Cone beam computed tomography for imaging orbital trauma--image quality and radiation dose compared with conventional multislice computed tomography.

We compared the image quality and radiation dose to the lens of the eye in patients with suspected orbital fractures who were imaged using cone beam computed tomography (CBCT) or conventional multislice computed tomography (CT). Although CBCT has a lower radiation dose than conventional CT, it is not known whether the image quality is comparable for diagnostic purposes. We identified fractures of the orbit (floor or roof, or both) in 6/10 patients who were scanned using CBCT and in 5/10 patients who were scanned using multislice CT (orbital floor and medial wall). Impingement of the rectus muscle on fracture lines was identified with both techniques, but retro-orbital haemorrhage was detected only on multislice CT. The mean radiation dose to the lens of the eye was 42% lower (range 23-53, SD 10) for CBCT than for multislice CT (p<0.001), and the effective dose (a measure of the risk of developing a radiation-induced cancer) was also significantly lower. CBCT can therefore be used to diagnose orbital fractures, and is associated with a significantly lower radiation dose than multislice CT.