LAUSR

Purpose Semiquantitative 18F-FET PET assessment using the tumor's SUV or tumor-to-background ratios (TBRs) can separate gliomas from peritumoral tissue or progression from pseudoprogression. This study investigated if point spread function (PSF) reconstruction of 18F-FET PET data affects SUV-based dignity assessment. Materials and Methods This study is a retrospective analysis of 87 glioma patients (female, 36; male, 51; age, 48 [13–81] years) undergoing 18F-FET PET/MRI for staging (n = 17) or restaging (n = 70). PET was reconstructed using ordered-subset expectation maximization with and without PSF. Lesions were delineated with semiautomated background-adapted thresholding relative to SUVmax; background was delineated contralaterally. Comparative measurements with a National Electrical Manufacturers Association International Electrotechnical Commission PET body phantom (sphere-to-background ratios, 8:1 and 4:1) were performed. Results PSF showed significantly higher tumor SUVmax (median difference, +0.1; interquartile range, 0.04–0.18), SUVmean (+0.05; 0.03–0.08), TBRmax|mean (+0.1; 0.04–0.2), and TBRmean|mean (+0.06; 0.03–0.09) than non-PSF (P < 0.001). Background SUVmean was unaffected. In patients and phantom, differences between PSF and non-PSF increased with TBR and decreased with lesion's PET volume. Differences only exceeded 0.2 SUV for SUVmax or 0.1 SUV for SUVmean if TBR was greater than 3 and lesion's PET volume was less than 10 mL (d = 27 mm). Dignity assessment by PSF and non-PSF was concordant in all patients examined for staging (cutoff, TBRmean|mean > 1.6; positive, 14; negative, 3) and restaging (cutoff, TBRmax|mean > 2.0; positive, 67; negative, 3). Conclusions PSF increased tumor SUVmax and SUVmean compared with non-PSF 18F-FET PET/MRI data, especially in small lesions with high TBR (>3). However, dignity assessment using established TBR cutoffs was not affected.