Camera-Based PPG Signal Extraction for Pulse Transit Time Measurement
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Solution Overview
Problem
Current methods for non-invasively measuring arterial stiffness and pulse wave velocity are limited in accuracy and reliability, particularly in monitoring cardiovascular health, as they often require multiple contact sensors and are prone to errors due to body movement and posture changes.
Innovation Solution
A device and method using a single optical imaging unit to detect motion, select regions of interest, extract photoplethysmographic signals, correct for motion, determine physical distances, and calculate pulse transit time and pulse wave velocity from multiple body parts, enabling continuous, unobtrusive, and accurate monitoring of cardiovascular health.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple contact sensors are used to measure pulse wave velocity, then measurement precision is improved, but device complexity and ease of operation deteriorate
Solution Approach 1:
The patent combines multiple sensing functions into a single optical imaging unit (camera) that captures images of multiple body regions simultaneously. This single device performs the function of multiple contact sensors by detecting photoplethysmographic signals from different locations in the captured images, thereby reducing device complexity while maintaining measurement capability
Solution Approach 2:
The patent replaces mechanical contact sensors with an optical imaging system. Instead of using physical sensors that require contact with the skin, the system uses a camera to optically detect blood volume changes through photoplethysmography, eliminating the need for mechanical attachment and reducing device complexity
2Measurement precision
If multiple contact sensors are placed on the body, then measurement precision is improved, but ease of operation deteriorates due to sensor placement and synchronization requirements
Solution Approach 1:
The patent merges multiple measurement locations into a single field of view of one camera. The imaging unit captures images of multiple body regions (e.g., forehead, chest, abdomen) simultaneously, eliminating the need to place and synchronize multiple separate sensors across different body locations
Solution Approach 2:
The system automatically identifies and selects regions of interest from the captured images without requiring manual sensor placement. The camera and processing system self-adjust to capture the necessary physiological signals from appropriate body regions, reducing operational complexity
3Reliability
If contact sensors are used for continuous monitoring, then measurement reliability is improved, but ease of operation deteriorates due to body movement and posture changes affecting sensor contact
Solution Approach 1:
The patent replaces contact-based mechanical sensing with non-contact optical sensing. The camera-based photoplethysmography system detects blood volume changes through light reflection without requiring physical contact, making it inherently robust to body movement and posture changes while maintaining continuous monitoring capability
Solution Approach 2:
The system dynamically adapts to body movement by continuously capturing images and automatically tracking regions of interest. The imaging unit can follow body parts as they move within the field of view, maintaining reliable signal acquisition despite changes in body position
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 provides reliable and efficient measurement of pulse transit time and pulse wave velocity, improving the accuracy and reliability of cardiovascular monitoring by using a single camera-based system that adjusts for body motion and posture, allowing for early detection of health deteriorations and providing comprehensive vital sign analysis.
Implementation Method 1
extract at least two photoplethysmographic, PPG, signals from at least two selected region of interest from the set of image frames
Data Source
AI summary
The present invention relates to a device and method for obtaining pulse transit time and/or pulse wave velocity information of a subject (14). Based on a set of image frames (19) of a subject (14) and detected motion of body parts of the subject (14) regions of interest are selected from different non-moving body parts and pulse transit time and/or pulse wave velocity information is obtained from acquired PPG signals extracted from different regions of interest and the respective determined physical distance between the respective regions of interest.