An image formation model for ultrasound superresolution using a polymer ball lens

Abstract

Ultrasonic superresolution images can be generated using a polymer ball lens. Here, we provide an image formation model for this superresolution imaging method. The imaging system is comprised of a circular flat transducer operating in pulse-echo mode with a central frequency of 1MHZ, and a ball lens centered in the beam axis of symmetry. The wavelength in water is λ0=1.5mm. The system experimentally achieves a resolution of 0.6λ0 in the focal plane at one wavelength away from the lens. Finite-element simulations are performed to compute the point-spread function of the system. The obtained numerical results are remarkably consistent with experimental data. For illustration purpose, the superresolution method is compared with a conventional ultrasonic system based on a spherically focused transducer. Our technique presents twice more resolution with a shorter depth-of-field of 2λ0. Possible applications that take advantage of these features are discussed, as well as some limitations of the proposed technique.