Premium
Local SAR reduction in parallel excitation based on channel‐dependent Tikhonov parameters
Author(s) -
Cloos Martijn Anton,
Luong Michel,
Ferrand Guillaume,
Amadon Alexis,
Le Bihan Denis,
Boulant Nicolas
Publication year - 2010
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.22346
Subject(s) - specific absorption rate , tikhonov regularization , flip angle , electromagnetic coil , channel (broadcasting) , physics , parallel communication , excitation , computational physics , transmission (telecommunications) , optics , reduction (mathematics) , head (geology) , materials science , nuclear magnetic resonance , acoustics , computer science , mathematical analysis , geometry , mathematics , antenna (radio) , telecommunications , inverse problem , geology , magnetic resonance imaging , medicine , quantum mechanics , geomorphology , radiology
Purpose To reduce the local specific absorption rate (SAR) obtained with tailored pulses using parallel transmission while obtaining homogenous flip angle distributions. Materials and Methods Finite‐element simulations on a human head model were performed to obtain the individual magnetic and electric field maps for each channel of a parallel transmit array. From those maps, SAR calculations were carried out for “spoke” pulses designed to homogenize the flip angle in an axial slice of a human brain at 7 T. Based on the assumption that the coil element nearest to the maximum local energy deposition is the dominant contributor to the corresponding hot spot, a set of channel‐dependent Tikhonov parameters is optimized. Resulting SAR distributions are compared to the ones obtained when using standard pulse design approaches based on a single Tikhonov parameter. Results In both the small‐ and large‐tip‐angle domain, the simulations show local SAR reductions by over a factor of 2 (4) for a well‐centered (off‐centered) head model at the expense of roughly 1% increment in flip‐angle spread over the slice. Conclusion Significant SAR reductions can be obtained by optimizing channel‐dependent Tikhonov parameters based on the relation between coil elements and SAR hot spot positions. J. Magn. Reson. Imaging 2010;32:1209–1216. © 2010 Wiley‐Liss, Inc.