Majumdar S, Genant H K
Department of Radiology, University of California, San Francisco 94143, USA.
Osteoporos Int. 1995 Mar;5(2):79-92. doi: 10.1007/BF01623308.
Osteoporosis is a common metabolic disorder with considerable associated morbidity and mortality. The loss of bone mineral integrity and the resultant occurrence of atraumatic fractures are typically symptomatic of the disease. Currently skeletal status is commonly assessed using non-invasive conventional radiography and scintigraphy as well as densitometric techniques such as quantitative computed tomography and dual-energy X-ray absorptiometry. But, apart from gross bone mineral density, the fine structure of trabecular bone also plays an important role in defining the biomechanical competence of the skeleton. Recently attention has been focused on deriving measures that provide information about not only trabecular bone density but also microstructure. Magnetic resonance imaging (MRI) is one such new technique which potentially may provide information pertaining to bone density and structure as well as to occult fracture detection. Cortical bone produces a signal void in MR images, due to the fact that it contains very few mobile protons that give rise to a signal in MRI; also the MR relaxation time T2 of these protons is very short which produces a very fast decay of the MR signal during image acquisition. However, the trabecular bone network affects the MR properties of bone marrow. The difference in the magnetic properties of trabecular bone and bone marrow generates local imperfections in the magnetic field. The MR signal from bone marrow is modified due to these imperfections and the MR relaxation time T2 of marrow is shortened. The extent of relaxation time shortening and hence loss of signal intensity is proportional to the density of trabecular bone and marrow interfaces and their spatial architecture. Recent investigation in this area include studies aimed at quantifying marrow relaxation times and establishing their relationship to trabecular bone density and structure. In addition, with advances in imaging software and hardware, MR images at in-plane resolutions of 78-200 microns may be obtained. The trabecular bone structure is clearly revealed in such images and studies aimed at the development of high-resolution MRI techniques combined with quantitative image analysis techniques are currently under way. These potentially useful techniques for assessing osteoporosis and predicting fracture risk are reviewed in this paper.
骨质疏松症是一种常见的代谢性疾病，伴有相当高的发病率和死亡率。骨矿物质完整性的丧失以及由此导致的非创伤性骨折的发生是该疾病的典型症状。目前，骨骼状态通常使用非侵入性的传统放射摄影和闪烁扫描以及密度测量技术（如定量计算机断层扫描和双能X线吸收法）进行评估。但是，除了骨矿物质密度外，小梁骨的精细结构在确定骨骼的生物力学能力方面也起着重要作用。最近，人们的注意力集中在获取不仅能提供小梁骨密度信息，还能提供微观结构信息的测量方法上。磁共振成像（MRI）就是这样一种新技术，它有可能提供有关骨密度和结构以及隐匿性骨折检测的信息。皮质骨在MR图像中产生信号缺失，这是因为它含有的可移动质子极少，而这些质子在MRI中会产生信号；而且这些质子的MR弛豫时间T2非常短，这会在图像采集过程中导致MR信号非常快速地衰减。然而，小梁骨网络会影响骨髓的MR特性。小梁骨和骨髓的磁性差异会在磁场中产生局部缺陷。由于这些缺陷，来自骨髓的MR信号会被改变，骨髓的MR弛豫时间T2也会缩短。弛豫时间缩短的程度以及信号强度的损失与小梁骨和骨髓界面的密度及其空间结构成正比。该领域最近的研究包括旨在量化骨髓弛豫时间并确定其与小梁骨密度和结构关系的研究。此外，随着成像软件和硬件的进步，可以获得平面分辨率为78 - 200微米的MR图像。在这些图像中，小梁骨结构清晰可见，目前正在开展旨在开发结合定量图像分析技术的高分辨率MRI技术的研究。本文对这些评估骨质疏松症和预测骨折风险的潜在有用技术进行了综述。
