Dental material artifacts on MR images.

Hinshaw, David B.; Holshouser, Barbara A.; Engström, Hans; Tjan, Anthony H.L.; Christiansen, Edwin L.; Catelli, W F

doi:10.1148/radiology.166.3.3340777

Cited by 56 publications

(42 citation statements)

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“…Artefact size can be classified in different categories, depending on the level of extinction and distortion. 15 However, categories such as artefacts ,2, 3-5 or .5 cm are imprecise. Also indicating the artefact size on a millimetre range is inefficient for clinical use, since further inaccuracies have to be expected with this method; data obtained from a software-based measurement tool need to be evaluated by the user to define the border of the artefact zone.…”

Section: Discussionmentioning

confidence: 99%

MRI with intraoral orthodontic appliance—a comparativein vitroandin vivostudy of image artefacts at 1.5 T

Zachriat¹,

Asbach²,

Blankenstein³

et al. 2015

Dentomaxillofacial Radiology

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Objectives: We investigated artefacts caused from orthodontic appliances at 1.5-T MRI of the head and neck region and whether the image quality can be improved utilizing the artefact-minimizing sequence WARP. Methods: In vitro tests were performed by phantom measurements of different orthodontic devices applying different types of MR sequences [echoplanar imaging (EPI), turbo spin echo (TSE) and TSE-WARP, gradient echo (GRE)]. Two independent readers determined after calibration the level of artefacts. Subsequently, the interobserver agreement was calculated. The measurement of artefacts was based on the American Society for Testing Materials Standard F 2119-07. For in vivo imaging, one test person was scanned with an inserted multibracket appliance. The level of artefacts for 27 target regions was evaluated. Results: In vitro: ceramic brackets and ferromagnetic steel brackets produced artefact radii up to 1.12 and 7.40 cm, respectively. WARP reduced these artefacts by an average of 32.7%. The Bland-Altman-Plot indicated that maximum measurement differences of 3 mm have to be expected with two calibrated observers. In vivo: the EPI sequence for brain imaging was not analysable. The TSE sequence of the brain did not demonstrate artefacts except for the nasal cavity. Conversely, the TSE sequence of the cervical spine revealed severe artefacts in the midface region. The GRE sequence appeared to be more susceptible to artefacts than did the TSE sequence. Conclusions: In vitro measurements allow an estimation of the in vivo artefact size. Orthodontic appliances may often remain intraorally when performing MRI. WARP showed a more significant effect in vitro than in vivo. Dentomaxillofacial Radiology (2015Radiology ( ) 44, 20140416. doi: 10.1259 Cite this article as: Zachriat C, Asbach P, Blankenstein KI, Peroz I, Blankenstein FH. MRI with intraoral orthodontic appliance-a comparative in vitro and in vivo study of image artefacts at 1.5 T. Dentomaxillofac Radiol 2015; 44: 20140416.

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Section: Discussionmentioning

confidence: 99%

MRI with intraoral orthodontic appliance—a comparativein vitroandin vivostudy of image artefacts at 1.5 T

Zachriat¹,

Asbach²,

Blankenstein³

et al. 2015

Dentomaxillofacial Radiology

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“…(3) For stationary spins, the program only recalculates the strength of the secondary magnetic field when the gradient amplitudes are changed. (4) During signal sampling, which is by far the largest part of the event sequence, the program uses "sine" and "cosine" look-up tables when the real and imaginary k-space signal amplitudes ( M y y . cos A and Mx,, * sin A) are calculated, provided that an integer representation (normally 10 bits of precision) of the angle A is chosen.…”

Section: Discussionmentioning

confidence: 99%

“…[5] where 5 = t y (G, x + G,,y + G, z ) , i.e., the angle offset at each spatial position at time t. Gi is the gradient amplitude and y is the gyromagnetic ratio. 4) Another problem related to the limited number of subvectors is effects caused by diffusion. The initial amplitude of each subvector was reduced by the diffusion factor exp(-Dy2G2T~/12), before the start of the event sequence, assuming a static gradient field with amplitude G, i.e., close to a metallic object, and an isotropic diffusion coefficient D (19).…”

Section: Problems Related To the Limited Number Of Spins In Each Voxelmentioning

confidence: 99%

A computer simulation program for mr imaging: application to rf and static magnetic field imperfections

Olsson¹,

Wirestam²,

Persson³

1995

Magnetic Resonance in Med

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A computer simulation program capable of demonstrating various artifacts, such as image distortion caused by metallic implants in MR imaging, is presented. The structure of the program allows for the implementation of various imaging situations as long as spins only experience weak interaction, i.e., the Bloch equations are obeyed. The raw data are obtained by repeatedly applying the Bloch equations to the magnetization vector of each point of the simulated object, throughout the pulse sequence. With only a limited number of spins in each voxel, the effects of intravoxel dephasing and rephasing require special attention, and algorithms for this have been implemented.

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“…dextermag.com/N3830), with the shape of rectangular prism and dimensions of 1.3 × 1.3 × 5.0 mm 3 with Ni coating and fully magnetized along the long axis. This material has an intrinsic coercivity of 2387 kA/m (corresponding to 3 T in a vacuum) at 20…”

Section: C Testing the Measurement Of Both Transverse And Longitudmentioning

confidence: 99%

Induced magnetic moment in stainless steel components of orthodontic appliances in 1.5 T MRI scanners

et al. 2015

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Purpose: Most orthodontic appliances are made of stainless steel materials and induce severe magnetic susceptibility artifacts in brain MRI. In an effort for correcting these artifacts, it is important to know the value of induced magnetic moments in all parts of orthodontic appliances. In this study, the induced magnetic moment of stainless steel orthodontic brackets, molar bands, and arch-wires from several vendors is measured. Methods: Individual stainless steel brackets, molar bands, and short segments of arch-wire were positioned in the center of spherical flask filled with water through a thin plastic rod. The induced magnetic moment at 1.5 T was determined by fitting the B 0 map to the z-component of the magnetic dipole field using a computer routine.

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Dental material artifacts on MR images.

Cited by 56 publications

References 0 publications

MRI with intraoral orthodontic appliance—a comparativein vitroandin vivostudy of image artefacts at 1.5 T

MRI with intraoral orthodontic appliance—a comparativein vitroandin vivostudy of image artefacts at 1.5 T

A computer simulation program for mr imaging: application to rf and static magnetic field imperfections

Induced magnetic moment in stainless steel components of orthodontic appliances in 1.5 T MRI scanners

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