Imaging assessment of bone quality in osteoporosis

Noninvasive and/or nondestructive techniques can provide structural information about bone beyond simple bone densitometry. Although bone densitometry provides important information about osteoporotic fracture risk, many studies indicate that bone mineral density only partly explains bone strength. Quantitative assessment of macrostructural characteristics, such as geometry, and microstructural features, such as relative trabecular volume, trabecular spacing, and connectivity, may improve the ability to estimate bone strength. Methods for quantitatively assessing macrostructure include (besides conventional radiographs) dualenergy x-ray absorptiometry (DXA) and computed tomography (CT), particularly volumetric quantitative computed tomography (vQCT). Methods for assessing microstructure of trabecular bone noninvasively and/or nondestructively include high-resolution computed tomography (hrCT), microcomputed tomography (μCT), high-resolution magnetic resonance (hrMR), and micromagnetic resonance μMR. Volumetric QCT, hrCT, and hrMR are generally applicable in vivo; μCT and μMR are principally applicable in vitro. Despite progress, problems remain. The important balances between spatial resolution and sampling size, or between signal-to-noise and radiation dose or acquisition time, need further consideration, as do the complexity and expense of the methods vs their availability and accessibility. Clinically, the challenges for bone imaging include balancing the advantages of simple bone densitometry vs the more complex architectural features of bone or the deeper research requirements vs the broader clinical needs. The biological differences between the peripheral appendicular skeleton and the central axial skeleton must be further addressed. Finally, the relative merits of these sophisticated imaging techniques must be weighed with respect to their applications as diagnostic procedures, requiring high accuracy or reliability, vs their monitoring applications requiring high precision or reproducibility.