A Comparison of Radiography, X-Ray Tomosynthesis, and CT for Intraorbital Metallic Foreign Body Screening

Objective: Before MRI examination, patients are often screened for intraorbital metallic foreign bodies (IMFBs) via questioning, clinical record review, and imaging when appropriate. This work compares the screening performance of digital radiography (DR), digital tomosynthesis (DT), and CT in detecting IMFBs composed of various metals and identifies their limits of detection. Methods: Fragments of aluminum, steel, and cobalt-cemented tungsten carbide were produced. A human skull model, with metal fragments embedded in grapes placed in each orbit, was submerged in a water bath to create a semi-anthropomorphic phantom. Phantom orbit images were acquired with DR, DT, and CT. Six experienced radiologists reviewed images and scored their confidence in detecting IMFBs. Receiver operating characteristic analysis was performed and a multireader, multicase analysis of variance was used to compare the modalities. Results: Performance comparison across modalities yielded area under the receiver operating characteristic curve values of 0.90, 0.79, and 0.78 for CT, DT, and DR, respectively. Pairwise comparison revealed that CT was superior to both DT and DR (P <.05). When stratified by metal type, a significant performance difference among modalities was only observed for steel. Steel fragments of mass 0.8 mg and smaller were not detected using DT or DR, but even the smallest steel fragments of 0.4 mg were detectable with CT. Conclusion: CT outperformed DT and DR in detecting IMFBs using a semi-anthropomorphic phantom. This performance difference is largely attributed to differences in detection of steel fragments. Since steel is often ferromagnetic, this distinction is relevant for imaging modality selection for orbit screening before MRI.