There is considerable overlap in the indications and the utility of MRA versus CTA. Either technique can be utilized for diagnosis and evaluation of atherosclerotic carotid vascular disease, vertebral artery stenosis, posttraumatic and spontaneous vessel dissection and preoperative evaluation for carotid vessel involvement with head and neck tumors.
CTA may be useful in evaluating degree of lumen stenosis similar to that with contrast enhanced MRA. However, when dense calcium deposits are present within an atherosclerotic plaque at the carotid bifurcation this may limit accurate quantitation of vessel lumen stenosis using CTA. For these cases, contrast enhanced MRA may be superior to CTA.
Posttraumatic vessel injury or vessel dissection can also be evaluated with either CTA or MRA. MRA has the advantage of being more specific for traumatic vessel dissection since it detects the presence of intramural hematoma. In the acute situation, however, CTA is more rapidly available in many emergency departments. cTa provides good SNR images of the neck and provides very rapid imaging of the cervical vessels with modern multi-row detector array CT scanners. In addition, there are not the critical safety concerns with CTA. Since many trauma patients may be unable to give a proper history, MR safety considerations may preclude use of MRA in the acute situation.
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