Metallic artifacts on magnetic resonance images caused by multibracket appliances

概要

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Magnetic resonance imaging (MRI) often produces artifacts as a result of the mechanism of image construction. They include disappearance and distortion of the image caused by substances existing in and around the subject. We examined the effects of multibracket appliances for orthodontic treatment on MRI using various combinations of materials. Three types of MRI sequences, which are often employed in maxillofacial and craniofacial examinations, were used for this study with a 1.5 Tesla MRI. The range of impairment in each image was measured, and the following results were obtained. In the Spin Echo T1 weighted (SE T1) images, Fast Gradient Echo T2 weighted (FGR T2) images and fluid attenuated inversion recovery (FLAIR) images, we observed the largest impairment with orthodontic appliances that had metal brackets, archwire bent keyhole loops, ligature wires and a palatal bar. The smallest impairments were observed in images with ceramic brackets, archwire bent L-loops, elastic ligatures and no palatal bar. Currently, most orthodontic appliances use metal brackets and stainless-steel wires. Therefore multibracket appliances become a factor for artifacts with MRI. These results suggest that we must take into consideration the type of materials and shape of arch-wires when doing MRI and be aware of the possibility for artifacts in images of the maxillofacial area of patients with multibracket appliances.