High-resolution gradient-recalled echo imaging at 9.4T using 16-channel parallel transmit simultaneous multislice spokes excitations with slice-by-slice flip angle homogenization

Tse, Desmond H. Y. , Wiggins, Christopher J. and Poser, Benedikt A. (2016) High-resolution gradient-recalled echo imaging at 9.4T using 16-channel parallel transmit simultaneous multislice spokes excitations with slice-by-slice flip angle homogenization. Magnetic Resonance in Medicine , . doi:10.1002/mrm.26501


Author Tse, Desmond H. Y.
Wiggins, Christopher J.
Poser, Benedikt A.
Title High-resolution gradient-recalled echo imaging at 9.4T using 16-channel parallel transmit simultaneous multislice spokes excitations with slice-by-slice flip angle homogenization
Journal name Magnetic Resonance in Medicine    Check publisher's open access policy
ISSN 1522-2594
0740-3194
Publication date 2016-10-23
Year available 2016
Sub-type Article (original research)
DOI 10.1002/mrm.26501
Open Access Status DOI
Total pages 9
Place of publication Hoboken, NJ, United States
Publisher John Wiley & Sons
Collection year 2017
Formatted abstract
Purpose
In order to fully benefit from the improved signal-to-noise and contrast-to-noise ratios at 9.4T, the challenges of math formula inhomogeneity and the long acquisition time of high-resolution 2D gradient-recalled echo (GRE) imaging were addressed.

Theory and Methods
Flip angle homogenized excitations were achieved by parallel transmission (pTx) of 3-spoke pulses, designed by magnitude least-squares optimization in a slice-by-slice fashion; the acquisition time reduction was achieved by simultaneous multislice (SMS) pulses. The slice-specific spokes complex radiofrequency scaling factors were applied to sinc waveforms on a per-channel basis and combined with the other pulses in an SMS slice group to form the final SMS-pTX pulse. Optimal spokes locations were derived from simulations.

Results
Flip angle maps from presaturation TurboFLASH showed improvement of flip angle homogenization with 3-spoke pulses over CP-mode excitation (normalized root-mean-square error [NRMSE] 0.357) as well as comparable excitation homogeneity across the single-band (NRMSE 0.119), SMS-2 (NRMSE 0.137), and SMS-3 (NRMSE 0.132) 3-spoke pulses. The application of the 3-spoke SMS-3 pulses in a 48-slice GRE protocol, which has an in-plane resolution of 0.28 × 0.28 mm, resulted in a 50% reduction of scan duration (total acquisition time 6:52 min including reference scans).

Conclusion
Time-efficient flip angle homogenized high-resolution GRE imaging at 9.4T was accomplished by using slice-specific SMS-pTx spokes excitations. Magn Reson Med, 2016. 
Keyword High-resolution GRE SMS-pTX
Magnitude least-squares
Parallel transmission
Simultaneous multislice
Spokes pulses
Ultrahigh-field MR
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: HERDC Pre-Audit
Centre for Advanced Imaging Publications
 
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