JP5634956B2 - Coil apparatus, gradient magnetic field coil for magnetic resonance imaging apparatus, manufacturing method thereof, and magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to a coil device having a coil body made of a thin conductor plate in which a gap between turns is provided between turns of a conductor portion, a gradient coil for a magnetic resonance imaging apparatus using the coil device, and manufacture of the gradient coil The present invention relates to a method and a magnetic resonance imaging apparatus having the gradient magnetic field coil.

  An MRI apparatus (magnetic resonance imaging apparatus) measures an NMR (nuclear magnetic resonance) signal generated by a nuclear spin constituting a tissue of a subject, particularly a human body, and has two forms and functions such as a head, abdomen, and extremities. It is an apparatus for imaging in a three-dimensional or three-dimensional manner. In imaging, the NMR signal is given different phase encoding and frequency encoding depending on the gradient magnetic field. The NMR signal measured as time series data is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  In such an MRI apparatus, a gradient magnetic field coil that generates a gradient magnetic field is installed close to a superconducting magnet that generates a static magnetic field. For this reason, when the gradient magnetic field changes with time, eddy currents are generated in conductors such as the heat shield plate, helium vessel, and outer wall of the superconducting magnet. The magnetic field generated by the eddy current changes the gradient magnetic field spatially and temporally in the space where the subject is placed. For this reason, when an eddy current occurs, image quality and local spectral performance deteriorate.

  On the other hand, conventionally, a coil pattern design method for a gradient magnetic field coil having high-speed gradient magnetic field switching characteristics while suppressing eddy current has been proposed (for example, see Patent Document 1).

  Further, while it is required to widen the space for the subject to enter, the magnet for generating the static magnetic field is required to be as small as possible due to the restriction of the installation position. For this reason, it is desired that the gradient magnetic field coil be reduced in size and thickness, and in the conventional MRI apparatus, a thin coil obtained by processing a conductive thin plate made of copper, aluminum, or the like is used as the gradient magnetic field coil.

  Such a thin coil is manufactured by subjecting a conductive thin plate to spiral pattern processing (laser processing or water jet processing) and then bending it into a cylindrical or elliptical cylinder shape with a roll machine or the like. In addition, in such a conventional gradient magnetic field coil, as a method of suppressing heat generation due to eddy current and heat generation due to energized pulsed large current, the coil conductor width in the high magnetic field region is changed from the coil conductor width in the low magnetic field region. Has also been proposed (see, for example, Patent Document 2).

JP-A-8-84716 JP 2009-183386 A

  In the gradient magnetic field coil made of the conventional conductive thin plate as described above, when the magnetic field generated when a large pulse current is applied intersects, an eddy current is generated and the temperature rises. In addition, this eddy current causes deterioration in image quality particularly during high-speed imaging.

  In order to suppress such eddy currents, it is effective to narrow the coil conductor width and limit the width in which current can be passed. Narrowing the coil conductor width is also effective from the viewpoint of suppressing current drift.

  However, if the coil conductor width is narrowed simply by increasing the gap between turns, the area of the conductor thin plate decreases, so the contact area between the roll machine and the conductor thin plate decreases when bending using a roll machine. However, the force is not sufficiently and evenly transmitted to the conductor thin plate, and there is a problem that the bending accuracy is deteriorated, for example, deformation occurs, resulting in a manufacturing error.

  The present invention has been made in order to solve the above-described problems, and a coil device capable of suppressing the current drift and the generation of eddy currents while sufficiently securing the area of the conductor thin plate, and its It is an object of the present invention to provide a gradient magnetic field coil for a magnetic resonance imaging apparatus using the coil device, a method for manufacturing the gradient magnetic field coil, and a magnetic resonance imaging apparatus having the gradient magnetic field coil.

The coil device according to the present invention includes a coil body that is formed of a thin conductor plate and has a turn-to-turn gap between turns of a conductor portion, and at least a portion between the turn gaps is in a direction of a current flowing through the conductor portion. It has a meandering shape.
A gradient magnetic field coil for a magnetic resonance imaging apparatus according to the present invention includes a coil body that is formed of a curved conductor thin plate and has a turn-to-turn gap between turns of a conductor portion, and at least a portion between the turn gaps. Has a meandering shape with respect to the direction of current flowing in the conductor portion.
The magnetic resonance imaging apparatus according to the present invention includes a gradient magnetic field coil having a coil body that is formed of a curved conductor thin plate and has a turn-to-turn gap between turns of a conductor portion, and at least between the turn gaps. A part has a shape meandering with respect to the direction of the current flowing through the conductor part.
In addition, the method for manufacturing a gradient magnetic field coil for a magnetic resonance imaging apparatus according to the present invention comprises a step of forming a spiral conductor portion by patterning a gap between turns on a conductor thin plate, and a pattern processed conductor thin plate. A step of bending, and when patterning the inter-turn gap, at least a part of the turn gap is formed in a meandering shape with respect to the direction of the current flowing in the conductor portion.

  In the coil device, the gradient magnetic field coil for the magnetic resonance imaging apparatus, the manufacturing method thereof, and the magnetic resonance imaging apparatus of the present invention, at least a part between the turn gaps has a meandering shape with respect to the direction of the current flowing through the conductor part. In addition, it is possible to limit the range in which the current substantially flows in the conductor portion while ensuring a sufficient area of the conductor thin plate, and to suppress the deviation of the energized current and the generation of the eddy current.

It is a block diagram which shows the MRI apparatus by Embodiment 1 of this invention. It is a perspective view which shows the mold body of the gradient magnetic field coil of FIG. It is a perspective view which shows the example of a pattern design of x main coil of FIG. FIG. 4 is a perspective view showing a first x main coil of FIG. 3. FIG. 5 is a development view showing the first x main coil of FIG. 4. FIG. 6 is a development view showing a part of the first x main coil of FIG. 5 in an enlarged manner. FIG. 7 is a development view showing an example in which a gap between turns is formed in a pattern different from FIG. 6. FIG. 6 is an explanatory diagram showing a portion through which a current substantially flows in the first x main coil of FIG. 5. It is explanatory drawing explaining the current drift. It is a perspective view which shows the example of a pattern design of z main coil of FIG. It is an expanded view which shows the 1st z main coil of FIG.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an MRI apparatus according to Embodiment 1 of the present invention. In the figure, the MRI apparatus has a static magnetic field generation system 2, a gradient magnetic field generation system 3, a sequencer 4, a transmission system 5, a reception system 6, and a computer 7.

  If the static magnetic field generation system 2 is a horizontal magnetic field system, it generates a uniform static magnetic field in the body axis direction. The static magnetic field generation system 2 includes a permanent magnet type, a normal conduction type, or a superconducting type static magnetic field generation magnet. The static magnetic field generating magnet is disposed around the subject 1.

  The gradient magnetic field generation system 3 includes a plurality of gradient magnetic field coils 8 that apply gradient magnetic fields in three axial directions of x, y, and z that are coordinate systems of the MRI apparatus, and a gradient magnetic field power source 9 that drives each gradient magnetic field coil 8. And have. The gradient magnetic field generation system 3 applies the gradient magnetic fields Gx, Gy, and Gz in the three axial directions of x, y, and z by driving the gradient magnetic field power supply 9 in accordance with a command from the sequencer 4.

  At the time of imaging, a slice direction gradient magnetic field pulse is applied in a direction orthogonal to the slice plane (imaging cross section), and the slice plane for the subject 1 is set. Then, a phase encoding direction gradient magnetic field pulse and a frequency encoding direction gradient magnetic field pulse are applied in the remaining two directions orthogonal to the slice plane and orthogonal to each other, and position information in each direction is encoded in the echo signal. The

  The sequencer 4 is a control unit that repeatedly applies a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined pulse sequence. The sequencer 4 operates under the control of the computer 7, and sends various commands necessary for collecting tomographic image data of the subject 1 to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6.

  The transmission system 5 irradiates the subject 1 with an RF pulse in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the living tissue of the subject 1. The transmission system 5 includes a modulator 10, a high frequency oscillator 11, a high frequency amplifier 12, and a high frequency coil (transmission coil) 13a on the transmission side.

  The high-frequency coil 13 a is disposed in the vicinity of the subject 1. The RF pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 10 at a timing according to a command from the sequencer 4. The amplitude-modulated RF pulse is amplified by the high frequency amplifier 12 and then supplied to the high frequency coil 13a. Thereby, the subject 1 is irradiated with the RF pulse.

  The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the living tissue of the subject 1. The reception system 6 includes a reception-side high-frequency coil (reception coil) 13 b, a signal amplifier 14, a quadrature phase detector 15, and an A / D converter 16.

  The high-frequency coil 13 b is disposed in the vicinity of the subject 1. The NMR signal in response from the subject 1 is induced by the electromagnetic wave irradiated from the high frequency coil 13a on the transmission side. The induced NMR signal is detected by the high-frequency coil 13 b and amplified by the signal amplifier 14. The amplified NMR signal is divided into two orthogonal signals by the quadrature detector 15 at a timing according to a command from the sequencer 4. The divided signals are converted into digital quantities by the A / D converter 16 and sent to the computer 7.

  The computer 7 performs various data processing, display and storage of processing results, and the like. Further, a display 17, a storage device 18 and an operation device 19 are connected to the computer 7.

  As the display 17, a CRT display, a liquid crystal display, or the like is used. As the storage device 18, an optical disk device, a magnetic disk device, or the like is used. As the operating device 19, a combination of a trackball or a mouse and a keyboard is used.

  When data from the reception system 6 is input to the computer 7, the computer 7 executes processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 1 as a result on the display 17. At the same time, image data is recorded in the storage device 18.

  The operating device 19 is disposed in the vicinity of the display 17. Various control information of the MRI apparatus and control information of processing performed by the computer 7 are input using the operation device 19. The operator interactively controls various processes of the MRI apparatus through the operation device 19 while looking at the display 17.

  In FIG. 1, the high-frequency coil 13a and the gradient magnetic field coil 8 on the transmission side are installed so as to surround the subject 1 in the static magnetic field space of the static magnetic field generation system 2 into which the subject 1 is inserted. ing. The high-frequency coil 13b on the reception side is installed so as to surround the subject 1.

  Further, the imaging target nuclide that is currently widely used in clinical practice is a hydrogen nucleus (proton) that is a main constituent of the subject. By imaging information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

  FIG. 2 is a perspective view showing a molded body of the gradient magnetic field coil 8 of FIG. 1, and in this example, an active shield type gradient magnetic field coil is shown. Here, the coordinate axes in the gradient magnetic field coil 8 are the origin of the center of the imaging region, the z-axis is the direction of the static magnetic field, and the x-axis and the y-axis are two axes orthogonal to the z-axis.

  The gradient magnetic field coil 8 includes three types of main coils, that is, an x main coil 20a, a y main coil 20b, and a z main coil 20c, and three types of shield coils, that is, an x shield coil 21a, a y shield coil 21b, and a z shield coil. 21c is used. These coils 20a to 20c and 21a to 21c are molded and integrated with resin or the like.

  The x main coil 20a, the y main coil 20b, and the z main coil 20c generate linear gradient magnetic fields in the corresponding directions in the imaging region. The x shield coil 21a, the y shield coil 21b, and the z shield coil 21c generate a gradient magnetic field in the corresponding direction.

  The shield coils 21a to 21c are installed outside the main coils 20a to 20c and in a space between the main coils 20a to 20c and the static magnetic field generating magnet, and prevent the leakage magnetic field from the main coils 20a to 20c. Fulfill.

  FIG. 3 is a perspective view showing a pattern design example of the x main coil 20a of FIG. By applying a current on such a pattern, it is possible to generate a desired magnetic field that linearly changes in the x-axis direction within the imaging region. In order to realize such a pattern, the first x main coil 22a, the second x main coil 22b, the third x main coil 22c, and the fourth x main coil 22d are used as the x main coil 20a. Is used.

  As each x main coil 22a-22d, what curved the thin coil which consists of conductor thin plates is used. As a material for the conductor thin plate, for example, a material that conducts electricity well, such as copper or aluminum, is used.

  FIG. 4 is a perspective view showing the first x main coil 22a of FIG. The first x main coil 22 a that is a coil body is constituted by a spiral conductor portion 23. Between the turns of the conductor portions 23 adjacent in the radial direction, a spiral inter-turn gap 24 is formed.

  The inter-turn gap 24 has a plurality of meandering shapes in which line segments along the current direction and line segments perpendicular to the current direction are alternately connected, in this example, a rectangular wave shape. In addition, a rectangular shape may be used instead of a rectangular wave shape. That is, the inter-turn gap 24 has a shape meandering with respect to the direction of the current flowing through the conductor portion 23. A hollow portion 25 is formed in the central portion of the first x main coil 22a.

  The thickness of the conductor thin plate is, for example, 2 to 3 mm. Moreover, the width dimension of the gap | interval 24 between turns is 1-2 mm, for example. Furthermore, the number of turns (number of turns) of the conductor portion 23 is, for example, about 15 to 30, but it is shown in the figure for the sake of simplicity.

  The second, third, and fourth x main coils 22b to 22d have the same or similar shape as the first x main coil 22a. A combination of such coils 22a to 22d generates a gradient magnetic field that linearly changes in the x direction in the imaging region.

  FIG. 5 is a development view showing the first x main coil 22a of FIG. When manufacturing the 1st x main coil 22a, the hollow part 25, the clearance gap 24 between turns, and a coil outer periphery line are first patterned into a flat conductor thin plate. The pattern processing can be performed by laser processing, water jet processing, or pallet punching processing. Further, the inter-turn gap 24 can be patterned in a single stroke from the outer peripheral side to the inner peripheral side or from the inner peripheral side to the outer peripheral side.

  FIG. 6 is an expanded view showing a part of the first x main coil 22a of FIG. The turns T1 and T2 are spiral adjacent turns, and the turn T2 is located outside the turn T1.

  The points A1, B1, C1, D1,... Are placed on the desired current outermost line to1 in the turn T1, and the points A2, B2, C2, D2,. Take ... The lines connecting the line segments A1-A2, B1-B2, C1-C2, D1-D2, A2-B2, B1-C1, and C2-D2 are used as the pattern processing locus. These may be curved lines instead of line segments.

  As a result, the locus of pattern processing becomes a one-stroke shape (continuous) of A1-A2-B2-B1-C1-C2-D2-D1-..., And the inter-turn gap 24 is cut along this locus. Then, the turn T1 and the turn T2 are electrically insulated.

  As a result, a pattern is formed in which the current is limited to the line width dw1 between the curves ti1 and to1 in the turn T1, and the current is limited to the line width dw2 between the curves ti2 and to2 in the turn T2. Can do. That is, in each turn, the rectangular wave-shaped inter-turn gap 24 makes it difficult for current to flow in the portion protruding inward and outward in the radial direction of the conductor portion 23, and only in the portion excluding the portion protruding inward and outward in the radial direction. A current flows substantially.

  Further, the line widths dw1 and dw2 in the same turn may be the same size or may be changed depending on the position. In the example of FIG. 5, the dimension (for example, 500 to 800 mm) in the z-axis direction is shorter than the dimension in the circumferential direction (for example, 1000 to 1500 mm) of the x main coil 22a, and a current substantially flows through the conductor portion 23. The width of the portion changes depending on the position in the circumferential direction. For example, the width of the portion through which the current substantially flows in the z-axis direction central portion (the portion on the long axis of the x main coil 22a) in FIG. ) Is substantially smaller than the width of the portion through which current flows.

  Here, if the inter-slit distances ds1 and ds2 are too wider than the line widths dw1 and dw2, the current meanders outside the desired current limiting region, and the linearity of the gradient magnetic field is disturbed or the eddy current increases. . For this reason, it is desirable that the inter-slit distances ds1 and ds2 be less than half of the desired line widths dw1 and dw2. That is, in each turn of the conductor portion 23, the size of one pulse width (one rectangular wave portion) of the rectangular wave-shaped inter-turn gap 24 (one meander width) is the inter-turn gap in the width direction of the conductor portion 23. It is desirable to make it less than or equal to half of the width dimension of the portion excluding the region where 24 is provided.

  Further, instead of setting the cutting locus to A2-B2, B1-C1, C2-D2, as shown in FIG. 7, it may be A1-B1, B2-C2, C1-D1. In this case, the pattern processing locus is a one-stroke writing pattern (continuous) of A2-A1-B1-B2-C2-C1-D1-D2-.

  6 and 7, the pattern processing method for the turns T1 and T2 has been described. By performing this for other turns of the coil, the pattern processing trajectory of the entire coil becomes as shown in FIG.

  After the pattern processing is performed in the shape shown in FIG. 5, the x main coil 22a as shown in FIG. 4 is formed by bending into a cylindrical or elliptical cylindrical shape with a desired curvature using a roll machine.

  FIG. 8 is an explanatory diagram showing a portion through which a current substantially flows in the first x main coil 22a of FIG. By patterning into a shape as shown in FIG. 5, a current flows in a region 29 as shown in FIG. 8, and the current is limited in the region 30. That is, the current is limited in the same manner as when pattern processing is performed on the boundary line between the region 29 and the region 30 in FIG. 8, and an effect of suppressing heat generation due to eddy current and heat generation due to a pulsed large current is obtained.

  FIG. 9 is an explanatory diagram for explaining current drift. In FIG. 9A, the current conducting region is limited between 33a and 34a. Moreover, in FIG.9 (b), the electric current supply area | region is restrict | limited between 33b and 34b. That is, the width of the energized region in FIG. 9B is narrower than that in FIG. 9A.

  In such a state, in a section with a large curvature, even if the designed current center is the curve 31, a drift occurs in the inner direction, and the actual current centers become curves 32 a and 32 b. In particular, in FIG. 9A, the curve 32 a greatly deviates from the curve 31. On the other hand, the pattern processing according to the first embodiment is equivalent to limiting the current conduction region as shown in FIG. 8B, and can suppress current drift.

  According to the above method, it is possible to reduce the portion where the conductor thin plate is cut off during pattern processing, and it is possible to prevent a reduction in the area of the conductor thin plate due to pattern processing. For this reason, when performing bending after pattern processing, the contact area between the roll of the roll machine and the conductor thin plate can be kept sufficiently, and the force of the roll is transmitted sufficiently and evenly to the conductor thin plate, so that bending can be performed with high accuracy. It can be performed.

  Further, the pattern processing trajectory can be written in a single stroke (continuous), the processing trajectory can be continuously processed without duplication, and the processing time can be shortened.

  The hollow portion 25 needs to be removed, but from the viewpoint of maintaining a contact area with the roll at the time of bending, it may be left at the time of patterning and removed after the bending. In this case, at the time of pattern processing, a slit may be made while leaving a part around the hollow portion 25, and the remaining portion may be cut after bending.

  In the above description, the method of forming the x main coil has been described. However, since the y main coil, the x shield coil, and the y shield coil have similar shapes, the same method can be applied.

  Further, FIG. 10 is a perspective view showing a pattern design example of the z main coil 20c of FIG. As the z main coil 20c, first and second z main coils (coil bodies) 35a and 35b having a solenoid shape are used.

When the same method as the above-mentioned x main coil 22a is applied to the first z main coil 35a, pattern processing as shown in FIG. 11 is applied to the conductor thin plate, and both ends in the longitudinal direction in FIG. Add) and make it cylindrical. Further, the second z main coil 35b can be manufactured in the same manner. Further, a z shield coil can be manufactured in the same manner.
However, for the z main coil and the z shield coil, the above-described method may not be applied, and a structure similar to the conventional structure (a structure in which a coil conductor is wound in a solenoid shape) may be used. In this case, at least one of the z main coil and the z shield coil may be formed of a tubular conductor, and the coolant may be circulated therein.

  Furthermore, in FIG. 4 and FIG. 5, the inter-turn gap 24 has a rectangular wave shape as a whole, but it does not necessarily have to be a rectangular wave shape as a whole. For example, since the width of the region 30 is small in the intermediate portion in the circumferential direction of FIG. 8, the inter-turn gap 24 does not have to meander.

In the above example, the rectangular wave-shaped inter-turn gap 24 is shown. However, a sinusoidal wave may be used as long as ds1 and ds2 are sufficiently smaller than dw1 and dw2.
Furthermore, in the above example, the gradient magnetic field coil for the magnetic resonance imaging apparatus has been described. However, the present invention can also be applied to a coil apparatus mounted on a device other than the magnetic resonance imaging apparatus.

  8 Gradient magnetic field coil, 22a 1st x main coil (coil body), 22b 2nd x main coil (coil body), 22c 3rd x main coil (coil body), 22d 4th x main coil (coil) Main body), 23 conductor portion, 24 inter-turn gap, 35a first z main coil (coil main body), 35b second z main coil (coil main body).

Claims (7)

A coil device comprising a coil body configured by a conductor thin plate and provided with a gap between turns of a conductor portion,
At least a portion between the turn gaps has a meandering shape with respect to the direction of current flowing through the conductor portion. A gradient magnetic field coil for a magnetic resonance imaging apparatus, comprising a coil body configured by a curved conductor thin plate and provided with a gap between turns of a conductor portion,
A gradient magnetic field coil for a magnetic resonance imaging apparatus, wherein at least a part between the turn gaps has a meandering shape with respect to a direction of a current flowing through the conductor portion. The inter-turn gap has a meandering shape multiple times,
In each turn of the conductor portion, the size of one meandering width between the turn gaps is half of the width size of the portion excluding the region where the inter-turn gap in the width direction of the conductor portion is provided. The gradient coil for a magnetic resonance imaging apparatus according to claim 2, wherein:   The gradient coil for a magnetic resonance imaging apparatus according to claim 2, wherein the inter-turn gap has a rectangular wave shape.   A magnetic resonance imaging apparatus comprising the gradient magnetic field coil according to any one of claims 2 to 4. Forming a spiral conductor portion by patterning a gap between turns in a thin conductor plate; and
A method of manufacturing a gradient coil for a magnetic resonance imaging apparatus, comprising: bending the patterned conductor thin plate,
Manufacturing a gradient coil for a magnetic resonance imaging apparatus, wherein when patterning the inter-turn gap, at least a part of the turn gap is meandered with respect to the direction of current flowing in the conductor portion Method.   The meandering gap between the turns is formed by alternately punching a portion along the direction of the current flowing through the conductor portion and a portion perpendicular to the direction of the current flowing through the conductor portion. Item 7. A method for producing a gradient coil for a magnetic resonance imaging apparatus according to Item 6.

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