PET/CT fusion error due to urinary bladder filling changes: Simple correction with a repeat section imaging

673 Objectives: Upward expansion of the urinary bladder (UB) in PET compared with CT images in the integrated PET/CT system due to continuous UB filling frequently results in considerable image fusion errors, particularly when oral contrast is used. A repeat pelvic section acquisition is investigated in this study as a practical solution to this problem. Methods: Whole body F-18 FDG scans of 31 consecutive patients (12 men, 19 women, mean age 60 ± 14 years) with known or suspected malignancy were analyzed. Scans were obtained using a dedicated PET/CT scanner (GE Discovery ST) with approximately 1litre oral contrast (1.5% water diluted Gastrographin®) given to 27 of the patients. All patient underwent a repeat 5-minutes pelvic section scan. Patients were asked to empty their UB prior to both scans. Three-dimension mid-UB CT and PET matching measurements in millimeter (mm) were obtained from the fused images, in addition to assessment of the anterior and posterior vertical dimensions change and UB walls displacement between CT and PET images. Results: The mean UB height was significantly increased (p Conclusions: The UB image fusion errors in PET/CT scans can be substantially resolved by a separate acquisition of a pelvis section presumably due to shorter time interval of UB scan completion between CT and PET. This repeat short scan should be considered for better localization of pelvic PET findings, particularly if FDG lesion is suspected above the UB.