Ultrasound compared with projection radiography for the detection of soft tissue foreign bodies - A technical note

Soft tissue foreign bodies (STFBs) present a diagnostic challenge depending on their composition. Untreated complications can arise, namely infection through to loss of function. General (projection) radiography is recommended as the first line imaging examination. However, some STFBs are radiolucent, leading to false negative radiographs. The aim of this in vitro study was to compare ultrasound with projection radiographs for the detection of a range of different types of STFB.

Ethical approval (for use of participants to evaluate images) was granted by the Higher Education Institute's departmental Ethics Committee. Seven hand phantoms were created from a water, gelatine and psyllium mix. A different STFB (radiolucent and radiopaque) was inserted into six phantoms, with the seventh being a control. Ultrasound and projection radiograph images were generated of each phantom. Participants (academics and radiography students) reviewed all images.

50 responses were received from a study population of approximately 400, (10 academics, 40 students). The ability of ultrasound to detect radiolucent foreign bodies performs well compared with projection radiography: sensitivity 94% versus 9%, specificity 90% versus 88%. For radiopaque foreign bodies the data was more mixed: sensitivity 96% versus 99%, specificity 90% versus 88%.

These data suggest that ultrasound is superior to projection radiography for the detection of radiolucent STFBs. Limitations include the lack of formal postgraduate ultrasound training within the study population and a lack of simulated bony structure within the hand phantoms.

Ultrasound has the potential to be a useful modality in the detection of STFBs, particularly radiolucent objects. There are associated challenges such as conducting ultrasound in the vicinity of a wound, but further exploration of this application of ultrasound is warranted.