MRI Gibbs \ Truncation Artifact
Gibbs artifact, also known as Truncation artifact or ringing artifact, is a common artifact observed in magnetic resonance imaging (MRI) images. It appears as a series of oscillations or ripples near sharp edges or high-contrast structures in the image. This artifact occurs due to the truncation of high-frequency information during the image reconstruction process, resulting in a phenomenon known as Gibbs phenomenon.
The appearance of Gibbs artifact in an MRI image can be described as a wavy pattern, often located near sharp transitions in the image, such as the edges of objects. The appearance of this artifact can depend on the type of imaging sequence used and the specific parameters used during image acquisition and reconstruction.
In axial brain imaging, bands may be observed around the edges due to the signal intensity difference between high signal fat in the scalp and low signal skull. These bands are caused by Gibbs artifact resulting from the truncation of high-frequency information.
In sagittal cervical spine imaging, a similar artifact can occur due to the signal intensity boundary between cerebrospinal fluid (CSF) and the spinal cord. This truncation artifact can mimic the appearance of a syrinx, which is a fluid-filled cavity within the spinal cord.
Here are some strategies to minimize or avoid Gibbs Artifact
Decrease pixel size by decreasing field of view (FOV): Gibbs artifact is more prominent when there are sharp edges or high-contrast structures in the image. By decreasing the FOV and subsequently reducing the pixel size, the artifact can be minimized. This approach allows for better sampling of high-frequency information and can help mitigate the ringing artifact.
Smoothing filters: Applying smoothing filters, such as Gaussian filters, can help reduce the oscillations and ringing associated with Gibbs artifact. These filters blur the sharp edges in the image, effectively smoothing out the artifact. However, it’s important to strike a balance between reducing the artifact and preserving important image details.
Fat suppression if one boundary is fat: If the Gibbs artifact is particularly prominent at the interface between fat and another tissue, using fat suppression techniques can help minimize its impact. Fat suppression methods, such as chemical shift selective saturation or inversion recovery-based techniques, selectively nullify the fat signal, thereby reducing the artifact near fat-tissue boundaries.
Increase matrix size: Increasing the matrix size can reduce the impact of chemical shift artifact. However, this may also lead to a reduction in SNR.
Increase the number of phase encoding steps: By acquiring more phase encoding steps during data acquisition, you can sample higher spatial frequencies and reduce the Gibbs artifact. However, this can lead to longer scan times.
References:
- Kellner E, Dhital B, Kiselev VG, Reisert M. Gibbs-ringing artifact removal based on local subvoxel-shifts. Magn Reson Med. 2016;76(5):1574-1581. doi: 10.1002/mrm.26054
- Pipe JG. Motion correction with PROPELLER MRI: application to head motion and free-breathing cardiac imaging. Magn Reson Med. 1999;42(5):963-969. doi: 10.1002/(sici)1522-2594(199911)42:5<963::aid-mrm17>3.0.co;2-4