Design and Implementation of Novel Ear Shims to Enhance the Functional MRI at 5T and beyond

Motivation: High-field MRI (≥5 T) suffers from severe B0 inhomogeneities caused by magnetic susceptibility differences, especially in the inferior temporal cortices (ITCs), external auditory canals (EACs), and mastoid air cells (MACs). Goal(s): To address the localized bifocal B0 inhomogeneities around EACs and MACs, a novel local passive shim approach using ear shims was proposed and implemented. Approach: By optimizing the mass ratio of the biocompatible silicone/pyrolytic graphite (PG) mixture and incorporating additional embedded PG plates, the ΔB0 fields were significantly compensated. Results: In vivo experiments demonstrated a significant reduction in signal voids around EACs and MACs in GRE-echo echo planar imaging (EPI). Impact: The novel earplug enhances B0 homogeneity in the temporal lobe region, greatly improving the image quality of fMRI and supporting neuroscience research related to the temporal lobe region.