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Correction for geometric distortion in echo planar images from B0 field variations
1Laboratory of Cardiac Energetics, NHLBI, National Institutes of Health, Bethesda, MD 20892, USA.
Magnetic Resonance in Medicine
|July 1, 1995
Summary
This study introduces a new method to correct geometric distortions in echo planar images caused by magnetic field variations. The technique uses field maps to unwarp images, improving alignment with standard scans.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Image Processing
- Medical Physics
Background:
- Echo planar imaging (EPI) is susceptible to geometric distortions.
- These distortions primarily arise from static magnetic field inhomogeneities.
- Pixel shifts, especially in the phase-encode direction, degrade image quality and alignment.
Purpose of the Study:
- To present a novel method for correcting geometric distortions in EPI.
- To enable accurate alignment of EPI data with conventionally acquired images.
- To demonstrate the efficacy of the unwarping technique across different magnetic field strengths.
Main Methods:
- Characterization of static magnetic field inhomogeneities using field maps.
- Development and application of an unwarping algorithm based on field map data.
- Acquisition and analysis of EPI data at 1.5 and 4 Tesla.
Main Results:
- Successful correction of geometric distortions in EPI.
- Demonstration of improved image alignment post-unwarping.
- Validation of the method at both 1.5T and 4T field strengths.
Conclusions:
- The described method effectively corrects EPI geometric distortions.
- Field map-based unwarping significantly enhances spatial accuracy.
- This technique is valuable for quantitative MRI and multi-modal image integration.
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