In vivo dark-field reflection-mode photoacoustic microscopy

Reflection-mode photoacoustic microscopy with dark-field laser pulse illumination and high-numerical-aperture ultrasonic detection is designed and implemented in noninvasively imaged blood vessels in the skin in viuo. Dark-field optical illumination minimizes the interference caused by strong photoacoustic signals from superficial structures. A high-numerical-aperture acoustic lens provides high lateral resolution, 45-120 mum in this system. A broadband ultrasonic detection system provides high axial resolution, estimated to be similar to15 mum. The optical illumination and ultrasonic detection are in a coaxial confocal configuration for optimal image quality. The system is capable of imaging optical-absorption contrast as deep as 3 mm in biological tissue. (C) 2005 Optical Society of America.