Gibbs or Truncation Artifacts

Gibbs or truncation artifacts are bright or dark lines that are seen parallel and adjacent to borders of abrupt intensity change, as when going from bright CSF to dark spinal cord on a T2-weighted image. In the spinal cord, this artifact can simulate a small syrinx to the unaware. It is also seen in other locations as at the brain/calvarium interface. This artifact is related to the finite number of encoding steps used by the Fourier transform to reconstruct an image. The more encoding steps, the less intense and narrower the artifacts. The first axial image is a phantom containing water, surrounded by air. The image was encoded 128 times in the horizontal direction and 256 times in the vertical direction. Note the prominent light and dark line along the sides that fade as they approach the top and bottom of the phantom. The second image was encoded 256 times in both directions. Minimal artifact is seen uniformly around the periphery of the phantom.
The diagram below shows the Gibbs effect resulting from a Fourier transformation of a sharp change in image intensity.