JPH08280648A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE: To provide a magnetic resonance imaging apparatus which can form a three-channel inclined magnetic field while enlargement in the axial direction and radial direction is suppressed and provides a small-sized inclined magnetic field coil such as that for head part. CONSTITUTION: A magnetic resonance imaging apparatus is provided with a small-sized inclined magnetic field coil 11 which is placed in a static magnetic field generated by means of a magnet and into which only a local site of a subject P to be examined is inserted. The coil 11 is provided with coils for generating a three channel inclined magnetic field consisting of coils x(11x...11x), coils y(11y...11y) and coils z(11z...11z) and at least the coils x(11x...11x) and the coils y(11y...11y) are formed by multiple winding of a flat conductive wire CP and both end parts in the magnetic field direction Z of the static magnetic field are arranged in the direction in which the longitudinal direction of the crosssectional face of the flat conductive wire CP intersects the magnetic field direction Z at right angles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging (MRI) apparatus equipped with a small gradient magnetic field coil suitable for a local region such as the head.

[0002]

2. Description of the Related Art Generally, in an MRI apparatus, a main static magnetic field has a linear gradient for the purpose of determining an arbitrary imaging cross section and applying position information to MR signals from a subject. A coil that generates this linear gradient magnetic field is a gradient magnetic field coil, and is installed in the bore of a magnet (for example, a superconducting magnet) for generating a main static magnetic field.

This gradient magnetic field coil is usually installed in advance as a coil for the whole body, but depending on the device, a head gradient magnetic field coil is inserted as a dedicated coil in the bore formed by this whole body gradient magnetic field coil. There is a structure that does. When using this dedicated coil, the whole body gradient coil is placed in a non-driven state. The head gradient magnetic field coil is formed in a substantially cylindrical shape so as to entirely cover only the head of the subject, and the gradient magnetic field is formed in a local space at the center of the main static magnetic field.

[0004]

However, the above-mentioned head gradient magnetic field coil covers the head (face) along the head, and it is intended to form three-channel gradient magnetic fields in the x, y, and z directions. Then, in each of the x, y, and z coils, the plate conductors must be sequentially arranged in the axial direction (z direction) of the magnet and wound many times, so that the axial length of the entire cylindrical head gradient magnetic field coil is increased. Becomes longer. When the head is inserted into the coil when the size is increased in the axial direction in this way, the shoulder of the subject hits the end of the coil, and the virus ring (Willis Circle) of the head is photographed at the center of the magnetic field inside the coil. There is a problem that it is not possible to align the areas, and proper photography cannot be performed.

If the axial length of the gradient magnetic field coil for the head is to be shortened, x, y,
Although it is unavoidable to reduce the number of z-coils (channels) and to give up the formation of the gradient magnetic field of three channels, if this is done, there is a limit to the shortening of the echo time that is important in imaging such as MR angiography.

It is also conceivable that the flat conductor wires of the x, y, and z coils are laminated and wound in the radial direction of the magnet, but this time, the radial size of the head gradient coil exceeds the physical limit. As a practical matter, it is difficult to wind 10 to 15 turns of flat conductor wire having a thickness of 2 mm and a width of 5 mm, for example. I needed to wind it.

The present invention has been made in view of such a conventional situation, and is a small-sized tilt for a head or the like capable of forming a 3-channel gradient magnetic field while suppressing an increase in the size in the axial direction and the radial direction. It is an object of the present invention to provide a magnetic resonance imaging apparatus including a magnetic field coil.

Another object of the present invention is to provide a magnetic resonance imaging apparatus having a head gradient magnetic field coil which can achieve the above-mentioned object and which can be easily aligned with the coil. To aim.

[0009]

In order to achieve one of the above-mentioned objects, magnetic resonance provided with a small gradient coil placed in a static magnetic field generated by a magnet and inserting only a local region of a subject. In the imaging apparatus, the coil is provided with a three-channel gradient magnetic field generating coil of an x coil, ay coil and az coil, and at least the x coil and the y coil are formed by multiple winding of a flat conductor wire,
Both ends of at least the x-coil and the y-coil in the magnetic field direction of the static magnetic field are arranged such that the longitudinal direction of the cross section of the flat plate conductor is orthogonal to the magnetic field direction.

In order to achieve another object, a magnet for generating a static magnetic field and a substantially cylindrical and small gradient magnetic field which is placed in the static magnetic field and into which only a local region of the subject is inserted. A gantry having a coil, a high-frequency coil placed in the cylindrical space of the gradient magnetic field coil, a tabletop on which the subject is placed, and a bed having a bed body that supports the tabletop so as to be vertically movable. In the magnetic resonance imaging apparatus, the tabletop is a lower tabletop slidable in the magnetic field direction of the static magnetic field with respect to the bed body, and an upper table slidable in the magnetic field direction with respect to the lower tabletop. A rest body which is formed in a double top plate structure with a top plate and places the local portion on the end of the upper top plate on the gantry side, and alignment between the diagnostic position of the local portion and the gradient magnetic field center. Positioning body for As well as location, provided a control means for controlling the vertical movement and sliding of the upper and lower top plate.

For example, the gradient coil has an x coil,
A three-channel gradient magnetic field generating coil of a y-coil and a z-coil is provided, and at least the x-coil and the y-coil are formed by multiple winding of a flat wire, and the magnetic field direction of the static magnetic field of at least the x-coil and the y-coil. The both ends of the flat wire are arranged such that the longitudinal direction of the cross section of the flat plate conductor is orthogonal to the magnetic field direction.

[0012]

According to one aspect of the present invention, a small-sized gradient magnetic field coil for inserting only a local portion of a subject is provided with three-channel gradient magnetic field generating coils of an x coil, ay coil and az coil. At least the x-coil and the y-coil are formed by multiple winding of a flat conductor wire, and at least both ends of the x-coil and the y-coil in the magnetic field direction of the static magnetic field have the longitudinal direction of the cross section of the flat conductor wire orthogonal to the magnetic field direction. It is arranged in the direction.

According to another aspect, the top plate is a lower top plate slidable in the magnetic field direction of the static magnetic field with respect to the main body of the bed, and an upper side slidable in the magnetic field direction with respect to the lower top plate. It is formed with a double top plate structure with the top plate. A rest body for mounting a local site such as a head on the gantry side end of the upper table and a positioning body for aligning the diagnostic position of the local site with the center of the gradient magnetic field are installed. Control means for controlling the vertical movement and sliding of the upper and lower top plates are further provided. At this time, the gradient magnetic field coil is provided with three-channel gradient magnetic field generating coils of an x coil, ay coil and az coil, and at least the x coil and the y coil are formed by multiply winding a flat conductor wire, and at least the x coil. And both ends in the magnetic field direction of the static magnetic field of the y coil are
The flat conductor wire is arranged such that the longitudinal direction of the cross section thereof is orthogonal to the magnetic field direction.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic resonance imaging apparatus according to an embodiment of the present invention will be described below with reference to FIGS.

A schematic configuration of a magnetic resonance imaging apparatus according to this embodiment is shown in FIG. This magnetic resonance imaging apparatus includes a gantry G and a bed B, a magnet part for generating a static magnetic field, a whole body gradient magnetic field part for adding a linear gradient magnetic field to the static magnetic field, and a selective excitation and MR signal reception. R for
An F signal transmission / reception unit, a head coil unit that adds a linear gradient magnetic field to the static magnetic field, and a control / calculation unit responsible for system control and image reconstruction.

The magnet section includes a superconducting magnet 1 provided in the gantry G and a static magnetic field power supply 2 for supplying a current to the magnet 1, and a cylindrical diagnostic space into which the subject P is inserted. A main static magnetic field H0 is generated in the Z-axis direction.

The whole body gradient magnetic field unit supplies three sets of whole body gradient magnetic field coils 3 in the X, Y, and Z-axis directions installed in the diagnostic space of the magnet 1, and a current to the gradient magnetic field coils 3. Gradient magnetic field power supply 4 and sequencer 5 for controlling this power supply 4
And a gradient magnetic field sequencer 5a therein. The sequencer 5a includes a computer, and receives a signal instructing a collection sequence related to the FE method, the high-speed SE method, or the like from a controller 6 (on which a computer is mounted) of the entire apparatus. As a result, the gradient magnetic field sequencer 5a controls the application and strength of each gradient magnetic field in the X, Y and Z axis directions according to the commanded sequence, and these gradient magnetic fields can be superimposed on the static magnetic field H0.

The RF signal transmitting / receiving section is a high-frequency coil 7 for the whole body, which is arranged in the photographing space inside the magnet 1, and this coil 7.
A transmitter 8T and a receiver 8R connected to each other, and an RF sequencer 5b (with a computer) that controls operation timings of the transmitter 8T and the receiver 8R. Under the control of the RF sequencer 5b, the transmitter 8T and the receiver 8R supply an RF current pulse having a Larmor frequency for exciting nuclear magnetic resonance (NMR) to the high frequency coil 7, while the high frequency coil 7 receives the RF current pulse. The received MR signal (high frequency signal) is subjected to various kinds of signal processing to form a corresponding digital signal.

The head coil portion is arranged in the bore (diagnosis space) and is provided with a head gradient magnetic field coil 11 and a QD head coil 12 as an RF coil which are coaxially provided. There is.

The entire head gradient magnetic field coil 11 is formed in a cylindrical shape as shown in FIGS. 2 and 3, and includes three sets of x, y, z coils 11x ... 11x, 11y ... 11y, 1
Bobbin B with 1z and 11z insulated from each other (see FIG. 5)
Is wrapped around. The positional relationship and winding device state of each of the x, y, and z coils 11x to 11z are shown in FIGS.

Among them, each of the x coils 11x ... 11x is formed in a saddle shape in which a flat plate conductor CP is wound a plurality of times, and is also opposed to each other in the X direction.
Two pairs of 11x are arranged in the z direction. At this time, each of the x coils 11x ... 11x is a flat plate as shown in an enlarged manner in a circular circle (a) in FIG. 5 (showing the a′-a ′ cross section and the a ″ -a ″ cross section in the figure). The longitudinal direction WD of the cross section of the conductive wire CP is orthogonal to the axial direction of the head gradient magnetic field coil 11 (that is, the Z-axis direction), and the coil 1 is always
1 is wound in multiple layers so as to face the entire radial direction R.

Each of the y coils 11y ... 11y is also formed in a saddle shape in which the flat plate conductor CP is wound a plurality of times, and two coil pairs 11y and 11y facing each other are arranged in the Z direction. This y coil 11y ...
Each of the 11t is also shown by enlarging a circular circle (b) in FIG. 5 (showing the cross section of the small circle b ′ and the b ″ -b ″ cross section in the same figure), as shown in FIG. The direction WD is orthogonal to the Z-axis direction and is wound in multiple layers so that the coil 11 is always oriented in the radial direction R.

As in the conventional case, the flat conductor CP having a thickness of about 2 to 3 mm (the length in the lateral direction of the cross section) and a width of about 5 mm (the length in the longitudinal direction of the cross section) has a current capacity. In consideration of the above, for example, the x coil 1 is wound for about 15 turns.
The 1x and y coils 11y are finished.

On the other hand, each of the z coils 11z and 11z is formed in a loop shape in which the plate conductor CP is also wound a plurality of times, and is arranged so as to face each other in the Z direction. This z
Each of the coils 11z and 11z is enlarged in an explanatory ellipse view (c) in FIG. 5 (showing a cross section of a small ellipse c ′ in FIG. 5), and the longitudinal direction WD of the cross section of the flat plate conductor CP is Z. It is wound a plurality of times in the same diameter plane so as to be parallel to the axial direction. The z coils 11z and 11z adopt the same winding method as the conventional one.

The above x coil, y coil, z coil 11x
As shown in FIGS. 2 and 3, lead wires 11 to 11z are connected to the connectors 13x, 13y, and 13z. The connectors 13x to 13z are connected to the gradient magnetic field power source 4 for each channel. The gradient magnetic field power source 4 responds to a command from the gradient magnetic field sequencer 5a to generate the gradient magnetic field coil 3 for the whole body.
Alternatively, a pulse current can be selectively supplied to the head gradient magnetic field coil 11, and a gradient magnetic field having a predetermined gradient can be created in each coil 3 or 11.

The entire head gradient magnetic field coil 11 is fixedly mounted on a bed rail 20 extending to the bed, and is inserted into the center of the cylindrical diagnostic space of the gantry G.

An RF shield body 14 such as a copper thin plate is attached to the inner peripheral surface of the head gradient magnetic field coil 11. Also, this coil 11 and the QD head coil 1
In the central part of 3, over a predetermined range in the circumferential direction,
Windows 11Aa and 12A for enhancing the habitability of the subject P are provided respectively.

At the upper part of the entrance of the diagnostic opening of the gantry G, a projector 18 for irradiating a light beam for positioning the subject P is provided as shown in FIG.

On the other hand, the bed B is provided with a top plate 21 on which the subject P is placed. This top plate 21 is, as shown in FIG.
It has a double structure of an upper top plate 21U and a lower top plate 21L made of a non-magnetic material. The upper table 21U is slidable in the Z-axis direction with respect to the lower table 21L by a slide mechanism, and the lower table 21L is also slidable in the Z-axis direction with respect to the main body of the bed B by a slide mechanism. Has become.

At the tip of the gantry G side of the upper top plate 21U,
A headrest 22 that is made of a non-magnetic material and has a size that can be inserted into the QD head coil 12 is extended. A pillow member 23 having a curved concave surface that substantially matches the roundness of the occipital region is provided on the upper surface of the tip portion of the headrest 22 so that the head HD of the subject P does not sway left and right as much as possible.

Further, from the back side of the headrest 22, as shown in FIGS. 2 and 3, a transparent F is formed so as to wrap the head HD.
An alignment semi-cylinder 24 made of RP is provided. The semi-cylinder 24 is used for alignment with the center of the gradient magnetic field, and may be cylindrical.

On the bed B, a vertical movement mechanism section (hydraulic cylinder or the like) 25 for vertically moving the top plate 21 based on a control signal.
And a slide mechanism unit (motor, which slides the upper top plate 21U and the lower top plate 21L independently based on a control signal).
Gears and the like) 26, and receive control signals from the bed controller 27, respectively.

Further, in addition to the controller 6 described above, the control / calculation unit inputs the digital data of the MR signal formed by the receiver 8R, calculates the image data, and stores the calculated image data. The storage unit 31, the display unit 32 for displaying an image, and the input unit 33 are provided. The arithmetic unit 30 specifically performs processing such as arrangement of actually measured data in a two-dimensional Fourier space, which is a memory space, and Fourier transform for image reconstruction. The controller 6 is a gradient magnetic field sequencer 5a and RF.
While controlling the sequencer 5b in synchronization with each other, the operation content and operation timing of both are controlled, and the bed controller 27
Send a drive command to.

Next, the function and effect of this embodiment will be described.

Now, assume that the head HD of the subject P is imaged using the head gradient magnetic field coil 11. First, the subject P
Is placed on the top plate 21 so that the imaged part of the head HD (for example, a virus ring) matches the reference position of the alignment semi-cylinder 24 (for example, the axial center position of the pre-marked semi-cylinder 24). . At this time, the position of the top plate 21 in the Z-axis direction is a predetermined initial position in which the alignment semi-cylinder 24 does not collide with the gantry G when the height of the top plate 21 is raised.

From this state, the couch controller 27 raises the tabletop 21 by a desired height so that the center position of the imaging region coincides with the center of the gradient magnetic field, and then the slide mechanism is moved. Using the part 26, the lower top plate 2
Gantry G is 1L (that is, upper plate 21U)
Slide horizontally towards the opening. This slide is manually instructed using, for example, the input device 33, and is performed until the reference position of the alignment semi-cylinder 24 matches the light beam position of the projector 18.

Z in the gantry G between the position of the light beam from the projector 18 and the gradient magnetic field center of the head gradient magnetic field coil.
Since the axial distance L (see FIG. 1) is known, when the inspector issues a final stage slide command from the input device 33 after alignment at the light beam position as described above, the slide mechanism unit 26 Then, only the upper top plate 21U of the top plate 21 is automatically inserted together with the subject P into the diagnostic opening. Since this insertion distance is set to the above known value L,
When the slide is stopped, the center of the desired imaged part of the head HD is exactly aligned with the center of the gradient magnetic field, and the imaged part is accurately entered in the FOV (Field Of View). The final slide for the known distance L can also be manually controlled.

After such positioning, a scan command is sent from the controller 6 to the sequencer 5, and the scan of the desired sequence is executed on the head HD.

In the head gradient magnetic field 11 of this embodiment, as described above, the x-coil and the y-coil are wound so that the longitudinal direction of the cross section thereof is orthogonal to the Z-axis, and therefore, the Z-axis direction. The size of the entire coil can be remarkably suppressed as compared with the conventional one. At the same time, the z-coils are wound side by side so that the longitudinal direction of the cross section is parallel to the Z-axis, as in the conventional case. Therefore, the radial distance orthogonal to the Z-axis is also within a limit value. Can be suppressed to As a result, the head gradient magnetic field coil 11 has a moderate size in both the Z-axis direction and the radial direction, and can secure a gradient magnetic field of three channels of x, y, and z, thereby shortening the echo time of MR angiography. Can be carried out suitably.

Further, at the time of alignment, the head HD is placed on the headrest 23, and the head HD does not collide with the QD head coil 12 or the like, which protects the head,
It can give the patient a sense of security. When the patient is slid into the diagnostic opening, the doubled lower top plate 12L slides to guide the head HD to the entrance of the opening, and the subsequent slide then turns to the upper top plate 21U.
Therefore, the lower top plate 21L does not touch the gantry G and misalign the positioning. Since the inspector only has to align the light beam from the projector 18 with the reference position on the alignment semi-cylinder 24, the QD head coil 12
Even if is fixed in advance in the head gradient magnetic field coil 11, the center position of the imaging region can be easily and accurately adjusted to the center position of the FOV by reducing the labor of the operation.

During the slide adjustment of the two-stage stance, the length of the head gradient magnetic field coil 11 in the Z-axis direction is suppressed as described above, so that the shoulder of the patient P does not touch the end of this coil. , The imaging region can be easily adjusted to the center of the gradient magnetic field. As a result, it is possible to obtain a high-quality MR scan image without causing the geometry inside the gantry G to be disturbed due to the shoulder hitting.

In the above embodiment, the small-sized gradient magnetic field coil for the head has been described, but naturally it may be a gradient magnetic field coil for other local parts such as knees and arms.

Further, in both the x-coil and the y-coil of the head gradient magnetic field coil in the above-described embodiment, the longitudinal direction of the cross section of the flat conductive plate is orthogonal to the Z-axis direction over the entire circumference of the saddle shape. I decided to arrange it like this, but at the middle position 90
It is possible to limit the orthogonal portion to only the return line portions at both ends in the Z-axis direction of the entire gradient magnetic field coil by arranging by twisting.

The x-coil and y-coil of the head gradient magnetic field coil in the above embodiment may have a winding pattern other than the saddle shape.

[0045]

As described above, according to the present invention,
It is possible to provide a magnetic resonance imaging apparatus including a small-sized gradient magnetic field coil for a head, which can form a three-channel gradient magnetic field while suppressing an increase in size in the axial direction and the radial direction. Further, the present invention can provide a magnetic resonance imaging apparatus having such a head gradient magnetic field coil and capable of easily performing alignment with the coil.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a head gradient magnetic field coil of the same embodiment (a diagram showing a cross section taken along line II-II in FIG. 3).

3 is a side view in the Z-axis direction as seen from the direction of the line III in FIG.

FIG. 4 is a sectional view in the Z-axis direction showing the arrangement of x, y, and z coils of the head gradient magnetic field coil.

5 is a schematic cross-sectional view showing a coil arrangement along line VV in FIG.

[Explanation of symbols]

 1 superconducting magnet 2 static magnetic field power supply 6 controller 11 head gradient magnetic field coil 11x x coil 11y y coil 11z z coil 12 QD head coil 18 projector 21 top plate 21U upper top plate 21L lower top plate 22 headrest 24 semi-cylindrical cylinder for alignment 25, 26 Drive mechanism section 27 Bed controller B Bed G Gantry P Subject (patient)

Claims (6)

[Claims] 1. A magnetic resonance imaging apparatus provided with a small gradient magnetic field coil placed in a static magnetic field generated by a magnet and inserting only a local region of a subject, wherein the coils are x-coil, y-coil and z-coil. A coil for generating a gradient magnetic field of three channels is provided, and at least the x coil and the y coil are formed by multiple winding of a flat wire, and at least both ends of the x coil and the y coil in the magnetic field direction of the static magnetic field are formed. A magnetic resonance imaging apparatus arranged such that a longitudinal direction of a cross section of the flat plate conductor is orthogonal to the magnetic field direction. 2. The magnetic resonance imaging apparatus according to claim 1, wherein each of the x-coil and the y-coil is two sets of coils facing each other, and the both ends are return lines of the coil. 3. A magnet for generating a static magnetic field, a substantially cylindrical and small gradient magnetic field coil that is placed in the static magnetic field and inserts only a local portion of a subject, and a cylindrical space of the gradient magnetic field coil. In a magnetic resonance imaging apparatus including a gantry having a high-frequency coil placed on, a table on which the subject is placed, and a bed having a bed body that supports the table in a vertically movable manner, the table is A double top plate structure having a lower top plate slidable in the magnetic field direction of the static magnetic field with respect to the bed body and an upper top plate slidable in the magnetic field direction with respect to the lower top plate Then, a rest body for mounting the local portion on the gantry side end of the upper top plate and a positioning body for positioning the diagnostic position of the local portion and the gradient magnetic field center are installed, and the upper side And lower top plate Magnetic resonance imaging apparatus provided with control means for controlling the vertical movement and the slide. 4. The gradient magnetic field coil is provided with a three-channel gradient magnetic field generating coil of an x coil, ay coil and az coil, and at least the x coil and the y coil are formed by multiple winding of a flat wire, and At least x
4. The magnetic resonance imaging apparatus according to claim 3, wherein both ends of the coil and the y coil in the magnetic field direction of the static magnetic field are arranged such that a longitudinal direction of a cross section of the flat plate conductor is orthogonal to the magnetic field direction. 5. The positioning body is formed of a transparent curved or cylindrical member that encloses the rest body and is fixed to the rest body and has a diameter that can be inserted into a diagnostic space formed by the high-frequency coil. The magnetic resonance imaging apparatus according to claim 3 or 4. 6. The light emitting device for projecting a light beam to the top plate, which is installed in the gantry and accesses the gantry, and the control means controls the irradiation position information of the light beam on the positioning body. The magnetic resonance imaging apparatus according to claim 5, further comprising: an upper top control means for sliding the upper top into the gantry by using distance data required for the alignment determined based on the above.