Tissue hydration estimation by spectral absorption bandwidth measurement

• US 20080076983A1
• Filed: 09/27/2006
• Published: 03/27/2008
• Est. Priority Date: 09/27/2006
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Debreczeny, Martin P., Baker, Clark R.
• Granted Patent: US 8,180,419 B2
• Time in Patent Office: Days
• US Class Current: 600/310
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: G01N 21/3554 for determining moisture content
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/359 using near infrared light

Abstract

A system and method are provided for determining tissue hydration. Specifically, in accordance with one aspect of the present invention there is provided a method for determining tissue hydration. The method includes detecting electromagnetic radiation scattered and reflected from the living tissue and using the detected electromagnetic radiation to determine spectral absorption bandwidth. The method also includes correlating the spectral absorption bandwidth to a tissue hydration index.

Claims

1. A method for determining tissue hydration comprising:

detecting electromagnetic radiation scattered and reflected from the living tissue;

using the detected electromagnetic radiation to determine spectral absorption bandwidth; and

correlating the spectral absorption bandwidth to a tissue hydration index.

2. The method of claim 1, comprising determining peak shift and correlating peak shift and the spectral absorption bandwidth to the tissue hydration index.

3. The method of claim 1, wherein emitting electromagnetic radiation comprises using light emitting diodes (LEDs) operating in the near-infrared spectrum having a spectral bandwidth of less than approximately 75 nm.

4. The method of claim 3, comprising using LEDs having emission peaks at 1500 nm and 1450 nm.

5. The method of claim 4 comprising using an additional LED having an emission peak at 1400 nm, the method comprising combining the measurements at the three wavelengths to provide an estimate of a lean water fraction in the tissue.

6. The method of claim 5, comprising:

linearly combining the logarithm of the measurements at the three wavelengths to produce a quantity related to the ratio of water-to-protein, (r), in the tissue; and

correlating the ratio to the lean water fraction, (f¹_w), by;

f¹_w=r/(1+r).

7. The method of claim 3, comprising using LEDs having emission peaks at 1550 nm, 1450 nm and 1400 nm.

8. The method of claim 3, comprising using LEDs having emission peaks at 1550 nm, 1430 nm and 850 nm.

9. The method of claim 3, comprising using LEDs having emission peaks at 1500 nm, 1450 nm, 1100 nm, and 1070 nm.

10. The method of claim 1, wherein emitting electromagnetic radiation comprises using at least one tunable laser.

11. The method of claim 1, wherein emitting electromagnetic radiation comprises using vertical-cavity surface-emitting lasers.

12. The method of claim 1, wherein emitting electromagnetic radiation comprises using a broadband source coupled with narrowband optical filters.

13. The method of claim 1, wherein emitting electromagnetic radiation comprises implementing NIR spectroscopy.

14. The method of claim 13, comprising using scanning-grating spectroscopy.

15. The method of claim 13, comprising using diode array spectroscopy.

16. The method of claim 13, comprising Fourier transform spectroscopy.

17. The method of claim 13, comprising Hadamard transform spectroscopy.

18. The method of claim 1, wherein detecting electromagnetic radiation comprises using an InGaAs detector.

19. The method of claim 3, comprising using at least two LEDs having emission peaks spaced 25 to 250 nm apart in the 1800 to 2100 nm region of the spectrum.

20. A system for measurement of living tissue comprising:

a sensor unit configured to emit and detect electromagnetic radiation; and

an hydration index unit coupled to the sensor unit and configured to determine spectral absorption bandwidth and correlate the spectral absorption bandwidth to living tissue hydration.

21. The system of claim 20, comprising a display configured to output a tissue hydration estimation.

22. The system of claim 20, wherein the sensor unit comprises at least one emitter and at least one detector.

23. The system of claim 20, wherein the at least one emitter operates in the 1300 nm to 1650 nm spectral region.

24. The system of claim 20, wherein the at least one emitter comprises a first LED operating at 1500 nm having a spectral bandwidth of less than 75 nm and a second LED operating at 1450 nm having a spectral bandwidth of less than 75 nm.

25. The system of claim 24, wherein the at least one emitter comprises a third LED operating at 1400 nm having a spectral bandwidth of 75 nm or less.

26. The system of claim 22, wherein the at least one detector comprises an InGaAs photodetector.

27. The system of claim 20, wherein the hydration index unit is configured to determine peak shift and correlate peak shift and spectral absorption bandwidth to hydration.

28. The system of claim 20, wherein the hydration index unit and the sensor unit are integrated into the same housing.

29. The system of claim 20, wherein the sensor unit comprises a tunable laser.

30. The system of claim 20, wherein the sensor comprises a broadband source coupled with narrowband optical filters.

31. The system of claim 20, wherein the sensor comprises a vertical-cavity surface-emitting laser.

32. The system of claim 20, wherein the sensor comprises a scanning-grating spectroscope.

33. The system of claim 20, wherein the sensor comprises a diode array spectroscope.

34. The system of claim 20, wherein the sensor comprises a Fourier transform spectroscope.

35. The system of claim 20, wherein the sensor comprises a Hadamard transform spectroscope.

36. A method for estimating analyte concentration comprising:

measuring the spectral absorption bandwidth of an analyte near an absorption band of the analyte, wherein measuring the spectral absorption bandwidth of the analyte comprises transmitting electromagnetic radiation into living tissue and using a photo sensitive detector to generate a photo electrical signal representative of the electromagnetic radiation detected; and

correlating the spectral absorption bandwidth of the analyte to a relative concentration level of the analyte.

37. The method of claim 36 comprising determining peak shift of the absorption band of the analyte and correlating the peak shift to the concentration of the analyte.

38. The method of claim 36 comprising calibrating the correlation of the spectral absorption bandwidth to the analyte concentration based on a determination of body fat or local fat.

39. The method of claim 36 comprising calibrating the correlation of the spectral absorption bandwidth to the analyte concentration based on a determination of body temperature.