Tracking and analysis of human head motion during Guided fMRI motor tasks

In this work, we studied human head motions during upper extremity motor task, conducted in functional magnetic resonance imaging (fMRI) studies. The experiments were performed on a mock up of the MRI bench. Three kinds of linear movements in the caudal-cranial, left-right and anterior-posterior directions, a reaching movement as well as single joint movements at shoulder, elbow and wrist, were investigated at three different speeds with the right arm. Optical markers tracked by a high-precision motion tracking system were used to detect head and arm movements. For each task, the head moved principally in the direction of right-caudal-posterior to left-cranial-anterior, parallel to the line from the right shoulder joint to the head. No principal rotation axis was observed. The translational and rotational head motions were 1.7 ~ 8.4 mm and 0.15deg ~ 0.96deg, respectively. We then applied a special head fixation to stabilize the head, and repeated all the experiments. The translational and rotational head motions were significantly suppressed by 78% and 73%, to the range of 0.3 ~ 2.4 mm and 0.04deg ~ 0.39deg.