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

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging
• Acoustics

Background:

• Echo-Planar Imaging (EPI) is crucial for fMRI and diffusion MRI.
• Rapid gradient switching in EPI causes noise and artifacts, worsening at ultra-high fields.
• Current methods to reduce these issues often require complex acquisition or reconstruction changes.

Purpose of the Study:

• To predict and demonstrate how minor timing modifications in multi-train EPI can reduce acoustic energy.
• To investigate the impact of timing changes on ghosting artifacts.
• To achieve these improvements without altering the fundamental acquisition or reconstruction design.

Main Methods:

• Developed an analytic model linking gradient train interference to acoustic energy.
• Integrated the model with acoustic transfer functions to predict scan noise.
• Validated predictions on 7T and 10.5T MRI systems by systematically varying timing parameters and measuring acoustic output and ghosting.

Main Results:

• Sub-millisecond timing shifts caused 2-fold to 47-fold changes in acoustic power.
• Doubling acquisition speed sometimes halved minimal acoustic energy.
• Navigator time shifting reduced ghosting up to 5-fold, correlating with acoustic resonance frequencies.

Conclusions:

• Minimal timing adjustments offer a simple, reconstruction-agnostic method to decrease acoustic noise and ghosting.
• This strategy expands the usable parameter space for EPI.
• The findings enable quieter, higher-quality EPI scans, particularly beneficial for ultra-high-field and high-speed MRI.