Radiology Tests Used For Kidney Stones:  XRay, Ultrasound, CT Scan, IVP and CT Urography

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Physicians have multiple ways to look at kidney stones.  The method often depends on the severity of the problem, the type of stone, and the presence or absence of symptoms.  

XRAY:  Standard xrays of the mid to lower abdomen will include the kidneys, ureter and bladder.  Xrays work by passing low doses of radiation through the patient's body onto a photographic negative.  When xrays pass through soft body tissues, they hit the film and cause it to turn black (exposure).  When a calcium stone or bone (which is also made of calcium) is present the xray cannot pass through and no exposure occurs.  The stone(s) and bones will appear white.  This technique can only detect stones which contain calcium.  It will miss pure uric acid or indinavir stones.  Xrays can be done quickly and cheaply and are a quick, inexpensive, and useful technique for monitoring growth of a kidney stone.

Ultrasound (U/S):  Ultrasound is performed by passing a probe over the kidneys, ureters, and bladder.  Sound waves are emitted from the probe and are integrated into an image of the urinary system that can be seen on a television screen.  This test can detect both calcium and non-calcium types of stones.  It often is not a good test to find a stone that is suddenly passing from the kidney through the ureter on its way to the bladder.  This is the time when stones hurt the most and cause people to seek immediate emergency medical assistance.  If the stone has been lodged in the ureter for some time, then it can detect obstruction.  In this situation the ureter is abnormally dilated.  It is used by some for routine monitoring of new stones or growth of old stones. It has the benefit of no radiation.  

Computerized Tomography (CT or CAT Scan): This is one of the best methods to detect kidney stones, especially when someone comes to the emergency room with severe pain (colic) due to a passing stone.  It is more sensitive than ultrasound or xray.  It is performed by placing the patient in an xray tube that creates several images of the kidneys, ureter, and bladder.  It can detect both calcium and non-calcium stone.  Although it may sometimes miss crixivan/indinavir stones.  It is more expensive than an xray and requires more radiation.  Since it scans many organs, it can sometimes detect non stone causes of severe pain. (View CT Image)

Intravenous Pyelogram (IVP): This is one of the older techniques for detecting kidney stone and still sometimes used.  A special dye is injected into a vein.  Then xrays are taken of mid to lower abdomen.  If a stone is present, a filling defect will be seen on the xray images.  It is very useful for detecting stones in the ureter, especially if not seen by CT scan.  This sometimes happens when the ureter is dilated/obstructed but no stone is seen.  One disadvantage is that the injected dye can cause allergic reactions, usually temporary kidney damage, and symptoms including nausea.  If the patient has kidney disease other than stones, sometimes it is better to perform a Retrograde Urogram.  In this test, a catheter is placed into the bladder and the dye is injected to visualize the bladder and ureters for stones. This technique avoids absorption of the dye outside of the urinary tract. (View IVP Image)

CT Urography: CT urography is a combination of CT and IVP.  An injection of intravenous dye is given which outlines the parts of the kidney, ureterers, and bladder where urine collects.  The images are viewed with a CT scanner. Traditional CT images are also generated.  This test is particularly helpful as a step in the evaluation for blood in the urine (hematuria).  It can show causes other than just stones.  It is particularly useful in the evaluation of a kidney (renal) diverticulum.  This is a pouch that develops inside the kidney.  Kidney stones and infections can form inside this pouch.  It can also be associated with pain.  (View IVP Image)