Detection of Intraorbital Foreign Bodies Using Magnetic Resonance Imaging and Computed Tomography

We analyze the detectability of intraorbital foreign bodies (OrbFBs) of various types and sizes using computed tomography (CT) and magnetic resonance imaging using a three-Tesla machine (MRI 3 T).

An ex vivo model of sheep eyes with preserved extraocular muscles and orbital fat tissue placed in the orbital cavity of the human skull was created for this study. Foreign bodies made of four different materials - plastic, bottle glass, stone and wood - each in three different sizes (large, intermediate and small) were inserted into the soft tissue of the orbit in the extraocular space. Each orbit was scanned by CT and MRI. Images were analyzed by a senior radiologist and underwent masked review by three oculoplastic surgeons.

Analysis of MRI and CT scans identified distinguishing characteristics for each of the four materials. This information was further integrated into a clinical algorithm. CT allowed easier identification of most of the embedded materials compared to MRI. Smaller OrbFB size was associated with lower detectability. Review of CT yielded 94.4% agreement between oculoplastic specialists in detecting OrbFbs using CT scans and allowed detection of most OrbFBs. In contrast, the overall agreement with MRI was lower: 66.7% with T1 MPRAGE, 50% with T1TSE, 88.9% with T2 TSE and 72.2% with T2 TSE FS. Plastic was the most difficult material to detect in all size categories.

CT offers a clear advantage over MRI for detecting and localizing nonmetallic OrbFBs of all sizes, except for plastic. Plastic OrbFBs can be detected with CT depending on size but are more visible in MRI scans.