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MRI Artifacts
  
Ultrasound Imaging Artifacts Open this link in a new window
Chemical Shift Artifact 
Quick Overview
Please note that there are different common names for this artifact.

Artifact Information
NAME Chemical shift, black boundary, spatial misregistration, relief
DESCRIPTION Black or bright band
REASON Chemical shift, opposed phase image
HELP Fat suppression, smaller water fat shift (high bandwidth), in phase image, SE sequences

During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.


Image Guidance
For artifact reduction helps a smaller water fat shift (higher bandwidth), a higher matrix, an in phase TE or a spin echo technique. Since the misregistration offset is present in the read out axis the patient may be rescanned with this axis parallel to the fat-water interface. Steeper gradient may be employed to reduce the chemical shift offset in mm. Another strategy is to employ specialized pulse sequences such as fat saturation or inversion recovery imaging. Fat suppression techniques eliminate chemical shift artifacts caused by the lack of fat signal.
See also Black Boundary Artifact and Magnetic Resonance Spectroscopy.


• View the DATABASE results for 'Chemical Shift Artifact' (7).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
  News & More:
What is chemical shift artefact? Why does it occur? How many Hz at 1.5 T?
   by www.revisemri.com    
Abdominal MRI at 3.0 T: The Basics Revisited
Wednesday, 20 July 2005   by www.ajronline.org    
Case Study 1 :
In this case study the chemical shift artifact is visible as a small dark or bright border at the interfaces of bone, fat and muscle, best seen in the upper part of the head. This scan is taken with maximum water fat shift.
 
Case Study 2 :
This image is the same slice as case 1, but scanned with minimum water fat shift. The interface borders are smaller, but the minimized water fat shift produces more noise and a less signal to noise ratio.
 
Case Study 3 :
In this gradient echo image the typical artifact appears as a black and bright border in the frequency direction right and left of the kidney.
 
Case Study 4 :
In this image the chemical shift artifact is seen as a small bright line in front of the femoral bone.
 
Similar Artifacts:
 • Black Boundary Artifact
 • Susceptibility Artifact
 • Metal Artifact
 • Partial Volume Artifact
  Corrupted Data (Artifact) top
 
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