Effects of the Medium-Wall Modulus Contrast on the Pulse Wave Imaging (PWI) of Aortic Phantoms

Abstract

Given its close correlation to cardiovascular pathologies, change in arterial stiffness has been deemed as a reliable biomarker for predicting cardiovascular events. The feasibility of using the ultrasound-based method of Pulse Wave Imaging (PWI) for estimating the arterial Pulse Wave Velocity (PWV) as surrogate of the wall stiffness has shown capacity for enhancing cardiovascular noninvasive diagnosis. The MoensKorteweg equation, which is the baseline for the modulus-PWV relationship, does not account for factors such as the stiffness of the surroundings and the continuous pulsatile flow; while these factors are prevalent in phantom and in vitro PWI studies and could affects the PWV measurements. The objective of the present study is to quantify the correlation between the wave propagations and the stiffness of the surrounding medium, under various flow speeds. The PWV results were quantified in terms of their r 2 and SNR, indicating the uniformity of the waves and variations in the measurements. The characteristic curves were developed in terms of the wall-to-medium modulus contrast that could be used as the reference for selecting the optimized gel and medium stiffness parameters that minimize the boundary conditions effects and maximize the SNR and r 2 .Keywords-Pulse Wave Imaging (PWI); Aortic phantom in vitro; Modulus contrast; Pulse wave propagation BackgroundChange in aortic stiffness has widely been reported as an independent indicator of all-cause and cardiovascular diseases (CVDs)-related mortalities such as primary coronary events, hypertension, aortic atherosclerosis and aneurysms [1][2][3][4][5][6][7][8], which can potentially leverage noninvasive estimation of arterial local stiffness and enhanced CVD diagnosis. Based on the formula known as the Moens-Korteweg (MK) equation, the velocity of the arterial pulse wave is correlated to the underlying wall stiffness [9,10], and therefore can be used as a surrogate measure to estimate the arterial wall stiffness. Pulse Wave Imaging (PWI) is a recent, noninvasive, ultrasound-based technique to obtain a visual map of the arterial pulsatile wave propagations, and to estimate the regional Pulse Wave Velocity (PWV) and wave propagation uniformity as denoted by the linear regression correlation coefficient, r 2 [11][12][13]. The feasibility of using PWI to effectively obtain a reliable estimate of PWV has been shown in different applications such as simulation models [14][15][16][17][18], in vitro and in vivo animal models [19][20][21], clinical studies [22][23][24][25], and arterial phantom experiments [13,21,26,27]. Mimicking the arterial pulsatile flow conditions in a laboratory setup and performing PWI in vitro or on arterial phantoms have been found to be useful in optimizing the PWI technique, and to be helpful in gaining a better insight on the in vivo and clinical findings [13,19,26,28,29]. In particular, tissue-mimicking arterial phantoms are effective and reliable substitutes for examining biological soft tissues of humans or animals [27]. Th...