This study aims to quantify the effects of geometry and stiffness of aneurysms on the pulse wave velocity (PWV) and propagation in fluid–solid interaction (FSI) simulations of arterial pulsatile flow. Spatiotemporal maps of both the wall displacement and fluid velocity were generated in order to obtain the pulse wave propagation through fluid and solid media, and to examine the interactions between the two waves. The results indicate that the presence of abdominal aortic aneurysm (AAA) sac and variations in the sac modulus affect the propagation of the pulse waves both qualitatively (eg, patterns of change of forward and reflective waves) and quantitatively (eg, decreasing of PWV within the sac and its increase beyond the sac as the sac stiffness increases). The sac region is particularly identified on the spatiotemporal maps with a region of disruption in the wave propagation with multiple short-traveling forward/reflected waves, which is caused by the change in boundary conditions within the saccular region. The change in sac stiffness, however, is more pronounced on the wall displacement spatiotemporal maps compared to those of fluid velocity. We conclude that the existence of the sac can be identified based on the solid and fluid pulse waves, while the sac properties can also be estimated. This study demonstrates the initial findings in numerical simulations of FSI dynamics during arterial pulsations that can be used as reference for experimental and in vivo studies. Future studies are needed to demonstrate the feasibility of the method in identifying very mild sacs, which cannot be detected from medical imaging, where the material property degradation exists under early disease initiation.

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Endovascular Aneurysm Repair (EVAR), a method for repairing Abdominal Aortic Aneurysm (AAA), has increasingly been performed on patients with suitable anatomy, and has generated a great deal of interest toward enhancing minimallyinvasive therapeutics. However, there exist clinical cases of patients with large affected zones where one single oversized endograft does not provide a proper solution, often due to highly curved and irregular geometries. Therefore, the clinical practice of endograft implantation in patients with extended regions of arterial damage constitutes the use of multiple standard-sized endografts, usually overlapping to ensure a full coverage of the diseased areas. While being a clinically appealing practice, there exist reports on the confounding effects of using multiple, overlapping stents and the increased risk of adverse clinical outcome. The impacts of using multiple, overlapping stents on hemodynamics visa-vis cardiovascular mechanics have not been fully examined, and we speculate that resulting local flow complications contribute to the escalation of such cases. In this article, we review the arterial hemodynamic parameters in physiological conditions, as well as under employment of single and multiple stents, and highlight the major concerning impacts on the quantified flow parameters. Even though stent overlap cannot always be avoided in clinical practice, an improved stent design and overlapping deployment strategies could potentially minimize flow complications and compounding pathological effects.

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...

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