Tissue Oximetry Apparatus and Method

• US 20080015424A1
• Filed: 07/20/2007
• Published: 01/17/2008
• Est. Priority Date: 03/14/2005
• Status: Active Grant

• Current Assignee: Peter Bernreuter
• Original Assignee: Peter Bernreuter
• Inventors: Bernreuter, Peter
• Granted Patent: US 8,055,321 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 2560/0238 Means for recording calibration data
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 2562/0242 for varying or adjusting the optical path length in the tissue
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/72 Signal processing specially adapted for physiological signals or for diagnostic purposes character recognition, recognising digital ink, document-oriented image-based pattern recognition G06V30/00; recognition or understanding of postal images G06V30/424
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence

Abstract

An apparatus and method for determining tissue oxygenation such as arterial and venous oxygenation and cerebral oxygenation. In one embodiment the optical properties of tissue are determined using measured light attenuations at a set of wavelengths. By choosing distinct wavelengths and using light attenuation information, the influence of variables such as light scattering, absorption and other optical tissue properties can be minimized.

Claims

1. Apparatus for measuring tissue oxygenation of a patient comprising:

a sensor interface adapted to be coupled to a patient tissue site and including at least one light emitter emitting light into tissue and at least one detector detecting light passing through tissue from said at least one emitter;

a processor for determining light attenuations LAwsj dependant on light detected at a selected wavelength, wsj;

a coupling device for coupling said sensor interface at said tissue site;

a data processor for generating a signal representative of tissue oxgenation based said determined light attenuations; and

a display device displaying a tissue oxygenation level.

2. The apparatus of claim 1 wherein said data processor includes means for generating a signal representative of tissue oxygenation and provides arterial oxygenation information based on pulsating changes of light attenuations.

3. The apparatus of claim 2 wherein said at least one emitter is an LED and said at least one detectors is a photodiode.

4. The apparatus of claim 2 wherein said means for generating a signal representative of tissue oxygenation uses a non-pulsating part of light attenuation in order to improve accuracy of said arterial oxygen information

5. The apparatus of claim 1 wherein said means for generating a signal representative of tissue oxygenation uses a nonpulsating part of light attenuation to determine tissue oxygenation.

6. The apparatus of claim 1 wherein said sensor interface is coupled to a chest band or head band.

7. The apparatus of claim 2 wherein said sensor coupling device is an arm band.

8. The apparatus of claim 7 wherein said armband is a wrist band.

9. The apparatus of claim 7 comprising:

elastic means for controlling a force applied to tissue through the sensor interface.

10. The apparatus of claim 2 wherein said at least one emitter emits light having at least three different wavelengths.

11. The apparatus of claim 2 wherein two determined light attenuations are added and two are subtracted to generate at least one measure related to oxygenation in tissue.

12. The apparatus of claim 2 wherein a pulse or heart rate is additionally determined.

13. The apparatus of claim 1 wherein said display device displays time.

14. An apparatus for measuring tissue oxygenation comprising:

a sensor interface including at least two emitters which emits light into tissue with at least two wavelengths, and at least one detector to receive light passing through said tissue;

a storage device for retaining information of sensor variation within said sensor interface; and

a processor for determining tissue oxygenation using said sensor variation information of said sensor interface.

15. Apparatus according to claim 14 wherein a wavelength emission intensity of at least one of said emitters is compensated for said by said means for calculating.

16. Apparatus according to claim 14 wherein a light emission intensity of at least one of said emitters is compensated for by said means for calculating.

17. Apparatus according to claim 14 wherein a light emission intensity of at least one of said emitters and a wavelength of at least one of said emitters is compensated for by said means for calculating.

18. Apparatus according to claim 17 wherein brain tissue oxygenation is determined using said sensor interface with at least one emitter/detector distance being greater than 3 cm and said sensor interface being provided at one side of a forehead, said apparatus measuring the oxygenation of one brain hemisphere.

19. Apparatus according to claim 18 wherein at least one emitter detector distance is about 1 cm long and a related path can be used to determine a light attenuation or additionally arterial oxygenation by evaluating a pulsatile part of detected light.

20. The apparatus of claim 17 wherein said apparatus performs calculation steps for at least one wavelength wsj of:

calculating light attenuation LA(A1,wsj) of light emitted in a first emitter and received at a first detector;

calculating light attenuation LA(A4,wsj) of light emitted in a second emitter and received at a second detector;

calculating light attenuation LA(A2,wsj) of light emitted in said first emitter and received at said second detector;

calculating light attenuation LA(A3,wsj) of light emitted in said second emitter and received at said first detector; and

computing the optical constitution of the tissue one which corresponds to a resulting light attenuation LAwsj at said wvavelength wsj by weighting and accumulating the light attenuations of LA(A2,wsj) and LA(A3,wsj) and subtracting therefrom the weighted and accumulated light attenuations LA(A1,wsj) and LA(A4, wsj).

21. Apparatus for measuring tissue oxygenation comprising:

a sensor adapted to be coupled to a forehead tissue including at least two light emitters placed apart from each other on said sensor with at least two different wavelengths for each emitter where each emitter has approximately the same wavelengths which emit light into said tissue and at least one detector for detecting light having passed through said tissue, whereby a distance of one said emitters and one of said at east one detector is chosen so that a light path penetrates through the tissue and whereby a distance between at least one emitter-detector pair is more than 20 millimeters;

means for calculating at least two signals which depend on detected light for selected wavelengths wsj for said at least one detector and said at least two emitters, wherein said at least two signals are calculated by adding or subtracting light attenuations;

calculating attenuation corresponding to In(intensity of steady state light received at the detector) for at least two possible light paths between said at least two light emitters and said at least one detector; and

means for generating an output representative of tissue oxygenation based on the at least said two signals.

22. Apparatus of claim 21 using at least two emitters and at least two detectors whereby for at least two of said wavelengths for each of the wavelengths the corresponding light attenuations for two light paths are added and the corresponding light attenuation for two further light paths are subtracted to generate a measure for said at least two signals.

23. The apparatus of claim 22 comprising:

means for calculating a ratio R indicative of tissue oxygenation in brain whereby said two signals are used.

24. The apparatus of claim 22 comprising:

means for calculating a measure of tissue oxygenation level using three different wavelengths with a multidimensional calibration dependant on attenuations of said three wavelengths or two ratios R based on ratios of light attenuations versus oxygenation.

25. The apparatus of claim 22 comprising:

means for calculating a measure of tissue constituents using additional wavelengths of light.

26. The apparatus of claim 22 wherein a calibration is based on empirical data.

27. The apparatus of claim 22 wherein said sensor includes at least one emitter detector distance of at least 4 cm and a second emitter detector distance, of at least 1.5 cm.

28. The apparatus of claim 21 wherein said sensor includes at least one emitter detector distance of at least 4 cm and a second emitter detector distance of at least 1.5 cm.

29. The apparatus of claim 21 wherein at least three of said at least one detector and said at least two emitters are approximately linearly aligned on the sensor.

30. The apparatus of claim 27 where at least 65% of a generated oxygenation signal is originated by brain tissue by adding and subtracting light paths through forehead tissue and brain tissue.

31. Apparatus of claim 28 for monitoring an oxygenation level of brain hemispheres of a subject with a pair of sensors placed on opposites side of the subject'"'"'s forehead.

32. Apparatus of claim 28 for monitoring an oxygenation level of brain hemispheres of a subject with a pair of sensors placed on opposites side of the subject'"'"'s forehead where the sensors include LED)s and photodetectors

33. Apparatus of claim 28 wherein an emitter-detector distance of the sensor placed on one side of the forehead to monitor a brain hemisphere is less than 20 mm long.

34. Apparatus of claim 28 having a means to calculate a measure for arterial oxygenation using a light signal related to an emitter-detector pair separated by a distance of no more than 20 mm.

35. The apparatus of claim 21 wherein for at least one wavelength wsj, said apparatus performs a method comprising:

determining a light attenuation LA(A1,wsj) of light emitted in a first emitter and received at a first detector;

determining a light attenuation LA(A4,wsj) of light emitted in a second emitter and received at a second detector;

determining a light attenuation LA(A2,wsj) of light emitted in said first emitter and received at said second detector;

determining a light attenuation LA(A3,wsj) of light emitted in said second emitter and received at said first detector; and

determining a optical constitution of the tissue which corresponds to a resulting light attenuation LAwsj at said wavelength wsj by weighting and accumulating light attenuations of LA(A2,wsj) and LA(A3,wsj) and subtracting therefrom the weighted and accumulated light attenuations LA(A1,wsj) and LA(A4,wsj)

36. The apparatus of claim 21 wherein at least one detector of said sensor includes an electrically isolated isolation layer and a grounded layer between said isolation layer and an area where said light intensity is detected.

37. The apparatus of claim 36 wherein said at least one detector is adapted for use to detect oxygenation of a brain hemisphere.

38. A method of determining tissue oxygenation comprising:

placing at least two detectors and at least two emitters on a tissue surface and determining a resulting light attenuation by adding a light attenuation measured at a first detector emitted by a first emitter, subtracting a light attenuation between said first emitter and a second detector, and further selecting pairs of detectors and emitters and adding or subtracting light attenuations;

subtracting a light attention from said resulting light attenuation for each detector and emitter pair having a light path which terminates at each detector for at least one light attenuation previously added to generate said resulting light attenuation; and

adding and subtracting light attenuations to determine a measure of tissue oxygenation.

39. The method of claim 38 wherein said detectors and emitters are rectangularly spaced.

40. The method of claim 38 wherein said detectors and emitters are spaced so that at least two light paths through tissue between said emitters and detectors are not crossing.

41. The method of claim 38 wherein said detectors and emitters are spaced to provide asymmetry in said light paths.