Last Updated: 2002-01-14 17:01:14 EST (Reuters Health) By Richard Woodman LONDON (Reuters Health)

Magnetic resonance imaging is a "highly accurate" technique for diagnosing deep vein thrombosis (DVT) and may be particularly helpful to pregnant women and travellers at risk of developing dangerous blood clots, British researchers said on Monday.

Professor Alan Moody and his team in the department of academic radiology at Nottingham University tested magnetic resonance direct thrombus imaging (MRDTI) in 101 patients with suspected DVT above and below the knee. The results were compared with those already obtained using venography by two experts who found that the MRDTI diagnosis was accurate throughout the lower leg venous system.

"The great advantages that MRDTI has over other methods to detect thrombosis are that it is non-invasive, quick and reliable," said Dr. Moody whose findings are published in the Annals of Internal Medicine. "MRI has this wonderful ability to pick out different characteristics of tissues and because of the way blood behaves, it gives out this very good signal of where the clot is," Dr. Moody told Reuters Health. The method "does not require contrast agent and is highly accurate and reproducible," the investigators point out in their journal report.

Although venography has largely been replaced by ultrasound, the researchers said that both techniques rely on changes secondary to a blood clot such as impaired blood flow. These results might be inconclusive below the knee, whereas MRDTI directly reveals the thrombus. They added in a news statement that MRDTI enables radiologists to diagnosis the disorder at an early stage even before symptoms are apparent. "Action can then be taken to prevent the clot [from] becoming larger and blocking the blood vessel, or the clot breaking off and travelling to the lungs and causing pulmonary embolism."

Although the study did not include pregnant women, Dr. Moody is confident that MRDTI could play an important role in monitoring blood clot formation. "DVT can be a major problem during pregnancy and in a few cases may be fatal," he said. The clots often originate in the pelvis, which are difficult to detect using ultrasound. "MRDTI produces good images of the pelvis and the pregnant mum would not need X-rays for us to see the blood vessels." DVT in travellers during long-haul flights causes great concern and the speed and reliability of MRDTI could, in the future, identify those most at risk, the researchers added. Dr. Moody said that the limited number and capital cost of MRI machines might limit widespread use of MRDTI at present. However, running costs were competitive at around US $1000 per hour, enough time to scan three or four patients.

Ann Intern Med 2002;136:89-97