Fast implementation of fully iterative scatter corrected OSEM for HRRT using GPU

Accurate scatter correction is especially important for high-resolution 3D PETs due to the lack of inter-slice septa. To address this problem, a fully 3D iterative scatter-corrected OSEM in which a 3D single scatter simulation (SSS) is alternatively performed with a 3D OSEM reconstruction until convergence was recently proposed. However, due to the computational complexity of both SSS and OSEM algorithms for a high-resolution 3D PET, it has not been widely used in practice. The main objective of this paper is, therefore, to accelerate the fully 3D iterative scatter-corrected OSEM using a Graphics Processing Unit (GPU) and verify its performance. For SSS implementation, a sinogram-driven approach is found to be more appropriate compared to a detector-driven approach, as fast linear interpolation can be performed in sinogram domain through the use of texture memory. Furthermore, a pixel-driven backprojector and a ray-driven projector can be significantly accelerated by assigning threads to voxels and sinograms, respectively. Using Nvidia´s GPU (Tesla C1060) and the Compute Unified Device Architecture (CUDA), the execution time of the SSS is less than 25(s), a single iteration of OSEM takes 25(s) for the span 9 HRRT geometry.