Hierarchical Shape Distributions for Automatic Identification of 3D Diastolic Vortex Rings from 4D Flow MRI
Vortex ring formation within the cardiac left ventricular (LV) blood flow has recently gained much interest as an efficient blood transportation mechanism and a potential early predictor of the chamber remodeling. In this work we propose a new method for
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Abstract. Vortex ring formation within the cardiac left ventricular (LV) blood flow has recently gained much interest as an efficient blood transportation mechanism and a potential early predictor of the chamber remodeling. In this work we propose a new method for automatic identification of vortex rings in the LV by means of 4D Flow MRI. The proposed method consists of three elements: 1) the 4D Flow MRI flow field is transformed into a 3D vortical scalar field using a well-established fluid dynamics-based vortex detection technique. 2) a shape signature of the cardiac vortex ring isosurface is derived from the probability distribution function of pairwise distances of randomly sampled points over the isosurface 3) a hierarchical clustering is then proposed to simultaneously identify the best isovalue that defines a vortex ring as well as the isosurface that corresponds to a vortex ring in the given vortical scalar field. The proposed method was evaluated in a datasets of 24 healthy controls as well as a dataset of 23 congenital heart disease patients. Results show great promise not only for vortex ring identification but also for allowing an objective quantification of vortex ring formation in the LV.
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Introduction
A growing body of evidence [1-6] suggests a critical role of vortex ring formation within cardiac left ventricular blood flow during diastole as a significant contributor to efficient blood transportation [2] and as a potential clinical biomarker for early prediction of cardiac remodeling and diastolic dysfunction [4,5]. A vortex is generally characterized by a swirling motion of a group of fluid elements around a common axis. Among different types of vortical flow structures, vortex rings are most abundant in nature due their stability [6]. In the LV, the asymmetrical redirection of blood flow through the LV results in the development of a vortex ring distal to the mitral valve (Fig.1) [1]. In fluid dynamics, different methods exist to define a vortex structure [7]. Most of these methods are based on a function of the velocity gradient tensor of the flow field. 4D Flow MRI enables non-invasive acquisition of the blood flow velocity field © Springer International Publishing Switzerland 2015 N. Navab et al. (Eds.): MICCAI 2015, Part II, LNCS 9350, pp. 467–475, 2015. DOI: 10.1007/978-3-319-24571-3_56
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M.S.M. Elbaz, B.P.F. Lelieveldt, and R.J. van der Geest
providing all three velocity components (in-plane and through-plane) over the three spatial dimensions and over the cardiac cycle [1]. Therefore, 4D Flow MRI provides all the flow field information needed for 3D vortex analysis [3]. A typical 3D vortex ring identification problem consists of three steps 1) convert the 3D velocity flow field into some 3D vortical scalar field in which a vortex is defined given some criteria; 2) manually (empirically) select an isovalue threshold that can define a vortex ring structure from the 3D vortical field. Given that different vortex structures may be present in the same flow field, the selected isovalue
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