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Gabriel Herl, M.Sc.

  • Research Planning
  • Project Management: Research Robot-CT-Systems

Centre for Applied Research

Technology Campus Plattling CT

Academic Staff

ITC2 0.16

0991/3615-391

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Zeitschriftenartikel

  • Julian Wittmann
  • Gabriel Herl
  • Jochen Hiller

Generation of a 3D model of the inside volume of shoes for e-commerce applications using industrial x-ray computed tomography

In: Engineering Research Express vol. 3 pg. 045058.

  • (2021)

DOI: 10.1088/2631-8695/ac43c8

In 2018, 47% of global internet users had purchased footwear products through the internet, making it the second most popular online shopping category worldwide right after clothing with 57%. In the same year, on average, about every sixth parcel delivered in Germany (16.3%) was returned. With the effort and costs that are associated with the return of shoes, the objective of reducing the number of returns for shoes promises an enormous economic potential and helps to reduce the CO2 emissions due to a lower traffic volume. This paper presents a workflow for determining the inside volume surface of shoes using industrial x-ray computed tomography (CT). The fundamental idea is based on the Region Growing (RG) method for the segmentation of the shoe's inner volume. Experiments are performed to illustrate the correlation of image quality and segmentation result. After obtaining the 3D surface model of an individual foot, the inner volume surface data of a scanned shoe can then be registered and evaluated in order to provide a reliable feedback for the customer regarding the accuracy of fit of a shoe and the individual foot on the basis of an overall 'metric of comfort' before buying online. This step is not part of the work at hand. Conclusions are drawn and suggestions for improving the robustness and the flexibility of the workflow are given, so it can be adapted to various shoe types and implemented in a fully automated measurement process in the future.
  • TC Cham
  • Fraunhofer AWZ CTMT
  • Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen
  • DIGITAL
Zeitschriftenartikel

  • Gabriel Herl
  • Jochen Hiller
  • M. Thies
  • J.-N. Zaech
  • M. Unberath
  • A. Maier

Task-Specific Trajectory Optimisation for Twin-Robotic X-Ray Tomography

In: IEEE Transactions on Computational Imaging vol. 7 pg. 894-907.

  • (2021)

DOI: 10.1109/TCI.2021.3102824

With the advent of robotic C-arm computed tomography (CT) systems in medicine and twin-robotic CT systems in industry, new possibilities for the realisation of complex trajectories for CT scans are emerging. These trajectories will increase the range of CT applications, enable optimisation of image quality for many applications and open up new possibilities to reduce scan time and radiation dose. In this work, trajectory optimisation methods for optimising both, task-based data quality and data completeness, are presented by combining two different metrics. On the one hand, task-based data quality is optimised with a proven observer model. On the other hand, a Tuy-based metric is utilised to optimise data completeness. Both metrics capture mutually exclusive properties of the trajectory which are necessary, but alone are not sufficient for trajectory optimisation. Hence, existing task-driven trajectory optimisation approaches require additional input to decide on an overall optimal trajectory, e.g. in most cases constraints on the trajectory. Advantages and disadvantages of the presented methods are investigated. It is shown that by combining both metrics, trajectory optimisation for arbitrary geometries becomes possible. In application examples it is shown that this can be used for trajectory optimisation of challenging scanning tasks involving metal parts as well as for trajectory optimisation to reduce the number of projections while ensuring task-dependently high image quality. In total, the results of this work enable new applications for X-ray CT, especially for twin-robotic CT systems which are able to benefit from a high number of degrees of freedom.
  • Maschinenbau und Mechatronik
  • Fraunhofer AWZ CTMT
  • DIGITAL
Zeitschriftenartikel

  • Gabriel Herl
  • Jochen Hiller
  • A. Maier

Scanning trajectory optimisation using a quantitative Tuybased local quality estimation for robot-based X-ray computed tomography

In: Nondestructive Testing and Evaluation vol. (Published 21 June 2020) pg. 1-17.

  • (2020)

DOI: 10.1080/10589759.2020.1774579

Robotic CT systems allow complex scanning trajectories. This work presents a workflow to automatically calculate optimised scanning trajectories for robotic CT systems. In particular, as a local quality estimation, this work introduces a quantitative measure to quantify local reconstruction quality based on the Tuy conditions. The proposed method is tested in two summation experiments using an STL model of a motorcycle. In both experiments, a trajectory is calculated using a quantitative Tuy-based local quality estimation and the reconstruction result is then compared to reconstructions using conventional scanning trajectories. The comparison results indicate that the proposed approach automatically finds trajectories that enable 3D reconstructions with high image quality using much less projection data, which allows a significant reduction of scanning time.
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
  • NACHHALTIG
Zeitschriftenartikel

  • A. Stock
  • Gabriel Herl
  • T. Sauer
  • Jochen Hiller

Edge-preserving compression of CT scans using wavelets

In: Insight - Non-Destructive Testing and Condition Monitoring (The British Institute of Non-Destructive Testing) vol. 62 pg. 345-351.

  • (2020)

DOI: 10.1784/insi.2020.62.6.345

This work addresses the subject of efficient storage of computed tomography (CT) data with an emphasis on the quality of surfaces. Industrial dimensional metrology often requires high measurement accuracy and it is shown that this is retained using wavelet-based compression methods. The applied techniques include a tensor product wavelet transform and soft wavelet shrinkage. In these tests, performed on real objects, dimensional CT measurements of compressed and uncompressed volumes were compared. The necessary storage space was reduced significantly with a negligible loss of accuracy. The storage space required for a multi-sphere phantom was decreased to 4.7% (from 638 MB to 30 MB), with an average deviation below 1 μm from the original volume.
  • Maschinenbau und Mechatronik
  • Fraunhofer AWZ CTMT
  • DIGITAL
  • NACHHALTIG
Beitrag in Sammelwerk/Tagungsband

  • Peter Landstorfer
  • Gabriel Herl
  • Jochen Hiller

Investigation of Non-circular Scanning Trajectories in Robot-based Industrial X-ray Computed Tomography of Multi-material Objects

  • (2019)
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
Zeitschriftenartikel

  • Gabriel Herl
  • Jochen Hiller
  • S. Kasperl
  • A. Maier

Reduktion von Metallartefakten durch multipositionale Datenfusion in der industriellen Röntgen-Computertomographie

In: tm - Technisches Messen vol. 87

  • (2019)

DOI: 10.1515/teme-2019-0137

Metallartefakte stellen eine große Herausforderung für das Messen mit Röntgen-Computertomographie dar. Dieser Beitrag stellt die Methode der multipositionalen Datenfusion zur Reduktion von Metallartefakten vor. Dazu werden mehrere Scans desselben Objekts bei unterschiedlicher Objekt-positionierung durchgeführt, aufeinander registriert und zur Fusion gemeinsam unter Betrachtung eines lokalen Gütemaßes rekonstruiert. In praxisnahen Experimenten wird der Mehrwert der Methode gezeigt. Insbesondere wird dargestellt, wie mit wenig Aufwand und ohne Vorwissen Kunststoffstrukturen trotz starker Metallartefakte sichtbar gemacht werden können, womit das Verfahren ein Alleinstellungsmerkmal gegenüber den existierenden Metallartefaktreduktionsverfahren aufweist.
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
Beitrag in Sammelwerk/Tagungsband

  • Gabriel Herl
  • Jochen Hiller
  • T. Sauer

Artifact reduction in X-ray computed tomography by multipositional data fusion using local image quality measures

  • (2019)
Metal artifacts are still a major problem in X-ray industrial computed tomography. In order to reduce metal artifacts and increase the image quality of X-ray CT-scans, we suggest using projection data from multiple scans with differently positioned object orientations. We present two different approaches for multipositional CT, which are especially effective for multimaterial objects with high absorbing metal parts. On one hand, we reconstruct the different scans separatly, estimate the local quality of the resulting volumes and then fuse these volumes to an optimized volume. On the other hand, we introduce smART (shrinking merged Algebraic Reconstruction Technique) and merge sinograms of different scans, estimate the reliability of each projection pixel and then reconstruct the merged sinogram with an adapted SART reconstruction method. We demonstrate our approaches on simulations and on measurement data and are able to show a significant reduction of image artifacts qualitatively and quantitatively with the help of dimensional measurement results.
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
Vortrag

  • Gabriel Herl
  • Simon Rettenberger
  • Jochen Hiller
  • T. Sauer

Metal artifact reduction by fusion of CT scans from different positions using the unfiltered backprojection

In: 8th Conference on Industrial Computed Tomography (iCT 2018)

Wels, Österreich

  • 06.-09.02.2018 (2018)
Metal objects or metal parts in an object are still a major problem of X-ray computed tomography (CT) because of so called metal artifacts. We propose a new method – a multipositional data fusion – for automatically fusing multiple CT volumes from different positions to reduce these metal artifacts. After scanning a specimen several times at different positions and reconstruction of every scan (e.g. by the filtered backprojection), we also perform an unfiltered backprojection. Based on the assumption that metal artifacts occur the most wherever X-rays are attenuated a lot, the unfiltered backprojection is used to autonomously estimate the likelihood of metal artifacts in every voxel of every scan. The different volumes are registered and then fused by weighted sum preferring the voxels with low values in the unfiltered backprojection results. In our tests on real objects, our method fully automatically created optimized volumes with significantly less metal artifacts. The multipositional data fusion was compared to the commercially multi spectra fusion of Werth Messtechnik GmbH and outperformed it in one of the use cases.
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
Beitrag in Sammelwerk/Tagungsband

  • A. Stock
  • Gabriel Herl
  • T. Sauer
  • Jochen Hiller

Edge preserving compression of CT scans using wavelets

  • (2018)

This work addresses the subject of efficient storage of computed tomography (CT) data with an emphasis on the quality of surfaces. Industrial dimensional metrology often requires high measurement accuracy and we show that this is retained using wavelet-based compression methods. The applied techniques include a tensor product wavelet transform and soft wavelet shrinkage. In our tests on real objects, we compared dimensional CT measurements of compressed and uncompressed volumes. We were able to reduce the necessary storage space significantly with a minimal loss of accuracy. For a multi sphere phantom, we decreased the storage space to 4.7% (from 638 MB to 30 MB) with an average deviation below 1 µm from the original volume.
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
Beitrag in Sammelwerk/Tagungsband

  • A. Stock
  • Gabriel Herl
  • T. Sauer
  • Jochen Hiller

Metal artifact reduction by fusion of CT scans from different positions using the unfiltered backprojection

  • (2018)

Metal objects or metal parts in an object are still a major problem of X-ray computed tomography (CT) because of so called metal artifacts. We propose a new method – a multipositional data fusion – for automatically fusing multiple CT volumes from different positions to reduce these metal artifacts. After scanning a specimen several times at different positions and reconstruction of every scan (e.g. by the filtered backprojection), we also perform an unfiltered backprojection. Based on the assumption that metal artifacts occur the most wherever X-rays are attenuated a lot, the unfiltered backprojection is used to autonomously estimate the likelihood of metal artifacts in every voxel of every scan. The different volumes are registered and then fused by weighted sum preferring the voxels with low values in the unfiltered backprojection results. In our tests on real objects, our method fully automatically created optimized volumes with significantly less metal artifacts. The multipositional data fusion was compared to the commercially multi spectra fusion of Werth Messtechnik GmbH and outperformed it in one of the use cases.
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL
Vortrag

  • A. Stock
  • Gabriel Herl
  • T. Sauer
  • Jochen Hiller

Edge preserving compression of CT scans using wavelets

In: International Symposium on Structural Health Monitoring and Nondestructive Testing

Saarbrücken

  • 04.-05.10.2018 (2018)
This work addresses the subject of efficient storage of computed tomography (CT) data with an emphasis on the quality of surfaces. Industrial dimensional metrology often requires high measurement accuracy and we show that this is retained using wavelet-based compression methods. The applied techniques include a tensor product wavelet transform and soft wavelet shrinkage. In our tests on real objects, we compared dimensional CT measurements of compressed and uncompressed volumes. We were able to reduce the necessary storage space significantly with a minimal loss of accuracy. For a multi sphere phantom, we decreased the storage space to 4.7% (from 638 MB to 30 MB) with an average deviation below 1 µm from the original volume.
  • Maschinenbau und Mechatronik
  • Fraunhofer AWZ CTMT
  • DIGITAL
Beitrag in Sammelwerk/Tagungsband

  • Gabriel Herl
  • Simon Rettenberger
  • Jochen Hiller

Fusion mehrerer Computertomographie-Aufnahmen zur Verbesserung der Bildqualität

pg. 29-32.

  • (2017)
  • Fraunhofer AWZ CTMT
  • Maschinenbau und Mechatronik
  • DIGITAL