Application of discrete complex image method algorithm to back-projection method in photoacoustic imaging

Photoacoustic imaging(PAI) is a hybrid imaging system depending on optics and ultrasound, and it is a method that has not reached yet the clinical stage with technological and commercial potential that can be used especially in cancer diagnosis and treatment. This method, which is based on optical and ultrasound imaging systems and includes nonionizing waves (harmless rays), is a new imaging technique with high resolution and contrast, which has been intensively researched in recent years. In this study, the tissue was modeled as a 2 layer planar structure under the continuity on the layer surface, initial condition at t=0 and radiation conditions at infinity. Subject to these conditions, layered acoustic Green's function were used to solve the photoacoustic wave equation. Since layered Green's functions are highly oscillating and slowly convergent integrals, the computation time takes long. The discrete complex image method which named as Discrete Complex Image Method(DCIM) was applied to shortened the computation time of layered Green's functions which need to be calculated repeatedly in the photoacoustic imaging and to obtain the closed form of Green's function. Green's functions were obtained as the sum of complex exponential terms using the Generalized Pencil of Function(GPOF) method, which is one of the procedure used when applying the DCIM. In addition, in order to calculate the surface wave contribution, firstly, coordinates of poles were found by Newton-Raphson method and contributions of these points were subtracted from Green's function, and surface wave contributions in the far and near field were examined. Then, Green's functions, which were obtained by DCIM, were used in the reconstruction algorithm and photoacoustic imaging was performed for a two-layer media and the distribution of the point source function was demonstrated.