Biomechanical modeling for the response of human thorax to blast waves

A simplified finite element model of a human thorax had been developed for probing into the mechani- cal response in simple and complex blast environments. The human thorax model was first created by CT images with blast loading applied via a coupled arbitrary Lagrangian- Eulerian method, allowing for a variety of loads to be considered. The goal is to analyze the maximum stress distri- butions of lung tissue and peak inward thorax wall velocity and to know the possible regions and levels of lung injury. In parallel, a mathematical model has been modified from the Lobdell model to investigate the detailed percentage of lung injury at each level. The blast loadings around the human tho- rax were obtained from the finite element model, and were then applied in the mathematical model as the boundary con- ditions to predict the normalized work of the human thorax lung. The present results are found in agreement with the modified Bowen curves and the results predicted by Axels- son＇s model.

Multi-level biomechanical models for rehabilitation engineering

Rehabilitation engineering aims in the upmost degree to restore the lost functions for those persons with physical disability. Biomechanical modeling has been widely used for different purposes in rehabilitation engineering to understand the bio-

A Biomechanical Model of Human Lung Deformation Utilizing Patient-Specific Elastic Property

A biomechanical model is developed and validated for breathing-induced deformation of human lung. Specifically, a subject-specific poro-elastic lung model is used to predict the displacement over the breathing cycle and compared with displacement derived from high resolution image registration. The lung geometry is derived from four-dimensional computed tomography (4DCT) scan dataset of two human subjects. The heterogeneous Young’s modulus is estimated using inverse analysis method. The numerical simulation uses fluid-structure interaction technique to solve the coupled airflow equations and structural dynamics of the lung tissue. The modelled displacement is validated by comparison with the 4DCT registration results.

Advanced 4-dimensional cone-beam computed tomography reconstruction by combining motion estimation, motioncompensated reconstruction, biomechanical modeling and deep learning

4-Dimensional cone-beam computed tomography(4D-CBCT)offers several key advantages over conventional 3DCBCT in moving target localization/delineation,structure de-blurring,target motion tracking,treatment dose accumulation and adaptive radiation therapy.However,the use of the 4D-CBCT in current radiation therapy practices has been limited,mostly due to its sub-optimal image quality from limited angular sampling of conebeam projections.In this study,we summarized the recent developments of 4D-CBCT reconstruction techniques for image quality improvement,and introduced our developments of a new 4D-CBCT reconstruction technique which features simultaneous motion estimation and image reconstruction(SMEIR).Based on the original SMEIR scheme,biomechanical modeling-guided SMEIR(SMEIR-Bio)was introduced to further improve the reconstruction accuracy of fine details in lung 4D-CBCTs.To improve the efficiency of reconstruction,we recently developed a U-net-based deformation-vector-field(DVF)optimization technique to leverage a population-based deep learning scheme to improve the accuracy of intra-lung DVFs(SMEIR-Unet),without explicit biomechanical modeling.Details of each of the SMEIR,SMEIR-Bio and SMEIR-Unet techniques were included in this study,along with the corresponding results comparing the reconstruction accuracy in terms of CBCT images and the DVFs.We also discussed the application prospects of the SMEIR-type techniques in image-guided radiation therapy and adaptive radiation therapy,and presented potential schemes on future developments to achieve faster and more accurate 4D-CBCT imaging.

Nonlinear Anisotropic Composite Biomechanical Modeling of Human Skin

A 3D nonlinear anisotropic composite biomechanical modeling of human skin was developed according to existing biomechanical experimental results,which can provide insights into the important structure-function relationship and parameters in skin tissue.A structural approach determines the macroscopic mechanical response of the skin tissue from its underlying structural components.The collagen fibers were embedded into a block of elastic gel matrix.The constitutive matrix of skin tissue consisted of both of collagen fiber and elastic gel block according to the rule that the collagen fibers were undulated with the ability to resist load only when completely straightened.The nonlinear and anisotropic mechanical responses were largely due to varying degree of fiber undulation.Statistical distributions were used to determine the extent of fiber undulation.The comparison of stress-strain plots between the modeling and experimental results showed the good coordination of the both.Some model parameters were discussed to compute the macroscopic mechanical response when the tissue block was subject to a simple deformation mode.

A model for potential non-contact ski injuries of the knee

Broadly accepted is that most knee injuries result from increased vertical forces,usually induced by an incidental ski fall,collision,or a high jump.We present a new non-contact knee injury mechanism that can happen during a ski turn.Such an injury is governed by a sudden inward turn of the inner ski and consequent swing of the inner leg followed by a nearly instant stop when locked by hip and knee joints.The model provides predictive results for a lateral tibial plateau compression fracture because several simplifications have been made.We confirmed that the modelled compression stresses at typical skiing conditions and with typical skiing equipment can provoke serious knee injuries.The awareness of skiers and skiing equipment industry of the described knee injury mechanism can act as an important injury-prevention factor.

Three-dimensional organ modeling based on deformable surfaces applied to radio-oncology

This paper describes a method based on an energy minimizing deformable model applied to the 3D biomechanical modeling of a set of organs considered as regions of interest (ROI) for radiotherapy. The initial model consists of a quadratic surface that is deformed to the exact contour of the ROI by means of the physical properties of a mass-spring system. The exact contour of each ROI is first obtained using a geodesic active contour model. The ROI is then parameterized by the vibration modes resulting from the deformation process. Once each structure has been defined, the method provides a 3D global model including the whole set of ROIs. This model allows one to describe statistically the most significant variations among its structures. Statistical ROI variations among a set of patients or through time can be analyzed. Experimental results are presented using the pelvic zone to simulate anatomical variations among structures and its application in radiotherapy treatment planning.

Effects of the windshield inclination angle on head/brain injuries in car-to-pedestrian collisions using computational biomechanics models

Car-to-pedestrian collision(CPC)accidents occur frequently,and pedestrians often suffer serious head/brain injuries.One major cause is the primary impact with the windshield.Here,we use an umerical sim ulation method to study the influence of the windshield in-clination angle of a passenger car on pedestrian head/brain injury due to CPC accidents.The range of the windshield inclination angle was set at 24°-50°,with an interval of 2°.The results show that the windshield angle significantly affects the pedestrian kine-matics and exerts different effects on the head injury when evaluating with various head injury criteria.Regarding the head peak linear/rotational acceleration and acceleration-based head injury criterion(HIC)/rotational injury criterion(RIC),the predictions at the secondary impact stage have no clear relationship with the windshield angle(R^(2)=0.04,0.07,0.03 and 0.26,respectively)and their distributions are scattered.In the primary impact,the peak linear acceleration and HIC show a weak trend of first decreasing and then increasing with the increasing of the windshield angle,and the rotational acceleration and RIC tend to remain relatively con-stant.Regarding the cum ulative strain dama ge measure(CSDM)criterion,the predictions at the primary impact are slightly lower than those at the secondary impact,and the trend of first decreasing and then increasing with the increase in the windshield angle is observed at both impact stages.When the windshield inclination angle is approximately 32°-40°,the head injury severity in both impact phases is generally lower than that predicted at other windshield angles.

细胞单层的静态与动态力学研究: 一个多尺度结构模型

上皮单层在伤口愈合和胚胎发育等各种生理活动中起着十分重要的作用.随着技术的快速发展,上皮单层的力学行为得到了广泛的关注与研究.在阶跃载荷作用下,上皮单层的蠕变响应表现出对时间的幂律依赖,且其幂律指数大于单细胞的幂律指数.而在静态载荷下,上皮单层的弹性模量比单细胞高出近两个数量级.到目前为止,仍然缺乏一个能够同时描述上皮单层动态和静态响应的力学模型.本文基于细胞的结构特征,建立了一个多尺度结构的细胞单层模型.所建模型能够自然地描述细胞单层的动态和静态力学行为.此外,本文还探讨了细胞骨架和细胞膜模量分别对单细胞和细胞单层的幂律流变学响应以及应力-应变关系的影响.这一工作为后续研究更复杂的上皮单层的力学行为奠定了基础.

Cranio-maxillofacial surgery simulation based on pre-specified target face configurations

This paper presents a novel method for assisting surgeons in automatically computing an optimal surgical plan by directly specifying the desired correction to a facial outline. First, the desired facial appearance is designed using a 3D sculpturing tool, while the cut regions of the skull are defined based on facial anatomy. Then, the deformation of the face meshes is performed using an improved biomechanical model in which virtual external forces are driven by the displacements corresponding to the differences of node coordinates between the original and specified face meshes, and free nodes and fixed nodes are defined in terms of the contact surfaces between the soft tissues and the bones within the cut regions. Finally, the shape of the contact surfaces is updated following the deformation of the soft tissues. After registering the deformable contact surfaces and the cut surfaces, the final positions of the cut bones are estimated. Evaluation of preliminary experimental results quantitatively shows the effectiveness of the proposed approach.