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Magn Reson Med. 2016 Oct;76(4):1158-69. doi: 10.1002/mrm.26020. Epub 2015 Oct 28.

Array-compressed parallel transmit pulse design.

Cao Z1,2, Yan X1,3, Grissom WA4,5,6,7.

Author information

1
Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.
2
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
3
Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA.
4
Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA. will.grissom@vanderbilt.edu.
5
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA. will.grissom@vanderbilt.edu.
6
Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA. will.grissom@vanderbilt.edu.
7
Department of Electrical Engineering, Vanderbilt University, Nashville, Tennessee, USA. will.grissom@vanderbilt.edu.

Abstract

PURPOSE:

To design array-compressed parallel transmit radiofrequency (RF) pulses and compare them to pulses designed with existing transmit array compression strategies.

THEORY AND METHODS:

Array-compressed parallel RF pulse design is proposed as the joint optimization of a matrix of complex-valued compression weights that relate a full-channel physical array to a reduced-channel virtual array, along with a set of RF pulses for the virtual array. In this way, the physics of the RF pulse application determine the coil combination weights. Array-compressed pulse design algorithms are described for four parallel transmit applications: accelerated two-dimensional spiral excitation, multislice RF shimming, small-tip-angle kT -points excitation, and slice-selective spokes refocusing. Array-compressed designs are compared in simulations and an experiment to pulses designed using four existing array compression strategies.

RESULTS:

In all cases, array-compressed pulses achieved the lowest root-mean-square excitation error among the array compression approaches. Low errors were generally achieved without increasing root-mean-square RF amplitudes or maximum local 10-gram specific absorption rate. Leave-one-out multisubject shimming simulations demonstrated that array-compressed RF shimming can identify useful fixed coil combination weights that perform well across a population.

CONCLUSION:

Array-compressed pulse design jointly identifies the transmit coil array compression weights and RF pulses that perform best for a specific parallel excitation application. Magn Reson Med 76:1158-1169, 2016. © 2015 Wiley Periodicals, Inc.

KEYWORDS:

RF pulse design; RF shimming; array compression; kT points pulses; optimization; parallel transmission; selective excitation; singular value decomposition; spokes pulses; tailored excitation

PMID:
26510117
PMCID:
PMC4848238
DOI:
10.1002/mrm.26020
[Indexed for MEDLINE]
Free PMC Article

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