Interstitial and cerebrospinal fluid exchanging process revealed by phase alternate labeling with null recovery MRI

Purpose To develop Phase Alternate LAbeling with Null recovery (PALAN) MRI methods for the quantification of interstitial to cerebrospinal fluid flow (ICF) and cerebrospinal to interstitial fluid flow (CIF) in the brain. Method In both T1-PALAN and apparent diffusion coefficient (ADC)-PALAN MRI methods, the cerebrospinal fluid (CSF) signal was nulled, while the residual interstitial fluid (ISF) was labeled by alternating the phase of pulses. ICF was extracted from the difference between the recovery curves of CSF with and without labeling. Similarly, CIF was measured by the T2-PALAN MRI method by labeling CSF, which took advance of the significant T2 difference between CSF and parenchyma. Results Both T1-PALAN and ADC-PALAN observed a rapid occurrence of ICF at 67±56 ms and 13±2 ms interstitial fluid transit times, respectively. ICF signal peaked at 1.5 s for both methods. ICF was 1153±270 ml/100ml/min with T1-PALAN in the third and lateral ventricles, which was higher than 891±60 ml/100ml/min obtained by ADC-PALAN. The results of the T2-PALAN suggested the ISF exchanging from ependymal layer to the parenchyma was extremely slow. Conclusion The PALAN methods are suitable tools to study ISF and CSF flow kinetics in the brain. ### Competing Interest Statement The authors have declared no competing interest.