Line-Focus Array Transducers for Effective Actuation of Tissue

Abstract

Acoustic radiation forces induced by ultrasound can be used to apply external forces to an object, and the viscoelastic property of the object can be evaluated by measuring the resultant regional displacement of the object using a different ultrasonic probe for measurement. However, according to safety guidelines for the use of ultrasound, the recommended intensity is below 1 W/cm2 for continuous waves. Therefore, to generate a measurable displacement or strain by acoustic actuation, a method of effectively applying acoustic radiation forces needs to be devised. A potential way to improve the efficiency of acoustic actuation is to use line-focus transducers. However, there are undesired fluctuations in the emitted sound field due to the finite aperture size with uniform apodization when a single-element line-focus transducer (SELFT) is used to emit plane waves, which are focused only in the elevational direction. To suppress such undesired fluctuations, in the present study, a pair of line-focus array transducers (LFATs) was constructed to realize spatially smoother radiation forces by applying an appropriate apodization. As a result, the three dominant undesired peaks in the sound field emitted from a SELFT were suppressed using the LFATs with the examined appropriate apodization, and the displacement distribution induced in a phantom, which was measured by the phased tracking method using the different ultrasonic probe, became spatially smooth.