Volumetric imaging with homogenised excitation and static field at 9.4 T

MAGMA. 2016 Jun;29(3):333-45. doi: 10.1007/s10334-016-0543-6. Epub 2016 Mar 19.


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.

Keywords: 3D EPI; B0 shimming; Flip-angle homogenisation; MPRAGE; Parallel transmission; Ultra-high field MR.

MeSH terms

  • Brain / diagnostic imaging*
  • Brain / pathology
  • Brain / physiopathology
  • Brain Mapping / methods
  • Calibration
  • Contrast Media / chemistry
  • Echo-Planar Imaging*
  • Humans
  • Image Enhancement / methods*
  • Image Interpretation, Computer-Assisted / methods
  • Imaging, Three-Dimensional
  • Radio Waves
  • Workflow


  • Contrast Media