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

• US 5,459,317 A
• Filed: 02/14/1994
• Issued: 10/17/1995
• Est. Priority Date: 02/14/1994
• Status: Expired due to Term

• Current Assignee: Ohio University, University of Iowa Research Foundation
• Original Assignee: Iowa Research Foundation, Ohio University
• Inventors: Arnold, Mark, Small, Gary W.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Bruce, David Vernon
• Application Number:
  US08/195,709
• Time in Patent Office: 610 Days
• Field of Search: 364/413.01, 364/413.02, 364/413.07, 364/413.09, 364/572, 364/576, 250/341.1, 250/341.8, 250/343, 250/347
• US Class Current: 250/341.1
• 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 are made using infrared radiation and a signal processing system that permits the construction of a device suited for home use. The level of a selected physiological chemical in a 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 such that the radiation is transmitted through or reflected from the test subject; (b) collecting data concerning the transmitted or reflected infrared radiation using a detector; (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 model to the digitally filtered data. The data collected may be in the form of an absorbance spectrum, i.e., a representation of the variation in absorbance as a function of wavelength; or in the form of an interferogram, i.e., a representation of infrared light intensity as a function of the retardation of the moving mirror in the interferometer, and thus of time.

Claims

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

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

(b) collecting data concerning the transmitted or reflected infrared radiation using a detector;

(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 model 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 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.

7. A method according to claim 1, wherein the chemical is glucose.

8. A method according to claim 7, 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.

9. A method according to claim 8, wherein the spectrum that is digitally filtered spans the region from 6500 to 5800 cm^-1.

10. A method according to claim 8, 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.

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

12. A method according to claim 11, wherein only a short segment of an entire interferogram is analyzed.

13. A method according to claim 11, 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 11, wherein the physiological chemical is glucose.

15. A method according to claim 14, 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.

16. A method according to claim 15, wherein the Gaussian function is selected to isolate the glucose-associated absorbance at 4400 cm^-1.

17. A method according to claim 14, wherein the interferogram is a short segment interferogram.

18. A method according to claim 1, wherein the collected spectrum 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

19. A device for measurement of glucose concentration in a sample being irradiated with near infrared radiation comprising:

(a) means for collecting data concerning near-infrared radiation transmitted through or reflected from the sample;

(b) means for digitally filtering the collected data to isolate a portion of data indicative of glucose;

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

(d) means for reporting the amount of glucose in the sample.

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

(a) means for irradiating a portion of the surface of the test subject with near-infrared radiation such that transmitted or reflected near-infrared radiation 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 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 sample.