I. Introduction
Medical ultrasound imaging is used extensively for diagnosing diseases in the cardiovascular system (e.g., arterial stenosis, insufficient heart valve function). The distribution and magnitude of the blood velocities contain valuable information for the diagnosing. Estimates of the blood velocities can be obtained from a set of acquired RF-signals by proper processing of these. Over the years a number of estimators have been proposed and used in various scanners. An exhaustive presentation of all these are out of the scope of this article, but they can be obtained from the literature [1], [2].