Quick Overview

A moiré pattern is an interference pattern created for example when two grids are overlaid at an angle, or when they have slightly different mesh sizes. The human visual system creates an imaginary pattern of roughly horizontal dark and light bands, the moiré pattern that appears to be superimposed on the lines.
In MRI, the appearance of moiré fringes can be caused by a variety of reasons e.g., inhomogeneity of the main magnetic field caused by a defect shielding (interference with RF pulses), interferences produced by aliasing, and interferences of echoes from different excitation modes (with different echo times).

Take spin echo-based techniques, or a surface coil. This artifact is often sensitive to shimming or susceptibility gradients.

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.

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

RF noise, which often appears as static on the image, can be caused by a medical device located anywhere in the MR procedure room. RF noise is a result of excessive electromagnetic emissions from the device that interference with the proper operation of the MR scanner. The interference is attenuated and aliased in the frequency direction.

In the first case try to eliminate the factor of disturbance, if the problem persists screen the magnet- and room shielding.

See also Signal to Noise Ratio.

The MRI equipment consists of following components:
Better MRI equipment and software design along with the latest information technology improves system maintenance and overall communication. Software and digital imaging and communications in medicine (DICOM) compatibility allows to network into hospital databases, helps to modify pulse sequences, data post processing, and archiving via picture archiving and communication system (PACS).

See also the related poll result: 'Most outages of your scanning system are caused by failure of'