Method and apparatus for adjusting signal variation of an electronically controlled infrared transmissive window

• US 6,917,038 B2
• Filed: 11/21/2002
• Issued: 07/12/2005
• Est. Priority Date: 11/21/2001
• Status: Expired due to Fees

• Current Assignee: OptiScan Biomedical Corporation
• Original Assignee: OptiScan Biomedical Corporation
• Inventors: Gable, Jennifer H., Braig, James R., Zheng, Peng, Hall, W. Dale, Witte, Kenneth G.
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Sung, Christine
• Application Number:
  US10/302,030
• Publication Number:
  US 20030146385A1
• Time in Patent Office: 964 Days
• Field of Search: 250/339.04, 250/339.01, 250/338.1, 250/336.1
• US Class Current: 250/339.04
• 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

Abstract

An analyte detection system non-invasively determines the concentration of an analyte in a sample generating a sample infrared signal indicative of the concentration of the analyte in the sample. The detection system includes a window assembly for receiving the sample infrared signal. The window assembly is adapted to allow the sample infrared signal to transmit therethrough, and generates a window infrared signal. The detection system further includes at least one detector configured to receive both the window infrared signal and the sample infrared signal transmitted through the window assembly. The detector is further adapted to generate a detector signal in response thereto. The detection system further includes a correction module configured to generate a corrected detector signal indicative of the concentration of the analyte in the sample.

Claims

1. An analyte detection system for non-invasively determining the concentration of an analyte in a sample, the sample generating a sample infrared signal indicative of the concentration of the analyte in the sample, the detection system comprising:

a window assembly for receiving the sample infrared signal, the window assembly adapted to allow the sample infrared signal to transmit therethrough, the window assembly generating a window infrared signal;

at least one detector configured to receive both the window infrared signal and the sample infrared signal transmitted through the window assembly, the detector further adapted to generate a detector signal in response thereto; and

a correction module configured to generate a corrected detector signal indicative of the concentration of the analyte in the sample.

2. An analyte detection system for non-invasively determining the concentration of an analyte in a sample, the sample generating a sample infrared signal indicative of the concentration of the analyte in the sample, the detection system comprising:

a window assembly for receiving the sample infrared signal, the window assembly adapted to allow the sample infrared signal to transmit therethrough, the window assembly generating a window infrared signal;

at least one detector configured to receive both the window infrared signal and the sample infrared signal transmitted through the window assembly, the detector further adapted to generate a detector signal in response thereto; and

a correction module configured to generate a corrected detector signal indicative of the concentration of the analyte in the sample, wherein the correction module generates a correction signal indicative of the window infrared signal, and the correction module generates the corrected detector signal in response to both the correction signal and the detector signal.

3. The analyte detection system of claim 2, additionally comprising at least one resistance temperature device coupled to the window assembly.

4. The analyte detection system of claim 2, wherein the window assembly comprises a heater and at least one monitor.

5. The analyte detection system of claim 4, wherein the monitor comprises an ammeter.

6. The analyte detection system of claim 4, wherein the monitor comprises a voltmeter configured to measure a voltage across the heater.

7. The analyte detection system of claim 4, wherein the monitor comprises a resistance monitor configured to measure a resistance of the heater.

8. The analyte detection system of claim 2, additionally comprising at least one reference detector channel configured to generate the correction signal in response to infrared radiation from the window assembly.

9. A method for improving the sensitivity of a noninvasive infrared analyte detection system having a window assembly and a plurality of detector channels, each detector channel generating a detector signal in response to infrared emissions from a sample and infrared emissions from the window assembly, the method comprising:

measuring a window signal for each detector channel, each window signal having a corresponding amplitude and a corresponding phase delay;

calculating a scaling factor for each detector channel, each scaling factor equal to the ratio of the corresponding window signal amplitude and a normalization signal amplitude; and

subtracting the product of the corresponding scaling factor and a phase-shifted window reference signal from each detector signal, thereby providing a corrected detector signal for each detector channel.

10. The method of claim 9, wherein the window signals are measured without a sample on the window assembly.

11. The method of claim 9, wherein the window signals are measured with a blanking sample on the window assembly.

12. The method of claim 9, wherein the normalization signal amplitude is measured concurrently with the measurement of the window signals.

13. The method of claim 9, wherein the normalization signal amplitude is generated by a resistance temperature device coupled to the window assembly.

14. The method of claim 9, wherein the window assembly comprises a heater and the normalization signal amplitude is indicative of a current flowing through the heater.

15. The method of claim 9, wherein determining the window reference phase shift comprises finding the value of the window reference phase shift which maximizes a sensitivity of the analyte detection system.

16. The method of claim 9, wherein determining the window reference phase shift comprises finding the value of the window reference phase shift which minimizes a sample signal amplitude.

17. The method of claim 9, wherein the window reference signal in measured with a sample on the window assembly.

18. A method for improving the sensitivity of a noninvasive infrared analyte detection system having a window assembly and a plurality of detector channels, each detector channel configured to generate signals in response to infrared emissions at a characteristic wavelength, the method comprising:

providing a reference detector channel, the reference detector channel configured to generate reference signals in response to infrared emissions at a reference wavelength;

measuring a reference window signal using the reference detector channel, the reference window signal having an amplitude corresponding to infrared emissions at the reference wavelength from the window assembly;

measuring a plurality of window signals using the plurality of detector channels, each window signal having an amplitude corresponding to infrared emissions at the characteristic wavelength of the detector channel from the window assembly;

calculating a scaling factor for each detector channel, each scaling factor equal to the ratio of the corresponding window signal amplitude and the reference window signal amplitude;

measuring a reference detector signal using the reference detector channel, the reference detector signal having an amplitude corresponding to infrared emissions at the reference wavelength from the sample and the window assembly;

measuring a plurality of detector signals using the plurality of detector channels, each detector signal having an amplitude corresponding to infrared emissions at the characteristic wavelength of the detector channel from the sample and the window assembly; and

calculating a corrected detector signal for each detector channel, the corrected detector signal equal to the corresponding detector signal minus the product of the scaling factor and the reference detector signal from each detector signal.

19. The method of claim 18, wherein the reference wavelength is approximately 5 microns.

20. The method of claim 18, wherein the reference detector channel is isolated from other portions of the analyte detection system.

21. The method of claim 18, wherein the reference window signal is measured with no sample on the window assembly.

22. The method of claim 18, wherein the reference window signal is measured with a blanking sample on the window assembly.

23. The method of claim 18, wherein the plurality of window signals are measured concurrently with the measurement of the reference window signal.

24. The method of claim 18, wherein the reference detector signal is measured with a sample on the window assembly.

25. The method of claim 18, wherein the plurality of detector signals is measured with a sample on the window assembly.

26. The method of claim 18, wherein the plurality of detector signals is measured concurrently with the measurement of the reference detector signal.

27. A method of enhancing the accuracy of an analyte measuring system, wherein said analyte measuring system comprises at least one infrared radiation detector and at least one window through which infrared radiation from a sample to be tested is received, said method comprising:

estimating at least one characteristic of the detector signal produced by infrared radiation generated by said window; and

compensating the total received detector signal using at least in part said estimated characteristic.

28. A method of enhancing the accuracy of an analyte measuring system, wherein said analyte measuring system comprises at least one infrared radiation detector responsive to infrared radiation in a wavelength range and at least one window through which infrared radiation from a sample to be tested is received, said method comprising:

reducing the response of the analyte measuring system to infrared radiation emitted by the window, wherein said reducing comprises increasing the transmission of the window in the wavelength range.

29. The method of claim 28, wherein the wavelength range is between approximately 8 microns and approximately 12 microns and the transmission of the window in the wavelength range is greater than approximately 60%.

30. The method of claim 28, wherein the wavelength range is between approximately 8 microns and approximately 12 microns and the transmission of the window in the wavelength range is greater than approximately 70%.

31. A method of enhancing the accuracy of an analyte measuring system, wherein said analyte measuring system comprises a first infrared radiation detector generating a first signal having a first phase shift in response to infrared radiation in a first wavelength range, a second infrared radiation detector generating a second signal having a second phase shift in response to infrared radiation in a second wavelength range, and at least one window through which infrared radiation from a sample to be tested is received, said method comprising:

reducing the response of the analyte measuring system to infrared radiation emitted by the window, wherein said reducing comprises selecting the first wavelength range and the second wavelength range such that the first phase shift and the second phase shift are approximately equal.

32. A method of enhancing the accuracy of an analyte measuring system, wherein said analyte measuring system comprises a first infrared radiation detector generating a first signal having a first phase shift in response to infrared radiation in a first wavelength range, a second infrared radiation detector generating a second signal having a second phase shift in response to infrared radiation in a second wavelength range, and at least one window through which infrared radiation from a sample to be tested is received, said method comprising:

reducing the response of the analyte measuring system to infrared radiation emitted by the window, wherein said reducing comprises selecting the first wavelength range and the second wavelength range such that the difference between the first phase shift and the second phase shift is minimized.

33. A method of enhancing the accuracy of an analyte measuring system, wherein said analyte measuring system comprises at least one infrared radiation detector responsive to infrared radiation in a wavelength range and at least one window through which infrared radiation from a sample to be tested is received, said sample coupled to said window, said method comprising:

stabilizing the coupling between the sample and the window by placing a fluid film between the sample and the window.

34. The method of claim 33, wherein the fluid film comprises mineral oil.