Apparatus and method for reproducibly modifying localized absorption and scattering coefficients at a tissue measurement site during optical sampling

• US 6,534,012 B1
• Filed: 08/02/2000
• Issued: 03/18/2003
• Est. Priority Date: 08/02/2000
• Status: Expired due to Fees

• Current Assignee: GLT Acquisition Corporation
• Original Assignee: Sensys Medical, Inc. (Sensys Medical Limited)
• Inventors: Abul-Haj, N. Alan, Hazen, Kevin H., Abul-Haj, Roxanne E., Acosta, George
• Primary Examiner(s): Warden, Jill
• Assistant Examiner(s): SINES, BRIAN J
• Application Number:
  US09/631,440
• Time in Patent Office: 958 Days
• Field of Search: 436/164, 436/165, 422/55, 422/68.1, 422/82.05, 422/50, 422/82.09, 422/108, 250/214.1, 250/341.8, 356/445, 600/316, 600/342, 600/445
• US Class Current: 422/82.05
• 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 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure

Abstract

An apparatus for varying localized absorption and scattering coefficients at a tissue measurement site in a controlled and reproducible manner during optical sampling of a tissue volume by controlling the pressure applied to a tissue measurement site by a spectroscopic analyzer allows applied pressure to be maintained at a constant level, or the applied pressure may be varied in a controlled, reproducible manner as a function of time. A rest for receiving a body part holds the body part in a fixed position and at a fixed elevation. A mechanical system advances a fiber optic probe until it makes contact with the body part with a constant amount of pressure. The applied force is supplied by a counterweight on a single arm balance. A temperature control allows the temperature of the fiber optic probe to be equilibrated with the temperature in the immediate vicinity of the tissue measurement site. Alternate embodiments allow the fiber optic probe to be brought into direct contact with the tissue measurement site, and displaced a known distance into the tissue. The invention is also embodied as a method in which the absorption and scattering coefficients for successive spectral measurements are calculated to determine optimum depth of penetration for detection of a target analyte.

Claims

1. An apparatus for varying localized absorption and scattering coefficients at a tissue measurement site in a controlled and reproducible manner during optical sampling comprising:

a subject interface for variably contacting with a tissue measurement site;

means for measuring specular reflectance or spectral data of tissue at said tissue measurement site;

means for varying and maintaining contact with said tissue measurement site by said subject interface in a controlled and reproducible manner according to any of said measured specular reflectance and said measured spectral data; and

means for reproducibly positioning said tissue measurement site relative to said subject interface.

2. The apparatus of claim 1, wherein said subject interface comprises:

a fiber optic probe surrounded by a housing, wherein said probe delivers light energy to said tissue measurement site and collects light energy transmitted or reflected from said tissue measurement site.

3. The apparatus of claim 2, wherein a tip of said fiber optic probe contacts said tissue measurement site, where said tissue measurement site is located on a limb of said subject.

4. The apparatus of claim 3, wherein said fiber optic probe is rectangular and wherein said probe tip contacts said limb in a lengthwise manner so that contact of said probe tip with said tissue measurement site is maximized, with a minimum of applied pressure to said tissue measurement site by said probe tip being required.

5. The apparatus of claim 2, wherein said housing comprises a cylinder surrounding said fiber optic probe and wherein said probe tip protrudes from a terminal surface of said housing.

6. The apparatus of claim 5, wherein said housing is fabricated from a lightweight, heat conductive material.

7. The apparatus of claim 6, wherein said housing further comprises means for heating said fiber optic probe so that probe temperature is equilibrated with surface temperature at said tissue measurement site.

8. The apparatus of claim 7, said subject interface further comprising means for detecting surface temperature at said tissue measurement site.

9. The apparatus of claim 2, wherein said means for varying and maintaining contact with said tissue measurement site by said subject interface in a controlled and reproducible manner comprises:

a single arm balance with a counter weight, said single arm balance comprising a hinged beam attached to an upright mount at a point of attachment, wherein a bearing element allows said hinged beam to rotate freely about a point of rotation defined by said point of attachment, and wherein said beam has a first end and a second end; and

a gimbal mount attached to said second end for receiving said subject interface;

wherein adjusting said counter weight varies the amount of pressure applied to said tissue measurement site by said fiber optic probe.

10. The apparatus of claim 9, wherein said subject interface floats on said gimbal mount so that the optical axis of said fiber optic probe is normal to a limb of said subject whereon the tissue measurement site is located when the fiber optic probe is pressing against said tissue measurement site.

11. The apparatus of claim 10, wherein said gimbal mount is equipped with a gimbal locking mechanism, said gimbal locking mechanism comprising any of a compression and a pinch element and wherein said gimbal locking mechanism is operative to maintain stability of said fiber optic probe tip against said tissue measurement site.

12. The apparatus of claim 9, wherein said counter weight comprises an adjustable weight attached at said first end of said hinged beam.

13. The apparatus of claim 9, wherein said counter weight comprises a larger weight that slides along said beam, where said beam has gradations for different pressure levels, and wherein a screw with a smaller weight attached at said first end allows fine adjustments to applied pressure.

14. The apparatus of claim 9, further comprising a beam movement brake mechanism, said beam movement brake mechanism comprising a friction plate, said friction plate being operative to lock said beam into a desired position by being compressed against said upright mount.

15. The apparatus of claim 1, wherein said means for reproducibly positioning said tissue measurement site relative to said subject interface comprises a limb guide for receiving a limb of said subject, whereon said tissue measurement site is located.

16. The apparatus of claim 15, wherein said limb guide comprises an arm guide, said arm guide comprising:

a platform mounted on a support structure;

an elbow guide;

a wrist guide and a hand guide, all detachably mounted on said platform; and

an aperture defined by said platform.

17. The apparatus of claim 16, wherein said arm guide receives said subject'"'"'s arm, so that the subject'"'"'s elbow is resting in the elbow guide, the subject'"'"'s wrist is resting on the wrist guide and the subject'"'"'s hand is resting on the hand guide such that a tissue measurement site on a lower surface of said arm is aligned with said aperture.

18. The apparatus of claim 17, wherein said subject interface, mounted on said means for varying and maintaining contact with said tissue measurement site protrudes upward through said aperture to contact said tissue measurement site.

19. The apparatus of claim 16, wherein said wrist guide and said hand guide are formed as a single unit, and wherein said unit is slideably mounted on said platform, so that said unit is positionable according to the length of said subject'"'"'s forearm.

20. The apparatus of claim 19, wherein said elbow guide and said assembly are ergonomically molded.

21. The apparatus of claim 20, wherein said elbow guide and said assembly are custom molded according to subject.

22. The apparatus of claim 17, wherein said subject'"'"'s arm is positioned such that the arm is at the subject'"'"'s side and flexed to an angle of ninety degrees.

23. The apparatus of claim 16, wherein said arm guide is adapted to receive one of a right arm and a left arm.

24. The apparatus of claim 2, wherein said means for reproducibly positioning said tissue measurement site relative to said subject interface comprises a platform, said platform being supported by and attached to said means for varying and maintaining contact with said tissue measurement site by said subject interface in a controlled and reproducible manner, said means for varying and making contact comprising:

a system for raising and lowering said platform so that said fiber optic probe may be brought into contact with said tissue measurement site and then displaced into skin at the tissue measurement site by a known amount, where said subject interface is fixedly mounted;

wherein said tissue measurement site is located on an arm of said subject.

25. The apparatus of claim 24, wherein said platform has detachably mounted thereon;

an elbow guide, a wrist guide and a hand guide for reproducibly positioning said arm, said wrist guide and said hand guide being slideable to accommodate arms of varying length; and

wherein said platform has an aperture through which said fiber optic probe protrudes in order to make contact with the tissue measurement site.

26. The apparatus of claim 25, wherein said elbow guide, said wrist guide and said hand guide are ergonomically molded.

27. The apparatus of claim 25, wherein said guides are custom molded according to subject.

28. The apparatus of claim 25, wherein said subject'"'"'s arm is positioned such that the arm is at the subject'"'"'s side and flexed to an angle of ninety degrees.

29. The apparatus of claim 25, wherein said system for raising and lowering said platform comprises a linear slide mechanism, said linear slide mechanism comprising an actuator arm and a plurality of vertical guides.

30. The apparatus of claim 29, said system for raising and lowering said platform further comprising an electric motor for driving said linear slide mechanism.

31. The apparatus of claim 30, wherein said motor is computer-controlled.

32. The apparatus of claim 31, wherein a zero point constitutes the elevation at which full contact between said arm and said fiber optic probe first occurs.

33. The apparatus of claim 32, said system further comprising:

an LED situated at one side of said arm;

a detector situated at the opposite side of said arm;

wherein a signal from said LED is aimed directly above said fiber optic probe, and detected by said detector.

34. The apparatus of claim 33, wherein said arm is lowered until said zero point is reached, said zero point constituting the elevation at which said LED signal is undetectable.

35. The apparatus of claim 32, wherein said zero point is determinable by analyzing successive spectral measurements for spectrally reflected light, and wherein an absence of spectrally reflected light indicates said zero point.

36. The apparatus of claim 32, wherein said subject'"'"'s arm is positioned at said zero point and subsequently lowered onto said fiber optic probe so that said probe is displaced into the skin of said tissue measurement site by a preferred amount, said preferred amount indicated by target values for absorption and scattering coefficients, said coefficients being calculated for successive spectral measurements.

37. The apparatus of claim 25, wherein said system for raising and lowering said platform comprises one of:

a hand crank;

a lever arm;

a scissors jack

a hinge point in conjunction with a linear drive; and

a worm drive.

38. The apparatus of claim 1, wherein said means for reproducibly positioning said tissue measurement site relative to said subject interface comprises a placement guide, said placement guide being reproducibly attachable to a subject'"'"'s body part whereon said tissue measurement site is located, said guide having an aperture through which said subject interface protrudes to contact said tissue measurement site, said placement guide also having one or more guide rods for reproducibly coupling an analyzer bearing said subject interface to said tissue measurement site.

39. The apparatus of claim 38, wherein said body part comprises a limb of said subject.

40. A method for varying localized absorption and scattering coefficients at a tissue measurement site in a controlled and reproducible manner during optical sampling of a tissue volume comprising the steps of:

providing a tissue measurement site;

providing a spectroscopic analyzer having a subject interface adapted to make contact with said tissue measurement site during measurement;

making an initial NIR spectral measurement, for which any of applied pressure to the tissue measurement site by said subject interface and degree of displacement into the tissue of the tissue measurement site by said subject interface is known and maintained during said initial measurement;

measuring NIR spectral data of tissue at said tissue measurement site;

varying and maintaining contact with said tissue measurement site by said subject interface in a controlled and reproducible manner according to said measured NIR spectral data;

calculating local absorbance and scattering coefficients for said measurements;

making one or more subsequent NIR spectral measurements in which any of applied pressure and displacement is varied by a known amount;

calculating absorbance and scattering coefficients for each measurement; and

determining an optimal sampling depth for detecting a target analyte, wherein a ratio of absorption coefficient to scattering coefficient is an indicator of said optimal depth.

41. The method of claim 40, wherein increased pressure at said tissue measurement site forces water from said sampled tissue volume, and wherein the local absorption coefficient decreases as water concentration within said tissue volume decreases.

42. The method of claim 41, wherein density of scattering centers within said sampled tissue increases as water concentration decreases, and wherein said scattering coefficient increases as density of scattering centers increases.

43. The method of claim 42, wherein said tissue measurement site is on a limb of a living subject.

44. The method of claim 43, wherein said limb is an arm.

45. The method of claim 42, wherein said subject interface comprises a fiber optic probe having a tip, and wherein said probe delivers light energy to said tissue measurement site and collects light energy transmitted or reflected from said tissue measurement site.

46. The method of claim 45, wherein said tip contacts said tissue measurement site.

47. The method of claim 42, wherein a guide positions said tissue measurement sight relative to said subject interface in a controlled and reproducible manner.

48. The method of claim 47, wherein said guide includes an aperture, wherein said subject interface protrudes through said aperture to contact said tissue measurement site.

49. The method of claim 42, wherein said applied pressure is varied and controlled by means of a single arm balance having an adjustable counter weight, said balance comprising a beam having a first end and a second end, wherein said pressure is controlled and varied by adjusting said counterweight.

50. The method of claim 49, wherein said balance further comprises a gimbal mount attached to an end of said balance, wherein said subject interface floats on said gimbal mount.

51. The method of claim 50, wherein said balance further comprises a locking mechanism so that said beam may be locked into a desired position.

52. The method of claim 42, wherein said degree of displacement is varied and controlled by a platform having one or more guides for reproducibly positioning said tissue measurement site, said platform being supported on and attached to a system for raising and lowering said platform so that said subject interface may contact said tissue measurement site and then be displaced into skin at the tissue measurement site by a known amount, where said subject interface is fixedly mounted.

53. The method of claim 52, wherein a zero point constitutes the first point of full contact between said subject interface and said tissue measurement site, wherein said tissue measurement site is first lowered to said zero point and subsequently lowered a further known amount to displace said subject interface further into the tissue measurement site.

54. The method of claim 52, wherein said means for raising and lowering said platform comprises a linear actuator, said linear actuator powered by an electric motor.

55. The method of claim 54, wherein said electric motor is digitally-controlled.

56. The method of claim 52, wherein said means for raising and lowering said platform comprises one of:

a hand crank;

a lever arm;

a scissors jack

a hinge point in conjunction with a linear drive; and

a worm drive.