Optical sampling interface system for in vivo measurement of tissue
View Patent ↗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.
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:
using ananalyzer to provide a tissue measurement;
determining a difference between said tissue measurement and a tissue template associated with a registration position;
mapping the 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 1 , wherein said step of determining a 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 5 , 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.
7. The method of claim 6 , wherein said reference analyte values are determined from an analysis of a blood or interstitial fluid sample.
8. The method of claim 6 , 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.
9. The method of claim 8 , 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.
10. The method of claim 4 , wherein c=1 and d=0.
11. 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.
12. The method of claim 1 , further comprising the optional step of detecting outliers.
13. The method of claim 1 , further comprising:
registering at least a portion of said analyzer to said registration position using means for registering.
14. The method of claim 13 , wherein said step of registering further comprises any of the steps of:
positioning said analyzer relative to said registration position using mechanical alignment;
positioning said analyzer relative to said registration position using optical alignment;
positioning said analyzer relative to said registration position using electrical alignment;
positioning said analyzer relative to said registration position using magnetic alignment.
15. The method of claim 13 , wherein said step of registering further comprises the step of:
using a guide.