Natural shear wave imaging using vocal tract vibrations: Introducing vocal passive elastography (V-PE) to thyroid elasticity mapping

Abstract

We present a shear wave elastography (SWE) approach for thyroid characterization that is inspired by passive elastography, which extracts elasticity from the natural vibrations in living tissues that are caused by cardiac motion, blood pulsatility, and muscle activity. On thyroid, this physiological noise is mainly due to the carotid pulsation, which is in the 1–10 Hz bandwidth and is located right next to the gland. In order to decrease the shear wavelength and increase the signal to noise ratio, we propose to create in the thyroid a complex shear wave field by using natural vocal tract vibrations. The nature of the sound can be easily modified to be narrow or broad band, with small or large amplitude. Using correlation-based algorithm and a sound sustained at 150 Hz, we have developed an innovative technique using ultrasound, allowing us to compute a 2D shear wave velocity map, superposed onto a B-mode ultrasound image of a volunteer's thyroid. Using our vocal passive elastography method, shear wave velocity was measured at every point within a mask surrounding the thyroid with a pixel resolution of 150 × 150 μm2. The mean shear wave speed value measured is 3.2 m/s, taking its value from 0.7 m/s to 8.8 m/s. The values obtained were in good agreement with comparative shear wave elastography (SWE) measurements.