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

Abstract

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 (CBVSS) is subject to error resulting from the effects of water diffusion from the intra- to extravascular space. CBVSS measurements were simulated in both fast- and no-water-exchange limits, and compared with measured CBVSS 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 T1 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.