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Blood-pool contrast agents help increase contrast and resolution of MRA

Best Practice
Maki, Jeffrey, M.D., Ph.D. University of Washington • USA

Non-contrast MR Angiography (MRA) techniques are highly flow-dependent, often require specialized equipment, and can be quite slow. Contrast-enhanced MRA, on the other hand, is fast, readily available, and well validated. Bloodpool contrast agents largely remain intravascular, and have a short enough T1 that they provide a steady state phase that can persist for more than 30 minutes, providing more time and equilibrium of contrast to achieve high spatial resolution.

 Jeffrey H. Maki, MD, PhD
Jeffrey H. Maki, MD, PhD

Jeffrey H. Maki, MD, PhD, is Professor of Radiology and Director of Body MRI at the

University of Washington Medical Center and Puget Sound VA Health Care Service.

Using Achieva 1.5T (Release 2.6), he performs MRA with a blood pool agent to look for atherosclerotic occlusive disease.

Agent is a confidence-booster

Blood pool agents enable steady state imaging well after the first pass. This reduces the

possibility of what Dr. Maki calls “timing” errors; effects often seen in first pass MRA, where distal vessels or vessels downstream of a stenosis or slowly filling collateralized vessels do not quite fill during the first pass, and can be easily misinterpreted as diseased.

“The ability to confidently see the entire vasculature free of these artifacts is extremely important,” he says. “Higher spatial resolution is easily achievable (up to 0.6 mm isotropic), and this allows an excellent evaluation of vessel morphology, including seeing and evaluating plaque in a way we are not used to seeing.”

"Vessels that looked occluded, he says, can often reveal tiny residual lumens, and stenoses

that didn’t look so severe on first pass can be better characterized."

“Clinically, it’s a whole new way of looking at things"

The impact from a clinical perspective is significant. “We have seen several cases where the steady state blood-pool images have changed the interventional plan,” says Dr. Maki. “For

example in one case there appeared to be an occluded left CFA with severe disease of the left SFA, and the surgical plan would have been to perform a fem-pop bypass.
Looking at the steady state images, however, the occlusion was real, but only very focal. Distally the SFA was normal, only appearing diseased due to the timing problems.”

While the concentration of contrast in steady state isn’t as high as in first pass, it’s high enough. “First pass only lasts as long as contrast is being injected, about 15-20 seconds,” says Dr. Maki. “There’s not much time to acquire data, and you’re very limited in spatial resolution.
That limitation can make accurate interpretation difficult. If the arteries are bright and you see the stenosis, then you may think you made a great MRA, but spatial resolution, say in the upper station, might be 1.4 x 2 x 2.4 mm. In comparison, when acquiring steady state images the resolution might be 0.8 x 0.8 x 0.8 mm – much, much higher resolution.”

“It’s really a whole new way of looking at things,” he concludes.

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Nov 10, 2011

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Best Practice
Achieva 1.5T
Release 2.6
ablavar, stenosis, Vascular

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