Noncontact SpO2 Measurement Using Synchronized Camera and LED Arrays
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Solution Overview
Problem
Current non-contact methods for measuring blood oxygen saturation (SpO2) suffer from low frame rates, sensitivity to ambient light, and poor signal-to-noise ratio, making it difficult to obtain accurate SpO2 values over a wide clinical range.
Innovation Solution
A device using a camera with synchronized near-infrared and orange LEDs for video recording of the facial area, processing photoplethysmography signals to determine SpO2 values from pulsatile to non-pulsatile components, providing high temporal resolution and signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If non-contact SpO2 measurement is implemented using camera and LED arrays, then physical contact is eliminated and measurement comfort is improved, but measurement precision deteriorates due to low frame rate and poor signal-to-noise ratio
Solution Approach 1:
The system uses synchronized periodic illumination from LED arrays at specific wavelengths (red 660nm and infrared 940nm) corresponding to the pulsatile nature of blood flow. The camera captures images at synchronized intervals to match the illumination cycle, enabling periodic extraction of photoplethysmography signals that reflect blood volume changes during cardiac cycles, thereby achieving accurate SpO2 measurement without physical contact
Solution Approach 2:
The system changes the illumination wavelength parameter by using dual-wavelength LED arrays (red and infrared) to differentiate between oxygenated and deoxygenated hemoglobin absorption characteristics. By capturing images at these specific wavelengths and analyzing the differential absorption, the system achieves precise SpO2 measurement while maintaining non-contact operation
2Adaptability or versatility
If ambient light conditions are present during measurement, then measurement versatility is improved for practical applications, but measurement precision deteriorates due to sensitivity to ambient light
Solution Approach 1:
The system employs synchronized periodic illumination and image capture to distinguish between ambient light and structured illumination signals. By capturing images at specific time intervals synchronized with the LED illumination cycle, the system can temporally separate and extract the periodic illumination signal from the ambient light background, maintaining measurement precision in practical lighting conditions
Solution Approach 2:
The system performs preliminary synchronization of camera exposure timing with LED illumination timing before actual measurement. By pre-configuring the camera to capture images only during the illumination pulse windows, the system prepares the measurement process to inherently reject ambient light that falls outside these synchronized time gates, thereby maintaining precision in versatile environmental conditions
3Device complexity
If low frame rate is used to reduce data processing load, then device complexity is reduced, but measurement precision deteriorates due to insufficient temporal resolution
Solution Approach 1:
Instead of processing all captured images, the system extracts only the specific photoplethysmography signal components related to blood volume changes at the pulsatile frequency. By isolating and extracting these relevant signal components from the image sequence using frequency-domain analysis, the system achieves accurate SpO2 measurement while minimizing data processing requirements, effectively separating the useful signal from unnecessary data
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 method achieves accurate non-contact SpO2 measurement over a wide range (80%-100%) with high temporal resolution and signal-to-noise ratio, validated through a pilot study, and is suitable for clinical settings without physical contact.
Implementation Method 1
one or more arrays of LEDs each having a first set of LEDs emitting near infrared (NIR), and the second set of LEDs emitting orange light
Implementation Method 2
A processor receives photoplethysmography (PPG) data signal values from the camera. The PPG data signal values are present in the reflected light and include pulsatile and non-pulsatile components
Implementation Method 3
The processor determines SpO2 values from the PPG data signal values from the measured ratios of pulsatile to non-pulsatile components of the PPG signals
Data Source
AI summary
A device for non-contact measurement of blood oxygen saturation (SpO2) in a mammalian subject including a camera and one or more arrays of LEDs each having a first set of LEDs emitting near infrared (NIR), and the second set of LEDs emitting orange light located in an optical path adapted to transmit reflected light from a subject to the camera. A controller transmits a camera trigger to the camera, and is further coupled to transmit control signals to the one or more arrays of LEDs. A processor receives photoplethysmography (PPG) data signal values from the camera. The PPG data signal values are present in the reflected light and include pulsatile and non-pulsatile components. The processor determines SpO2 values from the PPG data signal values from the measured ratios of pulsatile to non-pulsatile components of the PPG signals.