Micro-tomographic imaging for the nondestructive evaluation of trabecular bone architecture.

The structural properties of trabecular bone have been shown to vary significantly with age, anatomic location, and metabolic condition. Micro-computed tomography (microCT) is an emerging technique for the nondestructive assessment and analysis of the three-dimensional trabecular bone architecture. Within the framework of the European Union BIOMED I project "Assessment of Bone Quality in Osteoporosis," a total of 350 bone biopsies from five different anatomical locations were harvested post mortem from 70 donors (aged 23 to 92 years). These biopsies were measured using a newly devised compact micro-tomographic system, also referred to as desk-top microCT. Samples with a diameter from a few millimeters to a maximum of 18 mm and a length of up to 55 mm can be measured. For this study fresh, untreated bone biopsies with a diameter of 8 mm were measured micro-tomographically with a nominal isotropic resolution of 14 microns. For all samples, the volumes of interest (4 x 4 x 4 mm3) were binarized using a uniform threshold. Subsequently, standard structural indices such as bone volume density (BV/TV), bone surface density (BS/BV), trabecular plate number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp) and the degree of anisotropy (DA) were computed for all specimens incorporating mean intercept length (MIL) measurements. Regression analysis was used to estimate the correlations of single structural parameters with age or with a second parameter and also among different measurement sites. The nondestructive microCT measurements allowed not only to perform quantitative bone morphometry but also to assess other important microstructural features in the determination of the mechanical integrity of trabecular bone such as the incidence and prevalence of microcallus formations. The findings from the BIOMED I study are expected to improve our understanding of the relative importance of bone architecture, damage accumulation, and bone mineralization in the characterization of bone quality in the progress of age- and disease-related bone loss.