Sidelobe reduction for synthetic aperture focusing in high-frequency ultrasonic imaging

Synthetic aperture focusing with virtual sources has been previously employed to increase the penetration and to extend the depth of focus in high-frequency ultrasonic imaging, but the performance is limited by its high sidelobes. This paper introduces an adaptive weighing technique based on a focusing-quality index to suppress the sidelobes. The proposed technique is of particular value in high-frequency ultrasound where dynamic focusing using array transducer is not yet possible. Experimental data from a 50-MHz imaging system with a single-crystal transducer are used to demonstrate the efficacy of the proposed technique on both wire targets and speckle-generating objects. Both 50-MHz fundamental imaging and 50-MHz tissue harmonic imaging are tested. In vivo experiments were also performed on a mouse to further demonstrate the effectiveness. The principles and implementation issues of the new technique are also described.