Diagnostic Imaging Online
October 8, 2003
CE-MRA earns 'unreliable' label for measuring carotid stenosis
Evidence continues to mount that contrast-enhanced MR angiography for imaging the carotids is less robust than previously thought. Researchers are taking a second look at 3D time-of-flight MRA for assessing carotid artery stenosis.
Non-contrast-enhanced MRA carotid imaging with the time-of-flight (TOF) technique compares favorably with angiography, ultrasound, and excised plaques, according to Dr. Tiffany C. Townsend and colleagues at the San Francisco VA Medical Center. Yet gadolinium contrast-enhanced MRA (CE-MRA) has almost universally replaced TOF-MRA, because it reduces imaging time (25 seconds versus 10 minutes) and improves signal-to-noise ratio.
Researchers found alarming discrepancies between CE-MRA and TOF-MRA in measuring carotid stenosis and decided to test the two MR techniques against each other.
With each technique, they measured stenosis in 107 carotid arteries in 58 patients. There were 12 occluded arteries. In the remaining 95 arteries, CE-MRA showed a greater degree of stenosis than TOF-MRA in 42 arteries, a lesser degree in 14, and similar stenosis in 39.
The mean overestimated degree of severity by CE-MRA was 21% in patients with up to 29% stenosis, 35% in patients with 30% to 40% stenosis, and 38% in those with 50% to 69% stenosis.
Researchers performed experiments with carotid phantoms to test the contribution of imaging software to image quality. These experiments showed that the imaging parameters of CE-MRA, particularly the plane on which frequency encoding gradients were applied, reduced signal acquisition at the area of stenosis.
CE-MRA is an excellent screening technique, but only TOF-MRA should be used to determine the degree of carotid artery stenosis, said coauthor Dr. Joseph H. Rapp, vascular surgery chief at the San Francisco VA.
"I would not recommend any interventions based upon MRA -- or ultrasound -- alone," he said.
The study, published in the July issue of the Journal of Vascular Surgery, suggests that contrast-enhanced parameters be retooled before CE-MRA can be considered a reliable indicator of carotid artery stenosis. CE-MRA images then need to be compared with 3D TOF or ultrasound to add certainty to the diagnosis.
For more information from the Diagnostic Imaging archives:
MR-ultrasound duo could replace angio in carotids
MR angiography works in pediatric vascular abnormalities
MR alone may lead to inappropriate treatment for carotid artery stenosis
MR finds its way to open systems
-- By H.A. Abella
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