Methods and systems for improving the reliability of orthogonally redundant sensors

• US 9,649,059 B2
• Filed: 04/24/2014
• Issued: 05/16/2017
• Est. Priority Date: 12/16/2013
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Varsavsky, Andrea, Liu, Mike C., Zhong, Yuxiang, Yang, Ning, Li, Xiaolong
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Fardanesh, Marjan
• Application Number:
  US14/261,043
• Publication Number:
  US 20150164389A1
• Time in Patent Office: 1,118 Days
• Field of Search: None
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2560/0238 Means for recording calibration data
• CPC Class Codes: A61B 2562/06 Arrangements of multiple sensors of different types
• CPC Class Codes: A61B 5/0004 characterised by the type of physiological signal transmitted
• 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 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14556 by fluorescence A61B5/14555 takes precedence
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/1468 using chemical or electrochemical methods, e.g. by polarographic means A61B5/1486 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 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/4839 combined with drug delivery
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61M 2005/1726 the body parameters being measured at, or proximate to, the infusion site
• CPC Class Codes: A61M 2205/3306 Optical measuring means
• CPC Class Codes: A61M 2205/3584 using modem, internet or bluetooth
• CPC Class Codes: A61M 2205/3592 using telemetric means, e.g. radio or optical transmission
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/505 : Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2205/52 : with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2230/005 : Parameter used as control input for the apparatus
• CPC Class Codes: A61M 2230/201 : Glucose concentration
• CPC Class Codes: A61M 5/142 : Pressure infusion, e.g. using pumps
• CPC Class Codes: A61M 5/14244 : adapted to be carried by the patient, e.g. portable on the body
• 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: C12Q 1/006 : for glucose
• CPC Class Codes: G01N 21/00 : Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light G01N3/00 - G01N19/00 take precedence
• CPC Class Codes: G01N 21/59 : Transmissivity G01N21/25 takes precedence
• CPC Class Codes: G01N 21/84 : Systems specially adapted for particular applications
• CPC Class Codes: G01N 2201/127 : Calibration; base line adjustment; drift compensation
• CPC Class Codes: G01N 27/27 : Association of two or more measuring systems or cells, each measuring a different parameter, where the measurement results may be either used independently, the systems or cells being physically associated, or combined to produce a value for a further parameter
• CPC Class Codes: G01N 27/3274 : Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration coding of calibration information G01N33/48771
• 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

Abstract

Methods and systems for sensor calibration and sensor glucose (SG) fusion are used advantageously to improve the accuracy and reliability of orthogonally redundant glucose sensor devices, which may include optical and electrochemical glucose sensors. Calibration for both sensors may be achieved via fixed-offset and/or dynamic regression methodologies, depending, e.g., on sensor stability and Isig-Ratio pair correlation. For SG fusion, respective integrity checks may be performed for SG values from the optical and electrochemical sensors, and the SG values calibrated if the integrity checks are passed. Integrity checks may include checking for sensitivity loss, noise, and drift. If the integrity checks are failed, in-line sensor mapping between the electrochemical and optical sensors may be performed prior to calibration. The electrochemical and optical SG values may be weighted (as a function of the respective sensor'"'"'s overall reliability index (RI)) and the weighted SGs combined to obtain a single, fused SG value.

Claims

1. A continuous glucose monitoring system comprising:

an orthogonally redundant glucose sensor device comprising an optical glucose sensor and an electrochemical glucose sensor; and

a transmitter operatively coupled to said electrochemical and optical glucose sensors and having a housing, wherein the transmitter includes sensor electronics in said housing, said sensor electronics including at least one physical microprocessor that is configured to;

perform a status check on each of the electrochemical glucose sensor and the optical glucose sensor, wherein said status check on the electrochemical glucose sensor is based on at least one of a previous cal ratio a previous sensor accuracy, a sensitivity loss flag, and a dip flag for the electrochemical glucose sensor;

calculate a first reliability index for an output signal of the electrochemical sensor based on said status check for the electrochemical sensor;

calculate a second reliability index for an output signal of the optical sensor based on said status check for the optical sensor;

calibrate the output signal of the electrochemical sensor to obtain an electrochemical sensor glucose value (echem SG);

calibrate the output signal of the optical sensor to obtain an optical sensor glucose value (optical SG);

calculate a first weight based on said first reliability index and generate a weighted echem SG based on said first weight;

calculate a second weight based on said second reliability index and generate a weighted optical SG based on said second weight; and

calculate a single, fused sensor glucose value for the orthogonally redundant glucose sensor device based on said weighted echem SG and weighted optical SG.

2. The system of claim 1, wherein said weighted echem SG is calculated by multiplying said first weight by said echem SG, and wherein said weighted optical SG is calculated by multiplying said second weight by said optical SG.

3. The system of claim 1, wherein said single, fused sensor glucose value is calculated by adding said weighted echem SG to said weighted optical SG.

4. The system of claim 1, wherein the transmitter wirelessly transmits said single, fused sensor glucose value.

5. The system of claim 1, wherein the transmitter is configured to be worn on a body of a user.

6. The system of claim 1, further including a handheld monitor.

7. The system of claim 6, wherein the handheld monitor includes an integrated blood glucose meter.

8. The system of claim 7, wherein the transmitter wirelessly transmits said single, fused sensor glucose value to the hand-held monitor.

9. The system of claim 1, further including an insulin pump.

10. The system of claim 9, wherein the transmitter wirelessly transmits said single, fused sensor glucose value to the insulin pump.

11. The system of claim 10, wherein said glucose monitoring system is a closed-loop system.

12. The system of claim 1, wherein the optical glucose sensor includes an assay having a glucose receptor, a glucose analog, a first fluorophore, and a reference fluorophore different from said first fluorophore.

13. The system of claim 12, wherein said output signal of the optical glucose sensor is a ratio of the fluorescence signal from the first fluorophore to the fluorescence signal from the reference fluorophore.

14. The system of claim 1, wherein each of the electrochemical and optical sensors has a distal portion and a proximal portion, and wherein respective distal portions of the optical sensor and the electrochemical sensor are configured to be co-located within a user'"'"'s body.

15. The system of claim 1, wherein said status check on the electrochemical glucose sensor is based on a value of said output signal of the electrochemical glucose sensor.

16. The system of claim 1, wherein said cal ratio is defined as a meter glucose value divided by a difference between the electrochemical glucose sensor'"'"'s output signal and an offset.

17. The system of claim 1, wherein said status check on the optical glucose sensor is based on a value of said output signal of the optical glucose sensor.

18. The system of claim 1, wherein said status check on the optical glucose sensor is based on at least one of a previous cal ratio, a previous sensor accuracy, a sensitivity loss flag, and a dip flag for the optical glucose sensor.

19. The system of claim 18, wherein said cal ratio for the optical glucose sensor is defined as a meter glucose value divided by the optical glucose sensor'"'"'s output signal.

20. The system of claim 1, wherein the first reliability index is calculated based on a reliability index for each of sensor dip, sensor noise, sensor sensitivity loss, sensor cal ratio, and sensor accuracy for the electrochemical glucose sensor, and the second reliability index is calculated based on a reliability index for each of sensor dip, sensor noise, sensor sensitivity loss, sensor cal ratio, and sensor accuracy for the optical glucose sensor.

21. The system of claim 20, wherein, for both the electrochemical glucose sensor and the optical glucose sensor, the reliability index for each of sensor dip and sensor sensitivity loss has a value of either 0 or 1.0.

22. The system of claim 20, wherein, for both the electrochemical glucose sensor and the optical glucose sensor, the reliability index for each of sensor noise, sensor cal ratio, and sensor accuracy has a value between 0 and 1, inclusive.

23. The system of claim 1, wherein said first weight is a linear function of said first reliability index, said second weight is a linear function of said second reliability index, or both.

24. The system of claim 1, wherein said first weight is a non-linear function of said first reliability index, said second weight is a non-linear function of said second reliability index, or both.