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Specific absorption rate reduction in parallel transmission by k ‐space adaptive radiofrequency pulse design
Author(s) -
Homann Hanno,
Graesslin Ingmar,
Nehrke Kay,
Findeklee Christian,
Dössel Olaf,
Börnert Peter
Publication year - 2011
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.22663
Subject(s) - specific absorption rate , computer science , shim (computing) , reduction (mathematics) , image quality , transmission (telecommunications) , homogeneity (statistics) , optics , nuclear magnetic resonance , materials science , physics , mathematics , computer vision , telecommunications , image (mathematics) , medicine , geometry , machine learning , erectile dysfunction , antenna (radio)
The specific absorption rate (SAR) is an important safety criterion, limiting many MR protocols with respect to the achievable contrast and scan duration. Parallel transmission enables control of the radiofrequency field in space and time and hence allows for SAR management. However, a trade‐off exists between radiofrequency pulse performance and SAR reduction. To overcome this problem, in this work, parallel transmit radiofrequency pulses are adapted to the position in sampling k ‐space. In the central k ‐space, highly homogeneous but SAR‐intensive radiofrequency shim settings are used to achieve optimal performance and contrast. In the outer k ‐space, the homogeneity requirement is relaxed to reduce the average SAR of the scan. The approach was experimentally verified on phantoms and volunteers using field echo and spin echo sequences. A reduction of the SAR by 25–50% was achieved without compromising image quality. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.