Dental-CT: Image quality and absorbed radiation dose of different scan protocols.

Purpose: To develop a scan protocol for dental-CT which guarantees good ima ge quality at the lowest possible radiation dose. Methods: In an experiment al investigation Dental-CT (HSA, GE, Milwaukee, USA) of the mandible of two human skeletons positioned in a water tank were performed in order to defi ne the most advantageous scan protocol. Tube currents ranged from 40 to 200 mA and the scan technique was modified (axial mode or helical mode with pi tches of 1 to 3 and corresponding increments of 0.4 to 1.0 mm). 39 patients underwent a dental-CT with decreased current (80 mA) in the helical scan m ode (pitch 2, slice thickness 1 mm). Dose measurements were performed for t wo different scan protocols (A: axial, 130 mAs, B: helical, 80 mA, pitch 2) . Results: The preliminary investigations of image quality showed only a mi nor effect of the applied current. For the helical scan mode, pitches of mo re than 2 impaired image quality. A low increment had no advantages. There were no disadvantages in clinical practice using protocol B with decreased tube current. Absorbed radiation dose of dental CT performed with protocol B was decreased to one third in comparison to protocol A. Conclusions: A sc an protocol with a low tube current (e.g., 80 mA, for a rotation time of 1 s) and a helical scan mode (e.g., for a slice thickness of 1 mm with a pitc h of 2 and an increment of 1 mm) is recommended for performing dental-CT.