Acoustic-resolution photoacoustic imaging enables unique high-resolution visualization of chromophores in deep tissue. However, most current systems are bulky and use complex optical components for illumination. In this study, we developed a compact acoustic-resolution photoacoustic imaging system with simple fiber-based illumination. Around the ultrasound sensor attached to an acoustic lens, four optical fibers were placed in four directions 90° apart, and the sensor plane was covered with an optically and acoustically transparent plastic spacer. The imaging head is compact (diameter, 32 mm; height, 27mm) and lightweight (32 g) and is alignment-free, thus being suitable for in vivo applications. We assessed the uniformity and symmetry of photoacoustic excitation both by Monte Carlo simulation and experiments. A phantom study showed lateral and axial resolutions of the system to be 148 and 66 innodatamum, respectively. With the system, high-contrast visualization of blood vessels in rat skin was demonstrated in vivo.
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