Pearling

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Summary: The present invention relates to image segmentation, and more particularly, to segmentation of tubular structures in images. Tubular structures can appear as strokes or stroke-like structures in 2-dimensional images. As used herein, the term “stroke” refers to variable width curves in 2-dimensional images. Segmentation of stroke-like structures, such as blood vessels, is a fundamental problem in medical imaging, and is an important component of clinical applications involving diagnosis (e.g., stenosis, aneurysm, etc.), surgical planning, anatomical modeling and simulation, and treatment verification. Segmentation of stroke-like structures is a problem that also arises in other contexts including industrial applications and aerial/satellite image analysis. The present invention provides a method for segmenting tubular or stroke-like structures in images. Embodiments of the present invention are directed to segmenting stroke-like structures in images using pearling. Pearling is the generation an ordered series of pearls, which are variable-radius 2D disks, as a discrete representation of the stroke geometry. Pearling is robust to fluctuations in image intensities (due to noise, etc.) as the forces acting on a pearl are integrated over the region inside the pearl. Pearling is computationally efficient and well suited to user interactivity. Such interactivity can allow operator guidance of the segmentation in a particular direction, as well as operator correction of errant segmentation results. In one embodiment of the present invention, user inputs identifying a first region on the image inside of a tubular (stroke-like) structure and a second region of the image outside of the tubular structure are received. Based on the pixel intensities in the first and second regions, probability densities for inside and outside of the structure can be estimated. An ordered series of pearls are generated along the structure. Pearls are 2D disks, each having a center location and a radius determined based on local pixel intensities in the image. The probability densities are used to iteratively estimate the center point and the radius for each pearl. A continuous model of the structure is generated by interpolating the center locations and radii of the ordered series of pearls. The center locations and the radii of the ordered series of pearls can be interpolated using an iterative subdivision interpolation, which at each step introduces a new pearl between each pair of consecutive pearls in the ordered series of-pearls. The continuous model is output as a segmentation result and can be used in interactive segmentation.