Magnetic resonance image-forming system gradient field spherical harmonic coefficient obtaining method

Abstract

The invention relates to a method for acquiring spherical harmonic coefficient of gradient field of magnetic resonance imaging system, which comprises the following steps of : (a) constructing a water model coordinate system selecting a mark point Pc(u0, v0) closest to the image center as the original point Op, selecting the u axis direction of an MRI image as the c axis direction, selecting the v axis direction in the image as the r axis direction, and selecting the direction forming a right-handed coordinate system with the c and the r axes as the s axis direction; (b) calculating the MRI coordinates of the mark point Pi according to the water model coordinate system by following steps: (1) ignoring the rotation of the water model in the plane thereof and the translation of the original point; (2) considering the rotation by a theta angle in the plane of the water model around the center of Op and a shaft in the direction of a scan layer slice; and (3) considering the translation of the coordination original point of the water model; and (c) obtaining a linear equation group concerning spherical harmonic coefficients a and b if the magnetic field intensity parameters gamma, theta, phi and image coordinates of a certain point are known, and calculating the coefficients a and b by solving the linear equation group.

Description

technical field [0001] The invention relates to a coefficient acquisition method, in particular to a magnetic resonance imaging system gradient field spherical harmonic coefficient acquisition method. Background technique [0002] In the nuclear resonance system, the nonlinearity of the gradient field often causes the geometric distortion of the image. The geometric distortion of images is different whether on different magnetic resonance imaging machines or within different fields of view (FOV) of the same magnetic resonance imaging machine. Therefore, the image correction technology for the nonlinear problem of the gradient field is quite necessary in practical applications to improve the accuracy of magnetic resonance image navigation surgery and to judge the feasibility of multi-magnetic resonance image research. The basic process of magnetic resonance image gradient deformation correction is: first find the position offset of a limited number of control points in the m...

AI Technical Summary

Problems solved by technology

This method is to calculate the correction parameters for image correction according to the design parameters of the gradient coil, but the design parameters of the gradient coil are only one of the main factors of image deformation, and there are other factors that have not been taken into account

Therefore, there is still a certain difference between the actual calibration parameters and the design parameters

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