T2-weighted T1 mapping and automated segmentation of CSF: Assessment of solute gradients in the healthy brain

BACKGROUND: Cerebrospinal fluid (CSF) serves as a vehicle for nutrient delivery and waste clearance. The T1 relaxation rate R1 can be used to measure concentration of intrinsic solutes and extrinsic contrast agents. PURPOSE: To implement a method for R1 mapping and segmentation of CSF and to use this method to explore how R1 of CSF vary with CSF protein content and Gadobutrol after intrathecal administration. STUDY TYPE: Prospective cohort study, complemented by phantom analysis. POPULATION: Ten healthy control subjects (mean age 65.5, SD 4.4 years, range 57-72 years; five males and five females) and a protein-gradient phantom for study validation. FIELDSTRENGTH/SEQUENCE: 3T Philips Ingenia scanner; 3D T2W mixed inversion recovery spin-echo (T2W Mixed IRSE) sequence and 3D T1W turbo field echo (3D T1W-TFE). ASSESSMENT: R1 maps were calculated by combining inversion recovery and spin echo data. An automated segmentation method derived from FreeSurfer employed spin-echo data for CSF segmentation and T1W-TFE for anatomical reference. Through lumbar puncture, CSF was harvested for total protein measurements, and 0.25mmol Gadobutrol were injected intrathecally. Post contrast assessments were performed at 6h, 24h, 48h and 72h. STATISTICAL TESTS: One-way ANOVA, followed by a post-hoc Tukey HSD test, and simple linear regression analysis; significance level of 0.05. RESULTS: Intrinsic R1 values in the subarachnoid space were significantly higher than that in ventricles (p < 0.001) and correlated with lumbar protein concentration (p < 0.05). Peak Gadobutrol concentrations were 80 uM (SD 66) in ventricles, 146 uM (SD 70) in cerebellar SAS and 131 μM (SD 72) in cerebral SAS. Corresponding concentrations were 5.2 uM (SD 4.3), 13.0 uM (SD 6.9) and 30 uM (SD 15) at 72 hours after administration. DATA CONCLUSION: Intrinsic R1 of CSF in subarachnoid space correlated with protein content. Intracranial CSF enrichment after intrathecal administration of Gadobutrol showed a large variation among healthy volunteers.