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Kidneys, Ureters, and Bladder (KUB) Imaging

Practice Essentials

Various imaging studies can be used to evaluate patients with suspected renal or urinary tract disease.
 Renal angiography is the gold standard for direct visualization of the renal vasculature. It is invaluable in the diagnosis and prognosis of renal artery stenosis and renal vein thrombosis.
  Plain films of the abdomen are now rarely used to evaluate kidney and urinary tract disease. Renal ultrasonography is invaluable as a screening test for urinary tract dilatation (hydronephrosis), a hallmark of urinary tract obstruction. Ultrasonography remains the procedure of choice for evaluation of acquired or hereditary polycystic kidney disease.
 Color doppler ultrasonography is used to measure flow or velocity of blood in the main renal artery; it is primarily used to detect renal vascular occlusive disease.

Plain abdominal films are indicated for the evaluation of radiopaque kidney stones (calcium-containing stones, struvite, cystine). An advantage of the plain film is that it can be performed in pregnant and pediatric patients, since the amount of radiation exposure is limited. 

Intravenous pyelography (IVP) can be used to detect kidney stones and delineate the level of obstruction in patients with urinary tract obstruction. 

Computed tomography (CT) is an excellent tool to evaluate masses, traumatic injury to the kidney, stones, and pyelonephritis. CT scanning is superior to ultrasonography in identifying renal cysts, since it is capable of detecting small cysts (2-3 mm in diameter).

Magnetic resonance imaging (MRI) provides a useful alternative to CT scanning in individuals at risk for toxicity from intravenous contrast. 

Radionuclide scanning has been successfully used to evaluate renal perfusion in various settings, including renal artery stenosis and thrombosis. Radionuclide cystography is widely used by pediatric nephrologists to detect early vesicoureteral reflux in children.

Retrograde pyelography is an essential tool for localizing the site of urinary tract obstruction. It has been replaced by ultrasonography or CT scanning in most settings but is helpful in patients with a known pelvic malignancy when hydronephrosis is absent because of ureteral encasement.

Diuretic renography is widely used to discriminate functional versus anatomic obstruction after identification of a dilated upper urinary tract (usually with ultrasonography or CT scanning).
 Two important functional aspects of kidney function can be assessed: (1) clearance of each kidney and (2) the flow of urine through the urinary tract.

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