Development of real-time photoacoustic microscopy

Photoacoustic tomography detecting ultrasound signals generated from photon absorption provides optical absorption contrast in vivo for structural, functional and molecular imaging. Although photoacoustic tomography technology has grown fast in recent years, real-time photoacoustic imaging with cellular spatial resolution are still strongly demanded. We developed a photoacoustic microscopy which has video-rate imaging capability with cellular spatial resolution. The system consists of a single-element focused ultrasound transducer, a fiber-based light-delivery subsystem, a voice-coil translation stage, a motion controller, and a data acquisition subsystem. A compact cube is employed to split optical and acoustic beams. The mass of the entire scanning photoacoustic probe is less than 40 grams, which minimizes potential vibrations and inertial effects, therefore, makes it capable to scan fast. The imaging system is capable of acquiring 20 cross-sectional (B-scan) images per second over 9 mm, and up to 40 B-scan images per second over 1 mm. Focused laser beams provide a lateral resolution of five microns. Confocal deployment of optical and acoustic focuses provides higher SNR than optical scanning approach. Micron-sized carbon particles flowing in silicone tubing and in vivo blood flows were imaged in video-rate, which demonstrated the capability to image highly dynamic biological processes in vivo with cellular resolution. This real-time high-resolution photoacoustic imaging system provides a promising approach for various in vivo imaging and quantitative studies.