WO2005115239A1 - 磁気共鳴イメージング装置 - Google Patents
磁気共鳴イメージング装置 Download PDFInfo
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- WO2005115239A1 WO2005115239A1 PCT/JP2005/009523 JP2005009523W WO2005115239A1 WO 2005115239 A1 WO2005115239 A1 WO 2005115239A1 JP 2005009523 W JP2005009523 W JP 2005009523W WO 2005115239 A1 WO2005115239 A1 WO 2005115239A1
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- magnetic field
- vibration
- static magnetic
- imaging apparatus
- resonance imaging
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- 238000002595 magnetic resonance imaging Methods 0.000 title claims abstract description 66
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/387—Compensation of inhomogeneities
- G01R33/3873—Compensation of inhomogeneities using ferromagnetic bodies ; Passive shimming
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
- G01R33/3854—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils means for active and/or passive vibration damping or acoustical noise suppression in gradient magnet coil systems
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/3806—Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
- G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
Definitions
- the present invention relates to a magnetic resonance imaging apparatus, and more particularly to a magnetic resonance imaging apparatus that suppresses noise generated by driving a gradient coil.
- a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus) is a nuclear magnetic resonance phenomenon that occurs in nuclei of atoms constituting a subject when the subject is irradiated with an electromagnetic wave in a uniform static magnetic field.
- MR signals nuclear magnetic resonance signals
- magnetic resonance images (hereinafter, referred to as the MRI image).
- a gradient magnetic field is applied so as to overlap the static magnetic field.
- a gradient magnetic field coil is provided inside (a uniform static magnetic field side) a pair of static magnetic field sources arranged up and down. A pair is arranged facing up and down.
- each gradient magnetic field coil also has three sets of magnetic field generation coils.
- a gradient magnetic field power supply is connected to the gradient magnetic field coil, and a pulse current is applied to the MRI apparatus at an appropriate timing and voltage according to conditions at the time of imaging and inspection.
- a pulse-like current was applied to the gradient coil, Lorentz force was applied, and the gradient coil vibrated to generate noise.
- the gradient magnetic field coil is attached to the pole piece with a D piece made of a soft material such as rubber interposed therebetween, so that the vibration of the gradient magnetic field coil is not transmitted to the pole piece.
- Patent Document 1 described above, if the D-piece is too soft, the positional fluctuation due to the vibration of the gradient magnetic field coil becomes large, and the gradient magnetic field becomes large due to the large positional fluctuation. There is a problem that the disturbance causes out of the image artifact.
- Patent Document 3 also discloses a technique for preventing noise due to vibration of a gradient magnetic field coil.
- Patent Document 3 in the spectral characteristics of the current waveform applied to the gradient magnetic field coil, the intensity of the component of the frequency f that matches the natural frequency of the gradient magnetic field coil including the holding member is set to approximately 0. , Reduce noise.
- the axial direction of the holding member is set such that the frequency at which the intensity becomes substantially zero and the natural frequency of the gradient magnetic field coil in the spectral component of a specific current waveform match. It describes how to change the parameters related to the natural frequency, such as the length and the fixed location.
- Patent Document 1 JP-A-11 137535
- Patent Document 2 Japanese Patent No. 3156088
- Patent Document 3 JP-A-10-201735
- Patent Document 4 Japanese Patent Application Laid-Open No. 2002-360537
- Patent Document 3 The technology described in Patent Document 3 has the following problems. That is, in the MRI apparatus, it is necessary to perform imaging by applying a gradient magnetic field having various frequency components from a normal sequence to a high-speed sequence. For this reason, imaging using only a specific current waveform adjusted to suppress vibration cannot cope with various sequences.
- An object of the present invention is to realize a magnetic resonance imaging apparatus capable of suppressing noise caused by vibration of a gradient coil and improving image quality.
- the magnetic resonance imaging apparatus of the present invention includes a static magnetic field generating means for generating a static magnetic field in an imaging space, a gradient magnetic field generating means for generating a gradient magnetic field in an imaging space, and a high frequency magnetic field for generating a high frequency magnetic field It has a generating means, a signal receiving means for detecting a nuclear magnetic resonance signal, and a signal processing means for reconstructing an image using the detected nuclear magnetic resonance signal.
- a plurality of static magnetic field inhomogeneity correction members are provided between the static magnetic field generating means and the gradient magnetic field generating means, and the plurality of holes are provided.
- an anti-vibration member is provided.
- the magnetic resonance imaging apparatus of the present invention includes a static magnetic field generating means for generating a static magnetic field in the imaging space, a gradient magnetic field generating means for generating a gradient magnetic field in the imaging space, and a high frequency magnetic field High-frequency magnetic field generating means, a signal receiving means for detecting a nuclear magnetic resonance signal, and a control means for reconstructing an image using the detected nuclear magnetic resonance signal and generating a gradient magnetic field and a high-frequency magnetic field according to a plurality of pulse sequences And
- the magnetic resonance imaging apparatus further includes a vibration suppressing unit that changes a frequency characteristic or a vibration transmission characteristic of the vibration generated by the vibration of the gradient magnetic field generating unit.
- FIG. 1 is a schematic configuration diagram of an MRI apparatus to which the present invention is applied.
- FIG. 2 is a schematic perspective view of an MRI apparatus to which the present invention is applied.
- FIG. 3 is a schematic sectional view of an MRI apparatus according to the first embodiment of the present invention.
- FIG. 4 is a plan view showing only a shim tray and an anti-vibration damper in an MRI apparatus according to a second embodiment of the present invention, as viewed from a directional force of a static magnetic field.
- FIG. 5 is a diagram showing the relationship between the distance between shims and the distance from the center of the shim tray when trying to adjust the static magnetic field with a predetermined uniformity.
- FIG. 6 is a view showing only a shim tray and an anti-vibration damper in an MRI apparatus according to a third embodiment of the present invention, as viewed from a directional force of a static magnetic field.
- FIG. 7 is a view showing a fourth embodiment of the present invention, and is a view showing a form of a support means of a vibration damper.
- FIG. 8 is a view showing only a shim tray and an anti-vibration damper in an MRI apparatus according to a fifth embodiment of the present invention, as viewed from a directional force of a static magnetic field.
- FIG. 9 is a sectional view taken along the line BB of FIG. 8.
- FIG. 10 is a sectional view of a gantry according to a sixth embodiment of the present invention.
- FIG. 11 is an explanatory diagram of a vibration transmission path of a gradient magnetic field coil.
- FIG. 12 is a conceptual explanatory diagram concerning frequency characteristics of vibration of a gradient magnetic field coil and its transmission.
- FIG. 13 is a detailed explanatory view of a fixed state of the gradient coil.
- FIG. 14 is a block diagram of a control system according to a sixth embodiment of the present invention.
- FIG. 15 is an operation flowchart when imaging is performed using the MRI apparatus according to the sixth embodiment of the present invention.
- FIG. 16 is a sectional view of a gantry according to a seventh embodiment of the present invention.
- FIG. 17 is a schematic configuration diagram of a drive system when a hydraulic element is used as an actuator.
- FIG. 18 is an explanatory diagram in the case of using a piezoelectric element as an actuator.
- FIG. 19 is an explanatory diagram of a case where a piezoelectric element is used as an actuator.
- the MRI apparatus is roughly divided into a central processing unit (hereinafter abbreviated as a CPU) 1, a sequencer 2, a transmission system 3, a magnet 4 for generating a static magnetic field, a reception system 5, It comprises a magnetic field generation system 21 and a signal processing system 6.
- a CPU central processing unit
- sequencer 2 a transmission system 3
- magnet 4 for generating a static magnetic field
- reception system 5 It comprises a magnetic field generation system 21 and a signal processing system 6.
- the CPU 1 controls the sequencer 2, the transmission system 3, the reception system 5, and the signal processing system 6 according to a predetermined program.
- Sequencer 2 operates based on a control command from CPU1.
- the transmission system 3 includes a high-frequency oscillator 8, a modulator 9, and an irradiation coil 11, and modulates a reference high-frequency pulse from the high-frequency oscillator 8 with a modulator 9 according to a command from the sequencer 2.
- This amplitude-modulated high-frequency pulse is amplified through a high-frequency amplifier 10 to irradiate an irradiation coil 1
- the subject By supplying it to 1, the subject is irradiated with a predetermined pulsed electromagnetic wave.
- the static magnetic field generating magnet 4 is for generating a uniform static magnetic field in a predetermined direction around the subject 7.
- An irradiation coil 11, a gradient magnetic field coil 13, and a receiving coil 14 are arranged in the static magnetic field generating magnet 4.
- the gradient magnetic field coil 13 is included in the gradient magnetic field generation system 21, receives a current from the gradient magnetic field power supply 12, and generates a gradient magnetic field under the control of the sequencer 2.
- the receiving system 5 detects a high-frequency signal (NMR signal) emitted by nuclear magnetic resonance of nuclei of living tissue of the subject 7, and includes a receiving coil 14, an amplifier 15, and a quadrature phase signal. It has a detector 16 and an AZD translator 17. Then, a response high-frequency signal (NMR signal) from the subject 7 due to the electromagnetic wave irradiated from the irradiation coil 14 is detected by the receiving coil 14 arranged close to the subject 7, and the amplifier 15 and the quadrature phase detector 16 are detected. Is input to AZD Translator 17 via. Then, in AZD conversion 17, it is converted to digital quantity, and the signal is sent to CPU1.
- NMR signal high-frequency signal
- the signal processing system 6 includes an external storage device such as a magnetic disk 20, an optical disk 19 and the like, and a display 18 having a CRT or the like.
- an external storage device such as a magnetic disk 20, an optical disk 19 and the like
- a display 18 having a CRT or the like.
- the CPU 1 executes processing such as signal processing and image reconstruction, and displays an image of a desired tomographic plane of the subject 7 on the display 18 as well as , For example, on the magnetic disk 20 of an external storage device.
- FIG. 2 is a schematic perspective view of an open MRI apparatus to which the present invention is applied.
- the open-type MRI apparatus refers to a static magnetic field generating magnet, which is arranged vertically or across the imaging space (not shown in FIG. 2), and is opposed to the left and right, etc., perpendicularly to the aforementioned facing surface.
- This is an MRI apparatus that obtains an MRI image of a subject placed in the imaging space by disposing a magnetic field.
- the MRI apparatus has a magnet for generating a static magnetic field, a receiving coil for receiving an NMR signal, and the like, and includes a gantry 31 for accommodating a subject therein.
- a processing unit 33 for performing an image reconstruction operation to generate an MRI image based on an NMR signal obtained by a reception coil in a gantry 31;
- a monitor 34 and the like mounted on the monitor 33 for displaying the MRI image generated by the processing device 33 are provided.
- FIG. 3 shows that the magnetostatic source is arranged at the center by a static magnetic field source arranged vertically opposed as shown in FIG.
- a static magnetic field source arranged vertically opposed as shown in FIG.
- This is an example in which an open superconducting magnet 4 for generating a field is used, 35 is a uniform magnetic field space, 36a and 36b are upper and lower cryostats accommodating a superconducting coil, and 13 is an inclined magnetic field space 35.
- a gradient magnetic field coil for generating a magnetic field 39, a connecting pipe connecting the upper cryostat 36a and the lower cryostat 36b; 40, an RF coil fixture for fixing the RF coil 11 to the upper cryostat 36a and the lower cryostat 36b; 43 is a cover.
- Reference numeral 22 denotes a shim tray for disposing a large number of ferromagnetic shims (iron shims) in a large number of holes (screw holes).
- the shim tray 22 is provided between the static magnetic field generating magnet 4 and the gradient magnetic field coil 13. Be placed.
- Numeral 23 is disposed inside the hole formed in the shim tray 22 to reduce the noise generated by the vibration of the gradient magnetic field coil 13 propagating to the static magnetic field generating magnet and shaking the static magnetic field generating magnet and the like. This is an anti-vibration damper that also produces rubber and resin.
- the vibration transmissibility representing the performance of the vibration damper 23 is generally calculated according to the following equation (1) according to the value of the natural frequency of the system determined by the spring constant of the vibration damper 23 and the load of the support. I will decide.
- Tr is the vibration transmissibility
- fn is the natural vibration frequency of the system
- f is the vibration frequency
- K is the panel constant
- m is the support load.
- the equal loudness curve force is obtained.
- the sensitivity of the human ear to obtain the sound of 3 kHz to 5 kHz is higher than the highest sensitivity, and gradually lower at lower frequencies. It goes bad.
- the minimum frequency setting of the vibration to be damped is set to 3kHz, and a spring constant K (for example, 1Z10 or less) at which the vibration transmissibility is sufficiently small when the frequency is 3kHz is obtained. If this value is used as the upper limit of the panel constant, it is possible to reduce the noise of sounds with high ear sensitivity of about 3kHz to 5kHz.
- the vibration of the gradient magnetic field coil 13 itself must be suppressed to a small value.
- the frequency characteristics of the electromagnetic force acting on the gradient magnetic field coil 13 vary depending on the imaging sequence, the frequency characteristics at the resonance point (the frequency at which the vibration transmissibility is maximized (the natural vibration frequency)) of the anti-vibration damper 23 are set The forces at which the amplitude of the vibrations can be taken into account must be taken into account.
- the amplitude of the vibration at the resonance point is generally determined according to the following equation (2).
- F is the electromagnetic force applied to the gradient magnetic field coil
- Q is the ratio of the vibration amplitude at the resonance point to the displacement when the applied electromagnetic force is static.
- K is the panel constant
- X is the vibration amplitude.
- the allowable vibration amplitude of the gradient coil 13 is the same in any direction, for example, about ⁇ 0.1 mm.
- the lower limit of the constant can be obtained.
- the panel constant is set to a value between the upper limit and the lower limit of the spring constant.
- a large number of holes are formed in the shim tray 22 for improving the uniformity of the static magnetic field, and the vibration-damping damper having an appropriate panel constant is formed in the large number of holes.
- the arrangement area of the means can be secured, noise due to vibration of the gradient magnetic field coil 13 can be reduced, and image quality deterioration can be reduced.
- FIG. 4 is a plan view of only the shim tray 22 and the vibration damper 23 in the MRI apparatus according to the second embodiment of the present invention, as viewed from the direction of the static magnetic field.
- the second embodiment is also an example of the vertical magnetic field type MRI apparatus in which the direction of the static magnetic field is perpendicular to the direction of the body axis of the subject, as in the first embodiment. Since these are common to the first embodiment, their illustration is omitted.
- reference numerals 23a and 23b denote vibration dampers inserted into holes formed inside and outside the center of the shim tray 22, respectively, and 24 denotes a plurality of screw holes formed in the shim tray 22. This is a hole for placing the attached ferromagnetic shim (iron shim). These shim holes 24 are arranged at a certain interval in the radial direction from the center of the shim tray 22, and are also arranged at a constant interval in the angular direction. Therefore, when adjusting the magnetic field, the calculation of the position at which the ferromagnetic material is attached can be performed relatively easily.
- FIG. 5 shows that when the static magnetic field is to be adjusted with a predetermined uniformity, the density of the ferromagnetic shim (iron shim) must be set at the shim interval.
- FIG. The horizontal axis in FIG. 5 shows the distance from the center on the shim tray 22, and the vertical axis shows the arrangement interval of ferromagnetic shims (iron shims) (the reciprocal of the possible amount of shim per unit area).
- a ferromagnetic shim (iron shim) must be closely arranged. In other words, the distance between the ferromagnetic shim (iron shim) holes 24 must be smaller at the center.
- the distance between the shim holes 24 is smaller at the center than at the outer periphery of the shim tray 22.
- the space between the shim holes 24 is wider at the outer periphery of the shim tray 22 than at the center.
- the anti-vibration damper 23 inserted into the hole formed in the shim tray 22 has four inner dampers 23a (the first damper 23a) in accordance with the difference between the inner and outer shim holes 24. It consists of two types: a vibration isolating member) and four outer dampers 23b (a second vibration isolating member).
- the inner damper 23a has a circumferential length that allows for more space to place a ferromagnetic shim (iron shim) that is smaller than the radial length. .
- the four outer dampers 23b can make the space between the shim holes 24 wider than the inner side, so that they can be relatively freely arranged. In the case of FIG. 4, the circumferential width is larger than the radial length.
- the arrangement of the vibration isolating dampers 23a shown in FIG. 4 is rotationally symmetric about the center point of the shim tray 22, and a plurality (four in this example) are arranged at a predetermined angle (here, 90 degrees). Are the same as each other. Also, the panel constants of a plurality (four in this example) of outer vibration dampers 23b arranged at predetermined angles (here, 90 degrees) are the same. Preferably, the panel constants of all the inner and outer dampers 23a and 23b are the same.
- the weight of the gradient magnetic field coil 13 can be equally received at each position, so that the vibration damping performance of all the vibration dampers 23 can be equalized.
- the shims are arranged according to the shim arrangement density required for adjusting the static magnetic field with a predetermined uniformity, and the shims are arranged according to the distance between the shims. And a vibration damper, so that the static magnetic field Coordination with the shading means can be achieved.
- FIG. 6 is a diagram showing only the shim tray 22 and the vibration damper 23 of the MRI apparatus according to the third embodiment of the present invention when viewed from the direction of the static magnetic field.
- the inner vibration damper 23a has a shape in which the length in the circumferential direction is reduced in accordance with the force toward the center point of the shim tray 22.
- a ferromagnetic shim (iron shim) is arranged near the center of the shim tray 22. You can take more pace.
- FIG. 7 is a view showing a fourth embodiment of the present invention, showing a form of a support means of the vibration dampers 23a and 23b, and is a line AA of the vibration damper 23a shown in FIG.
- FIG. 7 is a view corresponding to a cross-sectional view taken along the line. It should be noted that not only the anti-vibration damper 23a but also the anti-vibration damper 23b have the same structure.
- the vibration-proof damper 23a has a shape in which the damper material 26 is sandwiched between two metal fittings 25a and 25b.
- the metal fittings 25a and 25b and the damper material 26 are fixed by bonding.
- the brackets 25a and 25b are fastened to the cryostats 36a and 36b and the gradient magnetic field coil 13 with bolts 27, respectively, so that the vibration-proofing of the gradient magnetic field coil 13 can be performed.
- the height of the vibration-damping damper 23a is made slightly higher than the height of the shim tray 22, so that the dimension in the height direction can be reduced, and the subject is arranged. Space can be expanded.
- the panel constant of the vibration isolating damper 23a having the same shape is smaller than the panel constant in the compression direction, and the panel constant in the shearing direction is, for example, 10: 1.
- the electromagnetic force acting on the gradient magnetic field coil 13 is almost the same in the vertical direction and the horizontal direction, optimizing the panel constant in the compression direction results in the panel constant in the shear direction being too small. As a result, the horizontal displacement of the gradient magnetic field coil 13 increases.
- the displacement of the gradient magnetic field generating coil 13 in the horizontal direction is applied to the outer peripheral portion of the shim tray 22 which can take a large length in the circumferential direction. Separately attach anti-vibration damper 23c for suppression purpose.
- FIG. 9 is a cross-sectional view taken along the line BB of FIG.
- the bracket 25a is a gradient magnetic field. It has a surface that is substantially parallel to the surface direction of the coil 13 and is attached to the gradient magnetic field coil 13, and a surface that is substantially perpendicular to the surface direction of the gradient magnetic field coil 13 and supports the damper material 26.
- the metal fitting 25b is substantially parallel to the surface direction of the lower cryostat 36b, and has a surface on which the lower cryostat 36b is mounted and a surface substantially perpendicular to the surface direction of the lower cryostat 36b and which supports the damper member 26. Have.
- FIG. 10 is a sectional view of a gantry 31 according to the sixth embodiment of the present invention.
- the same portions as those in the example shown in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.
- the difference between the example shown in FIG. 10 and the example shown in FIG. 3 is that the shim tray and the vibration damper are not disposed between the gradient magnetic field coil 13 and the upper and lower cryostats 36a and 36b. Instead of these, a gradient coil fixture 41 and an actuator 42 are provided.
- the actuator 42 changes the natural frequency of the fixed member according to the mode of the method of applying the current pulse to the gradient magnetic field coil 13, and the vibration is changed by the upper and lower cryostats 36 a and 36 b and the like. Changes the transfer function when it is transmitted to and resonates to produce noise.
- the weight of the gradient magnetic field coil 13 is relatively heavy, generally 30 to 400 kg, depending on the structure employed. It is designed to have high rigidity.
- the RF coil 11 is a force formed by attaching an electric element to a non-magnetic and non-conductive base material, and generally weighs about 10 to 50 kg.
- the cover 43 is formed of a non-metallic material such as FRP (fiber reinforced plastic) having a thickness of several mm, and is generally relatively lightweight, about 10 to 50 kg, and has low rigidity. ing. As described above, since the weight and the like of each component are different, the vibration characteristics are also greatly different.
- FIG. 12 (a) shows the frequency characteristics of the current pattern applied to the gradient coil 13 (or due to the current pattern applied to the gradient coil 13) when a certain imaging sequence is used. (Frequency characteristics of the vibration itself of the gradient magnetic field coil 13).
- FIG. 12 (b) shows the vibration generated in the gradient coil 13 shown in FIG.
- the ratio of transmission from the subject to the surgeon via the route that has passed until the sound is heard as noise is expressed as a transfer function.
- (I) in Fig. 12 (c) shows the frequency characteristics of noise actually heard by the subject and the surgeon.
- the frequency characteristic of (I) in FIG. 12 (c) is a result of multiplying FIG. 12 (a) by (I) in FIG. 12 (b).
- the peak frequency of the frequency characteristic of (I) in Fig. 12 (b) matches or is very close to the frequency of the peak part of the frequency characteristic in Fig. 12 (a). are doing.
- the transfer function in (I) of FIG. 12 (b) is changed by the method and means described later, as shown in (II) of FIG. 12 (b). This is changed so that the peak in FIG. 12 (a) and the peak in (II) in FIG. 12 (b) do not coincide with each other. As a result, the frequency characteristics of the noise actually heard by the subject and the operator are as shown in (II) of FIG. 12C, and the magnitude of the peak can be reduced.
- reference numeral 42a denotes a base for fixing the actuator 42 to the lower cryostat 36b.
- reference numeral 42a denotes a base for fixing the actuator 42 to the lower cryostat 36b.
- FIG. 13 only two gradient coil fixing devices 41 are shown. However, in actuality, a number sufficient to support the gradient coil 13 is required, and is omitted in FIG.
- the force actuator 42 is disposed above the base 42a.
- the tip on the side of the gradient magnetic field coil 13 is not in contact with the gradient magnetic field coil 13 in a normal state.
- the natural vibration mode generated in the gradient magnetic field coil 13 or the transfer function shown in FIG. 12 (b) is determined by the arrangement of the gradient magnetic field coil fixture 41.
- the actuator 42 when the actuator 42 is operated to bring the gradient magnetic field coil 13 into close contact with the gradient magnetic field coil 13 side of the actuator 42, the fixing condition of the gradient magnetic field coil 13 changes. As a result, when the natural vibration mode changes, the transfer function also changes.
- the frequency (peak frequency) at which the transfer function peaks and the frequency characteristics of the current pattern applied to the gradient coil 13 (determined in advance) It is possible to set so that the frequency of the peak in (1) shifts.
- the generated noise can be reduced, and the discomfort felt by the subject and the operator can be eliminated.
- FIG. 14 is a block diagram of a control system according to the sixth embodiment of the present invention.
- a CPU 1 that controls the entire system issues commands such as an imaging sequence and parameters to a sequencer 2 that controls a current applied to the gradient coil 13.
- commands such as an imaging sequence and parameters to a sequencer 2 that controls a current applied to the gradient coil 13.
- a control signal is supplied to a drive source 63 for driving the actuator 42, and an appropriate actuator is provided. 42 is brought into contact with the gradient coil 13.
- the sixth embodiment of the present invention does not directly cancel the vibration unlike the technique described in Japanese Patent Application Laid-Open No. 8-154518. Instead of controlling, control it statically. Therefore, high driving circuit Since a fast one is not required, it can be simplified.
- step 71 the operator inputs information such as a sequence to be shot and parameters to be shot via the display 18 or the like.
- the frequency characteristic of the current pattern applied to the gradient coil 13 is calculated when the imaging is performed using the sequence and parameters input in step 71.
- step 73 in order to make the vibration generated by the current no-turn applied with the frequency characteristic calculated in step 72 as loud noise to the subject and the operator, any actuator is used. To determine whether to decorate the transfer function.
- photographing is performed while driving the actuator 42 as determined in step 73.
- the transfer function between the gradient magnetic field coil 13 and the upper and lower cryostats 36a, 36b is changed according to the imaging sequence.
- the actuator 42 is configured to be driven so as to have the most appropriate value for suppressing the vibration of the magnetic field, so that the generation of noise due to the vibration of the gradient magnetic field coil can be suppressed in accordance with various sequences. Image quality can be improved.
- FIG. 16 is a sectional view of a gantry 31 according to the seventh embodiment of the present invention.
- the same portions as those in the example shown in FIG. 10 are denoted by the same reference numerals, and detailed description thereof will be omitted.
- the anti-vibration dampers 23 (23a, 23b) in the first to fifth embodiments of the present invention are used as the actuator 42, and the elastic modulus of the actuator 42 is changed. By doing so, the elastic modulus that can be most suppressed vibration according to various sequences, There is an example of control.
- the RF coil 11 and the cover 43 have a lower rigidity and weight.
- the higher the frequency the greater the effect of sound insulation. Therefore, when the vibration intensity of the gradient magnetic field coil 13 is the same, it is better to suppress the vibration peak on the lower frequency side to reduce the noise peak. can do.
- the human sensitivity to noise depends on the frequency. Therefore, the transfer function may be changed including its sensitivity.
- the noise generated varies depending on the location, it is possible to design the location to be subject to noise suppression taking into account the noise. For example, since the position of the ear of the subject is different depending on the imaging region of the subject, it is only necessary to select which actuator is brought into contact with each component according to the imaging region. At this time, it is also possible to take into account the level of noise reduction of the operator.
- a rubber damper or the like is arranged so as to be in contact with the gradient magnetic field coil 13, and by changing this temperature, the hardness of the rubber damper is changed and the frequency characteristic of the vibration of the gradient magnetic field coil 13 is changed.
- the effect of the present invention can also be obtained by changing.
- a method of changing the temperature a method of using a heater, a method of changing the temperature of a fluid inside a pipe wound around rubber, a method of using a Peltier element, or the like can be considered.
- a vibration damping effect can also be obtained, so that an effect of suppressing the transmission of vibration from the gradient coil 13 to the magnet (cryostat) can also be obtained.
- a piezoelectric element can be used as an actuator.
- FIG. 17 is a schematic configuration diagram of a drive system of the actuator 42 when a hydraulic element is used as the actuator 42.
- the CPU 1 outputs a command to the power supply 80 so as to have a dimension corresponding to the sequence to be executed, and in accordance with the power supplied from the power supply 80, the hydraulic pressure in which the pump 81 is the actuator 42.
- the hydraulic element 42 and the pump 81 are made of a non-magnetic material in consideration of the influence on the magnetic field uniformity.
- FIG. 18 is an explanatory diagram in the case where a piezoelectric element is used as the actuator 42.
- Piezoelectric elements have various structures based on an element in which a piezoelectric body is sandwiched between two electrodes, and include a monomorph type and a laminated type.
- the laminated piezoelectric element When applied to the present invention, it is desirable to use a stacked type in order to obtain a relatively large displacement.
- the laminated piezoelectric element includes an external electrode 83 and an internal electrode 84, and is formed by laminating several tens of LOO piezoelectric thin plates.
- the piezoelectric bodies are alternately stacked so that the polarization in the thickness direction is reversed. When a voltage is applied to the electrode, it is displaced in the stacking direction.
- a piezoelectric element has a hysteresis in the amount of displacement with respect to an applied voltage, as shown in Fig. 19, and therefore control needs to be performed in consideration of this.
- the MRI apparatus in which the gradient magnetic field coil 13 is provided on the cryostats 36a and 36b has been described.
- the present invention is also applicable to an MRI apparatus in which the gradient magnetic field coil 13 is installed on a support table fixed to a floor other than the cryostat.
- the actuator base may be provided between the support base and the gradient coil.
- An MRI apparatus using such a support table can reduce the transmission of vibration from the gradient coil 13 to the cryostats 36a and 36b, and thus has an effect of suppressing noise.
- the present invention can be used in combination with a known noise reduction technology (for example, a sequence-based noise reduction, a vacuum shielding technology, and the like), and further noise reduction can be achieved.
- a known noise reduction technology for example, a sequence-based noise reduction, a vacuum shielding technology, and the like
- the force is not used. Noise may be reduced if not closely attached to the gradient coil.
- the present invention is not limited to the above-described embodiments, and can be implemented in various modifications without departing from the spirit of the present invention.
- the present invention is directed to a horizontal magnetic field type tunnel type MRI apparatus, that is, an object arranged in an imaging space in a gantry by generating a static magnetic field in a generally cylindrical gantry along a central axis of the cylinder. It can also be applied to MRI equipment that obtains MRI images.
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Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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US11/628,097 US7755359B2 (en) | 2004-05-31 | 2005-05-25 | Magnetic resonance imaging apparatus with noise suppressing structure |
JP2006513899A JP4822439B2 (ja) | 2004-05-31 | 2005-05-25 | 磁気共鳴イメージング装置 |
Applications Claiming Priority (4)
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JP2004-160779 | 2004-05-31 | ||
JP2004160779 | 2004-05-31 | ||
JP2005-070214 | 2005-03-14 | ||
JP2005070214 | 2005-03-14 |
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WO2005115239A1 true WO2005115239A1 (ja) | 2005-12-08 |
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PCT/JP2005/009523 WO2005115239A1 (ja) | 2004-05-31 | 2005-05-25 | 磁気共鳴イメージング装置 |
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JP (1) | JP4822439B2 (ja) |
WO (1) | WO2005115239A1 (ja) |
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JPWO2016136465A1 (ja) * | 2015-02-25 | 2017-11-30 | 株式会社日立製作所 | 磁気共鳴イメージング装置、静磁場均一度調整方法、プログラム及び計算機 |
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DE102011089445B4 (de) * | 2011-12-21 | 2015-11-05 | Siemens Aktiengesellschaft | Verfahren und Gradientensystem zur Reduzierung von mechanischen Schwingungen in einem Magnetresonanzbildgebungssystem |
CA2871384C (en) | 2012-04-30 | 2020-04-21 | Children's Hospital Medical Center | Acoustic noise reducing rf coil for magnetic resonance imaging |
DE102013206555B4 (de) * | 2013-04-12 | 2018-03-01 | Siemens Healthcare Gmbh | Magnetresonanzscanner mit Antennensystem |
DE102013206557B4 (de) * | 2013-04-12 | 2017-03-23 | Siemens Healthcare Gmbh | Magnetresonanzscanner mit Antennensystem |
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JP6245993B2 (ja) * | 2014-01-09 | 2017-12-13 | 東芝メディカルシステムズ株式会社 | 磁気共鳴イメージング装置及びシムトレイ |
US10656225B2 (en) * | 2016-09-01 | 2020-05-19 | Canon Medical Systems Corporation | Magnetic resonance imaging apparatus |
CN112826494B (zh) * | 2020-12-30 | 2023-05-23 | 上海联影医疗科技股份有限公司 | Mr设备振动和声学噪声消减方法、系统、装置及存储介质 |
CN114994770A (zh) * | 2022-04-27 | 2022-09-02 | 吉林大学 | 一种频率域地空电磁探测用接收系统 |
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Also Published As
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JP4822439B2 (ja) | 2011-11-24 |
US7755359B2 (en) | 2010-07-13 |
US20080309343A1 (en) | 2008-12-18 |
JPWO2005115239A1 (ja) | 2008-03-27 |
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