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Correction for eddy current induced Bo shifts in diffusion-weighted echo-planar imaging
F Calamante1, D A Porter, D G Gadian
1Radiology and Physics Unit, Institute of Child Health, University College London Medical School, England. cfernan@ich.ucl.ac.uk
Abstract:
The importance of diffusion-weighted MRI in the assessment of acute stroke is well-recognized, and quantitative maps of the apparent diffusion coefficient (ADC) are now widely used. Echoplanar imaging provides a robust method of acquiring diffusion-weighted images free of motion artifact. However, initial experience with clinical MRI systems indicates that calculation of artifact-free ADC maps from a series of echo-planar diffusion-weighted images is not necessarily straight-forward. One of the problems is that frequency shifts resulting from eddy currents can cause misregistration of base diffusion-weighted images. In this study, an on-line correction method that overcomes this problem is described, and phantom and human images that demonstrate the validity of the technique are presented. The method uses a non-phase-encoded reference scan to correct the phase of each echo in the echo train, and can provide ADC maps that are free of misregistration artifacts, without the need for off-line postprocessing.
Insights
This study introduces an online method to correct eddy current-induced misregistration in diffusion-weighted MRI. This technique generates accurate apparent diffusion coefficient (ADC) maps for acute stroke assessment without postprocessing.
Area of Science:
- Radiology
- Medical Imaging
- Neuroimaging
Background:
- Diffusion-weighted MRI (DW-MRI) is crucial for acute stroke assessment.
- Quantitative apparent diffusion coefficient (ADC) maps are widely used.
- Echoplanar imaging (EPI) is effective for motion-artifact-free DW-MRI acquisition.
Purpose of the Study:
- To address challenges in calculating artifact-free ADC maps from EPI DW-MRI.
- To present an online correction method for eddy current-induced misregistration.
- To validate the technique using phantom and human imaging.
Main Methods:
- An online correction method using a non-phase-encoded reference scan.
- Correction of phase in each echo of the echo train.
- Acquisition of diffusion-weighted images using echoplanar imaging.
Main Results:
- The developed method effectively corrects frequency shifts from eddy currents.
- Misregistration artifacts in diffusion-weighted images are eliminated.
- Accurate ADC maps are generated without offline postprocessing.
Conclusions:
- The online correction method provides artifact-free ADC maps for clinical MRI.
- This technique enhances the reliability of quantitative diffusion MRI in stroke diagnosis.
- It simplifies the process of generating accurate ADC maps for acute stroke evaluation.