JPH0678896A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To provide gradient magnetic field power sources which independently supply currents in the magnetic resonance imaging device having a gradient magnetic field coil generating a gradient magnetic field fast in rising and high in magnetic field intensity in addition to ordinary gradient magnetic field coils. CONSTITUTION:This magnetic resonance imaging device is provided with a Gx coil 30a, Gy coil 30b and Gz coil 30c for generating the orthogonal triaxial gradient magnetic fields in ordinary photographing. The respective coils 30a, 30b, 30c are respectively connected to the Gx powder source 80a, Gy power source 80b and Gz power source 80c. The SGz coil 50 for generating the gradient magnetic field in the direction z fast in rising and high in magnetic field intensity in local photographing and a Gz power source 15 connected thereto are provided. A combined gradient magnetic field combining the gradient magnetic fields to be generated in the Gz coil 30c and the SGz coil 50 is used in the prescribed sequence for the local photographing.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic resonance imaging apparatus.

[0002]

2. Description of the Related Art FIG. 7 shows conventional magnetic resonance imaging (M
It is a block diagram showing the configuration of the RI) device. Also, FIG.
FIG. 9 is a block diagram showing a connection relationship between a gradient magnetic field coil and a gradient magnetic field power supply in the MRI apparatus shown in FIG. 7.

In FIG. 7, a conventional MRI apparatus includes a magnet assembly 1, a magnet controller 7, a gradient magnetic field power source 8, an RF transceiver 9, a sequencer 10, and a bed 1.
1, bed controller 12, computer system 1
3 and the console 14.

The magnet assembly 1 includes a magnet 2 for generating a uniform static magnetic field in an imaging region of the subject P, and a first gradient magnetic field coil for generating gradient magnetic fields in three directions (x, y, z directions). 3 and a body part RF coil 4 for generating an RF pulse (high frequency pulse) used to image a predetermined part (for example, abdomen) of the subject P. As shown in FIG. 8, the first gradient coil 3
Is an integrated Gx coil 3a, Gy coil 3b, G
It has a z-coil 3c.

For example, when photographing the head of the subject P,
The magnet assembly 1 further includes a head RF coil 6
And the SGz coil 5 (see FIG. 8) as the second gradient magnetic field coil. The SGz coil 5 generates a gradient magnetic field having a fast rising and a large magnetic field strength. Incidentally, such a coil is described in JP-A-1-20835.

The magnet controller 7 is directly connected to the computer system 13 and controls the magnet 2. The gradient magnetic field power source 8 includes a Gx power source 8a, a Gy power source 8b, and a Gy power source 8b.
It has a z power supply 8c and supplies a current to the first gradient magnetic field coil 3 and the SGz coil 5 as the second gradient magnetic field coil in order to generate various gradient magnetic fields. The gradient magnetic field power supply 8 is connected to the computer system 13 via a sequencer 10 that generates a preprogrammed signal.

The RF transceiver 9 is controlled by the sequencer 10, supplies RF pulses to the RF coils 4 and 6, and detects MR signals received by the RF coils 4 and 6.
Amplify. The MR signal detected and amplified by the RF transceiver 9 is digitally converted and output to the computer system 13. In the computer system 13, calculation processing is performed based on this digital signal, and the processing result is MR
An image or the like is displayed on the monitor (not shown) of the console 14.

The bed 11 is used for placing the subject P, is connected to the computer system 13, and is moved by the bed controller 12. As a result, the subject P is inserted into the magnet assembly 1. The above operation is performed by the operator inputting various commands and data from the console 14 to the computer system 13.

In the case of performing high-speed imaging or the like, it is necessary for the MRI apparatus to generate a gradient magnetic field Gz in the z direction which has a fast rise and a large magnetic field strength. Therefore, the imaging region of the subject P is limited to, for example, a local site such as the head, but the SGz coil 5 as the second gradient magnetic field coil having an opening diameter smaller than that of the first gradient magnetic field coil 3. Are used in MRI equipment.

The switch 30 is connected to the Gz coil 3a of the first gradient magnetic field coil 3 having an opening diameter larger than that of the second gradient magnetic field coil.
c is switched to connect to the SGz coil 5, which supplies current to the SGz coil 5 from the Gz power supply 8c. That is, the gradient magnetic field Gx in the x, y, and z directions,
Gy and Gz are generated by only one of the first gradient magnetic field coil 3 and the SGz coil 5 as the second gradient magnetic field coil.

[0011]

As described above, in the conventional MRI apparatus, the current is supplied from the Gz power supply to the SGz coil by switching the gradient magnetic field power supply. Therefore, in one sequence, for example, There is a problem that the gradient magnetic field in the same direction (z direction) cannot be generated in the first gradient magnetic field coil and the second gradient magnetic field coil at the same time or with a time difference.

The present invention has been made in view of the above circumstances, and in addition to a normal gradient magnetic field coil, it has a gradient magnetic field coil for generating a gradient magnetic field having a fast rising and a large magnetic field strength, and each coil is independent. It is an object of the present invention to provide a magnetic resonance imaging apparatus having a gradient magnetic field power supply that supplies an electric current.

[0013]

A magnetic resonance imaging apparatus according to the present invention is a magnetic resonance imaging apparatus for collecting magnetic resonance signals from a subject by applying a gradient magnetic field and a high frequency pulse to the subject placed in a static magnetic field. In the resonance imaging apparatus, a plurality of first gradient magnetic field power supplies each supplying a current, and at least one first gradient magnetic field generating at least one of three directions according to the current supplied from the first gradient magnetic field power supply. A first gradient magnetic field coil, at least one second gradient magnetic field power supply that supplies a current, and a second gradient magnetic field in at least one of the three directions according to the current supplied from the second gradient magnetic field power supply. The second gradient magnetic field coil and the second gradient magnetic field have a faster rise and larger magnetic field strength than the first gradient magnetic field, And a control means for controlling the first and second gradient magnetic field power supply.

[0014]

With the above-described structure, by simultaneously supplying currents to the first and second gradient magnetic field coils, a gradient magnetic field having a fast rising is generated in multiple steps and up to a large magnetic field strength in the same direction (z direction). It becomes easy to let. Therefore, the generation of the gradient magnetic field can be accurately controlled.

When it is necessary to generate a large magnetic field strength, the second gradient magnetic field coil is used, and when the magnetic field strength is small, it is necessary to generate the gradient magnetic field with multi-step magnetic field strength. It is possible to properly use the first gradient magnetic field coil.

In the gradient magnetic field generated by the first gradient magnetic field coil, for example, when the magnetic field strength is set to ¼ of the predetermined magnetic field strength, the rising time is also the time until it rises to the predetermined magnetic field strength. It becomes 1/4 of that. Therefore, the first
The gradient magnetic field generated by the gradient magnetic field coil can be matched with the fast rising gradient magnetic field generated by the second gradient magnetic field coil. Further, the generation of the gradient magnetic field by the multi-step magnetic field strength can be performed by controlling the current supplied to the first gradient magnetic field coil.

Further, since it is possible to generate a gradient magnetic field having a fast rising and a large magnetic field strength, it is possible to shorten the time until the acquisition of the MR signal. Further, the time taken to acquire the MR signal is shortened and the flow void is reduced, so that the resolution is improved in the MR angiography.

Furthermore, since it is unnecessary to change and connect the power cable from the gradient magnetic field power source connected to the predetermined gradient magnetic field coil to another gradient magnetic field coil, the burden on the operator is reduced. Furthermore, the noise of the gradient magnetic field power supply is reduced, and the effect of eddy current is reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a connection relationship between a gradient magnetic field coil and a gradient magnetic field power source in a magnetic resonance imaging (MRI) apparatus which is a first embodiment of the present invention. In FIG. 1, the first gradient magnetic field coil 30 has a Gx coil 30a, a Gy coil 30b, and a Gz coil 30c because it is necessary to generate a gradient magnetic field in the directions of three orthogonal axes (x, y, z axes). ing. These coils 30a,
30b and 30c are integrated. The gradient magnetic field power supply 80 has a Gx power supply 80a, a Gy power supply 80b, and a Gz power supply 80c. Each coil 30a, 30b, 30c
Is a Gx power supply 80a, a Gy power supply 80b, a Gz power supply 80c
Respectively connected to.

For local imaging of the subject's head, etc., z
In some cases, it may be necessary to accelerate the rising of the gradient magnetic field Gz in the direction and increase the magnetic field strength. Therefore, in the first embodiment, the SGz coil 50 is further provided as the second gradient magnetic field coil, and is connected to the SGz power supply 15 as a gradient magnetic field power supply different from the gradient magnetic field power supply 80.

In the first embodiment, the SGz coil 50, which is a z-direction gradient magnetic field coil, is used as the second gradient magnetic field coil. However, depending on a predetermined data acquisition sequence, not only one direction but also two directions. Alternatively, the gradient magnetic field coils in three directions may be configured as the second gradient magnetic field coil. This will be described later.

FIG. 2 shows the MR of the first embodiment of the present invention shown in FIG.
It is an example of a data collection sequence performed in the I device. In FIG. 2, the dotted line indicates the Gy coil 30b and the Gz coil 30c in the normal data acquisition sequence.
The gradient magnetic field strength (G / cm) generated in 1 is shown. The rising time is 1 ms and the maximum magnetic field strength is 1 G / cm.

Here, the rise time is 1/4, that is,
In order to change to 0.25 ms, the maximum magnetic field strength should be 0.
It should be 25 G / cm or less. But Gy
The formation of the synthetic gradient magnetic field in which the gradient magnetic fields generated by the coil 30b and the Gz coil 30c are synthesized is limited to the region 16 shown by hatching in FIG. 3 is a diagram showing the intensity distribution of the synthetic gradient magnetic field that can be generated in the MRI apparatus of the first embodiment of the present invention.

Therefore, instead of the Gz coil 30c, SG
When the z coil 50 is used, the rising time of the gradient magnetic field generated in the SGz coil 50 can be 0.25 ms and the magnetic field strength can be 1 G / cm.
Thus, the combined gradient magnetic field obtained by combining the gradient magnetic fields generated by the Gz coil 30c and the Gz coil 30c can be formed up to the region 17.

Although the angle α is limited to the angle α shown in FIG. 3 in the oblique photographing, a predetermined FOV (Field of View) can be maintained and the phase encode gradient application time can be shortened. If the gradient magnetic field in the y direction can also be generated using the second gradient magnetic field coil, imaging at a predetermined angle can be performed under the same conditions.

In the case of the first embodiment of the present invention, the SGz coil 5 is used.
The intensity of the gradient magnetic field generated by 0 is fixed at 1.0 G / cm, and the magnitude of the current supplied to the Gy coil 30b and the Gz coil 30c is adjusted to form a composite gradient magnetic field in the region 18 shown in FIG. be able to. In addition,
Similar to FIG. 3, FIG. 4 is a diagram showing the intensity distribution of the synthetic gradient magnetic field that can be generated in the MRI apparatus of the first embodiment of the present invention.

Further, the intensity of the gradient magnetic field generated by the SGz coil 50 is kept constant at 0.5 G / cm, and the Gy coil 30b is
By adjusting the magnitude of the current supplied to the Gz coil 30c and the Gz coil 30c, a composite gradient magnetic field can be formed in the region 19 shown in FIG.

As a result, the current supplied to the SGz coil 50 used as the second gradient magnetic field coil need only be switched in several stages, and the configuration of the sequencer and the gradient magnetic field power supply can be simplified. It can be realized without increasing the cost. Further, it is not necessary to change the connection of the power cable, and when the SGz coil 50 as the second gradient magnetic field coil is not used, normal imaging can be performed.

FIG. 5 shows M of the first embodiment of the present invention shown in FIG.
It is another example of the data collection sequence performed in the RI apparatus. As shown in FIG. 5, the gradient magnetic field generated by the Gz coil 30c (rise time 1 ms, maximum magnetic field strength 1
G / cm) as a lead gradient, a lead intensity of 0.5 G / cm, a data collection time of 6 ms,
When the gradient magnetic field indicated by the dotted line is generated in Gz shown in FIG. 5, the echo time TE becomes 8.5 ms.

On the other hand, in the phase compensation part, the gradient magnetic field generated by the SGz coil 50 (rise time 0.5 m
s, the magnetic field strength is 2 G / cm) and the gradient magnetic field shown by the solid line is generated in Gz shown in FIG. 5, the echo time TE becomes 6.25 ms, and only the gradient magnetic field generated by the Gz coil 30c is used. The echo time TE can be shortened as compared with the case where it occurs.

The gradient magnetic field (shown by the solid line) generated by the Gz coil 30c is used only for the data acquisition time. Since this gradient magnetic field does not require a large magnetic field strength, its rise time is set to 0.5 ms.

Further, by making the intensity of the gradient magnetic field in the phase compensation portion constant and changing the application time of the gradient magnetic field,
It is possible to simplify the configurations of the sequencer and the gradient magnetic field power supply without causing a significant increase in cost. Next, a second embodiment of the present invention will be described.

FIG. 6 shows an MRI which is a second embodiment of the present invention.
FIG. 3 is a block diagram showing a connection relationship between a gradient magnetic field coil and a gradient magnetic field power source in the apparatus. Compared to the first embodiment shown in FIG. 1, in the second embodiment shown in FIG. 6, the second gradient magnetic field coil 55 generates a gradient magnetic field having a fast rising and a large magnetic field strength in all the three orthogonal axes. , SGx coil 55a,
It has an SGy coil 55b and an SGz coil 55c.

Further, the gradient magnetic field power source 85 is provided for each coil 30.
In order to independently supply currents to a to 30c and 55a to 55c, G1 power supply 85a, G2 power supply 85b, G
3 Power supply 85c, G4 power supply 85d, G5 power supply 85e, G6
It has a power supply 85f.

The switching box 40 switches the current supplied from the gradient magnetic field power source 85 to the first and second gradient magnetic field coils 30 and 55. With this, it is possible to independently supply current from each power source of the gradient magnetic field power source 85 to a predetermined gradient magnetic field coil.

In the second embodiment, when the normal photographing is performed on a wide photographing area, the first gradient magnetic field power source G is used.
x coil 30a, Gy coil 30b, Gz coil 30c
Is used.

On the other hand, when it is necessary to generate a gradient magnetic field having a fast rising and a large magnetic field strength such as high-speed imaging, high-resolution MR angiography, or diffusion imaging, SGx coil 55a, SGy coil 55.
b, SGz coil 55c is used. In this case, the photographing area is narrowed, but the Gx coil 30a and the Gy coil 30 are
b. Compared with the imaging using the Gz coil 30c, a special power source is not required, the noise due to the gradient magnetic field generated during the imaging is reduced, and the eddy current flowing through the conductor in the magnet is also reduced. According to the present invention, various sequences can be selectively used according to the purpose. Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0039]

As described above, according to the present invention, by simultaneously supplying currents to the first and second gradient magnetic field coils, it is possible to increase the gradient magnetic field having a fast rise in the same direction (for example, z direction). It becomes easy to generate even a large magnetic field strength in stages. Therefore, the generation of the gradient magnetic field can be accurately controlled. When it is necessary to generate a gradient magnetic field having a large magnetic field strength, a second gradient magnetic field coil is used, and when a magnetic field strength is small, a gradient magnetic field having a multi-stage magnetic field strength needs to be generated. Is
It is possible to properly use the first gradient magnetic field coil.

In the gradient magnetic field generated by the first gradient magnetic field coil, for example, when the magnetic field strength is set to 1/4 of the predetermined magnetic field strength, the rising time of the gradient magnetic field is also the time required to rise to the predetermined magnetic field strength. It becomes 1/4. Therefore, the gradient magnetic field generated by the first gradient magnetic field coil can be matched with the fast rising gradient magnetic field generated by the second gradient magnetic field coil. Further, the generation of the gradient magnetic field having multi-step magnetic field strength can be performed by controlling the current supplied to the first gradient magnetic field coil.

Further, since it is possible to generate a gradient magnetic field having a fast rising and a large magnetic field strength, it is possible to shorten the time until the acquisition of MR signals. Further, the time taken to acquire the MR signal is shortened and the flow void is reduced, so that the resolution is improved in the MR angiography.

Further, since it is unnecessary to change and connect the power cable from the gradient magnetic field power source connected to the predetermined gradient magnetic field coil to another gradient magnetic field coil, the burden on the operator is reduced. Furthermore, the noise due to the gradient magnetic field generated during imaging is reduced, and the effect of eddy currents is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a connection relationship between a gradient magnetic field coil and a gradient magnetic field power source in an MRI apparatus that is a first embodiment of the present invention.

FIG. 2 is an example of a data acquisition sequence performed in the MRI apparatus of the first embodiment of the present invention shown in FIG.

FIG. 3 is a diagram showing an intensity distribution of a synthetic gradient magnetic field that can be generated in the MRI apparatus of the first embodiment of the present invention.

FIG. 4 is a diagram showing an intensity distribution of a synthetic gradient magnetic field that can be generated in the MRI apparatus of the first embodiment of the present invention.

5 is another example of the data acquisition sequence performed in the MRI apparatus of the first embodiment of the present invention shown in FIG.

FIG. 6 is a block diagram showing a connection relationship between a gradient magnetic field coil and a gradient magnetic field power source in an MRI apparatus that is a second embodiment of the present invention.

FIG. 7 is a block diagram showing the configuration of a conventional MRI apparatus.

8 is a block diagram showing a connection relationship between a gradient magnetic field coil and a gradient magnetic field power supply in the MRI apparatus shown in FIG.

[Explanation of symbols]

15 ... SGz power source, 30 ... First gradient magnetic field coil, 30a
... Gx coil, 30b ... Gy coil, 30c ... Gz coil, 40 ... Switching box, 50, 55c ... SGz coil, 55 ... Second gradient magnetic field coil, 55a ... SGx coil, 55b ... SGy coil, 80, 85 ... Gradient magnetic field Power supply, 80a ... Gx power supply, 80b ... Gy power supply, 80c ... G
z power supply, 85a ... G1 power supply, 85b ... G2 power supply, 85c
… G3 power supply, 85d… G4 power supply, 85e… G5 power supply, 8
5f ... G6 power supply, 100 ... sequencer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 8203-2G G01R 33/22 Y

Claims (3)

[Claims] 1. A magnetic resonance imaging apparatus for collecting a magnetic resonance signal from a subject by applying a gradient magnetic field and a radio frequency pulse to the subject placed in a static magnetic field. A first gradient magnetic field power supply; at least one first gradient magnetic field coil for generating a first gradient magnetic field in at least one of the three directions according to the current supplied from the first gradient magnetic field power supply; Two second gradient magnetic field power supplies, a second gradient magnetic field coil that generates a second gradient magnetic field in at least one of the three directions according to a current supplied from the second gradient magnetic field power supply, and the second gradient magnetic field The first
A magnetic resonance imaging apparatus comprising: a control unit that rises faster than a gradient magnetic field and has a large magnetic field strength, and that controls the first and second gradient magnetic field power supplies according to a predetermined sequence. 2. The second gradient magnetic field and the first gradient magnetic field in the same direction as the first gradient magnetic field and the second gradient magnetic field corresponding to the first gradient magnetic field and the second gradient magnetic field corresponding to the first gradient magnetic field in the same sequence at the same time or with a predetermined time difference.
The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is generated by a current supplied from a gradient magnetic field power supply. 3. A second of at least one of the three directions
The intensity of the gradient magnetic field is set to a predetermined value, the intensity of the first gradient magnetic field in the same direction as the direction of the second gradient magnetic field is changed, and
The magnetic resonance imaging apparatus according to claim 1, wherein the second gradient magnetic field is generated at the same time.