三次元動作解析の精度の検討

抄録

We have used three-dimensional (3-D) motion analysis to measure equilibrium function in patients with vertigo or dizziness. The reliability of the analysis depends on the accuracy of the values of reflective markers on 3-D coordinates. In this paper, we studied the reliability of the 3-D motion analysis method described above using two kinds of experiments. In our routine examinations, 2 CCD video cameras are used to record subjects. Thirty pictures were taken during a one-minute video recording.
Experiment 1: A subject carried a board with 3 reflective markers attached and walked around while being video recorded for 8.3 seconds. Distances between each pair of three markers were 14.8 cm and 13.6 cm, and these values were analyzed. Similarly, an angle of 90.5 degrees formed by two lines connecting each pair of markers was analyzed. The mean differences between the real value and analyzed value were calculated for the entire 8.3 seconds. Those differences of the two distances were 0.08 cm and 0.14 cm, while the difference of the angle was 0.5 degree.
Experiment 2: Analysis of the acceleration of a reflective marker in free falling was repeated twelve times. The analyzed values between 0.167 seconds and 0.267 seconds after the beginning of the falling were rather accurate. However, shapes of the marker were recorded as an ellipse 0.300 seconds after beginning the fall. Therefore, it became impossible to obtain accurate values of reflective markers in 3-D coordinates. One of the reasons for this phenomenon may be overexposure due to the slow shutter speed of CCD video cameras. Despite such a problems, our experiments indicated that 3-D motion analysis appeared to be sufficiently accurate to measure equilibrium function.