Metal foreign bodies may be present if they are ingested, inserted, or as a result of an injury.
Radiographic features
Nearly all metals are radiopaque and can be seen on plain radiographs and CT with the exception of aluminum, which may not be seen on plain radiographs 1,2.
Ultrasound
Metal foreign bodies are hyperechoic with posterior acoustic shadowing +/- reverberation artifact 1.
CT
Almost all metals are very high density 1:
- aluminum: 700-800 HU
- iron: ~3000 HU
- lead: 30,000 HU
As a result, metals except aluminum have associated beam hardening and streak artifacts 1.
MRI
Metal foreign bodies are typically low signal with most metals generating susceptibility artifact (gold and austenitic stainless steel do not). On GRE sequences blooming artifact can be present 1,2.
Treatment and prognosis
Metal foreign bodies can be treated conservatively, as they readily form foreign body granulomas and become essentially inert 2.
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