It is fortunate that many foreign bodies are radiopaque; most foreign bodies that can be missed during the initial clinical evaluation can be seen on plain films. 6 Plain films are readily available but must be obtained with appropriate technique and inspected carefully to detect small and faint foreign bodies. Metal, mammalian bone, some types of fish bones, teeth, pencil graphite, certain plastics, glass, gravel, sand, and aluminum are visible on plain radiographs 1-Z,8,9,l°,l1 and 12 (Table...42-1). Almost all glass is visible on radiographs if it is 2 mm or larger, and contrary to myth, glass does not have to contain lead to be visible on plain films. I5,7 A radiopaque fragment is more easily seen if it is positioned parallel to the central ray of the x-ray beam, which increases its apparent thickness.
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