Timing Is Everything: How Subtle Timing Changes in MRI Echo Planar Imaging Can Significantly Alter Mechanical...

Echo-Planar Imaging (EPI) is central to fMRI, diffusion MRI, and many dynamic clinical applications, yet rapid gradient switching induces strong mechanical vibrations, generates acoustic noise, and contributes to ghosting artifacts-effects that intensify at ultra-high fields. This study aims to predict how subtle timing changes in multi-train EPI can modulate acoustic energy and reduce ghosting without altering reconstruction or acquisition design.

We derived an analytic model describing the interference between short gradient trains and combined it with the system's acoustic transfer function to predict the acoustic energy of a scan. The model predicts cyclic variations in acoustic power resulting from small timing adjustments of slices and echoes. Validation was performed on a clinical 7 T and an investigational 10.5 T MRI systems by measuring acoustic output and ghosting-artifact levels while systematically sweeping timing conditions in single and multi-echo EPI protocols.

Sub-millisecond timing modifications produced large, predictable changes in the acoustic power; changes ranging from 2-fold to 47-fold. Intriguingly, under certain conditions, doubling the acquisitions per unit-time reduced the minimal acoustic energy two-fold. In addition, navigator time shifting reduced the ghosting-artifact intensity, up to 5-fold, exhibiting cyclic dependence corresponding to the dominant acoustic resonance frequency. These trends were consistent across both the 7 T and the 10.5 T systems.

Minimal timing adjustments provide an effective, reconstruction-agnostic strategy to reduce acoustic noise, to mitigate ghosting artifacts, and to expand feasible EPI parameters space. The proposed model paves the way towards quieter, higher-quality EPI scans, particularly valuable for ultra-high-field and high-speed imaging.