Concomitant magnetic-field-induced artifacts in axial echo planar imaging

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Physics

Background:

• Linear magnetic field gradients in MRI can generate higher-order magnetic fields.
• These fields can cause artifacts in echo planar imaging (EPI), particularly with horizontal solenoid magnets.
• Artifacts include axial image shift and intensity reduction, worsening with slice offset from the isocenter.

Purpose of the Study:

• To quantitatively analyze the impact of higher-order magnetic fields on EPI.
• To identify the cause of image shift, intensity reduction, and Nyquist ghosting in EPI.
• To develop and validate methods for artifact elimination in MRI.

Main Methods:

• Theoretical analysis based on Maxwell equations.
• Experimental validation using MRI scans.
• Computer simulations to verify predicted artifacts.
• Development and implementation of artifact correction techniques.

Main Results:

• Established a quantitative correlation between theoretical predictions and experimental observations of image artifacts.
• Confirmed the occurrence and severity of image shift and intensity reduction with increasing slice offset.
• Predicted and experimentally verified a novel Nyquist ghost artifact at large slice offsets.
• Demonstrated the effectiveness of developed methods in eliminating artifacts.

Conclusions:

• Higher-order magnetic fields are a significant source of artifacts in EPI.
• The developed methods successfully mitigate image shift, intensity loss, and Nyquist ghosting.
• Implementation on commercial scanners confirms the practical utility of these artifact correction techniques.