Multi-channel non-invasive tissue oximeter

Abstract

A method and apparatus for spectrophotometric in vivo monitoring of blood metabolites such as hemoglobin oxygen concentration at a plurality of different areas or regions on the same organ or test site on an ongoing basis, by applying a plurality of spectrophotometric sensors to a test subject at each of a corresponding plurality of testing sites and coupling each such sensor to a control and processing station, operating each of said sensors to spectrophotometrically irradiate a particular region within the test subject; detecting and receiving the light energy resulting from said spectrophotometric irradiation for each such region and conveying corresponding signals to said control and processing station, analyzing said conveyed signals to determine preselected blood metabolite data, and visually displaying the data so determined for each of a plurality of said areas or regions in a comparative manner.

The invention claimed is: 
     
       1. A method for comparative spectrophotometric in vivo monitoring and display of selected blood metabolites present in a plurality of different internal regions of the same test subject on a continuing and substantially concurrent basis, comprising the steps of:
 applying separate spectrophotometric sensors to a test subject at each of a plurality of separate testing sites and coupling each of said sensors to a control and processing station;   operating a selected number of said sensors on a substantially concurrent basis to spectrophotometrically irradiate at least two separate internal regions of the test subject during a common time interval, each of said regions being associated with a different of said testing sites;   separately detecting and receiving light energy resulting from said spectrophotometric irradiation for each of said at least two separate internal regions, and conveying separate sets of signals to said control and processing station which correspond to the separately detected light energy from said at least two separate internal regions;   separately and concurrently analyzing said conveyed separate sets of signals to separately determine quantified data representative of a blood metabolite in each of said at least two separate internal regions; and   concurrently visually displaying said separately determined quantified data for each of said at least two separate internal regions for direct concurrent mutual comparison, wherein said sensors are applied to a head of the test subject and are used to monitor two mutually separate regions within a brain of the test subject.   
     
     
       2. The method of  claim 1 , wherein said step of analyzing comprises quantitative determination of blood oxygenation levels within each of said at least two separate internal regions. 
     
     
       3. The method of  claim 2 , wherein said analyzing step includes producing separate quantitative value determinations for hemoglobin oxygen saturation for each of said at least two separate internal regions. 
     
     
       4. The method of  claim 3 , wherein said analyzing step includes production of ongoing graphical traces representing a plurality of said quantitative value determinations made at successive points in time. 
     
     
       5. The method of  claim 4  including the step of visually displaying a plurality of said graphical traces at substantially the same time and in predetermined relationship to one another to facilitate rapid and accurate visual comparison. 
     
     
       6. The method of  claim 5 , including the step of visually displaying a plurality of said quantitative value determinations at substantially the same time and in predetermined relationship to one another to facilitate rapid and accurate visual comparison. 
     
     
       7. The method of  claim 3 , including the step of visually displaying a plurality of said quantitative value determinations at substantially the same time and in predetermined relationship to one another to facilitate rapid and accurate visual comparison. 
     
     
       8. The method of  claim 1 , wherein said metabolite comprises hemoglobin oxygen. 
     
     
       9. The method of  claim 1 , wherein said sensors are positioned in locations proximate to different brain hemispheres and said two mutually separate regions are located in a different brain hemisphere. 
     
     
       10. The method of  claim 9 , wherein said metabolite comprises cerebral blood hemoglobin oxygenation. 
     
     
       11. An apparatus for concurrent comparative spectrophotometric in vivo monitoring of selected blood metabolites present in each of a plurality of different internal regions on a continuing basis, comprising:
 a plurality of spectrophotometric sensors, each attachable to a test subject at different test locations and adapted to separately but concurrently spectrophotometrically irradiate at least two different internal regions within the test subject associated with each of said test locations;   a controller and circuitry coupling each of said sensors to said controller for separately and individually but concurrently operating certain of said sensors to spectrophotometrically irradiate each of said different internal regions within the test subject associated with each of said test locations;   said sensors each further adapted to receive light energy resulting from the separate spectrophotometric irradiation of said sensors' associated one of said at least two different internal regions on a substantially concurrent basis with other said sensors, and to produce separate signals corresponding to the light energy received, said circuitry acting to convey said separate signals to said controller for separate analytic processing;   said controller adapted to analytically process said conveyed signals separately and determine separate quantified blood metabolite data therefrom for each of said sensors and said sensors' associated one of said at least two different internal regions; and   a visual display coupled to said controller and adapted to separately but concurrently display the quantified blood metabolite data determined for each of said sensors in a mutually-comparative manner, wherein said sensors are adapted to be applied to a head of the test subject and to monitor a brain of the test subject.   
     
     
       12. The apparatus of  claim 11 , wherein said controller is adapted to analyze said data to quantitatively determine blood oxygenation within said at least two different internal regions. 
     
     
       13. The apparatus of  claim 12 , wherein said controller is adapted to produce separate numeric value designations for hemoglobin oxygen saturation for said at least two different internal regions. 
     
     
       14. The apparatus of  claim 13 , wherein said controller and said display are adapted to produce ongoing graphical traces representing a plurality of said numeric value designations for the same region taken over a period of time. 
     
     
       15. The apparatus of  claim 14 , wherein said controller and said display are adapted to visually display at least two of said graphical traces on a substantially concurrent basis and in predetermined relationship to one another to facilitate rapid and accurate visual comparison. 
     
     
       16. The apparatus of  claim 15 , wherein said controller and said display are adapted to visually display at least two of said numeric value designations as well as at least two of said graphical traces on a substantially concurrent basis and in proximity to one another to facilitate rapid and accurate visual comparison. 
     
     
       17. The apparatus of  claim 13 , wherein said controller and said display are adapted to visually display at least two of said numeric value designations on a substantially concurrent basis and in predetermined relationship to one another to facilitate rapid and accurate visual comparison. 
     
     
       18. The apparatus of  claim 11 , wherein said sensors are adapted to provide signals to said controller which comprise at least two separate data sets that cooperatively define at least portions of a particular area within a given one of said at least two different internal regions. 
     
     
       19. The apparatus of  claim 18 , wherein said data sets provided by said sensors include a first set characterizing a first part of said particular area and a second set characterizing a second part of said particular area. 
     
     
       20. The apparatus of  claim 19 , wherein said second part of said particular area characterized by said second set includes at least part of said first part of said area. 
     
     
       21. The apparatus of  claim 11 , wherein said controller is adapted to determine blood oxygenation saturation in said brain. 
     
     
       22. The apparatus of  claim 11 , wherein at least two of said sensors are adapted to be positioned in locations associated with mutually different hemispheres of the brain and each of said sensors is operable to separately monitor at least portions of each of said different hemispheres. 
     
     
       23. The apparatus of  claim 22 , wherein said controller is adapted to determine cerebral blood oxygenation saturation within each of said different hemispheres. 
     
     
       24. The apparatus of  claim 22 , wherein said sensors are adapted to provide signals to said controller which comprise at least two data sets that cooperatively define at least portions of a particular area within the same hemisphere of said brain. 
     
     
       25. The apparatus of  claim 11 , wherein said sensors are adapted to be applied to the outside periphery of the test subject and to operate non-invasively. 
     
     
       26. A method for concurrent comparative in vivo monitoring of blood metabolites in each of a plurality of different internal regions in a selected test subject, comprising the steps of:
 spectrophotometrically irradiating each of a plurality of different testing sites on said test subject;   detecting light energy resulting from said spectrophotometric irradiation of said testing sites, and providing separate sets of signals to a control and processing station which are representative of the light energy received by each of said testing sites and which cooperatively define blood metabolite data for an individual one of at least two different internal regions;   analyzing said separate signals to determine quantified blood metabolite data representative of at least one defined region within said at least one test subject associated with each of at least two different of said testing sites, each said defined region being different from the other; and   concurrently displaying data sets for each of said at least two different internal regions at substantially the same time for direct mutual comparison, wherein said at least two different internal regions are located within different brain hemispheres of said test subject.   
     
     
       27. The method of  claim 26 , wherein said data sets include a first set which characterizes a first zone within one of said at least two different internal regions and a second set which characterizes a second zone that is at least partially within the same one of said at least two different internal regions. 
     
     
       28. The method of  claim 26 , wherein said spectrophotometric irradiation comprises application of at least two different wavelengths applied in an alternating sequence of timed pulses, and wherein detection of light energy corresponding to each of said at least two different wavelengths is done on a timed periodic basis using detection periods whose occurrence generally corresponds to that of said applied spectrophotometric irradiation. 
     
     
       29. The method of  claim 28 , wherein the duration of each of said detection periods is limited to a length which is less than that of each pulse of applied spectrophotometric irradiation. 
     
     
       30. The method of  claim 29 , wherein the duration of each of said detection periods is less than half that of a pulse of said applied spectrophotometric irradiation. 
     
     
       31. The method of  claim 30 , wherein a plurality of said detection periods are used during pulses of said applied spectrophotometric irradiation, and a corresponding energy detection occurs during each of a plurality of said detection periods. 
     
     
       32. The method of  claim 31 , further including the steps of averaging a selected number of energy detection event values to obtain a resultant value therefor, and using said resultant value to compute a metabolite value which is representative thereof. 
     
     
       33. The method of  claim 32 , wherein said display includes said computed representative metabolite value. 
     
     
       34. The method of  claim 33 , wherein said display is refreshed periodically by using a sequence of computed representative metabolite values which are based upon and represent the averaged detection event values produced during the different time intervals corresponding to the intervals of said periodic display refreshment. 
     
     
       35. Apparatus for spectrophotometric in vivo monitoring of a selected metabolic condition in each of a plurality of different test subject regions on a substantially concurrent basis, comprising:
 a plurality of spectrophotometric emitters, each adapted to separately spectrophotometrically irradiate a designated region within a test subject from a test location on said test subject;   a controller and circuitry coupling each of said emitters to said controller for individually operating selected ones of said emitters to spectrophotometrically irradiate at least two particular regions within the test subject;   a plurality of detectors, each adapted to separately receive light energy resulting from the spectrophotometric irradiation of said at least two particular regions, and to produce at least one separate set of signals for each one of said at least two particular regions; and circuitry acting to convey said at least one separate set of signals to said controller for analytic processing;   said controller adapted to analytically process said at least one separate set of signals to determine separate sets of quantified data representative of a metabolic condition in said at least two particular regions; and   a visual display coupled to said controller and adapted to display separate representations of said separate sets of quantified data for each of said at least two particular regions in a mutually-comparative manner and on a substantially concurrent basis, wherein at least two of said at least two particular regions are located in mutually separate regions of a brain of said test subject.   
     
     
       36. The apparatus of  claim 35 , wherein said controller includes a computer programmed to analyze said signals to separately determine a blood oxygenation state within each of said at least two particular regions. 
     
     
       37. The apparatus of  claim 36 , wherein said computer comprises a processor, data buffers, and a timing signal generator, said data buffers adapted to store data representative of said blood oxygenation state and said timing signal generator adapted to control actuation of said emitters and detectors. 
     
     
       38. The apparatus of  claim 36 , wherein said controller comprises a unitary device which includes said computer and said display. 
     
     
       39. The apparatus of  claim 38 , wherein said unitary device further includes a keyboard interface to said computer. 
     
     
       40. The apparatus of  claim 38 , wherein said unitary device further includes a data output interface. 
     
     
       41. The apparatus of  claim 40 , wherein said unitary device further includes an integral keyboard interface to said computer. 
     
     
       42. The apparatus of  claim 38 , wherein said display comprises a flat electroluminescent visual display screen. 
     
     
       43. The apparatus of  claim 42 , wherein said unitary device further includes an integral keyboard interface to said computer. 
     
     
       44. The apparatus of  claim 35 , wherein at least certain of said detectors and certain of said emitters comprise operational pairs, and said controller is arranged to operate the emitters and detectors of at least certain of said operational pairs in predetermined timed relationship while maintaining the emitters and detectors of other of said operational pairs in a non-operating condition. 
     
     
       45. The apparatus of  claim 44 , wherein said controller is adapted to sequence the operation of said at least certain of said operational pairs. 
     
     
       46. The apparatus of  claim 45 , wherein at least one of said operational pairs include a plurality of said detectors arranged at mutually spaced locations which are spaced at differing distances from the emitter of said at least one of said operational pairs. 
     
     
       47. The apparatus of  claim 46 , wherein said controller is adapted to operate the emitter and a selected number less than all of the detectors of at least one of said operational pairs substantially in unison while holding the other detectors of said at least one of said operational pairs in a non-operating condition, and said controller is further arranged to operate said other detectors substantially in unison with said emitter at another time during which said selected number of said detectors are maintained in a non-operating condition. 
     
     
       48. The apparatus of  claim 44 , wherein at least one of said operational pairs includes a first detector and a second detector, and wherein the first detector is located nearer the emitter than the second detector to thereby provide near and far detector groupings for said at least one of said operational pairs. 
     
     
       49. The apparatus of  claim 48 , wherein said controller is adapted to sequence the operation of said at least one of said operational pairs. 
     
     
       50. A system for evaluating oxygen saturation values in human tissue, the system comprising:
 a first emitter, a second emitter, a first detector, and a second detector, the first emitter being adapted to emit at least a first light into the human tissue, the second emitter being adapted to emit at least a second light into the human tissue;   the first detector being adapted to detect the first light propagated over a first mean path through a first region of the human tissue that is primarily confined to layers of skin, tissue, and skull outside a brain and to detect the second light propagated over a second mean path through a second region of the human tissue, the first mean path having a first length and the second mean path having a second length greater than the first length, the first detector being further configured to detect at least two different wavelengths of the first light;   the second detector being adapted to detect the first light propagated over a third mean path through a third region of the human tissue and to detect the second light propagated over a fourth mean path through a fourth region of the human tissue that is primarily confined to layers of skin, tissue, and skull outside the brain, the third mean path having a third length and the fourth mean path having a fourth length less than the third length, the second detector being further configured to detect at least two different wavelengths of the second light;   the first detector and the second detector being configured to produce a set of signals indicative of the first light and the second light detected by the first detector and the second detector;   the first detector and the second detector being spaced apart by a first distance and the first detector and the first emitter being spaced apart by a second distance, the first distance being greater than or approximately equal to the second distance, and   an oximeter unit being configured to receive the set of signals and to determine at least regional blood oxygen saturation values of the human tissue, represented by the second and third regions, based at least in part on the set of signals.   
     
     
       51. The system of claim 50, wherein the first emitter, the second emitter, the first detector, and the second detector are aligned in a plane. 
     
     
       52. The system of claim 51, wherein the first detector and the second detector are adapted to produce the set of signals when the second mean path and the third mean path intersect at a location below a tissue surface of the human tissue. 
     
     
       53. The system of claim 52, wherein the first detector and the second detector are adapted to produce the set of signals when the third mean path lies farther from the tissue surface than the second mean path along a line orthogonal to the surface of the tissue and between the first detector and the second detector. 
     
     
       54. The system of claim 51, wherein the first detector and the second detector are adapted to produce the set of signals when the second mean path lies substantially as far from a tissue surface as the third mean path at approximately a midpoint between the first detector and the second detector. 
     
     
       55. The system of claim 50, wherein the first length is substantially equivalent to the fourth length and the second length is substantially equivalent to the third length. 
     
     
       56. The system of claim 50, wherein the first and second emitters alternately emit at least the first light and at least the second light along a paring of mean paths and the pairing of mean paths includes at least the first mean path and the second mean path. 
     
     
       57. The system of claim 50, wherein the oximeter unit is adapted to remove one or more effects attributable to a portion of the human tissue in which the first mean path and the fourth mean path travel. 
     
     
       58. The system of claim 50, wherein the first light and the second light each include at least four different wavelengths and the first detector and the second detector are each adapted to detect the wavelengths of the first light and the second light. 
     
     
       59. The system of claim 50, wherein the first emitter comprises:
 a first narrow-bandwidth light-emitting diode (LED) configured to output a first center output wavelength of the first light;   a second narrow-bandwidth LED configured to output a second center output wavelength of the first light, the second center output wavelength being different than the first center output wavelength;   a third narrow-bandwidth LED configured to output a third center output wavelength of the first light, the third center output wavelength being different than the first and second center output wavelengths; and   a fourth narrow-bandwidth LED configured to output a fourth center output wavelength of the first light, the fourth center output wavelength being different than the first, second, and third center output wavelengths, the first detector and the second detector being adapted to detect each of the four center output wavelengths of the first light.   
     
     
       60. The system of claim 50, wherein the human tissue is a first human tissue, the set of signals is a first set of signals, and the regional blood oxygen saturation values are first regional blood oxygen saturation values, the system further comprising a third emitter, a fourth emitter, a third detector, and a fourth detector, the third emitter being adapted to emit at least a third light into a second human tissue, the fourth emitter being configured to emit at least a fourth light into the second human tissue;
 the third detector being adapted to detect the third light propagated over a fifth mean path through a fifth region of the second human tissue and to detect the fourth light propagated over a sixth mean path through a sixth region of the second human tissue, the fifth mean path having a fifth length and the sixth mean path having a sixth length, the third detector being further configured to detect at least two different wavelengths of the third light;   the fourth detector being adapted to detect the third light propagated over a seventh mean path through a seventh region of the second human tissue and to detect the fourth light propagated over an eighth mean path through an eighth region of the second human tissue, the seventh mean path having a seventh length and the eighth mean path having an eighth length, the fourth detector being further configured to detect at least two different wavelengths of the fourth light;   the seventh length being greater than the fifth length and the sixth length being greater than the eight length;   the third detector and the fourth detector being configured to produce a second set of signals indicative of the third light and the fourth light detected by the third detector and the fourth detector; and   the oximeter unit being configured to receive the second set of signals and to determine at least second regional blood oxygen saturation values of the second human tissue, represented by the sixth and seventh regions, based at least in part on the second set of signals.   
     
     
       61. The system of claim 60, wherein the oximeter unit includes a display configured to convey one or more superimposed trace lines indicative of at least the first regional blood oxygen saturation values and the second regional blood oxygen saturation values over time. 
     
     
       62. The system of claim 60, wherein the first human tissue includes a first brain hemisphere, the second human tissue includes a second brain hemisphere, the oximeter unit is capable of determining the first regional blood oxygen saturation values when the first emitter is adapted to emit light into the first brain hemisphere, the first regional blood oxygen saturation values being regional blood oxygen saturation values of the first brain hemisphere, and the oximeter unit is further capable of determining the second regional blood oxygen saturation values when the second emitter is adapted to emit light into the second brain hemisphere, the second regional blood oxygen saturation values being regional blood oxygen saturation values of the second brain hemisphere. 
     
     
       63. The system of claim 50, wherein the first emitter and the first detector form a first near coupling, the second detector is located farther from the first emitter than the first detector to form a first far coupling, the second emitter and the first detector form a second far coupling, and the second detector is located closer to the second emitter than the first detector to form a second near coupling. 
     
     
       64. The system of claim 50, wherein the first emitter and the second emitter are further adapted to transmit the first light and the second light along the first and fourth mean paths, respectively, that substantially avoid the second and third regions of the human tissue. 
     
     
       65. The system of claim 50, wherein the first detector is adapted to produce signals indicative of background light during a time that the first and second emitters are not emitting, and the oximeter unit is further configured to determine the regional blood oxygen saturation values using the signals indicative of background light. 
     
     
       66. The system of claim 50, wherein the first emitter and the second emitter are secured within different sensor bodies. 
     
     
       67. A method for evaluating oxygen saturation values in human tissue, the method comprising:
 detecting, with a first detector, at least two wavelengths of a first light propagated over a first mean path through a first tissue region, the first mean path being primarily confined to layers of skin, tissue, and skull outside the brain, and at least two different wavelengths of a second light propagated over a second mean path through a second tissue region, the first mean path having a first length and the second mean path having a second length;   detecting, with a second detector, at least two different wavelengths of the first light propagated over a third mean path through a third tissue region and at least two different wavelengths of the second light propagated over a fourth mean path through a fourth tissue region, the fourth mean path being primarily confined to layers of skin, tissue, and skull outside the brain, the third mean path having a third length and the fourth mean path having a fourth length;   the first length being less than the third length and the fourth length being less than the second length;   generating, with the first detector and the second detector, a set of signals indicative of the first light and the second light detected by the first detector and the second detector;   receiving, with an oximeter unit, the set of signals; and   determining, with the oximeter unit, at least regional blood oxygen saturation values for the tissue, represented by the second and third tissue regions, based at least in part on the set of signals.   
     
     
       68. The method of claim 67, wherein the set of signals is a first set of signals, and the regional blood oxygen saturation values are first regional blood oxygen saturation values, the method further comprising:
 detecting, with a third detector, at least two different wavelengths of a third light propagated over a fifth mean path through a fifth tissue region and at least two different wavelengths of a fourth light propagated over a sixth mean path through a sixth tissue region, the fifth mean path having a fifth length and the sixth mean path having a sixth length;   detecting, with a fourth detector, at least two different wavelengths of the third light propagated over a seventh mean path through a seventh tissue region and at least two different wavelengths of the fourth light propagated over an eighth mean path through an eighth tissue region, the seventh mean path having a seventh length and the eighth mean path having an eighth length;   the fifth length being less than the seventh length and the eight length being less than the sixth length;   generating, with the third detector and the fourth detector, a second set of signals indicative of the third light and the fourth light detected by the third detector and the fourth detector;   receiving, with an oximeter unit, the second set of signals; and   determining, with the oximeter unit, at least second regional blood oxygen saturation values for the tissue, represented by the sixth and seventh tissue regions, based at least in part on the second set of signals.   
     
     
       69. The method of claim 68, further comprising a step of displaying a first indicator of the first regional blood oxygen saturation values on a monitor of the oximeter unit and a step of displaying a second indicator of the second regional blood oxygen saturation values on the monitor. 
     
     
       70. The method of claim 68, wherein the step of determining, at the oximeter unit, at least the second regional blood oxygen saturation values includes removing one or more effects attributable to portions of the tissue in which the fifth mean path and the eighth mean path travel. 
     
     
       71. The method of claim 67, wherein the determining step includes removing one or more effects attributable to portions of the tissue in which the first mean path and the fourth mean path travel. 
     
     
       72. The method of claim 67, wherein the first light detected at the first detector includes a first center output wavelength, a second center output wavelength, a third center output wavelength, and a fourth center output wavelength, each center output wavelength being different and each center output wavelength being generated by a separate narrow-bandwidth light emitting diode.