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Patient safety concept for multichannel transmit coils
Author(s) -
Seifert Frank,
Wübbeler Gerd,
Junge Sven,
Ittermann Bernd,
Rinneberg Herbert
Publication year - 2007
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.21149
Subject(s) - specific absorption rate , radio frequency , radiofrequency coil , finite difference time domain method , electromagnetic coil , imaging phantom , rf power amplifier , amplitude , rf probe , computer science , phase (matter) , acoustics , power (physics) , physics , optics , telecommunications , amplifier , antenna (radio) , bandwidth (computing) , quantum mechanics
Purpose To propose and illustrate a safety concept for multichannel transmit coils in MRI based on finite‐differences time‐domain (FDTD) simulations and validated by measurements. Materials and Methods FDTD simulations of specific absorption rate (SAR) distributions in a cylindrical agarose phantom were carried out for various radio frequency (RF) driving conditions of a four‐element coil array. Additionally, maps of transmit amplitude, signal phase, and temperature rise following RF heating were measured by MRI. Results Quantitative agreement was achieved between simulated and measured field distributions, thus validating the numerical modeling. When applying the same RF power to each element of the coil array but systematically varying the RF phase between its elements, the maximum of the SAR distribution was found to vary by a factor of about 15. Conclusion Our results demonstrate that current RF safety approaches are inadequate to deal with the new challenge of multichannel transmit coils. We propose a new concept based on a systematic investigation of the parameter space for RF phases and amplitudes. In this way the driving conditions generating the highest local SAR values per unit power can be identified and appropriately considered in the RF safety concept of a given MRI system. J. Magn. Reson. Imaging 2007;26:1315–1321. © 2007 Wiley‐Liss, Inc.