K-space trajectories in 3D-GRASE sequence for high resolution structural imaging

Purpose: To propose and evaluate new k-space trajectories for 3D-GRASE to improve scan time over 3D-FSE/TSE for high resolution structural imaging. Methods: Five different Cartesian k-space trajectories were developed and evaluated. They combine ideas of existing k-space trajectories for 3D-GRASE and 3D-FSE/TSE. T2 and T2* are linearly or radially modulated in k space to achieve the desired contrast while including the autocalibration region needed for the parallel imaging reconstruction technique. Phase modulation among echoes was corrected in reconstruction to remove remaining artefacts. Simulation and in-vivo experiments on a 3T scanner were conducted to evaluate the performance of the different k-space trajectories. Results: Two of the proposed k-space trajectories for high resolution structural imaging with 3D-GRASE obtained images comparable to 3D-FSE with lower specific absorption rate (PD/T2: 41%/75%) and shorter acquisition time (PD/T2: 27%/20%). Conclusions: 3D-GRASE image quality strongly depends on the k-space trajectory. With an optimal trajectory, 3D-GRASE may be preferable over 3D-FSE/TSE for structural high-resolution MRI.