Surface Acoustic Wave Propagation Using Crawling Waves Technique in High Frequency Ultrasound

Ultrasonic surface acoustic wave elastography: A review of basic theories, technical developments, and medical applications

“…The concept of crawling-wave-based elastography was first introduced in 2004 as a shear wave elastography method 79 and later validated in 2018 as a surface wave elastography method. 44 It should be noted that both Rayleigh wave 80 and Scholte wave 81 can generate the crawling wave phenomenon and, therefore, be used in the crawling wave-based elastography for imaging superficial tissue.…”

“…The foundation of the crawling-wave-based elastography is to generate the slowly moving interference pattern from two SAWs propagating in opposite directions. 44,45 This technique assumes the linear interference of the surface waves. Because the crawling wave speed is related to its source surface wave speed, which is determined by the wave propagation medium's mechanical properties, it can be used for elastography purposes.…”

“…As shown in Figure 9, to generate a crawling wave on a tissue surface, a signal generator or wave generator (Tektronix AFG3252) produces two separate signals with a minimal frequency difference (0.3-0.5 Hz). 44,45 Then, each signal is passed to a digital amplifier (Type 2718, Bruel and Kjaer). The amplified signals are sent to the two different vibration sources or mini-shakers (Type 4810, Bruel and Kjaer).…”

“…The amplified signals are sent to the two different vibration sources or mini-shakers (Type 4810, Bruel and Kjaer). 44,45,82 For the experiment, these two shakers are placed at the surface of the phantom and vibrate generally to the surface of the medium, as demonstrated in Figure 8. Surface acoustic crawling waves propagating in opposite directions are generated due to the excitation.…”

“…It is a technique where surface wave speed is calculated from a dynamic wave interference of two surface waves propagating in opposite directions. 44,45 Recently, the Scholte-wave-based SAW elastography technique was proposed to generate SAWs at a liquid-tissue interface of target tissues and perform a comprehensive elastic characterization of both surficial tissue and deep tissue simultaneously. 46 As an emerging imaging method, ultrasonic SAW elastography is in its critical stage of development: several techniques have been proposed and validated, further development is in process, related clinical studies have just started, and potential medical applications are awaiting exploration.…”