Summary of EPI Artifacts
Please find below a summary of echo planar imaging (EPI) artifacts, based on Chapter 16.1.4 in Bernstein et al., 2004
More information sources on artifacts
For more information about and illustrative examples of EPI artifacts, see for example:
- Image Artifacts:
- Hornak, 2020, Chapter (http://www.cis.rit.edu/htbooks/mri/chap-11/chap-11.htm#11.3)
- Generation and illustration of some artifacts:
- JEMRIS: Example 1: Simulation of common MRI artifacts (https://www.jemris.org/ug_example_artifacts.html)
- Signal dropout:
- Weiskopf et al., 2006
EPI Distortion Correction
There are several approaches to correct for susceptibility artifacts, where static magnetic field inhomogeneities cause geometric distortions in EPI images (usually saved in BrainVoyager as FMR files).
EPI distortion correction via acquired field maps (anatabacus plugin)
This can be achieved in BrainVoyager with the anatabacus plugin using the pixelshift method by Zezzard & Balaban, 1995.
The pixelshift for each voxel is calculated using a B0 fieldmap and some acquisition parameters: phase encoding bandwidth and phase encoding direction of the EPI data, and echo time difference of the "fieldmap".
EPI distortion correction via estimated field maps (COPE plugin)
This can be achieved in BrainVoyager with the COPE plugin using EPI images acquired with opposite/reverse phase-encoding directions. This approach is based on image registration, see Breman et al, 2020
References
Bernstein, M. A., King, K. F., & Zhou, X. J. (2004). Handbook of MRI Pulse Sequences. Handbook of MRI Pulse Sequences, 1–1017. https://doi.org/10.1016/B978-0-12-092861-3.X5000-6
Breman, H. et al. (2020). An Image Registration-Based Method for EPI Distortion Correction Based on Opposite Phase Encoding (COPE). In: Špiclin, Ž., McClelland, J., Kybic, J., Goksel, O. (eds) Biomedical Image Registration. WBIR 2020. Lecture Notes in Computer Science(), vol 12120. Springer, Cham. https://doi.org/10.1007/978-3-030-50120-4_12
Hornak, J. P. (2020). Chapter 11: Image Artifacts. in The Basics of MRI. Retrieved July 5, 2024, from https://www.cis.rit.edu/htbooks/mri/
Jezzard, P., & Balaban, R. S. (1995). Correction for geometric distortion in echo planar images from B0 field variations. Magnetic resonance in medicine, 34(1), 65–73. https://doi.org/10.1002/mrm.1910340111
Weiskopf, N., Hutton, C., Josephs, O., & Deichmann, R. (2006). Optimal EPI parameters for reduction of susceptibility-induced BOLD sensitivity losses: a whole-brain analysis at 3 T and 1.5 T. NeuroImage, 33(2), 493–504. https://doi.org/10.1016/J.NEUROIMAGE.2006.07.029
Example 1: Simulation of common MRI artifacts. JEMRIS. (n.d.), Retrieved July 5, 2024, from https://www.jemris.org/ug_example_artifacts.html