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(a) Example of asymmetry of the frontal sinuses. Left one (blue arrow) is larger than right (yellow arrow); (b) Example of asymmetry of the: the nasal cavity (green arrow), the septum of a sphenoid sinus, mastoid cells, and the inner ear on the left (blue arrow) and the right (yellow arrow) (own source).
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The study of symmetrical and non-symmetrical effects in physics, mathematics, mechanics, medicine, and numerical methods is a current topic due to the complexity of the experiments, calculations, and virtual simulations. However, there is a limited number of research publications in computational biomechanics focusing on the symmetry of numerical h...
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Context 1
... inside of the skull also tends to present some degree of asymmetry. One example is the paranasal sinuses that are rarely symmetrical, usually separated by septum, and usually located slightly off the midline (Figure 2a). Another of the many examples of asymmetry may be the nasal cavity, the septum of the sphenoid sinus, or mastoid cells Figure 2b). ...
Citations
... Initial clinical presentation of optic neuropathy overlaps with glaucoma, optic neuritis, maculopathy and cataract. [17]. Asymmetry of skull base structures had previously been associated with genetic factors, epigenetic influences, and person's handedness [13][14]. ...
... The energy transfer from the electronic object to the human head follows the one-sided symmetry in the skull. The facial, brain, and skull symmetries are well explained by Ratajczak et al. [6]. ...
In this study, a new fractional-order model for human skull heat conduction is tackled by using a neural network, and the results were further modified by using the hybrid cuckoo search algorithm. In order to understand the temperature distribution, we introduced memory effects into our model by using fractional time derivatives. The objective function was constructed in such a way that the L2−error remained at a minimum. The fractional order equation was then calculated by using the proposed biogeography-based hybrid cuckoo search (BHCS) algorithm to approximate the solution. When compared to earlier simulations based on integer-order models, this method enabled us to examine the fractional-order (FO) cases, as well as the integer order. The results are presented in the form of figures and tables for the different case studies. The results obtained for the various parameters were validated numerically against the available literature, where our proposed methodology showed better performance when compared to the least squares method (LSM).
... The exact extent of symmetricity as quanti ed in Table 1 notes slightly higher induced values in the right vestibular network (i.e. the one proximate to the cathode) with a symmetricity ratio of 0.933 and 0.854 (considering mean and max values respectively). It is known that the human head is not perfectly symmetric with reported asymmetries (minor) in the skull and brain anatomies [32]. Given, our model geometry is directly derived from medical images, the asymmetricity in current ow pattern due to a symmetric montage is therefore, not unexpected. ...
Galvanic Vestibular Stimulation is a non-invasive electrical stimulation technique that is typically used to probe the vestibular system. While commonly delivered using two electrodes, additional electrode placements have been employed. Our objective was to systematically evaluate all known placements, compare induced current flow, and how it relates to the archetypal virtual and sway motions. The ultimate goal is to help users in having a better understanding of the effects of different configurations. We simulated seven placements using an ultra-high-resolution model. Induced electric field (EF) patterns at the cortical and the location of vestibular organs were determined. As expected, current flow patterns are electrode placement specific. Placements with two electrodes generally result in higher EF magnitude. Placements with four electrodes result in lower percentage of current entering the cranial cavity. Symmetric placements do not result in similar EF values in the left and the right organs highlighting inherent anatomical asymmetry. Asymmetric placements may result in as much as ~ 3-fold higher EF in one organ over the other. The percentage of current entering the cranial cavity varies between ~ 15–40% depending on the placement. Detailed analysis such as this may be used to help understand mechanism of action, guide stimulation strategy, ultimately resulting in quantitatively informed rational / optimal choices.
... However, since there is a stress concentration on the brain's gyri and sulci, the level of detail in the head is not sufficient for advanced brain injury analysis [56,57]. Moreover, unlike the presented aHEAD model, most available head models [58]. That is a significant simplification that influences the outcome of the results. ...
The human head is a highly complex structure, with a combination of hard and soft tissues and a variety of materials and interactions. Many researchers have used computational approaches to model the head, and several human finite element head models can be found in the literature. However, most of them are not geometrically accurate – for instance, the brain is simplified to a smooth spherical volume, which poses some concerns regarding boundary conditions and geometrical accuracy. Therefore, an advanced head model of a 28-year-old, designated as aHEAD 28 yo (aHEAD: advanced Head models for safety Enhancement And medical Development), has been developed. The model consists entirely of hexahedral elements for 3D structures of the head such as the cerebellum, skull and cerebrum, with detailed geometry of the gyri and sulci. Additionally, it is one of the first human head approaches published in the literature that includes cerebrospinal fluid simulated by Smoothed Particle Hydrodynamics (SPH) and a detailed model of pressurized bridging veins. To support the model’s credibility, this study is focused on physical material testing. A novel comprehensive experimental-computational approach is presented, which involves the brain tissue’s response to induced vibrations. The experiment successfully aimed to validate the material models used in the numerical analysis. Additionally, the authors present a kinematical model validation based on the Hardy experimental cadaver test. The developed model, along with its verification, aims to establish a further benchmark in finite element head modelling and can potentially provide new insights into injury mechanisms.
... The patient was a 23-year-old Hispanic male, with a height of 174 cm, without previous shoulder pathologies. We assume symmetry of the biomechanical conditions; thus, only one shoulder is studied [25]. DICOM files were used for obtaining the 3D model of bones using the imaging segmentation software 3D Slicer v4.11 [26], applying semi-automatic segmentation. ...
The glenohumeral joint (GHJ) is one of the most critical structures in the shoulder complex. Lesions of the superior labral anterior to posterior (SLAP) cause instability at the joint. Isolated Type II of this lesion is the most common, and its treatment is still under debate. Therefore, this study aimed to determine the biomechanical behavior of soft tissues on the anterior bands of the glenohumeral joint with an Isolated Type II SLAP lesion. Segmentation tools were used to build a 3D model of the shoulder joint from CT-scan and MRI images. The healthy model was studied using finite element analysis. Validation was conducted with a numerical model using ANOVA, and no significant differences were shown (p = 0.47). Then, an Isolated Type II SLAP lesion was produced in the model, and the joint was subjected to 30 degrees of external rotation. A comparison was made for maximum principal strains in the healthy and the injured models. Results revealed that the strain distribution of the anterior bands of the synovial capsule is similar between a healthy and an injured shoulder (p = 0.17). These results demonstrated that GHJ does not significantly deform for an Isolated Type II SLAP lesion subjected to 30-degree external rotation in abduction.
... The models prepared using the methods differ mostly in the cartilage description-FEM offers fully deformable cartilage, while MBS substitutes it with a constraint-often based on symmetrical shapes (ball socket joint or rigid/deformable contact pair [2][3][4][5][6][7][8]10,11,15]). It is worth noting that in FEM the bodies can experience large deformations, as in [28], while MBS covers mostly rigid bodies with flexible outer layer. ...
Experimental studies report that ligaments of the ankle joint are prestrained. The prestrain is an important aspect of modern biomechanical analysis, which can be included in the models by: applying symmetrical, arbitrary prestrains to the ligaments, assuming a strain-free location for the joint or by using experimental prestrain data. The aim of the study was to comparatively analyze these approaches. In total, 4 prestraining methods were considered. In order to do so, a symmetrical model of the ankle with six nonlinear cables and two sphere–sphere contact pairs was assumed. The model was solved in statics under moment loads up to 5 Nm. The obtained results showed that the arbitrary prestrains caused an unbalanced load for the model at rest, and in turn modified its rest location in an unpredictable way. Due to the imbalance, it was impossible to enforce the assumed prestrains and thus cartilage prestrain was required to stabilize the model. The prestraining had a significant effect on the angular displacements and the load state of the model. The findings suggest that the prestrain values are patient specific and arbitrary prestrains will not be valid for most models.
