A versatile approach for Monte Carlo simulation of tomographic systems

In this paper we present the design principles and the main features of a new Monte Carlo simulation code for tomography that, through a modular object oriented approach, maintains the efficiency of specialized solutions while incorporating features common to general Monte Carlo particle transport simulation packages such as the presence of a comprehensive geometrical modeling subsystem. The simulation of photon history through a heterogeneous medium is treated as a distinct case of particle transport, rather than a geometrical representation problem, leading to efficient tracing through voxel-based anthropomorphic phantoms. The approach is general and flexible allowing for a mixed voxel and surface based representation of the attenuation distribution (similarly for the activity distribution). Various variance reduction techniques are introduced.