Effective and flexible wall filter for pulsed Doppler signals

Wall filter design is a key for in vivo applications of the Color Flow Map (CFM) using pulsed Doppler ultrasound. Strong echoes from walls overshadow weak flow signals, introduce distortion, and limit capabilities of the CFM for small vessels. A new wall filter is introduced to completely reject frequencies outside of the selected areas in the two-dimensional Fourier domain of Doppler RF signals. The filter effectively eliminates wall effects and recovers Doppler information. An experiment was performed using a peripheral vascular Doppler flow phantom. Sixty-four tone bursts at 3.5 MHz with a PRF of 5 kHz were transmitted through a 19 mm diameter transducer focused in the center of the flow channel at angles of 70°. The transducer was weakly focused to simulate the situation of small vessels. The experiment supports the authors´ conclusion that the new wall filter provides improved velocity estimation and has great potential for flow characterization of small vessels