https://staff.aist.go.jp/k.chinzei/pdf/0011_jbiomech.pdf

Mechanical properties of brain tissue in-vivo: experiment and computer simulation

In order to create a useful computational tool that will aid in the understanding and perhaps prevention of head injury, it is important to know the quantitative influence of the constitutive properties, geometry and model formulations of the intracranial contents upon the mechanics of a head impact event. The University College Dublin Brain Trauma Model (UCDBTM) [1] has been refined and validated against a series of cadaver tests and the influence of different model formulations has been investigated. In total six different model configurations were constructed: (i) the baseline model, (ii) a refined baseline model which explicitly differentiates between grey and white neural tissue, (iii) a model with three elements through the thickness of the cerebrospinal fluid (CSF) layer, (iv) a model simulating a sliding boundary, (v) a projection mesh model (which also distinguishes between neural tissue) and (vi) a morphed model. These models have been compared against cadaver tests of Trosseille [2] an...

/pdf/influence-of-fe-model-variability-in-predicting-brain-motion-3yqf82azmp.pdf

Influence of FE model variability in predicting brain motion and intracranial pressure changes in head impact simulations

The accuracy of image-guided neurosurgery generally suffers from brain deformations due to intraoperative changes. These deformations cause significant changes of the anatomical geometry (organ shape and spatial interorgan relations), thus making intraoperative navigation based on preoperative images error prone. In order to improve the navigation accuracy, the authors developed a biomechanical model of the human head based on the finite element method, which can be employed for the correction of preoperative images to cope with the deformations occurring during surgical interventions. At the current stage of development, the two-dimensional (2-D) implementation of the model comprises two different materials, though the theory holds for the three-dimensional (3-D) case and is capable of dealing with an arbitrary number of different materials. For the correction of a preoperative image, a set of homologous landmarks must be specified which determine correspondences. These correspondences can be easily integrated into the model and are maintained throughout the computation of the deformation of the preoperative image. The necessary material parameter values have been determined through a comprehensive literature study. The authors' approach has been tested for the case of synthetic images and yields physically plausible deformation results. Additionally, they carried out registration experiments with a preoperative MR image of the human head and a corresponding postoperative image simulating an intraoperative image. The authors found that their approach yields good prediction results, even in the case when correspondences are given in a relatively small area of the image only.

Biomechanical modeling of the human head for physically based, nonrigid image registration

Resonance frequency analysis (RFA) has been used by several investigators to assess the boundary conditions of dental implants. The goal of the current study was to determine the vibrating behavior of a dental implant under various surrounding bone conditions. A 3D finite element (FE) model of a cylinder-type titanium implant was developed. In this model, the implant was embedded into a cubic section of bone. The model was first validated using a series of modal testing experiments. The effects of bony conditions on the resonance frequencies of the implant were computed with different bone types and bone densities. Our results show that the resonance frequency of the implant with type III surrounding bone decreased linearly (r=−0.996, P<0.01) from 17.9 kHz (without loss in bone density) to 0.6 kHz (90% loss in bone density) when the bone densities were decreased. On the other hand, without bone loss, the highest resonance frequency value (36.1 kHz) was found when the implant was placed into type I surrounding bone. In contrast, the resonance frequency of the implant with type IV bone quality was found to be 9.9 kHz, which is almost four-fold less than that found in the type I model. These results suggest that RFA could serve as a non-invasive diagnostic tool for detecting the stability of dental implants during the healing stages and in subsequent routine follow-up care after treatment.

Resonance frequency assessment of dental implant stability with various bone qualities: a numerical approach.

A review is presented of the existing finite-element (FE) models for the biomechanics of human head injury. Finite element analysis can be an important tool in describing the injury biomechanics of the human head. Complex geometric and material properties pose challenges to FE modelling. Various assumptions and simplifications are made in model development that require experimental validation. More recent models incorporate anatomic details with higher precision. The cervical vertebral column and spinal cord are included. Model results have been more qualitative than quantitative owing to the lack of adequate experimental validation. Advances include transient stress distribution in the brain tissue, frequency responses, effects of boundary conditions, pressure release mechanism of the foramen magnum and the spinal cord, verification of rotation and cavitation theories of brain injury, and protective effects of helmets. These theoretical results provide a basic understanding of the internal biomechanical responses of the head under various dynamic loading conditions. Basic experimental research is still needed to determine more accurate material properties and injury tolerance criteria, so that FE models can fully exercise their analytical and predictive power for the study and prevention of human head injury.

Finite-element models of the human head.

A head injury model consisting of the skull, the CSF, the brain and its partitioning membranes and the neck region is simulated by considering its near actual geometry. Three-dimensional finite-element analysis is carried out to investigate the influence of the partitioning membranes of the brain and the neck in head injury analysis through free-vibration analysis and transient analysis. In free-vibration analysis, the first five modal frequencies are calculated, and in transient analysis intracranial pressure and maximum shear stress in the brain are determined for a given occipital impact load.

Importance of partitioning membranes of the brain and the influence of the neck in head injury modelling

The experiment used four acid dyes, three basic dyes and two solvents, ethanol and toluene. The procedure was to stir a very small quantity 1 mm 3) o f powdered dye into 2 ml of the selected solvent and then to mix this with 2 ml o f D e 3140. The mixture was deposited as 'spots,' about 1.5 cm in diameter, on to clean microscope slides, which were then cured in moist air in a pressure chamber at 2 bar. Curing under pressure prevents bubbles appearing in the spots as a result of the contraction of the rubber during cure. The spot colours noted were those seen after 24 h; in most cases, however, the colour developed within a few minutes and was stable therafter, 48 h were allowed for cure.

S. Kumaresan

Papers

Importance of partitioning membranes of the brain and the influence of the neck in head injury modelling

Generation of geometry of closed human head and discretisation for finite element analysis

Mixed models in finite element analysis