ABSTRACT
This chapter introduces a universal back-projection algorithm for the three common geometries, namely planar, cylindrical, and spherical surfaces. This algorithm is extended straightforwardly to the limited-angle view case, in which the reconstruction may be incomplete and reconstruction artifacts may occur. The solid-angle weighting factor in the back-projection formula, however, can compensate for the variations in the detection views. It has to be pointed out that significant acoustic inhomogeneity of the sample may introduce reconstruction distortions, which, however, may be corrected or minimized using modified algorithms that take account of the acoustic inhomogeneity. The acoustic property of the tissue is often assumed to be homogenous as the speed of sound in soft tissue is relatively constant at 1.5 mm/µs. Photoacoustic (PA) computed tomography is based on the reconstruction of an internal PA source distribution from measurements acquired by scanning small-aperture ultrasound detectors over a surface that encloses the source under study.
