Development of a compact computed tomographic apparatus for dental use

Objective: To describe a compact computed tomographic apparatus (Ortho-CT) for use in dental practice. Methods: Ortho-CT is a cone-beam-type of CT apparatus consisting of a multifunctional maxillofacial imaging machine (Scanora(R), Soredex, Helsinki, Finland) in which the film is replaced with an X-ray imaging intensifier (Hamamatsu Photonics, Hamamatsu, Japan). The region of image reconstruction is a cylinder 32 mm in height and 38 mm in diameter and the voxel is a 0.136-mm cube. Scanning is at 85 kV and 10 mA with a 1 mm Cu filter. The scan time is 17 s comparable with that required for rotational panoramic radiography. A single scan collects 512 sets of projection data through 360 degrees and the image is reconstructed by a personal computer. The time required for image reconstruction is about 10 min. Results: The resolution limit was about 2.0 lp mm(-1) and the skin entrance dose 0.62 mGy. Excellent image quality was obtained with a tissue-equivalent skull phantom, roots, periodontal ligament space, lamina dura, and cancellous bone were clearly visualized. Conclusion: Ortho-CT provides three-dimensional images of excellent quality for dental use at a low entrance dose.