Abstract: A magnetic resonance imaging (MRI) system includes a main magnet system for generating a main magnetic field in an examination volume. A gradient coil system is arranged between the main magnet system and the examination volume and includes sub-gradient coils embedded in a binding material which has a glass temperature. A controller controls a temperature of the gradient coil system. A temperature-influencing unit influences the temperature of the gradient coil system on the basis of control signals supplied by the control unit. The control unit and the temperature-influencing unit control the temperature of the binding material of the gradient coil system to a value above the glass temperature during operation of the MRI system.

Abstract: The invention relates to a treatment room (7) suitable for recording images of a human or animal body on the basis of a magnetic resonance (MR) imaging technique, the walls (7a), the ceiling (7b) and the floor (7c) of the treatment room forming an electromagnetic shield for a magnetic resonance (MR) imaging system (1) arranged in the treatment room, which MR imaging system comprises at least a target area (5) in which a human or animal body can be placed, a housing (2, 3, 4) comprising at least one main magnetic unit and at least one gradient magnetic unit for generating one or more magnetic fields in the target area (5), and at least one radio-frequency (RF) pulse unit (6) for generating an electromagnetic RF pulse in the target area (5).

Abstract: At least one quantity which is characteristic of the temperature-dependent magnetic properties of magnetizable material which interacts with the magnetic fields of a magnetic resonance imaging device is determined in order to compensate the temporally varying strength of the main magnetic field of a main magnet of such a device. On the basis of this quantity a compensation signal is formed for the correction of the influence of the varying field strength on the imaging result.

Abstract: At least one quantity which is characteristic of the temperature-dependent magnetic properties of magnetizable material which interacts with the magnetic fields of a magnetic resonance imaging device is determined in order to compensate the temporally varying strength of the main magnetic field of a main magnet of such a device. On the basis of this quantity a compensation signal is formed for the correction of the influence of the varying field strength on the imaging result.

Abstract: At least one quantity which is characteristic of the temperature-dependent magnetic properties of magnetizable material which interacts with the magnetic fields of a magnetic resonance imaging device is determined in order to compensate the temporally varying strength of the main magnetic field of a main magnet of such a device. On the basis of this quantity a compensation signal is formed for the correction of the influence of the varying field strength on the imaging result.

Abstract: The MRI apparatus includes an actively shielded gradient system (40) with primary gradient coils and shielding coils (56). Despite the active shielding, such a system inevitably causes a magnetic field to some extent outside the shielding, so that eddy currents are generated in the conductive structures of the main magnet, said eddy currents causing heat dissipation and annoying noise. According to the invention, the gradient system also includes an eddy current shield (48) which consists of an electrically conductive, substantially closed plate; furthermore, the primary gradient coil (60) and the shielding coil (56) are arranged within the eddy current shield (48) and these three elements together constitute a mechanically rigid unit. As a result, eddy currents are avoided in the main magnet and annoying noise is strongly reduced.

Abstract: The invention relates to a method and a device for the imaging of a part of an object which is arranged in a steady magnetic field. The method according to the invention includes a step for filtering the shot noise from the measured MR signals. Filtering is performed by determining in a first step the value of a combination of a value of a parameter of a measuring point of the MR signal to be corrected and values of the parameter of measuring points in a vicinity of the measuring point. If the value of this combination exceeds a predetermined reference, the value zero is assigned to the value to be corrected. The invention is based on the idea that for a substantial part of the k space the corresponding MR signals behave as white noise. The reference is determined from the statistical distribution of the white noise. If the value of the combination exceeds the reference, it is assumed that a measuring point has been affected by shot noise.

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: The gradient coil system in a conventional MRI apparatus is optimized in respect of the shielding effect by the shielding coil of the system. Consequently, the system generally is not optimized in respect of the Lorentz forces occurring in the system, resulting in noise of a level such that it is annoying to the users. In order to avoid such noise, the system can be force-optimized. Because the shielding effect is partly lost in that case, however, eddy currents and hence disturbing noise would occur again. However, if the eddy currents are made to occur in acoustically insulated eddy current conductors which also have a large time constant for the decay of the eddy currents, the adverse effects of these eddy currents are adequately counteracted and the disturbing noise is reduced to an adequate extent. Particularly, the (cold) radiation shields of a cryogenic magnet system, arranged in vacuum, can be used as eddy current conductors. The vacuum then constitutes the acoustic insulation.

Abstract: Magnetic resonance imaging includes a system of gradient coils (3) for generating gradient fields in a measuring space (35), a power supply source (7) for the gradient coils, and a communication system for transferring acoustic information from at least a first region (39) in which the level of gradient noise generated by the gradient coils (3) is comparatively high to at least a second region (41). The communication system includes a reference signal generating device for generating a reference signal which is dependent on the gradient noise, a microphone (43) which is arranged in the first region (39) so as to pick up a mixture of sound information and gradient noise, and a sound reproduction device (65, 67), at least a part of which is situated in the second region (41).

Abstract: A magnetic resonance apparatus includes a magnet system (1) for generating a steady magnetic field in a measuring space (35), a gradient coil system (3) for generating gradient fields in the measuring space, and a power supply source (7) for the gradient coils (3) which comprises at least one gradient signal generator (9) and a number of gradient amplifiers (11), each of which is connected between an output of the gradient signal generator and at least one of the gradient coils.

Abstract: In a magnetic resonance apparatus, a coil system is added to a gradient coil system, as a result of which a measuring field range is adapted to the geometry of an object to be examined. For example, by addition of a Bo coil system to be activated simultaneously with the z-gradient system, an asymmetry is realized in the z-gradient field, as a result of which return of disturbing resonance signals from an object part located outside the gradient field operating range is avoided. Further, by addition of additional arc conductors, the z-gradient linearity range is displaced in the z-direction.

Abstract: In a magnetic resonance apparatus a gradient coil system in which "return" arc conductors, which contribute substantially less to the gradient field formation because they are situated further outwards radially and/or axially from the center of the system, are positioned to compensate for stray fields of "effective" are conductors, which are more centrally situated and which contribute more substantially to the gradient field formation. Due to both radial and axial displacement of the return arc conductors relative to the effective arc conductors, the measuring space of the apparatus can be conically shaped, so that a higher patient accessibility is achieved or a smaller diameter can be imparted to a central portion.

Abstract: In a gradient coil system for a magnetic resonance apparatus arc conductors of notably X coils and Y coils are stacked axially or radially so as to form rigid stacks. The arc conductors are interconnected by means of electrical conductors and the stacks are also interconnected, so that a rigid, self-supporting coil system is obtained. Because the coil system is composed of rigid elements, is comparatively open and does not require a coil former, the production of noise in a magnetic resonance apparatus comprising such a coil system is substantially reduced and field disturbances due to coil deformations are also reduced.