FDG is primarily excreted via the genitourinary system. FDG, unlike glucose at normal blood levels, 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. 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 kidneys can be correctly identified by the anatomic location and activity. Often variants such as absence, ectopy, or communicating renal cysts can be appreciated.

Possible limitations:

• It may be difficulty detecting renal lesions with a low sensitivity for the detection of disease near the kidneys.
• Dependant pooling of tracer in the superior renal poles due to imaging in the supine position could be interpreted as adrenal lesions.

Preventive measures:

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