JP2017113410A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MRI apparatus providing high uniformity of a static magnetic field.SOLUTION: The MRI apparatus includes an MRI body 200, a control device for controlling operation of the MRI body 200, and a bed on which a subject is placed. The MRI body 200 includes: static magnetic field generators 300, 400 for generating a static magnetic field on an observation area 204; gradient magnetic field generators 210, 211 for generating a gradient magnetic field; and RF pulse irradiation coils 214, 215. The static magnetic field generators 300, 400 include coils 320, 420 for generating magnetic fluxes, and magnetic materials 318, 418 for uniformizing the magnetic fluxes. Support mechanisms of the magnetic materials 318, 418 include heat generators 522, 524 at parts thereof, where the physical relationship of the magnetic materials 318, 418 is controlled by controlling heat-generating amounts of the heat generators 522, 524.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as MRI) apparatus.

  An MRI apparatus measures an NMR signal generated by spins of nuclei constituting a tissue of a human body as a subject, and images the form and function of, for example, the head, abdomen, and extremities in a two-dimensional or three-dimensional manner. It is a device to convert. In imaging of a subject, for example, NMR signals are given different phase encodings depending on a gradient magnetic field, are frequency-encoded, and are measured as time-series data. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform, for example. The obtained image is used for medical purposes such as diagnosis. For this reason, a high quality image is required.

  Since the intensity of the NMR signal generated by the nuclear spin is proportional to the intensity of the static magnetic field in the measurement region, it is necessary to increase the intensity of the static magnetic field in order to improve the resolution of the tomographic image. Therefore, a superconducting magnet device is used to generate a high-intensity static magnetic field. In addition, it is necessary to increase the magnetic field uniformity in the measurement region in order to improve the image quality of the tomographic image. For this purpose, a magnetic material is provided in the superconducting magnet device. Thus, a static magnetic field region having high strength and high static magnetic field uniformity is generated in the measurement region.

  Since the change in the position of the magnetic material leads to a decrease in the magnetic field uniformity of the static magnetic field, the magnetic material has been installed in the vacuum container so as not to be affected by the room temperature causing the expansion and contraction of the constituent members. Patent Document 1 discloses a configuration in which a magnetic material is arranged in a vacuum vessel.

JP 2010-233736 A

  The structure which arrange | positions a magnetic material in the vacuum vessel currently disclosed by patent document 1 tends to become an expensive structure. For this reason, the structure which arrange | positions a magnetic material outside a vacuum vessel can be considered. On the other hand, the configuration disclosed in Patent Document 1 has a structure in which the above-described magnetic material and the configuration that supports the magnetic material are not easily affected by external temperature because the vacuum vessel functions to prevent heat transfer. In the structure in which the magnetic material is arranged outside the vacuum vessel, the temperature of the examination room where the MRI apparatus is installed is easily transmitted, and the uniformity of the static magnetic field is lowered due to the influence of the temperature of the examination room. Challenges arise.

  An object of the present invention is to provide an MRI apparatus in which a decrease in the uniformity of a static magnetic field is suppressed or the uniformity of a static magnetic field is improved.

  An MRI apparatus of the present invention that solves the above problems includes an MRI main body, a control device that controls the operation of the MRI main body, and a bed on which a subject is placed. The MRI main body generates a static magnetic field in an observation region. A magnetic field generator, a gradient magnetic field generator for generating a gradient magnetic field, and an RF pulse irradiation coil. The static magnetic field generator has a coil for generating magnetic flux and a magnetic material for homogenizing the magnetic flux. In addition, a heating element is provided in a part of the support mechanism of the magnetic material, and the positional relationship of the magnetic material is controlled by controlling the heat generation amount of the heating element.

  ADVANTAGE OF THE INVENTION According to this invention, the MRI apparatus which can suppress the fall of the uniformity of a static magnetic field or can improve the uniformity of a static magnetic field can be provided.

It is explanatory drawing which shows an example of the MRI apparatus with which this invention was applied. It is arrow sectional drawing of the AA direction of the MRI main body described in FIG. It is a block diagram which shows the control system which controls the positional relationship of the upper iron core and lower iron core of FIG. It is a block diagram which shows the other Example of the control system shown in FIG. It is a flowchart which shows the further another Example of the control system shown in FIG. It is explanatory drawing explaining the arrangement | positioning state of a heater. It is explanatory drawing explaining the other arrangement | positioning state of a heater. It is explanatory drawing of the Example which can reduce a noise in addition to the maintenance and improvement of the uniformity of a static magnetic field. It is explanatory drawing which shows the structure of the upper side support part 370. FIG. It is explanatory drawing explaining the propagation path of noise. It is explanatory drawing of the other Example which can reduce a noise in addition to the maintenance and improvement of the uniformity of a static magnetic field. It is explanatory drawing explaining the propagation path of the noise in the Example shown in FIG.

1. 1. Introduction Next, an embodiment of the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in drawing referred performs the substantially same effect | action, and there exists a substantially the same effect. In order to avoid duplication of description, the description of the actions and effects relating to the configuration of the same reference numerals is omitted. Further, the following embodiments not only solve the problems of the invention described above and achieve the effects of the invention described above, but also solve problems other than the problems of the invention described above, and achieve effects other than the effects described above. The solution and effect of the problem will be described in the description of the embodiment.

2. Description of an MRI Apparatus that is an Embodiment of an MRI Apparatus to which the Present Invention is Applied Next, an overall configuration of an MRI apparatus 100 that is an embodiment of an MRI apparatus to which the present invention is applied will be described with reference to FIG. . The MRI apparatus 100 includes a control device 110, an MRI main body 200, and a bed 150. In addition to these configurations, there is an apparatus for supplying a refrigerant such as liquid helium for cooling the superconducting electromagnet described below. However, the illustration and explanation are omitted because the explanation is complicated.

  The control device 110 inputs information related to the subject, sets imaging conditions for imaging, controls the imaging operation of the MRI main body 200 according to the set imaging conditions, and image data detected by the imaging operation. The input device 124 that performs an operation for information input and an operation for imaging control, the input and state of information, a captured image, and the like are displayed. An input / output device 120 including a display device 122, an arithmetic processing device 130 that controls an imaging operation of the MRI main body 200 according to a set imaging condition, and an imaging control device 140. The arithmetic processing unit 130 not only controls the MRI main body 200 but also processes the captured data to form an image. The arithmetic processing unit 130 includes a storage device that stores data necessary for processing, and further performs processing for storing the processed result in the storage device in a searchable state. Illustration of these storage devices is omitted. The arithmetic processing device 130 controls the imaging operation of the MRI main body 200 via the imaging control device 140 according to the set imaging conditions. The operation of the imaging control device 140 will be described below.

  The bed 150 has a top plate 152 on which a subject to be examined is placed. By moving the top board 152 on which the subject is placed to an appropriate position, the subject can be moved to an appropriate position based on the imaging conditions. The top plate 152 on which the subject is placed can move in the Z-axis direction, which is the height direction, and is in the X-axis direction, which is the body axis direction. Can be moved to. The bed 180 may also have a structure that can move in the examination room or the hospital where the MRI main body 200 is arranged in a state where the patient is placed on the bed 180.

3 Description of Imaging Operation by Imaging Control Device 140 and MRI Main Body 200 3.1 Description of Imaging Control Device 140 and MRI Main Body 200 With reference to FIG. 1 and FIG. The configuration and operation of the MRI main body 200 will be described. The arithmetic processing device 130 sends a control signal for imaging the subject to the imaging control device 140 according to the set imaging conditions. The imaging control device 140 includes a sequencer 142, an RF current supply device 144 for supplying an RF current to the RF irradiation coil 214 and the RF irradiation coil 215 for irradiating a high frequency magnetic field (hereinafter referred to as RF) pulse, and a gradient magnetic field generation device. 210 and the gradient magnetic field generator 211 have a gradient magnetic field power source 146 for supplying a current for generating a gradient magnetic field, and a signal processing device 148 for processing the measured NMR signal.

  2 shows an AA cross-sectional view of the MRI main body 200 shown in FIG. 1 taken along the X-axis and the Y-axis in the Z-axis direction. In the present embodiment, the MRI main body 200 has a circular shape or a substantially circular outer shape centered on the Z axis, and an observation region 204 for imaging a subject's site is formed at the upper and lower central portions on the Z axis. Thus, an opening 202 which is a wider space is formed in the observation region 204 and its periphery.

  In order to obtain a clear image, it is desirable to generate a uniform and strong magnetic field in the observation region 204, and an upper superconducting magnet device 300 and a lower superconducting electromagnet 400 are provided. An upper RF pulse irradiation coil 214 and a lower RF pulse irradiation coil 215 are provided so as to sandwich the observation region 204, and an upper gradient magnetic field generator 210 and a lower gradient magnetic field generator 211 are further provided. Further, the upper iron core 318 of the upper superconducting magnet device 300 and the lower iron core 418 of the lower superconducting electromagnet 400 are provided so as to sandwich the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211. Although not shown in the drawing, an NMR receiving coil for receiving an NMR signal emitted by an NMR phenomenon close to the subject in a space sandwiched between the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 is provided. Provided.

3.2 Description of Superconducting Electromagnet According to One Embodiment to which the Present Invention is Applied In the MRI main body 200 shown in FIGS. 1 and 2, an upper superconducting electromagnet 300 that is a pair of superconducting magnets that generate a static magnetic field, The lower superconducting electromagnet 400 is disposed opposite to the Z-axis direction across the observation region 204, and has a symmetric shape and configuration. In the MRI apparatus 100 having such a structure, the opening 202 can be formed very widely, which gives the subject 102 an open feeling and improves the workability of imaging. As shown in FIG. 1, the top plate 152 of the bed 150 is disposed in the opening 202, but the bed 150 is not shown in FIG. Further, a cover is provided in the outermost peripheral portion of the configuration of FIG. 2 and the inside of the opening 202, but illustration of these covers is omitted in FIG.

  As shown in FIG. 2, an upper superconducting magnet device 300 and a lower superconducting electromagnet 400 are provided inside the MRI main body 200 at upper and lower positions along the Z-axis direction. In the Y-axis direction, struts are provided so as to be separated from each other in the left-right direction. The upper superconducting magnet device 300 and the lower superconducting electromagnet 400 are integrally fixed to each other by the left and right struts, and the upper superconducting magnet device. 300 is supported by the left and right columns. The upper superconducting magnet device 300 has a vacuum container 350 whose inside is a vacuum, and the lower superconducting electromagnet 400 has a vacuum container 450 whose inside is a vacuum. The vacuum vessel 350 and the vacuum vessel 450 are connected to each other by the vacuum vessel connecting pipe 250 at the left and right support columns.

  The left and right struts, in which the vacuum vessel connecting pipe 250 is formed, may be provided in a positional relationship with an angular difference of 180 degrees along the Y axis, but the opening on the bed 150 side is larger. In order to do so, the Y axis may be further shifted toward the opposite side of the bed 150. When it is moved further in the opposite direction of the bed 150, the left and right columns overlap each other on the opposite side of the bed 150. In other words, the upper superconducting magnet device 300 is supported by one column. In this state, the opening on the bed 150 side becomes very wide, but a large force due to the rotational moment acts on the support column, and the strength to withstand these forces is required.

  A coil container 332 and a coil container 432 are disposed inside the vacuum container 350 and the vacuum container 450, respectively. The coil container 332 and the coil container 432 are connected by a coil container 232 provided inside the vacuum container connecting pipe 250. The coil container 332, the coil container 432, and the coil container 232 are filled with a refrigerant 230 such as liquid helium. The upper portions of the coil container 332 and the coil container 232 have a disk shape that is substantially rotationally symmetric with respect to the Z axis, which is a common central axis, and the superconducting coil 320 for configuring the upper superconducting magnet device 300. A superconducting coil 322 is provided. Similarly, the lower part of the coil container 432 and the coil container 232 has a disk shape that is substantially axially symmetric with respect to the Z axis, and the superconducting coil 420 and the superconducting material for constituting the lower superconducting electromagnet 400. A coil 422 is provided.

  Upper superconducting magnet device 300 is composed of superconducting coil 320 or superconducting coil 322 and upper iron core 318, and lower superconducting electromagnet 400 is composed of superconducting coil 420 or superconducting coil 422 and lower iron core 418. Is done. The upper superconducting magnet device 300 and the lower superconducting electromagnet 400 can generate a strong magnetic field having a magnetic field strength of 0.7 T or more in the spherical observation region 204, and the uniformity of the magnetic field strength is as high as several ppm. Uniformity can be maintained. The direction of the magnetic field is parallel to the Z axis. As described above, the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 are provided so as to sandwich the observation region 204 which is a uniform magnetic field region, and the observation region 204 is set based on the current from the RF current supply device 144. On the other hand, a high frequency magnetic field pulse can be generated.

  Since a high vacuum state is maintained between the vacuum vessel 350 and the coil vessel 332, between the vacuum vessel 450 and the coil vessel 432, and between the vacuum vessel connecting pipe 250 and the coil vessel 232, heat transfer by convection can be performed. Can be prevented. As another heat transfer, heat transfer by radiation can be considered. Therefore, between the vacuum vessel 350 and the coil vessel 332, between the vacuum vessel 450 and the coil vessel 432, and between the vacuum vessel connecting pipe 250 and the coil vessel 232, respectively, the heat shield 334, the heat shield 434, and the heat shield are provided. 234 is provided. Each heat shield has, for example, a material and a structure that reflects light, and each heat shield may have a layered structure including a heat insulating material and a light reflecting material.

3.3 Description of Imaging Operation A uniform static magnetic field is formed in the observation region 204 by the upper superconducting magnet device 300 and the lower superconducting electromagnet 400. Further, by supplying a current for generating a gradient magnetic field from the gradient magnetic field power supply 146 to the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211, the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211 are supplied. Applies a gradient magnetic field for causing a spatial change of the magnetic field in the uniform magnetic field region for the purpose of providing spatial position information in imaging of the subject. The upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 receive an RF current from the RF current supply device 144 and apply an electromagnetic wave having a resonance frequency for causing an NMR phenomenon to the uniform magnetic field region. By such an operation, a cross section of the observation region inside the subject placed on the top plate 152 of the bed 150 can be imaged.

  That is, by superimposing the gradient magnetic field generated by the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211 on the observation region 204 which is a uniform magnetic field region, an observation region (usually a slice surface having a thickness of 1 mm is set. Only) is set to a predetermined magnetic field strength. Subsequently, the observation region is irradiated with an electromagnetic wave having a resonance frequency using the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 to cause an NMR phenomenon only on the slice plane which is the observation region, thereby generating hydrogen nuclei. The electromagnetic wave emitted by the spin is received by a receiving coil (not shown), signal processed by a signal processing device 148, and imaged based on the processing result.

4). Description of Upper Superconducting Magnet Device 300 and Lower Superconducting Electromagnet 400 Although the outlines of the upper superconducting magnet device 300 and the lower superconducting electromagnet 400 have already been described above, their structures will be described in more detail. The upper superconducting magnet device 300 and the lower superconducting electromagnet 400 form a target structure vertically with respect to a plane formed by the X axis and the Y axis passing through the center of the observation region 204. The upper superconducting magnet device 300 has an annular superconducting coil 320 or superconducting coil 322 whose central axis coincides with the Z axis passing through the center of the observation region 204, and the superconducting coil 320 or superconducting coil. 322 is accommodated in the coil container 332 and the coil container 232, and is disposed in the refrigerant 230 such as liquid helium.

  Similarly, the lower superconducting electromagnet 400 includes an annular superconducting coil 420 and a superconducting coil 422 whose center axis coincides with the Z axis passing through the center of the observation region 204. The coil 422 is housed in the coil container 432 or the coil container 232 and is disposed in a refrigerant 230 such as liquid helium. The coil container 332, the coil container 432, and the coil container 232 are disposed inside the vacuum container 350, the vacuum container 450, and the vacuum container connecting pipe 250, each of which is kept in a vacuum. The heat conduction between them is suppressed. In order to further enhance the effect of suppressing the heat conduction, the above-described heat shield 334, heat shield 434, and heat shield 234 are further provided between each coil container and each vacuum container.

  A magnetic material is generated by causing a constant permanent current to flow through the superconducting coil 320, the superconducting coil 322, the superconducting coil 420, and the superconducting coil 422, and the magnetic field in the observation region 204 is uniform. As with the upper iron core 318, the lower iron core 418, which is a magnetic material, is arranged so as to sandwich the observation region 204. The upper iron core 318 and the lower iron core 418 have complicated shapes in order to make the static magnetic field uniform, but are illustrated in a simple shape in the drawing.

  In this embodiment, the upper iron core 318 is supported by the upper support portion 370, and the upper support portion 370 is supported by the vacuum vessel top plate 254 of the vacuum vessel connection pipe 250. In this embodiment, the upper support portion 370 includes a top plate 372 and a support material 374, and the support material 374 is made of an annular plate made of a nonmagnetic material, and the upper iron core 318 is attached to the top plate 372. The upper iron core 318 is supported by the suspended structure. Further, in this embodiment, the lower iron core 418 is supported by a lower support portion 470 fixed to the vacuum vessel bottom plate 262 of the vacuum vessel connecting pipe 250, and the lower support portion 470 is, in this embodiment, the bottom plate 472 and the support material. The support member 474 is made of an annular plate made of a nonmagnetic material, and supports the lower iron core 418 with respect to the vacuum vessel bottom plate 262 in a constant state.

  The above-described vacuum vessel connecting pipe 250 has a vacuum vessel bottom plate 262 and a vacuum vessel top plate 254, and the vacuum vessel bottom plate 262 and the vacuum vessel top plate 254 have a vacuum vessel outer wall 252 and a vacuum vessel inner wall 256, As described above, the inside is maintained at a substantially vacuum. The coil container 232 and the heat shield 234 provided inside the vacuum container connecting pipe 250 are respectively supported by support members 240 made of a heat insulating material. Further, the vacuum vessel inner wall observation part 258 that is a portion of the vacuum vessel inner wall 256 facing the observation region 204 is recessed toward the outer periphery, and this structure makes the opening 202 wider. In this embodiment, an outer heater 522 and an inner heater 524, which will be described below, are arranged on the outer peripheral side of the vacuum vessel connecting pipe 250, and a heat insulating material 512 and a heat insulating material are provided further outside the outer heater 522 and the inner heater 524. 514 is provided, and the outer heater 522 and the inner heater 524 are covered with the heat insulating material 512 and the heat insulating material 514. The positions of the outer heater 522 and the inner heater 524 are not limited to this position, but are positioned between the upper superconducting magnet device 300 and the lower superconducting electromagnet 400 in this embodiment. A temperature sensor 530 and a temperature sensor 532 for controlling the heater, which will be described below, are fixed to a vacuum vessel outer wall 252 made of stainless steel and detect the temperature at a position slightly away from the outer heater 522. In this embodiment, the heat insulating material 512 covers not only the outer heater 522 but also the temperature sensor 530 and the temperature sensor 532, thereby preventing outside air from directly acting on the sensor. Since an outer cover is actually provided outside the FIG. 2, even if, for example, an air flow, that is, a wind exists outside the MRI apparatus 100, the wind does not directly hit the temperature sensor 530 or the temperature sensor 532.

  As shown in FIG. 1, columns for fixing the upper superconducting magnet device 300 and the lower superconducting electromagnet 400 are provided on the left and right, and the structure of the vacuum vessel connecting pipe 250 shown in FIG. The internal structure of the right pillar among the provided pillars is shown, but the internal structure of the left pillar among the pillars provided on the left and right, and the structure and arrangement of each heater and each temperature sensor are Z-axis and X-axis. The structure and arrangement are symmetrical with respect to the vacuum vessel connecting pipe 250 on the right side and each heater and each temperature sensor.

5. Description on Improvement of Uniformity of Static Magnetic Field The upper iron core 318 and the lower iron core 418 generate a static magnetic field in the observation region 204 by the superconducting coil 320, the superconducting coil 322, the superconducting coil 420, and the superconducting coil 422. The upper iron core 318 and the lower iron core 418 correct the magnetic field so that the static magnetic field in the observation region 204 becomes uniform. Since the magnetization of the magnetic material such as the upper iron core 318 and the lower iron core 418 changes based on the temperature change, the magnetic material is kept warm so that the temperature becomes constant. In a device using a permanent magnet device instead of a superconducting magnet, since the magnetic material part covers the entire magnet, the whole magnet is kept warm by a heater. In this embodiment, the nonmagnetic material of the superconducting magnet device is used. It is not always necessary to maintain the temperature to cope with the temperature change of the magnetization for the portion constituted by the above, and the required uniformity can be ensured even if the structure does not maintain the temperature by the heater. For this reason, in this embodiment, a structure in which the whole magnet is kept warm by a heater is not used. However, in order to improve the accuracy, it is of course possible to perform heat insulation with a heater. In this embodiment, since the heat retaining structure of the upper iron core 318 and the lower iron core 418 by the heater is not used, there is an effect that the structure is simplified, and there is an effect that the opening 202 can be set wider.

  The upper support portion 370 and the lower support portion 470 that support the upper iron core 318 and the lower iron core 418 expand and contract due to temperature changes, and as a result, the positions of the upper iron core 318 and the lower iron core 418 change. Changes in the positions of the upper iron core 318 and the lower iron core 418 immediately lead to deterioration of the uniformity of the static magnetic field. By maintaining the temperature of the vacuum vessel connecting tube 250, the upper support portion 370, and the lower support portion 470 at a predetermined reference temperature, distortion due to expansion and contraction of the vacuum vessel connecting tube 250, the upper support portion 370, and the lower support portion 470 is achieved. And the positions of the upper iron core 318 and the lower iron core 418 can be maintained at predetermined positions.

  The outer heater 522 and the inner heater 524 are planar heating elements, for example, heaters made of carbon graphite. The outer heater 522 and the inner heater 524 are fixed, for example, on the outer surface of the vacuum vessel connecting pipe 250, and heat based on the supplied current value is generated by supplying current to these heaters, and the vacuum vessel connecting pipe The temperature of 250 is maintained at the reference temperature. As the reference temperature, a temperature slightly higher than the room temperature where the MRI apparatus 100 is installed is desirable from the viewpoint of maintaining control accuracy. If the reference temperature is further increased, the subject may be adversely affected by the temperature. Therefore, it is desirable to set the reference temperature in a range of about 25 degrees to 35 degrees, and a range of 28 degrees to 34 degrees is more desirable.

  As described above, the heaters are disposed on the outer surfaces of the vacuum vessel connection pipes 250 provided on the left and right sides of the opening 202, and the temperature of the vacuum vessel connection pipe 250 is set to the reference temperature, thereby connecting the vacuum vessel provided on the left and right sides. Expansion and contraction due to temperature changes of the tube 250, the upper support portion 370, and the lower support portion 470 can be reduced, and the positions of the upper iron core 318 and the lower iron core 418 can be maintained at the reference positions. As a result, the deterioration of the uniformity of the static magnetic field can be reduced, or the uniformity of the static magnetic field can be improved more positively. In the present embodiment, the support material 374 constituting the upper support portion 370 is made of the same material with a bilaterally symmetric structure, and the occurrence of the inclination of the upper iron core 318 due to the influence of temperature is reduced. Also, the support material 474 that supports the lower iron core 418 with respect to the lower support portion 470 is also made of the same material with a symmetrical structure, and the tilt of the lower iron core 418 due to the influence of temperature is reduced. Yes. Moreover, the shift | offset | difference in the relative positional relationship of the upper side iron core 318 and the lower side iron core 418 can also be suppressed. Furthermore, the relative position change of the vacuum vessel connecting pipe 250, the upper support portion 370, and the lower support portion 470 can be reduced.

  FIG. 3 is a block diagram of a controller system 540 that controls the heaters attached to the vacuum vessel connecting pipes 250 respectively provided in the columns disposed on the left and right sides of the opening 202. The control system 540 includes a reference temperature setting unit 534 that sets a reference temperature for keeping the temperature of the vacuum vessel connecting pipe 250 constant in order to suppress thermal expansion and contraction, a temperature sensor 530 that measures the actual temperature, and a temperature sensor. Record a temperature sensor such as 532, a heater control device 550 for controlling the current supplied to the outer heater 522 and the inner heater 524 based on the measured value of the temperature sensor, and a control data map for controlling the supply current. And a recording device 552.

  Note that the control system 540 may actually be one of the functions executed by the arithmetic processing device 130. The reference temperature setting unit 534 may be a function of the input / output device 120. When the reference temperature for maintaining the temperature of the vacuum vessel connecting tube 250 is input from the input device 124 of the input / output device 120 and set, The reference temperature is recorded in the recording device included in the arithmetic processing unit 130. Once this reference temperature is set, it may be used repeatedly until a change operation is performed. In other words, once the MRI apparatus 100 is installed in a room for inspection, the inspection room is generally used continuously without being changed for a long time. The room temperature does not change greatly and is maintained at a temperature suitable for the subject. For this reason, the reference temperature input and set in the temperature sensor 532 can be used repeatedly. Many temperature sensors such as the temperature sensor 530 and the temperature sensor 532 may be provided. However, in a state where the temperature of the examination room in which the MRI apparatus 100 is installed does not change so much, the vacuum vessel connecting pipe 250 provided on the left and right of the opening 202 is provided. There will be no difference in temperature. In such a case, it is difficult for a large change to occur in the temperature of each part, so that highly accurate control is possible without increasing the number of temperature sensors. The same applies to the control of each heater to be controlled. It is possible to improve the control accuracy by finely controlling each heater individually. However, if the change in room temperature is small, that is, if the state does not change much, it is not possible to control each heater individually. The desired accuracy can be maintained even if the plurality of heaters are collectively controlled.

  When the temperature of the temperature sensor 530 or the temperature sensor 532 is measured, the current supplied to the outer heater 522 or the inner heater 524 is controlled by feedback control so that the measured temperature approaches the reference temperature set by the temperature sensor 532. To do. In this way, the temperature of the vacuum vessel connecting pipe 250 can be maintained at the reference temperature.

  Alternatively, a control map for determining the heater current using the reference temperature and the sensor output as control parameters is stored in the recording device 552 in advance, and the outer heater 522 and the inner heater 524 are controlled based on the search result of the control map. Anyway. By maintaining the temperature of the vacuum vessel connecting pipe 250 provided on the left and right of the opening 202 at the reference temperature, the expansion / contraction state of the vacuum vessel connecting pipe 250 can be maintained at the reference state, and the upper iron core 318 and the lower iron core can be maintained. The positional relationship of 418 can be maintained at a desirable positional relationship. As a result, the uniformity of the static magnetic field in the observation region 204 can be maintained.

  In order to maintain the uniformity of the static magnetic field, it is necessary to adjust the positional relationship between the upper iron core 318 and the lower iron core 418 in units of very small lengths. In the embodiments described in FIGS. 2, 3, 4, etc., the supporting means existing between the upper iron core 318 and the lower iron core 418, specifically, the vacuum vessel connecting pipes disposed on the left and right of the opening 202. The fine adjustment of 250 is performed using thermal expansion due to temperature change. By utilizing the thermal expansion, it is possible to make a fine extension and contraction of the length, which is the control amount accurately and stably with respect to the operation amount that is the temperature adjustment. By utilizing thermal expansion in this way, fine adjustment of the positional relationship between the upper iron core 318 and the lower iron core 418 can be performed in a very stable state with high accuracy.

  By maintaining the temperature environment in which the upper iron core 318 and the lower iron core 418 are arranged in a predetermined state by the control of FIG. 3, the positional relationship between the upper iron core 318 and the lower iron core 418 is maintained in a desirable relationship. The magnetic characteristics of the upper iron core 318 and the lower iron core 418 are maintained at predetermined characteristics. As a result, the planned uniformity of the static magnetic field can be obtained.

  The upper iron core 318 and the lower iron core 418 are mechanically connected by the upper support portion 370, the lower support portion 470, and the vacuum vessel connecting pipe 250. In other words, the upper iron core 318 and the lower iron core 418 are supported by the vacuum vessel connecting pipe 250, the upper support portion 370, and the lower support portion 470, and the positional relationship between the upper iron core 318 and the lower iron core 418 is determined by this support state. The vacuum vessel connecting pipe 250, the upper support portion 370, and the lower support portion 470 act as a support mechanism for the upper iron core 318 and the lower iron core 418. Since the positional relationship between the upper iron core 318 and the lower iron core 418 changes when any one of the support mechanisms is expanded or contracted, a heater may be provided in the upper support portion 370 or the lower support portion 470 as a large concept. However, depending on the location of expansion and contraction, new torsion or the like occurs due to expansion and contraction, and it becomes difficult to control the positional relationship between the upper iron core 318 and the lower iron core 418 with high accuracy.

  In the embodiment described in FIG. 2 and the like, the vacuum vessel connecting pipe 250 is provided with a heater. The reason is that, when expanded and contracted, the positional relationship between the upper iron core 318 and the lower iron core 418 shows a stable change, and a rapid twist or the like hardly occurs. By setting the position corresponding to the observation region 204 of the vacuum vessel connecting pipe 250 to the position to expand and contract, more stable control can be performed than to expand and contract other positions. This is the same for the embodiments other than FIG.

  Next, the control system 542 shown in FIG. 4 will be described. As described above, the uniformity of the static magnetic field can be maintained by keeping the positional relationship between the upper iron core 318 and the lower iron core 418 in a desirable relationship. In the control system 542, the positional relationship between the upper iron core 318 and the lower iron core 418 is measured by a sensor, and the deviation of the upper iron core 318 and the lower iron core 418 is corrected by a heater. The positional relationship between the upper iron core 318 and the lower iron core 418 is input in advance by the reference position setting unit 562 and recorded in a recording device such as the recording device 554. Next, the positional relationship between the actual upper iron core 318 and the lower iron core 418 is measured by the position sensor 560, and the recording device 552, the inner heater 524, etc. so that the measurement result becomes the positional relationship set by the reference position setting unit 562. The current supplied to the heater is controlled by the heater control device 550. In order to accurately measure the positional relationship between the upper iron core 318 and the lower iron core 418, a plurality of position sensors may be provided. A plurality of heaters for adjusting the length may be provided. For example, a control map that outputs the supply current to each heater as a control amount using the measurement result of the position sensor as a parameter in the recording device 554 is recorded in advance, and the supply current to each heater is retrieved from the control map by a map search. You may make it ask. Similar to the embodiment shown in FIG. 3, the heater control device 550 shown in FIG. 4 may be one of the processing functions of the arithmetic processing device 130 constituting the control device 110. In this case, the arithmetic processing unit 130 processes a function that needs to be processed, for example, in a time-sharing manner, and the one function to be processed is the processing content described in FIGS.

  The flowchart shown in FIG. 5 is one of the functions processed by the arithmetic processing unit 130, and is executed as a process for improving the uniformity of the static magnetic field as a pre-process for imaging the subject. When the process is started in step S100, a magnetic field state, for example, a static magnetic field state is detected in step S102. Based on the detection result, the necessity of correction regarding the uniformity of the static magnetic field is determined in step S104. If correction regarding the uniformity of the static magnetic field is not necessary, step S120, which is a post-processing end of step S104, is executed.

  On the other hand, if it is determined that correction regarding the uniformity of the static magnetic field is necessary, step S106 is executed. When large correction is required, it is difficult only by correction using shim coils, and correction related to the positions of the upper iron core 318 and the lower iron core 418 described with reference to FIGS. 3 and 4 is required. In this case, as described above, the expansion and contraction of the support means between the upper iron core 318 and the lower iron core 418, for example, the vacuum vessel connecting pipe 250, is controlled by the heater control. In step S108, a heater current value for expanding and contracting the vacuum vessel connecting pipe 250 is obtained by calculation, and current is supplied to heaters such as the outer heater 522 and the inner heater 524 based on the calculation result. Thereafter, correction by the shim coil is performed. In this embodiment, step S102 is executed again after step S108, and the determination of step S104 or step S106 is performed. If it is determined in step S106 that only shim coil control is required, step S110 is executed, the control amount of the shim coil is calculated, and control is executed. Thereafter, when the correction is completed, this is confirmed in step S104, and the process is terminated in step S120.

  FIG. 6 shows an example of the heater mounting position. In the above description, the vacuum vessel connection pipes 250 are provided on the left and right sides of the opening 202. In FIG. 6, the right vacuum vessel connection pipe is denoted by 250, and the left vacuum container connection pipe is denoted by 251. A coil vessel and a heat shield are provided inside the vacuum vessel connecting tube 250 and the vacuum vessel connecting tube 251, but these are omitted in FIG. Although described in FIG. 2, an outer heater 522 and an inner heater 524 are provided on the outer peripheral surface of the vacuum vessel connecting pipe 250 shown in FIG. 6, and the outer heater 523 and the inner heater 525 are similarly provided in the vacuum vessel connecting pipe 251. Is provided. By changing the amount of current between the outer heater 522 and the inner heater 524 provided in the vacuum vessel connecting pipe 250 and the outer heater 523 and the inner heater 525 provided in the vacuum vessel connecting pipe 251, The inclination of the side iron core 418 in the Y-axis direction can be adjusted.

  Instead of or in addition to the outer heater 522 and the inner heater 524, a heater 572 and a heater 574 may be provided. Furthermore, instead of or in addition to the outer heater 523 and the inner heater 525, a heater 573 and a heater 575 may be provided. By controlling the supply current to the heater provided in the vacuum vessel connection pipe 250 and the supply current to the heater provided in the vacuum vessel connection pipe 251, as described above, the upper iron core 318 and the lower iron core 418 in the Y direction. The tilt and positional relationship can be corrected. Further, by controlling the supply current of the heater 574 and the heater 575 with respect to the supply current of the heaters 572 and 573, the inclination and the positional relationship of the upper iron core 318 and the lower iron core 418 in the X-axis direction can be corrected. With such a structure, finer adjustments can be made.

  Another embodiment shown in FIG. 2 will be described with reference to FIG. In FIG. 2, a coil container 232 and a heat shield 234 are provided inside the vacuum container connecting pipe 250, but these are omitted in FIG. In FIG. 2, the outer heater 522 and the inner heater 524 are each composed of one heater, but in FIG. 7, these heaters are divided and arranged in the Z-axis direction. That is, a heater 526 and a heater 527 are provided on the surface of the vacuum vessel outer wall 252. In addition, a heater 528 and a heater 529 are also provided in the recess 258. Another sensor is provided at the position of the recess 258 corresponding to the center of the observation region 204 or the position of the vacuum vessel outer wall 252 corresponding to the center of the observation region 204, or the surface of the recess 258 or the vacuum vessel outer wall 252 is flat. It may have a special shape instead of a surface. The heater that heats the recess 258 and the vacuum vessel outer wall 252 is divided into a plurality of parts as shown in FIG. 7 and arranged in a balanced manner with respect to the upper iron core 318 and the lower iron core 418 in the vertical direction, which is the Z-axis direction. The positional relationship between the iron core 318 and the lower iron core 418 can be controlled with high accuracy.

6). Description of an embodiment that maintains static magnetic field uniformity and reduces noise Next, noise generated by the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211 using the embodiment shown in FIG. The reduction of the will be described. The description of the same configuration as that in FIG. 2 is omitted. In this embodiment, an upper gradient magnetic field generator 210 having a gradient magnetic field coil is fixed to the observation region 204 side of the upper iron core 318 of the upper superconducting magnet device 300 and the lower iron core 418 of the lower superconducting electromagnet 400 is fixed. A lower gradient magnetic field generator 211 having a gradient magnetic field coil is fixed on the observation region 204 side. The upper iron core 318 and the upper gradient magnetic field generator 210 are supported by an upper support portion 370, and the upper support portion 370 is supported by a vacuum vessel top plate 254 of a vacuum vessel connection tube 250 and a vacuum vessel top plate 354 of a vacuum vessel 350. Yes. The upper support 370 supports the upper RF pulse irradiation coil 214 in addition to the upper iron core 318 and the upper gradient magnetic field generator 210, but the upper RF pulse irradiation coil 214 is connected to the upper iron core 318 and the upper gradient magnetic field generator 210. Are supported in a completely separate structure.

  The upper support portion 370 includes a top plate 372 supported by the vacuum vessel top plate 254 and the vacuum vessel top plate 354, a support material 374 for supporting the upper iron core 318 and the upper gradient magnetic field generator 210, and a support material 374. Has a support member 272 and a support member 273 for supporting the upper RF pulse irradiation coil 214 provided separately. The support member 374 is made of an annular plate made of a nonmagnetic material and has a structure in which the upper iron core 318 and the upper gradient magnetic field generator 210 are suspended from the top plate 372. The support member 272 and the support member 273 have a structure in which the upper RF pulse irradiation coil 214 is suspended from the top plate 372 of the upper support portion 370.

  FIG. 9 shows the structure of the upper support portion 370 having a structure in which the upper iron core 318 and the upper gradient magnetic field generator 210 are suspended by the support material 374 and a structure in which the upper RF pulse irradiation coil 214 is suspended by the support material 374. The lower support 470 that supports the lower iron core 418 and the lower gradient magnetic field generator 211 described below and further supports the lower RF pulse irradiation coil 215 has the same structure as the upper support 370. The upper support portion 370 and the lower support portion 470 are disposed so as to be symmetric with respect to the observation region 204. As a representative of the lower support portion 470 and the upper support portion 370, the structure of the upper support portion 370 is shown in FIG.

  In FIG. 9, the upper gradient magnetic field generator 210 and the upper iron core 318 are fixed to the top plate 372 of the upper support portion 370 by a support member 374 made of a cylindrical stainless steel plate. The upper RF pulse irradiation coil 214 is fixed to the top plate 372 of the upper support portion 370 by a plate-like support material 272, a support material 273, and a support material 274 made of stainless steel. As shown in FIG. 8, a gap 212 is formed between the upper gradient magnetic field generator 210 and the upper RF pulse irradiation coil 214.

  The lower gradient magnetic field generator 211 and the lower iron core 418 are supported by a lower support portion 470 fixed to the vacuum vessel bottom plate 462 of the vacuum vessel 450 and the vacuum vessel bottom plate 262 of the vacuum vessel connecting pipe 250, and further, the lower RF The pulse irradiation coil 215 is also supported and fixed to the 462 and the vacuum vessel bottom plate 262 by the lower support portion 470. As described above, the lower support portion 470 has the same structure as the upper support portion 370, and the lower gradient magnetic field generator 211 and the lower iron core 418 are lowered by the support material 474 made of a cylindrical stainless steel plate. It is fixed to the bottom plate 472 of the side support portion 470. On the other hand, the lower RF pulse irradiation coil 215 is fixed to the bottom plate 472 of the lower support portion 470 by a plate-like support material 276 made of stainless steel, a support material 277, or the like. As shown in FIG. 2, a space 213 is formed between the lower gradient magnetic field generator 211 and the lower RF pulse irradiation coil 215.

  As shown in FIG. 8, the above-described vacuum vessel connecting pipe 250 has a vacuum vessel bottom plate 262 and a vacuum vessel top plate 254, and the vacuum vessel bottom plate 262 and the vacuum vessel top plate 254 have a vacuum vessel outer wall 252 and a vacuum vessel inner wall. 256, and the interior is maintained in a substantially vacuum as described above. The coil container 232 and the heat shield 234 provided inside the vacuum container connecting pipe 250 are respectively supported by support members 240 made of a heat insulating material. Further, the vacuum vessel inner wall observation part 258 that is a portion of the vacuum vessel inner wall 256 facing the observation region 204 is recessed toward the outer periphery, and this structure makes the opening 202 wider. As shown in FIG. 1, columns for fixing the upper superconducting magnet device 300 and the lower superconducting electromagnet 400 are provided on the left and right, and the structure of the vacuum vessel connecting pipe 250 shown in FIG. The internal structure of the right column among the provided columns is shown, but the internal structure of the left column among the columns provided on the left and right sides is made with respect to the vacuum vessel connecting pipe 250 by the Z axis and the X axis. The surface is symmetrical with respect to the surface.

7). Explanation on Causes of Noise Generation and Reduction of Noise In the MRI apparatus 100, the gradient magnetic field coils included in the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211 are supplied to the gradient magnetic field coil 146 from the gradient magnetic field power supply 146 with timing and voltage based on the inspection conditions. A pulsed current is applied. When a pulsed current is applied to the gradient coil, Lorentz force acts to generate vibration in the gradient coil. Since the Lorentz force tends to increase as the static magnetic field strength increases, in a MRI apparatus in which a strong static magnetic field by a superconducting magnet is used, vibration due to the gradient magnetic field coil becomes large, and this vibration is transmitted without being attenuated, When the upper RF pulse irradiation coil 214, the lower RF pulse irradiation coil 215, the wall 352 and the wall 452 are converted into air vibrations, a large noise 10 (see FIG. 10) and noise 12 (see FIG. 10) are generated. This gives an unpleasant feeling to the subject.

  The configuration in which air vibration is likely to be generated due to the vibration by the gradient magnetic field coil is the wall that is the surface on the opening 202 side of the upper RF pulse irradiation coil 214, the lower RF pulse irradiation coil 215, and the vacuum vessel 350 as described above. 352 and a wall 452 which is a surface on the opening 202 side of the vacuum vessel 450, both of which have a shape having a relatively large surface for vibrating air in the vicinity of the subject. Accordingly, vibrations generated by the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211, which are the vibration sources, cause individual numbers to be transmitted to the upper RF pulse irradiation coil 214, the wall 352 of the vacuum vessel 350, and the wall 452 of the vacuum vessel 450. Reduction is very important.

  The vibration transmission path and generation of noise will be described using the configuration shown in FIGS. 8 and 9 and the block diagram showing the vibration transmission shown in FIG. As described above, the upper gradient magnetic field generation device 210 and the lower gradient magnetic field generation device 211 can be given as examples of the vibration generation source. First, the vibration generated by the upper gradient magnetic field generator 210 will be described. When vibration is generated in the gradient magnetic field coil included in the upper gradient magnetic field generator 210, the vibration is transmitted to the top plate 372 via the upper iron core 318 and the support material 374, and the support material 272, the support material 273, and the support material are transmitted from the top plate 372. 274 is transmitted to the upper RF pulse irradiation coil 214 via the 274, and air vibration is generated by the upper RF pulse irradiation coil 214, resulting in noise 10. The vibration transmitted to the top plate 372 is transmitted to the vacuum vessel 350, vibrates the wall 352 of the vacuum vessel 350, and air vibration is generated by the vibration of the wall 352, and noise 12 is generated. Noises 10 and 12 generated by the upper RF pulse irradiation coil 214 and the wall 352 greatly affect the subject. Of course, noise is also generated from places other than the upper RF pulse irradiation coil 214 and the wall 352, but noise generated at a place far away from the noise 10 has little influence on the subject. For this reason, it is desirable to take measures against a noise generation source existing near the subject. As described above, the noise generation source existing near the subject is the wall 352 and the upper RF pulse irradiation coil 214, but the wall 452 and the lower RF pulse irradiation coil 215 described below are also close to the subject. It becomes an existing noise source.

  In the embodiment shown in FIGS. 8 and 9, the vibration generated by the upper gradient magnetic field generator 210 is transmitted to the support member 374 via the upper iron core 318, and the propagation path of the vibration transmitted from the support member 374 to the top plate 372 is very high. Has a long structure. A gap 212 is formed between the upper gradient magnetic field generator 210 and the upper RF pulse irradiation coil 214. It should be noted that the same effects as the effects of the upper gradient magnetic field generator 210 on the vibration are also generated for the vibration generated by the lower gradient magnetic field generator 211 described below.

  A gap 212 is formed between the upper gradient magnetic field generator 210 and the upper RF pulse irradiation coil 214. Note that the air gap 212 corresponds to the space 213 in terms of operational effects. The vibration generated by the gradient magnetic field coil inside the upper gradient magnetic field generation device 210 is transmitted from the surface of the upper gradient magnetic field generation device 210 to the air gap 212 and from the air gap 212 to the upper RF pulse irradiation coil 214 and is transmitted to the upper RF pulse irradiation coil. Noise is generated by vibrating the air in the opening 202 by the 214, but the attenuation of the vibration is large in the transmission path that vibrates the upper RF pulse irradiation coil 214 again from the upper gradient magnetic field generator 210 through the air vibration of the air gap 212. Become. For this reason, the noise caused by the vibration transmitted to the upper RF pulse irradiation coil 214 is small and the influence is small. As described below, the same effect can be obtained for the structure in which the space 213 is formed.

  In the transmission path through which vibration is transmitted from the upper gradient magnetic field generator 210 to the upper support portion 370 through the upper iron core 318, the length of the support member 374 in the Z direction is long. Since the vibration generated by the upper gradient magnetic field generator 210 has a wide bandwidth, it is difficult to dampen it even if it is intended to dampen the vibration using an elastic body. However, in this embodiment, since the support member 374 has a long transmission path, it has a characteristic of greatly suppressing transmission of vibrations other than a specific narrow band. For this reason, the connection portion between the upper iron core 318 and the support member 374, the connection portion between the support member 374 and the top plate 372, or the connection portion between the top plate 372 and the support member 273, the top plate 372, and the vacuum vessel top plate 354 is narrow. By suppressing the vibration in the band, the noise generated by the upper RF pulse irradiation coil 214 and the wall 352 can be greatly reduced. It is possible to attach a damping material to the wall of the support material 374, the top plate 372, the vacuum vessel top plate 354 and other vacuum vessels 350, and the support material 374, the top plate 372, the vacuum vessel top plate 354 and other vacuum vessels. A damping material can be used as the material of 350.

  As described above, the gradient magnetic field coil included in the lower gradient magnetic field generator 211 also generates a wide bandwidth vibration. However, as with the air gap 212, the lower gradient magnetic field generator 211 and the lower RF pulse irradiation coil 215 are arranged. A space 213 is formed. With this structure, vibration transmission from the lower gradient magnetic field generator 211 to the lower RF pulse irradiation coil 215 can be greatly reduced. Further, as described in the support member 374, a long vibration transmission path is formed by the support member 474. As a result, vibrations at other frequencies are greatly attenuated while leaving vibrations at specific frequencies. Therefore, as described above, in the connection of the lower iron core 418, the support material 474, the support material 474, the lower support portion 470, the bottom plate 472, the support material 277, the bottom plate 472, and the wall of the vacuum vessel 450, the vibration of a specific frequency. By suppressing the noise, the noise generated by the lower RF pulse irradiation coil 215 and the wall 452 can be greatly reduced. Further, the above-described vibration damping material may be attached to the plate material constituting the transmission path, or the plate material itself constituting the transmission path may be configured to use the vibration damping material.

  Further, by forming the support material 374, the support material 273, and the vacuum vessel 350 so that the vibration bandwidth transmitted by the support material 374 and the vibration bandwidth transmitted by the support material 273 and the vacuum vessel 350 are different, the upper gradient magnetic field is generated. It is possible to suppress the vibration of the generator 210 from being transmitted to the upper RF pulse irradiation coil 214 and the wall 352. The support material 374 is made of a plate that is long in the Z-axis direction, and the support material 272, the support material 273, and the vacuum vessel 350 are similarly made of a plate that is long in the Z-axis direction. Can be obtained. The same applies to the vibration generated by the lower gradient magnetic field generator 211. The support material 474, the support material 276, and the support material 277 vacuum vessel 450 are made of a plate that is long in the Z-axis direction. is important.

  The length of the support member 374 or the lower iron core 418 in the Z-axis direction is at least twice the length of the upper iron core 318 or the lower iron core 418 in the Z-axis direction, as shown in FIGS. It is about twice as long. The length of the support material 272, the support material 273, or the support material 276, or the support material 277 in the Z-axis direction is about twice or more and about three times the length of the upper iron core 318 or the lower iron core 418 in the Z-axis direction. There is a length of. The lengths of the vacuum vessel 350 and the vacuum vessel 450 in the Z-axis direction are about twice or more and about 3 times the length of the upper iron core 318 or the lower iron core 418 in the Z-axis direction. By having such a structure, the above-described effects can be obtained.

  In addition, as a background enabling such a structure, the upper iron core 318 which is a part of the upper superconducting magnet device 300 and the lower iron core 418 which is a part of the lower superconducting electromagnet 400 are replaced with the vacuum vessel 350 and the vacuum vessel 450. It is mentioned that it was made the structure which goes outside. By arranging the upper iron core 318 and the lower iron core 418 outside the vacuum vessel 350 and the vacuum vessel 450, the length of the support member 374 supporting the upper iron core 318 in the Z-axis direction can be increased. The vibration generated by the upper gradient magnetic field generator 210 and the lower gradient magnetic field generator 211 is moved upward via the top plate 372 and the bottom plate 472 fixed to the vacuum vessel top plate 254 and the vacuum vessel bottom plate 262 of the vacuum vessel connection pipe 250. A structure that can be transmitted to the RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 can be obtained. With this configuration, the noise generated by the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 and the noise generated by the wall 352 and the wall 452 can be greatly reduced.

  FIG. 11 shows another embodiment of the embodiment shown in FIGS. FIG. 12 is a block diagram showing a vibration transmission state and noise generation state in the embodiment of FIG. In FIG. 12, the description of the configuration common to FIG. 8 is omitted. In FIG. 8, the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 are supported by the support material 272, the support material 273, the support material 276, and the support material 277. For this reason, in the vibration transmission path shown in FIG. 10, the vibration transmitted to the top plate 372 and the bottom plate 472 is transmitted to the upper RF pulse irradiation coil 214 and the lower member via the support member 272, the support member 273, the support member 276, and the support member 277. It was transmitted to the side RF pulse irradiation coil 215. In another embodiment shown in FIG. 11, the upper RF pulse irradiation coil 214 is supported and fixed by the wall 352 of the vacuum vessel 350 and the recess 258 of the vacuum vessel inner wall 256 of the vacuum vessel connecting tube 250. Similarly, the lower RF pulse irradiation coil 215 is supported and fixed by the wall 452 of the vacuum vessel 450 and the recess 258 of the inner wall 256 of the vacuum vessel. In this structure, the vibration transmission path is the same from the upper gradient magnetic field generator 210 to the top plate 372 or from the lower gradient magnetic field generator 211 to the bottom plate 472. An air gap 212 is formed between the upper gradient magnetic field generator 210 and the upper RF pulse irradiation coil 214. Since the space 213 is formed between the lower gradient magnetic field generator 211 and the lower RF pulse irradiation coil 215, vibration is transmitted from the upper gradient magnetic field generator 210 to the upper RF pulse irradiation coil 214 via the gap 212. Is suppressed, and a space 213 is formed between the lower gradient magnetic field generator 211 and the lower RF pulse irradiation coil 215, so that the lower RF pulse irradiation is performed from the lower gradient magnetic field generator 211 via the space 213. Transmission of vibration to the coil 215 is suppressed.

  The vibration transmitted to the top plate 372 and the bottom plate 472 is transmitted to the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 via the vacuum vessel inner wall 256 of the vacuum vessel connecting pipe 250. Since the transmission path in the Z direction is long, the noise generated by the upper RF pulse irradiation coil 214 and the lower RF pulse irradiation coil 215 can be greatly reduced by the effects already described in FIG.

  The vibration transmitted to the top plate 372 is transmitted to the wall 352 through the vacuum vessel 350 and noise is generated in the wall 352, or further transmitted from the wall 352 to the upper RF pulse irradiation coil 214 to be transmitted to the upper RF pulse irradiation coil 214. Noise may occur. However, the action and effect already described with reference to FIG. 8 can greatly suppress the transmission of vibration to the wall 352, and the noise generated by the wall 352 and the upper RF pulse irradiation coil 214 can be greatly suppressed.

  Similarly, the vibration transmitted from the lower gradient magnetic field generator 211 to the bottom plate 472 is transmitted to the wall 452 through the vacuum vessel 450 to generate noise in the wall 452 or further from the wall 452 to the lower RF pulse irradiation coil 215. The lower RF pulse irradiation coil 215 noise is generated. However, the action and effect already described with reference to FIG. 8 can greatly suppress the transmission of the vibration of the wall 452, and can greatly suppress the noise transmitted from the wall 452 to the lower RF pulse irradiation coil 215.

8). Description of Still Another Embodiment Regarding Reduction of Noise Generation Although the embodiment shown in FIG. 8 and the embodiment shown in FIG. 11 have been described, the upper RF pulse irradiation coil 214 is used as a support material in the embodiment shown in FIG. Since the upper RF pulse irradiation coil 214 is fixed using the 272 and the support member 273, there is an advantage that the vacuum vessel 350 is not burdened. It is desirable that the inside of the vacuum vessel 350 is in a high vacuum state and does not impose a mechanical burden. In the structure shown in FIG. 11, the upper RF pulse irradiation coil 214 is fixed to the wall 352 of the vacuum vessel 350, and mechanical processing for fixing the upper RF pulse irradiation coil 214 to the wall 352 is performed. Necessary. On the other hand, since the inside of the vacuum vessel 350 is in a highly vacuum state, special considerations such as thickening the wall 352 are required when the above mechanical processing is performed. In the support structure shown in FIGS. 8 and 9, the upper RF pulse irradiation coil 214 is suspended by the support material 272 and the support material 273, and the tensile strength of the support material 272 and the support material 273 is used. The tensile strength of the metal plate constituting the support material 272 and the support material 273 is used. However, since the metal plate has a high tensile strength, there is an effect that a sufficient strength can be easily obtained even in a relatively thin state.

  On the other hand, in the structure of FIG. 8, a force in the compression direction acts on the support member 276 and the support member 277 that support the lower RF pulse irradiation coil 215. Further, there is a possibility that the weight of the subject 20 may be applied on the lower RF pulse irradiation coil 215. In order to support the lower RF pulse irradiation coil 215 with the support material 276 or the support material 277, the support material 276 or the support material is used. It is necessary to increase the thickness to obtain a strength of 277. From this viewpoint, the lower RF pulse irradiation coil 215 shown in FIG. 8 is supported by the support material 276 and the support material 277, and the lower RF pulse irradiation coil 215 is supported by the wall 452 of the vacuum vessel 450 and the vacuum vessel as shown in FIG. A structure supported by the recess 258 of the connecting pipe 250 is preferred. Therefore, it is more effective to use a combination of the structure of FIG. 8 and FIG. 11 in which the upper RF pulse irradiation coil 214 is supported by the structure of FIG. 8 and the lower RF pulse irradiation coil 215 is supported by the structure of FIG.

  DESCRIPTION OF SYMBOLS 100 ... MRI apparatus, 110 ... Control apparatus, 120 ... Input / output apparatus, 122 ... Display apparatus, 124 ... Input apparatus, 130 ... Arithmetic processing apparatus, 140 ... Imaging control Device: 142 ... Sequencer, 144 ... RF current supply device, 146 ... Gradient magnetic field power supply, 148 ... Signal processing device, 150 ... Bed, 152 ... Top plate, 200 ... MRI main body, 202 ... opening, 204 ... observation region, 210 ... upper gradient magnetic field generator, 211 ... lower gradient magnetic field generator, 214 ... upper RF pulse irradiation coil, 215 ... Lower RF pulse irradiation coil, 230 ... refrigerant, 232 ... coil container, 240 ... support member, 250 ... vacuum vessel connecting tube, 252 ... vacuum vessel outer wall, 254 ... vacuum Container top plate, 256 ..Vacuum vessel inner wall, 258... Recessed portion, 262... Vacuum vessel bottom plate, 272 .. support material, 273 .. support material, 276 .. support material, 277. ..Upper superconducting magnet device, 318 ... upper iron core, 320 ... superconducting coil, 322 ... superconducting coil, 332 ... coil container, 334 ... heat shield, 350 ... vacuum Vessel, 352 ... wall, 354 ... vacuum vessel top plate, 370 ... upper support, 372 ... top plate, 374 ... support material, 400 ... lower superconducting electromagnet, 418 ... Lower iron core, 420 ... Superconducting coil, 422 ... Superconducting coil, 432 ... Coil container, 434 ... Heat shield, 450 ... Vacuum container, 452 ... Wall, 462 ... Vacuum vessel bottom plate, 470 ... Lower support, 4 2 ... bottom plate, 474 ... bottom plate support material, 512 ... heat insulating material, 514 ... heat insulating material, 522 ... outer heater, 524 ... inner heater, 526 ... heater, 527 ... ..Heater, 530 ... temperature sensor, 532 ... temperature sensor, 534 ... reference temperature setting unit, 540 ... control system, 550 ... heater control device, 552 ... recording device. 560 ... Position sensor, 562 ... Reference position setting unit, 554 ... Recording device, 572 ... Heater, ... 573, 574 ... Heater, 575 ... Heater.

Claims (14)

An MRI main body, a control device for controlling the operation of the MRI main body, and a bed for placing a subject;
The MRI main body includes a static magnetic field generator that generates a static magnetic field in an observation region, a gradient magnetic field generator that generates a gradient magnetic field, and an RF pulse irradiation coil.
The static magnetic field generator has a coil for generating magnetic flux and a magnetic material for equalizing the magnetic flux,
An MRI apparatus characterized in that a heating element is provided in a part of the support mechanism of the magnetic material, and the positional relationship of the magnetic material is controlled by controlling the amount of heat generated by the heating element.   2. The MRI apparatus according to claim 1, further comprising: a vacuum vessel, wherein the coil of the static magnetic field generation device is configured by a superconducting coil, the superconducting coil is disposed inside the vacuum vessel, and the magnetic material is An MRI apparatus, which is disposed outside the vacuum container. The MRI apparatus according to claim 2,
The vacuum vessel has an upper vacuum vessel and a lower vacuum vessel arranged above and below the observation region,
The superconducting coil has an upper superconducting coil and a lower superconducting coil arranged above and below the observation region. The upper superconducting coil is provided inside the upper vacuum vessel, and The side superconducting coil is provided inside the lower vacuum vessel,
The magnetic material has an upper magnetic material and a lower magnetic material which are arranged above and below the observation region and arranged outside the upper vacuum vessel or the lower vacuum vessel,
An upper superconducting magnet device is made by the upper superconducting coil and the upper magnetic material, and a lower superconducting electromagnet is made by the lower superconducting coil and the lower magnetic material,
The upper magnetic material and the lower magnetic material are supported by the support mechanism,
The support mechanism includes a vacuum vessel connecting tube that connects the upper vacuum vessel and the lower vacuum vessel, an upper support portion that fixes the upper magnetic material to the vacuum vessel connecting tube, and the lower support for the vacuum vessel connecting tube. A lower support portion for fixing the side magnetic material,
An MRI apparatus, wherein the heating element is provided in the vacuum vessel connecting pipe. The MRI apparatus according to any one of claims 1 to 3,
An MRI apparatus comprising a detecting means for detecting a state of the magnetic material, and a current supplied to the heating element is controlled based on a detection result of the detecting means. The MRI apparatus according to claim 4, wherein
The detection means is a temperature sensor, and further includes a reference temperature setting unit for setting a temperature higher than the room temperature where the MRI apparatus is placed as a reference temperature. The detection result of the temperature sensor and the reference temperature setting unit The MRI apparatus is characterized in that the current supplied to the heating element is controlled based on the reference temperature set by. The MRI apparatus according to claim 4, wherein
The MRI apparatus, wherein the detection means is a position sensor that detects a position state of the magnetic material, and a current supplied to the heating element is controlled based on a detection result of the position sensor. The MRI apparatus according to claim 4, wherein
The detection means is a magnetic field state detection means for detecting a state of a static magnetic field, and an electric current supplied to the heating element is controlled based on a detection result of the magnetic field state detection means. apparatus.   8. The MRI apparatus according to claim 1, wherein the heating element is covered with a heat insulating material.   9. The MRI apparatus according to claim 8, wherein the heating element is a heater made of carbon graphite.   10. The MRI apparatus according to claim 1, wherein the RF pulse irradiation coil is disposed on the observation region side of the gradient magnetic field generator, and the gradient magnetic field generator, the RF pulse irradiation coil, An MRI apparatus characterized in that a gap is formed between the two. The MRI apparatus according to claim 10, wherein
The static magnetic field generator has an upper superconducting magnet device and a lower superconducting magnet device arranged in the vertical direction across the observation region,
The RF pulse irradiation coil has an upper RF pulse irradiation coil and a lower RF pulse irradiation coil,
The upper superconducting magnet device includes an upper vacuum vessel, an upper superconducting coil provided inside the upper vacuum vessel, and an upper iron core,
The lower superconducting magnet device has a lower vacuum vessel, a lower superconducting coil provided inside the lower vacuum vessel, and a lower iron core,
The gradient magnetic field generator has an upper gradient magnetic field generator and a lower gradient magnetic field generator,
The upper iron core and the upper gradient magnetic field generator are supported by an upper first support member, and the lower iron core and the lower gradient magnetic field generator are supported by a lower first support member,
The MRI apparatus, wherein the upper RF pulse irradiation coil and the lower RF pulse irradiation coil are supported by a member other than the upper first support member and the lower first support member. The MRI apparatus according to claim 11,
A vacuum vessel connecting pipe connecting the upper vacuum vessel and the lower vacuum vessel is provided,
A top plate fixed to the upper part of the vacuum vessel connecting pipe is provided,
The upper first support member is supported by the top plate;
The MRI apparatus, wherein the upper RF pulse irradiation coil is supported by the top plate by an upper second support member.   13. The MRI apparatus according to claim 12, wherein the upper first support member has a cylindrical shape, one of the cylindrical shapes is fixed to the top plate, and the upper iron core and the upper gradient magnetic field are fixed to the other cylindrical shape. An MRI apparatus, characterized in that the generator is supported. The MRI apparatus according to claim 13,
An opening having the observation region is formed,
The upper vacuum vessel and the lower vacuum vessel are arranged facing each other across the opening,
The MRI apparatus, wherein the lower RF pulse irradiation coil is fixed to the opening side of the lower vacuum vessel.

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