Potential hazards and artifacts of ferromagnetic and nonferromagnetic surgical and dental materials and devices in nuclear magnetic resonance imaging.

Abstract

The risks to patients with metal surgical implants who are undergoing nuclear magnetic resonance (NMR) imaging and the artifacts caused by such implants were studied. Twenty-one aneurysm and other hemostatic clips and a variety of other materials (e.g., dental amalgam, 14 karat gold) were used. Longitudinal forces and torques were found to be exerted upon 16 of the 21 clips. With five aneurysm clips, forces and torques sufficient to produce risk of hemorrhage from dislocation of the clip from the vessel or aneurysm, or cerebral injury by clip displacement without dislodgement were identified. The induced ferromagnetism was shown to be related to the composition of the alloys from which the clips were manufactured. Clips with 10-14% nickel are evidently without sufficient induced ferromagnetism to cause hazard. The extent of NMR imaging artifacts was greater for materials with measurable ferromagnetic properties, but metals without measurable ferromagnetism in our tests also resulted in significant artifacts. Dental amalgam and 14 karat gold produced no imaging artifacts, but stainless steels in dentures and orthodontic braces produced extensive artifacts in the facial region.

Quantification of Force and Torque Applied by a High-Field Magnetic Resonance Imaging System on an Ultrasonic Motor for MRI-Guided Robot-Assisted Interventions

“…The torque was measured using the same method as in [23] except that the system was placed at the center of the bore. The angle of rotation, ϕ, was measured, and the torque was then calculated using (4).…”

Aneurysm Clips: Evaluation of Magnetic Field Interactions With an 8.0 T MR System

“…These clips were specifically selected for this investigation because they represent various types of clips made from nonferromagnetic or weakly ferromagnetic materials that are used in patients for temporary or permanent treatment of aneurysms or arteriovenous malformations. Additionally, these aneurysm clips have been reported to be safe for patients undergoing MR procedures using MR systems with static magnetic field strengths of 1.5 T or less (3)(4)(5)(6)(7)(8)(9)(10).…”

“…For the assessment of translational attraction, each aneurysm clip was suspended by a 30 cm long piece of thread and attached to a plastic protractor so that the angle of deflection from the vertical could be measured (2)(3)(4)6,7). This test was conducted at the position in the 8.0 T MR system where the spatial gradient of the magnetic field was determined to be at a maximum.…”

“…THE PRESENCE of an intracranial aneurysm clip in a patient or individual in the MR environment represents a potentially hazardous situation (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). For example, aneurysm clips made from martensitic stainless steels are an absolute contraindication to the use of MR procedures because excessive, magnet-related forces can displace them, causing serious injury or death (1,(3)(4)(5)(6)(7)(8)(9)(10).…”

“…For example, aneurysm clips made from martensitic stainless steels are an absolute contraindication to the use of MR procedures because excessive, magnet-related forces can displace them, causing serious injury or death (1,(3)(4)(5)(6)(7)(8)(9)(10). By comparison, aneurysm clips classified as "nonferromagnetic" or "weakly ferromagnetic" (eg, those made from Phynox, Elgiloy, austentitic stainless steels, titanium alloy, or commercially pure titanium) are considered safe for patients undergoing MR procedures using MR systems with static magnetic fields of 1.5 T or less (3)(4)(5)(6)(7)(8)(9)(10).…”