Regional cerebral blood volume: A comparison of the dynamic imaging and the steady state methods

Accurate assessment of regional cerebral blood volume (rCBV) is of critical importance in the study of cerebrovascular disease and other disorders of the central nervous system, Currently, magnetic resonance imaging [MRI) is able to measure rCBV non-invasively with two commonly used methods: the dyn amic imaging (DI) and steady state (SS) approaches. In this study, two ques tions were investigated. First, how do partial volume effects between gray matter (GM) and white matter (WM) and between epicortical vessels and brain parenchyma affect the estimation of rCBV when using the SS approach? Secon d, how comparable are the ratios of rCBV in GM to rCBV in WM (rCBV GM/WM) o btained with the two methods? We used a paramagnetic contrast agent, OPTIMA RK (Mallinckrodt, St. Louis, MO), at a dose of 0.2 mmol/kg in anesthetized pigs (n = 6) to obtain rCBV maps using both methods. When a 10% rCBV thresh old was used to minimize effects from large epicortical vessels, and tissue segmentation was used to separate GM from WM, rCBV values of 4.8 +/- 0.3% and 3.3 +/- 0.5% were obtained for GM and WM, respectively, with the SS app roach. Significantly higher rCBV values for both GM (P < 0.001) and WM (P < 0.01) were observed when the contribution from large epicortical vessels w as not removed. When tissue segmentation and rCBV thresholding were used on SS data, an rCBV GM/WM ratio of 1.5 +/- 0.2 was obtained. This value did n ot differ significantly from the rCBV GM/WM ratio of 1.8 +/- 0.6 obtained u sing the DI approach. J, Magn, Reson, Imaging 1999;9:44-52, (C) 1999 Wiley- Liss, Inc.