Vascular stents and stent grafts: a vascular surgeon's view

Gadopentetate dimeglumine-enhanced three-dimensional MR-angiography: dosing, safety, and efficacy

Noninvasiveness, inherent three-dimensionality allowing reformations in any desired plane, and safe contrast agents, coupled with high diagnostic accuracy have driven the rise in popularity of contrast-enhanced MR angiography (CE-MRA) within the medical community. Reflecting its dominant market share as a paramagnetic contrast agent, gadopentetate dimeglumine (Gd-DTPA) has been used for the majority of clinically-performed MRA exams. Over the period January 1994 to February 2002, a total of 172 original studies describing the use of gadolinium-enhanced MRA in more than three human subjects were identified. Of these, 117 described the use of Gd-DTPA as the contrast agent for MRA. A total of 4046 subjects who received Gd-DTPA for MRA are described in these studies. Analysis of these data demonstrate Gd-DTPA to be a safe contrast agent for MRA when applied in a dose ranging from 0.1 to 0.3 mmol/kg of bodyweight. The documented clinical results show Gd-DTPA to be efficacious in the assessment of the arterial system. The effectiveness of Gd-DTPA-enhanced MRA extends beyond the detection, localization, and characterization of arterial disease, and encompasses choice and planning of appropriate therapy, as well as evaluation of therapeutic effectiveness.

Vascular complications arising from maldeployed stents

The authors present 6 unusual vascular complications secondary to maldeployed or undeployed vascular stents. They retrospectively reviewed patients referred for complications of vascular stent placement from September 1998 to March 1999. Information on patient history was obtained from a computerized database and clinical document file. Radiographic information was obtained from arteriograms, ultrasound, and computed tomography imaging. Case 1 describes an undeployed stent in the superior mesenteric artery with subsequent thrombosis in addition to celiac occlusion secondary to attempted balloon angioplasty. Case 2 refers to a malpositioned stent placed in the aortic arch and proximal left common carotid artery. Case 3 involves an undeployed coronary stent that migrated to the right distal posterior tibial artery, causing vascular occlusion and chronic pain. In Case 4, an attempted stent placement into the left iliac artery resulted in an undeployed stent lodged across the aortic bifurcation. Case 5 illustrates a partially deployed stent occluding the left renal artery that was unamenable to further angioplasty. Case 6 demonstrates arterial dissection with a pseudoaneurysm following stent placement for right subclavian stenosis. Five patients required operative intervention. Increased use of stents may escalate the number of complications requiring operative intervention. Foreign bodies can migrate distally and potentiate thrombotic occlusion of vessels. Caution must be used not only at the time of deployment but also in the follow-up period. Continued surveillance becomes important after vascular stent placement.

Vascular stents as RF antennas for intravascular MR guidance and imaging

Stent deployment is used to improve the immediate and long-term results of vascular interventions in various vascular sites. X-ray angiography as an imaging modality is often limited in providing an accurate assessment with regard to vessel size, plaque calcification, or stent deployment. In this study, the potential of using the stent endoprothesis as a radiofrequency (RF) receive-only probe for MR guidance and lesion imaging was investigated. Three different principles were developed to visualize stents actively, the first employing the stent as a loop antenna, the second employing the stent in an electrical dipole configuration, and the third employing the stent in a hybrid configuration as a coaxial line antenna. The three configurations resulted in different signal characteristics. Based on two of these antenna configurations, stent deployment devices were built and evaluated in in vitro as well as in vivo sheep experiments. Active stent visualization allows real-time MR guidance through the vessel tree and monitoring of stent deployment. In addition, the stent antenna may become useful for high resolution imaging of the vessel wall. Magn Reson Med 42:738-745, 1999.