Gradient Non-Linearity Artifact / Image Distortion Artifact
Gradient nonlinearity artifact in MRI refers to an imaging artifact that arises due to the nonuniformity of the magnetic field generated by the gradient coils. Gradient coils are responsible for spatially encoding the MRI signal, but their magnetic fields may not be perfectly linear across the imaging volume, resulting in the distortion of the acquired images.
This artifact can have various implications:
Image distortion: The nonuniform magnetic field caused by gradient nonlinearity can lead to geometric distortions in the MRI images. This distortion can affect the accuracy of anatomical measurements and spatial relationships between structures.
Misalignment of structures: The distorted images may result in the misalignment of anatomical structures, making it difficult to precisely identify and assess abnormalities or perform accurate image-guided interventions.
Inaccurate quantitative analysis: Gradient nonlinearity can also impact quantitative analysis, such as volumetric measurements or diffusion tensor imaging (DTI). The distorted images may yield inaccurate measurements and hinder the reliability of quantitative assessments.
Here are some strategies to minimize or avoid Gradient Non-Linearity Artifact
Image distortion correction: Post-processing techniques, such as distortion correction algorithms, can be applied to the acquired images to mitigate the effects of gradient nonlinearity. These algorithms map the distorted image back to its true anatomical shape using information about the gradient nonlinearity profile.
Imaging protocol optimization: Adjusting the imaging parameters, such as reducing the field of view (FOV) or using thinner slices, can help minimize the impact of gradient nonlinearity. Choosing imaging sequences that are less susceptible to this artifact, such as spin echo rather than echo planar imaging (EPI), can also be beneficial.
Gradient calibration: Regular calibration of the gradient coils can help reduce the impact of gradient nonlinearity. Manufacturers provide calibration sequences or software tools that allow for correcting the nonuniformity in the magnetic field.
References:
- Chen, N. K., & Wyrwicz, A. M. (2001). Correction of geometric distortion in gradient-echo images for stereotactic neurosurgery. Journal of Magnetic Resonance Imaging, 13(6), 909-917.
- Sommer, K., Gassert, F., Rudin, M., & Sprenger, T. (2015). Impact of gradient nonlinearity correction on apparent diffusion coefficient measurements. Magnetic Resonance Imaging, 33(3), 307-312.