Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods

Liu, F. and Crozier, S. (2004) Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods. Physics In Medicine And Biology, 49 10: 1835-1851. doi:10.1088/0031-9155/49/10/001


Author Liu, F.
Crozier, S.
Title Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods
Journal name Physics In Medicine And Biology   Check publisher's open access policy
ISSN 0031-9155
Publication date 2004-01-01
Sub-type Article (original research)
DOI 10.1088/0031-9155/49/10/001
Volume 49
Issue 10
Start page 1835
End page 1851
Total pages 17
Editor Beddoe, A.
Place of publication Bristol
Publisher IOP Publishing
Language eng
Subject C1
291500 Biomedical Engineering
671402 Medical instrumentation
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.
Keyword Engineering, Biomedical
Radiology, Nuclear Medicine & Medical Imaging
Dyadic Greens-function
Magnetic Stimulation
Surface Coil
Human-body
Volume Conductor
Computation
Excitation
Deposition
Gradients
Brain
Q-Index Code C1

 
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Created: Wed, 15 Aug 2007, 13:52:23 EST