Patent Application
20120113411
The present disclosure relates generally to medical diagnostic sensors and, more particularly, to energy efficient spectrophotometric sensors.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor and sense certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring and sensing many such physiological characteristics. One category of monitoring and sensing devices includes spectrophotometric monitors and sensors. This category of device typically measures the absorption and/or reflection of energy at particular, discrete wavelengths within the electromagnetic spectrum and may allow one or more physiological parameters to be determined based upon these measurements. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring and sensing devices have become an indispensable part of modern medicine.
One technique for monitoring certain physiological characteristics of a patient using spectrophotometric devices is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin (SpO2) in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the “pulse” in pulse oximetty refers to the time varying amount of arterial blood in the tissue during each cardiac cycle.
Pulse oximeters typically utilize a non-invasive sensor that transmits light through a patient's tissue and that photoelectrically detects the absorption and/or scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed and/or scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed and/or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms. This determination may be performed in a monitor coupled to the sensor that receives the necessary data for the blood constituent calculation.
Conventional pulse oximeter sensors have a multitude of electronic components that are part of the sensor, for example light emitting diodes (LEDs), resistors, capacitors, inductors, and so forth. Metals are also typically contained in the sensor as part of the wiring, the electronic components, the sensor body, and in other sensor components. However, electronic devices, as well as devices containing metallic components, may be unsuitable for use in certain medical environments. For example, electronic devices, such as pulse oximetry sensors, may be unsuitable for use inside magnetic resonance imaging (MRI) scanners where the presence of electromagnetic fields and/or magnetic materials may result in distortion or degradation of the image being created.
Advantages of the disclosed techniques may become apparent upon reading the following detailed description and upon reference to the drawings in which:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
The present disclosure describes a fiber optic sensor that may be used inside environments that are unsuitable for devices containing metal or electronic circuitry. In particular, embodiments of the present disclosure are typically free of electronics or metals as part of the sensor body. Instead, as discussed herein, such sensors may utilize fiber optic waveguides to transmit light into and out of such sensitive environments, such as the imaging bore of a magnetic resonance imaging (MRI) system.
Present embodiments may apply to a variety of spectrophotometric sensors, for example, pulse oximetry sensors. Moreover, as disclosed herein, the data of interest that may be observed using a spectrophotometric sensor may similarly vary depending on the capabilities of each device. For example, a pulse oximetry sensor may transmit absorption data that may be used to derive measurements of pulse rate, blood oxygen saturation, and/or total hemoglobin, and so forth. Because the embodiments presently disclosed may eliminate the need for the electronics and the metals found in conventional sensors, fiber optic sensors may be used in a wide variety of medical environments, including MRI scanners.
With the foregoing in mind,
In one embodiment, the sensor 12 does not include metallic, magnetic, and/or electronic components. For example, the sensor 12 may be formed from a polymeric composition (e.g., plastics, thermoplastics, or other polymeric materials, such as polyurethane, polypropylene, nylon, and so forth), though other suitable non-metallic and/or non-magnetic materials may also be used. The sensor 12 may also include or be formed using a thermoplastic elastomer or other conformable material. In such embodiments, the thermoplastic elastomer may include compositions such as thermoplastic polyolefins, thermoplastic vulcanizate alloys, silicone, thermoplastic polyurethane, as well as other suitable non-metallic and/or non-magnetic compositions.
The system 10 may include a patient monitor 18 that is connected to the sensor 12 via a fiber optic connection 20. The patient monitor 18 may include a display 22, a memory, a processor, and various monitoring and control features for processing data acquired via the sensor 12. Based on light received from the sensor 12, the patient monitor 18 may display patient diagnostic measurements and perform various additional algorithms. For example, when the system 10 is configured for pulse oximetry, the patient monitor may perform blood oxygen saturation calculations, pulse measurements, and other measurements based on the received light. Furthermore, to upgrade conventional operation provided by the monitor 18 to provide additional functions, monitor 18 may be coupled to a multi-parameter patient monitor 24 via a cable 26 connected to a sensor input port or via a cable 28 connected to a digital communication port, for example.
Turning to
The terminal portion 14 of the fiber optic element 30 may be manufactured by cutting the end of a fiber optic fiber at an angle of θ1 and by removing a section 34 of the fiber's jacket 36 so as to expose the cladding 38. In one embodiment, the terminal portion 14 of the fiber optic element 30 may have an angle θ1 of approximately 45°. However, in other embodiments, the angle θ1 may be between 30° and 60°. Any number of methods may be used for cutting the fiber at an angle of θ1. For example, ceramic scissors, an angled cutting jig, a laser cutter, a robotic fiber cutter, as well as other suitable fiber cutting techniques may be used to cut the terminal portion 14 at the angle θ1.
In one embodiment, the end of the cut fiber may be polished to enhance the reflectivity of the boundary surface 40. In another embodiment, it may be coated or capped with a reflective layer so that the reflectivity of the boundary surface 40 is enhanced. Enhancing the reflectivity of the boundary surface 40 may allow for more emitted rays of light to reflect into the patient tissue 32. In yet another embodiment, the cut fiber may not need to be further polished or cut, based on the reflectivity of the boundary surface 40. That is, the cut may result in a boundary surface 40 having sufficient reflectivity so as to suitably reflect the rays of light into the patient tissue 32. Indeed, the polishing, coating, and/or capping of the boundary surface 40 may be based on the reflectivity already present in the boundary surface 40. That is, the boundary surface 40 may already have a certain amount of reflectivity, and so only minimal (or no) polishing, coating, and/or capping may be needed.
As discussed above, in one embodiment, a tissue facing portion of the fiber optic element 30 has a section 34 where the fiber's jacket 36 that has been removed, exposing the cladding 38. Any number of methods may also be used to remove the section 34 of the fiber's jacket 36. For example, hand-held cable strippers, hand-held cable slitters, a robotic stripper, a robotic slitter, as well as other jacket removal techniques may be used to remove the section 34 of the jacket 36 and to expose the cladding 38. In one embodiment, the exposed cladding 38 is placed up against the patient tissue 32 at section 34, physically contacting the patient tissue 32. In another embodiment, the exposed cladding 38 does not physically contact the patient tissue 32 and there is an air gap between the exposed cladding 38 and the patient tissue 32 at section 34. Additionally, a light coupling medium, such as a gel, may be used to enhance the coupling efficiency of the cut fiber with the patient tissue. Accordingly, the gel coating may be disposed on the ends of the cut fiber, approximately on the terminal portion 14 and/or terminal portion 16.
Emitted rays of light may enter the patient tissue 32 at an angle θ2. The angle θ2 may vary in embodiments having the boundary surface 40 coated or capped with a reflective layer and in embodiments having the boundary surface 40 left uncoated and uncapped. In certain embodiments, angle θ2 may be derived based on the law of reflection of light and Snell's Law. Snell's law of refraction may take into account the refractive index of the core 44, the refractive index of the cladding 38, the refractive index of the environment (e.g., air) immediately adjacent to the terminal portion 14, and the refractive index of the patient tissue 32 (in embodiments where the exposed cladding 38 is physically contacting the patient) in order to derive angle θ2. The angle θ1 and/or the coating applied to the terminal portion 14 fiber optic element 30 may be selected taking into account the law of reflection and/or Snell's law to provide a desired angle θ2 for entry of light into the patient tissue 32.
Turning to
In one embodiment, the terminal portion 16 of the fiber optic element 30 may have an angle θ3 of approximately 45°. However, in other embodiments, the angle θ3 may be between 30° and 60°. The terminal portion 16 may be formed using one or more of the cutting techniques noted above, e.g., by use of ceramic scissors, an angled cutting jig, a laser cutter, a robotic fiber cutter, or other suitable fiber cutting techniques. In addition, as previously noted, the terminal portion 16 of the cut fiber may be polished or otherwise finished (such as by coating or capping the terminal portion 16 with a reflective layer) to enhance reflectivity of the boundary surface 40. By enhancing the reflectivity of the boundary surface 40, more light may be collected and reflect through the fiber optic element 30.
Further, as discussed above, a tissue facing portion of the fiber optic element 30 has a section 34 where the fiber's jacket 36 has been removed to expose the cladding 38. In one embodiment, the exposed cladding 38 may be placed up against the patient tissue 32 at section 34, physically contacting the patient tissue 32. In another embodiment, the exposed cladding 38 does not physically contact the patient tissue 32 and there is an air gap between the exposed cladding 38 and the patient tissue 32 at section 34. In one such embodiment, the removal of the section 34 of the fiber jacket 36 allows light to be collected from the patient tissue 32. The collected light may then pass through the cladding 38 at section 34 and into the fiber optic element 30.
Collected rays of light may enter the fiber optic element 30 from the patient tissue 32 an angle θ4. The angle θ4 may vary in embodiments having the boundary surface 40 coated or capped with a reflective layer and in embodiments having the boundary surface 40 left uncoated and uncapped, as discussed above. That is, in certain embodiments, angle θ4 may be derived based on Snell's law of refraction, taking into account the refractive index of the core 44, the refractive index of the cladding 38, the refractive index of the environment (e.g., air) immediately adjacent to the terminal portion 16, and the refractive index of the patient tissue 32 (in embodiments where the exposed cladding 38 is physically contacting the patient). The angle θ3 and/or the coating applied to the terminal portion 16 of fiber optic element 30 may be selected taking into account the law of reflection and/or Snell's law to provide a desired angle θ4 by which light may be collected from the patient tissue 32.
With the foregoing implementations of terminal portions of a fiber optic element in mind,
In one embodiment, the terminal portions 14, 16 may be secured to the patient tissue 32 by a bandage with stiffening elements to prevent the terminal portions from dislodging or otherwise moving out of position. In other embodiments, such as the depicted embodiment, the terminal portions 14, 16 may be secured to the patient tissue 32 by a clip-style holder or other rigid sensor body. Any structure that allows for a relatively secure attachment to the patient tissue 32 may be used to affix the terminal portions 14, 16.
Turning to
In one embodiment, a time processing unit (TPU) 52 may provide timing control signals to light drive circuitry 54 within the monitor 18. Light drive circuity 54 may contain a set of emitters (e.g., LEDs) which may be capable of emitting light through fiber optic element 48. Light drive circuity 54 may control which wavelength of light is emitted by turning on a suitable LED configured to emit light near a certain wavelength. Light drive circuitry 54 may also control when light is emitted, and if multiple light sources are used, the multiplexed timing for the different light sources. Light emitted from the light drive circuitry 54 may be transmitted through fiber element or fiber bundle 48 to the sensor 12 and may be reflected out of the light emitting terminal portion 14 into the patient tissue 32 as described with respect to
The TPU 52 may also control the gating-in of signals from the detector 56 through an amplifier 58 and a switching circuit 60. These signals may be sampled at the proper time, depending upon which of multiple light sources is illuminated, if multiple light sources are used. The received signals from the detector 56 may be passed through an amplifier 62, a low pass filter 64, and an analog-to-digital converter 66 for amplifying, filtering, and digitizing the received signals. The digital data may then be stored in a queued serial module (QSM) 68, for later downloading to the RAM 70 as the QSM 68 fills up. In an embodiment, there may be multiple parallel paths for separate amplifiers, filters, and A/D converters for multiple light wavelengths or spectra received. This raw digital diagnostic data may be further sampled by the circuitry of the monitor 18 into specific diagnostic data of interest, such as pulse rate, blood oxygen saturation, and so forth.
In various embodiments, based at least in part upon the value of the received signals corresponding to the light detected by detector 56, a microprocessor 72 may calculate a physiological parameter of interest using various algorithms. These algorithms may utilize coefficients, which may be empirically determined, corresponding to, for example, the wavelengths of light used. In one embodiment, these algorithms may be stored in the ROM 74.
The monitor 18 may include control inputs 76 such as a switch, dial, buttons, a keyboard, a mouse, a trackball, or a network port 78 providing instructions from a remote host computer communicating through a network interface card (NIC) 80. A display 22 may be used to show the physiological measurements, alarm limits, and other information of interest to a caregiver. Nonvolatile memory 82 may store caregiver preferences, patient information, or various parameters, discussed above, which may be used in the operation of the monitor 18. Software for performing the configuration of the monitor 18 and for carrying out the techniques described herein may also be stored on the nonvolatile memory 82, or may be stored on the ROM 74. The nonvolatile memory 82 and/or RAM 70 may also store historical values of various discrete medical diagnostic data points. By way of example, the nonvolatile memory 82 and/or RAM 70 may store values of corresponding to the pulse rate, blood oxygen saturation, and total hemoglobin, and others.
While the disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments provided herein are not intended to be limited to the particular forms disclosed. Indeed, the disclosed embodiments may not only be applied to measurements of blood oxygen saturation, but these techniques may also be utilized for the measurement and/or analysis of other blood constituents or other constituents suitable for spectrophotometric analysis. For example, using the same, different, or additional wavelengths, the present techniques may be utilized for the measurement and/or analysis of carboxyhemoglobin, met-hemoglobin, total hemoglobin, fractional hemoglobin, intravascular dyes, and/or water content. Rather, the various embodiments may cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims.
