Early dynamic PET/CT and 18F-FDG blood flow imaging in bladder cancer detection: a novel approach

The standard PET/CT and 18F-FDG scanning protocols for patients with cancer call for data acquisitions to start 50 to 60 minutes postinjection (PI) of the radiopharmaceutical. This prolonged incubation period allows the concentration of high activity tracer to accumulate in the urinary bladder rendering identification of bladder lesions very difficult, if not impossible. The objective of this study was to identify bladder cancer using a novel PET/CT and 18F-FDG scanning protocol that takes advantage of the angiogenesis observed in malignancies and the kidneys' physiology of delayed excretion of 18F-FDG into the urinary bladder.

Early dynamic PET/CT and 18F-FDG scans were performed on 7 consecutive male patients with pathology-confirmed bladder cancer. A series of 5 dynamic scans of 2 minutes each, starting at injection time, were obtained on each patient's urinary bladder. Areas of increased 18F-FDG blood flow to the bladder walls were considered suspicious for cancer.

Using pathologic report as the gold standard, this new protocol resulted in 5 true positives, 1 true negative, and 1 false positive. The average maximum standard uptake values (SUVmax ± SD), at 2 to 4 minutes postinjection, of bladder wall areas with increased and normal blood flow were 2.7 ± 0.7 and 1.1 ± 1.3 g/mL, respectively. Also, the average activity concentration ratios (tumor/blood vessel) of suspected cancerous regions versus time showed a linear pattern with a slope of 2.9.

Early dynamic FDG PET images can demonstrate bladder lesions that are obscured by urine activity on routine images at 1 hour.