Abstract: An ultrasound imaging system with pixel oriented processing is provided in which a method of producing a Doppler velocity image is accomplished by emitting unfocused acoustic signals into a medium over substantially an entire field; receiving scattered and reflected ultrasonic signals on a transducer array in response to the emission; processing the received ultrasonic signals to extract information to construct a Doppler velocity signal corresponding to at least one point in the medium; and generating on a display device the Doppler velocity image from the processed Doppler velocity signal. Acquisition sequences and signal processing algorithms are described that provide improved quantification of fluid flow parameters, including improved discrimination between regions of blood flow and tissue. Very high frame rate Spectral Doppler and Vector Doppler acquisition modes for real-time and post-acquisition visualization over a large field of view are described.