Foreign body

  • Metal and glass are radio opaque.
  • Wood and plastic radiolucent
  • 15 % of wood foreign bodies detected on radiograph
  • Radiograph go to imaging tool
  • Ultrasound lesser role – often difficult because of wounds accessibility etc. when looking, use a linear high frequency transducer
  • Metals show streak artefacts on CT and susceptibility artefacts on MR. MRI is generally not preferred for detection, especially should be avoided for evaluation of foreign bodies around CNS and orbit
  • Wood and glass show geometric signal drop in MRI.
  • Wood over time can absorb fluid and become denser
  • MRI has role in detecting foreign body inflammation, granuloma formation and abscess
  • Ultrasound can give clue to type of foreign body. Reverberation artefacts seen in smooth objects like glass. Posterior shadowing with irregular surface like wood. Plastic has marked posterior shadowing