Physiology and Experimental Medicine, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada.
J Magn Reson Imaging. 2012 Oct;36(4):805-24. doi: 10.1002/jmri.23718.
Conventional MR images are qualitative, and their signal intensity is dependent on several complementary contrast mechanisms that are manipulated by the MR hardware and software. In the absence of a quantitative metric for absolute interpretation of pixel signal intensities, one that is independent of scanner hardware and sequences, it is difficult to perform comparisons of MR images across subjects or longitudinally in the same subject. Quantitative relaxometry isolates the contributions of individual MR contrast mechanisms (T1, T2, T2) and provides maps, which are independent of the MR protocol and have a physical interpretation often expressed in absolute units. In addition to providing an unbiased metric for comparing MR scans, quantitative relaxometry uses the relationship between MR maps and physiology to provide a noninvasive surrogate for biopsy and histology. This study provides an overview of some promising clinical applications of quantitative relaxometry, followed by a description of the methods and challenges of acquiring accurate and precise quantitative MR maps. It concludes with three case studies of quantitative relaxometry applied to studying multiple sclerosis, liver iron, and acute myocardial infarction.
常规磁共振图像是定性的，其信号强度取决于几种互补的对比机制，这些机制可以通过磁共振硬件和软件进行操作。在缺乏用于绝对解释像素信号强度的定量指标的情况下，该指标不依赖于扫描仪硬件和序列，因此很难在不同受试者或同一受试者的纵向进行磁共振图像的比较。定量弛豫度分离了单个磁共振对比机制（T1、T2、T2）的贡献，并提供了图谱，这些图谱独立于磁共振协议，具有物理解释，通常以绝对值表示。除了提供用于比较磁共振扫描的无偏度量外，定量弛豫度还利用磁共振图谱与生理学之间的关系，为活检和组织学提供了一种非侵入性替代方法。本研究概述了定量弛豫度的一些有前途的临床应用，接着描述了获取准确和精确的定量磁共振图谱的方法和挑战。最后，通过三个定量弛豫度应用于多发性硬化症、肝脏铁和急性心肌梗死研究的案例研究进行了总结。
