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

The received radio frequency signal is too strong, parts of the signal get lost by converting from analog to digital, resulting in a washed out image.

Auto-prescanning usually adjusts the amplification at the receiver in a way, that the received signal could be processed without any loss. Else the receiver gain must be corrected manually.

See also Data Clipping Artifact, Artifact Overview and Artifacts Reduction Index.

(RE MRI) There are several approaches to speeding up the MRI data acquisition process by repeating the excitation by RF pulses in times short compared to T1, typically using small flip angles and gradient echo refocusing. When TR is also on the order of or shorter than T2, the repeated RF pulses will tend to refocus transverse magnetization remaining from prior excitations, setting up a condition of steady state free precession, and a dependence of signal strength (and image contrast) on both T1 and T2.
This can be modified in various ways, particularly:
1) to spoil the tendency to build up a steady state by reducing coherence between excitations, e.g. by variation of the phase or timing of consecutive RF pulses or of the strength of spoiler gradient pulses, thus increasing the relative dependence of signal strength on T1 or
2) acquire the signal when it is refocusing immediately prior to the next RF pulse, thus increasing the relative dependence of signal strength on T2.

See also Ultrafast Gradient Echo Sequence.

The portion of the MRI equipment that detects and amplifies the RF signals picked up by the receiver coil. Includes a preamplifier, MR signal amplifier, and demodulator. Phase sensitive detectors (electronic device in which the output is dependent on the instantaneous difference in phase between two input signals) are used to down-convert the MR signal to audio-frequencies prior to digitization.

See also MRI Equipment.

Quick Overview

Artifacts either by distorting the k-space trajectory (i.e. due to imperfect shimming) or as a consequence of the reduced bandwidth in the phase encode direction, commonly with EPI sequences.
While a standard spin warp-based sequence has an infinitely large bandwidth in the phase encode direction (about 1 or 2 kH), the bandwidth in EPI is related to the time between the gradient echoes (about a millisecond).
Hence even small frequency offsets can result in significant shifts of the signal in the phase encoding direction. Segmentation can introduce ghosting if there are significant difference in the amplitude and phase of the signal. This can be a particular problem when trying to acquire the segments in rapid succession.

Suitable choices of excitation schemes and/or subsequent correction can help to reduce this artifact. The signal from fat can easily be offset by a large fraction of the FOV, and must be suppressed. The effect of frequency offsets can be reduced by collecting data with more than one excitation, which effectively increases the bandwidth in the phase encoding direction.

Quick Overview

Materials with magnetic susceptibility cause this artifact. There are in general three kinds of materials with magnetic susceptibility: ferromagnetic materials (iron, nickel etc.) with a strong influence and paramagnetic/diamagnetic (aluminium, platinum etc./gold, water, most organic compounds etc.) materials with a minimal/non influence on magnetic fields. In MRI, susceptibility artifacts are caused for example by medical devices in or near the magnetic field or by implants of the patient. These materials with magnetic susceptibility distort the linear magnetic field gradients, which results in bright areas (misregistered signals) and dark areas (no signal) nearby the magnetic material.

Use a spin echo or a fast spin echo sequence, because gradient echo sequences are more sensitve to susceptibility artifacts. A high bandwidth (small water fat shift) and a short echo time help also to reduce this artifact.
In some cases it is even beneficial to use a gradient echo sequence, e.g. a cavernom contains some iron-rich haemosiderin, which also causes a signal void on gradient echo sequences and for this purpose increases the diagnostic image quality.