A layered media approach to photoacoustic tomography

Photoacoustic tomography is a rapidly emerging imaging technique that can benefit a wide range of biomedical applications. In this method, illumination of an object with a pulsed optical field induces an acoustic pressure wave related to the heating of the object (optical absorption). From knowledge of the resultant pressure wave measured in a region away from the acoustic source, the object's spatially varying optical absorption properties are estimated by use of an image reconstruction algorithm. Most existing analytic reconstruction algorithms for photoacoustic tomography assume the object of interest possesses homogeneous acoustic properties. In this work, photoacoustic tomography is considered in the case that the primary acoustic source is embedded in a planar layered medium whose speed of sound and densities are known. Exact propagation models valid for acoustic wave propagation in dispersive and absorptive layered media are presented that account for multiple reflections between the layers. Using the angular spectrum method, an inversion model is presented for acoustic data acquired on a plane parallel to the layered medium. The acquired data are shown to be simple linear combinations of plane waves generated at the source.