Quantification of T₁ and T₂ of subarachnoid CSF: Implications for water exchange between CSF and brain tissues

Abstract

PurposeTo quantify the T1 and T2 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.MethodsCSF T1 was measured using inversion recovery, and CSF T2 was assessed using T2‐preparation. T1 and T2 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 T1 and T2 that were unrelated to brain‐CSF exchange. Simulations were conducted to investigate the relationship between the brain‐CSF exchange rate and the apparent T1 and T2 values of SAS CSF.ResultsThe CSF T1 and T2 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 T1 (p = 0.006) and T2 (p < 0.0001) than CSF in the frontal horns. Phantom experiments showed negligible (< 6 ms for T1; < 1 ms for T2) spatial variations in T1 and T2, suggesting that the T1 and T2 differences between SAS and frontal horns were largely attributed to physiological reasons. Simulations revealed that faster brain‐CSF exchange rates lead to shorter apparent T1 and T2 of SAS CSF. However, the experimentally observed T2 difference between SAS and frontal horns was greater than that attributable to typical exchange effect, suggesting that the T2 shortening in SAS may reflect a combined effect of exchange and deoxyhemoglobin susceptibility.ConclusionQuantification of SAS CSF relaxation times may be useful to assess the brain‐CSF exchange.