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Session: Arteries
Session starts: Thursday 24 January, 10:30
Presentation starts: 10:30
Room: Lecture room 536

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Anne Saris (Radboudumc)
Rik Hansen (Radboudumc)
Stein Fekkes (Radboudumc)
Jan Menssen (Radboudumc)
Maartje Nillesen (Radboudumc)
Chris de Korte (Radboudumc)

Abstract:
Atherosclerosis is the primary cause of ischemic heart failure and stroke in westernized societies. It starts with the formation of lipid-rich accumulations in the vessel wall, which can grow and mature into plaques. These plaques can become unstable and rupture which can result in a stroke or myocardial infraction. It is known that certain arterial segments are more susceptible to plaque development [1, 2]. For example, at inner curves of vessels, downstream of a stenosis and at the outer walls of bifurcations, disturbed flow occurs. These regions are characterized by low wall shear stress (WSS) and they are more prone to atherosclerosis [1, 2]. For early detection of atherosclerosis, visualization and quantification of complex flow and the resulting WSS seems important. Conventional B-mode and Doppler ultrasound imaging allow visualization of plaque geometry and estimation of blood velocities. However, complex flow patterns cannot be visualized and quantified using the conventional techniques. This limitation originates from the angle dependency of these techniques, where only the velocity component along the US beam direction is estimated. With the aim of capturing the complex flow patterns that are associated with plaque development and progression, we developed a technique for the quantification of 2D blood velocities in the carotid artery. We performed 8000 angled plane wave ultrasound acquisitions (-20° and 20°) per second using a 7.8 MHz linear array transducer connected to a Verasonics Vantage 256 research ultrasound system. Adaptive clutter filtering was performed, where the velocity cut-off point was set dynamically based on the tracked vessel wall velocity. Inter-frame displacements were estimated using a 2-step cross-correlation-based algorithm. Subsequently, 2D blood velocities were obtained by either compounding axial displacement estimates obtained at both angles, or by projecting the angled estimates obtained at only one angle. This is decided adaptively, were RF signal power and velocity variance thresholding are used to determine the quality is the angled displacement estimates. The performance of the method was evaluated experimentally using a straight tube flow setup. Thereafter, initial in vivo evaluation was performed in healthy carotid arteries (n = 2), early-stage stenosed arteries (n = 1) and arteries which underwent endarterectomy with stent placement (n = 2). Straight vessel experiments demonstrated the technique performed with a maximum velocity magnitude bias of -3.7% (2.8% standard deviation) and an angle bias of -0.16° (0.41° standard deviation). In vivo, complex flow patterns were visualized in both healthy and diseased carotid arteries and quantified using a vector complexity measure that increased with increasing wall irregularity. This measure is a first example of new potentially clinical relevant parameters which might aid in early detection of atherosclerosis. REFERENCES [1] SS Dhawan, et al., Expert Rev Cardiovasc Ther, 8:545-56, 2010 [2] CJ Slager, et al., Nat Clin Pract Cardiovasc Med, 2: 456-64, 2005