Self-Fluence-Compensated Functional Photoacoustic Microscopy

Optical-resolution photoacoustic microscopy (OR-PAM) can image blood oxygen saturation (sO(2)) in vivo with high resolution and excellent sensitivity and offers a great tool for neurovascular study and early cancer diagnosis. OR-PAM ignores the wavelength-dependent optical attenuation in superficial tissue, which cause errors in sO(2) imaging. Monte Carlo simulation shows that variations in imaging depth, vessel diameter, and focal position can cause up to similar to 60% decrease in sO(2) imaging. Here, we develop a self-fluence-compensated OR-PAM to compensate for the wavelength-dependent fluence attenuation. We propose a linearized model to estimate the fluence attenuations and use three optical wavelengths to compensate for them in sO(2) calculation. We validate the model in both numerical and physical phantoms and show that the compensation method can effectively reduce the sO(2) errors. In functional brain imaging, we demonstrate that the compensation method can effectively improve sO(2) accuracy, especially in small vessels. Compared with uncompensated ones, the sO(2) values are improved by 10 similar to 30% in the brain. We monitor ischemic-stroke-induced brain injury which demonstrates great potential for the pre-clinical study of vascular diseases.