Correcting B0 Field Distortions in MRI Caused by Stainless Steel Orthodontic Appliances at 1.5 T Using Permanent Magnets \u2013 A Head Phantom Study

Zhiyue J Wang,Michael C Morriss,Nancy K Rollins,Youngseob Seo,Rami R Hallac,Rajiv Chopra,Yonatan Chatzinoff,Trung Nguyen,Khyana Price,Yong Jong Park,Ana Nava

doi:10.1038/s41598-018-23890-6

Abstract

Susceptibility artifacts caused by stainless steel orthodontic appliances (braces) pose significant challenges in clinical brain MRI examinations. We introduced field correction device (FCD) utilizing permanent magnets to cancel the induced B0 inhomogeneity and mitigate geometric distortions in MRI. We evaluated a prototype FCD using a 3D-printed head phantom in this proof of concept study. The phantom was compartmented into anterior frontal lobe, temporal lobe, fronto-parieto-occipital lobe, basal ganglia and thalami, brain stem, and cerebellum and had built-in orthogonal gridlines to facilitate the quantification of geometric distortions and volume obliterations. Stainless steel braces were mounted on dental models of three different sizes with total induced magnetic moment 0.15 to 0.17 A·m2. With braces B0 standard deviation (SD) ranged from 2.8 to 3.7 ppm in the temporal and anterior frontal lobes vs. 0.2 to 0.3 ppm without braces. The volume of brain regions in diffusion weighted imaging was obliterated by 32–38% with braces vs. 0% without braces in the cerebellum. With the FCD the SD of B0 ranged from 0.3 to 1.2 ppm, and obliterated volume ranged from 0 to 6% in the corresponding brain areas. These results showed that FCD can effectively decrease susceptibility artifacts from orthodontic appliances.

Highlights

Brain magnetic resonance imaging (MRI) is often acquired while orthodontic appliances are in place for a wide variety of medical conditions
The susceptibility artifacts manifest in MR imaging and spectroscopy in many different ways, including severe geometric distortions and obliteration of tissue volumes especially in techniques using EPI readout, excessive line broadening in MR spectroscopy, failure of chemical shift selective excitation or saturations, etc[4]
The prototype field correction device (FCD) consists of permanent magnets and plastic materials providing structural support

Summary

Introduction

Brain magnetic resonance imaging (MRI) is often acquired while orthodontic appliances are in place for a wide variety of medical conditions. MRI relies on a highly uniform magnetic field to acquire images with diagnostic quality, but most stainless steel orthodontic appliances have large magnetic susceptibility www.nature.com/scientificreports/. The susceptibility artifacts manifest in MR imaging and spectroscopy in many different ways, including severe geometric distortions and obliteration of tissue volumes especially in techniques using EPI readout, excessive line broadening in MR spectroscopy, failure of chemical shift selective excitation or saturations, etc[4]. All of these problems can be addressed by restoring B0 field homogeneity. We present quantitative results on the improvement of B0 homogeneity and geometric distortions using a FCD prototype on a head phantom

Methods

Results

Conclusion