Remote PPG Vital Sign Detection Using Modulated Illumination
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Solution Overview
Problem
Remote photoplethysmography (PPG) systems face challenges in achieving robust and accurate vital sign measurements due to low signal-to-noise ratio, interference from ambient light, and motion, particularly in healthcare settings where high accuracy and reliability are critical.
Innovation Solution
A system utilizing a detection unit with high sampling rates and large dynamic range, combined with HF-modulated radiation sources and a low-resolution 2D sensor array, to generate demodulated detection signals that are robust to ambient light and motion, allowing for the extraction of vital signs through statistical measures from multiple wavelength or polarization channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If remote PPG systems use camera-based detection to measure vital signs, then unobtrusiveness and ease of operation are improved, but signal-to-noise ratio deteriorates due to low signal strength and ambient light interference
Solution Approach 1:
The system modulates the illumination light at a specific frequency and synchronously demodulates the detected signal at the same frequency. This periodic action allows the system to distinguish the vital sign signal from ambient light interference, improving signal-to-noise ratio while maintaining remote, unobtrusive operation.
Solution Approach 2:
The system introduces a modulated illumination source as an intermediary that carries encoded vital sign information. By modulating the light and using synchronous demodulation, the system creates an intermediate representation that separates the weak vital sign signal from ambient noise, improving measurement reliability without contact.
2Measurement precision
If contact PPG devices are used to measure vital signs, then measurement precision is improved, but ease of operation deteriorates due to cable restrictions and subject discomfort
Solution Approach 1:
The system replaces the mechanical contact-based PPG device with an optical remote sensing system. Instead of using cables and physical sensors attached to the subject, the system uses modulated light illumination and camera-based detection to capture vital signs remotely, eliminating mechanical constraints while maintaining measurement precision through optical detection and synchronous demodulation.
3Adaptability or versatility
If remote PPG systems operate in challenging environmental conditions with motion and ambient light, then adaptability is improved, but measurement precision deteriorates due to motion artifacts and illumination variations
Solution Approach 1:
The system uses periodic modulation of the illumination light and synchronous demodulation at the same frequency. This creates a frequency-selective detection mechanism that is immune to ambient light variations and motion artifacts, as these do not occur at the specific modulation frequency. The system can therefore operate robustly in challenging environmental conditions while maintaining measurement precision.
Solution Approach 2:
The system processes the demodulated signal to extract vital signs and can use quality indicators to assess signal reliability. The feedback from signal quality assessment allows the system to distinguish between accurate vital sign measurements and artifacts caused by motion or poor illumination, maintaining precision despite environmental challenges.
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
The system provides reliable and robust vital sign measurements, even in challenging environmental conditions, by effectively filtering out ambient light and motion artifacts, enhancing the accuracy and reliability of remote PPG systems.
Implementation Method 1
an illumination unit configured to illuminate a skin region of the subject, said illumination unit comprising a first radiation source and a second radiation source, which are configured to emit differently modulated electromagnetic radiation in two or more wavelength channels
Implementation Method 2
a detection unit configured to detect electromagnetic radiation reflected from the skin region of the subject and to generate detection signals
Implementation Method 3
a processing unit configured to demodulate the detection signals corresponding to the modulation applied by the illumination unit to obtain demodulated detection signals
Implementation Method 4
Plethysmography generally refers to the measurement of volume changes of an organ or a body part and in particular to the detection of volume changes due to a cardio-vascular pulse wave traveling through the body of a subject with every heartbeat
Data Source
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AI summary
The present invention relates to a system and method for determining at least one vital sign of a subject. To improve the ambient light robustness, said system comprises an illumination unit (2) configured to illuminate a skin region of the subject, said illumination unit comprising a first radiation source (20) and a second radiation source (21), which are configured to emit differently modulated electromagnetic radiation in two or more wavelength channels and/or in two or more polarization channels, a detection unit (4) configured to detect electromagnetic radiation reflected from the skin region of the subject and to generate detection signals, wherein the detection unit (4) comprises a plurality of detection elements and wherein a detection signal is generated per detection element or group of two or more detection elements, a processing unit (11) configured to demodulate the detection signals corresponding to the modulation applied by the illumination unit to obtain demodulated detection signals, and a vital signs determination unit (5) configured to determine, per wavelength or polarization channel, a statistical measure from said demodulated detection signals at the same instant of time and to extract a vital sign from said statistical measures.