Biochemical (and functional) imaging of articular cartilage.
Biochemical (and functional) imaging of articular cartilage.
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DOI：
10.1055/s-2001-19043
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发表时间：
2001-12-01
影响因子：
1.4
通讯作者：
Xia, Y
中科院分区：
文献类型：
--
作者：
Gray, M L;Burstein, D;Xia, Y
在未来几十年中，磁共振成像（MRI）无损生化成像将为当今使用的破坏性组织学和生化检测提供辅助或替代。许多 MRI 方法显示图像对比度，尽管受到生化成分的影响，但通常并不特定于生化状态的特定测量。其中最广泛使用的是 T2 加权成像，它可以不同程度地揭示胶原蛋白超微结构、水合（或胶原蛋白含量），并在较小程度上揭示糖胺聚糖 (GAG) 浓度（这些生化指标中的每一个都是软骨功能完整性的重要决定因素）。该技术（以及本文讨论的其他技术）缺乏特异性，阻碍了改进软骨评估策略的努力。然而，三种方法可以对软骨生化状态进行非常具体的测量。本文详细探讨的这三种方法均植根于将图像信号强度与特定生化特征联系起来的生物物理理论。质子密度成像直接测量水含量（水合作用），该参数可能会随着显着退化而增加约 5%。魔角成像可测量 T2 的角度依赖性，可以提供胶原蛋白（或大分子）超微结构的特定测量。目前获得角度依赖性的困难阻碍了其在临床上的使用。软骨的延迟钆增强 MRI 提供了 GAG 分布的具体测量方法。该方法测量带电造影剂的分布，进而反映与 GAG 相关的电荷分布。该技术可用于临床环境，正在进行的研究将探索其在监测治疗效果和疾病进展方面的效用。尽管这些技术目前还没有进入常规临床应用，但新出现的数据表明，未来将出现针对患者的软骨生化分析，这在 20 年前几乎是不可想象的。
Over the coming decades nondestructive biochemical imaging by magnetic resonance imaging (MRI) will provide an adjunct or surrogate for the destructive histologic and biochemical assays used today. A number of MRI methods demonstrate image contrast that, although influenced by the biochemical composition, is not normally specific to a particular measure of the biochemical state. The most widely used of these is T2-weighted imaging, which variably reveals collagen ultrastructure, hydration (or collagen content), and, to a lesser extent, glycosaminoglycan (GAG) concentration (each of these biochemical metrics is an important determinant of the functional integrity of cartilage). The lack of specificity of this technique (and others discussed herein) confounds efforts to improve strategies for evaluating cartilage. However, three methods permit a very specific measure of the cartilage biochemical state. Each of these three methods, explored in detail in this article, is rooted in a biophysical theory that relates the image signal intensity to a specific biochemical feature. Proton-density imaging directly measures water content (hydration), a parameter that might increase approximately 5% with significant degeneration. Magic-angle imaging, in which the angle dependence of T2 is measured, can provide a specific measure of collagen (or macromolecular) ultrastructure. The difficulty in getting the angle dependence presently precludes its use clinically. Delayed gadolinium-enhanced MRI of cartilage provides a specific measure of the distribution of GAGs. This method measures the distribution of a charged contrast agent, which in turn reflects the distribution of charge associated with GAG. This technique can be used in a clinical setting, and ongoing studies will explore its utility in monitoring therapeutic efficacy and disease progression. Although none of these techniques are presently in routine clinical use, emerging data provide promise that the future will see patient-specific biochemical analysis of cartilage, an outcome almost unimaginable 20 years ago.