# Shear Wave Elastography Implementation on a Portable Research Ultrasound System: Initial Results
## 1 Introduction
### Background and Motivation  
A substantial improvement has been achieved in the field of SWE in last two decades and many approaches for SWE implementation have been reported by various research groups. Each method differs with regard to push beam generation, data acquisition scheme, shear wave tracking methods and the SWS reconstruction algorithm that are used. In [14], [PERSON] et al. used a single focused push beam to generate the ARF. However, as a  
Figure 1: A general measurement procedure of the SWE technique. result of focusing, the shear waves were generated in close proximity to the focal point of the push beam. Therefore, high-quality elasticity map reconstruction was only possible within a limited depth-of-field (DOF). To address this issue, a new push beam generation method was proposed by [PERSON] et al. in in [15], called supersonic shear imaging (SSI). In SSI, a sequence of beams that are focused at consecutive depths is used to generate a broad shear wavefront over a high axial extent to cover an extended field of view (FOV). In addition, an imaging rate of several thousand frames per second (FPS) is utilized in this method to track the shear waves. It allows for the capture of real-time shear wave propagation within the whole FOV using a single acquisition scheme, which has been introduced by the same group before in [16]. Although a single SSI acquisition covers a large part of the FOV, there is still a lack of shear waves in the beam axis. Therefore, the authors proposed the use of three acquisitions, each with a different push beam lateral position [4]. An alternative approach was proposed by another group in a series of works [7; 8; 9], in which multiple beams that are arranged in a comb pattern are used to generate shear waves. As the comb push beam-induced shear waves propagate within the whole FOV, a comprehensive elasticity map is reconstructed by applying only one acquisition. Nevertheless, the unfocused comb push beams feature a low penetration in depth, while the focused beams have limited DOF. Recent developments have shown that even more complex beam patterns, such as Bessel beams, can be used for a better optimized shear wave energy distribution within the FOV and improved power efficiency [17]. The practical implementation of the SWE technique is a complex engineering task and poses a number of technical challenges. Firstly, the generation of the ARF involves the transmission of high-energy and long transmit sequences using a wide aperture (many probe elements driven simultaneously). Consequently, it requires robust transmit capabilities in the ultrasound system and can cause significant heat dissipation in the driving electronics and the probe itself. Secondly, shear wave propagation tracking requires high-frame rate imaging (a minimum of 1000 FPS and typically \(>\)5000 FPS). This leads to a significant amount of data being captured and transferred from the ultrasound system to a PC for further processing. The huge dataset to be processed by the software and the complex nature of the elastography reconstruction algorithms demand high computational performance in order to reconstruct elasticity maps, especially in real-time applications. Two-dimensional SWE has been successfully developed and commercialized by several leading companies, including the Philips (Amsterdam, The Netherlands) EPIQ series and Affiniti 70, the SuperSonic Imagine (Aix-en-Provence, France) Aixplorer and MACH series, the Canon Medical Systems (Otawara, Japan) Aplio series, the Siemens (Erlanden, Germany) ACUSON series and the General Electric (Boston, MA, USA) LOGIQ series. Nevertheless, these devices are all advanced clinical cart scanners with proprietary processing algorithms and thus, are not useful for research purposes.