Posture Calibration Matrix for Implantable Medical Sensors
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Solution Overview
Problem
Existing medical devices face challenges in accurately determining patient posture due to varying orientations of implantable or wearable devices, which affects the interpretation of sensor measurements and can lead to incorrect diagnosis or treatment.
Innovation Solution
A multi-dimensional posture sensor system that includes a calibration circuit and processor to measure sensor outputs from different device axes, calculate coordinate transformations, and determine a calibration transformation to accurately determine patient posture without requiring trigonometric calculations, allowing for precise alignment with the gravitational field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a posture sensor is implanted or worn on a patient, then posture information can be obtained for monitoring patient condition, but the device orientation varies due to different mounting positions which reduces measurement accuracy
Solution Approach 1:
The patent applies preliminary action by performing a calibration procedure before normal operation. The device measures sensor outputs at multiple known orientations (e.g., 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) and pre-calculates a calibration matrix that maps device coordinates to body coordinates. This preliminary calibration enables accurate posture determination despite varying device mounting positions.
Solution Approach 2:
The patent changes the parameter representation by transforming sensor outputs from device coordinate system to body coordinate system using a calibration matrix. The calibration matrix contains transformation parameters that account for the specific device orientation relative to the patient's body, allowing accurate posture measurement regardless of how the device was mounted.
2Measurement precision
If coordinate transformations are calculated to compensate for device orientation, then posture determination accuracy improves, but device complexity increases due to additional calibration circuits and processing
Solution Approach 1:
The patent applies self-service by implementing the calibration and coordinate transformation functions within the implantable device itself. The calibration circuit measures sensor outputs and calculates the calibration matrix autonomously, and the processor applies the transformation during normal operation. This eliminates the need for external calibration equipment or complex external processing systems.
Solution Approach 2:
The patent replaces mechanical alignment procedures with electronic calibration. Instead of requiring precise mechanical mounting of the device at a specific orientation, the system uses electronic sensor measurements and computational transformation to achieve accurate posture determination. This substitution of mechanical precision with electronic calibration simplifies the physical mounting requirements.
3Measurement precision
If trigonometric calculations are used to determine device orientation angles, then accurate coordinate transformation can be achieved, but computational burden and processing time increase
Solution Approach 1:
The patent performs the computationally intensive trigonometric calculations during the preliminary calibration phase rather than during real-time operation. The calibration matrix is pre-calculated using trigonometric functions at known orientations, and then this matrix is applied through simple matrix multiplication during actual posture measurement, significantly reducing real-time processing requirements.
Solution Approach 2:
The patent transitions from dynamic trigonometric calculations to static matrix multiplication. The calibration matrix captures all the complex trigonometric relationships in a fixed set of parameters, allowing real-time posture determination to use efficient matrix operations instead of repeated trigonometric computations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and reliable posture determination in medical devices, improving patient monitoring and reducing errors in interpreting cardiac activity and other physiological parameters by compensating for device orientation variations.
Implementation Method 1
a multi-dimensional posture sensor configured to provide an electrical sensor output representative of alignment of respective first, second, and third non-parallel axes of the device with the gravitational field of the earth
Data Source
AI summary
A device can include a multi-dimensional posture sensor that provides an electrical sensor output representative of alignment of first, second, and third non-parallel axes of the device with the gravitational field of the earth, and a processor that includes a calibration circuit and a posture circuit. The calibration circuit measures a first sensor output for the first device axis and a second sensor output for one of a second device axis while the subject is in a first specified posture, measures sensor outputs for the first, second, and third device axes while the subject is in a second specified posture, calculates one or more coordinate transformations, generates transformed sensor outputs using the coordinate transformations, and calibrates the posture sensor by calculating a calibration transformation using the first and second sensor outputs and the transformed sensor outputs. The posture circuit determines a subsequent posture of the subject using the posture sensor.