title: Volumetric imaging with homogenised excitation and static field at 9.4 T.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands. desmond.tse@maastrichtuniversity.nl.
authors.forename: Desmond H Y
authors.initials: DH
authors.lastname: Tse
authors.affiliation: Scannexus BV, Maastricht, The Netherlands.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Wiggins
authors.affiliation: Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: Dimo
authors.initials: D
authors.lastname: Ivanov
authors.affiliation: German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Brenner
authors.affiliation: High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Hoffmann
authors.affiliation: High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.|Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Mirkes
authors.affiliation: High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.
authors.forename: Gunamony
authors.initials: G
authors.lastname: Shajan
authors.affiliation: High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.|Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Scheffler
authors.affiliation: Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.|Scannexus BV, Maastricht, The Netherlands.
authors.forename: Kâmil
authors.initials: K
authors.lastname: Uludağ
authors.affiliation: Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: Benedikt A
authors.initials: BA
authors.lastname: Poser
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D001931:Brain Mapping / Q000379:methods; D002138:Calibration; D003287:Contrast Media / Q000737:chemistry; D017352:Echo-Planar Imaging; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional; D011846:Radio Waves; D057188:Workflow
chemical_list: D003287:Contrast Media
keywords: 3D EPI; B0 shimming; Flip-angle homogenisation; MPRAGE; Parallel transmission; Ultra-high field MR