Abstract: A magnetic resonance imaging scanner includes a generally cylindrical main magnet assembly (10) that defines a cylinder axis (16). A first set of shims (60) are rigidly positioned inside the magnet assembly (10) at about a first distance (d1) relative to the cylinder axis (16). A second set of shims (62) are rigidly positioned inside the main magnet assembly (10) at about a second distance (d2) relative to the cylinder axis (16). The second distance (d2) is different from the first distance (d1). A generally cylindrical radio frequency coil (26) is arranged inside the main magnet assembly (10) at about a third distance (d3) relative to the cylinder axis (16). A plurality of gradient coils (20) are arranged inside the main magnet assembly (10) at about a fourth distance (d4) relative to the cylinder axis (16).

Abstract: A novel method is described for simulation of an electric stimulation of the nerve system subject to the rate of change of gradient fields. A gradient signal is filtered and a stimulation signal is derived, which is compared with a predetermined stimulation threshold value. An indicator signal is generated if the threshold value is exceeded. Therefore the time dependent and spatially dependent electric fields as defined by the scanning sequence and the gradient coil properties are calculated. A vector combination of said calculated electric field components from each gradient coil axis is performed, which results in a temporal diagram of the total electric field at various spatial locations within the gradient coil. The stimulation probability at each location from said temporal diagram and said stimulation signal is then calculated, and said stimulation probability is compared with the stimulation threshold value at each location within the gradient coil.

Abstract: The invention relates to a gradient coil arrangement for the generation of a gradient magnetic field for an MR arrangement with at least two gradient coils arranged on a cylinder surface with a substantially circular cross section. In order to enable adjustment of gradient fields extending as linearly as possible in the area of an object to be examined without having to modify the entire mechanical structure of the MR arrangement and without having to increase the power required to feed the gradient coil arrangement, it is proposed according to the invention to configure the gradient coils so as to be asymmetrical in relation to a central plane lying horizontally through the longitudinal axis of the cylinder.