Dielectric shading at 3 T: the dark patch in the abdomen
A dark or bright area in the middle of a large body part at 3 T is often the RF field and not disease.
Dielectric (standing wave) shading
A dark area in the middle of the abdomen or pelvis at 3 T, worse with ascites, pregnancy or large body size.
At 3 T the RF wavelength in tissue (about 26 cm) is close to body size. Waves interfere and B1 is not uniform.
- Multi-channel RF transmission (parallel transmit / RF shimming)
- Dielectric pad on the abdomen
- Scan the patient at 1.5 T
Pads take set-up time.
This page is one entry from the MRI Technologist Reference
The full reference has 31 protocols, 9 dynamic study timelines, 19 artifacts, 16 scanner problems and 15 safety topics, as a PDF in English and Arabic plus an interactive tool.
Educational reference. It does not replace your site protocols, the radiologist's instructions, the MR safety officer, or the manufacturer's instructions for any implant, device or contrast agent. Parameter values are typical starting points at 1.5 T and must be adapted to the scanner, coil and patient.