Accuracy verification of an automatic head-positioning system for a normalized measurement of jaw movement by an X-ray television

When measuring jaw movement by means of an X-ray television, the patient's head is immobilized, using a fixation jig. This, however, restricts the patient's jaw movement. To avoid this, we have been investigating a simple method, in which a head-position sensor and a robotized chair are used. Head-position is monitored by PSD camera-based photostereometry. If measurements are inconsistent, the robot-chair automatically corrects to within 5 degrees of freedom. Even this corrected head-position, however, has a certain margin of error, due to the mobility of the head, relative to the head support. To compensate for this, we employed an iterative method in that the positioning is repeated until the determined position converges. Through experiments using several subjects, this compensation was verified to converge in six iterations, and to be effective for the reduction of overall mobility errors.