bonej.org .
Degree of anisotropy (DA) is a measure of how highly oriented
substructures are within a volume. Trabecular bone varies its
orientation depending on mechanical load and can become
anisotropic. This plugin uses the mean intercept length (MIL)
method for determining anisotropy. Briefly, a large number of
vectors of the same length originating from a random point within
the sample are drawn through the sample. When each vector hits a
boundary between foreground and background, an intercept is counted
for that vector. The mean intercept length on that vector is then
the vector length divided by the number of boundary hits. A cloud
of points is built up, where each point represents the vector times
its mean intercept length. Fitting an ellipsoid to the point cloud, construction of a material anisotropy tensor and subsequent eigendecomposition
results in eigenvalues giving the lengths of the ellipsoid's axes and eigenvectors giving the orientation of the axes. DA is calculated as 1 - length of the shortest axis
/ length of the longest axis. New random points with the same
vectors are sampled and DA updated with the new MIL counts until
either the minimum number of sampling points is reached or the
coefficient of variation of DA falls below a threshold.
Odgaard A (1997) Three-dimensional methods for quantification of cancellous bone architecture. Bone 20: 315-28. doi:10.1016/S8756-3282(97)00007-0.
Harrigan TP, Mann RW (1984) Characterization of microstructural anisotropy in orthotropic materials using a second rank tensor. J Mater Sci 19: 761-767. doi:10.1007/BF00540446.
