Remote PPG Vital Sign Detection Using Dual-Modulated Light Sources
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Solution Overview
Problem
Conventional remote photoplethysmography (rPPG) systems face challenges in detecting and tracking suitable skin areas, especially in noisy and motion-prone environments, leading to unreliable vital sign measurements.
Innovation Solution
A system utilizing two radiation sources emitting differently modulated electromagnetic radiation from different directions with the same emission spectrum, combined with a demodulation unit and processing unit to separate skin and non-skin signals, enables reliable extraction of vital signs by demixing the detected signals using blind-source separation techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional rPPG systems are used to measure vital signs contactlessly, then patient comfort and freedom of movement are improved, but signal strength decreases and noise increases making detection unreliable
Solution Approach 1:
The system segments the reflected light signal into multiple wavelength components using a spectrometer, separating the PPG signal from noise and background illumination. This spectral segmentation enables reliable extraction of vital signs despite the contactless measurement configuration.
Solution Approach 2:
The system uses periodic modulation of the light source at a frequency distinct from the camera's frame rate, creating a modulated signal that can be demodulated to extract the PPG waveform. This periodic action enhances signal detection reliability in the contactless configuration.
2Adaptability or versatility
If conventional rPPG systems are used in motion-prone environments, then patient mobility is improved, but signal quality deteriorates due to motion artifacts and background interference
Solution Approach 1:
The system performs preliminary spectral analysis and noise filtering before extracting the PPG signal. By preprocessing the signal to remove background illumination and motion artifacts, the system maintains measurement precision even when patients are mobile.
Solution Approach 2:
The system uses feedback from the spectral analysis to adaptively adjust signal processing parameters, enhancing the PPG signal while suppressing motion artifacts and background interference in real-time during patient movement.
3Device complexity
If single wavelength light sources are used in rPPG, then device complexity is reduced, but measurement precision decreases for determining multiple vital signs
Solution Approach 1:
The system uses a broadband light source that provides multiple wavelengths simultaneously, enabling the measurement of multiple vital signs (pulse rate, SpO2, respiratory rate) with a single illumination system. This multi-functional approach maintains device simplicity while enhancing measurement precision.
Solution Approach 2:
The system transitions from temporal signal analysis to spectral domain analysis by using a spectrometer. This dimensional change from time-domain to frequency-domain measurement enables precise determination of multiple vital signs using the full spectral information from a single broadband light source.
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 reliability of vital sign determination by reducing noise and improving signal strength, even in challenging conditions such as motion and background interference, providing accurate measurements of physiological parameters like SpO2 and pulse rate.
Implementation Method 1
The determination of vital signs is performed by transmitting electromagnetic radiation through or reflected from a patient and detecting the transmitted or reflected electromagnetic radiation
Implementation Method 2
Electromagnetic radiation is transmitted through or reflected from a patient and detected by a sensor
Implementation Method 3
The absorption of blood, for these wavelengths, is larger than the absorption of the surrounding tissue. Thus, the variations in blood volume during the cardiac cycle affect the transmission or reflection correspondingly
Data Source
AI summary
The present invention relates to a system and method for determining a vital sign of a subject. To improve the detection of electromagnetic radiation reflected from or transmitted through skin of a subject (110) at least two differently modulated radiation sources (112, 114) are used. For both camera and single-element sensors, this allows access (after demodulation) to different mixtures of skin and non-skin reflections/transmissions that can be de-mixed and successively allows the skin-only signal to be used for photo-plethysmography, PPG, extraction. Thus, a sensor (130) detects the reflected or transmitted electromagnetic radiation and a demodulation unit (140) and processing unit (150) enable to determine a vital sign (160) from said detection signal.