Remote PPG Skin Pixel Selection for Accurate Blood Oxygen Saturation
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Solution Overview
Problem
Conventional non-contact PPG devices typically achieve a lower signal-to-noise ratio and average blood oxygen saturation values over large skin areas, which may include 'old' blood, making them less representative of the arterial blood oxygen saturation, especially in critical care settings like NICUs where accurate and immediate SpO2 measurements are crucial.
Innovation Solution
A remote PPG system that selects specific skin pixels or regions representative of 'new' blood by identifying areas with the fastest arterial blood perfusion and disregarding those with delayed perfusion, thereby determining a more accurate systemic blood oxygen saturation by averaging or weighting the signals from these selected pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If non-contact PPG devices measure blood oxygen saturation by averaging values over large skin areas, then the measurement covers a broader region, but the accuracy decreases due to inclusion of 'old' blood with delayed perfusion
Solution Approach 1:
The patent applies local quality by differentiating between different regions of the skin based on their perfusion characteristics. Instead of treating the entire skin area uniformly, the system identifies and weights specific regions (those with fastest arterial blood perfusion) more heavily in the calculation, giving them higher quality/importance in representing true arterial blood oxygen saturation while reducing the influence of areas with delayed perfusion
Solution Approach 2:
The patent segments the skin area into multiple pixels or regions and evaluates each individually based on its perfusion characteristics. By dividing the measurement area into discrete elements and selectively weighting them according to their arterial blood flow speed, the system can exclude or de-emphasize regions containing 'old' blood while maintaining coverage of the broader skin area
2Ease of operation
If non-contact PPG devices use remote measurement, then the unobtrusiveness and ease of operation improve, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent changes the parameter of signal selection by applying dynamic weighting to different spatial regions based on their perfusion characteristics. By adjusting the weight parameters according to arterial blood flow speed, the system enhances the signal quality from regions with fast perfusion (higher signal-to-noise ratio) while suppressing contributions from regions with delayed perfusion, thereby improving overall measurement reliability while maintaining the unobtrusive remote measurement approach
3Measurement precision
If conventional pulse oximeters are attached directly to the subject, then the measurement accuracy improves, but the ease of operation deteriorates due to limited freedom of movement
Solution Approach 1:
The patent replaces the mechanical contact-based measurement system with an optical remote measurement system using a camera or photo detector disposed away from the subject. This substitution eliminates the need for physical attachment and cables, providing complete freedom of movement while maintaining measurement capability through non-contact optical detection of blood volume changes
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 a more responsive and accurate measurement of blood oxygen saturation, reducing noise levels and differentiating dynamic changes in oxygen saturation across the body, enabling earlier and more precise detection of hypoxic events or other changes in arterial blood oxygenation.
Implementation Method 1
an imaging unit for detecting electromagnetic radiation emitted or reflected from one or more skin portions of the subject
Implementation Method 2
a radiation source for directing electromagnetic radiation to the subject
Data Source
Figure 1
Figure 2~3B
Figure 4A~4C
AI summary
The present invention relates to a device and a method for determining blood oxygen saturation of a subject. The proposed device comprises an interface (32) for receiving a data stream (26) derived from detected electromagnetic radiation (16) emitted or reflected from one or more skin portions of the subject (12), said data stream (26) comprising a data signal per skin pixel for a plurality of skin pixels of said one or more skin portions, a data signal representing the detected electromagnetic radiation (16) emitted or reflected from the respective skin pixel over time, an analyzer (34) for determining the change in blood oxygen saturation of said plurality of skin pixels based on the data signals of said plurality of skin pixels, a selector (36) for selecting a group of skin pixels comprising either the skin pixels showing the fastest change in blood oxygen saturation or said plurality of skin pixels except for skin pixels showing the slowest change in blood oxygen saturation, and a processor (38) for determining the blood oxygen saturation of the subject based on the data signals of the selected group of skin pixels.