Apparatus and method for quantification of tissue hydration using diffuse reflectance spectroscopy

• US 20030060693A1
• Filed: 06/25/2002
• Published: 03/27/2003
• Est. Priority Date: 07/22/1999
• Status: Active Grant

• Current Assignee: GLT Acquisition Corporation
• Original Assignee: Sensys Medical, Inc. (Sensys Medical Limited)
• Inventors: Wenzel, Brian J., Ruchti, Timothy L., Monfre, Stephen L., Blank, Thomas B.
• Granted Patent: US 6,675,029 B2
• Time in Patent Office: Days
• US Class Current: 600/322
• CPC Class Codes: A61B 5/0062 Arrangements for scanning
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/1075 for measuring dimensions by non-invasive methods, e.g. for determining thickness of tissue layer A61B8/0858 takes precedence
• 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
• CPC Class Codes: A61B 5/444 Evaluating skin marks, e.g. mole, nevi, tumour, scar
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: G01N 21/3554 for determining moisture content
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 21/4785 Standardising light scatter apparatus; Standards therefor
• CPC Class Codes: G01N 21/49 within a body or fluid
• CPC Class Codes: G01N 2201/129 Using chemometrical methods

Abstract

An apparatus and method for non-destructively estimating a tissue property, such as hydration, of a living subject utilizes in vivo spectral measurements made by irradiating skin tissue with near infrared (NIR) light. The apparatus includes a spectroscopic instrument in conjunction with a subject interface. The resulting spectra are passed to an analyzer for further processing, which includes detecting and eliminating invalid spectral measurements, and preprocessing to increase the signal-to-noise ratio. Finally, an estimation model developed from an exemplary set of measurements is applied to predict the tissue hydration for the sample. The method of tissue hydration measurement provides additional information about primary sources of systematic tissue variability, namely, the water content of the epidermal layer of skin and the penetration depth of the incident light. Tissue hydration measurement is therefore suitable for further spectral analysis and quantification of biological and chemical compounds, such as analytes.

Claims

1. An apparatus for estimating a tissue property non-destructively, based on spectral measurements, comprising:

means for measuring a spectrum at a selected tissue site on a subject;

an estimation model developed from a calibration set of exemplary samples and independent measurements; and

an analyzer, wherein processing is applied to said spectrum and said model subsequently applied to determine an estimate of said tissue property.

2. The apparatus of claim 1, wherein said spectral measurements comprises near IR (NIR) measurements.

3. The apparatus of claim 1, wherein spectral energy returned from said site is either transmitted through or reflected from said tissue site.

4. The apparatus of claim 1, wherein spectral energy returned from said site is diffusely reflected from said site.

5. The apparatus of claim 1, wherein said means for measuring a spectrum comprises:

an energy source;

means for separating energy into a plurality of targeted wavelengths, wherein said energy at said targeted wavelengths is transmitted to said tissue site;

at least one sensor element, said sensor element adapted to detect energy returned from said site as an analog signal and convert said detected energy to a current;

means converting said current to a voltage; and

means for converting said voltage to a digital signal.

6. The apparatus of claim 5, wherein said energy source and said energy separating means together comprise a plurality of LED'"'"'s, said LED'"'"'s controlled by an LED driver and a master sequence.

7. The apparatus of claim 6, wherein said plurality of LED'"'"'s comprises an LED array, each LED of said array producing energy centered at a specific targeted wavelength.

8. The apparatus of claim 6, wherein each of said plurality of LED'"'"'s is successively illuminated.

9. The apparatus of claim 6, said LED driver controls current flow to each of said LED'"'"'s.

10. The apparatus of claim 6, wherein illumination interval for each LED is controlled according to parameters specified by said master sequence.

11. The apparatus of claim 6, wherein sequence of illumination for said array is controlled according to parameters specified by said master sequence.

12. The apparatus of claim 6, wherein said LED'"'"'s have a peak wavelength of approximately 1.07 μ

m, 1.22 μ

m, and 1.25 μ

m, respectively.

13. The apparatus of claim 12, wherein said LED array transmits energy in a wavelength range of approximately 700-2500 nm.

14. The apparatus of claim 6, wherein each of said LED'"'"'s is equipped with an optical filter.

15. The apparatus of claim 14, wherein said filters have center wavelengths of approximately 1080 nm, 1180 nm, and 1280 nm respectively,

wherein the full width half maximum of said filters ranges from approximately 11 to 14.8 nm.

16. The apparatus of claim 6, further comprising means for conducting energy from said energy source toward said measurement site.

17. The apparatus of claim 16, wherein said means for conducting energy comprises a plurality of illuminating fiber optics, each of said illuminating fiber optics having a probe end.

18. The apparatus of claim 6, wherein said sensor element comprises one or more detectors.

19. The apparatus of claim 18, wherein said detectors comprise InGaAs detectors, and wherein an illuminating surface of said LED'"'"'s comprises a point of illumination, and a detecting surface of said InGaAs detectors comprises a point of detection, and wherein a distance from a point of illumination to a point of detection is approximately 40 μ

m-1 mm.

20. The apparatus of claim 6, wherein said means for directing energy transmitted or reflected from said tissue measurement site and said reference toward said detecting means comprises a plurality of detecting fiber optics, each of said detecting fiber optics having a probe end, and wherein said detection fiber optics radially surround said LED'"'"'s at specific distances.

21. The apparatus of claim 17, further comprising a sample probe head and a reference probe head, said sample probe head comprising a subject interface, wherein said subject interface contacts said site, and wherein said reference probe head is adapted to collect a spectrum of a reference standard.

22. The apparatus of claim 21, wherein each LED has a plurality of associated illuminating fibers, wherein a first portion of said associated illuminating fibers couples said LED to said sample probe head and a second portion of said illuminating fibers couples said LED to said reference probe head.

23. The apparatus of claim 22, wherein said sample probe head comprises the probe ends of said first portion of associated illuminating fibers for each LED, and the probe ends of a plurality of detecting fibers, wherein said detecting fibers surround said illuminating fibers, wherein said probe ends form a closed, packed arrangement.

24. The apparatus of claim 22, wherein said reference probe head comprises the probe ends of said second portion of illuminating fibers for each LED and a plurality of detection fibers, wherein said probe ends form a closed packed arrangement such that said detecting fibers completely surround each of said illuminating fibers

25. The apparatus of claim 9, wherein said means for converting said current to a voltage comprises an analog front end.

26. The apparatus of claim 25, further comprising a phase modulating lock-in amplifier, wherein said voltage signal is received from said analog front end and a reference signal is received from said LED driver wherein said lock-in amplifier amplifies signals that are in phase with said reference signal so that the signal-to-noise ratio is increased, and a direct current output is supplied to a digitizing means.

27. The apparatus of claim 26, wherein said digitizing means comprises a 16-bit analog to digital converter.

28. The apparatus of claim 6, wherein said analyzing means comprises a processor programmed to perform said processing and said estimate determination, said processor including a power supply and an attached display device for displaying said estimate or a message indicating an invalid scan.

29. The apparatus of claim 28, wherein said master sequence is executed on said processor and said power supply supplies current to said LED'"'"'s through said LED driver.

30. The apparatus of claim 28, wherein said processing includes any of:

absorbance calculation;

preprocessing; and

outlier detection.

31. The apparatus of claim 5, wherein said energy source comprises one of:

an LED array and a quartz halogen lamp.

32. The apparatus of claim 5, wherein said separating means comprises one of a monochromator, a spectrometer, a spectrograph, an interferometer, and successive illumination through the elements of an LED array.

33. The apparatus of claim 5, wherein said energy is transmitted to said site through one of:

direct illumination;

a light pipe;

one or more fiber optics;

a lens system; and

a light directing mirror system.

34. The apparatus of claim 5, wherein said sensor element comprises one or more detectors, said detectors responsive to a plurality of targeted wavelengths.

35. The apparatus of claim 5, further comprising means for directing said returned energy, said means for directing comprising one of:

one or more optical detectors; and

one or more fiber optics.

36. The apparatus of claim 5, wherein said converting means comprises one or more analog circuits.

37. The apparatus of claim 5, wherein said digitizing means comprises an analog-to-digital converter.

38. The apparatus of claim 5, wherein said analyzer comprising a data-processing system programmed to perform said analysis.

39. The apparatus of claim 5, further comprising a reference standard.

40. The apparatus of claim 39, wherein processing includes absorbance calculation through a reference spectrum.

41. The apparatus of claim 39, wherein said reference standard is external to remainder of said apparatus.

42. The apparatus of claim 39, wherein said reference standard is internal to said apparatus.

43. The apparatus of claim 1, said property comprising hydration of living tissue.

44. The apparatus of claim 1, said property comprising stratum corneum hydration.

45. The apparatus of claim 1, wherein said means for measuring a spectrum comprises:

a polychromatic light source, wherein polychromatic light is transmitted to said tissue site;

means for separating polychromatic light returned from said site into a plurality of targeted wavelengths;

at least one sensor element, said sensor element adapted to detect light at said plurality of targeted wavelengths as an analog signal and convert said detected light to a current;

means converting said current to a voltage; and

means for converting said voltage to a digital signal.

46. The apparatus of claim 42, wherein said source comprises and LED array.

47. The apparatus of claim 1, wherein said model is based on one of:

multiple linear regression;

principal component regression; and

partial least squares regression.

48. The apparatus of claim 1, said tissue property comprising one of:

body fat;

body composition;

thickness of subcutaneous layer;

chronological age of a subject;

photo-aging of skin;

photo-damage to skin;

skin temperature;

skin thickness;

body fat;

skin cancer detection;

blood volume estimation;

tissue circulation and rate of perfusion;

tissue turgor;

tissue elasticity;

tissue edema;

sex determination;

dermal hydration;

epidermal hydration

tissue deformity;

tissue cholesterol;

sweat;

free and bound water;

orientation of collagen fibers; and

tissue analyte determination, analytes including at least one of;

glucose, cholesterol, triglycerides, sodium, urea, elastin and collagen.