Patent Application
20150038852
The current invention relates to the field of medical technology. More specifically, the present invention provides methods and devices/systems for real time monitoring of tissue treatment, as well as for differentiating between treatment effects on multiple tissue types and/or layers (e.g., unidirectionally oriented collagen and planar collagen).
A major challenge in modern medicine concerns the controlled treatment of biological tissues through application of temperature change. Numerous medical conditions exist which can optionally be treated through use of such thermotherapy. Such treatments hold special promise for modification of collagen fibers both in planar arrangements (e.g., in dermal layers) and in unidirectional strands (e.g., in tendons and ligaments). A wide range of treatment procedures has been, and continues to be, developed to utilize thermotherapy.
While thermotherapy and related treatment regimes have the potential for wide ranging application, they also, however, have the disadvantage in that it is difficult to track their progress. In other words, the extent of desired tissue modification (e.g., collagen denaturation of a specific area) and the extent of undesired tissue modification (e.g., damage to adjacent tissues, etc.) are difficult or impossible to track even in applications where there is direct visualization of the tissues being treated. Furthermore, lack of real time monitoring of such modifications is even more problematic.
Thus, there is a continuing need for better and more controllable methods and systems/devices to allow monitoring, especially real time monitoring, of tissue treatments such as thermotherapy. The current invention provides these and other benefits which will be apparent upon examination.
In various embodiments herein, the invention comprises methods of monitoring a change in one or more structures (e.g., collagen) in a tissue (e.g., skin, a capsule, a vascular wall, a vaginal or urethral wall, etc.) through exposing the tissue and thus, the structure(s) to light and measuring the light reflected from one or more structures in the tissue; exposing the structures to treatment which could putatively alter them (e.g., by denaturing them); exposing the treated structures to light again and measuring the light reflected from the treated structures; and comparing the light reflected from the structures before treatment and the light reflected from the structures during or after treatment. In particular embodiments, the tissue can comprise a first and a second structure (e.g., an overlaying structure such as dermal collagen, mucosal collagen, synovial collagen, etc. and an underlying or deeper structure such as a tendon, a ligament, a fascia, or an aponeurosis, etc.). In the various embodiments, the different structures can be monitored simultaneously or sequentially or only one of the structures can be monitored.
In some embodiments herein, the invention comprises methods to determine the minimum Degree of Linear Polarization (DoLP) of a biological structure. In such methods, the structure is exposed to a first light at a first polarization angle and the birefringence of the light reflected back from the structure is measured. The reflected light is measured at four different angles of a detection polarizer (I−45, I+45, I0, and I+90). From the reflected light, Q, U, and I are calculated by the equations: Q=I0−I90, U=I+45−I−45, and I=I0+I90 and the DoLP from the reflected birefringence is calculated as:
The structure being monitored is then exposed to a second light at a slightly different polarization angle than the first exposure light (which second exposure light can be, e.g., 1 degree greater, 2 degrees greater, 3 degrees greater, etc. than the first exposure light) and another DoLP is calculated. In such embodiments, such steps are repeated (i.e., exposure of the structure to light—calculation of DoLP at that exposure—exposure of the structure to a light of slightly different polarization angle, and so on) over a range of 80 or more degrees. The minimum DoLP of the biological structure thus corresponds to the lowest measured DoLP value from this process. The minimum DoLP can substantially correspond to an orientation angle of 45 degrees relative to the birefringence axis orientation of the biological structure being monitored.
In some embodiments, the invention comprises monitoring a change in birefringence status of a biological structure, which change in birefringence status corresponds to a structural or physical change in the biological structure. In such embodiments, a first minimum DoLP is determined as outlined above. Next the structure being monitored (e.g. a tendon of collagen within a tissue) is subjected to treatment (e.g., thermotherapy) and second minimum DoLP is determined as outlined above. The first minimum DoLP is then compared with the second minimum DoLP. Again, a difference between the measured minimum DoLPs, thus, indicates a change in birefringent status of the structure, e.g., due to a change in the structure of the biological structure being monitored (e.g., denaturation) due to the treatment received.
In other embodiments, the invention includes methods of determining the maximum Linear Polarization Angle (θ) of a biological structure (e.g., the sample induced rotation of the linear polarization angle). In such methods, the structure is exposed to a first light at a first polarization angle and a reflected birefringence that is reflected from the structure is measured at I−45, I+45, I0, and I+90, wherein Iφ is the reflected birefringence measured by a detection polarizer at polarization angle φ. From the four different measurements of the reflected birefringence, Q, U, and I are computed (Q=I0−I90, U=I+45−I−45, and I=I0+I90) and θ is calculated from the equation 2θ=tan−1 (U/Q). In such embodiments, the structure is exposed to a second light at a second polarization angle (which is greater than the first angle of the first light) and another θ is calculated. Such steps are repeated, each with an incrementally different (e.g., greater) polarization angle until a range of at least 80 degrees is covered. The maximum θ of the biological structure thus corresponds to the greatest value of θ measured. In such embodiments, the maximum θ substantially corresponds to an orientation angle of 45 degrees relative to the birefringence axis orientation of the biological structure.
In some embodiments, the invention comprises monitoring a change in birefringence status of a biological structure, which change in birefringence status corresponds to a structural or physical change in the biological structure. In such embodiments, a first maximum θ is determined as outlined above. The structure being monitored (e.g., a tendon within a tissue) is then subjected to treatment (e.g., thermotherapy) and a second maximum θ is found as described above. The first maximum θ is then compared with the second maximum θ. The difference, if any, between the measured maximum θs, thus, indicates a change in birefringent status of the structure, e.g., due to a physical or structural change from the treatment in the structure being monitored.
In some embodiments herein, the invention includes methods of determining the minimum Degree of Vertical Polarization (DoVP) and/or minimum Degree of Horizontal Polarization (DoHP) of a biological structure. In such methods the structure is exposed to a first light at a first polarization angle; a birefringence that is reflected from the structure is then measured (at angle at I−45, I+45, I0, and I+90, wherein Iφ is the reflected birefringence measured by a detection polarizer at polarization angle φ); Q, U, and I are computed from the measured reflected birefringence by determining Q=I0−I90, U=I+45−I−45, and I=I0+I90; a DoVP and/or a DoHP is determined from the measured reflected birefringence, wherein the
and the
the structure is exposed to a second light at a second polarization angle (which is greater than the first angle); and another DoVP and/or DoHP is calculated. Such exposure and calculation steps are then repeated over a range of 80 or more degrees. In such methods, the minimum DoVP and/or minimum DoHP of the biological structure corresponds to the lowest value of DoVP and/or DoHP measured and the minimum DoVP and/or minimum DoHP substantially corresponds to an orientation angle of 45 degrees relative to the birefringence axis orientation of the biological structure.
In other embodiments, the invention includes monitoring a change in birefringence status of a biological structure (which change corresponds with a structural or physical change in the biological structure due to a treatment). In such embodiments, a first minimum DoVP and/or DoHP is determined as described above. The structure being monitored (e.g., a tendon or a layer or planar collagen) is then subjected to treatment (e.g., thermotherapy) and a second minimum DoVP and/or DoHP is determined (again as described above). The first minimum DoVP and/or DoHP and the second minimum DoVP and/or DoHP are then compared. Any difference between the two measurements can thus indicate a change in the birefringent status of the structure being monitored due to the treatment received.
In other embodiments, the invention includes determination of the angular dependence of a birefringence of a biological structure relative to an input polarization. Such embodiments include exposing the biological structure to a first light at a first polarization angle; measuring a reflected birefringence that is reflected from the biological structure at the first polarization angle at I−45, I+45, I0, and I+90, wherein Iφ is the reflected birefringence measured by a detection polarizer at polarization angle φ; computing Q, U, and I from the measured reflected birefringence, wherein Q=I0−I90, U=I+45−I−45, and I=I0+I90; computing a DoLP, θ, DoVP, or DoHP from the measured reflected birefringence, wherein
2θ=tan−1(U/Q);
exposing the biological structure to a second light at a second polarization angle, which second angle is greater than the first angle; and, repeating steps a-e over a range of at least 5 degrees.
In other embodiments, the invention includes monitoring a change in birefringence status of a biological structure (which change corresponds with a structural or physical change in the biological structure due to a treatment). In such embodiments, a first angular dependence of a birefringence of the biological structure relative to an input polarization is determined as described above. The structure being monitored is then subjected to a treatment and a second angular dependence (again similar to above) is determined. The first angular dependence and the second angular dependence are then compared. Any differences between the two measurements can thus indicate a change in the birefringent status of the structure being monitored due to the treatment received.
In the various embodiments herein, the light to which the biological structure being monitored is exposed to, can also pass through one or more other biological structures. Such additional biological structures through which the light passes can optionally also be birefringent biological structures. For example, the biological structure being monitored can be, e.g., a tendon and the additional biological structure through which the light passes can be, e.g., skin layers such as epidermis, dermis, etc. In various embodiments wherein the light passes through an overlying structure to an underlying structure (again, e.g., a layer of skin collagen over an underlying tendon), both of the structures can optionally be monitored, e.g., for possible alteration due to treatment. In other embodiments, just one of the structures is monitored (e.g., either of them). Additionally, either one or both of the structures can optionally targeted for treatment. Additionally, either one or both of the structures can be monitored through determination of DoLP, θ, DoVP, DoHP, or the angular dependence of the birefringence of the biological structure(s) relative to an input polarization.
In the various embodiments herein, the biological structure(s) being monitored can comprise collagen structures. The structures can be one or more of: dermal collagen, mucosal collagen, synovial collagen, cartilage, a tendon, a ligament, a fascia, or an aponeourosis. In the various embodiments, the biological structure(s) can comprise, e.g., skin, a fascia, an aponeurosis, a tendon, a ligament, a capsule, a cartilaginous structure, a vascular wall, a vaginal wall, an introitus, a uterus, a urethra, a soft palate, a turbine, a gastrointestinal tract, including sphincters, or a structure of the airway.
Also, in the various embodiments comprising altering a polarization angle of the light to which the monitored structures are exposed, the degree to which the polarization angle is changed (e.g., in each determination of DoLP, etc.) can be, e.g., less than 1 degree, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, 10 degrees, 15 degrees, or 20 degrees or more greater than the first polarization angle. Thus, the increments over which birefringence is measured can be quite fine. Additionally, no matter the increments in which it is done, the range over which the birefringence is measured can be, e.g., 5 degrees or less, over 5 degrees, over 10 degrees, over 20 degrees, over 30 degrees, over 40 degrees, over 50 degrees, over 60 degrees, over 70 degrees, over 80 degrees, over 85 degrees, over 90 degrees, over 95 degrees, or over 100 degrees.
In the various methods herein (e.g., determination of DoLP, 0, DoVP, DoHP or the angular dependence of the birefringence of the biological structure(s) relative to an input polarization) the degree of linear polarization can be estimated from measurements other than Q, I, and U. Thus, in some embodiments, the measurement of reflected birefringence (from a biological structure) by a detection polarizer can be measured at +1 degree and +46 degrees, etc. Also, in some such embodiments, the reflected birefringence measurement by a detection polarizer can be measured at just 2 points (e.g., 0 and +45, etc.) or just 3 points rather than at 4 points (e.g., 0, −45, +45, 90).
In the various methods described herein the degree of polarization (DoP) is used as a general term to describe the combination of two or more measurements of light intensity. The two or more measurements can differ according to the states of the input (excitation) polarization, detection (emission) polarization, or the sample orientation. In some embodiments herein the methods are carried out by exposing a biological structure to light at a first input polarization state, with the structure at a first sample orientation state. Light reflected from the biological structure is then collected and detected at a first output polarization state. The input polarization state, output polarization state, or sample orientation state are changed to at least one additional state and at least one additional measurement of light reflected from the biological structure is performed. The degree of polarization is computed by combining at least two of these reflected light measurements at two different states. Finally, the degree of polarization is related to the degree of birefringence of the biological structure. In some embodiments herein, the degree of birefringence is then repeatedly measured in order to assess the effect of or provide feedback for one or more treatment methods.
In some embodiments herein, the methods are carried out by systems/devices that include a computer processor. Such computer processor comprises an instruction set to calculate, e.g., the DoLP, θ, DoVP, DoHP or the angular dependence of the birefringence of the biological structure(s) relative to an input polarization at particular polarization angles. The instruction set can include instructions to determine, e.g., the minimum or maximum DoLP, θ, DoVP, DoHP or the angular dependence of the birefringence of the biological structure(s) relative to an input polarization. In the various embodiments herein, the computer processor outputs its results (e.g., the calculations of DoLP, etc. at particular polarization angles, the minimum or maximum DoLP, etc.) to a user. The output can be, e.g., in printed form, an email or text message, displayed on a screen or monitor, etc.).
In certain embodiments herein, the methods can monitor the effect of any of a number of different treatments to a biological structure. Such treatments can include, but are not limited to, e.g., application of physical energy, application of radio frequency waves, application of ultrasound, application of heat, application of cold, or application of a cosmeceutical. In some embodiments, the treatment is passage of time.
In other embodiments of the methods herein, the light to which the biological structures is exposed (and the reflected light from the structures) is polarized light (e.g., linear polarized light, circularly polarized light, etc.). In some embodiments, the light to which the structure(s) are exposed (and optionally the light reflected back from the structure) is infra-red light, UV light, light of a wave length from about 800 to about 1100 nm, or fluorescence.
In some embodiments herein the invention comprises methods of monitoring a change in a biological structure in a tissue (e.g., a collagen structure). In such embodiments, the tissue is exposed to a first light; a first reflected light reflected from the structure is measured; the tissue is exposed (and/or the structure) is exposed to one or more treatments that can (or that can putatively) alter the physical characteristics of the structure; the tissue is exposed to a second light; a second reflected light reflected from the structure is measured; and the first reflected light and the second reflected light are compared in order to monitor any change in the structure. In such embodiments, the tissue can optionally include a second biological structure and both or either one of the two structures can be monitored for change induced by the treatment. The treatment can be directed to either one or both of the biological structures. However, even if the treatment is directed to only structure in particular (e.g., a tendon), it will be appreciated that an overlying structure (e.g., collagen layers in the skin) could possibly be impacted by the treatment and can therefore be monitored for change as well. In various embodiments, the two structures can be monitored simultaneously or sequentially. Furthermore, in some instances, one structure is closer to the source of the monitoring light and/or closer to the treatment application. In some embodiments, the structure can comprise, e.g., collagen, dermal collagen, mucosal collagen, synovial collagen, cartilage, a tendon, a ligament, a fascia, or an aponeourosis. The tissue can optionally include, e.g., skin, a fascia, an aponeurosis, a tendon, a ligament, a capsule, a cartilaginous structure, a vascular wall, a vaginal wall, an introitus, or a urethra. Also in such embodiments, the treatment can comprise one or more of, e.g., application of physical energy, application of radio frequency waves, application of ultrasound, application of heat, application of cold, or application of a cosmeceutical.
In other embodiments of the methods herein, the light to which the biological structures is exposed (and the reflected light from the structures) is polarized light (e.g., linear polarized light, circularly polarized light, etc.). Thus, in some embodiments, comparing the light comprises comparing the polarization of the light. In some embodiments, the light to which the structure(s) are exposed (and optionally the light reflected back from the structure) is infra-red light, UV light, light of a wave length from about 800 to about 1100 nm, or fluorescence. Also, in some embodiments of such methods, the comparison of the first and second reflected lights comprises determination of DoLP, θ, DoHP, DoVP or the angular dependence of the birefringence of the biological structure(s) relative to an input polarization.
In the various methods herein, the treatment that is monitored can comprise, e.g., application of physical energy, application of radio frequency waves, application of ultrasound, application of heat, application of cold, or application of a cosmeceutical. In some embodiments, the “treatment” is the passage of time (i.e., no additional modification such as thermotherapy is performed to the structure). The light applied to the tissues herein (e.g., via laser) can comprise infra red light, light of wavelength of about 800 to about 1100 nm, UV light, etc. Furthermore, in the methods herein, the light applied to the tissues to monitor status of structures (e.g., collagen) can comprise polarized light (e.g., linearly polarized, circularly polarized, etc.).
In various embodiments of the methods herein, e.g., when utilizing polarized light, the status and/or change in status of different collagen structures can be monitored through use of differently polarized light. For example, the status of one collagen layer (e.g., a dermal layer) is optionally monitored when the light exposed onto the tissue is at one polarization, while the status of another collagen layer (e.g., an underlying tendon) is optionally monitored when the light is at another polarization. In various embodiments, the polarization is switched back and forth between two or more polarization settings to monitor different collagen structures/layers in a tissue.
In the various embodiments herein, the information on collagen structure is gathered (i.e., the collagen is monitored) without invasion of the tissue or collagen structure or with only minimal invasion of the tissue/structure. Furthermore, the various collagen structures can be monitored through one or more layers of untargeted tissue (e.g., overlaying tissue and/or other collagen layers).
The information gathered by the methods and devices/systems of the invention can be used to, e.g., guide clinical decisions (including decisions concerning the continuation/cessation of treatment of the tissues; the effectiveness or lack thereof of the treatments; etc.). Thus, in various embodiments, treatment can be altered, e.g., discontinued when a percent change in measured collagen change is noted through, e.g., a percent change in polarization/birefringence of the light reflected from the structure. In other embodiments, treatment can be stopped when a certain desired result is reached in the structure being treated and/or when a certain percent change in the treated structure and/or in another ancillary structure (e.g., an overlaying dermal collagen layer) is reached. Again, such percent change is optionally indicated by a percent change in polarization/birefringence of the light reflected from the treated (or otherwise monitored) structure. In some embodiments herein, the methods comprise a feed-back control over treatment.
In the various embodiments herein, the methods can include steps for orienting the polarization of the light exposed on the tissue relative to the strand orientation of a collagen layer in the tissue (e.g., in parallel with the collagen orientation in a tendon, etc.).
In other embodiments, the methods include the use of a plurality of source-detector distances in differentiating between changes in various collagen structures. Also, the methods include wherein wavelength dependence of birefringence is measured for various collagen structures.
In yet other aspects, the invention includes methods of determining the collagen content in a tissue wherein a measurement of birefringence provides an estimation of the collagen content. Furthermore, the invention also includes embodiments comprising methods of monitoring collagen status through measurement of birefringence which, in turn, is used as a guidance for treatment of the collagen layer being treated and/or of ancillary/nearby tissues/structures such as other collagen structures.
In other embodiments herein, the invention comprises a system or device for monitoring a change in one or more structures in a tissue (e.g., collagen structures). Such systems can include: a light source component (configured to emit light to the tissue); one or more light polarizer components (configured to polarize light that is emitted from the light source or used for light reflected back from the tissue and to be set at particular angles of φ); one or more lens components (configured to focus light that is emitted from the light source or to focus light that is reflected from the tissue); a light detection component that is configured to detect light reflected from the tissue (e.g., light that has also optionally traveled through other components such as lens(es), polarizers, etc.); a lock-in amplifier component that is configured to amply the light reflected from the tissue; and, a computer or processor component which has an instruction set that is programmed to instruct one or more of: direct the light source to expose the tissue to a first light at a particular polarization; direct the detection component to measure the polarization of a first reflected light from the one or more structures; direct the light source to expose the tissue to a second light at a particular polarization; direct the detection component to measure the polarization of a second reflected light for the one or more structures; and, compare the first reflected light and the second reflected light, thereby monitoring the changes in the one or more structures (based on changes in the polarization of the light) and to output the results to a user (e.g., on a monitor or readout, on a printout, on a disc or other medium, etc.). In many embodiments, the computer component is programmed to direct the emission and detection of the second light after the tissue that comprises the structure has been exposed to a treatment (e.g., RF treatment, exposure to a cosmeceutical, application of physical energy, application of radio frequency waves, application of ultrasound, application of heat, application of cold, etc.). In some instances, the “treatment” can merely be the passage of time rather than application of a particular therapy or the like.
In other embodiments herein, the invention comprises a system or device for monitoring the degree of birefringence in one or more structures in a tissue (e.g., collagen structures). Such systems can include: a light source component (configured to emit light to the tissue); one or more light polarizer components (configured to polarize light that is emitted from the light source or used for light reflected back from the tissue and to be set at particular angles or used to rotate the polarization of light prior to sample excitation or prior to emission detection); a light detection component that is configured to detect light reflected from the tissue (e.g., light that has also optionally traveled through other components such as polarizers, polarization rotators, etc.); and, a computer or processor component which has an instruction set that is programmed to instruct one or more of: direct the detection component to measure a first reflected light at a particular polarization state from the one or more structures following exposure of the light source to the tissue to light at a particular polarization state; direct the detection component to measure additional reflected light at a particular polarization state from the one or more structures following exposure of the light source to the tissue to light at particular polarization state; and, compare the first reflected light and the additional reflected light, thereby monitoring the degree of birefringence in the one or more structures and to output the results to a user (e.g., on a monitor or readout, on a printout, on a disc or other medium, etc.). In many embodiments, the computer component is programmed to direct additional measurement of the degree of birefringence after or while the tissue that comprises the structure is exposed to a treatment (e.g., RF treatment, exposure to a cosmeceutical, application of physical energy, application of radio frequency waves, application of ultrasound, application of heat, application of cold, etc.). In some instances, the “treatment” can merely be the passage of time rather than application of a particular therapy or the like.
The computer can also be programmed to control one or more of the various components present in the various embodiments of the invention. Thus, the computer can optionally control, e.g., the intensity of the light emitted, the timing and duration of the light emitted, the degree of polarization of the light emitted to the tissue, the angle setting of the detection polarizer through which birefringent light is transmitted to the detector, etc. In some embodiments, the system/device of the invention comprises multiple polarizer components, e.g., optionally in the light path prior to tissue exposure (e.g., light polarizer components that polarize light from the light source prior to the light exposing the tissue) and/or optionally in the light path of the light reflected back from the tissue towards the detector (e.g., light polarizer components that are set at preset angles such as +45 degrees, −45 degrees, 0 degrees, 90 degrees, etc.) The polarizer components can be directed/controlled by one or more polarizer rotators (which in turn can be optionally controlled by instructions either directly from the user or from instructions from the computer component which can also be input from the user). In some embodiments, the systems/devices of the invention can comprise multiple lenses. Thus, in some embodiments, the systems/devices can optionally have a lens that focuses light from the light source prior to the light exposing the tissue and/or can optionally have a lens that focuses the light that is reflected back from the tissue. In some embodiments, the systems/devices can comprise one or more mirrors (e.g., to direct light to and/or from the light source, the tissue, etc.). Of course, particular embodiments herein do not comprise mirrors. Some embodiments also comprise one or more polarization compensator components (e.g., that are each operably connected to a polarizer component). In the various embodiments, the system or device of the invention can be used to monitor tissues having a first and at least a second collagen structure. In such embodiments, the computer component can be programmed to direct the light source and polarization components to expose the tissue to a first light at a first polarization orientation and a second light at a second polarization orientation. Furthermore, in such embodiments, the computer component is programmed to differentiate changes in the first collagen structure from changes in polarization of the first light and changes in the second collagen structure from changes in polarization of the second light. In various embodiments, the systems/devices of the invention monitor a change in one or more structures in a tissue (e.g., due to treatment of the tissue). Such change can be, e.g., a change in DoLP, a change in θ, a change in DoHP, a change in DoVP, or a change in the angular dependence of the birefringence of the biological structure(s) relative to an input polarization.
In some embodiments, the systems or devices or methods herein comprise instrument calibration or correction to improve the accuracy of the measurement of the degree of birefringence. Such calibrations or corrections may be determined in advance of the measurement of the sample of interest (e.g. biological structures), and may employ calibration standards (e.g. mirrors, Teflon, or other reflective materials). The calibration may involve additive or multiplicative correction or a combination of the two. In some embodiments, multiple measurements made on the sample of interest are used to self-calibrate or self-correct the determined degree of birefringence.
In particular embodiments, the systems herein can comprise systems such as (or similar to) the ones illustrated in
These and other features of the invention will become more fully apparent when the following detailed description is read in conjunction with the accompanying figures and claims.
The ability to accurately monitor (and thereby more accurately control) tissue treatments such as thermotherapy, especially in real time, is significant in the productive treatment of a number of disease states/medical conditions, e.g., treatment of joint trauma. Furthermore, the ability to accurately monitor the effect of such products as cosmeceuticals on tissues (whether during and/or after treatment/application of such) is quite significant. Various embodiments of the current invention utilize tracking of changes of reflected light from biological structures, or from multiple biological structures, to track corresponding changes in such structures arising from treatment. Of course, it will be appreciated that even though the various embodiments herein are primarily described as useful for tracking progress of tissue treatment and the like, that the benefits of the invention also extend to, e.g., monitoring the condition of a subject's tissue or the presence and/or progression of a disease state or medical condition, whether or not any treatment is administered.
In particular embodiments herein, the invention uses birefringence of light reflected from one or more layers of collagen tissue to monitor treatment progress on collagen. Optionally such changes are tracked in real time, e.g., during treatment of the tissue. In yet other embodiments, the invention uses optical monitoring procedures other than birefringence and/or tracks changes after treatment has occurred (e.g., rather than as treatment is occurring). The invention includes the methods of monitoring treatment effects as well as systems and devices that implement such methods. Overall, the invention results in increased monitoring ability for tracking of tissue treatment.
Before describing the present invention in detail, it is to be understood that the invention herein is not necessarily limited to use with particular light sources, thermotherapy treatments, etc., which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not necessarily intended to be limiting. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a laser” optionally includes a combination of two or more lasers, and the like.
The term “subject” as used herein includes, but is not limited to, a mammal, including, e.g., a human, non-human primate (e.g., monkey), mouse, pig, cow, goat, rabbit, rat, guinea pig, hamster, horse, monkey, sheep, or other non-human mammal, or a non-mammal, including, e.g., a non-mammalian vertebrate, such as a bird, reptile, or amphibian. In some embodiments, the methods and systems/devices of the invention are used to monitor non-human animals. Many commercially important animals are susceptible to medical conditions, e.g., joint trauma, whose treatment is optionally monitored with the current invention.
The term “footprint” as used herein refers to the tissue area monitored by the current invention. It will be appreciated that such area can vary in different embodiments depending on, e.g., size of illumination beam used, etc. Furthermore, it will also be appreciated that such monitoring footprint need not be, and often is not, the same size as a treatment footprint, i.e., a tissue area that is being treated by, e.g., thermotherapy, etc.
As will be appreciated, the above terms, as well as additional terms, are detailed/described further below.
In the various embodiments of the present invention, changes in biological structures (e.g., collagen structures) are monitored by directing light into a tissue and collecting the light after it has interacted with the structures within the tissue. In particular embodiments, the collected light is measured in order to monitor the status of and/or changes in the structures within the tissue. In the various embodiments herein, more than one structure can be monitored simultaneously or sequentially, e.g., during the course of a treatment process that involves the tissue or during the course of the progression of a disease state or medical condition.
Particular embodiments of the invention monitor, through exposure to light, the status and/or change in status of collagen. As discussed further below, collagen is a uniaxial birefringent material whose optic axis (or slow axis), in which direction light travels most slowly, is parallel to the long axis of its triple helix while its fast axis, the one in which direction light travels most quickly, is perpendicular to its triple helix axis. The difference in refractive index, Δn, between the slow and fast axes of collagen is approximately 3×10−3. See, e.g., D. J. Maitland and J. T. Walsh, “Quantitative Measurements of Linear Birefringence During Heating of Native Collagen” Lasers in Surgery and Medicine, 20:310-318 (1997). The phase shift (δ) introduced between light traveling along the slow vs. fast axes can be related to the thickness of the collagen sample (d) and the wavelength of light (λ) according to Equation 1.
Linearly polarized light that is oriented parallel to the collagen optic axis (hereafter referred to as 0 degree orientation) will undergo no polarization rotation upon interaction with the collagen. However, linearly polarized light at a 45 degree orientation will undergo maximal polarization rotation. According to Equation 1, linearly polarized light with 800 nm wavelength and 45 degree orientation relative to the optic axis will undergo a 90 degree rotation (or 180 degree phase shift) after traveling through only 130 μm of collagen. Collagen layers in humans can vary in thickness depending on their type and location. For example, collagen layers in skin can be ˜200 microns in thickness, while tendons can be ˜2-3 mm in thickness. As explained below, various embodiments of the invention can monitor at various depths. Thus, some embodiments of the invention can monitor, e.g., 1-2 mm within a tendon, etc.
Again, as discussed further below, the birefringence of collagen is lost upon denaturation. Therefore, the embodiments herein can monitor changes in birefringence of a tissue (e.g., before and after thermotherapy) in order to track the progression of collagen denaturation by heating. Thus, for example, a tendon can be monitored before treatment and the birefringence thus determined can be compared to the birefringence determined after (or during) treatment to thereby monitor changes if any in the tendon (such as denaturation of its collagen). See Maitland, supra.
Various embodiments of the invention utilize the change in birefringence due to denaturation to monitor, e.g., the progress or effectiveness of treatments and the like. In particular embodiments, the baseline or starting status birefringence of a structure (e.g., a collagen layer) and the structure's response to treatment are both monitored by directing, e.g., a linearly polarized laser light into the tissue which comprises the structure, collecting the light after it has interacted with the structure(s), and measuring polarization-dependent properties of the collected light (e.g., the extent or degree of depolarization, the amount of polarization rotation, etc.). In various applications, the starting status of the structure is typically the status before any treatment is applied to it. However, the starting status can also optionally be from a point after treatment has started. Thus, for example, monitoring can optionally be implemented in the middle of a course of treatment of a tissue and be used to track changes occurring after the start of monitoring.
In various embodiments, the monitoring can be done non-invasively (e.g., by directing light upon skin, etc.), while in other embodiments, the monitoring can involve an invasive act (e.g., a monitoring probe or component inserted (e.g., arthroscopically) into a subject to monitor a tendon, vessel wall, etc.).
In some embodiments, the invention can be used to determine collagen content in a tissue (e.g., whether or not any treatment has been or is to be administered). For example, light properties such as birefringence can be measured in multiple subjects and/or at multiple sites within a subject to create a measurement guide of collagen content/status based on the light property measured (i.e., as opposed to changes in such property used in some embodiments herein). Based on multiple readings (between the level of the light property measured and collagen content), such measurement guide thus allows a practitioner to measure or estimate the collagen level in a tissue. The measure/estimate of collagen (based on the light property measured) can be done prior to any treatment to the subject or to compare with an average measurement (e.g., as in comparing diseased tissue against non-diseased tissue, etc.). Thus, a practitioner can use such measurement to advise whether treatment should even be undertaken, whether or to what extent treatment may be successful, etc. The readings taken to construct the measurement guide can optionally be normalized for subject status (e.g., based on age, ethnicity, gender, etc.) and tissue type or location (e.g., dermal collagen in the face, dermal collagen in the hands, etc.).
In certain embodiments, e.g., those comprising linearly polarized laser light, the light can be used to distinguish between birefringence from a superficial layer of collagen (e.g. an epidermal, dermal, mucosal, synovial, or intimal structure) and a deeper layer in which collagen is substantially oriented in linear strands (e.g. tendons, ligaments, fascia, aponeurosis, etc.). In some embodiments, one layer of collagen is targeted for treatment while the other is anticipated to remain untreated. However, it will be appreciated that both layers can be targeted for treatment. In various embodiments, the structures targeted for treatment as well as the structures not targeted for treatment can be monitored by embodiments of the current invention. Of course, in some embodiments, the invention monitors only a single structure rather than multiple structures (e.g., a tendon rather than a tendon and an overlying dermal collagen layer) even if such monitoring of a single structure is done through another structure (e.g., monitoring of a tendon or fascia underneath skin, etc.).
It will be appreciated, that while for ease of description, the current description herein primarily describes the structure type that is monitored as collagen, other structures are optionally included in the various embodiments. Thus, it is contemplated that the invention can also find use with monitoring of, e.g., pathological tissue such as tumors that are treated with thermotherapy. In such embodiments, it is thought that the methods and systems of the invention will track such tissues via, e.g., birefringence or other optical methods such as fluorescence. Furthermore, in some embodiments the structure monitored can comprise keratin and/or elastin. Additionally, while particular light (e.g., linearly polarized laser light) and light properties (e.g., changes in birefringence, etc.) are detailed in the discussion herein, those of skill in the art will appreciated that other light types, and/or light-dependent properties are included within the spirit and purview of the application and scope of the appended claims. Thus, different light properties can be measured rather than polarization-dependent properties. Additionally, the light used to monitor changes in the structure(s) can be, e.g., non-polarized, linearly polarized, or circularly polarized light. Furthermore, the light used can be, e.g., at a single wavelength, i.e., monochromatic (or substantially monochromatic), or at a multiplicity of wavelengths. In embodiments comprising use of polarization-dependent properties, such properties can include, e.g., the difference between the absorbed intensity of two light beams having mutually perpendicular linear polarizations, the difference between the absorbed intensity of two light beams having left and right circular polarizations, the rotation of the polarization of a linearly polarized input light beam, the extent of depolarization of a polarized light bean, or the polarization ellipticity of a circularly polarized input light beam.
In various embodiments, the methods of the invention comprise placement and orientation of the various system components (e.g., light emitter and detector) in relation to the tissue/structure being monitored. As will be appreciated, such placement/orientation can involve movement of the tissue being monitored and/or movement of one or more components of the devices/systems herein. Also, while the various embodiments herein are primarily discussed in terms of generalized systems of components, particular embodiments can comprise self-contained devices (e.g., a handheld probe and/or a handheld probe operationally connected to a unit having laser components, etc.). See below. Furthermore, as mentioned throughout, the various methods of the invention and the various devices/systems of the invention can be used topically on subjects (i.e., noninvasively) and/or can be used internally within subjects (i.e., invasively either through incisions or the like or through orifices of the subjects).
By determining a baseline status measurement of a tissue structure's birefringence, the various embodiments of the invention allow comparison of such values with measurements taken after/during a treatment (or even taken at a later date) to establish the impact (if any) of a given intervention. Thus, the monitoring can be real time during the treatment and/or after the treatment. Additionally, in some embodiments by simultaneously monitoring birefringence at multiple polarization settings while delivering a treatment (e.g. radiofrequency, ultrasound, light) the treatment can be terminated when either the target structure (e.g., a tendon) or a non-target or secondary target structure (e.g., a superficial layer such as dermal, synovial, mucosal collagen, etc.) has reached the desired change in birefringence or has exceeded a threshold change in birefringence, in either instance indicating a change in the particular structure. Thus, through use of some embodiments, a particular collagen containing structure can be treated while simultaneously avoiding damage to other collagen containing structures located above or below the targeted structure.
Also, it will be appreciated that various embodiments of the invention herein can include systems having multiple light sources and detector/polarizer component paths as well as systems having adjustable light sources and detection/polarizer component paths to allow monitoring of multiple tissue structures and/or tissue structures in multiple locations or depths.
One step in various methods herein includes the determination of birefringence of the tissue being monitored. The determination of the tissue birefringence can be accomplished by the devices/systems of the invention in several ways. Many of the embodiments of the invention can be grouped into one of two general categories: embodiments using the extent of depolarization of a polarized light beam in order to determine tissue (e.g., collagen) orientation and embodiments using the amount of polarization rotation of a polarized light beam in order to determine tissue orientation. However, it should be appreciated that the various embodiments herein typically share many qualities and aspects. For example, the various embodiments herein can, unless stated otherwise, all use similar light sources, wave plates, polarizers and other components. See below. Also, each general classification group of embodiments comprises specific embodiments wherein multiple tissue layers can be monitored simultaneously or concurrently and specific embodiments wherein only a single tissue is monitored (however, optionally through one or more other tissues). Other areas of similarities will be apparent to those of skill in the art.
Degree of Linear Polarization as Function of Collagen Axis Orientation
As stated above, one class of embodiments herein comprises determination of tissue orientation (by monitoring of which any change such as denaturation can be tracked) through determination of the extent or degree of depolarization of a polarized light by the tissue. Thus, in some embodiments, the methods and devices of the invention determine the degree of linear polarization of light reflected from a tissue (e.g., a tendon of collagen) as a function of the orientation of the tissue (e.g., the orientation of the axis of the collagen). Light diffusely reflected from tissue such as collagen travels through a wide range of possible path lengths when it is reflected. As can be seen from equation 1 above, the effect of polarized light transmitted at a 45 degree orientation from the axis of orientation of a tissue traveling through a range of depths of the tissue will be polarization rotation over a wide range of angles. Since only about 130 μm of collagen is required to induce a 90 degree change in polarization rotation (at a wavelength of 800 nm), light scattered from a thicker slab of collagen (e.g. 1 mm) will undergo a mixture of all possible polarization rotations. Thus, when monitored, the integrated result seen by a detector will be a large reduction in the degree of linear polarization. However, at 0 degree orientation between the polarized light and the tissue axis, there is no birefringent effect. Therefore, at this 0 degree orientation, polarized light can be expected to be less depolarized within the tissue. These effects can be seen in polarized images of rat tails. See, e.g., P. J. Wu, and J. T. Walsh, Jr., “Stokes Polarimetry Imaging of Rat Tail Tissue in a Turbid Medium”, J. Biomed. Optics, 11 (2006).
Therefore, in some embodiments, the methods and devices of the invention utilize the following method of searching for the tendon (or other tissue) orientation: search for the minimum (or maximum) degree of linear polarization as a function of sample orientation. The degree of linear polarization (DoLP) is defined as:
and Iφ is the signal measured on the detector when the detection polarizer (e.g., P2 in
The above-defined quantities, Q, U, and I, are 3 of the 4 values, collectively referred to as the “Stokes vector,” (see, e.g., Kliger, et al., “Polarized Light in Optics and Spectroscopy,” Academic Press (New York), 1990) that completely define the polarization state of a light beam (the fourth value is the difference in intensity between left and right circularized light). Q and U can also be used to compute the linear polarization angle, 0:
2θ=tan−1(U/Q) (Equation 6)
Thus, in some embodiments, the linear polarization angle is determined through the methods and devices herein as a way of determining the polarization rotation induced by a birefringent tissue sample and thus the tissue's orientation. Equation 6 provides a way of estimating the polarization rotation. It should be noted that using equations 2 and 6, the same data (Q and U) can equivalently be used to compute either DoLP or θ, and either could be used to determine the birefringent axis of collagen.
An exemplary arrangement of system components to implement such equations is shown in
Thus, in some embodiments, the methods and devices of the invention can determine, e.g., the orientation of the birefringent axis of a tendon by:
Example 1 below, illustrates the determination of the axis of orientation of a tendon using the above.
As detailed above, various embodiments of the invention present methods and devices to detect and monitor collagen orientation and denaturation. Additional embodiments of the invention present automation and instrumentation to carry out such detecting and monitoring. For example, results of use of one such exemplary embodiment are described in Example 2. Furthermore, Example 3 shows the results of bovine tendon measured through various skin-like (“phantom”) materials. These embodiments illustrate the increasing penetration depth through which tendon birefringence can be measured by various embodiments of the invention.
As can be seen from Example 2, various embodiments of the invention comprise systems (e.g., comprised of light sources, detectors, polarization manipulators, computers/processors, etc.) that can automatically carry out the various methods of the invention (e.g., of determination of collagen strand orientation and changes in such thus indicating degree of denaturation of such, etc.). Of course, it will be appreciated that the precise system configuration in Example 2 should not necessarily be taken as limiting and that other embodiments can optionally comprise additional, alternative, or fewer system components depending upon the specific needs of the embodiment. Also it should be noted that while the graphs for Example 2 are presented in terms of sample orientation, they could also be presented in terms of PR1 orientation. Thus, the graphs represent the relative angle between the input linear polarization and the sample orientation.
In addition to illustrating an exemplary automated system of the invention, Example 2 also shows that embodiments of the invention can monitor the decrease in birefringence of a tissue (e.g., a tendon) due to denaturation.
Tendon Measurements Through “Phantom” Skin Layers
As illustrated in Example 3, various embodiments of the invention can monitor tissue layers (e.g., collagen in tendons) through a number of various intervening layers (e.g., skin). Example 3 demonstrates that various embodiments of the invention can optionally be used for a number of non-invasive procedures such as tendon measurement through an intervening layer.
As shown in Example 3, in some embodiments, the methods and devices of the invention can split the measurement of the Degree of Linear Polarization (DoLP) into 2 parts: the Degree of Vertical Polarization (DoVP) and the Degree of Horizontal Polarization (DoHP). Such split terms can be defined as:
where Q, U, and I are as defined above. Of course, it will be appreciated that other embodiments which include determination of degree of linear polarization can also use DoVP and DoHP (e.g., the determinations in Examples 1, 2, and 4 could have made calculations of DoVP/DoLP, etc.). Measurement of DoHP and DoVP as a function of angle is thought to result in curves having the same amplitude but offset in phase by 90 degrees. Splitting the DoLP into its horizontal and vertical components can optionally add in reliability when determining the amplitude of the change in the degree of polarization with sample orientation. This is particularly true if the DoVP and DoHP functions are simultaneously fit to a model function where certain parameters are held fixed, such as: (1) the relative amplitudes of the fitting function, and (2) the relative phases of the fitting function.
In various embodiments (optionally both those monitoring degree of polarization and those monitoring amount of polarization rotation) the methods and systems of the invention can comprise monitoring at various depths into the tissue being examined. For example, a split sampling lens (see
Measurement of Dermal Collagen Through an Epidermis Layer
Automated Sample/Polarization Orientation
From
In such embodiments, rather than setting the sample orientation with a manual rotation stage, polarization rotator PR1 can be added just after first polarizer P1. Such rotator device can comprise a half-wave plate mounted in a computer-controlled rotation stage. This arrangement allows the sample to remain stationary while the relative polarization of the input beam is varied (e.g., by rotating PR1). Such embodiments are thought to have the advantage of interrogating the same sample volume throughout the measurement, whereas in other embodiments the sample is moved relative to the input beam each time the sample rotation stage is adjusted. Thus, in embodiments comprising such rotators, in addition to the advantage of automating the measurement, the measurement error is also thought to decrease. Also, in the current embodiments, when the laser beam is oriented at angles other than 0 (vertical) and 90 degrees (horizontal), mirrors M1-M3, PM, and the sampling lens cause partial depolarization of the light. Therefore, placing quarter-wave plate C in front of second polarizer PR2 largely compensates for this depolarization effect. In other embodiments, additional compensators can be also used (e.g. a quarter-wave plate between PR1 and MD in order to further increase instrument sensitivity.
Software Flow Diagram
An exemplary flow diagram summarizing and generalizing the steps involved in automated measurement of the orientation of a collagen sample (e.g., as with the embodiment characterized in
Alternative Instrument Configurations
The various instrument configurations described in the embodiments comprising determination of DoLP, polarization angle, etc. are designed to allow rapid measurement of the degree of linear polarization in a tissue (e.g., a tendon) sample. The measurements being collected by the various embodiments include 3 of the 4 Stokes vectors, (see, e.g., Kliger, et al., “Polarized Light in Optics and Spectroscopy”, Academic Press (New York), 1990) whereas a full Stokes measurement would include circular polarization in addition to linear. Since the relative input linear polarization is also being varied in the methods described here, the measurement can further be characterized as a partial determination of the Mueller matrix. See Kliger, supra. Measurement of the full 4×4 Mueller matrix requires characterization of all 4 Stokes vectors while varying the input polarization between at least 4 characteristic states of linear and circular polarization. Thus, in some embodiments of the invention, the methods and devices of the invention can comprise measurement of the full 4×4 Mueller matrix in monitoring tissue birefringence. Such embodiments can comprise, e.g., rapidly rotating quarter wave plates (e.g., in both the excitation and detection arms of the systems) to be used along with Fourier analysis. Other embodiments can comprise photoelastic polarization modulators or liquid crystal retarders instead or rotating quarter wave plates. In some embodiments Fourier analysis can be used to determine the elements of the Mueller matrix.
Monitoring of Multiple Tissues in Embodiments Comprising Determination of Degree of Depolarization
As is common to both general embodiment classifications herein, the embodiments wherein tissue orientation is determined and monitored through measurement of the extent or degree of depolarization can be used to simultaneously or concurrently monitor two or more tissue structures (e.g., a tendon and an overlying dermal collagen layer). Thus, in such embodiments, the point where DoLP (or DoVP/DoHP) is determined to be at a maximum corresponds to where the polarized light beam is parallel with, e.g., the collagen strands in a tendon. The amount of DoLP, etc. at that point is mainly due to, e.g., dermal, synovial, or mucosal collagen (e.g., from an overlying layer above the tendon). Thus, any change to this maximum reading can also be tracked during treatment to thereby monitor any changes in the overlying structure. In some embodiments wherein multiple tissue layers are monitored at the same time, the DoP can be characterized as a function of orientation angle. Thus, rather than just looking for a minimum or maximum the function would be fit to a model. In addition, in some embodiments it can be helpful to fit the DoP as a function of orientation angle to a model, where the model includes depolarization effects from both layers. Some simple examples of such models include: (1) A planar collagen layer plus a linear collagen layer can be modeled as a combination of an angle independent depolarization (planar layer) plus a sinusoidally varying DoP with sample angle (linear layer). (2) Two stacked linear collagen layers can be modeled as a combination of 2 sinusoidally varying DoP functions that differ in phase (corresponding to a difference in the orientation of the optical axes of the two layers). (3) A partially linear/partially planar collagen structure plus a fully linear collagen structure can be modeled as a small amplitude sinusoid plus a large amplitude sinusoid, again with phase difference indicative of the orientation of the birefringent axes. In more detailed models, the orientation dependence of the DoP resulting from each birefringent structure can be modeled as a distribution of sine functions (or other periodic functions), in order to account for the degree of disorder in the collagen orientation within the structure.
The various embodiments comprising determination of DoP demonstrate that the angular orientation of a tendon sample can be determined with high accuracy (<<5 degrees) by measuring the degree of linear polarization while varying the angle of input polarization relative to the sample orientation. As shown by the Examples, this angular variation has the expected 90 degree periodicity and diminishes as the tendon sample is heated (denatured). Also as demonstrated, measurement of tendon samples with embodiments of the invention through several skin “phantoms” can be done including measurement through: (1) at least 7 mm thick gelatin, (2) at least 0.5 mm thick Teflon, and (3) at least 2 mm thick 2% Intralipid (which has light scattering properties similar to human skin, see Troy, supra). The invention also provides a method for simultaneously fitting DoVP and DoHP curves which provides better reliability than use of DoLP alone in some embodiments. Embodiments of the invention also showed measurement of dermal collagen in skin.
Orientation of Monitoring Polarization Relative to Collagen Axis
The other general classification of embodiments herein comprises determination of tissue (e.g., collagen in a tendon) orientation by tracking the amount of polarization rotation at a number of angles. In some such embodiments, the invention comprises methods and devices/systems to simultaneously or concurrently monitor multiple tissue structures. Thus, for example, some embodiments can monitor a collagen tendon while also monitoring an overlying dermal collagen layer. In some such embodiments, the monitoring comprises determining (on a multi-layer tissue such as tendons under skin) the linear polarization orientation (of the applied light used) at which birefringence of the reflected light from the targeted structure (i.e., the structure that is targeted for treatment, such as linear collagen in a tendon) is minimized Minimum birefringence will be observed when the light polarization of the applied light is oriented parallel to the linear strand direction (or at 90 degree increments from such polarization). In such embodiment, the birefringence measured at the polarization orientation that gives minimal birefringence is mainly due to dermal, synovial, or mucosal collagen in the illustration. In other words, the birefringence seen is that arising from the planar overlying layer of collagen rather than from the targeted structure such as a tendon. In such embodiments, in order to achieve greatest sensitivity to the birefringence from light reflected from the structure targeted for treatment (e.g., sub-dermis, tendon, ligament, fascia, aponeurosis, etc.) the polarization of the applied light can be rotated by 45 degrees from the prior determined angle. As will be appreciated, the ability to track changes in birefringence (e.g., arising from structural changes such as denaturation) in more than one structure allows monitoring to ensure that not only is the targeted structure not altered beyond a particular point (and/or that a targeted structure is altered up to a particular point), but also that another particular structure (e.g., an overlying one) is not altered beyond a particular point (or is altered up to a particular point) as well.
In such embodiments, the polarization of a laser relative to the strand axis of a tendon (or other highly oriented collagen material being targeted by treatment such as RF) is first oriented, by searching for the angle of minimum (or maximum) birefringence. Once oriented, the degree of polarization rotation induced by the collagen at 45 degrees vs. 0 degrees is used to contrast the birefringence of the tendon relative to that of more superficial dermal collagen. The search procedure for both locating the optic axis of the collagen and for monitoring its subsequent changes in response to treatment such as RF heating, involves rotation of the angle of a polarizer in front of a detector, while searching for a minimum signal level.
An illustrative embodiment of system components to implement such embodiments is diagrammed in
A sample consisting of a half-wave plate with a mirror on top, was used to test the performance of the instrument. As expected, at 0 degree orientation, the sample had no effect on the laser beam polarization, whereas at 45 degree orientation, the sample rotated the laser beam polarization by approximately 90 degrees. In addition to these expected findings, it was also unexpectedly found that the degree of linear polarization was being substantially reduced at the 45 degree orientation. Further experiments traced the source of this unexpected depolarization to 2 factors: (1) mirror reflections at angles other than 90 degrees were causing mixing of polarization states, and (2) optical imperfections in the sampling lens were causing some polarization scrambling. Use of quarter and half-wave compensator optics can thus be used to correct such effects.
When changing the sample to bovine tendon (frozen after harvesting; then thawed in phosphate buffered saline before measurement) a high degree of depolarization was observed at all orientation angles with the system arrangement in
The flowcharts in
The light reflected from the structures within the tissue can be collected via a second polarization preserving optical fiber (e.g., fiber 1609 in
Once Target and Threshold values are determined, the polarization of the light can optionally be oriented to be parallel to the linear organization of a target structure (e.g., oriented with the direction of linear organization in a tendon to undergo treatment). See Box 101. Of course, such “matching up” is optional and the starting measurements can begin at any polarization orientation. In either embodiment, the resulting polarization measurement (i.e., the measurement of the polarization of light reflected back from the tissue/structure being treated) is measured once it reaches the detector.
After the optional visual orientation, a polarization search (Box 103 and substeps) is performed. In the polarization search, the angle of polarizer 1601, see
Once, or even before, the LOCBi and DCBi have been determined, Target values are set for the percent change desired for the linearly oriented collagen. As stated, the values may be previously set values, or may be values selected by the user through a user interface. From the desired percent change, the “final linearly-oriented collagen birefringence,” or LOCBf, is calculated by:
LOCBf=LOCBi(1|Target/100) Equation 9
Next a Threshold value for the desired maximum allowable percent change in the DCBi is determined. Again, this can be a stored value, or can be selected through a user interface. From the maximum percent change the “minimum dermal collagen birefringence,” or DCBm, is calculated by;
DCBm=DCBi(1−Threshold/100) Equation 10
After the above values are determined, treatment of the tissue/biological structure(s) begins. See Box 109. As explained throughout, the particular treatment that is monitored by the current invention should not be taken as limiting. In particular embodiments, the treatment comprises RF energy with surface cooling.
Simultaneous with the treatment application, steps 110 through 115 are performed in particular embodiments. Thus repeated birefringence measurements with the polarization-rotating device alternately set the “0” and “45” positions are done. The birefringence measurements are optionally performed at a rate that is high (e.g., in a millisecond time scale) compared to the effect of the treatment. Alternatively, the treatment application and birefringence measurements can be performed sequentially, with each treatment step being small (e.g., less than 1/10th of the target percent change) compared to the overall desired treatment level. In various embodiments, the monitoring footprint is smaller than the treatment footprint, while in other embodiments, the monitoring footprint is optionally the same size as or even bigger than the area being treated. It will be appreciated that in some embodiments, the monitoring can be done at numerous set positions simultaneously or sequentially during the treatment to monitor a broader area of the treatment footprint.
As indicated in steps 114 through 116, treatment is stopped when either the birefringence measurement with the polarization-rotating device set to the “45” position falls below the target setting, LOCBf or when the birefringence measurement with the polarization-rotating device set to the “0” position falls below the minimum setting, DCBm, Alternately, a secondary threshold can be used to signal a stop in treatment. For example, the secondary threshold may be based on the length of time of treatment or the total energy deposited.
In addition, a feedback loop is optionally used to independently adjust the amount of heating (energy) or cooling delivered to the tissue being treated to maximize the desired changes in LOCB while minimizing the undesirable effects on DCB.
Other Methods and Algorithms for Monitoring Birefringence
Besides the measurements and computed functions described elsewhere in this document for assessing tissue birefringence (e.g. DoLP, DoVP, DoHP, Δθ), numerous alternative methods and functions may also be effective. In order to further describe these measurements and methods, three angles are considered: (1) δ, the angle between the linear polarization axes of the excitation and detected light, (2) φ, the detection polarization angle (relative to vertical polarization), and (3) γ, the angle of rotation of the sample within the sample holder (positioned just above the sample lens). In what follows, the detected light intensity as a function of angles is denoted as Iδ(φ,γ). In certain embodiments described above, measurements made at different detection polarization angles, φ, were used to compute a function such as the degree of polarization (DoP), and then the dependence of the DoP on the sample angle, γ, was used as an indicator of sample birefringence. More generally, however, a DoP function can be determined by selecting one variable out of any of δ, φ, or γ and making at least 2 measurements of detected intensity as a function of this variable. Then, by choosing a 2nd variable out of the same set (δ, φ, and γ) and measuring the DoP function at 2 or more different values, the birefringence of the sample may be assessed.
In one embodiment, the angle between the linear polarization axes of the excitation and detected light, g is varied between two angles, 90 degrees apart. The DoP function is computed from these two measurements according to:
DoP(φ,γ)=Ix(φ,γ)/I(φ,γ) Equation 11
where I(φ,γ)=Ix(φ,γ)+Ix+90(φ,γ). The detection polarization angle, φ, is then varied across a range of angles with DoP being re-measured at each new angle. A measurement of porcine skin is shown in
DoB(φ,γ)=DoP(φ1,γ1)−DoP(φ2,γ2) Equation 12
Rather than varying the detection angle, φ, to determine the degree of birefringence, the sample orientation angle, γ, could instead be varied. A comparison of
I=I
x
+I
x+90 Equation 13
In many cases, it will be useful to use the angle-independent intensity, I, to normalize the angular-dependent intensities, Iδ(φ,γ) in computing a DoP function, so that the function is independent of the intensity of the light source used to perform the measurement.
Alternate DoP functions include ratios of the intensities measured at 2 angles:
DoP=Iδ1(φ1,γ1)/Iδ2(φ2,γ2) Equation 14
where at least one of the angles δ, φ, and γ is different for the two measurements. In one embodiment a ratio of the intensities measured with the angle δ at 2 values 90 degrees apart is used as the DoP function:
DoP=Iδ(φ1,γ1)/Iδ+90(φ1,γ1) Equation 15
In a similar manner the DoB function is defined as any combination of at least two measurements of DoP. In many cases the measurements of DoP will include 2 measurements at angles (e.g. δ, φ or γ) that are 45 degrees apart. This is because for a uniaxial birefringent material such as collagen, the maximum and minimum birefringence are expected to occur 45 degrees apart. In one alternate embodiment, the DoB function is computed from a ratio of DoP measurements determined at 2 or more angles:
DoB=DoP(1)/DoP(2) Equation 16
Instrument Calibration
Besides the sample being measured, components of the instrument may also cause depolarization of the light being measured. Half-wave and quarter-wave plates may be used to compensate for this depolarization. For example, it is expected that when a mirror is used as the “sample” the DoLP should have a unity value at all orientation angles. Referring to “FIG. 2”, for example, with a mirror on the sampling lens, SL, the compensators, C1 and C2, can be rotated about the axis of the transmitted light to maximize the measured DoLP. This process is then repeated at all excitation polarization angles to be measured.
Alternatively, or in addition to the use of compensator optics, numerical methods for correcting the measured birefringence may also be applied. In one embodiment a multiplicative correction is determined using a mirror in place of the sample, and in subsequent measurements the correction is applied to other sample types. Example algorithms for applying multiplicative correction to the measured intensity, I, are:
where the superscripts S and M refers to the sample and mirror, respectively and the subscript refers to the polarization angle (any of δ, φ, or γ). In the absence of a subscript, the symbol I refers to the angle-independent intensity, which may be computed according to:
I
S
=I
0
S
+I
90
S Equation 18 a
I
M
=I
0
M
+I
90
M Equation 18b
In other embodiments, the numerical correction algorithm that is suitable may be additive rather than multiplicative:
In further embodiments, a correction algorithm with both additive and multiplicative terms is suitable:
Correction factors a and d may be determined by using a mirror in place of the sample and setting the relative angle between the excitation and detection polarization axes, δ, to zero. Correction factors b and c may also be determined using a mirror in place of the sample, but with the angle δ set to 45 degrees. The correction factors may then be computed from the mirror measurements according to:
where parentheses are used to indicate the angle δ.
The above-described algorithms employ a mirror in place of the sample with the expectation that the mirror will reflect the excitation light without substantially depolarizing it. In an alternative embodiment a material that is expected to be fully depolarizing is instead employed as the calibration standard. One standard suitable for this purpose is a Teflon block. The Teflon block may optionally include a material embedded in the block that forces the excitation photons to travel through a long path before reaching the detection optics, thereby ensuring substantial depolarization of the detected light. Suitable materials are substantially non-transmissive of the excitation light. An example of such a material is a strip of black ABS plastic, embedded to a depth of several millimeters in the Teflon block.
In other embodiments of the invention, reference materials providing known amounts of depolarization are employed, such as quarter and half wave plates. In other embodiments, combinations of standards are measured, where to standards provide multiple levels of known depolarization.
In yet further embodiments of the invention, self-correcting algorithms are applied, that allow multiple measurements made on the same sample to be combined to compensate for instrument imperfections. One such algorithm is described in Example 5. In this example, measurements of Iδ on porcine skin as a function of φ are collected at two sample orientations, γ=0° (
The resulting function, Rδ(φ), shown in
The description of various embodiments of the systems/devices of the invention and their uses herein presents the basic components of the invention in a number of exemplary monitoring arrangements. In various such illustrations, the embodiment is described as arranged to monitor (e.g., as for tracking progress of a treatment) a tissue structure such as collagen in a tendon. In other illustrations, the embodiment is described as arranged to monitor a tissue beneath another tissue (e.g., a tendon beneath a dermal skin layer or a dermal collagen layer beneath the epidermis). In yet other illustrations, the embodiment is described as arranged to monitor both an underlying structure (e.g., a tendon, etc.) and an overlying layer structure (e.g., a dermal layer of collagen) as for monitoring a treatment that could possibly affect both layers (e.g., a transdermal thermotherapy application, e.g., via RF treatment). Of course, it will be appreciated that the various component arrangements in the embodiments should not necessarily be taken as limiting. Also, as further explained herein, the monitoring done by/through use of the embodiments herein can be to monitor treatment to an overlying structural layer or to an underlying structural layer, or to more than one structural layer. The invention can also be used to monitor treatment other than thermotherapy, etc. Finally, while the various embodiments present several devices/components and arrangements, it will be appreciated that not all such features or arrangements are necessarily present in all embodiments unless specifically stated.
An overview of several basic electrical components present in various embodiments herein is shown in
As stated previously, not all embodiments will necessarily comprise all elements/components listed herein or described in
It will also be appreciated that the digital and analog signals labeled in the Figures should not be taken to indicate strict requirements and that any of the various connections is optionally analog or digital. Digital signals are convenient for long-distance corruption-free transmission of signals, while analog signals are more often used over shorter distance to accomplish the direct interface with mechanical or optical components.
The use of an excitation polarizer, e.g., polarizer 1601, and its controller, e.g., controller 1701, are also optional in some embodiments. In some embodiments, if the light source is already inherently polarized (as is typical for lasers), then these components can be optional. Furthermore, in some embodiments, even if an excitation polarizer is included, its controller is optional. Similarly, in some embodiments a controller for the detection polarizer is optional.
The location of the polarization rotator (e.g. 1602 in
Although optical fibers (e.g., 1604 and 1609 in
In the various embodiments, a lens (e.g., detection lens 1606) to couple light into the detector (e.g., detector 1605) can also be optional. In some embodiments, if the active area of the detector were large enough, the need for such a lens would be removed. However, because there is generally a trade-off between the size of the active area of a detector and its dark noise, the focusing of light onto a detector with small active area is frequently desirable to achieve highest signal to noise ratios.
Additional components and arrangements of components in the systems of the invention are described throughout. For example,
Light Sources
In typical embodiments herein, the monitoring of tissue (e.g., as in tissue treatment through change in particular biological structures) is accomplished by light excitation and detector or camera observation. It will be appreciated that the invention is not necessarily limited by particular type or specific example of illumination used. Thus, in various embodiments, the light source can comprise, e.g., a laser, an edge-emitting laser diode (e.g., as opposed to a vertical cavity emitting laser diode, VCSEL), a resonant cavity LED, a gas laser (e.g. HeNe), a Nd-YAG laser (e.g., 1064, 532, or 355 nm), an YLF laser (e.g., 1053), a non-laser excitation source such as an LED, halogen or xenon arc lamp, etc.
In the various embodiments, the light source utilized can comprise a monochromatic light of a wavelength that allows for deep penetration into tissue (for example a light having a wavelength of from about 800 to about 1100 nm). Those of skill in the art will be familiar with numerous light emission devices (e.g., vertical cavity surface emitting lasers, VCSEL, having a wavelength of about 850 nm) that can be used in various embodiments of the invention. Depending upon, e.g., the type of tissue to be monitored, whether the monitoring is done topically, endoscopically, or arthroscopically, etc., the intensity/power of the light can be correspondingly chosen or adjusted.
In particular embodiments, the wavelength of light emitted by the light source falls within the range of 700 to 1100 nm. This wavelength region is bracketed on the short wavelength side by regions of strong hemoglobin absorption and on the long wavelength side by increasingly strong water absorption bands. The relatively low tissue absorption observed within the 700 to 1100 nm range allows light to penetrate below the skin layer to probe underlying structures in particular embodiments. Photon penetration depth into a tissue can depend on the scattering and absorption coefficients at the laser wavelength. The optical properties of tissue have been well characterized (see, e.g. “Optical-Thermal Response of Laser Irradiated Tissues,” ed. A. J. Welch, M. van Gernert, Springer, 1995) and many theoretical models have been developed to estimate tissue penetration (see, e.g. “Photon Migration in Tissues,” ed. Britton Chance, Springer, 1989). Furthermore, the penetration depth of detected photons can also depend on the source-detector spacing as discussed further herein.
In some embodiments of the invention, regions of strong absorption by collagen are specifically targeted. Thus, collagen absorption bands can be selectively targeted through larger birefringence effects and use of dichroism effects. Selective absorption by collagen can sometimes be difficult to achieve because in the UV region, other proteins as well as water will contribute to any measured tissue absorbance (or reflectance). Nonetheless, the enhancement of the birefringent effect observed in the UV justifies the choice of this wavelength region in particular embodiments. This is particularly true in applications where superficial collagen structures, such as the dermis, or connective tissue lying just below the skin surface (e.g. elbow) are being targeted. In such cases, the strong absorption of the excitation light can actually serve as an advantage, preventing interference from deeper-penetrating photons which will have had greater opportunity to depolarize through scattering.
Use of UV dichroism in some embodiments of the current invention can require the use of an excitation source(s) with access to a range of wavelengths. Suitable sources can include: (1) a plurality of discrete wavelength sources, (2) tunable sources, and (3) broadband sources whose wavelength region is selected or tuned by a secondary mechanism, such as an optical filter. In some embodiments, the light source can consist of a pair of laser diodes with emission wavelengths at 340 and 400 nm. Collagen absorption at 340 nm is high compared to absorption at 400 nm. See, e.g., Georgakoudi, et al., “NAD(P)H and Collagen as in Vivo Quantitative Fluorescent Biomarkers of Epithelial Precancerous Changes” Cancer Research, 62: 682-687, 2002. The difference between the birefringence observed at the two wavelengths can thus be used as the birefringence signal of interest. Otherwise, the implementation of the invention can be similar to that described for other embodiments herein.
As an alternative to the use of linearly polarized light, circularly polarized light can also be employed in the embodiments herein. Although in particular applications, the use of circularly polarized light can make it more difficult to distinguish between the birefringence due to collagen in skin and that in connective tissue, the triple helical nature of collagen is particularly suited to interact with circularly polarized light and, thus, the increased ease of making the measurement makes its usage beneficial in some embodiments. In such embodiments, no alignment of the polarization relative to the sample is typically necessary, and the measured signal is the differential absorption of the “left” and “right” circularly polarized light.
In other embodiments of the invention, a near infrared protein vibrational absorption band is targeted. For example, by the choice of a light source at 1680 nm, collagen amino acid C—H vibrational absorption can be targeted. Birefringence may thereby be enhanced. Although lipid and water absorption can possibly also contribute to the light absorbance in this spectral region, such contributions can be accounted for in the monitoring processes.
Lenses
In the various embodiments herein, a number of different lenses and lens types are optionally used. For example, split sampling lenses, which are described in more detail above, are used in some embodiments herein. See, e.g.,
Polarizers
In various embodiments herein, the light used to monitor the tissue can be generally substantially linearly polarized from an emitting device (e.g., a laser). However, particular embodiments can also optionally include a polarizer (e.g., polarizer 1601 in
While the rotation of the polarization can be accomplished by a number of ways, certain embodiments rotate the polarizers and/or polarization rotator either manually or mechanically. Thus, in particular embodiments herein, a polarizer and/or a polarization rotator in a suitable housing is rotated by a suitable DC motor or the like, operating at a speed coordinated with the image capture component. One embodiment of the polarization rotator consists of a wave plate (e.g. half wave plate, quarter wave plate) mounted in a rotatable housing. In yet other embodiments, other devices, such as liquid crystals (such as, but not limited to, those manufactured by Meadowlark Optics (Frederick, Colo.)) or electro-optic or acousto-optic devices (such as, but not limited to, those manufactured by Hinds Instruments (Hillsboro, Oreg.)) can be used to rotate the polarization of the light. With such devices, the polarization can be rotated by varying the voltage or acoustic pulses across the device. Again, control of the rotation can be done manually by a user or can be controlled by the computer component (which, in turn, is optionally controlled by input from the user).
Detection Devices
In the various embodiments herein, the reflected light that returns from the tissues/structures being monitored is captured in a detection device. In turn, the detection device typically relays such information to the computer component of the system. The detection device can comprise, e.g., a CCD camera or the like. Those of skill in the art will be familiar with numerous types and examples of detection devices capable of capture of light emission that can optionally be used with the current invention. Recitation of a particular type or example of detection device in various illustrations herein should therefore not be taken as limiting. For example, the detecting device of the system/devices herein can comprise, e.g., a PIN photodiode (e.g., operated in either photovoltaic or photocurrent modes), an avalanche photodiode, a phototransistor, a photomultiplier tube, or a CMOS array. In the 300-1100 nm spectral range silicon is generally the active detector element for photodiodes. Beyond 1100 nm, silicon becomes unresponsive and alternative materials are typically used. Indium Gallium Arsenide (InGaAs) is an optional choice for detection in the 800-2500 nm range. Germanium is alternate active material for detection in the near infrared spectral region. Thus, various detector devices herein, depending upon the embodiment, can comprise one or more of such elements.
Computer
As noted above, the various components of the present system can be coupled to an appropriately programmed processor or computer that functions to instruct the operation of these instruments in accordance with preprogrammed or user input instructions, receive data and information from these instruments, and interpret, manipulate and report this information to the user. As such, the computer is typically appropriately coupled to these instruments/components (e.g., including analog to digital or digital to analog converters as needed).
The computer optionally includes appropriate software for receiving user instructions, either in the form of user input into set parameter fields, e.g., in a GUI, or in the form of preprogrammed instructions, e.g., preprogrammed for a variety of different specific operations. The software then converts these instructions to appropriate language for instructing the correct operation to carry out the desired operation (e.g., of light illumination and birefringence capture, autofocusing, etc.).
The computer also optionally receives the data from one or more sensors/detectors included within the system, and interprets the data, either provides it in a user understood format (e.g., on a display or computer printout), or uses that data to initiate further instructions, in accordance with the programming, e.g., such as in control of illumination, temperatures, rotation of polarizers, and the like.
In embodiments of the present invention, the computer typically includes software for the monitoring and control of light illumination and capture. Additionally the software is optionally used to control movement of the illumination/capture footprints over a tissue surface, e.g., in coordination with the treatment being monitored. The computer also typically provides instructions, e.g., to any heating/cooling component and autofocus system, etc.
Any controller or computer optionally includes a monitor which is often a cathode ray tube (“CRT”) display, a flat panel display (e.g., active matrix liquid crystal display, liquid crystal display), or the like. Data produced from the current systems, e.g., degree of birefringence or change in birefringence of an area, is optionally displayed in electronic form on the monitor. Additionally, the data gathered from the system can be outputted in printed form. The data, whether in printed form or electronic form (e.g., as displayed on a monitor or deposited on tape, CD, or disc), can be in various or multiple formats, e.g., curves, histograms, numeric series, tables, graphs and the like.
Computer circuitry is often placed in a box which includes, e.g., numerous integrated circuit chips, such as a microprocessor, memory, interface circuits. The box also optionally includes a hard disk drive, a floppy disk drive, a high capacity removable drive such as a writeable CD-ROM, and other common peripheral elements. Inputting devices such as a keyboard or mouse optionally provide for input from a user and for user selection of sequences to be compared or otherwise manipulated in the relevant computer system.
It will be appreciated that the computer component in the systems/devices herein does not necessarily refer to a Personal Computer (PC), but can also or instead comprise a microcontroller or microprocessor.
Automation
Although the methods of the invention can be performed manually, in particular embodiments, such steps as placement of the light and detection components are performed in an automated fashion. Thus, the light emission and capture, polarization changes, adjustment of the light penetration and location on the tissue, etc. are all optionally automated. For example, polarization-rotating devices under electrical control are well known in the field of optics. Automation allows the birefringence measurements to be performed rapidly, so that near-continuous feed-back may be provided for a treatment method being monitored. Furthermore, the birefringence measurement can be performed simultaneously and in close proximity with the application of RF energy due to the weak interaction between RF and optical fields.
Housing
Placement and movement of the various components of the devices/systems herein is optionally controlled and secured by, e.g., an armature, scaffolding, or housing in which the components are located. In particular embodiments, the components, or at least part of the components, are handheld. Handheld and other manipulable components can be used to move over an area to be monitored (e.g., a subject's skin surface) or within an area to be monitored (e.g., within a subject's body). In some embodiments, one or more component of the system comprises a component that can be endoscopically or arthroscopically inserted into a subject. In some embodiments, the systems herein can optionally comprise one or more components to help stabilize and/or locate the one or more other components of the system in relation to the tissue area being monitored. Thus, some embodiments can comprise stabilizers, mounted platforms (e.g., for a subject), straps, etc.
Thus, it will be appreciated that the various components herein, e.g., the light emitting components, heating/cooling components, polarizers, etc., are typically arranged on a scaffolding or framework and optionally enclosed within a housing. The particular configuration of such framework and/or housing can optionally vary in different embodiments based upon, e.g., the particular components, their size, etc. In typical embodiments however, the framework keeps the various components secure and in the proper location and orientation while also optionally aiding in the movement of the components when necessary.
Heating and Cooling
In some embodiments, the systems herein comprise a heating/cooling component (and optionally a heating/cooling control component) having heating/cooling capabilities. In some embodiments, the heating/cooling component can optionally regulate the temperature of the other components of the systems/devices, e.g., the light emitter, the computer, etc. For example, the heating/cooling component can optionally regulate the temperature of the CCD camera. Such temperature control elements can also optionally help regulate the surface of the tissues whose treatment is being monitored.
Probe Geometry
As explained above, different embodiments of the invention can optionally comprise different arrangement of components in the systems/devices. Thus, some embodiments of the invention use more than one source-detector separation in the probe geometry to provide a supplemental or independent method of targeting particular collagen-containing structures. In one embodiment, two source-detector separations are employed. For example, the first source-detector separation and be approximately 1-2 mm, thereby causing the measured birefringence to be primarily due to dermal collagen, while the second source-detector separation can be approximately 2-5 mm, so that the measured birefringence reflects contributions from both dermal collagen and underlying targeted connective tissue structures.
Polarization-sensitive methods of measuring the structure and conformation of molecules are well known by those of skill in the art. For example, circular dichroism can be used as a method of measuring changes in protein structure. This technique involves measuring the differential absorption of left and right circularly polarized light. Chiral (or “optically active”) molecules will respond differently to these two types of polarization, particularly in wavelength regions matching the energy difference between electronic or vibrational states of the molecule. Far-UV (<250 nm) circular dichroism, in which wavelength range amide electronic bonds are absorptive, can be of particular use in probing the secondary structure of proteins, such as distinguishing alpha-helical, beta-sheet, and globular conformations of proteins. Near-UV (>250 nm) circular dichroism is more sensitive to the protein conformation surrounding aromatic amino acids (tryptophan, tyrosine, phenylalanine) and di-sulfide linkages between cysteine residues.
Linear dichroism is useful for the optical characterization of samples containing molecules aligned in a particular direction. Thus, in some embodiments of the current invention, the differential absorption of linearly polarized light (“parallel” and “perpendicular”) is measured. In wavelength regions matching the energy difference between electronic or vibrational states of the molecule, those molecules oriented with a transition dipole parallel to the light polarization will absorb parallel polarized light more strongly than perpendicularly polarized light.
Linear and circular dichroism are two examples of the more general optical properties of birefringence. In birefringent materials, light of different polarizations travels through the material at different speeds. For linearly polarized light, interaction with a birefringent material can result in rotation of the polarization of the light. The interaction of circularly polarized light with birefringent materials results in elliptically polarized light. Birefringence is referred to as dichroism when light at different wavelengths responds differently to the interaction with the birefringent material. Dichroism effects are generally strongest in spectral regions coincident with the energy separating electronic or vibrational molecular transitions, because in these regions the index of refraction is most rapidly changing. As explained throughout, the current invention uses birefringence in particular embodiments. See above.
The methods and systems/devices of the invention can be used in a number of different treatment programs for a number of different medical conditions. Thus, it will be appreciated that recitation of particular treatments or the like herein should not necessarily be taken as limiting. Heat and cold treatments have been widely used in the medical field and numerous well-established therapeutic modalities exist that take advantage of such treatments. See, e.g., Hayashi, et al., “The effect of thermal heating on the length and histologic properties of the glenohumeral joint capsule” Am J Sports Med, 25(1):107-12, 1997; Naseef, et al., “The thermal properties of bovine joint capsule. The basic science of laser- and radiofrequency-induced capsular shrinkage” Am J Sports Med, 25(5):670-4, 1997; and Oloff, et al., “Arthroscopic monopolar radiofrequency thermal stabilization for chronic lateral ankle instability: a preliminary report on 10 cases” J Foot Ankle Surg, 39(3):144-53, 2000. Light, ultrasound, radio frequency, shockwaves, magnetism and other forms of energy have been used to modify tissue temperatures in order to achieve benefits such as stimulation of different biological responses, ablation of tissue, or induction of necrosis. For instance, wound healing response stimulation, collagen stimulation, collagen denaturation, collagen contraction, disruption of fat cells for aesthetic purposes, reduction of benign or malign tumors and the like are all well established medical procedures achieved by temperature variation. The current invention aids such procedures, and others, and increases their usefulness and applicability by allowing monitoring (optionally real time monitoring) of the changes brought about by the treatments. Moreover, in typical embodiments, the current invention can be non-invasive (or minimally invasive) in regard to the tissue being treated, thus avoiding more damaging monitoring processes such as biopsies.
As detailed above, the current invention can, in many embodiments, be used to monitor treatment of collagen structures in various tissues. Besides water, collagen is the main component of skin, cartilage, and connective tissue (including, ligaments, tendons, and the like). Trauma, ageing, and other clinical entities can damage collagen's structure through thinning and disorientation of collagen fibers, myxoid degeneration, hyaline degeneration, chondroid metaplasia, calcification, vascular proliferation, and fatty infiltration, etc. See, e.g., Hashimoto, et al., “Pathologic evidence of degeneration as a primary cause of rotator cuff tear” Clin Orthop Relat Res, (415):111-20, 2003.
As is well known in the art, thermotherapy can cause collagen denaturation and contraction by well-known mechanisms of action. See, e.g., Allain, et al., “Isometric tension developed during heating of collagenous tissues. Relationships with collagen cross-linking” Biochim Biophys Acta, 533(1):147-55, 1978; Allain, et al., “Isometric tensions developed during the hydrothermal swelling of rat skin” Connect Tissue Res, 7(3):127-33, 1980; Chen, et al., “Heat-induced changes in the mechanics of a collagenous tissue: isothermal, isotonic shrinkage” J Biomech Eng, 120(3):382-8, 1998; Cooper, et al., “Correlation of thermal properties of some human tissue with water content” Aerosp Med, 42(1):24-7, 1971; Hayashi, et al., “The biologic response to laser thermal modification in an in vivo sheep model” Clin Orthop Relat Res, (373):265-76, 2000; Hayashi, et al., “The effect of nonablative laser energy on joint capsular properties. An in vitro mechanical study using a rabbit model” Am J Sports Med, 23(4):482-7, 1995; Hayashi, et al., “The mechanism of joint capsule thermal modification in an in-vitro sheep model” Clin Orthop Relat Res, (370):236-49, 2000; and Hayashi, et al., “The effect of nonablative laser energy on the ultrastructure of joint capsular collagen” Arthroscopy, 12(4):474-81, 1996.
The use of collagen denaturation/contraction through energy-based treatment modalities can be used in a number of important applications in fields ranging from neurosurgery and orthopedics to ophthalmology, aesthetic medicine, and surgery of the gastrointestinal tract. See, e.g., Avitall, et al., “Physics and engineering of transcatheter cardiac tissue ablation” J Am Coll Cardiol, 22(3):921-32, 1993; Avitall, et al., “The safety and efficacy of multiple consecutive cryo lesions in canine pulmonary veins-left atrial junction” Heart Rhythm, 1(2):203-9, 2004; Avitall, et al., “Linear lesions provide protection from atrial fibrillation induction with rapid atrial pacing” J Cardiovasc Electrophysiol, 13(5):455-62, 2002; Brodkey, et al., “Reversible Heat Lesions With Radiofrequency Current. A Method Of Stereotactic Localization” J Neurosurg, 21:49-53, 1964; Daoud, et al., “Catheter ablation of ventricular tachycardia” Curr Opin Cardiol, 10(1):21-5, 1995; Lesh, “Interventional electrophysiology—state-of-the-art” Am Heart J, 126(3 Pt 1):686-98, 1993; Moraci, et al., “Trigeminal neuralgia treated by percutaneous thermocoagulation. Comparative analysis of percutaneous thermocoagulation and other surgical procedures” Neurochirurgia (Stuttg), 35(2):48-53, 1992; Saxon, et al., “Results of radiofrequency catheter ablation for atrial flutter” Am J Cardiol, 77(11):1014-6, 1996; Seegenschmiedt, et al., “The current role of interstitial thermo-radiotherapy” Strahlenther Onkol, 168(3):119-40, 1992; and Sweet, et al., “Controlled thermocoagulation of trigeminal ganglion and rootlets for differential destruction of pain fibers. 1. Trigeminal neuralgia” J Neurosurg, 40(2):143-56, 1974. Those of skill in the art will be familiar with other applications/procedures utilizing temperature induced denaturation/contraction of collagen. Such applications/procedures are optionally monitored through use of the methods and systems of the current invention.
One common procedure to denature/contract collagen uses temperature generated through radiofrequency energy. Such energy can be applied to an area to be treated, e.g., through direct contact with the targeted structure via a surgical incision. Recently, some technologies have offered the ability of providing therapeutic heat levels through an overlying tissue (e.g., heat/energy applied transcutaneously, transsynovially, transmucosally, transintimaly, etc.) with the goal not only of treating the desired collagen but also preserving the integrity of non-targeted structures (e.g., skin, subcutaneous tissue, and other tissues depending on the targeted structure). See, e.g., Chen, et al., “Heat-induced changes in the mechanics of a collagenous tissue: isothermal, isotonic shrinkage. J Biomech Eng,” 120(3):382-8, 1998; Naseef, et al., “The thermal properties of bovine joint capsule. The basic science of laser- and radiofrequency-induced capsular shrinkage” Am J Sports Med,” 25(5):670-4, 1997; and Oloff, et al., “Arthroscopic monopolar radiofrequency thermal stabilization for chronic lateral ankle instability: a preliminary report on 10 cases” J Foot Ankle Surg, 39(3):144-53, 2000. However, visualization of the treated structure is often impossible and, even when direct visualization is possible, the fact that most collagen changes are not visible to the naked eye is problematic. Various embodiments of the current invention are especially useful in monitoring such procedures. The invention recognizes the baseline condition of a structure while also determining the impact of the provided treatment on the structure and optionally on other underlying or overlying structures. For example, by distinguishing between the collagen in superficial layers of tissue and the collagen in deeper structures, some embodiments of the current invention can aid in defining the clinical endpoint of a treatment based on changes to the structure being treated and/or on changes to nearby structures.
The fundamental unit of collagen consists of tropocollagen polypeptides organized into a triple helix. This triple helical structure is stabilized by intramolecular bonds, principally hydrogen bonds. The triple helices are further organized by intermolecular bonding. See, e.g., Arnoczky, et al., “Thermal modification of connective tissues: basic science considerations and clinical implications” J Am Acad Orthop Surg, 8(5):305-13, 2000. In tissues such as ligaments and tendons, the association of neighboring helices is largely parallel, resulting in unidirectional strands, while in other tissues such as capsular and dermal collagen, the collagen helices are less unidirectional, being instead confined within a plane.
Application of heat to tissue collagen in the range of 60 to 90° C., results in denaturation of the higher order protein structure. The intramolecular hydrogen bonds stabilizing the triple helices are particularly susceptible to disruption, while the intermolecular bonds are generally more heat stable. Therefore, application of heat has the effect of unraveling the triple helical structure of collagen while maintaining overall strand integrity. The result for ligaments, tendons, and other linearly oriented collagen structures is shortening of the collagen along the long axis and thickening of the collagen along the short axis. See, Arnoczky, supra. For collagen oriented within a plane, such as capsular and dermal collagen, contraction of the planar sheet is observed in response to heat, with thickening in the direction perpendicular to the plane.
During thermal treatments of tissue, the extent of collagen denaturation/contraction is affected by the temperature reached and/or the duration of the treatment provided. See Wall, et al., “Thermal modification of collagen.” J Shoulder Elbow Surg, 8(4):339-44, 1999. In addition, due to the variation in collagen composition, particularly the extent of intramolecular cross-linking, the extent of collagen denaturation/contraction can be difficult to predict in advance even if the temperature profile is fully characterized. Thus, various embodiments of the current invention are beneficial to such treatments because they can monitor the presence and extent of any denaturation that occurs during or as a result of treatment and thereby allows medical practitioners to more accurately administer treatment.
Monitoring of Tissue Changes Arising from Chemical/Cosmeceutical Use
Treatment of tissues through epidermal/dermal or percutaneous application of lotions, creams, or other substances is wide spread in the general populace and within the medical community. Many conditions can be treated by the application of different chemicals that are anticipated to induce changes in tissues including the skin, subcutaneous fat, or connective structures. See, e.g., Fang, et al., “Efficacy and irritancy of enhancers on the in-vitro and in-vivo percutaneous absorption of curcumin” J Pharm Pharmacol, 55(5):593-601, 2003, and Schottelius, et al., “An aspirin-triggered lipoxin A4 stable analog displays a unique topical anti-inflammatory profile” J Immunol, 169(12):7063-70, 2002. For instance, the cosmetics industry provides a wide variety of so called “cosmeceuticals” to increase collagen production. See, e.g., Katayama, et al., “A pentapeptide from type I procollagen promotes extracellular matrix production” J. Biol. Chem., 268(14):9941-9944, 1993. However, no objective measurement of effectiveness has previously been available to users. Thus, the current invention can optionally be used to monitor changes, if any, caused by use of cosmeceuticals or the like. For example, using the present invention, a baseline measurement can be taken of the collagen status of a tissue, the cosmeceutical or other putative treatment can then be applied/performed and additional measurements of the collagen status can be performed to detect any change. Again, it will be appreciated that the invention can monitor change before the treatment, during the treatment, and/or after the treatment of the tissue.
The current invention in similar or alternate embodiments can be used to track other optical properties of tissue for similar purposes (i.e., fluorescence, turbidity and the like). By applying same principles and concepts, but different optical properties and therefore equations, the current invention can be used to measure the baseline content of such a targeted tissue, measure its evolution over time (treated or untreated) and measure the impact of different therapeutic interventions.
For that purpose the current invention will take advantage of reflectance and transmittance of light as it is specific to various tissues. For instance fat has distinct properties than dermis (Near-infrared optical properties of ex vivo human skin and subcutaneous tissues measured using the Monte Carlo inversion technique C Rebecca Simpson et al 1998 Phys. Med. Biol. 43 2465-2478).
As a matter of examples and not to be taken as a limiting list, the following tissues could be monitored by the present invention in its preferred or alternate embodiments: urethra, vaginal wall, uterus, skin, fat, fascias, ligaments, tendons, cartilage, capsules, soft palate, turbines, gastrointestinal tract including sphincters, structures of the airway, and nerves among others.
By relying on a relative change in birefringence as a monitoring guide to therapeutic action, some embodiments of the invention avoid the pitfalls associated with attempts to non-invasively measure the absolute birefringence of collagen. In particular, skin and tissue are known to strongly scatter electromagnetic waves in the UV to IR range. With each scattering event, the light polarization becomes randomized to some extent, with the result that multiply scattered light may become entirely depolarized. The extent of polarization randomization will affect the size of the measured birefringence signal. Therefore, variations of tissue scattering properties observed from person-to-person or even site-to-site on the same person can make it difficult to make an absolute measure of birefringence of collagen through intervening tissue structures. In various embodiments of the present invention, however, each time the probe is applied, an initial determination of birefringence (as by either the DoP or polarization rotation methods described above) can be made, and RF energy (or any other energy source) can be applied to target a percent change in the birefringence. The number of times that the treatment is reapplied to the same tissue thus determines that net change in collagen denaturation. By relying only on a relative change in the birefringence, as induced by a therapeutic procedure, various embodiments of the present invention avoid the potential inaccuracy associated with an absolute measurement.
Use of the Invention with Various Treatments
As will readily be appreciated by those of skill in the art, the current invention can be used as a diagnostic and/or research tool or in conjunction with therapeutic/prophylactic modalities that aim at changing collagen characteristics. In such embodiments the invention can measure collagen's birefringence in various ways at a baseline and can be used for repeated measurements to establish changes in collagen content or characteristics within the studied tissue to determine the impact of a given intervention. As stated above, the treatment that is tracked with the current invention can treat one or more layers of tissue (e.g., collagen). In situations where only one structural layer is treated, such layer can be superficial to a structural layer that is to not be treated or vice versa. The treatments monitored through the current invention can be those that induce wound healing, induce collagen denaturation/renewal, induce collagen deposition, etc. Again, recitation of particular treatment methods/goals should not necessarily be taken as limiting.
In some embodiments, the invention provides a kit or an article of manufacture containing materials useful for the methods described herein and/or comprising examples of the systems/devices described herein. Such kits can optionally comprise one or more containers, labels, and instructions, as well components for monitoring of treatment.
The kits can also optionally comprise one or more light sources, polarizers, lenses, polarization rotators, fiber optics, light detectors, computers, etc. as well as optionally other components. The kits can optionally include scaffolding, armature or other organizational structures to controllably position and/or move the various components of the systems/devices of the invention.
In many embodiments, the kits comprise instructions (e.g., typically written instructions) relating to the use of the kit to determine and/or monitor changes in tissue (e.g., collagen). In some embodiments, the kits comprise a URL address or phone number or the like for users to contact for instructions or further instructions.
The following examples are offered to illustrate, but not to limit the claimed invention. It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
The instrument configuration diagrammed in
In the measurements, the input polarization angle was maintained at vertical (0 degrees). The orientation angle of the input polarization relative to the sample optic axis was changed by manually rotating the sample on top of the sampling lens (SL). The Stokes vector values were measured by manually rotating the polarizer (P2) in front of the detector, and manually recording the lock-in amplifier readings.
The “mirror” sample was a 1″ mirror suspended about 5 mm above the sampling lens. The “HWP” sample was a half wave plate placed directly over the sampling lens with a ½″ mirror placed on top of the half wave plate. The “Teflon” sample was an 8 mm thick, 1.5″ diameter disk of Teflon placed directly on top of the sampling lens. The “bovine tendon” sample was suspended about 3 mm above the sampling lens.
The results are summarized in Table 1. As expected, the “mirror” sample was unaffected by rotation relative to the input polarization. In contrast the “HWP” sample was strongly orientation dependent: both DoLP and θ decreased when the optic axis was rotated from 0 to 45 degrees. For this sample, the response was also measured at orientations between 0 and 100 degrees, in 5 degree increments. The results are displayed in
Also in this example, Teflon was used to test the effect of a non-birefringent but strongly scattering material. The DoLP in Table 1 indicates that the scattering in Teflon resulted in substantial depolarization of the laser light, but no orientation dependence was observed either for DoLP or 0.
The three bovine tendon measurements shown in Table 1 were performed on the same piece of tendon, but with re-hydration and repositioning of the sample between measurements. Although the detected light was substantially depolarized at both orientations, a reproducible reduction in DoLP from the 0 degree orientation to the 45 degree orientation was observed. In 2 of the 3 measurements, a substantial change in polarization rotation (θ) was also observed. It should be noted that not all bovine tendon samples that were tried showed significant orientation effects.
The instrument outlined in
A LabView (National Instruments, Austin, Tex.) computer program was written to sequentially set the voltage of the liquid crystal polarization rotator (PR in
An example measurement is shown in
Collagen birefringence is known to diminish with heating/denaturation. The “untreated” bovine tendon sample shown in
Example 3 demonstrates measurement of tendon birefringence through an intervening layer. The ability of measuring birefringence through an intervening layer (e.g., skin) is important in, e.g., non-invasive orthopaedic applications. In this example several skin “phantoms” were tested. These phantom materials included gelatin, Teflon® (DuPont, Wilmington, Del.) and Intralipid® (Kabivitrum, Alameda, Calif.) mixed with gelatin. Gelatin was used because it is composed of denatured collagen, the primary protein constituent found in skin. Teflon was used due to its ready availability in multiple thicknesses and the fact that, like skin, it is highly scattering and weakly absorptive at 808 nm. However, unlike skin, Teflon has little or no natural birefringence. 2% Intralipid in gelatin was used as a phantom mimicking the primary constituents of tissue (water, collagen, and fat) and having similar scattering properties to skin. See, e.g., T. L. Troy and S. N. Thennadil, “Optical Properties of Human Skin in the NIR Wavelength Range of 1000 to 2200 nm,” J. Biomed. Opt., 6:167 (2001). The measurements performed in Example 3 were done on the same system arrangement as that of Example 2.
Teflon was also examined as an intervening “skin” phantom layer. A series of different thicknesses of Teflon, ranging in thickness from 0.1 to 5 mm, were used. For each experiment, the Teflon sample was first placed in the sampling well and measured alone to verify that no significant birefringence effect was observed. After such measurement, a section of bovine tendon was placed on top of the Teflon, weighed down to keep the layers in close contact with each other, and a second measurement was performed. In addition to varying the thickness of Teflon through which the measurement was made, the gap between the sampling lens and the sampling well was varied in different experiments. Increasing this gap had the effect of increasing the overlap between the source beam and the detection cone, which in turn affected the depth of penetration of the measurement.
A measurement of tendon birefringence through a 0.5 mm thickness of Teflon is shown in
where Q, U, and I are as defined above in the specification. Determination of the amplitude of the change in the degree of polarization with sample orientation was found to be more reliable by simultaneously fitting the DoVP and DoHP curves than by fitting the DoLP curve alone. The DoVP and DoHP curves were fit to sine functions, with the angle set to 4 times the orientation angle, and further constrained to have relative phases separated by 45 degrees and the same amplitude.
Comparing
A measurement of tendon birefringence was also made through a skin phantom that had been reported to have similar scattering properties to human skin; namely 2% Intralipid. The Intralipid was embedded in gelatin in order to make a solid layer upon which a bovine tendon sample could be placed. Shown in
A measurement of birefringence of dermal collagen through an actual skin layer was done for Example 4. The component arrangement in Example 4 was the same as that shown in
For example 5, the birefringence of porcine skin was repeatedly measured as it was undergoing thermal treatment. The instrument was configured as diagrammed in
Fresh porcine skin was purchased from a local butcher and used on the same day (without freezing). Samples included some subcutaneous fat. A roughly 20 mm disk of skin was cut out with scissors and held in place with elastic straps with the skin side facing the window. The window was glued onto a 1″ OD plastic tube to make a small (˜10 mL) sample chamber. The sample chamber was filled with phosphate buffered saline (PBS) and a resistive heater and thermocouple attached to an aluminum disk were immersed in the PBS, above the sample. The resistive heater and thermocouple were attached to a temperature controller. A second thermocouple was placed inside the fat layer of the skin sample to monitor the actual skin temperature. A small stirring device was used to help maintain a uniform temperature within the heating bath.
The DoP function used for this example is shown in Equation 22. This function is a ratio of Iδ(φ)/I measurements collected with the sample orientation, γ, set at 0 (
DoB=Rδ=0(φ=−25°)−Rδ=0(φ=20°) Equation 23
The temperature of the porcine skin sample was raised in steps and monitored. The resulting DoB following each treatment step is shown in
A non-invasive measurement of the birefringence of skin on the forearm of a live subject is shown in
While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be clear to one skilled in the art from a reading of this disclosure that various changes in form and detail can be made without departing from the true scope of the invention. For example, all the techniques and apparatus described above may be used in various combinations. All publications, patents, patent applications, or other documents cited in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication, patent, patent application, or other document were individually indicated to be incorporated by reference for all purposes.
This application is a Continuation of Ser. No. 12/806,811, filed Aug. 19, 2010, which is a Continuation in Part of U.S. Ser. No. 12/380,014, filed Feb. 20, 2009, which claims priority to and benefit of U.S. Provisional Patent Application Ser. No. 61/066,593, filed on Feb. 20, 2008; and claims priority to and benefit of U.S. Provisional Patent Application Ser. No. 61/274,704 filed on Aug. 19, 2009, the disclosures of all of which are incorporated herein in their entireties for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61066593 | Feb 2008 | US | |
| 61274704 | Aug 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12806811 | Aug 2010 | US |
| Child | 14331044 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12380014 | Feb 2009 | US |
| Child | 12806811 | US |
