[Systematics of imaging artifacts in MRT caused by metallic vascular implants (stents)].

PURPOSE: Imaging artifacts in magnetic resonance tomography (MRT) caused by metallic vascular implants (stents) were characterized systematically in dependence on the material and the construction of the implants as well as with respect to different measurement protocols and for different static field strength B (0).
METHODS: Twelve stents, different in material (stainless steel, nitinol, Co-alloy) and/or construction, were examined at B (0) = 0.2 T and 1.0 T with two 2D gradient echo (GE) sequences (TE = 4 and 10 ms), one 3D GE sequence and one spin echo (SE) sequence. The stents were put into water with Gd-DTPA contrast agent. The dependence on the orientation was analyzed for the 9 possibilities of an orthogonal alignment of the stent axis, the direction of B (0), the slice, the read out, and the phase encoding direction. Special interest was given to the visibility of the stent lumen at forced rf excitation, as well as to the influence of broken struts on the signal obtained.
RESULTS: For the examined stents GE technique showed, due to spin dephasing regions a total signal loss ranging up to 8 mm away from the stent mashes. The value depends on the stent material, the stent orientation in the scanner and grows with voxel size, echo time and B (0). In SE technique dephasing artifacts vanish and wrong spatial encoding gets visible, rf shielding is more pronounced. The visibility of the stent lumen ranges from nearly unperturbed down to a complete signal loss. An improvement is possible using enlarged flip angles. Broken struts can not be imaged significantly. DISCUSSION: The MR representation of metallic stents commercially available at the time, especially of nitionol stents, can be optimized with a suitable adaptation of the imaging parameters. However, a profound improvement can only be expected from new stent material and design.