Application of electrochemical impedance spectroscopy in sensor systems, devices, and related methods

Patent metadata

Field	Value
Publication number	US-10172544-B2
Application number	US-201715701775-A
Country	US
Kind code	B2
Filing date	Sep 12, 2017
Priority date	Jun 8, 2012
Publication date	Jan 8, 2019
Grant date	Jan 8, 2019

Abstract

A diagnostic Electrochemical Impedance Spectroscopy (EIS) procedure is applied to measure values of impedance-related parameters for one or more sensing electrodes. The parameters may include real impedance, imaginary impedance, impedance magnitude, and/or phase angle. The measured values of the impedance-related parameters are then used in performing sensor diagnostics, calculating a highly-reliable fused sensor glucose value based on signals from a plurality of redundant sensing electrodes, calibrating sensors, detecting interferents within close proximity of one or more sensing electrodes, and testing surface area characteristics of electroplated electrodes. Advantageously, impedance-related parameters can be defined that are substantially glucose-independent over specific ranges of frequencies. An Application Specific Integrated Circuit (ASIC) enables implementation of the EIS-based diagnostics, fusion algorithms, and other processes based on measurement of EIS-based parameters.

First claim

What is claimed is:

1. A method of calculating a single, fused sensor glucose value based on respective glucose measurement signals of a plurality of redundant sensing electrodes, comprising:
performing respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of redundant sensing electrodes to obtain values of at least one impedance-based parameter for each said sensing electrode;
measuring the electrode current (Isiq) for each of the plurality of redundant sensing electrodes;
calibrating each of the measured Isiqs by using a blood glucose (BG) value to obtain respective calibrated sensor glucose values;
calculating a plurality of reliability indices for each said sensing electrode based on said values of the at least one impedance-based parameter, said plurality of reliability indices including a dip reliability index that is calculated by:
calculating a first similarity index to determine an amount of divergence between respective Isigs of at least a first one and a second one of said plurality of redundant sensing electrodes;
calculating a second similarity index to determine an amount of divergence between respective values of the at least one impedance-based parameter for said at least first one and second one of said plurality of redundant sensing electrodes;
mapping said first similarity index to said second similarity index; and
mapping said second similarity index to said first similarity index; and

calculating said single, fused sensor glucose value based on said plurality of reliability indices and calibrated sensor glucose values of each of the plurality of redundant sensing electrodes.

2. The method of claim 1 , wherein said impedance-based parameter is 1 kHz real impedance.

3. The method of claim 2 , wherein said plurality of reliability indices include a bound check reliability index and a noise check reliability index.

4. The method of claim 3 , wherein calculation of said bound check reliability index and noise check reliability index includes determining whether each said measured Isig and said values of the 1 kHz real impedance fall within respective predetermined ranges for a bound check and a noise check.

5. The method of claim 4 , wherein said predetermined range for the 1 kHz real impedance bound check is between 0.3e+4 and 2e+4.

6. The method of claim 1 , wherein said plurality of reliability indices include a sensitivity-loss index that is calculated based on each said electrode's imaginary impedance.

7. The method of claim 6 , wherein said imaginary impedance is measured at about 1 kHz over a period of time.

8. The method of claim 1 , wherein a low-pass filter is applied to said single, fused sensor glucose value.

9. The method of claim 1 , wherein each said respective EIS procedure is performed for a range of frequencies.

10. The method of claim 1 , wherein said plurality of reliability indices include a bound check reliability index and a noise check reliability index, and wherein said bound check reliability index and noise check reliability index are calculated based on values of 1 kHz imaginary impedance and 1 kHz real impedance.

11. The method of claim 10 , wherein calculation of said bound check reliability index and noise check reliability index is further based on values of 0.105 Hz imaginary impedance and 0.105 Hz real impedance.

12. The method of claim 11 , wherein calculation of said bound check reliability index and said noise check reliability index includes determining whether said values of the 0.105 Hz real impedance fall between 2e+4 and 7e+4.

13. The method of claim 11 , wherein calculation of said bound check reliability index and said noise check reliability index includes determining whether said values of the 0.105 Hz imaginary impedance fall between −2e+5 and 0.25e+5.

14. The method of claim 11 , wherein calculation of said bound check reliability index and noise check reliability index is further based on values of Nyquist slope.

15. The method of claim 14 , wherein calculation of said bound check reliability index and said noise check reliability index includes determining whether said values of Nyquist slope fall between 2 and 5.

16. The method of claim 1 , wherein calculation of said dip reliability index is additionally based on the measured Isig for each said electrode.

17. The method of claim 1 , wherein, prior to calibrating the measured Isigs, said Isigs are first filtered to remove any EIS-induced spikes therein.

18. The method of claim 1 , wherein one or more of the at least one impedance-based parameter are substantially glucose-independent.

19. The method of claim 1 , further including calculating, for each of the plurality of electrodes, a weight based on said plurality of reliability indices for each said electrode.

20. The method of claim 19 , wherein said single, fused sensor glucose value is calculated based on the respective weights and calibrated sensor glucose values of each of the plurality of redundant sensing electrodes.

Assignees

• Medtronic Minimed Inc

Inventors

• Yang Ning
• Gautham Raghavendhar
• Liang Bradley C
• Shah Rajiv

Classifications

• A61B5/1473

  invasive, e.g. introduced into the body by a catheter · CPC title

• A61B5/14865

  invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors · CPC title

• A61B5/7221 Primary

  Determining signal validity, reliability or quality (preventing, reducing or removing noise induced by motion artefacts A61B5/7207; noise originating from a therapeutic or surgical apparatus A61B5/7217) · CPC title

• A61B5/6852

  Catheters · CPC title

• G01N27/028

  Circuits therefor (measuring impedance per se G01R27/02) · CPC title