Magnetic resonance angiography of nonferromagnetic iliac artery stents andstent-grafts: A comparative study in sheep

Purpose: To compare nonferromagnetic iliac artery prostheses in their suita bility for patency monitoring with magnetic resonance angiography (MRA) usi ng conventional angiography as a reference. Methods: In experiment 1, three Memotherm stents were inserted into the ili ac arteries of each of six sheep: two "tandem" stents on one side and a sin gle stent on the other side. In experiment 2, four prostheses (normal and l ow-porosity Corvita stent-grafts, Memotherm, ZA-stent) were inserted in eac h of 11 sheep. Patency was monitored before and 1, 3, and 6 months after in sertion with 3D phase-contrast and two 2D time-of-flight sequences (TOF-1: TR/TE 18/6.9, TOF-2: 13/2.5) with and without contrast at 1.5 T. On 206 cor onal MIP images (72 pre-, 134 post-stenting), three readers analyzed 824 il iac segments (206 x 4) for patency and artifacts. Results: There was no difference in the number of artifacts between tandem and single iliac Memotherm stents. The ZA-stent induced significantly fewer artifacts than the other prostheses (p < 0.00001). With MRA, patency of th e ZA-stent was correctly diagnosed in 88% of cases, which was almost compar able to nonstented iliac segments (95%), patency of the Memotherm stent in 59%, and of the Corvita stent-grafts in 57% and 55%. The TOF-2 sequence wit h contrast yielded the best images. Conclusion: MRA compatibility of nonferromagnetic prostheses depends strong ly on the design of the device. MRA may be used to monitor the patency of i liac ZA-stents, whereas iliac Memotherm stents and Corvita stent-grafts app ear to be less suited for follow-up with MRA.