Pulsatile motion artifact reduction in 3D steady-state-free-precession-echo brain imaging.

An image can be made from the echo of a steady-state-free-precession and pulse sequences for this purpose have been implemented on various commercial systems under such names as "CE-FAST" and "SSFP" (herein generically termed SSFP-Echo). Such sequences can be employed to achieve strong T2-weighting with reduced T2* effects, but are limited by their sensitivity to flow and motion which produce artifacts. Simple considerations indicate that this sensitivity is primarily related to the (implementation-dependent) moments of the imaging gradients. In this work, MR imaging of the brain using a standard implementation of the sequence with large moment "crusher" gradients on the slice select axis (to dephase the FID of the SSFP) is compared to a modified implementation with reduced moment gradient pulses and different radiofrequency (RF) phase cycling. Asymmetric echo acquisition and narrowed bandwidth was used to further reduce gradient moments. The sensitivity of this sequence to flow and motion artifacts, especially for motion perpendicular to the slice, is thus expected to be significantly reduced. The modified sequence was found to have flow and motion artifacts reduced by a factor of five in the axial plane and a factor of two in the coronal plane. These modifications can thus significantly reduce the flow and motion artifacts commonly seen in conventional images of the SSFP echo with little or no penalty in scan time or signal-to-noise ratio.