Continuous Emission Ultrasound for M-Mode Imaging Based on an Inverse Problem Approach

Conventionally, ultrasound imaging techniques rely on pulse-echo (PE) acquisitions. PE paradigm provides a straight-forward access to the in-depth tissue structure, though limited for ultrafast phenomenon imaging. The first limitation is the pulse repetition frequency, directly proportional to the imaging framerate. Secondly, because of the small duty cycle, every region of the imaged medium does not produce any echo during most of the acquisition time. Continuous emission ultrasound imaging (CEUI) has been recently investigated to tackle these constraints for M-Mode and B-Mode imaging, relying on an uninterrupted insonification of the medium.Resulting recorded signals become, compared to PE, a "chaotic" spatio-temporal mixture of contribution from different regions in the field-of-view, backscattered at different times, and potentially received at the same time. Until now, to retrieve an image, proposed methods relied on a spatio-temporal dependent pulse compression for each estimated pixel, by looking for the signature of a short segment of the emitted waveform, in the received echoes. Repeating this process for a set of emitted segments enables to obtain images with a temporal resolution up to three orders of magnitude higher compared to ultrafast US imaging strategies with PE.This paper proposes a novel way to retrieve M-Mode images with continuous emission in order to tackle the trade-off between the gain in temporal resolution with its significant contrast degradation. An inverse problem approach enables to improve image consistency by estimating jointly all pixels from a same column of the M-Mode and enforcing temporal coherence between successive estimated states of the medium.