Parallel imaging techniques in functional MRI.

Originally developed for increased scanning velocity in cardiac imaging, parallel imaging (PI) techniques have recently also been applied for the reduction of artifacts in single-shot techniques. In functional brain imaging (fMRI) techniques, PI has been used for several purposes. It has been applied to reduce the distortions caused by the length of the echo-planar imaging readout, diminution of the gradient-related acoustic noise, as a means to increase acquisition speed or to increase the achievable brain coverage per unit time. In this article, the different applications of PI techniques in fMRI are reviewed, together with the basic theoretical background and the recently developed hardware necessary to achieve rapid, high signal-to-noise ratio PI-fMRI.