Patent Application
20110237910
1. Technical Field
This invention relates in general to apparatus and methods for non-invasively examining biological tissue utilizing near-infrared spectroscopy techniques, and in particular to a relatively stabilized laser diode light source for use with such apparatus and methods.
2. Background Information
Near-infrared spectroscopy (NIRS) is an optical spectrophotometric method that can be used to continuously monitor biological tissue characteristics such as the oxygenation level within the tissue. The NIRS method is based on the principle that light in the red/near-infrared range (660-1000 nm) can pass easily through skin, bone and other tissues where it encounters hemoglobin located mainly within micro-circulation passages; e.g., capillaries, arterioles, and venuoles. Hemoglobin exposed to light in the near-infrared range has specific absorption spectra that vary depending on its oxygenation state; i.e., oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) each act as a distinct chromophore. By using light sources that transmit near-infrared light at specific different wavelengths, and by measuring changes in transmitted or reflected light attenuation, concentration changes of the oxyhemoglobin and deoxyhemoglobin can be monitored as well as total or absolute values of tissue oxygenation levels can be determined or calculated. The ability to continually monitor or determine cerebral oxygenation levels, for example, is particularly valuable for those patients subject to a condition in which oxygenation levels in the brain may be compromised, leading to brain damage or death.
A NIRS system typically includes a sensor portion having a light source and one or more light detectors for detecting reflected and/or transmitted light. The light signal is created and sensed in cooperation with the overall NIRS system that includes a monitor portion having a computer or processor that runs an algorithm for processing signals and the data contained therein to, for example, calculate or determine the hemoglobin oxygenation concentration or saturation levels. Typically the monitor portion is separate from the sensor portion. Light sources such as light emitting diodes (LEDs) or laser diodes that produce light emissions in the wavelength range of 660-1000 nm are typically used. Each light source produces an infrared light signal at a particular wavelength at which a known absorption response is produced depending on the amount of oxygen concentration in the hemoglobin. Several different specific wavelengths are typically employed, for example, at 690 nm, 780 nm, 805 nm, and 850 nm. Thus, a corresponding number of light sources are employed in the sensor portion, with these light sources usually being located together. One or more photodiodes or other types of light detectors detect light reflected from or passed through the tissue being examined, and oftentimes the photodiodes are located at specific, predetermined different distances from the light source location. The NIRS system processor cooperates with the light source and detector to create, detect and analyze the signals, for example, in terms of their intensity and wave properties. U.S. Pat. Nos. 6,456,862 and 7,072,701, both of which are hereby incorporated by reference in their entirety, each disclose a NIRS system (e.g., a cerebral oximeter) and a methodology for analyzing the signals within the NIRS system to produce an indication of tissue oxygenation levels to a system user, typically a clinician.
However, a spectrophotometric system such as a cerebral oximeter that utilizes a laser system containing one or more laser diodes may demonstrate instability in operation for various reasons. For example, the output of the laser system may become unstable over time in terms of its wavelength and power output due to various factors, including environmental (e.g., temperature). Also, oftentimes the individual laser diode(s) is located apart from the sensor portion of the overall system and, as such, the laser diode output may be coupled directly by an optical fiber to the sensor portion. Therefore, problems may exist, for example, in the connection or coupling of the laser diode output to the optical fiber, for example, due to stripped cladding of the optical fiber, improper centering of the optical fiber in the connector, or use of an improper connector. Also, instabilities in the optical fiber itself may exist, for example, due to bending, temperature, and mode variance. In general, it is known that when the sensor portion of the spectrophotometric system is directly connected to the laser diode light source by an optical fiber of a few meters in length, an unstable light output can occur. Any sufficient degree of instability in the overall laser system output can cause corresponding errors in the overall spectrophotometric system, particularly those that utilize differential wavelength algorithms.
In addition, some oximetry monitors are multi-channel devices with a plurality of sensor portions, with each channel being associated with a different particular sensor portion. These devices often employ parallel sets of optical, electronic, and software subsystems, each dedicated to a different channel/sensor portion. The “parallel” approach, although straightforward to implement, can have several disadvantages. For example, replication of hardware in each parallel channel increases the cost, the size, and the complexity of the device, and the opportunity for a component to fail. In addition, each channel will have its own distinct spectrophotometric characteristics such as central wavelength, spectral bandwidth, and modal profile. These characteristics can vary from channel to channel, and can also vary independently as a function of time and environmental conditions. These variances in spectrophotometric characteristics will very likely result in measurement discrepancies between channels. The variances per channel within the monitor portion may also be additive to variances in the sensor portion for each channel.
What is needed, therefore, is a laser system light source that contains multiple light sources that can provide different discrete wavelengths for use in a spectrophotometric system such as a cerebral oximeter, where the laser system provides a relatively stable and consistent light radiation output in terms of output parameters such as, for example, power, intensity and radiation pattern, and a system that provides uniformity between channels.
According to the present invention, a spectroscopy system that may be used for spectrophotometric monitoring of tissue includes a monitor portion and a sensor portion. The spectroscopy system is described hereinafter as a cerebral oximeter operable to monitor brain tissue. The spectroscopy system is not limited to a cerebral oximeter embodiment, however, and may be utilized in other spectroscopic applications. The sensor portion generally includes one or more channels, each having a light source and one or more light detectors. The sensor portion may attach to a human to sense light signals from the light source that have traversed biological tissue, the light signals ultimately being used by the system to determine biological tissue blood hemoglobin oxygenation levels. The monitor portion generally includes a processor for determining or calculating tissue oxygenation levels from the sensed light signals, together with a visual display to indicate the determined oxygenation levels in various forms. The light source may comprise a plurality of laser diodes, LEDs, or the like, each providing infrared light at a particular wavelength. A laser beam combiner may couple the plurality of laser diode output light signals into one optical fiber. To stabilize the output of each of the laser diodes in the laser beam combiner, an optical fiber light stabilizer may be coupled to the combined laser diode output. The light stabilizer may include several meters of multimode optical fiber wrapped around a circular spool. The optical fiber coupled to a laser diode is typically “underfilled” when the laser light enters the optical fiber (i.e., usually only the lower-order propagation modes or paths are utilized in the optical fiber) since the laser diode radiation output has a lower numeral aperture (NA) compared to the optical fiber. The optical fiber light stabilizer redistributes the propagation modes so that the higher-order modes are filled until an equilibrium mode distribution is established. The propagation modes nearest to the axis of the fiber core are referred to as the lower-order modes, while the paths with the relatively greatest deviation (i.e., highest angles from the core axis) are referred to as the higher-order modes. The resultant laser system light output typically demonstrates a relatively high degree of stability when modal equilibrium is achieved. A light sensor (e.g., a photodiode) may also provide feedback with respect to the laser diode output, which allows for compensation of any laser diode light output instability independently of optical fiber related instabilities.
With an underfilled optical fiber, the light may “jump” between lower and higher modes due to temporary fiber bending or temperature changes, which causes instability in the laser system output. The optical fiber light stabilizer corrects this problem by redistributing the light into an equilibrium mode distribution. Such an equilibrium mode distribution may also be achieved with a relatively large amount (e.g., 1000-2000 meters) of uncoiled optical fiber. For example, a laser diode connected to a multimode optical fiber cable a few meters in length with a numeral aperture (NA) of 0.22 (conic light output of 12.7 degrees) will fill only the lower modes, resulting in an output NA of 0.18 (10.4 degrees) or less, depending on the laser light launch NA. By attaching the laser diode to the optical fiber light stabilizer comprising the same optical fiber but at a longer length (e.g., 20 meters) wrapped around a spool with a radius that is at least approximately equal to (e.g., or slightly larger than) the minimum long term bend radius of the optical fiber, the light output will reach an equilibrium mode distribution with an output NA of approximately 0.22 (12.7 degrees), resulting in a relatively more stable output.
According to an aspect of the present invention, a spectroscopic system that monitors oxygenation levels in biological tissue is provided. The system includes a sensor portion and a monitor portion. The sensor portion includes a plurality of sensor assemblies. Each sensor assembly has at least one light signal outlet, and at least one light detector adapted to sense light and produce detected signals. The monitor portion includes a processor, a light source adapted to produce light signals at a plurality of different wavelengths, and an optical switch with two or more output ports and an input port. Each switch output port is adapted to be connected to the light signal outlet of a particular one of the sensor assemblies. The switch input port is in communication with the light source. In some embodiments, the monitor portion includes a multiplexer having a plurality of input ports and an output port. Each multiplexer input port is adapted to be connected to a particular one of the light detectors in each sensor assembly. The multiplexer output port is in communication with the processor. The optical switch is adapted to selectively route light signals from the light source to each switch output port. The processor is adapted to process the detected signals to determine oxygenation levels within the biological tissue.
According to another aspect of the present invention, a method for spectrophotometrically determining an oxygenation level in biological tissue of a human subject is provided. The method includes the steps of: a) providing a plurality of laser output signals each at a predetermined wavelength of light; b) combining the plurality of laser output signals into a combined laser output signal; c) providing the combined laser output signal to an optical fiber, where the combined laser output signal propagates through the optical fiber; d) stabilizing the combined laser output signal within the optical fiber by redistributing modes of the combined laser output signal until an equilibrium mode distribution is established in the combined laser output signal propagating within the optical fiber; e) passing the stabilized laser output signal through an optical switch having a plurality of output ports; f) directing the laser output signal from each switch output port to a channel dedicated to that output port; g) selectively emitting the laser output signal from each channel into particular regions of biological tissue of the human subject; h) sensing for the laser output signal after it has passed through the biological tissue of the human subject, and producing detected signals corresponding to sensed laser output signals; i) multiplexing the detected signals into a processor; and j) determining the oxygenation level in the region of biological tissue of the human subject associated with each channel using the detected signals within the processor.
According to another aspect of the present invention, a method for spectrophotometrically determining an oxygenation level in biological tissue of a human subject is provided. The method includes the steps of: a) selectively providing a plurality of laser output signals each at a predetermined wavelength of light; b) providing the laser output signals to an optical fiber, where the laser output signals propagate through the optical fiber; c) stabilizing the laser output signals within the optical fiber by redistributing modes of the laser output signals until an equilibrium mode distribution is established in the laser output signals propagating within the optical fiber; d) emitting the laser output signals into the biological tissue of the human subject; e) sensing for the laser output signals after they have passed through the biological tissue of the human subject, and producing detected signals corresponding to sensed laser output signals; and f) determining the oxygenation level in the region of biological tissue of the human subject using the detected signals and a processor adapted to process the detected signals to determine the oxygenation level.
According to an aspect of the present invention, a spectroscopic system that monitors oxygenation levels in biological tissue is provided. The system includes a sensor portion, a monitor portion, and at least one optical fiber light stabilizer. The sensor portion includes at least one sensor assembly, which sensor assembly has at least one light signal outlet, and at least one light detector adapted to sense light and produce detected signals. The monitor portion has a processor in communication with the light detector in the sensor assembly, and a light source adapted to produce laser light signals at a plurality of different wavelengths. The optical fiber light stabilizer is adapted to stabilize the laser light signals. The processor is adapted to process the detected signals to determine oxygenation levels within the biological tissue.
These and other features and advantages of the present invention will become apparent in light of the drawings and detailed description of the present invention provided below.
Referring to
Referring to
The multiple laser beam combiner 40 includes a plurality of laser diodes 48, a laser output monitor photodiode 50, and a fiber optic connector 52 (e.g., an SMA-type connector). An example of an acceptable combiner 40 is the multiple laser beam combiner provided by Princetel, Inc. of Lawrenceville, N.J., U.S.A. The Princetel laser beam combiner 40 typically has three or four laser diodes 48, and all of the laser diode light output signals are combined into a single laser beam or output light signal using beamsplitters and polarizing filters within the combiner 40. A lens inside the combiner 40 focuses the laser light output into the optical fiber 44 via the SMA connector 52. Alternative versions of the fiber optic connector 52 could be used, such as an APC connector, which reduces back reflection of light entering back into the laser combiner 40, potentially causing interference to laser diode power control and monitoring. An APC connector has an angled (e.g. about 8 degrees) polished fiber optic face, which redirects back reflected light in a different direction or axis from the output light signal that is entering into the APC connector by internal reflection. For example, an SMA connector could be polished at an angle of 8 degrees to function as an APC connector. The NIRS sensor assembly 14 optically interfaces to the spectrophotometric system monitor portion 12 via the optical fiber connector coupler 46, which may be part of a detachable connector 54 that connects the monitor portion 12 with the sensor portion 10. The detachable connector 54 may be part of the connector housing 16 of
The laser diodes 48 are electrically actuated by laser diode power control drivers 56 via an electrical cable harness 58. A laser diode sequencer control 60 connects to the laser diode drivers 56 to provide laser diode pulse timing and control. The laser light from the multiple laser beam combiner 40 propagates through the optical fiber light stabilizer 44 and through the optical fiber connector coupler 46 to the NIRS sensor assembly 14. In the sensor assembly 14, the laser diode light propagates through a single core multimode optical fiber cable 62. The laser diode light is emitted out of the sensor assembly 14 at the light source outlet 17 and into the human subject (
Referring to
The optical fiber light stabilizer 42, which is relatively rugged mechanically, provides for a relatively stable and consistent laser diode light output in terms of parameters such as power, intensity, and radiation pattern, which helps to ensure accuracy of NIRS system monitored parameters. For example, the relatively high degree of output light stability allows for accurate differential wavelength tissue oxygenation signal processing, such as that described in the aforementioned U.S. Pat. No. 6,456,862. Due to the increased output light stability, another advantage is that the discrete laser diode light output wavelengths may be spaced relatively closer together, which provides for relatively accurate tissue oxygenation spectrophotometric measurement, despite the closer wavelength dependent light absorption coefficient values. Closer spaced wavelengths also allow for relative reduction of wavelength dependent light pathlength differences, which may cause errors in tissue oxygenation spectrophotometric measurements. Another advantage is that different discrete wavelengths of light from the laser diodes 48 may be combined and interfaced to a single core multimode output optical fiber 44. Further, the different discrete wavelengths of light may pass through the optical fiber 44 in a homogeneous manner, such that the output light intensity from the single core multimode optical fiber 44 for all wavelengths is proportional to the input light intensity for all wavelengths, even if the input radiation profile or input NA are different for each wavelength. Still further, a homogeneous and relatively stable light output radiation profile or output NA may be achieved, even if the input radiation profile or input NA are lower and individually different for each wavelength. This is done by providing for relatively constant and high optical fiber modal filling by spreading the lower input modes to also fill higher modes until the optical fiber modes are filled; that is, a relatively large number of all of the modes or possible light guide pathways in the optical fiber 44 are utilized. Another advantage is that relatively homogeneous and stable light output intensity may be provided during rapid, transient, or gradual temperature changes, or during rapid, transient, or gradual optical fiber mechanical stress, such as fiber bending or vibration. A further advantage is that different optical sensors, each of a particular configuration used for biological tissue oxygenation measurement, may be interchangeably utilized without having to be individually calibrated.
In an alternative embodiment, as shown in
Referring to
The optical switch 88 includes a signal input port 96 and “N” number of output ports 98, where “N” is an integer equal to or greater than two. The optical switch 88 is connected and adapted to receive light signals from the laser beam combiner 40 via an optical fiber 44, which fiber is connected to the signal input port 96. Each output port 98 is connectable to a sensor assembly 14 (e.g., via an optical fiber connector 46 as described above) for purposes of sending a light signal to the light signal outlet 17 of the respective sensor assembly 14. The optical switch 88 further includes a control signal port 100 for receiving control signals from a switch/multiplexer sequence control 101. These control signals determine through which output port 98 light emitted from the combiner 40 is directed.
The multiplexer 90 includes “N” number of signal input ports 102, a signal output port 104, and a control signal port 106. Each signal input port 102 is connected to a cable coupler 66 via electrical conduit 108. Each coupler 66 is adapted to connect to, and receive signals from, the shielded electrical conduit 64 of a respective one of the sensor channels 92, 94. The signal output port 104 is connected to signal processor 72. The control signal port 106 is adapted to receive control signals from the switch/multiplexer sequence control 101 that determine which one of the signals received by the input ports 102 is directed to the signal processor 72. As indicated above, in some embodiments a pre-amplifier 70 is disposed to receive the detector signals from the sensor assembly 14 prior to such signals reaching the signal processor 72. The signal processor 72 is adapted to process the detector signals from a given sensor assembly 14 (received via the multiplexer 90) in the manner described above, with the signals from each detector 20 processed independently of the signals from other sensor assemblies.
The signal processor 72 and the CPU or monitor processor 74 convert the received signals into physiological parameters by various spectrophotometric methods (e.g., those of U.S. Pat. Nos. 6,456,862 and 7,072,701), and the resultant physiological parameters (e.g., tissue oxygenation concentration or saturation levels) may be visually displayed on the user display 32. Also, light sampled by the laser output monitor photodiode 50 could be used as the input intensity (Io) signal utilized in spectrophotometric type algorithms such that described in U.S. Pat. No. 6,456,862.
In the embodiment shown in
Referring to
Although the present invention has been illustrated and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention. For example, the present spectrophotometric system and method has been described above in detail in terms of a cerebral oximeter useful to determine the oxygenation of biological tissue. The present spectrophotometric system and method is not limited to the described cerebral oximeter embodiment, however, and can be used alternatively to determine other tissue characteristics, or used to determine the presence of other substances that can be spectrophotometrically identified.
Applicant hereby claims priority benefits under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/316,633 filed Mar. 23, 2010, the disclosure of which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61316633 | Mar 2010 | US |
