Fundamentals Of MRI Studies: MRI Artifacts

OVERVIEW

This page is dedicated to discussing the various different types of MRI artifacts that can occur.

  • Gibbs (truncation) artifact
  • Ghosting (Nyquist, or N/2) artifact
  • Chemical shift artifact
  • Zipper artifacts 
  • Spike noise artifacts
  • Aliasing (“wrap-around”) artifact 
GIBBS ARTIFACT

What is it?

A Gibbs (truncation) artifact occurs as a consequence of using Fourier transforms to reconstruct MR signals into representative images. It appears as multiple fine parallel lines that are immediately adjacent to high contrast interfaces.

Example of Gibbs artifact on MRI (image source)

Not only can this artifact be distracting, it can also mimic the appearance of a syrinx in the spinal cord which can be problematic clinically.

Example of pseudo-syrinx created by Gibbs artifact (left pane). This artifact is resolved by increasing the image matrix (right page, image source).

How to solve it: This artifact can be resolved by

  • Specifying more phase encodings
  • Awaiting more samples during frequency encoding (increased matrix)
  • Pre/post reconstruction image filtration.
GHOSTING (NYQUIST, OR N/2) ARTIFACT

What is it?

A ghosting (Nyquist, or N/2) artifact is most often caused by some type of motion and appears as an image copy/multiple copies of an image that can blur the image.

Example of ghosting in an abodminla MRI that is caused by respiration (image source)

How to solve it: This artifact can be resolved by

  • Having patients hold still
  • Having patient’s hold breath
  • Pharmaceuticals to reduce bowel motion.
CHEMICAL SHIFT ARTIFACT

What is it?

A chemical shift artifact will appear as a bright or black band at the interfaces of fatty tissue/non-fatty tissue. The bright band will be present on the side of the fatty tissue, and the black band will be present on the non-fatty tissue. This is caused by the resonant frequency of fat that mimics frequency-encoding.

Examples of chemical shift artifact on an abdominal MRI scan (image source)

How to solve it: This artifact can be resolved by

  • Inverting phase-encode and frequency-encode directions to view pathology in an improved fashion
ZIPPER ARTIFACTS 

What is it?

These appear as a strip of noise in an image. These are caused by extraneous RF signals near the MRI machine during readout.

Example of zipper artifact on MRI (image source)

How to solve it: This artifact can be resolved by

  • Making sure door to scanner room is closed
  • Make sure equipment in room is checked for RF emissions (such as contrast pumps etc).
  • Call medical physics staff/field engineer to find RF leak.
SPIKE NOISE ARTIFACT

What is it?

Series of bands alternating between light and dark bands superimposed over an image.

Example of spike artifact on MRI (image source)

How to solve it: This artifact can be resolved by

  • Calling field engineer to check for vibrating metal/loose wires in MRI machine
ALIASING (“WRAP-AROUND”) ARTIFACT 

What is it?

An aliasing (“wrap-around) artifact is when an structure (outside the field of view) wraps around the image on the side opposite it it’s anatomical location.

 

A head MRI showing the wrap around artifact. The posterior portion of the skull is outside the field of view of the MRI image, however has wrapped around the anterior side of the image (image source).

How to solve it: This artifact can be resolved by

  • Orient the thinner axis of anatomy along the phase-encoding direction
  • Enlarge the field of view
  • Exclude all anatomy from the top view slices (for 3D ahead exams)
  • Use spatial saturation bands to null tissues outside the field of view.
ARTIFACT

What is it?

How to solve it: This artifact can be resolved by

 

 

 

Page Updated: 08.06.2017