Photoacoustic tomography provides both structural and functional imaging in vivo based on optical absorption contrast.
A novel imaging system that incorporates a two-dimensional matrix ultrasound probe for combined photoacoustic and
ultrasonic three-dimensional (3D) volumetric imaging is presented. The system consists of a tunable dye laser pumped
by a Nd:YAG laser, a commercial ultrasound imaging system (Philips iU22) with a two-dimensional matrix transducer
(Philips X7-2, 2500 elements, 2-7 MHz), and a multichannel data acquisition system which allows us to acquire RF
channel data. Compared with alternative 3D techniques, this system is attractive because it can generate co-registered 3D
photoacoustic and ultrasound images without mechanical scanning. Moreover, the lateral resolution along the azimuth
and elevational directions are measured to be 0.77 ± 0.06 mm and 0.96 ± 0.06 mm, respectively, based on reconstructed
photoacoustic images of phantoms containing individual human hairs. Finally, in vivo 3D photoacoustic sentinel lymph
node mapping using methylene blue dye in a rat model is demonstrated.