Three-dimensional T1 mapping demonstrates the transfer of oxygen into cerebrospinal fluid during hyperoxia

This study developed a non-invasive magnetic resonance imaging technique to investigate the transfer of oxygen into cerebrospinal fluid (CSF) in healthy subjects. Alterations in CSF T1 (longitudinal relaxation time) were induced by 100% hyperoxia and measured using a 3D SPACE sequence at 3T in 20 subjects, thereby demonstrating oxygen diffusion from blood to CSF. T1 mapping was performed at high resolution (0.9-mm isotropic) to capture anatomical details of the CSF spaces and was also repeated more rapidly at a lower resolution (3-mm isotropic) to capture the temporal dynamics of T1 changes. Region-dependent reductions in T1 were observed, indicating increased oxygen concentration. These occurred most prominently and rapidly in the cortical subarachnoid space, stabilising within approximately 7 minutes of initiating hyperoxia, suggesting that oxygen diffusion primarily occurs via pial arteries. Slower changes, commencing after approximately 10 minutes, occurred in the posterior lateral ventricles, where choroid plexus is found. In addition to providing insights into the structure of CSF and dynamics of blood-CSF oxygen exchange, this methodology could, in the future, offer a valuable tool for characterising the passive diffusion (oxygen permeability) properties of cerebral blood vessel walls, thereby providing a potential marker of cerebrovascular integrity.