Resolution adapted finite element modeling of radio frequency interactions on conductive resonant structures in MRI

• Published in: Magnetic resonance in medicine 2012-05, Vol.67 (5), p.1444-1452
• Main Authors: Ruoff, Jürgen, Würslin, Christian, Graf, Hansjörg, Schick, Fritz
• Format: Article
• Language: English
• Subjects: Electric Conductivity; Finite Element Analysis; heating; Image Interpretation, Computer-Assisted - methods; magnetic resonance compatibility of implants; magnetic resonance compatibility of instruments; Magnetic Resonance Imaging - methods; magnetic resonance safety; Manufactured Materials; Metals; Prostheses and Implants; Radio Waves; radiofrequency simulations; Reproducibility of Results; Sensitivity and Specificity
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.23109

Prediction of interactions between the radiofrequency electromagnetic field in magnetic resonance scanners and electrically conductive material surrounded by tissue plays an increasing role for magnetic resonance safety. Testing of conductive implants or instruments is usually performed by standardized experimental setups and temperature measurements at distinct geometrical points, which cannot always reflect worst‐case situations. A finite element method based on Matlab (The Mathworks, Natick, MA) and the finite element method program Comsol Multiphysics (Stockholm, Sweden) with a spatially highly variable mesh size solving Maxwell's full‐wave equations was applied for a comprehensive simulation of the complete geometrical arrangement of typical birdcage radiofrequency coils loaded with small conductive structures in a homogenous medium. Conductive implants like rods of variable length and closed and open ring structures, partly exhibiting electromagnetic resonance behavior, were modeled and evaluated regarding the distribution of the B1‐ and E‐field, induced currents and specific absorption rates. Numerical simulations corresponded well with experiments using a spin‐echo sequence for visualization of marked B1‐field inhomogeneities. Even resonance effects in conductive rods and open rings with suitable geometry were depicted accurately. The proposed method has high potential for complementation or even replacement of common experimental magnetic resonance compatibility measurements. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.