Calibration-free quantification of absolute oxygen saturation based on the dynamics of photoacoustic signals
Photoacoustic tomography (PAT) is a hybrid imaging technique that has broad preclinical and clinical applications. Based on the photoacoustic effect, PAT directly measures specific optical absorption, which is the product of the tissue-intrinsic optical absorption coefficient and the local optical fluence. Therefore, quantitative PAT, such as absolute oxygen saturation (sO_2) quantification, requires knowledge of the local optical fluence, which can only be estimated through invasive measurements or sophisticated modeling of light transportation. In this Letter, we circumvent this requirement by taking advantage of the dynamics in sO_2. The new method works when the sO_2 transition can be simultaneously monitored with multiple wavelengths. For each wavelength, the ratio of photoacoustic amplitudes measured at different sO_2 states is utilized. Using the ratio cancels the contribution from optical fluence and allows calibration-free quantification of absolute sO_2. The new method was validated through both phantom and in vivo experiments.
Additional Information© 2013 Optical Society of America. Received May 17, 2013; accepted June 29, 2013; posted July 3, 2013 (Doc. ID 190637); published July 29, 2013. The authors appreciate Prof. James Ballard's close reading of the manuscript. This work was sponsored in part by National Institutes of Health grants DP1 EB016986 (NIH Director's Pioneer Award), R01 EB008085, R01 CA134539, U54 CA136398, R01 CA157277, and R01 CA159959. L. W. has financial interests in Microphotoacoustics, Inc. and Endra, Inc., which, however, did not support this work. Konstantin Maslov has a financial interest in Microphotoacoustics, Inc., which, however, did not support this work.
Published - ol-38-15-2800.pdf