JP2706631B2 - Open access magnetic resonance imaging system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus (MRI apparatus) which has easy access to a patient and has at least two open sides so that radiotherapy can be easily performed. More specifically, the present invention relates to an MRI apparatus using superconducting coils for generating opposing parallel end plates and a uniform strong magnetic flux field.

[0002]

BACKGROUND OF THE INVENTION In medical diagnosis, nuclear magnetic resonance (NM)
R) or Magnetic Resonance Imaging (MRI) requires the generation of a very strong static main magnetic field that passes through the patient's body.
A time-varying magnetic field is superimposed on the first or main magnetic field. In addition, patients are exposed to RF electromagnetic waves that vary in time and in a particular pattern. Under the influence of magnetic and RF waves, it is observed that the nuclear spins of the nuclei are distributed. According to this method, it is possible to examine whether there is a tumor in a soft tissue and a tract of a body.

[0003] In MRI, the magnetic field must be a strong magnetic field, typically on the order of about 1 kilogauss or more. Magnetic fields in excess of 10 kilogauss (1 Tesla) are sometimes required. In addition, the magnetic field must be uniform and the non-uniformity must not exceed 100 ppm. Furthermore, this uniformity must cover the majority of the patient, and preferably has a diameter sphere volume (DSV) on the order of about 0.3-0.5 m.

[0004] In the past, these strong magnetic fields have been generated using permanent magnets, resistive magnets or superconducting magnets. Permanent magnets are typically the least expensive, require the least space, and have the lowest maintenance costs because they do not require liquid refrigerant. Permanent magnets, however, have limited magnetic field strength, are subject to instability over time, are extremely heavy, and are expensive for magnetic forces exceeding 0.20 Tesla. Resistance magnets are also relatively inexpensive, but supply of power and water is cumbersome and costly. In addition, the strength of resistive magnets is limited, often producing undesirable fringe fields and becoming unstable over time. The superconducting solenoid magnet has a strong magnetic field, is uniform, and has good stability over time. However, current superconducting solenoid magnets are expensive to manufacture and require cumbersome liquid cooling support systems. Regarding the structure of medical MRI magnet,
Generally, two different shapes or structural examples are used. One type of support structure is known in the art as an open access structure. Such structures typically include opposing parallel magnetic pole faces mounted on opposing parallel support plates. At least one, usually four, columns support the support plate and provide a return path for magnetic flux. Such an open structure is preferred by the patient because it is open and accessible from four sides. In such a configuration, the magnetic flux lines generally pass substantially orthogonal to the patient's longitudinal (ie, head-to-toe) axis.

[0005] Another type of MRI magnet that does not have opposing magnetic pole faces or has an open access structure resembles a large conventional solenoid. The solenoid structure has a generally cylindrical shape, and an electrically conductive wire is spirally wound. The magnetic flux lines are generated by the current passing through the wire,
The magnetic flux lines travel through the central opening of the cylinder substantially parallel to the longitudinal axis of the patient. It is known that such enclosed solenoid structures can impart claustrophobia to patients.

[0006] Different types of magnet systems have been proposed for use with each of these structures. In the past, apertured access structures typically consisted of mounting permanent magnets on opposing pole faces. For example, Breneman
U.S. Pat. No. 4,943,774 discloses such an apertured access MRI structure utilizing permanent magnets. The support structure is made from a ferromagnetic material such as high performance structural steel.

A superconducting magnet can be formed in the enclosed solenoid type structure. Such superconducting magnets must be cooled to a temperature near absolute zero (-273 ° C.) so that the wound wire loses resistance to current flow. Thus, a relatively small diameter wire carries a large current and can induce a high magnetic field. The superconducting wire is typically wrapped around the circumference of a cylindrical structure enclosed in a cryocontainer. Such an enclosed solenoid type structure may employ a pair of main superconducting coils and one or more auxiliary coils. Iron or other ferromagnetic material can be mounted in the patient storage opening as a shim to adjust the shape of the magnetic field. These measures are required to induce a uniform magnetic field having magnetic flux lines that are substantially parallel to each other and extend through the patient's body.

[0008] Another type of enclosure is Danby.
No. 4,766,378. In one embodiment of this patent, parallel opposing pole faces are mounted on opposing parallel circular support plates. A substantially continuous support frame is disposed between the support plates and provides a return path for the support members and magnetic flux to the pole faces. The enclosed patient storage space is located between the pole faces formed by the openings in the support frame. To generate a magnetic field, a superconducting wire is wound around each pole face and enclosed in a cryocontainer. The continuous support frame is generally circular in shape and forms the magnetic field so as to induce a uniform magnetic field within the enclosed patient area. This structure is similar to an open access MRI magnet in that the magnetic flux lines pass substantially perpendicular to the patient's body. However,
The problem with this type of structure is that the patient's feeling of confinement is more pronounced than with a solenoid type structure. In addition, the structure can be bulky and relatively heavy, and the placement itself can be difficult in a regular hospital without significant changes in location. A further disadvantage is that there is no access for additional medical personnel to perform intermittent radiation therapy.

[0009] The present invention uses a superconducting magnet,
It is an object of the invention to propose an open access MRI magnet system which produces a magnetic field of uniform intensity without the use of a heavy and confining support frame and without supplying a liquid refrigerant to the system. In addition, the open access frames can be used to provide accessibility to intermittent radiation therapy.
Accordingly, one object of the present invention is to provide an open access MR.
It is an object of the present invention to provide an open access MRI magnet having a uniform magnetic flux field generated by a superconducting magnet cooled without using a liquid refrigerant as an I magnet. Another object of the present invention is an open access MRI magnet, which is open to intermittent radiation therapy and has a structure that is not confined to a patient.
An object of the present invention is to provide an open access MRI magnet capable of generating a strong magnetic flux field on the order of 0.5 Tesla. Another object of the present invention is to provide an MR that is simple and inexpensive to install, build and operate.
To provide an I magnet.

[0010]

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an open access superconducting MRI magnet. The MRI magnet includes one or more superconducting coil assemblies for generating a magnetic flux field and a pair of opposed spaced apart supports for supporting the superconducting coil assemblies and providing a return path for the flow of magnetic flux. End plates and posts connecting the end plates. A patient storage area is formed between the end plate and the superconducting coil assembly, the superconducting coil assembly generating a magnetic flux field parallel to a polar axis substantially orthogonal to the end plate and the patient. I have. The end plates, in combination with the loose shims attached to them, provide homogeneity for magnetic flux lines in the patient storage area. In this regard, the end plates serve the same function as the pole faces used in prior art permanent magnets.

In a preferred embodiment, a superconducting coil assembly is associated with each end plate. The superconducting coil assembly includes a toroidal vacuum-tight container, insulation means, and one or more temperature shield members mounted within the vacuum container. A coil of superconducting wire is mounted within the thermal shield and is connected to a controller that includes a power source and a continuation switch for generating a continuous current path in the superconducting wire. The coil of superconducting wire, the heat shield member and the continuation switch are cooled by a combination of conduction and convection by contact with a heat conductor or by contact with helium gas piping. 2 cooling sources
It is a stepped type Gifford McMahon type cryocooler. The cryocooler cools the gas just before it circulates around the superconducting winding.

The end plates and struts provide a return path for the magnetic flux generated by the superconducting coil assembly. The magnetic flux field is between 0.20 and
It can be configured to provide a diameter sphere volume (DSV) having a substantially uniform and strong magnetic field in the range of 0.5 Tesla. In addition, access to the patient storage area is substantially open, and the patient has access to multiple medical personnel and additional equipment.
The open access frame is less restrictive for the patient and provides easier access when performing intermittent radiation therapy.

[0013]

1 and 2, there is shown a freely accessible (open access) superconducting MRI magnet apparatus constructed in accordance with the present invention and designated generally by the numeral 10. Superconducting magnet device 1
0 includes an open access frame 16 for supporting an upper superconducting coil assembly 18 and a lower superconducting coil assembly 20.

The open access frame 16 is formed from a ferromagnetic material that can be easily magnetized (ie, magnetically soft). The preferred material for frame 16 is low carbon steel. Open access frame 16
Are upper end plates 22 for supporting the upper and lower superconducting coil assemblies 18 and 20, respectively.
And a lower end plate 24. Each of the upper end plate 22 and the lower end plate 24 may have a generally rectangular or square outer peripheral profile. The upper end plate 22 and the lower end plate 24 are parallel to each other and are generally perpendicular to a vertical polar axis 26 passing through the center of the open access frame 16.

The open access frame 16 also includes four columns 28a, 28b, 28 fixedly attached to the upper end plate 22 and the lower end plate 24.
c, 28d. Alternatively, the open access frame 16 can be formed with a smaller number of struts (1-3). The patient storage area 12 is defined by an upper end plate 22 and a lower end plate 24 and four columns 28a, 28b, 28c, 28d. The columns 28a, 28b, 28c, 28d have a cylindrical shape as a whole, and are arranged in a rectangular pattern parallel to each other. Prop 28a, 28b, 28
c, 28d are located sufficiently far from each other so that the patient can access from each of the four sides of the strut frame 16. By way of example, as shown in phantom in FIG. 1, the patient support device 30 can be positioned between any two struts to place the patient in a reclined position between the superconducting coil assemblies 18,20. It is possible to support. Such a structure also allows access to apply radiation intermittently from different sides of the patient support device 30.

The struts 28a, 28b, 28c, 28d not only serve to support the end plates 22, 24, but also provide a return path for the magnetic flux generated by the superconducting coil assemblies 18, 20. ing. As shown in FIG. 2, a stepped structure can be formed in the end plates 22 and 24 to effectively bridge the return path of the magnetic flux without substantial magnetic flux leakage. In addition, as shown in FIG.
The columns 28a, 28b, 28c, 28d are (Brenem
transition plates 92, 94 similar to those described in U.S. Pat. No. 4,943,774) to connect to the upper end plate 22 or the lower end plate 24. .

Referring to FIG. 3, each of the superconducting coil assemblies 18 and 20 includes an annular vacuum-tight container 32 formed of a non-magnetic material, and one or more superconducting superconducting members mounted in the container. A coil of wire 36 is included. Further, a sustain switch 38 is electrically connected to the superconducting wire 36. In such superconducting coil assemblies 18, 20, the coil of superconducting wire 36 can be cooled to a temperature close to zero absolute temperature, at which point resistance to current is substantially zero.

The vacuum-tight container 32 for each superconducting coil assembly 18, 20 is toroidal in overall shape, and is mounted on mounting block 42 or other suitable mounting means on upper support plate 22 or lower support plate 22, respectively. It is mounted on the side support plate 24. Each vacuum vessel 32 is adapted to be permanently evacuated by a suitable vacuum source such as a vacuum pump (not shown). A suitable material for the vacuum vessel 32 is aluminum or stainless steel. In addition to being vacuum tight, each vacuum vessel 32 is insulated by a super-insulating agent (aluminized mylar) or the like. One or more metal temperature shields 44 can also be mounted within the vacuum vessel 32 as additional thermal barriers. Vacuum vessel 32 may be formed with a sealed top plate 46 that provides access to coil leads and instruments located therein.

The temperature shield 4 is provided on the support strap 96.
4 can be installed. Such a support strap is shown schematically in FIG. 3, which is cited for its construction (RL Creedon).
And similar to those disclosed in U.S. Pat. No. 4,622,824.

Each continuous coil of superconducting wire 36 is helically wound within toroidal container 32. The coil of superconducting wire 36 can be formed from a material such as a low or high temperature superconductor that exhibits superconductivity below the superconducting transition temperature. For low-temperature superconductors,
This transition temperature is about 8K. For high-temperature superconductors, the temperature is about 60K. By way of example, one suitable low temperature superconductor is copper with niobium titanium fibers in the wire. One suitable high temperature superconductor is YBCO. Alternatively, any material suitable for superconductivity can be utilized in this application, as long as the coil is provided with the proper operating temperature.

The coil of superconducting wire 36 is formed with a longitudinal axis, which is designated as a vertical polar axis 26. Further, each coil of superconducting wire 36 lies in a plane substantially parallel to the plane of upper end plate 22 and the plane of lower end plate 24. Superconducting coil assembly 1
8, 20 are also electrically connected to the continuation switch 38. Referring to FIG. 6 and FIG.
Are the external power lead 108 and the superconducting power lead 1
The power supply 10 is electrically connected to a DC power supply 70. The outer leads 108 are made from typical copper conductors, while the superconducting leads 110 can be made from a superconducting material with a high transition temperature. External lead wire 10
8 and the superconducting lead 110 can be joined at a joining point 132. A continuous switch 38 is configured to maintain a continuous current flow in the superconducting wire 36 coils of the upper and lower superconducting coil assemblies 18, 20 without continually consuming power from the DC power supply 70. A physically smaller non-inductive superconducting coil comprises a superconducting wire 36 comprising a main coil and a superconducting lead 1.
Junction points 134, 136, 138 and 14 for 10
0 is connected. Continue switch 38 is in thermal contact with heating element 74, which is connected to lead 142
And has its own DC power supply 76. When the heating element 74 is energized, it causes the continuation switch 38 to rise above its transition temperature, so that the switch 38 functions as an open switch. Heating element 74
Is de-energized, the continuation switch 38 drops below its transition temperature and thus functions as a close switch. As will be apparent to those skilled in the art, once a current is induced in the main coil of superconducting wire 36, a continuous switch 38
Even if is closed, a continuous current flow can be maintained without consuming any power.

Referring again to FIG. 2, energizing the coil of superconducting wire 36 on the upper and lower superconducting coil assemblies 18, 20 causes the upper and lower end plates 22,
A magnetic flux field is generated which is emitted substantially perpendicular to the plane of 24.
The return of the magnetic flux is provided by the upper and lower end plates 22, 24 and the struts 28a, 28b, 28c, 28d. The magnetic flux field created by the superconducting wire 36 provides a substantially uniform magnetic field within the true spherical volume (DSV) 54. The center of the DSV 54 is located in the middle of the upper and lower superconducting coil assemblies 18 and 20 and is 0.3 to
Preferably it has a diameter of 0.5 m.

In order to generate a magnetic field with magnetic flux lines that are substantially parallel to the perpendicular polar axis 26 and extend in the DSV section so as to be parallel to each other, these magnetic flux lines are formed in such a shape. There is a need to. Thus, the magnetic flux forming device includes an upper rose shim 64 and a lower rose shim 66 fixedly mounted on the upper end plate 22 and the lower end plate 24, respectively. The rose shim 64,
66 is generally made from a ferromagnetic material. The loose shims 64, 66 can be, but are not limited to, flat to cylindrical. Thus rose-shaped shim 6
4, 66 are formed like washers having an inner diameter portion and an outer diameter portion. The dimensions of the inner diameter of the rose shims 64, 66 can be as required to provide a magnetic field with the desired characteristics. Further, as shown in FIG. 2, the shims 64, 66 may be formed with transition plates 98, 100 stacked to further impart a magnetic field shape.

A schematic representation of a typical magnetic flux field generated by an MRI superconducting magnet is shown in FIG. Such a magnetic field feature is characterized by a DS located within the patient storage area 12.
This means that the magnetic flux lines are parallel lines in V54. Further, FIG. 7 illustrates the operation when the loose shims 64 and 66 form the magnetic flux lines. 7 illustrates the operation of a typical post 28b and the operation of the upper end plate 22 in bridging the return flux flow.

An alternative embodiment of an MRI magnet having a two-post open access frame is shown in FIGS. 4 and 5 and designated by reference numeral 78. Two pillars M
The RI magnet device 78 is substantially similar in structure to the four-post open access MRI magnet device 10 described above, only the structure of the support frame 80 is different. The support frame 80 includes an upper end plate 82 for an upper superconducting coil assembly 86 and a lower end plate 84 for a lower superconducting coil assembly 88. Patient access into the two-post MRI magnet device 78 is provided from two sides.

FIG. 8 illustrates an embodiment of a preferred apparatus used to cool various components of apparatus 10 in accordance with the present invention. The present invention does not consume liquid coolant,
This involves lowering the components to the required temperature by the cryocooler 100. The cryocooler 100 is preferably a multi-stage cryocooler capable of gradually achieving a low temperature, for example, Gifford-McMahon.
Type two-stage cryocooler has its first or main stage 1
A temperature of about 40K can be achieved at 02 and a temperature of about 4K at the second or sub-stage 104 thereof. The cooling capacity of the cryocooler 100 at these temperatures is about 30 watts in the main stage and 0.5 watts in the sub stage. The cryocooler 100 has its cooling station in a vacuum vessel 32. As shown, the vacuum vessel is in the form of an upper torus section and a lower torus section connected by a passage section. FIG. 8 schematically shows the entire vacuum vessel, and FIG. 9 shows only one side of the upper and lower sections for simplicity.

In the embodiment of FIG. 8, the components of the apparatus 10 are cooled by complete conduction by making thermal conductive contact with a plurality of solid thermal conductors connected to the cryocooler 100. These solid thermal conductors can take the form of cables, bars or other solid shapes. Specifically, a copper bar or plate 106 is fastened in thermal conductive contact with second stage 104 of cryocooler 100. A thermally conductive cable 112, shown as a branch cable, is fastened in thermal contact with the first stage 102 of the cryocooler at point 118. Thermally conductive cable 114, again shown as a branch cable, has a cryocooler 1 at point 124.
The second stage 104 is in thermal conductive contact with the second stage 104. Finally, the heat conductive cable 116 is fastened to make a heat conductive contact with the first stage 102 of the cryocooler 100 at point 130.

The continuation switch 38 is mounted on the copper plate 106. Connection points 134, 136, 138, 140
Is also mounted on the copper plate 106 in order to keep the junctions at the lowest possible temperature and to minimize the current decay caused by resistance at these junctions. Thermally conductive cable 112 is connected to points 120 and 122
Are mounted in thermal conductive contact with a heat shield 44, which surrounds the upper and lower superconducting coils 18, 20 and maintains itself at a temperature of about 40K. Alternatively, cable 112 may be heat shield 4
4 can be coated around. As the thermally conductive cable 114 is shown schematically at points 126 and 128, the upper and lower superconducting coils 18, 2
0 and are mounted in thermal conduction contact on the periphery of the upper and lower superconducting coils 18, 20.
Is maintained at a temperature of or near 4K. Ideally, the cable 114 should pass twice around each superconducting coil 18,20. Finally, the heat conductive cable 11
6 is fastened in thermal conductive contact with superconducting power lead 110 to maintain the lead below 50K.

FIG. 9 shows a second embodiment of the present invention. In this embodiment, the upper and lower superconducting coils 1 are provided.
The cooling of 8, 20 is performed by combining conduction and convection using a cooling circuit consisting of a pipe 170 for pumping a fluid such as helium gas into the pipe 170. The cooling fluid passes through the counter-flow heat exchanger 144 and also around the main stage 102 and sub-stage 104 of the cryocooler 100 to bring the temperature of the fluid,
The temperature is lowered to about 4K, which is lower than the transition temperature of the upper and lower superconducting coils 18 and 20. Heat exchanger 1
44 is arranged in the vacuum vessel 32. More specifically, a cooling fluid in the form of a gas is pumped by a compressor (not shown) into an inlet 146 of a heat exchanger 144, the nominal temperature of which is about 300K at point 154. And the nominal pressure is about 20 atmospheres.

The incoming fluid then passes to the first section 15
0, where the inlet pipe is in thermal contact with the outlet pipe, causing the temperature of the incoming fluid to drop to about 45K at point 156. The first section of the heat exchanger 144 can be made of stainless steel. The incoming fluid then circulates through the heat exchanger 144 and exits, after which the cryocooler 100
Passing around the main stage 102 of the
At about 40K. Here, the fluid is returned to the second section 152 of the heat exchanger 144. The second section 152 of the heat exchanger 144 may be copper or stainless steel tubing, but this second section also places the inlet pipe in thermal conductive contact with the outlet pipe and directs the incoming fluid at point 160 to about 4.5K. Temperature.

The cooling fluid is then conveyed by piping 170 past the sub-stage 104 of the cryocooler 144, reducing its temperature to about 4K, and then conveyed around the upper superconducting coil 18. You. The tubing 170 is shown schematically wound around the coil 18. Since the pipe 170 is in thermal conductive contact with the coil 18, the temperature of the fluid is raised to about 4.5K. Piping 170 then returns again to pass around sub-stage 104 and the temperature is reduced to about 4K, after which piping 170 passes around lower superconducting coil 20 and at point 162 heat exchanger 144 Return to.

At the return point 162, the effluent is at about 4.5K before it passes through the second section 152 of the heat exchanger 144, causing the second section 152 to reach point 1
Flow out at about 40K at 64. Finally, the effluent enters the first section 150 of the heat exchanger 144 at about 455K at point 166 and exits the first section 150 at 168 at a nominal temperature of about 300K. From the outlet 148, the fluid returns to the compressor via a needle valve as a gas at a nominal pressure of about 2 atmospheres. Cooling of the other cooled components of the device is achieved by conduction only by using a solid thermal conductor as described above.

In order to operate the MRI superconducting magnet device 10, the upper and lower superconducting coil assemblies 18, 20
Is cooled and maintained at a temperature of about 4K. A current flow is then generated by energizing the DC power supply 70 through the coil of superconducting wire 36. Once the current has flowed out and stabilized, the continuation switch assembly 38 is closed and a continuous current flow is achieved without consuming power in the coil of superconducting wire 36 as described above. When a current flows through the superconducting wire 36, a magnetic flux field is induced. The magnetic flux field is formed by rose shims 64, 66 such that the magnetic flux lines are substantially parallel to one another in DSV 54. About 21 in the coil of the superconducting wire 36
With a typical capacitance value of 8,000 amp turns, a magnetic flux field in the range of about 0.35 Tesla is generated. For the disclosed MRI superconducting magnet device 10, a magnetic flux field in the range of 0.20 to 0.50 Tesla is preferred.

A return path for the magnetic flux field generated by the current in the coil of superconducting wire 36 is provided by open access frame 16. The return path is supported by the columns 28a, 28b, 2 of the open access frame 16.
8c, 28d and upper and lower end plates 2
2 and 24.

In operation, the patient storage area 12 is accessible from four sides. Thus, additional medical equipment and personnel can be accessed for the patient. Medical techniques that require such accessibility, such as interference radiotherapy, are therefore easier to implement than conventional MRI magnet devices that are substantially blocked.

Thus, the present invention provides an open access MRI magnet system utilizing opposing parallel end plates and superconducting coils to generate a strong and uniform magnetic flux field. The MRI magnet device is easily accessible by the patient and is open on at least two sides, so that the patient is less susceptible to claustrophobia during use and easier to carry out interfering radiation therapy . Furthermore, the control unit for the superconducting wire includes a continuation switch to reduce power consumption. Cooling of the components of the apparatus 10 can be achieved without the consumption of liquid coolant. In addition, due to the open-access structure and the relatively low perimeter height, the building will need less modification during installation.

While only certain embodiments of the present invention have been described herein, it would be easy for those skilled in the art to devise various modifications and adaptations without departing from the scope and spirit of the claims. There will be.

[Brief description of the drawings]

FIG. 1 is a perspective view of the main structural elements of a four-post open access superconducting MRI magnet device constructed in accordance with the present invention, with the patient support device shown in phantom.

FIG. 2 is a partial schematic view taken along section line 2-2 of FIG. 1;

FIG. 3 is an enlarged partial view of FIG. 2 showing details of the superconducting coil in a schematic cross section.

FIG. 4 illustrates a two-post open access superconducting MRI magnet device constructed in accordance with the present invention.

FIG. 5 is a plan view of FIG. 4;

FIG. 6 is an electrical schematic diagram of a superconducting coil and a continuous switch of an MRI magnet device constructed according to the present invention.

FIG. 7 is a schematic diagram showing a distribution of a magnetic flux field and a return path of the magnetic flux field.

FIG. 8 is a schematic diagram of a conduction cooling device according to the first embodiment of the present invention.

FIG. 9 is a schematic view of a conduction cooling device according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 16 open access frame 18 upper superconducting coil assembly 20 lower superconducting coil assembly 22 upper end plate 24 lower end plate 28a to 28d strut 12 patient storage area 32 toroidal vacuum tight container 38 continuous switch 36 super Conductive wire 44 temperature shield 64,66 loose shim 26 polar axis 100 cryocooler 102 first stage of cryocooler 104 second stage of cryocooler 106,112,114,116 solid thermal conductor 70 power supply

 ──────────────────────────────────────────────────の Continuation of the front page (72) Inventor En-Hoel. United States of America 520, Santa Carina, Solana Beach, California (56) References JP-A-3-284243 (JP, A) JP-A-6-233747 (JP, A)

Claims (2)

(57) [Claims] 1. An open access magnetic resonance imaging apparatus, comprising an upper end plate and a lower end plate in a substantially open ferromagnetic frame, wherein the plates are horizontally spaced and at least A frame defining a patient storage area therebetween, which is substantially parallel to one another and which allows access to additional medical equipment and personnel, and said upper and lower end plates, respectively; The first and second toroidal coils of superconducting wires mounted on the first and second coils create a magnetic flux field along a vertical polar axis, and the return path for the magnetic flux field is Provided by the struts and the upper and lower end plates, wherein the superconducting wires are provided with coils having a low transition temperature; and A magnetic flux generator for forming the magnetic flux field to provide substantially parallel magnetic flux lines within a storage area, the magnetic flux generator including a rose shim mounted on each of the end plates. A cryocooler; and first and second solid heat conductors attached to the cryocooler, the heat conductors being in thermal conductive contact with the first and second superconducting coils, respectively. Mounted so that the superconducting coil is cooled by conduction heat transfer, thereby causing the superconducting coil to maintain a temperature below the low transition temperature of the superconducting wire. An open access magnetic resonance imaging apparatus having first and second solid thermal conductors. 2. An open access magnetic resonance imaging apparatus, comprising an upper end plate and a lower end plate in a substantially open ferromagnetic frame, wherein the plates are horizontally spaced and at least A frame defining a patient storage area therebetween, which is substantially parallel to one another and which allows access to additional medical equipment and personnel, and said upper and lower end plates, respectively; The first and second toroidal coils of superconducting wires mounted on the first and second coils create a magnetic flux field along a vertical polar axis, and the return path for the magnetic flux field is Provided by the struts and the upper and lower end plates, wherein the superconducting wires are provided with coils having a low transition temperature; and A magnetic flux generator for forming the magnetic flux field to provide substantially parallel magnetic flux lines within a storage area, the magnetic flux generator including a rose shim mounted on each of the end plates. A cryocooler; a tubular cooling circuit mounted in heat conductive contact with the cryocooler, circulating a cooling fluid around the superconducting coil, and combining the superconducting coil with a combination of convection and conduction heat transfer. A tubular cooling circuit for cooling the superconducting coil at a temperature lower than the low transition temperature, and in fluid communication with the cooling circuit for pre-cooling the cooling fluid upstream of the cryocooler. An open access magnetic resonance imaging apparatus comprising: a counterflow heat exchanger, wherein the exchanger comprises a counterflow heat exchanger housed within one of the vacuum vessels.