Segmentation and tracking of mitral valve leaflets in echocardiographic sequences: active contours guided by optical flow estimates

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Abstract
In this paper we present a technique for detecting and tracking the mitral leaflet boundaries in echocardiographic sequences of images covering a complete cardiac cycle. The developed method is based on the active contour framework. This approach requires initial placement of the contour in vicinity of a feature of interest (a leaflet boundary in this case). Contour shape and position are then modified by the energy minimization process. Active contour can be used for tracking by selecting the optimal solution from the previous frame as an initial position in the present one. Such approach fails when displacements of the feature between two consecutive frames are too large as is the case with mitral valve leaflets. We propose a technique for tracking leaflets and other fast moving objects that takes advantage of the velocity information obtained by optical flow estimation. Singh's multiresolution optical flow estimation technique is used since it can estimate large velocities. The algorithm has been tested on several sequences from transesophageal echocardiography. The advantage of utilizing velocity information proves to be important in frames where leaflet motion is large. The contour inertia and stiffness suppress sporadic inaccuracies in velocity estimates which results in a well-behaved contour.

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