JPH09131332A - Rf coil for magnetic resonance imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce complicatedness in setting for installing a signal receiving coil on a sample to obtain a target image. SOLUTION: A coil 41 is composed of plural conductors 41a-41d, 51a, 51b to be separable and changeable, and different coils are composed by combination of the connected conductors, so either coil is used to obtain a target image. For example, a surface coil is composed of the conductors 41a-41d, and an image around the surface of a sample is taken by this surface coil at a high sensitivity. Next, a connection part 42 and a cross part 43 of the coil are removed, the conductors 51a and 51b are connected to the conductors 41b and 41c to compose a solenoid coil, and an image of a cross sectional surface surrounded by this solenoid is taken at a high sensitivity. Sensitivity distribution of the signal receiving can thus be changed without changing setting of the sample. By thus composing the different coils integrally preliminarily, either coil can be set to function by changing a switch.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an RF coil for a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus).

[0002]

2. Description of the Related Art An MRI apparatus irradiates an atomic nucleus constituting a living tissue with a high frequency to cause magnetic resonance, and a magnetic resonance signal (hereinafter referred to as an NMR signal) generated by the magnetic resonance is received by a receiving coil. The image is reconstructed by performing an operation such as Fourier transform on the NMR signal, and is widely used to obtain a tomographic image or spectroscopy at an arbitrary portion of the subject.

In such an MRI apparatus, in order to receive an NMR signal generated from a human body with high sensitivity, it is necessary to attach a receiving coil to an arbitrary imaging site of a subject. For this reason, receiving coils of various shapes (reception systems) and sizes are used. For example, there are solenoid coils and saddle type coils for the whole body or head, and surface coils (surface coils) and phased array coils for local use. Further, the present inventor has proposed a dedicated coil for photographing a specific part such as a breast (Japanese Patent Laid-Open No. 02-302246).

[0004]

These receiving coils are
The surface coil has a unique sensitivity distribution, and for example, the surface coil is suitable for capturing a limited area near the body surface with high sensitivity. However, since the region with sensitivity is limited to the vicinity of a certain part, if the region of interest deviates from the center of sensitivity,
The subject must be set again. Further, when it is desired to take a deeper image next to the image near the body surface, a solenoid type coil capable of taking a deeper image must be replaced, and in this case as well, the subject must be set again.

As described above, in the conventional receiving coil, when one coil is set, the area of the sensitivity distribution of the coil is photographed, and it is impossible to change the coil sensitivity distribution according to the region of interest. .

Therefore, it is an object of the present invention to provide a coil for an MRI apparatus which can change the sensitivity distribution of the receiving coil without resetting the subject and can easily obtain a desired image.

[0007]

In order to achieve the above object, in the present invention, an RF coil for an MRI apparatus is composed of conductors forming two or more different coils, and one part of the conductor is used for the other part. Either the detachable coil or two or more different coils are switched to connect to the device. That is, the first aspect of the RF coil for an MRI apparatus of the present invention is an RF coil including a coil section and a connecting section for connecting the coil section to a tuning circuit of a magnetic resonance imaging apparatus, and the RF coil is detachable. The above conductors are formed, and different conductor combinations are connected to the tuning circuit when the two or more conductors are attached and detached. A second aspect of the RF coil for an MRI apparatus of the present invention includes at least two different types of coils as a coil unit, and the connecting unit includes means for switching each coil to connect to the tuning circuit. .

The RF coil for the MRI apparatus has a different sensitivity distribution by setting the subject, taking an image with one coil, attaching a conductor forming another coil to this coil, and connecting the coil to the MRI apparatus. You can continue shooting with another coil. When the coil section includes two or more different types of coils, the subject is set, and then the coil is switched at the connection portion to capture an image with a desired coil, for example, the vicinity of the body surface of the subject is imaged. After that, the image of the cross section can be continuously photographed at the same time, and the sensitivity distribution of the coil can be substantially changed and photographed. The RF coil of the present invention can be applied not only as a receiving coil but also as an irradiation coil for applying a high frequency magnetic field of the subject.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing an embodiment of an MRI apparatus to which the present invention is applied. This MRI apparatus includes a static magnetic field generating magnetic circuit 2, a gradient magnetic field generating system 3, and a transmitting system 4.
1, a reception system 5, a signal processing system 6, a sequencer 7, and a central processing unit (CPU) 8.

The static magnetic field generating magnetic circuit 2 is for generating a uniform static magnetic field around the subject 1 in an arbitrary direction. Inside the static magnetic field generating magnetic circuit 2, a gradient magnetic field coil 9 for generating a gradient magnetic field, an RF coil of the receiving system 5 (hereinafter referred to as a receiving coil) 15, an RF coil of a transmitting system 4 (hereinafter referred to as an irradiation coil). 14 is set.

The gradient magnetic field generating system 3 includes a gradient magnetic field coil 9 having a structure capable of independently applying a gradient magnetic field in mutually orthogonal Cartesian coordinate axis directions, that is, in the X axis direction, the Y axis direction, and the Z axis direction, and a gradient magnetic field. It is composed of a gradient magnetic field power supply 10 for supplying a current to the coil 9 and a sequencer 7 for controlling the gradient magnetic field power supply 10.

The transmission system 4 comprises a high-frequency oscillator 11, a modulator 12, a high-frequency amplifier 13 and an irradiation coil 14, and a high-frequency pulse from the high-frequency generator 11 is passed through the high-frequency amplifier 13 according to a command from the sequencer 7. Amplified and supplied to the irradiation coil 14, the subject 1 is irradiated with a predetermined pulsed electromagnetic wave.

The receiving system 5 comprises a receiving coil 15, an operational amplifier 16, a quadrature detector 17, and an A / D converter 18. When the receiving coil 15 detects the NMR signal from the subject 1, the signal is converted into a digital amount by the A / D converter 18 via the operational amplifier 16 and the quadrature phase detector 17, and the timing of the command from the sequencer 7 is given. 2 sampled by the quadrature detector 17 at
The data is converted into various series data and sent to the CPU 8.
Although the receiving coil 15 is shown at a position away from the subject in the figure, it is actually placed near the subject.

The signal processing system 6 has an external storage device 20 such as a magnetic disk 20a and a magnetic tape 20b, a display 21 including a CRT and a keyboard 22.

The sequencer 7 operates based on a control command from the CPU 8 and sends various commands necessary for collecting data of a tomographic image of the subject 1 to the transmission system 4 and the gradient magnetic field generation system 3 of the static magnetic field generation magnetic circuit 2. It is sent to the receiving system 5.

The CPU 8 controls each of the sequencer 7, the transmission system 4, the reception system 5, and the signal processing system 6 according to a predetermined program.

When the data from the receiving system 5 is input to the CPU 8, the CPU 8 executes signal processing, image reconstruction processing, etc., and displays the resulting desired sectional image of the subject 1 on the display 21. The data is stored in, for example, the magnetic disk 20a of the external storage device 20.

Next, the above M as a first aspect of the present invention.
A specific configuration example of the receiving coil 14 used in the RI apparatus will be described with reference to FIG. The receiving coil shown in FIG. 1 is a coil that functions as either a planar coil or a solenoid coil. FIG. 1A shows a state in which the surface coil 41 is formed, and a conductor 41 forming the surface coil 41 is shown.
a, 41b, 41c and 41d, the conductors 41a and 41b form one loop, and the conductors 41c and 41d form a loop having a winding direction opposite to that of the one loop.
These conductors 41a to 41d are fixed to the surface of an insulating member, such as an FRP, which has a shape adapted to the applicable part. The cross section 42 in which two loops formed by two sets of conductors cross each other and the connection section 43 for connecting the receiving coil to a tuning circuit (not shown) are formed from a conductor pattern formed on an insulating substrate such as FRP. The conductors 41a to 41d are configured to be detachable from the fixed insulating member. Then, a surface coil is configured in the state of FIG. 4A in which the cross portion 42 and the connecting portion 43 are connected to the conductors 41a to 41d,
An NMR signal (a high-frequency magnetic field pulse in a direction substantially parallel to the surface coil) is received from a subject region near the surface coil, and is sent to an operational amplifier 16 and a quadrature phase detector 17 of the MRI apparatus via a tuning circuit. The tuning circuit is a circuit for tuning the resonance frequency of the receiving coil with the NMR frequency.

On the other hand, FIG. 2B shows a state in which a solenoid coil is constructed. The cross portion 42 and the connecting portion 43 in FIG.
A and 51b are attached. Conductors 51a, 51b
Is also fixed to an insulating member such as FRP like the conductors 41a to 41d, and the shape of both ends of such a substantially U-shaped insulating member is the same as the cross portion 42 and the connecting portion 43.
The cloth portion 42 and the connecting portion 43 can be fitted to the removed portion. In the fitted state (b), the conductors 51a and 51b are connected to the conductors 41b and 41c, respectively, and the conductors 41b and 51a and the conductors 41c and 51b are connected.
Each form a loop in the same direction, and the conductor 51a
One end of each of 51 and 51b serves as a connection part to the tuning circuit. This solenoid coil also receives an NMR signal, which is a high-frequency magnetic field pulse in the same direction as the surface coil, and sends it to the MRI apparatus via the tuning circuit. Conductor 4 that was part of the surface coil
Since 1a and 41d are not electrically connected to any conductor, they do not interfere with the solenoid coil.

In the figure, the conductors 51a and 51b forming the solenoid coil are conductors 41a forming the surface coil.
Among 41 to 41d, the example in which the conductors 41b and 41c on the inner side are connected has been described. However, the conductors 41a and 41d on the outer side or any two conductors may be connected depending on the region of interest to be imaged. May be. Further, the example in which the solenoid coil is composed of two loops has been described, but the solenoid coil may be composed of a single loop by changing the conductor to be connected and the connecting portion, or may be composed of three or more loops.

Further, in FIG. 1, a coil having a rectangular conductor shape is shown, but the shape of the conductor can be arbitrarily changed according to the shape of the portion to which it is applied. For example, FIGS. 2 (a) and 2 (b)
Shows a modified example of the receiving coil similar to that of FIG. 1, in which a surface coil for the breast and a solenoid coil for the body are combined. In the surface coil for the breast, the two conductors 41'b and 41'c in the center have an uneven shape conforming to the shape of the breast, and the outer conductors 41a and 41d form loops having different winding directions. ing. In this embodiment, the cross section 44 where the two loops cross is a connection section with the tuning circuit. The connection section 44 and the conductor 4 are connected to each other.
1'b, 41'c of the connecting portion 44 side and the opposite end portion 45,
It is configured to be removable. The connecting portion 44 and the opposite end portion 45 are separated from each other, and conductors 51a and 51b forming a solenoid coil can be connected to this portion. As a result, a body-building solenoid coil as shown in FIG. 2B is constructed. Even in the coil shown in FIG. 2, the fixing of the conductor to the FRP or the like and the configuration of the connecting portion or the like are similar to those in FIG.
It is similar to the coil.

In the receiving coil constructed as described above,
First, in the state of the surface coil as shown in FIG. 1A or FIG. 2A, setting is performed so that the region of interest of the subject is near the surface coil, and imaging is performed. For example, FIG.
In the case of the breast receiving coil shown in (a), the receiving coil is laid prone so that the breast of the subject can be accommodated in the recess of the receiving coil.
The bed is moved to the measurement space in the static magnetic field generating magnetic circuit 2 of the MRI apparatus. Next, the sequencer 7 of FIG. 2 drives the gradient magnetic field generation system 3 and the transmission system 4 in a predetermined pulse sequence to excite the nuclear spins that compose the tissue of the subject, and the NMR with position information generated from the tissue is given. The signal is received by the receiving coil 14. The signal processing system 6 uses the received NMR signal to perform calculations such as Fourier transform, and reconstructs a cross-sectional image of the subject. This cross-sectional image shows the receiving coil 1
4 is an image reflecting the sensitivity distribution of the surface coil which is 4,
When it is necessary to obtain an image with a different sensitivity distribution based on this image, the bed is moved outward from the measurement space, and then the surface coil connecting portion 44 and the end portion 45 of FIG.
The other conductors 51a and 51b so as to cover the subject.
Connect. This sets the solenoid coil for the body, but at this time it is not necessary to move the subject. Then, similarly to the case of imaging on the surface coil, imaging is performed by the MRI apparatus to obtain a tomographic image by solenoid coils having different sensitivities. In this way, it is possible to perform imaging with coils having different sensitivity distributions at once without resetting the subject. Further, since the coil conductor is divided in the receiving coil of the present embodiment, it is extremely easy to mount on the subject.

In the above embodiment, the case where two different types of coils are formed by exchanging a part of the coil conductor, that is, the surface coil and the solenoid coil, has been described. ) In the surface coil, the outer conductors 41a and 41d are disconnected from the inner conductors 41b and 41c, and another conductor different in size and shape from the outer conductors 41a and 41d is used as the inner conductors 41b and 41c. It is also possible to exchange the conductors so as to form coils having the same method but different sensitivity distributions, such as connecting to.

Next, as a second aspect of the present invention, a concrete configuration example of a receiving coil in which two different coils are integrally provided and can be switched by a switch (means for connecting to a tuning circuit) is shown in FIG. Will be described with reference to.

The receiving coil shown in FIG. 4A is composed of four conductors 61a to 61d forming a plane and conductors 71a and 71b perpendicular to the plane. An equivalent circuit of this receiving coil is shown in FIG. 4B, and an equivalent circuit of this receiving coil is shown in FIG. 4B at one end of the conductor 61b. Switches Sw1 and Sw2 for connecting the conductor 61b to one of the conductor 61a and one end of the conductor 71a are provided at one end of the conductor 61b, and the other end of the conductor 61b is connected to a tuning circuit. Switches Sw3 and Sw4 for connecting one to the other end of the conductor 61a and the conductor 71b are provided for connecting either one to the other of the connecting portions with the tuning circuit. Switch Sw1 is O
When N, Sw3 is ON and Sw2 and Sw4 are OFF.
When Sw2 is ON, Sw4 is ON and Sw
1, Sw3 is turned off.

Similarly, the conductor 61c is attached to one end of the conductor 61c.
Are connected to either one of the conductor 61d and one end of the conductor 71b, and the other end of the conductor 61c is connected to one of the connecting portions with the tuning circuit. Switches Sw7 and Sw8 are provided at the other end of 71b for connecting one of them to the other of the connecting portions with the tuning circuit. When Sw5 is ON, Sw7 is ON, Sw6,
If Sw8 is OFF and Sw6 is ON, Sw8
Is ON, and Sw5 and Sw7 are OFF. The switch may be a mechanical switch or a switching element such as a diode, and these can be switched manually or automatically by a command from the keyboard 22. Further, the conductor and the switch can be integrally formed on an insulating member such as FRP.

The receiving coil configured as described above is set so that the region of interest of the subject is in the vicinity of the receiving coil, and then imaged by MRI. At this time, by turning on the switches Sw1, Sw3, Sw5, and Sw7, a surface coil connected in the order of conductors 61a → 61b → 61c → 61d is formed, and an image having high sensitivity near the coil surface is formed by this surface coil. Can be obtained. Further, by turning on the switches Sw2, Sw4, Sw6, and Sw8, a solenoid coil formed of the conductors 61b and 71a and a solenoid coil formed of the conductors 61c and 71b are formed, and the solenoids of these coils can be set without performing setting of the receiving coil again. An image having high sensitivity can be obtained in the cross section surrounded by the solenoid coil. As described above, in the receiving coil of the present embodiment, it is possible to easily obtain an image by two different types of coils by simply switching the switch without moving the bed or moving the subject.

In the receiving coil shown in FIG. 4, the conductor shape can be appropriately changed such as a circle or a shape having unevenness, and the number of conductors forming the solenoid coil is limited to two. is not. Furthermore, the combination of different coils is not limited to the surface coil and the solenoid, but may be a combination of coils of the same type such as two surface coils having different shapes.

In the above embodiments, the case where the RF coil of the present invention is applied to the receiving coil has been described, but the present invention can be applied to an irradiation coil.

[0031]

As described above, according to the present invention, M
By making it possible to replace part of the conductor of the RI coil, or by switching different integrated coils with a switch, it is possible to perform imaging with coils with different sensitivity distributions without re-setting the subject. Can be Particularly, when the conductor of the coil is divided, the ease of attachment to the subject can be improved. On the other hand, when the coils of two or more types are integrated, it is possible to perform imaging by the coils of different types only by switching the switch, and the operability is good.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an RF coil according to the first aspect of the present invention, in which (a) shows a usage state of a surface coil,
FIG. 6B is a diagram showing a usage state of the solenoid coil.

FIG. 2 is a diagram showing another embodiment of the RF coil according to the first aspect of the present invention, in which (a) shows a usage state of a surface coil,
FIG. 6B is a diagram showing a usage state of the solenoid coil.

FIG. 3 is a schematic configuration diagram showing an embodiment of an MRI apparatus to which the RF coil of the present invention is applied.

4A and 4B are diagrams showing an embodiment of an RF coil according to a second aspect of the present invention, in which FIG. 4A is an overall configuration diagram and FIG. 4B is an equivalent circuit diagram.

[Explanation of symbols]

 1 --- Subject 14 --- RF coil (reception coil) 42, 44 --- Connection part

Claims (2)

[Claims] 1. An RF coil comprising a coil part and a connecting part for connecting the coil part to a tuning circuit of a magnetic resonance imaging apparatus, the RF coil comprising two or more detachable conductors. R for magnetic resonance imaging apparatus, characterized in that different combinations of conductors are connected to the tuning circuit at the time of mounting and demounting, respectively.
F coil. 2. An RF coil comprising a coil portion and a connecting portion for connecting the coil portion to a tuning circuit of a magnetic resonance imaging apparatus, wherein the coil portion includes at least two different types of coils, and the connection is provided. An RF coil for a magnetic resonance imaging apparatus, characterized in that the unit is provided with means for switching each coil and connecting to the tuning circuit.