Dielectric effect artifact

Case contributed by Dr Matt A. Morgan

Presentation

Asymptomatic cirrhotic patient with ascites. Rule out hepatocellular carcinoma.

Modality: MRI

Central low signal in this cirrhotic patient with ascites.  Patient was imaged on a 3T system.

Case Discussion

This is not a problem with windowing and leveling, but the dielectric effect artifact, an inherent limitation of higher field MRI systems. 

As the field strength of an MRI unit increases, its radiofrequency (RF) wavelength in tissue decreases:

  • 1.5 T: 52 cm
  • 3.0 T: 26 cm
  • 7.0 T: 11 cm

As the wavelength decreases to the point where it approximates the abdominal diameter (at 3.0 T, ~26 cm), constructive and destructive interference patterns may result, and in body MRI imaging, this most often results in a darkening/shading of the central portion of the image.

To improve the artifact, the easiest solution is often to just switch the patient to a lower field system (e.g. 1.5 T) .

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Case Information

rID: 32988
Case created: 23rd Dec 2014
Last edited: 10th Sep 2015
Inclusion in quiz mode: Included

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