Asymmetric arrangement of permanent-magnetic elements for a magnetic resonance apparatus

Abstract

A main field magnet arrangement for a one-sided magnet resonance device produces a homogeneous magnetic field B in a working volume ( ). The working volume ( ) and the main field magnet ( ) are disposed on different sides of a plane E and the main field magnet ( ) has a geometric shape which permits disposal of a radio frequency (RF) receiver coil system and optionally a gradient coil system on the same side of the plane E as the main field magnet ( ). Field-generating elements of permanent-magnetic material form a radially outer part ( ) and a radially inner part ( ) relative to an axis A extending through the center of the working volume ( ), wherein the surface, facing the working volume ( ), of the radially inner part ( ) is axially further spaced apart from the center of the working volume ( ) than the surface of the radially outer part ( ) facing the working volume ( ), such that a depression ( ) is formed in the radially inner part ( ) in the axial direction. At least the radially inner part ( ) of the field-generating elements is made from permanent-magnetic material, the axes of the prismatic rods forming a grid of lines having a grid constant a. The surfaces of the prismatic rods, facing the working volume ( ), of the radially inner part ( ) of the field-generating elements have different axial separations from the center of the working volume ( ) which deviate from a rotationally-symmetrical distribution about the axis A, with the grid of lines extending in two main directions over at least four grid constants. Such an arrangement is particularly suited for use in a magnetic resonance tomography system for examining e.g. skin.