Optical sampling interface system for in vivo measurement of tissue

• US 20050049466A1
• Filed: 08/12/2004
• Published: 03/03/2005
• Est. Priority Date: 08/14/1997
• Status: Active Grant

• Current Assignee: Alexander D. Lorenz, George Acosta, Marcy Makarewicz, Mutua Mattu, Stephen L. Monfre, Thomas B. Blank, Timothy L Ruchti
• Original Assignee: Alexander D. Lorenz, George Acosta, Marcy Makarewicz, Mutua Mattu, Stephen L. Monfre, Thomas B. Blank, Timothy L Ruchti
• Inventors: Ruchti, Timothy L., Monfre, Stephen L., Blank, Thomas B., Lorenz, Alexander D., Acosta, George, Mattu, Mutua, Makarewicz, Marcy
• Granted Patent: US 7,233,816 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. A method of compensating measurement bias in noninvasive analyte measurement, said bias resulting from variations in 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.

2. The method of claim 1, wherein said variations in sampled volume result from differences in placement of either an optical probe, or an optical probe placement guide between measurements.

3. The method of claim 1, 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.

4. The method of claim of claim 1, 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.

5. The method of claim 4, wherein said tissue template is determined through one or more tissue measurements combined according to a predetermined data selection criterion during each measurement period.

6. The method of claim 4, wherein c=1 and d=0.

7. The method of claim 1, 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.

8. The method of claim 7, wherein said reference analyte values are determined from an analysis of a blood or interstitial fluid sample.

9. The method of claim 7, 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.

10. The method of claim 9, 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.

12. The method of claim 1, wherein said measurement site is on any of:

a dorsal surface of a forearm;

a volar surface of a forearm; and

a torso.

13. The method of claim 1, further comprising the optional step of detecting outliers.