The invention further relates to a medical imaging system comprising an MRI magnet system.

An MRI magnet system as well as a medical imaging system comprising an MRI magnet system of the types mentioned in the opening paragraphs are known from international patent application WO-A1-03/050555 Al. In this patent application an MRI magnet system of the open type is described. The functional lines for supplying electrical energy as well as cooling water to the two gradient coil units are indicated simply as individual electrical cables and cooling channels extending through a central passage. During installation of such an MRI magnet system however one is faced with practical problems regarding these functional lines. More specifically during installation the gradient coil unit is placed within a recess of the associated main coil unit. This means that the lower gradient coil unit is lowered whereas the upper gradient coil unit is lifted in the respective recesses.

The practical problems apply especially to the installation of the lower gradient coil unit from which the lines, which are quite lengthy and of limited flexibility which makes them hard to handle in general, should extend through the central passage and underneath the main coil unit to the outside of the main coil unit in order to be able to functionally connect the electrical cables and cooling channels to electrical power supply and cooling water supply respectively. Due to these problems also de-installation of the gradient coil unit from the remaining part of the MRI magnet system is usually hard to perform, meaning that maintenance to the gradient coil unit usually takes place when the gradient coil unit is in its functional position and that a gradient coil unit may not be readily replaced. In this respect reference also is made to WO-A1-03/023433 which describes a Nuclear Magnetic Resonance

(NMR) system having a coolant vessel of a cryostat within an outer vacuum vessel. The outer vessel is detachable from the rest of the cryostat without the need to purge the coolant vessel.

This allows the gradient coils to be serviced or changed as necessary without the need to purge the remainder of the cryostat, yet requires the separate disconnecting (and later on separate connecting) of the coolant line for the gradient coils on top of the MRI system.

The main object of the invention is to make installation of an MRI magnet system, more specifically the assembling of the main coil unit and the associated gradient coil unit, easier resulting in less time being necessary for the installation of an MRI magnet system.

Another object of the invention is to make the gradient coil unit easily removable from the remaining part of the MRI magnet system and/or replaceable with another gradient coil unit, especially for maintenance purposes.

In order to achieve these objects, a magnetic resonance imaging (MRI) magnet system in accordance with the invention is characterized in that the functional line comprises at least one male type connecting member and at least one female type connecting member, a first of said connecting members being mounted in a first fixed position relative to the main coil unit and a second of said connecting members being mounted in a second fixed position relative to the gradient coil unit, said first position and second position being such that, in the assembled position of the main coil unit and the gradient coil unit, the first and second connecting member engage with each other.

In order to achieve these objects, a medical imaging system according to the invention is characterized in that the MRI magnet system used therein is an MRI magnet system in accordance with the invention.

Due to these characterizing features, the installation of an MRI magnet system can take place much easier and quicker than is the case with a MRI magnet system according to the prior art since there is no need anymore to guide any cables or channels during the assembling of the main coil system and the associated gradient coil system, since before this assembling all cables or channels can be put in place and during the assembling of the main coil system and the gradient coil system, the male type connecting member and the female type connecting member will interact by engaging with each other in order to establish the necessary functional connection.

Although the above advantages could apply to all types of MRI magnet systems, they apply in particular to MRI magnet systems of the open type. For this reason the MRI magnet system according to the invention preferably is of the open type having a central axis, two essentially toroidal-shaped, spaced main coil units coaxial with the central axis and defining therebetween an imaging volume, and for each main coil unit a gradient coil unit coaxial with the associated main coil unit and located between the associated main coil unit and the imaging volume.

Preferably the main coil unit comprises a first intermediate body which interconnects a remaining portion of the main coil unit and the associated gradient coil unit and comprises the first connecting member. By making use of a first intermediate body, the remaining portion of the main coil unit can be embodied more or less like conventional main coil units. This prevents the need of a drastic redesign of conventional main coil units in order to make them suitable for the present invention.

In order to prevent or at least limit the transfer of disturbing sound causing vibrations between the main coil unit and the gradient coil unit, the first intermediate body preferably is resiliently mounted to the remaining portion of the main coil unit.

According to another preferred embodiment, the gradient coil unit comprises a second intermediate body which interconnects a remaining portion of the gradient coil unit and the associated main coil unit and comprises the second connecting member. This results in a similar advantage as is achieved with the above indicated preferred embodiment in which the main coil unit comprises the first intermediate body. By using the second intermediate body, the remaining portion of the gradient coil unit can be embodied more or less similar to gradient coil units according to the prior art.

Preferably the second intermediate body is rigidly mounted to the remaining portion of the gradient coil unit. In this way a correct relative positioning between the gradient coil unit and the main coil unit can be achieved.

In embodiments of an MRI magnet system of the open type, each main coil unit preferably comprises a first intermediate body, which interconnects a remaining portion of the respective main coil unit and the associated gradient coil unit and comprises the first connecting member, and each main coil unit further comprises a housing having a central passage coaxial with the central axis, said first intermediate body being arranged in the central passage of the housing of the respective main coil unit. The presence of said central passage allows the accommodation of different elements, such as the first intermediate body, within this central passage. In this way, the available space is efficiently used without using

space between the two main coil units, which space should be available for a patient as much as possible.

In the following, preferred embodiments of an MRI magnet system in accordance with the invention will be described in detail, by way of example only and not intended to limit the scope of the present invention, with reference to the accompanying drawings in which: Fig. 1 is a schematic vertical cross section of the lower half of an MRI magnet system of the open type in accordance with the invention; Fig. 2 is a partially exploded view of the MRI magnet system of Fig. 1 ; Fig. 3 is a fully exploded view of the MRI magnet system of Fig. 1 ; Fig. 4 is a detailed perspective view, partly broken away, of a cylindrical intermediate body to be used with an MRI magnet system according to the invention; Fig. 5 is a detailed perspective view, partly broken away, of the cylindrical intermediate body according to Fig. 4 in combination with part of the gradient coil unit of the MRI magnet system.

Figs. 1,2 and 3 schematically show in vertical cross section the lower substantially disc-shaped half 1 of an MRI magnet system of the open type in fully assembled condition, partially exploded condition and fully exploded condition, respectively. Such an MRI magnet system comprises, in its complete condition, another half spaced above half 1 and having in between the two halves an imaging volume. The two halves, which face each other, are connected with each other by a column on a circumferential position of the two halves.

Half 1 comprises a main coil unit 2 comprising a trunk section 4, a gradient coil unit 3 and an RF coil unit 5. The main coil unit 2 comprises a substantially toroidal- shaped housing 6 having a central cylindrical passage 7. Within the housing 6, a main coil (not shown) is present which is cooled to cryogenic temperatures by immersing the main coil in a cryogenic fluid. The gradient coil unit 3 is essentially conical-shaped, although alternatively it could have another shape like a disc-shape.

At its upper side, half 1 is provided with a recess 8 shaped in correspondence with the gradient coil unit 3 so as to allow the gradient coil unit 3 to be totally inserted in the

recess 8. On top of the gradient coil unit 3, in the fully assembled state according to Fig. 1, the RF coil unit 5 is present, which is essentially disc-shaped and the upper surface 9 of which is aligned with the upper surface 10 of the main coil unit 2, whereas the lower surface 11 of the RF coil unit 5 sits in close proximity to (yet without contacting) the upper surface 12 of the gradient coil unit 3 by mechanically connecting the RF coil unit 5 at its circumference to the housing 6 of the main coil unit 2.

Within the context of the present invention it is superfluous to elaborate in detail on the technical functionality of the different coils, having in mind that this knowledge is already very well known to persons skilled in the art.

Trunk section 4 is cylindrical and is mainly made of stainless steel and serves as a first intermediate body between a remaining portion of the main coil unit 2 and the gradient coil unit 3, which are consequently not directly connected. During installation, first of all trunk section 4 is removably mounted within the central passage 7. To this end, at the upper end and the lower end of the central passage 7, an upper flexible annular mount 13 and a lower flexible annular mount 14 are respectively bonded to the housing 6. The trunk section 4 is mounted to the annular mounts 13,14 using radial bolts (not shown) from inside to out.

The trunk section 4 comprises at its upper end a central mounting pillar 15 partly protruding from the central passage 7 in the recess 8 of the main coil unit 2. On top of the mounting pillar 15, a central hole 20 is present having an internal screw thread. Around the base of the mounting pillar 15, a tube-shaped cavity 21 is located within which the trunk section 4 comprises, within the height of central passage 7, first functional connecting members, in the embodiment shown plugs 18, which are mounted in first fixed positions relative to the main coil unit 2 when the trunk section 4 is mounted to the remaining portion of the main coil unit 2. Such plugs 18 could be used for the provision of electrical energy and/or cooling water to the gradient coil unit 3, both electrical energy and cooling water being necessary in order for the gradient coil unit 3 to function. Plugs 18 are connected to functional connections 23 which connect plugs 18 to appropriate functional sources in the main coil unit 2 or outside the MRI magnet system.

The gradient coil unit 3 has at its lower side an integrated central stump 16.

Central stump 16 is made from stainless steel and serves as a second intermediate body between a remaining portion of the gradient coil unit 3 and the main coil unit 2. The stump 16 partly extends in the body of the gradient coil unit 3 and is connected to horizontally oriented anchor ribs 17 for fixing the stump 16 internally to the gradient coil unit 3. Centrally within stump 16, a central passage 22 is provided which is closed at its top. Due to said

passage 22 the stump 16 has at its lower end 24 an essentially tube-shaped appearance. The length and the diameter of passage 22 correspond to the length and the diameter of mounting pillar 15. At radially outward positions with respect to the passage 22, corresponding to the positions of the first functional connecting members or plugs 18, stump 16 is provided with second functional connecting members, in the embodiment shown downwardly open sockets 19, which are mounted in second fixed positions relative to the gradient coil unit 3 as the stump 16 is in a fixed position relative to the gradient coil unit 3.

By lowering gradient coil unit 3, starting from the situation shown in Fig. 2, onto the trunk section 4, first of all mounting pillar 15 of trunk section 4 will start extending into passage 22 of gradient coil unit 3. Further lowering will result in the tightly fitting extension of the lower tube-shaped part 24 of stump 16 within the tube-shaped cavity 21 of the trunk section 4 as well as in the interengaging of plugs 18 and sockets 19. Finally gradient coil unit 3 will be bolted to the trunk section 4 by mounting bolt 25 cooperating with the screw thread of hole 20 and the RF coil unit will be mounted on top of the gradient coil unit 3.

As will be clear to the person skilled in the art, the installation of the gradient coil unit 3 as described above will automatically result in the establishment of the necessary functional connections between the gradient coil unit 3 and the appropriate functional sources in the main coil unit 2 or outside the MRI magnet system. This is the result of the fact that said first fixed positions of the plugs 18 relative to the main coil unit 2 and said second fixed positions of the sockets 19 relative to the gradient coil unit 3 are such that, in the assembled position of the main coil unit 2 and the gradient coil unit 3, the plugs 18 and the sockets 19 engage with each other.

Fig. 4 shows an alternative embodiment for a first intermediate body 30 which can be used instead of the trunk section 4 in the embodiments of Figs. 1,2 and 3. The housing of the main coil unit of the MRI magnet system to be used in combination with this intermediate body 30 comprises a central passage like the central passage 7 in Figs. 1, 2 and 3, having at its upper and lower end, inwardly projecting flanges 31 and 32 respectively.

Within the central passage, a tube-like member 33 is mounted. Tube-like member 33 consists of two sub tube parts 33a and 33b. These parts 33a and 33b are interconnected by bolts (not shown) extending through inwardly projecting flanges 34a, 34b being located at the lower end of part 33a and at the upper end of part 33b, respectively. At the upper end of part 33a and at the lower end of part 34a, tube-like member 33 comprises outwardly projecting flanges 35a, 35b on the outside of flanges 31,32, respectively. In between flange 31 and

flange 35a, on the one hand, and flange 32 and flange 35b, on the other hand, a resilient sealing ring 37,38 is enclosed.

A disc-shaped plate 39 is mounted against the lower side surface of flange 34b. At the upper side of plate 39 six upwardly extending first connecting members, in the embodiment shown electrical plugs 40, are present at radial outside positions of the plate 39.

At the locations of these plugs 40, the flange 34a, 34b is interrupted. Underneath the plate 39, second connecting members, in the embodiment shown electrical connection elements 41, are mounted to the plate 39, and are electrically connected with associated plugs 40 and adapted to be electrically connected to electrical cables (not shown). Underneath the connection elements 41, a ring 42 is located which is mechanically coupled to plate 39 via bars 44. Ring 42 is provided with holes 43 at positions corresponding with the positions of connection elements 41 for guidance of electrical cables connected to the connection elements 41 on one end and to an appropriate electrical power source on the other end.

Fig. 5 shows the intermediate body 30 in combination with a gradient coil unit 50 having a conical main part 51 and a cylindrical trunk 52 underneath this main part 51. The outer diameter of the trunk 52 corresponds to the inner diameter of tube part 33a, such that trunk 52 closely fits therein. Trunk 52 is provided with sockets 53 at positions corresponding with the positions of plugs 40. By lowering the gradient coil unit 50 upon the intermediate part 30 during installation of the MRI magnet system in question, not only a correct positioning of the gradient coil unit 50 with respect to the intermediate part 30 and consequently with respect to the main coil unit will take place, but also a proper electrical connection will be made between an electrical source outside the MRI magnet system and the gradient coil unit 51.