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Capturing three-dimensional (3D) imaging is essential in the broad field of cranio-maxillofacial surgery. Laser scanners and stereophotogrammetry are more and more relevant for capturing (facial) soft tissues. For this purpose, a 3D laser scanning imaging system, using a nonhazardous laser, with a precise texture reproduction and in some models with colour capturing, can replace 3D imaging with radiation in many cases. This chapter gives an overview on the different applications of laser scanning in maxillofacial surgery. The following topics will be pointed out: the method of laser scanning; the laser scanning of plaster models, impressions and skull models; the laser scanning for oral surgical planning and for the assessment of facial swelling after oral surgery; the laser scanning of malformations; the laser scanning in facial aesthetics and epithetic procedures; and the laser scanning in orthodontic treatment and orthognathic surgery. 3D laser scanners are still commonly used, but recently other devices, often based on stereophotogrammetry or 3D camera systems, became often superior. Due to shorter acquisition times, these systems are less vulnerable to motion artefacts and, thereby, more suitable for capturing small children or less cooperative patients.

During therapy of distoclusion entailing a rigid, fixed orthodontic appliance, the mandibular fossa and condyle are ideally remodeled, while dentoalveolar effects occur through adaptive mechanisms. Adaptive processes, especially in the fossa region, have not been adequately investigated. Our magnetic resonance imaging (MRI) investigation aimed to assess the effects of therapy with a functional mandibular advancer (FMA) on mandibular fossa morphology. We monitored via MRI the therapeutic course of 25 patients at three time points. Visual findings and metric assessments were carried out in the sagittal plane. Three-dimensional (3D) reconstructions of the joint structure of two exemplary patients were also made. Visual examinations of the MRI slices at the three time points revealed no changes in fossa shape in any of the 50 temporomandibular joints. Lateral comparisons showed that the morphology of the fossae of all 25 patients was identical. Metric analysis demonstrated no significant alterations in width, depth, or in their ratio, not even laterally. Nine measurements of the distances between the porion, mandibular fossa, and articular eminence revealed no significant changes in total or on the left and right sides, or intralaterally. The visual findings and metric analyses of parasagittal MRI slices did not indicate any morphological changes in the mandibular fossa or articular eminence in patients with distoclusion treated via a rigid, fixed orthodontic appliance. However, special reworking of the MRI data facilitated reconstruction of the surfaces of joint structures in 3D. This new method makes it possible to depict more accurately and noninvasively the adaptive mechanisms not ascertainable via metric methods and to assess them as 3D structures.

Osteoradionecrosis (ORN) is a serious side effect of oncologic radiation therapy. Often, surgical removal of the affected skeletal tissue is indicated. In cranio-maxillofacial surgery, partial or total resection of the upper or lower jaw implies a severe impairment of the patient‘s quality of life. Up to now, clear display of ORN is still a challenge. This part of the project is dedicated to medical visualization of progressing ORN for clinical diagnosis. Currently, clinical diagnosis of ORN is mostly based on computer tomography (CT). With regard to its high advantages as e.g. reduced radiation dose, we additionally evaluate cone beam computer tomography (CBCT). After registration on a suitable reference and refined image processing and segmentation, all patient’s CT-/CBCT-data are subjected to various rendering techniques configured for the respective purpose, namely visualization of destructive and/or sclerotic skeletal alterations, consideration of cortical or trabecular bone, and analysis based on CT or CBCT. Recent achievements within the project were demonstrated with special focus on evaluation of both, CT and CBCT as well as on close cooperation with the clinical setting.

Hintergrund Kraniomandibulare Dysfunktionen (CMD) betreffen einen erheblichen Teil der Bevolkerung. In den letzten Jahrzehnten haben computerassistierte Methoden fur die Diagnostik und Therapieplanung zunehmend Eingang in die klinische Praxis gefunden.

Bei Patienten mit kraniomandibularer Dysfunktion (CMD) sind eine umfangreiche Anamnese, eine klinische Untersuchung, aber auch die Bildgebung sehr wichtig. In den vergangenen Jahren konnten grose Fortschritte in der CMD-Diagnostik erzielt werden. Dieser Beitrag erlautert den aktuellen Stand verschiedener bildgebender Verfahren und deren Stellenwert. Dazu gehoren die konventionelle Rontgenaufnahme/Panoramaschichtaufnahme, die digitale Volumentomographie und Computertomographie, der (hochauflosende) Ultraschall, die nuklearmedizinische Bildgebung und die Magnetresonanztomographie.

In dentistry, clinical radiographs (also called X-ray images) reflect the intensity loss of an X-ray when being transmitted through the mandibular objects, and this loss is quantified in terms of grey values. While such images are standardly used for pathology detection by the experienced dentist, we here present a new method for getting more quantitative information out of such 2D radiographs, “extending” them into the third dimension. This “extension” requires consistent combination of X-ray physics (namely, X-ray intensity loss quantification along paths orthogonal to the panoramic clinical image and X-ray attenuation averaging for composite materials) with anatomically known upper and lower limits of vascular porosities in cortical and trabecular bone compartments. Correspondingly computed ranges of overall organ thicknesses are extremely narrow, suggesting adequate estimation of thickness characteristics from 2D radiographic panoramas used clinically, while predicted cortical and trabecular thickness ranges vary by ±8.47% and ±16.13%, respectively. The proposed method also identifies variations between thicknesses at similar anatomical locations left and right of the face's symmetry axis, and molar regions turn out to be thicker than those close to incisors. This paves the way to more detailed diagnostic activities, e.g. in combination with Finite Element simulations.

The minimal invasive procedure of vertebroplasty is a surgical technique to treat compression fractures of vertebral bodies. During the treatment, liquid bone cement gets injected into the affected vertebral body and therein cures to a solid. In order to investigate the treatment and the impact of injected bone cement, an integrated modelling and simulation framework has been developed. The framework includes (i) the generation of microstructural computer models based on microCT images of human cancellous bone, (ii) computational fluid dynamics (CFD) simulations of bone cement injection into the trabecular structure and (iii) non-linear finite element (FE) simulations of the subsequent bone cement curing. A detailed description of the material behaviour of acrylic bone cements is provided for both simulation stages. A non-linear process-dependent viscosity function is chosen to represent the bone cement behaviour during injection. The bone cements phase change from a highly viscous fluid to a solid is described by a non-linear viscoelastic material model with curing dependent properties. To take into account the distinctive temperature dependence of acrylic bone cements, both material models are formulated in a thermo-mechanically coupled manner. Moreover, the corresponding microstructural CFD- and FE-simulations are performed using thermo-mechanically coupled solvers. An application of the presented modelling and simulation framework to a sample of human cancellous bone demonstrates the capabilities of the presented approach.

Serious mandibular diseases such as tumor or osteonecrosis often require segmental or marginal mandibulectomy, the latter with improved outcome thanks to preserved mandibular continuity. Nevertheless, gradual osteolytic and/or osteosclerotic skeletal changes frequently indicate repetitive resections. Based on the fundamental adaptivity of bone to mechanical loads, the question arose whether resection-related anatomical alterations trigger relevant pathological skeletal adaptations. For a clinical case after mandibular box resection due to progressive osteoradionecrosis (ORN), routine biomechanical loading was simulated by finite element method, respecting pathology-related anatomy, tissue properties, and biting capacity. By 3D-visualization of the mandible’s pathological development from follow-up-CT’s over four years, remarkable correspondences of skeletal resorptions and increased unphysiological strain were revealed. Higher unphysiological load was correlated with more serious and earlier skeletal alterations. Three months post-operatively, serious buccal destruction at the distal resection corner occurred in correspondence with dominant tensile strain. At the resection, elevated strain caused by reduced alveolar height corresponded to skeletal compromise, observed 8–9 months post-operatively. ORN-related lesions, diagnosed before resection, entailed unphysiological strain coinciding with local skeletal alterations. Simulations with “healthy” instead of pathological tissue coefficients induced quantitative improvements of 25–33%, but without fundamental change. These results suggest a decisive contribution of resection-related biomechanical skeletal adaptations to this patient’s mandibular decline with hemimandibulectomy about 2.5 years after the first resection. However, mechanical stress concentrations in sharp angles as the distal resection corner and reduced stability due to decreased alveolar height generally bear the danger of pathological biomechanics and severe skeletal adaptations for patients after mandibular box resection.

Due to muscular deformation and movement, standard radiology provides only a snapshot of a probably never recurring situation. The scope of this project is dynamic rendering of muscular structures, starting from 4D-radiology, namely 3D+time, to macroscopic visualization and simulation based thereon. As full real time 4D-MRI is still beyond the technical possibilities for most human muscles, we follow kind of multi level approach. The first step is the analysis of muscular tissue of cadaveric preparations where validation can be performed by direct comparison. Secondly, nearly static, but living muscular tissue is studied based on standard 3DMRI. The first step towards time dependency are ex post composed series of static MRI where the muscle goes back to relaxed position between the acquisition steps. This is followed by so called “quasi-continuous” acquisition where, though not real time, the muscle does not go back to its original state, however remains in stretched position during acquisition. The final goal is full real time data acquisition. The radiological acquisition is followed by highly detailed image processing, segmentation, and visualization where the deforming muscular tissue is subjected to direct volume rendering with special transfer functions. The applied methods are demonstrated for the flexion of a human ankle joint and deforming human upper arm musculature. The visualization techniques proved to be well suited for capturing dynamics, but additional radiological research is strongly needed. The area of application of 4D-modeling ranges from biomechanics to medical diagnosis and therapy of muscular disorders. Key words: 4D-visualization, dynamic MRI, sequential MRI, upper arm musculature, ankle joint flexion, lower leg musculature, biceps brachii muscle, gastrocnemius muscle, direct volume rendering, 3D-reconstruction

Objective: To demonstrate feasibility of near-real-time oculodynamic magnetic resonance imaging (od-MRI) in depicting extraocular muscles and correlate quantitatively the motion degree in comparison with clinical testing in patients with diplopia. Methods: In 30 od-MRIs eye movements were tracked in the horizontal and sagittal plane using a a TrueFISP sequence with high temporal resolution. Three physicians graded the visibility of extraocular muscles by a qualitative scale. In 12 cases, the maximal monocular excursions in the horizontal and vertical direction of both eyes were measured in od-MRIs and a clinical test and correlated by the Pearson test. Results: The medial and lateral rectus muscles were visible in the axial plane in 93% of the cases. The oblique, superior and inferior rectus muscles were overall only in 14% visible. Horizontal (p = 0,015) and vertical (p = 0,029) movements of the right eye and vertical movement of the left eye (p = 0,026) measured by od-MRI correlated positively to the clinical measurements. Conclusions: Od-MRI is a feasible technique. Visualization of the horizontal/vertical rectus muscles is better than for the superior/inferior oblique muscle. Od-MRI correlates well with clinical testing and may reproduce the extent of eye bulb motility and extraocular muscle structural or functional deteriorations. Key Points • Oculodynamic MRI technique helps clinicians to assess eye bulb motility disorders • MRI evaluation of eye movement provides functional information in cases of diplopia • Oculodynamic MRI reproduces excursion of extraocular muscles with good correlation with clinical testing • Dynamic MRI sequence supplements static orbital protocol for evaluation of motility disorders

Active and passive experiments on skeletal muscles are in general arranged on isolated muscles or by consideration of the whole muscle packages, such as the arm or the leg. Both methods exhibit advantages and disadvantages. By applying experiments on isolated muscles it turns out that no information about the surrounding tissues are considered what leads to insufficient specifications of the isolated muscle. Especially, the muscle shape and the fibre directions of an embedded muscle are completely different to that of the same isolated muscle. An explicit advantage, in contrast, is the possibility to study the mechanical characteristics in an unique, isolated way. On the other hand, by applying experiments on muscle packages the aforementioned pros and cons reverse. In such situation, the whole surrounding tissue is considered in the mechanical characteristics of the muscle which are much more difficult to identify. However, an embedded muscle reflects a much more realistic situation as in isolated condition. Thus, in the proposed work to our knowledge, we, for the first time, suggest a technique that allows to study characteristics of single skeletal muscles inside a muscle package without any computation of the tissue around the muscle of interest. In doing so, we use magnetic resonance imaging data of an upper arm during contraction. By applying a three-dimensional continuum constitutive muscle model we are able to study the biceps brachii inside the upper arm and validate the modelling approach by optical experiments.

Introduction: The main objectives of this study were to generate individual finite element models of extracted human upper first premolars, and to simulate the distribution of the hydrostatic pressure in the periodontal ligament (PDL) of these models for evaluation of the risk of root resorption. Methods: The individual extracted teeth were from a previous in vivo study that investigated root resorption after application of continuous intrusive forces. The results of experimental examination and simulations were compared on these identical tooth roots. The applied force system was 0.5N and 1.0N of intrusive force. Results: The simulated results during intrusion of 0.5N showed regions near the apical thirds of the roots with hydrostatic pressure over the human capillary blood pressure. These regions correlated with the electron microscopies of previous studies performed in Brazil with the identical teeth. An increased force of 1.0N resulted in increased areas and magnitudes of the hydrostatic pressure. Conclusions: The key parameter indicating beginning root resorption used in this study was an increased value for hydrostatic pressure in the PDL.

An approach of 3D-visualization of the temporomandibular joint (TMJ) with special focus on the articular disc based on magnetic resonance imaging (MRI) was developed for the purpose of diagnosis support. Mandibular condyle and fossa were reconstructed as 3D-surfaces. Articular disc, retrocondylar tissue, and the lateral pterygoid muscle were visualized by means of direct volume rendering. By simultaneous visualization of both, the bony surfaces and the soft tissue, anterior disc displacement could be recognized in 3D-context. Additional superposition of the 3D-visualization with the original 2D-MRI slices allowed for a combination with conventional diagnostics. The method was tested for clinical T1-, T2-, and proton density weighted MRI data from four independent medical institutions. For all cases, the skeletal anatomy could be reproduced. Applied validation approaches showed good results. Anterior disc displacement could be clearly depicted as well as the incidence of reduction of the disc. By several experienced observers, the approach was rated as significant. Although partially non-standard in the clinical routine the new method provided promising results for efficient diagnosis support. Its validity in the medical practice, namely, its impact for dislocation/deformity of the mandibular disc will be further analyzed.

To visualize the temporomandibular joint (TMJ) and the surrounding tissues in detail utilizing high-resolution MR images for the diagnosis of soft- and hard-tissue abnormalities. Clinically routine MR slices are processed by tissue segmentation and three-dimensional (3D) reconstruction and viewed with visualization software.A 1.5 T MRI system was used. The double-echo procedure for taking oblique sagittal images was applied to obtain both proton density-weighted (PDW) and T2 weighted (T2W) images simultaneously, with separate examinations in both open and closed mouth positions. Diagnosis of the abnormality in the placement and morphology of articular discs and the joint effusion status is usually performed using multiple MRI slices. Clinically routine continuous MR slices were processed by segmentation, reconstruction and visualization algorithms, and the mandibular condyle, fossa, articular disc and other intra-articular tissues were visualized on the 3D and two-dimensional (2D)-3D fusion images.In a clinical case, the anterior disc displacement without reduction, with mouth open and closed, was clearly depicted in the 3D images. Also 2D-3D superposed images with changeable tissue transparency successfully depicted the stereoscopic TMJ morphology in three dimensions.High-resolution PDW- and T2W MR images could be processed by tissue segmentation and 3D-reconstruction procedures, and the resultant images showed the anatomical details in an easily recognizable way. By the simultaneous visualization of both bony surfaces and soft tissues, disc displacement and deformity can be recognized in a 3D context. The additional superposition of the 3D visualization with the original 2D MR slices allows for a combination with conventional diagnostics.

Fixed functional orthopedic appliances used in 6 to 9 month-long treatments to correct distoclusion keep the mandible permanently in the therapeutically-desired protruded position. The principal aim of this approach is to achieve an increase in length of the lower jaw by stimulating mandibular growth. Ideally, adaptive mechanisms in adolescents and young adults result in condylar remodeling. Alternatively, however, therapeutically-undesirable alterations in the condyle position within the articular fossa may also occur. Thus the aim of this magnetic resonance imaging (MRI) study was twofold: 1) to verify the effects that the treatment with a fixed functional orthopedic appliance used to correct distoclusion has on the topographic relationship of mandibular condyle and glenoid fossa, and 2) to analyze morphologic changes in the condyle.Treatment progress in 20 patients was monitored by MRI at four defined points in time. Visual inspection and metric analysis were performed in three planes (axial, frontal, parasagittal) shown on the MRIs. 3D-reconstruction of the condyle surfaces based on the MRI data sets at hand was done in selected cases.Upon assuming the therapeutically-desired position, the condyles were caudally and ventrally displaced from their centric position within the fossa. At the end of treatment, they had returned to their original position. When assessed laterally, statistical analysis revealed no significant differences between the joints on the right and left sides. Neither the anterior nor posterior joint space among all 40 joints exhibited significant changes in width compared to the baseline findings. Visual inspection in the axial, frontal, and sagittal planes revealed changes in the exterior form of 31 of the 40 condyles analyzed. On the whole, while morphologic changes were observed in all three planes, they were most marked in the axial plane. Metric analysis of the 2D-MRIs, on the other hand, revealed no significant changes in width, depth, or height in the plane in question. This is why we reconstructed the condyle structure three-dimensionally on a trial basis. For purposes of analysis, we super imposed the reconstructions of the condyle surfaces at the various control points on each other. By processing the data in this manner, an alternative approach for evaluating morphologic changes was created. CONCLUSIONS AND PROSPECTS: In patients treated with a rigid, fixed functional orthopedic appliance (FMA) for skeletal Class II malocclusion, both joints returned to a physiologic condyle-fossa relationship post-treatment. The improved occlusion was not achieved at the price of unphysiologic repositioning in the temporomandibular joint. Visual inspection suggested that morphologic changes in the condyle may have occurred as treatment progressed, but this was not confirmed by 2D metric analysis. However, by means of 3D-reconstruction of the condylar surfaces and their superposition, detailed visualization of adaptive mechanisms and their non-invasive evaluation in 3D may become feasible in clinical routine.

We here present a strategy for reliable prediction of elastic properties from X-ray attenuation coefficients visualized in Computer Tomographic images, as basis for Finite Element models. By example, we show the distribution of the axial normal stress throughout a human mandible, due to a bite on the leftmost premolar. Remarkably, this distribution is not heavily altered if we replace the inhomogeneous material distribution by one discerning merely cortical and trabecular bone, but it is strongly affected by the consideration of material anisotropy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We provide a case study for the generation of pure hexahedral meshes for the numerical simulation of physiological stress scenarios of the human mandible. Du to its complex and very detailed free-form geometry, the mandible model is very demanding. This test case is used as a running example to demonstrate the applicability of a combinatorial approach for the generation of hexahedral meshes by means of successive dual cycle eliminations, which has been proposed by the second author in previous work. We report on the progress and recent advances of the cycle elimination scheme. The given input data, a surface triangulation obtained from computed tomography data, requires a substantial mesh reduction and a suitable conversion into a quadrilateral surface mesh as a first step, for which we use mesh clustering and b-matching techniques. Several strategies for improved cycle elimination orders are proposed. They lead to a significant reduction in the mesh size and a better structural quality. Based on the resulting combinatorial meshes, gradient-based optimized smoothing with the condition number of the Jacobian matrix as objective together with mesh untangling techniques yielded embeddings of a satisfactory quality. To test our hexahedral meshes for the mandible model within an FEM simulation we used the scenario of a bite on a ‘hard nut.’ Our simulation results are in good agreement with observations from biomechanical experiments.

A new modular software concept for individual numerical simulation of the human mandible using the finite element method (FEM) is presented. The main task is an individual analysis of regional stress and stress-compatibility on the basis of computed tomographic data in individual patients. Simulation should, however, also be possible in parallel with biomechanical experiments, or for further research projects. For this purpose, rapid and uncomplicated generation of the FEM model, easy modification of input data, and short computation times are required. Practical use in the clinical setting makes appreciable additional demands on the individual software components.

Different mechanisms have been hypothesized as contributing to abduction deficit in high myopia: the size of the eye within the orbit, tightness of the medial rectus muscles, decompensation of longstanding esotropia, and inferior displacement of the lateral rectus muscle. Using oculodynamic magnetic resonance imaging, enhanced by computer-aided visualization, we demonstrate globe restriction by the medial orbital wall on abduction in a patient with high myopia.

A new method is presented for “extending” 2D radiographs into the third dimension. Pixel grey values, reflecting X-ray intensity losses, are converted into average attenuation coefficients, and the latter are related to vascular porosities in cortical and trabecular bone. These conversions contain information on cortical and overall mandibular thicknesses, pixel-specific bounds for which can be finally assessed from the pixel brightness. Computed thickness profiles allow for localizing potential abnormalities in the mandible, as incentive for further, targeted examination.

Objective The objective of this study was to reduce metal-induced streak artifact on oral and maxillofacial x-ray computed tomography (CT) images by developing the fast statistical image reconstruction system using iterative reconstruction algorithms. Study Design Adjacent CT images often depict similar anatomical structures in thin slices. So, first, images were reconstructed using the same projection data of an artifact-free image. Second, images were processed by the successive iterative restoration method where projection data were generated from reconstructed image in sequence. Besides the maximum likelihood-expectation maximization algorithm, the ordered subset-expectation maximization algorithm (OS-EM) was examined. Also, small region of interest (ROI) setting and reverse processing were applied for improving performance. Results Both algorithms reduced artifacts instead of slightly decreasing gray levels. The OS-EM and small ROI reduced the processing duration without apparent detriments. Sequential and reverse processing did not show apparent effects. Conclusions Two alternatives in iterative reconstruction methods were effective for artifact reduction. The OS-EM algorithm and small ROI setting improved the performance.

This contribution deals with the simulation based investigation of processes related to the surgical treatment of vertebroplasty. In this regard, a simulation framework has been developed, which includes the generation of microstructural computer models of cancellous bone structures, the simulation of bone cement injection by computational fluid dynamics (CFD) methods and finite element (FE) simulations of bone cement curing processes. The modelling and computation strategy is illustrated and different material modelling approaches for the representation of acrylic bone cements as a non-linear fluid and a non-linear viscoelastic solid with curing dependent properties are outlined. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Introduction The finite element method is a promising tool to investigate the material properties and the structural response of the periodontal ligament (PDL). To obtain realistic and reproducible results during finite element simulations of the PDL, suitable bio-fidelic finite element meshes of the geometry are essential. Methods In this study, 4 independent coworkers generated altogether 17 volume meshes (3-dimensional) based on the same high-resolution computed-tomography image data set of a tooth obtained in vivo to compare the influence of the different model generation techniques on the predicted response to loading for low orthodontic forces. Results It was shown that the thickness of the PDL has a significant effect on initial tooth mobility but only a remarkably moderate effect on the observed stress distribution in the PDL. Both the tooth and the bone can be considered effectively rigid when exploring the response of the PDL under low loads. The effect of geometric nonlinearities could be neglected for the applied force system. Conclusions Most importantly, this study highlights the sensitivity of the finite element simulation results for accurate geometric reconstruction of the PDL.

Within a clinical study, 30 pre- and post-operative CT-data sets were acquired directly before and 6 – 11 weeks after surgical maxillary expansion. The pre- operative data were rigidly registered on the post-operative ones. Subsequent 3D-reconstruction showed the skeletal changes due to the surgery. By an approach developed in the group, new bone formation in the osteotomy gap could be visualized. New bone could be clearly differentiated from preexistent bone. New bone formation was non-uniform along the osteotomy lines, but approximately symmetric. The more symmetrical the osteotomy was performed, the more symmetrical bone formation was observed. Actual research is dedicated to the patterns of new bone formation with regard to the applied surgical device and technique.

Aim: Tumor surgery at the skull base is a demanding field due to the complex and delicate anatomical hard and soft tissue structures in this region. The tumorous structure is mostly difficult to reach and the possibility of complete tumor resection is often only limited. The precise planning of the operative interventions and the following treatment, also a better prediction of the surgical results are aims of an advanced tumor treatment. The post-operative outcome with optimal quality of life (aiming for complete tumor resection) is even more difficult. In this article, a work-flow and new diagnostic methods are introduced.

Based on so called “quasi-continuous MRI” of a highly trained volunteer, 4D-visualization of a moving human foot due to ankle joint flexion is provided. In particular, visualization of the pedestrial superficial soft tissue as well as of the skeletal tissue is given. By our approach, we inter alia contribute to various kind of simulation of the lower leg by providing realistic boundary conditions.

A special visualization approach for tumors in the cranio-maxillofacial region, e.g. skull base infiltrating tumors of large dimensions, was developed for diagnosis support as well as surgery and therapy planning.

This project is dedicated to computer aided support of functional diagnostics of the entire human orbit, inter alia with focus on the extra-ocular muscles and the optic nerve. Therefore, radiological imaging by MRI has to be referred to. Three approaches were followed, firstly highly resolved 3D-reconstruction of the ocular anatomy, further so called oculodynamic MRI with radiological acquisition of only one MRI slice but including near real-time eye movements, thirdly sequential MRI with full 4D-visualization. The oculo-dynamic MRI has already been integrated in the clinical setting as part of routine MRI examination. The full 4D-approach which was rated as very promising by clinical experts has been successfully applied for a control.

Despite complex hierarchical organization of bone and wood, it was recently possible to identify a few elementary components at the micro and nanolevel of these material classes for the explanation of the diversity of macroscopic (poro-)elastic properties of different bones and woods [2, 3]. The mechanical properties (i.e. elasticity) of these elementary components are (up to experimental scattering) the same across a variety of different bones and woods, respectively; they are ’universal’, i.e., independent of tissue-type, species, and anatomical location. The mechanical interaction between these elementary components (mechanical morphology) and the dosages of these components in different tissues determine the macroscopic material properties. Having in mind that, as regards bone, these dosages are dependent on complex biochemical control cycles (defining the metabolism of the organism), the purely mechanical theory can be linked to biology, biochemistry, and, on the applied side, to clinical practice. Drug-driven or genetically driven changes in metabolisms lead to changes in the dosages of elementary components. The effects of these metabolic changes on the mechanical behavior of skeletal (sub)systems under well-defined loading conditions (e.g., downfall of elderly persons with osteoporosis) can then be studied by feeding structural models (e.g., Finite Element models [4]) of whole bones with the aforementioned macroscopic material properties - the output of the micromechanical models. This is probably highly relevant for patient-specific non-invasive bone disease diagnosis and therapy. As regards wood, our nano-to-macro approach is expected to support optimization of technological processes, such as drying.

For soft tissue organs, standard 3D-reconstructions can only provide a snapshot of a dynamically deforming structure. A reasonable possibility to overcome this drawback is the transition forward from 3D-reconstruction to 4D-visualization, i. e. rendering time dependent behavior based on dynamical radiological data sets. This article is dedicated to dynamical visualization of craniofacial soft tissue, namely human eye movement (MRI) and real time visualization of the downward movement of a volunteer’s mandible (256 row 4D-CT, NIRS, Chiba, Japan). Within several considered approaches for presentation of the results, stereoscopic realization of the 4D-visualization was regarded as providing best diagnostic impact and acceptance.

Percutaneous vertebroplasty is a common clinical procedure to treat vertebral compression fractures and osteoporotic vertebral bodies. However, this operation technique is accompanied by different complications due to lack of knowledge about the complicated behaviour of bone cement within the human body. To contribute to a better understanding of the processes that take place inside the body during a vertebroplasty, a detailed model of the thermomechanical behaviour of acrylic bone cement has been developed. All important effects are covered, that influence the behaviour of acrylic bone cement during the injection in a human vertebral body. Implemented in the opensource CFD-code OpenFOAM®, first results show that this comprehensive simulation of the minimal invasive injection is capable to accurately predict the cement distribution and temperature field of acrylic bone cement inside the vertebral body. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Objectives, When metallic prosthetic appliances and dental fillings exist in the oral cavity, the appearance of metal-induced streak artefacts are not avoidable in CT images. The study was to develop a method for artefact reduction using the statistical reconstruction on MD (multi-detectors row) CT images., Methods, Adjacent CT images often depict similar anatomical structures. Therefore, reconstructed images with weak artefacts were attempted using projection data of an artefact-free image in a neighboring thin slice. Images with moderate and strong artefacts were continuously processed in sequence by successive iterative restoration where projection data was generated from the adjacent reconstructed slice. First, the basic maximum likelihood-expectation maximization (ML-EM) algorithm was applied. Next, the ordered subset-expectation maximization (OS-EM) algorithm was examined. Alternatively, a small region of interest (ROI) setting was designated. Finally, the GPGPU (general purpose graphic processing unit) machine was applied in both situations., Results, The algorithms reduced metal-induced streak artefacts on MDCT images when the sequential processing method was applied. The OS-EM and small ROI reduced the processing duration without apparent detriments. GPGPU realized the high performance., Conclusions, A statistical reconstruction method was applied for the streak artefact reduction. The alternatives of algorithms applied were effective. Both software and hardware tools, such as OS-EM, small ROI and GPGPU achieved fast artefact correction.

In the present paper, a method to compare displacement results of a muscle contraction simulation with results of optical experiments is proposed. A human skeletal muscle has been reconstructed to a volume element out of real two-dimensional MRI data. The surrounding tissue has also been taken into account in order to describe the interaction with other components in a realistic way. These regions of the interface have been supported by several spring stiffness. The numerical model has been fitted by this stiffness on one significant node. The results shown satisfied agreement with the optical experiments. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Within the biomechanics of bony organs, individual tissue anisotropy and inhomogeneity are intensively discussed subjects. This paper is dedicated to the impact of a fully anisotropic and inhomogoneous material description on the structural behaviour of an elderly partially edentulous human mandible. Radial, axial, and circumferential trajectories of orthotropic elasticity were reconstructed from kind of inner skeleton derived from the organ's geometry and from coherent structures recognisable from the spatial distribution of the grey values coming from computer tomography (CT). Based on recent micromechanical research driven forward by the second author, CT numbers were transferred into inhomogeneous stiffness tensor components reflecting individual tissue properties. These coefficients were considered as local orthotropic elastic coefficients in reference to coordinate systems formed by the anisotropic trajectories of elasticity. For the sake of a complete anisotropic material description over the whole organ, the tensor components were transformed into a global base frame which allows assembling an overall patient-specific stiffness matrix. Various sensitivity analysis revealed that the more the anisotropy is considered the more the mandible is spared from loading which indicates kind of mechanical optimality of the mandible with respect to tissue anisotropy. In the opposite, the consideration of individual inhomogeneous tissue properties resulted in intensification of load concentrations due to pathological alterations of the organ which gives rise to the suggestion of self-energising processes of bone resorption. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural mechanics simulation of bony organs is of general medical and biomechanical interest, because of the interdependence of the inner architecture of bone and its functional loading already stated by Wolff in 1892. This work is part of a detailed research project concerning the human mandible. By adaptive finite element techniques, stress/strain profiles occurring in the bony structure under biting were simulated. Estimates of the discretization errors, local grid refinement, and multilevel techniques guarantee the reliability and efficiency of the method. In general, our simulation requires a representation of the organ's geometry, an appropriate material description, and the load case due to teeth, muscle, or joint forces. In this paper, we want to focus on the influence of the masticatory system. Our goal is to capture the physiological situation as far as possible. By means of visualization techniques developed by the group, we are able to extract individual muscle fibres from computed tomography data. By a special algorithm, the fibres are expanded to fanlike (esp. for the musc. temporalis) coherent vector fields similar to the anatomical reality. The activity of the fibres can be adapted according to compartmentalisation of the muscles as measured by electromyological experiments. A refined sensitivity analysis proved remarkable impact of the presented approach on the simulation results. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)