Gibbs and truncation artifacts

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 is manifest in the reconstructed image in the form of 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.

Remedy

• 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

History and etymology

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

See also

• truncation artifact (CT)