Aneurysm Clip Motion during Magnetic Resonance Imaging: In Vivo Experimental Study with Metallurgical Factor Analysis

Abstract

Because of various mechanical, metallurgical, and commercial constraints, aneurysm clips are manufactured from different alloys, including several stainless steel and cobalt alloys. Some of the steels contain volume fractions of the crystal phase known as martensite. Martensitic alloys have body-centered cubic structure, are prone to stress corrosion failure, and are ferromagnetic. Martensitic steel can be displaced like a compass needle when exposed to a magnetic field such as that generated during magnetic resonance imaging (MRI). The force exerted by the magnetic field is proportional to the volume fraction of the magnetic phase. We investigated the martensitic content and magnetic field-induced displacement of 12 common aneurysm clips. Four clips of each of the following types were examined: Sugita, Sundt-Kees Multi-Angle, Heifetz (two types), Vari-Angle McFadden, Yasargil (two types), Scoville, Mayfield, Vari-Angle, Pivot, and Kapp. Phase homogeneity and crystal structure were analyzed by x-ray diffraction using a Phillips x-ray diffractometer. Clip deflection in an Oxford Research Systems MRI spectrometer was measured in our in vivo rat abdominal aortic aneurysm model. Results showed that the volume fraction of the martensitic phase in the various clips correlated with the magnitude of the deflection. Among the clips examined, the Yasargil, Sugita, Heifetz Elgiloy, and Vari-Angle McFadden had a nonmartensitic composition and did not deflect in the magnetic field. The Scoville contained 5% martensite and deflected only marginally. Martensite comprised 35% of the Mayfield clip, which deflected 45 degrees, and 90% of the Heifetz, Vari-Angle, Pivot, and Sundt-Kees Multi-Angle clips, which deflected approximately 70 degrees or slipped off the aneurysm.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance safety update 2002: Implants and devices

“…These factors can greatly influence the MR safety aspects of these implants. While certain aneurysm clips are a contraindication for the MR environment, others classified as nonferromagnetic or weakly ferromagnetic are deemed safe for patients or individuals exposed to MR systems operating at 1.5 Tesla or less (1)(2)(3)(4)(5)8,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24).…”

“…Previous reports investigating magnetic qualities of aneurysm clips indicated that aneurysm clips made from stainless steel alloy, Phynox, Elgiloy, commercially pure titanium, and titanium alloy were safe at 1.5 Tesla (1)(2)(3)5,8,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23). However, as previously discussed, few studies have been performed to evaluate magnetic field interactions for implants in association with MR systems operating above 1.5 Tesla.…”

Clinical safety of cardiac magnetic resonance imaging at 3 T early after stent placement for acute myocardial infarction

“…Even in that case, safety concerns cannot be excluded. Indeed, the literature reports that some devices once thought to have no ferromagnetic potential have been found to possess some of the qualities of ferrous metal [13,[17][18][19]. Explanations for this phenomenon have included the metallurgical composition of different alloys, heat treatment and the degree of cold working during the manufacturing process.…”

Aneurysm clips

“…The previous qualitative studies measuring the magnetic field in the MR unit and the movements of the clips may provide practical information regarding the magnetic characteristics of aneurysm clips (Dujovny et al 1984(Dujovny et al , 1985(Dujovny et al , 1994(Dujovny et al , 1996. However, their results should not be considered fully reliable, for the reasons explained earlier.…”