FDG is primarily excreted via the genitourinary system. Fluoro-deoxy-glucose, unlike normal glucose, is poorly reabsorbed by the kidneys allowing filtered FDG to be excreted in the urine. This can result in intense concentrated tracer activity in the renal collecting systems, ureters, and bladder. The activity can be influenced by the level of renal function, hydration, compliance of the collecting system, and in some cases the patient's position. Normally the ureters can be correctly identified by the anatomic location. Activity extends in a cranio-caudal direction in the abdomen and may be contiguous or irregular. Urinary diversions can be appreciated. Altered anatomy following suregery can also be seen.

Possible limitations:
Misinterpretation of focal ureteral activity for abdominal/retroperitoneal lymph node uptake.

Preventive measures:

• Void immediately prior to scanning.
• Good hydration and in some cases diuresis (furosemide) can help reduce activity by facilitating FDG clearance.
• Delayed dual time point imaging to demonstrate clearance of activity can clear any doubt.