Bladder

Despite the patient voiding just prior to imaging, the bladder will typically be filled with hypermetabolic urine by the time it is imaged on the PET portion of the exam, markedly limiting its evaluation. 

Moreover, because of the time delay between the CT portion of the exam and the completion of the PET exam, the bladder will be more distended on the PET images than on the CT images, leading to “misregistration” when the images are fused, another limitation of bladder assessment with PET/CT.

Assessment of potential bladder malignancy with PET/CT imaging heavily relies on the CT appearance of the bladder rather than on its metabolic activity (e.g. focal wall thickening). 

Some advocate improved bladder lesion conspicuity with marked hydration of the patient prior to imaging and/or bladder catheterization during the exam.   We do not employ either of these techniques.

We do, however, recommend manual manipulation of image intensity of the bladder during interpretation (as is done when evaluating the brain) to try to differentiate hypermetabolic urine from a potentially FDG-avid bladder wall mass.

Cystoscopy will typically be required to further evaluate a potential lesion suspected on PET/CT.