Abstract
In industrial Computed Tomography (CT), scattered radiation causes a loss of quality of the reconstructed 3D volume. Scatter is caused by photon-matter interaction, whereby a photon is deflected from its initial propagation direction. The most prominent contributor to scattered radiation in the scope of photon energies occurring in industrial CT is Compton Scattering. With the used Beam Hole Array (BHA) technology for scatter correction, scatter intensities are determined by subtracting the primary intensities, which are gathered behind small apertures from the total intensities, which are gathered in the absence of the apertures. Intensities measured behind the apertures are assumed to be scatter free, since the transversal components of the radiation are strongly reduced. The scatter correction is performed by subtracting scatter intensities from primary intensities in the projection image. Improvements are evaluated for a newly developed test specimen considering image quality metrics and dimensional accuracy. The contrast could be improved especially for small structures. Cupping artifacts that express as systematic offset of grey values rising with the penetration length were reduced. Measurement deviations towards tactile references were decreased.
Zusammenfassung
In der industriellen Computertomographie (CT) ist die Streustrahlung ein prominenter Effekt, der zu einem Verlust von Bildqualität führt. Der Mechanismus der Streustrahlung beruht auf Photon-Materie-Interaktionen, insbesondere dem Compton-Effekt, durch welchen Röntgenphotonen von ihrer geradlinigen Ausbreitungsrichtung abgelenkt werden. Mittels eines Streustrahlengitters, hier mittels eines sogenannten Beam Hole Arrays (BHA), lassen sich Streuintensitäten ermitteln. Hierzu werden die Intensitäten in den abgeschatteten Bildbereichen hinter den hochabsorbierenden Strukturelementen des BHAs gemessen. Die Streustrahlenkorrektur basiert auf einer Subtraktion der gemessenen Streuintensitäten von den Gesamtintensitäten, welche unter Abwesenheit des Streustrahlengitters ermittelt werden. Um den Einfluss des Korrekturverfahrens auf die Bildqualität zu bewerten, werden Untersuchungen anhand eines entwickelten Prüfkörpers durchgeführt. Die Veränderungen werden durch Bildqualitätsmetriken und dimensionelle Messabweichungen quantifiziert. Die Ergebnisse zeigen eine Verbesserung des Bildkontrasts speziell bei kleinen geometrischen Strukturen. Sogenannte Cupping-Artefakte, die fälschlicherweise ein Absinken der Grauwerte im Bereich homogenen Materials beschreiben, werden signifikant reduziert. Ebenso sinken Messabweichungen gegenüber einer taktilen Referenzmessung.
Funding statement: This work did not receive any specific grant.
About the authors
Manuel Kaufmann is a Research Associate at Fraunhofer IPA since 2018. His research interest lays on dimensional metrology applications and inspection processes in the context of industrial quality assurance. In his preceding Master thesis, he researched a method for scatter correction for Industrial Computed Tomography. In his current PhD study at the University of Stuttgart, he researches Virtual Assembly algorithms.
Carla Pfaffelhuber is a Research Associate at Dr. Ing. h.c. F. Porsche AG and the University of Stuttgart since 2021. Her PhD study is focused on methodologies for managing the sustainability goals in vehicle projects. In her Master thesis, she researched the benefit gathered by scatter correction in the context of Industrial Computed Tomography at Dr. Ing. h.c. F. Porsche AG.
Ingo Vater is associated with Dr. Ing. h.c. F. Porsche AG in Weissach. His work is focused on the Field Management of Non Destructive Testing, for example the Industrial Computed Tomography, in the context of the automotive industry.
Wolfram Wiest is associated with Dr. Ing. h.c. F. Porsche AG in Weissach. His work is focused on the application of the Industrial Computed Tomography in the context of the automotive industry.
Hendrik Höhe is associated with Dr. Ing. h.c. F. Porsche AG in Weissach. His work is focused on the application of the Industrial Computed Tomography in the context of the automotive industry.
Dr.-Ing. Ira Effenberger is group leader of the research group “3D data processing” at Fraunhofer IPA. One main research activity of her group is the intelligent and automated analysis of 3D data sets for measurement and testing solutions. As experienced scientist Dr. Effenberger has coordinated national and European research projects, e. g. for industrial Computed Tomography data evaluation. In her PhD she focused on automated geometry-based measurement sequences and 3D data evaluation for multi-sensor CMMs.
References
1. Kruth, J. P.; Bartscher, M.; Carmignato, S.; Schmitt, R.; Chiffre, L. de ; Weckenmann, A. Computed tomography for dimensional metrology. CIRP Annals 2011, 60, 821–842, doi:10.1016/j.cirp.2011.05.006.Search in Google Scholar
2. Feldkamp, L. A.; Davis, L. C.; Kress, J. W. Practical cone-beam algorithm. J. Opt. Soc. Am. A 1984, 1, 612, doi:10.1364/JOSAA.1.000612.10.1364/JOSAA.1.000612Search in Google Scholar
3. Demtröder, W. Experimentalphysik 2; Springer: Berlin, Heidelberg, 2013, ISBN 978-3-642-29943-8.10.1007/978-3-642-29944-5Search in Google Scholar
4. Beyerer, J.; Puente León, F. Die Radontransformation in der digitalen Bildverarbeitung (The Radon Transform in Digital Image Processing). at - Automatisierungstechnik 2002, 50, doi:10.1524/auto.2002.50.10.472.Search in Google Scholar
5. Demtröder, W. Experimentalphysik 3; Springer: Berlin, Heidelberg, 2010, ISBN 978-3-642-03910-2.10.1007/978-3-642-03911-9Search in Google Scholar
6. Krieger, H. Grundlagen der Strahlungsphysik und des Strahlenschutzes; Springer: Berlin, Heidelberg, 2019.10.1007/978-3-662-60584-4Search in Google Scholar
7. Klein, O.; Nishina, Y. Über die Streuung von Strahlung durch freie Elektronen nach der neuen relativistischen Quantendynamik von Dirac. Z. Physik 1929, 52, 853–868, doi:10.1007/BF01366453.Search in Google Scholar
8. Hsieh, J. Computed tomography. Principles, design, artifacts, and recent advances, 2nd ed.; Wiley Interscience; SPIE Press: Hoboken N. J., Bellingham Wash., 2009, ISBN 9780819475336.Search in Google Scholar
9. Attix, F. H. Introduction to Radiological Physics and Radiation Dosimetry; Wiley, 1986.10.1002/9783527617135Search in Google Scholar
10. Lifton, J. J.; Malcolm, A. A.; McBride, J. W. An experimental study on the influence of scatter and beam hardening in x-ray CT for dimensional metrology. Meas. Sci. Technol. 2016, 27, 15007, doi:10.1088/0957-0233/27/1/015007.Search in Google Scholar
11. Schörner, K.; Goldammer, M.; Stierstorfer, K.; Stephan, J.; Boni, P. Scatter Correction Method by Temporal Primary Modulation in X-Ray CT. IEEE Trans. Nucl. Sci. 2012, 59, 3278–3285, doi:10.1109/TNS.2012.2218127.Search in Google Scholar
12. Krämer, A.; Böhmler, P.; Lanza, G. Optimierung von Aufnahmeparametern mittels projektionsbasierter Qualitätskenngrößen in der industriellen Computertomographie. In 18. GMA/ITG-Fachtagung Sensoren und Messsysteme 2016, Nürnberg; AMA Science, Ed., 2016; pp 383–390.10.5162/sensoren2016/5.4.1Search in Google Scholar
13. Fleßner, M.; Müller, A.; Helmecke, E.; Hausotte, T. Evaluating and visualizing the quality of surface points determined from computed tomography volume data. In Proceedings of the MacroScale 2014: - Recent developments in traceable dimensional measurements; PTB, Ed.; Wien, 2015.Search in Google Scholar
14. Reiter, M.; Weiß, D.; Gusenbauer, C.; Erler, M.; Kuhn, C.; Kasperl, S.; Kastner, J. Evaluation of a histogram-based image quality measure for X-ray computed tomography. In Conference on Industrial Computed Tomography (ICT) 2014; Kastner, J., Ed.; Shaker: Aachen, 2014; pp 273–282, ISBN 978-3-8440-2557-6.Search in Google Scholar
15. DIN EN ISO 15708-1, 2019: Zerstörungsfreie Prüfung – Durchstrahlungsverfahren für Computertomographie. Beuth: Berlin, 2019.Search in Google Scholar
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