An Optimized Mismatched Filter for Continuous Emission Ultrasound Imaging

Current echography imaging techniques rely on pulse-echo acquisitions. Despite their direct insight into the in-depth structure of tissues, they are subject to two significant limitations. The first is related to the pulse repetition frequency, and consequently, to the imaging framerate. Secondly, they are unable to capture phenomena during most of the acquisition time because of the small duty cycle and, as a consequence, the short wave tissue interaction duration. To address these challenges, we recently proposed a new paradigm, denoted continuous emission ultrasound imaging (CEUI). The concept of CEUI has been demonstrated for motion-mode imaging for a single input-single-output device. CEUI relies on the continuous transmission of an encoded signal. Then, the received signal requires to be decoded. At first, the decoding capacities of existing pulse compression approaches have been evaluated. However, these standard methods do not take into account a main consequence of continuous coded insonification: the interference of other parts of the emission beyond the one being used for decoding, resulting into image quality loss. In this paper, we propose a mismatched filter designed to reduce integrated sidelobe ratio (ISLR) of a specific point spread function of the imaging system. The latter incorporates the impact of emission segments that interfere on a single decoding step. Simulation results show a significant enhancement of the ISLR by 7 dB compared to the matched filter and 5.5 dB compared to classical mismatched filter, while reducing the mainlobe width by 60% and respectively 25%.