Positron emission tomography (PET) imaging has a wide applicability in oncology, cardiology and neurology. However, a major drawback when imaging very active regions such as the bladder and the bone is the spill in effect, leading to inaccurate quantification and obscured visualisation of nearby lesions. Therefore, this thesis aims at investigating and correcting for the spill in effect from high activity regions to the surroundings, as a function of activity in the hot region, lesion size and location, system resolution as well as application of post-filtering, using the background correction technique. This thesis involved analytical simulations for the digital XCAT2 phantom, and validation acquiring data from NEMA phantoms and patient datasets with the GE Signa PET/MR and Siemens Biograph mMR/mCT scanners. Reconstructions were done using the ordered subset expectation maximisation (OSEM) algorithm. Dedicated point spread function (OSEM+PSF) and the background correction (OSEM+PSF+BC) were incorporated into the reconstruction for spill in correction. For region of interest (ROI) analysis, a semi-automated ellipsoidal ROIs were drawn on the exact location of the lesions, and these were used to extract the standardized uptake value
(SUV). The bias, recovery coefficient (RC), coefficient of variation (CoV) and contrast-to-noise ratio (CNR) were computed from the SUVs, and these were used as figures of merit to compare the performances of all the reconstruction algorithms. The thesis revealed that: (i) lesions within 15-20 mm from the hot region are predominantly affected by the spill in effect, leading to an increased bias and impaired lesion visualisation within the region; (ii) the spill in effect is further influenced by the ROI selection, increasing activity in the hot region, reduced resolution and application of post-filter; (iii) the spill in effect is more evident for the SUVmax than the SUVmean; (iv) for proximal lesions (within 2 voxels around the hot region), PSF has no major improvement over OSEM because of the spill in effect, coupled with the Gibbs effect; (v) with OSEM+PSF+BC, the spill in contribution from the hot region was removed in all cases (irrespective of ROI-selection, proximity of lesion to hot source, or application of post-filter), thereby facilitating stability in quantification and enhancing the contrast in lesions with low uptake. This thesis therefore concludes that the BC technique is effective in correcting for the spill in effect from hot regions to surrounding regions of interest. It is also robust to ROI-induced errors and post-filtering.
