JP5498614B2 - Magnetic resonance imaging system - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging (MRI) apparatus for medical diagnosis and a sound insulation method thereof, and in particular, a silent magnetic resonance imaging apparatus capable of greatly suppressing noise generated due to driving of a gradient magnetic field coil. About.

  A magnetic resonance imaging apparatus for medical diagnosis is an imaging apparatus based on the magnetic resonance phenomenon of nuclear spins in a subject, and is non-invasive and is not exposed to X-ray exposure like an X-ray device. An image can be obtained. For this reason, its usefulness has been demonstrated in abundance in clinical settings in recent years.

  In general, a magnetic resonance imaging apparatus for obtaining an MR image includes a gantry for inserting a subject into an imaging space, and an apparatus body that cooperates with the gantry. The gantry includes a static magnetic field magnet such as a superconducting magnet for generating a static magnetic field in a diagnostic space, a gradient magnetic field coil that generates a linear gradient magnetic field superimposed on the static magnetic field, and an RF that transmits a high-frequency signal and receives an MR signal It has a coil. At the time of imaging, the static magnetic field magnet, the gradient magnetic field coil, and the RF coil are driven along a desired pulse sequence. That is, according to the pulse sequence, a linear gradient magnetic field in each direction of the x, y, and z axes is superimposed on a subject placed in a static magnetic field, and the nuclear spin of the subject is magnetically excited with a high-frequency signal having a Larmor frequency. The A magnetic resonance (MR) signal generated with this excitation is detected, and a two-dimensional tomographic image of the subject is reconstructed based on this signal.

  In such magnetic resonance imaging, in recent years, there is a great need for speeding up imaging in order to shorten the time required for imaging. In response to this, a pulse sequence involving high-speed switching (high-speed inversion) of a gradient magnetic field pulse such as a high-speed echo planar imaging (EPI) method has been developed, and some have been successfully put into practical use.

  When a gradient magnetic field pulse is generated, an electromagnetic force acts on the gradient magnetic field coil at the rising or inversion thereof. This electromagnetic force causes mechanical distortion in the coil unit, and the whole unit vibrates starting from this. Due to the vibration of the coil unit, there is a problem that air vibration occurs and noise is generated.

  In particular, when the gradient magnetic field pulse is reversed at a high speed, the vibration increases, so that the noise generated increases as the speed increases. This noise may give a very uncomfortable feeling or anxiety to the subject (patient) lying in the imaging space of the gantry.

  For this reason, in order to eliminate such noise, there is an attempt to seal the entire unit of the gradient magnetic field coil in a vacuum vessel and to eliminate vibration or noise air propagation based on the vacuum space.

However, the conventional noise countermeasures described above still have the following unsolved problems.
In a sealed container that seals a gradient magnetic field coil in a vacuum space, a container and covers that form the vacuum space are jointed to a cover and a casing of a static magnetic field magnet. The gradient magnetic field coil itself is also supported by a static magnetic field magnet container and covers.

  For this reason, a part of the vibration (noise) generated by the gradient magnetic field coil is blocked in the vacuum space, but another part of the vibration propagates to the static magnetic field magnet or the like via the support part of the gradient magnetic field coil. . Therefore, there is a problem that the static magnetic field magnet vibrates together with the vibration generated in the gradient magnetic field coil, and the entire gantry becomes a vibration source, and generates a large noise.

  In addition, the O-ring structure is used to seal the inside of the part where the cover of the sealed container is joined to the cover of the static magnetic field magnet. However, the airtightness is not sufficient, and sufficient vacuum is obtained. Can not do it. For this reason, the effect of preventing air propagation of noise is not sufficient.

  As described above, the gradient magnetic field coil is accommodated in the sealed container for noise prevention. However, the coil in the container cannot be confirmed from the outside. Therefore, it is necessary to remove the container cover in order to confirm and adjust the position of the gradient magnetic field coil, and the work load is large.

  Further, if the degree of vacuum is increased in order to increase the noise prevention effect, the sealed container may be deformed. In order to prevent the deformation, if the strength of the sealed container is increased, the size of the container becomes larger and heavier this time. Therefore, the degree of vacuum cannot be made too high.

  In the above description, noise mainly using a gradient coil is described, but there are other vibration sources. For example, a superconducting coil is widely used as a static magnetic field magnet, and this superconducting coil is housed in a cryostat. The displacer of the cold head of the cryostat performs piston movement by the pressure of helium gas. This piston motion was propagated to a container such as an 80k shield and generated noise. At present, no special measures are taken against the noise generated by the cold head as a vibration source.

  Further, the gantry is composed of many parts. Many of these parts are made of metal. When a potential difference is generated between the metal parts when the metal parts are fastened, so-called B radio waves are generated by vibration using a gradient magnetic field coil as a main generation source, and are picked up by the RF coil. There is also a problem that the image quality is deteriorated when electrons are mixed into the signal line.

  Further, in order to magnetically shield the RF coil, a magnetic shield is disposed on the outside thereof. This magnetic shield generally has a structure in which a plurality of thin strip-shaped copper plates are attached in parallel with a predetermined interval on the surface of a resin substrate, and a capacitor is inserted between adjacent copper plates. In some cases, a thin strip-shaped copper plate is opposed to the front and back surfaces of a resin substrate as a dielectric, and a plurality of them are attached in parallel at a predetermined interval, thereby realizing a capacitor structure between the front and back surfaces. However, in any of these structures, there is also a problem that a sufficient shielding effect cannot be obtained due to insufficient capacity of the capacitor.

  As a vibration source, not only the gradient magnetic field coil described above but also an eddy current due to a leakage magnetic field from the gradient magnetic field coil is generated in the conductive material of the circuit unit including the tuning circuit of the RF coil. Cause vibration. Currently, no countermeasures are taken against this vibration.

  In addition, the vacuum pump for exhausting the air inside the sealed container needs to be maintained at a relatively high frequency, and under the situation where the load on the pump increases with the spread of the high-speed sequence, this pump Reducing the frequency of maintenance is also a future issue.

  Further, the degree of vacuum of the sealed container is inevitable to change over time due to the operating condition of the pump, the variation in airtightness of the sealed container, and various other factors. Due to the fluctuation of the degree of vacuum, the magnetic field intensity also fluctuates, so that the resonance frequency fluctuates, and there is a concern about the deterioration of the image due to this. However, at present, no special measures are taken against the deterioration of the image quality due to the change in the degree of vacuum.

  An object of the present invention is to satisfactorily suppress noise caused by a gradient magnetic field coil or the like in a magnetic resonance imaging apparatus.

The present embodiment relates to a magnetic resonance imaging apparatus having a static magnetic field magnet, a gradient magnetic field coil, a high frequency coil, and a sealed container that houses the gradient magnetic field coil, and a pump for exhausting the internal air of the sealed container Means for generating an MR signal from a subject according to an arbitrarily set imaging condition and driving the gradient coil and the high-frequency coil to collect the MR signal, and operating the pump according to the imaging condition A pump control unit that changes a pattern; and a control unit that drives the gradient coil and the high-frequency coil according to a pulse sequence selected from a plurality of types of pulse sequences. The on-time of the pump is changed according to the pulse sequence.

1 is a diagram showing a basic configuration of a magnetic resonance imaging apparatus according to a preferred embodiment of the present invention. The longitudinal cross-sectional view of the mount based on 1st Embodiment. The enlarged view in the broken line of FIG. The figure which shows the structure of the airtight container which concerns on 2nd Embodiment. The perspective view of the airtight container which concerns on 3rd Embodiment. FIG. 6 is a cross-sectional view showing the joining of the sealed container of FIG. 5 and a static magnetic field magnet container. The longitudinal cross-sectional view of the cryostat of the static magnetic field magnet which concerns on 4th Embodiment. The internal structure figure of the dynamic vibration absorber of FIG. The internal structure figure of the cold head part by the other example of 7th Embodiment. The longitudinal cross-sectional view of the mount frame which concerns on 6th Embodiment. The longitudinal cross-sectional view of the gradient magnetic field coil unit which concerns on 7th Embodiment. The figure which shows the generation principle of a noise electromagnetic wave in 7th Embodiment. The figure which shows the tuner copper plate of FIG. 11, and its connection component. The figure which shows the example of a connection of metal components in 7th Embodiment. The figure which shows the other example of a connection between metal components in 7th Embodiment. The figure which shows the example of insulation connection of metal components in 7th Embodiment. The figure which shows the other insulated connection example of metal components in 7th Embodiment. The figure which shows the further another insulation connection example of metal components in 7th Embodiment. The perspective view of RF shield concerning an 8th embodiment. The longitudinal cross-sectional view of the mount frame of the magnetic resonance imaging apparatus which concerns on 9th Embodiment. The systematic diagram of the vacuum pump of the airtight container which concerns on 10th Embodiment. The figure which shows the pressure change in an airtight container in 10th Embodiment. In 10th Embodiment, the timing chart of ON / OFF of a vacuum pump and opening and closing of a valve | bulb. The principal part block diagram of the magnetic resonance imaging apparatus which concerns on 11th Embodiment. The principal part block diagram of the magnetic resonance imaging apparatus which concerns on 12th Embodiment. The figure which shows the variation of the operation pattern of a vacuum pump in 12th Embodiment.

  Hereinafter, a magnetic resonance imaging apparatus according to the present invention will be described with reference to the drawings according to preferred embodiments. First, a basic configuration of the magnetic resonance imaging apparatus will be described with reference to FIG. The magnetic resonance imaging apparatus includes a gantry 14 having an imaging space for inserting and placing a subject to be imaged, a bed 18 disposed adjacent to the gantry 14, and operations of the gantry 14 and the bed 18. A control processing unit (computer system) for controlling and processing MR signals. Note that the gantry 14 is typically formed with an imaging space penetrating in a substantially cylindrical shape at the inner central portion thereof. For this cylindrical imaging space, the axial direction is Z, and the X direction (left-right method) and Y direction (vertical direction) orthogonal to the Z direction are defined.

The gantry 14 is supplied with a current from the static magnetic field power source 2 and enters a static magnetic field H0 in the imaging space. A static magnetic field magnet 1 is provided. The static magnetic field magnet 1 is typically composed of a superconducting magnet. The overall shape of the static magnetic field magnet 1 is formed in a substantially cylindrical shape. A gradient coil 3 is disposed in the bore of the magnet 1. The gradient magnetic field coil 3 includes three sets of coils 3x, 3y, and 3z for receiving a current supply from the gradient magnetic field power source 4 and generating gradient magnetic fields related to the XYZ axes. The gradient magnetic field coil 3 is housed in a sealed container whose inside is maintained in a vacuum or a state close thereto by a vacuum pump for noise countermeasures.

  A high frequency coil (RF coil) 7 is arranged further inside the gradient magnetic field coil 3. A transmitter 8T and a receiver 8R are connected to the RF coil 7. The transmitter 8T supplies the high-frequency coil 7 with a current pulse that vibrates at a Larmor frequency for exciting nuclear magnetic resonance (NMR) under the control of the sequencer 5. The receiver 8R receives the MR signal (high frequency signal) via the high frequency coil 7, performs various signal processing, and forms a corresponding digital signal.

  The sequencer 5 is placed under the control of a controller 6 that manages the entire apparatus. An input device 13 is connected to the controller 6. The operation can select a desired pulse sequence from a plurality of types of pulse sequences such as a spin echo method (SE) and an echo planer method (EPI) via the input device 13. The controller 6 sets the selected pulse sequence in the sequencer 5. The sequencer 5 controls the application timing of each gradient magnetic field in the X, Y, and Z-axis directions, its intensity, the application timing of the high-frequency magnetic field, the amplitude, the duration, and the like according to the set pulse sequence.

  The arithmetic unit 10 inputs the MR signal (digital data) formed by the receiver 8R, arranges measured data in a two-dimensional Fourier space formed by a built-in memory, Fourier transform for image reconstruction, etc. To generate image data and spectrum data. The storage unit 11 stores the calculated image data. The display device 12 displays an image.

  Next, an embodiment relating to a magnetic resonance imaging apparatus having the above basic configuration will be described.

(First embodiment)
FIG. 2 shows a longitudinal sectional view of the gantry of the magnetic resonance imaging apparatus according to the first embodiment. The gradient magnetic field coil 102 may be a non-shield type or an active shield type. The gradient coil 102 has an x coil, a y coil, and a z coil as its windings. The x coil, y coil and z coil are impregnated into a bobbin having a cylindrical shape.

  The gradient magnetic field coil 102 having a substantially cylindrical shape is supported on a heavy concrete base 125 installed on the floor surface. Further, the gradient magnetic field coil 102 is accommodated in the sealed container 133. The sealed container 133 includes a liner 131 having a substantially cylindrical shape that constitutes an inner wall thereof, and a vacuum lid 132 thereof. The back surface of the sealed container 133 is closed with an inner wall 117 of a cryostat 116 for placing a static magnetic field magnet (here, a superconducting coil) in a cryogenic environment. A side wall 118 of the cryostat 116 is joined to the vacuum lid 132 by a joining plate 135. The hermetic container 133 and the gantry base 125 are joined together by a vacuum bellows 134 in order to keep the hermeticity of the hermetic container 133.

  The air inside the sealed container 133 is exhausted by a vacuum pump, and the inside of the sealed container 133 is held in a vacuum or a state close thereto. This prevents noise from propagating through the gradient magnetic field coil 102 as a source.

  An RF coil 103 is disposed on the inner surface of the liner 131, a high frequency magnetic field is applied to the subject via the RF coil 103, and MR signals from the subject are received.

  In such a configuration, a vacuum leak is likely to occur at a connection portion between the side wall 118 of the cryostat 116 and the bonding plate 135. In order to prevent this vacuum leak, an O-ring 108 for vacuum sealing is sandwiched between the side wall 118 of the cryostat 116 and the bonding plate 135. However, the surface accuracy of the side wall 118 of the cryostat 116 is not so high. Therefore, the contact accuracy of the O-ring 108 with the side surface 118 of the cryostat 116 is not so high, and the sealing performance of the O-ring 108 is not sufficient.

  On the other hand, in this embodiment, as shown in FIG. 3, an annular flange 106 is welded to the side wall 118 of the cryostat 116 (reference numeral 107), and the joining plate 135 of the sealed container 133 is connected to the flange 106. Is fixed by a bolt 109 via an O-ring 108. The flange 106 can be formed with high accuracy by machining or the like. Therefore, since the flange 106 can make good contact with the O-ring 108, the sealing performance of the O-ring 108 can be maximized. Further, since the connection between the side wall 118 of the cryostat 116 and the flange 106 is performed by welding, the airtightness between them is ensured. Therefore, the substantially vacuum state inside the sealed container 133 can be maintained, and the air propagation of vibration and noise can be well shielded.

(Second Embodiment)
FIG. 4A shows the appearance of the sealed container of the gradient coil according to the second embodiment. As a countermeasure against noise, the gradient magnetic field coil is accommodated in an airtight container 201 that is maintained in a substantially vacuum state. For this reason, conventionally, in order to confirm the position of the gradient magnetic field coil, it was necessary to partially disassemble the sealed container 201.

  On the other hand, in this embodiment, each of the side walls 207 of the sealed container 201 is cut out into a pair of left and right circles. In this portion, a window 202 made of glass or fiber reinforced plastic that transmits visible light is fitted. Through this window 202, the position of the gradient magnetic field coil in the sealed container 201 can be easily visually recognized from the outside.

  As shown in FIG. 4B, the gradient magnetic field coil 204 is attached with a scale 206 representing its position. The scale 206 can be viewed through the window 202. While observing the scale 206, the relative position of the gradient magnetic field coil 204 with respect to the static magnetic field magnet 205 can be objectively grasped.

  As shown in FIG. 4C, the leg 203 of the sealed container 201 has a base 212. A support column 213 that supports the gradient magnetic field coil 204 is fitted in a hole vertically formed in the base 212 so as to be movable up and down. A thread is cut on the outer periphery of the support column 213, and a screw 215 is engaged with the thread on the cross axis. By rotating the dial 214 at the tip of the screw 215, the support column 213 moves up and down together with the gradient coil 204 inside the container 201. Thereby, the relative position of the gradient magnetic field coil 204 can be adjusted with respect to the static magnetic field magnet 205.

  Thus, even if the container is not disassembled, the gradient magnetic field coil can be visually recognized from the outside, and the position can be adjusted, so that the chance of airtightness deterioration can be reduced. Thereby, the airtightness of a container is ensured and the shielding effect of the air propagation of a vibration and noise can be made high.

  Further, as shown in FIG. 4D, the side wall 207 of the hermetic container 201 is joined to the static magnetic field magnet container 217 via the joining plate 235, and the corner portion that joins the side wall 207 and the joining plate 235 is joined. Make a round. Similarly, a round is given not only to the joint portion between the side wall 207 and the joining plate 235 but also to the corner portion where the cylindrical inner wall (liner) of the sealed container 201 and the joining plate 235 are joined. By these, the tolerance with respect to atmospheric pressure of the airtight container which accommodates the gradient magnetic field coil can be improved.

(Third embodiment)
In FIG. 5, the external appearance of the sealed container of the gradient magnetic field coil which concerns on 3rd Embodiment is shown. The gradient magnetic field coil is accommodated in the sealed container 301. In order to prevent noise from propagating through the gradient magnetic field coil 102, the air inside the sealed container 301 is exhausted by a vacuum pump, and the inside of the sealed container 133 is maintained in a vacuum or a state close thereto. Thereby, the airtight container 133 receives atmospheric pressure. For this reason, the strength of the sealed container 133 is important. In the second embodiment, the window 302 is attached to the side wall 204 of the sealed container 133. In the present embodiment, in order to increase the strength of the portion of the window 302, the side wall 304 around the window 302 is formed in a convex portion 303 having a round shape such as a half pipe, so that the periphery of the window 302 is formed. The strength of this part is reinforced.

  By this reinforcement, the degree of vacuum (internal pressure) of the sealed container 301 can be sufficiently increased (decreased), and the shielding effect of vibration and noise air propagation can be increased.

  Further, as shown in FIG. 6, the sealed container 301 includes a liner 309 having a substantially cylindrical shape that constitutes an inner wall thereof, and a vacuum lid 307 thereof. The back surface of the sealed container 301 is closed with an inner wall of a cryostat 306 for placing a static magnetic field magnet (here, a superconducting coil) in a cryogenic environment. A side wall 311 of the cryostat 306 is joined to the vacuum lid 307.

  In the actual manufacturing process, the length L2 of the opening portion of the sealed container 301 into which the cryostat 306 is fitted may not match the length L1 of the cryostat 306. In this case, the airtightness of the container 301 is reduced, and a vacuum leak occurs. In order to solve this problem, in the present embodiment, an annular packing 310 can be further sandwiched between the liner 309 and the vacuum lid 307 of the sealed container 301. Therefore, when the length L2 of the opening portion of the sealed container 301 into which the cryostat 306 is fitted does not match the length L1 of the cryostat 306, the liner 309 and the vacuum cover 307 of the sealed container 301 with the packing 310 having an appropriate width interposed therebetween. By joining, the length L2 of the opening portion of the sealed container 301 into which the cryostat 306 is fitted can be easily matched to the length L1 of the cryostat 306.

  By this packing 310, the accuracy of joining the sealed container 301 and the cryostat 306 can be improved, and the hermeticity of the container 301 can be improved. Thereby, the shielding effect of air propagation of vibration and noise can be enhanced.

(Fourth embodiment)
The gradient magnetic field coil is not the only source of vibration and noise in the magnet mount. For example, there is a superconducting coil heat exchanger employed as a static magnetic field magnet. 7 and 8 are cross-sectional views of the heat exchanger according to the present embodiment. Superconducting coil 401 is housed in cryostat 404. The cryostat 404 is configured to surround the outer periphery of a liquid nitrogen tank that accommodates the superconducting coil 401 together with liquid nitrogen by heat radiation shields 402, 405, and 406.

  The cryostat 404 is provided with a heat exchanger 407 that absorbs heat from the shield 402 and exhausts the heat to the outside. The heat exchanger 407 includes a cylinder 408 whose bottom is in contact with the shield 402, a cylinder 408 that covers the cylinder 408, a cold head 411 that is cooled by helium gas He, and a cylinder 408 that includes a bottom thereof. A displacer 409 that makes a piston motion with the pressure of the helium gas He between the cold head 411 and a vacuum bellows 410 are included.

  The displacer 409 absorbs heat from the shield 402 when the displacer 409 is at the bottom. The displacer 409 transfers heat to the cold head 411 when the displacer 409 is at the top. By repeating such an operation, heat can be exhausted from the shield 402.

  As described above, since the displacer 409 performs a piston motion in the cylinder 408, vibration is generated. This vibration propagates mechanically to the shields 402, 405, 406. As a result, noise is generated.

  In order to absorb this vibration, a dynamic vibration absorber 414 is mounted on the cold head 411. This dynamic vibration absorber 414 has an elastic body, for example, a spring 412 connected to the cold head 411 so that the expansion / contraction direction of the spring 412 is substantially parallel to the piston movement direction of the displacer 409. A weight 413 is connected. When the displacer 409 performs a piston motion, the weight 413 moves up and down following the piston motion. As a result, the vibration of the cold head 411 using the displacer 409 as a generation source is absorbed by the dynamic vibration absorber 414, and as a result, noise is reduced.

  Usually, the displacer 409 performs a piston motion at the frequency of the commercial power source. In the dynamic vibration absorber 414, the elasticity of the spring 412 and the mass of the weight 413 are set so as to resonate with vibration generated by the displacer 409 that performs piston movement at this frequency. Thereby, vibration can be effectively absorbed.

  As shown in FIG. 9, two cylinders 408-1 and 408-2, displacers 409-1 and 409-2, and cold heads 411-1 and 411-2 are provided, that is, two heat exchangers are provided. Even if these two heat exchangers are arranged so that the piston motion axes face each other, and the displacers 409-1 and 409-2 are moved in the opposite phase to each other, vibration is reduced. It can be done.

(Fifth embodiment)
FIG. 10 shows a longitudinal sectional view of a gantry of a magnetic resonance imaging apparatus according to the fifth embodiment. The gradient coil 502 has an x coil, a y coil, and a z coil as its windings. The x coil, y coil and z coil are impregnated into a bobbin having a cylindrical shape. The gradient magnetic field coil 502 having a substantially cylindrical shape is supported on a heavy concrete base 525 installed on the floor surface. The gradient magnetic field coil 502 is accommodated in the sealed container 533. The sealed container 533 includes a liner 531 having a substantially cylindrical shape constituting the inner wall thereof, and a vacuum lid 532 thereof. The back surface of the sealed container 533 is closed by an inner wall 517 of a cryostat 516 for placing a static magnetic field magnet (here, a superconducting coil) in a cryogenic environment. A side wall 518 of the cryostat 516 is joined to the vacuum lid 532 by a joining plate 535. The hermetic container 533 and the gantry base 525 are connected by a vacuum bellows 534 in order to maintain the hermeticity of the hermetic container 533.

  The vibration of the gradient coil 502 propagates mechanically to the sealed container 533. The frequency of vibration of the gradient coil 502 is equivalent to the alternating frequency of the gradient magnetic field of the pulse sequence. The liner 531 and the vacuum lid 532 of the hermetic container 533 do not resonate with the vibration of the gradient magnetic field coil 502, that is, the natural frequency of the liner 531 and the vacuum lid 532 with respect to the vibration frequency of the gradient magnetic field coil 502. Weights 541, 542, 543, and 544 are discretely attached to the liner 531 and the vacuum lid 532 so that the natural frequencies of the natural frequencies are different from each other.

  The weight 544 attached to the vacuum lid 532 is, for example, a nonmagnetic metal piece. In addition, annular gel-like substances 541, 542, and 543 are attached to the liner 53 along the inner wall thereof. The place where the substances 541, 542, and 543 are mounted is outside the RF coil 503 in order to avoid a decrease in the Q value of the RF coil 503.

  According to such a structure, the liner 531 and the vacuum lid 532 of the sealed container 533 do not resonate with respect to the vibration of the gradient coil 502. Therefore, noise is reduced.

  Note that the thickness of the liner 531 and the vacuum lid 532 may be partially reduced instead of or in addition to attaching weights to the liner 531 and the vacuum lid 532. In short, the point of this embodiment is to partially increase or decrease the masses of the liner 531 and the vacuum lid 532 in order to shift the natural frequency. In addition to the shift of the natural frequency, beams and braces may be inserted for reinforcement.

(Sixth embodiment)
FIG. 11 is a longitudinal sectional view of a gantry of a magnetic resonance imaging apparatus according to the sixth embodiment. The gradient coil 602 has an x coil, a y coil, and a z coil as its windings. The x coil, y coil and z coil are impregnated into a bobbin having a cylindrical shape. The gradient magnetic field coil 602 having a substantially cylindrical shape is supported on a heavy concrete base 625 installed on the floor surface. The gradient magnetic field coil 602 is accommodated in the sealed container 633. The sealed container 633 includes a liner 631 having a substantially cylindrical shape, a vacuum lid 632 having a substantially annular plate shape, and a back casing 634 having a substantially cylindrical shape. A cryostat 616 for placing a static magnetic field magnet (a superconducting coil in this case) in a cryogenic environment is disposed outside the back casing 634 of the sealed container 633. An RF coil 635 is disposed on the inner surface of the liner 631, a high frequency magnetic field is applied to the subject via the RF coil 635, and MR signals from the subject are received.

  The point of this embodiment is that the inner wall of the cryostat 616 is not used for the sealed container 633 that houses the gradient magnetic field coil 602, in other words, the sealed container 633 is configured completely separately from the cryostat 616. It is in. When the inner wall of the cryostat 616 is used for the sealed container 633 that accommodates the gradient magnetic field coil 602, vacuum leakage is likely to occur at the joint due to the low surface accuracy and dimensional error of the cryostat 616. However, in this embodiment, since the cryostat 616 is not joined to the sealed container 633, that is, the sealed container 633 is manufactured independently, high airtightness is achieved without depending on the low surface accuracy and dimensional error of the cryostat 616. be able to.

(Seventh embodiment)
The seventh embodiment is made for the purpose of preventing generation of B radio waves and induction electrons due to rubbing of metal parts in the gantry, and is a magnetic resonance apparatus that physically vibrates or propagates the vibrations. It can be applied to fastening all metal parts constituting the gantry.

  The gantry is composed of a large number of metal parts, and metal screws are mainly used to fasten these parts. For example, as shown in FIG. 12A, when a copper tuner plate 724 is attached to a metal mount frame 724, conventionally, a metal screw 723 and a metal insert 722 are generally used. Many capacitors are provided in the gantry, and metal screws are often used when the capacitors are attached to a tuner plate or the like, or when the connector of the RF coil tuner is fastened to the tuner plate. In this way, metal screws are used in most places for fixing parts in the gantry. As shown in FIG. 12B, the metal screws and the metal parts, and further, the metal parts are vibrated as described above. So that the so-called B radio wave is generated. This B radio wave is picked up by the RF coil and may cause image artifacts, but until recently, it was not considered as a problem. However, in order to realize higher speed and higher strength of the gradient magnetic field in recent years, higher voltage has progressed, and accordingly, B radio waves tend to become stronger. At present, image artifacts due to the strong B radio noise have already been enlarged to a degree that cannot be ignored. Further, there is a problem that not only the B radio wave but also, for example, electrons induced by contact and vibration between the connector and the tuner plate are mixed in the signal line as they are, and image artifacts are generated.

  This embodiment is made for the purpose of preventing the generation of B radio waves and induction electrons that cause such noise.

  As is well known, the gantry is a magnet device that mainly includes a static magnetic field magnet, a gradient magnetic field coil, and an RF coil, and includes many metal parts. There are a huge number of places where these metal parts are attached to other parts. This attachment location can be roughly divided into two types. As shown in FIGS. 13 and 14, one is attached to the copper plates 709 and 710 constituting the RF coil, and the RF coil copper plates 709 and 710 and the capacitor 711 are attached. Mounting, mounting of RF coil copper plate 710 and lead copper plate 703, mounting of lead copper plate 703 and copper plate 704 of RF coil tuner, mounting of copper plate 704 of RF coil tuner and connector 706, copper plate 704 of RF coil tuner and capacitor 715 It is a place that requires the electrical connection as well as physically fixing the parts as represented by the attachment, and the other purpose is simply to physically fix the parts, This is a place where no electrical connection is required.

  In the former part, it is most preferable to use solder 705 for attachment. In this case, since there is no friction between the components, the B radio wave is not generated and induction electrons are not generated. However, there are places where solder cannot be used because of its weak fastening force. Screws are used at this point.

  FIG. 15 shows an example in which the metal parts 731 and 732 are attached to each other using a resin screw 733 as an example. Conventionally, since a metal screw is used, it is inevitable that B radio waves and induction electrons are generated due to friction between the metal screw and the metal part 731 and between the metal screw and the metal part 732. However, in this example, since the resin screw 733 is used, these occurrences can be prevented.

  As another example, FIG. 16 shows an example in which metal parts 731 and 732 are attached to each other using a metal screw 734, and in order to avoid contact between the metal screw 734 and the metal part 731, A resin spacer 735 is used, and a resin tap 736 is used to avoid contact between the metal screw 734 and the metal part 732. In this example, while using the metal screw 734, the metal screw 734 and the metal component 731 and the metal screw 734 and the metal component 732 are insulated by the resin members 735 and 736, Generation of B radio waves and induction electrons can be prevented.

  Of course, any of the attachment methods shown in FIGS. 15 and 16 may be adopted, or both methods may be described. Further, the effect of reducing the generation of B radio waves and induction electrons can be expected even if the mounting method shown in FIG. 15 and FIG. .

  In the latter attachment point, that is, the point where the electrical connection is not required mainly for the purpose of physically fixing the parts, for example, as shown in FIG. However, by sandwiching an insulating sheet 739 between the metal parts 737 and 738, it is only necessary to prevent generation of B radio waves and induction electrons due to friction between the metal screw and the metal part as in the conventional case. It is also possible to prevent generation of B radio waves and induction electrons due to friction between the metal parts 737 and 738.

  In the example of FIG. 18, an example in which the metal parts 737 and 738 are attached to each other using the metal screw 734 is shown. In order to avoid contact between the metal screw 734 and the metal part 737, a substantially cylindrical shape is used. A resin spacer 740 is used, and a resin tap 741 is used to avoid contact between the metal screw 734 and the metal part 738. In this example, while using the metal screw 734, the metal screw 734 and the metal component 737 and the metal screw 734 and the metal component 738 are insulated by the resin members 740 and 741, Generation of B radio waves and induction electrons can be prevented.

  Of course, any of the attachment methods shown in FIGS. 17 and 18 may be adopted, or both methods may be described. Moreover, even if it does not employ | adopt the attachment method of FIG. 17, FIG. 18 to all the said locations in a mount, but only employ | adopts only to one part, it can anticipate the effect of reducing generation | occurrence | production of B electric wave and an induction electron. .

  In addition to attaching metal parts to each other, the metal screw and the metal screw, which have been generated in the past, can be applied by using the attachment method shown in FIGS. 17 and 18 at the place where the metal parts and resin parts such as coil bobbins are attached. Generation of B radio waves and induction electrons due to friction with parts can be prevented.

(Eighth embodiment)
The eighth embodiment relates to an improvement of the RF shield arranged on the outer periphery of the RF coil. The RF shield is typically composed of a copper tube in order to magnetically isolate the RF coil from the outside and shield electromagnetic noise coming from the outside into the RF coil. In this copper tube, an eddy current is generated due to high-speed switching of the gradient magnetic field, and the gradient magnetic field is distorted. In order to shorten the time constant of this eddy current, many slits are formed in the copper cylinder.

  In addition, a magnetic field having a relatively low frequency such as a gradient magnetic field (up to about 100 KHz) passes, and a high frequency magnetic field of several MHz to several tens of MHz such as an excitation pulse is cut off, that is, the low frequency impedance is increased and the high frequency impedance is decreased. In order to do this, a capacitor is connected between the copper plates across the slit. As another conventional configuration of the RF shield, a capacitance is formed between the front and back surfaces by pasting a plurality of copper plates with a gap (slit) on the surface of the dielectric substrate and further pasting a plurality of copper plates on the back surface. There is also an RF shield.

  High-speed imaging methods such as echo-planar imaging (EPI) are required, for example, for cardiac imaging, and this requires an extremely rapid gradient magnetic field response. For this reason, it is necessary to provide a large number of slits with fine steps (intervals). However, if a large number of slits are provided, the capacity decreases as the copper plate area decreases, and thereby, high-frequency short-circuiting in individual slits becomes incomplete. As a result, the shielding function is incomplete.

This embodiment implements both an increase in the number of slits and prevention of a decrease in capacity.
FIG. 19 shows a partial perspective view of the RF shield according to the present embodiment. A plurality of copper plates 802 are attached to the surface of the dielectric substrate 801 with a predetermined gap (slit) 805 therebetween. Similarly, a plurality of copper plates 803 are attached to the back surface of the dielectric substrate 801 with a predetermined gap (slit) 806 therebetween. A capacitor is formed between the copper plates 802 and 803 facing each other with the dielectric substrate 801 interposed therebetween.

  Further, a capacitor 804 is connected between adjacent copper plates 802 on the surface of the dielectric substrate 801. Similarly, a capacitor 805 is connected between adjacent copper plates 803 on the back surface of the dielectric substrate 801.

  In this configuration, the total capacitance of the front side capacitor 804, the back side capacitor 805, and the capacitance between the front side copper plate 802 and the back side copper plate 803 is sufficient to complete a high frequency short circuit. It can be secured as a capacity.

(Ninth embodiment)
FIG. 20 is a longitudinal sectional view of the gantry of the magnetic resonance imaging apparatus according to the ninth embodiment. The gradient coil 902 has an x coil, a y coil, and a z coil as its windings. The x coil, y coil and z coil are impregnated into a bobbin having a cylindrical shape. The gradient magnetic field coil 902 having a substantially cylindrical shape is supported on a heavy concrete base 925 installed on the floor surface. The gradient magnetic field coil 902 is accommodated in the sealed container 933. The sealed container 933 includes a liner 931 having a substantially cylindrical shape that constitutes an inner wall thereof, and a vacuum lid 932 thereof. The back surface of the sealed container 933 is closed by an inner wall 917 of a cryostat 916 for placing a static magnetic field magnet (here, a superconducting coil) in a cryogenic environment. A side wall 918 of the cryostat 916 is joined to the vacuum lid 932 by a joining plate 935. The hermetic container 933 and the gantry base 925 are joined together by a vacuum bellows 934 in order to keep the hermeticity of the hermetic container 933.

  An RF coil 903 is disposed on the inner surface of the liner 931. A transmitter and a receiver are connected to the RF coil 903. The transmitter is provided to supply the RF coil 903 with a high-frequency current pulse corresponding to the Larmor frequency in order to bring the nuclear magnetization of the subject into an excited state by the high-frequency magnetic field. A phase selector, a frequency converter, an amplitude modulator, and a high-frequency power amplifier are included. In addition, the receiver includes a pre-amplifier, an intermediate frequency converter, a phase detector, a low-frequency amplifier, a low-pass filter, and an AD converter in order to receive the MR signal from the subject via the RF coil 903. Is done.

  These transmitters and receivers are housed in an RF unit 940. The RF unit 940 is placed near the RF coil 903 in order to shorten the cable and reduce power loss and noise. Conventionally, as indicated by a dotted line in FIG. 20, the RF unit is attached to the vacuum lid 932 near the edge of the opening 941. However, this place is the place where the leakage magnetic field from the gradient coil 902 is the largest. The RF unit 940 includes many conductive parts, and eddy currents are generated in these conductive parts due to a leakage magnetic field from the gradient magnetic field coil 902. As a result, the conductive parts vibrate due to Lorentz force. This vibration is transmitted to the sealed container 933 and noise is generated.

The purpose of this embodiment is to reduce noise generated by the RF unit 940 as a source.
The RF unit 940 is not a vacuum lid 932 close to the edge of the opening 941, but is further physically separated from the hermetic container 933, here in the radial direction of the gantry cylinder from the central axis (Z axis). It is outside 903 and is located near the opening 941 and immediately below it. Specifically, the RF unit 940 is installed on a heavy concrete base 925 or a separate dedicated base.

  This installation location is less affected by the leakage magnetic field from the RF coil 903 than the conventional installation location. Therefore, the RF unit 940 reduces the vibration of the conductive parts. Moreover, since the RF coil 903 is physically separated from the sealed container 933 and is attached to the heavy concrete base 925, minute vibrations of the RF coil 903 are hardly transmitted to the sealed container 933. .

Therefore, noise generated from the RF unit 940 can be reduced.
(10th Embodiment)
As described above, the gradient magnetic field coil is housed in a sealed container in which internal air is exhausted by a vacuum pump for noise countermeasures. The higher (lower) the degree of vacuum (pressure) in the sealed container, the greater the noise shielding effect. In order to increase the degree of vacuum in the sealed container, conventionally, the vacuum pump is continuously operated during scanning. This continuous operation shortens the life of the vacuum pump. Using a vacuum pump with reduced capacity cannot increase the degree of vacuum in the sealed container, and the noise shielding effect is reduced.

In the present embodiment, the noise shielding effect is maintained as long as possible by reducing the load on the vacuum pump.
FIG. 21 shows a vacuum pump and a piping system according to this embodiment. The hermetic container 1001 is connected to the vacuum pump 1002 via the main tube 1003. An electromagnetic valve 1004 is disposed in the middle of the main tube 1003. A branch tube 1005 is connected to the main tube 1003, and the tip of the branch tube 1005 is opened via an electromagnetic valve 1006.

  The operation of the vacuum pump 1002, the opening and closing of the electromagnetic valve 1004, and the opening and closing of the electromagnetic valve 1006 are under the control of the pump / valve control unit 1020. The vacuum pump 1002 repeats operation (ON) and stop (OFF) alternately as shown in FIG. 22 according to the control of the pump / valve control unit 1020. The length of the operation period T1 and the length of the stop period T2 are set in advance so that the pressure in the sealed container 1001 does not exceed a predetermined upper limit value. The length of the operation period T1 and the length of the stop period T2 can be arbitrarily adjusted.

Thus, by operating the vacuum pump 1002 intermittently rather than continuously, the maintenance frequency of oil, oil filters, etc. can be reduced as compared with the case where the vacuum pump 1002 is continuously operated.
As shown in FIG. 23, the opening / closing of the electromagnetic valve 1004 and the opening / closing of the electromagnetic valve 1006 are related to such intermittent operation of the vacuum pump 1002 by the pump / valve control unit 1020.

  First, the electromagnetic valve 1006 of the branch tube 1005 is opened and closed in synchronization with the intermittent operation of the vacuum pump 1002. That is, the electromagnetic valve 1006 is closed in synchronization with the switching of the vacuum pump 1002 from OFF to ON, and is opened in synchronization with the switching of the vacuum pump 1002 from ON to OFF.

  On the other hand, the electromagnetic valve 1004 of the main tube 1003 is opened by a time T3 later than the switching timing of the vacuum pump 1002 from OFF to ON in order to reduce the load of the vacuum pump 1002, and the vacuum pump 1002 It is closed at a timing earlier than the timing of switching from ON to OFF by time T4. These time differences T3 and T4 are set to an arbitrary time from several seconds to several minutes.

  By opening the electromagnetic valve 1004 with a delay of time T3 from the switching timing of the vacuum pump 1002 from OFF to ON, the vacuum pump 1002 is turned on for a relatively short period of time T3 (pre-vacuum period). The lubrication in the vacuum pump 1002 can be completed. This is because the exhaust target is a small volume from the pump inlet to the electromagnetic valve 1004. Then, after the time T3 has elapsed since the start of on, the valve 1004 of the main tube 1003 is opened, and the exhaust operation (main main volume of the volume from the electromagnetic valve 1004 to the sealed container 1001 and the volume of the sealed container 1001 is targeted). However, since the lubrication in the vacuum pump 1002 has already been completed at this time, the main vacuum operation can be smoothly performed. Therefore, the load on the vacuum pump 1002 can be reduced.

  Next, the valve 1004 of the main tube 1003 is closed after a predetermined time (T1-T4) has elapsed since the vacuum pump 1002 was turned on, that is, at a timing earlier than the timing when the vacuum pump 1002 was turned off. This means that the sealed container 1001 is separated from the vacuum pump 1002 in a state where the pressure of the sealed container 1001 is sufficiently reduced. As a result, it is possible to prevent an abrupt increase in pressure in the sealed container 1001 due to the stop of the vacuum pump 1002.

(Eleventh embodiment)
FIG. 24 shows the configuration of the main part of the magnetic resonance imaging apparatus according to the eleventh embodiment. The gantry 1101 includes a static magnetic field magnet 1102 that generates a static magnetic field H0, a gradient magnetic field coil 1103 that receives current supply from a gradient magnetic field power supply (G-amp) 1105, an RF coil 1104, and a shim coil power supply (Shim-amp) 1107. And a plurality of shim coils 1116 that generate a magnetic field that corrects static magnetic field inhomogeneity by receiving a current supply from.

  The gradient magnetic field coil 1103 is housed in a hermetic container 1115 whose inside is maintained in a vacuum or a state close thereto by a vacuum pump 1111 for noise countermeasures. A plurality of vacuum sensors (vacuum gauges) 1112 for measuring the internal pressure are discretely arranged inside the sealed container 1115. The degree of vacuum data measured by the degree of vacuum sensor 1112 is sent to and stored in the storage unit 1113. In addition, the storage unit 1113 stores operation state data from the vacuum pump 1111 together with the vacuum degree data. The operation status data represents the operation time of the vacuum pump 1111.

  The maintenance information generation unit 1114 generates maintenance information of the sealed container 1115 and the vacuum pump 1111 in a timely manner based on the vacuum degree data and the operation status data stored in the storage unit 1113. The maintenance information generation unit 1114 determines that the vacuum level (pressure) in the sealed container 1115 from the vacuum level data indicates that the vacuum pump 1111 and the sealed container 1115 have no noise when the noise in the imaging region does not fall below a predetermined pressure corresponding to, for example, 99 dB. Maintenance information that prompts maintenance is generated. Further, the maintenance information generating unit 1114 calculates the cumulative operation time from the operation status data, and generates maintenance information that prompts maintenance of the vacuum pump 1111 when the cumulative operation time exceeds a predetermined value. The maintenance information is, for example, a message for prompting maintenance of the sealed container 1115 and the vacuum pump 1111 and is displayed on the display 1110.

  The receiver 1108 collects MR signals (high frequency signals) via the RF coil 1104, performs preprocessing such as detection and AD conversion, and outputs them to the processor 1109. The processor 1109 processes the collected MR data and generates an image and a spectrum. These images and spectra are sent to the display 1110 and displayed.

  In addition to the main function of generating an image and spectrum, the processor 1109 has a function of correcting the phase of MR data collected by the receiver 1108 and performing a frequency shift based on the vacuum degree data. When the degree of vacuum changes, the intensity H0 of the static magnetic field also changes accordingly. When the strength H0 of the static magnetic field changes, the resonance frequency f0 of protons, for example, under a static magnetic field on which no gradient magnetic field is superimposed changes accordingly. The processor 1109 holds data representing the relationship between the vacuum degree measured in advance and the resonance frequency f0, and specifies the resonance frequency (corrected resonance frequency) f0 corresponding to the vacuum degree data with reference to this relationship data. To do. Based on the corrected resonance frequency f0, MRS (MR spectroscopy) corrects the phase of MR data collected by the receiver 1108 and shifts the frequency. A spectrum is generated based on the corrected data. In practice, data collection is repeated several times, phase correction and frequency shift are individually performed for each data, a plurality of spectra are generated, and the plurality of spectra are added. In EPI (Echo Planar Imaging), an EPI image is generated based on the acquired data, and the EPI image is shifted in the phase encoding direction (the position shift of the EPI image is large in the PE direction but slightly in the RO direction) To do). In practice, data collection is repeated several times, EPI images are individually generated for each data, each image is individually shifted in the phase encoding direction, and the plurality of EPI images are added and subtracted. Similarly, in the case of the phase image, the phase shift amount is calculated based on the corrected resonance frequency f0, and the phase image is corrected based on the phase shift amount.

  Thus, according to this embodiment, maintenance information can be generated in a timely manner. Moreover, phase and frequency correction can be applied according to the fluctuation of the degree of vacuum.

(Twelfth embodiment)
FIG. 25 shows the configuration of the main part of the magnetic resonance imaging apparatus according to the twelfth embodiment. The gantry 1201 includes a static magnetic field magnet 1202 that generates a static magnetic field H 0, a gradient magnetic field coil 1203 that receives a current supply from a gradient magnetic field power supply (G-amp) 1205, and an RF connected to a transceiver (RF-amp) 1208. A coil 1204 and a plurality of shim coils 1216 that receive a current supply from a shim coil power supply (Shim-amp) 1207 and generate a magnetic field that corrects static magnetic field inhomogeneity are incorporated.

  The gradient magnetic field coil 1203 is housed in an airtight container 1215 whose inside is maintained at a vacuum or a state close thereto by a vacuum pump 1211 for noise countermeasures. A plurality of vacuum sensors (vacuum gauges) 1212 for measuring the internal pressure are discretely arranged inside the sealed container 1215. Based on the vacuum degree data measured by the vacuum degree sensor 1212, the real-time manager 1210 waits for execution of the pulse sequence to the sequence controller 1209 that controls the gradient magnetic field power source 1205, the transceiver 1208, and the shim coil power source 1207 according to the pulse sequence. Outputs a command such as The real-time manager 1210 controls the operation of the vacuum pump 1211 based on the measured vacuum degree data. The system manager 1213 is provided for controlling the entire system in accordance with an operator instruction input via the console 1214.

First, real-time control of the real-time manager 1210 will be described. The real-time manager 1210 performs the following functions.
(1) Prior to the start of scanning, the vacuum pump 1211 starts operation. At this time, until the degree of vacuum in the sealed container 1215 (the pressure inside the sealed container) falls below a predetermined value, the sequence controller 1209 is instructed to start scanning. Do not give out. That is, the real-time manager 1210 issues a scan start command to the sequence controller 1209 for the first time when the degree of vacuum exceeds a predetermined value. (2) When performing a pulse sequence sensitive to magnetic field fluctuations such as MRS and EPI, the vacuum pump 1211 is continuously operated, particularly during scanning. (3) When the degree of vacuum exceeds a predetermined value during scanning, a command to stop scanning is issued to the sequence controller 1209. (4) When the degree of vacuum is lower than the predetermined value, the vacuum pump 1211 is operated before the start of scanning, and the scan start command is not issued to the sequence controller 1209 until the degree of vacuum reaches the predetermined value.

  (5) The operation pattern of the vacuum pump 1211 is properly used according to the imaging conditions (type of pulse sequence, number of averages, dynamic imaging, etc.). For example, when a pulse sequence such as spin echo that is not very sensitive to magnetic field fluctuations is performed, the pump 1211 is intermittently operated as shown in FIG. For example, the vacuum pump 1211 is operated for the period ΔT1, and then the operation is stopped for the period Δt1. This operation / stop is repeated alternately. When performing a pulse sequence that is relatively sensitive to magnetic field fluctuations, as shown in FIG. 26B, the operation period ΔT2 and the stop period Δt2 of the pump 1211 are shortened from ΔT1 and Δt1, thereby reducing the magnetic field fluctuation width. Furthermore, when performing a pulse sequence that is very sensitive to magnetic field fluctuations such as MRS and EPI, the pump 1211 is continuously operated as shown in FIG. Furthermore, when performing a pulse sequence that is very sensitive to magnetic field fluctuations such as MRS and EPI, instead of continuously operating the pump 1211, the pump 1211 is stopped so that the inside of the sealed container is at atmospheric pressure. May be. In this case, a noise reduction effect cannot be expected, but at least magnetic field fluctuations are eliminated. Note that the real-time manager 1210 holds in advance information on image quality parameters (magnetic field inhomogeneity, center frequency, phase shift) corresponding to atmospheric pressure so that image reconstruction can be performed satisfactorily even at atmospheric pressure. The transmitter / receiver 1208 adjusts the shim coil current, the center frequency and phase of the high-frequency current pulse of the transmitter / receiver 1208, and the reference frequency and phase of the receiving system.

  (6) The pump 1211 is operated / stopped according to the comparison result between the measured degree of vacuum and a predetermined value. That is, when the measured degree of vacuum exceeds the upper limit value, the pump 1211 is operated. Conversely, when the measured degree of vacuum is lower than the lower limit value, the pump 1211 is stopped. Thereby, the fluctuation | variation of a vacuum degree can be restrained in the range between an upper limit and a lower limit. The upper limit value and the lower limit value can be changed according to the shooting conditions, similarly to (5).

  (7) Further, when the vacuum level does not fall below a predetermined value even if the pump 1211 is continuously operated, a warning is generated by voice or image display.

  The real-time manager 1210 also has a function of performing the following correction according to the degree of vacuum. (1) The magnetic field inhomogeneity changes depending on the degree of vacuum. The relationship between the degree of vacuum and the magnetic field inhomogeneity is measured in advance and held in the real-time manager 1210. The real-time manager 1210 refers to this relationship, identifies the magnetic field inhomogeneity according to the degree of vacuum, and adjusts the shim coil current that flows through the shim coil 1207 according to the identified magnetic field inhomogeneity. Thereby, the magnetic field inhomogeneity can be corrected immediately. In practice, the relationship between the degree of vacuum and the magnetic field inhomogeneity is discretely measured, and the magnetic field inhomogeneity is obtained from the discrete values by linear interpolation. (2) When the degree of vacuum changes, the strength of the static magnetic field changes accordingly, and for example, the proton resonance frequency B0 changes under a static magnetic field on which no gradient magnetic field is superimposed. The real-time manager 1210 adjusts the center frequency and phase of the high-frequency current pulse of the transmission system of the transceiver 1208 according to the resonance frequency B0 corresponding to the degree of vacuum. Also, the reference frequency and phase of the receiving system are adjusted.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Furthermore, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some constituent requirements may be deleted from all the constituent requirements shown in the embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Static magnetic field power supply, 3 ... Gradient magnetic field coil 3, 4 ... Gradient magnetic field power supply, 5 ... Sequencer, 6 ... Controller, 7 ... RF coil, 8T ... Transmitter, 8R ... Receiver, 10 ... Arithmetic unit, 11 ... storage unit, 12 ... display, 13 ... input device, 14 ... gantry, 18 ... bed.

Claims (5)

In a magnetic resonance imaging apparatus having a static magnetic field magnet, a gradient magnetic field coil, a high-frequency coil, and a sealed container that houses the gradient magnetic field coil,
A pump for exhausting the internal air of the sealed container;
Means for driving the gradient coil and the high-frequency coil to generate an MR signal from the subject and collect the MR signal according to an arbitrarily set imaging condition;
A pump control unit that changes an operation pattern of the pump according to the photographing condition;
Said gradient coil and said RF coil, and ingredients Bei and a control unit for driving in accordance with the selected pulse sequence from among a plurality of types of pulse sequences,
The pump controller
In response to said selected pulse sequence, magnetic resonance imaging apparatus you and changing the on time of the pump. In a magnetic resonance imaging apparatus having a static magnetic field magnet, a gradient magnetic field coil, a high-frequency coil, and a sealed container that houses the gradient magnetic field coil,
A pump for exhausting the internal air of the sealed container;
Means for driving the gradient coil and the high-frequency coil to generate an MR signal from the subject and collect the MR signal according to an arbitrarily set imaging condition;
A pump control unit that changes an operation pattern of the pump according to the photographing condition;
Said gradient coil and said RF coil, and ingredients Bei and a control unit for driving in accordance with the selected pulse sequence from among a plurality of types of pulse sequences,
The pump controller
When the selected pulse sequence is a first pulse sequence, the pump is operated, when the selected pulse sequence is the second pulse sequence, characterized by stopping the pump magnetic Qi resonance imaging device. The magnetic resonance imaging apparatus according to claim 2 , further comprising a vacuum gauge that detects a degree of vacuum of the sealed container. The magnetic resonance imaging apparatus according to claim 3 , further comprising a processing unit that corrects a phase and / or frequency of data collected through the high-frequency coil in accordance with the detected degree of vacuum. The controller is
4. The magnetic resonance imaging apparatus according to claim 3, wherein when the detected degree of vacuum does not satisfy a predetermined condition, driving of the gradient coil and the high-frequency coil and data collection are stopped.

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