Design of a high frequency array based photoacoustic microscopy system for micro-vascular imaging

The rapidly expanding field of photoacoustic imaging includes a technique called photoacoustic microscopy. Photoacoustic microscopy is a hybrid imaging modality with sub-millimeter resolution that possesses the contrast benefit of optical imaging and the resolution benefit of ultrasonic imaging. This technique can be used to image the structure and dynamics of microvessels involved in angiogenesis within biological tissue. In this paper we present results of a new high frequency array based photoacoustic microscopy system (PAM) using an Nd:YLF pumped tunable dye laser, a 30MHz piezo composite linear array and a custom multi-channel receiver system. Using offline delay and sum beamforming and beamsteering, phantom images were obtained from a 6microm carbon fiber in water at a depth of 8mm. The measured axial and lateral spatial resolution of the system was 103+/-5microm and 45+/-5microm, respectively. In vivo B-scans were obtained from vessels within a human hand as well as 3D photoacoustic images of vessels 3mm below the skin surface in a Sprague Dawley Rat.