Abstract
Inhomogeneities of the main magnetic field cause geometric distortion in echo-planar imaging, a method central to functional MRI. A number of correction methods have been proposed, most of which are based on the acquisition of a fieldmap providing the local offsets to the main magnetic field. Here, accelerated multiecho echo-planar imaging is used, with echo times short enough to enable the construction of a fieldmap of comparable quality from the data themselves. This way, each volume in a time series can be unwarped using a fieldmap obtained from that volume, avoiding volume-to-volume field-motion interactions that invalidate reference data in conventional approaches that use a single, static, fieldmap. The combination of accelerated acquisition with dynamic distortion correction yields volumes with very low distortion at repetition times similar to conventional echo-planar imaging. The method is applied to data acquired at 3 and 7 T and is shown to effectively correct image geometry. Furthermore, it is shown that dynamic distortion correction yields better temporal signal stability than correction using a static fieldmap in the presence of subject motion.
Original language | English |
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Pages (from-to) | 1247-1254 |
Number of pages | 8 |
Journal | Magnetic Resonance in Medicine |
Volume | 68 |
Issue number | 4 |
DOIs | |
Publication status | Published - Oct 2012 |
Externally published | Yes |
Keywords
- Algorithms
- Artifacts
- Brain
- Electron Spin Resonance Spectroscopy
- Humans
- Image Enhancement
- Image Interpretation, Computer-Assisted
- Reference Values
- Reproducibility of Results
- Sensitivity and Specificity
- Signal Processing, Computer-Assisted