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

The choroid plexus (ChP) plays an important role in the glymphatic system of the human brain as the primary source of the cerebrospinal fluid (CSF) production. Development of a non-invasive imaging technique is crucial for studying its function and age-related neurofluid dynamics. This study developed a relaxation-selective intravoxel incoherent motion (IVIM) technique to assess tissue and fluid compartments in the ChP in a prospective cross-sectional study involving 83 middle-aged to elderly participants (age: 61.5 ± 17.1 years old) and 15 young controls (age: 30.7 ± 2.9 years old). Using a 3T MRI scanner, IVIM, FLAIR-IVIM, LongTE-IVIM, and VASO-LongTE-IVIM were employed to measure diffusivity and volume fractions of fluid compartments and evaluate aging effects on microvascular perfusion and interstitial fluid (ISF). FLAIR-IVIM identified an additional ISF compartment with free-water-like diffusivity (2.4 ± 0.9 x10 -3 mm 2 /s). Older adults exhibited increased ChP volume (2320 ± 812 mm 3 vs 1470 ± 403 mm³, p=0.0017), reduced perfusion (6.5 ± 4.7 vs 3.6 ± 2.9 x10⁻³ mm²/s, p=0.0088), decreased ISF volume fraction (0.58 ± 0.09 vs 0.67 ± 0.06, p=0.0042), and lower tissue diffusivity (1.16 ± 0.14 vs 1.29 ± 0.17 x10 -3 mm²/s, p=0.031) compared to younger adults. Relaxation-selective IVIM may offers enhanced specificity for characterizing age-related changes in ChP structure and fluid dynamics.