Optical measurement of tissue pH

• US 5,813,403 A
• Filed: 11/08/1995
• Issued: 09/29/1998
• Est. Priority Date: 11/08/1995
• Status: Expired due to Term

• Current Assignee: Polestar Technologies Inc., University Of Massachusetts
• Original Assignee: Polestar Technologies Inc.
• Inventors: Soller, Babs R., Micheels, Ronald H.
• Primary Examiner(s): Bahr, Jennifer
• Assistant Examiner(s): YARNELL, BRYAN KEITH
• Application Number:
  US08/555,102
• Time in Patent Office: 1,056 Days
• Field of Search: 128/633, 128/634, 128/664, 128/665, 128/666, 356/39-41, 356/300, 356/306, 356/319, 356/326
• US Class Current: 600/310
• 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 5/0086 using infrared radiation
• CPC Class Codes: A61B 5/14539 for measuring pH

Abstract

The invention provides an optical method and apparatus for determining the pH of a tissue. The method includes the step of first irradiating the tissue with optical radiation. The radiation may first pass through skin covering the tissue of interest, or may irradiate the tissue directly. Radiation reflected from the tissue is then collected to determine a reflection spectrum. pH is then determined by comparing this spectrum to a mathematical model relating optical properties to pH of the tissue.

Claims

1. A non-invasive method for determining the localized pH of a sample tissue disposed underneath a covering tissue of a patient, said method comprising:

irradiating the sample tissue with optical radiation not substantially absorbed by the covering tissue such that the radiation propagates through the covering tissue to irradiate the sample tissue;

collecting radiation from the sample tissue which passes through the covering tissue to determine an optical spectrum; and

,

processing the optical spectrum and a mathematical model to determine the localized pH of the sample tissue, said model relating optical spectra to known pH values of interstitial fluid in tissue.

2. The method of claim 1, wherein said processing includes comparing the optical spectrum to the mathematical model to determine the pH of the sample tissue.

3. A method of claim 1, wherein the covering tissue is skin.

4. A method of claim 1, wherein the optical radiation is infrared radiation.

5. A method of claim 4, wherein the infrared radiation is between 700 nm and 1100 nm.

6. A method of claim 1, wherein the mathematical model is determined prior to said irradiating by collecting multiple optical spectra, each occurring at a known pH value, from a representative sample, and then processing the optical spectra and known pH values with a mathematical algorithm to determine the model.

7. A method of claim 6, wherein the mathematical algorithm is a partial least-squares fitting algorithm.

8. A method of claim 6, wherein the model comprises a linear or non-linear mathematical equation relating pH to the reflectivity or absorptivity of the sample tissue.

9. A method of claim 6, wherein the representative sample is a sample tissue of the patient.

10. A method of claim 6, wherein the representative sample is a solution or a second tissue.

11. A method of claim 1, wherein the sample tissue comprises muscle or organ.

12. A method of claim 1, wherein the localized pH is in a pH range of about 5.8 to 7.6.

13. A method of claim 1, further including determining a level of ischemia of the sample tissue from said localized pH.

14. A method of claim 1, wherein said step of collecting radiation from the sample tissue comprises collecting radiation reflected from the sample tissue.

15. A method of claim 1, wherein the optical radiation is between 400 nm and 2000 nm.

16. A method for determining the localized pH of a sample tissue, said method comprising:

irradiating the sample tissue with optical radiation;

collecting radiation from the sample tissue to determine an optical spectrum; and

,

processing the optical spectrum and a mathematical model to determine the localized pH of the sample tissue, said model relating optical spectra to known pH values of interstitial fluid in tissue.

17. A method of claim 16, wherein the mathematical model is determined prior to said irradiating by collecting multiple optical spectra, each occurring at a known pH value, from a representative sample, and then processing the optical spectra and known pH values with a mathematical algorithm to determine the model.

18. A method of claim 17, wherein the representative sample is a sample tissue of the patient.

19. A method of claim 17, wherein the representative sample is a solution or a second tissue.

20. A method of claim 16, wherein the step of irradiating the sample tissue with optical radiation includes invasively accessing the sample tissue to irradiate the sample tissue.

21. A method of claim 20, wherein the sample tissue is accessed with an endoscope.

22. A method of claim 16, further including determining a level of ischemia of the sample tissue from said localized pH.

23. A device for determining the pH of a sample, said device comprising:

an array of light sources for delivering radiation to the sample, wherein each of said light sources delivers radiation at a unique set of optical wavelengths;

a power supply;

a modulation system in electrical contact with each of said light sources and said power supply, said modulation system configured to modulate electrical power delivered from said power supply to each of said light sources at a unique frequency;

a detection system comprising a first optical detector configured to receive radiation delivered from each light source and from the sample, said detection system, after receiving radiation from the sample, generating a first set of radiation-induced electrical signals, each corresponding to radiation delivered from a separate light source, said detection system further including phase-sensitive detection electronics in electrical contact with said first optical detector to detect radiation generated at the unique frequency, said phase-sensitive detection electronics being incorporated in a lock-in amplifier;

a signal processor for receiving the first set of electrical signals and, in response, generating a first set of digital electrical signals; and

,

a microprocessor configured to receive the first set of digital electrical signals to calculate the pH of the sample, said microprocessor being programmed to first process the first set of digital electrical signals to determine a first spectrum and then compare the first spectrum or a spectrum determined from the first spectrum to a mathematical model to determine the pH of the sample.

24. A device of claim 23, wherein said microprocessor is additionally programmed to calculate the mathematical model prior to processing the first set of digital electrical signals.

25. A device of claim 23, wherein said device further comprises a lens configured to focus radiation from said light sources into a fiber optic cable.

26. A device of claim 25, wherein said fiber optic cable comprises a delivery fiber for delivering radiation to the sample, and a signal fiber for delivering radiation reflected by the sample to said first optical detector.

27. A device of claim 23, wherein said light sources deliver infrared wavelengths.

28. A device of claim 27, wherein the infrared wavelengths are between 700 nm and 1100 nm.

29. A device of claim 27, wherein each light source delivers infrared radiation having a bandwidth of between about 10 and 100 nm.

30. A device of claim 23, wherein each light source is a light-emitting diode.

31. A device of claim 23, wherein each light source is a diode laser.

32. A device of claim 23, wherein said array of light sources comprises between 2 and 20 light sources.

33. A device of claim 23, wherein said detection system comprises a second optical detector configured to detect radiation directly from each of said light sources, said second optical detector, in response to the radiation, generating a second set of radiation-induced electrical signals, each corresponding to radiation delivered from a separate light source.

34. A device of claim 33, wherein said signal processor is additionally configured for receiving the second set of electrical signals and, in response, generating a second set of digital electrical signals.

35. A device of claim 34, wherein said microprocessor is additionally programmed to process the second set of digital electrical signals to determine a reference spectrum and then calculate a ratio between the reference spectrum and the first spectrum.

36. A device of claim 33, wherein said device further comprises a reference fiber for delivering radiation from said light sources to said second optical detector.

37. A device of claim 23, wherein said radiation from the sample comprises reflected radiation.

38. A portable device for determining the pH of a sample, said device comprising:

a mount having a series of holes extending therethrough;

an array of light sources attached to said mount and positioned to deliver radiation to the sample through said series of holes;

a power supply electrically coupled to said mount;

a modulation system electrically coupled to said mount and arranged to modulate electrical power delivered from said power supply to each of said light sources;

a detection system comprising a first optical detector attached to said mount and positioned to receive radiation from the sample, said detection system, after receiving sample radiation, generating a first set of electrical signals, each corresponding to sample radiation delivered from a separate light source and received from the sample;

a signal processor electrically coupled to said mount for receiving the first set of electrical signals and, in response, generating a first set of digital signals; and

a microprocessor configured to receive the first set of digital signals and to calculate the pH of the sample, said microprocessor being programmed to process the first set of digital signals to determine a sample spectrum and then compare the sample spectrum to a mathematical model to determine the pH of the sample.

39. A device of claim 38, wherein said power supply, said modulation system, said signal processor, and said microprocessor are attached to said mount.

40. A device of claim 38, wherein said array of light sources are positioned such that said radiation delivered by each said light source is aimed at a common spot on a tissue sample.

41. A device of claim 38, wherein said first optical detector is located on an outer, tissue facing surface of said mount.

42. A device of claim 38, wherein said detection system comprises a second optical detector arranged to detect reference radiation directly from each of said light sources, said second optical detector, in response to the radiation, generating a second set of electrical signals, each corresponding to reference radiation delivered from a separate light source.

43. A device of claim 42, wherein said second optical detector is located on an inner, non-tissue facing surface of said mount.

44. A device of claim 42, wherein said mount comprises a mounting plate comprising said series of holes and a cover attached to said mounting plate, said array of light sources being attached to said cover, said cover including a reflective surface arranged to reflect radiation from each of said light sources to said second optical detector.

45. A device of claim 42, wherein said signal processor receives the second set of electrical signals and, in response, generates a second set of digital signals, said microprocessor being additionally programmed to process the second set of digital reference signals to determine a reference spectrum and then calculate a ratio between the reference spectrum and the sample spectrum.

46. A device of claim 39, wherein said array of light sources are evenly spaced and arranged in a circular pattern, and said series of holes are evenly spaced and arranged in a circular pattern.

47. A method for determining the localized pH of a sample tissue, said method comprising:

irradiating the sample tissue with optical radiation;

collecting radiation from the sample tissue to determine an optical spectrum; and

,

processing the optical spectrum and a mathematical model to determine the localized pH of the sample tissue, said model relating optical spectra to known pH values of muscle or organ cells.

48. A portable device for determining the pH of a sample, said device comprising:

a mount;

an array of light sources attached to said mount;

a fiber optic cable attached to said mount, said fiber optic cable including a delivery fiber for delivering radiation to the sample, a reference fiber, and a signal fiber;

a lens attached to said mount, said lens configured to focus radiation from said light sources into said fiber optic cable,

a power supply electrically coupled to said mount;

a modulation system electrically coupled to said mount and arranged to modulate electrical power delivered from said power supply to each of said light sources;

a detection system comprising a first optical detector attached to said mount and coupled to said signal fiber for receiving radiation from the sample, said detection system, after receiving sample radiation, generating a first set of electrical signals, each corresponding to sample radiation delivered from a separate light source and received from the sample, and a second optical detector attached to said mount and coupled to said reference fiber for receiving radiation directly from each of said light sources, said second optical detector, in response to the radiation, generating a second set of radiation-induced electrical signals, each corresponding to radiation delivered from a separate light source;

a signal processor electrically coupled to said mount for receiving the first set of electrical signals and, in response, generating a first set of digital signals, and for receiving the second set of electrical signals and, in response, generating a second set of digital electrical signals; and

a microprocessor configured to receive the first set and the second set of digital signals and to calculate the pH of the sample, said microprocessor being programmed to process the first set of digital signals to determine a sample spectrum and then compare the sample spectrum to a mathematical model to determine the pH of the sample, said microprocessor additionally being programmed to process the second set of digital electrical signals to determine a reference spectrum and then calculate a ratio between the reference spectrum and the first spectrum.

49. A device of claim 48, wherein said power supply, said modulation system, said signal processor, and said microprocessor are attached to said mount.

50. A device of claim 48, wherein at least a portion of said fiber optic cable comprises a delivery fiber surrounded by radially and symmetrically disposed fibers.

51. A device of claim 50, wherein said delivery fiber is surrounded by radially and symmetrically disposed reference fibers in the region where said fiber optic cable receives radiation from said light sources.

52. A device of claim 50, wherein said delivery fiber is surrounded by radially and symmetrically disposed signal fibers in the region where said fiber optic cable delivers radiation to the sample.

53. A device of claim 48, wherein said array of light sources is arranged on said mount such that incident irradiation irradiates said lens in a symmetric, ring-like pattern disposed radially around a center of said lens.

54. A device of claim 48, further comprising a housing attached to said mount, said lens being supported by said housing.