Relaxation‐Selective Intravoxel Incoherent Motion Imaging of Microvascular Perfusion and Fluid Compartments in the Human Choroid Plexus

The choroid plexus (ChP) is critical to the glymphatic system of the human brain through its primary function as the source of cerebrospinal fluid (CSF) production, which plays an important role in brain waste clearance. Developing noninvasive imaging techniques to assess ChP is crucial for studying its function and age‐related neurofluid dynamics. In this study, we developed a relaxation‐selective intravoxel incoherent motion (IVIM) technique to assess tissue and fluid compartments in the ChP of 83 middle‐aged to elderly participants (age: 61.5 ± 17.1 years) and 15 young controls (age: 30.7 ± 2.9 years). Using a 3‐T MRI scanner, we implemented T1‐ and T2‐selective IVIM approaches, including Fluid‐Attenuated Inversion Recovery IVIM (FLAIR‐IVIM), LongTE‐IVIM, and Vascular Space Occupancy‐LongTE‐IVIM (VASO‐LongTE‐IVIM), to measure diffusivity and volume fractions of fluid compartments in ChP. Our results showed that FLAIR‐IVIM identified an additional interstitial fluid (ISF) compartment with free‐water‐like diffusivity in ChP. We then evaluated the aging effects on microvascular perfusion and ISF in ChP. Compared to younger adults, older adults exhibited increased ChP volume, reduced perfusion, decreased ISF volume fraction, and lower tissue diffusivity. Relaxation‐selective IVIM may offer enhanced specificity for characterizing age‐related changes in ChP structure and fluid dynamics.