Is CTA or contrast enhanced MRA better?
It depends on local preferences and expertise. CTA is quicker than MRA, and therefore is generally preferred for evaluation of potentially unstable or claustrophobic patients, but it exposes patients to ionizing radiation. CTA is superior when there are indwelling metallic stents in the artery. Stents, particularly stainless steel stents, lead to blooming artifact on MRA. CTA is also useful to assess the burden of atherosclerotic calcification, which is useful, for example, for preoperative planning of abdominal aortic aneurysm (AAA). Paradoxically, MRA is better for evaluating heavily calcified arteries that are also small, such as arteries of the calf. This is because it is difficult to distinguish between heavy calcification and iodinated contrast material on CTA, particularly when an artery is heavily calcified.
The spatial resolution of CTA can be as small as 0.6 mm, whereas MRA is typically on the order of 1 mm. MRA is more amenable to postprocessing because it is easier to subtract background structures. Both CTA and MRA can offer a snapshot of organ perfusion, but MRA offers more dynamic information without radiation exposure.
MRA allows image acquisition in any plane, whereas CTA provides only for image acquisition in the axial plane. However, multiplanar reconstructions and reformations can subsequently be created in any plane of interest.
