ILATO - Improving Limited Angle computed Tomography by Optical data integration
Project of Visualization and Numerical Geometry Group
D-A-CH, a joint project financed by the DFG, German Research Foundation, and the SNSF, Swiss National Science Foundation, Switzerland
Members at IWRAndreas Beyer, Hubert Mara, Susanne Krömker, Hans Georg Bock
Project partnersYu Liu (ETH Zurich, and Empa), Konrad Wegener (ETH Zurich), Philipp Schütz (Luzern University of Applied Sciences and Arts), Alexander Flisch (Empa), Urs Sennhauser (Empa)
PublicationsA. Beyer, H. Mara, S. Krömker: ILATO Project: Fusion of Optical Surface Models and Volumetric CT Data, in: Computing Research Repository CoRR, 2014
Abstract, Fulltext PDF
Y. Liu, P. Schütz, A. Flisch, U. Sennhauser: Exploring the limits of limited-angle computed tomography complemented with surface data, in: 11th European Conference on Non-destructive Testing (ECNDT), 2014
Abstract, Fulltext PDF
Short description of the projectILATO is an acronym of Improving Limited Angle computed Tomography by Optical data integration. By measuring the intensity of X-ray beam after it travels through an object, the attenuation values of a specimen are acquired.
The 3D information is reconstructed from a series of 2D projections mostly on a circular trajectory. This is accomplished via inverse radon transformation. Limited angle computed tomography is indicated whenever measurements from certain angles are impossible. Incomplete data from the limited angle CT measurement poses problems to the reconstruction which introduces blurred edges and other artifacts.
Surface representations acquired from optical scans are processed according to the corresponding CT trajectory to inspect all rays intersecting the object and to calculate the exact ray length in material. This information enables enhanced reconstruction to deliver a superior volumetric representation of the specimen.
A surface mesh acquisition of the object obtained via structured light optical scan is not limited in angle but cannot reveal the volumetric structure inside. To support the volumetric data reconstruction algorithm a surface mesh acts as a mask defining boundaries of the reconstructed image. For registration purposes of the outer boundary of CT data with the surface of the optical scan a Volume-Enclosing Surface ex-Traction Algorithm (VESTA; B. R. Schlei) is implemented and tested against a commercial marching cube algorithm.
The goal of the project is to correct certain defects in reconstructing limited angle CT scans which occur from insufficient information. As attenuation measurement based imaging techniques collect data only as footprints of each ray and limited angle CT does not provide a full set of projection directions, reconstruction algorithms tend to introduce an elongation which can be observed as an anisotropic magnification effect in the resulting representation of the object.
The project focuses on the registration of optically acquired surfaces with data acquired from computed tomography in order to enhance image quality and shorten acquisition times in X-ray based industrial quality inspection.
The challenges are the correct setup,
the registration of data sets created with considerably different imaging techniques, and the improvement of the applied methods.
All the extracted information is used to gain an improved visualization in the sense of less noise and sharper edges especially in the areas where the limited angle reconstruction suffers from insufficient information.
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