Noncontrast renal artery MRA shows potential

A noncontrast, flow-dependent FIESTA sequence offers a safe and effective alternative to gadolinium-enhanced MR angiography for renal artery evaluations.

That conclusion, drawn from a Japanese study of 63 patients with suspected renal tumors, should come as good news to physicians who are making treatment decisions for patients with severely compromised renal function. Such patients comprise nearly all of the roughly 500 patients with confirmed or suspected nephrogenic systemic fibrosis, a devastating skin disease associated with exposure to gadolinium-based MR contrast media.

Dr. Takayuki Masui, a radiologist at Seirei Hamamatsu General Hospital in Hamamatsu, presented results at the 2008 International Society for Magnetic Resonance in Medicine meeting suggesting that images produced with noncontrast FIESTA MRA with a flow-preparation pulse (Flow-Prep) are clinically equivalent to images produced with conventional gadolinium-enhanced 3D gradient-echo imaging.

Imaging was performed on a 1.5T GE scanner with an eight-channel, phased-array body coil to identify the number and location of renal arteries. The exams aided planning of renal tumor surgery.

Noncontrast MRA was obtained in two steps. ECG-gated, axial 2D phased-contrast cine MRI of the aorta was acquired above the renal arteries during a 15-second breath-hold. Aortic peak-flow velocity and its delay time after the R-wave on the electrocardiogram were then measured. Masui followed with a respiration-triggered, ECG-gated, Flow-Prep 3D FIESTA sequence, obtained in the coronal plane. Total imaging times ranged from 2.5 to four minutes.

Two radiologists subjectively evaluated the images from the noncontrast and contrast approaches. Assessments were based on a five-point scale. Evaluations were repeated for the ability to recognize anatomy at two points along the aorta and at five levels for the renal arteries.

Four noncontrast FIESTA studies were judged nondiagnostic because of ECG failure. Otherwise, the noncontrast and contrast approaches showed nearly the same overall image quality and resistance to artifacts, Masui said.

Both techniques consistently recognized the aorta from the diaphragm to the bifurcation. Noncontrast and contrast MRA recognized the same number of renal arteries in 59 of 63 patients. No differences were seen in the ability to characterize the proximal to mid renal arteries.

Noncontrast MRA rendered a better depiction of the peripheral renal arteries than contrast-enhanced MRA, but overlaps of veins and soft tissues were easier to discriminate with the contrast-enhanced approach.

In response to a question, Masui admitted that FIESTA is flow-dependent and would not be well suited for imaging vessels involving varying flow, such as the carotid arteries.

Besides eliminating any risk of side effects to contrast agents, one of the advantages of noncontrast MRA is the feasibility of repeated administration-even within a single study-with different parameters to optimize image quality, according to Masui.

"Noncontrast MRA using Flow-Prep FIESTA with successfully triggered ECG gating can be used for the examination of the renal arteries," he said.

-By James Brice