Correction of head movements in multi-slice EPI and single-slice gradient-echo functional MRI

The authors have investigated 2D and 3D registration techniques based on either simple rotational/translational movements or movements modeled as a first or second order polynomial to correct for assumed rigid and nonrigid body motion in fMRI. Data acquired with two different multi-slice echo planar imaging (EPI) systems and a single-slice conventional gradient-echo system (all at 1.5 T) were used to develop and evaluate the registration techniques. Two sets of data were acquired with EPI. In the first set, the subjects were asked to keep their head as stationary as possible while in the second set, subjects were asked to randomly move their head with displacements being on the order of 1 cm. Images from the second set were registered and compared to those obtained from the first set. Results show that 2D and 3D motion corrected images show lower variance to mean ratio than uncorrected images and that in most cases, polynomial based nonrigid body correction produces the lowest variance to mean ratios.