We propose a new technique to measure the 3D motion of marker points along a straight path within an object
using x-ray stereo projections. From recordings of two x-ray projections with 90° separation angle, the 3D
coordinates of marker points can be determined. By synchronizing the x-ray exposure time to the motion event,
a moving marker leaves a trace in the image of which the gray scale is linearly proportional to the marker
velocity. From the gray scale along the motion path, the 3D motion (velocity) is obtained. The path of motion
was reconstructed and compared with the applied waveform. The results showed that the accuracy is in order of
5%. The difference of displacement amplitude between the new method and laser vibrometry was less than 5μm.
We demonstrated the method on the malleus ossicle motion in the gerbil middle ear as a function of pressure
applied on the eardrum. The new method has the advantage over existing methods such as laser vibrometry
that the structures under study do not need to be visually exposed. Due to the short measurement time and the
high resolution, the method can be useful in the field of biomechanics for a variety of applications.