Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods
- 29 April 2004
- journal article
- Published by IOP Publishing in Physics in Medicine & Biology
- Vol. 49 (10) , 1835-1851
- https://doi.org/10.1088/0031-9155/49/10/001
Abstract
The precise evaluation of electromagnetic field (EMF) distributions inside biological samples is becoming an increasingly important design requirement for high field MRI systems. In evaluating the induced fields caused by magnetic field gradients and RF transmitter coils, a multilayered dielectric spherical head model is proposed to provide a better understanding of electromagnetic interactions when compared to a traditional homogeneous head phantom. This paper presents Debye potential (DP) and Dyadic Green's function (DGF)-based solutions of the EMFs inside a head-sized, stratified sphere with similar radial conductivity and permittivity profiles as a human head. The DP approach is formulated for the symmetric case in which the source is a circular loop carrying a harmonic-formed current over a wide frequency range. The DGF method is developed for generic cases in which the source may be any kind of RF coil whose current distribution can be evaluated using the method of moments. The calculated EMFs can then be used to deduce MRI imaging parameters. The proposed methods, while not representing the full complexity of a head model, offer advantages in rapid prototyping as the computation times are much lower than a full finite difference time domain calculation using a complex head model. Test examples demonstrate the capability of the proposed models/methods. It is anticipated that this model will be of particular value for high field MRI applications, especially the rapid evaluation of RF resonator (surface and volume coils) and high performance gradient set designs.Keywords
This publication has 23 references indexed in Scilit:
- Different excitation and reception distributions with a single‐loop transmit‐receive surface coil near a head‐sized spherical phantom at 300 MHzMagnetic Resonance in Medicine, 2002
- Electric fields induced in a spherical volume conductor by temporally varying magnetic field gradientsPhysics in Medicine & Biology, 2002
- Effect of RF coil excitation on field inhomogeneity at ultra high fields: a field optimized TEM resonatorPublished by Elsevier ,2002
- Calculations of B1 distribution, SNR, and SAR for a surface coil adjacent to an anatomically‐accurate human body modelMagnetic Resonance in Medicine, 2001
- Sensitivity and Power Deposition in a High-Field Imaging ExperimentJournal of Magnetic Resonance Imaging, 2000
- A spherical slot array applicator for medical applicationsIEEE Transactions on Microwave Theory and Techniques, 1995
- Electromagnetic dyadic Green's function in spherically multilayered mediaIEEE Transactions on Microwave Theory and Techniques, 1994
- Gradient-Coil Design by Simulated AnnealingJournal of Magnetic Resonance, Series A, 1993
- Electric field induced in a spherical volume conductor from arbitrary coils: application to magnetic stimulation and MEGMedical & Biological Engineering & Computing, 1992
- Electromagnetic fields of surface coil in vivo NMR at high frequenciesMagnetic Resonance in Medicine, 1991