Mapping of arterial transit time by intravascular signal selection.

The arterial transit time ((a)) is a potentially important physiological parameter which may provide valuable information for the characterization of cerebrovascular diseases. The present study shows that (a) can be measured by arterial spin labeling (ASL) applied quasi-continuously in an amplitude-modulated fashion at the human neck. Imaging was performed using short repetition times and excitation flip angles of 90 degrees, which resulted in the selection of an ASL signal of mostly intravascular origin. Model-independent estimates of (a) were obtained directly from the temporal shift of the ASL time series. An extended two-compartment perfusion model was developed in order to simulate the basic features of the proposed method and to validate the evaluation procedure. Vascular structures found in human (a) maps, such as the circle of Willis or cerebral border zones, hint at the sensitivity of the method to most sizes of arterial vessels. Group-averaged values of (a) measured from the carotid bifurcation to the tissue of interest in selected regions of the human brain ranged from 925ms in the insular cortex to 2000ms in the thalamic region. Copyright (c) 2014 John Wiley & Sons, Ltd.