using ultrasound measurements to determine the conduit diameter, as a function of time, at a longitudinal position of the conduit;

using ultrasound measurements to determine fluid velocity, as a function of time, in a volume element at said longitudinal position of the conduit, the ultrasound measurements to determine fluid velocity being effected by tracking objects within the fluid flow in successive frames sampling the volume element, to obtain displacement vectors for the objects, in which the objects being tracked comprise red blood cells, white blood cells, or platelets, wherein the ultrasound measurements for determining fluid velocity comprise a series of B-mode images or B-mode RF data, and further comprise displacement vectors obtained by correlating the locations of the tracked objects in successive frames of the B-mode images or B-mode RF data;

determining a measure of wave intensity as a function of change in determined conduit diameter and corresponding change in fluid velocity.