MAGNETIC-RESONANCE ANGIOGRAPHY - FIELDS O F EXPLORATION, MAIN INDICATIONS AND LIMITS

Magnetic resonance angiography (MRA) has become a widely accepted tech nique with regards to the other available noninvasive techniques in th e diagnosis of vascular disease. This paper proposes a review of the d ifferent indications of this technique in arterial and venous diseases . Among several MRA pulse sequences, the most frequently used until to day consisted of a time-of-flight technique which provided angiograms without any injection of intravascular contrast medium. It required to be performed in a plane perpendicular to the main axis of the vessel to be optimal. New techniques, such as contrast medium bolus-enhanced acquisitions allow examination of vascular segments in a plane paralle l to their course (coronal for the aorta and lower limb arteries). An increasing number of clinical applications has raised since the implem entation of MRA techniques on MR devices; some of them art widely acce pted, whereas some others remain under the scope of extensive validati on. With a high level of accuracy in grading carotid artery stenosis, MRA is now routinely used in cerebral arterial occlusive diseases and has in part replaced contrast angiography. MRA of the venous system of the brain plays a major role in the diagnosis and follow up of dural venous thrombosis. Other vascular brain diseases, such as vascular mal formations, yet have limited uses. Carotid artery dissections are fair ly demonstrated with MRA, which can be used for diagnosis as well as f or follow-up. The accuracy of MRA in the diagnosis of venous thrombosi s of the cervical/mediastinal veins has been reported as high as 100 % . Moreover, MRA allows a precise assessment of collateral vessels in c ase of complete cervical/mediastinal venous thrombosis. MRA is able to explore most normal and diseased coronary arteries. With further MRA techniques improvements, coronary MRA should become an integral part o f the evaluation of patients with ischemic heart disease. CineMRI, a M RA variant. is a valuable technique in the assessment of left and righ t ventricular function. In addition. this technique allows indirect as sessment of pulmonary hypertension. Several reports have emphasized th e value of MRA in the diagnosis and follow-up of aortic dissections, a nd in the preoperative assessment of abdominal aortic aneurysms; The c apability of MRA to diagnose renal artery disease has been emphasized in several studies. anti this technique is non accepted in the work-up of renovascular hypertension and renal failure, A major advantage of MRA over spiral CT is the lack of nephrotoxicity. Early clinical MR in vestigations of the arteries in the lower extremities using time-of-fl ight MRA showed that severe stenoses or occlusions could be diagnosed accurately, However, the mean limitation of this technique was the len gth of time required for acquisitions. in particular when long vascula r segments were examined (until 2 hours), New bolus-enhanced subtracti on techniques hold promise since they provide angiograms similar to th ose of digital subtraction angiography in less than 20 minutes. The po tential contribution of MRA in pulmonary embolism is under considerati on. In thromboembolic disease. pulmonary MRA is able to demonstrate pr oximal emboli until segmental pulmonary arteries, but concurrence with spiral CT remains a major challenge in this disease. MRA provides ima ges similar to those of pulmonary angiography, whereas spiral CT could not. Another main advantage of MRA over spiral CT is that deep venous thrombosis is accurately assessed by MRA, Lower limb veins and pulmon ary arteries can be examined in a single examination by MRA. The rapid ly changing nature of MRA techniques is an evidence. Hence. clinical i ndications of MRA at present can rapidly change in this environment. M RA has an increasing number of current clinical roles in patient manag ement. This method holds promise for more extensive use in the future. The method is likely to replace most of routine conventional diagnost ic angiography performed Lit the present time.