In Vivo Dynamic D 2 O ‐ MRI for Quantifying Apparent CSF Water Renewal Across Ventricular and Extraventricular Compartments

Purpose The choroid plexus has long been regarded as the principal source of cerebrospinal fluid (CSF), yet this view remains unresolved. We developed a dynamic indirect D 2 O MRI approach to quantify regional apparent CSF water renewal in vivo in rats at 9.4 T. Methods Rats were scanned at 9.4 T using spin‐echo echo‐planar imaging during intravenous D 2 O infusion (10.69‐s temporal resolution, 150 × 150 μm 2 in‐plane resolution). A deliberately long echo time (TE = 150 ms) was used to preferentially suppress signals from brain parenchyma, blood, and interstitial fluid, thereby enhancing sensitivity to signal changes in CSF compartments. After relaxation correction, regional apparent CSF water renewal rates were estimated using a one‐compartment kinetic model. Results D 2 O‐induced signal attenuation was regionally heterogeneous. The ambient and supracerebellar cisterns (AC + SC) exhibited the largest signal reduction, reaching 47.32% ± 15.70% of baseline, whereas the lateral ventricles (LVs) showed smaller reductions (LV1: 68.73% ± 18.72%; LV2: 72.64% ± 15.07%). The estimated apparent CSF water renewal rates were low and comparable between the bilateral ventricles (LV1: 0.20 ± 0.20 μL/min; LV2: 0.26 ± 0.21 μL/min), but markedly higher in the AC + SC region (4.38 ± 3.95 μL/min; p < 0.01 vs. LVs). The third and fourth ventricles also showed relatively small signal changes. Conclusion Dynamic D 2 O MRI enabled noninvasive assessment of apparent CSF water renewal in vivo. The total apparent renewal rate was higher in AC + SC than in the LVs. These results suggest that extraventricular CSF compartments contribute substantially to apparent CSF water renewal.