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

• US 9,357,958 B2
• Filed: 02/27/2013
• Issued: 06/07/2016
• Est. Priority Date: 06/08/2012
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Yang, Ning, Gautham, Raghavendhar, Liang, Bradley C., Shah, Rajiv
• Primary Examiner(s): Breene, John
• Assistant Examiner(s): MORGAN, JEFFREY CHAD
• Application Number:
  US13/778,416
• Publication Number:
  US 20130332085A1
• Time in Patent Office: 1,196 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2562/0214 Capacitive electrodes
• CPC Class Codes: A61B 2562/04 Arrangements of multiple sensors of the same type
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/14503 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors A61B5/1459, A61B5/1464, A61B5/1473, A61B5/1482, A61B5/14865 take precedence
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/1473 invasive, e.g. introduced into the body by a catheter A61B5/1482 takes precedence
• CPC Class Codes: A61B 5/14865 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/4839 combined with drug delivery
• CPC Class Codes: A61B 5/6849 in combination with a needle set
• CPC Class Codes: A61B 5/6852 Catheters
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• 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
• CPC Class Codes: A61B 5/7242 using integration
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B
• CPC Class Codes: A61M 2005/1726 the body parameters being measured at, or proximate to, the infusion site
• CPC Class Codes: A61M 5/14244 adapted to be carried by the patient, e.g. portable on the body
• CPC Class Codes: A61M 5/14276 : specially adapted for implantation
• CPC Class Codes: A61M 5/1582 : Double lumen needles
• CPC Class Codes: A61M 5/1723 : using feedback of body parameters, e.g. blood-sugar, pressure measurement of body parameters A61B5/00
• CPC Class Codes: G01N 27/026 : Dielectric impedance spectroscopy electrochemical impedance spectroscopy for measuring corrosion G01N17/02
• CPC Class Codes: G01N 27/028 : Circuits therefor measuring impedance per se G01R27/02
• CPC Class Codes: G01N 27/416 : Systems G01N27/27 takes precedence
• CPC Class Codes: G01N 27/4163 : checking the operation of, or calibrating, the measuring apparatus G01N27/3274, G01N27/4175 and G01N33/0006 take precedence
• CPC Class Codes: G01N 33/49 : Blood chemical methods for determining blood cell populations G01N33/5094; chemical analysis of blood groups or blood types G01N33/80
• CPC Class Codes: G01N 33/66 : involving blood sugars, e.g. galactose
• CPC Class Codes: G01N 33/96 : involving blood or serum control standard
• CPC Class Codes: G01R 35/00 : Testing or calibrating of apparatus covered by the other groups of this subclass
• CPC Class Codes: G01R 35/005 : Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

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.

Claims

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 (Isig) for each of the plurality of redundant sensing electrodes;

independently calibrating each of the measured Isigs to obtain respective calibrated sensor glucose values;

performing a bound check and a noise check on said measured Isig and said values of the at least one impedance-based parameter and assigning a bound-check reliability index and a noise-check reliability index to each said sensing electrode;

performing signal-dip analysis based on one or more of said at least one impedance-based parameter and assigning a dip reliability index to each said sensing electrode;

performing sensitivity-loss analysis based on one or more of said at least one impedance-based parameter and assigning a sensitivity-loss index to each said sensing electrode;

for each of the plurality of electrodes, calculating a total reliability index based on said electrode'"'"'s bound-check reliability index, noise-check reliability index, dip reliability index, and sensitivity-loss reliability index;

for each of the plurality of electrodes, calculating a weight based on said electrode'"'"'s total reliability index; and

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

2. The method of claim 1, wherein each said Isig is calibrated by using a blood glucose (BG) value.

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

4. The method of claim 1, wherein said at least one impedance-based parameter includes at least one of real impedance, imaginary impedance, and Nyquist slope.

5. The method of claim 4, wherein values are obtained for real impedance at 1 kHz and for real impedance at 0.105 Hz.

6. The method of claim 4, wherein values are obtained for imaginary impedance at 1 kHz and for imaginary impedance at 0.105 Hz.

7. The method of claim 1, wherein said bound check and noise check include determining whether each said measured Isig and said values of the at least one impedance-based parameter fall within respective predetermined ranges for said bound check and noise check.

8. The method of claim 1, wherein, prior to calculation of said single, fused sensor glucose value, a low-pass filter is applied to the total reliability index for each of the plurality of redundant electrodes.

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

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

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

12. The method of claim 1, wherein said signal-dip analysis is additionally based on the measured Isig for each said electrode.

13. The method of claim 1, wherein said signal-dip analysis is performed based on each said electrode'"'"'s real impedance at about 1 kHz.

14. The method of claim 1, wherein said sensitivity-loss analysis is performed based on each said electrode'"'"'s imaginary impedance at about 1 kHz over a period of time.

15. 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 (Isig) for each of the plurality of redundant sensing electrodes;

calibrating each of the measured Isigs to obtain respective calibrated sensor glucose values;

calculating a bound-check reliability index and a noise-check reliability index for each said sensing electrode based on said measured Isig and said values of the at least one impedance-based parameter;

calculating a dip reliability index for each said sensing electrode 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;

calculating a sensitivity-loss index for each said sensing electrode based on one or more of said at least one impedance-based parameter;

for each of the plurality of electrodes, calculating a total reliability index based on said electrode'"'"'s bound-check reliability index, noise-check reliability index, dip reliability index, and sensitivity-loss reliability index; and

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

16. The method of claim 15, wherein said impedance-based parameter is 1 kHz real impedance.

17. The method of claim 16, wherein said bound check and noise check include determining whether each said measured Isig and said values of the 1kHz real impedance fall within respective predetermined ranges for said bound check and noise check.

18. The method of claim 17, wherein said predetermined range for the 1 kHz real impedance bound check is between 0.3e+4 and 2e+4.

19. The method of claim 15, wherein said sensitivity-loss analysis is performed based on each said electrode'"'"'s imaginary impedance.

20. The method of claim 19, wherein said imaginary impedance is measured at about 1 kHz over a period of time.