The blood-brain barrier (BBB) regulates the transfer of solutes and essential nutrients into the brain. Growing evidence supports BBB dysfunction in a range of acute and chronic brain diseases, justifying the need for novel research and clinical tools that can non-invasively detect, characterize, and quantify BBB dysfunction in-vivo. Many approaches already exist for measuring BBB dysfunction in man using positron emission tomography and magnetic resonance imaging (e.g. dynamic contrast-enhanced MRI measurements of gadolinium leakage). This review paper focusses on MRI measurements of water exchange across the BBB, which occurs through a wide range of pathways, and is likely to be a highly sensitive marker of BBB dysfunction. Key mathematical models and acquisition methods are discussed for the two main approaches: those that utilize contrast agents to enhance relaxation rate differences between the intravascular and extravascular compartments and so enhance the sensitivity of MRI signals to BBB water exchange, and those that utilize the dynamic properties of arterial spin labelling to first isolate signal from intravascular spins and then estimate the impact of water exchange on the evolving signal. Data from studies in healthy and pathological brain tissue are discussed, in addition to validation studies in rodents.

中文翻译：

---

使用 MRI 测量跨血脑屏障的水交换

血脑屏障 (BBB) 调节溶质和必需营养素向大脑的转移。越来越多的证据支持一系列急性和慢性脑部疾病中的 BBB 功能障碍，证明需要能够在体内无创检测、表征和量化 BBB 功能障碍的新型研究和临床工具的必要性。许多方法已经存在用于使用正电子发射断层扫描和磁共振成像（例如钆泄漏的动态对比增强 MRI 测量）来测量人体 BBB 功能障碍。这篇综述论文重点介绍了 BBB 水交换的 MRI 测量，它通过多种途径发生，并且可能是 BBB 功能障碍的高度敏感标志物。讨论了两种主要方法的关键数学模型和采集方法：那些利用造影剂来增强血管内和血管外隔室之间的弛豫率差异从而增强 MRI 信号对 BBB 水交换的敏感性的那些，以及那些利用动脉自旋标记的动态特性首先从血管内自旋中分离信号然后估计的那些水交换对演化信号的影响。除了啮齿动物的验证研究外，还讨论了健康和病理脑组织研究的数据。以及利用动脉自旋标记的动态特性首先从血管内自旋中分离信号，然后估计水交换对演化信号的影响的那些。除了啮齿动物的验证研究外，还讨论了健康和病理脑组织研究的数据。以及利用动脉自旋标记的动态特性首先从血管内自旋中分离信号，然后估计水交换对演化信号的影响的那些。除了啮齿动物的验证研究外，还讨论了健康和病理脑组织研究的数据。