The Influence On The Mechanical Properties Of The Vertebral Finite Element Model Aroused By Different Attribute Assignment Methods

Background:The technique of finite element analysis has been widly used in the medical field,and CT data sets has been tightly connected with three-dimensional reconstruction, especially in the part to construct skeleton model.3Dimensional finite element model can not only be used to analyze the stress and strain situation of normal bone but also can analyze the risk factor for fracture and the Micro between fixation and fracture.Finite element modeling means that a digital model with the mechanical properties consistent with the physical model reality is found for calculating in computer. A digital model is created using the finite element method in the virtual environment. This model has the following requirements:First, the mechanics are integrated;Second,the result is valid. In other words, a good finite element model found has two missions, it has a complete mechanical information and this model can be quickly calculated in computer. So a successful madel not only has a good sharp near to truth but aslo has good mechanical material properties near to real situation.The visualization technology of Three-dimensional reconstruction to medical images can convert medical image datas to graphics or images displayed on the screen. Computer graphics, image processing, computer vision, and human-computer interaction technology are used in this process.Materialise’s interactive medical image control system(MIMICS) is a3D image generation and editing processing software,it is is highly integrated and easy-to-use. Many medical imaging (CT, MRI) data can be entered in to found3D models. With the development of the technology for three-dimensional (3D) finite element (FE) modelling, computerized tomography (CT) datasets have been widely used in building the finite element (FE) modeling of bones, and three-dimensional (3D) finite element (FE) modeling has commonly been employed to assess the stress state,fracture risk of bone structures and micromotions at the implant interface, such as long bones, spine, and so on. In the early period, computerised tomography (CT) was just used to generate bone geometry,when assigning material properties into a FE model as an important step to generate bone FE modelling, was done by most of the investigators according to the the general experience data access to previous experimental literature or experiment. Recently, Marom et al. has found that CT scans is of high advantange in bone modeling. CT images not only provide accurate information about bone geometry, but also can be related to the mechanical properties of bone, and moreover CT scanning is a mildly invasive routine diagnostic method which permits the modeling of human bones in vivo.So it was considered an in-house program code, e.g., BONEMAT,AMAB, and others, can be used to connect the CT dataset and FE dataset. The assignment program can be in accordance with the gradation value of the CT data to determine the material properties of the finite element model,determines all CT image pixels that fall inside an element volume and assigns to the element the average value of these pixels. The program is aimed to use the CT dataset and FE dataset to assign the Young’s modulus to each element, to modify the FE dataset. As each element type has a different data structure, the implementation of this method needs advanced programming or manual manipulations. Before running the assignment program, the users need to create a FE model first. The values of the Young’s modulus are discretised into a number of distinct values. For each element, the average value of the Young’s modulus over the element is calculated from the CT dataset and rounded to a value and assigned to this element. To account for the spatial variation of material properties within an element.But now,there isn’t a specific standard to say that how to use this CT based modal and how much parts divided in the modal is best and most suitable to the finite element analysis.Finite element modeling of spineSome important operation techniques used in this experiment weresystematically recorded and edited in this article,obviously,to grasp all these operation techniques should be very usefully to improve the quality of three-dimensional models,and raise the efficiency of finite elementmodeling.Finite Element Analysis as animportant experimental method in the field of medical biomechanice, give the model logical material attributes to simulate the invivo conditions.Finite element modelong was a necessary requirement for finite element analysis,and it aimed at providing a"public platform" for all kinds of finite element analysis.The spine was used to demonstrate the general process of human bone finite element modeling in in this section.The surface smoothing processing operation as well as its relationships with the finite element modeling were focused indetail,as well as the corresponding three-dimensional model of the ideal finite element model using Geomagic software processing.The influence on the mechanical properties of the vertebral finite element model aroused by different material attributes assigned gradients of automatic assignment methodObjective:To appraise the influence on the mechanical properties of the vertebral finite element model aroused by different material attributes assigned gradients of automatic assignment method.Methods:An adult human spine(T12-L5) was scanned by a computerised tomography scanner, the3D model of each vertebra was generated from the CT dataset in a software routine, MIMICS. After that, the models were modified in the software routine called Geomagic, and were exported into the ANSYS general purpose FE package to generate the three mesh using the method:FVMESH. And then go back to the software routine MIMICS, the models were separated it into2,4,8,10,50,100,200,400gradients to assign the material attribute. At last, finite element analyses were performed on the workstation (computer) using ANSYS.Result:There are obvious distinction (P<0.05) between the different von mises stresses of different gradients in the CT HU-method, the von mises stresses from2copies and400copies were significantly different from the datasets of other number of copies.Conclusions:In the process of finite element analysis, taking into account the time and accuracy, an appropriate sub-method should be chosen in practical applications. According to this experiment,10parts is a good choose. It can meet the fast and accurate requirements clinical work to3D model.Compare the influence on the mechanical properties of the vertebral finite element model aroused by manual assignment method and automatic assignment methodObjective:To appraise the influence on the mechanical properties of the vertebral finite element model aroused by manual assignment method and automatic assignment method.Methods:An adult human spine(T12～L5) was scanned by a computerised tomography scanner, the3D model of each vertebra was generated from the CT dataset in a software routine, MIMICS. After that, the models were modified in the software routine called Geomagic, and were exported into the ANSYS general purpose FE package to generate the three mesh using the method:FVMESH. To assign material attributes there are two methods:First, the extra-elements were chose to assign the material as cortical bone,and the other part was assigned the material as spongy bone;Second, go back to the software routine MIMICS, the models were separated into10parts to assign the material attribute. At last, finite element analyses were performed on the workstation (computer) using ANSYS.Results:There are obvious distinction (P<0.05) between the two von mises stresses of different methods, the von mises stresses of cortical bone from the first method were significantly higher then that from the second method, the von mises stresses of spongy bone from the first method were significantly lower then that from the second method from the datasets of other number of copies.Conclusion:There are obvious distinction between the two von mises stresses of different methods, the von mises stresses of cortical bone from the first method were significantly higher then that from the second method, the von mises stresses of spongy bone from the first method were significantly lower then that from the second method from the datasets of other number of copies.The lines from the second method are more convergence.