Synchronised biplanar x-ray videos can be used to quantify three-dimensional movement. This can either be done by tracking the position of small radio-opaque markers, or by so-called rotoscoping: superimposing the 3D-shape of the object to match its views in the two x-ray projection plane in 3D-graphics software.
Methods to perform 3D-kinematic analyses, and to generate 3D-animations of the results have been developped at Brown University. These methods are commonly referred to as XROMM (X-ray Reconstruction of Moving Morphology). Several of these tools are illustrated below, but more information can be found on the XROMM and XROMM wiki webpages of Brown University.
The undistortion and 3D-calibration objects available in the 3D2YMOX room (see at the bottom of the Technical information page) are compatible with the analysis software XMA-lab. Undistortion removes any type of skewing of the image due to the x-ray image intensifier and its downstream series of lenses:
The 3D-calibration procedure uses a grid with metal spheres at known positions, and four symbols (circle, cross, triangle, square) to define the orientation of the Cartesian reference frame. The centres of the spheres are automatically determined by XMA-lab, while manual clicking on the symbols sets the reference frame:
Based on images of the external surface of our small lego cube placed in the same position and orientation as in the X-ray calibration, it is possible to add 'normal' optical cameras to the 3D calibration scene, i.e. in the same reference frame as the X-ray videos. More detailed information on the small lego cube can be found here (Small_lego_cube_information_sheet_v5.pdf), and a protocol to do a 3D calibration in XMAlab using the small cube's surface coordinates can be found here (Creating a calibration file from 3D surface coordinates using GOM Inspect v2.pdf).
The CAD file of the small lego cube registered in the frame of the x-ray marker reference file can be downoaded in GOM format here (legocube_small_GOM_v2.ginspect) and in a version using STL files (no color textures) here (Lego_cube_small_STL_files.zip).