Design Of An MRI Simulator And Imaging Simulation In Low-field System

Computer simulation of magnetic resonance imaging becomes more and more important by time. It doesn’t need the actual MR equipment and the experimental conditions can be changed without the limits of the equipment. Simulators based on the Bloch equation are time consuming and the operation is complex. The purpose of the paper is to design a compact and easy used magnetic resonance imaging simulator based-on Bloch equation, which using less iscromats within each object voxel. It is used for the virtual magnetic resonance imaging (MRI) study in case of low-field with regard on main field inhomogeneity. The main contents of this paper are summarized as follows.This paper implements an MRI simulator. The simulator is divided into four different modules. The control module concerns the virtual object, main magnetic field, k-space and the signal bandwidth manipulations and definitions. The MRI sequence module implements the difference sequences. The magnetization vector computation module contains core of the algorithm. The last module is used to handle image reconstruction. Software of this simulator is written with C language. The structure of this program is clear and it guarantees the program flexibility.The simulator kernel algorithm is based on discrete time solution of the Bloch equation to iteratively calculate the magnetization vector of object voxels at different time. We simulated free induction decay signal and spin echo signal to test and verify the performance of the simulator. Adjusting the sequence parameters of SE sequence, we obtained images in different contrast. The experimental results fit well with the theoretical analysis, which shows the correctness of the simulation algorithm.We assumed two field inhomogeneity models (linear model and square mode) to simulate their impact on imaging. The results demonstrated that the inhomogeneity mode determines the style of the image distortion and the inhomogeneity intensity determines the degree of distortion. Because the impact of magnet aging and environmental factors such as temperature, the main field inhomogeneity of low-filed MRI systems has no specific pattern. It can provide a reference for the analysis of the main field inhomogeneity in practical MRI imaging by analyzing characteristics of the results of different inhomogeneity modes.