Data rebinning and reconstruction in 3-D PET/CT oncological studies: a Monte Carlo evaluation

An accurate identification and interpretation of neoplastic lesions by PET is related to PET image quality, and depends on several factors including data processing for image formation. The aim of this work was to assess the influence of data rebinning and reconstruction on lesion detectability and quantification for a high-resolution 3-D PET/CT system, in order to optimize 3-D PET/CT oncological protocols. Oncological ¹⁸F-FDG PET studies were Monte Carlo (MC) simulated, based on a normal-weight oncological patient study, varying lesion size, lesion-to-background ratio, statistics, and including or not attenuation and scatter effects. Single slice rebinned (SSR), Fourier rebinned (FORE) and Fully 3-D (3-D) sinograms were considered. Reconstruction was carried out using ordered subset expectation maximization (OSEM) and attenuation weighting OSEM (AWOSEM). Human observers evaluated images in terms of clinical parameters characteristic of lesion detectability and quantification: lesion number and lesion size. By comparison with the known activity map (input for MC simulations), identified lesions were classified as true and false positive; the true positive fraction (TPF) and sensitivity were derived, as indices of lesion detectability. % maximum number of lesions identified with erroneous size (MAX_ls) and % errors on lesion-to-background ratio (εLBR) were calculated as quantitative indices for lesion characterization. The results show that, when images corrected for scatter and attenuation are considered, 2-D rebinning allows more lesions to be identified than 3-D, with the best detectability found using FORE+AWOSEM: in this case, sensitivity was found equal to 0.43, higher than with SSR+OSEM (0.30), SSR+AWOSEM (0.23), FORE+OSEM (0.35) and 3-D (0.18 for both OSEM and AWOSEM). Quantitatively, smaller MAX_ls and smaller εLBRs were found using FORE+AWOSEM, in comparison to 3-D+AWOSEM (p=0.125 for both parameters); FORE+OSEM presented the smallest εLBRs. Our findings, from one single simulated patient with lesions in the abdomen, suggest that, in the considered case, FORE is more suitable for lesion detectability and quantification than 3-D, FORE+AWOSEM presenting better performance for lesion detectab- ility and spatial characterization, FORE+OSEM for the quantification of lesion activity concentration.