A Deep Learning Approach for Beamforming and Contrast Enhancement of Ultrasound Images in Monostatic Synthetic Aperture Imaging: A Proof-of-Concept.

Goal: In this study, we demonstrate that a deep neural network (DNN) can be trained to reconstruct high-contrast images, resembling those produced by the multistatic Synthetic Aperture (SA) method using a 128-element array, leveraging pre-beamforming radiofrequency (RF) signals acquired through the monostatic SA approach. Methods: A U-net was trained using 27200 pairs of RF signals, simulated considering a monostatic SA architecture, with their corresponding delay-and-sum beamformed target images in a multistatic 128-element SA configuration. The contrast was assessed on 500 simulated test images of anechoic/hyperechoic targets. The DNN's performance in reconstructing experimental images of a phantom and different in vivo scenarios was tested too. Results: The DNN, compared to the simple monostatic SA approach used to acquire pre-beamforming signals, generated better-quality images with higher contrast and reduced noise/artifacts. Conclusions: The obtained results suggest the potential for the development of a single-channel setup, simultaneously providing good-quality images and reducing hardware complexity.

Experimental and simulation study of harmonic components generated by plane and focused waves.

Although there is increasing interest in the use of plane waves (PW) in high-frame-rate imaging, not much experimental data is available about their behavior in terms of nonlinear propagation. This paper presents a detailed study of fundamental and harmonic components of the ultrasound beam associated to PW transmission from a linear array. Simulations and hydrophone measurements of PW propagation in water were performed and compared to the results obtained for focused waves (FWs) at various levels of peak negative pressure (PNP). Experimental results confirm that, at comparable PNP, the amplitudes of the harmonics reached by PWs are always higher, over extended regions, than those achieved with FW. For example, at MI = 0.2 the PW second harmonic turns out to be 9 dB higher at 25 mm depth (i.e. in the focal region), and 20 dB higher at 40 mm depth. Simulations additionally show that when ultrasound waves propagate through blood or muscle, the situation is in general reversed but, at low MI, the second harmonic amplitude can still be higher in PW than in FW. Furthermore, it is shown that increasing the array aperture size yields higher harmonic growth in PW compared to FW.