Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor
Background:In the diagnosis and primary health care of an individual, estimation of the pulse rate and blood oxygen saturation (SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow>&...
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| Format: | Article |
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MDPI AG
2022-10-01
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| Series: | Sensors |
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| Online Access: | https://www.mdpi.com/1424-8220/22/20/7796 |
| _version_ | 1797470021328306176 |
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| author | Mukul Sarkar Maher Assaad |
| author_facet | Mukul Sarkar Maher Assaad |
| author_sort | Mukul Sarkar |
| collection | DOAJ |
| description | Background:In the diagnosis and primary health care of an individual, estimation of the pulse rate and blood oxygen saturation (SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula>) is critical. The pulse rate and SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula> are determined by methods including photoplethysmography (iPPG), light spectroscopy, and pulse oximetry. These devices need to be compact, non-contact, and noninvasive for real-time health monitoring. Reflection-based iPPG is becoming popular as it allows non-contact estimation of the heart rate and SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula>. Most iPPG methods capture temporal data and form complex computations, and thus real-time measurements and spatial visualization are difficult. Method:In this research work, reflective mode polarized imaging-based iPPG is proposed. For polarization imaging, a custom image sensor with wire grid polarizers on each pixel is designed. Each pixel has a wire grid of varying transmission axes, allowing phase detection of the incoming light. The phase information of the backscattered light from the fingertips of 12 healthy volunteers was recorded in both the resting as well as the excited states. These data were then processed using MATLAB 2021b software. Results: The phase information provides quantitative information on the reflection from the superficial and deep layers of skin. The ratio of deep to superficial layer backscattered phase information is shown to be directly correlated and linearly increasing with an increase in the SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula> and heart rate. Conclusions: The phase-based measurements help to monitor the changes in the resting and excited state heart rate and SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula> in real time. Furthermore, the use of the ratio of phase information helps to make the measurements independent of the individual skin traits and thus increases the accuracy of the measurements. The proposed iPPG works in ambient light, relaxing the instrumentation requirement and helping the system to be compact and portable. |
| first_indexed | 2024-03-09T19:30:51Z |
| format | Article |
| id | doaj.art-930804974615467a86b2fdd8088277ee |
| institution | Directory Open Access Journal |
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| language | English |
| last_indexed | 2024-03-09T19:30:51Z |
| publishDate | 2022-10-01 |
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| spelling | doaj.art-930804974615467a86b2fdd8088277ee2023-11-24T02:26:11ZengMDPI AGSensors1424-82202022-10-012220779610.3390/s22207796Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging SensorMukul Sarkar0Maher Assaad1Electrical Engineering Department, IIT Delhi, Hauz Khas, New Delhi 110016, IndiaDepartment of Electrical and Computer Engineering, Ajman University, Ajman P.O. Box 346, United Arab EmiratesBackground:In the diagnosis and primary health care of an individual, estimation of the pulse rate and blood oxygen saturation (SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula>) is critical. The pulse rate and SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula> are determined by methods including photoplethysmography (iPPG), light spectroscopy, and pulse oximetry. These devices need to be compact, non-contact, and noninvasive for real-time health monitoring. Reflection-based iPPG is becoming popular as it allows non-contact estimation of the heart rate and SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula>. Most iPPG methods capture temporal data and form complex computations, and thus real-time measurements and spatial visualization are difficult. Method:In this research work, reflective mode polarized imaging-based iPPG is proposed. For polarization imaging, a custom image sensor with wire grid polarizers on each pixel is designed. Each pixel has a wire grid of varying transmission axes, allowing phase detection of the incoming light. The phase information of the backscattered light from the fingertips of 12 healthy volunteers was recorded in both the resting as well as the excited states. These data were then processed using MATLAB 2021b software. Results: The phase information provides quantitative information on the reflection from the superficial and deep layers of skin. The ratio of deep to superficial layer backscattered phase information is shown to be directly correlated and linearly increasing with an increase in the SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula> and heart rate. Conclusions: The phase-based measurements help to monitor the changes in the resting and excited state heart rate and SpO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>2</mn></msub></semantics></math></inline-formula> in real time. Furthermore, the use of the ratio of phase information helps to make the measurements independent of the individual skin traits and thus increases the accuracy of the measurements. The proposed iPPG works in ambient light, relaxing the instrumentation requirement and helping the system to be compact and portable.https://www.mdpi.com/1424-8220/22/20/7796polarizationCMOS image sensorimaging sensorswire grid polarizersoximeterpulse oximeter |
| spellingShingle | Mukul Sarkar Maher Assaad Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor Sensors polarization CMOS image sensor imaging sensors wire grid polarizers oximeter pulse oximeter |
| title | Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor |
| title_full | Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor |
| title_fullStr | Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor |
| title_full_unstemmed | Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor |
| title_short | Noninvasive Non-Contact SpO<sub>2</sub> Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor |
| title_sort | noninvasive non contact spo sub 2 sub monitoring using an integrated polarization sensing cmos imaging sensor |
| topic | polarization CMOS image sensor imaging sensors wire grid polarizers oximeter pulse oximeter |
| url | https://www.mdpi.com/1424-8220/22/20/7796 |
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