Study of a convergent subsetized list-mode EM reconstruction algorithm

We have implemented a convergent subsetized (CS) list-mode reconstruction algorithm, based on previous work on complete-data OS-EM reconstruction. The first step of the convergent algorithm is exactly equivalent (unlike the histogram-mode case) to the regular subsetized list-mode EM algorithm, while the second and final step takes the form of additive updates in image space. A hybrid algorithm based on the ordinary and the convergent algorithms is also proposed, and is shown to combine the advantages of the two algorithms: it is able to reach a higher image quality in fewer iterations while maintaining the convergent behavior, making the hybrid approach a good alternative to the ordinary subsetized list-mode EM algorithm. Reconstructions using various LOR-driven projection techniques (Siddon method, trilinear and bilinear interpolation) were considered and it was demonstrated that in terms of FWHM, the Siddon technique is inferior to the other two algorithms, with the bilinear interpolation technique performing nearly similarly as the trilinear while being considerably faster.