MRI Eddy Current Artifact
Eddy current artifact in MRI is caused by the interaction of the gradient magnetic fields with the conductive materials present in the imaging subject or surrounding the MRI scanner. When the gradient magnetic fields are switched on or off rapidly, eddy currents are induced in the conductive materials, including the metallic components of the MRI scanner and the biological tissues of the patient. These eddy currents can produce additional magnetic fields that cause image distortions and signal losses, resulting in the eddy current artifact.
The appearance of eddy current artifact can vary depending on the imaging sequence used and the location of the artifact. Some common features of the artifact include geometric distortions, signal losses, and blurring of the image. In some cases, the artifact may appear as ghosting or smearing of the image, particularly in diffusion-weighted imaging and echo-planar imaging.
Here are some strategies to help avoid or minimize Eddy Current Artifacts
Proper gradient system calibration: Accurate calibration of the MRI system’s gradient coils is essential for minimizing eddy current artifacts. Regular calibration routines, such as pre-scan calibrations, can help optimize the gradient performance and reduce the impact of eddy currents.
Proper sequence design: The design of MRI sequences can influence the occurrence of eddy current artifacts. Optimize the sequence parameters, such as gradient timing, rise time, and duty cycle, to minimize eddy current effects. Sequences that use shorter echo times (e.g., spin echo) may be less susceptible to these artifacts compared to sequences with longer echo times (e.g., echo planar imaging).
Echo train length (ETL) optimization: Eddy currents can be more pronounced in fast imaging techniques with longer echo trains. Reducing the echo train length (ETL) or using techniques such as partial Fourier imaging can help mitigate eddy current artifacts.
References:
- Jezzard, P., Barnett, A. S., & Pierpaoli, C. (1998). Characterization of and correction for eddy current artifacts in echo planar diffusion imaging. Magnetic Resonance in Medicine, 39(5), 801-812. doi: 10.1002/mrm.1910390518. PMID: 9581612.
- Sodickson, D. K., & Manning, W. J. (1997). Simultaneous acquisition of spatial harmonics (SMASH): fast imaging with radiofrequency coil arrays. Magnetic resonance in medicine, 38(4), 591-603.
- Bernstein, M. A., King, K. F., & Zhou, X. J. (2018). Handbook of MRI pulse sequences. Elsevier.
