Ferromagnetic metal will cause a
magnetic field inhomogeneity, which in turn causes a local signal void, often accompanied by an area of high
signal intensity, as well as a
distortion of the image.
They create their own
magnetic field and dramatically alter
precession frequencies of protons in the adjacent tissues. Tissues adjacent to
ferromagnetic components become influenced by the induced
magnetic field of the metal
hardware rather than the parent field and, therefore, either fail to
precess or do so at a different
frequency and hence do not generate useful signal. Two components contribute to
susceptibility artifact, induced
magnetism in the
ferromagnetic component itself and induced
magnetism in protons adjacent to the component.
Artifacts from metal may have varied appearances on
MRI scans due to different type of metal or configuration of the piece of metal.
The biocompatibility of metallic alloys, stainless steel, cobalt chrome and titanium alloy is based on the presence of a constituent
element within the alloy that has the ability to form an adherent oxide coating that is stable, chemically inert and hence biocompatible. In relation to imaging titanium alloys are less
ferromagnetic than both cobalt and stainless steel, induce less
susceptibility artifact and result in less marked image degradation.
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Further Reading:
Case Study 1 :
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