Susceptibility artifacts occur as the result of microscopic gradients or
variations in the magnetic field strength that occurs near the interfaces
of substance of different magnetic susceptibility. Large susceptibility artifacts
are commonly seen surrounding ferromagnetic objects inside of diamagnetic
materials (such as the human body). These gradients cause dephasing of spins
and frequency shifts of the surrounding tissues. The net result are bright
and dark areas with spatial distortion of surrounding anatomy. These artifacts
are worst with long echo times and with gradient echo sequences.
Clicking the icon will show an axial MRI of the head in a patient with mascara on her eyelids. Susceptibility artifacts from the mascara obscure the front half of the globes.