Laser-scanning optical-resolution photoacoustic microscopy

We have developed a laser-scanning optical-resolution photoacoustic microscopy that can potentially be easily integrated with several existing optical microscopic modalities. During data acquisition, the ultrasonic transducer is kept stationary and only the laser light is raster-scanned by an x-y galvanometer scanner. In this configuration, the field-of-view is limited by the beam diameter of the ultrasonic detector, which is related to the active element size, numerical aperture, and the center frequency of the ultrasonic transducer. The spatial resolution is determined by the size of the optical focus. A lateral resolution of 7.8 μm and a circular field-of-view with a diameter of 6 mm were achieved in an optically clear medium. Using a laser system working at a pulse repetition rate of 1024 Hz, the data acquisition time for an image consisting of 256×256 pixels was less than two minutes. In vivo imaging of microvasculature in mouse ears were also achieved.