Receive coil arrays and parallel imaging for functional magnetic resonance imaging of the human brain

The use of multiple small receive coils has several advantages over a single larger (e.g. birdcage) coil. With an array of small receive coils, image signal-to-noise ratio (SNR) can be optimized throughout the field-of-view and the image acquisition process can be accelerated by use of parallel imaging (PI) techniques. In an accelerated PI experiment, data are undersampled during acquisition. Subsequently, artifact-free images are reconstructed based on the independently acquired signals from the elements of the receive coil array. PI techniques have recently been applied to functional MRI (fMRI) experiments of the human brain in order to improve the performance of commonly used single-shot techniques like echo-planar imaging (EPI). Potential benefits of PI-fMRI include the reduction of geometrical distortions due to off-resonance signals, the reduction of signal-loss in areas with substantial signal inhomogeneity, increases of the spatial and temporal resolution of the fMRI experiment and reduction of gradient acoustic noise. Although the loss in SNR, inherent to PI, can severely compromise MRI image quality, the effect on fMRI quality, which is governed by the temporal stability of the signal, is often not as severe. On the other hand, PI's potential in mitigating the often severe image artifacts present in single-shot fMRI render it an important tool, in particular with the recent surge in high field MRI applications.