Zebra Artifact / Zebra Stripes

The “zebra” artifact, frequently referred to as the ” Zebra stripes” or “striping artifact,” is a phenomenon observed in MRI characterized by a distinctive pattern of alternating light and dark stripes or bands on the image. These stripes can be mainly seen at the periphery of the MRI image, presenting as curved bright and dark bands. However, the inhomogeneity of the magnetic field, in combination with aliasing, can sometimes also produce a centrally located artifact.

The genesis of the zebra artifact is multifaceted. It can emerge due to the inhomogeneity of the main magnetic field, as well as from the wrap-around or aliasing of signals from areas outside the coil that play a role in image formation. This specific phenomenon where signals from outside the intended field-of-view contribute to artifact formation is also known as the Moiré fringe artifact.

The primary causes or sources of the zebra artifact include:

Gradient Nonlinearity: This is one of the most common causes of zebra artifacts. The gradients used to encode spatial information in the MRI scanner might not be perfectly linear, causing distortions in the spatial encoding of the signal.

Magnetic Field Inhomogeneity: Variations or inhomogeneities in the magnetic field can lead to inconsistencies in the signal, resulting in striped artifacts.

RF Coil Malfunctions: Problems with the radiofrequency (RF) coil, such as improper tuning or hardware malfunctions, can produce uneven signal reception, leading to zebra artifacts.

Hardware-related issues: Imperfections in the gradient coil can lead to these striping patterns. These coils are critical for spatially encoding MRI signals, and any inconsistency can manifest as artifacts.

Calibration and algorithm issues: The malfunction or incorrect calibration of correction algorithms, particularly those designed to correct gradient non-linearity, can introduce the zebra artifact.