Local SAR in parallel transmission pulse design
Name
Adalsteinsson_Local SAR.pdf
Size
4.73 MB
Format
Adobe PDF
Checksum (MD5)
1226e435ece5a3f389db5bf8b1b1a7ba
Author(s)
Lee, Joonsung
Gebhardt, Matthias
Adalsteinsson, Elfar
Wald, Lawrence
Date Issued
November 2011
Journal
Magnetic Resonance in Medicine
Publisher
Wiley Blackwell
Citation
Lee, Joonsung, Matthias Gebhardt, Lawrence L. Wald, and Elfar Adalsteinsson. “Local SAR in Parallel Transmission Pulse Design.” Magnetic Resonance Medicine 67, no. 6 (June 2012): 1566–1578.
Version
Author's final manuscript
Abstract
The management of local and global power deposition in human subjects (specific absorption rate, SAR) is a fundamental constraint to the application of parallel transmission (pTx) systems. Even though the pTx and single channel have to meet the same SAR requirements, the complex behavior of the spatial distribution of local SAR for transmission arrays poses problems that are not encountered in conventional single-channel systems and places additional requirements on pTx radio frequency pulse design. We propose a pTx pulse design method which builds on recent work to capture the spatial distribution of local SAR in numerical tissue models in a compressed parameterization in order to incorporate local SAR constraints within computation times that accommodate pTx pulse design during an in vivo magnetic resonance imaging scan. Additionally, the algorithm yields a protocol-specific ultimate peak in local SAR, which is shown to bound the achievable peak local SAR for a given excitation profile fidelity. The performance of the approach was demonstrated using a numerical human head model and a 7 Tesla eight-channel transmit array. The method reduced peak local 10 g SAR by 14–66% for slice-selective pTx excitations and 2D selective pTx excitations compared to a pTx pulse design constrained only by global SAR. The primary tradeoff incurred for reducing peak local SAR was an increase in global SAR, up to 34% for the evaluated examples, which is favorable in cases where local SAR constraints dominate the pulse applications.
MIT Department
Harvard University--MIT Division of Health Sciences and Technology
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Terms of Use
Creative Commons Attribution-Noncommercial-Share Alike
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1002/mrm.23140
