A dual echo approach to motion correction for functional connectivity studies

The effect of subject head movement on functional connectivity as measured by BOLD (blood oxygen level dependent) fMRI was investigated; movement mainly introduced increases in connectivity into the dataset. The effect of movement on connectivity is an important consideration when comparing patients suffering from neurological conditions to healthy controls, since it is well known that patients affected by such conditions are prone to move more in the scanner than healthy subjects. A method of motion correction utilising a dual echo EPI sequence is described. The first echo is acquired soon after the slice excitation (TE(1)=10ms) when BOLD contrast is low and the MR signal is mainly sensitive to movement related effects, while the second echo is acquired at an echo time (TE(2)=30ms) at which the MR signal is sensitive to both BOLD and movement related effects. To correct for additional signal variance introduced by subject movement, the second echo image is divided by the first echo image at each time point across the length of the scan. This procedure is easy to implement and requires no extra scan time. This method proved superior to the standard means of correction whereby realignment parameters and their first order derivatives are used as covariates of no interest in a linear regression model.