TU-H-206-08: Quantitative Impact of Biliary Stent Artefacts On MR Images.

PURPOSE: Biliary stents may cause artifacts in MR-images. These artifacts are caused by differences in susceptibility (artifact-1), eddy currents during read-out (artifact-2) and eddy currents due to the excitation pulse (artifact-3), which all are MRI sequence-dependent. In this study, we investigated and quantified the magnitude of these artifacts as a function of the distance from biliary stents, using a sequence-independent approach where possible.

METHODS: Eight phantoms were made containing different commercial biliary stents made of nitinol, platinol, stainless steel or polyethylene. To quantify artifact-1 sequence-independently, we acquired ΔB0-maps and T2*-maps. To maximize artifact-2, the phantom was placed 130mm off center. We then compared signal ratios from acquisitions with gradients in directions that induced eddy currents and acquisitions with gradients in directions that did not induce eddy currents, to assess the contribution of artifact-2. We acquired B1-maps to quantify the effect of artifact-3.These experiments were performed at 3T. The ΔB0-maps and T2*-maps were also acquiered at 1.5T.Finally, we acquired ΔB0-maps, T2*-maps and clinical MR-images in vivo in two pancreatic cancer patients with platinol stents.

RESULTS: Artifact-1 was dominant over the other artifacts. The stainless steel stent showed the largest artifact-1: decreased T2* and ΔB0>75Hz up to 20mm from the stent's edge which results in signal shifts>3voxels for typical diffusion weighted images with bandwidth BW=25Hz/voxel. The other stents showed a decreased T2* up to 8.5mm/5.1mm (3T/1.5T) from the edge of the stent and had a BW<95Hz/55Hz, resulting in signal shifts <0.2voxels for sequences with BW>500Hz/275Hz at 3T/1.5T. The plastic stent showed no artifacts. In vivo, the changes in B0 and T2* induced by the stent were larger than typical variations in B0 and T2* induced by anatomy.

CONCLUSION: We presented a sequence-independent measure to quantify susceptibility artifacts. Other artifacts are negligible compared to susceptibility artifacts for biliary stents.