MRA evolves to meet changing clinical needs

Contrast-enhanced MR angiography is the primary method of assessing vascular disease at many hospitals worldwide. While advances in technology ensure that CT angiography draws its share of devotees, MRA continues to win hearts and minds among radiologists who prefer the radiation-free imaging approach.

Scheduling difficulties may sometimes lead to CTA or conventional angiography performed in patients who would otherwise undergo MRA, said Dr. Martin Prince, chief of MRI at the Presbyterian Hospital and Weill Cornell Medical Center in New York City. Claustrophobic patients, or those with pacemakers or metallic implants, may also be referred to other modalities. Otherwise, MRA is the modality of choice for nonemergency cases outside the coronary arteries.

A key strength of CE-MRA is that the same type of approach can be used for practically every clinical indication, said Dr. James Meaney, a radiologist at St. James's Hospital in Dublin. All CE-MRA examinations at St. James's are performed with a heavily T1-weighted fast spoiled gradient echo imaging sequence.

"You may alter parameters such as spatial resolution, scan planes, and the location of your imaging box, but basically the same robust technique works for all regions of interest," he said.

While a "one size fits most" approach might apply to sequence choice, quality MRA still requires time, effort, and expertise. Opinions vary as to the best way for radiologists and MR technologists to learn their craft. Suggested strategies include hands-on training courses, work-shadowing of experienced colleagues, and even free MRA examinations for friends and family. Refresher courses may also be required to stay abreast of evolving techniques.

Protocols should be reviewed and revised on a regular basis, said Dr. Tim Leiner, a radiologist at Maastricht University Hospital in the Netherlands. Routine protocols should also be established for specific clinical indications. Imaging the lower legs first in patients with critical ischemia, for example, will help surgeons determine the viability of a bypass.

"Clinicians will remember the one bad case you send them more than all the good ones put together," he said.

Development of smarter processing software should make it easier to interpret MRA in the future, according to Leiner. Semiautomated evaluations can remove the need for individual stenoses to be measured manually.

Radiology residents at University Hospital Grosshadern in Munich are taught to measure the area of stenoses. This method provides a more accurate assessment of obstruction than simply diameter measurements, said Dr. Stefan Schoenberg, chief of MRI at the Munich hospital. Use of isotropic data sets also helps avoid any under- or overestimation of stenotic size that can result from geometric distortion of voxels.

The future of MRA, however, will mean much more than straightforward stenosis measurements or aneurysm detection, according to Dr. Jonathan Gillard, a neuroradiologist at Cambridge University Hospitals Foundation Trust in the UK. Advances in medicine will mean that clinicians need to know the cause of any arterial disease before they can select the most appropriate treatment. Developments in high-resolution plaque imaging are pointing the way.

"You can have two people, both with a 60% stenosis in the carotid artery," he said. "One may be symptomatic and have had a ministroke, the other not. The actual measurement doesn't tell you why they are different. But if you look at the causes of narrowing and the different types of plaque, then it becomes clear why some people have a higher risk of plaque rupture and clot-formation."