Advanced imaging of bone macro and micro structure.

In the past decade, considerable progress has been made in the development of methods for assessing the skeleton noninvasively so that osteoporosis can be detected early, its progression and response to therapy carefully monitored, or the risk of fracture effectively ascertained. Bone mineral density (BMD) of the peripheral, central, or entire skeleton as well as the trabecular or cortical bone envelopes, can now be evaluated with a high degree of accuracy and precision, and the strength of bone and the propensity to fracture can be reliably estimated. Noninvasive and/or nondestructive techniques are capable of providing macro or micro structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, numerous studies indicate that bone strength is only partially explained by BMD. Quantitative assessment of macrostructural characteristics such as geometry, and microstructural features such as relative trabecular volume, trabecular spacing, and connectivity, may improve our ability to estimate bone strength. The methods available for quantitatively assessing macrostructure include (besides conventional radiographs, which are not considered in this review) computed tomography and particularly volumetric quantitative computed tomography (vQCT). Methods for assessing microstructure of trabecular bone noninvasively and/or nondestructively include high-resolution computed tomography (hrCT), micro computed tomography (mCT), high-resolution magnetic resonance (hrMR), and micro magnetic resonance (mMR). vQCT, hrCT, and hrMR are generally applicable in vivo, and mCT and mMR are principally applicable in vitro.