Rate of metallic foreign bodies found on orbital radiographs prior to MRI.

OBJECTIVE: The purpose of this research is to more precisely quantify the positivity rate for conventional radiographs (CR) of the orbit performed for the purpose of pre-MR screening in patients at risk of having a radio-opaque orbital foreign body (ROFB).

METHODS: By review of electronic medical records, we identified 47,237 patients who had undergone orbital CR for clearance of ROFB prior to MRI. The reports from these examinations were manually reviewed, and the examinations with positive findings were re-interpreted by a CAQ-certified head and neck radiologist. The rate of ROFB found in these examinations was reported and compared to historical estimates in the literature.

RESULTS: 328 of the 47,237 examinations (0.69 %) were originally interpreted as positive for ROFB. Upon re-review, only 39 of the 47,237 examinations (0.083 %, 95 % CI 0.06 %-0.11 %) contained ROFB that were in locations that posed a risk to ocular or vascular structures or were in an equivocal location. Almost all of the patients with false-positive initial interpretations had been denied MRI.

DISCUSSION: The rate of ROFB discovered on clearance CR of the orbits prior to MRI is far less than previously estimated in the radiology literature. More conservative guidelines for MR clearance may be useful to reduce costs, mitigate imaging delays, and avoid unnecessary denial of imaging.