2019 Volume 58 Issue 2 Pages 58-65
Objectives: The purpose of this study was to develop a method for evaluating the image quality of multi-detector computed tomography （MDCT） protocols for dental implant treatment planning. Methods: In experiment 1, an aluminum phantom composed of 12 steps, with 7 holes in each step, was scanned with two CT units. The numbers of undetectable holes on superimposed images were counted after the optimal threshold grey value had been determined using the just-noticeable difference （JND） method. The results were compared with those obtained by 7 observers. In experiment 2, we used two 12-step phantoms, with 7 holes in each step. One was made of aluminum, and the other was made of Teflon （polytetrafluoroethylene）. They were scanned with a CT scanner at a tube voltage of 120kV, and the tube current was set at 200, 150, 100, 50, or 10mA. Results: On superimposed CT images, the numbers of undetectable holes according to the aforementioned method exhibited predictable relationships with the values obtained by the observers. The number of undetectable holes decreased as the tube current increased up to 150mA in both the aluminum and Teflon phantoms. There was no significant difference in the number of undetectable holes between 150mA and 200mA. Considering the administered radiation dose, a tube current of 150mA was considered appropriate for use in our hospital. Conclusions: Our JND-based method can be used to evaluate the image quality of MDCT. This technique, which involves aluminum and Teflon phantoms, is expected to be an effective way of determining the optimal MDCT protocol.