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RF Current Density Imaging in Homogeneous Media
Author(s) -
Scott G. C.,
Joy M. L. G.,
Armstrong R. L.,
Henkelman R. M.
Publication year - 1992
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910280203
Subject(s) - displacement current , nuclear magnetic resonance , imaging phantom , current density , current (fluid) , eddy current , radio frequency , magnetic field , materials science , specific absorption rate , rf power amplifier , electrical conductor , dielectric heating , dielectric , physics , optics , optoelectronics , computer science , antenna (radio) , amplifier , cmos , quantum mechanics , composite material , thermodynamics , telecommunications
MRI has proven capable of imaging quasistatic volume current densities in electrolytic and biological media. In this paper, the feasibility of extending the method to image RF current density at the Larmor frequency is studied. RF current imaging could be relevant to MR power absorption and safety and to hyperthermia analysis, as well as creating dielectric and conductivity‐dependent tissue contrast. The approach is to deliberately induce or inject RF currents in a sample synchronous with an MR pulse sequence and measure the resulting transverse RF magnetic field components. Current density is extracted by computing the curl of the magnetic fields. The preliminary theory has been developed for uniform media where both displacement and conduction currents exist while skin effects or eddy currents are absent. If the derivative in the B O direction of the RF magnetic field component parallel to B O is negligible, then sufficient information exists to reconstruct the RF current density component that is parallel to B O without rotating the sample. The relative phase of the current can also be estimated. The method has been proven feasible by successfully imaging a uniform 85.6‐MHz current density in a salt water phantom. The experiment conforms closely to capacitively coupled hyperthermia heating.© 1992 Academic Press,Inc.