Presentation
Asymptomatic cirrhotic patient with ascites. Rule out hepatocellular carcinoma.
Patient was imaged on a 3T system. Dielectric effect artifact centrally (also motion artifact with ghost images in the phase encoding direction). Central low signal in this cirrhotic patient with ascites.
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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