Shading artifact

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Shading artifact in MRI refers to loss of signal intensity in one part of the image, leading to dark shading in this portion of the image.

Causes
  • uneven excitation of nuclei within the field; due to RF pulses applied at flip angles other than 90 and 180 degrees
  • abnormal loading of coil or coupling of coil at a point (as with a large patient whom touches one side of the coil)
  • inhomogeneity in the magnetic field
  • overflow of analog to digital converter
Axis
  • frequency encoding
  • phase encoding

Remedy

  • load the coil correctly
  • use the proper size coil for patient size and the examined part
  • prevent the patient touching the coil (you can use foam pads between patient and coil)
  • shimming to reduce inhomogeneity of the magnetic field
  • use the proper scanning parameters to set proper amplitude of applied RF pulses (less amplification to avoid analog to digital converter over flow)

See also