Acoustic Spectrum and Ghosting in EPI: Timing is Everything (and it is Not Just Echo Spacing)

Motivation: Gradient echo-trains in EPI cause mechanical vibration, loud sounds, ghosting artifacts, and even mechanical failure. A better understanding of the vibration modes can help mitigate ghosting and/or disturbing sounds. Goal(s): Modeling acoustic spectrum for a given gradient-waveform can predict the acoustic modes. Approach: A simple model of sinusoidal echo-trains was introduced for multi-slice and multi-echo acquisition to predict acoustic modes. The effect of subtle timing changes was examined to reduce undesired acoustic peaks. Results: The model agrees well with measurements around the 1st-harmonics, however, some peaks were amplified, probably due to system resonances. Significant ghost reduction was achieved using the model prediction. Impact: Subtle control of slice timing and echo-times can reduce EPI-ghosting artifacts. Furthermore, proper modeling of acoustic modes, should allow replacing the current restrictive forbidden echo-spacings logic in sequences with a less restrictive vibration power-prediction.