Noninvasive Non-Contact SpO₂ Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor.

Area of Science:

• Biomedical Optics
• Medical Imaging
• Physiological Monitoring

Background:

• Accurate estimation of pulse rate and blood oxygen saturation (SpO2) is crucial for primary healthcare.
• Non-contact, noninvasive methods like photoplethysmography (iPPG) are essential for real-time health monitoring.
• Existing iPPG methods often involve complex computations, hindering real-time spatial visualization.

Purpose of the Study:

• To propose a novel reflective mode polarized imaging-based iPPG method.
• To enable non-contact, real-time estimation of heart rate and SpO2.
• To overcome limitations of current iPPG techniques in real-time measurements and spatial visualization.

Main Methods:

• Designed a custom image sensor with wire grid polarizers for polarization imaging.
• Recorded phase information of backscattered light from fingertips of 12 volunteers using polarized light.
• Processed data using MATLAB 2021b to analyze superficial and deep skin layer reflections.

Main Results:

• Phase information quantitatively reflects light scattering from superficial and deep skin layers.
• The ratio of deep to superficial backscattered phase information linearly correlates with SpO2 and heart rate.
• Demonstrated real-time monitoring of heart rate and SpO2 changes in resting and excited states.

Conclusions:

• Phase-based measurements enable real-time monitoring of heart rate and SpO2.
• Using the ratio of phase information enhances measurement accuracy by normalizing individual skin traits.
• The proposed iPPG system operates in ambient light, allowing for compact and portable device design.