Localization of spherical photoacoustic sources in acrylamide gels using time domain measurements

Photoacoustic imaging may be used to detect tumor masses in biological tissue. In particular, time of flight measurements of the photoacoustic waves may indicate tumor location. Here we use time of flight information to localize spherical photoacoustic sources in tissue phantoms. A Q-switched, frequency-doubled Nd:YAG laser operating at 532 nm with a pulse duration of 5 ns irradiated absorbing spheres 2 mm in diameter. The spheres were in mineral oil or turbid acrylamide blocks. A PVDF acoustic transducer was built and used to detect the acoustic waves. The position of the detector was translated so that the time of flight information from two acoustic waveforms from the source could be correlated by a convolution algorithm. This convolution resulted in a two dimensional map indicating the position of the source. Source location was indicated to within 5% of the true location for acoustic propagation distances of 20 mm. An image source is also indicated when the true source was in proximity to a reflecting boundary.