JP6163553B2 - High frequency coil and magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (MRI) technique, and more particularly to a resonance frequency adjustment technique for a high-frequency coil.

  The MRI apparatus is a medical diagnostic imaging apparatus that causes magnetic resonance to occur in a nuclear spin in an arbitrary cross section that crosses an examination target, and obtains a tomographic image in the cross section from a generated nuclear magnetic resonance signal. When a high-frequency magnetic field is irradiated through a high-frequency coil while applying a gradient magnetic field to a subject placed in a static magnetic field, a nuclear spin in the subject, for example, a nuclear spin of a hydrogen atom is excited, and the excited nuclear spin When the phase returns to an equilibrium state, a circularly polarized magnetic field is generated as a nuclear magnetic resonance signal. In the MRI apparatus, this nuclear magnetic resonance signal is detected by a high-frequency coil, and signal processing is performed to image the distribution of hydrogen nuclei in the living body.

  The MRI apparatus is called a hamburger type or a tunnel type depending on the shape of a magnet that generates a static magnetic field. Among these, tunnel-type MRI apparatuses have been increasing in popularity in recent years, can provide high-quality images, and have become popular. In this tunnel type MRI apparatus, as a high-frequency coil, for example, a birdcage type coil (see, for example, Patent Document 1), a TEM coil having a pipe pattern in a pipe shape (for example, see Non-Patent Document 1), a partial cylindrical type coil ( For example, Patent Document 2) is used.

  In the tunnel type MRI apparatus, the examination space in which the subject is arranged is determined by the inner diameter of the high frequency coil arranged inside the magnet. It is desirable that the examination space is as large as possible in order to increase the comfort during examination and to provide a space for installing treatment equipment. However, in the birdcage type coil, since the resonance frequency depends on the inner diameter of the coil, it becomes difficult to adjust the resonance frequency so that it resonates at a high frequency while keeping the inner diameter large as the resonance frequency set with increasing magnetic field increases. ing. In this respect, the TEM coil and the partial cylindrical coil are resonated by generating capacitive coupling between the high-frequency shield and the coil pattern, so that the resonance frequency does not depend on the inner diameter of the coil. Therefore, there is no restriction like a birdcage type coil.

  By the way, in the high frequency coil of the MRI apparatus, it is essential to adjust the resonance frequency at the time of installation or maintenance according to the magnetic field strength unique to the apparatus. In the case of a pipe-shaped TEM coil, for example, a coaxial line is formed by inserting a dielectric and a bar-shaped conductor inside the pipe-shaped coil pattern, and the capacity generated in the coaxial line is changed by moving the bar-shaped conductor. (For example, refer nonpatent literature 1). As another method for changing the capacitance, a method using a trimmer capacitor can be easily considered.

U.S. Pat. No. 4,916,418 International Publication No. 2012/023385

J. et al. T. T. Vaughan et al., “High frequency volume coils for clinical magnetic resonance magnetic resonance and imaging in the field of magnetic resonance imaging and spectroscopy in the field of magnetic resonance imaging and spectroscopy.” 32, p. 206-218

  In an MRI apparatus, in order to obtain sufficient irradiation intensity, a high voltage of several kV may be applied to a high-frequency coil. At that time, it is necessary to avoid the occurrence of discharge in the high frequency coil. In order to guarantee a withstand voltage against the power of the electromagnetic wave to be irradiated, it is necessary to secure a distance greater than the maximum distance (hereinafter referred to as the maximum discharge distance) at which discharge occurs between conductors that cause capacitive coupling. When the coil pattern is a pipe-shaped TEM coil, a thickness larger than three times the maximum discharge distance is required due to its structure.

  Further, since the trimmer capacitor uses a screw, there is a backlash and hysteresis of capacitance change occurs in the rotation direction. Therefore, it is difficult to adjust the capacity. Furthermore, a high-voltage trimmer capacitor having a large variable capacitance is expensive and large in size. Therefore, there is a limit to the inspection space that can be secured while maintaining insulation. In order to avoid this, if a trimmer capacitor is disposed outside the tunnel of the MRI apparatus, the circuit configuration becomes complicated, which hinders the design of a high-frequency coil that realizes a uniform irradiation intensity distribution.

  Thus, if the function of adjusting the resonance frequency is added to the high frequency coil, the inspection space is sacrificed accordingly.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of adjusting a resonance frequency without sacrificing an inspection space in a high-frequency coil of a tunnel type MRI apparatus.

  The present invention includes a cylindrical high-frequency shield, a coil pattern disposed on a cylindrical virtual surface having the same central axis as that of the high-frequency shield, and a frequency adjusting member. The high-frequency coil is formed by the high-frequency shield and the coil pattern. A high-frequency coil of a tunnel type MRI apparatus that forms a resonance loop for determining the resonance frequency of the MRI apparatus is provided. The frequency adjusting member is disposed in a space between the high-frequency shield and the coil pattern so that the coupling capacitance between them can be adjusted, and thereby the resonance frequency of the resonance loop can be adjusted.

  Further, a resonance frequency of the high-frequency coil is provided using a frequency adjusting member disposed in a space between the high-frequency shield and the coil pattern provided in the high-frequency coil so that the coupling capacitance between the high-frequency shield and the coil pattern can be adjusted. A method for adjusting a resonance frequency of a high frequency coil for adjusting the frequency is provided.

  According to the present invention, in the tunnel type MRI apparatus, the resonance frequency of the high frequency coil of the tunnel type MRI apparatus can be adjusted without sacrificing the inspection space.

It is an external view of the MRI apparatus of 1st embodiment. It is a block diagram which shows schematic structure of the MRI apparatus of 1st embodiment. It is explanatory drawing for demonstrating the connection relation of the high frequency coil of 1st embodiment, a high frequency signal distribution / synthesis | combination device, a transmission / reception switching device, a transmitter, and a receiver. (A) And (b) is explanatory drawing explaining the structure of the frequency adjustment member in a coaxial TEM coil. It is explanatory drawing for demonstrating the structure of the high frequency coil of 1st embodiment, (a) is the figure which looked at the high frequency coil from the central-axis direction, (b) is a perspective view of a high frequency coil. , (C) is a perspective view of a part of the high-frequency coil. (A) is explanatory drawing for demonstrating arrangement | positioning and a motion of the frequency adjustment member in 1 resonance loop of the high frequency coil of 1st embodiment, (b) is the frequency adjustment member of 1st embodiment. It is explanatory drawing for demonstrating the shape of this, (c) is explanatory drawing for demonstrating arrangement | positioning of the frequency adjustment member of 1st embodiment. (A)-(d) is explanatory drawing for demonstrating the positional relationship of the frequency adjustment member of 1st embodiment, and a coil pattern (coil conductor). It is explanatory drawing for demonstrating the resonant frequency change of the resonant loop according to the movement of the frequency adjustment member of 1st embodiment. It is explanatory drawing for demonstrating the other example of the moving direction of the frequency adjustment member of 1st embodiment. It is explanatory drawing for demonstrating the modification of the frequency adjustment member of 1st embodiment. (A) to (d) is an explanatory view for explaining a modification of the frequency adjusting member of the first embodiment. It is explanatory drawing for demonstrating the modification of the frequency adjustment member of 1st embodiment. It is explanatory drawing for demonstrating the modification of the high frequency coil of 1st embodiment. It is explanatory drawing for demonstrating the shape of the frequency adjustment member of the modification of the high frequency coil of 1st embodiment. It is explanatory drawing for demonstrating the mode of the movement of the frequency adjustment member of the modification of the high frequency coil of 1st embodiment. It is a block diagram which shows schematic structure of the MRI apparatus of 2nd embodiment. It is explanatory drawing for demonstrating the connection relation of the high frequency coil of 2nd embodiment, a transmission / reception switching device, a transmitter, and a receiver. It is explanatory drawing for demonstrating the structure of the high frequency coil of 2nd embodiment. It is explanatory drawing for demonstrating the structure of the partial cylindrical coil of the high frequency coil of 2nd embodiment, (a) is the figure seen from the central-axis direction, (b) is a perspective view. It is a block diagram which shows schematic structure of the modification of the MRI apparatus of 1st and 2nd embodiment.

<< First Embodiment >>
Hereinafter, a first embodiment of the present invention will be described. In all the drawings for explaining the embodiments of the present invention, the same reference numerals are given to the parts having the same functions unless otherwise specified, and the repeated explanation thereof is omitted.

<Device configuration>
First, the overall configuration of the MRI apparatus of this embodiment will be described. FIG. 1 is an external view of the MRI apparatus of the present embodiment. In the drawing, the z-axis direction of the coordinate system 900 is the static magnetic field direction. The MRI apparatus 100 of the present embodiment includes a static magnetic field forming unit 110 that forms a static magnetic field in a space (hereinafter referred to as an examination space) in which the subject 101 is disposed, and a table 120. The static magnetic field forming unit 110 uses a horizontal magnetic field type, for example, a superconducting magnet. The subject 101 is inserted into the examination space in the tunnel formed by the static magnetic field forming unit 110 while being laid on the table 120 and imaged. In the following description, the direction of the static magnetic field is the z direction, the direction orthogonal to the z direction on the surface of the table 120 is the x direction, and the direction orthogonal to the table surface is the y direction.

FIG. 2 is a block diagram showing a schematic configuration of the MRI apparatus 100 of the present embodiment. The same elements as those in FIG. 1 are denoted by the same reference numerals. In this figure, 920 represents the direction of the static magnetic field (B ₀ ).

  In addition to the static magnetic field forming unit 110 and the table 120 described above, the MRI apparatus 100 according to the present embodiment transmits a high-frequency magnetic field to the examination space via a transmission / reception coil and a gradient magnetic field application unit that applies a gradient magnetic field to the examination space. In addition, a transmission / reception unit that receives a nuclear magnetic resonance signal generated from the subject 101 via a transmission / reception coil, and a control unit that controls operations of the gradient magnetic field application unit, the high-frequency magnetic field transmission unit, and the signal reception unit are provided. Furthermore, you may provide the shim part which adjusts a static magnetic field uniformity.

  The gradient magnetic field application unit includes a gradient magnetic field coil 130 and a gradient magnetic field power supply 131. The gradient coil 130 applies a gradient magnetic field to the examination space by a gradient magnetic field control current supplied from the gradient magnetic field power supply 131.

  The shim unit is configured by a shim coil 140 and a shim power supply 141. The shim coil 140 applies a shim magnetic field to the examination space by a shim control current supplied from the shim power supply 141.

  The transmission / reception unit includes a transmission / reception coil 150, a transmission / reception switch 151 that switches on / off of a high-frequency signal in accordance with transmission and reception timings, a transmitter 152, a receiver 153, and a high-frequency signal distributor / synthesizer 154. .

  The transmission / reception coil 150 is connected to two transmission / reception switches 151 via a high-frequency signal distributor / synthesizer 154, and the transmission / reception switch 151 is connected to the transmitter 152 and the receiver 153, respectively. The high-frequency signal for high-frequency magnetic field irradiation is applied to the transmission / reception coil 150 through the transmission / reception switch 151 and the high-frequency signal distributor / synthesizer 154, and the subject 101 is irradiated with the high-frequency magnetic field. The nuclear magnetic resonance signal generated from the subject 101 by the irradiated high frequency magnetic field is detected by the transmission / reception coil 150, and the detected signal passes through the high frequency signal distributor / synthesizer 154 and transmission / reception switch 151, and is received by the receiver 153. Are amplified and detected. The signal detected by the receiver 153 is transmitted to the control unit via an A / D converter (not shown).

  In the transmission / reception coil 150 of the present embodiment, a transmission coil that generates a high-frequency magnetic field and a reception coil that receives a signal from the subject 101 may be provided separately or may be shared by a single coil. Hereinafter, in this embodiment, a case where a single coil is also used will be described as an example. The detailed configuration of the transmission / reception coil 150 will be described later.

  The control unit includes a computer 170 and a sequencer 160. Further, a display device 171 and a storage device 172 are connected to the computer 170.

  The computer 170 controls the operation of the entire MRI apparatus 100 and performs signal processing such as image reconstruction on the received signal. The result is stored in the storage device 172 and displayed on the display device 171. The operation is controlled by issuing an instruction to the sequencer 160 in accordance with a pulse sequence stored in the storage device 172 in advance. The storage device 172 also stores measurement conditions used when the computer 170 instructs the sequencer 160.

  In accordance with an instruction from the computer 170, the sequencer 160 instructs each device so that each device operates at a predetermined timing and intensity. Specifically, a command is sent to the gradient magnetic field power supply 131, the shim power supply 141, the transmission / reception switch 151, the receiver 153, and the transmitter 152. Further, the magnetic resonance frequency used as a reference for detection in the receiver 153 is set by the sequencer 160.

  The transmission / reception coil 150 of this embodiment is demonstrated. FIG. 3 is an explanatory diagram for explaining a connection relationship among the high-frequency coil 200 used as the transmission / reception coil 150, the high-frequency signal distributor / synthesizer 154, the transmission / reception switch 151, the transmitter 152, and the receiver 153. The high-frequency signal distributor / synthesizer 154 includes a QD hybrid 181 and two 0-180 degree distributor / synthesizers as shown in FIG. The two 0-180 degree distribution / synthesis circuits are divided into a first 0-180 degree distribution / synthesis circuit (first 0-180 degree distribution / synthesis circuit) 182 and a second 0-180 degree distribution / synthesis circuit, respectively. (Second 0-180 degree distribution / combination circuit) 183.

  The QD hybrid 181 is a circuit with two inputs and two outputs. When there is one input signal, the signal is divided into two signals having a signal waveform phase difference of 90 degrees and output, and there are two input signals. The phase of one signal is shifted by 90 degrees and synthesized with the other signal, and the synthesized signal is output. Further, the first 0-180 degree distribution / synthesis circuit 182 and the second 0-180 degree distribution / synthesis circuit 183 function to distribute one high-frequency signal to two high-frequency signals having a signal waveform phase difference of 180 degrees. And a function of synthesizing and outputting two high-frequency signals after shifting one phase by 180 degrees.

  The transmitter 152 and the receiver 153 are each connected to the QD hybrid 181 via the transmission / reception switch 151. Two outputs of the QD hybrid 181 are connected to inputs of a first 0-180 degree distribution / combination circuit 182 and a second 0-180 degree distribution / combination circuit 183, respectively. The two outputs of the first 0-180 degree distribution / combination circuit 182 are connected to two opposing first feeding points 184, respectively. The two outputs of the second 0-180 degree distribution / combination circuit 183 are respectively connected to two second feed points 185 arranged at 90 degrees with respect to the central axis 910 from the two first feed points 184. The The high frequency coil 200 will be described later.

  The transmission / reception switch 151 is ON / OFF controlled in accordance with an instruction from the sequencer 160. The instruction is that the transmission / reception switch 151 connected to the transmitter 152 is turned on when the high-frequency signal is irradiated, and the transmission / reception switch 151 connected to the receiver 153 is turned on when the nuclear magnetic resonance signal is detected. To be made.

<High frequency coil>
In the present embodiment, the configuration of the high-frequency coil 200 is devised, and in the tunnel-type MRI apparatus 100, the transmission / reception coil 150 that can easily adjust the resonance frequency without sacrificing the size of the examination space into which the subject 101 enters is provided. Realize.

  Prior to the description of the high-frequency coil 200 of the present embodiment, a configuration (frequency adjustment unit) related to a frequency adjustment function of a coaxial TEM coil whose coil pattern is a pipe shape will be described. FIG. 4A is an external view of the coaxial TEM coil 800. As shown in the figure, the coaxial TEM coil 800 is provided with a plurality of pipe-like coil patterns 810 having rod-like conductors 820 inside at a predetermined distance from the high-frequency shield 830.

  FIG. 4B shows a cut surface of the coaxial TEM coil 800. 4B is a view showing a cross section passing through the center of the coaxial line of the coaxial TEM coil 800, and is a cross-sectional view taken along line AA of FIG. The coaxial TEM coil 800 is arranged in the order of a pipe-shaped coil pattern part 810A, a rod-shaped conductor 820, a pipe-shaped coil pattern part 810B, and a high-frequency shield 830 from the side closer to the center axis of the tunnel. Here, the high-frequency shield 830 and the rod-shaped conductor 820 are at the same potential.

  As described above, a maximum discharge distance must be ensured between conductors having different potentials. Therefore, in the coaxial TEM coil 800, the high-frequency shield 830 and the rod-shaped conductor 820 must ensure the maximum discharge distance between the pipe-shaped coil pattern 810, respectively. That is, an interval 840A between the pipe-shaped coil pattern portion 810A and the rod-shaped conductor 820, an interval 840B between the rod-shaped conductor 820 and the pipe-shaped coil pattern 810B, an interval 840C between the pipe-shaped coil pattern portion 810B and the high-frequency shield 830, The three intervals must be larger than the maximum discharge distance. Therefore, the thickness (840A + 840B + 840C) of the conventional coaxial TEM coil 800 is larger than three times the maximum discharge distance. Therefore, the coaxial TEM coil 800 cannot expand the inspection space beyond this limit.

  Next, details of the high-frequency coil 200 used as the transmission / reception coil 150 in this embodiment will be described.

  FIG. 5A to FIG. 6C are diagrams for explaining the configuration of the high-frequency coil 200 of the present embodiment. 5A is a view of the high-frequency coil 200 viewed from the z-axis direction, FIG. 5B is a perspective view of the high-frequency coil 200, and FIG. It is a perspective view of a part. FIGS. 6A and 6C are enlarged views of a part of the high-frequency coil 200. FIG. In each figure, the z direction is the direction of the static magnetic field 920 as described above. Moreover, in order to avoid complication, in each figure, structures other than the description object are suitably abbreviate | omitted or shown transparently.

  As shown in these drawings, the high-frequency coil 200 includes a cylindrical high-frequency shield 210, a coil pattern 220, and a frequency adjusting member 240 that adjusts the resonance frequency of the high-frequency coil 200. The coil pattern 220 includes a high-frequency coil. A plurality of coil conductors 230 are disposed substantially parallel to the central axis 910 at intervals on a cylindrical virtual plane having the same shield 210 and central axis 910, and the virtual plane includes the high-frequency shield. 210, the frequency adjusting member 240 is configured by at least one of a conductor and a dielectric, and is coupled to the space between the high frequency shield 210 and the coil pattern 220 in the space between the high frequency shield 210 and the coil pattern 220. The capacity is arranged to be adjustable. The subject 101 enters a cylindrical examination space on the central axis 910 side with respect to the coil pattern 220.

  Hereinafter, in the present embodiment, the high-frequency shield 210 is cylindrical, and the virtual surface on which the coil conductor 230 is disposed is a cylindrical surface. FIG. 5A shows an example in which 16 coil conductors 230 are provided. However, the number of coil conductors 230 is not limited to this. For example, it may be 8 or 24.

  As shown in FIG. 5B, the coil conductor 230 is a plate-shaped conductor, and is arranged so that a main plane (hereinafter referred to as a plate surface) of the plate-shaped conductor is in contact with the virtual surface. It arrange | positions at equal intervals in the circumferential direction of a surface. In addition, since the virtual plane and the high frequency shield 210 have a coaxial cylindrical shape, the coil pattern 220 is arranged with a certain distance from the high frequency shield 210. The length of each coil conductor 230 in the z direction is determined by the design of the sensitivity region in the z direction. However, it is shorter than the length of the high frequency shield 210 in the z direction. The difference between the lengths in the z direction is at least the length in the z direction of a frequency adjusting member 240 described later.

  Further, as shown in FIGS. 5A and 5C, each coil conductor 230 is connected to the high-frequency shield 210 via the first capacitor 250. Two first capacitors 250 are disposed inside the coil conductor 230 in the z direction. A resonance loop 260 is formed by the coil conductor 230, the high-frequency shield, and the two first capacitors.

  The value of the first capacitor 250 is adjusted so that the high-frequency coil 200 resonates at the same frequency as the resonance frequency of the MRI apparatus 100. Here, the inductance of the resonance loop 260 is omitted. Further, in the present embodiment, the first capacitor 250 is disposed inside the end portion of the coil conductor 230 by a predetermined distance that is larger than the length in the z direction of a frequency adjusting member 240 described later.

  In FIG. 5C, FIG. 6A, and FIG. 6C, the frequency adjustment member 240 is hatched. The frequency adjustment member 240 is disposed in a space between the high frequency shield 210 and the coil conductor 230 as shown in FIG.

  In the present embodiment, the resonance frequency of the resonance loop 260 is adjusted by moving the frequency adjustment member 240. That is, the frequency adjusting member 240 is disposed so that the position of the high-frequency shield 210 and the coil pattern 220 (coil conductor 230) relative to at least one of the high-frequency shield 210 and the coil pattern 220 can be changed. For this reason, the frequency adjustment member 240 is disposed at a position where it can be easily moved, for example, at the end of the coil conductor 230 in the z direction, as shown in FIG. Here, a case where one coil conductor 230 is arranged is illustrated. However, the frequency adjusting member 240 may not be arranged for all the coil conductors 230. FIG. 6A is a view of the resonance loop 260 as seen in a cross section passing through the central axis 910 and the first capacitor 250. The resonance loop 260 of interest is depicted from the x direction.

  FIG. 6B is a three-dimensional depiction of the frequency adjustment member 240. The frequency adjusting member 240 is configured by at least one of a conductor and a dielectric as described above. Here, the case where it comprises with a conductor is illustrated. Its shape is a partial cylindrical shape as depicted in FIG.

  The frequency adjusting member 240 has an outer diameter equal to the inner diameter of the high-frequency shield 210 and an inner diameter larger than the diameter of the virtual surface on which the coil conductor is disposed. It has a shape cut out at a corner in parallel to the central axis 910 and cut to a predetermined length in the direction of the central axis 910. The center angle at the time of cutting is an angle at which the frequency adjusting member 240 arranged in the adjacent coil conductor 230 does not interfere and a desired variable capacitance can be realized.

  In the present embodiment, the frequency adjusting member 240 is disposed so as to be in contact with the inner surface of the high-frequency shield 210 as shown in FIG. Thus, the frequency adjusting member 240 is connected to the high frequency shield 210 and a low resistance, and is disposed so as to be capacitively coupled to the coil pattern 220 (coil conductor 230). Accordingly, the difference between the inner diameter of the hollow cylinder from which the frequency adjusting member 240 is cut out and the diameter of the imaginary plane is set to be equal to or greater than the maximum discharge distance.

  The capacitive coupling destination of the frequency adjustment member 240 is not limited to the coil pattern 220 (coil conductor 230). It may be capacitively coupled to the high frequency shield 210. That is, the frequency adjusting member 240 of the present embodiment may be disposed so that either one of the high-frequency shield 210 and the coil pattern 220 (coil conductor 230) is connected to a low resistance, and the other is capacitively coupled.

  When the frequency adjusting member 240 is connected to the coil conductor 230 with a low resistance, the frequency adjusting member 240 has an outer diameter smaller than the inner diameter of the high-frequency shield 210 by a predetermined amount, and the inner diameter is a virtual position where the coil conductor 230 is disposed. A high-frequency shield 210 equal to the surface and a hollow cylinder coaxial with the virtual surface are cut out and created.

<Frequency adjustment method>
Next, the frequency adjustment method of the high frequency coil 200 by the frequency adjustment member 240 of the present embodiment will be described.

The high-frequency coil 200 in this embodiment includes the same number of resonance loops 260 as the coil conductors 230. For example, in the example of FIG. 5A, it is composed of 16 resonance loops 260. Each resonance loop 260 is connected through a high-frequency shield 210. For this reason, the resonance frequency of the high frequency coil 200 can be adjusted by changing at least one resonance frequency of the resonance loop 260. The resonance frequency f _R of each resonance loop 260 is expressed by the following equation (1) using the inductance L and capacitance C of the resonance loop 260.

A coupling capacitance generated between the frequency adjusting member 240 and the coil conductor 230 is defined as C _f . Since the resonance loop 260 is a parallel resonance circuit in which the first capacitor 250 and the coupling capacitance C _f are connected in parallel, the coupling capacitance C _f additionally contributes to the capacitance C in the equation (1).

In general, the capacitance C _pp of a parallel plate capacitor (capacitor) is expressed by the following equation (2).
C _pp = ε × S _pp / d _pp (2)
Here, S _pp is the area of the electrode plates, d _pp is the distance between the electrode plates, and ε is the dielectric constant of the material filled between the electrode plates. From equation (2), the capacitance of the capacitor changes due to changes in the area and distance of the electrode plates constituting the capacitor, the dielectric constant of the substance between the electrode plates, and the like.

  In the present embodiment, by changing the area S (hereinafter referred to as the overlapping area) where the frequency adjustment member 240 and the coil conductor 230 overlap, the coupling capacitance between the frequency adjustment member 240 and the coil conductor 230 is changed, and resonance is achieved. The resonance frequency of the loop 260 is changed. As shown in FIG. 6A, the area S is changed by moving the frequency adjusting member 240 in the z direction in a state where the frequency adjusting member 240 is disposed in contact with the inner surface of the high frequency shield 210.

  FIGS. 7A to 7D are views of the coil pattern 220 (coil conductor 230) and the frequency adjusting member 240 as viewed from the direction of the central axis 910. FIG. Here, the focused frequency adjusting member 240 shown in FIG. 5A is depicted from the y direction. Here, only the inner cylindrical surface of one coil conductor 230 and the frequency adjusting member 240 constituting the coil pattern 220 is depicted.

By moving the frequency adjusting member 240 in the z direction while maintaining physical contact with the high frequency shield 210, the overlapping area with the coil conductor 230 changes. As a result, the coupling capacitance C _f changes, and accordingly, the resonance frequency f _R of the resonance loop 260 of Expression (1) also changes. Therefore, the resonance frequency f _R of the resonance loop 260 can be adjusted by moving the frequency adjustment member 240. As a result, the resonance frequency of the high-frequency coil 200 configured by the resonance loop 260 can be adjusted.

FIG. 8 is a graph 710 showing a change in the resonance frequency f _R of the resonance loop 260 with respect to the position z _R of the frequency adjusting member 240. In the graph 710, (a) to (d) correspond to the position of the frequency adjusting member 240 in FIGS. 7 (a) to 7 (d), respectively. The position z _R is the frequency adjustment member 240 in each of FIGS. 7A to 7D with reference to the right end position of the coil pattern 220 (coil conductor 230) in FIG. 7A. This is the position of the right end.

Strictly speaking, the coupling capacitance between the frequency adjusting member 240 and the coil pattern 220 (coil conductor 230) is not determined solely by their overlapping areas. For example, as shown in FIG. 7C and FIG. 7D, even when the overlapping area is 0, capacitive coupling occurs not a little depending on the distance between the frequency adjusting member 240 and the coil pattern 220. And the coupling capacity varies depending on the distance between the two. However, when the overlapping area is dominant to the capacitance C _f as in the present embodiment, the resonance frequency f _R changes abruptly while the overlapping occurs, as shown by a graph 710 in FIG.

Here, a simulation result of calculating a change in the resonance frequency of the resonance loop 260 is shown. For simplicity, it focuses only on the one of the resonant loop 260, a frequency adjusting member 240, in a state where no state and inserted inserts a capacitor of the capacitance C _f, and compares the resonance frequency.

The model used for the calculation is as follows. The resonance loop 260 was a rectangular loop having a long side of 500 mm and a short side of 10 mm, and the width of the coil conductor 230 constituting the long side was 50 mm. The capacity of the two first capacitors 250 connecting the coil conductor 230 and the high frequency shield 210 is 27 pF. The first capacitor 250 is disposed on each of the two short sides of the resonance loop 260. The capacitor of inserting capacitor C _f is a parallel plate capacitor the air layer is 3mm in electrode plates with 50mm square.

In such resonant loop 260, when no insert a capacitor of the capacitance C _f, the impedance peak was present in the frequency 131MHz. On the other hand, inserting a capacitor of the capacitance C _f, the equation (2), the capacitance C _f becomes 7.38PF. The capacitance C _f, is added in parallel to one of the short sides. Thus, in the resonance loop 260, a capacitance of 27 pF is arranged on one of the short sides and a capacitance of 34.38 pF is arranged on the other side. In this state, the resonance loop 260 has an impedance peak at a frequency of 124 MHz.

  From the above, it was shown that the resonance frequency of the resonance loop 260 is reduced by inserting the frequency adjusting member 240.

  In the present embodiment, when the high frequency coil 200 is manufactured, attached to the MRI apparatus 100, attached to the site of the MRI apparatus 100, or maintained, the frequency adjusting member 240 is used to adjust the resonance frequency of the high frequency coil 200. Make adjustments.

  As described above, the high-frequency coil 200 of the present embodiment includes the cylindrical high-frequency shield 210, the coil pattern 220, and the frequency adjusting member 240, and the coil pattern 220 includes the high-frequency shield 210 and the central axis. A plurality of coil conductors 230 arranged in parallel to the central axis at intervals on a cylindrical virtual surface having the same frequency, the virtual surface being disposed inside the high-frequency shield, and the frequency adjusting member 240 is composed of at least one of a conductor and a dielectric, and is disposed in a space between the high-frequency shield 210 and the coil pattern 220 so that the coupling capacitance between the high-frequency shield 210 and the coil pattern 220 can be adjusted. Is done.

  Thus, in the high frequency coil 200 of the present embodiment, the frequency adjusting member 240 that adjusts the resonance frequency is disposed between the high frequency shield 210 and the coil pattern 220 (coil conductor 230). Therefore, the examination space is not compressed by the frequency adjusting member 240.

  The coil conductor 230 is a plate-like conductor, and the plate-like conductor is disposed so that the plate surface is in contact with the virtual surface. Thus, according to the present embodiment, the coupling capacity with the frequency adjusting member 240 is increased by making each coil conductor 230 constituting the coil pattern 220 into a plate shape, and the adjustment width of the resonance frequency of the high-frequency coil 200 is increased. I can take it big.

  The frequency adjusting member 240 is disposed so that the relative position between at least one of the high-frequency shield 210 and the coil pattern 220 can be changed, and the area overlapping the coil conductor 230 can be changed by changing the relative position. May be. For this reason, in the high frequency coil 200 of this embodiment, the resonance frequency can be adjusted only by moving the frequency adjusting member 240 so that the overlapping area changes.

  Further, at this time, in the high-frequency coil 200 of the present embodiment, the frequency adjusting member 240 is connected to one of the high-frequency shield 210 and the coil pattern 220 with a low resistance and is capacitively coupled to the other. May be.

  Therefore, the high-frequency coil 200 of the present embodiment only needs to ensure a maximum discharge distance between the high-frequency shield 210 and the coil pattern 220 that are capacitively coupled. That is, in the high frequency coil 200 of the present embodiment, the frequency can be adjusted by a simple method using the space between the coil pattern 220 and the high frequency shield 210 without increasing the distance between them. For this reason, compared with the conventional coaxial TEM coil which provides a frequency adjustment member inside a coil pattern, the distance between the outer diameter of the high frequency coil 200 and an internal diameter can be shortened. Therefore, the high-frequency coil 200 of the present embodiment is a high-frequency coil having a larger inner diameter than the conventional coaxial TEM coil, and accordingly, a wide inspection space can be secured.

  The high-frequency shield 210 and the coil pattern 220 are connected via at least two first capacitors 250, and each of the first capacitors 250 is predetermined from the end in the central axis direction of the plate conductor. The frequency adjusting member 240 may change the relative position on the outer side in the central axis direction from the position where the first capacitor 250 is disposed.

  As described above, in the high-frequency coil 200 of the present embodiment, the first capacitor 250 is connected to the inner side from the end of the coil pattern 220 by at least the length of the frequency adjustment member 240 in the z direction. For this reason, even when the width of the coil pattern 220 is occupied by the connection of the plurality of first capacitors 250, the frequency adjusting member 240 is moved from the connection position to the end portion, and the resonance frequency of the resonance loop 260 is set. Can be adjusted. Therefore, adjustment of the resonance frequency is easy, and there are few restrictions on the design of the high-frequency coil 200.

  Further, since the resonance frequency is adjusted by moving the frequency adjusting member 240, the change rate of the capacitance with respect to the insertion distance of the frequency adjusting member 240 can be adjusted by selecting the distance between the frequency adjusting member 240 and the coil pattern 220. it can. From this point, it can be said that adjustment is easy.

  Further, as described above, in the present embodiment, the coupling capacitance is adjusted by the frequency adjusting member 240 by changing the overlapping area of the frequency adjusting member 240 and the coil conductor 230. The overlapping area is changed by moving the frequency adjusting member 240 in the z direction. At this time, the frequency adjusting member 240 is moved while maintaining physical contact with the high frequency shield 210. Therefore, in this embodiment, the distance between the frequency adjusting member 240 and the coil pattern 220 is constant during capacity adjustment, and the thickness of the air layer therebetween is maintained. Therefore, in the high frequency coil 200 of the present embodiment, the withstand voltage does not change during frequency adjustment.

  For example, when the dielectric breakdown voltage is 2.9 kV / mm, the dielectric breakdown voltage is 8.7 kV if the air layer is 3 mm. That is, by providing a space of at least 3 mm between the coil conductor 230 and the frequency adjusting member 240, the frequency adjusting member 240 of the present embodiment is smaller in space and higher than a general trimmer capacitor (for example, about 7 kV). A variable capacitor with a withstand voltage is realized. Note that 2.9 kV / mm is a dielectric breakdown voltage of the air layer sandwiched between parallel plates at 127 MHz, which is the resonance frequency of hydrogen, which is the main imaging nuclide in the MRI apparatus.

  As described above, the high frequency coil 200 of the present embodiment can adjust the resonance frequency with a simple configuration without sacrificing the inspection space. For this reason, it is possible to easily perform adjustments according to the installation environment, such as during installation, maintenance, and other MRI apparatuses arranged in the vicinity.

  In a tunnel type MRI apparatus, if the tunnel diameter is small, the examination space inside the tunnel MRI apparatus is also narrowed, which may give a great stress to a patient as a subject. It is particularly stressful for fat people and those with claustrophobia. In addition, a tight posture may be imposed even when photographing with the joint bent or photographing with the shoulder or elbow as the center of the magnetic field. However, according to the present embodiment, it is possible to provide a high-frequency coil that can ensure a wider inspection space than in the past. Therefore, the stress given to these patients can be reduced.

  Furthermore, according to the present embodiment, since a wide examination space can be provided, it is possible to secure a space for installing a treatment device inside the MRI apparatus. Therefore, it becomes easy to install a contrast agent injector device and a non-magnetic treatment device to perform precise diagnosis and treatment.

  Further, the high frequency coil of this embodiment can adjust the resonance frequency without using a trimmer capacitor. And the screw is not used for position adjustment of the frequency adjustment member 240 used for adjustment of the resonance frequency. For this reason, unlike the case where adjustment is performed using a trimmer capacitor, the inspection space is not narrowed, the design becomes difficult, and complicated adjustment in consideration of the hysteresis of capacitance change is not required.

  Further, in this embodiment, the overlapping area of the frequency adjusting member 240 and the coil conductor 230 is changed, the coupling capacitance between them is changed, and the resonance frequency of the high frequency coil 200 is adjusted. The change in the coupling capacity between the two depends on the amount of change in the overlapping area. Further, the amount of change in the overlapping area depends on the area of the frequency adjusting member 240 facing the coil conductor 230. Since the frequency adjustment member 240 of the present embodiment has the above-described configuration, the area of the frequency adjustment member 240 can be changed without narrowing the inspection space. Therefore, according to this embodiment, the adjustment range of the resonance frequency can be easily changed while maintaining the withstand voltage and the inspection space.

<Modification of moving direction>
The moving direction of the frequency adjusting member 240 is not limited to the z direction. As long as the overlapping area with the coil conductor 230 can be changed while maintaining physical contact with the high-frequency shield 210, it may be moved in any direction. For example, as shown in FIG. 9, the z direction may be a vertical direction, that is, the circumferential direction of the high-frequency coil 200 (the x direction in the resonance loop 260 focused here). In this case, the overlapping area between the coil conductor 230 and the frequency adjusting member 240 is changed by moving the frequency adjusting member 240 between the coil conductors 230.

  In the present embodiment, since the outer diameter of the frequency adjusting member 240 is configured to be equal to the inner diameter of the high frequency shield 210, the frequency adjusting member 240 is circumferentially maintained in physical contact with the high frequency shield 210. Can move. Further, since the hollow cylindrical cylinder that is coaxial with the coil pattern 220 is cut out, the coil pattern 220 and the frequency adjusting member 240 can be moved in any direction while the frequency adjusting member 240 is kept in contact with the high frequency shield 210. The vertical distance of is constant. Accordingly, the withstand voltage and the inspection space are maintained.

<Configuration of frequency adjusting member, modification of shape>
In the present embodiment, the case where the frequency adjustment member 240 is configured by a uniform conductor has been described as an example, but the material and configuration of the frequency adjustment member 240 are not limited to this.

  For example, the content of the conductor constituting the frequency adjusting member 240 may be a cavity. Further, if the inner cylindrical surface and the outer cylindrical surface are connected and the shape can be maintained, the four surfaces that support the inner cylindrical surface and the outer cylindrical surface may be omitted. For example, it may be connected in an I shape with one thick pillar at the center between the inner cylindrical surface and the outer cylindrical surface. Alternatively, the shape of the frequency adjusting member 240 may be made of a material that can be easily shaped, such as an epoxy resin, and the periphery thereof may be covered with a thin conductor such as a copper tape. With this configuration, the frequency adjusting member 240 can be manufactured at a low cost without losing the effects described in the above embodiment.

  Further, the frequency adjusting member 240 of the present embodiment is formed by cutting the hollow cylinder at a predetermined center angle and cutting it to a predetermined length, but the shape is not limited to the shape obtained by this method.

  For example, in the above-described embodiment, the center angle at the time of cutting is determined so that the frequency adjusting member 240 arranged in the adjacent coil conductor 230 does not interfere, but the center angle to be cut out is made larger and the adjacent frequency adjusting member is 240 may be connected.

  Further, the hollow cylinder may not be cut out in parallel with the central axis 910 of the cylinder. For example, you may cut out so that the projection surface of an inner cylindrical surface may become a triangle. With this configuration, the amount of change in the coupling capacity with respect to the movement distance in the z direction can be increased.

  Moreover, in the said embodiment, although the height of the frequency adjustment member 240 is constant, you may change height. By providing a change in height in the direction of moving the frequency adjusting member 240 during adjustment, the amount of change in the coupling capacitance relative to the amount of movement can be changed.

  Even when the height is changed, an interval of at least the maximum discharge distance is secured between the frequency adjusting member 240 and the coil pattern 220 (coil conductor 230).

  Furthermore, the shape of the frequency adjusting member 240 may not be a partial cylindrical shape. For example, even in the case of a rectangular parallelepiped, a part of the high frequency shield 210 is in physical contact with the coil pattern 220 (coil conductor 230) and a necessary capacity may be formed at a distance that does not discharge.

<Modification of material of frequency adjustment member>
In the above embodiment, the frequency adjusting member 240 has been described by taking as an example the case of being made of a conductor, but the material is not limited to a conductor. For example, you may be comprised with the dielectric material. An example of the frequency adjusting member 241 in this case is shown in FIG. The shape is the same as that of the frequency adjusting member 240 of the above embodiment. The dielectric used is, for example, a material having a dielectric constant larger than that of air, such as a fluororesin.

  The frequency adjusting member 241 may include a dielectric, and may be configured to change a dielectric constant between the high frequency shield 210 and the coil pattern 220 using the dielectric. In this case, by changing the amount of insertion of the frequency adjusting member 241 between the coil conductor 230 and the high frequency shield 210, the coupling capacitance between the two is changed. This corresponds to changing the dielectric constant ε in the above equation (2). As a result, the resonance frequency of the resonance loop 260 changes, and the resonance frequency of the high-frequency coil 200 changes.

  The method of changing the amount of insertion of the frequency adjusting member 241 is the same as in the above embodiment. That is, the frequency adjusting member 241 is moved so as to change the area overlapping with the coil conductor 230 while maintaining physical contact with either the high-frequency shield 210 or the coil conductor 230.

  According to this modification, since the frequency adjustment member 241 does not include a conductor, the coil pattern 220 (coil conductor 230) and the high-frequency shield 210 are short-circuited in addition to the effect obtained by the frequency adjustment member 240 formed of a conductor. Risk can be eliminated. Therefore, the frequency adjustment member 241 and any one of the coil pattern 220 and the high-frequency shield 210 need not be separated by the maximum discharge distance, and a wider inspection space can be secured.

  In this modification, a fluororesin is used as the dielectric, but the present invention is not limited to this. Any dielectric material can be used. Depending on the dielectric constant of the dielectric used for the frequency adjusting member 241, the rate of change of the coupling capacitance by changing the overlapping area can be changed. Therefore, the material is selected according to the change range to be realized.

  The frequency adjustment member 241 has the same shape as the frequency adjustment member 240, but the shape is not limited thereto. The frequency adjusting member 241 may have any shape as long as the variable capacitance due to the insertion of the frequency adjusting member 241 exerts a desired frequency change and fits between the coil pattern 220 and the high frequency shield 210. The coil pattern 220 and the high-frequency shield 210 may be in contact with each other.

  In addition, when the frequency adjusting member 241 is formed of a dielectric, when changing the coupling capacitance between the coil pattern 220 and the high frequency shield, the frequency adjusting member 241 is not moved, and the frequency created with a material having a different dielectric constant is used. By replacing with the adjusting member 241, the dielectric constant between them may be changed.

  Further, the frequency adjusting member may be a combination of a dielectric and a conductor. Examples of the frequency adjusting member 242 in this case are shown in FIGS. 11 (a) to 11 (d).

  The frequency adjusting member 242 includes a conductor part 242A and a dielectric part 242B. The overall shape of the frequency adjustment member 242 is the same as that of the frequency adjustment member 240 of the above embodiment. However, the inner diameter of the hollow cylinder from which the frequency adjusting member 242 is cut out is the same as the virtual plane on which the coil conductor 230 is disposed. That is, the frequency adjusting member 242 is disposed so as to fill the gap between the high frequency shield 210 and the coil pattern 220.

  11A to 11D, the frequency adjusting member 242 has a multilayer structure, and the number (ratio) of the conductor portion 242A and the dielectric portion 242B and the arrangement thereof. Change the order.

  FIG. 11A and FIG. 11B are examples in which the dielectric portion 242B is disposed on the coil pattern 220 side and capacitive coupling is performed between the frequency adjusting member 242 and the coil pattern 220 (coil conductor 230). FIG. 11C shows an example in which the dielectric portion 242B is disposed on the high frequency shield 210 side, and the high frequency shield 210 and the frequency adjusting member 242 are capacitively coupled.

  FIG. 11D shows an example in which dielectric portions 242B are arranged on both sides of the coil pattern 220 and the high-frequency shield 210. In this case, the frequency adjusting member 242 is capacitively coupled to both the coil pattern 220 (coil conductor 230) and the high frequency shield 210. With this configuration, the voltage applied to the coupling capacitance can be dispersed, and the risk of discharge can be reduced.

The change in the number and arrangement means that the distance between the conductor portion 242A of the frequency adjusting member 242 and the coil pattern 220 (in the direction of the central axis) is changed and the amount of dielectric between the two is changed. That is, this change corresponds to the change of the dielectric constant ε and the change of the distance d _{pp in} the above formula (2). As a result, the coupling capacitance generated between the two changes. Due to the capacitance change, the resonance frequency of the resonance loop 260 changes, and the resonance frequency of the high-frequency coil 200 can be adjusted.

  At this time, the coupling capacitance may be changed by replacing the dielectric part 242B of the frequency adjusting member 242 with a dielectric having a different dielectric constant.

  According to this modification, the resonance frequency of the high-frequency coil 200 is adjusted by changing the layer configuration of the frequency adjustment member 242 having a multilayer structure. Therefore, a space for moving the frequency adjusting member 242 is not necessary. Therefore, even when the moving space of the frequency adjusting member 242 is limited and it is difficult to change the overlapping area, the resonance frequency of the high-frequency coil 200 can be easily adjusted without sacrificing the size of the inspection space. it can.

  Further, by using a dielectric having a higher withstand voltage than the air layer, for example, a fluororesin, as the dielectric portion 242B of the frequency adjusting member 242, the withstand voltage between the high frequency shield 210 and the coil pattern 220 is increased. Can do. When the withstand voltage is increased, the maximum discharge distance is decreased. Therefore, according to the frequency adjusting member 242, the thickness of the high-frequency coil 200 can be further reduced, and the inspection space can be increased.

<Modification of frequency adjustment member connection>
Moreover, in the said embodiment, although the frequency adjustment member 240 is comprised so that it may be connected to at least one of the high frequency shield 210 or the coil pattern 220 by low resistance, it is not limited to this structure. A configuration example in this case is shown in FIG.

  In the present modification, as shown in the drawing, the frequency adjusting member 243 includes a member portion 243A and a flexible conductor portion 243B. The surface of the member portion 243A with respect to the coil pattern 220 is the same as that of the frequency adjustment member 240. The flexible conductor portion 243B is joined to the member portion 243A and the high-frequency shield 210 with solder. At this time, the member portion 243A is configured to be movable in the z direction while maintaining a vertical distance from the coil pattern 220. The flexible conductor portion 243B is made of, for example, a copper wire. Continuity between the member portion 243A and the high-frequency shield 210 is maintained with respect to movement in the z direction.

  The frequency adjustment member 243 is electrically connected to the high frequency shield 210 at the surface facing the coil pattern 220. For this reason, it functions similarly to the frequency adjustment member 240. Here, since the member portion 243A of the frequency adjusting member 243 and the high frequency shield 210 have the same potential, it is not necessary to increase the maximum discharge distance.

  According to this modification, since the connection can be made more securely than physical contact, in addition to the effects brought about by the frequency adjusting member 240, contact failure and contact resistance change can be prevented.

  In addition, the frequency adjustment member 240 arrange | positioned with respect to all the coil conductors 230 may not be the same shape, a raw material, and a structure. The shape described in the above embodiment and any shape, material, and configuration described in each modification may be used.

<Modification of the first capacitor>
In the present embodiment, the first capacitor 250 is connected inside the end portion of the coil pattern 220 (coil conductor 230) in order to secure the moving space of the frequency adjusting member 240, but is not limited to this configuration. .

  For example, the connection position of the first capacitor 250 may be the end of the coil conductor 230 as long as the width of the frequency adjustment member 240 can be secured without occupying the entire width of the coil conductor 230. Thereby, the freedom degree of high frequency coil 200 manufacture increases.

  In the present embodiment, the number of the first capacitors 250 is two, but the number is not limited to two. It is sufficient that the resonance frequency of the resonance loop 260 can be adjusted to a desired value. Therefore, if the necessary capacity can be provided by the frequency adjusting member 240, the first capacitor 250 may be omitted. Further, instead of using the first capacitor 250, the space between the coil pattern 220 (coil conductor 230) and the high-frequency shield 210 may be filled with a dielectric to cause capacitive coupling.

<Modification of coil pattern shape>
In the above-described embodiment, the case where the plurality of coil conductors 230 constituting the coil pattern 220 are arranged on a virtual surface having a cylindrical shape coaxial with the high-frequency shield 210 has been described as an example. The shape is not limited to this. For example, an elliptic cylinder shape may be sufficient.

  FIG. 13 shows the arrangement of the high-frequency shield 210, the coil pattern 224, the first capacitor 250, and the subject 101 of the high-frequency coil 204 in this case. Also in this modification, the frequency adjusting member 244 is provided for at least one of the plurality of coil conductors 234 constituting the coil pattern 224. Here, in order to avoid complexity, the frequency adjusting member 244 is not described.

  The high-frequency shield 210 has a cylindrical shape and is the same as that in the above embodiment. The coil pattern 224 includes a plurality of coil conductors 234 arranged on the virtual elliptic cylinder surface having the same high-frequency shield 210 as the central axis 910 and having a major axis in the x direction and a minor axis in the y direction. The coil conductor 234 is disposed substantially parallel to the direction of the central axis 910 as in the above embodiment. The length in the z direction is the same as in the above embodiment.

  The first capacitor 250 is arranged so as to connect the high-frequency shield 210 and the coil pattern 224 on the inner side by a predetermined distance from the end of the coil conductor 234 as in the above embodiment.

  A frequency adjustment member 244 of this modification is shown in FIG. As the shape of the coil pattern 224 changes, the shape of the frequency adjustment member 244 also changes. That is, the frequency adjusting member 244 of this modification has a cylindrical surface shape whose outer surface has an outer diameter equal to the inner diameter of the high-frequency shield 210, and the inner surface has a hollow cylinder that maintains the same distance as a virtual surface on which the coil conductor 234 is disposed. Is cut out at a predetermined central angle and cut into a predetermined length in the direction of the central axis 910.

  In this case, the material of the frequency adjusting member 244 may be a conductor only, a conductor hollow, a dielectric, or a combination of a conductor and a dielectric, as in the above embodiment.

  Further, the resonance frequency of the resonance loop 264 is changed by a method of moving the frequency adjusting member 244 in the z direction, changing the amount of dielectric, or changing the dielectric constant, as in the above embodiment.

  Also in this modification, the frequency adjustment member 244 may be moved in a direction other than the z direction, and the overlapping area between the frequency adjustment member 244 and the coil conductor 234 may be changed. That is, in the case of this modification, even if the frequency adjustment member 244 is moved in the z direction, the distance from the coil pattern 224 does not change. Therefore, the coupling capacitance with the coil pattern 224 can be changed by changing the overlapping area with the coil pattern 224 by this movement.

  However, in the case of this modification, when the frequency adjustment member 244 is moved in a direction other than the z direction, the distance between the frequency adjustment member 244 and the coil pattern 224 changes due to the movement.

  FIG. 15 shows a case where the frequency adjusting member 244 is moved in the circumferential direction of the high frequency shield 210 as an example. The frequency adjusting member 244A before movement indicated by a solid line in the drawing is moved in the circumferential direction toward the short axis side of the ellipse. The frequency adjusting member 244B after movement is indicated by a dotted line. As shown in the figure, the distance between the frequency adjustment member 244B after movement and the coil pattern 224 (coil conductor 234) is compared with the distance between the frequency adjustment member 244A and coil pattern 224 (coil conductor 234) before movement. growing. Therefore, in the case of this modification, the coupling capacity can be reduced by moving the frequency adjusting member 244 in the circumferential direction toward the short axis side of the ellipse. Therefore, compared with the case where the coil conductor 230 is arrange | positioned on the cylindrical virtual surface, the freedom degree of adjustment increases and it can change a coupling capacity more efficiently. Depending on the distance between the frequency adjusting member 244 and the coil pattern 224 (coil conductor 234) and the curvature of the ellipse, the frequency adjusting member 244 can be adjusted coarsely when moved in the z direction and finely adjusted when moved in the circumferential direction.

  On the other hand, when the frequency adjusting member 244 is moved in the circumferential direction to the long axis side, the distance from the coil pattern 224 (coil conductor 234) is reduced. Therefore, a stopper 274 and the like are provided on the long axis side so that the distance between the frequency adjusting member 244 and the coil pattern 224 (coil conductor 234) does not become the maximum discharge distance or less. This prevents discharge from occurring.

  As described above, even if the shape of the virtual surface on which the coil conductor 234 is arranged is an elliptical cylinder, by changing the shape of the frequency adjusting member 244 according to the shape, the high-frequency coil is the same as in the case of the high-frequency coil 200. The resonance frequency of 204 can be changed. Therefore, the same effect as the above embodiment can be obtained.

  Furthermore, when the shape of the virtual surface on which the coil conductor 234 is disposed is an elliptic cylinder, the examination space into which the subject 101 enters is also an elliptic cylinder as shown in FIG. In particular, when the shape is an elliptical cylinder having a long axis in the horizontal direction, the shape of the examination space is similar to the cross-sectional shape of the subject 101, and brings openness and comfort to the subject 101. For this reason, in this modification, in addition to the effect of the high-frequency coil 200, a more comfortable examination space can be provided for the subject 101.

  Furthermore, in the high-frequency coil 204 of this modification, when the frequency adjusting member 244 is moved in the circumferential direction, the distance between the frequency adjusting member 244 and the coil pattern 224 (coil conductor 234) also changes, so that it is more efficient. Thus, the coupling capacity can be changed.

  In the present modification as well, the shape of each frequency adjusting member 244 is not limited to the above shape as long as the distance between adjacent conductors is not less than the maximum discharge distance, as in the above embodiment. The size may be adjusted as long as the capacity can be adjusted within a desired range. Further, the shape of each frequency adjusting member 244 provided in each coil conductor 234 may be different.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described. The high-frequency coil of this embodiment includes a plurality of channels in which the transmission / reception coil can independently control the amplitude and phase.

  The MRI apparatus of the present embodiment has basically the same configuration as the MRI apparatus 100 of the first embodiment. However, the configuration of the high frequency coil is different. Hereinafter, the present embodiment will be described focusing on the configuration different from the first embodiment. Also in this embodiment, the direction of the static magnetic field 920 generated by the horizontal magnetic field type static magnetic field forming unit 110 is the z direction of the coordinate system 900. Hereinafter, in the present embodiment, a case where the transmission / reception coil includes four channels (4ch) will be described as an example. The number of channels is not limited to 4 channels. For example, there may be 8 channels.

<Device configuration>
FIG. 16 is a block diagram showing a schematic configuration of the MRI apparatus 105 of the present embodiment. The MRI apparatus 105 of the present embodiment has basically the same configuration as the MRI apparatus 100 of the first embodiment. However, since the high-frequency coil 205 of the present embodiment used as the transmission / reception coil 150 has four channels and drives each channel independently, instead of the transmission / reception switch 151, the transmitter 152, and the receiver 153, Each includes a 4ch transmission / reception switch 155, a 4ch transmitter 156, and a 4ch receiver 157. The high-frequency signal distributor / synthesizer 154 is not provided.

  FIG. 17 is an explanatory diagram for explaining a connection relationship between the high-frequency coil 205 of the present embodiment, the 4ch transmission / reception switch 155, the 4ch transmitter 156, and the 4ch receiver 157 used as the transmission / reception coil 150. The high-frequency coil 205 of this embodiment includes four partial cylindrical coils 280 that can transmit and receive a high-frequency signal independently. Details of the partial cylindrical coil 280 will be described later. Each partial cylindrical coil 280 includes a feeding point 186.

  The 4ch transmitter 156 has a function of independently controlling the amplitude and phase of the four signals, and is a circuit that outputs four high-frequency signals. The 4ch receiver 157 is a circuit for A / D converting four high-frequency signals, and the output is sent to the computer 170. The 4ch transmission / reception switching unit 155 is a circuit having a function of switching signal lines of 4 inputs and 4 outputs. The 4ch transmission / reception switch 155 supplies the high frequency signal supplied from the 4ch transmitter 156 to the feeding point of each partial cylindrical coil 280. In addition, a high-frequency signal output from the feeding point of each partial cylindrical coil 280 is output to the 4ch receiver 157.

<High frequency coil>
18 and 19 are diagrams for explaining details of the configuration of the high-frequency coil 205 of the present embodiment. FIG. 18 is a view of the high-frequency coil 205 as viewed from the z direction. Here, the z direction is the direction of the static magnetic field 920 as described above. FIG. 19A illustrates the partial cylindrical coil 280 from the z direction, and FIG. 19B is a perspective view of the partial cylindrical coil 280.

  The high-frequency coil 205 of this embodiment is composed of four partial cylindrical coils 280. Each partial cylindrical coil is spaced from an adjacent partial cylindrical coil 280, and includes a plane defined by the x axis and the z axis in FIG. 18 including the central axis 910, and a plane defined by the y axis and the x axis. On the other hand, they are arranged in plane symmetry. Each partial cylindrical coil 280 of this embodiment is driven as one channel of the high-frequency coil 205.

  Each partial cylindrical coil 280 includes a coil pattern 225, a connection conductor 282, a first capacitor 250, a partial cylindrical conductor 281, and a frequency adjustment member 245. In FIG. 18, the frequency adjustment member 245 is omitted to avoid the complexity of the drawing. The partial cylindrical conductor 281 is disposed so as to contact the inner surface of the high-frequency shield 215. For this reason, the partial cylindrical conductor 281 can be regarded as being integral with the high-frequency shield 215.

  Therefore, the high-frequency coil 205 of this embodiment includes a cylindrical high-frequency shield 215, a coil pattern 225, and a frequency adjustment member 245 that adjusts the resonance frequency of the high-frequency coil 205, and the coil pattern 225 includes the high-frequency shield 215. And a plurality of coil conductors 235 arranged substantially parallel to the central axis 910 at intervals on a cylindrical virtual surface having the same central axis 910 as the virtual surface, The frequency adjusting member 245 is disposed on the inner side, and is configured by at least one of a conductor and a dielectric. A coupling capacitance between the high frequency shield 215 and the coil pattern 225 is provided in a space between the high frequency shield 215 and the coil pattern 225. Adjustable arrangement.

  Further, the connection conductor 282 connects the adjacent partial cylindrical coils 280. A second capacitor 283 is inserted into the connection conductor 282 between two adjacent partial cylindrical coils 280. The value of the second capacitor 283 is adjusted so that magnetic coupling does not occur between two adjacent partial cylindrical coils 280.

  Thus, the coil pattern 225 of this embodiment is separated so that the high-frequency coil 200 functions as a multi-channel coil that is not coupled to each other.

  Also in this embodiment, the subject 101 enters the cylindrical examination space on the central axis 910 side with respect to the coil pattern 225. Moreover, the coil conductor 235 which comprises the coil pattern 225 is a plate-shaped conductor, and is arrange | positioned so that the plate | board surface of a plate-shaped conductor may contact | connect a virtual surface. In addition, the coil conductors 235 are arranged at equal intervals in the circumferential direction of the virtual plane. The length of each coil conductor 235 in the z direction is the same as that of the coil conductor 230 of the first embodiment. FIG. 18 illustrates a case where each partial cylindrical coil 280 includes five coil conductors 235, respectively. However, the number of coil conductors 235 is not limited to this. For example, 10 or 1 may be sufficient.

  In this embodiment, the high-frequency shield 215 has an elliptic cylinder shape, and the virtual plane on which the coil conductor 235 is arranged is described as an example of an elliptic cylinder surface. In the present embodiment, the distance between the high-frequency shield 215 and the virtual plane on which the coil conductor 235 is arranged decreases from the central axis 910 toward the outside along the x direction. As in the first embodiment, these shapes may both be cylindrical, the high frequency shield 215 may be cylindrical, and the virtual plane may be elliptical.

  Also in this embodiment, two first capacitors 250 are inserted. As shown in FIG. 19B, the two first capacitors 250 are respectively disposed on the inner side in the z direction by a predetermined distance from both end portions of each coil conductor 235 in the z direction. Thus, the resonance loop 265 is configured by the coil conductor 235, the two first capacitors 250, and the partial cylindrical conductor 281. In the example of FIG. 18, each partial cylindrical coil 280 has five coil conductors 235. For this reason, each partial cylindrical coil 280 is provided with five resonance loops.

  Note that the first capacitor 250 is adjusted such that the resonance frequency of the partial cylindrical coil 280 formed of the plurality of resonance loops 265 matches the resonance frequency of the nuclide that is to be imaged by the MRI apparatus 105.

  When a high frequency signal is applied to the partial cylindrical coil 280, a high frequency current flows through each resonance loop 265. At this time, since each coil pattern 225 is short-circuited to both ends of the adjacent coil pattern 225 by the connection conductor 282, all potentials generated at the end portions of the coil patterns 225 are the same. Therefore, the partial cylindrical coil 280 resonates in a mode in which the high-frequency currents flowing through all the resonance loops 265 have the same phase (hereinafter referred to as an in-phase mode).

  As shown in FIG. 19B, the frequency adjusting member 245 of the present embodiment is disposed outside the first capacitor 250 on one side in the z direction. In this figure, the case where three frequency adjustment members 245 are arrange | positioned at each partial cylindrical coil 280 is illustrated. Further, as shown in FIG. 19A, the frequency adjusting member 245 is connected to the high frequency shield 215 (partial cylindrical conductor 281) with a low resistance as in the case of the frequency adjusting member of the first embodiment. 225 (coil conductor 235) has a constant distance.

  Also in the present embodiment, the frequency adjusting member 245 is disposed so that the relative position with respect to at least one of the high-frequency shield 215 and the coil pattern 225 can be changed, as in the first embodiment. For example, it is arranged to be movable in the z direction, and the area overlapping with the coil conductor 235 can be changed. Also in this embodiment, by changing the overlapping area, the coupling capacitance with the coil conductor 235 is changed, and the resonance frequency of the resonance loop 265 is changed. Thereby, the resonance frequency of the partial cylindrical coil 280 is changed. In the present embodiment, the resonance frequencies of the partial cylindrical coils 280 are matched so that the high frequency coil 205 resonates as a whole at the same frequency.

  The moving direction when changing the overlapping area is not limited to the z direction. That is, the overlapping area can be changed by moving the frequency adjusting member 245 in a predetermined direction in a state where the frequency adjusting member 245 is connected to either the high frequency shield 215 or the coil pattern 225 with a low resistance, as in the first embodiment. That's fine.

  However, when the virtual plane on which the high-frequency shield 215 and the coil conductor 235 are arranged is an ellipse as in the present embodiment, the frequency adjustment member 245 and the coil conductor 235 or the high-frequency shield are present when there is a major axis direction component in the moving direction. The distance from 215 should not be less than the maximum discharge distance.

  As described above, the high-frequency coil 205 of the MRI apparatus 105 of the present embodiment includes the cylindrical high-frequency shield 215, the coil pattern 225, and the frequency adjustment member 245, and the coil pattern 225 includes the high-frequency shield. 215 includes a plurality of coil conductors 235 arranged in parallel with the central axis at intervals on a cylindrical virtual surface having the same central axis as 215, and the virtual surface is disposed inside the high-frequency shield 215. The frequency adjusting member 245 includes at least one of a conductor and a dielectric, and a coupling capacitance between the high-frequency shield 215 and the coil pattern 225 is formed in a space between the high-frequency shield 215 and the coil pattern 225. Are arranged to be adjustable.

  Therefore, according to the present embodiment, as in the first embodiment, in the tunnel type MRI apparatus, the resonance of the high frequency coil that resonates by generating capacitive coupling between the high frequency shield and the coil pattern while ensuring a wide inspection space. The frequency can be adjusted.

  The coil pattern 225 is separated so that the high-frequency coil 205 functions as a coil of a plurality of channels that are not coupled to each other. The four partial cylindrical coils 280 constituted by the coil pattern 225 and the partial cylindrical conductor 281 on the high-frequency shield 215 can independently adjust the phase and strength.

  Therefore, according to this embodiment, in addition to the effects of the high-frequency coil 200 of the first embodiment, the irradiation intensity and phase from each partial cylindrical coil 280 are adjusted to make the irradiation magnetic field uniform to the examination space. Can be improved. In addition, the specific absorption rate of electromagnetic waves with respect to the subject 101 can be reduced. In addition, selective excitation or the like can be realized as the number of channels increases.

  Further, as described above, the resonance frequency of each partial cylindrical coil 280 is adjusted so as to coincide with the resonance frequency of the nuclide to be imaged by the MRI apparatus 105. However, since the resonance frequency of each partial cylindrical coil 280 varies depending on various factors such as the inductance of the coil pattern 225, the value of the first capacitor 250, and the connection position, there is a mismatch in resonance frequency due to manufacturing errors.

  As described above, in the present embodiment, the resonance frequency of each partial cylindrical coil can be adjusted by the frequency adjusting member 245. Therefore, since the resonance frequency of each partial cylindrical coil 280 can be adjusted to a desired value, it can be easily adjusted even when there is a mismatch in the resonance frequency. Therefore, according to the present embodiment, it is possible to realize a high-frequency coil 205 having a plurality of channels with high resonance frequency matching.

  Further, as illustrated in the present embodiment, when the virtual plane on which the high-frequency shield 215 and the coil conductor 235 are arranged is an elliptic cylinder shape, as shown in FIG. 18, the examination space into which the subject 101 enters is also an elliptic cylinder shape. Become. In particular, when the shape is an elliptical cylinder having a long axis in the horizontal direction, the shape of the examination space is similar to the cross-sectional shape of the subject 101, and brings openness and comfort to the subject 101. For this reason, according to this embodiment, in addition to the effect which the high frequency coil 200 has, the test | inspection space comfortable for the subject 101 can be provided.

  In the present embodiment, the number of frequency adjusting members 245 is three for each partial cylindrical coil 280, but the number is not limited thereto. If the variable amount of the resonance frequency of the partial cylindrical coil 280 is sufficient, for example, the variable amount is 2 MHz with respect to the resonance frequency of 127 MHz, and the mode in which the partial cylindrical coil 280 resonates is within the range in which the common mode is maintained, It suffices that at least one partial cylindrical coil 280 is arranged. For example, one coil conductor 235 may be disposed as in the first embodiment.

  In the present embodiment, various modifications are possible as in the first embodiment.

  In the present embodiment, the case where both ends of all the coil patterns 225 are connected by the connection conductor 282 has been described as an example, but the present invention is not limited to this configuration. The coil pattern 225 in each partial cylindrical coil 280 should just become the same electric potential, for example, only one edge part may be connected.

  In this embodiment, only the first capacitor and the second capacitor are used. However, the present invention is not limited to this. For example, a capacitor may be inserted into the coil pattern 225 or the connection conductor 282 to prevent eddy currents.

  The four partial cylindrical coils 280 can independently adjust the phase and intensity in the 4ch transmitter 156. Further, the adjacent partial coil 280 is decoupled by the second capacitor 283 so as not to be magnetically coupled. For this reason, if a high-frequency signal having the same intensity with the phase shifted by 90 degrees is input to the four partial cylindrical coils 280, the same QD irradiation as in the first embodiment can be performed.

  In each said embodiment, although the high frequency coil was used as the transmission / reception coil 150, it is not limited to this. For example, in a transmitter coil and receiver coil separation type MRI apparatus, the transmitter coil may be used as a transmitter coil that only transmits RF pulses. In that case, for example, a detuning circuit is provided, and the high frequency coil is switched on and off by this detuning circuit.

  FIG. 20 is a block diagram showing a schematic configuration of the transmission coil and reception coil separation type MRI apparatus 106. The MRI apparatus 106 is the same as any one of the MRI apparatuses of the above embodiments except for the configuration related to the transmission of RF pulses and the reception of NMR signals.

  The configuration relating to the RF pulse transmission and the reception of the nuclear magnetic resonance signal includes the transmitter 152 and the receiver 153 of the first embodiment, and the detuning circuit driving device 158.

  However, in this modification, the transmitter 152 is directly connected to the transmission coil 191. The receiver 153 is directly connected to the receiving coil 192. The detuning circuit driving device 158 includes the transmission coil 191 and the transmission coil 191 according to the timing at which the transmitter 152 transmits a high-frequency signal to the transmission coil 191 and the timing at which the receiver 153 receives the signal detected by the reception coil 192, respectively. The receiving coil 192 is brought into a tuning state and a detuning state.

  Thus, by providing the transmission coil 191 and the reception coil 192 separately, the reception coil 192 can be disposed near the subject 101. Thereby, a signal can be received at a closer position, and the signal-to-noise ratio can be improved.

  Note that the modifications described in the above embodiments may be used in combination.

  DESCRIPTION OF SYMBOLS 100: MRI apparatus, 101: Subject, 105: MRI apparatus, 106: MRI apparatus, 110: Static magnetic field formation part, 120: Table, 130: Gradient magnetic field coil, 131: Gradient magnetic field power supply, 140: Shim coil, 141: Shim Power: 150: Transmission / reception coil, 151: Transmission / reception switch, 152: Transmitter, 153: Receiver, 154: High frequency signal distributor / synthesizer, 155: 4ch transmission / reception switch, 156: 4ch transmitter, 157: 4ch receiver 158: Detuning circuit drive device, 160: Sequencer, 170: Computer, 171: Display device, 172: Storage device, 181: QD hybrid, 182: First 0-180 degree distribution / synthesis circuit, 183: Second 0 -180 degree distribution / combination circuit, 184: first feeding point, 185: second feeding point, 186: feeding point, 186: second feeding point 191: Transmitting coil 192: Reception coil 200: High frequency coil 204: High frequency coil 205: High frequency coil 210: High frequency shield 215: High frequency shield 220: Coil pattern 224: Coil pattern 225: Coil pattern , 230: Coil conductor, 234: Coil conductor, 235: Coil conductor, 240: Frequency adjustment member, 241: Frequency adjustment member, 242: Frequency adjustment member, 242A: Conductor part, 242B: Dielectric part, 243: Frequency adjustment member 243A: member portion, 243B: flexible conductor portion, 244: frequency adjustment member, 244A: frequency adjustment member, 244B: frequency adjustment member, 245: frequency adjustment member, 250: first capacitor, 260: resonance loop, 264: resonance Loop, 265: Resonant loop, 274: Su 280: Partial cylindrical coil, 281: Partial cylindrical conductor, 282: Connection conductor, 283: Second capacitor, 710: Graph, 800: Coaxial TEM coil, 810: Pipe-shaped coil pattern, 810A: Pipe-shaped coil Part of pattern, 810B: Part of pipe-shaped coil pattern, 820: Bar-shaped conductor, 830: High frequency shield, 840A: Interval, 840B: Interval, 840C: Interval, 900: Coordinate system, 910: Central axis, 920: Static magnetic field

Claims (13)

A cylindrical high-frequency shield,
Coil pattern,
A frequency adjusting member,
The coil pattern includes a plurality of coil conductors arranged in parallel to the central axis at intervals on a cylindrical virtual surface having the same central axis as the high-frequency shield,
The virtual surface is disposed inside the high-frequency shield,
The frequency adjusting member is composed of only a conductor or a combination of a conductor and a dielectric, and a coupling capacity between the high frequency shield and the coil pattern can be adjusted in a space between the high frequency shield and the coil pattern. And the high frequency coil characterized by being arrange | positioned so that a relative position with at least one of the said high frequency shield and the said coil pattern can be changed . The high frequency coil according to claim 1,
The coil conductor is a plate-shaped conductor,
The high frequency coil, wherein the plate-like conductor is arranged so that a main plane of the plate-like conductor is in contact with the virtual plane. The high frequency coil according to claim 1 ,
The high-frequency coil, wherein the frequency adjusting member is arranged so that an area overlapping the coil conductor can be changed. The high frequency coil according to claim 1 ,
The high-frequency coil, wherein the frequency adjusting member is arranged to be able to change a distance from at least one of the high-frequency shield and the coil pattern. The high frequency coil according to claim 1,
The frequency adjusting member includes a dielectric, and is configured to be capable of changing a dielectric constant between the high-frequency shield and the coil pattern by the dielectric. The high frequency coil according to claim 1,
The high-frequency coil, wherein the frequency adjusting member is arranged to be electrically connected to one of the high-frequency shield and the coil pattern, and to be capacitively coupled to the other. The high frequency coil according to claim 1,
The high frequency coil, wherein the frequency adjusting member is disposed so as to be capacitively coupled to the high frequency shield and the coil pattern. The high frequency coil according to claim 1 ,
The high frequency shield and the coil pattern are connected via at least two capacitors,
Each of the capacitors is disposed at a predetermined distance from an end of the coil conductor in the central axis direction,
The high-frequency coil according to claim 1, wherein the frequency adjusting member changes the relative position outside the capacitor in the central axis direction. The high frequency coil according to claim 1,
The high frequency coil, wherein the high frequency coil is separated so as to function as a coil of a plurality of channels that are not coupled to each other. The high frequency coil according to claim 1,
The high-frequency shield is cylindrical,
The high-frequency coil according to claim 1, wherein the virtual surface is one of a cylindrical surface and an elliptical cylindrical surface. The high frequency coil according to claim 1,
The high frequency shield has an elliptical cylindrical shape,
The high-frequency coil, wherein the virtual surface is an elliptical cylindrical surface. A static magnetic field forming unit that forms a static magnetic field in a space in which the subject is disposed;
A gradient magnetic field application unit for applying a gradient magnetic field to the space;
A high-frequency magnetic field transmitter that transmits a high-frequency magnetic field to the subject via a transmission coil;
A signal receiving unit for receiving a nuclear magnetic resonance signal generated from the subject via a receiving coil;
A control unit that controls operations of the gradient magnetic field application unit, the high-frequency magnetic field transmission unit, and the signal reception unit,
It said transmission coil, a magnetic resonance imaging apparatus characterized by claims 1 11 is a high frequency coil according to any one. A static magnetic field forming unit that forms a static magnetic field in a space in which the subject is disposed;
A gradient magnetic field application unit for applying a gradient magnetic field to the space;
A high-frequency magnetic field transmitter for transmitting a high-frequency magnetic field to the subject via a transmission / reception coil;
A signal receiving unit that receives a nuclear magnetic resonance signal generated from the subject via the transmitting and receiving coil;
A control unit that controls operations of the gradient magnetic field application unit, the high-frequency magnetic field transmission unit, and the signal reception unit,
The transceiver coil is a magnetic resonance imaging apparatus characterized by claims 1 11 is a high frequency coil according to any one.

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