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.

Quick Overview

The saturation effect of inflowing blood in 3D inflow MRA.

Smaller 3D Volume or scans with e.g. tilt optimized nonsaturated excitation. In multi chunk scans TONE decreases this artifact or allows thicker chunks.

Quick Overview

Two types of audio-frequency problems are possible:
1. Modulation of the MR signal at an audio rate
2. Audio signal component at digitizer input
Problem 1 looks like ghosts, weak copies of the real image, displaced along the phase encoding direction. The number and intensity of the ghosts depends upon the relationship between the period of the audio modulation and the repetition time.
Problem 2 shows up as lines or spots at the appropriate points along the frequency direction. If there is no correlation between the audio period and TR, lines are generated or discrete spots occur.

Both problems can be lessened by use of AC-line synchronization (line trigger).

Data clipping artifacts give images a washed-out, non-uniform appearance. If the receiver gain increase, so that the signal level is larger than the maximum ADC value, the reconstructed image brightness was scaled to compensate this. The overall intensity loss as well as the extensive signal is reconstructed outside of the object. This effect is called 'clipping' because on a plot of signal amplitude vs. time, it looks like the top and bottom of the echo has been 'clipped off' with scissors.

See Radio Frequency Overflow Artifact.

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.