Cerebrospinal fluid‐tissue exchange 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 the water exchange between cerebrospinal fluid (CSF) and other surrounding tissues in the brain. Method In both T 1 ‐PALAN and apparent diffusion coefficient (ADC)‐PALAN MRI methods, the cerebrospinal fluid signal was nulled, whereas the partial recovery of other tissues with shorter T 1 (T 1 ‐PALAN) or lower ADC values (ADC‐PALAN) was labeled by alternating the phase of pulses. The water exchange was extracted from the difference between the recovery curves of CSF with and without labeling. Results Both T 1 ‐PALAN and ADC‐PALAN observed a rapid occurrence of CSF water exchange with the surrounding tissues at 67 ± 56 ms and 13 ± 2 ms transit times, respectively. The T 1 and ADC‐PALAN signal peaked at 1.5 s. The CSF water exchange was 1153 ± 270 mL/100 mL/min with T 1 ‐PALAN in the third and lateral ventricles, which was higher than 891 ± 60 mL/100 mL/min obtained by ADC‐PALAN. T 1 ‐PALAN ∆S values for the rostral and caudal ventricles are 0.015 ± 0.013 and 0.034 ± 0.01 ( p = 0.022, n = 5), whereas similar values in both rostral and caudal lateral ventricles were observed by ADC‐PALAN (3.9 ± 1.9 × 10 −3 vs 4.4 ± 1.4 × 10 −3 ; p = 0.66 and n = 5). Conclusion The PALAN methods are suitable tools to study CSF water exchange across different compartments in the brain.