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Colon Visualization Using Shape Preserving Flattening Joseph Marino and Arie Kaufman Stony Brook University

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Introduction Virtual colonoscopy is a popular non-invasive colon screening method Various colon flattening methods proposed – Cylindrical projections of segments [Vilanova Bartoli et al.] – Mass-spring unfolding [Umemoto et al.] – Conformal mapping [Haker et al., Hong et al.] Need methods to visualize flattened colons

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Related Work Visualize conformally flattened colon meshes – Shape characteristics are of utmost importance Polygonal rendering of flattened meshes – Use per-vertex normals of original surface mesh – Encode geometric properties as color at each vertex E.g., curvature These methods do not have the quality or look of the VC endoluminal view

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Generating 2D Views Use volumetric ray casting – Similar to endoluminal view Obtain view position for each ray – For each column of pixels in final image Average original 3D positions of each pixel These form a flattened centerline along the entire colon Use these as view point for ray casting (each column uses its average position value)

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2D Surface Views Opaque transfer function – Typical colon surface view – Structures identifiable due to shape preserving map This rendering is more natural to view and of higher quality than a simple mesh rendering

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Further 2D Views Using ray casting also allows for other rendering effects – E.g., electronic biopsy rendering Given two flattened colons with a one-to-one and onto correspondence, obtaining matching views in 2D is trivial

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Integration for 3D Navigation Flattened colon can help guide 3D navigation For a location on the flattened colon, obtain the view frustum to view that location in the endoluminal view View position either on flattened centerline or volumetric skeleton

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Obtaining View Frustums Given: location p on the surface viewpoint o on centerline (closest to p) neighboring centerline points c 0 and c 1

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Corresponding View Frustums If one-to-one and onto mapping between two flat colons Given view frustum on supine, find corresponding view frustum in prone Similar to previous

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Conclusion Methods to integrate shape preserving flattening into VC system Flattened 2D view with same look and feel as typical 3D endoluminal view Use 2D flattened mesh to assist in navigation in the 3D endoluminal view

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Acknowledgements This work has been supported by NIH grant R01EB7530 and NSF grants IIS , CCF The datasets are provided through the NIH, courtesy of Dr. Richard Choi, Walter Reed Army Medical Center.

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