A method for accurate 3-D reconstruction of skeletal morphology and movement
Brainerd, E.L., Gatesy, S.M., Metzger, K.A., Baier, D.B., and Hedrick, T.L.
Accurate 3-D skeletal movement data would be valuable for many areas of biomechanics research. Bone movement sometimes can be inferred from external movement, but loose skin introduces artifacts and many bones are too deep in the body to be tracked externally. We are developing a method "CTX imaging" for visualizing skeletal position during rapid movement. CTX combines bone shape data from CT scans with bone position data from biplanar x-ray video. The result is an accurate movie of 3-D bones moving in 3-D space. Here we describe our work on a marker-based CTX method. Two OEC 9400 C-arm cinefluoroscopes were retrofitted with high-speed video cameras (1000 fps) and arranged such that the intersection of the x-ray beams covers a basketball-sized volume. The steps in marker-based CTX are: 1) at least three radiopaque spheres (1 mm) are surgically implanted into each bone of interest; 2) biplanar x-ray movies of animal movement are collected; 3) distortions introduced by fluoroscope and camera are removed from the movies and XYZ coordinates of the markers are measured; 4) the animal is CT scanned and digital 3-D bone models are made with the markers in still place; 5) the data from marker motion capture (steps 1-3) are used to position and orient the 3-D bone models (from step 4), resulting in an accurate (±0.1 mm) reconstruction of bone position over time. We are also working on a markerless CTX method that will not require surgical implantation of radiopaque spheres.
Ecology & Evolutionary Biology - Brown University