Methods for noninvasively measuring analyte levels in a subject

• US 20060276696A1
• Filed: 06/02/2006
• Published: 12/07/2006
• Est. Priority Date: 08/11/2004
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: GlucoLight Corporation
• Inventors: Schurman, Matthew J., Shakespeare, Walter J., Bennett, William Henry
• Granted Patent: US 8,036,727 B2
• Time in Patent Office: Days
• US Class Current: 600/316
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters

Abstract

A method for noninvasively measuring analytes such as blood glucose levels includes using a non-imaging OCT-based system to scan a two-dimensional area of biological tissue and gather data continuously during the scanning. Structures within the tissue where measured-analyte-induced changes to the OCT data dominate over changes induced by other analytes are identified by focusing on highly localized regions of the data curve produced from the OCT scan which correspond to discontinuities in the OCT data curve. The data from these localized regions then can be related to measured analyte levels.

Claims

1. A method for calibrating optical coherence tomography (OCT) measurements using a plurality of light wavelengths to identify a tissue for measurement, comprising:

obtaining at least a first and a second OCT scattering profile based on light attenuated by a subject'"'"'s tissue as a function of depth at a first and a second wavelength of light respectively, the tissue having a different attenuation coefficient at the first selected wavelength relative to the second selected wavelength; and

identifying a localized region corresponding to a tissue location for OCT measurement calibration based upon differential comparison of the first and second OCT scattering profiles.

2. The method of claim 1, wherein the localized region corresponding to the tissue location undergoes light attenuation changes due to the presence of a measurable analyte.

3. The method of claim 2, wherein the measurable analyte is blood glucose.

4. The method of claim 1, wherein the tissue has a different absorption coefficient at the first selected wavelength relative to the second selected wavelength.

5. The method of claim 1, further comprising:

normalizing the first and second OCT scattering profiles prior to differential comparison to obtain first and second normalized profiles; and

identifying a localized region corresponding to a tissue location for OCT measurement calibration based upon differential comparison of the first and second normalized profiles.

6. The method of claim 5, further comprising:

obtaining a difference profile by subtraction of one normalized profile from the other normalized profile.

7. The method of claim 6, further comprising:

identifying at least one extrema point in the difference profile.

8. The method of claim 7, wherein the step of identifying the localized region corresponding to the tissue location further comprises corresponding the localized region with at least one depth associated with the at least one extrema point.

9. The method of claim 1, wherein the step of identifying the localized region further comprises:

corresponding at least one offset location with the localized region; and

identifying at least one interval on an OCT scattering profile using the at least one offset location, the at least one interval and at least one offset location defining a localized region of the OCT scattering profile to be correlated with a particular attenuation coefficient.

10. The method of claim 9, wherein the step of identifying at least one interval on the OCT scattering profile further comprises using the at least one interval and the at least one offset location to define a slope corresponding with the particular attenuation coefficient.

11. The method of claim 9, wherein the particular attenuation coefficient is a scattering coefficient.

12. The method of claim 1, further comprising:

obtaining a first and a second blood glucose measurement to correlate with the first and the second OCT scattering profiles respectively.

13. The method of claim 12, further comprising:

calibrating OCT measurements by using a correlation between the first and second blood glucose measurements and the first and second OCT scattering profiles to correspond the OCT measurements with blood glucose levels.

14. The method of claim 1, wherein the step of obtaining at least the first and the second normalized OCT scattering profile further comprises using the first and the second selected wavelengths of light such that the tissue has a larger scattering coefficient than absorption coefficient at the first selected wavelength, and a larger absorption coefficient for the second selected wavelength relative to the first selected wavelength.

15. The method of claim 1, wherein the step of obtaining at least the first and the second scattering profiles further comprises attenuating light at the first and second selected wavelengths based at least in part on a presence of a selected analyte associated with the tissue.

16. The method of claim 15, wherein the analyte is at least one of water and hemoglobin.

17. The method of claim 1, wherein the tissue includes at least one of vascular tissue, at least one component of blood, and dermal tissue surrounding vascular tissue.

18. The method of claim 17, wherein vascular tissue comprises a blood vessel wall.

19. A method for determining an absorption coefficient in optical coherence tomography (OCT) measurements using a plurality of light wavelengths, comprising:

obtaining a first and a second OCT scattering profile based on light reflected from a subject'"'"'s tissue as a function of depth at a first and a second selected wavelength respectively, the tissue having a larger scattering coefficient than absorption coefficient at the first selected wavelength;

determining a scattering coefficient from the first OCT scattering profile;

estimating a scattering coefficient in the second OCT scattering profile based on the scattering coefficient of the first OCT scattering profile; and

determining an absorption coefficient in the second OCT scattering profile using the estimated scattering coefficient of the second OCT scattering profile.

20. The method of claim 19, wherein the scattering coefficient of the tissue at the first wavelength is at least about 5 times greater than the absorption coefficient of the tissue at the first selected wavelength.

21. The method of claim 19, wherein the step of determining the scattering coefficient from the first OCT scattering profile further comprises calculating the slope of a plot of a function of reflected intensity versus depth.

22. The method of claim 19, wherein the step of estimating the scattering coefficient in the second OCT scattering profile further comprises using a scattering theory with the scattering coefficient of the first OCT scattering profile to estimate the scattering coefficient of the second OCT scattering profile.

23. A method for calibrating optical coherence tomography (OCT) measurements using a plurality of light wavelengths to identify a tissue for measurement, comprising:

obtaining at least a first and a second OCT measurement based on light attenuated by a subject'"'"'s tissue as a function of time at a first and a second wavelength of light respectively, the tissue having a larger absorption coefficient at the first selected wavelength relative to the second selected wavelength, the absorption coefficient depending upon the presence of an analyte;

converting the first OCT measurement into an analyte measurement as a function of time; and

using the analyte measurement to calibrate scattering coefficient determinations from the second OCT measurement as a function of time.

24. The method of claim 23, wherein the analyte is water.

25. The method of claim 23, wherein the scattering coefficient of the tissue is at least about 5 times greater than the absorption coefficient of the tissue at the second selected wavelength.