Focused Acoustic Driver to Generate High-Frequency Shear Waves in Deep Regions for Magnetic Resonance Elastography

INTRODUCTION Magnetic resonance elastography (MRE) is a phase-contrast technique that can noninvasively visualize shear waves patterns within tissue [1]. Accurate values of tissue stiffness are calculated by the equations of motion from the shear wave pattern of a single frequency [2]. In order to generate shear waves within tissue, various external drivers have been proposed [3]. To acquire an accurate shear modulus map (defined as an elastogram) in high spatial resolution in deep regions, external drivers must generate a precisely controlled high frequency (higher than 100 Hz) and a large amplitude vibration. Also, for clinical use, drivers tend to be of a simple and robust design. Currently, there are no drivers that satisfy all these conditions. For example, electromechanical and pneumatic approaches demonstrate the feasibility of applying MRE to deep-lying organs, although these drivers cannot match the precise control of a piezoelectric actuator in terms of frequency, amplitude and phase. Whereas small displacements are a drawback in piezoelectric materials, and the need for mechanical amplification increases the design complexity [4]. In this study, we develop a simple and robustly designed focused acoustic driver to enhance shear wave amplitude in deep regions by high frequency using a piezoelectric actuator. To confirm the performance of the proposed driver, phantom studies are performed.