Phase-apodisation technique to extend depth of field for high-frequency ultrasound imaging

The quality of focusing in high-frequency ultrasound imaging is significantly affected by the length of the depth of field (DOF). A dual-concentric transducer combined with a phase-apodisation scheme is presented to achieve the extended DOF maintaining signal-to-noise ratio. As a preliminary study, computational simulation by using a Field-II program is conducted to demonstrate the feasibility. A dual-concentric transducer is composed of a disc- and a ring-type element with confocal apertures. When two input signals with 0 degrees and 180 degrees phases are simultaneously applied to the inner and outer elements, a bifocal-zone is generated in the axial direction. The overall -6 dB DOF is 40% longer compared with a single element transducer. Thus, the proposed scheme can be a potential approach to increase the DOF for high-frequency ultrasound imaging.