Evolvement Rule Of Hematoma Stress Distribution And Prediction Of Tissue Damage After Intracerebral Hemorrhage

Intracerebral hemorrhage?ICH?is a subtype of stroke,occurs within the brain tissue.Because of high morbidity and mortality,the researches on the causes of bleeding,injury mechanisms,and treatments are highly concerned.After ICH ictus,brain injury can be divide into two parts:primary brain injury which caused by mechanical compression of hematoma in early stage?in 4h?and secondary brain injury which casused by thrombin,erythrocytes,haemoglobin,and inflammation in later stage.Physical damage of brain tissue,caused by mass effect,is one of the significant factors of brain injury after ICH.But because of the suddenness of ICH,it is hardly to observe the dynamic process of ICH in clinical practice and trials,and no direct and effective observation techniques can be used to measure the physical damage due to mass effect.Based on the computed tomography?CT?image data of hematoma location after ICH,a mathematical-physical model is established by biomechanical method.From perspective of mechanics,the temporal and spatial variations between the distibution of stress and strain in brain tissue and hematoma enlargement after ICH is studied.According to strain energy theory and theories of mathematics and physics,the constitutive equation describing the undamaged deformation of brain tissue is presented.and the strain threshold of tensile injury in deformation is predicted under different load.The study on the evolvement rule of hematoma stress distribution will help to understand the process of brain injury after ICH ictus,help to predict physical damage caused by mechanical compression from hematoma enlargment.The results will provide new research ideas for the study of nature history,intervention and prognosis.The main research content and results are as follows:?1?According to geometric characteristics of brain structure and hematoma location,a finite element analysis model is proposed for analyzing the evolvement rule of hematoma stress distribution.Using CT images from ICH patients as data recourses,and region growing method is applied to segment CT images.Defining brain parenchyma as homogeneous medium,and skull as boundary constrain,the detail features of geometry such as superficial sulci and gyri of brain are simplified,and then finite element mesh was obtained by manual operation.2D model comprised 43138-node quadrilateral elements,and 13,373 nodes.The grid type is CPE8H.Through rebuilding the image by 3D Slicer,the space location of hematoma in finite element model was confirmed.The hematoma volume is calculated to be 18.69 mL as a loading boundary condition in finite element analysis.Through the processing of CT image,the geometric features are extracted,and then the clinical data are transformed into numerical model.?2?Constitutive equation for analyzing brain tissue deformation after ICH.Brain parenchyma can be considered an incompressible isotropic material.According to the mechanical properties of brain parenchyma,hyperelastic models such as polynomial models and Ogden model,which based on strain energy density function,were applied to fit stress and strain data of human brain tissue.The fitting results are verified by cross validation.With the purpose of optimal constitutive equation determination which could apply to simulate the relationship of stress and strain in ICH,an evaluation function was created to evaluate each fitting result.The parameters of models,which well suited for describing the deformation of gray matter and white matter under uniaxial tension,compression and simple shear,were obtained after fitting stress and strain data at strain rate 0.5s^-1,5s^-1 and 30 s^-1 respectively.The results shown that polynomial model?N=2?,reduced polynomial model?N=2?,Yoeh model and Mooney-Rivlin model can be a good fit to the experimental data under uniaxial tension,compression.Reduced polynomial model?N=2?,Ogden model and Yeoh model,based on the results of the evaluation function,were chosen as constitutive equations and the modal parameters are determined.The constitutive equation of brain tissue provides the necessary condition for the establishment of finite element analysis model.?3?In order to study the evolvement rule of hematoma stress distribution after ICH,based on the finite element model and constitutive equation above and Monro-Kellie doctrine,finite element analysis is used to simulate hematoma enlargement by adopting Ogden model as constitutive equation.The result indicate that the stress distributed around hematoma location.With hematoma volume increasing,stress distribution gradually concentratet towards the direction of hematoma enlargenent.When the tissue deformation reaches tolerance limit,the tissue is torn,and then stress release.The process continues to circulate until bleeding termination.The result indicates that the physical damage is caused by repeated mechanical oppression.When the hematoma volume larger than 568.111mm³,stress concentration is observed in precornu and postcornu on the side of hematoma location.This result suggest that the lesion caused by tissue deformation may not be only restricted to the border zone of hematoma.After ICH,with hematoma enlargement,the demand of external forces,which results in hematoma enlargement,is gradually decreasing.This result suggests that the function of reducing blood pressure as a standard treatment is limited in preventing or decreaseing bleeding.After simulating hematoma volume increasing from 0.114 to 3907mm³,the results show that raised intracranial pressure is not enough to inhibit hematoma enlargement.This suggested that intracranial pressure may not play a pivotal role in termination of ICH.The volume of hematoma obtained by finite element simulation was much less than the actual volume.The result indicates there are signifsiant difference between the hematoma volume obtained from CT images and the actual bleeding amount.?4?Physical damage threshold of brain tissue determination and damage prediction.Based on the finite element analysis of the tensile test acted on brain tissue and data fitting,strain energy loss in the process of tissue deformation had been studied,strain was to serve as the standard to predict structural damage of brain tissues.According to energy conservation law and strain energy theory,the deformation of white matter is supposed to meet the hyperelastic constitutive law when??1.15,then the difference of strain energy density between measurement and model results were compared.The level of damage in stretch could be divided into four phases:Undamage???1.343?,Slight damage?1.343???1.615?,Serious damage?1.615???2.241?and Fracture???2.241?.Stress threshold of each level had been determined.2D finite element model was applied to analyze the process of bleeding in the brain according to the level of damage.The results shown that the level of damage associated with hematoma growth direction,and the damage distribution area???0.343?concentrated at the ends of the hematoma,as a fan-shaped distribution.The prediction method of tissue physical damage can help to understand the natural progress of ICH.