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 magnetic resonance imaging facilitates a pre-compensating phase encoding of spuriously generated magnetizations. The method includes generating a preparatory excitation of spins represented upon an RF-excitation line, applying subsequently a temporary magnetic compensation gradient as represented along a phase-encoding axis, generating subsequently an RF excitation pulse as represented upon the RF-excitation line, applying subsequent to the RF excitation pulse, and before an acquisition interval for receiving magnetic resonance signals, a phase-encoding gradient as represented along the phase-encoding axis. The phase-encoding gradient is substantially the same magnitude as, and opposite in direction relative to, the direction of the temporary magnetic compensation gradient. The last step includes receiving magnetic resonance signals during the acquisition interval as represented along the RF-excitation line.

Abstract: In an MRI apparatus for medical purposes it is desirable to minimize the length of the magnet system for generating the main field, inter alia in order to keep the accessibility of the region to be examined in the imaging volume as high as possible for the attending staff. In order to save costs it is also desirable to make the diameter of the magnet system as small as possible. According to the invention a short, actively shielded magnet system is obtained in that the turns of the magnet system are situated in an imaginary U-shaped space 43 with the opening of the U facing the axis 35. The current component in the bottom 37 of the U has a value which is smaller than that of the current component in the limbs 47a, 47b of the U. The inner space 49 of the U does not contain a current for generating a contribution to the main field in the measuring space 29 of the apparatus.

Abstract: The design of a gradient system may be aimed at a high degree of linearity of the gradient field or a high speed during the generating of the gradient pulses, depending on the wishes of the user. These two wishes imply contradictory design criteria. In order to comply with both user wishes, the gradient system 32, 34, 36, 38 according to the invention is constructed so as to include a gradient coil 32 having a comparatively poor linearity, and a correction coil 36 which is intended to correct the linearity of the gradient coil; the linearity of the correction coil 36 itself thus is not important. The linearity of the system is enhanced, relative to that of the gradient coil alone, by addition of the fields of the two coils 32, 36. If a high speed is desired at the expense of the linearity, the gradient coil 32 alone may be activated; if a high linearity is desired at the expense of the speed, both coils 32, 36 can be switched on.

Abstract: Magnetic resonance apparatus includes a magnet system for generating a steady magnetic field in a measuring space, which steady magnetic field is oriented mainly parallel to one of the axes of an orthogonal coordinate system, a gradient system with gradient coil systems and with a controlled source for supplying the gradient coil systems with excitation currents with a predetermined variation in time. The gradient coil systems include a number of linear gradient coil systems, each of which is arranged to generate a main gradient field which is dependent on the location of the field in the measuring space in such a manner that a magnetic field formed by superposition of one of the main gradient fields on the steady magnetic field can be described, as a function of the coordinates of the coordinate system, as a series containing first-order terms and higher-order terms, the first-order terms having predetermined coefficients which are equal to zero for two of the coordinates.

Abstract: Magnetic resonance apparatus includes an essentially cylindrical magnet system (2) for generating a steady magnetic field (H) in a measurement space (28), a coil system (4) for generating gradient fields in the measurement space, and at least one RF coil (10) which is arranged in the immediate vicinity of the measurement space. In order to increase the homogeneity of the main magnetic field (H), approximately annular first elements (44) of a magnetically conductive material are provided within the magnet system (2) so as to extend coaxially with respect to the axis (9) of the magnet system. In order to minimize the amount of magnetically conductive material required, the first elements (44) are situated in the immediate vicinity of the RF coil (10).

Abstract: An extremely efficient magnet system having a comparatively large angle of aperture can be obtained for magnetic resonance imaging by a reduction of fields of all orders in a common approach affecting active and passive as well as positive and negative oriented coil elements. Passive soft-magnetic ring segments are arranged in two pairs and located within a plurality of larger diameter active magnetic coils. The active coils include a central coil and outer coils wherein the outer coils are smaller than the central coil. The coils are in a helium Dewar vessel and arranged such that the system has an aperture of about 90.degree.. The central active coil may have a larger radius than the smaller outer coils.

Abstract: In a magnetic resonance apparatus comprising a superconducting magnet system (1) for generating a steady magnetic field there is also included a superconducting shielding coil system (22) in order to compensate for magnetic field variations induced in the magnet by external magnetic flux variations. The shielding coil system (22) comprises coil sections (24) of different diameters.