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Imaging of the inner structure of cave bear teeth by novel non-destructive techniques

Elisabeth Leiss-Holzinger, Karin Wiesauer, Henrike Stephani, Bettina Heise, David Stifter, Benjamin Kriechbaumer, Stefan J. Spachinger, Christian Gusenbauer, and Gerhard Withalm

Plain Language Abstract

For the determination of the age-at-death of cave bears, various derivatives of bones are suited such as the skull or the baculum (penis bone). Typically, the most durable derivatives are teeth. During their lifetime, cement is deposited on the roots continually. Periodical variations in the nutrition in the course of the year can cause a deficiency of minerals in the cement, which enables us to distinguish annual increments like in trees. Up to now, it was necessary to cut off the roots of teeth to etch and stain the resulting surface to study these annuli. In this work, several non-destructive methods are compared to better visualize the microstructure in teeth. The spacings between the annuli can be less than 10 μm. Therefore, optical coherence tomography (OCT), a high-resolution (2.7 µm in air), non-destructive and contactless technology for two and three dimensional (2D, 3D) imaging, was applied. The OCT results were compared to X-ray micro computed tomography (µ-CT) and terahertz imaging (THz). While OCT could clearly detect the annuli, µ-CT images did not show any annuli but provided an excellent undistorted topography of enamel, dentin and cement in true aspect ratio. Compared to OCT, THz imaging exhibits much larger penetration depths up to centimeters, but with a lower resolution of about 1 mm. Thus, THz imaging provides insight into the internal structure of cave bear teeth on a larger scale, combined with the potential of spectroscopic evaluation. In conclusion we can say that the combination of these complementary methods is suited for a highly informative non-destructive characterization of teeth.

Resumen en Español

Obtención de imágenes de la estructura interna de los dientes del oso de las cavernas mediante nuevas técnicas no destructivas

El potencial de las técnicas no destructivas de obtención de imágenes, como la obtención de imágenes por tomografía de coherencia óptica (OCT), tomografía computarizada de rayos X micro-3D (μ-CT) y terahercios (THz), ha sido tenido en cuenta para tareas de diagnóstico de estructuras y de edad en el campo de la paleontología. En particular, OCT, una tecnología de alta resolución, no destructiva y que no establece contacto con el objeto para la obtención de imágenes de dos y tres dimensiones (2D, 3D), fue evaluada para investigar las microestructuras del cemento dental, concretamente de dentición del oso de las cavernas. OCT, con una resolución de profundización en el rango de micras, mostró su capacidad para permitir el conteo de las líneas de acreción anuales de cemento y, por lo tanto, para determinar la edad del individuo. Como método adicional, también se presenta la tecnología THz que exhibe una notoriamente mayor profundidad de penetración, la cual alcanza un rango centimétrico, pero con una resolución más baja respecto a OCT. De este modo, la obtención de imágenes por THz proporciona una idea de la estructura interna de los dientes del oso de las cavernas en una escala más grande. Además, para completar la variedad de técnicas no destructivas de obtención de imágenes consideradas en el presente estudio, se ha aplicado μ-CT para el análisis de las estructuras dentarias, y así obtener unos resultados para compararlos con los obtenidos con OCT y THz. La combinación de estos métodos complementarios es muy adecuada para la caracterización no destructiva de la dentición.

Palabras clave: tomografía; coherencia óptica; imágenes; terahercios; tomografía computarizada de rayos X; análisis de datos; elementos dentales; tridimensional (3D)

Traducción: Enrique Peñalver

Résumé en Français

Imagerie de la structure interne des dents d'ours des cavernes par des nouvelles techniques non destructives

Le potentiel des techniques d'imagerie non-destructives, comme la tomographie par cohérence optique (OCT), X-ray micro-3D tomodensitométrie (μ-CT) et l'imagerie térahertz (THz) a été considéré pour les tâches diagnostiques structurelles et de l'âge dans le domaine de la paléontologie. En particulier l'OCT, une technologie à haute résolution, non destructive et sans contact pour l'imagerie en deux ou trois dimensions (2D, 3D), a été évaluée pour l'enquête de microstructures de cément dentaire, illustré par des dents d'ours des cavernes. OCT avec une résolution de profondeur dans l'ordre du micron a montré sa capacité à compter les lignes d'apposition annuelle constituée du cément et donc de déterminer l'âge de l'individu. Comme autre méthode également la technologie THz est présentée, présentant une beaucoup plus grande profondeur de pénétration de plusieurs centimètres, mais avec une résolution plus faible, contrairement à l'OCT. Ainsi, l'imagerie THz donne un aperçu de la structure interne des dents d'ours des cavernes sur une plus grande échelle. En outre, pour compléter la variété des techniques d'imagerie non destructives considérées, μ-CT a été appliqué à l'analyse des structures de dents, en comparaison aux résultats de l'OCT et à l'imagerie THz. La combinaison de ces méthodes complémentaires est bien adaptée à la caractérisation non destructive des dents.

Mots-clés: tomographie; cohérence optique; imagerie; térahertz; Rayons X de tomographie assistée par ordinateur; analyse des données; dent (dents); trois dimensions (3D)

Translator: Kenny J. Travouillon

Deutsche Zusammenfassung

Abbildung der inneren Struktur eines Höhlenbärenzahns mit neuen zerstörungsfreien Techniken

Das Potential von zerstörungsfreien Abbildungstechniken wie optischer Kohärenztomographie (OCT), Röntgen-Mikro-3D-Computertompgraphie (μ-CT) und Terahertz-Abbildung (THz) wurde in der Paläontologie für Struktur-und Altersdiagnosen in Betracht gezogen. Besonders OCT, eine hochauflösende, zerstörungsfreie und kontaktfreie Technologie zur 2D und 3D Abbildung wurde für die Untersuchung von dentalen Zementmikrostrukturen am Beispiel eines Höhlenbärenzahns evaluiert. OCT mit einer Tiefenauflösung im Mikrometerbereich war fähig die jährlichen Anlagerungslinien aus Zement sichtbar zu machen und das Alter des Individuums zu bestimmen. Als zusätzlich Methode wird auch die THz Technologie vorgestellt, die mit bis zu einigen Zentimetern eine viel höhere Durchdringungstiefe aufweist, jedoch eine geringere Auflösung im Vergleich zu OCT hat. Somit gibt die THz Abbildung einen Einblick in die interne Struktur des Höhlenbärenzahns im größeren Maßstab. Um die Vielfalt der in Betracht gezogenen zerstörungsfreien Abbildungstechniken zu komplettieren, wurde darüber hinaus μ-CT zur Zahnstrukturanalyse im Vergleich zu den mit OCT und THz erzielten Ergebnissen eingesetzt. Die Kombination dieser sich ergänzenden Methoden ist für eine zerstörungsfreie Charakterisierung von Zähnen gut geeignet.

Schlüsselwörter: Tomographie; Optische Kohärenz; Abbildung; Terahertz; Röntgen-Computertomographie; Datenanalyse; Zahn (Zähne); dreidimensional (3D)

Translator: Eva Gebauer

Arabic

in progress

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Orientation of measurement planes with respect to the tooth. The red area signifies the surface area scanned by OCT.

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FIGURE 2. Specimen GS 26-1. Root of a right lower M1 of a senile individual of Ursus ingressus from Gamssulzen cave (Lower Austria). 2.1. Comparison between 3D volume rendering of µ-CT and OCT (λ c =850 nm) data. 2.2. - 2.4. Axial cross sections of the mesial root by µ-CT at position i)-iii) as depicted in 2.1. The regions marked in red show the area scanned by OCT presented in Figure 3.

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FIGURE 3. Specimen GS 26-1.Comparison between axial cross-sectional µ-CT and OCT (λ c =850 nm) images on the distal root at position i-iii, as depicted in Figure 1. 3.1. The cross section close to the collum dentis shows enamel but no annuli. 3.2.-3.3. The cross-sectional images ii) and iii) show annuli.

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FIGURE 4. Specimen GS 26-1. 4.1. Volume rendering of the 3D µ-CT. The red area marks the region scanned by OCT. 4.2. Sectional view of 3D OCT data. (see animations for OCT scan). 4.3. µ-CT axial cross-sectional scans and 4.4. µ-CT en-face scan. (see animations for animated µ-CT scan).

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FIGURE 5. Axial cross-sectional OCT image (λ c =1300 nm) in the lower third of the tooth radix of specimen. 5.1. GS 26-1 (distal). 5.2. GS 108-1 (mesial). 5.3. GS 108-2 (mesial). The camera images on the left show the OCT scanning region. The OCT images have a lateral dimension of 4 mm. The depth scale bar is stretched according to a refractive index of 1.6, leading to an image depth of about 1mm. The microscope images are 1x1 mm² in true aspect ratio. The depth scale of OCT images and microscope image is identical.

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FIGURE 6. 6.1-2: Comparison between the commercial system at 1300 nm (6.1) and the Lab system at 800 nm (6.2), exemplified by cross-sectional images of the specimen GS 26-1. The arrow in 6.2 indicates a fine structure that cannot be resolved by the 1300 nm system. 6.3-4: Comparison between the commercial system (6.3) and the PS-OCT system at 1500 nm, exemplified by by cross-sectional images of the specimen GS 108-2. 6.4. shows the reflectivity image, and 6.5. the retardation image. The arrow in 6.3 indicates an annual ring, while the arrows in 6.5 indicate birefringence of the tooth.

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FIGURE 7. Specimen GS 108-2, right lower m1 of a young adult individual of Ursus ingressus from Gamssulzen cave (Lower Austria). Comparison between 7.1. transmitted pulse amplitude, 7.2. time delay of THz measurement and 7.3. µ-CT.

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FIGURE 8. Image processing and hyper spectral data analysis: 8.1. Combined input data set containing hyper spectral data; 8.2. Overall features (main amplitude, phase slope, phase intercept, echo pulse delay, wavelet scaling factor); 8.3. Reduced feature set after applying the wavelet based feature reduction method; 8.4. Result of automatic classification by applying the two step partitional clustering method (k=20) based on the reduced feature set. For comparison: see animation of the result applying a Preclustering-based agglomerative hierarchical clustering method (40 clusters and 100 preclusters).

figure8

 

FIGURE 4. Specimen GS 26-1. 4.2. Sectional view of 3D OCT data. (Click on image for OCT scan animation).

figure4.2 

4.4. µ-CT en-face scan. (click on animation for animated µ-CT scan).

figure4.4 

 

FIGURE 8. Image processing and hyper spectral data analysis: 8.4. Result of automatic classification by applying the two step partitional clustering method (k=20) based on the reduced feature set. For comparison: click on image for animation of the result applying a Preclustering-based agglomerative hierarchical clustering method (40 clusters and 100 preclusters).

figure8 

 

leissElisabeth Leiss-Holzinger
Research Center for Non-Destructive Testing GmbH
Science Park 2/2.OG
Altenberger Straße 69
4040 Linz
Austria
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Elisabeth Leiss-Holzinger studied Technical Physics at the Vienna University of Technology. In the frame of her research in the field of magnetism, she started to develop sensors and numerical methods. Actually, she is working at the Research Center for Non Destructive Testing GmbH (RECENDT) in Linz, Austria. She focuses on the development of optical non-destructive testing techniques that apply interferometric technologies. This involves optical coherence tomography and, lately, multimodal OCT/photacoustic imaging. In the field of material characterization she is experienced in interdisciplinary cooperations and multimodal approaches.

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wiesauerKarin Wiesauer
Research Center for Non-Destructive Testing GmbH
Science Park 2/2.OG
Altenberger Straße 69
4040 Linz
Austria
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Karin Wiesauer received her PhD in technical sciences from the Johannes-Kepler-University in Linz, Austria, at the Department of Semiconductor Physics. Several years, she had been working in the field of OCT with special expertise in PS- and transversal measurements, and with well-founded experience in materials research. At the Research Center for Non Destructive Testing GmbH (RECENDT) in Linz, she built-up a new group for THz spectroscopy. After passing a postgraduate education at the medical university of Vienna, she is actually working as medical physicist at the hospital Krankenhaus der Barmherzigen Schwestern at the department of therapeutic radiology and oncology.

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stephaniHenrike Stephani
Fraunhofer Institute for Industrial Mathematics
Fraunhofer-Platz 1
67663 Kaiserslautern
Germany
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After studying mathematics at the University of Potsdam, Henrike Stephani did a joint Ph.D. at the Johannes Kepler University in Linz and the Technical University in Kaiserslautern on hyperspectral image analysis. She is now working as the deputy head of the image processing department of the Fraunhofer Institute for Industrial Mathematics (ITWM) in Kaiserslautern, Germany. The work there includes several industrial machine learning topics as well as the continuing work within the research field of hyperspectral image analysis, in cooperation with various universities.

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heiseBettina Heise
FLLL at Johannes Kepler University Linz and CDL MS-MACH
Altenberger Strasse 69
4040Linz
Austria
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and Research Center for Non-Destructive Testing GmbH
Science Park 2/2.OG
Altenberger Straße 69
4040 Linz
Austria
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Bettina Heise is Senior Scientist at the Johannes Kepler University (JKU) Linz. She is related to the physics and mathematics department as well as to the Recendt GmbH Linz , Austria. Her research interests cover the field of optical imaging and signal processing, where she has got experience in national and international scientific cooperations. Now, she is affiliated to CDL MS-MACH at JKU, where she works in in field of coherent microscopy.

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stifterDavid Stifter
CDL MS-MACH
Altenberger Strasse 69
4040 Linz
Austria
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David Stifter is Associate Professor at the Center for Surface and Nanoanalytics (ZONA) and head of the Christian Doppler Laboratory for Microscopic and Spectroscopic Material Characterization (CDL-MS-MACH) at the Johannes Kepler University Linz, Austria. His research interests are focused on the development of novel linear and non-linear optical microscopy techniques, as well as material characterization on the nano-scale in general, with electron-spectroscopic and -microscopic techniques.

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kriechbaumerBenjamin Kriechbaumer
University of Applied Sciences Upper Austria
Linz Campus
Garnisonstraße 21
4020 Linz
Austria
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Benjamin Kriechbaumer studied Biomedical Engineering at the University of Applied Sciences Linz, where his main interests were Biomechanics and Molecular Analysis. At the Research Center for Non Destructive Testing GmbH (RECENDT) in Linz he performed THz measurements. He is currently working as Field-Technical engineer at Sorin Group Austria GmbH.

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spachingerStefan J. Spachinger
University of Applied Sciences Upper Austria
Wels Campus
Stelzhamerstraße 23
4600 Wels
Austria
no e-mail available

Stefan Spachinger studied at the Upper Austria University of Applied Sciences in Wels. The main fields of his interest were X-ray computed tomography for industrial applications and high resolution X-ray computed tomography. At the Graz University of Technology, he focused on the comparison between experimental parameters and numerical thermo-dynamic modelling of the welding process.

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gusenbauerChristian Gusenbauer
University of Applied Sciences Upper Austria
Wels Campus
Stelzhamerstraße 23
4600 Wels
Austria
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Christian Gusenbauer studied Technical Physics at the Johannes Kepler University of Linz. Currently he is studying Medical Physics at the Medical University of Vienna. His main research interests are computed tomography, metrology, non-destructive testing of metals and image data processing.

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withalmGerhard Withalm
Institute of Palaeontology
University of Vienna
Althanstraße 14
1090 Wien
Austria
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Dr. Gerhard Withalm was born in Vienna (Austria) and attended school in his hometown Baden. Later on he studied biology and (vertebrate) paleontology at the University of Vienna (Austria). In 1995 he was rewarded with the Othenio-Abel-Prize of the Austria Academy of Sciences. From 1995 on Gerhard Withalm was assistant to Gernot Rabeder, the chair of paleobiology, at the Institute of Palaeontology in Vienna and prepared his thesis on the evolution of metapodial bones within the cave bear group and started to work with X-ray computed tomography. At the same time he started his own lectures on paleopathology and the evolution of birds, an activity, which lasted until 2010. Since then he is dealing with selected subjects of vertebrate paleontology due to the necessity to earn money.

 

TABLE 1. Examined teeth of Ursus ingressus Rabeder et al. (2004) from Gamssulzen cave in Lower Austria (Austria). All specimens are lower first molars (M1) of the right side (dext.) or of the left side (sin.).

 table1

TABLE 2. Comparison between applied measurement methods.

 table2