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Tissue Deformation (tissue + deformation)
Selected AbstractsA Computational Framework for Patient-Specific Analysis of Articular Cartilage Incorporating Structural Information from DT-MRIGAMM - MITTEILUNGEN, Issue 2 2009David M. Pierce Abstract Accurate techniques for simulating sof t biological tissue deformation are an increasingly valuable tool in many areas of biomechanical analysis and medical image computing. To model the morphology and the material response of human articular cartilage a phenomenological and patient-specific simulation approach incorporating the collagen fibre fabric is proposed. We then demonstrate a unique combination of ultra-high field Diffusion Tensor Magnetic Resonance Imaging (17.6T DT-MRI) and a novel numerical approach incorporating the empirical data to predict the collagen fibre fabric deformation for an indentation experiment (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Altered T Wave Dynamics in a Contracting Cardiac ModelJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003NICOLAS P. SMITH Ph.D. Introduction: The implications of mechanical deformation on calculated body surface potentials are investigated using a coupled biophysically based model. Methods and Results: A cellular model of cardiac excitation-contraction is embedded in an anatomically accurate two-dimensional transverse cross-section of the cardiac ventricles and human torso. Waves of activation and contraction are induced by the application of physiologically realistic boundary conditions and solving the bidomain and finite deformation equations. Body surface potentials are calculated from these activation profiles by solving Laplace's equation in the passive surrounding tissues. The effect of cardiac deformation on electrical activity, induced by contraction, is demonstrated in both single-cell and tissue models. Action potential duration is reduced by 7 msec when the single cell model is subjected to a 10% contraction ramp applied over 400 msec. In the coupled electromechanical tissue model, the T wave of the ECG is shown to occur 18 msec earlier compared to an uncoupled excitation model. To assess the relative effects of myocardial deformation on the ECG, the activation sequence and tissue deformation are separated. The coupled and uncoupled activation sequences are mapped onto the undeforming and deforming meshes, respectively. ECGs are calculated for both mappings. Conclusion: Adding mechanical contraction to a mathematical model of the heart has been shown to shift the T wave on the ECG to the left. Although deformation of the myocardium resulting from contraction reduces the T wave amplitude, cell stretch producing altered cell membrane kinetics is the major component of this temporal shift. (J Cardiovasc Electrophysiol, Vol. 14, pp. S203-S209, October 2003, Suppl.) [source] Time series analysis of jaw muscle contraction and tissue deformation during mastication in miniature pigsJOURNAL OF ORAL REHABILITATION, Issue 1 2004Z. J. Liu summary, Masticatory muscle contraction causes both jaw movement and tissue deformation during function. Natural chewing data from 25 adult miniature pigs were studied by means of time series analysis. The data set included simultaneous recordings of electromyography (EMG) from bilateral masseter (MA), zygomaticomandibularis (ZM) and lateral pterygoid muscles, bone surface strains from the left squamosal bone (SQ), condylar neck (CD) and mandibular corpus (MD), and linear deformation of the capsule of the jaw joint measured bilaterally using differential variable reluctance transducers. Pairwise comparisons were examined by calculating the cross-correlation functions. Jaw-adductor muscle activity of MA and ZM was found to be highly cross-correlated with CD and SQ strains and weakly with MD strain. No muscle's activity was strongly linked to capsular deformation of the jaw joint, nor were bone strains and capsular deformation tightly linked. Homologous muscle pairs showed the greatest synchronization of signals, but the signals themselves were not significantly more correlated than those of non-homologous muscle pairs. These results suggested that bone strains and capsular deformation are driven by different mechanical regimes. Muscle contraction and ensuing reaction forces are probably responsible for bone strains, whereas capsular deformation is more likely a product of movement. [source] Sensitivity of the Early Life Stages of Macroalgae from the Northern Hemisphere to Ultraviolet Radiation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Michael Y. Roleda The reproductive cells of macroalgae are regarded as the life history stages most susceptible to various environmental stresses, including UV radiation (UVR). UVR is proposed to determine the upper depth distribution limit of macroalgae on the shore. These hypotheses were tested by UV-exposure experiments, using spores and young thalli of the eulittoral Rhodophyceae Mastocarpus stellatus and Chondrus crispus and various sublittoral brown macroalgae (Phaeophyceae) with different depth distribution from Helgoland (German Bight) and Spitsbergen (Arctic). In spores, the degree of UV-induced inhibition of photosynthesis is lower in eulittoral species and higher in sublittoral species. After UV stress, recovery of photosynthetic capacity is faster in eulittoral compared to sublittoral species. DNA damage is lowest while repair of DNA damage is highest in eulittoral compared to sublittoral species. When the negative impact of UVR prevails, spore germination is inhibited. This is observed in deep water kelp species whereas the same UVR doses do not inhibit germination of shallow water kelp species. A potential acclimation mechanism to increase UV tolerance of brown algal spores is the species-specific ability to increase the content of UV-absorbing phlorotannins in response to UV-exposure. Growth rates of young Mastocarpus and Chondrus gametophytes exposed to experimental doses of UVR are not affected while growth rates of all young kelp sporophytes exposed to UVR are significantly lowered. Furthermore, morphological UV damage in Laminaria ochroleuca includes tissue deformation, lesion, blistering and thickening of the meristematic part of the lamina. The sensitivity of young sporophytes to DNA damage is correlated with thallus thickness and their optical characteristics. Growth rate is an integrative parameter of all physiological processes in juvenile plants. UV inhibition of growth may affect the upper distribution depth limit of adult life history stages. Juveniles possess several mechanisms to minimize UVR damage and, hence, are less sensitive but at the expense of growth. The species-specific susceptibility of the early life stages of macroalgae to UVR plays an important role for the determination of zonation patterns and probably also for shaping up community structure. [source] Advances in collision detection and non-linear finite mixed element modelling for improved soft tissue simulation in craniomaxillofacial surgical planningTHE INTERNATIONAL JOURNAL OF MEDICAL ROBOTICS AND COMPUTER ASSISTED SURGERY, Issue 1 2010Shengzheng Wang Abstract Background There is a huge demand to develop a method for assisting surgeons in automatically predicting soft tissue deformation in terms of a bone-remodelling plan. Methods This paper introduces several novel elements into a system for the simulation of postoperative facial appearances with respect to prespecified bone-remodelling plans. First, a new algorithm for efficient detection of collisions, using the signed distance field, is described. Next, the penalty method is applied to determine the contact load of bone on facial soft tissue. Finally, a non-linear finite mixed element model is developed to estimate the tissue deformation induced by the prescribed bone remodelling plan. Results The performance of the proposed collision detection algorithm has been improved in memory requirements and computational efficiency compared with conventional methods. In addition, the methodology is evaluated over both synthetic and real data, with simulation performance averaging <0.5 mm pointwise error over the facial surface in six mid-face distraction osteotogenesis procedures. Conclusions The experimental results support the novel methodological advancements in collision detection and biomechanical modelling proposed in this work. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||