In vivo Combined Photoacoustic and Doppler Ultrasound Imaging

The long-term goal of our research is to develop photoacoustic and Doppler ultrasound imaging methods for noninvasive estimation of the oxygen consumption rate (MRO2) in vivo. Previously, we have demonstrated a combined photoacoustic and high-frequency Doppler ultrasound system and shown the feasibility of flow velocity and oxygen saturation (sO(2)) estimation using double-ink flow phantoms. In this work, the results of in vitro sheep blood experiments are presented. Blood oxygen flux has been estimated at different sO(2) levels and mean flow speeds, and the uncertainty of the measurement has been quantified. In vivo experiments have been performed on Swiss Webster mice to provide co-registered photoacoustic and Doppler flow images with imaging depths of similar to 2mm. Doppler bandwidth broadening technique has been used to obtain transverse flow velocity. The diameter of the blood vessel is similar to 500 mu m and the mean flow speed is 15cm/s. We are working towards sO(2) estimation in vivo and 3D oxygen consumption imaging of tumors at depths beyond OR-PAM.