System model for laser-scanning photoacoustic microscopy

In this work we derive a system model for a laser-scanning, optical-resolution photoacoustic microscopy system. We use the model to derive a simple image reconstruction algorithm and then analyze the depth resolution achievable by this algorithm. There has recently been development of high-frequency photoacoustic microscopy (PAM) systems with the ability to image biological tissue at a microscopic scale. The imaging depths achievable (a few mm) are shallower than in photoacoustic tomography (which has lower spatial resolution), but deeper than conventional optical microscopy. PAM usually employs a focused single-element high-frequency ultrasonic transducer and a spatially overlapped optical illumination. These existing PAMs require mechanical scanning of the ultrasonic-optical assembly, which is relatively slow and also not compatible with other optical microscopic modalities such as confocal microscopy, two-photon microscopy, and optical coherence tomography. Recently one of us (H.Z.) has developed a laser-scanning OR-PAM (LSOR-PAM) to demonstrate the feasibility of employing optical scanning in PAM. In LSOR-PAM, the ultrasonic detector is kept stationary and only the laser light is raster-scanned within the FOV during data acquisition. Further improvements in image quality and the development of image quality metrics will benefit from the system model derived in this work.