Quantification of T and T of subarachnoid CSF: Implications for water exchange between CSF and brain tissues.

Purpose: To quantify the T and T values of CSF in the subarachnoid space (SAS) at 3 T and interpret them in the context of water exchange between CSF and brain tissues.

Methods: CSF T was measured using inversion recovery, and CSF T was assessed using T -preparation. T and T values in the SAS were compared with those in the frontal horns of lateral ventricles, which have less brain-CSF exchange. Phantom experiments were performed to examine whether there were spatial variations in T and T that were unrelated to brain-CSF exchange. Simulations were conducted to investigate the relationship between the brain-CSF exchange rate and the apparent T and T values of SAS CSF.

Results: The CSF T and T values were 4308.7 ± 146.9 ms and 1885.5 ± 67.9 ms, respectively, in the SAS and were 4454.0 ± 187.9 ms and 2372.9 ± 72.0 ms in the frontal horns. The SAS CSF had shorter T (p = 0.006) and T (p < 0.0001) than CSF in the frontal horns. Phantom experiments showed negligible (< 6 ms for T ; < 1 ms for T ) spatial variations in T and T , suggesting that the T and T differences between SAS and frontal horns were largely attributed to physiological reasons. Simulations revealed that faster brain-CSF exchange rates lead to shorter apparent T and T of SAS CSF. However, the experimentally observed T difference between SAS and frontal horns was greater than that attributable to typical exchange effect, suggesting that the T shortening in SAS may reflect a combined effect of exchange and deoxyhemoglobin susceptibility.

Conclusion: Quantification of SAS CSF relaxation times may be useful to assess the brain-CSF exchange.