A new object model for Monte Carlo simulation of SPECT imaging system

A new object model is proposed for Monte Carlo programs based on combinations of simple-geometry (SG), shaped-based (SB) and voxel-based (VB) models. The SG model describes the object as a primitive of quadratic shape and the SB model describes the boundaries by mathematical expression. Both are used to describe regular and irregular shaped objects including more primitives than usually used. The VB model involves a segmented description to model a complex shape using uniform regions. The authors introduce a hierarchical data structure to organize the relationships with no restriction on the intersection set. A tree scanning method is proposed to compute efficiently the sampled emission location. An adjacent tree is associated with the hierarchical tree to reduce the computational time for the calculation of the intersection locations. The aim of this work is to extend the simulations from simple geometry sources to more clinically realistic situations. The implementation is validated for SPECT simulations. A brain phantom illustrates the results