Volumetric imaging with homogenised excitation and static field at 9.4 T

Tse, Desmond H. Y., Wiggins, Christopher J., Ivanov, Dimo, Brenner, Daniel, Hoffmann, Jens, Mirkes, Christian, Shajan, Gunamony, Scheffler, Klaus, Uludag, Kamil and Poser, Benedikt A. (2016) Volumetric imaging with homogenised excitation and static field at 9.4 T. Magnetic Resonance Materials in Physics Biology and Medicine, 29 3: 333-345. doi:10.1007/s10334-016-0543-6

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Author Tse, Desmond H. Y.
Wiggins, Christopher J.
Ivanov, Dimo
Brenner, Daniel
Hoffmann, Jens
Mirkes, Christian
Shajan, Gunamony
Scheffler, Klaus
Uludag, Kamil
Poser, Benedikt A.
Title Volumetric imaging with homogenised excitation and static field at 9.4 T
Journal name Magnetic Resonance Materials in Physics Biology and Medicine   Check publisher's open access policy
ISSN 0968-5243
1352-8661
Publication date 2016-06-01
Year available 2016
Sub-type Article (original research)
DOI 10.1007/s10334-016-0543-6
Open Access Status DOI
Volume 29
Issue 3
Start page 333
End page 345
Total pages 13
Place of publication Heidelberg, Germany
Publisher Springer
Collection year 2017
Language eng
Formatted abstract
Objectives
To overcome the challenges of B0 and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B0 and flip-angle homogenisation was implemented on a human 9.4 T scanner.

Materials and methods
Imaging was performed with a 9.4 T human MR scanner (Siemens Medical Solutions, Erlangen, Germany) using a 16-channel parallel transmission system. B0- and B1-mapping were done using a dual-echo GRE and transmit phase-encoded DREAM, respectively. B0 shims and a small-tip-angle-approximation kT-points pulse were calculated with an off-line routine and applied to acquire T1- and T2*-weighted images with MPRAGE and 3D EPI, respectively.

Results
Over six in vivo acquisitions, the B0-distribution in a region-of-interest defined by a brain mask was reduced down to a full-width-half-maximum of 0.10 ± 0.01 ppm (39 ± 2 Hz). Utilising the kT-points pulses, the normalised RMSE of the excitation was decreased from CP-mode’s 30.5 ± 0.9 to 9.2 ± 0.7 % with all B1+ voids eliminated. The SNR inhomogeneities and contrast variations in the T1- and T2*-weighted volumetric images were greatly reduced which led to successful tissue segmentation of the T1-weighted image.

Conclusion
A 15-minute B0- and flip-angle homogenisation workflow, including the B0- and B1-map acquisitions, was successfully implemented and enabled us to reduce intensity and contrast variations as well as echo-planar image distortions in 9.4 T images.
Keyword 3D EPI
B0 shimming
Flip-angle homogenisation
MPRAGE
Parallel transmission
Ultra-high 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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