Magnetic resonance imaging apparatus

Abstract

To provide a magnetic resonance imaging apparatus that can change heat exchange efficiency between a refrigerant for a superconducting coil and a radiation shield.SOLUTION: A magnetic resonance imaging apparatus according to an embodiment comprises a superconducting coil, a first container, a radiation shield, a second container, first piping, second piping, third piping, and a switching part. The first container houses the superconducting coil, immerses the superconducting coil in refrigerant liquid, and contains refrigerant gas generated by vaporization of the refrigerant liquid. The radiation shield houses the first container. The second container houses the radiation shield. The first piping guides the refrigerant gas in the first container to the outside of the radiation shield. The second piping is connected to the first piping, and passes the refrigerant gas from the first piping in such a manner that the refrigerant gas can exchange heat with the radiation shield. The third piping is connected to the first piping, and discharges the refrigerant gas from the first piping to the outside. The switching part guides the refrigerant gas from the first piping to the second piping or the third piping.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and drawings relate to a magnetic resonance imaging apparatus. [Background technology]

[0002] A magnetic resonance imaging apparatus is equipped with a superconducting magnet that can generate a stronger magnetic force than a normal electromagnet. The superconducting magnet operates at extremely low temperatures, and is therefore housed in a refrigerant container filled with a refrigerant (e.g., liquid helium).

[0003] The refrigerant container is housed in a radiation shield to reduce heat penetration into the refrigerant container. The radiation shield generates heat due to eddy current loss caused by the generation of gradient magnetic fields during imaging. If the temperature of the radiation shield rises during imaging, the quality of the images obtained by the magnetic resonance imaging apparatus may deteriorate. Therefore, the temperature of the radiation shield during imaging must be maintained within a predetermined temperature range (hereinafter, "maintained at a steady state"). Patent Document 1 proposes a configuration in which a pipe for discharging evaporated refrigerant to the outside is arranged in the radiation shield to keep the radiation shield cooled.

[0004] In peripheral equipment including superconducting magnets, evaporated refrigerant may be temporarily released into the outside air during initial cooling, injection, excitation / demagnetization, when a quench occurs, or when the refrigerator stops (due to transportation, intermittent operation of the refrigerator, power outage, malfunction, etc.).

[0005] Furthermore, for peripheral equipment including superconducting magnets, there are times when the cooling efficiency of the radiation shield needs to be increased and times when it is not necessary to increase the cooling efficiency of the radiation shield. Examples of times when the cooling efficiency of the radiation shield needs to be increased include when performing initial cooling, when a quench occurs, and when the refrigerator stops. On the other hand, examples of times when the cooling efficiency of the radiation shield does not need to be increased include when performing additional liquid injection and when performing excitation / demagnetization.

[0006] The configuration of Patent Document 1 cannot switch the cooling efficiency of the radiation shield depending on the situation as described above. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-74019 Summary of the Invention [Problem to be solved by the invention]

[0008] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to make it possible to change the heat exchange efficiency between the refrigerant of the superconducting coil and the radiation shield in a magnetic resonance imaging apparatus. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in each embodiment described below can also be positioned as other problems. [Means for solving the problem]

[0009] A magnetic resonance imaging apparatus according to an embodiment includes a superconducting coil, a first container, a radiation shield, a second container, a first pipe, a second pipe, a third pipe, and a switching unit. The first container houses the superconducting coil, immersing the superconducting coil in a refrigerant liquid and containing a refrigerant gas formed by evaporation of the refrigerant liquid. The radiation shield houses the first container. The second container houses the radiation shield. The first pipe directs the refrigerant gas in the first container to the outside of the radiation shield. The second pipe is connected to the first pipe and passes the refrigerant gas from the first pipe so that heat exchange occurs with the radiation shield. The third pipe is connected to the first pipe and discharges the refrigerant gas from the first pipe to the outside. The switching unit directs the refrigerant gas from the first pipe to the second pipe or the third pipe. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the first embodiment. [Figure 3] FIG. 3 is a perspective view showing a first example of arrangement of piping covering the radiation shield according to the first embodiment. [Figure 4] 4A and 4B are perspective views showing a second example of the arrangement of piping covering the radiation shield according to the first embodiment. Fig. 4A is a diagram showing an example of the arrangement of piping on the outer cylinder and end plate of the radiation shield, among the second example of the arrangement. Fig. 4B is a diagram showing an example of the arrangement of piping on the inner cylinder of the radiation shield, among the second example of the arrangement. [Figure 5] FIG. 5 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to a first modified example of the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to a second modified example of the first embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the second embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the third embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the third embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the third embodiment. [Figure 12] FIG. 12 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the third embodiment. [Figure 13] FIG. 13 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the third embodiment. [Figure 14] FIG. 14 is a cross-sectional view showing the configuration of a static magnetic field magnet and its surroundings according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A magnetic resonance imaging apparatus according to an embodiment will be described with reference to the accompanying drawings. In the following embodiments, parts with the same reference numerals operate in the same manner, and redundant description will be omitted as appropriate.

[0012] [First embodiment] 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus 1 according to the first embodiment. The magnetic resonance imaging apparatus 1 includes a magnet gantry 100, a control cabinet 300, a console 400, a bed 500, and an RF (Radio Frequency) coil 13.

[0013] The magnetic gantry 100 has a static magnetic field magnet 10, a gradient magnetic field coil 11, and a WB (Whole Body) coil 12. These components are housed in a cylindrical housing.

[0014] The control cabinet 300 includes gradient magnetic field power supplies 31 (for the X axis 31x, for the Y axis 31y, and for the Z axis 31z), a coil selection circuit , an RF receiver 32, an RF transmitter 33, and a sequence controller .

[0015] The console 400 includes a processing circuit 40, a memory circuit 41, a display 42, and an input device 43. The console 400 functions as a host computer. The bed 500 includes a bed body 50 and a top board 51.

[0016] The static magnetic field magnet 10 of the magnetic gantry 100 has a roughly cylindrical shape and generates a static magnetic field within a bore into which a subject, e.g., a patient, is transported. The bore is the space inside the cylinder of the magnetic gantry 100. The static magnetic field magnet 10 incorporates a superconducting coil 15, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply (not shown) to the superconducting coil. Thereafter, when the static magnetic field magnet 10 transitions to the persistent current mode, the static magnetic field power supply is disconnected from the static magnetic field magnet 10. Once transitioned to the persistent current mode, the static magnetic field magnet 10 continues to generate a large static magnetic field for a long period of time, e.g., for more than one year.

[0017] The gradient magnetic field coil 11 also has a roughly cylindrical shape and is fixed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 applies gradient magnetic fields to the subject in the directions of the X-axis, Y-axis, and Z-axis by currents supplied from gradient magnetic field power supplies 31x, 31y, and 31z, respectively.

[0018] The bed body 50 of the bed 500 can move the top plate 51 in the vertical and horizontal directions. Before imaging, the subject placed on the top plate 51 is moved to a predetermined height. Then, during imaging, the top plate 51 is moved horizontally to move the subject into the bore.

[0019] The WB coil 12, also called a whole-body coil, is fixed in a roughly cylindrical shape so as to surround the subject inside the gradient coil 11. The WB coil 12 transmits RF pulses transmitted from the RF transmitter 33 toward the subject. It also receives magnetic resonance signals, i.e., MR (Magnetic Resonance) signals, emitted from the subject due to excitation of hydrogen nuclei.

[0020] The magnetic resonance imaging apparatus 1 includes an RF coil 13 as shown in FIG. 1 in addition to the WB coil 12. The RF coil 13 is a coil placed close to the body surface of the subject. The RF coil 13 includes a plurality of element coils. These element coils are arranged in an array inside the RF coil 13, and are therefore sometimes called PACs (Phased Array Coils). There are several types of RF coils. For example, the RF coil 13 includes a body coil placed on the chest, abdomen, or legs of the subject as shown in FIG. 1, and a spine coil placed on the back of the subject.

[0021] The RF transmitter 33 generates an RF pulse based on an instruction from the sequence controller 34. The generated RF pulse is transmitted to the WB coil 12 or the RF coil 13 and applied to the subject. The application of the RF pulse generates an MR signal from the subject. The RF coil 13 or the WB coil 12 receives this MR signal.

[0022] The MR signals received by the RF coil 13, more specifically, the MR signals received by each element coil in the RF coil 13, are transmitted to the coil selection circuit 36 ​​via cables provided on the tabletop 51 and the bed body 50. The coil selection circuit 36 ​​selects the signal output from the RF coil 13 or the signal output from the WB coil 12 in accordance with a control signal output from the sequence controller 34 or the console 400.

[0023] The selected signal is output to the RF receiver 32. The RF receiver 32 converts the channel signal, i.e., the MR signal, from analog to digital (AD) and outputs it to a sequence controller 34. The digitalized MR signal is also called raw data. The AD conversion may be performed inside the RF coil 13 or in the coil selection circuit 36.

[0024] The sequence controller 34 scans the subject by driving the gradient magnetic field power supply 31, the RF transmitter 33, and the RF receiver 32 under the control of the console 400. When raw data is received from the RF receiver 32 by the scan, the sequence controller 34 transmits the raw data to the console 400.

[0025] The sequence controller 34 includes a processing circuit (not shown). This processing circuit is configured with hardware such as a processor that executes a predetermined program, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit).

[0026] The console 400 includes a memory circuitry 41, an input device 43, a display 42, and a processing circuitry 40. The memory circuitry 41 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), and an external storage device such as an HDD (Hard Disk Drive) or an optical disk device. The memory circuitry 41 stores various types of information and data, as well as various programs executed by a processor included in the processing circuitry 40.

[0027] The input device 43 includes various devices such as a mouse, keyboard, trackball, touch panel, etc., which are used by the operator to input various information and data. The display 42 is a display device such as a liquid crystal display panel, a plasma display panel, an organic EL panel, etc.

[0028] The processing circuit 40 is a circuit including, for example, a CPU or a dedicated or general-purpose processor. The processor realizes various functions described below by executing various programs stored in the storage circuit 41. The processing circuit 40 may be configured with hardware such as an FPGA or an ASIC.

[0029] Fig. 2 is a cross-sectional view showing the configuration of a static magnetic field magnet 10 and its surroundings according to the first embodiment. The static magnetic field magnet 10 shown in Fig. 2 corresponds to the static magnetic field magnet 10 located above the magnetic gantry 100 among the static magnetic field magnets 10 shown in Fig. 1. Therefore, in Fig. 2, a bore is formed below the static magnetic field magnet 10, and a subject is placed in this bore. As shown in Fig. 2, the static magnetic field magnet 10 includes a superconducting coil 15, a refrigerant container 16, a radiation shield 17, a vacuum container 18, and pipes P1, P2, and P3. The superconducting coil 15 generates a static magnetic field for the subject.

[0030] Refrigerant container 16 accommodates superconducting coil 15, immerses superconducting coil 15 in a refrigerant liquid (liquid refrigerant), and contains a refrigerant gas, which is a gas formed by vaporizing the refrigerant liquid. The refrigerant liquid is, for example, liquid helium, and cools superconducting coil 15 to an extremely low temperature of about 4 K. Refrigerant container 16 is an example of a first container.

[0031] Radiation shield 17 is maintained at a temperature higher than the temperature of the refrigerant liquid but sufficiently lower than the outside air, for example, at about 30 to 80 K, to prevent radiant heat from entering from the outside. Outside air is an example of the outside. Radiation shield 17 is made of, for example, aluminum. Vacuum container 18 has a vacuum inside and houses radiation shield 17. Radiation shield 17 has a vacuum inside and houses refrigerant container 16. Vacuum container 18 is an example of a second container.

[0032] The pipe P1 delivers the refrigerant gas in the refrigerant container 16 to the outside of the radiation shield 17. In Fig. 2, the pipe P1 is connected to the outer surface of the outer cylinder of the refrigerant container 16, passes through the radiation shield 17, and extends to the outside of the vacuum container 18. The pipe P1 is thermally connected to the radiation shield 17. The pipe P1 is an example of a first pipe.

[0033] The pipe P2 is connected to the pipe P1 and passes the refrigerant gas introduced from the pipe P1 so as to be able to exchange heat with the radiation shield 17. In FIG. 2, the pipe P2 branches off from the pipe P1, penetrates the vacuum vessel 18 inward, circles around the radiation shield 17, then penetrates the vacuum vessel 18 outward, and is connected to an outlet EP. That is, the pipe P2 passes the refrigerant gas introduced from the pipe P1 so as to be able to exchange heat with the radiation shield 17, and then discharges the refrigerant gas to the outside. The pipe P2 is an example of a second pipe. Note that, although the illustration is simplified in FIG. 2, a pipe (not shown) is provided indoors from the MRI room in which the magnetic resonance imaging apparatus 1 is installed to the outdoors as a pipe for discharging the refrigerant gas to the outside, and this pipe is connected to an outlet EP that is open to the outdoors. The outdoors is an example of the outside. Note that the pipe P2 may or may not be in contact with the radiation shield 17 as long as it is able to exchange heat with the radiation shield 17.

[0034] 3 and 4 are diagrams showing examples of the arrangement of piping P2 that surrounds the radiation shield 17. Fig. 3 is a perspective view showing a first example of the arrangement of piping P2 that covers the radiation shield 17 according to the first embodiment. The radiation shield 17 is installed inside the static magnetic field magnet 10 and has a cylindrical shape. The outer surface of the radiation shield 17 is covered by the piping P2.

[0035] The radiation shield 17 is made up of an outer cylinder 171, end plates 172R and 172L, and an inner cylinder 173. The outer cylinder 171 is the outer surface of the radiation shield 17. The end plates 172R and 172L are both side surfaces of the radiation shield 17 and are formed in a doughnut shape. The end plate 172R is the right end plate. The end plate 172L is the left end plate. The inner cylinder 173 is the inner surface of the radiation shield 17. For ease of explanation, when the radiation shield 17 in Figure 3 is viewed diagonally from the front left, the top of the end plate 172L will be called the 0 degree position, and the positions will be called the 45 degree position, 90 degree position, etc. in clockwise order.

[0036] 3, pipes P2 are arranged at positions of 0, 90, 180, and 270 degrees on the outer cylinder 171 of the radiation shield 17. Meanwhile, pipes P2 are arranged at positions of 45, 135, 225, and 315 degrees on the inner cylinder 173 of the radiation shield 17. Eight pipes P2 that connect the pipes P2 of the outer cylinder 171 and the pipes P2 of the inner cylinder 173 are arranged on the end plates 172L and 172R of the radiation shield 17.

[0037] For example, the end plate 172R is provided with a pipe P2 that connects the pipe P2 arranged at the 0-degree position on the outer cylinder 171 with the pipe P2 arranged at the 45-degree position on the inner cylinder 173. The end plate 172L is provided with a pipe P2 that connects the pipe P2 arranged at the 45-degree position on the inner cylinder 173 with the pipe P2 arranged at the 90-degree position on the outer cylinder 171. In this way, the pipe P2 arranged at the outer cylinder 171 and the pipe P2 arranged at the inner cylinder 173 are all connected together.

[0038] FIG. 4 is a perspective view showing a second arrangement example of the piping P2 covering the radiation shield 17 according to the first embodiment. FIG. 4(A) shows an example of the arrangement of the piping P2 in the outer cylinder 171, end plate 172R, and end plate 172L of the radiation shield 17, among the second arrangement examples. Meanwhile, FIG. 4(B) shows an example of the arrangement of the piping P2 in the inner cylinder 173 of the radiation shield 17, among the second arrangement examples. For convenience of explanation, FIGS. 4(A) and 4(B) are separated, but in reality they are integrated. In other words, the configuration of FIG. 4(A) and the configuration of FIG. 4(B) can be used in combination.

[0039] 4(A), the pipe P2 is arranged in a spiral shape on the outer cylinder 171 of the radiation shield 17. The pipe P2 is arranged in the outer cylinder 171 over two turns from the 0 degree position on the end plate 172L to the 0 degree position on the end plate 172R.

[0040] 4(B), a pipe P2 is arranged in a spiral shape in the inner cylinder 173 of the radiation shield 17. The pipe P2 is arranged in the inner cylinder 173 over two turns from the 0 degree position on the end plate 172L to the 0 degree position on the end plate 172R.

[0041] 4(A), a spiral-shaped pipe P2 is arranged on the end plate 172R. The spiral-shaped pipe P2 connects the pipe P2 arranged at the 0-degree position of the outer cylinder 171 with the pipe P2 arranged at the 0-degree position of the inner cylinder 173. In addition, a spiral-shaped pipe P2 is arranged on the end plate 172L. The spiral-shaped pipe P2 connects the pipe P2 arranged at the 0-degree position of the outer cylinder 171 with the pipe P2 arranged at the 0-degree position of the inner cylinder 173.

[0042] In this way, the pipe P2 arranged in the outer cylinder 171 is connected to the pipe P2 arranged in the inner cylinder 173. The valves 22 and 23 shown in FIG. 2 are installed on both ends of the pipe P2 arranged in the outer cylinder 171. The first and second arrangement examples of the pipe P2 described above are examples for the purpose of explanation, and the present invention is not limited to these.

[0043] Returning to Fig. 2, the pipe P3 is connected to the pipe P1 and directly discharges the refrigerant gas introduced from the pipe P1 to the outdoors. In Fig. 2, the pipe P3 branches off from the pipe P1, passes outside the static magnetic field magnet 10, and then connects to the discharge port EP. The pipe P3 is an example of a third pipe.

[0044] The valves 21, 22, and 23 cooperate to introduce the refrigerant gas introduced from the pipe P1 into the pipe P2 or the pipe P3. The valves 21, 22, and 23 are an example of a switching unit.

[0045] Valve 21 is installed in pipe P1 near the portion where pipe P2 is connected, and opens and closes according to the pressure of the refrigerant gas in pipe P1. Valve 21 allows refrigerant gas to pass from the inside to the outside of pipe P1 when the pressure of the refrigerant gas in pipe P1 exceeds a predetermined threshold. Valve 21 does not allow refrigerant gas to flow back from the outside to the inside of pipe P1. Valve 21 is, for example, a check valve that opens and closes according to a predetermined operating pressure.

[0046] The valve 22 guides the refrigerant gas introduced from the pipe P1 to the pipe P2 or the pipe P3. That is, the valve 22 forms a path from the pipe P1 to the pipe P2 or a path from the pipe P1 to the pipe P3. The valve 22 is, for example, a switching valve such as a three-way valve.

[0047] Valve 23 is installed in pipe P2 between static magnetic field magnet 10 (vacuum vessel 18) and discharge port EP, and opens and closes according to the pressure of the refrigerant gas in pipe P2. Valve 23 passes the refrigerant gas from pipe P2 to the discharge port EP side when the pressure of the refrigerant gas in pipe P2 exceeds a predetermined threshold. Valve 23 does not allow the refrigerant gas to flow back from the discharge port EP side of pipe P2 to pipe P2. Valve 23 may be, for example, a check valve.

[0048] The valves 21 and 23 may be valves that are manually opened and closed (ball valves, globe valves, etc.).

[0049] 2, valve 21 is open, valve 22 forms a path from pipe P1 to pipe P2, and valve 23 is open. As a result, the refrigerant gas in refrigerant container 16 passes through pipes P1 and P2 and is then discharged to the outside from outlet port EP. In this case, the refrigerant gas passes through pipe P2, allowing heat exchange with radiation shield 17.

[0050] In other words, the static magnetic field magnet 10 includes at least pipes P1, P2, and P3 through which a refrigerant gas capable of heat exchange with the radiation shield 17 flows, and a valve 22 capable of switching the path through which the refrigerant gas flows. The valve 22 switches the path through which the refrigerant gas flows when the sensible heat of the refrigerant gas needs to be used to increase the efficiency of heat exchange with the radiation shield 17 (for example, during initial cooling, quenching, when the refrigerator is stopped, imaging, etc.). This increases the efficiency of heat exchange between the refrigerant gas and the radiation shield 17, and increases the cooling efficiency of the radiation shield 17. As a result, the time required for the temperature of the radiation shield 17 to reach a steady state (80 K in this embodiment) can be shortened.

[0051] FIG. 5 is a diagram showing the configuration of the static magnetic field magnet 10 and its periphery according to the first embodiment. The configuration in FIG. 5 is the same as that in FIG. 2. As in FIG. 2, valve 21 is open. However, unlike FIG. 2, valve 22 forms a path from pipe P1 to pipe P3, and valve 23 is closed. As a result, the refrigerant gas in refrigerant container 16 passes through pipes P1 and P3, and is then discharged to the outside air from outlet port EP. In this case, the refrigerant gas does not pass through pipe P2, and so heat exchange only takes place with radiation shield 17 at the location where pipe P1 passes.

[0052] According to this, when there is no need to increase the heat exchange efficiency with the radiation shield 17 (for example, when additional refrigerant is being poured in, magnetization, demagnetization, etc.), it is possible to not increase the heat exchange efficiency between the refrigerant gas and the radiation shield 17, and therefore not increase the cooling efficiency of the radiation shield 17. As a result, it is possible to prevent the temperature of the radiation shield 17 from dropping too much compared to the steady state due to the injection of refrigerant into the refrigerant container during additional refrigerant pouring, magnetization, demagnetization, etc. As a result, it is possible to shorten the time required for the temperature of the radiation shield 17 to reach the steady state (80 K in this embodiment).

[0053] [First Modification of the First Embodiment] Fig. 6 is a cross-sectional view showing the configuration of the static magnetic field magnet 10a and its surroundings according to a first modified example of the first embodiment. In Fig. 2, the pipe P1 extends to the outside of the vacuum vessel 18 and connects to the pipes P2 and P3 outside the static magnetic field magnet 10a. In other words, the branch point from the pipe P1 to the pipes P2 and P3 is located outside the vacuum vessel 18. In this way, the refrigerant gas passing through the pipe P2 is once affected by the outside air (for example, its temperature increases) and then exchanges heat with the radiation shield 17.

[0054] 6, after passing through the radiation shield 17 to the outside, the pipe P1 is arranged so as to immediately run along the outer surface of the radiation shield 17 and connect to the pipes P2 and P3. In other words, the branch point from the pipe P1 to the pipes P2 and P3 is located inside the vacuum vessel 18. The pipe P2 then circles the radiation shield 17 inside the vacuum vessel 18 (without going outside the vacuum vessel 18). This allows the refrigerant gas passing through the pipe P2 to exchange heat with the radiation shield 17 at a lower temperature than in the configuration of FIG. 2 without being affected by the outside air.

[0055] [Second Modification of First Embodiment] Fig. 7 is a cross-sectional view showing the configuration of a static magnetic field magnet 10b and its surroundings according to a second modified example of the first embodiment. The piping P2 is preferably made of a material that prevents refrigerant gas from leaking into the static magnetic field magnet 10b. As shown in Fig. 7, the portion of the piping P2 that circumscribes the radiation shield 17 may have high thermal conductivity, and the portion that does not circumscribe the radiation shield 17 may have low thermal conductivity.

[0056] For example, the pipe P2 in contact with the radiation shield 17 may be reconnected to a pipe made of copper or aluminum, which has high thermal conductivity. This increases the efficiency of heat exchange between the refrigerant gas passing through the pipe P2 and the radiation shield 17. On the other hand, the pipe P2 not in contact with the radiation shield 17 may be reconnected to a pipe made of stainless steel (SUS: Steel Use Stainless), which has low thermal conductivity. This prevents heat from entering the pipe P2 from the outside air when the pipe P2 is exposed to the outside air.

[0057] The static magnetic field magnets 10, 10a, and 10b according to the first embodiment have a pipe P2 that runs around the radiation shield 17 and discharges the refrigerant gas into the outside air when discharging the refrigerant gas in the refrigerant container 16 into the outside air, in addition to a pipe P3 that directly discharges the refrigerant gas into the outside air. This allows the refrigerant gas that should be discharged to adjust the pressure inside the refrigerant container 16 to be effectively used for cooling the radiation shield 17. Furthermore, the heat exchange efficiency between the refrigerant gas and the radiation shield 17 can be intentionally changed as needed.

[0058] Second Embodiment FIG. 8 is a cross-sectional view showing the configuration of a static magnetic field magnet 10c and its surroundings according to the second embodiment. Comparing the first embodiment with the second embodiment, the arrangement and operation of the valves are different. As shown in FIG. 8, valves 24 and 25 work together to introduce refrigerant gas introduced from pipe P1 into pipe P2 or pipe P3. Valves 23, 24, and 25 are an example of a switching unit.

[0059] Valve 24 is installed near the portion of pipe P2 that connects to pipe P1, and opens and closes according to the pressure of the refrigerant gas introduced from pipe P1. Valve 24 allows the refrigerant gas to pass into pipe P2 when the pressure of the refrigerant gas introduced from pipe P1 exceeds a predetermined threshold. Valve 24 does not allow the refrigerant gas to flow back from pipe P2 to pipe P1. Valve 24 may be, for example, a check valve. Valve 24 is an example of a first valve.

[0060] Valve 25 is installed near the portion of pipe P3 that connects to pipe P1, and opens and closes according to the pressure of the refrigerant gas introduced from pipe P1. Valve 25 allows the refrigerant gas to pass into pipe P3 when the pressure of the refrigerant gas introduced from pipe P1 exceeds a predetermined threshold. Valve 25 does not allow the refrigerant gas to flow back from pipe P3 to pipe P1. Valve 25 is, for example, a check valve. Valve 25 is an example of a second valve.

[0061] The valve 23 is installed in the pipe P2 between the static magnetic field magnet 10c (vacuum vessel 18) and the discharge port EP, and opens and closes according to the pressure of the refrigerant gas in the pipe P2. The valve 23 passes the refrigerant gas from the pipe P2 to the discharge port EP side when the pressure of the refrigerant gas in the pipe P2 exceeds a predetermined threshold. The valve 23 does not allow the refrigerant gas to flow back from the discharge port EP side of the pipe P2 to the pipe P2. For example, a check valve is used as the valve 23. The valve 23 is an example of a third valve. The discharge port EP of the pipe P2 is an example of a part that discharges the refrigerant gas to the outside.

[0062] Valve 24 opens when the pressure of the refrigerant gas exceeds a first threshold. Valve 25 opens when the pressure of the refrigerant gas exceeds a second threshold that is higher than the first threshold. For example, the first threshold of valve 24 is set to 7000 [Pa], and the second threshold of valve 25 is set to 20000 [Pa]. As a result, when the pressure of the refrigerant gas in refrigerant container 16 exceeds 7000 [Pa], the refrigerant gas flows to pipe P2 on the radiation shield 17 side. When the pressure of the refrigerant gas further exceeds 20000 [Pa], the refrigerant gas flows not only through pipe P2 but also through pipe P3, and is directly discharged to the outside.

[0063] Furthermore, valve 23 opens when the pressure of the refrigerant gas exceeds a third threshold value that is greater than the first threshold value. When the pressure of the refrigerant gas exceeds the first threshold value, the refrigerant gas accumulates in pipe P2. Then, when the temperature of the refrigerant gas rises and the pressure of the refrigerant gas exceeds the third threshold value, the refrigerant gas is discharged to the outside air. In FIG. 8, valves 23 and 24 are open and valve 25 is closed, so the refrigerant gas passes through pipes P1 and P2 and is then discharged to the outside air from outlet port EP.

[0064] According to the static magnetic field magnet 10c of the second embodiment, if the operating pressures of the three valves 23, 24, and 25 can be determined, check valves may be used for the three valves. This eliminates the need for switching valves, eliminating the need for manual switching of the refrigerant gas path. Next, when the pressure inside the refrigerant container 16 increases and the refrigerant gas is discharged to the outside air, it first passes through pipe P2 and circulates around the radiation shield 17 before being discharged to the outside air. When the pressure of the refrigerant gas further increases, it passes through pipe P3 and is directly discharged to the outside air. This allows the refrigerant gas that should be discharged to adjust the pressure inside the refrigerant container 16 to be preferentially used to cool the radiation shield 17. Furthermore, since the refrigerant gas is temporarily retained in pipe P2, the heat exchange efficiency between the refrigerant gas and the radiation shield 17 can be improved.

[0065] Third Embodiment In the first and second embodiments, the pipe P2 is configured to go around the entire radiation shield 17. However, in the third embodiment, the pipe P2 circumscribes a part (a predetermined part) of the radiation shield 17.

[0066] Fig. 9 is a cross-sectional view showing the configuration of a static magnetic field magnet 10d and its surroundings according to the third embodiment. As shown in Fig. 9, the piping P2 is circumscribed by the outer casing 171 of the radiation shield 17. For example, during transportation of the magnetic resonance imaging apparatus 1, the refrigerator provided in the radiation shield 17 does not operate, and therefore the outer casing 171 of the radiation shield 17 is likely to heat up. With the above configuration, in such a case, the outer casing 171 of the radiation shield 17 can be cooled.

[0067] Fig. 10 is a cross-sectional view showing the configuration of the static magnetic field magnet 10e and its surroundings according to the third embodiment. As shown in Fig. 10, the pipe P2 is circumscribed by the end plate 172 of the radiation shield 17. For example, during transportation of the magnetic resonance imaging apparatus 1, the refrigerator provided in the radiation shield 17 does not operate, and therefore the end plate 172 of the radiation shield 17 is likely to heat up. With the above configuration, in such a case, the end plate 172 of the radiation shield 17 can be cooled.

[0068] FIG. 11 is a cross-sectional view showing the configuration of a static magnetic field magnet 10f and its surroundings according to the third embodiment. As shown in FIG. 11, the piping P2 circumscribes the inner cylinder 173 of the radiation shield 17. For example, when the magnetic resonance imaging apparatus 1 is imaging a subject, the inner cylinder 173 closer to the gradient magnetic field coil 11 is more likely to heat up than the outer cylinder 171 due to eddy current loss in the radiation shield 17 caused by the application of a gradient magnetic field. Furthermore, when a quench occurs, in which the magnetic force generated by the static magnetic field magnet 10 suddenly decreases, the inner cylinder 173 of the radiation shield 17 closer to the position where the superconducting coil 15, which has a large number of coil turns, is disposed is more likely to heat up due to eddy current loss than the outer cylinder 171. With the above configuration, the inner cylinder 173 of the radiation shield 17 can be cooled in such cases.

[0069] Fig. 12 is a cross-sectional view showing the configuration of a static magnetic field magnet 10g and its surroundings according to the third embodiment. As shown in Fig. 12, the pipe P2 circumscribes both outer sides of the inner cylinder 173 of the radiation shield 17 in the cylindrical axial direction. For example, both outer sides of the radiation shield 17 are more likely to heat up than the inner side (center) in the axial direction. With the above configuration, in such a case, both outer sides of the inner cylinder 173 of the radiation shield 17 can be cooled.

[0070] Fig. 13 is a cross-sectional view showing the configuration of a static magnetic field magnet 10h and its surroundings according to the third embodiment. As shown in Fig. 13, the pipe P2 circumscribes the inner axial (center) surface of the inner cylinder 173 of the radiation shield 17. For example, depending on the arrangement of the gradient magnetic field coil 11, the inner axial side of the radiation shield 17 may generate heat due to eddy currents caused by the gradient magnetic field. In such cases, the above configuration allows the inside of the inner cylinder 173 of the radiation shield 17 to be cooled.

[0071] According to the third embodiment, the static magnetic field magnets 10d to 10h are equipped with at least a pipe P2 for flowing a heat-exchangeable refrigerant gas to a predetermined portion where the efficiency of heat exchange with the radiation shield 17 should be increased, and a valve 22 capable of switching the path for flowing the refrigerant gas. This increases the efficiency of heat exchange with the radiation shield 17, and can increase the cooling efficiency of the radiation shield 17.

[0072] [Fourth embodiment] 14 is a cross-sectional view showing the configuration of the static magnetic field magnet 10i and its surroundings according to the fourth embodiment. As shown in FIG. 14, the static magnetic field magnet 10i according to the fourth embodiment further includes a control device 20, in contrast to the first to third embodiments.

[0073] In the fourth embodiment, sub-pipes P21, P22, and P23 branch off from the pipe P1 instead of the pipe P2 in the first to third embodiments. That is, the pipe P2 branches off into the sub-pipes P21, P22, and P23 downstream of the connection portion with the pipe P1. The sub-pipes P21, P22, and P23 are configured to circumscribe different portions of the radiation shield 17, exchange heat with the radiation shield 17, merge after the heat exchange, and connect to an outlet EP that discharges the refrigerant gas to the outside air. The sub-pipe P21 circumscribes the outer cylinder 171 of the radiation shield 17. The sub-pipe P22 circumscribes the end plate 172 of the radiation shield 17. The sub-pipe P23 circumscribes the inner cylinder 173 of the radiation shield 17. The sub-pipes P21, P22, and P23 are examples of multiple second sub-pipes.

[0074] The valves 261, 262, and 263 are respectively installed at positions before the sub-pipes P21, P22, and P23 exchange heat with the radiation shield 17, and open and close in response to instructions from the control device 20. The valve 27 is installed on the pipe P3 and opens and closes in response to instructions from the control device 20. The valves 261, 262, 263, and 27 are configured to be able to adjust the flow rate of refrigerant gas. The flow rate of refrigerant gas can be adjusted, for example, according to the opening degree of the valve. The valves 261, 262, 263, and 27 may be any valve whose opening and closing can be controlled by the control device 20, and may be, for example, an electric valve or a solenoid valve. The valves 261, 262, and 263 are an example of a plurality of first valves. The valve 27 is an example of a second valve.

[0075] The control device 20 selects the valve to be opened from among the valves 261, 262, 263, and 27, and instructs the selected valve to open the circuit. The control device 20 adjusts the flow rate of the refrigerant gas at the valves 261, 262, 263, and 27.

[0076] Valves 231, 232, and 233 are installed near the confluence of sub-pipes P21, P22, and P23, respectively, and open and close according to the pressure of the refrigerant gas in each of sub-pipes P21, P22, and P23. When the pressure of the refrigerant gas in each of sub-pipes P21, P22, and P23 exceeds a predetermined threshold, valves 231, 232, and 233 allow refrigerant gas to pass from the inside to the outside of each of sub-pipes P21, P22, and P23. Valves 231, 232, and 233 do not allow refrigerant gas to flow back from the outside to the inside of each of sub-pipes P21, P22, and P23. Valves 231, 232, and 233 may be, for example, check valves. Even if the operating pressures of the valves 231, 232, and 233 are the same, if the pressure losses of the sub-pipes P21, P22, and P23 are different, it is believed that more refrigerant gas will flow through the pipe with the smaller pressure loss, even when the valves 261, 262, and 263 are fully opened. Therefore, it is desirable to make the pressure losses of the sub-pipes P21, P22, and P23 as similar as possible. This allows for adjustment of the flow rate of refrigerant gas. Furthermore, the shape, length, and cross-sectional area of ​​the sub-pipes P21, P22, and P23 may be changed. This allows for adjustment of the pressure loss of the refrigerant gas flow. For example, to minimize the pressure loss, the cross sections of the sub-pipes P21, P22, and P23 are generally circular.

[0077] According to the fourth embodiment, the static magnetic field magnet 10i includes sub-pipes P21, P22, and P23 that pass heat-exchangeable refrigerant gas through predetermined portions where the efficiency of heat exchange with the radiation shield 17 should be increased, a path for flowing the refrigerant gas, portions of the radiation shield 17, and a valve capable of switching the flow rate, and a control device 20. This increases the efficiency of heat exchange between the refrigerant gas and the radiation shield 17, and increases the cooling efficiency of the radiation shield 17.

[0078] According to at least one of the embodiments described above, in a magnetic resonance imaging apparatus, it is possible to change the heat exchange efficiency between the refrigerant of the superconducting coil and the radiation shield.

[0079] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0080] 1...Magnetic resonance imaging device 10...Static magnetic field magnet 15...Superconducting coil 16...Refrigerant container 17...Radiation shield 18...Vacuum container 20...Control device 171...Outer cylinder 172, 172R, 172L...end plate 173…Inner cylinder 21, 22, 23, 231, 232, 233, 24, 25, 261, 262, 263, 27...Valves P1, P2, P3...piping P21, P22, P23...Sub-pipes

Claims

1. a superconducting coil; a first container that accommodates the superconducting coil, immerses the superconducting coil in a refrigerant liquid, and contains a refrigerant gas that is vaporized from the refrigerant liquid; a radiation shield that houses the first container; a second container that houses the radiation shield; a first pipe that guides the refrigerant gas in the first container to the outside of the radiation shield; a second pipe connected to the first pipe and allowing the refrigerant gas from the first pipe to pass through the second pipe so as to be able to exchange heat with the radiation shield; a third pipe connected to the first pipe and discharging the refrigerant gas from the first pipe to the outside; a switching unit that directs the refrigerant gas from the first pipe to the second pipe or the third pipe; A magnetic resonance imaging apparatus comprising:

2. the second pipe allows the refrigerant gas from the first pipe to pass through the radiation shield so as to be able to exchange heat, and then discharges the refrigerant gas to the outside; The switching unit is a first valve that is installed in the second pipe near a portion where the second pipe is connected to the first pipe and that opens and closes in response to the pressure of the refrigerant gas from the first pipe; a second valve that is installed in the vicinity of a portion of the third pipe that is connected to the first pipe and that opens and closes in response to the pressure of the refrigerant gas from the first pipe; a third valve that is installed in the second pipe between the second container and a portion that discharges the refrigerant gas to the outside and that opens and closes in response to the pressure of the refrigerant gas; Equipped with 2. The magnetic resonance imaging apparatus according to claim 1.

3. the first valve opens when the pressure of the refrigerant gas exceeds a first threshold value; The second valve opens when the pressure of the refrigerant gas exceeds a second threshold value that is greater than the first threshold value.

3. The magnetic resonance imaging apparatus according to claim 2.

4. the first valve opens when the pressure of the refrigerant gas exceeds a first threshold value; The third valve opens when the pressure of the refrigerant gas exceeds a third threshold value that is greater than the first threshold value.

3. The magnetic resonance imaging apparatus according to claim 2.

5. the second pipe circumscribing a predetermined portion of the radiation shield; 2. The magnetic resonance imaging apparatus according to claim 1.

6. the predetermined portion is an outer cylinder, an end plate, an inner cylinder, or a part of the inner cylinder of the radiation shield.

6. A magnetic resonance imaging apparatus according to claim 5.

7. a portion of the second pipe that is in circumscribing contact with the radiation shield has a high thermal conductivity, and a portion of the second pipe that is not in circumscribing contact with the radiation shield has a low thermal conductivity; 2. The magnetic resonance imaging apparatus according to claim 1.

8. Further comprising a control device, the second pipe is branched into a plurality of second sub-pipes downstream of a connection portion with the first pipe, and the plurality of second sub-pipes are configured to circumscribe different portions of the radiation shield to exchange heat with the radiation shield, and to discharge the refrigerant gas to the outside after the heat exchange; The switching unit is a plurality of first valves that are respectively installed at positions before the plurality of second sub-pipes exchange heat with the radiation shield and that open and close in response to instructions from the control device; a second valve installed in the third pipe and opened and closed in response to an instruction from the control device; Equipped with the control device selects a valve to be opened from among the plurality of first valves and the plurality of second valves, and instructs the selected valve to open the valve.

2. The magnetic resonance imaging apparatus according to claim 1.

9. the plurality of first valves and the second valve are configured to be able to adjust the flow rate of the refrigerant gas, the control device adjusts the flow rates of the refrigerant gas in the plurality of first valves and the second valve.

9. The magnetic resonance imaging apparatus according to claim 8.

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