Multifocal optical-resolution photoacoustic microscopy in reflection mode

Abstract

Compared with single-focus optical-resolution photoacoustic microscopy (OR-PAM), multifocal OR-PAM utilizes both multifocal optical illumination and an ultrasonic array transducer, significantly increasing the imaging speed. Here we present a reflection-mode multifocal OR-PAM system based on a microlens array that provides multiple foci and an ultrasonic array transducer that receives the excited photoacoustic waves from all foci simultaneously. By using a customized microprism to reflect the incident laser beam to the microlens array, we align the multiple optical foci confocally with the focal zone of the ultrasonic array transducer. Experiments show our reflection-mode multifocal ORPAM system is capable of imaging microvessels in vivo, and it can image a 9 mm x 5 mm x 2.5 mm volume at 16 μm lateral resolution in ~4 min, limited by the signal multiplexing ratio and laser pulse repetition rate.