Numerical approach to investigate MR imaging artifacts from orthopedic implants at different field strengths according to ASTM F2119.

Objective: This study presents an extended evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment.

Methods: The numerical approach is validated by comparing the artifact shape of the simulations and measurements of two metallic orthopedic implants at three different field strengths (1.5 T, 3 T, and 7 T).

Development and evaluation of a numerical simulation approach to predict metal artifacts from passive implants in MRI.

Objective: This study presents the development and evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment that can be applied to improve the testing procedure for MR image artifacts in medical implants according to ASTM F2119.

Methods: The numerical approach is validated by comparing simulations and measurements of two metallic test objects made of titanium and stainless steel at three different field strengths (1.5T, 3T and 7T).

Safety evaluation of a new setup for transcranial electric stimulation during magnetic resonance imaging.

Background: Transcranial electric stimulation during MR imaging can introduce safety issues due to coupling of the RF field with the stimulation electrodes and leads.

Objective: To optimize the stimulation setup for MR current density imaging (MRCDI) and increase maximum stimulation current, a new low-conductivity (σ = 29.4 S/m) lead wire is designed and tested.

[Test methods to determine magnetic resonance (MR) safety and MR image compatibility of implants/devices].

Methodical Innovations: In the present article, interactions associated with magnetic resonance (MR) procedures and MR test procedures for implants/devices are examined.

Performance: Since 2012, many interactions of items with MR procedures have been physically described and translated into standardized ASTM and ISO testing procedures. Despite the standardized procedures, the determination of the test method to use is an important decision.

Radiofrequency induced heating around aneurysm clips using a generic birdcage head coil at 7 Tesla under consideration of the minimum distance to decouple multiple aneurysm clips.

Purpose: To evaluate radiofrequency (RF) induced tissue heating around aneurysm clips during a 7T head MR examination and to determine the decoupling distance between multiple implanted clips.

Methods: A total of 120 RF exposure scenarios of clinical relevance were studied using specific absorption rate and temperature simulations. Variations between scenarios included 2 clips (18.

Radio frequency induced heating of an insulated wire during magnetic resonance imaging.

Radio frequency (RF) induced power deposition near straight insulated leads excited by different incident electrical field profiles was investigated. 3-D electromagnetic (EM) simulations were used to obtain implant models as well as RF-induced power depositions calculated as the integral of power loss density. For the investigated setups up to 400% discrepancy between the implant model predictions and EM simulation values was observed.

Variation of radio frequency induced power deposition due to second surrounding tissue.

We investigated RF-induced power deposition (p) generated by insulated leads with different lengths located in proximity to two tissues. The first tissue surrounding the leads was shaped as a cylinder with a diameter of 11 mm and located in a very large box filled with the second tissue. Lead electromagnetic models and p substantially depended on electrical properties of both tissues.

In vitro and in silico assessment of RF-induced heating around intracranial aneurysm clips at 7 Tesla.

Purpose: To examine radiofrequency-induced tissue heating around intracranial aneurysm clips during a 7 Tesla (T) head MR examination.

Methods: Radiofrequency (RF), temperature simulations, and RF measurements were employed to investigate the effects of polarization and clip length on the electric field (E-field) and temperature. Heating in body models was studied using both a conservative approach and realistic exposure scenarios.

Experience with magnetic resonance imaging of human subjects with passive implants and tattoos at 7 T: a retrospective study.

Object: Over the last decade, the number of clinical MRI studies at 7 T has increased dramatically. Since only limited information about the safety of implants/tattoos is available at 7 T, many centers either conservatively exclude all subjects with implants/tattoos or have started to perform dedicated tests for selected implants. This work presents our experience in imaging volunteers with implants/tattoos at 7 T over the last seven and a half years.

A phantom and animal study of temperature changes during fMRI with intracerebral depth electrodes.

Background: MRI is routinely used in patients undergoing intracerebral electroencephalography (icEEG) in order to precisely locate the position of intracerebral electrodes. In contrast, fMRI has been considered unsafe due to suspected greater risk of radiofrequency-induced (RF) tissue heating at the vicinity of intracerebral electrodes. We determined the possible temperature change at the tip of such electrodes during fMRI sessions in phantom and animals.

Testing methods for MR safety and compatibility of medical devices.

Magnetic resonance (MR) safety and image compatibility are important issues when using medical devices in the environment of magnetic resonance imaging (MRI). MR testing of medical devices is required for device approval by the FDA and the EU notified bodies. Testing methods have been established for basic issues and were published as first ASTM International standards (formerly ASTM, the American Society of Testing and Materials).