Practically feasible histogram-mode and list-mode EM reconstructions with full motion compensation

Abstract

With continuous improvements in spatial resolution of PET scanners, small patient movements during PET imaging become a significant source of resolution degradation. This work explores incorporation of motion information into EM reconstruction algorithms. Precorrection of the data for attenuation and normalization as well as weighted schemes, in which these correction factors are incorporated into the system matrix, are considered. An important issue addressed is the existence of LORs corresponding to no actual pairs of detectors and their motion-induced "interaction" with the detectable LORs. An example of this is a scanner design with gaps existing in-between the detector heads. It is shown that to properly account for such LORs in histogram-mode and list-mode EM reconstructions, in addition to motion-correction of the data, the algorithms themselves must be modified. This modification is implemented by including time-weighted sensitivity correction factors. A practically feasible method for calculation of sensitivity factors is derived based on image-space monitoring of voxel motion during the scan.