Magnetic susceptibility artifact

Magnetic susceptibility artifact refers to a distortion in the MR image especially seen while imaging metallic orthopedic hardware or dental work. This results from local magnetic field inhomogeneities introduced by the metallic object into the otherwise homogeneous external magnetic field B0. These local magnetic field inhomogeneities are known as magnetic susceptibility and are a property of the object being imaged.

In terms of magnetic susceptibility, most materials can be classified as diamagnetic, paramagnetic, superparamagnetic, or ferromagnetic.

Water is considered (weakly) diamagnetic.

Paramagnetic materials, which have unpaired electrons, concentrate local magnetic forces and thus increase the local magnetic field, i.e. have increased magnetic susceptibility.

Superparamagnetic materials contain particles with a much stronger magnetic susceptibility than that of paramagnetic materials, e.g. SPIO (superparamagnetic iron oxide) has been used in liver imaging.

Ferromagnetic materials contain large solid or crystalline aggregates of molecules with unpaired electrons exhibit “magnetic memory,” by which a lingering magnetic field is created after their exposure to an external magnetic field. Examples of ferromagnetic metals include iron, nickel, and cobalt, all of which distort magnetic fields, thereby causing severe artifacts on MR images.

See also

MRI physics

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