A computer simulation program for mr imaging: application to rf and static magnetic field imperfections

Abstract

A computer simulation program capable of demonstrating various artifacts, such as image distortion caused by metallic implants in MR imaging, is presented. The structure of the program allows for the implementation of various imaging situations as long as spins only experience weak interaction, i.e., the Bloch equations are obeyed. The raw data are obtained by repeatedly applying the Bloch equations to the magnetization vector of each point of the simulated object, throughout the pulse sequence. With only a limited number of spins in each voxel, the effects of intravoxel dephasing and rephasing require special attention, and algorithms for this have been implemented.

Efficient simulation of magnetic resonance imaging with Bloch–Torrey equations using intra-voxel magnetization gradients

“…It should be noted that in [2,10], intra-voxel dephasing is accounted for by shortening the transverse magnetization according to the current field gradients in the voxel during each sample time. This accumulative damping of the signal models continuous dephasing correctly, but cannot account for rephasing (e.g., a gradient echo cannot be generated from a single voxel) as it does only keep track of the magnitude of the magnetization vector.…”

“…Thereby, the isochromats differ by frequency offset due to different spatial offsets in the field gradients of the imaging sequence. This isochromat summation (ISUM) was adapted in a number of subsequent studies [2,3,[6][7][8][9][10][11]. In general, the accuracy of the simulation increases with the number of isochromats and hence with simulation time (ST), which is the time required to complete the simulation.…”

Medical Images Simulation, Storage, and Processing on the European DataGrid Testbed

“…It is used as an educational tool in medical and technical environments [38]. By offering an analysis independent of the multiple parameters involved in the MR technology, MRI simulation permits the investigation of artifact causes and effects [9,32]. Likewise simulation may help in the development and optimization of MR sequences [9].…”

Nonlinear Identification of NMR Spin Systems by Adaptive Filtering

“…Ĥ 1 (n), Ĥ 2 (n), X 1 (n), and X 2 (n) are defined by Eqs. [7], [8], [9], and [10], respectively. ␦ 3 is a positive factor that must satisfy 0 Ͻ ␦ 3 Ͻ 2/(N x 2 ) 3 to assure the stability of the adaptive filter.…”