Method and apparatus for tissue oximetry

• US 20050059868A1
• Filed: 07/02/2004
• Published: 03/17/2005
• Est. Priority Date: 07/09/2003
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: GlucoLight Corporation
• Inventors: Schurman, Matthew J.
• Granted Patent: US 7,356,365 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

In accordance with the invention, the oxygenation of blood-profused tissue is measured by shining light into the profused tissue and analyzing the light reflected within the tissue. The light is reflected by cell walls in the tissue and is partially absorbed by hemoglobin in the blood. Since the extent of absorption is sensitive to the extent of hemoglobin oxygenation, measurement and processing of the reflected light provides a measure of the oxygenation of the blood. In one embodiment, the method is applied to measure the oxygenation of blood within the tympanic membrane (ear drum).

Claims

1. A method of tissue oximetry on a human or animal subject comprising the steps of:

providing light of at least two different wavelengths, the light of the two wavelengths having different absorption and different reflectivity from oxygenated hemoglobin and deoxygenated hemoglobin, respectively;

splitting the light into a sample beam and a reference beam;

illuminating tissue of the subject with the sample beam;

collecting reflected light from within the illuminated tissue;

interfering the reflected light with reference light from the reference beam; and

measuring the interfered light and processing the measurements to determine the oxygen content of hemoglobin in the tissue.

2. The method of claim 1 wherein the light is provided by one or more low coherence sources.

3. The method of claim 2 wherein the reference light is adjusted in phase to constructively interfere with reflected light that is reflected from within the tissue.

4. The method of claim 1 further comprising the step of moving the sample beam to vary the region of the tissue being illuminated so as to reduce the effect of speckle.

5. A method of tissue oximetry on a subject comprising the steps of:

providing a low coherence interferometer comprising a sample arm, a sample arm probe coupled to the sample arm, a reference arm, a reference arm reflector and one or more detectors;

providing a light source for illuminating tissue of the subject and the reference arm;

positioning the sample arm probe, to sample the light reflected from within the tissue;

interfering light reflected from the tissue and light from the reference arm reflector to select light reflected within tissue comprising blood; and

detecting and processing the interfered light to yield a measurement of blood oxygenation.

6. The method of claim 5 wherein processing comprises processing by computer or microprocessor.

7. The method of claim 5 further comprising the step of increasing the absorption profile by adjusting the pathlength of the reference arm.

8. An apparatus for tissue oximetry of an animal or human subject comprising:

one or more sources of light to provide light at two different wavelengths that respectively absorb and reflect differently from oxygenated hemoglobin;

a first light path to direct a beam of light from the sources onto the tissue of the subject and to receive reflected light from the tissue;

a second light path to direct a beam of reference light from the sources through a phase adjuster;

an interferometer to interfere the reflected light with the phase adjusted reference light, the phase adjustment of the reference light chosen to select by constructive interference, the light reflected from tissue comprising blood;

one or more photodetectors to measure the interfered light; and

a processor to determine the oxygenation of the blood from the measurements,.

9. The apparatus according to claim 8 wherein the sources are low coherence sources and the interferometer comprises a low coherence interferometer.

10. The apparatus according to claim 8 wherein the interferometer comprises:

a beam splitter to split the light into a sample beam and a reference beam, sample light guides to direct a beam of light from the sources onto the tissue of the subject and to receive light reflected from within the tissue, and a reference light path to direct the reference beam into interference with the reflected light.

11. The apparatus of claim 8 wherein the beam splitter comprises a 2×

2 optical splitter.

12. The apparatus of claim 8 wherein the reference light path comprises a reflector to adjust the path length.

13. The apparatus of claim 8 further comprising a photodetector to measure the interfered light.

14. The apparatus of claim 13 where the photodetector comprises a photodiode.

15. The apparatus of claim 8 wherein at least one light source comprises a light emitting diode (LED) or a superluminescent diode (SLED).