The present invention relates generally to systems and methods for assessing blood flow in blood vessels, for assessing vascular health, for conducting clinical trials, for screening therapeutic interventions for adverse effects, and for assessing the effects of risk factors, therapies and substances, including therapeutic substances, on blood vessels, especially cerebral blood vessels, all achieved by measuring various parameters of blood flow in one or more vessels and analyzing the results in a defined matter. The relevant parameters of blood flow include mean flow velocity, systolic acceleration, and pulsatility index. By measuring and analyzing these parameters, one can ascertain the vascular health of a particular vessel, multiple vessels and an individual. Such measurements can also determine whether a substance has an effect, either deleterious or advantageous, on vascular health. In one of many embodiments, the present invention further provides an expert system for achieving the above.