SENSOR-UNSPECIFIC CALIBRATION METHODS AND SYSTEMS

• US 20170181671A1
• Filed: 12/28/2015
• Published: 06/29/2017
• Est. Priority Date: 12/28/2015
• Status: Abandoned Application

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Mung, Jay, Lu, Yunfeng, Korjani, Mohammad Mehdi, Varsavsky, Andrea
• Application Number:
  US14/980,114
• Publication Number:
  US 20170181671A1
• Time in Patent Office: Days
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1473 invasive, e.g. introduced into the body by a catheter A61B5/1482 takes precedence
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F

Abstract

An unscented Kalman filter is used to enable sensor calibration independently of the actual design of the subject sensors. By utilizing an unscented Kalman filter, an underlying calibration methodology is developed that is sensor-unspecific, such that a single calibration methodology and related systems may be used to calibrate various sensors, without the need to re-calculate a calibration factor for each specific sensor, and without the need to design a separate filtering mechanism to compensate for noise. In this way, various calibration inputs can be allowed to change over time without the need to change the codebase on which the calibration methodology otherwise operates. In multi-electrode systems, the methodology may incorporate a fusion algorithm to provide a single, fused sensor glucose value. The fusion algorithm may incorporate, and/or work in conjunction with, Electrochemical Impedance Spectroscopy (EIS) procedures.

Claims

1. A method for real-time calibration of a glucose sensor for measuring the level of glucose in a body of a user, said sensor including physical sensor electronics, a microcontroller, and a working electrode, the method comprising:

measuring, by said physical sensor electronics, the electrode current (Isig) for the working electrode;

obtaining a plurality of blood glucose (BG) values for said user, wherein said BG values include noise;

applying, by said microcontroller, an unscented Kalman filter to said plurality of BG values and determining an estimated calibration factor (CF) value based on said Isig and BG values; and

calculating, by said microcontroller, a calibrated sensor glucose (SG) value associated with said Isig based on said estimated CF value.

2. The method of claim 1, wherein said microcontroller further applies said unscented Kalman filter to compensate for said BG noise.

3. The method of claim 1, wherein said Isig includes noise, and said microcontroller further applies said unscented Kalman filter to compensate for said Isig noise.

4. The method of claim 1, wherein said estimated CF value is further determined based on an offset value that correlates said Isig, BG, and CF values.

5. The method of claim 4, wherein said offset value is unspecific to said sensor.

6. The method of claim 5, wherein said estimated CF value is unspecific to said sensor.

7. The method of claim 1, wherein the sensor includes a plurality of working electrodes.

8. The method of claim 7, further including calculating, for each of the plurality of working electrodes, a respective calibrated sensor glucose (SG) value based on said estimated CF value.

9. The method of claim 8, wherein said estimated CF value is unspecific to said sensor.

10. The method of claim 8, further including fusing the respective calibrated SG values for the plurality of working electrodes to calculate a single, fused sensor glucose value.

11. The method of claim 10, further including performing, by said microcontroller, respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of working electrodes to obtain values of at least one impedance-based parameter for each said working electrode, and calculating said single, fused sensor glucose value based on said values of the at least one impedance-based parameter.

12. The method of claim 7, wherein the sensor electronics measure respective Isig values for each of the plurality of working electrodes, and the microcontroller applies said unscented Kalman filter to said plurality of BG and Isig values to determine said estimated calibration factor value based on said Isig and BG values.

13. The method of claim 12, further including performing, by said microcontroller, respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of working electrodes to obtain values of at least one impedance-based parameter for each said working electrode, and calculating said single, fused sensor glucose value based on said values of the at least one impedance-based parameter.

14. A program code storage device comprising:

a computer-readable medium; and

computer-readable program code, stored on the computer-readable medium, the computer-readable program code having instructions which, when executed, cause a physical microcontroller to perform a method for real-time calibration of a glucose sensor for measuring the level of glucose in a body of a user, said sensor including physical sensor electronics, said physical microcontroller, and a working electrode, by;

obtaining, from said physical sensor electronics, the electrode current (Isig) for the working electrode;

obtaining a plurality of blood glucose (BG) values for said user, wherein said BG values include noise;

applying an unscented Kalman filter to said plurality of BG values and determining an estimated calibration factor (CF) value based on said Isig and BG values; and

calculating a calibrated sensor glucose (SG) value associated with said Isig based on said estimated CF value.

15. The device of claim 14, wherein the computer-readable program code has instructions which, when executed, further cause the microcontroller to apply said unscented Kalman filter to compensate for said BG noise.

16. The device of claim 14, wherein said Isig includes noise, and the computer-readable program code has instructions which, when executed, further cause the microcontroller to apply said unscented Kalman filter to compensate for said Isig noise.

17. The device of claim 14, wherein said estimated CF value is further determined based on an offset value that correlates said Isig, BG, and CF values.

18. The device of claim 17, wherein said offset value is unspecific to said sensor.

19. The device of claim 18, wherein said estimated CF value is unspecific to said sensor.

20. The device of claim 14, wherein the sensor includes a plurality of working electrodes.

21. The device of claim 20, wherein the computer-readable program code has instructions which, when executed, further cause the microcontroller to calculate, for each of the plurality of working electrodes, a respective calibrated sensor glucose (SG) value based on said estimated CF value.

22. The device of claim 21, wherein said estimated CF value is unspecific to said sensor.

23. The device of claim 21, wherein the computer-readable program code has instructions which, when executed, further cause the microcontroller to fuse the respective calibrated SG values for the plurality of working electrodes to calculate a single, fused sensor glucose value.

24. The device of claim 23, wherein the computer-readable program code has instructions which, when executed, further cause the microcontroller to perform respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of working electrodes to obtain values of at least one impedance-based parameter for each said working electrode, and to calculate said single, fused sensor glucose value based on said values of the at least one impedance-based parameter.

25. The device of claim 20, wherein the computer-readable program code has instructions which, when executed, further cause the microcontroller to obtain respective Isig values for each of the plurality of working electrodes and to apply said unscented Kalman filter to said plurality of BG and Isig values to determine said estimated calibration factor value based on said Isig and BG values.

26. The device of claim 25, wherein the computer-readable program code has instructions which, when executed, further cause the microcontroller to perform respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of working electrodes to obtain values of at least one impedance-based parameter for each said working electrode, and to calculate said single, fused sensor glucose value based on said values of the at least one impedance-based parameter.