SU‐C‐19A‐03: Evaluation of Common Material Magnetic Susceptibility Effects for Immobilization Devices Used in MRI‐Guided Therapies

Abstract

Purpose:Phase variations induced by magnetic susceptibility differences of materials used for immobilization can result in localized signal dropout and spatial distortions on MR images. The goal of this study was to determine an optimal material for immobilization device construction that minimizes the effect of susceptibility on adjacent tissues.Methods:A total of 30 thermoset and thermoplastic material samples were included in the study. Each material sample was precision machined to dimensions of 11.1 × 23.8 × 123.8 mm3. During imaging, the samples were placed adjacent to a ball phantom with the long axis oriented parallel to the magnetic field. Imaging was performed at 3T using a GRE‐EPI sequence (FOV/matrix: 24cm2/128×128, TE/TR: 59/2000ms, rBW: 125 kHz, TH: 3mm). High order shimming was optimized once prior to acquisition. Phase images were reconstructed and unwrapped offline. Relative phase induced by the ith material was determined by subtracting the mean phase over a 3×3 kernel at the phantom center from the mean phase over a 3×3 kernel at a position of maximal phase‐induced change. Phase differences (Δϕ) induced by the ith material were determined by subtracting the relative phase with no sample from the relative phase with sample. Mann‐Whitney and Kruskal‐Wallis tests were used to determine whether significant differences in Δϕ existed between and among material categories.Results:In general, glass‐cloth resin reinforced materials produced the smallest phase differences, with G‐9 fiberglass producing the smallest phase difference of all materials studied. Significant phase differences were found between thermoset and thermoplastic materials (p=0.0002). Within the thermosets group, significant differences were found between glass‐cloth based materials relative to other thermosets (p=0.0157).Conclusions:Glass‐cloth resinreinforced thermosets, specifically G‐9 fiberglass, produced the smallest phase differences of all materials studied, and are recommended for construction of immobilization devices used in MR imaging and MRIguided therapies.Funding provided by Advancing a Healthier Wisconsin.