B(0)-fluctuation-induced temporal variation in EPI image series due to the disturbance of steady-state free precession.

Steady-state free precession (SSFP) can develop under a train of RF pulses, given the condition TR < T(2). SSFP in multi-shot imaging sequences has been well studied. It is shown here that serial single-shot echo-planar imaging (EPI) acquisition can also develop SSFP, and the SSFP can be disturbed by B(0) fluctuation, causing voxel-wise temporal variation. This SSFP disturbance is predominantly present in cerebrospinal fluid (CSF) regions due to the long T(2) value. By applying a sufficiently strong crusher gradient in the EPI pulse sequence, the temporal variation induced by SSFP disturbance can be suppressed due to diffusion. Evidence is provided to indicate that physiological motions such as cardiac pulsation and respiration could affect the voxel-wise time courses through the mechanism of SSFP disturbance. It is advised that if the disturbance is observed in serial EPI images, the crusher should be made stronger to eliminate the unwanted temporal variation.