Fundamental efficiency of new-style limited-cone-beam CT (3DX). Comparison with helical CT

Limited-cone-beam CT named 'Ortho-CT' has been used clinically for more than 2 years. On the basis of this experience we developed the new-style limited-cone-beam CT for practical use named '3DX Multi image micro CT' (3DX). Purpose of this study was to evaluate the fundamental efficiency of this new-style limited-cone-beam CT in comparison with helical-CT. The resolutions of 3DX was evaluated with MTF (Modulation transfer function). 3DX were compared with helical CT about the fundamental efficiency. The subjective image quality was evaluated with the anatomical landmarks which included inner ear, temporomandibular joint (TMJ), and the maxillary first molar and mandibular first molar. Five dental radiologists and two otolaryngologists evaluated the quality of 3DX image in comparison with that of helical CT images on the same observation point. The five-point scale used ranged from point one (inferior) to five (superior). The skin doses of 3DX and helical CT were measured using TLD on the Rando phantom. The resolution of 3DX was 3.1 line pair/mm (horizontal) and 4.2 line pair/mm (vertical). The subjective image quality of 3DX was better than that of helical CT at every observational point. The minimum score was 3.46 and maximum score was 4.03. There was a significant difference in every observation point (p<0.05). The skin doses were 1.19 mSv with 3DX and 160.0 mSv with helical CT. The skin dose of 3DX was very low compared with that of helical CT. The image showed very high resolution in comparison with that of helical CT. The skin dose was under the one-percent as against helical CT. This system is very useful for diagnosis of tooth and bone in dental and otological field. (author)