Magnetic resonance imaging and computed tomography in a model of wooden foreign bodies in the orbit

Wooden foreign bodies in the orbit are not detectable by standard roentgenography. Reports in the literature on the ability of computed tomography (CT) to detect orbital wooden foreign bodies have varied. To evaluate whether magnetic resonance imaging (MRI) would offer any advantage over CT in detecting wood in the orbit, MRI and CT were performed on an in vitro model of wooden foreign bodies in the orbit. Woods of different types and sizes were studied in vegetable fat backgrounds chosen to simulate orbital fat. On CT, most types of wood were hypodense to fat. Appropriate window settings were critical in the detection of wood by CT: in this model, a window width of 1000 Hounsfield units was optimal. On MRI. all types of wood were hypointense to fat. Small pieces of wood were surrounded by an MRI truncation artifact consisting of hyperintense spots. TI-weighted images demonstrated wood better than T2-weighted images and required less scanning time than either proton density or T2-weighted images. MRI was superior to CT in detecting the smallest pieces of wood. The role of MRI in the detection of orbital wooden foreign bodies in clinical practice remains to be determined.