By Brenda Tilke

New infusion MRA techniques (IMRA) may become diagnostically acceptable alternatives to digital subtraction angiography (DSA) for carotid artery examinations, according to an award-winning scientific exhibit shown at the RSNA meeting.

Contrast-enhanced breath-hold infusion MRA carotid artery exams were performed with new fast-gradient MR systems and compared to two-dimensional time-of-flight MRA and DSA in more than 30 patients at Long Island Jewish Medical Center in New Hyde Park, NY.

For the IMRA exams, the team used a 1.5-tesla GE EchoSpeed Signa System with a volume neck coil. The IMRA pulse sequence featured enhanced three-dimensional GRE sequence with TR 4/TE 1.9 msec, 26 partitions, zip factor of 2 and effective slice thickness of 0.8 mm, with a 75% to 50% phase field-of-view acquisition. Imaging time was about 15 to 20 seconds.

The contrast dose was 0.2mmol/kg of Gd-DTPA administered intravenously with an MR compatible injector. Scan delay varied between 10 and 15 seconds.

This IMRA protocol was compared against a routine time-of-flight MRA scanning technique and biplane DSA with selective common carotid arteriography. The comparisons showed IMRA had several advantages over routine MRA. These included better images of ulcerations, better correlation with angiography, better signal-to-noise, and better estimation of the length and degree of internal carotid artery stenosis. IMRA also had no in-plane saturation and no misregistration or flow-related artifacts.

IMRA is not completely problem-free, however. The team found problems with venous contamination and postprocessing artifacts. The study's authors strongly urged that IMRA source images be reviewed to control for these artifacts.

They said timing is the most important factor for IMRA. Late scan delay creates venous contamination that obscures anatomy.