Advanced imaging of the macrostructure and microstructure of bone

Noninvasive and/or nondestructive techniques are capable of providing more macro- or microstructural information about bone than standard bone densito metry. Although the latter provides important information about osteoporoti c fracture risk, numerous studies indicate that bone strength is only parti ally explained by bone mineral density. Quantitative assessment of macro- a nd microstructural features may improve our ability to estimate bone streng th. The methods available for quantitatively assessing macrostructure inclu de (besides conventional radiographs) quantitative computed tomography (QCT ) and volumetric quantitative computed tomography (vQCT). Methods for asses sing microstructure of trabecular bone noninvasively and/or nondestructivel y include high-resolution computed tomography (hrCT), micro-computed tomogr aphy (mu CT), high-resolution magnetic resonance (hrMR), and micromagnetic resonance (mu MR). vQCT, hrCT and hrMR are generally applicable in vivo; mu CT and mu MR are principally applicable in vitro. Although considerable pr ogress has been made in the noninvasive and/or nondestructive imaging of th e macro- and microstructure of bone, considerable challenges and dilemmas r emain. From a technical perspective, the balance between spatial resolution versus sampling size, or between signal-to-noise versus radiation dose or acquisition time, needs further consideration, as do the trade-offs between the complexity and expense of equipment and the availability and accessibi lity of the methods. The relative merits of in vitro imaging and its ultrah igh resolution but invasiveness versus those of in vivo imaging and its mod est resolution but noninvasiveness also deserve careful attention. From a c linical perspective, the challenges for bone imaging include ba la nci ng t he relative advantages of sim pie bone densitometry against the more comple x architectural features of bone or, similarly, the deeper research require ments against the broader clinical needs. The considerable potential biolog ical differences between the peripheral appendicular skeleton and the centr al axial skeleton have to be addressed further. Finally, the relative merit s of these sophisticated imaging techniques have to be weighed with respect to their applications as diagnostic procedures requiring high accuracy or reliability on one hand and their monitoring applications requiring high pr ecision or reproducibility on the other. Copyright (C) 2000 S. Karger AG. B aser.