Search

Surgical treatment of endocrine orbitopathy can be performed by way of resecting orbital walls, which effectively releases superfluous tissue from the surgically enlarged orbital space allowing the eyeballs to move back. Existing approaches aim to select an optimal surgical strategy based on statistical correlations between the extent of the surgical procedure and the resulting bulbus displacement but do not provide an individual surgery plan or predict surgery outcome. In this retrospective study, we performed a quantitative analysis of pre- and post-surgery 3D tomographic data of six patients and applied explorative biomechanical modeling of orbital mechanics to dissect factors influencing patient-specific outcome. Our experimental results showed a large variability of the backward eyeball displacement in dependency on the amount of orbital volume flow, which could partially be described by computational simulation. Our detailed analysis revealed that patients with regular fat tissue show a good correlation between bulbus displacement and relative volume of decompressed tissue, which, in turn, correlates with decrease in hydrostatic pressure. In contrast, patients with fibrotic tissue exhibit significantly reduced and computationally less predictable eyeball translation in response to surgical tissue decompression. Based on the results of this study we see a great potential for quantitative planning of surgical exophthalmos treatment using 3D biomechanical modeling. Conventional approaches to planning of soft tissue interventions consider, however, only the patient's 3D anatomy and widely disregard individual tissue properties. Further investigations are required to establish reliable procedures for assessment of individual tissue properties and incorporating them into patient-specific models of orbital mechanics. • Outcome of three-wall resection for treatment of endocrine exophthalmos depends on individual mechanical properties of orbital tissue. • Patients with fibrotic/malignant tissue exhibit significantly reduced and computationally less predictable post-OP eyeball translation. • Patients with regular fat tissue show better correlation between eyeball displacement and the relative volume of decompressed tissue. • Our biomechanical simulations are in good conformity with post-surgery outcome for patients with regular fat tissue. [ABSTRACT FROM AUTHOR]

A typical problem in the registration of MRI and X-ray mammography is the nonlinear deformation applied to the breast during mammography. We have developed a method for virtual deformation of the breast using a biomechanical model automatically constructed from MRI. The virtual deformation is applied in two steps: unloaded state estimation and compression simulation. The finite element method is used to solve the deformation process. However, the extensive computational cost prevents its usage in clinical routine. We propose three machine learning models to overcome this problem: an extremely randomized tree (first model), extreme gradient boosting (second model), and deep learning-based bidirectional long short-term memory with an attention layer (third model) to predict the deformation of a biomechanical model. We evaluated our methods with 516 breasts with realistic compression ratios up to 76%. We first applied one-fold validation, in which the second and third models performed better than the first model. We then applied ten-fold validation. For the unloaded state estimation, the median RMSE for the second and third models is 0.8 mm and 1.2 mm, respectively. For the compression, the median RMSE is 3.4 mm for both models. We evaluated correlations between model accuracy and characteristics of the clinical datasets such as compression ratio, breast volume, and tissue types. Using the proposed models, we achieved accurate results comparable to the finite element model, with a speedup of factor 240 using the extreme gradient boosting model. These proposed models can replace the finite element model simulation, enabling clinically relevant real-time application. • Prediction of breast deformation using machine learning models. • Estimation of the unloaded state from a gravity-loaded magnetic resonance imaging. • Simulation of realistic mammographic compression of an MRI based biomechanical model. • A speedup of factor 240 and prediction error in average in the range below 4 mm are achieved. • A clinical database with 516 breasts was used to train and evaluate the models. [ABSTRACT FROM AUTHOR]

Background Anterior vertebral body growth modulation is a fusionless instrumentation to correct scoliosis using growth modulation. The objective was to biomechanically assess effects of cable tensioning, screw positioning and post-operative position on tridimensional correction. Methods The design of experiments included two variables: cable tensioning (150/200 N) and screw positioning (lateral/anterior/triangulated), computationally tested on 10 scoliotic cases using a personalized finite element model to simulate spinal instrumentation, and 2 years growth modulation with the device. Dependent variables were: computed Cobb angles, kyphosis, lordosis, axial rotation and stresses exerted on growth plates. Supine functional post-operative position was simulated in addition to the reference standing position to evaluate corresponding growth plate’s stresses. Findings Simulated cable tensioning and screw positioning had a significant impact on immediate and after 2 years Cobb angle (between 5°–11°, p < 0.01). Anterior screw positioning significantly increased kyphosis after 2 years (6°–8°, p = 0.02). Triangulated screw positioning did not significantly impact axial rotation but significantly reduced kyphosis (8°–10°, p = 0.001). Growth plates' stresses were increased by 23% on the curve's convex side with cable tensioning, while screw positioning rather affected anterior/posterior distributions. Supine position significantly affected stress distributions on the apical vertebra compared to standing position (respectively 72% of compressive stresses on convex side vs 55%). Interpretation This comparative numerical study showed the biomechanical possibility to adjust the fusionless instrumentation parameters to improve correction in frontal and sagittal planes, but not in the transverse plane. The convex side stresses increase in the supine position may suggest that growth modulation could be accentuated during nighttime. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this study was the simulation of the implantation of intrastromal corneal-ring segments for patients with keratoconus. The aim of the study was the prediction of the corneal curvature recovery after this intervention. Methods Seven patients with keratoconus diagnosed and treated by implantation of intrastromal corneal-ring segments were enrolled in the study. The 3D geometry of the cornea of each patient was obtained from its specific topography and a hyperelastic model was assumed to characterize its mechanical behavior. To simulate the intervention, the intrastromal corneal-ring segments were modeled and placed at the same location at which they were placed in the surgery. The finite element method was then used to obtain a simulation of the deformation of the cornea after the ring segment insertion. Finally, the predicted curvature was compared with the real curvature after the intervention. Results The simulation of the ring segment insertion was validated comparing the curvature change with the data after the surgery. Results showed a flattening of the cornea which was in consonance with the real improvement of the corneal curvature. The mean difference obtained was of 0.74 mm using properties of healthy corneas. Conclusions For the first time, a patient-specific model of the cornea has been used to predict the outcomes of the surgery after the intrastromal corneal-ring segments implantation in real patients. [ABSTRACT FROM AUTHOR]

Excessive mobility of the bladder neck and urethra are common features in stress urinary incontinence. We aimed at assessing, through computational modelling, the bladder neck position taking into account progressive impairment of the pelvic ligaments. Magnetic resonance images of a young healthy female were used to build a computational model of the pelvic cavity. Appropriate material properties and constitutive models were defined. The impairment of the ligaments was simulated by mimicking a reduction in their stiffness. For healthy ligaments, valsalva maneuver led to an increase in the a angle (between the bladder necksymphysis pubis and the main of the symphysis) from 91.8° (at rest) to 105.7°, and 5.7 mm of bladder neck dislocation, which was similar to dynamic imaging of the same woman (a angle from 80° to 103.3°, and 5 mm of bladder neck movement). For 95% impairment, they enlarged to 124.28° and 12 mm. Impairment to the pubourethral ligaments had higher effect than that of vaginal support (115° vs. 108°, and 9.1 vs. 7.3 mm). Numerical simulation could predict urethral motion during valsalva maneuver, for both healthy and impaired ligaments. Results were similar to those of continent women and women with stress urinary incontinence published in the literature. Biomechanical analysis of the pubourethral ligaments complements the biomechanical study of the pelvic cavity in urinary incontinence. It may be useful in young women presenting stress urinary incontinence without imaging evidence of urethral and muscle lesions or organ descend during valsalva, and for whom fascial damage are not expected. [ABSTRACT FROM AUTHOR]

Highlights: [•] We developed a sensor home equipped with an embedded video-surveillance system. [•] We developed a fall detection algorithm and a body axis tracking algorithm. [•] We measured behaviors of 19 children aged 11–50 months old at the sensor home. [•] Fall database includes 105 incidents, and its browser enables conditional searches. [•] The database enables accurate estimation of injury risk resulting from fall. [ABSTRACT FROM AUTHOR]

Abstract: Background: The Nuss procedure corrects pectus excavatum using a pre-bent bar that generates stress on the chest wall. To investigate the biomechanical effects after the Nuss procedure, we designed a three-dimensional finite element analysis model to analyze the distribution of stress and strain induced in the chest wall. Methods: Three patients with pectus excavatum aged 8, 7, and 7years, were enrolled in this study. The greatest upward displacements of their sternums after the operation were measured from computed tomography images and chest X-ray films. Based on these displacements, we constructed three finite element analysis models for analyzing biomechanical changes in the thoracic cage after the Nuss procedure. Findings: The simulation results indicated that greatest strain occurred at the third through seventh cartilages, especially where they join the sternum and ribs. A high bilateral stress distribution was also found over the backs of the third to the seventh ribs near the vertebral column. Interpretation: The stress and strain induced by the Nuss procedure can be analyzed using our finite element analysis model. Although the stress and strain may have some influence on chest and spine development, a more detailed finite element analysis model is recommended for future study to improve the accuracy of our simulation results. [Copyright &y& Elsevier]

Abstract: Optimal control simulations of the standing long jump were developed to gain insight into the mechanisms of enhanced performance due to arm motion. The activations that maximize standing long jump distance of a joint torque actuated model were determined for jumps with free and restricted arm movement. The simulated jump distance was 40cm greater when arm movement was free (2.00m) than when it was restricted (1.60m). The majority of the performance improvement in the free arm jump was due to the 15% increase (3.30 vs. 2.86m/s) in the take-off velocity of the center of gravity. Some of the performance improvement in the free arm jump was attributable to the ability of the jumper to swing the arms backwards during the flight phase to alleviate excessive forward rotation and position the body segments properly for landing. In restricted arm jumps, the excessive forward rotation was avoided by “holding back” during the propulsive phase and reducing the activation levels of the ankle, knee, and hip joint torque actuators. In addition, swinging the arm segments allowed the lower body joint torque actuators to perform 26J more work in the free arm jump. However, the most significant contribution to developing greater take-off velocity came from the additional 80J work done by the shoulder actuator in the jump with free arm movement. [Copyright &y& Elsevier]

• Hybrid neuroprostheses based on FES and exoskeleton may accelerate rehabilitation. • Detailed musculoskeletal models may replicate relevant features of experiments. • Simulations provide further information of unachievable metrics in gait experiments. • Open-source simulation environment to quantify and compare controllers performance. Lower-limb rehabilitation programs are beneficial in restoring function for people with neurological disorders. Combining techniques and equipment, such as active orthoses and functional electrical stimulation (FES), promises to accelerate the therapy outcome while simultaneously reducing therapists' physical burden. However, there are still challenges related to inadequate stimulation response characteristics and the trade-off between weight, size, and active orthoses performance. Moreover, it is often unachievable to obtain specific metrics in experimental environments, and it seems there is still no consolidated simulation environment for these applications. Here we explore an open-source simulation framework to investigate further FES and active orthoses controlling knee motion of a detailed musculoskeletal model. We modeled, implemented, and compared tracking errors and correlations of four FES controllers for two slow speeds (0.1 m/s and 0.3 m/s), showing a higher correlation with the reference for the higher speed (0.89) than for the lower speed (0.73). Further, we observed that the simulation environment presented a similar behavior compared to experiments, as higher errors during the knee flexion and hip extension. These results are compatible with the expected behavior from real experiments, showing that muscle-drive simulations may generate a wealth of data and elucidate the principles that govern muscle coordination to improve rehabilitation outcomes. [ABSTRACT FROM AUTHOR]

Vergence-accommodation conflict (VAC) is the main contributor to visual fatigue during immersion in virtual environments. Many studies have investigated the effects of VAC using 3D displays and expensive complex apparatus and setup to create natural and conflicting viewing conditions. However, a limited number of studies targeted virtual environments simulated using modern consumer-grade VR headsets. Our main objective, in this work, is to test how the modern VR headsets (VR simulated depth) could affect our vergence system, in addition to investigating the effect of the simulated depth on the eye-gaze performance. The virtual scenario used included a common virtual object (a cube) in a simple virtual environment with no constraints placed on the head and neck movement of the subjects. We used ocular biomechanics and eye tracking to compare between vergence angles in matching (ideal) and conflicting (real) viewing conditions. Real vergence angle during immersion was significantly higher than ideal vergence angle and exhibited higher variability which leads to incorrect depth cues that affects depth perception and also leads to visual fatigue for prolonged virtual experiences. Additionally, we found that as the simulated depth increases, the ability of users to manipulate virtual objects with their eyes decreases, thus, decreasing the possibilities of interaction through eye gaze. The biomechanics model used here can be further extended to study muscular activity of eye muscles during immersion. It presents an efficient and flexible assessment tool for virtual environments. [ABSTRACT FROM AUTHOR]