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 T₁ -PALAN and apparent diffusion coefficient (ADC)-PALAN MRI methods, the cerebrospinal fluid signal was nulled, whereas the partial recovery of other tissues with shorter T₁ (T₁ -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 T₁ -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 T₁ and ADC-PALAN signal peaked at 1.5 s. The CSF water exchange was 1153 ± 270 mL/100 mL/min with T₁ -PALAN in the third and lateral ventricles, which was higher than 891 ± 60 mL/100 mL/min obtained by ADC-PALAN. T₁ -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 $\Delta S$ 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.