Optical sampling interface system for in vivo measurement of tissue

• US 20030069484A1
• Filed: 06/12/2002
• Published: 04/10/2003
• Est. Priority Date: 05/02/2000
• Status: Active Grant

• Current Assignee: GLT Acquisition Corporation
• Original Assignee: Sensys Medical, Inc. (Sensys Medical Limited)
• Inventors: Ruchti, Timothy L., Monfre, Stephen L., Blank, Thomas B., Lorenz, Alexander D., Acosta, George, Mattu, Mutua, Makarewicz, Marcy
• Granted Patent: US 7,206,623 B2
• Time in Patent Office: Days
• US Class Current: 600/310
• CPC Class Codes: A61B 2560/0233 Optical standards
• CPC Class Codes: A61B 2562/12 Manufacturing methods specially adapted for producing sensors for in-vivo measurements
• CPC Class Codes: A61B 2562/146 for optical coupling
• 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 5/0071 by measuring fluorescence emission
• 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 5/01 Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue clinical contact thermometers G01K13/20
• CPC Class Codes: A61B 5/061 Determining position of a probe within the body employing means separate from the probe, e.g. sensing internal probe position employing impedance electrodes on the surface of the body A61B1/00158 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 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/6833 Adhesive patches
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure

Abstract

An optical sampling interface system minimizes and compensates error resulting from sampling variations and measurement site state fluctuations. Components include: An optical probe placement guide having an aperture wherein the optical probe is received, facilitates repeatable placement accuracy on surface of a tissue measurement site with minimal, repeatable disturbance to surface tissue. The aperture creates a tissue meniscus that minimizes interference due to surface irregularities and controls variation in tissue volume sampled; an occlusive element placed over the tissue meniscus isolates the meniscus from environmental fluctuations, stabilizing hydration at the site and thus, surface tension; an optical coupling medium eliminates air gaps between skin surface and optical probe; a bias correction element applies a bias correction to spectral measurements, and associated analyte measurements. When the guide is replaced, a new bias correction is determined for measurements done with the new placement. Separate components of system can be individually deployed.

Claims

1. An optical probe placement guide for repeatably coupling an optical probe to a targeted measurement site, comprising:

a mount having a contact surface, at least a portion of said contact surface being in contact with a surface proximate said measurement site during use; and

an aperture, defined by said mount, adapted to receive said optical probe, wherein an area defined by said aperture comprises said measurement site.

2. The guide of claim 1, wherein said measurement site comprises a tissue measurement site and wherein surface tissue at said measurement site comprises skin, skin surface comprising stratum corneum.

3. The guide of claim 2, further comprising means for occluding said aperture when it is not occluded by said optical probe.

4. The guide of claim 3, said means for occluding said aperture comprising an occlusion plug.

5. The guide of claim 4, wherein shape and dimensions of a portion of said occlusion plug adapted to be received by said aperture mimics shape and dimensions of said aperture.

6. The guide of claim 3, further comprising means for removably attaching said plug at an exterior surface of said guide.

7. The guide of claim 6, wherein said means for attaching comprises any of:

magnets attached to said plug and said guide;

VELCRO;

adhesives; and

snaps.

8. The guide of claim 4, wherein said plug is adapted to fit snugly within said aperture without additional attachment means.

9. The guide of claim 4, wherein said guide induces a tissue meniscus within said aperture.

10. The guide of claim 9, wherein said plug is adapted to stabilize hydration level of the stratum corneum across surface of said meniscus.

11. The guide of claim 1, further comprising means for removably attaching said guide at said measurement site.

12. The guide of claim 11, wherein said means for attaching comprises an adhesive.

13. The guide of claim 11, wherein said means for attaching comprises any of:

at least one strap;

at least one armband; and

at least one suction element.

14. The guide of claim 1, wherein size and shape of said aperture are matched to those of said optical probe, said probe fitting snugly into said aperture, so that a mechanical registration in an x-y plane of said probe relative to said measurement site is provided.

15. The guide of claim 1, further comprising at least one mechanical stop, said stop preventing over-penetration of said probe toward said measurement site, and providing registration along a z-axis of said probe relative to said measurement site.

16. The guide of claim 1, further comprising optical registration means wherein said probe is registered relative to said measurement site along any of x-, y- and z-axes.

17. The guide of claim 1, further comprising magnetic registration means along any of x-, y- and z-axes.

18. The guide of claim 1, further comprising means for monitoring surface temperature proximate said measurement site.

19. The guide of claim 1, wherein an optical coupling medium optically couples said probe to said measurement site.

20. An optical sampling interface system comprising:

means for controlling variations in sample volume;

means for controlling surface reflection of an optical signal;

means for stabilizing at least one surface condition at said measurement site;

wherein sampling error is minimized, eliminated, reduced or compensated.

21. The system of claim 20, wherein said means for controlling variations in sample volume comprises an optical probe placement guide for repeatably coupling an optical probe to a targeted measurement site, said guide comprising:

a mount having a contact surface, at least a portion of said contact surface being in contact with a surface proximate said measurement site during use; and

an aperture, defined by said mount, adapted to receive said optical probe, wherein an area defined by said aperture comprises said measurement site;

wherein said guide is removably attached at said measurement site.

22. The system of claim 21, wherein means for attaching said guide comprises any of:

an adhesive;

at least one strap;

at least one armband; and

at least one suction element.

23. The system of claim 21, wherein size and shape of said aperture are matched to those of said optical probe, said probe fitting snugly into said aperture, so that a mechanical registration in an x-y plane of said probe relative to said measurement site is provided, said guide further comprising at least one mechanical stop, said stop preventing over-penetration of said probe toward said measurement site, and providing registration along a z-axis of said probe relative to said measurement site.

24. The system of claim 21, said guide further comprising optical registration means wherein said probe is registered relative to said measurement site along any of x-, y-, and z-axes.

25. The system of claim 20, said means for controlling surface reflection comprising an optical coupling medium.

26. The system of claim 25, wherein said optical coupling medium comprises an optical coupling fluid.

27. The system of claim 26, wherein said optical coupling fluid comprises:

one or more perfluoro compounds, wherein a quantity of said optical coupling fluid is placed at an interface of an optical probe and a measurement site, so that said probe and said measurement site are tightly optically coupled.

28. The system of claim 20, wherein said means for stabilizing at least one surface condition comprises means for stabilizing surface hydration.

29. The system of claim 28, wherein said means for stabilizing surface hydration comprises an occlusion plug, said occlusion plug adapted to be received by an aperture in an optical probe placement guide between measurements, so that said measurement site is occluded and evaporation of surface moisture is prevented.

30. The system of claim 29, wherein shape and dimensions of a portion of said occlusion plug adapted to be received by said aperture mimics shape and dimensions of said aperture.

31. The system of claim 29, wherein said occlusion plug is removably attached at an exterior surface of said guide.

32. The system of claim 28, wherein said means for stabilizing surface hydration comprises any of:

ultrasound treatment at the measurement site;

means for applying water to said surface;

means for applying a topical applicant that elevates surface tissue hydration

means for accelerating passive occlusion; and

means for applying water/solute mixtures to said surface that drive water and/or solute into an outer layer of said surface.

33. The system of claim 20, wherein said means for stabilizing at least one surface condition comprises a cover for said measurement site, wherein evaporation of surface moisture from said site is prevented.

34. The system of claim 20, wherein said means for stabilizing at least one surface condition comprises means for stabilizing surface temperature.

35. The system of claim 20, wherein said measurement site comprises a tissue measurement site and wherein surface tissue at said measurement site comprises skin, skin surface comprising stratum corneum.

36. The system of claim 35, further comprising means for correcting measurement bias resulting from one or both of variations in sampled volume and measurement conditions.

37. The system of claim 36, wherein said means for correcting measurement bias comprises:

a noninvasive measurement system;

a tissue template; and

a calibration model;

wherein measurement bias is compensated by;

determining difference between a tissue measurement and a tissue template;

mapping resulting difference to a measurement of a target analyte according to a calibration model; and

applying a baseline adjustment to said analyte measurement.

38. The system of claim 37, wherein variations in sampled volume result from differences in placement of either an optical probe, or an optical probe placement guide between measurements.

39. The system of claim 37, wherein said tissue template is determined through one or more tissue measurements combined according to a predetermined data selection criterion during a measurement period.

40. The system of claim 37, wherein said calibration model is determined from a calibration set of exemplary paired data points each consisting of a pre-processed and bias corrected tissue measurement and an associated reference analyte value determined from an analysis of a blood or interstitial fluid sample.

41. The system of claim 37, wherein said baseline adjustment is associated with said tissue template and said calibration model.

42. A method of compensating measurement bias in noninvasive analyte measurement, said bias resulting from variations sampled volume and measurement conditions between measurements, comprising the steps of:

providing a tissue measurement;

determining difference between said tissue measurement and a tissue template;

mapping resulting difference to a measurement of a target analyte according to a calibration model; and

applying a baseline adjustment to said analyte measurement.

43. The method of claim 42, wherein said variations in sampled volume result from differences in placement of either an optical probe, or an optical probe placement guide between measurements.

44. The method of claim 42, further comprising the step of preprocessing said tissue measurement and tissue template before determining the difference between said tissue measurement and tissue template, preprocessing comprising any of:

derivative calculation;

selecting wavelengths and wavelength regions specific to the target analyte; and

scatter correction.

45. The method of claim of claim 42, wherein said step of determining difference between said tissue measurement and a tissue template comprises:

determining difference between the tissue template and a preprocessed spectrum according to;

z=x−

(cx_t+d);

wherein x comprises a pre-processed spectrum or a selected set of features, x_t comprises a tissue template associated with a measurement period.

46. The method of claim 45, wherein said tissue template is determined through one or more tissue measurements combined according to a predetermined data selection criterion during each measurement period.

47. The method of claim 45, wherein c=1 and d=0.

48. The method of claim 42, further comprising the step of:

providing an associated set of reference analyte values, said values combined according to said predetermined data selection criterion to form a measurement bias adjustment.

49. The method of claim 48, wherein said reference analyte values are determined from an analysis of a blood or interstitial fluid sample.

50. The method of claim 48, wherein said analyte values are combined according to same strategy used to create said tissue template, wherein an analyte bias adjustment, b, is formed according to

ŷ

=g(z)+b

where g;

^M→

¹ is a calibration model used to map z to an estimate ŷ

. of the target analyte.

51. The method of claim 50, wherein said model is determined from a calibration set of exemplary paired data points each consisting of a pre-processed and bias corrected tissue measurement (z) and an associated reference analyte value (y) determined from an analysis of a blood or interstitial fluid sample.

52. The method of claim 42, wherein said measurement site is on any of:

a dorsal surface of a forearm;

a volar surface of a forearm; and

a torso.

53. The method of claim 42, further comprising the optional step of detecting outliers.

54. An apparatus for minimizing optical sampling error at a tissue measurement site due to fluctuations of surface conditions, comprising any of:

an occlusive plug, said plug adapted to be received by an aperture for an optical probe, between measurements;

an occlusive patch applied over the measurement site;

a topical medium application to the measurement site that elevates surface tissue hydration; and

an application of ultrasound treatment to the measurement site.

55. The apparatus of claim 54, wherein shape and dimensions of a portion of said occlusion plug adapted to be received by said aperture mimic shape and dimensions of said aperture.

56. The apparatus of claim 54, wherein said plug is adapted to fit snugly within said aperture without additional attachment means.

57. The apparatus of claim 54, further comprising means for removably attaching said plug at an exterior surface of an apparatus defining said probe aperture.

58. The apparatus of claim 57, wherein said means for attaching comprises any of:

magnets attached to said plug and said apparatus bearing said probe aperture;

VELCRO;

adhesives; and

snaps.

59. The apparatus of claim 57, wherein said apparatus bearing said probe aperture induces a tissue meniscus within said aperture.

60. The apparatus of claim 59, wherein said plug is adapted to stabilize hydration level of surface tissue across surface of said meniscus.

61. The apparatus of claim 54, wherein said aperture is defined by an optical probe placement guide.

62. The apparatus of claim 54, wherein said occlusion patch is applied over said measurement site

63. The apparatus of claim 54, wherein said occlusion patch is attached through any one of adhesives, tape, straps, suction.

64. The apparatus of claim 54, wherein said ultrasound is applied to the measurement site prior to a measurement period.

65. The apparatus of claim 54, wherein said topical applicants include any of skin toner, alpha hydroxy acid solutions, water, lotions and skin creams.

66. The apparatus of claim 54, wherein said topical applicants include topical analgesic formulations.