Mike Heath DMU, Auckland radiology Group, Auckland, NZ

Introduction
In recent years ultrasound has established itself as an excellent modality for the detection of superficial non-radiopaque foreign bodies (FB) with reported sensitivities and specificities in the order of 90% (1,2). This review will briefly discuss imaging modalities for various types of superficial FB and then the ultrasound features of FB diagnosis. An emphasis will be placed on scan technique highlighting potential pitfalls with suggestions on how to minimise false positive and negatives. Consideration will also be given to findings which can help the referring physician.

Conclusion
Ultrasound is a sensitive test for the investigation of suspected superficial FB. It is the examination of choice for the non-radiopaque FB such as wood and plastic. Virtually all FB types can be detectd by ultrasound and the modality may be of use for specific localisation. Plain X-ray should reveal 100% of metal FB and is overall more sensitive for the detection of glass, fish bones, pencil lead and other high density materials.

Localisation of a detected FB for the clinician can be assisted by marking its length and orientation on the skin surface with an indelible marker and a depth from the skin surface indicated. Ultrasound can be of further assistance in searching for information that will influence management.

A negative ultrasound review does not exclude the presence of a FB and meticulous care has to be given to scan technique in order to overcome potential pitfalls. Further evaluation should be considered in the context of a negative ultrasound and strong clinical suspicion. Suspicious but inconclusive ultrasound findings coupled with a good clinical history should also prompt MR or CT evaluation contingent on expected FB type.