Zoomed imaging with calibration-free destructive B1+ shimming for rapid fMRI

Motivation: High-resolution MRI enables precise studies of specific brain regions but this comes at a cost of increased acquisition time. Goal(s): We examined if calibration-free destructive interferences can be introduced with simple static B1-shims for zoomed fMRI acquisitions. Approach: We optimised destructive B1 phase offsets and implemented these whilst assessing image quality in MPRAGE, tSNR in an EPI timeseries, flip angle distributions and |B1|. Results: Calibration-free destructive shims allowed reducing the field-of-view (50%) and acquisition-time (35%), while retaining good signal (higher B1 and similar tSNR) in the target (visual cortex). Impact: The calibration-free destructive B1 shims can be applied across brain regions with standard head coils and therefore translate across neuroscientific studies, while reducing acquisition-time and signal contributions from noise-prone areas. This may flexibly improve the spatial resolution and signal quality.