3-Dimension Visualization Of Ventricles And Modeling Of Cardiac Electricity Simulation

Electrocardiogram forward problem and inverse problem has been one of the difficulties in electrocardiogram sphere and has restricted electrocardiogram's development from experiential science to experimental science. In short, the research on electrocardiogram problems is on the relationship of cardiac electrical source and cardiac electrical field, in which the analysis of cardiac electrical field by the distribution and change of cardiac electrical source is called ECG Forward Problem, and inversely, the analysis and derivation of cardiac electrical source by the distribution and change of cardiac electrical source is called Inverse Problem. Clinical Electrocardiogram diagnosis is an Inverse Problem, which became the mainstream of Cardiac Electricity research in early stage. However, the resolving of Cardiac Electricity problems are closely related to the research on Cardiac Electricity Forward Problem, which has been increasingly paid attention to recently with the development of experimental techniques and other studies related to Cardiac Electricity, such as Cardiac Electrophysiology, Biological Modeling and Simulation, especially in the recent year the large amount of Cardiac Electrical Modeling and Simulation have upgraded the Forward Problem to a new altitude. Cardiac Electricity Modeling and Simulation has become the important method and means in the research ofelectrocardiogram Forward Problem, which is a hot spot in the Cardiac Electricity sphere. But due to the biological complexity of cardiac electrical activity, Cardiac Electricity Modeling and Simulation is still on the preliminary stage.Tracing back to the development course of Cardiac Electrical Modeling and Simulation, people tried to describe cardiac electrical activities with dipole physical models and later on multiple dipoles and congregate dipoles, all of these are called physical models. As these models are all approximate physical models and cannot reflect the structure and function of concrete cells and the heart, so interpretation based on these models has only some qualitative analysis function and cannot make quantitative analysis. Modeling and Simulation based on cell electrical physiology makes it possible to get quantitative analysis.Modeling and Simulation based on cell electrophysiology simulates cardiac electrical activities by incorporating the cell AP model and excitement propagation model into the heart structure, which touches the essence of cardiac electrical activities. It makes research on cardiac electrical activities at the cell level and can explain many complicated problems which many physical models are incapable of, and the results are evidently better than the physical models. So it is the developing trend in present cardiac electrical modeling and simulation. This modeling and simulation comes into being based on the understanding of electrical activities of the single cell and the enhancement of computer's computation capability, and at the same time, be restricted by the above two factors. Whatever models are the approximation of the real object to some extent, simulation models based on cell electrophysiology is no exception. At present there are large distance between the models and the reality, owing to two reasons: one is the understanding level, for example, the understanding of the conduction system, the cell electrophysiology, the impulse propagation between cells, and the heart structure is still not completely clearand needs to be more thorough; the other is the limitation of the computer's computation capability which cannot attain the resolution of cell level.Modeling and Simulation of cardiac electrical activities based on cell electrophysiology has been recognized highly by the researchers and become the hot spot. But among them, many are based on the 2-dimension or the local small sphere of cardiac muscle cells. Simulation based on the 3-dimension electrical activities of the whole heart or ventricles has begun and many overseas researchers are working on it. The research is still under exploration and the models needs to be unceasingly improved. There is still no domestic systematic research on the 3-dimensional simulation of cardiac electrical activities based on the cell electrophysiology with the anatomic structure and the distribution direction of heart muscle fibers.This task is to establish a 3-dimension simulation model of quasi cell level based on cell electrophysiology and anatomic structure (spatial resolution is 0.25 X 0.25 X 0.25mm, and the number of the nodes for the model is 180 X 136 X125, among which the number of the nodes for cells is 1039192) and simulate the electrical activity of ventricle. Cardiac electricity simulation based on cell electrophysiology includes many sub models: the heart's geometry model, the cardiac conduction system model, the action potential model of the cardiac cells, and the impulse spreading model. This dissertation is evolved on these sub-models, expatiated as the following: Research on the scientific computation visualization of the cardiac electricity simulation, and implement many means of 3-dimension display of the simulation with volume rendering and surface rendering. As surface rendering method reflects the real condition of the light reflection from the object with the sense of brightness and darkness and has better 3D visual effects, so we put emphasis on the surface rendering techniques, improve the Marching Cubes algorithm of surface rendering with proposal of anaccelerate algorithm to quicken the calculation speed. Moreover, we also put forth an algorithm which can directly calculate the normal direction from the edge surface. The approach has a high display speed. And we make use of the color brightness to display images with evident 3D effects with different colors for different parts to display the Isochronic surfaces map of the ventricular activation.We design the geometry model of the ventricles based on the anatomic structure. The ventricles wall has three layers: endocardial, midmyocardial, and epicardial myocytes, the cells of each layer have different action potential duration(APD), which play an important role in the formation of ECG So we proposes a layer-partition method and set up the ventricle geometry model with three layers. First make the detection of the endocardium and epicardium by the senary tree searching algorithm, and then separate the endocardium and the epicardium manually, and detect the slice layer neighboring to the endocardium, and at the same time detect the slice neighboring to the epicardium by the senary tree searching algorithm. After several alternate searching, the leftover is the midmyocardial myocytes (M cells). Now we find the boundary of the endocardium and midmyocardium, and build the transition strips between the endocardium and midmyocardium and the transition strips between the epicardium and the midmyocardium.Design the Purkinje conduction system with fractal theory. Fractal theory can delineate the complex phenomena seemingly impossible to be described. The structure described by fractal theory has self-resemblance characteristic between local and whole. Ventricle Purkinje system is a tree-shape system with self-resemblance property. Purkinje fibers' distribution is a branchstructure, with sub branches attached to parent branches, and the distribution has multi-scale property. We reasonably select the location of the fractal tree and the root and put forth the growing algorithm of the fractal tree on the endocardiac surface, and build the ventricle conduction system based on the fractal theory.? Implement the numerical solution of action potential equation of the single cell. There are many action potential models cardiac cells, among which some of the models deal with small number of ion channels and gated variables, the structure is simple, the calculation amount is little, but the effect is poor, while some others include many types of ion channels, the structure is complex, and the calculation amount is large. We choose M-N-T AP mathematical model of 1975 as Purkinje cell model and LRI AP model of 1991 as ventricle cell model, owing to their moderation of model complexity, calculation amount and model effects. And make numerical solution of the two models, protract the action potential curves of the single cells, and regulate the action potential duration (APD), suiting for the epi,mid,endo cardiac cells respectively.? We build the cells excitement propagation model. Excitement propagation between the cells is mainly is through the gap junction. There are mainly four types of gap junctions in the ventricle: the gap junction between the Purkinje cells, the gap junction between the Purkinje cells and the ventricle muscle cells, the axial gap junction between the ventricle muscle cells, and the radial gap junction between the ventricle muscle cells. We set up these gap junction models by programming, and decide the values of all types of gap junction according to the reported excitement propagation speeds.? Incorporating the sub-models into a whole simulation model of ventricleelectrical activities. Accord with the collateral calculation thought, we implement the whole propagation procedure of the ventricle with C language programming, calculating the isochronic surfaces map of the excitement of the whole ventricles, taking into consideration of the anisotropy of excitement propagation because of the difference of the axial and radial spreading of ventricle muscle, and lay the foundation for the later calculation ofECGThe main purpose of this dissertation is to build the 3-dimension simulation mode of ventricle electrical activities based on the anatomic structure, and provide a platform as well as a tool for the research of other abnormal cardiac electrical activities, and lay sound foundation for the later research work.The simulation of this dissertation is mainly carried out on PC. It takes over 500 hours to simulate ventricle electrical activities of Is long, so it is very difficult to make the programs. In the programming procedure, we take the strategies of first the revision of the sub-models and then the incorporating of the whole cardiac electrical simulation model as to enhance the speed and finally obtain the satisfactory isochronic surfaces maps.