MR imaging artifacts, ferromagnetism, and magnetic torque of intravascular filters, stents, and coils.

Abstract

Experiments were conducted in which various intravascular filters, stents, and coils were imaged using magnetic resonance (MR) spin-echo technique at 0.35 T. These devices were also evaluated for ferromagnetism (at 0.35, 1.5, and 4.7 T), magnetic torque (at 0.35 and 1.5 T), and magnetically induced migration within a plastic tube (at 0.35 and 1.5 T for the Greenfield filter [GF]). The stainless-steel GF was evaluated in vitro for its propensity to perforate canine inferior venae cavae (IVC). Magnetic force and torque at 1.5 T did not dislodge the GF or result in perforation of canine IVC by the GF. Beta-3 titanium alloy (used in a new percutaneous version of the GF) is apparently one of the best-suited metals for use with MR imaging because of its lack of ferromagnetism (up to 4.7 T) and absence of MR imaging artifacts (at 0.35 T). Devices composed of Elgiloy (Mobin-Uddin filter), nitinol, and MP32-N (Amplatz filter) alloys all created mild artifacts. Devices fashioned from 304 and 316L (GF and Palmaz stent) stainless-steel alloys created severe "black-hole" artifacts, with the 304 alloy devices also showing marked image distortion. Generally, the greater the ferromagnetism of a device, the greater its magnetic susceptibility artifact.

Biomedical implants and devices: Assessment of magnetic field interactions with a 3.0‐Tesla MR system

“…Many different types of intravascular and intracavitary coils and stents have been evaluated for safety with MR systems at 1.5-T or less (6,14,18,19,(37)(38)(39)(40)(41)(42). Additionally, a GDC tested at 3.0-T was reported to be safe for this environment (21).…”

“…Thus, it is unlikely that they would become moved or dislodged as a result of being attracted by static magnetic fields of MR systems up to 1.5-T (6,14,18,19,(37)(38)(39)(40)(41)(42). Furthermore, there has never been a report of such an incident.…”

MR Evaluation Ex Vivo and In Vivo of a Covered Stent-Graft for Abdominal Aortic Aneurysms: Ferromagnetism, Heating, Artifacts, and Velocity Mapping

“…Nitinol is a nickel-titanium alloy (55% nickel and 45% titanium) (17). The Vanguard stent-graft was selected because it is routinely used at our center for endovascular treatment of AAA.…”

“…The stent-graft was suspended by a fine string, attached at the estimated center of mass, to a specially constructed device (a plastic protractor mounted on a wooden stand) and placed at the portal of the magnet bore (15)(16)(17)24,26). The accuracy of this device is Ϯ0.5°.…”

“…Previous studies have shown that MRI is safe if the metallic implant exhibits none, or negligible, ferromagnetism, in the sense that the metallic implant is not affected by the static magnetic field (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). With respect to heating, patients may safely undergo MRI if the metallic implant is not or is only slightly (Յ1.0°C) heated when tested ex vivo (16,(22)(23)(24)(25)(26)(27)(28)(29).…”