Genant Harry K, Jiang Yebin
University of California, San Francisco, San Francisco, CA 94143, USA.
Ann N Y Acad Sci. 2006 Apr;1068:410-28. doi: 10.1196/annals.1346.038.
Noninvasive and/or nondestructive techniques can provide structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, many studies indicate that bone mineral density (BMD) 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 our ability to estimate bone strength. Methods for quantitatively assessing macrostructure include (besides conventional radiographs) dual 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 (micro-CT), high-resolution magnetic resonance (hrMR), and micromagnetic resonance (micro-MR). vQCT, hrCT, and hrMR are generally applicable in vivo; micro-CT and micro-MR 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 versus their availability and accessibility. Clinically, the challenges for bone imaging include balancing the advantages of simple bone densitometry versus the more complex architectural features of bone, or the deeper research requirements versus 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, versus their monitoring applications, requiring high precision or reproducibility.
非侵入性和/或非破坏性技术能够提供除简单骨密度测定之外的有关骨骼的结构信息。虽然骨密度测定能提供有关骨质疏松性骨折风险的重要信息，但许多研究表明，骨矿物质密度（BMD）只能部分解释骨骼强度。对宏观结构特征（如几何形状）和微观结构特征（如相对骨小梁体积、骨小梁间距和连通性）进行定量评估，可能会提高我们估计骨骼强度的能力。定量评估宏观结构的方法包括（除传统X线片外）双能X线吸收法（DXA）和计算机断层扫描（CT），尤其是容积定量计算机断层扫描（vQCT）。非侵入性和/或非破坏性评估骨小梁微结构的方法包括高分辨率计算机断层扫描（hrCT）、显微计算机断层扫描（micro-CT）、高分辨率磁共振成像（hrMR）和显微磁共振成像（micro-MR）。vQCT、hrCT和hrMR一般适用于活体；micro-CT和micro-MR主要适用于体外。尽管取得了进展，但问题依然存在。空间分辨率与采样大小之间，或信噪比与辐射剂量或采集时间之间的重要平衡，以及这些方法的复杂性和成本与其可用性和可及性之间的平衡，都需要进一步考虑。在临床上，骨成像面临的挑战包括平衡简单骨密度测定的优势与骨骼更复杂的结构特征，或者更深层次的研究需求与更广泛的临床需求。外周附属骨骼与中央中轴骨骼之间的生物学差异必须进一步加以研究。最后，必须权衡这些复杂成像技术在作为诊断程序（要求高精度或可靠性）与监测应用（要求高精确度或可重复性）方面的相对优缺点。
