Selective averaging for the diffusion tensor measurement

The multishot echo planar imaging sequence was often used in the high-resolution diffusion measurements. However, it is susceptible to motion artifacts because of the requirements of combining the raw data from different acquisitions into one complete k-space data set. Conventional solutions used cardiac gating but greatly extended the total acquisition time. Here we propose a selective averaging algorithm based on the information in the navigator echoes. The data were sampled continuously without cardiac gating. Contributions contaminated by motion were detected by a thresholding algorithm and were discarded during postprocessing. The data were then averaged in the modulus or complex format. Diffusion tensor imaging (DTI) data with isotropic spatial resolution were acquired in phantom as well as from two normal volunteers. The information in the navigator echoes proved to be a good indicator for the extent of motion contamination. Differences were noticed between modulus and complex averaging in DTI quantification, but both showed reduced artifact and improved signal-to-noise ratio.