Patent Application
20070123776
The present invention relates to probes, especially ultrasonic probing devices that are operated or controlled using non-electrical transmission methods. More particularly, the present invention relates to an ultrasonic probing device with a miniature cross-section that is suitable for intravascular medical operations including diagnostics such as monitoring of coronal artery, or general vascular dimensions. The probing device is small enough to fit inside or be incorporated within a standard guidewire such as used in intervascular procedures.
Catheters having ultrasound capability at or adjacent to their tips that is affected by the transmittance of optical waves to and reception of optical signals from the tip of the catheter while converting the optical waves into ultrasonic waves and the ultrasound back into an optical signal are known in the art. An example of which is U.S. Pat. No. 5,944,687 “Opto-Acoustic Transducer for Medical Applications” disclosed by Benett et al. describing an optically activated transducer for generating acoustic vibrations in a biological medium. The transducer is located at the end of an optical fiber that may be located within a catheter. Energy for operating the transducer is provided optically by laser light transmitted through the optical fiber to the transducer. Pulsed laser light is absorbed in the working fluid of the transducer to generate thermal stress and consequent expansion of the transducer head such that it applies forces against the ambient medium. The transducer returns to its original state by a process of thermal cooling. Celliers et al. teaches in U.S. Pat. No. 6,022,309 “Opto-Acoustic Thrombolysis” a catheter-based device for generating an ultrasound excitation in biological tissue. Pulsed laser light is guided through an optical fiber to provide the energy for producing the acoustic vibrations. The optical energy is deposited in a water-based absorbing fluid, e.g. saline, thrombolytic agent, blood or thrombus, and generates an acoustic impulse in the fluid through thermoelastic and/or thermodynamic mechanisms. An additional patent disclosed by Sinofsky et al. named “Device for Use in Laser Angioplasty” discloses an apparatus for use in removing atherosclerotic plaque deposits in a blood vessel that comprises a high power laser, an elongated, flexible catheter adapted to be inserted into, and advanced through the blood vessel, a plurality of circumferentially arrayed optical fibers extending axially through the catheter, and an ultrasonic transducer at the distal end of the catheter for transmitting acoustical energy toward a selected area of the inner surface of a blood vessel in response to laser energy coupled through any one of the optical fibers and impinging upon the transducer. A detector proximal to the ultrasonic transducer is responsive to ultrasonic energy reflected from the blood vessel and produces a signal indicative of the tissue interfaces of the blood vessel. Laser energy can be transmitted from the high power laser through the same optical fiber used for the diagnostic procedure to ablate plaque in the blood vessel.
In a disclosure incorporated herein as a reference, PCT/IL02/00018 “Ultrasonic Transducer Probe”, Aharoni et. al. (not yet published) describe a compact cross-sectioned electromagneticl acoustic arrangement for generating and detecting ultrasound waves using an electromagnetic waveguide. The Acoustic generator comprises a source of electromagnetic radiation, a waveguide coupled to the source and at least one absorbing region defined in said waveguide, said region being selectively absorbing for portions of said radiation meeting at least one certain criterion and having significantly different absorbing characteristics for radiation not meeting said criterion, both of said radiation being suitable for conveyance through said waveguide, wherein said absorbing region converts said radiation into an ultrasonic acoustic field. Optionally, said region comprises a volumetric absorber. Alternatively or additionally, said region comprises plurality regions. The phenomenon of converting electromagnetic radiation to ultrasound is comprehensively described in PCT/IL02100018. It is emphasized that the devices described in the prior art differ from the acoustic generator described in PCT/IL02/00018 disclosure in at least one of the following aspects:
In addition, prior art primarily relies on technologies that require a relatively large cross-section. Consequently, a central guide wire is used in order to guide the devices into the artery. Therefore, these designs necessarily require a significantly larger diameter than the guide wire itself. The ability to reduce the cross-section of the device, for example if it can be made to the guidewire itself, has many significant advantages for intravascular diagnostics and in particular for monitoring coronal artery dimensions as well as other medical applications.
It is an object of the present invention to provide a new and unique ultrasonic transducer having a very small cross-section for diagnostics such as dimensional monitoring of an artery along its length.
It is another object of the present invention to provide a new and unique probe for diagnostics such as dimensional monitoring having a distributed array of sensing regions so as to monitor the variation of artery parameters over an extended artery length. The distributed array of sensing regions eliminates the need to mechanically relocate the device along in the artery in order to monitor artery cross-sectional parameters over a specified artery length.
It is thus provided in accordance with a preferred embodiment of the present invention a probing device for insertion into a duct having a physical structure to determine local parameters associated with the physical structure of the duct at a selected region of the duct, and in particular variations in the physical structure along a predetermined length of interest, the probing device comprising:
Furthermore, in accordance with a preferred embodiment of the present invention, at least some of said at least one of a plurality of transmitters and said plurality of receivers are combined in the form of receiving and transmitting transducers.
Furthermore, in accordance with a preferred embodiment of the present invention, at least some of the transducers are piezo-electric transducers.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said at least one of a plurality of transmitters, comprises an absorbing region within an optical fiber, the absorbing region made from material, which converts optical signals to acoustic signals. Furthermore, in accordance with a preferred embodiment of the present invention, each of said at least one of a plurality of transmitters, comprises at least one of a plurality of absorbing regions within an optical fiber, the absorbing regions made from material, which converts optical signals to acoustic signals.
Furthermore, in accordance with a preferred embodiment of the present invention, the absorbing regions are made of material that absorbs at different optical spectra, such that at least one of the absorbing regions are activated to generate acoustic signals at a certain optical spectrum, and other absorbing regions are activated to generate acoustic signals at one or more different optical spectra.
Furthermore, in accordance with a preferred embodiment of the present invention, the absorbing regions are made of material selected from the group containing: Copper-doped material with absorption spectrum at about 450 nm or shorter wavelengths, Alexandrite-doped material with absorption at about 850 nm or longer wavelengths, and Yitterbium-doped material with absorption in the range 1,000-1300 nm.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said plurality of receivers comprises at least one of a plurality of optical fibers through which light can traverse and be modulated by the echoes.
Furthermore, in accordance with a preferred embodiment of the present invention, each one of said fibers, serving as a receiver, includes a reflecting element that effectively limits the extents of the fiber.
Furthermore, in accordance with a preferred embodiment of the present invention, the reflecting element comprises a Bragg grating optical element.
Furthermore, in accordance with a preferred embodiment of the present invention, at least some of said fibers serving as receivers are staggered along the length of interest to sensitize them to different regions along the length of interest.
Furthermore, in accordance with a preferred embodiment of the present invention, signals are processed by subtracting signals of two detecting fibers, such that the resulting signal corresponds to their region where the two fibers do not overlap.
Furthermore, in accordance with a preferred embodiment of the present invention, said fibers, serving as receivers, each include two reflecting elements and two types of light propagating in the fiber effectively forming two detection channels; the distal reflecting element serves to effectively limit the extent of the fiber for one of the detecting channels, and the proximal reflecting element serves to effectively limit the extent of the fiber for the other detecting channel; the differential signal between these two channels effects a sensitive region local to the separation of the two reflecting elements.
Furthermore, in accordance with a preferred embodiment of the present invention, at least some of said sensitive local regions are staggered along the length of interest to sensitize them to different regions along the length of interest.
Furthermore, in accordance with a preferred embodiment of the present invention, received signals are processed to account for different phases in each receiver in conjunction with a knowledge of physical separation between the receivers so as to effect a circumferential resolution in the device.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a Bragg grating optical element, and the two channels are differentiated by wavelength.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a polarization-dependent reflector, and the two channels are differentiated by polarization.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a spatially selective element, reflecting one or more guided modes, and the two channels are differentiated by guided modes.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said plurality of receivers comprises at least one of a plurality of optical fibers through which light can traverse and be modulated by the echoes and which incorporates several wavelength-dependent reflectors, such that each effectively limits extent of a certain optical wavelength traveling in the fiber; the position of at least some of these reflecting elements is distributed along the length of the interest, sensitizing each wavelength to a different positions along the length of interest.
Furthermore, in accordance with a preferred embodiment of the present invention, the received signals are processed to account for the different phases in each receiver in conjunction with a knowledge of physical separation between the receivers so as to effect a circumferential resolution in the device.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said at least one of a plurality of transmitters, comprises at least one absorbing region within a multicore optical fiber, the absorbing region made from material, which converts optical signals to acoustic signals, and wherein at least one of the cores serve as at least one receiver.
Furthermore, in accordance with a preferred embodiment of the present invention, some of the cores serving to generate the acoustic signals have larger lateral cross section than those serving for detection.
Furthermore, in accordance with a preferred embodiment of the present invention, the cores in the said multicore optical fiber, serving as receivers, include a reflecting element that effectively limits the extent of each of the receiver cores and sensitizes each on to a different positions along the length of interest.
Furthermore, in accordance with a preferred embodiment of the present invention, the reflecting element comprises a Bragg grating optical element.
Furthermore, in accordance with a preferred embodiment of the present invention, said cores, serving as receivers, include two reflecting elements and two types of light propagating in each core effectively forming two detection channels; the distal reflecting element serves to effectively limit the extents of the core for one of the detecting channel, and the proximal reflecting element serves to effectively limit the extent of the core for the other channel; the differential signal between these two channels effects a sensitive region local to the separation of the two reflecting elements.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a Bragg grating optical element, and the two channels are differentiated by wavelength.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a polarization-dependent reflector, and the two channels are differentiated by polarization.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a spatially selective element, selectively reflecting one or more guided modes, but not reflecting other such modes, and the two channels are differentiated by different guided modes.
Furthermore, in accordance with a preferred embodiment of the present invention, said predetermined length of the elongated structure extends to approximately 30 mm.
Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a probing device for insertion into a duct having a physical structure to determine local parameters associated with the physical structure of the duct at a selected region of the duct, and in particular variations in the physical structure along a predetermined length of interest, the probing device comprising:
Furthermore, in accordance with a preferred embodiment of the present invention, said plurality of transmitters and said at least one of a plurality of receivers are combined in the form of receiving and transmitting transducers.
Furthermore, in accordance with a preferred embodiment of the present invention, at least some of the transducers are piezo-electric transducers.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said plurality of transmitters, comprises an absorbing region within an optical fiber, the absorbing region made from material, which converts optical signals to acoustic signals.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said plurality of transmitters, comprises at least one of a plurality of absorbing regions within an optical fiber, the absorbing regions made from material, which converts optical signals to acoustic signals.
Furthermore, in accordance with a preferred embodiment of the present invention, the absorbing regions are made of material that absorbs at different optical spectra, such that at least one of the absorbing regions are activated to generate acoustic signals at a certain optical spectrum, and other absorbing regions are activated to generate acoustic signals at one or more different optical spectra.
Furthermore, in accordance with a preferred embodiment of the present invention, the absorbing regions are made of material selected from the group containing: Copper-doped material with absorption spectrum at about 450 nm or shorter wavelengths, Alexandrite-doped material with absorption at about 850 nm or longer wavelengths, and Yitterbium-doped material with absorption in the range 1,000-1300 nm.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said at least one of a plurality of receivers comprises at least one of a plurality of optical fibers through which light can traverse and be modulated by the echoes.
Furthermore, in accordance with a preferred embodiment of the present invention, said fibers, serving as receivers, each include two reflecting elements and two types of light propagating in the fiber effectively forming two detection channels; the distal reflecting element serves to effectively limit the extent of the fiber for one of the detecting channels, and the proximal reflecting element serves to effectively limit the extent of the fiber for the other detecting channel; the differential signal between these two channels effects a sensitive region local to the separation of the two reflecting elements.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said fibers serving as receivers are staggered along the length of interest to sensitize them to different regions along the device.
Furthermore, in accordance with a preferred embodiment of the present invention, the received signals are processed to account for the different phases in each receiver in conjunction with a knowledge of their physical separation so as to effect a circumferential resolution in the device.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a Bragg grating optical element, and the two channels are differentiated by wavelength.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a polarization-dependent reflector, and the two channels are differentiated by polarization.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a spatially selective element, selectively reflecting one or more guided modes, and the two channels are differentiated by guided modes.
Furthermore, in accordance with a preferred embodiment of the present invention, each one of said fibers, serving as a receiver, includes a reflecting element that effectively limits the extents of the fiber.
Furthermore, in accordance with a preferred embodiment of the present invention, the reflecting element comprises a Bragg grating optical element.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said fibers serving as receivers are staggered in their length to sensitize them to different regions along the length of interest.
Furthermore, in accordance with a preferred embodiment of the present invention, signals are processed by subtracting signals of two adjacent detecting fibers, such that the resulting signal corresponds to their region where the two fibers do not overlap.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said plurality of receivers comprises an optical fiber through which light can traverse and be modulated by the echoes and which incorporates several wavelength-dependent reflectors, such that each effectively limits extent of a certain optical wavelength traveling in the fiber; the position of these reflecting elements is distributed along the predetermined length of the device, sensitizing each wavelength to a different positions along the assembly.
Furthermore, in accordance with a preferred embodiment of the present invention, the received signals are processed to account for the different phases in each receiver in conjunction with a knowledge of their physical separation so as to effect a circumferential resolution in the device.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said at least one of a plurality of transmitters, comprises at least one absorbing region within a multicore optical fiber, the absorbing region made from material, which converts optical signals to acoustic signals, and wherein several of the cores serve as one or more receivers.
Furthermore, in accordance with a preferred embodiment of the present invention, some of the cores serving to generate the acoustic signals have larger lateral cross section than those serving for detection.
Furthermore, in accordance with a preferred embodiment of the present invention, the cores in the said multicore optical fiber, serving as receivers, include a reflecting element that effectively limits the extent of each of the receiver cores and sensitizes each on to a different positions along the assembly.
Furthermore, in accordance with a preferred embodiment of the present invention, the reflecting element comprises a Bragg grating optical element.
Furthermore, in accordance with a preferred embodiment of the present invention, said fiber, serving as receiver, includes two reflecting elements and two types of light propagating in the fiber effectively forming two detection channels; the distal reflecting element serves to effectively limit the extents of the fiber for one of the detecting channel, and the proximal reflecting element serves to effectively limit the extent of the fiber for the other channel; the differential signal between these two channels effects a sensitive region local to the separation of the two reflecting elements.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a Bragg grating optical element, and the two channels are differentiated by wavelength.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a polarization-dependent reflector, and the two channels are differentiated by polarization.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one of the two reflecting elements comprises a spatially selective element, reflecting one or more guided modes, and the two channels are differentiated by guided modes.
Furthermore, in accordance with a preferred embodiment of the present invention, said predetermined length of the elongated structure extends to approximately 30 mm.
Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a system for determining local parameters associated with a physical structure of a duct at a selected region of the duct, and in particular their variation of a predetermined length of interest, the system comprising:
Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a method for determining local parameters associated with a physical structure of a duct at a selected region of the duct, and in particular variations in the physical structure along a predetermined length of interest, the method comprising:
processing data associated with the echoes by the processing unit to determine parameters associated with a physical structure of a duct at the desired region.
In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention as defined in the appending Claims. Like components are denoted by like reference numerals.
a-2d illustrate a preferred embodiment of the present invention using a bundle of separate optical fibers each capable of transmitting and receiving ultrasound.
a illustrates a longitudinal sectional view of an ultrasonic probing device in accordance with a preferred embodiment of the present invention having a set of absorbing regions and a plurality of waveguiding structures within one assembly.
b illustrates an axial cross-sectional view of the probing device shown in
c illustrates an axial cross-sectional view of the probing device shown in
a-4f illustrate the signal forms resulting from the build-up in signal cross-talk for different sensing elements in the probe of the present invention.
a and 5b illustrate cross-sectional views of a probing device in accordance with a preferred embodiment of the present invention centered in the artery lumen (
a and 10b illustrate a schematic representation of the spectral absorption curves for materials suitable for use in wavelength division transmitting core as a part of a preferred embodiment for the present invention.
Confinements in the cross-section of arteries occur as a result of a variety of artery illnesses, such as plaque or thrombosis. This situation often requires intravascular intervention. Typically, the surgeon must locate and measure the confined regions in order to properly position a device for expanding the artery, such as inflating balloons or by a device for applying artery-wall support such as a stent. The ability to measure and monitor the dimensions of the artery in preparation for, during, and/or after the procedure of balloon inflation or stent positioning presents a significant advantage for the surgeon. In accordance with a preferred embodiment of the present invention, a probe is provided for diagnostic operations such as monitoring the dimensions of the artery; a feature of this probe relates to its relatively small cross-section. In fact, the cross-section is small enough so as to allow the entire probe to fit inside a standard guidewire (whose typical diameter is in the order of 1 French, i.e. about 0.34 mm) that is used to guide surgery tools through arteries. Adding sensing features to the guidewire significantly improves its performance and applicability, combining its conventional mechanical function: guiding different surgical tools to a selected location within the artery, with sensing and diagnostic capabilities: locating the malignant region, mapping the extent of the malignant artery, and, for example, measuring the external and internal artery diameters. More advanced diagnostic operations, such as accurate imaging of the artery cross-section, or even characterization of the malignant tissue, can be implemented with a similar concept using a greater number of sensing elements and suitable signal analysis procedures.
State of the art dedicated diagnostic tools must be inserted along the guidewire to the required position to provide various sensing functions. Such diagnostic tools must be removed before surgical tools are inserted. A guidewire with sensing features in accordance with the present invention alleviates the necessity for the entire procedure of inserting and removing the diagnostic tools. Moreover, by using the device of the present invention, the surgeon can monitor the artery simultaneously with any treatment operations. These capabilities provides for a real-time process control tool that need not be removed prior to the insertion of any surgical tool.
In practice the lumen measurements that are most significant to the surgeon relate to the minimal, maximal, and average lumen diameter, and the artery wall-thickness at every artery section. Such statistical values are sufficient for most practical purposes. Optionally, additional angular details, such as the variation of the distance to the internal wall around the circumference of the artery's cross-section, may also be important. As the amount of data collected by the probe at every artery section increases, it can provide more information on the geometry of the artery's cross-section; essentially if the full potential of the data generated by the present invention is exploited, a high-resolution imaging probe can be implemented. The basic diameter/wall-thickness measurements are sufficient for identifying a malignant area when the measurements are distributed over a sufficient length of the artery. Typically, a malignant region in the artery is limited to several millimeters in length; it is very seldom that narrowed regions extend to an inch (25 mm). Consequently, a sensor with the capability of detecting the variation of the artery dimensions over a distance exceeding one inch (25 mm), preferably on the order of thirty millimeters, is capable of identifying the non-uniform and non-monotonic change in a malignant artery profile.
The required distributed sensing capability can be achieved, in principle, by moving a single sensor within a device such as a catheter over the required artery length. This method is referred to as “pull-back”, where a catheter incorporating a sensor near its distal tip is drawn back by pulling the proximal end over the distance of interest. While it is possible to use the “pull-back” procedure in connection with a probe of the present invention, such a procedure would compromise some of the inherent advantages of the present invention. The device of the present invention combines mechanical guiding and diagnostic functions. The “pull-back” procedure requires the surgeon to re-insert the device through the malignant region after each measurement. In the preferred embodiments of the present invention, as is comprehensively discussed herein, an array of sensing regions distributed over the length of the probe serve to monitor artery parameters along a predetermined length without the need for any scanning motion.
The underlying concept of the present invention relates to a series of local sensors, each comprising transmitting means and receiving means, distributed along a predetermined length, and designed to acquire information pertinent to the cross-section of the artery at the location of each sensor. Although each of these sensors performs a simple, elementary measurement, the overall data acquired using this arrangement is sufficient to provide significant information on the artery structure and its variations along a predetermined length. Only a basic performance is required of each transducer. Therefore the transducers can be physically very small, rendering the device of the present invention suitable for insertion, interrogation and mapping of minute bodily ducts.
Notwithstanding the basic concept of minimal transducer capabilities to minimize the size of the probing device of the current invention, the probing device can encompass broader application capabilities. As described in the following, phase information gathered from different sensors can be used to enhance the lateral as well as the circumferential resolution of the basic device. Furthermore, the detected ultrasound carries information related to the composition, texture and other material properties of the artery walls. Therefore, in addition to extracting the profile of the artery, the present probing device is also capable of characterizing its material properties; this is an invaluable capability for differentiating between malignant and healthy regions within the duct.
A variety of different technologies may be used to Implement the individual sensors in the distributed arrangement of the present invention, including, but not limited to, piezoelectric devices, acousto-magnetic devices, EMAT (electromagnetic acoustic transducers), and acousto-optic devices. Nevertheless, as mentioned in the following, in cases where the sensor is to be disposable, opto-acoustic methods, relying on optical fiber technologies, have a favorable advantage.
An ultrasonic probing device having distributed sensors, in accordance with a preferred embodiment of the present invention, is based on electromagnetic waveguides that transmit radiation to generate ultrasonic signals from distributed ultrasonic transducers. For convenience only, and without loss of generality, we refer in the following to optical waveguides, specifically optical fibers, and light as an example of such waveguides and such radiation. Nevertheless the meaning of these expressions is maintained in its broader sense whereby “light” should be taken here to represent any form of electromagnetic radiation, and “optical fiber”, or “fiber”, any form of electromagnetic waveguide. The echoes of these ultrasonic signals are reflected off the walls of the artery and a portion of them is redirected back onto the probe. These signals, in turn, modulate designated portions of the light traveling in the probe. By demodulating the reflecting light of the probe as it exits on return from the sensing region of the device, it is possible to detect the ultrasonic echoes and diagnose various parameters of the artery, including, for example, the dimension of the artery lumen and its wall-thickness. Although it is conceptually straight-forward to implement such a device with piezo-electric transducers, such implementation requires the insertion of wires through the device. The fundamental advantage of the proposed acousto-optic arrangement is the absence of any such wiring, potentially simplifying the construction and minimizing its manufacturing costs in high-volume-production. The production cost is most significant when a disposable device is desired, such as is common with similar medical invasive devices.
There are different ways to implement the distributed probing device of the present invention. In general, the preferred embodiments can be classified into three major arrangements (and combinations thereof): a) a distributed array of sensors, each capable of transmitting and receiving ultrasonic signals independently of the rest of the sensors; b) one transmitting arrangement that transmits ultrasonic signals and a plurality of receiving sensors; and c) a plurality of independent transmitters generating ultrasonic waves and one receiver that detect received signals. The approach of configuration (a) is advantageous as it generates a set of independent ultrasonic signals that can be analyzed in one recursive procedure. Nevertheless, as the compactness of the sensor is of primary importance here, the use of one of the other two arrangements, which necessarily require less physical sensors, may be more suitable in many cases. Naturally any combination of the above classes can also be useful, such as a small number of transmitters in connection with a larger number of receivers and any permutation of such an arrangement.
Fundamentally, a transmitter is constructed within the probe of the present invention, by providing one or more absorbing regions within an optical waveguide. Light pulses transmitted through a fiber can cause the absorbing region to generate ultrasound signals. The basic thermo-elastic effect exploited in the probe and various transmitting configurations have been comprehensively described in PCT/IL02/00018 (not yet published). The following succinct description is repeated here for completeness. In the present invention, the description is limited to the phenomenon of thermo-elastic generation of ultrasound: light incident on an absorbing region heats it abruptly. Provided the heating is significantly faster than the thermal dissipation processes (conduction and radiation), a condition that can readily be met in practice, thermal stresses are generated. The thermal stresses propagate as acoustic waves. Absorbing regions that absorb the incident radiation of different geometries and embodiments are possible. There can be one absorbing region, or a plurality of absorbing regions that are dense enough to absorb all the intensity of the incident radiation such that no portion of the absorbed wavelength is transmitted past the absorbing region. Alternatively, a portion of the energy at the absorbed wavelength is transmitted through the region, while another portion is absorbed. Another alternative is that multiple absorbing regions can be provided for a specific wavelength, each region absorbs a portion of the light and transmits a portion of the light. The absorbency of the regions may be designed to provide a uniform (or patterned) thermal distribution so as to generate a specific form of ultrasonic field.
Reference is now made to
The desired effect of a distributed electromagnetic radiation-based ultrasonic probing device can be implemented in a variety of configurations. In general one can provide a set of independent sensing and detecting elements each capable of either generating ultrasound signals or detecting at a specified position, or alternatively capable of both functions. Such an exemplary embodiment is shown in
An alternative preferred embodiment comprises a monolithic probing device assembly as illustrated in
Referring now to
When an electromagnetic pulse is transmitted through core 38 while the ultrasonic probing device is in a duct (as shown in
Cores 32 are elongated and pass along waveguide 30. In order to better understand the positioning of detecting cores 32, reference is now made to
The distribution of lengths of cores 32 (as described in
Reference is now made to
It is noted, however, that for a good subtraction performance, the different timing of the signals due to the different locations of each detector need to be accounted for. Assuming the detecting cores are evenly distributed around the transmitting core, the direct XMT signal is expected to arrive in all cores simultaneously. Nevertheless the timing difference between the detection in one core and its reference core is directly related to the effective point of reflection from the artery (see below) and relative distance from this point to each core. To estimate the severity of these effects for typical core geometries we return to the example values of
The description above refers to a one-dimensional model for the ultrasonic echoes. This model applies to the special case where the artery lumen is a perfect circle and the probe is positioned coaxially to the lumen. In this case the one-dimensional model holds as all the reflections from the circumference of the artery wall arrive at the same time to the probe, and the result is the waveforms shown in
Returning to
Reference is now made to
To avoid the effect of time differences between the detecting core and the reference core we consider a modified preferred embodiment in which transmission and detection cores are arranged in a similar manner to the arrangement of
A further possibility relates to a system with one or more transmitting regions in each core, with the same core sustaining also the detection signals. Here frequency-filtering regions are required to multiplex and demultiplex the detection and generation signals and associate them with different regions in the length of the fiber. Naturally, multiple-application of such multiple detection/transmission fibers can be deployed in one ensemble.
The distribution of the detection cores across the cross-section of the fiber introduces a relative timing delay between the same signal portions arriving at each core. For a basic implementation, which assumes that these errors are sufficiently small to be ignored, these phase differences are model errors. Nevertheless, this situation can be turned around and the phase delays between cores can be used to decode the angular information related to these phase differences. This can provide for a degree of angular resolution of the signal. In principle there can be up to N−1 angular segments for N cores. Similarly, if the sensing regions are made closer together they can be formed into a phase array in the longitudinal direction. In this manner the guidewire can also be made into a two-dimensional imaging system.
Reference is now made to
Reference is now made to
Reference is now made to
As was discussed in PCT/IL02100018, incorporated herein by reference, the absorber geometry and characteristics can take different forms. In a preferred embodiment of the invention shown herein, different absorbers are provided for different wavelengths. Optionally, each absorber can be designed to absorb several relevant wavelengths. Optionally, there is a spatial overlap between the absorbers for different wavelengths, for example a 0.1 mm region that absorbs a first wavelength includes a 0.05 mm sub-region that absorbs a second wavelength in addition to the first wavelength. Such overlap potentially increases the design flexibility in controlling the acoustic transmission envelope, direction and/or frequency.
Furthermore, the absorption can be volumetric in nature, such that the absorption is gradual along the direction of propagating of the radiation, rather than the energy being absorbed on a surface or boundary layer of the volume. Optionally, the volume is selectively absorbing of wavelength, polarization and/or does not block the entire cross-section of a light guide used to provide the light.
As discussed in PCT/IL02/00018, incorporated herein by reference, a reflector may be provided distal to an absorber, to reflect radiation that is not absorbed by the absorber on the forward pass, back into the same region for further absorption. Optionally, the radiation is made to reverberate several times through the absorber. This may be accomplished, for example, by two reflectors positioned on either side of the absorber. Alternatively a polarization-based two-pass reflecting system can be implemented by providing a polarization-changing element at the distal reflector and/or at the entrance to an absorber (or integrated into the absorber), so that the radiation inside the absorber has a polarization that is reflected by a polarization dependent reflector provided at the entrance to the absorbing volume. Such a polarization dependent reflector may also be provided at the exit from the absorbing volume. Optionally, the reflector(s) and/or the number, size and/or density of the absorbing volume(s) are selected to control the uniformity of the waves generated by one or more regions. A particular region may include absorber density variations along its length and/or cross-section, alternatively or additionally to changes in wavelength-dependent behavior. In a preferred embodiment of the present invention, a plurality of absorbers is included in each of the distributed sensor location and placed along the wave-guide. The type, dimensions and relative positions of these absorbers may be used to determine the characteristics of the generated ultrasound. Suitable arrangements can optionally determine the directionality, spectral contents, waveform, and the intensity of the ultrasonic radiation. A potential benefit of multiple or extended regions is better heat dissipation, possibly allowing higher ultrasonic peak-power to be effectively used.
In a preferred embodiment of the invention, a plurality of absorbers act in concert to provide a desired energy field distribution and/or wave propagation direction. For example, the distance between two absorbing regions may be related to a desired acoustic wavelength to be generated. The absorbing regions that act in concert may be absorbing a same wavelength of radiation or different wavelengths. Alternatively or additionally, the number, spacing and/or length of the regions may be used to select the wavelength spectrum generated in one or more directions. Alternatively or additionally, the regions in the same or different fibers may be used to steer the ultrasonic waves, for example, using phase differences between the regions.
In a preferred embodiment of the present invention, a plurality of absorbers are used to generate a strong acoustic wave while maintaining a low average acoustic radiation power, which radiation power is desirably below a break-down point of the absorbing target The plurality of absorbers allows the target to accumulate a larger overall acoustic power while maintaining the peak power level at each region below a specified threshold.
In a preferred embodiment of the present invention, the ultrasound is generated without any free-space propagation of light, with light going directly from a wave-guide to an absorbing volume. Alternatively, spaces are defined in the waveguide, for example if the waveguide is hollow or by providing air (or vacuum or other fluids or gasses) spaces, such as expansion spaces, adjacent the target.
An aspect of some embodiments of the present invention relates to control ultrasound properties by spatial and density design of absorbing volumes. In a preferred embodiment of the present invention, the control includes one or more uniformity, frequency, number of cycles, directivity and waveform. In another preferred embodiment of the present invention, the control is achieved by providing multiple and suitably spaced absorbing volumes, possibly with different volumes being addressable using different wavelengths, polarizations and/or via different fibers. Alternatively or additionally, the volumes have controlled densities, which may be matched, for example, to the expected relative intensity of an electromagnetic wave at the volume. It should be noted that this control contrasts with that suggested in the art for fluid based systems, in which the absorption depth is fixed and a single volume is used. While the use of solids is desirable in many embodiments of the invention, other material phases, such as gas or liquid may be used. In the example of absorption outside of a catheter, the density of absorbing material may be controlled in order to achieve a desired radiation volume.
An aspect of some embodiments of the present invention relates to providing multiple absorbing regions in a waveguide, for generation of ultrasound from each of the regions.
An aspect of some embodiments of the invention relates to providing multiple electro-magnetic radiation waves in a wave-guide, such that a plurality of functions is provided. The multiple waves may have different polarization and/or wavelengths. In an exemplary embodiment of the invention, one of the waves is used for the generation of ultrasound and another wave is used for detection of ultrasound or treatment based on the radiation. Such treatment may be, for example, treatment using the radiation, treatment using heat or treatment using high-powered ultrasound generated from the radiation. In a preferred embodiment of the invention, ultrasound radiation is generated from the electromagnetic wave during forward traveling of the electro-magnetic wave.
An aspect of some embodiments of the present invention relates to an acousto-optical medical probe that provides a distributed sensing capability over an extended length of the device. The device is incorporated into a mechanical structure such that it can mechanically serve as guide-wire with provisions for independent insertion into an artery and serving as a guide over which, surgical tools can be slide into position. Alternatively, ultrasound detection and/or generation may be by an external probe. In an exemplary embodiment of the invention, the acoustic radiation and light radiation are provided using a same optical fiber.
Reference is made to
It should be noted that in many embodiments of the present invention, the ultrasonic probing device having distributed sensors may comprise only a single fiber having a relatively small diameter. Optionally, this fiber can be coated with various materials, such as anti-coagulants and biocompatible polymers. Alternatively or additionally, a hollow waveguide can be used.
A coupler or switch 112 is provided for coupling the light to probe 114 and couple detection light from probe 114 to a detector 104. A dedicated processor 103 is provided for data analysis and demultiplexing. A controller 106 controls the generation and detection sequences. Optionally, a computer (e.g., a microcontroller) 102 is provided, with a suitable display 101, for a user interface and/or for storing recorded signals, images and other data.
The multi-core or multi-waveguide characteristics of the distributed ultrasonic probing device, requires a specialized connector to couple probe 190 with the other components and in order to separate the radiation for the generation of ultrasonic signals and the detection of the acoustic signals. In principle, a standard multi-core arrangement can be used, where a mechanical connector is designed to register the angular direction so as to ensure the matching of different cores within the fiber on both sides of the connector. This approach suffers two drawbacks: a) multi-core connectors typically incorporate an inherent relatively large misalignment of the cores; and b) introducing a connector to the end of the device limits its use as a mechanical guide wire: any mechanical connector is significantly larger than the diameters allowed for standard guide wires, substantially 0.34 mm.
Reference is now made to
Reference is now made to
Reference is now made to
A fourth alternative overcomes the inherent uncertainty of the internal alignment of the different fiber cores. It is this uncertainty in the actual position of the internal cores that make it necessary for the alignment procedures of each core described in the previous two alternatives. To overcome the manufacturing tolerance issues it is proposed to include two connecting systems as shown in
Multicore fibers are available commercially, but mainly for situations where the satellite cores are used for incoherent pumping operation. Here attention is necessary to implement highly accurate connectors for the satellite cores, which need to carry interferometric signals. Two different approaches are introduced to the manufacture of the multicore fiber for the use as a distributed probing device: a) prepare a multicore perform which can then be pulled to effect a multicore fiber (
It is noted that some of the embodiments above described may describe a best mode contemplated by the inventors and therefore include structure, acts or details of structures and acts that may not be essential to the invention and which are described as examples. Structure and acts described herein are replaceable by equivalents, which perform the same function, even if the structure or acts are different, as known in the art. Therefore, the scope of the invention is limited only by the elements and limitations as used in the claims. When used in the following claims, the terms “comprise”, “include”, “have” and their conjugates mean: “including but not limited to”.
| Number | Date | Country | Kind |
|---|---|---|---|
| 155329 | Apr 2003 | IL | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL04/00172 | 2/23/2004 | WO | 12/14/2006 |
