Nonlinear oxygen saturation measurement for functional photoacoustic microscopy (Conference Presentation)

Optical-resolution photoacoustic microscopy can measure oxygen saturation () in vivo, offering an important tool to assess tissue oxygenation and health condition. Limited by available wavelengths for fast OR-PAM, the accuracy of sO2 imaging may be degraded by absorption saturation due to high absorption in the blood. Here, we report a nonlinear model to solve the saturation problem and increase the accuracy of measurement. The absorption saturation is analyzed by comparing a nonlinear and linear photoacoustic model using numerical simulation, which shows the nonlinear model has an improved accuracy than the linear model when the absorption is high. Phantom experiments on bovine blood further validate the accuracy of the nonlinear sO2 measurement method. In vivo experiments are conducted in the mouse ear. The values in a pair of arteries and veins are calculated using both linear and nonlinear methods, showing that the nonlinear method measures the arterial value closer to normal physiological condition than the conventional linear model. The nonlinear model requires the use of three or more wavelengths (532nm, 545nm, and 558nm in this work). As a result, we demonstrate the saturation effect in OR-PAM can be compensated via a nonlinear model, which may advance the application of functional optical-resolution photoacoustic microscopy.