Method and apparatus for monitoring blood constituent levels in biological tissue
View Patent ↗In accordance with the invention, a low coherence interferometer is used to non-invasively monitor the concentration of glucose in blood by shining a light over a surface area of human or animal tissue, continuously scanning the light over a two dimensional area of the surface, collecting the reflected light from within the tissue and constructively interfering this reflected light with light reflected along a reference path to scan the tissue in depth. Since the reflection spectrum is sensitive to glucose concentration at particular wavelengths, measurement and analysis of the reflected light provides a measure of the level of glucose in the blood. The measurement of glucose is taken from multiple depths within blood-profused tissue, and sensitivity is preferably enhanced by the use of multiple wavelengths. Noise or speckle associated with this technique is minimized by continuously scanning the illuminated tissue in area and depth.
1. A method of monitoring blood constituent concentration within a biological tissue comprising:
providing light having scattering properties sensitive to the blood constituent concentration within the biological tissue;
directing the light over an area of the biological tissue;
causing a reflected portion of the light to interfere with a reference beam;
obtaining interferometric, non-image measurements from at least one tissue depth, the non-image measurements including at least scatter measurements of the light; and
processing the non-image measurements to determine the blood constituent concentration within the biological tissue.
2. The method of claim 1 wherein said providing light comprises providing light from one or more sources that is split into a sample beam and the reference beam, and further wherein said directing the light comprises scanning the sample beam over a two-dimensional area, the method further comprising:
varying the phase of the reference beam before causing the reflected portion of the light to interfere with the reference beam.
3. The method of claim 2 further comprising:
adjusting the reference beam to constructively interfere with reflected light from a selected depth within the biological tissue.
4. The method of claim 1 wherein the two-dimensional area is aligned with a skin surface.
5. The method of claim 1 wherein said directing the light over an area comprises scanning the biological tissue to reduce speckle.
6. The method of claim 5 further comprising:
scanning multiple depths within the biological tissue to reduce speckle.
7. The method of claim 1 wherein the light comprises low coherence light.
8. The method of claim 1 wherein the light comprises at least two different wavelengths including a first wavelength having measurably different scattering properties for hemoglobin-containing tissue or indicators of such tissue relative to a second wavelength.
9. The method of claim 8 wherein the at least two different wavelengths comprise at least one wavelength at about 1310 nm, at about 1450 nm, and in a range from about 820 nm to about 960 nm.
10. The method of claim 1 wherein the light comprises at least one of infrared light and near infrared light.
11. The method of claim 1 wherein the reflected portion of the scanned light comprises light reflected from blood-perfused tissue.
12. The method of claim 1 further comprises:
measuring changes in a hydration level of the biological tissue.
13. The method of claim 12 wherein said processing the light measurements comprises compensating for changes in hydration level of the biological tissue.
14. An apparatus for measuring blood constituent concentration of a human or animal subject comprising:
at least one light source for providing a sample beam and a reference beam, the at least one light source providing at least one wavelength of light, the at least one light source configured to direct the sample beam to tissue of the subject;
a phase shifter configured to adjust the phase path of the reference beam;
a scanner to scan the sample beam over a two-dimensional area of the subject's tissue;
an interferometer to constructively interfere a reflected sample beam from the subject tissue with the reference beam;
at least one photodetector to detect the interfered light; and
a processor to calculate blood constituent concentration based at least partly on non-image measurements of the detected interfered light.
15. The apparatus of claim 14 wherein the at least one light source comprises a low coherence source.
16. The apparatus of claim 14 , wherein the interferometer comprises a low coherence interferometer.
17. The apparatus of claim 14 further comprising:
a beam splitter to split light from the at least one light source into the sample beam and the reference beam;
wherein the phase shifter is configured to direct the reference beam to interfere with the reflected sample beam.
18. The apparatus of claim 17 wherein the beam splitter comprises a 2×2 optical splitter.
19. The apparatus of claim 14 wherein the phase shifter comprises an adjustable reflector.
20. The apparatus of claim 19 wherein the reflector is configured to scan multiple depths within the subject tissue.
21. The apparatus of claim 14 wherein the photodetector comprises a photodiode.
22. The apparatus of claim 14 wherein the at least one light source comprises a light emitting diode (LED).
23. The apparatus of claim 14 wherein the at least one light source comprises a superluminescent diode (SLED).
24. The apparatus of claim 14 wherein the scanner comprises a movable lenslet array which can be translated or rotated rapidly to reduce speckle.
25. The apparatus of claim 14 wherein the scanner comprises a movable diffractive optical element which can be translated or rotated rapidly to reduce speckle.
26. The apparatus of claim 14 wherein the scanner is configured to scan the sample beam such that the two-dimensional area is aligned with a skin surface.
27. The apparatus of claim 14 wherein the scanner is configured to scan the sample beam to reduce speckle.
28. The apparatus of claim 14 wherein the apparatus is configured to produce non-imaged interfered light.