CT detection and location of intraorbital foreign bodies. Experiments with wood and glass.

The series comprises 27 patients examined by CT to detect, locate or exclude a foreign body. 22 of them actually had an orbital foreign body. In three cases CT was the primary method and showed the foreign body correctly, while in 18 it was first detected in plain films and CT was performed to locate it. 20 metallic foreign bodies were hyperdense in appearance. Two cases had wooden foreign bodies, one with a density of +10 HU and the other hypodense with a value of about -434 to -446 HU. The latter piece of wood was first interpreted falsely as a bubble of gas. The results proved that the detection of metal is easy, but differentiation between wood and gas is problematical. Experiments conducted to determine the CT densities of different pieces of wood gave results varying from -618 HU to +23 HU. The highest densities obtained for glass varied from +522 HU to +2000 HU. The density of a plastic lens was -105 HU.