Deep Vein Thrombosis Diagnosis Cat Scans

CAT scan is a term people commonly use to refer to computerized axial tomography (CAT) scans. The scan itself combines an X-ray with a computer to produce cross-section views of various sections of the body. If necessary, the procedure can generate 3-D images of the body’s internal organs.

When used only on specific parts of the body, CAT scans pose no significant danger. However, repeated full-body scans can increase the risk of CAT scan radiation-induced cancer.

CAT Scans and DVT

A CAT scan machine is only one tool that physicians use to diagnose deep vein thrombosis (DVT). The size of a blood clot (pulmonary embolism), its location and its symptoms affect a CAT scan’s ability to detect the clot. Other imaging techniques such as ultrasound and MRI may locate blood clots. Certain blood tests may locate them as well.

Despite a CAT scan’s powerful ability to display the body’s internal organs, the only conclusive diagnosis for DVT is a venography, a procedure that produces X-rays of the veins.

Spiral CAT Scans

A newer procedure called a spiral CAT scan is being used to diagnose DVT. This type of scan is very fast and provides a higher definition of internal structures than a standard CAT scan. Blood vessels and internal tissues display in greater detail in a spiral CAT scan.

In a spiral CAT scan, a CAT scan technologist injects a dye that contains iodine into a patient’s arm vein while he is being scanned. It usually takes less than 30 seconds to complete the scan. After the scan, a physician can receive the results with 30 minutes.

Pros and Cons Spiral CAT Scans

One advantage of the spiral CAT scan is its non–invasive nature. Another is its accuracy rate in diagnosing most pulmonary emboli in the main branches of the pulmonary arteries.

Disadvantages include the dye possibly causing allergic reactions in patients with kidney disease if they cannot normally eliminate the dye through urine. Another is the fact that spiral CAT scans are not as accurate in detecting emboli in the smaller arteries in the lung, where 16 percent to 30 percent of pulmonary emboli occur.

Other Procedures to Diagnose DVT

In addition to CAT scans, the diagnostic procedures to diagnose DVT include:

  • Magnetic Resonance Imaging (MRI): An MRI scan uses magnetism, radio waves and a computer to produce images of body structures. MRIs have proved to be especially effective in diagnosing DVT in the thigh and pelvic veins. While not as widely used as CAT scans, MRIs can assist in diagnosing kidney patients who may be allergic to the dye used in spiral CAT scans.
  • Nuclear Medicine Lung Scans (V/Q Scan): A nuclear medicine lung scan analyzes air flow in the lungs (V for ventilation) and blood flow through the lungs (Q for perfusion). The ventilation scan analyzes where an inhaled aerosol is distributed within the lungs. The blood-flow analysis determines if a pulmonary embolus is blocking blood from entering the lung.

    In many patients with a pulmonary embolus, the ventilation scan shows normal but the perfusion scan shows abnormal. Therefore, a spiral CAT scan may be ordered before deciding the best way to treat a pulmonary embolism.

  • Pulmonary Angiography: Pulmonary angiography is the most accurate test for DVT. In this test, a long catheter is passed through a vein in the groin, up the venous system, through the right side of the heart and into the pulmonary arteries. The arteries are then injected with a dye that is visible on X-rays. Any areas in the pulmonary arteries that don’t fill with dye contain a blood clot.

    Pulmonary angiography can be risky and costly. Because radiologists with special training must perform the procedure, it is not available in all hospitals.


DeNoon, Daniel J. (2004). CT Scan Radiation Risks? Retrieved June 21, 2007, from the CBS News Web site:

Medical Editorial Board (2006). X-Ray, Ultrasound, CAT Scan, MRI and D dimer Testing. Retrieved June 21, 2007, from the Deep Vein Thrombosis Symptoms Web site:

Shiel, William C. Deep Vein Thrombosis. Retrieved June 21, 2007, from the Web site: