Noise Cancellation Circuitry for Optical Tissue Oxygenation Sensors
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Solution Overview
Problem
Optical sensors used for monitoring tissue oxygenation are susceptible to motion artifacts, making it challenging to reliably measure tissue oxygenation in ambulatory patients, as movement alters the optical pathway and introduces noise in the sensor signals.
Innovation Solution
The implementation of noise cancellation circuitry in conjunction with optical sensors, which uses second derivatives of light attenuation to derive calibrated measurements of tissue oxygen saturation and total hemoglobin concentration, and employs adaptive noise cancellation techniques to reduce noise in the sensor signals, thereby improving the accuracy of tissue oxygenation monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical sensors are used to monitor tissue oxygenation in ambulatory patients, then valuable diagnostic and therapeutic data can be obtained, but motion artifacts introduce noise that degrades measurement accuracy
Solution Approach 1:
A noise reference sensor is introduced as an intermediary element that specifically detects motion artifacts without measuring tissue oxygenation. The noise cancellation processor uses this intermediary sensor's output to identify and remove motion-related noise from the primary optical sensor signal, thereby preserving measurement precision while maintaining reliability in ambulatory conditions
Solution Approach 2:
The invention extracts the motion artifact component from the composite optical sensor signal by using the noise reference sensor to isolate motion-related variations. This extracted noise component is then subtracted from the primary signal, separating the desired tissue oxygenation information from the unwanted motion artifacts and improving measurement precision
2Measurement precision
If motion sensing is added to detect and cancel noise, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
Instead of using a single complex sensor, the invention employs two simpler optical sensors with distinct functional qualities: one optimized for tissue oxygenation measurement and another optimized for motion artifact detection. This local differentiation of sensor functions achieves noise cancellation while keeping individual sensor components relatively simple
Solution Approach 2:
The noise reference sensor acts as a simplified copy or proxy that replicates the motion artifact signal without needing to measure tissue oxygenation. This copying approach allows the system to capture motion noise characteristics using a less complex sensor configuration, reducing overall device complexity while maintaining measurement precision
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
This approach enables reliable monitoring of tissue oxygenation by reducing motion-induced noise, allowing for accurate and stable measurements even in non-uniform tissues and ambulatory patients, enhancing the effectiveness of tissue oxygenation monitoring and therapy management.
Implementation Method 1
measuring light attenuation for at least four different wavelengths
Implementation Method 2
computing two second derivatives of the light attenuation
Data Source
AI summary
A medical device system and associated method are used for monitoring tissue oxygenation. An optical sensor produces a signal corresponding to tissue light attenuation. A processor receives the optical sensor signal and computes a first measure of light attenuation at a first light wavelength and a second measure of light attenuation at a second light wavelength. In one embodiment, noise cancellation circuitry receives the first measure and the second measure and generates a guessed ratio of the first and second measures. Using the first measure, the second measure and the guessed ratio, the noise cancellation circuitry provides a peak output power when the guessed ratio corresponds to an actual ratio of the first and second measures.