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Field-map correction in read-out segmented echo planar imaging for reduced spatial distortion in prostate DWI for
Robert V Bergen1, Lawrence Ryner1, Marco Essig2
1Department of Physics & Astronomy, University of Manitoba, Canada; Medical Physics, CancerCare Manitoba, Canada.
Magnetic Resonance Imaging
|December 18, 2019
Summary
Magnetic field map corrections significantly reduce geometric distortion in diffusion-weighted echo planar imaging (DW-EPI) and read-out segmented echo planar imaging (RS-EPI). This enhanced accuracy is crucial for MRI-guided radiotherapy applications.
Area of Science:
- Magnetic Resonance Imaging
- Medical Physics
- Radiotherapy
Background:
- Diffusion-weighted echo planar imaging (DW-EPI) is prone to geometric distortions caused by low phase-encoding bandwidth.
- Read-out segmented echo planar imaging (RS-EPI) mitigates but does not eliminate these distortions, necessitating further correction for precise applications like radiotherapy.
Purpose of the Study:
- To evaluate the efficacy of magnetic field map corrections in reducing geometric uncertainty for DW-EPI and RS-EPI.
- To assess the potential of these corrected images for MRI-guided radiotherapy.
Main Methods:
- Magnetic field maps were generated using gradient echo images.
- Distortion corrections were applied to RS-EPI images.
- Geometric accuracy was evaluated in a prostate phantom and in vivo using a T2-weighted spin echo as ground truth.
Main Results:
- Field map-corrected RS-EPI reduced maximum distortion by an average of 5 mm compared to DW-EPI across 10 patients.
- Significant reduction in geometric distortions was observed with field mapping in RS-EPI compared to RS-EPI alone (p ≤ 0.05).
Conclusions:
- Magnetic field map corrections substantially improve the geometric accuracy of RS-EPI.
- The enhanced geometric precision enables better fusion of diffusion-weighted MRI with other imaging modalities (MR, CT) for radiotherapy planning and delivery.
