FAST IMPLEMENTATIONS OF RECONSTRUCTION-BASED SCATTER COMPENSATION IN FULLY 3D SPECT IMAGE-RECONSTRUCTION

Accurate scatter compensation in SPECT can be performed by modelling t he scatter response function during the reconstruction process. This m ethod is called reconstruction-based scatter compensation (RBSC). It h as been shown that RBSC has a number of advantages over other methods of compensating for scatter, but using RBSC for fully 3D compensation has resulted in prohibitively long reconstruction times. In this work we propose two new methods that can be used in conjunction with existi ng methods to achieve marked reductions in RBSC reconstruction times. The first method, coarse-grid scatter modelling, significantly acceler ates the scatter model by exploiting the fact that scatter is dominate d by low-frequency information. The second method, intermittent RBSC, further accelerates the reconstruction process by limiting the number of iterations during which scatter is modelled. The fast implementatio ns were evaluated using a Monte Carlo simulated experiment of the 3D M CAT phantom with Te-99m tracer, and also using experimentally acquired data with Tl-201 tracer. Results indicated that these fast methods ca n reconstruct, with fully 3D compensation, images very similar to thos e obtained using standard RBSC methods, and in reconstruction times th at are an order of magnitude shorter. Using these methods, fully 3D it erative reconstruction with RBSC can be performed well within the real m of clinically realistic times (under 10 minutes for 64 x 64 x 24 ima ge reconstruction).