JP4817966B2 - MRI apparatus and high frequency coil for MRI apparatus - Google Patents

Description

  The present invention relates to an MRI apparatus and a high-frequency coil for the MRI apparatus that enable imaging of an imaging target having a non-cylindrical shape.

  The magnetic resonance imaging (MRI) method is based on a magnetic resonance signal (MR signal) generated by exciting a nuclear spin of a living tissue placed in a static magnetic field with a high-frequency signal having the Larmor frequency. To reconstruct the image data. The MRI apparatus is an image diagnostic apparatus that obtains diagnostic information by the MRI method. The MRI apparatus can obtain not only anatomical information but also a lot of diagnostic information such as biochemical information and functional information. Therefore, the MRI apparatus has become indispensable in the field of diagnostic imaging today.

  In order to generate high-quality image data by the MRI apparatus, it is necessary to efficiently detect a weak MR signal generated in a living body, and many technical devices have been made for that purpose. Different types of high-frequency coils used for detecting MR signals are used depending on the direction of the static magnetic field. If the static magnetic field is horizontal, a saddle coil is used. When the static magnetic field is vertical, a solenoid coil is used. A high-frequency coil for transmitting a high-frequency signal and a high-frequency coil for receiving an MR signal may be provided separately. However, since the transmission timing and the reception timing are different, the same high-frequency coil is used. It is also possible to use it.

  On the other hand, a QD volume coil is known as a high-sensitivity high-frequency coil. The volume coil for the static magnetic field in the horizontal direction is generally a bird cage type. The bird cage type includes two end rings and at least four rods (elements). The rod is arranged in a state substantially parallel to the static magnetic field direction (horizontal direction), and both ends thereof are connected to the two end rings, respectively. In particular, when there are four rods, it is also called a slotted tube resonator. In such a volume coil, a cylindrical imaging region having a relatively uniform high-frequency magnetic field distribution is formed therein.

  By the way, when imaging an imaging target inside a birdcage type high frequency coil, it is desirable that each rod be as close to the surface of the imaging target as possible. However, when imaging an imaging target having a non-cylindrical shape such as a part including the lower leg and foot, a high-frequency coil having an inner diameter corresponding to the size of the foot must be used. Will leave. In such a situation, when a high-frequency coil is used as an irradiation coil, a larger transmission power is required than when a high-frequency coil having a smaller inner diameter is used. When a high frequency coil is used as a receiving coil, the S / N of the detected MR signal deteriorates.

  On the other hand, a method using a surface coil has been developed as a method for detecting MR signals with high sensitivity. However, the sensitivity distribution in the surface coil is usually non-uniform and correction thereof is not easy, and it is difficult to obtain good quality image data.

As a method for solving such problems, a cylindrical high-frequency coil 500 as shown in FIG. In the cylindrical high-frequency coil 500, the end ring 504 has an inner diameter corresponding to the thickness of the lower leg 501. A part of the rod 503 is bent outward in accordance with the shape of the foot 502. According to this cylindrical high-frequency coil 500, the rod 503 can be made to approach over the entire area of the lower leg 501 and the foot 502.
US Pat. No. 5,277,183

  However, in the cylindrical high-frequency coil 500, the spatial distribution of the high-frequency magnetic field formed by the current flowing through the rod 503 in the region formed by bending the rod 503 is non-uniform. The non-uniformity of the high frequency magnetic field affects the quality of the reconstructed image data.

  The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to detect MR signals generated in an imaging target having a non-cylindrical shape uniformly and with high sensitivity. is there.

  In order to achieve the above object, according to a first aspect of the present invention, in a high frequency coil for a magnetic resonance imaging apparatus, two end members made of a conductive material and arranged opposite to each other, and the conductive material are formed in a rod shape. A plurality of rod members each having both ends connected to the two end members, and an additional member having both ends connected to one of the rod members. The additional member is arranged so as to form a second imaging region outside the first imaging region formed by the end member and the rod member.

  In order to achieve the above object, according to a second aspect of the present invention, in a high-frequency coil for a magnetic resonance imaging apparatus, two end members made of a conductive material and disposed opposite to each other, and the conductive material are formed in a rod shape. And at least a plurality of rod members having both ends connected to the two end members, and a conductive member formed in a rod shape, and both ends connected to one of the rod members A member and an impedance element inserted into each of the plurality of rod members and the additional member, and the additional member is located outside a first imaging region formed by the end member and the rod member. Arranged to form a second imaging region.

  In order to achieve the above object, a third aspect of the present invention is a high frequency coil for a magnetic resonance imaging apparatus, wherein two end members made of a conductive material and arranged opposite to each other, and the conductive material are formed in a rod shape. It is formed by forming at least four rod members whose both ends are respectively connected to the two end members and a conductive member in a rod shape, and both ends are connected to one of the rod members. A second addition having a first addition member and a conductive member formed in a rod shape, both ends of which are connected to one of the rod members different from the connection of the first addition member. A first plane that is hypothesized so that the rod members are substantially parallel to each other and the first and second rod members of the rod members are opposed to each other. U The third and fourth rod members are substantially orthogonal to a second plane that is assumed to be two opposite sides, and the first and second additional members are connected to the first and third rod members, respectively. The first additional member is connected to each other, and the first additional member is crossed to form a first crossing portion, and the first additional member positioned between the first crossing portion and the first rod member is connected to each other. A third plane imaginary with a part and the first rod member as a side and a fourth plane imaginary with the remaining part of the first additional member as a side are directed in different directions, and The fourth plane is substantially parallel to the first plane, the second additional member is crossed so as to form a second crossing portion, and the second crossing portion and the third rod member are Virtually using a part of the second additional member and the third rod member located between the sides as a side The fifth plane and the sixth plane imaginary with the remaining part of the second additional member as a side are directed in different directions, and the sixth plane is substantially parallel to the second plane. It was.

  In order to achieve the above object, the fourth aspect of the present invention reconstructs image data based on MR signals radiated from an imaging target placed in a region where a static magnetic field, a gradient magnetic field, and a high frequency magnetic field are formed. In the magnetic resonance imaging apparatus, the high-frequency coil according to any one of the first to third inventions is used for at least one of forming the high-frequency magnetic field and detecting the MR signal.

  According to the present invention, an MR signal generated in an imaging object having a non-cylindrical shape can be detected uniformly and with high sensitivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The first feature of the present embodiment is that an additional imaging region is provided outside the cylindrical main imaging region by adding two extension rods to two rods included in a general birdcage type high-frequency coil. Is to form. The additional imaging region is suitable for imaging the toe portion of the foot, for example.

  The second feature of the present embodiment is that the high-frequency magnetic field formed in the main imaging region and the high-frequency magnetic field formed in the additional imaging region are made uniform by individually adjusting the high-frequency current flowing through the rod and the extension rod. There is to control.

  In the following, the case where the human lower leg and foot are the imaging target will be described, but the present invention is not limited to this and may be another imaging target.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus 100 in the present embodiment, and FIGS. 2 to 14 are diagrams for explaining a high-frequency coil.

  The MRI apparatus 100 includes a static magnetic field generation unit 1, a gradient magnetic field generation unit 2, a transmission / reception unit 3, a calculation / storage unit 4, a bed 5, an input unit 6, a display unit 7, and a control unit 8.

  The static magnetic field generation unit 1 includes a main magnet 11 and a static magnetic field power supply 12. For example, a superconducting magnet is used as the main magnet 11. The static magnetic field power supply 12 supplies a current to the main magnet 11. The main magnet 11 is operated by the current supplied from the static magnetic field power supply 12 and forms a strong static magnetic field around the subject 150.

  The gradient magnetic field generator 2 includes a gradient magnetic field coil unit 21 and a gradient magnetic field power supply 22. In the gradient magnetic field coil unit 21, three types of coils corresponding to the X, Y, and Z axes orthogonal to each other are combined. The gradient magnetic field power supply 22 individually supplies current to the three types of coils of the gradient magnetic field coil unit 21. The gradient magnetic field power supply 22 individually changes the current corresponding to each of the three types of coils in accordance with the control signal supplied from the control unit 8. Thereby, the gradient magnetic fields along the X, Y, and Z axes can be set to have arbitrary gradients. The gradient magnetic fields of the X, Y, and Z axes correspond to, for example, the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr, respectively. The gradient magnetic field Gs is used to arbitrarily determine an imaging cross section. The gradient magnetic field Ge is used to change the phase of the magnetic resonance signal in accordance with the spatial position. The gradient magnetic field Gr is used to change the frequency of the magnetic resonance signal in accordance with the spatial position. These gradient magnetic fields are superimposed on the static magnetic field formed by the main magnet 11.

  The transmission / reception unit 3 includes a high-frequency coil 31, a transmitter 32 and a receiver 33. The high frequency coil 31 receives a high frequency signal from the transmitter 32 and irradiates the subject 150 with an RF pulse. The high frequency coil 31 detects an MR signal radiated from the subject 150. The transmitter 32 includes a reference signal generator, a modulator, a power amplifier, and the like. The transmitter 32 generates the above-described high-frequency signal by modulating a reference signal having the same frequency as the magnetic resonance frequency (Larmor frequency) determined by the static magnetic field strength of the main magnet 11 with a selective excitation waveform. The MR signal detected by the high frequency coil 31 is input to the receiver 33. The receiver 33 performs A / D conversion after performing signal processing on the MR signal. The above signal processing includes intermediate frequency conversion, phase detection, filtering, and the like. The receiver 33 further includes a 90 ° phase shifter for performing phasing (phase alignment) on two MR signals whose phases detected by the high frequency coil 31 are different by 90 °.

  The calculation / storage unit 4 includes a high-speed calculation circuit 41 and a storage circuit 42. The high-speed arithmetic circuit 41 reconstructs the MR signal transmitted from the receiver 33 via the control unit 8 by two-dimensional Fourier transform, and generates real space image data. The storage circuit 42 includes an MR signal storage circuit 421 and an image data storage circuit 422. The MR signal storage circuit 421 stores the MR signal sent from the receiver 33. The image data storage circuit 422 stores the image data generated by the high speed arithmetic circuit 41.

  The bed 5 moves the subject 150 to an arbitrary position in the body axis direction in order to set a desired imaging position. The bed 5 can carry the subject 150 out of the main magnet 11 through an opening formed in the main magnet 11.

  The input unit 6 includes a console including various input devices such as a switch, a keyboard, or a mouse, and a display panel. The input unit 6 inputs various instructions and information designated by the operator. The instruction and information input by the input unit 6 include, for example, a patient ID, an instruction to start imaging, imaging conditions such as an imaging method and a pulse sequence, information on a display method, an instruction for moving the bed 5, and the like.

  The display unit 7 includes a display storage circuit, a conversion circuit, and a monitor. The image data stored in the image data storage circuit 422 is supplied to the display unit 7 by the control unit 8. Also, incidental information such as various characters and numbers input from the input unit 6 is supplied to the display unit 7 by the control unit 8. The display unit 7 combines the supplied image data and the accompanying information in a display storage circuit to generate display image data. The conversion circuit performs D / A conversion and television format conversion on the display image data to obtain an image signal. The monitor displays an image according to the image signal. As a monitor, a CRT or a liquid crystal display is used.

  The control unit 8 includes a main control circuit 81 and a sequence control circuit 82. The main control circuit 81 includes a CPU and a storage circuit, and controls the entire apparatus. The storage circuit of the main control circuit 81 stores information related to the imaging method, pulse sequence, image data display method, and the like input from the input unit 6. The CPU of the main control circuit 81 supplies pulse sequence information based on information input at the input unit 6 to the sequence control circuit 82. The pulse sequence information represents, for example, the magnitude, application time, application timing, and the like of the high-frequency current applied to the gradient magnetic field coil unit 21 and the high-frequency coil 31. The sequence control circuit 82 includes a CPU and a storage circuit. The storage circuit of the sequence control circuit 82 stores the pulse sequence information supplied from the main control circuit 81. The CPU of the sequence control circuit 82 controls the gradient magnetic field power source 22, the transmitter 32, and the receiver 33 according to the pulse sequence information.

  Next, the high frequency coil 31 will be described in detail.

  FIG. 2 is a perspective view showing the appearance of the high-frequency coil 31. FIG. 3 is a perspective view showing a schematic configuration of the high-frequency coil 31. 4 is a diagram showing a schematic configuration of the high-frequency coil 31 as viewed from the direction of the arrow shown in FIG.

  The high frequency coil 31 is configured by housing the end rings Ef and Eb, rods R1, R2, R3, and R4 and extension rods R3x and R4x shown in FIGS. 3 and 4 in a case 311 shown in FIG.

  The case 311 includes a main portion 311a having a cylindrical shape and a protruding portion 311b having a cubic shape. The main portion 311a has an inner diameter such that the lower leg can be inserted and the inner wall of the main portion 311a and the lower leg are close to each other. The protrusion 311b is disposed at a position where the toe portion of the foot is positioned when the lower leg is inserted into the main portion 311a. The protrusion 311b has a space formed therein, and this space is connected to the space inside the main portion 311a. The space inside the protrusion 311b has a size such that the toe portion can be inserted as shown in FIG. 2 and the inner wall of the protrusion 311b and the toe portion are close to each other.

  The end rings Ef, Eb and the rods R1, R2, R3, R4 are accommodated in the main portion 311a in the state shown in FIG. 3 so as to be located around the space inside the main portion 311a. The extension rods R3x and R4x are accommodated in the protrusion 311b in the state shown in FIG. 3 so as to be positioned around the space inside the protrusion 311b.

  The end rings Ef and Eb are each formed by forming a conductive material in a ring shape. The end rings Ef and Eb have similar shapes to each other and are arranged to face each other. The planes imaginary inside the end rings Ef and Eb are parallel to each other.

  Each of the rods R1, R2, R3, and R4 is formed by forming a conductive material into a linear rod shape. Each of the rods R1, R2, R3, R4 is once connected to the end ring Ef at equal intervals. The other ends of the rods R1, R2, R3, R4 are connected to the end ring Eb at equal intervals. The rods R1, R2, R3, R4 are all arranged along the direction in which the end rings Ef, Eb are arranged. That is, the rods R1, R2, R3, R4 are parallel to each other. With such an arrangement, the plane P1 hypothesized with the rods R1 and R3 as two sides and the plane P2 hypothesized with the rods R2 and R4 as two sides are orthogonal to each other.

  Each of the extension rods R3x and R4x is formed by forming a conductive material into a rod shape. Both ends of the extension rod R3x are connected to the rod R3. Both ends of the extension rod R4x are connected to the rod R4. The extension rods R3x and R4x are bent into a shape that satisfies the following conditions.

  (1) The extension rods R3x cross each other to form a crossing portion CR1.

  (2) A portion of the extension rod R3x that is located between the crossing portion CR1 and the rod R3 and a plane P3 that is assumed to be the side of the rod R3, and a virtual portion that is the side of the remaining portion of the extension rod R3x. Plane P4 to be formed.

  (3) The plane P4 is substantially parallel to the plane P1 and not parallel to the plane P3.

  (4) The extension rods R4x cross each other to form a crossing portion CR2.

  (5) A portion of the extension rod R4x that is located between the crossing portion CR2 and the rod R4 and a plane P5 that is assumed to be the side of the rod R4, and the remaining portion of the extension rod R4x is assumed to be the side. A plane P6 is formed.

  (6) The plane P6 is substantially parallel to the plane P2 and not parallel to the plane P5.

  (7) The plane P4 and the plane P6 are orthogonal to each other in the space inside the protrusion 311b.

  With such a structure, the high-frequency coil 31 forms first and second imaging regions in the space inside the main portion 311a and the space inside the protrusion 311b, respectively. The first and second imaging regions are connected to each other.

  The above is the principle structure of the high frequency coil 31.

  In addition, although the above is ideal for various shapes and positional relationships, the shapes may change from the above, or the positional relationships may deviate from the above.

  FIG. 5 is a diagram illustrating a specific configuration of the high-frequency coil 31. The configuration shown in FIG. 5 is achieved based on the above-described principle structure.

  The configuration of the high-frequency coil 31 shown in FIG. 5 is different from that shown in FIG. 2 in that both ends of the rods R1, R2, R3, and R4 are bent and the capacitors C11, C12, C13, C14, C15, and C21. , C22, C23, C24, C25, C33, C34, C35, C43, C44, C45, C34x, and C44x.

  Both ends of the rods R1, R2, R3, and R4 are bent at right angles in the same direction. The rods R1, R2, R3, and R4 have similar shapes. One end of the rod R1 and one end of the rod R3, the other end of the rod R1 and the other end of the rod R3, one end of the rod R2 and one end of the rod R4, and the other end of the rod R2 and the other end of the rod R4 are linear. Are lined up. The relative positional relationship between the intermediate portions of the rods R1, R2, R3, and R4 is the same as the principle structure.

  Capacitors C13 and C15 are respectively disposed in the vicinity of both ends of the rod R1. Capacitors C23 and C25 are arranged in the vicinity of both ends of the rod R2. Capacitors C33 and C35 are arranged in the vicinity of both ends of the rod R3. Capacitors C43 and C45 are arranged in the vicinity of both ends of the rod R4. Capacitors C14, C24, C34, and C44 are disposed in the vicinity of the center of each of rods R1, R2, R3, and R4. Thereby, the capacitors C13, C14, C15 are connected in series by the rod R1. Capacitors C23, C24, and C25 are connected in series by rod R2. Capacitors C33, C34, and C35 are connected in series by a rod R3. Capacitors C43, C44, and C45 are connected in series by a rod R4.

  The capacitor C34 is disposed between the positions where both ends of the extension rod R3x are connected. The capacitor C44 is disposed between positions where both ends of the extension rod R4x are connected.

  Both ends of the capacitor C13 are connected to cables connected to the transmitter 32 and the receiver 33 via impedance matching capacitors C11 and C12, respectively. Both ends of the capacitor C23 are connected to cables connected to the transmitter 32 and the receiver 33 via impedance matching capacitors C21 and C22, respectively.

  That is, the high frequency current generated in the transmitter 32 is supplied to the high frequency coil 31 from both ends of the capacitor C13 or the capacitor C23 via the cable. The MR signal detected by the high frequency coil 31 is supplied from both ends of the capacitor C13 or both ends of the capacitor C23 to the receiver 33 via a cable. In the following, the channel through the capacitor C11 and the capacitor C12 is referred to as a first power supply channel, and the channel through the capacitor C21 and the capacitor C22 is referred to as a second power supply channel.

  FIG. 6 is an electrical equivalent circuit diagram of the high-frequency coil shown in FIG.

  As shown in FIG. 6, capacitors C11, C12, C13, C21, C22, C23, C34x and C44x are variable capacitance type elements, respectively. Although not shown in FIG. 5, the high frequency coil 31 includes capacitors C01 and C02 for isolation. As these capacitors C01 and C02, variable capacitance type elements are respectively used.

  Both ends of the capacitor C01 are connected to a portion of the rod R1 located between the capacitors C13 and C14 and a portion of the rod R4 located between the capacitors C43 and C44, respectively. Both ends of the capacitor C02 are connected to a portion of the rod R2 located between the capacitors C23 and C24 and a portion of the rod R3 located between the capacitors C33 and C34, respectively.

  Capacitors C13 and C23 are used for tuning (resonance frequency adjustment) for each of the first and second power supply channels. That is, the capacity of the capacitor C13 is such that the resonance frequency determined by the capacitor capacity inserted in series with the rods R1, R3 and the extension rod R3x and the inductance component of each rod and end ring substantially matches the Larmor frequency of the high-frequency current. Adjusted. However, in FIG. 6, the inductances of the rods R1, R2, R3, R4 and the extension rods R3x, R4x are not shown.

  Capacitors C11, C12, C21, and C22 are used to match the impedances of the first and second power supply channels with the impedances of the transmitter 32 and the receiver 33, respectively. For example, by adjusting the capacitances of the capacitors C11, C12, C21, and C22, the impedances of the first and second power supply channels are set to 50 ohms.

  High-frequency currents having phases different from each other by 90 degrees are supplied from the transmitter 32 to the first power supply channel and the second power supply channel, respectively. By such power supply, a rotating high-frequency magnetic field is formed in each of the first imaging region and the second imaging region. This makes it possible to irradiate a uniform RF pulse with half the power compared to the case where there is one power supply channel.

  On the other hand, two MR signals whose phases are different from each other by 90 degrees are output from the high-frequency coil 31 to the first power supply channel and the second power supply channel. The two MR signals are phased (the phase difference of 90 degrees is corrected to 0 degree) by the receiver 33 and then added. As a result, a sensitivity (S / N) that is √2 times as high as that in the case of one power supply channel is obtained, and uniform image data can be generated.

  That is, by adjusting the capacitances of the capacitors C01 and C02, the high-frequency current sent from the transmitter 32 to the first power supply channel via the capacitors C11 and C12 is supplied to the rod R1 and the rod R3 and the extension rod R3x. The high-frequency current supplied and sent to the second power supply channel via the capacitors C21 and C22 is supplied to the rod R2, the rod R4, and the extension rod R4x.

  Next, the high-frequency current flowing through the extension rods R3x and R4x and the high-frequency magnetic field formed by this high-frequency current will be described.

  FIG. 7 is a diagram illustrating a state in which a high-frequency current is generated in the high-frequency coil 31 by power supply from the first power supply channel. FIG. 8 is a diagram showing how a high-frequency magnetic field is formed by the high-frequency current shown in FIG.

  The high-frequency current supplied from the transmitter 32 via the capacitor C11 flows in the order of, for example, the end ring Ef, the rod R3 and the extension rod R3x, the end ring Eb, and further the rod R1, and then the transmitter C via the capacitor C12. Return to 32. At this time, a high-frequency magnetic field B1 as shown in FIG. 8 is formed for the first imaging region based on the high-frequency current flowing through the rod R3 and the rod R1. Further, a high frequency magnetic field B2 is formed for the second imaging region based on the high frequency current flowing through the extension rod R3x.

  On the other hand, FIG. 9 is a diagram illustrating a state in which a high-frequency current is generated in the high-frequency coil 31 by power supply from the second power supply channel. FIG. 10 is a diagram showing how a high-frequency magnetic field is formed by the high-frequency current shown in FIG.

  The high-frequency current supplied from the transmitter 32 via the capacitor C21 flows in the order of, for example, the end ring Ef, the rod R4 and the extension rod R4x, the end ring Eb, and further the rod R2, and then the transmitter C via the capacitor C22. Return to 32. At this time, a high-frequency magnetic field B1 ′ as shown in FIG. 10 is formed for the first imaging region based on the high-frequency current flowing through the rod R2 and the rod R4. Further, a high frequency magnetic field B2 ′ is formed for the second imaging region based on the high frequency current flowing through the extension rod R4x.

  Next, the operation of forming the high frequency magnetic field B2 on the second imaging region will be described in more detail.

  FIG. 11A is a diagram showing an equivalent circuit when the extension rod R3x is arranged such that the extension rod R3x and a part of the rod R3 form a rectangular loop. Forming the crossing portion CR1 is equivalent to twisting the extension rod R3x in the state shown in FIG. 11 (a) as shown in FIG. 11 (b). Further, by bending at the crossing portion CR1, the equivalent circuit of the actual extension rod R3x is as shown in FIG.

  The extension rod R3x is constituted by the extension rod R3xa and the extension rod R3xb, and the high-frequency magnetic field B2 in the second imaging region is formed by synthesizing the high-frequency magnetic field by the extension rod R3xa and the high-frequency magnetic field by the extension rod R3xb. However, since the influence of the high-frequency magnetic field by the extension rod R3xb is more dominant than the high-frequency magnetic field by the extension rod R3xa, the high-frequency magnetic field by the extension rod R3xb is set as the high-frequency magnetic field B2. In order to match the direction of the high-frequency magnetic field B2 more accurately with the direction of the high-frequency magnetic field B1, the angle between the plane P3 and the plane P4 may be adjusted.

  By changing the capacitance of the capacitor C34x, the strength of the high-frequency magnetic field B2 changes. That is, by appropriately adjusting the capacitance of the capacitor C34x, the strength of the high-frequency magnetic field B1 and the strength of the high-frequency magnetic field B2 can be made equal.

  The high frequency magnetic field B2 formed by the extension rod R3x has been described above, but the same applies to the high frequency magnetic field B2 'formed by the extension rod R4x.

  When the capacitances of the capacitors C34x and C44x are changed so that the strengths of the high-frequency magnetic fields B2 and B2 ′ are equal to the strengths of the high-frequency magnetic fields B1 and B1 ′, the impedance and resonance frequency of each power supply channel are also changed accordingly. Change. For this reason, when changing the capacities of the capacitors C34x and C44x, the impedance of the power supply channel is adjusted by changing the capacities of the capacitors C11, C12, C21 and C22, the resonance frequency is adjusted (tuning) by changing the capacities of the capacitors C13 and C23, and Therefore, it is necessary to adjust the isolation between the power supply channels by changing the capacitances of the capacitors C01 and C02. In addition, when adjustment using only the above-described capacitors is impossible due to large differences in impedance and resonance frequency, it is desirable to adjust the capacitance values of other capacitors inserted in series in each rod.

  Finally, since the high-frequency coil 31 viewed from the feeding channels 1 and 2 is equivalent, the high-frequency magnetic field B1 and the high-frequency magnetic field B1 ′ are substantially equal, and the high-frequency magnetic field B2 and the high-frequency magnetic field B2 ′ are substantially equal. Become.

  As described above, the state in which the high-frequency magnetic field is formed by the high-frequency coil 31 when irradiating the imaging object with the RF pulse has been described, but the same applies to the detection of the MR signal generated in the imaging object. That is, the high frequency coil 31 can detect an MR signal with a magnetic field similar to the high frequency magnetic field formed during transmission. That is, for the first imaging region, the high-frequency coil 31 can detect an MR signal with a magnetic field in the same direction as the high-frequency magnetic field B1 and an MR signal with a magnetic field in the same direction as the high-frequency magnetic field B1 ′. For the second imaging region, the high-frequency coil 31 can detect an MR signal with a magnetic field in the same direction as the high-frequency magnetic field B2 and an MR signal with a magnetic field in the same direction as the high-frequency magnetic field B2 ′. And the sensitivity regarding these MR signals is uniform.

  As described above, according to this embodiment, it is possible to form a high-frequency magnetic field in each of the first and second imaging regions. In addition, it is possible to detect MR signals in each of the first and second imaging regions. In both the first and second imaging regions, the spatial distribution of the high-frequency magnetic field in the region can be made uniform. In both the first and second imaging regions, the MR signal detection sensitivity can be made uniform. Thus, the first and second imaging regions can be imaged with uniform image quality in the respective regions.

  In the case of the high frequency coil disclosed in US Pat. No. 5,277,183, it is impossible to independently control the high frequency current flowing through the bent rod. For this reason, the high-frequency magnetic field in the cylindrical imaging region formed by the linear rod and the high-frequency magnetic field in the imaging region newly formed by the bent rod cannot be made uniform. For this reason, in the high frequency coil shown in FIG. 15, the image quality changes in each of the two imaging regions.

  However, according to the present embodiment, the high-frequency magnetic fields of the first and second imaging regions can be made uniform. In addition, the detection sensitivities of the MR signals in the first and second imaging regions can be made uniform. Thus, it is possible to image the entire first and second imaging regions with uniform image quality.

  Furthermore, according to the present embodiment, high-frequency magnetic fields in directions orthogonal to each other can be formed in each of the first and second imaging regions. In each of the first and second imaging regions, MR signals with magnetic fields orthogonal to each other can be detected. Thus, high-quality imaging by the QD method is possible for both the first and second imaging regions.

  Furthermore, according to this embodiment, the directions of the high-frequency magnetic fields formed in the first and second imaging regions are the same. In each of the first and second imaging regions, MR signals with magnetic fields in the same direction can be detected. Thus, the image quality regarding each of the first and second imaging regions can be made uniform.

  The present invention is not limited to the above embodiment, and various modifications can be made as follows.

(First modification)
FIG. 12 shows a modification of the rod R3 to which the extension rod R3x is added. FIG. 12 (a) shows an external view and FIG. 12 (b) shows an electrical equivalent circuit diagram.

  In the modification shown in FIG. 12A, the rod R3 'is provided in parallel with the rod R3. The end ring Ef, the end ring Eb, the rod R3, the additional rod R3 ', and the extension rod R3x are each made of a thin copper plate. Capacitors C34, C34 ', and C34x are inserted into the rod R3, the additional rod R3', and the extension rod R3x, respectively.

  In this case, it is desirable to add additional rods to the rod R4 and the rods R1 and R2. A plurality of additional rods may be added to one rod.

  By adding additional rods in this way, the number of rods forming the first imaging region can be partially increased, thereby improving the magnetic field uniformity in the first imaging region. In addition, the magnetic field uniformity in the first imaging region can be improved by forming the various rods with thin plate conductors.

(Second modification)
FIG. 13 is a diagram illustrating a first example of the configuration of the high-frequency coil in which the extension rods R3x and R4x are detachable in an electrical equivalent circuit diagram.

  This high-frequency coil includes a main unit 31a shown in FIG. 13A, an attachment / detachment unit 31b shown in FIG. 13B, and an attachment / detachment unit 31c shown in FIG. 13C.

  The main unit 31a cuts the rod R3 between the capacitors C33 and C34 and between the capacitors C34 and C35 in the high-frequency coil 31, and between the capacitors C43 and C44 and between the capacitors C44 and C45. The rod R4 is cut at each of the positions, and a part of the rod R3, a part of the rod R4, the capacitors C34, C44, C34x, C44x and the extension rods R3x, R4x are removed from the high frequency coil 31. . Note that portions corresponding to a part of the rod R3 are referred to as rods R3a and R3b. Parts corresponding to part of the rod R4 are referred to as rods R4a and R4b. Joints J11 and J12 are attached to the ends of the rods R3a and R3b. Joints J13 and J14 are attached to the ends of the rods R4a and R4b.

  The detachable unit 31b is configured by a portion removed from the high frequency coil 31 in the main unit 31a. Parts corresponding to the rods R3 and R4 are referred to as rods R3c and R4c, respectively. Joints J21 and J22 are attached to both ends of the rod R3c. Joints J23 and J24 are attached to both ends of the rod R4c.

  The detachable unit 31b includes rods R3d and R4d corresponding to parts of the rods R3 and R4 removed from the high-frequency coil 31 in the main unit 31a, and capacitors C36 and C46. Further, joints J31 and J32 are attached to both ends of the rod R3d, respectively. Joints J33 and J34 are attached to both ends of the rod R4d. Capacitors C36 and C46 are inserted into rods R3d and R4d, respectively.

  By attaching the detachable unit 31b to the main unit 31a by joining the joints J21, J22, J23, and J24 to the joints J11, J12, J13, and J14, a high-frequency coil that functions similarly to the high-frequency coil 31 is configured. When the extension rods R3x, R4x are not necessary, the detachable unit 31c is mounted on the main unit 31a by joining the joints J31, J32, J33, J34 to the joints J11, J12, J13, J14. Capacitors C36 and C46 are characterized in that rod R1, rod R2, rod formed by jointing rods R3a, R3b, and R3d, and rod formed by jointing rods R4a, R4b, and R4d. May be determined to function in a balanced manner for transmission and reception in the first imaging region.

(Third Modification)
FIG. 14 is a diagram illustrating a second example of the configuration of the high-frequency coil in which the extension rods R3x and R4x are detachable in an electrical equivalent circuit diagram.

  This high frequency coil includes a main unit 31d shown in FIG. 14A and a detachable unit 31e shown in FIG. 14B.

  The main unit 31d cuts the extension rods R3x, R4x in the high-frequency coil 31 at both ends thereof, removes the extension rods R3x, R4x and the capacitors C34x, C44x from the high-frequency coil 31, and replaces the capacitors C34, C44 with capacitance. It has a configuration obtained by providing variable type capacitors C37 and C47. Joints J15, J16, J17, and J18 are attached to locations where the extension rods R3x and R4x are cut off.

  The detachable unit 31e is configured by a portion removed from the high frequency coil 31 in the main unit 31d. Joints J41 and J42 are attached to both ends of the extension rod R3x. Joints J43 and J44 are attached to both ends of the rod R4x.

  By attaching the detachable unit 31e to the main unit 31d by joining the joints J41, J42, J43, and J44 to the joints J15, J16, J17, and J18, a high-frequency coil that functions similarly to the high-frequency coil 31 is configured. At this time, the capacities of the capacitors C37 and C47 are set to be the same as the capacities of the capacitors C34 and C44.

  When the extension rods R3x and R4x are unnecessary, the main unit 31d is operated alone without attaching the detachable unit 31e. At this time, the capacitances of the capacitors C37 and C47 may be determined so that the rods R1, R2, R3, and R4 function in a balanced manner for transmission and reception in the first imaging region.

(Other variations)
The high frequency magnetic fields B1 and B2 may be adjusted by the capacitance of the capacitors inserted into the rods R1, R2, R3, R4, or the capacitance of the capacitors inserted into the additional rods added to the rods R1, R2, R3, R4.

  The number of rods parallel to the rods R1, R2, R3, R4 may be increased. The number of increasing rods can be arbitrary.

  The end rings Ef and Eb may be divided into two parts, and they may be jointable. That is, the high frequency coil 31 may be divided into two units that can be attached to and detached from each other. In this way, by dividing the two units, it becomes easy to insert the imaging target into the high-frequency coil 31.

  Instead of the end rings Ef and Eb, loop-shaped members that are not ring-shaped may be used.

  The end ring Eb may be replaced with a plate-like member.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram showing the overall configuration of an MRI apparatus in an embodiment of the present invention. The perspective view which shows the external appearance of the high frequency coil shown by FIG. The perspective view which shows schematic structure of the high frequency coil shown by FIG. The figure which shows a mode that the schematic structure of the high frequency coil shown by FIG. 3 was seen from the direction of the arrow shown in FIG. The figure which shows the specific structure of the high frequency coil shown by FIG. FIG. 6 is an electrical equivalent circuit diagram of the high-frequency coil shown in FIG. 5. The figure which shows a mode that a high frequency current arises in the high frequency coil shown by FIG. 5 by the electric power feeding from a 1st electric power feeding channel. The figure which shows a mode that a high frequency magnetic field is formed with the high frequency current shown by FIG. The figure which shows a mode that a high frequency current arises in the high frequency coil shown by FIG. 5 by the electric power feeding from a 2nd electric power feeding channel. The figure which shows a mode that a high frequency magnetic field is formed with the high frequency current shown by FIG. The figure for demonstrating the electromagnetic effect | action in the extension rod shown by FIG. The figure which shows the structure of the high frequency coil in a 1st modification. The figure which shows the structure of the high frequency coil in a 2nd modification. The figure which shows the structure of the high frequency coil in a 3rd modification. The figure which shows the conventional structural example of a cylindrical high frequency coil.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field generation part, 2 ... Gradient magnetic field generation part, 3 ... Transmission / reception part, 4 ... Calculation / storage part, 5 ... Bed, 6 ... Input part, 7 ... Display part, 8 ... Control part, 31 ... High frequency coil, 31a, 31d ... main unit, 31b, 31c, 31e ... detachable unit, 100 ... MRI apparatus, 150 ... subject, 311 ... case, 311a ... main part, 311b ... projection, C01, C02, C11-C15, C21- C25, C33 to C35, C43 to C45, C34x, C44x, C34 '... capacitor, CR1, CR2 ... crossing portion, Ef, Eb ... end ring, J11-J18, J21-J24, J31-J34, J41-J44 ... Joint , P1 to P6 ... plane, R1 to R4, R3 '... rod, R3x, R4x ... extension rod.

Claims (20)

In a high frequency coil for a magnetic resonance imaging apparatus,
Two end members made of a conductive material and arranged opposite to each other;
A plurality of rod members each formed by forming a conductive material in a rod shape and having both ends connected to the two end members;
An electrically conductive member is formed in a rod shape, and includes an additional member having both ends connected to one of the rod members,
The high-frequency coil according to claim 1, wherein the additional member is disposed so as to form a second imaging region outside a first imaging region formed by the end member and the rod member. The additional members are connected to different rod members, and a plurality of the additional members are provided.
The high frequency coil according to claim 1, wherein the second imaging region is formed by the plurality of additional members.   Two of the plurality of additional members are arranged such that the first and second high-frequency magnetic fields formed by the two additional members in the second imaging region are substantially orthogonal to each other. The high frequency coil according to claim 2. The plurality of rod members form third and fourth high-frequency magnetic fields substantially orthogonal to each other in the first imaging region;
The said two additional members are arrange | positioned so that the said 1st and 2nd high frequency magnetic field may respectively become a substantially the same direction as a said 3rd and 4th high frequency magnetic field, The said 2nd addition member is characterized by the above-mentioned. High frequency coil. Two of the plurality of additional members each include a loop portion capable of virtually imagining the first and second planes inside, respectively.
The high frequency coil according to claim 2, wherein the two additional members are arranged such that the first and second planes are substantially orthogonal to each other. The plurality of rod members include at least four rod members, and the four rod members are a third plane that is assumed to be two sides of the two rod members, and the remaining two rod members. Are arranged so as to be substantially orthogonal to a fourth plane that is assumed to be two sides,
The high frequency coil according to claim 5, wherein the two additional members are arranged such that the first and second planes are parallel to the third and fourth planes, respectively.   2. The high-frequency coil according to claim 1, wherein the two end members and the plurality of rod members are defined in shape and arrangement so that the first imaging region has a cylindrical shape. The two end members each have a ring shape,
The high-frequency coil according to claim 1, wherein the rod member is disposed along a cylindrical cylindrical surface virtually assumed with the two end members as both ends.   An additional rod member formed by forming a conductive member in a rod shape, connected to the rod member to which the additional member is connected, and forming the first imaging region together with the rod member. Item 4. The high frequency coil according to Item 1. In a high frequency coil for a magnetic resonance imaging apparatus,
Two end members made of a conductive material and arranged opposite to each other;
At least a plurality of rod members each formed by forming a conductive material into a rod shape and having both ends connected to the two end members,
An additional member formed by forming a conductive member into a rod shape, and having both ends connected to one of the rod members;
An impedance element inserted into each of the plurality of rod members and the additional member;
The high-frequency coil according to claim 1, wherein the additional member is disposed so as to form a second imaging region outside a first imaging region formed by the end member and the rod member.   The impedance element has characteristics and arrangement determined so that the distribution of the high-frequency magnetic field in the first imaging region and the distribution of the high-frequency magnetic field in the second imaging region are substantially uniform. The high frequency coil according to claim 10. The additional members are connected to different rod members, and a plurality of the additional members are provided.
The impedance element is inserted into each of the plurality of additional members,
The high frequency coil according to claim 10, wherein the second imaging region is formed by the plurality of additional members.   The high-frequency coil according to claim 10, wherein the impedance element inserted into the rod member to which the additional member is connected is disposed between positions where both ends of the additional member are connected to each other.   The high frequency coil according to claim 10, wherein a plurality of impedance elements are inserted into each of the plurality of rod members.   The high-frequency coil according to claim 10, wherein at least a part of the impedance element is an element capable of changing impedance.   The high-frequency coil according to claim 10, wherein the impedance element is a capacitor. In a high frequency coil for a magnetic resonance imaging apparatus,
Two end members made of a conductive material and arranged opposite to each other;
Formed of a conductive material in the form of a rod, and at least four rod members each having both ends connected to the two end members;
A first additional member formed by forming a conductive member in a rod shape, and having both ends connected to one of the rod members;
A conductive member is formed in a rod shape, and includes a second additional member having both ends connected to one of the rod members different from that to which the first additional member is connected,
The rod members are substantially parallel to each other, and the first and second rod members of the rod members are assumed to have two sides facing each other, and a first flat surface and third and fourth of the rod members. The second virtual plane so that the rod members of the two are opposed to each other are substantially orthogonal to each other,
The first and second additional members are connected to the first and third rod members, respectively;
The first additional member crosses to form a first crossing portion, a part of the first additional member positioned between the first crossing portion and the first rod member, and the The third plane imaginary with the first rod member as a side and the fourth plane imaginary with the remaining part of the first additional member as a side are in different directions, and the fourth plane Is substantially parallel to the first plane,
The second additional member crosses so as to form a second crossing portion, and a part of the second additional member positioned between the second crossing portion and the third rod member, The fifth plane imaginary with the third rod member as a side and the sixth plane imaginary with the remaining part of the second additional member as a side are oriented in different directions, and the sixth plane Is a high-frequency coil substantially parallel to the second plane. In a magnetic resonance imaging apparatus that reconstructs image data based on an MR signal emitted from an imaging target placed in a region where a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field are formed,
A magnetic resonance imaging apparatus using the high frequency coil according to claim 1 for at least one of forming the high frequency magnetic field and detecting the MR signal. In a magnetic resonance imaging apparatus that reconstructs image data based on an MR signal emitted from an imaging target placed in a region where a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field are formed,
A magnetic resonance imaging apparatus using the high-frequency coil according to claim 10 for at least one of forming the high-frequency magnetic field and detecting the MR signal. In a magnetic resonance imaging apparatus that reconstructs image data based on an MR signal emitted from an imaging target placed in a region where a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field are formed,
A magnetic resonance imaging apparatus using the high-frequency coil according to claim 17 for at least one of forming the high-frequency magnetic field and detecting the MR signal.

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