Improving the performance of diffusion-weighted inner field-of-view echo-planar imaging based on 2D-selective radiofrequency excitations by tilting the excitation plane.

PURPOSE: To improve the performance and flexibility of diffusion-weighted inner field-of-view (FOV) echo-planar imaging (EPI) based on 2D-selective radiofrequency (RF) excitations by 1) using higher gradient amplitudes for outer excitation lines, and 2) tilting the excitation plane such that the unwanted side excitations do not overlap with the current image slice or other slices to be acquired.
MATERIALS AND METHODS: Acquisitions with a conventional (untilted) and the improved setup were compared and inner FOV diffusion tensor measurements were performed in the human brain and spinal cord with voxel sizes of 1.0 × 1.0 × 5.0 mm(3) and 0.6 × 0.6 × 5.0 mm(3) on a 3 T whole-body magnetic resonance imaging (MRI) system.
RESULTS: With the modified setup, the 2D-selective RF excitations can be considerably shortened (e.g., from 26 msec to 6 msec) which 1) avoids profile distortions in the presence of magnetic field inhomogeneities, and 2) reduces the required echo time and increases the signal-to-noise ratio accordingly, e.g., by about 20% in the spinal cord.
CONCLUSION: Tilting the excitation plane and applying variable gradient amplitudes improves the applicability of inner FOV EPI based on 2D-selective RF excitations.