MRI IN CYLINDRICAL COORDINATES

Abstract

We obtained the nuclear density distribution of a disk in 25 ms by using an one-dimensional (1D) imaging technique in the cylindrical coordinates, A magnetic field gradient coil implementing the cylindrical coordinates in MRI was devised by simply changing the direction of current flow at the central part of a solenoid for easy construction. The current distributions, which give the maximum field gradient in the radial direction and the ratio of the field gradient in the radial direction to that in the axial direction, were found numerically as a function of the solenoid length and the number of turns of reverse current at the center. The ratio of the radial gradient and the axial gradient of the designed coil is large enough to produce an undistorted 1D image in the radial direction of a slice perpendicular to the axis. The reverse current prevents the image from being shifted in a spectrum. The gradient coil gives images which agree with theoretical expectations within 5% error. Our result is applicable to the imaging of dynamic objects with cylindrical symmetry which do not change substantially during the order of milliseconds.