Dynamic B0 Shimming of the Motor Cortex and Cerebellum with a Multicoil Shim Setup for BOLD fMRI at 9.4T

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

BOLD activation map in motor cortex and cerebellum during finger tapping from a single subject. The overlaid t‐value map is restricted to the voxels with t > 3 (P < .001 uncorrected). Better shimming with the multicoil is reflected in a larger activated cluster with higher t‐values. Activation maps are slightly smoothed for a better presentation.

In this work, we showed that a multicoil shim setup can be a proper choice for dynamic shimming of 2 spatially distant areas with different inhomogeneity distributions. We compare geometric distortions, tSNR, and the results of fMRI experiment at 9.4T with and without dynamic shimming using a 16‐channel multicoil shim setup. Dynamic shimming in this context describes slice‐specific shimming, that is, the shim values are optimized for individual slices and rapidly switch to proper settings from slice to slice. An fMRI study with 2 slice groups covering the motor cortex and the cerebellum was performed during a finger tapping task. Finger tapping is an appropriate way to target the cerebellar‐motor cortex network, given that it represents an excellent motor task which requires precise control of speed, force, and range of movement. Amount of residual image distortions and improvement in tSNR in the case of dynamic shimming were investigated for all the measurements. Shim settings were optimized for each slice individually and applied using the multicoil shim setup during measurement. Both regions were covered within the same measurement for reliable evaluation.

1.
Aghaeifar A, Bause J, Leks E, Grodd W, Scheffler K.
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.

 

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