Automatic Functional and Anatomical Registration for fMRI using Optimized 3D Flyback Echo Planar Imaging

INTRODUCTION: Echo planar imaging (EPI) is the most widely used method for functional MRI (fMRI). However, functional images are often distorted because EPI is highly sensitive to field inhomogeneities, eddy currents, and gradient delays. The slow traversal in kspace along the phase encode (PE) direction exacerbates these distortions. Hence, functional and anatomical image registration is complicated by these distortions and by the fact that each image is obtained with a different imaging sequence. Special fMRI sequences [1, 2] as well as linear [3, 4] and non-linear [5-7] registration methods have been developed to address this problem. However, none of these methods automatically yield usable anatomical and functional images that may be directly overlaid onto each other with no post-processing. This work investigates the use of an optimized 3D flyback EPI trajectory with echo time shifting (ETS) [8] to solve this issue efficiently and with no post-processing. Here, the robustness of flyback EPI to eddy currents and gradient delays is combined with the high SNR efficiency and reduced signal dropout offered by passband steady-state free precession (SSFP) fMRI [912], although the same optimization method applies to GRE BOLD. The result is high quality functional and high resolution anatomical images that have minimal distortions and are inherently self co-registered.