Published in:
01-09-2013 | Original Article
Foreign bodies: radiopaque compared to what?
Published in: Pediatric Radiology | Issue 9/2013
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Background
The term “radiopaque” is commonly used when discussing foreign bodies and lists of radiopaque and non-radiopaque materials are sometimes created, but radiopacity is not a binary concept. A more fundamental understanding of radiopacity is necessary for the work-up of foreign bodies.
Objective
To demonstrate that “radiopaque” is a relative term.
Materials and methods
Twenty foreign bodies of various sizes, shapes and materials were placed in a basin. Radiographs were obtained of the objects with 0, 2.5, 5 and 10 cm depth of water in the basin to simulate the appearance of a foreign body in human tissue. The progressively changing appearance of the objects was observed.
Results
All of the objects were radiographically visible in the empty basin. Different objects demonstrated different appearances when immersed in progressively deeper levels of water, illustrating the effect of the surrounding water as well as the effects of object shape, size, orientation and composition.
Conclusion
The concept of radiopacity seems simple and the term “radiopaque” is sometimes used to describe an all or none phenomenon. However, radiopacity is a comparative concept implying relative X-ray attenuation. Accurate understanding of the radiographic appearance of foreign bodies requires one to keep in mind the concepts of relative X-ray attenuation and contrast resolution.