JPH09201346A - High frequency coil, and magnetic resonance inspection device using same coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RF coil with which a high frequency magnetic field can be applied or signal-received only to a necessary part to be photographed clinically. SOLUTION: In an RF coil comprising three rings of conductor parts 1-3 respectively separated by plural capacitors 8-10 and connected to each other by linear conductors 4-7, diodes 11-14, 15-18 are connected to the ring 2 and the linear conductors 4-7 in series, feeding to this is controlled, so a part to be used as the RF coil for signal receiving or radiation can be selected. Danger such as heat generation of a subject, or burning or electric shock on the subject or an operator by application of a high frequency magnetic field can thus be eliminated. In addition, selection of the coil usage part can be performed while checking on an operation panel, thereby a radiation part and/or signal receiving part can be checked while checking through a monitor to improve operability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency coil of an inspection apparatus using nuclear magnetic resonance, and particularly to a magnetic resonance inspection apparatus (hereinafter referred to as MRI apparatus) suitable for obtaining a tomographic image or spectrum of a specific region of a subject. Called) high frequency coil.

[0002]

2. Description of the Related Art An MRI apparatus irradiates a subject placed in a static magnetic field with a high-frequency magnetic field to generate a nuclear magnetic resonance signal (hereinafter referred to as an NMR signal) generated from a nuclear spin of atoms constituting the tissue of the subject. That is) is detected and imaged. Therefore, the MRI apparatus includes a high-frequency coil (hereinafter, referred to as an RF coil) that irradiates a subject with a high-frequency magnetic field and an RF coil that detects an NMR signal that is a high-frequency signal. The MRI apparatus is provided with separate RF coils for irradiation and reception (cross coil method), or 1
There are two RF coils for irradiation and reception (single coil system), and coils of various shapes are used depending on these systems and the site to which they are applied.

For example, as an irradiation RF coil, in order to make a high-frequency magnetic field applied to a subject uniform, irradiation is performed by a whole-body coil such as a saddle type (saddle type) coil or a birdcage type coil, while receiving an NMR signal. At times, a small coil, such as a local surface coil, is used to increase the reception sensitivity (Japanese Patent Laid-Open No. 61-61).
95234). In some cases, the birdcage type whole-body coil is used for both irradiation and reception.

[0004]

When such a whole-body coil is used for irradiation, the excitation of the subject extends to a site unnecessary for imaging, so SAR (Specific Absor)
The problem of heat generation of the human body such as ption ratio may occur. In particular, with the recent widespread adoption of high-speed imaging, the power applied to the RF coil has also increased, and it is necessary to prevent the risk of burns and electric shock to the subject and operator due to excessive power. Is occurring.

By the way, conventionally, a method has been known in which a field of view is changed by switching a diode as a surface coil dedicated to reception, but such an example is not known for a whole body coil. Furthermore, there is no example in which the irradiation area and the reception area are switched between the irradiation and reception. Therefore, problems such as unnecessarily exciting a wide area and a narrow visual field in the longitudinal direction during reception occur. In particular, in the case of the single coil system, the field of view in the longitudinal direction is narrowed, which causes a problem that the high frequency magnetic field distribution becomes nonuniform.

During MR angiography of the head or thigh (hereinafter referred to as "angio"), when the whole body is excited by the whole body coil, unnecessary signals due to blood flowing from the heart outside the imaging field of view are generated. Were mixed in, and the image quality was deteriorated.

Therefore, the RF coil of the present invention can excite only a clinically necessary imaging region, and prevents the application of an unnecessary high-frequency magnetic field to the subject, thereby solving the problem of causing the subject to generate heat. In addition, it is an object of the present invention to prevent application of unnecessary power to the irradiation coil to prevent the risk of burns, electric shock and the like. Moreover, even if the same RF coil is used for both irradiation and reception in the whole-body coil, it is also an object to take an image with high sensitivity. Further, in the case of angiography, it is an object to avoid unnecessary excitation and reduce blood flow noise from the heart to obtain a good image.

[0008]

The RF coil of the present invention comprises:
A static magnetic field generating means for applying a uniform static magnetic field and a gradient magnetic field generating means for generating a gradient magnetic field having different strengths depending on positions are used to irradiate the subject with a high-frequency magnetic field in order to cause a nuclear magnetic resonance phenomenon in the subject, And / or a high-frequency coil for detecting a nuclear magnetic resonance signal generated in a subject by irradiation, including a plurality of conductors and a plurality of capacitors that form a plurality of resonators that resonate at a predetermined frequency. There is provided a plurality of switch means connected to at least a part of the plurality of resonators to selectively activate one of the plurality of resonators and deactivate the other resonator.

Depending on the part to which the high-frequency coil is applied and whether the high-frequency coil is used for irradiation or reception, it is possible to drive an appropriate switch means to activate a desired resonator. . As a result, unnecessary excitation can be prevented, the safety of the device can be improved, and unnecessary signals can be prevented from being mixed in particularly during angiography.

The RF coil of the present invention comprises three or more ring-shaped conductors, a plurality of linear conductors that connect each ring-shaped conductor, and a ring-shaped conductor and / or a capacitance that divides the linear conductor. Applied to an RF coil, any two ring-shaped conductors of a plurality, preferably three or more ring-shaped conductors or a part thereof and a linear conductor connecting the two ring-shaped conductors or a part thereof A plurality of switch means are provided for electrically disconnecting a part of the ring-shaped conductor and / or the linear conductor from the resonator so that the resonator constituted by (3) is activated. Here, the ring-shaped conductor is not limited to a circle, and may be any conductor that forms a loop such as an ellipse or a rectangle.

The resonator in the operating state can be composed of any two ring-shaped conductors and a plurality of linear conductors connecting the ring-shaped conductors, and the ring-shaped conductor is further divided by capacitance. If you use some of them,
It is also possible to configure each of the ring-shaped conductors and a linear conductor that connects them. As a coil formed of each part of such a ring-shaped conductor and a linear conductor that connects them, there is, for example, a surface type RF coil.

The structure of such an RF coil can be determined by on / off controlling a predetermined one of a plurality of switch means. A diode is preferably used as the switch means in terms of easiness of control and the like, but the switch means is not limited to this, and a known switch means such as a relay or a coaxial switch can be used. The diode is connected in series with the ring conductor and / or the linear conductor, and the conductor is directly connected by turning on / off.
It can be used as a switch means for disconnecting it, or can be used in combination with a resonance circuit of capacitance and conductance.

In the case of a diode connected in series with a ring-shaped conductor and / or a linear conductor, if the diode is on, the conductor acts as a connected one, and if it is off, the conductor acts as a disconnected one.

On the other hand, when the diode is used in combination with the resonance circuit, the conductance connected in series and the diode are connected in parallel to the capacitance connected in series to the conductor. Here, the conductance and the capacitance form a resonance circuit that resonates in parallel at the frequency of the resonator when the diode is on, and have a high impedance. As a result, the conductor in which such a resonance circuit is introduced is not connected (opened). State). When the diode is reverse-biased and turned off, it is equivalent to not connecting an inductance, and the conductor is connected by capacitance.

When a diode is used as the switch means, a diode drive means for supplying power to the diode is provided. The diode driving means may be provided for each diode, or when a plurality of diodes are connected in series to the ring-shaped conductor, it is possible to supply power to each diode from one place of the ring-shaped conductor.

In the present invention, the diode is preferably a combination of a plurality of diodes. For example, the anodes of two diodes are used as one set connected to each other, and in this case, the diode driving means supplies a positive voltage to the connection point of the two diodes and a negative voltage to each cathode side. When the RF coil of the present invention is used as an irradiation coil, a relatively large voltage is applied to the diode in the off state during irradiation, so a reverse voltage is applied so that the diode does not turn on due to such voltage. Will be required. In this case, it may occur that a reverse voltage of several hundred volts must be applied. Therefore, as described above, two diodes are connected in the forward direction, a negative voltage is applied to the connection point, and a positive voltage is applied to the cathode side. The diode can also be prevented from turning on.

The diode driving means for supplying power to the diode is connected to a control line from a controller such as a calculator and supplies power to the diode in the forward direction or the reverse direction according to the imaging conditions and the imaging procedure. Further, it is possible to provide different control lines for irradiation and for reception to supply power at different time timings according to the photographing procedure.

By controlling the diodes in this manner, it is possible to selectively connect or disconnect the respective conductor portions forming the plurality of resonators, and thereby bring any resonator into an operating state. You can For example, when the RF coil includes a plurality of ring-shaped conductors, a coil including any two ring-shaped conductors and a linear conductor that connects the two ring-shaped conductors can be activated. The coil configuration can be changed by changing the combination of the two ring-shaped conductors. Therefore, when the RF coil of the present invention is an irradiation coil, the irradiation area can be changed, and when it is a reception coil, the sensitivity distribution can be changed. Further, when each part of the ring-shaped conductor divided by the capacitance connects a diode to each other, a part of the two ring-shaped conductors and a line connecting them are fed by feeding a reverse direction to some of the diodes. A coil composed of the strip conductor can be activated.

As described above, the RF coil according to the present invention has the capacitance for dividing the ring-shaped conductor and the ring-shaped conductor and / or
Or in combination with a diode connected to a linear conductor,
It is possible to realize resonators having various shapes such as a surface coil and a whole body coil, and long and short various volume of whole body type coils. Further, such an RF coil can be used for both irradiation and reception,
The shape, volume, etc. can be freely selected according to the examination site of the subject and depending on the irradiation purpose or the reception purpose. This avoids unnecessary high magnetic field irradiation,
The shooting sensitivity can also be increased.

The RF coil of the present invention further comprises means for tuning the active resonator to the desired frequency. As such means, a ring-shaped conductor, a plurality of linear conductors, a ring-shaped conductor and / or a capacitance dividing the linear conductor tunes a resonator operated by turning on / off the switch means to a desired resonance frequency. It is possible to construct a combination of a capacitance and an inductance as described above, or to provide a means for tuning the capacitance such as a variable capacitance.

The RF coil of the present invention has a power feeding means for feeding power to the coil itself, and preferably has a plurality of power feeding means. These plurality of power feeding means are R of the present invention.
Corresponding to the change in the coil configuration of the F coil, the F coil serves as a power feeding means for each coil.

The RF coil of the present invention can be arbitrarily modified as long as the function of the coil is not hindered.
As an aspect, at least one of the ring-shaped conductors has a deformed shape corresponding to the shape of the subject. For example, by partially deforming the shape of the ring-shaped conductor, an RF coil having a shape suitable for angiography can be obtained.

Furthermore, the RF coil of the present invention is an RF coil that both irradiates and receives a high frequency signal, and has a different coil configuration during irradiation and during reception. In this case, for example, at the time of reception, the coil configuration may be made in a narrower area than that at the time of irradiation to increase the sensitivity.

The MRI apparatus of the present invention uses the R as described above.
An F coil is provided, and together with this RF coil, magnetic field generating means for applying a uniform static magnetic field to the subject,
And a magnetic field generating means for generating a gradient magnetic field having different strength depending on the position. In this MRI device, the irradiation area can be changed, and the sensitivity distribution in the case of reception can be changed.
Since the coil is provided, unnecessary application of a high-frequency magnetic field to the subject can be prevented, and the region of interest can be imaged with high sensitivity.

The MRI apparatus of the present invention preferably includes control means for independently controlling power supply to each of the diodes included in the RF coil, and more preferably, a ring-shaped conductor, a linear conductor and these of the RF coil. It is provided with an operation panel that displays the on / off state of the diodes connected to the conductors and is selectable to turn on or off any of the diodes.
The operation panel displays, for example, the shapes of the constituent coils on the captured image of the subject. Based on the display on the operation panel, the operator can perform on / off control of the diode in order to irradiate the required area with RF or to detect the NMR signal with high sensitivity from the required area. Therefore, the selection operation has good operability and is reliable.

A further preferred MRI apparatus of the present invention comprises display means for displaying a coil configuration determined by turning on or off a diode. The display means displays on the screen which part is the irradiation coil and which part is the reception coil as a result of which diode is turned on after the operation by the operation panel. This allows
The operator can monitor the coil configuration currently in operation and finally judge the adequacy of the selected resonator, and can operate with good operability.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the RF coil of the present invention will be described with reference to the schematic circuit diagram of FIG. This RF coil has three ring-shaped conductors (hereinafter,
Called a ring. ) 1 to 3 and four linear conductors (hereinafter, referred to as rungs) 4 to 7 that connect these rings.

The rings 1 and 3 are divided into four by inserting appropriately adjusted capacitances 8 and 10 in the conductor portions between the connection points with the rungs 4 to 7, respectively.

In the ring 2, two capacitances 9 are inserted between the connection points with the rungs 4 to 7, respectively, and are divided into eight by a total of eight capacitances. Then, diodes 11 to 14 as switching means are connected in series to the conductor portion between the two capacitances between the connection points. Each diode 11-14 is shown in FIG.
As shown in (a), it is connected to a power supply circuit (diode drive means) 71 for supplying power via an inductance. The diode is 70 in FIG.
The capacitance on both sides is indicated by 410, and the diodes 11-14 and the capacitance 9 in FIG.
Respectively. Such an inductance of the power supply circuit 71 is added to the diodes 11 to 14 so as to have a high impedance with respect to a predetermined resonance frequency. In the ring 2, since the capacitors 410 are located on both sides of the diode, the bias current does not flow and the direct current is cut off.

The rungs 4 to 7 have diodes 15 to 18 at the conductor portions located between the ring 2 and the ring 3, respectively.
Are connected in series, and these diodes 15-18
Is also connected to the power feeding circuit via an inductance like the diodes 11 to 17.

The RF coil of FIG. 1 constructed as described above has diodes 11 to 14 connected to the ring 2 and diodes 15 to 18 connected to the rungs 4 to 7 between the ring 2 and the ring 3. By controlling on / off,
Long resonator composed of ring 1, ring 3 and rungs 4-7 connecting these rings 1, 3 and short resonance composed of ring 1, ring 2 and rungs 4-7 connecting these rings 1, 2. It is possible to construct a saddle type surface coil composed of a vessel and a part of the rings 1 and 3 and a rung.

When the coil configuration changes as described above (the resonators in the operating state are different), it is necessary that any of the resonators can be tuned at a desired resonance frequency. Therefore, each capacitance 8-10
Or select the capacitance of
It is desirable that a part of 10 to 10 be a variable capacitance or that a variable capacitance is separately connected to perform tuning according to a change in coil configuration.

Next, a power feeding means for feeding power to such an RF coil will be described. Generally, there are a method of feeding power to the RF coil via a capacitance to a feeding point provided on a conductor and a method of inductive coupling of feeding another coil close to the conductor.
Since the coil configuration of the F coil can be changed by driving the diode as described above, it is preferable to provide a plurality of power feeding means corresponding to the plurality of coil configurations. In the case of capacitive coupling, it is possible to supply power to each resonator by providing a feed point by capacitive coupling on the rungs in the rings 1 to 3 or in the vicinity thereof. In this case, it is also possible to switch each power supply means with a switch or a relay to supply power to the RF coil, so that it is possible to supply power only to the rings that make up the resonator, and not to supply power to unnecessary rings. . Further, in the case of inductive coupling, another coil, which is a power feeding means, may be brought close to the vicinity of the ring which is in an operating state depending on the coil configuration. The inductive coupling is easier to handle than the capacitive coupling in that the feeding point does not have to be directly connected to the RF coil.

In any case, the RF coil can be QD-ized by supplying power to the three rings at positions of 90 degrees with respect to the circumferential direction.

In the illustrated embodiment, the case where a single diode is connected in series to the conductor as the switch means (FIG. 2A) has been described. However, the inductance and the diode are connected in parallel with the capacitance dividing the conductor. A series circuit may be connected. Such an embodiment is shown in FIG.
Here, the power feeding circuit 71 is composed of an inductor having a high impedance, and turns on the diode 70 by forward bias. In this case, by appropriately selecting the inductance 72, the capacitance 420 and the inductance 72 cause parallel resonance at a desired frequency when the diode 70 is on, and a high impedance can be obtained at both ends of the capacitance 420. As a result, the conductor loop into which such a circuit is inserted is substantially opened. Further, by reverse-biasing the diode 70 from the power feeding circuit 71 and turning it off, it is equivalent to not connecting the inductance 72, and the conductor loop into which this circuit is inserted is closed. Therefore, when the switch means has the configuration shown in FIG. 2B, the diode is turned on contrary to the case of FIG. 2A (the state shown in FIG. 2B).
With this, the conductor loop is opened, and the diode is turned off to close the conductor loop.

When an RF coil is used as an irradiation coil, a relatively large voltage of about several hundreds of volts may be applied during irradiation, and when a single diode is used as the diode structure (see FIG. 2). (A) and (b), there is a possibility that a diode that has been turned off by applying a reverse voltage may also turn on. In order to prevent this, it is necessary to set the reverse bias voltage applied to the diode to several hundred volts, but this makes the configuration of the power feeding circuit difficult and is not preferable from the viewpoint of safety. Therefore, as shown in FIGS. 2 (c) and 2 (d) as the configuration of the diode,
Connect the two diodes 70, 70 with their anodes connected to each other,
It is preferable to provide feeding points at three places, that is, the connection point and each cathode side. In such a configuration, when the diode is turned on, a positive voltage is applied to the connection point and a negative voltage is applied to both ends as illustrated. On the other hand, when turning off the diode, a negative voltage is applied to the connection point and a positive voltage is applied to both ends. As a result, it is possible to prevent the diode from turning on even with a large reverse voltage during irradiation. still,
Although two diodes are shown in FIGS. 2C and 2D, a plurality of diodes in the same direction can be further added between these diodes and the feeding point. As a result, it is possible to make it stronger against the reverse voltage.

Next, the application of the RF coil configured as described above to the MRI apparatus will be described. The RF coil of the present invention can be used as both an irradiation / reception coil of an MRI apparatus, an irradiation-dedicated coil or a reception-dedicated coil. In the following, when the RF coil of FIG. 1 is used as an irradiation coil for the whole body. Will be described.

First, a resonator to be constructed is selected according to the photographing area. Since it is suitable to use a long resonator when irradiating in a wide area, in this case, the diodes 11 to 14 connected to the ring 2 are connected to the power feeding means 71 (see FIG. 2).
(A)) Power is supplied in the opposite direction to turn off and diodes 15-18 connected to the rungs 4-7
Are turned on by supplying power in the forward direction by the power supply means.
As a result, a long resonator constituted by the ring 1 and the ring 3 can be used as the irradiation coil as shown by the thick line in FIG. On the other hand, if only a narrow area is imaged, it is suitable to use a short resonator, and in such a case, the diodes 11 to 1 connected to the ring 2 are used.
4 is fed in the forward direction to turn on, and the diodes 15 to 18 connected to the rungs 4 to 7 are fed in the reverse direction to turn off. As a result, FIG.
A short resonator constituted by the ring 1 and the ring 2 as shown by the thick line in (b) can be used as the irradiation coil.
In addition, here, in order to simplify the description, the diodes 11 to 11
When a single diode is used as 18 (see FIG.
Although (a)) has been described, since it is applied as an irradiation coil, it is desirable that the configuration of the diode is as shown in FIG. 2 (c) or (d).

Regardless of which resonator is active, the capacitance is adjusted to tune the nuclear magnetic resonance frequency. When there are a plurality of power feeding points, power is fed from the power feeding point corresponding to the resonator to be activated.

As described above, when the RF coil of the present invention is used as an irradiation coil, a short irradiation coil composed of the ring 1 and the ring 2 or the ring 1 and the ring 3 is formed depending on the size of the region to be excited. Can be a long irradiation coil configured by, for example, when imaging a narrow area using a head coil, a neck coil, a knee coil or a local surface coil as a receiving coil, only the corresponding part is excited Therefore, it is possible to prevent unnecessary RF irradiation. Alternatively, by exciting only a specific region, blood flow noise from the heart or the like can be prevented by inflow imaging of angio and image quality can be improved. Further, since the space excited when excited in a narrow region is ½ of the space excited when excited in a wide region, the irradiation power becomes ¼.

The RF coil of the present invention can be applied not only as a whole body irradiation coil but also as a local irradiation coil.

Next, a case where the RF coil of FIG. 1 is applied to a receiving coil will be described.

In this case, another R installed for irradiation is used.
In order to avoid the coupling with the F coil, all the diodes 11 to 1 of the RF coil of this embodiment are irradiated at the time of irradiation.
8 is fed in the opposite direction through the inductance,
Open the loop in the detection direction for decoupling so that the irradiation magnetic field is not disturbed. Next, at the time of reception, a predetermined diode is appropriately turned on and the other diodes are turned off according to the size of the region of interest. The configuration of a short resonator using the rings 1 and 2 in the case of imaging a narrow area and the configuration of a long resonator using the rings 1 and 3 in the case of imaging a wide area are the same as those described above. It is similar to the case of the coil.

Although the irradiation coil and the reception coil have been described above, the irradiation / reception combined coil can be similarly applied.

Generally, the filling factor η of the resonator is
Since it is inversely proportional to the volume of the resonator, in the RF coil shown in FIG. 1, the filling factor η changes depending on the length of the resonator, and in the short resonator, the filling factor η improves.
The sensitivity S of the RF coil is proportional to the filling factor η. Therefore, in this embodiment, the volume of the short resonator is half the volume of the long resonator, so that the sensitivity S is doubled. The symbol of Q in this equation indicates the Q value of the resonator.

[0046]

[Equation 1] Similarly, if the volume of the resonator becomes 1/2 and 1/3,
The sensitivity is doubled and tripled. Further, since the voltage V and the sensitivity S are proportional to each other, the irradiation power P that can be expressed by the following equation is reduced to 1/4.

P = V ² / R Therefore, the short resonator has a higher sensitivity than the long resonator and requires less irradiation power.

Further, for example, when the thigh is photographed with a raw image and the region of interest is narrow, a long resonator is used to illuminate a wide region, and then a short resonator is used to illuminate a narrow region. You may. In this case, the diodes 11 to 14 connected to the ring 2 are turned on at the time of irradiation, and the rungs 4 to 7 are turned on.
The diodes 15 to 18 connected to are turned off, and when receiving, the diodes 11 to 14 are turned off.
The on / off of the diode is controlled so that 5 to 18 are turned on.

In this way, even when an image is taken in a wide area at the time of taking an original image, it is possible to take an image in a narrow area while setting the subject when taking an image for diagnosis. Since the shooting can be performed in such a narrow area, the filling factor is improved. In principle, in the present embodiment, shooting in a narrow area can be performed with twice the sensitivity as in a wide area.

Next, a case where the RF coil shown in FIG. 1 is used as a surface coil will be described. In order to use the RF coil of FIG. 1 as a surface coil, for example, the diode 11 connected to the ring 2 is turned on, and the other diodes 12 to 14 connected to the ring 2 and the diodes connected to the rungs 4 to 7 are connected. Turn off 15-18. As a result, as shown by the thick line in FIG.
A saddle type surface coil can be configured by the rung 4 and the rung 7 between and, and the divided portion of the ring 1 and the ring 2 including the diode 11.

The surface coil constructed in this case corresponds to the lower side in FIG. 1, and in the case where the photographing area is on the lower side, the patient can be photographed with high sensitivity while lying down. As the surface coil, not only the one for irradiating and receiving the lower side as described above, but also the diode 13 connected to the ring 2 is turned on, and the other diodes 11, 12 and 14-1.
By turning off 8, the upper surface coil can be similarly constructed. Also, by turning on the diode 12 or 14 connected to the ring 2 and turning off all the other diodes, the side surface coil can be similarly configured. Further, it is possible to form a surface coil having a long rung length by turning on a necessary portion of the diode connected to the rung between the ring 2 and the ring 3.

Similar to the case of the whole body coil, such a surface coil can be used for both irradiation and reception, can be used only for irradiation, and can be used only for reception. Further, not only can it be used as a surface coil during irradiation and reception, but it can also be used as the above-mentioned whole-body coil during irradiation and used as the above-mentioned surface coil during reception. When used as a receive-only coil, as described for the whole-body coil, when irradiation is performed by another irradiation coil, all the diodes 1
It is necessary to feed power to 1 to 18 in the opposite directions via the inductances 19 to 26, open the loop in the detection direction and perform decoupling so that the irradiation magnetic field is not disturbed.

As described above, the RF coil according to the present invention includes a capacitance that divides the ring-shaped conductor and a ring-shaped conductor and / or
Or in combination with a diode connected to a linear conductor,
It is possible to realize resonators of various shapes such as a surface coil and a whole body coil, and long and short various volumes of the whole body coil.

Although not shown, the ring 1 and the ring 2
When a diode similar to that is provided or when a diode is provided on the rungs 4 to 7 between the rings 1 and 2 in the same manner as between the rings 2 and 3, these diodes are turned off to disconnect the ring 1. A short resonator consisting of ring 2, ring 3 and rungs 4-7 connecting these rings 2, 3 can be operated as an RF coil.

In the illustrated embodiment, the RF coil composed of three rings has been described, but the number of rings may be four or more. Further, in this embodiment, the capacitances 8 to 10 are respectively connected to the rings 1 to 3, but diodes may be connected instead of connecting these capacitances, and diodes are connected to each ring and each rung. You may. Especially when it is used as a surface coil or when there are four or more rings, it is better to have diodes in series in the other rings.

FIG. 4 shows another embodiment of such an RF coil. This RF coil is also provided with a ring and a rung connecting each ring, and each ring is divided into four parts by a capacitance. Regarding the points, the use of an inductance as a bias power supply means of the diode connected to the ring, the point where the direct current is cut off by the capacitance so that the bias current does not flow across the diode, etc., the RF coil of FIG. Is the same as. This RF coil is largely different from the example shown in FIG. 1 in that diodes are connected in series to all the rings forming the RF coil and no diodes are connected to the rungs. Further, in this embodiment, the number of rings is four.

Specifically, the rings 27 to 30 divided by the diode, and the rung 201 connecting these rings are connected.
~ 204, diode 4 connected in series with ring 27
7-50, diode 5 connected in series with ring 28
1 to 54, diode 5 connected in series with ring 29
5 to 58, diode 5 connected in series with ring 30
9 to 62, eight capacitances 210 arranged at both ends of each of the diodes 47 to 50 and connected in series to the ring 27, eight capacitances 220 arranged at both ends of each of the diodes 51 to 54 and connected in series to the ring 28, Eight capacitances 230 arranged at both ends of each of the diodes 55 to 58 and connected in series to the ring 29, eight capacitances 240 arranged at both ends of each of the diodes 59 to 62 and connected in series to the ring 30, each diode 47 to Inductors (not shown) for feeding power to the respective 62 are provided. Further, each inductance is connected to a controller and can be supplied with power independently.

In the illustrated embodiment, a single diode is connected to the conductor in series as in FIG. 1, but
The configuration of the diode as the switch means may be any of the configurations shown in FIGS. 2 (a) to 2 (d) similarly to the embodiment of FIG. 1, and particularly when this RF coil is used as the irradiation coil, In order to prevent the off diode from turning on by the applied voltage, it is preferable to combine a plurality of diodes as shown in FIGS. 2 (c) to 2 (d).

As with the RF coil shown in FIG. 1, the RF coil shown in FIG. 4 can form various resonators having different lengths and positions depending on how to combine the rings by selecting ON / OFF of the diodes. Moreover, since the number of rings is larger than that of the RF coil in FIG. 1 and the diode is connected to each ring, various coil configurations are possible. That is, in the case of a whole body coil, it consists of a combination of two rings (rings 27 and 29, rings 27 and 28, rings 28 and 30, and rings 28 and 29, or rings 29 and 30) and a rung that connects them. You can make street resonators. For example, the resonator constituted by the rings 27 and 29 turns on the diodes 47 to 50 connected in series to the ring 27 and the diodes 59 to 62 connected in series to the ring 30, and connects them in series to the ring 28. It can be obtained by turning off the connected diodes 51 to 54 and the diodes 55 to 58 connected in series to the ring 29. The same applies to other resonators,
The diode connected to the ring that constitutes the resonator may be turned on, and the diodes connected to the other rings may be turned off.

It is also possible to construct a saddle type surface coil by using a part of any two rings. For example, by turning on the diodes 47 and 51 and turning off the other diodes, the rings 27 and 2
A lower surface coil is obtained, which is constituted by a part of each of 8 and the rungs 201, 202.

When the above-described six types of resonators are formed or when the surface coil is formed, the resonance frequency of each resonator is an appropriate capacitance according to the resonator using the capacitances 210, 220, 230 and 240. It is possible to combine or tune these capacitances as variable capacitances to the desired resonant frequency.

As in the case of the RF coil shown in FIG. 1, such a whole body coil or surface coil can be used for both irradiation and reception, can be used only for irradiation, and can be used only for reception.

The method of feeding power to this RF coil is also the same as that described above. For example, by providing feeding means by inductive coupling in the vicinity of each of the rings 27 to 30, it is possible to feed power to each of the configured resonators. Is. Also, by providing a plurality of power supply means and switching them with switches or relays to supply power to the RF coil, power can be supplied only to the rings that make up the resonator, and unnecessary rings are not supplied. .

In the embodiments described above, the method of feeding power to the individual diodes through the feeding circuit is adopted as the method of feeding the diodes. However, when a plurality of diodes are inserted in the ring, the ring is fed. It is also possible to feed these multiple diodes from one location. Such an embodiment is shown in FIG.

The RF coil shown in FIG. 5 has three rings 6.
Four rungs 301 to 3 that connect each ring with 3 to 65
04 is similar to the RF coil of FIG. 1, but the diode, which is the switch means for closing or opening the conductor loop, is not connected to the rung and the ring 6
Connected to 4 and 65. That is, four capacitances 310 are connected to the ring 63 and have the same configuration as the ring 1 of the RF coil of FIG. 1, but four diodes 325 to 328 are serially connected to the ring 64 at intervals of 90 ° in the circumferential direction. A circuit 108 including a capacitance and an inductance is connected in series between the diodes. The ring 65 also has the same configuration as the ring 64, and four diodes 331 to 334 are connected in series, and a circuit 108 including a capacitance and an inductance is connected in series to a conductor portion between each diode. . In addition, capacitances 311 to 314 are provided between the rings 63 and 64 on each of the rungs 301 to 304.
Capacitance 321-32 between the rings 64 and 65
4 are connected.

Further, inductances 66 and 67 for supplying power to the diodes and capacitances 68 and 69 having large capacitances are connected to the rings 64 and 65, respectively, and power is supplied to the diodes connected to the rings. Each has one. In this embodiment, since the circuit 108 including the capacitance and the inductance is connected in series with the conductor forming the ring as a high impedance, the ring is opened by supplying a bias current from one feeding point. Therefore, the method of supplying power to the diode can be simplified.

Next, as another embodiment of the RF coil of the present invention, an RF coil having an asymmetric shape in which a part of the ring is deformed will be described with reference to FIG. This RF coil is an example applied to a head coil, and has a shape that does not hinder the shoulder of the subject. With such a shape, the thoracic spine that is clinically required for the head coil
-Enables up to the third shooting.

This RF coil has four rings 73 to 7
6 and four rungs 501 to 504 for connecting the rings, and the rings 73 and 74 have the structure shown in FIG.
Since it is exactly the same as the rings 27 and 28 in the coil, description thereof will be omitted.

The ring 75 and the ring 76 share a part so that both sides are open in the figure, and the upper and lower sides of both rings are curved and deformed so as to extend along the axial direction of the subject, Ring 75 extends less than ring 76. As a result, when the parts of the rings 73 and 74 are attached to the head of such an RF coil, the shared parts of the rings 75 and 76 are located on the shoulders of the human body, and the curved parts are located above the vertebrae and the chest. It is arranged to be located in. As a result, it is possible to image the top of the head and the chest while avoiding the shoulder of the subject.

Also in the shared portion of the rings 75 and 76 and the conductors of the curved portions, the diodes 99 to 104 and the capacitances 530 and 54 at both ends of these diodes are provided.
0 is connected, and the point that an inductance as a power feeding means is connected to these diodes is similar to the above.

In the RF coil of the present invention constructed as described above, when the position of the tip of the ring 76 extending along the axial direction of the subject is a position including the upper side of the chest which does not include the heart, it is angio. Suitable for in-flow photography. That is, when angiography is performed with a large irradiation coil at the time of angiography, the heart is also illuminated, which causes deterioration of image quality due to blood flow noise from the heart. However, the RF coil having the above-described shape does not need to illuminate the heart and is necessary. This is because only the area can be illuminated. On the other hand, when the image is taken with a small resonator for both transmission and reception, the field of view becomes narrow, and when the coil is made larger, the filling factor is lowered and the sensitivity is lowered. This can be solved by irradiating in a range and receiving in a narrow range with a small resonator to improve sensitivity.

For example, during irradiation, the diodes 91 to 94 connected to the ring 73 and the diodes 103 and 104 connected to the ring 76 are turned on by forward bias, and the diodes 95 to 98 connected to the ring 74 are turned on.
And the diodes 99, 100 connected to the ring 75,
101 and 102 are turned off by reverse bias.
By supplying power in this way, the ring 73 and the ring 76 are
It is possible to obtain an irradiation coil configured to irradiate a wide range. However, even in this case, unlike the conventional whole body coil, it is possible to efficiently excite only the region necessary for imaging.

Next, at the time of reception, the diodes 91 to 94 connected to the ring 73 and the diodes 100, 103, 102 and 104 connected to the ring 76 are turned off by reverse bias, and the diode 9 connected to the ring 74 is turned on.
5 to 98 and the diodes 99 and 101 connected to the ring 75 are turned on by forward bias. As a result, it is possible to obtain a receiving coil having a high sensitivity for receiving in a narrow range constituted by the ring 74 and the ring 75.

The RF coil shown in FIG. 6 can be used not only for irradiation and reception but also for irradiation and reception as in the case of the other RF coils of the present invention described above. Further, the combination of rings is not limited to the one described above, and various combinations are allowed. That is, it is only necessary to select a coil to be constructed in consideration of size and shape according to the purpose of photographing, and to control ON / OFF of the diode according to the selected coil. Further, the method of supplying power to the diode can be changed in addition to the method of using the inductance, or the method of supplying power to each ring.

Next, the MRI apparatus of the present invention will be described. The MRI apparatus of the present invention includes a static magnetic field generating means for generating a uniform static magnetic field in a space where a subject is placed, a gradient magnetic field generating means for generating a gradient magnetic field having different strengths depending on positions, and R
An F coil and a computer that controls the gradient magnetic field generating means and the driving means of the RF coil in accordance with a predetermined sequence, and calculates a tomographic image and a spectrum of a subject specific portion based on the NMR signal received by the RF coil. It is the same as the conventional MRI apparatus in that it is provided, but it is provided with the above-mentioned RF coil as an RF coil and further with a control means for driving a diode provided in this RF coil.

The control means of the diode is composed of a controller such as a calculator, and its control line is connected to the diode drive means so that the diode is fed in the forward direction or in the reverse direction according to the photographing conditions and the photographing procedure. Control the drive means. This control method is as described above as an example of using the RF coil. The control means is provided with an operation panel that enables selection of turning on / off of the diode.

The operation panel can also be used as the operation panel of the MRI apparatus. Further, as shown in FIG.
The display unit has a display unit that displays the shapes 601-603 of the entire F coil and also displays the measurement site 610 of the subject on the screen. The operator selects a resonator to be activated (ON) or a resonator to be inactivated (OFF) while looking at the display portion of the operation panel 600, and drives a diode from an operation console (not shown). It is possible to control the power supply to the means such as the inductance. The shape of the RF coil is, for example, a portion 602 where the resonator is turned on.
Is shown with a solid line, and the parts 601, 603 that are turned off
Can be indicated by a dotted line, and in this way, the operator can make a selection while confirming whether the resonator is on or off.

Any display method may be used as long as the on / off state of the resonator can be identified, for example, the color is changed by turning on / off. When the RF coil is used for both irradiation and reception, it is preferable that the RF coil resonator on / off selection operation can be performed independently for irradiation and reception.

Further, the operation panel does not have to use the schematic diagram as shown in FIG. 6, but may be one in which a name or the like is input and selected in an interactive screen format.

Further, it is preferable that the MRI apparatus of the present invention comprises display means for displaying the RF coil constituted by such a diode selection operation. The display means 700 may be an independent monitor for displaying the RF coil configuration, but it is preferable that the display means 700 also serves as a monitor for displaying an image of the MRI apparatus, and is configured as a sub-screen of the imaging screen. be able to. FIG. 7 shows an example of such a display means 700.

The display means 700 displays a subject 710 in the center of the image pickup screen, and child screens for displaying the coil shape at the time of irradiation and the coil shape at the time of reception are provided at the upper left and lower left of the screen, respectively. Here, the irradiation coil and the reception coil are displayed in different shapes, but the same shape may be used. Also in this display means, a portion 701 selected as an irradiation coil during irradiation is shown by a solid line, and portions 702 and 703 not selected as an irradiation coil are shown by dotted lines. Similarly, a portion 705 selected as a receiving coil at the time of reception is shown by a solid line, and portions 704 and 706 not selected as a receiving coil are shown by a dotted line. The operator displays the subject 7 by the display on the display unit 700.
10, the irradiation coil and the receiving coil can be recognized at the same time, and it is possible to check the operation of selecting the resonator on / off performed separately by the operation panel 600 shown in FIG. 7.

This display can be applied to the case where the RF coil is also used for irradiation and reception, and the case where it is used for either one.
When the RF coil of the present invention is dedicated to irradiation or reception, it may be either one of the two child screens on the left side of the screen. Further, the display method is not limited to this example, and any method may be used as long as the object, the irradiation coil selection state and / or the reception coil selection state can be simultaneously confirmed.

[0083]

According to the RF coil of the present invention, an R including a plurality of conductors and a capacitance forming a plurality of resonators.
By providing a plurality of switch means for selectively activating one of the plurality of resonators and deactivating the other resonators in the conductor portion of the F coil, one RF coil can be formed by switching the switch means. However, it can be used as an irradiation coil that excites only a clinically necessary imaging region and as a reception coil that detects only a region of interest. Thereby, the irradiation power of the coil can be reduced and the filling factor can be improved. As a result, it is possible to prevent an unnecessary high-frequency magnetic field from being applied to the subject and reduce the problem of causing the subject to generate heat. In addition, it is possible to prevent unnecessary power from being applied to the irradiation coil and eliminate the risk of burns, electric shock, and the like. Further, when the receiving coil is used, the sensitivity can be improved by selectively using a narrow area.

In particular, in the RF coil of the present invention, a plurality of switch means are connected to the conductor of the RF coil which is composed of three or more ring-shaped conductors, linear conductors connecting these conductors, and a capacitance dividing these conductors. As a result, it is possible to construct a practical RF coil having a large degree of freedom in selecting the resonator to operate.

Further, the RF coil of the present invention can be used as both an irradiation coil and a reception coil, and can be operated as both a whole body coil and a surface coil depending on the switching method of the switch means. The coil configuration used correspondingly can be changed. For example, when applied to a whole-body coil, the length of the resonator can be different between irradiation and reception, regardless of whether it is for irradiation or reception. It is possible to configure a short resonator corresponding to. This makes it possible to shoot with high sensitivity.

In the case of inflow imaging of angios such as the head, neck and thighs, the image can be taken without irradiating the heart even in the cross method, so that the image quality based on the blood signal from the heart is used. Deterioration can be prevented.

According to the MRI apparatus of the present invention, since the RF coil as described above is provided, the R
High-quality images can be obtained by minimizing F irradiation. Further, the resonator to be operated can be selected while observing the display on the operation panel overlaid on the captured image, and the operability is good. In addition, a region that needs to be imaged for diagnosis and a portion that operates as an irradiation coil and / or a reception coil are displayed on the monitor, so that the region can be easily confirmed.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram of one embodiment of an RF coil of the present invention.

FIGS. 2A to 2D are diagrams showing a method of supplying power to a diode in the RF coil of the present invention.

3A to 3C are diagrams showing different coil configurations of the RF coil shown in FIG. 1;

FIG. 4 is a schematic circuit diagram of another embodiment of the RF coil of the present invention.

FIG. 5 is a schematic circuit diagram of another embodiment of the RF coil of the present invention.

FIG. 6 is a schematic circuit diagram of an asymmetric RF coil of the present invention.

FIG. 7 is a diagram showing a display example of an operation panel for selecting a resonator of an RF coil in the MRI apparatus of the present invention.

FIG. 8 is a diagram showing a display example of display means in the MRI apparatus of the present invention.

[Explanation of symbols]

1 to 3 ··· Ring conductor (ring) 4 to 7 ··· Line conductor (rung) 8 to 10 ··· Capacitance 11 to 18 ··· Diode 19-26 ..... Diode driving means (inductance) 600 ..

Claims (13)

[Claims] 1. A static magnetic field generating means for applying a uniform static magnetic field and a gradient magnetic field generating means for generating a gradient magnetic field having different intensities depending on positions are used together with a high frequency magnetic field for causing a nuclear magnetic resonance phenomenon in a subject. Irradiate the subject and /
Alternatively, a high-frequency coil for detecting a nuclear magnetic resonance signal generated in the subject by irradiation, comprising a plurality of conductors and a plurality of capacitances constituting a plurality of resonators resonating at a predetermined frequency, of the plurality of conductors A high-frequency coil comprising a plurality of switch means connected to at least a part of the plurality of resonators to selectively activate one of the plurality of resonators and deactivate the other resonator. 2. A static magnetic field generating means for applying a uniform static magnetic field and a gradient magnetic field generating means for generating a gradient magnetic field having different intensities depending on positions are used to generate a high frequency magnetic field for causing a nuclear magnetic resonance phenomenon in a subject. Irradiate the subject and /
Or a high-frequency coil for detecting a nuclear magnetic resonance signal generated in the subject by irradiation, wherein a plurality of ring-shaped conductors, a plurality of linear conductors coupling the respective ring-shaped conductors, a ring-shaped conductor and / or a wire A plurality of ring-shaped conductors or a part thereof and a line conductor connecting the two ring-shaped conductors or a part thereof. A high-frequency coil, comprising switch means for electrically disconnecting a part of the ring-shaped conductor and / or the linear conductor from the resonator so that the resonator is in an operating state. 3. The switch means includes a diode connected in series to the ring-shaped conductor and / or the linear conductor,
The high frequency coil according to claim 1 or 2, comprising a diode driving means for supplying power to the diode. 4. The switch means comprises an inductance connected in parallel with the capacitance, a diode connected in series with the inductance, and a diode driving means for feeding the diode, and the capacitance connected in parallel and the diode. The inductance forms a resonance circuit that resonates at the same resonance frequency as the resonator when the diode is turned on.
The described high frequency coil. 5. The diode comprises a set of diodes to which respective anodes are connected, and the diode driving means supplies a positive voltage to a connection portion of the set of diodes,
The high frequency coil according to claim 3, wherein a negative voltage is supplied to each cathode side. 6. The capacitance of claim 1 or 2, wherein the capacitance comprises means for tuning the resonator to a desired frequency when one of the plurality of resonators is activated. High frequency coil. 7. The high frequency coil according to claim 1, further comprising a plurality of power supply means for supplying power to the high frequency coil. 8. The high frequency coil according to claim 2, wherein at least one of the ring-shaped conductors has a shape deformed corresponding to the shape of the subject. 9. A high-frequency coil for irradiating and receiving a high-frequency signal, wherein the resonator structure at the time of irradiation and the resonator structure at the time of reception are different from each other. 10. A static magnetic field generating means for applying a uniform static magnetic field to a subject, and a gradient magnetic field generating means for generating a gradient magnetic field having different intensities depending on positions.
A magnetic resonance inspection apparatus comprising: the high-frequency coil as described in the above item. 11. The magnetic resonance examination apparatus according to claim 10, further comprising control means for independently controlling power supply to each of the switch means provided in said high frequency coil. 12. A display means for displaying on / off states of a ring-shaped conductor, a line-shaped conductor, and a diode connected to these conductors of the high-frequency coil, and comprising selection means for turning on or off an arbitrary diode. The magnetic resonance inspection apparatus according to claim 10 or 11, characterized in that. 13. The magnetic resonance examination apparatus according to claim 10, further comprising display means for displaying a coil configuration determined by turning on or off the diode.