By Charles Bankhead

MRI more accurately identifies leaks in abdominal aortic stent grafts than CT angiography (CTA), and requires further evaluation as the initial noninvasive imaging modality for that indication, according to a team of French radiologists.

In 24 patients with stent graft repair of abdominal aortic aneurysm, MRI correctly identified 12 leaks, compared to seven of 24 identified by CTA, Dr. Jean-Paul Beregi reported at the RSNA scientific sessions. MRI detected all seven leaks identified by CTA, but CTA missed five of the 12 leaks seen on MRI. All leaks were confirmed by conventional angiography.

"MRI appears to be more sensitive than CTA for detection of leaks after stent grafting of abdominal aortic aneurysm," said Beregi, a radiologist at University Hospital in Lille, France. "All relevant information can be obtained in 10 minutes, and MRI has the advantage of reducing exposure to radiation and to ionic contrast material."

The findings came from follow-up evaluations of patients who had stent graft procedures for repair of abdominal aortic aneurysm. In each case, the graft was evaluated by both MRI and CTA. All patients had follow-up imaging at one month, and most also had subsequent imaging evaluations at six or 12 months.

MRI evaluation included T1- and T2-weighted turbo spin-echo, MR angiography, and axial T1-weighted spin-echo after intravenous injection of gadolinium. Helical CT was performed in arterial and delayed phases.

At one-month follow-up, thrombus appeared as a heterogeneous signal on T1- and T2-weighted MRI sequences, and gadolinium uptake was seen in eight of 24 patients. CT detected leaks in five of the eight cases. A similar disparity in detection accuracy was seen in imaging studies performed at six and at 12 months, Beregi said.