Magnetic susceptibility artifact
Citation, DOI & article data
Magnetic susceptibility artifacts (or just susceptibility artifacts) refer to a variety of MRI artifacts that share distortions or local signal change due to local magnetic field inhomogeneities from a variety of compounds.
They are especially encountered while imaging near metallic orthopedic hardware or dental work, and result from local magnetic field inhomogeneities introduced by the metallic object into the otherwise homogeneous external magnetic field B0. These local magnetic field inhomogeneities are a property of the object being imaged, rather than of the MRI unit itself.
A common susceptibility-related artifact, deliberately sought to make small lesions more conspicuous, is the blooming artifact.
Types of magnetic susceptibility
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 and 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.
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