Method and apparatus for non-invasive determination of physiological chemicals, particularly glucose

• US 6,061,582 A
• Filed: 06/11/1997
• Issued: 05/09/2000
• Est. Priority Date: 02/14/1994
• Status: Expired due to Term

• Current Assignee: Ohio University, University of Iowa Research Foundation
• Original Assignee: Ohio University, University of Iowa Research Foundation
• Inventors: Arnold, Mark, Small, Gary W.
• Primary Examiner(s): Dvorak, Linda C. M.
• Assistant Examiner(s): YARNELL, BRYAN KEITH
• Application Number:
  US08/860,850
• Time in Patent Office: 1,063 Days
• Field of Search: 600/310, 600/314-316, 600/322, 600/323, 600/326-328, 600/339, 600/341, 600/473, 600/476, 600/478, 356/39-41
• US Class Current: 600/316
• 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 5/7257 using Fourier transforms
• CPC Class Codes: G01J 3/45 Interferometric spectrometry
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/359 using near infrared light

Abstract

Non-invasive measurements of physiological chemicals such as glucose in a test subject are made using infrared radiation and a signal processing system. The level of a selected physiological chemical in the test subject is determined in a non-invasive and quantitative manner by a method comprising the steps of: (a) irradiating a portion of the test subject with near infrared radiation; (b) collecting data concerning the irradiated light on the test subject; (c) digitally filtering the collected data to isolate a portion of the data indicative of the physiological chemical; and (d) determining the amount of physiolgocial chemical in the test subject by applying a defined mathematical model to the digitally filtered data. The collected data is in the form of either an absorbance spectrum or an interferogram.

Claims

1. A method for non-invasive quantitative detection of a physiological chemical in a test subject comprising the steps of:

(a) irradiating an exterior surface of a portion of the test subject with near-infrared radiation such that the radiation is transmitted through or reflected from the portion of the test subject;

(b) collecting data concerning the infrared radiation transmitted through or reflected from the portion of this subject using a detector, wherein the collected data is from an absorbance spectrum or an interferogram;

(c) digitally filtering the collected data to isolate a portion of the data indicative of the physiological chemical; and

(d) determining the amount of physiological chemical in the test subject by applying a defined mathematical mode to the digitally filtered data.

2. A method according to claim 1, wherein the digital filtering is performed by a Fourier filtering process.

3. A method according to claim 1, wherein the collected data is in the form of an absorbance spectrum.

4. A method according to claim 3, wherein the spectrum is digitally filtered by performing a Fourier transform on the absorbance spectrum;

multiplying the transformed spectrum by a Gaussian function; and

applying an inverse Fourier transformation to the multiplied transformed spectrum.

5. A method according to claim 4, wherein the mathematical model applied to the digitally filtered spectrum applies coefficients developed using a partial least squares regression multivariate calibration procedure.

6. A method according to claim 5, wherein the spectrum that is digitally filtered spans the region from 6500 to 5800 cm^-1.

7. A method according to claim 6, wherein the magnitude of the digitally filtered spectrum is compared to a standard value using a series of regression coefficients developed using a partial least squares regression multivariate calibration procedure.

8. A method according to claim 1, wherein the collected data is in the form of a single beam spectrum.

9. A method according to claim 1, wherein the collected data is in the form of an interferogram.

10. A method according to claim 9, wherein only a short segment of an entire interferogram is analyzed.

11. A method according to claim 10, wherein the digital filtering step comprises the steps of performing a fast Fourier transform on the interferogram to obtain a transformed spectrum;

multiplying the transformed spectrum with a Gaussian function to select for a peak diagnostic for the physiological chemical; and

applying an inverse Fourier transform to the multiplied, transformed spectrum.

12. A method according to claim 11, wherein the Gaussian function is selected to isolate the glucose-associated absorbance at 4400 cm^-1.

13. A method according to claim 9, wherein the digital filtering step comprises the steps of performing a fast Fourier transform on the interferogram to obtain a transformed spectrum;

multiplying the transformed spectrum with a Gaussian function to select for a peak diagnostic for the physiological chemical; and

applying an inverse Fourier transform to the multiplied, transformed spectrum.

14. A method according to claim 1, wherein the collected data is an interferogram and the digital filtering is performed directly on the interferogram to select out waveforms within the interferogram having a frequency equal to ##EQU4## where the wavenumber has units of cm^-1, mirror velocity is the velocity of mirror travel in the interferometer used to generate the interferogram expressed in units of cm/sec.

15. A method according to any of claims 1-5 or 6-14, wherein the chemical is glucose.

16. An apparatus for the non-invasive measurement of one or more physiological chemical in a test subject, comprising,

(a) means for irradiating an exterior surface of a portion of the test subject with near-infrared radiation such that near infrared radiation transmitted through or reflected from the exterior surface of the portion of the test subject is available for collection;

(b) means for collecting data concerning the transmitted or reflected near-infrared radiation;

(c) means for digitally filtering the collected data to isolate a portion of the data indicative of the physiological chemical;

(d) means for applying a defined mathematical model to the digitally filtered data, whereby the amount of chemical in the test subject is determined; and

(e) means for reporting the amount of chemical in the test subject.