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Off-resonance image artifacts in interleaved-EPI and GRASE pulse sequences
1Department of Radiology, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Magnetic Resonance in Medicine
|August 1, 1996
Summary
Echo-time shifting (ETS) in MRI sequences can cause ghosting artifacts due to phase discontinuities. This study quantifies these artifacts and provides recommendations to limit them, improving image quality.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Medical Physics
- Image Reconstruction
Background:
- Echo-time shifting (ETS) is employed in Gradient and Spin Echo (GRASE) and interleaved Echo Planar Imaging (EPI) sequences to mitigate off-resonance effects.
- Despite ETS, residual phase discontinuities persist, potentially leading to image artifacts.
Purpose of the Study:
- To quantitatively evaluate the magnitude and form of image artifacts arising from phase discontinuities in ETS-enhanced MRI sequences.
- To derive general conditions for artifact occurrence based on the functional form of phase evolution.
Main Methods:
- Calculation of point spread functions and simulated images for two sequence structures.
- Evaluation of artifacts as a function of off-resonance frequency and data sampling period.
Main Results:
- Periodic phase discontinuities, even with ETS, can degrade image quality by causing ghosting artifacts at edges.
- These ghosting artifacts resemble those typically seen with periodic motion.
Conclusions:
- Recommendations are provided to limit ghosting artifacts caused by phase discontinuities in ETS-enhanced MRI.
- Optimizing sequence parameters can mitigate artifacts and improve diagnostic image quality.