Photoacoustic imaging of inhomogeneities embedded in breast tissue phantoms

A novel photoacoustic breast phantom was developed using poly(vinyl alcohol) gel prepared by a simple technique that imparts optical scattering to the gel without the neccessity for scattering particles. Tumour simulating gel samples of suitable absorption coefficient were also prepared using a second technique, by adding appropriate quantities of dye at the time of formation; the samples were then cut into spheres. The optical absorption coefficient of the spheres was chosen as between 4 - 7 times that of breast tissue. A breast phantom with a thickness of 60 mm, embedded with such 'tumours' was developed for studying the applicability of photoacoustics in mammography. Time resolved photoacoustics, in a transmission mode, was used to image the inhomogeneities. Light excitation was from a liquid-light guide coupled Nd:YAG laser at 1064 nm, with a 5 ns pulse duration. The guide was mechanically scanned across the surface of the phantom, with the time-of-flight signals recorded using a PVDF based detector array. A modified delay and sum beamforming algorithm was used to reconstruct the photoacoustic sources. Results of these experiments are discussed.