This invention provides methods for non-invasive, real-time measuring and/or monitoring of local blood flow in a subject. Methods of the invention generally include the steps of obtaining Doppler shift images of at least two planes intersecting blood vessels at the scanned location; determining Doppler angles using the Doppler shift images; and then using the Doppler angles thus determined together with the Doppler shift signals to arrive at a measure of the volumetric blood flow. Also provided are systems and software for performing the methods.