Dynamic B0 shimming of the motor cortex and cerebellum with a multicoil shim setup for BOLD fMRI at 9.4T

Magn Reson Med. 2020 May;83(5):1730-1740. doi: 10.1002/mrm.28044. Epub 2019 Nov 11.

Abstract

Purpose: We assessed how improved static magnetic field (B0 ) homogeneity with a dynamic multicoil shimming can influence the blood oxygen level dependent (BOLD) contrast to noise when echo planar imaging (EPI) sequence is used for a motor task functional MRI study. We showed that a multicoil shim setup can be a proper choice for dynamic shimming of 2 spatially distant areas with different inhomogeneity distributions.

Methods: A 16-channel multicoil shim setup is used to provide improved B0 homogeneity by dynamic slice-wise shimming. The performance of dynamic B0 shimming was investigated in 2 distinct brain regions, the motor cortex and the cerebellum, in the same experiment during a finger-tapping task. Temporal SNR (tSNR), geometric distortion of the EPIs, and results of an analysis with a general linear model before and after shimming with the multicoil were compared.

Results: Reduced B0 deviation by 30% and 52% in the cerebellum and motor cortex, respectively, resulted in higher tSNR and a reduction of distortions in the EPI. Statistical analysis applied to the EPIs showed higher t values and increased number of voxels above significance threshold when shimming with the multicoil setup.

Conclusions: Improved B0 homogeneity leads to higher tSNR and enhances the detection of BOLD signal.

Keywords: B0 inhomogeneity; BOLD signal; multicoil; shimming; temporal SNR; ultrahigh field.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Brain
  • Cerebellum / diagnostic imaging
  • Echo-Planar Imaging
  • Image Processing, Computer-Assisted
  • Magnetic Resonance Imaging*
  • Motor Cortex* / diagnostic imaging