Ex Vivo Evaluation of Mechanical Anisotropic Tissues with High-Frequency Ultrasound Shear Wave Elastography

Abstract

The use of imaging devices to assess directional mechanics of tissues is highly desirable. This is because the directional mechanics depend on fiber orientation, and altered directional mechanics are closely related to the pathological status of tissues. However, measuring directional mechanics in tissues with high-stiffness is challenging due to the difficulty of generating localized displacement in these tissues using acoustic radiation force, a general method for generating displacement in ultrasound-based elastography. In addition, common ultrasound probes do not provide rotational function, which makes the measurement of directional mechanics inaccurate and unreliable. Therefore, we developed a high-frequency ultrasound mechanical wave elastography system that can accommodate a wide range of tissue stiffness and is also equipped with a motorized rotation stage for precise imaging of directional mechanics. A mechanical shaker was applied to the elastography system to measure tissues with high-stiffness. Phantom and ex vivo experiments were performed. In the phantom experiments, the lateral and axial resolution of the system were determined to be 144 μm and 168 μm, respectively. In the ex vivo experiments, we used swine heart and cartilage, both of which are considered stiff. The elastography system allows us to acquire the directional mechanics with high angular resolution in the heart and cartilage. The results demonstrate that the developed elastography system is capable of imaging a wide range of tissues and has high angular resolution. Therefore, this system might be useful for the diagnostics of mechanically anisotropic tissues via ex vivo tests.

Elasticity and Viscoelasticity Imaging Based on Small Particles Exposed to External Forces

“…In these methods, a static, quasi-static, or dynamic force is applied to the tissue, and the deformation caused by the applied force is detected using a traditional imaging technique such as MRI or ultrasound imaging. Many attempts have been made to develop elasticity imaging methods with distinct capabilities, especially using ultrasound technology [3,4]. Some of these methods include vibro-acoustography [5], shear wave elasticity imaging (SWEI) [6], acoustic radiation force impulse imaging (ARFI) [7], harmonic motion imaging (HMI) [8], supersonic shear imaging (SSI) [9], and shear wave spectroscopy (SWS) [10].…”