Photoacoustic imaging of oxygen saturation (sO2) in deep tissue has broad preclinical and clinical applications. Because the magnitude of photoacoustic signal is proportional to the product of optical absorption coefficient and local fluence, quantitative imaging of oxygen saturation usually requires knowledge of the local optical fluence. Especially in deep biological tissue, wavelength dependent optical attenuation of biological tissue presents a challenge to measure the absolute oxygen saturation. Here, we present a new method to measure the sO2 without knowing the local fluence. We measure photoacoustic signals at different wavelengths and different sO2 values. Because the optical fluence at each optical wavelength does not change with a certain sO2, the unknown optical fluence at one wavelength can be cancelled via taking the ratio between two photoacoustic amplitudes at the same optical wavelength but different sO2 values. Three wavelengths, i.e. 760,798,820nm, have been utilized to quantify the absolute sO2. Compared with conventional two-wavelength method, the proposed three wavelength dynamic sO2 method has a better performance on the estimation of absolute sO2. Preliminary phantom experiments have validated the feasibility of this method. This new method enables calibration-free quantitative imaging of absolute sO2 in deep biological tissue.
Guoha Wen and Lidai Wang, "Quantitative photoacoustic measurement of absolute oxygen saturation in deep tissue (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 104941B (Presented at SPIE BiOS: January 29, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2287319.5752218870001.
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