Shear wave elasticity measurements from natural pulsatility of human carotid artery: a preliminary ex vivo study. R. Ternifi, J-P Remenieras, E. Nicolas, E. Simon, S. Callé UMR INSERM U 930, Université François-Rabelais de Tours, PRES Centre-Val de Loire Université, Tours, FRANCE redouane.ternifi@etu.univ-tours.fr Abstract: Mechanical properties of biological tissues exhibiting natural movements such as brain pulsatility or artery wall motion, and particularly tissue elasticity, can be estimated using ultrafast passive elastography processing. Indeed, determination of local tissue elasticity is becoming increasingly important in the diagnosis of tissue disease. In this work, we studied the shear wave propagation due to natural artery wall movement and evaluated the performance of two different methods to estimate local elasticity. The aim was to test the feasibility of measuring the Shear Wave Velocity (SWV) using an ultrafast ultrasound imaging system. Keywords: shear wave velocity, tissue pulsatility imaging, elastography, ultrasound. I. INTRODUCTION In vivo determination of local tissue elasticity is becoming increasingly important in the diagnosis of tissue disease. Today several ultrasound diagnostic imaging manufacturers propose an elastography imaging mode on their systems. In the particular case of the measurement of elastic properties of arteries, which have a major role in the cardiovascular system [1], elastography techniques have been extended to measure the deformation of tissue around arteries due to the internal blood pressure to study vascular dynamics [2]. The viscoelastic properties of arteries have been extensively investigated in clinical research. Recently, serious attention has been directed to measure more precisely arterial stiffness. Deng et al. have shown in an ex vivo study that the elastic properties of the arterial wall are varying with respect to the blood pressure [2]. They developed also a new concept of shear wave imaging to estimate a local arterial stiffness. This theoretical model of shear wave propagation in the arterial wall has been proposed and validated experimentally in vitro on phantom and in vivo on one healthy volunteer [3]. In this study, we aim to develop an ultrasound method with up to 1 kHz frame rate to detect Shear Wave Velocity (SWV) and to evaluate local tissue elasticity. The performance of the Fourier transform and cross-correlation techniques has been tested on the detection of a shear wave emitted by a pulsating phantom mimicking a pulsatility of human carotid arteries. II. MATERIAL AND METHODS This work describes our initial investigations to measure SWV from a pulsating artery. The phantom is composed with an ex vivo human carotid surrounded by a calibrated viscoelastic gel (12 cm in length, 6 cm in large and 6 cm in height; Young Modulus E = 10 kPa). As shown in figure (1), each end of the carotid was connected to silicone tubes to apply pulsatile hydraulic pressures with a flow pump. We measured the SWV in the phantom surrounding the carotid during internal stress stimuli such as cardiac pulse propagation. The wall pulsation of the carotid, induced by the flow pump, was used as an internal source of mechanical stress. One short pulse duration was generated in this experience. As an indicator of mechanical properties, local SWV can be calculated from the time delay measured between the successive ultrasound echoes at a fixed distance.