Single-Wavelength Blood Oxygen Saturation Sensing With Combined Optical Absorption and Scattering

Blood oxygen saturation (SO2) reflects the oxygenation level in blood transport and tissue. Previous studies have shown the capability of non-invasive quantitative measurements of SO2 by multi-wavelength photoacoustic (PA) spectroscopy for diagnosis of brain, tumor hemodynamics, and other pathophysiological phenomena. Here, we report a newly proposed method by combining PA and scattered light signals wherein imposing a hypothesis that scattering intensity is linear to the concentrations of oxygenated hemoglobin and deoxygenated hemoglobin weighed by blood scattering coefficients. A rigorous theoretical relationship between PA and scattering signals is thus established, making it possible that SO2 can be measured with only one excitation wavelength after calibration. To verify the theory basis, both dual-ink phantoms and fresh porcine blood sample have been employed in the experiments. The phantom experiment is able to quantify the concentration of mixed red–green ink that is in precise agreement with pre-set values. The
in vitro
experiment with fresh porcine blood was conducted, and the results of the proposed single-wavelength method achieved reasonable accuracy with 5%–8% errors. These demonstrated that the proposed single-wavelength SO2 detection method is able to provide non-invasive, accurate measurement of blood oxygenation combining optical absorption and scattering.