Gradient systems for magnetic resonance imaging systems

Abstract

The invention describes a gradient system for a magnetic resonance imaging system, the gradient system comprising a plurality of pairs of gradient coils (25x, 25y, 25z), wherein each pair of gradient coils (25x, 25y, 25z) comprises a center plane (23) and is arranged on opposite sides of an examination region (M1, M2, M3, M4, M5, M6) such that the center planes (23) of the two gradient coils (25x, 25y, 25z) of the pair are at an angle greater than 10° to each other, so that the gradient system (20) is V-shaped. The invention also describes a magnetic resonance imaging system having such a gradient system.

Description

Technical Field

[0001] The present invention describes a gradient system for a magnetic resonance imaging system ("MRI system"), in particular a gradient system for an MRI system having two or more examination regions, and such an MRI system. Background Art

[0002] The principles of magnetic resonance imaging (MRI) have been used for imaging and other measurements for more than four decades. Despite this longevity and the importance of this measurement method, only two magnet designs are currently used in clinically used MRI systems or MRI scanners: the C-magnet format and the solenoid. The operation of this type of MRI scanner remains problematic for clinical workflow.

[0003] The most serious problems that occur are related to the extensive stray magnetic fields surrounding these scanners. To deal with this problem and avoid accidents and damage, hospital administrations must delineate strictly controlled areas in and around MRI examination rooms by limiting access to people and equipment. Damage can occur if metal or magnetic parts are attracted by the strong magnets of the MRI scanner and accelerated in the direction of the scanner volume.

[0004] Another problem is that MRI scanners using a solenoid magnet design "enclose" the patient in a narrow patient corridor, which can be particularly claustrophobic. This claustrophobia may be so severe in some patients that an MRI scan cannot be performed. In addition, due to the narrow examination corridor, the access of medical personnel to the patient is severely limited, which is not conducive to interventional or therapeutic procedures, especially for real-time MRI imaging.

[0005] Typically, MRI scanners use self-shielded, solenoid-type superconducting magnets to reduce the strength of the leakage magnetic field caused by the coils of the basic field magnet. Actively shielded basic field magnets are much more expensive than unshielded basic field magnets. In addition, the shielding coils reduce the efficiency of the basic magnetic field that can be used for measurements in the inspection channel. The diameter of an active shielding magnet (about 220 cm) is larger than the diameter of an unshielded magnet (about 145 cm).

[0006] An alternative design for an MR scanner is to use a C-shaped magnet. The C-shaped magnet can be a permanent magnet or an electromagnet including two Helmholtz coils. The C-shaped magnet has two pole pieces that create a vertical base magnetic field in their space. A similar structure is a portal magnet, which is mechanically more robust and can also be implemented using superconducting Helmholtz coils in some embodiments. C-shaped magnets and portal magnets have the advantage of open access to the patient and additionally reduce the sense of claustrophobia. However, such a structure requires a very strong mechanical structure to offset the huge magnetic attraction between the two opposing base field magnets. In order to reduce the expansion of stray magnetic fields, these magnet architectures typically use an iron yoke to guide and enclose the magnetic field lines outside the imaging volume. The iron yoke is one of the most cost-effective shielding members. The disadvantage of such a yoke is the large size, weight and volume of the MR scanner.

[0007] A while ago, a method for solving these problems was proposed. The method is based on an MRI system with a toroidal magnetic field. Unlike the prior art of MR magnets using solenoids or Helmholtz-pair magnet coils, toroidal coils tend to confine the magnetic field to a torus with only small and not very far stray magnetic fields. This system not only overcomes the problems of stray magnetic fields and lightweight construction, but also provides the opportunity to implement two or more examination areas in a single MRI system. An example of such an MRI system is a basic field magnet device with three, four, six or eight (e.g., identical) basic field magnet segments, which are arranged in a star shape with rotational symmetry (e.g., 60° for six magnets and six examination areas) around a central axis. The basic magnetic field has a main direction extending in the form of a toroidal magnetic field.

[0008] There are local gradient systems with coil pairs arranged in parallel on the left and right side of the patient. However, although such known gradient systems can also be used for these new MRI systems, there are currently no gradient systems that work in an optimal way with these MRI systems. Summary of the invention

[0009] The object of the present invention is to improve known MRI systems to enable an improved gradient system, in particular for generating a spatially non-constant magnetic field, preferably for an MRI system having more than one examination region.

[0010] This object is achieved by a gradient system according to an embodiment and a magnetic resonance imaging system according to an embodiment.

[0011] A gradient system for a magnetic resonance imaging system according to the invention comprises several pairs of gradient coils, wherein the gradient coils in each pair comprise a central plane and are arranged at opposite sides of an examination region such that the central planes of the two gradient coils in the pair make an angle greater than 10° with respect to each other, such that the gradient system is V-shaped.

[0012] Although gradient systems are very advantageous for star-shaped magnet arrangements, they are also advantageous for conventional MRT systems.

[0013] The expression "pairs of gradient coils" means that there are two gradient coils for each gradient axis. Typically, a gradient system creates gradients in the X, Y and Z directions to achieve a gradient vector with X, Y and Z contributions. Therefore, preferably, there are pairs of X gradient coils, pairs of Y gradient coils and pairs of Z gradient coils. Obviously, two gradient coils designed to create the same gradient (and arranged on different sides of the examination region) form a pair.

[0014] To clarify the position in the 3D coordinate system, there is a reference to the center plane of the gradient coil. The center plane of the coil is the plane of the loop of the coil (or at least the average middle plane). Looking at a planar gradient coil, the center plane is the plane of the coil, looking at a Helmholtz coil, the center plane is the plane of the windings of the coil, where the magnetic field is perpendicular to the plane.

[0015] The gradient coils in each pair (i.e., the X, Y and / or Z gradient coils) are arranged on opposite sides of the examination region. The examination region of the gradient system is the region between the gradient coils, since in normal use in an MRT scanner, the examination region for an MRI examination will be between the gradient coils.

[0016] The gradient coils are arranged in a special way: they are not aligned in parallel as in the prior art, but so that the center planes of the two coils in the pair are at an angle greater than 10° to each other. Thus, the gradient system is V-shaped. For a better understanding, it is defined here that the "front side" of the gradient system is the mouth of the V-shape and the "back side" is the opposite side, where the gradient coils in the pair are closest to each other. The vector of the X-axis points to the front side of the gradient system.

[0017] Of course, the gradient system should also include additional components that the prior art gradient systems also include for optimal operation. These components are, for example, dedicated gradient power amplifiers, shim coils or holding structures for each axis GPAx, GPAy and GPAz.

[0018] The advantage of such a gradient system is that it generates special gradient fields which can be used for spatially resolvable gradients. However, this is very advantageous for MRI scanners with an inclined arrangement of the basic field magnets, such as in a star arrangement as described above.

[0019] A magnetic resonance imaging system comprises: at least one examination region, preferably two or more examination regions; and a gradient system according to the invention in at least one examination region. A preferred MRI scanner of such a magnetic resonance imaging system comprises an inclined arrangement of basic field magnets, for example a star-shaped arrangement. An MRI scanner with an annular MR scanner architecture is particularly preferred. In a star-shaped arrangement of basic field magnets with an annular magnetic field, the front side of the gradient system should point outside the annular magnetic field.

[0020] Particularly advantageous embodiments and features of the invention are given by the dependent claims, as disclosed in the following description. Features of different claim categories may be combined as appropriate to give further embodiments not described herein.

[0021] According to a preferred gradient system, each centering gradient coil is arranged in a mirror-image arrangement on opposite sides of the examination region, so that the center planes of the two centering gradient coils are symmetrical about an angle bisector. The angle bisector divides the angle spanned by the respective center planes into two angles of equal measure. The preferred gradient system has the shape of an isosceles triangle (with an open hypotenuse).

[0022] According to a preferred gradient system, the gradient coil is a dual-plane gradient coil. This has the advantage that the gradient system does not require a lot of space.

[0023] Preferably, the central planes of the gradient coils on one side of the examination region are parallel to each other, in particular when the gradient coils are dual-plane gradient coils.

[0024] Preferably, the gradient system comprises two or three pairs of gradient coils (eg X, Y and Z gradient coils), wherein all pairs of gradient coils are arranged at the same angle to each other, ie the angles between the center planes are equal.

[0025] According to a preferred gradient system, several gradient coils are formed as local coils, preferably as local gradient coils for head imaging.Preferably, the gradient coils are integrated into a headrest of a patient chair and / or are mechanically attached to a headrest of a patient chair.

[0026] Alternatively or additionally, it is preferred that several gradient coils are formed to cover the side of the entire field of view (or at least a part of the FoV) of the examination region, preferably being mechanically and / or permanently attachable to the MRI scanner. Preferably, the gradient coil system has two building blocks symmetrically located on the right side (such as block 1) and the left side (such as block 2) of the examination region. The right block 1 and the left block 2 are preferably mirror-image pairs. Each block preferably integrates at least one gradient coil for one axis. Typically, each block integrates three gradient coils for all three axes. This means that block 1 includes a stack of planar gradient coils, for example, the right half of the X, Y and Z gradient coils. In particular for a V-shaped basic magnet arrangement, the examination region (or each examination region) has a V-shaped gradient coil system attached to the basic field magnet and including two blocks. Such a V-shaped architecture of the gradient coils makes better use of the available magnetic field space in the examination region, which is shaped like a triangular prism or a trapezoidal prism. For a local gradient system, each block (1, 2) includes a stack of planar gradient coils, for example, each block integrates half of an X, Y and Z gradient coil pair.

[0027] The preferred gradient system comprises magnetic field shimming coils and / or active shielding coils, wherein these coils are preferably arranged parallel to the gradient coils (i.e., the center planes of these coils are parallel to the center planes of the gradient coils). With respect to the previous example, the gradient system block (1, 2) may also integrate magnetic field shimming coils and / or active shielding coils designed to attenuate stray gradient fields outside the imaging volume that would otherwise penetrate into adjacent examination regions and / or the imaging volume.

[0028] According to a preferred gradient system, the gradient coil is formed by a plurality of loops of conductors. It is obvious that preferably only one long conductor is wound into several loops, however, an open loop connected to another loop may also be present. In the following, the loops of the coil are designated as "loops in a group", wherein any reference to a moving action is intended to be understood as a change of a subsequent loop. The following design is preferred (alternatively or additionally).

[0029] The loops of the gradient coil for the X-gradient comprise two sets of inverted loops adjacent in the X-direction, preferably wherein the radius of the loops in a set increases, and the outer conductors in the X-direction (front and rear) remain substantially on the sides of the gradient coil. This means that the shape of such a coil is reminiscent of a butterfly.

[0030] The loops of the gradient coil for the Y gradient include two sets of inverted loops adjacent in the Y direction, preferably wherein the radius of the loops in a set increases, and the outer conductor in the Y direction remains substantially at the side of the gradient coil (the side being perpendicular to the front and rear sides). This means that the coil will look like the coil for the X gradient rotated only 90°.

[0031] The loops of the gradient coils for the Z gradient comprise enlarging loops in a group, preferably wherein the centre of the loops remains substantially in the centre of the gradient coil. This means that the coils can be coaxial but become larger at least in the X direction.

[0032] In the following, a more preferred special design of the coil is described. This special design generates a field which increases in the direction of the mouth of the V-shape of the gradient system (towards the front side).

[0033] With respect to gradient coils for X-gradients, the distance of the field-dependent conductors in a loop in a group steadily decreases at least in the direction of the opening of the V-shape of the gradient system (in the direction towards the front side). The field-dependent conductors are those parts of the loop that determine the magnetic field of the gradient.

[0034] With regard to the gradient coils for the Z-gradient, the distances of the field-dependent conductors in a group of loops decrease steadily at least in the direction of the opening of the V-shape of the gradient system (in the direction towards the front).

[0035] Regarding the gradient coil for Y gradient, the radius of a group of loops increases in the X direction and in the Y direction, and the outer conductor at the opening of the V shape is substantially maintained at the opening side (ie, at the front side) and at a side perpendicular to the front side.

[0036] Various hardware or software tools can be used to further fine-tune these line patterns to meet some additional constraints such as gradient linearity to reduce stray fields, the amplitude of mechanical vibrations, and the level of peripheral nerve stimulation or acoustic noise.

[0037] The described line pattern distribution can eliminate the inherent nonlinearity of the gradient field in the radial direction or along the local X-axis. Such nonlinearity is only produced by V-shaped gradient coils when the line pattern density along the X-axis is approximately constant.

[0038] For the X and Z gradient coils, the special loop shaping described can eliminate the nonlinear component along the X axis by modifying the wire spacing along the X axis from a constant spacing to a more quadratic spacing, where the wire density increases approximately quadratically with the radial distance to the symmetry axis (e.g., the symmetry axis of the annular base magnet). For the Y gradient coil, the exemplary solution adds an additional wire distribution with a constant spacing along the X axis. This is similar to the wire pattern of the magnet coil used to generate the static magnetic field Bo.

[0039] According to a preferred magnetic resonance imaging system, the gradient system comprises several gradient coils covering the sides (or at least a part of the sides) of the entire field of view of the examination region, preferably being mechanically and / or permanently attachable to an MRI scanner of the magnetic resonance imaging system.

[0040] According to a preferred magnetic resonance imaging system, the center plane of the gradient coils of the gradient system of at least one side of the examination region is arranged parallel to the basic field magnet of the MRI scanner of the magnetic resonance imaging system. Therefore, the MRI scanner has an inclined basic field magnet and the gradient system follows the arrangement of the basic field magnet.

[0041] The preferred opening angle of the V-shape of the gradient system is 120° (e.g., for a star-shaped MRI scanner with 3 examination regions), 90° (e.g., for a star-shaped MRI scanner with 4 examination regions), 72° (e.g., for a star-shaped MRI scanner with 5 examination regions), 60° (e.g., for a star-shaped MRI scanner with 6 examination regions) or 45° (e.g., for a star-shaped MRI scanner with 8 examination regions).

[0042] According to a preferred magnetic resonance imaging system, the magnetic resonance imaging system is designed such that a gradient system in an examination region, preferably a gradient system in each examination region, operates asynchronously and / or independently from a gradient system in another examination region of the magnetic resonance imaging system.

[0043] Preferably, the gradient system comprises a central control unit which is designed to coordinate all gradient activities, preferably to coordinate the independent operation of different gradient systems, in particular even to coordinate the minimization and / or correction of crosstalk terms between gradient systems. The term "independent operation" means that the MR sequences running in the examination region are not necessarily identical or synchronized or interleaved. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It should be understood, however, that the accompanying drawings are designed only for illustrative purposes and not as a limitation of the scope of the present invention.

[0045] Figure 1 A simplified MRI system according to an embodiment of the present invention is shown.

[0046] Figure 2 An exemplary embodiment of a magnetic resonance tomography system with a star-shaped basic field magnet arrangement is shown.

[0047] Figure 3 A detailed schematic representation of the individual basic field magnet segments of a star-shaped basic field magnet arrangement is shown.

[0048] Figure 4 A further exemplary embodiment of a magnetic resonance scanner having two examination regions is shown.

[0049] Figure 5A schematic example of a gradient system according to the invention is shown.

[0050] Figure 6 A schematic representation of a planar coil for an X-gradient according to the invention is shown.

[0051] Figure 7 A schematic representation of a planar coil for a Y-gradient according to the invention is shown.

[0052] Figure 8 A schematic representation of a planar coil for a Z-gradient according to the invention is shown.

[0053] Fig. 9 An alternative winding of the gradient coil for the X-gradient is shown.

[0054] Fig.10 An alternative winding of the gradient coil for the Y-gradient is shown.

[0055] Fig.11 An alternative winding of the gradient coil for the Z-gradient is shown.

[0056] In the drawings, like reference numerals refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0057] Figure 1 A schematic representation of a magnetic resonance imaging system 1 ("MRI system") is shown. The MRI system 1 comprises an actual magnetic resonance scanner (data acquisition unit) 2 having an examination space 3 or a patient channel in which a patient or a test person is located on a driven couch 8 and in which an actual examination object O is located.

[0058] The magnetic resonance scanner 2 is usually equipped with a basic field magnet system 4, a gradient system 6 and an RF transmission antenna system 5 and an RF reception antenna system 7. In the exemplary embodiment shown, the RF transmission antenna system 5 is a whole-body coil permanently installed in the magnetic resonance scanner 2, in contrast to which the RF reception antenna system 7 is formed as a local coil (here only represented by a single local coil) to be arranged on a patient or test subject. In principle, however, a whole-body coil can also be used as an RF reception antenna system and the local coils can be switched to different operating modes respectively.

[0059] The basic field magnet system is typically designed so that it generates a basic magnetic field in the longitudinal direction of the patient, i.e. along the longitudinal axis of the magnetic resonance scanner 2 extending in the z direction. The gradient system 6 usually comprises individually controllable gradient coils in order to be able to switch (activate) gradients independently of one another in the x-direction, the y-direction or the z-direction.

[0060] The MRI system 1 shown here is a full-body system with a patient channel into which the patient can be completely introduced. In principle, however, the invention can also be used at other MRI systems, for example, at MRI systems with a C-shaped housing with lateral openings, and in smaller magnetic resonance scanners in which only one body part can be located.

[0061] Furthermore, the MRI system 1 has a central control device 13 for controlling the MRI system 1. The central control device 13 comprises a sequence control unit 14 for controlling the measurement sequence. With the sequence control unit 14, a series of radio frequency pulses (RF pulses) and gradient pulses can be controlled according to a selected pulse sequence.

[0062] In order to output the individual RF pulses of the pulse sequence, the central control device 13 has a radio frequency transmission device 15, which generates and amplifies the RF pulses and feeds the RF pulses to the RF transmission antenna system 5 via a suitable interface (not shown in detail). In order to control the gradient coils of the gradient system 6, the control device 13 has a gradient system interface 16. The sequence control unit 14 communicates with the radio frequency transmission device 15 and the gradient system interface 16 in a suitable manner to transmit the pulse sequence.

[0063] Furthermore, the control device 13 has a radio frequency receiving device 17 (likewise communicating in a suitable manner with the sequence control unit 14 ) for acquiring magnetic resonance signals for the individual measurements (ie raw data), which are received in a coordinated manner from the RF receiving antenna system 7 within the scope of the pulse sequence.

[0064] The reconstruction unit 18 receives the acquired raw data and reconstructs magnetic resonance image data for the measurement from the acquired raw data. The reconstruction is usually performed based on parameters that can be specified in a corresponding measurement or control protocol. For example, the image data can then be stored in a memory 19.

[0065] The central control device 13 can be operated via a terminal 10 having an input unit and a display unit 9, and thus the entire MRI system 1 can also be operated by an operator via the terminal 10. MR images can also be displayed at the display unit 9, and measurements can be planned and started with the aid of the input unit (possibly in combination with the display unit 9), and in particular, suitable control protocols can be selected (and possibly modified) using a suitable series of pulse sequences PS as described above.

[0066] The MRI system 1 according to the invention, in particular the control device 13, can have several additional components that are not shown in detail but are usually present in such systems, for example, a network interface to connect the entire system to a network and to be able to exchange raw data and / or image data or respectively parameter maps, but also additional data (for example patient-related data or control protocols).

[0067] The manner of acquiring suitable raw data by radiating RF pulses and generating gradient fields and reconstructing MR images from the raw data is known to those skilled in the art and therefore does not need to be explained in detail herein.

[0068] Figure 2 An exemplary embodiment of a magnetic resonance tomography system 1 with a star-shaped basic field magnet arrangement 40 is shown.

[0069] Here, a magnetic resonance scanner 2 is shown, the functions of which can be controlled by a control device 13. In principle, the control device 13 can be controlled in the same manner as in accordance with Figure 1 The control device 13 in the conventional MR system is constructed in a similar manner and has the same components as the control device 13. Likewise, the control device 13 may also have appropriate terminals, etc. (not shown here).

[0070] The basic field magnet arrangement 40 of the magnetic resonance scanner 2 in the figure comprises six (here identical) basic field magnet segments 44, which in this embodiment are arranged in a star shape with a rotational symmetry of 60° around a central axis A. The basic magnetic field B0 indicated by the arrow has a basic field main direction R0, which extends in the form of a circular or annular magnetic field.

[0071] Figure 3 Shown is a detailed schematic representation of the individual basic field magnet segments 44 of the star-shaped basic field magnet arrangement 40. Here, six coil arrangements can be considered as basic field magnet segments 44 of the basic field magnet arrangement 40.

[0072] It should be noted that Figure 3 In the embodiment, the basic magnetic field B0 does not form a circle, but forms a hexagonal outline in each of the inspection regions M1, M2, M3, M4, M5, M6. The field lines of the basic magnetic field B0 form parallel lines.

[0073] This "six-pack" annular MRI scanner allows up to six patients to be scanned simultaneously in six imaging volumes (examination regions), wherein the homogeneity of the magnetic field B0 is high enough for performing MR imaging sequences, as is known from the prior art. Figure 1The process described herein is an acquisition and image reconstruction method to acquire raw data and reconstruct MR images.

[0074] For each imaging volume, there is a local coordinate system XYZ associated with it, as exemplarily depicted here for only one imaging volume. The local Z axis extends parallel to the static magnetic field B0 and points in the same direction as the static magnetic field B0. The Y axis is parallel to the rotational symmetry axis of the six-set magnet system, while the X axis corresponds to the radial direction pointing out of the magnet from the center of symmetry.

[0075] Arrows and contour lines depict the overall distribution of the static magnetic field B0 in a cross-sectional plane cut through the middle of the magnet. The local magnetic field vectors depicted by small arrows show the distribution of the local magnetic field size (arrow size) and its direction (arrow orientation).

[0076] A significant advantage of such a symmetrical arrangement is the structural stability when the basic magnetic field B0 is switched on. The magnetic forces between the individual basic field magnet segments 44 cancel each other out in the direction of the main magnetic field direction R0. Each basic field magnet segment 44 is attracted by its two adjacent basic field magnet segments, each with the same force. The resulting forces act inwardly toward the column 43 and can be well compensated at the column 43 by appropriate structural reinforcement.

[0077] Based on Figure 2 and Figure 3 Such a magnetic resonance imaging system 1 with a basic field magnet arrangement 40 allows six different examination regions M1, M2, M3, M4, M5, M6 (see Figure 2 ), wherein in the example shown, measurements for an object O (a patient as shown or an inanimate object) take place at an examination region M4, wherein the patient stands upright here against a vertical wall of the basic field magnet arrangement 40. Theoretically, measurements can be taken at all six examination regions M1, M2, M3, M4, M5, M6 simultaneously. A central column 43 holds the basic field magnet segments 44 in place and can also include technical components, such as electrical connections or even a power supply.

[0078] In each case, a measuring device 12 (shown only symbolically) or the components required for this purpose at the examination regions M1, M2, M3, M4, M5, M6, respectively (e.g., HF coils) can be located at the examination regions M1, M2, M3, M4, M5, M6, the transmitting coils of the RF transmission system, the RF receiving coils of the RF receiving system and / or a common RF transmitting / receiving coil. Likewise, this can include gradient coils and / or shim coils. All these components can be controlled cooperatively by a common control device 13.

[0079] Of course, the magnetic resonance scanner 2 can also have more than six examination areas M1, M2, M3, M4, M5, M6, its height can be lower, or it can be designed for examining small areas of the body, for example, for head examination or examination of limbs, female breasts, prostate, liver, kidneys or other organs. The star-shaped basic field magnet arrangement 40 can also be positioned to lie flat.

[0080] An example of a gradient system 20 according to the invention is shown around a patient's head in an examination region M4. The V-shape of the gradient system 20 follows the angle between the two basic field magnet segments 44, namely 60°.

[0081] Another example of a gradient system 20 according to the invention is shown in an adjacent examination region M3. The gradient system 20 comprises a large gradient coil that covers the entire field of view of the examination region M3 and is mechanically and permanently attached to the basic field magnet segment 44 of the MRI scanner 2. Each examination region M1, M2, M3, M4, M5, M6 can have such a V-shaped gradient system 60 attached thereto, and such a V-shaped gradient system 60 comprises two blocks: a right block and a mirror-imaged left block. The V-shaped architecture of the gradient system 60 according to the invention makes better use of the magnetic field space available in the examination region, which is shaped like a triangular prism or a trapezoidal prism. As for the local gradient system 20, each block comprises a stack of planar gradient coils 25x, 25y, 25z (see the following figures), for example, each block integrates half of an X, Y and Z gradient coil pair. Furthermore, the block may also integrate magnetic field shimming coils and / or active shielding coils designed to attenuate stray gradient fields outside the imaging volume that would otherwise penetrate adjacent examination regions and / or the imaging volume. The gradient system 20 may also include a dedicated gradient power amplifier for each axis GPAx, GPAy and GPAz and for each examination region, preferably all gradient power amplifiers being controlled by a common central unit.

[0082] Figure 4 Another exemplary embodiment of a magnetic resonance scanner 2 with two examination regions M1, M2 is shown. Here, only the lower half of the basic field magnet arrangement 40 is designed in a star shape as a group 41 of basic field magnet segments 44, while another basic field magnet segment 44 protrudes upward and serves both to guide the basic magnetic field B0 and as part of a wall W between the two examination regions M1, M2, in which two patients are located as objects O to be examined. It can be seen in the illustration that the lower part of the wall W between the two patients is formed by the housing wall 30 of the magnetic resonance scanner 2, and the basic field magnet segments 44 are integrated between the examination regions M1, M2. The wall W can be used not only as a privacy barrier, but also as an acoustic shield or RF shield.

[0083] The basic magnetic field B0 of the magnetic resonance scanner 2 becomes weaker toward the outside—which can be used for position coding—and is uniform in the longitudinal direction (orthogonal to the image plane). The shape of the basic magnetic field B0 is essentially the same in the two examination regions M1, M2, the only difference being that the course (in a direction through the surface on which the patient O lies) is reversed. In addition, the dimensions of the magnetic resonance scanner 2 can be selected to be completely different.

[0084] Here, the basic magnetic main field direction R0 is also circular. The special feature of this embodiment is that the patient O is not in a confined space, but can freely look toward the ceiling. The inhomogeneity of the basic magnetic field B0, which is usually caused by the curvature, can be used as described above for spatial encoding resolution in one spatial direction.

[0085] Due to the open design of the magnetic resonance scanner 2 and the annular magnetic field, this arrangement allows easy and almost unrestricted access to the patient. Due to the symmetrical construction, the magnetic force is largely Figure 2 The magnetic forces are either compensated in this way or they are transferred to areas where they can be structurally well reinforced.

[0086] An example of a gradient system 20 according to the invention is shown in two examination regions M1 , M2 . The V-shape of the gradient system 20 again follows the angle between the two basic field magnets 44 , ie here 90°.

[0087] Figure 5 A schematic example of a gradient system 20 according to the invention is shown. The gradient system 20 comprises several pairs of gradient coils 25x, 25y, 25z, wherein the gradient coils 25x, 25y, 25z in each pair comprise a center plane 23 and are arranged on opposite sides of an examination region M1, such that the center planes 23 of the two gradient coils 25x, 25y, 25z in the pair are at an angle of about 60° to each other here, such that the gradient system 20 is V-shaped.

[0088] Figure 6 , Figure 7 and Figure 8 A schematic representation of planar gradient coils 25x, 25y, 25z for X-gradient, Y-gradient and Z-gradient is shown. The gradient coils 25x, 25y, 25z are formed by current conductors 21. The gradient coils can be connected to a gradient power supply (not shown) via power connectors 22. The gradient system 60 should include all three gradient coils 25x, 25y, 25z for generating gradient vectors having contributions in the X, Y and Z directions (see, for example, Figure 5 ). The arrow at conductor 21 always shows a predefined direction of the current.

[0089] Figure 6A gradient coil 25x for an X gradient is shown. The gradient coil 25x is shaped so that the radius of subsequent loops increases perpendicularly to the field-dependent conductor 21 (here the center conductor 21 with arrows pointing to the bottom). The center of the subsequent loops moves in the direction of the center of the gradient coil 25x.

[0090] Figure 7 A gradient coil 25y for a Y gradient is shown. The gradient coil 25y is shaped so that the radius of subsequent loops increases perpendicularly to the field-dependent conductor 21 (here the center conductor 21 with arrows pointing left / right). The center of the subsequent loop moves in the center direction of the gradient coil 25y.

[0091] Figure 8 A gradient coil 25z for a Z gradient is shown. The gradient coil 25z is shaped so that the radius of subsequent loops increases perpendicularly to the field-dependent conductor 21 (here the conductor 21 with the arrow pointing to the bottom). The center of the subsequent loops remains substantially at the center of the gradient coil 25z.

[0092] Use Figure 6 , Figure 7 and Figure 8 As shown in the line pattern, the generated gradient field may be slightly nonlinear along the radial direction or along the local X-axis due to the V-shape of the gradient system 20. This is not a serious limitation for this solution, since the prior art of MRI provides various image reconstruction methods adapted to nonlinear gradient fields. In addition, MR imaging using nonlinear gradients may provide additional advantages, such as variable spatial resolution, faster data acquisition using nonlinear signal encoding, and weak peripheral nerve stimulation.

[0093] Fig. 9 , Fig.10 and Fig.11 Alternative windings for the gradient coils 25x, 25y, 25z are shown. Figure 6 , Figure 7 and Figure 8 25x, 25y, 25z as a reference are shown in the figure, and gradient coils 25x, 25y, 25z with alternative windings are shown on the right. Since the coils are arranged in a V shape, the magnetic field of the left coil that generates the linear gradient field becomes weaker in the direction of the x-axis (the mouth of the V, i.e., the front side). Since the distance between the conductors 21 increases from left to right, the right coils 25x, 25y, 25z generate a linear gradient field in a V-shaped configuration. In order to achieve a constant gradient field, the left side of the right gradient coil 25x, 25y, 25z should point in the direction of the x-axis.

[0094] Fig. 9An alternative winding of a gradient coil 25x for an X-gradient is shown. The alternative winding is shaped so that the radius of subsequent loops increases perpendicular to the field-dependent conductor 21 (here the center conductor 21 with the arrow pointing to the bottom) with a non-constant distance between adjacent conductors. The center of the subsequent loop moves in the direction of the center of the gradient coil 25x. Thus, the distance of the field-dependent conductors 21 in a group of loops steadily decreases at least in the direction towards the front side of the gradient system 2.

[0095] Fig.10 An alternative winding of a gradient coil 25y for a Y gradient is shown. The alternative winding is shaped so that the radius of subsequent loops increases perpendicular to the field-related conductor 21 (here the center conductor 21 with an arrow pointing to the left) with a non-constant distance between adjacent conductors. Due to the V-shape of the gradient system, the center of the subsequent loops moves toward the center and to the right. Thus, the radius of the loops in a group increases in the X direction as well as in the Y direction, and the outer conductor 21 remains substantially at the front side of the gradient system.

[0096] Fig.11 An alternative winding of a gradient coil 25z for a Z gradient is shown. The alternative winding is shaped so that the radius of subsequent loops increases perpendicular to the field-dependent conductor 21 (here the center conductor 21 with arrows pointing up and down) with a non-constant distance between adjacent conductors. The center of the subsequent loops remains substantially in the center of the gradient coil 25z. Thus, the distance of the field-dependent conductors in a group of loops decreases steadily at least in the direction towards the front side of the gradient system.

[0097] Can be further optimized by hardware or software tools Figures 6 to 11 The initial pattern shown satisfies the additional constraints. Figures 9 to 11 The line pattern depicted, the generated gradient field is slightly nonlinear along the radial direction or along the local X-axis. This is not a serious limitation for the use of this solution in prior art MRI systems, because the prior art of MRI provides various image reconstruction methods adapted to nonlinear gradient fields. In addition, MR imaging using nonlinear gradients can provide additional advantages, such as variable spatial resolution, faster data acquisition using nonlinear signal encoding, and weak peripheral nerve stimulation.

[0098] exist Figures 9 to 11 The alternative gradient coils 25x, 25y, 25z depicted on the right side of FIG. 2 are optimized to also generate linearly varying gradient fields along the radial / local x-axis.

[0099] Although the present invention has been disclosed in the form of preferred embodiments and variations thereof, it will be appreciated that many additional modifications and variations may be made to the present invention without departing from the scope of the present invention. For the sake of clarity, it will be appreciated that the use of expressions throughout this application that are not qualified by quantifiers does not exclude a plurality, and "comprising" does not exclude other steps or elements. Reference to a "unit" or "device" does not exclude the use of more than one unit or device.

Claims

1. A magnetic resonance imaging system (1), comprising: Two or more examination regions (M1, M2, M3, M4, M5, M6) and a gradient system (20) in each examination region, the gradient system (20) comprising a plurality of pairs of gradient coils (25x, 25y, 25z), wherein the gradient coils (25x, 25y, 25z) in each pair comprise a central plane (23) and are arranged on opposite sides of the examination region (M1, M2, M3, M4, M5, M6) such that the central planes (23) of the two gradient coils (25x, 25y, 25z) in the pair are at an angle greater than 10° to each other, such that the gradient system (20) is V-shaped, and The gradient system comprises a plurality of gradient coils (25x, 25y, 25z) covering the sides of the entire field of view of the examination region (M1, M2, M3, M4, M5, M6).

2. The magnetic resonance imaging system (1) according to claim 1, wherein: The gradient coils (25x, 25y, 25z) in each pair are arranged in a mirror-image arrangement on opposite sides of the examination region (M1, M2, M3, M4, M5, M6) so that the center planes (23) of the two gradient coils (25x, 25y, 25z) in the pair are symmetrical about the angle bisector.

3. The magnetic resonance imaging system (1) according to one of the preceding claims, wherein: The gradient coil (25x, 25y, 25z) is a dual-plane gradient coil (25x, 25y, 25z).

4. The magnetic resonance imaging system (1) according to claim 3, wherein: The central planes (23) of the gradient coils (25x, 25y, 25z) on one side of the examination region (M1, M2, M3, M4, M5, M6) are parallel to each other.

5. The magnetic resonance imaging system (1) according to one of claims 1, 2 and 4, wherein: Several gradient coils (25x, 25y, 25z) are formed as local coils, and / or Therein, several gradient coils (25x, 25y, 25z) formed to cover the sides of the entire field of view of the examination area (M1, M2, M3, M4, M5, M6) can be mechanically and / or permanently attached to the MRI scanner (2).

6. The magnetic resonance imaging system (1) according to claim 5, wherein: Several gradient coils (25x, 25y, 25z) are formed as local gradient coils (25x, 25y, 25z) for head imaging.

7. The magnetic resonance imaging system (1) according to one of claims 1, 2, 4 and 6, comprising magnetic field shimming coils and / or active shielding coils.

8. The magnetic resonance imaging system (1) according to claim 7, wherein: The magnetic field shimming coils and / or active shielding coils are arranged parallel to the gradient coils (25x, 25y, 25z).

9. The magnetic resonance imaging system (1) according to one of claims 1, 2, 4, 6 and 8, wherein: Gradient coils (25x, 25y, 25z) are formed by a plurality of loops of a conductor (21).

10. The magnetic resonance imaging system (1) according to claim 9, wherein: - the loops of the gradient coils (25x, 25y, 25z) for the X gradient include two sets of inverted loops adjacent to each other in the X direction, - the loops of the gradient coils (25x, 25y, 25z) for the Y gradient include two sets of inverted loops adjacent to each other in the Y direction, - The loops of the gradient coils (25x, 25y, 25z) for the Z-gradient consist of a group of enlarged loops.

11. The magnetic resonance imaging system (1) according to claim 10, wherein: The radius of the loop of a set of gradient coils (25x, 25y, 25z) for X-gradient increases, and the outer conductor (21) in the X-direction is substantially maintained at the side of the gradient coils (25x, 25y, 25z).

12. The magnetic resonance imaging system (1) according to claim 10, wherein: The radius of the loop of the gradient coils (25x, 25y, 25z) for Y gradient in a group increases, and the outer conductor in the Y direction is basically maintained at the side of the gradient coils (25x, 25y, 25z).

13. The magnetic resonance imaging system (1) according to claim 10, wherein: The center of the loop of the gradient coil (25x, 25y, 25z) for the Z gradient is maintained substantially at the center of the gradient coil (25x, 25y, 25z).

14. The magnetic resonance imaging system (1) according to one of claims 10 to 13, wherein: With respect to the gradient coils (25x, 25y, 25z) for the X-gradient and / or the gradient coils (25x, 25y, 25z) for the Z-gradient, the distances of the field-dependent conductors (21) in a group of loops decrease steadily at least in the direction of the opening of the V-shape of the gradient system (20), and / or In particular, regarding the gradient coils (25x, 25y, 25z) for the Y gradient, the radius of the loops in a group also increases along the X direction toward the opening of the V-shape, and the outer conductor is basically maintained at the opening.

15. The magnetic resonance imaging system according to claim 3, wherein: Several gradient coils (25x, 25y, 25z) covering the sides of the entire field of view of an examination region (M1, M2, M3, M4, M5, M6) are mechanically and / or permanently attached to an MRI scanner (2) of the magnetic resonance imaging system (1).

16. The magnetic resonance imaging system according to one of claims 1, 2, 4, 6, 8, 10 to 13 and 15, wherein: The central plane (23) of the gradient coils (25x, 25y, 25z) of the gradient system (20) on at least one side of the examination area (M1, M2, M3, M4, M5, M6) is parallel to the basic field magnet of the MRI scanner (2) of the magnetic resonance imaging system (1).

17. The magnetic resonance imaging system according to one of claims 1, 2, 4, 6, 8, 10 to 13 and 15, wherein: The magnetic resonance imaging system (1) is designed such that a gradient system (20) in the examination region (M1, M2, M3, M4, M5, M6) operates asynchronously and / or independently of a gradient system (20) in another examination region (M1, M2, M3, M4, M5, M6) of the magnetic resonance imaging system (1).

18. The magnetic resonance imaging system according to claim 17, wherein: The magnetic resonance imaging system (1) is designed so that a gradient system (20) in each examination region (M1, M2, M3, M4, M5, M6) operates asynchronously and / or independently of a gradient system (20) in another examination region (M1, M2, M3, M4, M5, M6) of the magnetic resonance imaging system (1).

19. The magnetic resonance imaging system according to one of claims 1, 2, 4, 6, 8, 10 to 13, 15 and 18, comprising a central control unit (13) designed to coordinate all gradient activities.

20. The magnetic resonance imaging system according to claim 19, wherein: The central control unit (13) is designed to coordinate the independent operation of the different gradient systems (20).

21. The magnetic resonance imaging system according to claim 19, wherein: The central control unit (13) is designed to coordinate the minimization and / or correction of even cross-interference terms between the gradient systems (20).

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