Blood Oxygen Saturation Measurement Using Polarization-Dependent Optical Sectioning

Abstract

Blood oxygen saturation (SpO2) measurement is a routinely performed clinical procedure involved in the diagnosis of several critical diseases. However, the most commonly used SpO2 measuring device, known as oximeter, becomes unreliable in the absence of proper body contact. A non-contact, non-invasive, real-time device is desirable for accurate measurement and continuous monitoring of SpO2. This paper presents a polarized imaging-based integrated solution for SpO2 measurement. The polarization filters are used to separate light components reflecting from deep and superficial layers of skin. The ratio of intensities of the two components is found to have a linear relationship with SpO2 levels. In contrast to the existing SpO2 measurement techniques, the proposed method uses a single light source. The experiments are performed with 15 human subjects (11 male and 4 female) using different wavelengths of light. A statistically significant relationship is observed between SpO2 and the intensity ratios for red light (correlation coefficient $\textrm {r = 0.6426}$ with p = 0.001965 and mean error = 0.0626). The experiments are repeated using white light, and a similar relationship is observed ( $\textrm {r = 0.5603}$ with p = 0.00947 and mean error = −0.9289). Furthermore, the Bland–Altman analysis shows that the results of the proposed method are consistent with the reference data. This suggests that a real-time integrated polarized imaging-based SpO2 measurement device can be developed based on the proposed method.