JP2002102207A - High frequency coil for nuclear magnetic resonance imaging device and the same device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency coil for an MRI device capable of effectively executing decoupling with a small-sized RF coil in the MRI device provided with a vacuum container for suppressing a noise accompanying the application of an inclined magnetic field and the MRI device. SOLUTION: The high frequency coil 4 for the whole body constitutes a bird cage shape constituted of two ring parts 411 and 412 facing each other and a plurality of straight line parts 421 and 422-42n with both ends connected with connection points of peripheral edge parts of the ring parts 411 and 412, as one example. Closed loops except element loops E1 and E2-En and not all but a prescribed number of element loops of the element loops E1 and E2-En are provided with switches 43. In the figure, the E1, E4, E7 and E10 are left as the prescribed number of the element loops, constituting the 'closed loops'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear magnetic resonance imaging apparatus, and more particularly to a high-frequency coil for transmitting a high-frequency signal or receiving an NMR signal.

[0002]

2. Description of the Related Art A nuclear magnetic resonance imaging apparatus (hereinafter, referred to as a nuclear magnetic resonance imaging apparatus)
“MRI (Magnetic Resonance I)
A “magnetizing device”) is a nuclear magnetic resonance signal (NMR) obtained by applying an excitation magnetic field (RF magnetic field) and a gradient magnetic field to a subject arranged in a static magnetic field space.
(Nuclear Magnetic Resonan
ce) signal) to reconstruct a nuclear magnetic resonance imaging image (tomographic image) relating to the subject.

[0003] Such an MRI apparatus has an air core (imaging space) H in a gantry G as shown in FIG. The air core H has a main magnet 3 for forming a strong static magnetic field, a high-frequency coil 4 for whole body for applying an RF magnetic field, and a gradient magnetic field coil (gradient magnetic field applying means) 5 having a central axis L as a coaxial axis. Are arranged. Subject P
Is placed on a top plate (not shown) and is introduced into the air core H. In addition, a small RF coil may be provided on the top plate separately from the whole-body high-frequency coil 4 for observing other small parts such as the elbow and knee of the subject P, for example. This small RF coil can be configured, for example, for reception only, or can be configured to perform both transmission and reception.

In the MRI apparatus having such a configuration, it is necessary to perform a process of "de-coupling" the small RF coil and the whole-body high-frequency coil 4. This “decoupling” is performed by, for example, so-called “de-tuning”, that is, a technique achieved by shifting (detuning) the resonance frequency between the small RF coil and the whole-body high-frequency coil 4. More specifically, as a technique for performing such detuning, a whole-body high-frequency coil 4 is used.
Is often short-circuited to an RF shield 4a attached to the outside thereof. In any case, such measures are required to avoid the occurrence of other problems such as deterioration of detection sensitivity due to electromagnetic coupling or coupling between the whole-body high-frequency coil 4 and the small RF coil. That's why.

On the other hand, in the MRI apparatus having the above configuration, the noise generated by the gradient coil 5 may be regarded as a problem. The noise is a pulse sound generated when the gradient coil 5 is normally driven based on a pulse sequence. This generally reaches 90 dB or more, and gives unnecessary pain or fatigue to the subject during the MRI examination.

Therefore, conventionally, as shown in FIG. 14, the gradient magnetic field coil 5 is connected to the outer wall V of the vacuum vessel.
There has been proposed a means for shutting off the noise by adopting a configuration in which the noise is enclosed in a region surrounded by the inner wall Va. According to such a configuration, the RF shield 4a is installed in the vacuum vessel together with the gradient coil 5. The reason for this arrangement is that it is preferable that the whole-body high-frequency coil 4 and the RF shield 4a be installed as far apart as possible.

[0007]

However, in the case where the above configuration is adopted, there are the following problems. That is, the whole-body high-frequency coil 4 is disposed outside the vacuum vessel, while the RF shield 4a is disposed inside the vacuum vessel. Therefore, the whole-body high-frequency coil 4 and the RF shield 4a are provided for the purpose of detuning. Is required to provide many conducting wires penetrating the inner wall Va of the vacuum vessel.

However, in this case, firstly, it may be difficult to maintain a predetermined degree of vacuum in the vacuum container.
Secondly, the installation work of the MRI apparatus becomes complicated and troublesome, and the maintenance work after the installation becomes difficult.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an MRI apparatus equipped with a vacuum container for suppressing noise accompanying the application of a gradient magnetic field as described above. To provide a high-frequency coil for an MRI apparatus and an MRI apparatus capable of effectively performing the above.

[0010]

The present invention employs the following means in order to solve the above problems. That is, the high frequency coil for a nuclear magnetic resonance imaging apparatus according to claim 1 includes a plurality of conductor members assembled so as to cover a substantially cylindrical space and to form a plurality of closed loops through which a current can return. For all of the closed loops, a switch capable of interrupting a current flowing through them is provided.

A high-frequency coil for a nuclear magnetic resonance imaging apparatus according to claim 2 includes a plurality of conductor members assembled so as to cover a substantially cylindrical space and to form a plurality of closed loops through which current can flow. Regarding the “closed loop excluding the shortest circumference closed loop having the smallest circumference” among the plurality of closed loops, a switch capable of interrupting at least current flowing through the closed loop is provided.

Further, in the high-frequency coil for a nuclear magnetic resonance imaging apparatus according to the third aspect, in the high-frequency coil according to the second aspect, the plurality of conductor members include two ring portions, each facing each other, and these ring portions. At the connection point at the peripheral edge of each part, a birdcage shape composed of a plurality of linear parts whose both ends are connected is configured, and the shortest circumference closed loop is two linear parts adjacent to each other among the linear parts. An element loop surrounded by four connection points with the ring portion, wherein the switch is provided for a predetermined number, but not all, of the element loops.

According to a fourth aspect of the present invention, in the high frequency coil for a nuclear magnetic resonance imaging apparatus, two or more switches are provided for at least one of the element loops. The high-frequency coil according to claim 5 is the high-frequency coil according to claim 3 or 4, wherein the switch is
Two or more element loops adjacent to each other are provided so as not to be left as a closed loop.

On the other hand, a nuclear magnetic resonance imaging apparatus according to claim 6, wherein a high-frequency coil for applying an excitation magnetic field to a subject arranged in a static magnetic field space, and a gradient magnetic field for applying a gradient magnetic field to the subject. Application means, and
Shielding means for preventing the coupling of the high-frequency coil and the gradient magnetic field applying means, and a vacuum vessel in which the high-frequency coil is provided outside thereof, and wherein the shielding means and the gradient magnetic field applying means are disposed therein. The high-frequency coil includes a plurality of conductor members arranged so as to cover a substantially cylindrical space and to form a plurality of closed loops through which a current can flow, and can interrupt a current flowing through the plurality of closed loops. The plurality of conductor members are composed of two ring portions, each facing each other, and a plurality of linear portions, both ends of which are connected to a connection point at a peripheral portion of each of these ring portions. An element configured to have a birdcage shape, wherein the switch is surrounded by four connection points of two adjacent linear portions and the ring portion of the linear portions. It is characterized in that provided for the closed-loop and elements loop a predetermined number, but not all of the elements loop excluding the loop.

According to a seventh aspect of the present invention, there is provided a nuclear magnetic resonance imaging apparatus, comprising: a high-frequency coil for applying an excitation magnetic field to a subject disposed in a static magnetic field space; and a gradient magnetic field for applying a gradient magnetic field to the subject. A nuclear magnetic resonance imaging apparatus provided with an application unit, wherein the gradient magnetic field application unit, the high-frequency coil, and a shielding unit provided between the high-frequency coil and the gradient magnetic field application unit are disposed inside the vacuum container. It is characterized by having.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. In the drawings referred to in the following description, the same reference numerals should be used when indicating the same target as the target indicated by the reference numerals used in FIG. And

FIG. 1 is a schematic diagram showing a configuration example of an MRI apparatus according to the present embodiment. In FIG. 1, the MRI apparatus includes a bed 1, a gantry G, a control unit 6, and the like. The bed 1 is provided with the top plate 1a on which the subject P is placed as described above. The top plate 1a is movable along the body axis direction of the placed subject P, and the movement causes the subject P to move to the air core portion (imaging space portion) H of the gantry G. It can be inserted. Also,
Around the air core H, the main magnet 3, the whole body high frequency coil 4, and the gradient magnetic field coil (gradient magnetic field applying means) 5 are provided concentrically with the axis L of the air core H being coaxial. I have.

The main magnet 3 forms a strong static magnetic field in the air core H. In the present embodiment, a permanent magnet,
Any of an electromagnet, a superconducting magnet, and the like can be applied.

The whole-body high-frequency coil 4 is a coil for applying an RF magnetic field (excitation magnetic field) for causing nuclear magnetic resonance absorption in the subject P in the static magnetic field. This whole-body high-frequency coil 4 is connected to a transmitter 4T via a duplexer 4D, and is driven discretely with respect to time, that is, based on a pulse signal. A receiver 21 is connected to the whole-body high-frequency coil 4 via the duplexer 4D, and receives an NMR signal regarding the subject P obtained by applying an RF magnetic field.

As shown in FIG. 2, the whole-body high-frequency coil 4 of the present embodiment includes two opposed ring portions 411 and 412, and these ring portions 411 and 41.
2 connection points 411p ₁ , 411p ₂ ,
.., 411 _pn and 412 p ₁ , 412 p ₂ ,.
_pn , a plurality of linear portions 42 ₁ , 42 connected to both ends thereof
_2, ..., 42 covers a substantially cylindrical space by the _n, are configured in a shape similar to it were "birdcage". Note that the ring portions 411 and 412 and the plurality of linear portions 42 ₁ , 42 ₂ ,.
2 _n is formed by a conductive wire such as copper,
It is still the “conductor member” of the whole-body high-frequency coil 4. In addition, the above-described configuration is widely known as being generally referred to as a “bird-cage type”.

The ring portions 411 and 412 are as described above.
As shown in FIG.
And 412F are parallel to each other. Straight section 4
2₁, 42_Two, ..., 42_nOf the ring portion 411
One connection point at the edge (for example, 411p_Two)When,
At the periphery of the ring portion 412 corresponding to the position
One connection point (for example, 412p_Two)
The surface 411F surrounded by the ring portions 411 and 412;
And 412F. did
Accordingly, these straight portions 42₁, 42_Two, ..., 42_nAre each
They are in a parallel relationship. In addition, these linear portions 42₁, 42_Two,
…, 42_nOn the periphery of the ring portions 411 and 412
Are provided at predetermined intervals. Note that this
Straight section 42 ₁, 42_Two, ..., 42_nEach and the ring part 4
Whole-body high-frequency coil 4 separated from 11 and 412
Each area of the side surface is hereinafter referred to as an element loop E1,
E2,..., En. For example, Element
Troop E1 has four connection points 411p₁, 412
p₁, 412p_TwoAnd 411p_TwoClosed loop surrounded by
Becomes

A capacitor (not shown) is inserted at an appropriate position in the whole-body high-frequency coil 4 so as to resonate with the inductance of a conductor member constituting the whole-body high-frequency coil 4. Regarding the insertion of this capacitor, it is conceivable to adopt various well-known methods,
Generally, it can be classified into a high-pass type, a low-pass type, and a band-pass type. In the present invention, any of the embodiments may be adopted.

The gradient magnetic field coil 5 is a coil for applying different magnetic fields (Gx, Gy, Gz) for each of the three orthogonal axes (x, y, z) defined in the air core H. The degree of the inclination is set by the gradient magnetic field power supply system 51. Position localization of the NMR signal received by the whole-body high-frequency coil 4 or the small-sized RF coil 2 to be described later can be performed based on the degree of the inclination described above.

Further, in the MRI apparatus of the present embodiment, in the gantry G, the gradient magnetic field coil 5 is disposed in a region surrounded by the outer wall V and the inner wall Va of the vacuum vessel as shown in FIG. (See also FIG. 14). This is a configuration for preventing noise generated by the gradient coil 5 from reaching the air core H as described in the section of the related art. The whole-body high-frequency coil 4 is disposed outside the vacuum vessel, and an RF shield (shielding) for preventing coupling between the whole-body high-frequency coil 4 and the gradient coil 5 is provided inside the vacuum vessel. Means 4a. In the following, an MRI apparatus including such a vacuum vessel will be particularly referred to as a “silent MRI apparatus”.

On the other hand, in the present embodiment, the receiver 21
, And provided on the top plate 1a.
A small RF coil 2 used for receiving MR signals is provided. It should be noted that the small RF coil 2 receives a transmission signal from the transmitter 4T via a duplexer, which is omitted in the drawing, via a switch, and uses this signal for transmission. Is also possible. Small RF matching knee area as shown in FIG.
The coil 2 can reduce the transmission energy by transmitting from the coil 2, and has an imaging advantage that the unnecessary portion of the nuclear spin is not excited. It is. In the case of a surface coil or the like, the flip angle of an RF pulse changes in accordance with the sensitivity distribution of the coil, and the NMR signal intensity is weakened. The RF coil 2 is configured to perform only reception.

Incidentally, in FIG. 1, the small RF coil 2 is configured to cover the knee of the subject P. However, in order to observe other small parts such as the elbow of the subject P, for example, The one that matches the shape of the corresponding small part may be used.

In the present embodiment, in the above-described case, the coupling of both coils 4 and 2 for the purpose of preventing the present invention is generated.

Incidentally, in the MRI apparatus according to the present embodiment, in addition to the above-mentioned various components, as shown in FIG.
The transmitter 4T, the sequencer 7 for driving the gradient magnetic field power supply system 51, etc., and the overall control of the above-mentioned various components, and the NM of the whole-body high-frequency coil 4 or the small RF coil 2
The control unit 6 includes an image generating unit (not shown) for reconstructing a tomographic image based on the R signal reception result, and a display unit D for displaying the tomographic image and the like.

Further, the operation of the MRI apparatus having the above configuration example is not directly related to the gist of the present invention and is well known, so that the detailed description thereof will be omitted. Briefly, the top plate 1
is inserted into the air core H of the gantry G to which a static magnetic field is applied by the main magnet 3 together with the top plate 1a to align the nuclear magnetic moment in the subject P with the top plate 1a. The precession of the Larmor of the magnetic moment about the direction of the static magnetic field is generated, and an RF magnetic field is applied to the whole body high-frequency coil 4 (or the small RF coil 2) to apply magnetic resonance absorption (spin excitation). This causes the NMR signal obtained at this time to be received by the whole-body high-frequency coil 4 or the small RF coil 2, and the tomographic image of the subject P is reconstructed by the image generation means in the control unit 6. In addition, by applying the gradient magnetic field of the gradient magnetic field coil 5, it becomes possible to perform position localization at the time of forming the tomographic image.

Further, noise generated by driving the gradient magnetic field coil 5 (driving based on a pulse sequence) is reduced by disposing the coil 5 in the vacuum vessel. Therefore, the subject P can receive the examination comfortably.

In the following, the structure of the whole-body high-frequency coil 4 and the operation and effect thereof, which are characteristic elements of the present invention, will be described in more detail.

FIG. 3 shows one of the ring portions 411 and 412 of the whole-body high-frequency coil 4 shown in FIG. As described with reference to FIG. 2, the whole-body high-frequency coil 4
, 412 and the straight portions 42 ₁ , 42 ₂ ,..., 42 ₁₂ , so that the developed view of FIG. 3 is “ladder-like” to “amidashi”. Therefore, the element loop E1 at the left end and the element loop E1 at the right end in the drawing are "the same". Further, FIG. 3 shows the whole-body high-frequency coil 4 having the element loop number “12” as an example. Incidentally, a birdcage-type whole-body high-frequency coil 4 as shown in FIG.
It may be referred to as an "element" whole-body high-frequency coil.

As shown in FIG. 3, the whole-body high-frequency coil 4 has ring portions 411 and 412 as conductor members.
A plurality of switches 43 are connected in series with the linear portions 42 ₁ , 42 ₂ ,..., 42 ₁₂ . This switch 43
As a specific embodiment, for example, the one shown in FIG. 4 can be adopted. In this figure, a switch 43 has a PIN
A diode 431 and an inductor 432 are provided.
A control line (not shown) is connected to the end of the inductor 432.

The switch 43 can cut off (decoupling) the electromagnetic coupling or coupling between the whole-body high-frequency coil 4 and the small-sized RF coil 2.

In the case of FIG. 3, the element loops E2, E3, E5 and E9 and the closed loop "including" these element loops E2, E3, E5 and E9 (for example, defined by the entire circumference of the element loops E9 and E10) (Closed loop), since the switch 43 is disposed, it is possible to prevent coupling from occurring in at least these loops. That is, in order to prevent the coupling between the small-sized RF coil 2 and the whole-body high-frequency coil 4, all the loops constituting the whole-body high-frequency coil 4 are connected to the switch 43 so as to be cut off. This is a preferable index in a general sense.

The purpose of the present invention is to connect or dispose the switch 43 to a conductor member constituting the whole-body high-frequency coil 4 so as not to cause the above-mentioned coupling. The point is to propose a technique for detuning the high-frequency coil 4. Hereinafter, the “preferred connection mode” will be described.

First, an example shown in FIG. 5 will be described as a premise. According to this figure, a ring portion 411 as a conductor member is shown.
Are connected to twelve switches 43 in series. At first glance, it seems that all of the element loops E1,..., E12 constituting the whole-body high-frequency coil 4 are cut off, but this corresponds to the ring portion 412 as shown by the thick line in FIG. It can be seen that a large closed loop remains. This is apparent from the perspective view shown in FIG. 2 instead of the developed view in FIG. Therefore, in such a case, it cannot be expected to effectively prevent the coupling. That is, when considering a suitable connection / arrangement mode of the switch 43, it is always necessary to always keep in mind the form of the whole-body high-frequency coil 4 as a three-dimensional body.

In the embodiment as shown in FIG. 5, as described above, a sufficient decoupling could not be performed because the closed loop related to the ring portion 412 remained. As shown, in addition to the switch 43 shown in FIG.
It can be seen that connection or insertion into the ring portion 412 as a conductor member is sufficient. In this way, it is possible to break all the closed loops constituting the whole-body high-frequency coil 4, so that complete decoupling can be performed. In the present invention, the connection arrangement of the switch 43 is also included in the range.

However, the switch 43 in FIG.
This arrangement cannot be denied to be inefficient.
That is, according to such means, although it is certain to achieve the purpose of implementing decoupling, it is necessary to prepare a large number of switches 43 inevitably. It will be extra (expensive). In addition, the configuration of the whole-body high-frequency coil 4 itself is unnecessarily complicated.

The present inventors propose a more suitable arrangement of the switch 43 under the awareness of the problem concerning the configuration shown in FIG. This “more suitable switch 43
In order to realize the “arrangement mode”, the general idea acting on the background is as follows. That is, FIGS. 2 and 3
Of the various closed loops observed in the whole-body high-frequency coil 4 shown in FIG. 2, if the circumference or the area is small, the degree of coupling with the small RF coil 2 becomes small, so that the occurrence of defects is remarkable. It is not something that is not. Here, the term "various closed loops" refers to, for example, a closed loop defined by the entire circumference of the element loops E2, E3, and E4, as indicated by a broken line in FIG. 7, or a dashed line in FIG. The presence of a closed loop or the like that includes such ring portions 411 and 412 as its path.

Based on this, and in the case shown in FIG. 7 and the like, the element loops E1, E2,.
If it is confirmed again that each of the E12s is a “closed loop having the smallest circumference”, it is presumed that some of them do not need to be cut off by the switch 43.

In FIG. 8, based on the above general idea, four element loops E1, E4, E7 indicated by thick lines are shown.
No switch 43 is provided for E10 and E10, and a "closed loop" is established and left. At this time, the high-frequency current may certainly flow in these element loops E1, E4, E7, and E10, but at least when the "closed loop corresponding to the ring portion 412" shown in FIG. By comparison, it is easily presumed that the influence on the above-mentioned inconvenience is much smaller. In addition, as a result of actually using such a whole-body high-frequency coil 4, it was confirmed that practically sufficient decoupling can be realized.

In FIG. 8, the switch 43k provided especially in the element loop E5
The role of (or the switch 43 provided another in the loop E5) is significant. That is, as shown in FIG. 9, if the state where the switch 43k is removed is temporarily realized, a large closed loop as shown by a thick line in FIG.
This is because they are left as in FIG. From this, it is understood that it is necessary to connect and arrange two switches 43 for a closed loop having the smallest circumference, that is, at least one of the element loops. By doing so, a large loop as shown in FIG. 9 will not be left.

In connection with the above, it can be generally said that it is not preferable that two or more of the element loops E1,... That is, as shown in FIG. 10, the switch 43 is not provided for two adjacent element loops such as element loops E2 and E3, E5 and E6, E8 and E9, E11 and E12,
If the cutoff cannot be performed, a closed loop as shown by a thick line in the figure remains. As is clear in such a case, it can be said that the decoupling effect is slightly inferior to that in FIG. 8, and it is preferable to avoid such a form if possible.

Further, as a modification of FIG. 8, it is more preferable to adopt a connection mode of the switch 43 as shown in FIG. In this figure, the element loop E11
Is different from FIG. 8 in that another switch 43j is further connected to the switch. Although the element loop E11 has already been cut off by the presence of the switch 43m, the provision of such a switch 43j makes it possible to maintain symmetry with the installation of the switch 43k. Thus, the decoupling effect can be more reliably enjoyed.

As described above, according to the high-frequency coil 4 for whole body of the present embodiment, the element loops E1,.
For some of E12, the existence of a closed loop as the element loop (shortest circumference) is permitted, but by determining the connection / arrangement mode of the switch 43 so as not to leave at least a large closed loop, As a whole, a sufficient decoupling effect can be obtained. This can reduce the number of switches 43 to be installed as compared with FIG.
There is no increase in the manufacturing cost and no complicated structure.

The decoupling achieved by the present embodiment is achieved by the switch 4 in the high-frequency coil 4 for whole body.
This is based only on making the connection mode 3 suitable. Therefore, the decoupling between the whole-body high-frequency coil 4 and the small-sized RF coil 2 can be realized without any problem even in the silent MRI apparatus provided with the vacuum container as shown in FIG.

In the above embodiment, the description has been made exclusively of the "12-element" whole-body high-frequency coil. However, the present invention is not limited to such an embodiment. The present invention is applicable in principle to a whole-body high-frequency coil 4 having any number of elements.

In the above description, the so-called "bird cage type" whole-body high-frequency coil 4 has been described. However, the present invention is not limited to such an embodiment. That is, as is well known, the whole-body high-frequency coil 4
As for the form of the “NMR probe”, generally speaking, various forms have been proposed even at present, and since “decoupling” is required for these forms, the present invention is basically applicable to Applicable.

As the above-mentioned various NMR probes, for example, an S probe having a cylindrical conductor member as shown in FIG.
And a TR (Slotted Tube Rotator) type probe. In this case, it is preferable to connect a switch as indicated by reference numeral 49k in the figure.
More generally, a QD (Quadrature) probe and a multi-surface coil probe configured by combining a plurality of tuning coils are also described.
Decoupling is required, and the present invention can be applied.

By the way, in the above-mentioned embodiment, the whole body high-frequency coil 4 and the small RF coil 2
Although the aim was to achieve decoupling with this, this object can also be achieved by another viewpoint or method. Hereinafter, this will be described as another embodiment different from the above.

FIG. 13 shows an MR according to another embodiment.
The outline of the I device is shown. FIG. 13 shows a state in which the gantry G is viewed from the front and a part of the inside of the gantry G is seen through, similarly to FIG. 14 described in the section of the related art. What is the arrangement of the whole-body high-frequency coil 4. That is, in FIG. 14, the whole-body high-frequency coil 4 is connected to the air core H
On the side. However,
In FIG. 13, this high-frequency coil 4 for whole body is also
It differs from FIG. 14 in that it is arranged in a vacuum vessel (in a region surrounded by the outer wall V and the inner wall Va).

In this embodiment, when decoupling the whole-body high-frequency coil 4 and the small-sized RF coil 2, the whole-body high-frequency coil 4 and the RF shield 4a are short-circuited in the same manner as in the conventional method. Then, the whole-body high-frequency coil 4 may be detuned. This is because, in this case, unlike FIG. 14, a situation in which a conducting wire penetrating the wall Va is provided to realize the short circuit is avoided. 13, the whole-body high-frequency coil 4 and the RF shield 4
Since both a are arranged in the vacuum vessel, it is not necessary for the conductor connecting them to penetrate the inner wall Va.

As described above, according to another embodiment of the present invention shown in FIG. 13, decoupling between the whole-body high-frequency coil 4 and the small-sized RF coil 2 can be achieved by the same method as in the related art.

However, in the embodiment shown in FIG. 13, there is a point that requires some attention. That is, in this case, discharge may occur at both ends of the capacitor constituting the whole-body high-frequency coil 4. Therefore, in order to prevent this discharge, it is preferable to perform an appropriate molding treatment on the whole-body high-frequency coil 4.

[0056]

As described above, according to the high frequency coil for an MRI apparatus and the MRI apparatus of the present invention, decoupling between the high frequency coil and the small RF coil can be effectively achieved. As the method, either by arranging the switch effectively on the conductor member forming the high-frequency coil, or by arranging the high-frequency coil and the shielding means and the conducting wire connecting both in the vacuum vessel, obtain.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration example of a nuclear magnetic resonance imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration example of a whole-body high-frequency coil.

FIG. 3 is a development view of the high-frequency coil for whole body shown in FIG. 2;

FIG. 4 is a circuit diagram illustrating a configuration example of a switch provided in the whole-body high-frequency coil.

5 is an explanatory diagram showing one connection mode of the switch shown in FIG. 4 to a high-frequency coil for whole body.

FIG. 6 is an explanatory diagram showing a connection mode of switches different from that of FIG. 5;

FIG. 7 is an explanatory diagram showing a “closed loop” assumed in a whole-body high-frequency coil.

FIG. 8 is an explanatory diagram showing a connection mode of switches different from those in FIGS. 5 and 6;

9 is an explanatory diagram illustrating a case where one switch 43k is removed from the connection state of the switches illustrated in FIG. 8;

FIG. 10 is an explanatory diagram showing a connection mode of a switch in which an adjacent element loop is left as a closed loop.

FIG. 11 is an explanatory diagram illustrating a connection mode of a switch that is a modification example of FIG. 8;

FIG. 12 is a perspective view showing a configuration example of an STR type probe.

FIG. 13 is a schematic diagram showing a configuration example of a nuclear magnetic resonance imaging apparatus according to another embodiment of the present invention.

FIG. 14 is a schematic diagram showing a configuration example of a conventional nuclear magnetic resonance imaging apparatus.

[Explanation of symbols]

P subject 1 bed 1a top plate 2 small RF coil 3 main magnet 4 whole-body radio frequency coil 411 ring portion _{42 1, 42 2, ...,} 42 n linear portion _{411p 1, 411p 2, ...,} 411p n and 412p ₁ ,
412p _2, ..., 412p _n connection points E1, E2, ..., En element loop (shortest circumference closed loop) 43 Switch 431 PIN diode 432 inductor 5 gradient coils (gradient magnetic field application means) 6 control unit 7 sequencer G gantry V vacuo Outer wall of container Va Inner wall of vacuum container

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuto Nakabayashi 1385-1 Higashiyama, Shimoishigami, Otawara-shi, Tochigi F-term in Toshiba Nasu Plant (reference) 4C096 AB34 AB47 CA66 CB19 CC01 CC05 CC16

Claims (7)

[Claims] 1. A high-frequency coil for a nuclear magnetic resonance imaging apparatus for transmitting a high-frequency signal or receiving an NMR signal, wherein the coil covers a substantially cylindrical space and forms a plurality of closed loops through which a current can flow. A high-frequency coil, comprising: a plurality of assembled conductor members; and a switch capable of cutting off a current flowing through all of the plurality of closed loops. 2. A high-frequency coil for a nuclear magnetic resonance imaging apparatus for transmitting a high-frequency signal or receiving an NMR signal, wherein the coil covers a substantially cylindrical space and forms a plurality of closed loops through which a current can flow. A plurality of assembled conductor members, and regarding a closed loop excluding the shortest circumference closed loop whose circumference is the smallest among the plurality of closed loops, a switch capable of interrupting at least a current flowing through the closed loop is provided. Features high frequency coil. 3. A birdcage comprising: a plurality of conductor members each including two ring portions facing each other; and a plurality of straight portions connected to both ends of the ring portions at a connection point on a peripheral edge thereof. The shortest perimeter closed loop is an element loop surrounded by four connection points between two linear portions adjacent to each other and the ring portion among the linear portions, wherein the switch is 3. The high-frequency coil according to claim 2, wherein a predetermined number, not all of the element loops, are provided. 4. The high-frequency coil according to claim 3, wherein two or more switches are provided for at least one of the element loops. 5. The high-frequency coil according to claim 3, wherein the switch is provided so that two or more adjacent element loops are not left as a closed loop. 6. A high-frequency coil for applying a magnetic field for excitation to a subject arranged in a static magnetic field space, and a gradient magnetic field applying means for applying a gradient magnetic field to the subject, A shielding means for preventing coupling of the gradient magnetic field applying means, and a vacuum vessel in which the high-frequency coil is provided outside thereof and the shielding means and the gradient magnetic field applying means are provided therein; Is composed of a plurality of conductor members arranged to cover a substantially cylindrical space and to form a plurality of closed loops through which a current can flow, and a switch capable of interrupting a current flowing through the plurality of closed loops. The plurality of conductor members, two ring portions each facing each other, at a connection point in the peripheral edge of each of these ring portions,
The switch has a birdcage configuration including a plurality of straight portions connected at both ends thereof, and the switch is surrounded by four connection points between two adjacent straight portions and the ring portion of the straight portions. A nuclear magnetic resonance imaging apparatus is provided for a predetermined number of element loops which are not all of the closed loops except for the element loops and the element loops. 7. A nuclear magnetic resonance imaging apparatus comprising: a high-frequency coil for applying a magnetic field for excitation to a subject arranged in a static magnetic field space; and a gradient magnetic field applying means for applying a gradient magnetic field to the subject. The nuclear magnetic resonance apparatus according to claim 1, further comprising: a vacuum vessel in which the gradient magnetic field applying means, the high-frequency coil, and shielding means provided between the high-frequency coil and the gradient magnetic field applying means are disposed. Imaging device.