Quantitative CBV measurement from static T₁ changes in tissue and correction for intravascular water exchange

The steady-state (SS) approach has been proposed to measure quantitative cerebral blood volume (CBV)- However, it is known that the CBV value in SS (CBV_ss) is subject to error resulting from the effects of water diffusion from the intra- to extravascular space. CBV_ss measurements were simulated in both fast-and no-water-exchange limits, and compared with measured CBV_ss values to determine which limiting case is appropriate. Twenty-eight patients were scanned with a segmented Look-Locker echo-planar imaging (LL-EPI) sequence before and after the injection of 0.1 mmol/kg of a T₁-shortening contrast agent. Signal changes and T ₁ values of brain parenchyma and the blood pool were measured pre- and postcontrast. These signal changes and T₁ values, in combination with the simulated results, were used to estimate water-exchange rates. We found that the intra- to extravascular water-exchange rates in white matter (WM) and gray matter (GM) were 0.9 and 1.6 s^-1, respectively. With these water-exchange rates, the fast-water-exchange limit of the CBV values showed good agreement with the simulation (r = 0.86 in WM, and 0.78 in GM). The CBV values with the correction for water-exchange effects were recalculated as 2.73 ± 0.44 and 5.81 ± 1.12 of quantitative cerebral blood water volume (%) in WM and GM, respectively.