Purpose: To investigate and compare digital x-ray tomosynthesis (DT) to 2-view radiography (DR) and CT as a candidate modality for detecting tungsten carbide, steel, and aluminum fragments in the orbits for orbital metal screening prior to MRI.
Methods: A semi-anthropomorphic head phantom was created by placing a human skull model into a water bath. Shaving fragments of aluminum, steel, and tungsten carbide were created. Varying sized fragments of aluminum (0.1-0.7mg, 0.04-0.26mm³), steel (0.4-0.7mg, 0.05-0.09mm³), and tungsten carbide (1.3-8.1mg, 0.08-0.52mm³) were embedded in table grapes, with one fragment in each grape. The grapes were placed into the skull and images were acquired with our institution’s orbit CT protocol, 2-view facial bone DR protocol, and with a facial DT protocol. Resulting images were reviewed by a radiologist to qualitatively evaluate comparative detectability on each modality. For each set of grapes with different fragments embedded, repeatability was investigated by acquiring repeat images after repositioning of the grapes, the skull, and/or no repositioning.
Results: For the fragment sizes investigated, tungsten carbide was detectable on all modalities. Steel fragments were detectable on CT, and the largest steel fragment was just detectable on DT but not DR. The largest aluminum fragment was just detectable on CT but not on DT or DR. Repeatability tests indicated consistency in detectability of fragments on CT, while detection of fragments on DT was more position dependent.
Conclusion: With respect to detectability of orbital metal fragments, DT performance was found to lie in between that of DR and CT. DT may be an appropriate modality for orbital metal screening, providing a balance between the radiation dose, detection capabilities, and cost of DR and CT. Expansion of this work into a formal detectability study with multiple observers and a wider range of fragment sizes is warranted.