Gibbs and truncation artifacts

Last revised by Roland Zhang on 10 Nov 2023

Gibbs artifact, also known as truncation artifact or ringing artifact, is a type of MRI artifact. It refers to a series of lines in the MR image parallel to abrupt and intense changes in the object at this location, such as the CSF-spinal cord and the skull-brain interface.

The MR image is reconstructed from k-space which is a finite sampling of the signal subjected to inverse Fourier transform in order to obtain the final image. At high-contrast boundaries (jump discontinuity in mathematical terms), the Fourier transform corresponds to an infinite number of frequencies. Since MR sampling is finite, the discrepancy manifests in the reconstructed image as a series of lines. These can appear in both phase-encode and frequency-encode directions.

The more encoding steps, the less intense and narrower the artifacts. Figure 1 shows the Gibbs effects resulting from Fourier transforming a sharp change in image intensity. Figure 2 shows prominent light and dark line along the sides that fade as they approach the top and bottom of the phantom. Figure 3 shows minimal artifact seen uniformly around the periphery of the phantom as a result of increasing the matrix size in the phase direction.

  • increasing the matrix size (i.e. sampling frequency for the frequency direction and number of phase-encoding steps for the phase direction)

  • use of smoothing filters (2-D exponential filtering, Gegenbauer reconstruction etc.)

  • if fat is one of the boundaries, use fat suppression

Josiah Willard Gibbs (1839-1903) 5 was an American mathematician and physicist.

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