Motion artifacts reduction in DWI using navigator echoes: a robust and simple correction scheme

NMR signal phase variation caused by macroscopic motion of an object during application of the diffusion gradient is a well-known effect in diffusion-weighted imaging (DWI) using the standard pulsed gradient spin-echo sequence (PGSE). This phase error causes severe ghost artifacts in the output image when phase encoding techniques, such as two dimensional Fourier transform (2DFT) imaging, are used. One possible way to eliminate the motion effects is the navigator echo technique. The method is based on estimating the phase error from the navigator echo and using it for the correction of the image echo. The phase errors (zero and first order) for the phase correction of the image echo are usually evaluated from the navigator echo after Fourier transform (FT) in the readout direction, correcting for both translation and rotation. We present here a simple algorithm which enables evaluation and correction in the time domain of phase errors induced by motion. This approach has the advantage of improved correction of motional artifacts and minimized sensitivity to noise and inaccurate setting up of the experiment.