Passive ultrasound aided acoustic resolution photoacoustic microscopy imaging for layered heterogeneous media

Abstract

Photoacoustic imaging reconstructions usually assume a known speed-of-sound (SOS) distribution; however, in most cases, the SOS distribution is not revealed and is difficult to estimate from photoacoustic signals. In this paper, we propose passive ultrasound aided acoustic resolution photoacoustic microscopy which simultaneously reconstructs SOS distributions and photoacoustic images for layered heterogeneous media. The passive ultrasound is a kind of laser-induced acoustic wave generated by a transducer absorbing the backscattered light. It can be used to measure the layer thicknesses due to its sensitivity to structural information and broad bandwidth and further determine the SOS distributions. After estimating the SOS distributions, a phase shift plus interpolation is employed to reconstruct the photoacoustic image for heterogeneous media. Without introducing additional hardware, this method can be conveniently incorporated into a conventional photoacoustic imaging system. A curved shell immersed in water is adopted as a layered heterogeneous phantom, and the proposed method reconstructs the targets (carbon rods) under this shell. Under the test of a 5 MHz focused transducer (NA 0.25), the maximum reconstruction deviation of 1.2 mm carbon rods is only 0.15 mm.