An MR-SAFE nitinol guidewire design for intravascular applications

Abstract

Magnetic resonance imaging (MRI) o ers excellent soft tissue contrast and radiation free imaging. Conventional guidewires employ long metallic materials for versatility and mechanical characteristics, and are subject to RF-induced heating, therefore are inappropriate for use in MR. This work describes the design and testing of a metallic guidewire that is intrinsically MR-safe with preserved mechanical performance. The MR-safe guidewire was constructed using nitinol rod segments less than a quarter wavelength of RF transmission at 1.5 T within the body to eliminate standing wave formation, hence RF heating. The insulated nitinol segments were connected by short nitinol tubes for a sti ness-matched guidewire core. Mechanical integrity was tested in vitro according to ISO standards. RF-safety was evaluated in vitro according to ASTM standards, and in vivo in swine in a 1.5T MR system. Tests were performed on the prototype and a commercially available guidewire (Glidewire, Terumo, Japan) for comparison. Mechanical tests demonstrated that the segmented-core guidewire behaves similarly to its comparator. In vitro and in vivo RF heating tests con rmed that RF heating is under 2◦C as required by US Food and Drug Administration. The feasibility of an intrinsically safe passive metallic MRI guidewire design is demonstrated. The prototype exhibits negligible heating at high ip angles in conformance with FDA guidance documents (<2◦C), yet mechanically resembles a highperformance conventional metallic guidewire. This may represent a signi cant advance once applied to clinical MRI catheterization.|Keywords : Interventional MRI, intravascular guidewire, RF-safety, catheterization.