MRIを用いた脳内水動態のマクロレベルでの可視化

抄録

The glymphatic system has been proposed as a draining system in the brain like the lymphatic system in the body. The water dynamics (inflow and outflow) should be an important key; however, the exact dynamics of intracranial water especially for extracellular and cerebrospinal fluid (CSF) are still unknown.

Water molecules labeled by a stable isotope of oxygen-17 (O-17) can be visualized by MRI. When it is used as an exogenous tracer, temporal changes in tracer concentration can be elucidated. By using intravenous injection of O-17 labeled water, we found the different kinetics of CSF between subarachnoid and intraventricular spaces in humans. By using intrathecal injection, we also found the different washout of CSF between patients with idiopathic normal pressure hydrocephalus and Alzheimer's dementia.

In the animal study, different water kinetics have been noted between AQP4 knocked out and wild type (WT) mice in the water intoxication model, and between amyotrophic lateral sclerosis model and WT mice. These differences are probably due to the differences in permeability or retention of water in the brain. Further studies are now being planned to trace the outflow of water dynamics in detail in the animal study after the intrathecal injection of O-17 labeled water.