Methods and systems for improving the reliability of orthogonally redundant sensors
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.
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;
calculate a first reliability index for the output signal of the electrochemical sensor 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;
calculate a second reliability index for the 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 calculate a weighted echem SG based on said first weight;
calculate a second weight based on said second reliability index and calculate a weighted optical SG based on said second weight; and
calculate a single, fused sensor glucose value based on said weighted echem SG and said weighted optical SG.
2. 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.
3. 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.
4. The system of claim 3 , 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.
5. The system of claim 1 , wherein 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.
6. 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.
7. 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.
8. 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.
9. The system 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, and wherein said output signal of the optical glucose sensor is a ratio of the assay fluorescence signal to the reference fluorescence signal.
10. 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.
11. The system of claim 1 , wherein the transmitter is worn on a body of a user.
12. The system of claim 1 , further including a handheld monitor.
13. The system of claim 12 , wherein the handheld monitor includes an integrated blood glucose meter.
14. The system of claim 13 , wherein the transmitter transmits said single, fused sensor glucose value to the hand-held monitor.
15. The system of claim 1 , further including an insulin pump.
16. The system of claim 15 , wherein the transmitter transmits said single, fused sensor glucose value to the insulin pump.
17. The system of claim 16 , wherein said glucose monitoring system is a closed-loop system.
18. The system of claim 1 , wherein the transmitter wirelessly transmits said single, fused sensor glucose value.
19. The system of claim 1 , wherein the sensor device is configured to be either implanted or subcutaneously disposed in a body of a user.