Kwan-Jin Jung1, Tiejun Zhao2
1Scientific Imaging Brain Research
(SIBR), Department of Psychology, Carnegie Mellon University, Pittsburgh, PA,
United States; 2MR R&D Collaborations, Siemens Medical
Solutionsn USA, Siemens Healthcare, Pittsburgh, PA, United States
Parallel imaging with acceleration was noted to pronounce the ripple artifact near the susceptibility-affected region in the gradient echo EPI for BOLD fMRI. Using the extended EPI sequence, which collected extended readouts outside the regular data acquisition window, the pronounced ripple artifact was analyzed and found to be caused by an increased echo shift in the pre-TE period in accelerated parallel imaging. This was also confirmed by theoretical derivation of the echo shift due to the magnetic field susceptibility. A new EPI sequence was developed to reduce the ripple artifact as well as to restore the signal level to the level of un-accelerated parallel imaging by applying the acceleration asymmetrically only to the post-TE period. The un-accelerated portion in the pre-TE period utilized the delay for the optimum BOLD sensitivity at 3T, maintaining the same slice coverage as the conventional acceleration in both pre- and post-TE periods.