Bilateral Low-Accumulation Bladder Artifacts Due to High Radioactivity of Urine on ¹⁸F-FDG PET/CT

Despite their clinical significance, the prevalence of bilateral low-accumulation bladder artifacts and the factors contributing to their occurrence in routine ¹⁸F-FDG PET/CT examinations have not been comprehensively studied. The aim of this study was to determine the prevalence of bilateral low-accumulation bladder artifacts and identify factors associated with their occurrence in clinical ¹⁸F-FDG PET/CT scans. Methods: Patients (n = 112) who underwent ¹⁸F-FDG PET/CT for clinical purposes were retrospectively evaluated. PET images were reconstructed using 4 methods: 3-dimensional ordered-subset expectation maximization (OSEM) without time-of-flight (TOF); OSEM with TOF; Bayesian penalized likelihood (BPL) without TOF; and BPL with TOF. For non-TOF OSEM, PET images were reconstructed with and without scatter correction (SC). The SUV_max in the bladder was compared in patients with and without bilateral low-accumulation bladder artifacts. Phantom experiments with 2 external shapes were conducted, and the relationship between the radioactivity (0, 20, 50, 120, and 280 kBq/mL) of the ¹⁸F-FDG solution in the bladder-simulated sphere and the occurrence of the low-accumulation artifacts was evaluated. Results: The prevalence of bilateral bladder artifacts was significantly lower in PET images reconstructed with TOF OSEM (7 patients; 6.3%), non-TOF BPL (3 patients; 2.7%), and TOF BPL (0 patients) compared with non-TOF OSEM (39 patients; 34.8%) (P < 0.001). Artifacts were also observed on PET images without SC. The median bladder SUV_max in patients with artifacts was significantly higher than that of patients without artifacts (59.8 vs. 28.5; P < 0.001). In phantom experiments using a rectangular model, bilateral bladder artifact intensity increased as the radioactivity in the simulated bladder increased on non-TOF reconstructions with and without SC. No artifacts were observed in experiments using a spheric phantom. Conclusion: Bilateral low-accumulation bladder artifacts were observed in approximately 35% of clinical ¹⁸F-FDG PET/CT images reconstructed with non-TOF OSEM. Artifact occurrence was associated with radioactivity in the urinary bladder, independent of SC, and influenced by body shape. TOF and BPL reconstructions reduced artifact prevalence.