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Using Magnetic Resonance Direct Thrombus Imaging To Diagnose Deep-Vein Thrombosis in the Lower Legs FREE

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The summary below is from the full report titled “Diagnosis of Lower-Limb Deep Venous Thrombosis: A Prospective Blinded Study of Magnetic Resonance Direct Thrombus Imaging.” It is in the 15 January 2002 issue of Annals of Internal Medicine (volume 136, pages 89-98). The authors are DGW Fraser, AR Moody, PS Morgan, AL Martel, and I Davidson.


Ann Intern Med. 2002;136(2):I26. doi:10.7326/0003-4819-136-2-200201150-00001
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What is the problem and what is known about it so far?

Blood clots (thrombi) sometimes form in leg veins (deep-vein thrombosis, or DVT) and can then break free, eventually coming to rest in the blood vessels of the lungs. This problem, called pulmonary embolism, can be fatal. It is important to diagnose DVT rapidly and accurately because treatment with blood thinners is very effective in preventing complications. Some tests for DVT are painful, and they may provide uncertain answers that often require additional tests to be sure of the diagnosis. To measure the reliability of the answers provided by a new test, researchers compare its results to a diagnostic “gold standard,” which in the case of DVT is contrast venography. In performing contrast venography, doctors inject the leg veins with a liquid that shows the veins on an x-ray and outlines any clots. Magnetic resonance imaging is a rapid and accurate technique for visualizing structures inside the body. It has recently been used to detect thrombi without the need to inject anything into the body; this technique is called magnetic resonance direct thrombus imaging (MRDTI).

Why did the researchers do this particular study?

To find out whether MRDTI is as reliable as traditional methods for diagnosing DVT.

Who was studied?

The study group was selected from 338 consecutive patients who were suspected of having DVT and who underwent contrast venography. The final study group included everyone in whom contrast venography showed DVT, plus some randomly selected patients who had negative results on contrast venography.

How was the study done?

After contrast venography and other confirmatory tests, MRDTI was performed within 48 hours. The MRDTI scans were interpreted by an experienced radiologist and by a nonradiologist trained to read these scans; neither of them knew the patient's diagnosis or the results of contrast venography.

What did the researchers find?

Compared with results of contrast venography, the radiologist correctly identified DVT on MRDTI in 96% of cases and the nonradiologist identified it in 94% of cases. In four cases, both reviewers diagnosed DVT when none was present on contrast venography. The MRDTI technique also appeared to be more accurate than contrast venography in detecting blood clots in the groin veins.

What were the limitations of the study?

A few patients had clots only in the calf or in the groin veins, resulting in some uncertainty about the reliability of MRDTI in these areas. If MRDTI is actually more accurate than the previous “gold standard,” contrast venography, evaluation of this new test may underestimate its reliability.

What were the implications of the study?

Magnetic resonance direct thrombus imaging identifies nearly all blood clots in the legs and seldom gives false-positive results. It is very promising as a test for blood clots in the legs, but its higher cost and lack of availability may limit its widespread use.

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