Experimental measurement of human head motion by binocular stereo vision method

X-ray computed tomography, also known as CT scan, is an imaging procedure which utilizes computer-processed X-rays to produce images of inner areas of the body. Treatments to some diseases require CT resolution to be smaller than 40μm. However, at present, such resolution is hard to reach partly due to unavoidable movements of human bodies. This paper focuses on the movements of human heads. We experimented with volunteers and tried to compare the minimal movements of their heads in different states (sitting, lying with or without rigid fixation). We measured the rotations and shifts of the volunteers´ heads, and described the heads´ mean absolute excursions within different time intervals. We also tried to explain the tiny and cyclic movements. The conclusions are as follows. First, it is heartbeat that results in the tiny cyclic motions of human heads. Second, lying and fixation can greatly reduce head motions. Moreover, the longer it takes to complete the scan, the more severe the motions. The average excursion of a lying volunteer´ head without fixation can reach 100μm in 1 second. If resolution higher than 50μm is needed, we must not only apply fixation but also complete the scan in less than 10 seconds. However, no matter what fixations we apply and how fast the volunteers are scanned, an excursion of over 25μm exists. Hence it is essential to develop a new CT method if we want to reach a higher resolution.