Head to head, MR beats CT for endoleak detection, sizing

March 8, 2004

MR scored significantly better than unenhanced biphasic CT scans to detect aneurysmal endoleaks and to rate their size, according to researchers from the University of Mainz, Germany.Because of these differences, even within the various CT protocols,

MR scored significantly better than unenhanced biphasic CT scans to detect aneurysmal endoleaks and to rate their size, according to researchers from the University of Mainz, Germany.

Because of these differences, even within the various CT protocols, researchers recommend that reporting standards be created for endoleaks associated with endovascular repair of abdominal aortic aneurysms.

Dr. Michael B. Pitton and colleagues evaluated 118 patients with endovascular repair of AAA. Follow-up was within 48 hours postintervention, at three, six, and 12 months, and annually thereafter.

Researchers analyzed 252 complete data sets including CT (unenhanced, arterial, and late contrast enhanced) and MR. Consensus reading of CT and MR was defined as the diagnostic reference standard.

With respect to this standard, 141 of the 252 data sets demonstrated evidence of endoleaks, Pitton said during a Monday morning scientific session at the European Congress of Radiology.

Endoleak rate was 56%. MRI detected 52%, biphasic CT detected 24%, while uniphasic and arterial late results were even less.

MR sensitivity to detect endoleak was 95%, followed by 43.3% for biphasic CT, and 37.6% and 34% for uniphasic late CT and uniphasic arterial CT, respectively. MR scored nearly 95% negative predictive value, while the CT protocols ranged between 55% and 58%.

MR underrated size in 2.5% of cases, while that rate jumped to 40% for CT. The accuracy of endoleak sizing was 96.4% for MR; 57.5% for biphasic CT; 56.8% for uniphasic late CT; and 55.2% for uniphasic arterial CT.

Endoleaks not detected by MR were due to calcification of the thrombus or calcification in the vessel wall adjacent to the stent, Pitton said.

Spiral CT protocol was 3-mm slices, reconstruction interval at 2 mm, unenhanced, arterial, and late-contrast enhanced scans. MR sequences included transversal T2-weighted spin-echo, T1-weighted FLASH 2D unenhanced, T1-weighted FLASH 2D contrast enhanced, and FLASH 3D angio on a 1.5T scanner.

In another study, Dr. Zhonghua Sun and colleagues from the University of Ulster and the Royal Victoria Hospital in the U.K. determined that axial CT images were best in preoperative situations compared with virtual intravascular endoscopy.

However, virtual intravascular endoscopy provided important information post-stent grafting. The 3D relationship of the suprarenal stent struts to the aortic ostia - in particular the renal and superior mesenteric arteries - was clearly visualized, Sun said.

"Virtual intravascular endoscopy findings might aid clinicians to accurately assess the effect of suprarenal stent grafting on the renal arteries," he said.

Sun and colleagues evaluated 47 patients with AAA undergoing aortic stent grafting with contrast enhanced single-slice CT. Virtual intravascular endoscopy proved inferior to axial CT images to visualize normal arterial branches, measure aneurysm sac size and neck length as well as diameter, assess vessel patency, and detect the presence of endoleaks.

Virtual intravascular endoscopy proved superior to axial CT and other 3D imaging methods in the visualization of configuration of stent struts relative to the ostia and the number of stent wires crossing the ostia in more than 80% of cases.