Quick Overview

Uneven intensity or brightness may occasionally be noted on high field MRI e.g. of the brain. There are various causes of localized inhomogeneous brightness across the MRI images such as improper tuning of the RF transceiver, unbalanced deposition of the RF energy due to incorrect geometry and localized attenuation due to positioning or anatomical variants.

Tuning of the RF transceiver, a homogeneity correction filter and better positioning of the scanned object and/or coil in the scanner.

Quick Overview
Please note that there are different common names for this artifact.

Patient motion is the largest physiological effect that causes artifacts, often resulting from involuntary movements (e.g. respiration, cardiac motion and blood flow, eye movements and swallowing) and minor subject movements.
Movement of the object being imaged during the sequence results in inconsistencies in phase and amplitude, which lead to blurring and ghosting. The nature of the artifact depends on the timing of the motion with respect to the acquisition. Causes of motion artifacts can also be mechanical vibrations, cryogen boiling, large iron objects moving in the fringe field (e.g. an elevator), loose connections anywhere, pulse timing variations, as well as sample motion. These artifacts appear in the phase encoding direction, independent of the direction of the motion.

Motion artifacts can be flipped 90° by swapping the phase//frequency encoding directions.
The artifacts can be reduced by using breath holding, cardiac synchronization or respiratory compensation techniques: triggering, gating, retrospective triggering or phase encoding artifact reduction. Flow effects can be reduced by using gradient moment nulling of the first order of flow, gradient moment rephasing or flow compensation, depending of the MRI system.
Peristaltic motion can be reduced with the intravenous injection of an anti-spasmodic (e.g. Buscopan).
By using multiple averages, respiratory motion can be reduced in the same way that multiple averages increase the signal to noise ratio. Noticeable motion averaging is seen when four averages are obtained, six averages are often as good as respiratory compensation techniques and higher averages will continue to improve image quality.
In some cases will help a presaturation of the anatomy that was generating the motion.

See also Phase Encoded Motion Artifact.

A signal to noise improvement method that is accomplished by taking the average of several FID's made under similar conditions to suppress the effects of random variations or random artifacts.

Quick Overview

Zipper artifacts appear as dashed lines. There are various causes for this MRI artifact.
Most of zipper artifacts result from inhomogeneities of the magnetic field caused by interferences with radio frequency from various sources ('your radio is working in the scanner room means your shielding is not working'). Software and equipment problems can also cause zipper lines in both directions.

Scanning room door during the acquisition of images is closed, shielding is working, and all disturbing devices are removed?

See also Room Shielding, Active Shielding, Radio Frequency Shielding.

See Black Boundary Artifact.