APPLICATIONS OF INNOVATIVE BUILDING MATERIAL AND COMPUTER VISION METHODS IN GEOTECHNICAL ENGINEERING

Ph.D

Content-aware approach for improving biomedical image analysis: an interdisciplinary study series

Biomedicine is a highly interdisciplinary research area at the interface of sciences, anatomy, physiology, and medicine. In the last decade, biomedical studies have been greatly enhanced by the introduction of new technologies and techniques for automated quantitative imaging, thus considerably advancing the possibility to investigate biological phenomena through image analysis. However, the effectiveness of this interdisciplinary approach is bounded by the limited knowledge that a biologist and a computer scientist, by professional training, have of each other’s fields. The possible solution to make up for both these lacks lies in training biologists to make them interdisciplinary researchers able to develop dedicated image processing and analysis tools by exploiting a content-aware approach. The aim of this Thesis is to show the effectiveness of a content-aware approach to automated quantitative imaging, by its application to different biomedical studies, with the secondary desirable purpose of motivating researchers to invest in interdisciplinarity. Such content-aware approach has been applied firstly to the phenomization of tumour cell response to stress by confocal fluorescent imaging, and secondly, to the texture analysis of trabecular bone microarchitecture in micro-CT scans. Third, this approach served the characterization of new 3-D multicellular spheroids of human stem cells, and the investigation of the role of the Nogo-A protein in tooth innervation. Finally, the content-aware approach also prompted to the development of two novel methods for local image analysis and colocalization quantification. In conclusion, the content-aware approach has proved its benefit through building new approaches that have improved the quality of image analysis, strengthening the statistical significance to allow unveiling biological phenomena. Hopefully, this Thesis will contribute to inspire researchers to striving hard for pursuing interdisciplinarity

Investigation of x-ray computed tomography for Portland cement phase quantification

Cementitious materials are often characterized through the use of advanced analytical techniques to understand the macro-, micro-, and nano-scale properties, including phase formation during hydration, and subsequent potential deterioration mechanisms which can affect service life. A major limitation with using such analytical techniques to quantify solid phases in cementitious systems is that many techniques are destructive in nature. If one wants to monitor changes over time, samples must be extracted from different locations of the same sample, or from a different sample, at different times. This limitation can hinder the ability continually monitor the desired property. One method to extract quantifiable information non-destructively is x-ray computed tomography (x-ray CT). X-ray CT is a non-destructive, non-contact technique that uses computer-processed x-rays to produce three-dimensional tomographic images of specific zones of a sample. This technique has been successfully used in many different aspects of research, including medicine, geo-sciences, and materials science. The use of x-ray CT has been applied to cementitious systems but has been predominately limited to qualitative or semi-quantitative analysis. Quantification of cementitious properties has been hindered through two means, spatial resolution and low contrast between solid phases, including the unhydrated and hydrated phases. This low contrast has often led to quantification of void space within the cementitious sample. The work presented in this dissertation addresses methods to resolve the expected low contrast in x-ray CT images on cementitious and the potential for segmentation of the four main hydration products found in portland cement. This was achieved through an investigation of different image segmentation algorithms and a creative use of contrast agents to be bound into specific hydration products using a synchrotron x-ray CT. Advancements in x-ray CT optics and data collection are continually improving image resolution, therefore it is not discussed in this dissertation. Published literature on the use of x-ray CT in cementitious materials often does not include a thorough description of the image processing procedures used for analysis. The use of arbitrary, histogram-based threshold values can lead to biased segmentation and misclassification of the voxels in the image volume. Presented in this dissertation is a method to deconstruct the greyscale values of a histogram into individual Gaussian curves in an unbiased manner. The greyscale values of laboratory synthesized calcium-silicate-hydrate (C-S-H), calcium hydroxide (CH), monosulfate (AFm), and ettringite (AFt) were determined to provide a baseline for threshold values. Pure phase, binary, and quaternary mixture samples of the four aforementioned phases were studied. A Gaussian probability density function was applied to each phase and proportioned to the known mass of each phase in the binary and quaternary mixtures. Intersections of the Gaussian curves was determined as the threshold value. Quantification of binary mixtures was successfully done with exception to C-S-H and AFm mixtures. Low contrast between the phases was observed leading to difficulties accurately quantifying such mixtures. Similar success was observed in quaternary mixtures of phases. However, difficulties in segmentation were compounded segmenting AFm, C-S-H, and CH in these mixtures. One method to resolve low contrast is to incorporate the use of contrast agents. Success in the medical field, and other limited successes in geo-sciences, provided the motivation to determine methods to incorporate contrast agents into portland cement hydrates. Literature reports a myriad of ions which can be incorporated into the structure of C-S-H, AFm, and AFt through various mechanisms, including substitution and absorption. Due to the limitations in segmenting AFm and C-S-H in their pure form, investigations for incorporating contrast agents to improve segmentation was done. Iodine was selected as the contrast agent to be substituted for the sulfate ion in AFm. Dual energy scans above and below the absorption edge of iodine was done, and the use of image subtraction allowed for quick and accurate segmentation of the C-S-H and modified AFm phases. However, difficulties segmenting C-S-H and CH were observed in quaternary mixtures of AFt, CH, C-S-H, and a modified AFm using the Gaussian deconstruction method to determine threshold values for segmentation. Lastly, due to the difficulties achieving consistent results during segmentation when using histogram-based threshold values, a study determining the feasibility of local segmentation algorithms was done on binary and quaternary mixtures of the four phases. These algorithms often result in more desirable results by accounting for the spatial arrangement of the greyscale values throughout the image volume. Two local segmentation algorithms, watershed and Bayesian Markov random fields, were compared to the Gaussian deconstruction method. Results indicated both local segmentation algorithms resulted in more accurate quantification of the four phases, thus providing promise for future applications to hydrating portland cement

Characterization of Bone Material Properties and Microstructure in Osteogenesis Imperfecta/Brittle Bone Disease

Osteogenesis imperfecta (OI) is a genetic disorder primarily associated with mutations to type I collagen and resulting in mild to severe bone fragility. To date, there is very little data quantifying OI cortical bone mechanics. The purpose of this dissertation was to investigate bone microstructure, mineralization, and mechanical properties in adolescents with OI. Characterization studies were performed on small osteotomy specimens obtained from the extremities during routine corrective surgeries. Nanoindentation was used to examine the longitudinal elastic modulus and hardness at the material level for mild OI type I vs. severe OI type III. Both modulus and hardness were significantly higher (by 7% and 8%, respectively) in mild OI cortical bone compared to the more severe phenotype. Lamellar microstructure also affected these properties, as the younger bone material immediately surrounding osteons showed decreased modulus (13%) and hardness (11%) compared to the older interstitial material. A high resolution micro-computed tomography system utilizing synchrotron radiation (SRµCT) was described and used to analyze the microscale vascular porosity, osteocyte lacunar morphometry, and bone mineral density in OI vs. healthy individuals. Vascular porosity, canal diameter, and osteocyte lacunar density were all two to six times higher in OI cortical bone. Osteocytes were also more spherical in shape. Finally, three-point bending techniques were used to evaluate the microscale mechanical properties of OI cortical bone in two different orientations. Elastic modulus, flexural yield strength, ultimate strength, and crack-growth toughness were three to six times higher in specimens whose pore structure was primarily oriented parallel vs. perpendicular to the long bone axis. There was also a strong negative correlation between the elevated vascular porosity of OI cortical bone and its elastic modulus, flexural yield strength, and ultimate strength. This relationship was independent of osteocyte lacunar density and tissue mineral density. In summary, these findings highlight new material and microstructural changes within OI cortical bone that help contribute to its fragility. They also underscore a deep connection between bone structure and mechanical integrity at multiple length scales

Forum Bildverarbeitung 2022

Bildverarbeitung verknüpft das Fachgebiet die Sensorik von Kameras – bildgebender Sensorik – mit der Verarbeitung der Sensordaten – den Bildern. Daraus resultiert der besondere Reiz dieser Disziplin. Der vorliegende Tagungsband des „Forums Bildverarbeitung“, das am 24. und 25.11.2022 in Karlsruhe als Veranstaltung des Karlsruher Instituts für Technologie und des Fraunhofer-Instituts für Optronik, Systemtechnik und Bildauswertung stattfand, enthält die Aufsätze der eingegangenen Beiträge

Applications of x-ray computed microtomography to material science: devices and prespectives

2006/2007The three-dimensional visualization of the inner microstructural features of objects and materials is an aspect of relevant interest for a wide range of scientific and industrial applications. X-ray computed microtomography (μ-CT) is a powerful non-destructive technique capable to satisfy these needs. Once the complete reconstruction of the sample is available, a quantitative characterisation of the microstructure is essential. Through digital image processing tools, image analysis software or custom developed algorithms, it is possible to obtain an exhaustive geometrical, morphological and topological description of the features inside the volume, or to extract other particular parameters of interest (e.g. porosity, voids distribution, cell size distribution, average struts length, connectivity between the cells, tortuosity). This thesis was carried out at the third-generation Elettra Synchrotron Radiation Facility (Trieste, Italy), where a hard X-ray imaging beamline is available. The experience developed at this beamline has leaded scientists to design a complementary state-of-the-art μ-CT facility based on a micro-focus X-ray source, working both in absorption and phase contrast mode. In this dissertation a detailed description of this facility is given together with a rigorous characterization of the imaging system capabilities, in terms of the actual achievable spatial resolution, in order to optimize the working parameters for the different experiments. The main artefacts that concur to the degradation of the quality of the reconstructed images have been considered (e.g. beam hardening effects, ring artefacts, uncertainness associated with the cone-beam geometry): procedures are presented in order to eliminate, or at least to reduce, the causes of these artefacts. The aspects related to the digital image processing of the reconstructed data are intensively developed in this study: appropriated methodologies have been elaborated capable to deal with the different three-dimensional data of complex porous media, providing a correlation between the microstructure and the macroscopic behaviour of the observed materials. Three representative examples obtained with the described methods are used to demonstrate the application of μ-CT, combined with the developed image processing tools, to material science: the geometrical and morphological characterisation of polyurethane foams employed in the automotive industry due their vibro-acoustic properties; a new approach to characterize the resonance spruce wood microstructure in order to study its acoustical behaviour; finally, the possibility of revealing defects in hybrid-friction stir welded aluminium joints, guiding the optimization of the process parameters.La visualizzazione tridimensionale della struttura interna di oggetti e materiali costituisce un aspetto di notevole interesse per una ampia gamma di applicazioni scientifiche ed industriali. La microtomografia computerizzata a raggi X (μ-CT) rappresenta una potente tecnica di indagine adeguata a soddisfare tali richieste. Una volta completata la ricostruzione del campione in esame, è essenziale poter fornire una caratterizzazione quantitativa della microstruttura evidenziata. Attraverso gli strumenti messi a disposizione dalle moderne tecniche di analisi di immagine, per mezzo di software dedicati o algoritmi personalizzati, è possibile ottenere una descrizione esaustiva della geometria, morfologia e topologia degli elementi microstrutturali presenti, che consenta l’estrazione dei parametri di interesse per la particolare applicazione (porosità, distribuzione dei vuoti, dimensione degli elementi, lunghezze caratteristiche, grado di interconnessione, tortuosità etc.). Il presente lavoro di tesi è stato svolto presso il laboratorio di luce sincrotrone di terza generazione Elettra (Trieste, Italia), dove è disponibile una linea sperimentale dedicata all’imaging con raggi X duri. L’esperienza acquisita da parte dei ricercatori di questa linea ha consentito poi la progettazione di una stazione per μ-CT complementare, allo stato dell’arte e basata su una sorgente di radiazione a microfuoco, capace di operare con modalità di raccolta delle immagini sia in assorbimento sia in contrasto di fase. In questa tesi viene fornita una dettagliata descrizione della stazione, accompagnata da una rigorosa caratterizzazione del sistema impiegato per l’acquisizione e la ricostruzione delle immagini, in termini di risoluzione spaziale raggiungibile, così da consentire l’ottimizzazione dei parametri critici di lavoro nelle differenti condizioni sperimentali. Vengono poi presi in considerazione i principali artefatti che contribuiscono al deterioramento della qualità delle immagini ottenute (come il beam hardening, gli artefatti ad anello, gli artefatti legati all’incertezza geometrica associata al fascio conico etc.): vengono quindi proposti dei metodi per l’eliminazione, o almeno la riduzione, delle cause che li determinano. Nella tesi inoltre sono sviluppati in maniera approfondita gli aspetti connessi al trattamento dei dati digitali raccolti: sono state infatti elaborate delle metodologie appropriate, capaci di trattare i diversi tipi di dato provenienti dall’analisi di mezzi porosi, determinanti per la comprensione della correlazione tra la microstruttura del materiale ed il suo comportamento macroscopico. Infine, vengono proposti tre esempi rappresentativi per dimostrare l’efficacia dell’applicazione della μ-CT, in combinazione con gli strumenti di analisi di immagine messi a punto, alla scienza dei materiali: la caratterizzazione geometrica e morfologica di schiume di poliuretano impiegate nell’industria automobilistica come isolante vibro-acustico; un nuovo approccio rivolto alla caratterizzazione della struttura del legno di risonanza al fine di studiarne il comportamento acustico; la possibilità di mettere in luce i difetti in giunti di saldatura di leghe d’alluminio realizzati con la tecnica ibrida friction stir welding/TIG in maniera da ottimizzare i parametri di processo.XX Ciclo197

3D Characterisation of microcracks in concrete

The nature of microcracks that developed in concrete is not well understood. One reason for this is the lack of suitable techniques to detect and characterise the microcracks. Conventional methods include imaging polished cross sections with scanning electron microscopy and optical microscopy. However, these techniques only provide a two-dimensional representation of a three-dimensional structure, which significantly reduces the insights from such analysis. Another reason is that the development of microcracks may be associated with various complex forms of concrete deterioration during service life, e.g. due to mechanical loading, drying, thermal effects and chemical reactions. This complicates laboratory scale experiments and inducing “realistic” microcracks in concrete samples becomes very difficult. The aim of this study is to develop new techniques for three-dimensional quantitative characterisation of microcracks and to apply these to understand the properties of microcracks in concrete. A thorough literature review was conducted to identify the causes of microcracking in concrete, mechanisms of microcrack initiation and propagation, transport properties of micro-cracked concrete and methods to characterise microcracks in two dimensions (2D) and three dimensions (3D). Materials and experimental procedures for inducing different types of microcracks, sample preparation for imaging and image analysis of microcracks are discussed. The feasibility of three-dimensional techniques such as focused ion beam nanotomography (FIB-nt), broad ion beam combines with serial sectioning (BIB), X-ray microtomography (μ-CT) and laser scanning confocal microscopy (LSCM) for imaging microcracks were investigated. A new approach that combines LSCM with serial sectioning was proposed to enhance the capability of LSCM for imaging microcracks in 3D. A major focus of this thesis was dedicated to microcracks induced by autogenous shrinkage because this has been previously neglected due to the dominant role of drying shrinkage. Nonetheless, the increasing use of high strength concretes containing low water/binder ratio, complex binder systems and multiple chemical admixtures in recent years has highlighted the problem of autogenous shrinkage in these concretes. This study presents a first attempt on direct characterisation and understanding of the microcracks caused by autogenous shrinkage in 3D. Various concrete samples were produced and sealed cured to induce autogenous shrinkage. The water/binder ratio, cement type and content, and aggregate particle size distribution were varied to vary the magnitude of autogenous shrinkage and degree of microcracking. Linear deformation measurement was performed to correlate autogenous shrinkage with degree of microcracking. Samples were imaged in 2D using laser scanning confocal microscope (LSCM) and in 3D with X-ray microtomography (μ-CT). Subsequently, 2D and 3D image analysis was employed to quantify microcracks > 1 μm in width. A major challenge was to isolate the microcracks that are inherently connected to pores and air voids. Therefore, an algorithm was developed to separate microcracks from pores, and to extract quantitative data such as crack density, orientation degree, distribution of width and length, as well as connectivity and tortuosity. The results show that use of supplementary cementitious materials and low water/binder ratio can increase linear deformation and the amount of the microcracks. The thesis discusses the effect of autogenous shrinkage on the characteristics of the induced microcracking, which is critical to understanding the transport properties and long-term durability of concretes containing supplementary cementitious materials.Open Acces