INTRA- AND INTER-ITERATION 3D OSEM PET IMAGE RECONSTRUCTION

Most of the recent medical imaging modalities use noninvasive means to obtain the activity information inside human organs, so doctors may detect the initial symptoms of a disease as early as possible and give appropriate treatment. PET is to use radio-isotopes which can emit positrons in its clinical and research uses. By injecting the nuclear medicine drug formed by labeling a radioelement to molecules of deoxidized glucose to a patient and after the cells in the patient body absorbing it through metabolic functions, the detectors will receive annihilation coincidence events formed from the number of the positrons generated from the response of the labeled deoxidized glucose molecules. The most critical module of the modality therefore is the procedure regarding how to reconstruct good quality images using the collected projection information. However, in the reconstruction process, MLEM involves massive data in considerable number of iterations in order to yield accurate images and takes quite a long time in computation. Ordered Subsets Expectation Maximization (OSEM) was proposed to accelerate the reconstruction process by expediting the convergence while maintaining the same image quality as those produced by MLEM. Since then, OSEM iterative algorithm has become the de facto reconstruction method adopted by most PET installations. To further improve the image quality, both clinical and research data have been acquired in 3D mode on the majority of the current systems. The accompanied computational load of iterative reconstruction increases considerably resulting from the 3D OSEM method. Attributed to the fact of the recent technological advancement, many high-performance parallel methods have been proposed to speed up the reconstruction process. These methods in general are to partition data into several sets before applying any parallel acceleration. They do not take on the nature of OSEM method to identify the intrinsic data dependencies. This project intends to analyze the iterative natures of the 3D OSEM method, particularly the intra- and inter-iteration aspects of the reconstruction method along with the latest shared-memory parallel machine architecture. Experiments will be conducted to demonstrate its superior performance over the existing methods.