The proliferation of cone-beam CT (CBCT) has created interest in performance optimization, with x-ray scatter identified among the main limitations to image quality. CBCT often contends with elevated scatter, but the wide variety of imaging geometry in different CBCT configurations suggests that not all configurations are affected to the same extent. Graphics processing unit (GPU) accelerated Monte Carlo (MC) simulations are employed over a range of imaging geometries to elucidate the factors governing scatter characteristics, efficacy of antiscatter grids, guide system design, and augment development of scatter correction. Variance reduction yielded improvements in MC simulation efficiency ranging from similar to 17-fold (for SA CBCT) to similar to 35-fold (for Head and C-arm), with the most significant acceleration due to interaction splitting (similar to 6 to similar to 10-fold increase in efficiency). The benefit of a more extended geometry was evident by virtue of a larger air gap-e.g., for a 16 cm diameter object, the SPR reduced from 1.5 for ADD = 12 cm (MSK geometry) to 1.1 for ADD = 22 cm (Head) and to 0.5 for ADD = 60 cm (C-arm). Grid efficiency was higher for configurations with shorter air gap due to a broader angular distribution of scattered photons-e.g., scatter rejection factor similar to 0.8 for MSK geometry versus similar to 0.65 for C-arm. Grids reduced cupping for all configurations but had limited improvement on scatter-induced streaks and resulted in a loss of CNR for the SA, Breast, and C-arm. Relative contribution of forward-directed scatter increased with a grid (e.g., Rayleigh scatter fraction increasing from similar to 0.15 without a grid to similar to 0.25 with a grid for the MSK configuration), resulting in scatter distributions with greater spatial variation ...
Biology and Biomedicine
cone-beam ct; x-ray scatter; antiscatter grid; image quality; monte carlo; gpu; flat-panel detectors; computed-tomography; breast ct; micro-ct; digital radiography; coherent scattering; radiation-therapy; photon transport