Blind Autofocus for Photoacoustic Imaging in Stratified Medium

To facilitate photoacoustic imaging in heterogeneous media such as transcranial imaging and breast imaging, an increasing number of heterogeneous photoacoustic methods have been proposed. Nonetheless, prevailing reconstruction methods require prior knowledge of the speed of sound (SOS) distribution, which is often impractical in industrial applications. To mitigate the dependency on prior knowledge of the SOS distribution, this article introduces the blind autofocus method. This method employs a passive ultrasound technique to obtain the temporal matrix of SOS and stratified traversal of SOS values to determine the optimized spatial matrix of SOS. The feasibility of this approach in reconstructing the initial pressure in heterogeneous media is evaluated through simulation and experiments. The results demonstrate the capability of the blind autofocus method in achieving high-quality reconstruction in a 3-D stratified medium.