Direct evidence from kinetic D2O-MRI modeling that the choroid plexus is not the major source of cerebrospinal fluid

The role of the choroid plexus (CP) as the primary source of cerebrospinal fluid (CSF) remains controversial. Here, we used dynamic indirect D2O magnetic resonance imaging (MRI) at 9.4T to investigate whole-brain CSF dynamics in rats. Spin-echo echo-planar imaging (SE-EPI) was performed during intravenous D2O infusion with a temporal resolution of 10.69 s and an in-plane resolution of 150 x 150 {micro}m. An echo time of 150.0 ms was employed to effectively suppress signals from brain parenchyma, blood, and interstitial fluid, resulting in preferential visualization of CSF. The ambient and supracerebellar cisterns (AC+SC) exhibited the greatest signal attenuation, reaching 47.32 {+/-} 15.70% of baseline, whereas the lateral ventricles (LV1, LV2) showed smaller reductions (68.73 {+/-} 18.72%-72.64 {+/-} 15.07% of baseline). CSF production rates were quantified using a one-compartment perfusion model. Estimated secretion rates were 0.11 and 0.13 {micro}L/min in the lateral ventricles and 1.30 {micro}L/min in the AC+SC region, indicating a 5.42-fold higher CSF production outside the ventricles. These findings provide direct in vivo evidence that the lateral ventricles are not the primary site of CSF production. The proposed D2O-based dynamic SE-EPI approach is safe, non-invasive, cost-effective, and suitable for widespread application.