Three-Dimensional Evaluation of Dental Metallic Artifacts on Magnetic Resonance Images : Effects of Frequency and Phase-Encoding Direction

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The purpose of this study was to clarify the effects of imaging direction on susceptibility artifacts caused by dental metallic materials in magnetic resonance images. Magnetic resonance images of five silver alloy cubes (each 5 mm in diameter) were obtained using a 1.5-Tesla superconducting magnetic resonance imager. The images were divided into two groups and comparisons of shapes and artifact volumes were performed. In the perpendicular group (Per-group), the direction of the static magnetic field (B0) and the frequency-encoding direction were perpendicular, while in the Parallel group (Pal-group), the direction of B0 and the frequency-encoding direction were parallel. Metal artifacts in both groups consisted of a signal void around the cubes and a high-signal area along B0, although the shapes were different between the groups. The magnitude of the artifacts tended to be larger, although not significantly larger, in the Pal-group than in the Per-group. We concluded that the directions of the static magnetic field and frequency encoding have effects on the three-dimensional extension of metallic artifacts in magnetic resonance images.