HR-pQCT assesses peripheral sites (distal radius and distal tibia). The technique has all the advantages of quantitative CT; it makes a volumetric assessment of bone mineral density (rather than the areal measurement made by DXA), it is less affected by overlying soft tissue than DXA, and it can separate cortical and trabecular compartments. Because it measures peripheral sites in a purpose-built device, it can use high energy radiation to obtain high resolution images, with a low effective radiation dose. The voxel size was about 80 microns in the first generation scanners and 60 microns in the second generation. This resolution can image trabecular and cortical microstructure, to quantify trabecular number, thickness and structural homogeneity, and cortical porosity. Before HR-pQCT this level of microstructural detail could only be obtained in vivo by bone biopsy. HR-pQCT images can also be reconstructed into Finite Element models, for virtual testing of bone stiffness and strength. The earliest clinical studies gave new insights into age- and gender-specific changes in bone microstructure. For example, in men, trabecular thickness decreases with ageing but trabecular number is preserved, whereas in women, trabecular number decreases which has a greater impact on bone strength. HR-pQCT studies have increased our understanding of bone fragility in young women with idiopathic osteoporosis and obese children, as well as in older adults. They have also helped to understand the mechanism of action of different osteoporosis drugs. HR-pQCT is unlikely to become a widely-used clinical technique, but it is an important addition to the research tool kit.
Clinical imaging of bone microarchitecture with HR-pQCT. Nishiyama KK, Shane E. Curr Osteoporos Rep 2013 11:14755. doi: 10.1007/s11914-013-0142-7
Osteoporosis drug effects on cortical and trabecular bone microstructure: a review of HR-pQCT analyses. Lespessailles E, Hambli R, Ferrari S. Bonekey Rep. 2016;5:836. doi: 10.1038/bonekey.2016.59.