C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands; Leiden Institute for Brain and Cognition (LIBC), Leiden, Netherlands; Department of Radiology, Leiden University Medical Center, Leiden, Netherlands.
C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands; Department of Radiology, Leiden University Medical Center, Leiden, Netherlands.
Neuroimage. 2021 Dec 15;245:118755. doi: 10.1016/j.neuroimage.2021.118755. Epub 2021 Nov 24.
The study of brain clearance mechanisms is an active area of research. While we know that the cerebrospinal fluid (CSF) plays a central role in one of the main existing clearance pathways, the exact processes for the secretion of CSF and the removal of waste products from tissue are under debate. CSF is thought to be created by the exchange of water and ions from the blood, which is believed to mainly occur in the choroid plexus. This exchange has not been thoroughly studied in vivo. We propose a modified arterial spin labeling (ASL) MRI sequence and image analysis to track blood water as it is transported to the CSF, and to characterize its exchange from blood to CSF. We acquired six pseudo-continuous ASL sequences with varying labeling duration (LD) and post-labeling delay (PLD) and a segmented 3D-GRASE readout with a long echo train (8 echo times (TE)) which allowed separation of the very long-T CSF signal. ASL signal was observed at long TEs (793 ms and higher), indicating presence of labeled water transported from blood to CSF. This signal appeared both in the CSF proximal to the choroid plexus and in the subarachnoid space surrounding the cortex. ASL signal was separated into its blood, gray matter and CSF components by fitting a triexponential function with Ts taken from literature. A two-compartment dynamic model was introduced to describe the exchange of water through time and TE. From this, a water exchange time from the blood to the CSF (T) was mapped, with an order of magnitude of approximately 60 s.
脑清除机制的研究是一个活跃的研究领域。虽然我们知道脑脊液（CSF）在现有的主要清除途径之一中起着核心作用，但 CSF 的分泌和组织中废物清除的确切过程仍存在争议。CSF 被认为是由血液中的水和离子交换产生的，据信这主要发生在脉络丛中。这种交换在体内还没有得到彻底研究。我们提出了一种改良的动脉自旋标记（ASL）MRI 序列和图像分析方法，用于追踪被转运到 CSF 的血液水，并对其从血液到 CSF 的交换进行特征描述。我们采集了六个具有不同标记持续时间（LD）和标记后延迟（PLD）的伪连续 ASL 序列，以及一个具有长回波链（8 个回波时间（TE）的分段 3D-GRASE 读出，允许分离非常长 T CSF 信号。在长 TE（793ms 及更高）处观察到 ASL 信号，表明存在从血液转运到 CSF 的标记水。该信号既出现在脉络丛附近的 CSF 中，也出现在皮层周围的蛛网膜下腔中。通过拟合 Ts 取自文献的三指数函数，将 ASL 信号分离为其血液、灰质和 CSF 成分。引入了一个双室动力学模型来描述随时间和 TE 的水交换。由此，绘制了从血液到 CSF 的水交换时间（T），其量级约为 60s。
