Prior-shape based segmentation of various objects in ultrasound images after speckle-reduction using level-set based curvature evolution
Medical ultrasound images are noisy with speckle, acoustic noise and other artifacts. Reduction of speckle in particular is useful for CAD algorithms. We use two algorithms, namely, mean curvature evolution of the ultrasound image surface and a variation of the mean-curvature flow, to reduce speckle. The premise is that when we view the ultrasound image as a surface, the speckle appears as a high-curvature jagged layer over the true objects intensities and will reduce quickly on curvature evolution. We compare the two speckle reduction algorithms. We apply the speckle reduction to an image of a cyst and a 4-chamber view of the heart. We show significant, if not complete, speckle reduction, while keeping the relevant organ boundaries intact. On the speckle-reduced images, we apply a segmentation algorithm to detect objects. The segmentation algorithm is two-stepped. In the first step we choose a prior-shape and optimize the pose parameters to maximize the edge-pixels the curve falls into, using gradient ascent. In the second step, a radial motion is used to draw the contour points to the local-edges. We apply the algorithm on a cyst and obtain satisfactory results. We compare the total area inside the boundary output of our segmentation algorithm and to the total area covered by a hand-drawn boundary of the cyst, and the ratio is about 97%.