Sidelobe Reduction for Limited Diffraction Pulse-Echo Systems

Conventional focused transducers have a sharp focal spot with low sidelobes but, they have a short depth of field. Commercial medical scanners obtain increased depth of field by combining several images in a montage, each obtained at a different focal depth. Therefore, to get low sidelobes over a large depth of field several transmits must be used, which decreases the frame rate. Limited diffraction beams such as Bessel beams and X waves obtain good resolution over very large depth of field but, they have high sidelobes. We have developed a summation-subtraction method for decreasing the sidelobes. The method requires three transmits, decreasing the frame rate to one third. Although others have tried the same technique, we apply it to limited diffraction beams and obtain an analytic description.