Ultrasonic doppler imager having a spatially smoothed control signal for an adaptive tissue rejection filter

An ultrasonic Doppler flow (i.e. blood) imaging and/or measuring system capable of adaptively suppressing stationary or slowly-moving non-flow (i.e. blood) signals having variable spectra from the recovered ultrasonic echoes. In accordance with the invention, the tissue signals are suppressed using a tissue rejection filter arrangement having an attenuation characteristic which is controlled based upon measured estimates of at least one spectral characteristic of the tissue signals to be removed, thereby maximizing the rejection of tissue movement signals and minimizing undesired attenuation of the blood flow signals. In accordance with an embodiment of the invention, data representative of the tissue signal movement, e.g., the spectral estimates of the tissue signals, are spatially averaged before being used to control the tissue rejection filter arrangement. In accordance with an alternative embodiment of the invention, the spatial averaging algorithm itself is adaptively changed, for example, in response to changes in the value of the power estimate of the tissue movement signals. In accordance with an even further alternative embodiment of the invention, a plurality of parallel beamforming channels are used for developing multiple sets of color flow beamlines substantially simultaneously with one another which scan an area, and velocity estimates from at least two of the sets which are representative of movement in adjacent portions in the scanned area are averaged for developing a control signal which adaptively controls the tissue rejection filter.