A method of determining volume flow rate of a bodily fluid in a biological conduit includes determining a cross-sectional area of a biological conduit using a velocity vector map representing moving entities or moving fluid portions in a bodily fluid flowing within the biological conduit, calculating an average speed of the moving entities or moving fluid portions in the bodily fluid flowing across the determined cross-sectional area of the biological conduit, and calculating volume flow rate of the bodily fluid in the biological conduit from the determined cross-sectional area and the calculated instantaneous or average speed. A series of velocity vector maps may be collected over time so as to generate a flow rate profile representing flow rate as a function of time.
