Magnetic field homogenization of the human prefrontal cortex with a set of localized electrical coils

Abstract

The prefrontal cortex is a common target brain structure in psychiatry and neuroscience due to its role in working memory and cognitive control. Large differences in magnetic susceptibility between the air‐filled sinuses and the tissue/bone in the frontal part of the human head cause a strong and highly localized magnetic field focus in the prefrontal cortex. As a result, image distortion and signal dropout are observed in MR imaging. A set of external electrical coils is presented that provides localized and high‐amplitude shim fields in the prefrontal cortex, with minimum impact on the rest of the brain when combined with regular zero‐ to second‐order spherical harmonics shimming. The experimental realization of the new shim method strongly minimized or even eliminated signal dropout in gradient‐echo images acquired at settings typically used in functional magnetic resonance at 4 T. Magn Reson Med, 2009.