Volumetric imaging with homogenised excitation and static field at 9.4 T

Desmond H. Y. Tse*, Christopher J. Wiggins, Dimo Ivanov, Daniel Brenner, Jens Hoffmann, Christian Mirkes, Gunamony Shajan, Klaus Scheffler, Kamil Uludag, Benedikt A. Poser

*Corresponding author for this work

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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 T 2 (*) -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 B 1 (+) voids eliminated. The SNR inhomogeneities and contrast variations in the T1- and T 2 (*) -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.

Original languageEnglish
Pages (from-to)333-345
Number of pages13
JournalMagnetic Resonance Materials in Physics Biology and Medicine
Volume29
Issue number3
Early online date19 Mar 2016
DOIs
Publication statusPublished - Jun 2016

Keywords

  • Ultra-high field MR
  • Parallel transmission
  • B-0 shimming
  • Flip-angle homogenisation
  • MPRAGE
  • 3D EPI
  • ECHO-PLANAR
  • HUMAN BRAIN
  • NUCLEAR-MAGNETIC-RESONANCE
  • SUSCEPTIBILITY
  • FUNCTIONAL MRI
  • NOISE RATIO
  • RF PULSES
  • PARALLEL-TRANSMISSION
  • GEOMETRIC DISTORTION
  • GRADIENT-ECHO

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