Positive visualization of MR-compatible nitinol stent using a susceptibility-based imaging technique

MR-compatible metallic implanted devices, such as the endovascular stent grafts, are commonly used for the treatment of arterial occlusive diseases (1). Computed tomography (CT) is currently the standard imaging modality to assess the stent restenosis and localize the metallic implanted devices (2). In addition, the improved computed tomography technique, such as synchrotron radiation computed tomography (3), allows for a more accurate assessment of the stent and size measurement of different aortic stent grafts. The dual energy computed tomography angiography (DECTA) which can obtain better image quality in peripheral arterial stenting when compared to conventional CTA (4). However, CT requires exposure to ionizing radiation and has limited soft tissue contrast (5-8). In recent years, several MR techniques have been proposed for scanning the patients with implanted MR compatible stent because of their superior soft tissue contrast. MR angiography (MRA) and contrast-enhanced MRA techniques are respectively proposed by some scholars to image MR compatible metallic stents (9-11) non-invasively. The results show that intraluminal loss of signal and artifacts of most of the SFA (superficial femoral artery) stents do not markedly limit assessment of stent lumen by MRA at 1.5 and 3T. MRA can be considered a valid technique for the detection of relevant in-stent restenosis. Furthermore, the inversion recovery with on-resonant water suppression (IRON) with conventional T1-weighted (T1w) MRA is proposed for visualization of peripheral nitinol stents (12). IRON-MRA provides an improvement of the in-stent lumen visualization with an ‘open-close-open’ design, which reveals a complete in-stent signal loss in T1W MRA. However, the fat-saturated T2-weighted imaging can limit assessment of in-stent pathology of the cobalt-chromium stents because of the metal artifact (13). Additionally, these conventional MR techniques neither accurately localize the position of the implanted devices nor assess the stent restenosis due to the susceptibility and radiofrequency (RF) shielding artifacts caused by the stent graft. Therefore, a reliable MR technique for visualizing the metallic devices and assessing the stent restenosis would be highly beneficial