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Session: Poster session II
Session starts: Thursday 24 January, 16:00

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Luuk van Knippenberg (Eindhoven University of Technology)
Ruud van Sloun (Eindhoven University of Technology )
Arthur Bouwman (Catharina Hospital Eindhoven)
Massimo Mischi (Eindhoven University of Technology )

Abstract:
Doppler ultrasound is an important technique for non-invasive quantification of blood flow, which is of major clinical importance in the assessment of cardiovascular condition. However, a major disadvantage of flow estimation using Doppler ultrasound is the operator-dependency in achieving a longitudinal image in which both the Doppler angle (beam-to-flow angle α) and vessel diameter (flow area) can be accurately estimated. Instead, keeping the probe correctly positioned in the short axis is much easier and has the advantage of capturing the whole flow profile of a vessel while measuring the vessel area simultaneously [1]. Therefore, cross-sectional imaging would be preferable to longitudinal imaging if α can be estimated. In this work, we propose a solution that is based on modelling of the common carotid artery as a cylinder, which intersects with the ultrasound plane, resulting in an ellipse on the B-mode image. The ellipse characteristics (semi-major axis a, semi-minor axis b and tilt β) are used to estimate α by solving a least-squares problem. To prove theoretical feasibility a geometric model was simulated in MATLAB, where both the cylinder (r=5 mm) and imaging plane can be arbitrarily rotated and α is estimated from the resulting intersection. In addition, the propagation of erroneous estimates of b (5% error, 0.25 mm) was evaluated. Finally, blood flow through a tilted and rotated vessel was simulated using Field II software [2][3]. In the geometrical model, α was estimated perfectly (zero error with respect to reference), although the sign of the Doppler angle could not be determined (i.e. 60° vs 120°). For a 5% error introduced in b, the error in estimating α increased as α approached 90°, from 1.6° at a Doppler angle of 30° up to 8.0° at 70°. In the Field II simulation (α=135° and r=5 mm), the estimates were αest=132.6° and rest=4.9mm. The proposed method to estimate the Doppler angle from cross-sectional ultrasound images shows promise and satisfactory results in these theoretical experiments. However, further research should be performed to evaluate how sensitive this method is to errors in the estimated ellipse parameters and how this method performs in vivo. References [1] R. Schorer, A. Badoual, B. Bastide, A. Vandebrouck, M. Licker, and D. Sage, “A feasability study of color flow doppler vectorization for automated blood flow monitoring,” J. Clin. Monit. Comput., vol. 31, no. 6, pp. 1167–1175, 2017. [2] J. A. Jensen, D.- Lyngby, P. Medical, B. Engineering, J. A. Jensen, and I. Technology, “Field: A Program for Simulating Ultrasound Systems,” Pap. Present. 10th Nord. Conf. Biomed. Imaging Publ. Med. Biol. Eng. Comput., vol. 34, pp. 351–353, 1996. [3] J. A. Jensen and N. B. Svendsen, “Calculation of pressure fields from arbitrarily shaped, apodized, and excited ultrasound transducers,” IEEE Trans. Ultrason. Ferroelec., Freq. Contr., vol. 39, no. 2, pp. 262–267, 1992.