Measuring the change in CBV upon cortical activation with high temporal resolution using look-locker EPI and Gd-DTPA

A method of simultaneously measuring the changes in cerebral blood volume (CBV) and T-2* that occur on brain activation with high temporal resolution was developed. The method involves measuring the change in the longitudinal relaxation time (T-1) that occurs following a bolus injection of Gd-DTPA and converting this measurement to a change in blood volume assuming fast exchange. The sequence was optimized for the measurement of changes in CBV with high temporal resolution. A change in CBV of 27 +/- 4% on activation of the primary visual cortex (V1) was measured across four subjects. The time course of changes in T-2* showed a poststimulus undershoot (P = 0.008) corresponding approximately to a period over which CBV was still elevated above baseline, but falling (P = 0.01). The effects of perfusion, nonfulfillment of the assumption of fast exchange and of intrinsic T, changes on activation on the model used to calculate the change in CBV are discussed. (C) 2003 Wiley-Liss, Inc.