Patent ID: 6107800
Filing Date: 2000-08-22
Classification: G01R

Abstract:
A gradient coil system for use in a magnetic resonance (MR) apparatus having a magnet system for generating a steady magnetic field B.sub.0 in a measuring space and oriented mainly parallel to a z-axis of an orthogonal coordinate system having coordinates labeled x, y and z, the gradient coil system comprising:a plurality of linear gradient coils, wherein each linear gradient coil generates a magnetic field oriented mainly parallel to the z-axis and with a lowest-order spatial variation comprising a first-order term depending on one direction,a plurality of additional gradient coils, wherein each additional gradient coil generates a magnetic field whose component in the direction of the steady magnetic field has a lowest-order spatial variation comprising one or more second-order terms depending on one or more directions in a predetermined manner, andcontrol means for supplying the linear gradient coils and the additional gradient coils with excitation currents having predetermined amplitudes and time variations during an MR imaging experiment,such that the amplitude of the total magnetic field generated can be represented by the series.vertline.B.sub.tot .vertline.=B.sub.0 +G.sub.x x+G.sub.y y+G.sub.z z+Ax.sup.2 +By.sup.2 +Cz.sup.2 +HOT,where G.sub.x, G.sub.y and G.sub.z are first-order coefficients having predetermined values at least one of which is not zero, and where A, B and C are second-order coefficients, and where HOT are third-order and higher-order terms, andsuch that any two of the second-order coefficients can be given predetermined values.