Magnetic Resonance Angiography

            Magnetic resonance imaging is less invasive than traditional angiography and therefore provides a potential favorable alternative to traditional angiography. MRA has been used by peripheral vascular surgeons to image the vasculature of the lower extremity as well as to image the carotid arteries in the head and neck. MR is also commonly used to image vascular malformations. ^9-11

MRA is not a standardized technique as there are various protocols which are used to evaluate the lower extremities.  Time of flight MRA is based on the contrast formation by the inflow of unsaturated spins (blood) into surrounding saturated spins (perivascular tissue). Acquisition of images is available in 2-dimensional or 3-dimensional mode. Two-dimensional MRA can cover large anatomic areas within reasonable time but is sensitive to changes in flow direction. Three-dimensional imaging can overcome these limitiations but requires contrast agents such as gadolinium to improve visualization. ¹⁰ A recent meta-analysis found that MRA is highly accurate for detection of stenosis greater than 50% or occlusion within the entire lower extremity arterial tree. Furthermore, as expected, gadolinium-enhanced MRA yielded consistently better results. ^1-4   

While MRA is less invasive than traditional angiography, and typically less expensive, there are still several drawbacks to this technique.  Long acquisition times, poor spatial relations, inability to detect intravascular calcifications as well as inability to allow a three dimensional view of the vessels and bones together all limit the utility of MRA. In addition, patients with pacemakers or hardware (i.e. external fixators and intramedullary rods) cannot be evaluated by magnetic resonance imaging. Furthermore, patients who are prone to claustrophobia typically do not tolerate the imaging study.

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