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• Hardware Issues

• Software problems

• Physiological phenomena

• Physics limitations

Sources of Artifacts:

calibration, power stability

Example of Hardware Issues

programming errors

Example of Software problems

blood flow

Example of Physiological phenomena

Gibbs and susceptibility

Example of Physics limitations

Chemical Shift Artifact

• Frequency-encoding direction

• The different resonant frequency of fat & water is transformed into spatial difference.

Dark and bright

Chemical Shift Artifact Appearance

Aliasing or "Wrap-around"

Occurs when the field of view (FOV) is smaller than the body part being imaged causing the region beyond to project on the other side of the image.

Phase direction (duplication of phase values)

Wrap Around Artifact aka Aliasing Axis

Anatomy outside FOV

Wrap Around Artifact aka Aliasing Appearance

Black Line Artifact

An artificially created black line located at fat-water interfaces such as muscle-fat interfaces.

Ring of dark signal

Chemical Misregistration Artifact aka Out-of-Phase, Black Boundary, or India Ink Appearance

Gibbs or Truncation Artifact

Bright or dark lines that are seen parallel & next to borders of abrupt intensity change.

Rippling artifact

Truncation Artifact aka Gibbs Appearance

Zipper Artifacts

Most are related to hardware or software problems beyond the radiologist control.

Motion Artifacts

Bright noise or repeating densities usually oriented in the phase direction.

• Arterial pulsations

• CSF pulsations

• swallowing

• breathing

• peristalsis

• physical movement.

Motion Artifacts Examples:

Motion Artifacts

• Mitigation:

• Arterial and CSF pulsation artifacts can be reduced with flow compensation and cardiac gaiting.

Slice-overlap (cross-slice) Artifacts

Loss of signal seen in an image from a multi-angle, multi-slice acquisition.

Cross-talk Artifact

Result of imperfect slice excitation

Adjacent slices

Cross Excitation Artifact Appearance

Magic Angle Effects

Seen most frequently in tendons and ligaments that are oriented at a 55° angle to the main magnetic field.

55° increasing the signal.

The dipolar interactions go to zero at about

Phase and frequency direction

Magic Angle Artifact Axis

• T1W

• PDW

• GRE

Magic Angle Artifact Occurs on sequences with short TEs:

Entry slice (Inflow) artifact

Unsaturated spins in blood or CSF entering the initial slices results in greater signal than reduces on subsequent slices.

Field inhomogeneity

• Mitigation:

• Shimming, area of interest in near isocenter

Coil

Use volume vs. surface coil, allow space between coil and body.

Dielectric

use phased array coils, software compensation

RF Overflow Artifacts (Clipping)

Causes a nonuniform, washed-out appearance to an image.

Moire fringes

are an interference pattern most commonly seen when doing gradient echo images.

Central Point Artifact

A focal dot of increased or decreased signal in the center of an image.

Quadrature ghost artifact

Another amplifier artifact caused by unbalanced gain in the two channels of a quadrature coil.

180 degree "ghost."

Combining two signals of different intensity causes some frequencies to become less than zero causing

Susceptibility Artifacts

Variations in the magnetic field strength that occurs near the interfaces of substance of different magnetic susceptibility such as ferromagnetic foreign bodies.

Zebra Artifacts

Band-like, usually oblique stripes.

Eddy Current Artifacts

Varying magnetic field from gradients can induce electrical currents in conductors such as the cryostat causing distortion of the gradient waveforms.

Precompensation

A "distorted" gradient waveform is used which corrects to normal with the eddy current effects.

Shielded gradients

Active shielding coils between gradient coils and main gradients.

Diastolic Pseudogating

Change in intensity of blood in large vessel such as the aorta from slice to slice when there is synchronization of the cardiac cycle and the pulse sequence,

heart rate (TR=1/HR)

repetition rate

Gadolinium "Pseudolayering"

Three density layers in the bladder after Gd

dark

Low conc. Gd top layer

bright

Med conc. Gd middle layer

dark

High conc. Gd lower layer near ureters

"ON"

THE MAGNETIC FIELD IS AT FULL POWER ALWAYS ....IT IS ALWAYS

GRADIENT FIELD

• INDUCED CURRENTS (PERIPHERAL NERVOUS SYSTEM)

• AUDITORY DAMAGE

RF FIELD

• RF POWER DEPOSITION

• BURNS

Zone 1

THIS REGION INCLUDES ALL AREAS THAT ARE FREELY ACCESSIBLE TO THE GENERAL PUBLIC.

Zone 2

Unscreened MRI patients also may be attenders