RF artifacts caused by metallic implants or instruments which get more prominent at 3 T: an in vitro study

Graf, Hansjörg; Lauer, Ulrike A.; Berger, Alexander; Schick, Fritz

doi:10.1016/j.mri.2004.12.009

Cited by 70 publications

(78 citation statements)

References 12 publications

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“…Thin sections should be acquired to achieve low through-plane displacement by decreasing the voxel size and reducing intra-voxel dephasing [31], though this reduces the SNR and is concomitant with a longer examination time as the number of averages needs to be raised to obtain a sufficient SNR.…”

Section: Mr Parametersmentioning

confidence: 99%

“…Therefore, the frequency encoding direction can be changed, e. g. anterior to posterior, to minimize artifact in the region of interest. The frequency encoding matrix should be increased to 512 with a corresponding adaptation of the phase encoding axis to achieve the smallest voxel size [31]. However, small voxels and increased receiver bandwidth are associated with a decreased SNR, which in turn can be alleviated with an increasing number of excitations.…”

Section: Mr Parametersmentioning

confidence: 99%

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CT and MRI Techniques for Imaging Around Orthopedic Hardware

Duong

Sutter

Skornitzke

et al. 2017

Fortschr Röntgenstr

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ZUSAMMENFASSUNGOrthopädische Implantate verringern die Bildqualität in der Schnittbildgebung. Bei steigendem Einsatz von orthopädi-schen Implantaten in einer alternden Bevölkerung ist eine Metallartefaktreduktion von zunehmender Bedeutung. Im folgenden Review möchten wir einen Überblick über die wesentlichen Artefakte in der Computertomografie und Magnetresonanztomografie sowie die neuesten Standards zur Verbesserung der Bildqualität geben. Alle Schritte der Bildakquisition von Gerätewahl über Scanvorbereitungen und -parameter bis hin zur Bildverarbeitung beeinflussen das Ausmaß der Metallartefakte. Technische Fortschritte wie die Dual-energy-Computertomografie mit der Option der Virtuellen monochromatischen Bildgebung sowie neue Implantatmaterialien bieten weitere Möglichkeiten der Metallartefaktreduktion in CT und MRT. Dezidierte MetallartefaktSequenzen beinhalten Algorithmen zur Artefaktreduktion und zur Verbesserung der Bildqualität des umgebenden Gewebes und sind essenzielle Werkzeuge in der orthopä-dischen Bildgebung zur frühzeitigen Detektion von postoperativen Komplikationen. ABSTR AC TOrthopedic hardware impairs image quality in cross-sectional imaging. With an increasing number of orthopedic implants in an aging population, the need to mitigate metal artifacts in computed tomography and magnetic resonance imaging is becoming increasingly relevant. This review provides an overview of the major artifacts in CT and MRI and state-ofthe-art solutions to improve image quality. All steps of image acquisition from device selection, scan preparations and parameters to image post-processing influence the magnitude of metal artifacts. Technological advances like dual-energy CT with the possibility of virtual monochromatic imaging (VMI) and new materials offer opportunities to further reduce artifacts in CT and MRI. Dedicated metal artifact reduction sequences contain algorithms to reduce artifacts and improve imaging of surrounding tissue and are essential tools in orthopedic imaging to detect postoperative complications in early stages.

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Section: Mr Parametersmentioning

confidence: 99%

Section: Mr Parametersmentioning

confidence: 99%

CT and MRI Techniques for Imaging Around Orthopedic Hardware

Duong

Sutter

Skornitzke

et al. 2017

Fortschr Röntgenstr

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“…16 In this study, an undesirable MRI phenomenon was used to measure induced currents. A uniform RF field is desired during an MRI scan, but in the presence of a wire, RF fields due to the induced current produces nonuniform RF fields, and consequently, a nonuniform flip angle 17 distribution in the vicinity of the wire. This nonuniform flip angle distribution was measured using the double angle method 18 in the vicinity of the wire.…”

Section: Iiib Experimental Verification Of Motlimmentioning

confidence: 99%

Modeling of radio‐frequency induced currents on lead wires during MR imaging using a modified transmission line method

Açıkel

Atalar

2011

Medical Physics

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Purpose: Metallic implants may cause serious tissue heating during magnetic resonance (MR) imaging. This heating occurs due to the induced currents caused by the radio-frequency (RF) field. Much work has been done to date to understand the relationship between the RF field and the induced currents. Most of these studies, however, were based purely on experimental or numerical methods. This study has three main purposes: (1) to define the RF heating properties of an implant lead using two parameters; (2) to develop an analytical formulation that directly explains the relationship between RF fields and induced currents; and (3) to form a basis for analysis of complex cases. Methods: In this study, a lumped element model of the transmission line was modified to model leads of implants inside the body. Using this model, leads are defined using two parameters: impedance per unit length, Z, and effective wavenumber along the lead, k t . These two parameters were obtained by using methods that are similar to the transmission line theory. As long as these parameters are known for a lead, currents induced in the lead can be obtained no matter how complex the lead geometry is. The currents induced in bare wire, lossy wire, and insulated wire were calculated using this new method which is called the modified transmission line method or MoTLiM. First, the calculated induced currents under uniform electric field distribution were solved and compared with method-of-moments (MoM) calculations. In addition, MoTLiM results were compared with those of phantom experiments. For experimental verification, the flip angle distortion due to the induced currents was used. The flip angle distribution around a wire was both measured by using flip angle imaging methods and calculated using current distribution obtained from the MoTLiM. Finally, these results were compared and an error analysis was carried out. Results: Bare perfect electric, bare lossy, and insulated perfect electric conductor wires under uniform and linearly varying electric field exposure were solved, both for 1.5 T and 3 T scanners, using both the MoTLiM and MoM. The results are in agreement within 10% mean-square error. The flip angle distribution that was obtained from experiments was compared along the azimuthal paths with different distances from the wire. The highest mean-square error was 20% among compared cases. Conclusions: A novel method was developed to define the RF heating properties of implant leads with two parameters and analyze the induced currents on implant leads that are exposed to electromagnetic fields in a lossy medium during a magnetic resonance imaging (MRI) scan. Some simple cases are examined to explain the MoTLiM and a basis is formed for the analysis of complex cases. The method presented shows the direct relationship between the incident RF field and the induced currents. In addition, the MoTLiM reveals the RF heating properties of the implant leads in terms of the physical features of the lead and electrical properties of the medium.

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“…Dynamic tracking of ferromagnetic materials is mostly used due to significant magnetic susceptibility artifacts when present inside the MRI during imaging [10] . Moreover, image acquisition delays offer a great challenge for real-time interventional MRI.…”

Section: Introductionmentioning

confidence: 99%

MRI-based dynamic tracking of an untethered ferromagnetic microcapsule navigating in liquid

Dahmen

Belharet

Folio

et al. 2016

International Journal of Optomechatronics

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The propulsion of ferromagnetic objects by means of MRI gradients is a promising approach to enable new forms of therapy. In this work, necessary techniques are presented to make this approach work. This includes path planning algorithms working on MRI data, ferromagnetic artifact imaging and a tracking algorithm which delivers position feedback for the ferromagnetic objects, and a propulsion sequence to enable interleaved magnetic propulsion and imaging. Using a dedicated software environment, integrating path-planning methods and real-time tracking, a clinical MRI system is adapted to provide this new functionality for controlled interventional targeted therapeutic applications. Through MRI-based sensing analysis, this article aims to propose a framework to plan a robust pathway to enhance the navigation ability to reach deep locations in the human body. The proposed approaches are validated with different experiments.

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RF artifacts caused by metallic implants or instruments which get more prominent at 3 T: an in vitro study

Cited by 70 publications

References 12 publications

CT and MRI Techniques for Imaging Around Orthopedic Hardware

CT and MRI Techniques for Imaging Around Orthopedic Hardware

Modeling of radio‐frequency induced currents on lead wires during MR imaging using a modified transmission line method

MRI-based dynamic tracking of an untethered ferromagnetic microcapsule navigating in liquid

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