Table 1.
Commonly used trabecular parameters
| Parameter | Symbol (unit) | Description |
|---|---|---|
| Bone volume fraction | BV/TV | The proportion of trabecular bone voxels relative to the total number of voxels in a given region or volume of interest (VOI) |
| Degree of anisotropy | DA | DA describes the trabecular orientation in 3D space. Anisotropic structure has a preferred orientation to the trabecular struts, while isotropic structures show symmetry of the orientation in all directions. DA is usually calculated using the mean intercept length (MIL) algorithm (see Harrigan & Mann, 1984), where the eigenvectors give the main directions. DA is reported as a dimensionless value, with fully isotropic structure represented by 0 or 1, and higher values representing relatively more anisotropic structures |
| Trabecular thickness | Tb.Th (mm) | The mean thickness of the trabecular struts in a given region or VOI. This is typically measured via ‘sphere‐fitting’, i.e. by the diameter of spheres that can be fully contained within the structure |
| Trabecular separation | Tb. Sp (mm) | The mean width of the spaces between adjacent trabeculae in a given region or VOI |
| Trabecular number | Tb.N (mm−1) | The number of trabecular struts per mm. It is calculated as the inverse of the mean distance between the mid‐axes of the trabecular struts |
| Structure model index | SMI | SMI is a dimensionless measure of the relative proportion of plate‐like vs. rod‐like structures in a given region or VOI. Values typically range from 0 (idealised plates) to 3 (idealised rods), and can be positive or negative values. Negative values indicate a more concave or closed structure, like a honeycomb; positive values indicate a more convex and open structure |
| Connectivity density | Conn.D | The number of interconnected trabeculae per unit volume (Odgaard & Gundersen, 1993) |
| Trabecular bone pattern factor | Tb.Pf (mm−1) | A proxy measure of trabecular connectivity within a given region or VOI. Lower values indicate greater connectivity and structural integrity within the trabecular structure; higher values indicate greater fragmentation and the presence of isolated trabecular struts. It can also have positive (connected structures are more convex) or negative (connected structures are more concave) values and the basis of its calculation is similar to SMI (Hahn et al. 1992). Thus, changes in SMI and Tb.PF values are closely correlated. Importantly, Odgaard (1997) demonstrates that quantification of Tb.Pf in 2D is not representative of connnectivity in 3D |
| Bone surface density | BS/BV | The ratio of trabecular bone surface area relative to total trabecular bone volume in a given region or VOI |