Dual-Orientation Fusion of Dual-Frequency Ultrashort Ultrasound Pulses for Super-Resolution Imaging

In ultrasound imaging, it is an everlasting pursuit to achieve higher and higher resolutions to visualize finer structures within the imaged area. However, the current mainstream approach to super-resolution ultrasound imaging heavily relies on ultrasound localization microscopy, which necessitates costly contrast agents and thousands of image syntheses for each super-resolution image. Consequently, this method suffers from low frame rates. In this study, we propose a novel super-resolution imaging technique that leverages a focused dual-frequency transducer and a dual-angle fusion method. This article outlines the design and fabrication process of a 0.9/3.9 MHz dual-frequency transducer with a focal point located approximately 17.5 mm away. The effectiveness of the super-resolution imaging method was validated using a customized phantom, successfully discerning copper wires that were spaced 0.15 mm apart. The axial resolution is 0.05 mm ( $0.13~\lambda $ ) and the lateral resolution is 0.23 mm ( $0.60~\lambda $ ) compared to the high-frequency wavelength. This design offers a promising approach for super-resolution ultrasound imaging without the need for contrast agents.