Noninvasive measurement of arterial cerebral blood volume using Look-Locker EPI and arterial spin labeling

This paper describes a method of noninvasively measuring regional arterial cerebral blood volume fractions (CBVa) in vivo using the combination of Look-Locker echo-planar imaging (LL-EPI) with arterial spin labeling (ASIL). Using this technique the arterial inflow curve is rapidly sampled and the regional CBVa is measured, while tissue perfusion signals are suppressed. Two methods of spin labeling (LL-EPI flow-sensitive alternating inversion recovery (LL-EPI-FAIR) and LL-EPI signal targeting using alternating radiofrequency (LL-EPI-STAR)) are assessed and their advantages discussed. The application of vascular crushing to LL-EPI-FAIR is described and used to validate the insensitivity of the sequence to the perfusion difference signal. LL-EPI-STAR is used to assess changes in CBVa in response to a finger-tapping task. LL-EPI-STAR signal difference curves are shown to have a shortened vascular transit delay and increased peak signal change on activation. A 33 +/- 14% increase in CBV, on activation is found. CBVa is measured with a 6-s temporal resolution and the temporal response is compared with the BOLD signal change. CBVa is shown to increase more rapidly and return to baseline significantly faster than the BOLD signal change, which supports the suggestion that a change in CBVa is an input to the BOLD response. Magn Reson Med 58:41-54, 2007. (c) 2007 Wiley-Liss, Inc.