Analysis of local bone ultrastructure in the context of the trabecular microarchitecture.

<p>(A) Gray values from synchrotron radiation-based computed tomography (SR CT), which represent local mineralization levels. Linear range: 1–2.5∙10⁴ (a.u.). (B) Distance to bone surface. Linear range: 0–70 μm. (C) Distance to skeleton. Linear range: 0–200 μm. (A-C) Blue (bottom) and yellow (top) represent the minimum and maximal values respectively, where intermediate values are interpreted according to the linear colormap provided at the right border. (D) Local surface curvature. Convex and concave geometries have positive and negative values for the local surface curvature, respectively. (C-D) Distance to skeleton and local surface curvature is heavily affected by the 3D geometry of the trabecular microarchitecture and cannot be easily interpreted in 2D. (E-F) Alignment of the ultrastructure with trabecular microarchitecture. (E) The normals to the bone surface of a trabecula, whose structure and ultrastructure orientation are depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159838#pone.0159838.g002" target="_blank">Fig 2C</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159838#pone.0159838.g002" target="_blank">Fig 2D</a>, respectively. (F) The alignment is quantified by the angle of the ultrastructure orientation to the surface normal for each surface element, in the form of a histogram. The orange line visualizes the threshold value of 75° between the two vectors, above which the ultrastructure was considered to be perpendicular to the bone surface and thus aligned with the trabecular microarchitecture.