Persistence for ultrasonic flow imaging

An improved technique for providing persistence to velocity signals obtained by an ultrasound imaging system is disclosed. The velocity signals with appropriate persistence are then used to form an image on a display device so as to accurately depict fluid flow. The persistence technique intelligently decides whether or not to provide persistence to the velocity signals. In making these persistence determinations, the persistence technique not only avoids distorting the velocity values with corrupt signals, but also preserves directional flow information. The persistence technique can also make use of various thresholds to reduce errors (e.g., flash artifacts or random noise) as well as persistence of such errors.