Padmavathi Sundaram, Presenter: Nothing to Disclose

Eftychios Dimitrios Sifakis, Abstract Co-Author: Nothing to Disclose

David Seungwon Paik PhD, Abstract Co-Author: Nothing to Disclose

Christopher Frederick Beaulieu MD, Abstract Co-Author: Nothing to Disclose

Sandy Napel PhD, Abstract Co-Author: Nothing to Disclose

Normal haustral folds complicate both visual and computer-aided detection (CAD) of polyps in CTC data. We present a method to straighten and flatten the colon by simulating stretching of the colonic surface using a quasistatic Finite Element Model (FEM). The output of our algorithm is a 3D fold-free surface that can be displayed as a single image and/or subjected to a CAD algorithm.

We created several mathematical phantoms using MATLAB 7.0.1, with folds and polyps modeled as half sine functions and hemispheres, respectively. The phantoms had folds, polyps on flat regions and polyps on folds. We also tested our algorithm on a subvolume of actual patient data, acquired under our IRB during a research CTC scan at our institution, containing a 6.9 mm polyp. Our algorithm stretches the surface in a direction normal to the direction of the folds, resulting in flattening the folds, with minimal distortion to polyps. A spatially invariant response to pulling from both ends is essential, otherwise structures closer to the edges being pulled will be more distorted than those farther away. Thus, we implemented a quasistatic assumption in our FEM so as to neglect inertial effects. To evaluate our methods we measured the curvature and size of the polyps (diameters) and folds (heights) before and after simulated stretching.

On phantom and patient data, our method shows reductions in fold height and curvature ranging from 54.4% to 70.3%, and 36.3% to 86.1% respectively. Polyp size and curvature were reduced by only 0% to 16%, and 0% to 20%, respectively. The output of our algorithm is a 3D surface that can be viewed as a single image.

Our physics-based method to flatten the colonic surface using a quasistatic finite element model suppresses folds while leaving polyps relatively undistorted, and has the potential to improve the efficiency of interpretation by reducing visual clutter and sources of false positive detections by CAD. Continued development is warranted.

Sundaram, P, Sifakis, E, Paik, D, Beaulieu, C, Napel, S, Fold Removal in CT Colonography (CTC): A Physics-based Approach.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4415303.html