Abstract:
A magnetic resonance imaging magnet assembly ( 100 ) comprising: —a magnet ( 102 ) adapted for generating a main magnetic field for aligning the magnetic spins of nuclei of a subject ( 502 ) located within an imaging volume ( 504 ); and —a gradient coil ( 103 ) for generating a gradient magnetic field for spatial encoding of the magnetic resonance signal of spins of nuclei within the imaging volume, wherein the gradient coil is adapted to be mounted into the magnet, wherein the gradient coil comprises: —a first gradient coil section ( 112 ), wherein the first gradient coil section comprises a first rigid element ( 113 ), —a second gradient coil section ( 114 ), wherein the second gradient coil section also comprises a second rigid element ( 115 ), —a connecting element ( 116, 300, 302, 304, 400 ) for joining the two half gradient coils, wherein the connecting element comprises an elastic material ( 116 ), wherein the elastic material is in contact with the first rigid element and the second rigid element.

Description:
TECHNICAL FIELD 
     The invention relates to magnetic resonance imaging systems, in particular to the design of gradient coils for such systems. 
     BACKGROUND OF THE INVENTION 
     A static magnetic field is used by Magnetic Resonance Imaging (MRI) system to align the nuclear spins of atoms as part of the procedure for producing images within a subject. This static magnetic field is referred to as the B 0  field or the main field. 
     Magnetic field gradient coils are used to generate spatially and temporally variying magnetic fields which are used to spatially encode the nuclear spins being imaged. This spatial encoding is part of what allows the reconstruction of images from magnetic resonance imaging signals. 
     However Magnetic Resoance Imaging is typically performed in a large magnetic field. As current flows through a magnetic field gradient coil the Lorentz force on the coil may be enormous. Gradient coils are typically mounted on or embedded within a rigid carrier to which these forces are transferred. During operation the large forces exerted by the Lorentz for can cause acoustic vibrations in the gradient coil and the rigid carrier. These acoustic vibrations may sound like a large knocking, thumping, or clicking sound during the use of the magnetic resonance imaging system. 
     It is commonly known that increasing the strength of the B 0  field used for performing a magnetic resoance imaging scan offers the opportunity of increasing the spatial resolution and contrast resolution of the diagnostics images. This increase in resolution and contrast benefits physicians using a magnetic resoance image to diagnose a patient. However as the strength of the B 0  field increases, so do the Lorentz forces acting on the gradient coil during use. As the B 0  field increases so does the noise generated by the gradient coils during operation. 
     In the journal article Michael Poole, Richard Bowtell, Concepts in Magnetic Resonance Part B, Vol. 31B(3), page 162-175, 2007 a method of designing gradient coils using the boundary element is disclosed. The minimization of a functional during the design process which imposes torque-balancing of the gradient coil is disclosed. 
     In U.S. Pat. No. 5,764,059, an acoustically screened magnetic coil which is adapted to be placed in a static magnetic field is disclosed. Essentially a combination of active and magnetic screening for gradient coils is disclosed. A closed loop of the gradient coil carrying current is arranged such that the two different parts of the loop are mechanically coupled, dimensioned and arranged such that the Lorentz forces experienced by the magnetic equipment are substantially reduced and preferably cancelled. the US patent application US2004/0113618 shows a gradient coil system having two structurally independent sub-coils. These sub-coils are attached separately from one another so that an (RF) antenna system can be arranged between them. 
     SUMMARY OF THE INVENTION 
     The invention provides for a magnetic resonance imaging magnet assembly, a magnetic resonance imaging system, and a gradient coil in the independent claims. Embodiments are given in the dependent claims. 
     Magnetic resonance gradient coils exhibit mechanical resonance modes. This leads to increased acoustic noise at particular operating frequencies. Typically, gradient coils do not exhibit much mechanical damping, leading to enhanced vibration amplitudes at resonances. There is therefore a need to dampen such resonances. Attempts to dampen resonances have been largely unsuccessful, because the entire structure is optimized to withstand large Lorentz forces without mechanical failure. For example in U.S. Pat. No. 5,764,059 column 10 lines 20 through 21 it is written: “Thus contrary to intuition, a light coupling structure of high strength is required.” The design taught in U.S. Pat. No. 5,764,059 teaches a method of balancing forces between coils, but does not address the problems associated with acoustic resonances in the mechanical structure. 
     The use of the light coupling structure in U.S. Pat. No. 5,764,059 teaches away from the solution used by embodiments of the invention to dampen resonances: According to some embodiments of the invention a mechanical damping structure may be introduced into region of the coil where no large forces are transmitted, and where significant relative motion occurs for damping material to be effective. It is preferable if damping layers are not bridged by conductors, since their mechanical stiffness would cancel the effect of the damping material. For a cylindrical gradient coil, the natural location for a damping layer is the z=0 mid-plane of the coil, but conventional gradient coils experience large bending forces acting on the mid-plane. The z direction is defined as being aligned with the axis of symmetry of a cylindrical magnet. 
     In some embodiments, the acoustic noise emission of the gradient coils can be reduced by incorporating a mechanical damping material or elastic material, which reduces the mechanical quality factor of the structure. In some embodiments, a cylindrical gradient coil is split mechanically in the z=0 mid-plane and the two halves are joined using an elastic or lossy material. A prerequisite for such a mechanical split is that each of the halves of the gradient coils does not experience net magnetic translational or rotational forces in the field of the main field magnet. This requirement can be met by suitable magnetic design of the coil systems. 
     A gradient coils built according to the invention may have the following features:
     1. On splitting the coil about the z=0 plane, each half coil shall be force and torque-balanced when operated in the field of the magnet to which the coil is matched   2. The two halves of the coil are joined using mechanically lossy or elastic material such as to dampen the mechanical resonance modes of the coil. This lossy or elastic material may be incorporated in the form of a relatively thin layer of rubber.   

     Balancing net translational forces on gradient coils can be achieved by incorporating appropriate design constraints in the gradient design software. In a similar way, the net rotational forces can be constrained, if the coil is modeled as two independent halves. Solutions exhibiting zero torque can be found if the length of the coil is typically equal to or greater than the length of the superconducting main field magnet. The range of solutions increases if conductors are allowed to be placed on the end and mid-plane flanges of the gradient coil. Zero torque solutions can even be found for coils having an asymmetric cross-section. The damping layer at the joint between the two coils can be a layer of rubber-like material. Pre-stressing or compressing may enhance the effect of a damping layer. Alternatively, the two halves of the coil can be joined by a thin-walled short cylinder, placed either on the outside or on the inside of the coil structure, using a lossy or material for the lap joint between the coil and the joining cylinder. 
     A processor is an electronic component which is able to execute a program or machine executable instruction. References to the computing device comprising “a processor” should be interpreted as possibly containing more than one processor. The term computing device should also be interpreted to possibly refer to a collection or network of computing devices each comprising a processor. Many programs have their instructions performed by multiple processors that may be within the same computing device or which may even distributed across multiple computing device. 
     A computer-readable storage medium as used herein is any storage medium which may store instructions which are executable by a processor of a computer or computing device. The computer-readable storage medium may be a computer-readable non-transitory storage medium. The computer-readable storage medium may also be a tangible computer readable medium. In some embodiments, a computer-readable storage medium may also be able to store data which is able to be accessed by the processor of the computing device. An example of a computer-readable storage medium include, but are not limited to: a floppy disk, a magnetic hard disk drive, a solid state hard disk, flash memory, a USB thumb drive, Random Access Memory (RAM) memory, Read Only Memory (ROM) memory, an optical disk, a magneto-optical disk, and the register file of the processor. Examples of optical disks include Compact Disks (CD) and Digital Versatile Disks (DVD), for example CD-ROM, CD-RW, CD-R, DVD-ROM, DVD-RW, or DVD-R disks. The term computer readable-storage medium also refers to various types of recording media capable of being accessed by the computer device via a network or communication link. For example a data may be retrieved over a modem, over the internet, or over a local area network. 
     Computer memory is an example of a computer-readable storage medium. Computer memory is any memory which is directly accessible to a processor. Examples of computer memory include, but are not limited to: RAM memory, registers, and register files. 
     Computer storage is an example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. Examples of computer storage include, but are not limited to: a hard disk drive, a USB thumb drive, a floppy drive, a smart card, a DVD, a CD-ROM, and a solid state hard drive. In some embodiments computer storage may also be computer memory or vice versa. 
     In one aspect the invention provides for a magnetic resonance imaging magnet. The magnet is adapted for generating a main magnetic field for aligning the magnetic spins of nuclei of a subject located within an imaging volume. The magnet may be a superconducting magnet, a permanent magnet, or a resistive electromagnet, or a combination of any of the three. The magnet assembly further comprises a gradient coil for generating a magnetic field for a spatial encoding of the magnetic resonance signal of the spins of nuclei within the imaging volume. The gradient coil is adapted to be mounted into the magnet. The gradient coil comprises a first gradient coil section. The gradient coil further comprises a second gradient coil section. The first gradient coil section comprises a first rigid element and the second gradient coil section comprises a second rigid element. For a cylindrically shaped gradient coil, the first and second rigid elements may be rigid tubes. 
     The gradient coil further comprises a connecting element for joining the two half gradient coils. The connecting element comprises an elastic material. The elastic material is in contact with both the first and second elements. An example of an elastic material is rubber. The gradient coil may comprise three separate sets of coils. Each set of coils generates a gradient magnetic field in one of three spatial directions. They may be orthogonal and they may coincide with the geometric axes of x, y and z. 
     Each of the first and second gradient coil sections may contain coil windings of each of the at least three gradient coil systems. This embodiment may be advantageous because dividing the coil into two sections changes the resonant properties of the gradient coil. This may lead to a reduction in acoustic noise during operation of the magnetic resonance imaging magnet assembly. For example during use a series of loud thumping or clicking sounds is heard when data is acquired with the magnetic resonance imaging system. Embodiments of the invention may reduce this acoustic noise and make it more comfortable for a patient to be examined in a magnetic resonance imaging system. 
     In another embodiment both the first and second gradient coil sections comprise coil windings. The first and second gradient coil sections comprise inner and outer windings. The inner windings provide the magnetic field for creating the gradient magnetic fields during operation. The outer windings may be shield windings which cancel the magnetic field from the gradient coil from inducing eddy currents in other parts of the magnetic resonance imaging magnet assembly. Such a gradient coil is known in the art as an active shielded gradient coil. The coil windings comprise flange conductors. The flange conductors are portions of the coil windings that go between the inner and outer windings. The flange conductors are designed such that the flange conductors are adapted to balance a torque exerted on the gradient coil by the main magnetic field during operation of the gradient coil. This embodiment is advantageous because each of the first and second gradient coil sections are each torque balanced. This will lead to less mechanical motion of the first and second gradient coil sections. This may lead to a reduction in noise during operation of the magnetic resonance imaging system. 
     In another embodiment the coil windings of the first gradient coil section are rigidly attached to the first rigid element and the coil windings of the second gradient coil sections are rigidly attached to the second rigid element. This embodiment is advantageous because when current passes through a gradient coil and the gradient coil is in a large magnetic field there are Lorentz forces exerted on the coil winding. By having the coil windings rigidly attached to the rigid material the forces on the coil winding are transferred to the rigid material. In some embodiments the coil windings are fixed to the surface of the rigid elements and in other embodiments the coil winding are fully or partially embedded in the rigid elements. 
     In another embodiment the first and second rigid elements are elastically mounted to the magnet. This embodiment is advantageous because the use of elastic material to join the first and second gradient coil sections to the magnet reduces the transfer of mechanical vibrations between the gradient coil sections and the magnet. This may lead to reduced acoustic noise during operation of the magnetic resonance imaging magnet. 
     In another embodiment the connecting element comprises a viscous element that joins the first and second rigid elements. This embodiment is advantageous because the viscous element may dissipate acoustic vibrations between the first and second gradient coil sections. This may have the effect of reducing acoustic noise generated by the magnetic resonance imaging magnet assembly during use. The viscous element may be a material that is elastic and lossy. The viscous element may also be a mechanical element designed to dissipate energy. For instance small shock absorbers may be positioned between the first and second gradient coils to dissipate energy. 
     In another embodiment the connecting element comprises a lap joint. A lap joint as used herein is an overlapping joint that connects two elements. For instance two elements may dovetail or have a notch which fits together. In one variant the first and second gradient coil sections are cylindrical. A larger cylinder overlaps both the first and second gradient coil sections and this overlapping cylinder forms the lap joint. 
     In another embodiment the elastic material of the connecting element is compressed. For instance a flange system with bolts or threaded rods may be used to compress an elastic or for instance a rubber element between the first and second gradient coil sections. This embodiment is advantageous because it forms a joint that changes the acoustic resonance of the gradient coil and also may dissipate acoustic energy being transmitted between the first and second gradient coil sections. 
     In another embodiment the first and second gradient coil sections are electrically isolated. This embodiment is advantageous because this prevents mechanical energy by being transmitted by the connections between the first and second gradient coil sections. 
     In another embodiment the first and second gradient coil sections are connected electrically using bus bars. The bus bars are mounted elastically to the first and second rigid elements. This embodiment is advantageous because the first and second gradient coils can be connected electrically without acoustically coupling them. This may reduce the acoustic noise generated by the magnetic resonance imaging magnet assembly during operation. 
     In another embodiment the first and second gradient coil sections have separate cooling water connections and electrical power connections. That is to say that the coils which make up each of the first and second gradient coil sections are powered separately. For instance the z coil in the first gradient coil section may be connected to a gradient coil power supply and the z coil of the second gradient coil section may also be connected separately to the same or a different power supply. By having separate cooling water connections and electrical power connections the acoustic coupling between the first and second gradient coil sections may be reduced. This may have the benefit of reducing the acoustic noise generated by the magnetic resonance imaging magnet assembly during operation. 
     In another embodiment the first gradient coil section and the second gradient coil section are torque balanced for Lorentz forces in the magnetic field of the magnet. The first gradient coil section and the second gradient coil section are translational force balanced for Lorentz forces in the magnetic field of the magnet. This is advantageous because during use the magnets will not exert force on each other and this may have the effect of reducing noise generated by the magnetic resonance imaging magnet assembly. 
     In another embodiment the elastic material couples vibrations between the first gradient coil section and the second gradient coil section. This has the effect of reducing the acoustic noise generated by the magnetic resonance imaging magnet assembly during operation. This is because the resonant frequency of the gradient coil is changed by doing this. 
     In another embodiment the elastic material is a visco-elastic material. This embodiment is advantageous because the elastic material is lossy. That is to say that acoustic energy being transmitted between the two gradient coil sections is dissipated within the elastic material. This may have the effect of reducing the acoustic noise generated by the magnetic resonance imaging magnet assembly during operation. 
     In another aspect the invention provides for a magnetic resonance imaging system. The magnetic resonance imaging system comprises a magnetic resonance imaging magnet assembly according to an embodiment of the invention. The magnetic resonance imaging system further comprises a radio frequency system for acquiring magnetic resonance data. Magnetic resonance data is defined herein as being the recorded measurements of radio frequency signals emitted by atomic spins by the antenna of a Magnetic resonance apparatus during a magnetic resonance imaging scan. A Magnetic Resonance Imaging (MRI) image is defined herein as being the reconstructed two or three dimensional visualization of anatomic data contained within the magnetic resonance data. This visualization can be performed using a computer. 
     The radio frequency system is adapted to connect to a radio frequency antenna. The radio frequency system may be the combination of a transmitter and a receiver or it may be a transceiver. Accordingly the radio frequency antenna may be a single antenna which is used to send and receive radio signals or it may be a separate transmit and receive antenna. The magnetic resonance imaging system further comprises a magnetic field gradient coil power supply for supplying current to the magnetic field gradient coil. The magnetic resonance imaging system further comprises a computer system adapted for constructing images from the magnetic resonance data. The computer system is adapted for generating magnetic resonance images of the subject using the magnetic resonance data. The advantages of this embodiment have been previously discussed. 
     In another aspect the invention provides for a gradient coil for generating a magnetic field for spatial encoding of the magnetic spins of nuclei within an imaging volume of a magnetic resonance imaging system. The gradient coil is adapted to be mounted into a magnet of the magnetic resonance imaging system. The gradient coil comprises a first gradient coil section. The first gradient coil section comprises a first rigid element. The gradient coil comprises a second gradient coil section. The second gradient coil section also comprises a second rigid element. The gradient coil further comprises a connecting element for joining the first and second gradient coil sections. The connecting element comprises an elastic material. The elastic material is in contact with the first and second rigid elements. The advantages of this gradient coil have been previously discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which: 
         FIG. 1  shows a cross-sectional view of a magnetic resonance imaging magnet assembly according to an embodiment of the invention; 
         FIG. 2  shows a perspective, cross-sectional view of the windings of an embodiment of a magnet assembly according to the invention; 
         FIG. 3A  shows an example of lap joints according to an embodiment of the invention; 
         FIG. 3B  shows a further example of lap joints according to an embodiment of the invention; 
         FIG. 3C  shows a further example of lap joints according to an embodiment of the invention; 
         FIG. 4  shows an example of a compression joint which compresses the connecting element according to an embodiment of the invention; and 
         FIG. 5  shows a functional block diagram of a magnetic resonance imaging system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent. 
       FIG. 1  shows a cross-sectional view of a magnetic resonance imaging magnet assembly  100  according to an embodiment of the invention. The magnet assembly  100  comprises a magnet  102  and a gradient coil  103 . The magnet  102  shown in this FIG. is a magnet with a cylindrical symmetry. The axis of symmetry  104  of the magnet  102  is shown. The magnet  102  comprises a cryostat  106 . The cryostat  106  is surrounded by an insulation system which may comprise a vacuum  108 . The insulation system may also comprise a liquid nitrogen tank or vessel. Inside the cryostat  106  are superconducting coils  110 . 
     The gradient coil  103  comprises a first gradient coil section  112  and a second gradient coil section  114 . The first gradient coil section  112  and the second gradient coil section  114  are joined by a connecting element  116 . The first gradient coil section comprises a first rigid element  113 . The second gradient coil section comprises a second rigid element  115 . The connecting element joins the rigid elements  113 ,  115  of the first and second gradient coil sections  112 ,  114 . Both of the gradient coil sections  112 ,  114  are shown as having both outer windings  118  and inner windings  120 . All of the outer windings  118  and the inner windings  120  are rigidly connected to the rigid elements  113  and  115 . Bus bars  122  are used to connect the outer windings  118  of the first and second gradient coil sections  112 ,  114 . Likewise bus bars  122  are also used for connecting the inner windings  120  of the first and second gradient coil sections  112 ,  114 . The gradient coil  103  is shown as being mounted to the magnet  102  using the elastic mounts  126 . 
     The elastic mounts  126  may be elastic or they may also be visco-elastic in which case acoustic energy is dissipated in the elastic mounts. Likewise the connecting element may be an elastic or viscous element. It may be an elastic element, or it may be a visco-elastic element. The connecting element  116  serves during operation to change the resonant properties of the gradient coil  103 . This may have the effect of reducing acoustic noise generated within the magnet assembly  100 . 
       FIG. 2  shows a cross-sectional view of the windings  200  of an embodiment of a magnet assembly according to the invention. Inner coils of the magnet are labeled  110 ′. Outer coils of the magnet are labeled  110 ″. The regions labeled  208  show the location of where the rigid element would be. The inner  120  and outer  118  windings are shown inside and outside of the region  208 . The inner windings  120  is the primary layer of the gradient coil windings and the outer windings  118  are the shield layer of the gradient coil windings. 
     The axis labeled  210  is a rotational axis of symmetry for the magnet assembly. This axis is located on a plane which divides the gradient coil into the first gradient coil section  112  and the second gradient coil section  114 . The magnet has mirror- and rotational symmetry. The symmetry plane of the magnet coincides with the mid-plane of the gradient coil. 
       202  is a flange conductor. In this embodiment, the end flange conductor  202  of the gradient coil is located somewhere within the volume enclosed by the inner coil of the magnet  110 ′ further from the mid-plane of the magnet. Without the end flange conductors the gradient coil would need to be made longer to achieve torque balancing. The further from the mid-plane of the magnet, the less homogeneous the magnetic field is. In homogeneities of the magnetic field can be used to design a gradient coil which is torque balanced. 
       204  is also a flange conductor. The flange conductor  204  is clearly not running radially outwards. The flange conductor  204  starts and stops on a shield coil  118  winding. 
       206  is a flange conductor near the mid-plane of the gradient coil. 
     The flange conductor labeled  206  is near the mid-plane of the gradient coil. The mid-plane of the gradient coil is where the gradient coil is split into the first and second gradient coil sections. The gradient coil also features a recessed section of the primary gradient coil windings near the split between the first  112  and second  114  gradient coil sections. 
       FIGS. 3   a ,  3   b  and  3   c  show examples of lap joints  300 ,  302 ,  304  which join the first gradient coil section  112  to the second gradient coil section  114 . In  FIG. 3   a  a section of a cylindrical gradient coil is shown. The first gradient coil section  112  is joined to the second gradient coil section  114  by an overlapping lap joint  300 . A connecting element  116  is shown as connecting the first gradient coil section  112  with the second gradient coil section  114 . 
       FIG. 3   b  is very similar to  3   a  except instead of using the overlapping joint a tongue-in-groove lap joint  302  is used. Then a connecting element  116  connects the first gradient coil section  112  to the second gradient coil section  114 . 
     In  FIG. 3   c  a different style lap joint  304  is shown. In the embodiment shown in  FIG. 3   c  a connecting cylinder  306  is used to join the first gradient coil section  112  with the second gradient coil section  114 . A connecting element  116  connects the first gradient coil section  112  to the connecting cylinder  306 . The connecting cylinder  306  is then connected via another section of  116  to the second gradient coil section  114 . In this embodiment the connecting element  116  is shown as two distinct pieces. However, in some embodiments a single piece of connecting element could be used. Also shown is connecting element  116 ′ which is between the first gradient coil section  112  and the second gradient coil section  114 . This connecting element  116 ′ is optional. In addition the embodiment of  FIG. 3   c  could be combined with the embodiments shown in  FIG. 3   a  or  3   b.    
       FIG. 4  shows an example of a compression joint  400  which joins the first gradient coil section  112  to the second gradient coil section  114 . In this embodiment the connecting element  116  is compressed. Both the first gradient coil section  112  and the second gradient coil section  114  have flanges  408 . Going around the circumference of the gradient coil there may be a number of bolts  402  which are tightened using nuts  404 . The combination of the bolt  402  and the nut  404  is used to place the connecting element  116  under compression. The bolts  402  and the nuts  404  are vibrationally isolated from the first and second gradient coil sections  112 ,  114  by vibration isolation elements  406 . In this example the vibration isolation elements  406  may simply be large rubber washers which prevent the bolt  402  and the nut  404  from coming in direct contact with either the first gradient coil section  112  or the second gradient coil section  114 . 
       FIG. 5  shows a functional block diagram of a magnetic resonance imaging system  500  according to an embodiment of the invention. The magnetic resonance imaging system comprises a magnetic resonance imaging magnet assembly according to an embodiment of the invention. The magnet assembly comprises a magnet  102  and a gradient coil  103 . As was explained before the gradient coil comprises a first gradient coil section  112  and a second gradient coil section  114  that is joined by a connecting element  116 . The gradient coil  103  is mounted in the magnet  102  using elastic mounts  126 . In other embodiments the ends of the gradient coil  103  may be mounted to the magnet  102  using rigid mounts. However, elastic mounts  126  have the advantage that they provide vibration isolation between the gradient coil  103  and the magnet  102 . 
     The magnet  102  has an imaging zone  504 . Within the imaging zone  504  the magnetic resonance imaging system  500  can acquire magnetic resonance data  536 . A subject  502  is shown partially within the imaging zone  504  and the subject  502  is supported by a subject support  506 . The gradient coil  103  is connected to a gradient coil power supply  508  which supplies current to the gradient coil  103 . In this example the first gradient coil section  112  and the second gradient coil section  114  are connected separately to the gradient coil power supply  508 . The first and second gradient coil sections may also be supplied independently with a cooling fluid such as water. Alternatively the first and second gradient coil sections may be supplied by a single good cooling system. 
     The magnetic resonance imaging system  500  also comprises a radio frequency transceiver  510  which is connected to an antenna  512 . The combination of the radio frequency transceiver  510  and the antenna  512  allows the manipulation or the orientation of magnetic spins within the imaging zone  504 . The radio frequency transceiver  510  and the antenna  512  also allow the reception of magnetic resonance signals from within the imaging zone  504  also. 
     The gradient coil power supply  508  and the radio frequency transceiver  510  are connected to the hardware interface  516  of a computer system  514 . Through the hardware interface  516  the computer system  514  is able to record the magnetic resonance symbols as magnetic resonance data  536 . The computer system further comprises a microprocessor  520  which is connected to the hardware interface  516 , computer storage  518 , computer memory  522  and a user interface  524 . The storage may be for example a hard drive. The memory  522  may be random access memory. The user interface  524  is an interface which a user uses to interact with the computer system  514 . This interface may comprise such things as a display unit such as a computer display. It may also contain input devices such as a mouse, keyboard, or touch pad. 
     The computer storage  518  contains a program for the execution of software for controlling the magnetic resonance imaging system  500 . The storage  518  further contains a magnetic resonance image  534 . This image  534  may be rendered on a display of the user interface  524 . Also within the storage  518  is magnetic resonance data  536  which was acquired by the magnetic resonance imaging system  500 . The memory  522  contains a copy of the program  532 . The program  532  in memory is labeled as  526 . The program  526  contains a module  528  for controlling the operation of the magnetic resonance imaging system. The program  526  also contains a module  530  for performing image reconstruction. This is the reconstruction of magnetic resonance data  536  into a magnetic resonance image  534 . While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
     Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope. 
     LIST OF REFERENCE NUMERALS 
     
         
           100  magnetic resonance imaging magnet assembly 
           102  magnet 
           103  gradient coil 
           104  axis of symmetry 
           106  cryostat 
           108  vacuum 
           110  superconducting coils 
           110 ′ inner coils of magnet 
           110 ″ outer coils of magnet 
           112  first gradient coil section 
           113  first rigid element 
           114  second gradient coil section 
           115  second rigid element 
           116  connecting element 
           116 ′ connecting element 
           118  outer windings 
           120  inner windings 
           122  bus bar 
           124  flange conductor 
           126  elastic mount 
           200  windings of magnet assembly 
           202  flange conductor 
           204  flange conductor 
           206  flange conductor 
           208  location of rigid element 
           210  axis of rotational symmetry 
           300  overlapping lap joint 
           302  tongue in groove lap joint 
           304  lap joint 
           306  connecting cylinder 
           400  compression joint 
           402  bolt 
           404  nut 
           406  vibration isolation elements 
           500  magnetic resonance imaging system 
           502  subject 
           504  imaging zone 
           506  subject support 
           508  gradient coil power supply 
           510  radio frequency transceiver 
           512  antenna 
           514  computer system 
           516  hardware interface 
           518  storage 
           520  processor 
           522  memory 
           524  user interface 
           526  program 
           528  control module 
           530  image reconstruction module 
           532  program 
           534  magnetic resonance image 
           536  magnetic resonance data