Quantitative evaluation of patient movement during simulated acquisition of cephalometric radiographs.

The objective of this study was to perform the quantitative three-dimensional analysis of the patients' movements at the different time points during the simulated acquisition of cephalometric radiographs. Fifty-three subjects (32 men, 21 women) were divided into four groups according to their age (Group 1: 9-12, Group 2: 13-19, Group 3: 20-25, and Group 4: 26-30 years old). The experiment (Exp) consisted in providing the subjects with three different kinds of verbal instructions as follows; Exp 1: they were simply instructed not to move, Exp 2: detailed instructions were provided, and Exp 3: they were specifically instructed to clench their molars. The amount of their movement during the 20 s of the cephalomatric X-ray exposure was measured using an optical marker and tracker. The maximum movement was analyzed three-dimensionally at 0.5, 2, 5, 10, 15, and 20 s. There was minimal vibrating movement every 0.3-0.5 s and relatively large movement every 3-5 s. The youngest group showed the largest amount of movement among the four age groups, and their movement was more significant in the up and down direction (p < 0.05). There was no significant difference in the amount of movement according to the instructions. The longer exposure time showed the larger amount of the movement. Children can show the significant movements during X-ray taking, and the longer exposure time can also result in the larger movement during acquisition of cephalometric radiographs. Therefore, the shorter exposure time is recommended in order to improve image quality.