Abstract
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Objectives: High-activity bladder is known as a potential source of artifacts on 18F-FDG PET/CT. Recently we noticed high-intensity artifacts extending from bladder to nearby air region in rectum or small intestine, which has not been previously reported. The purpose of this study were to assess the incidence and magnitude of this peribladder artifact on 18F-FDG PET/CT images, and to evaluate the impact of Time-of-Flight (TOF) reconstruction on this artifact. Materials and Methods: One hundred six consecutive patients (mean age, 64 ± 15 years; M/F=63/43) who underwent 18F-FDG PET/CT for clinical purpose were retrospectively studied. PET/CT examinations were performed with Discovery PET/CT 690. The PET data were acquired from head to proximal thigh for 2 min per one bed position. PET images were reconstructed using CT attenuation correction and 3D-OSEM (3 iterations, 16 subsets, and 5-mm Gaussian filter) with and without TOF. Areas of high 18F-FDG accumulation extending from bladder to nearby air region without any pathological causes were considered artifact. Two experienced observers evaluated the presence or absence of the artifact on PET/CT images. When an artifact was indicated, a manually positioned circular region of interest was used to measure the maximum standardized uptake value (SUVmax), which was used to quantify the magnitude of the effect. In addition, bladder activity was also measured in all subjects.
Results: The peribladder artifacts were observed in 12 (11%) of 106 patients on PET images without TOF reconstruction. Example of the artifacts is shown in Figure 1. The mean SUVmax of the artifacts was 6.5 ± 2.9. The bladder SUVmax in patients with peribladder artifacts was significantly higher than that in patients without the artifacts (74.9 ± 61.1 vs 46.3 ± 35.2, p=0.036). Using TOF reconstruction, the artifacts disappeared in 4 (33%) of 12 patients. The mean SUVmax of peribladder artifacts on PET images with TOF was significantly lower than that without TOF (4.0 ± 1.5 vs 6.5 ± 2.9, p=0.0002).
Conclusions: High-activity bladder can lead to an artifact of apparently increased radiotracer uptake in the peribladder region on 18F-FDG PET/CT. This artifact is mitigated by TOF reconstruction. Awareness of the peribladder artifact is important for precise evaluation in pelvis on 18F-FDG PET/CT.