High flip angle imaging of metallic stents: implications for MR angiography and intraluminal signal interpretation.

Intraluminal stent signal characterization by MRI is generally hampered by signal loss from the metallic stent material. This signal loss is related to magnetic susceptibility and RF shielding. Even when stent materials with low magnetic susceptibility are used, RF shielding can still be problematic. In this article we have shown that high flip angle imaging enables morphology assessment and tissue characterization in stents made of stainless steel 316L, NiTinol, and ABI-alloy.

Thrombolysis of occluded synthetic bypass grafts in the lower limb: technical success and 1-year follow-up in 32 patients.

PURPOSE: To evaluate prospectively the technical success and clinical outcome of thrombolysis for acute occlusion of synthetic arterial bypass grafts in the lower limb. METHODS: Thirty-two consecutive patients (27 men; median age 65 years, range 41-80) with occluded polytetrafluoroethylene bypass grafts were treated with direct-catheter thrombolysis (100,000-IU bolus of urokinase with 100,000-IU/h infusion) followed by ancillary interventions to treat underlying stenosis whenever necessary. All patients received oral anticoagulation to maintain the international normalized ratio at 3.0 to 4.0. Clinical follow-up and duplex ultrasound examinations were performed at 3-month intervals up to 1 year. RESULTS: Thrombolysis was technically successful in 27 (84%) patients; 3 of the 5 failed patients had amputations. Mean duration of urokinase therapy was 36+/-14 hours. In 18 patients, underlying stenoses (11 distal anastomosis, 5 proximal anastomosis, and 3 inflow) were treated, 15 by an endovascular procedure and 3 surgically. Four major complications occurred: groin hematoma, sepsis, transient renal dysfunction, and a hemorrhage at the proximal anastomosis after urokinase treatment. At 1 year, 21 bypass grafts had reoccluded (20% patency rate on intention-to-treat basis); 3 reocclusions resulted in amputation (overall 19% amputation rate). CONCLUSIONS: Thrombolysis in the setting of acute lower limb bypass graft occlusion is associated with good initial technical success rates and satisfactory clinical results. However, the re-occlusion rate within 1 year is high.

MR-velocity mapping in vascular stents to assess peak systolic velocity. In vitro comparison of various stent designs made of Stainless Steel and Nitinol.

INTRODUCTION: Peak systolic velocity (PSV) measurements of blood flow inside vascular stents allow reliable detection of in-stent re-stenosis. The purpose of this in vitro study was to evaluate the feasibility of obtaining PSV measurements inside vascular stents made of Stainless Steel and Nitinol, using a velocity encoded MR technique. MATERIALS/METHODS: In a flow phantom, stents of Stainless Steel and Nitinol were studied. The phantom was integrated into a closed-tubing circuit driven by a MR dedicated pulsatile flow pump. MR imaging was performed on a 1.5 T system. The PSV in the tube without stent was used as the gold standard to determine the accuracy and the variability (paired t-test and Pittman's test) of the PSV measurements inside the stents. RESULTS: PSV values inside the stents showed percentual difference in mean of -15 to 21% (P < 0.05) at a pump setting of 10 and 20 ml/s. CONCLUSION: PSV measurements can be accurately obtained inside stents made of Stainless Steel and Nitinol. MR-velocity measurements may be used in patients to non-invasively evaluate stent patency and in-stent re-stenosis.