Methods and systems for improving the reliability of orthogonally redundant sensors

• US 10,426,385 B2
• Filed: 04/07/2017
• Issued: 10/01/2019
• 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, Li, Xiaolong, Liu, Mike C., Zhong, Yuxiang, Yang, Ning
• Primary Examiner(s): Winakur, Eric F
• Assistant Examiner(s): Fardanesh, Marjan
• Application Number:
  US15/481,868
• Publication Number:
  US 20170209080A1
• Time in Patent Office: 907 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 method of calibrating an optical glucose sensor of an orthogonally redundant sensor device for determining the concentration of glucose in a body of a user, wherein the sensor device further includes an electrochemical glucose sensor and sensor electronics having at least one physical microprocessor, the method comprising:

(a) receiving, by said microprocessor, a first signal from the electrochemical glucose sensor and a second signal from the optical glucose sensor;

(b) receiving, by said microprocessor, a meter glucose value, said meter glucose value being indicative of the user'"'"'s blood glucose (BG) level;

(c) pairing said meter glucose value with said second signal;

(d) performing, by said microprocessor, a validity check on the paired meter glucose value and second signal and accepting said paired meter glucose value and second signal when said validity check is satisfied;

(e) calculating, by said microprocessor, a mapped value for the second signal based on the first signal and said accepted meter glucose value; and

(f) calibrating the mapped value of the second signal based on said first meter glucose value.

2. The method of claim 1, wherein the microprocessor performs said validity check when the first and second signals are not in an initialization period.

3. The method of claim 2, wherein the microprocessor determines that the second signal is past the initialization period when the second signal'"'"'s rate of change at start-up is below a calculated threshold.

4. The method of claim 2, wherein, in step (e), said mapped value of the second signal is calculated based on one or more values for the first signal that were generated after the initialization period and before said first meter glucose value.

5. The method of claim 1, further including, prior to step (e), calculating a correlation value between said first and second signals by said microprocessor.

6. The method of claim 5, wherein the microprocessor calculates said correlation value by performing linear fitting of the second signal to the first signal, and then calculating the coefficient of determination between the second signal and the first signal.

7. The method of claim 6, wherein, if the correlation value is less than a calculated threshold, then the microprocessor determines that the first and second signals do not correlate well with each other, saves said meter glucose value and second signal to a buffer, and does not perform steps (e) and (f), and wherein, if the correlation value is greater than a calculated threshold, then the microprocessor determines that the first and second signals correlate well with each other, and performs said mapping in step (e).

8. The method of claim 7, wherein the buffer is a first-in-first-out (FIFO) buffer, and has a calculated size.

9. The method of claim 7, wherein, to perform said mapping, the microprocessor performs a linear regression calculation on stored values of said first and second signals so as to obtain a first slope value and a first offset value, said stored values being values of said first and second signals that were generated before said first meter glucose value.

10. The method of claim 9, wherein the microprocessor calculates said mapped value for the second signal by using the relation (mapped signal)=(first signal+first offset)*(first slope).

11. The method of claim 10, wherein, in step (f), the mapped value for the second signal is calibrated so as to generate an optical sensor glucose value by using the relation (optical sensor glucose value)=(mapped value of second signal+fixed offset)*(second slope), wherein said second slope is calculated based on a paired meter glucose value and second signal value.

12. The method of claim 11, wherein said fixed offset is empirically derived from in vivo or in vitro data.

13. The method of claim 1, wherein step (e) is performed when said meter glucose value is a first meter glucose value of one or more meter glucose values, and wherein, when said meter glucose value is not the first meter glucose value but a subsequent meter glucose value of said one or more meter glucose values, the microprocessor performs a validity check on said subsequent meter glucose value and its paired second signal, and then saves the paired subsequent meter glucose value and second signal to a first-in-first-out (FIFO) buffer.

14. The method of claim 13, further including calculating an absolute difference between the subsequent meter glucose value and the immediately preceding meter glucose value that was saved in the buffer.

15. The method of claim 14, wherein, when said absolute difference is greater than a calibration threshold, the microprocessor performs linear regression based on all meter glucose value-second signal pairs inside the buffer to obtain a third slope value and a third offset value, and wherein, when said third slope and offset values are within a predetermined range, the microprocessor calculates an optical sensor glucose value by using the relation (optical sensor glucose value)=(second signal+third offset)*(third slope).

16. The method of claim 15, wherein, when said absolute difference is lower than said calibration threshold, the microprocessor obtains a glucose value from the electrochemical sensor, calculates an absolute difference between that electrochemical sensor glucose value and said subsequent meter glucose value, and, when the absolute difference between that electrochemical sensor glucose value and the subsequent meter glucose value is greater than said calibration threshold, saves the electrochemical sensor glucose value and its paired second signal to the buffer, such that said electrochemical sensor glucose value is treated as an additional meter glucose value in the buffer.

17. The method of claim 16, wherein the microprocessor performs linear regression based on all meter glucose value-second signal pairs inside the buffer to obtain a fourth slope value and a fourth offset value, and wherein, when said fourth slope and offset values are within a predetermined range, the microprocessor calculates an optical sensor glucose value by using the relation (optical sensor glucose value)=(second signal+fourth offset)*(fourth slope).

18. The method of claim 1, wherein the optical glucose sensor includes an assay fluorophore and a reference fluorophore, wherein the assay fluorophore generates an assay fluorescence signal and the reference fluorophore generates a reference fluorescence signal.

19. The method of claim 18, wherein said second signal is a ratio of the assay fluorescence signal to the reference fluorescence signal.

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