The limited cone-beam CT known as Ortho-CT has been used in clinical examination since 1997. On the basis of this experience, we developed a new style of limited cone-beam CT for practical use, called “3DX Multi image micro CT” (3DX). The purpose of this study was to introduce this new style of limited cone-beam X-CT by comparing it to the prototype (Ortho-CT). Material and Methods: 3DX was compared with Ortho-CT regarding the fundamental efficiency. The skin doses of 3DX and Ortho-CT were measured using TLD on a Rando phantom. The resolutions of both systems were evaluated with MTF (modulation transfer function). The subjective image quality was evaluated on the following anatomical landmarks : the inner ear, temporomandibular joint (TMJ), maxillary first molar, mandibular first molar. Five dental radiologists and two otolaryngologists evaluated the quality of 3DX images comparing then with that of Ortho-CT images for the same observation point. The five-point scale ranged from one point (inferior) to five (superior). Results: The skin doses were 1.07 mSv with 3DX and 1.19 mSv with Ortho-CT. The skin dose of “3DX” was almost the same as that of Ortho-CT. The resolutions of Ortho-CT were 0.6 line pair/mm (horizontal) and 0.9 line pair/mm (vertical) on the MTF (0.5). The resolution of 3DX was 1.1 line pair/mm (horizontal) and 1.3 line pair/mm (vertical). The subjective image quality of 3DX was better than that of Ortho-CT at every observation point. The minimum score was 3.46, and maximum score was 4.17. There were significant differences with every observation point (p<0.05). Conclusion: On the basis of the clinical experience of Ortho-CT, a new style of limited cone-beam X-CT called “3DX” was developed by us for practical use. The skin dose is almost the same as in the prototype system. The images show very high resolution compared to those of the prototype system. We think that this system is very useful for diagnosis of hard tissue for dental purposes and otology.
