Correlating Contact and Non-Contact PPG Signals for Noise Reduction
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Solution Overview
Problem
Imaging photoplethysmography (iPPG) signals are often noisy due to environmental illumination and body movement, making it challenging to accurately detect physiological responses such as allergic reactions, strokes, migraines, stress, emotional responses, pain, and blood pressure using non-contact sensors like cameras.
Innovation Solution
A system comprising a head-mounted contact photoplethysmography device and a camera, physically coupled to smartglasses or a smart-helmet, measures photoplethysmogram signals from the skin and captures images of the head, allowing for the detection of physiological responses by correlating imaging photoplethysmogram signals with contact signal fiducial points, even in noisy environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If non-contact sensors (cameras) are used to obtain iPPG signals, then ease of operation and user comfort are improved, but measurement precision deteriorates due to environmental illumination and body movement noise
Solution Approach 1:
The patent introduces an intermediary contact PPG sensor that provides a reliable reference signal to mediate between the noisy non-contact iPPG measurements and the ground truth physiological data. This contact sensor acts as a mediator that captures the same physiological information through direct skin contact, eliminating the need for complex noise filtering algorithms while maintaining measurement accuracy.
Solution Approach 2:
The system uses a contact PPG sensor to create a reference copy of the physiological signal that can be used to validate and correct the non-contact iPPG measurements. By having two parallel measurement paths (contact and non-contact), the system can identify and eliminate noise components in the iPPG signal by comparing against the clean contact reference signal.
2Measurement precision
If contact PPG devices are used to obtain PPG signals, then measurement precision is improved, but ease of operation deteriorates due to skin contact requirements
Solution Approach 1:
The patent merges the advantages of both contact and non-contact PPG measurement approaches into a single integrated system. The contact PPG sensor provides accurate reference measurements when needed, while the non-contact camera provides continuous monitoring capability. The system intelligently combines data from both sensors to achieve both high measurement precision and ease of operation.
Solution Approach 2:
The head-mounted device serves multiple functions: it acts as both a contact PPG sensor (when placed on the skin) and a non-contact iPPG camera (when positioned away from the skin). This multi-functional design allows the same device to adapt to different measurement needs and user preferences, providing both accuracy and ease of operation depending on the situation.
3Reliability
If iPPG signals are used for physiological response detection, then reliability of non-contact monitoring is improved, but measurement precision deteriorates due to signal noise from environmental factors
Solution Approach 1:
The system implements feedback by continuously comparing the non-contact iPPG signal with the contact PPG reference signal. When discrepancies are detected (indicating noise contamination), the system uses the contact reference to correct or reject the noisy measurements. This feedback mechanism ensures that reliability is maintained through continuous validation against a known good reference.
Solution Approach 2:
The contact PPG sensor performs preliminary measurement to establish the true physiological signal before the non-contact iPPG measurement is processed. By having the reference measurement ready in advance, the system can pre-identify noise components in the iPPG signal and apply appropriate correction filters before final analysis, improving measurement precision while maintaining reliability.
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 enhances the accuracy of iPPG signal detection, enabling reliable monitoring of physiological responses over extended periods, improving the ability to detect conditions like strokes, migraines, and stress through improved signal correlation and noise reduction.
Implementation Method 1
A photoplethysmogram signal (PPG signal) is an optically obtained plethysmogram that is indicative of blood volume changes in the microvascular bed of tissue. A PPG signal is often obtained by using a pulse oximeter, which illuminates the skin and measures changes in light absorption.
Implementation Method 2
Another possibility for obtaining the PPG signal is using an imaging photoplethysmography (iPPG) device. As opposed to typical PPG devices, which usually come in contact with the skin, iPPG does not require contact with the skin and is obtained by a non-contact sensor, such as a video camera.
Data Source
AI summary
Disclosed herein are systems and methods for detecting a physiological response using different types of photoplethysmography sensors. Examples of physiological responses that may be detected include an allergic reaction, a stroke, a migraine, stress, certain emotional responses, manifestation of pain, and blood pressure. In one embodiment, a head-mounted contact photoplethysmography device measures a signal indicative of photoplethysmogram signal at a first region that includes exposed skin on a user's head (PPG signal). A camera, located more than 10 mm away from the user's head, captures images of a second region that includes exposed skin on the user's head. A computer detects the physiological response based on: (i) imaging photoplethysmogram signals (iPPG signals) recognizable in the images, and (ii) correlations between the PPG signal and the iPPG signals.