Dielectric effect artifact

Dielectric effect artifact is an MRI artifact encountered most often on body MRI with 3 T units.

Artifact

At 3 T, the radiofrequency (RF) wavelength measures 234 cm in air, and the speed and wavelength of the RF field is shortened to ~26 cm within the body as a result of dielectric effects. However, this 26 cm field of view is approximately the cross-sectional diameter of most body imaging studies.

With patient abdominal diameters that exceed the RF wavelength (e.g. patients with cirrhosis and ascites or pregnant patients), constructive and destructive interference patterns may emerge. In body MRI this may lead to darkening/shading at the center of the image.

At 7.0 T, the RF wavelength in tissue decreases to ~11 cm.

Improvement

• switch imaging to a <3.0 T system
• drain ascites before imaging a patient with cirrhosis to decrease the chance of the artifact occurring