A new model for tracing first-order Compton scatter in quantitative SPECT imaging

A new model for tracing the first-order Compton scatter was implemented based on the Klein-Nishina formula and Siddon method. This model significantly improved the accuracy with comparable computing effort to our previous work. It further extended our previous work in tracing all attenuation factors within each bin view subtended by collimator holes. Therefore, this model simulates SPECT data accurately up to the first-order scatter which dominates the total scatter contribution. If a central-ray approximation is applied for the attenuation factors within the bin view, this model, based on photon propagation physics, is a most efficient approach, for compensation of object-specific attenuation and system-specific resolution variation in quantitative SPECT image reconstruction. This model was tested by simulations based on a thorax phantom derived from a patient chest CT image with a heart insert and a resolution kernel of a parallel-hole collimator. The simulation of 128 projections (each with 128 bins) on an elliptical orbit from an 128² phantom array took approximately six hours on an HP/735 computer by tracing all pixels for both scatter and attenuation factors (without the central-ray approximation). The 3D simulation for 64 projections each with 64×32 bins from an 64²×32 phantom array finished in less than four days. This accurate analytical simulation model for SPECT imaging offers the options of studying the effects of attenuation, scatter, and detector-resolution variation individually