WO2011016398A1

WO2011016398A1 - Magnetic resonance measurement device

Info

Publication number: WO2011016398A1
Application number: PCT/JP2010/062903
Authority: WO
Inventors: 久晃越智; 悦久五月女; 博幸竹内; 秀太羽原; 良孝尾藤; 幸生金子; 哲彦高橋
Original assignee: 株式会社日立メディコ
Priority date: 2009-08-05
Filing date: 2010-07-30
Publication date: 2011-02-10
Also published as: JPWO2011016398A1; JP5258968B2

Abstract

Disclosed is a feature that, in a tunnel MRI device, ensures a comfortable examination space without increasing the production cost of the MRI device and without sacrificing performance. In a tunnel MRI device, within a gradient coil that has a cylindrical inner wall, RF coils that are two partial-cylinder loop RF coils with an angle of view of less than 180 degrees and that are provided with a plurality of rungs within the loop are disposed facing each other. At this point, in response to the target application, the disposed locations of the two loop RF coils are determined.

Description

Magnetic resonance measuring device

The present invention relates to a high-frequency magnetic field coil for transmitting and / or receiving electromagnetic waves, and a magnetic resonance measuring apparatus (hereinafter referred to as “MRI apparatus”) using the same.

An MRI apparatus arranges a subject in a uniform static magnetic field generated by a magnet, irradiates the subject with an electromagnetic field to excite nuclear spins within the subject, and nuclear magnetic resonance, which is an electromagnetic wave that generates nuclear spins. A signal is received and the subject is imaged. Superconducting magnets and permanent magnets are widely used as magnets, and typical shapes include a cylindrical type and a counter type. A tunnel type (horizontal magnetic field type) MRI apparatus that uses a magnet that generates a static magnetic field in the horizontal direction with a cylindrical shape, and an MRI apparatus that uses a magnet that generates a static magnetic field in the vertical direction with an opposing type. It is often called an open type (vertical magnetic field type) MRI apparatus.

Also, irradiation of electromagnetic waves and reception of nuclear magnetic resonance signals are performed by an RF coil that transmits (irradiates) and receives radio frequency (RF) electromagnetic waves. If there is a difference in the excited state of the nuclear spin depending on the region of the subject, unevenness of the image contrast and artifacts occur. In order to avoid these, the RF coil is required to improve the irradiation efficiency and the irradiation uniformity, and various shapes of transmission RF transmission coil, reception RF reception coil, or RF transmission / reception coil that combines both are provided. Has been developed.

As a shape with high uniformity of irradiation intensity, for example, a so-called birdcage type RF coil is known (see, for example, Patent Document 1). The birdcage type RF coil disclosed in Patent Document 1 includes a linear conductor (lang) and an arcuate conductor (ring) disposed on a cylindrical RF base. The rung extends in the central axis direction (z-axis direction) of the RF base, and the rings are disposed at both ends of the rung. A nonmagnetic resin such as acrylic or FRP is used for the RF base.

In the high-pass type of birdcage type RF coils, capacitors are arranged on the ring, and these are tuned to form an RF coil that resonates at a desired frequency. An example of this high-pass birdcage RF coil 100 is shown in FIG. FIG. 22A is an explanatory diagram for explaining the appearance, and FIG. 22B is an explanatory diagram viewed from the z-axis direction. As shown in this figure, the high-pass birdcage type RF coil 100 is composed of two loop conductors,

rings

110 and 120, and a plurality of (12 in FIG. 22) linear conductors parallel to the z-axis. And a rung 130. The

rings

110 and 120 are arranged so as to face each other so that the central axis of the loop is common and the central axis is parallel to the z-axis, and are connected by a rung 130. In FIG. 22, the RF base is omitted. The plurality of rungs 130 are arranged at equal intervals. Incidentally, in the figure, z-axis direction of the coordinate axes, the orientation 140 of the static magnetic field B ₀ which the magnet of the MRI device generates. A plurality of first capacitors Cr are arranged between the connection points of the plurality of rungs 130 and the

rings

110 and 120, and the feeding point 150 is arranged in one of the first capacitors. Since the RF coil 100 is easy to tune, it is widely used in horizontal magnetic field type MRI apparatuses.

A QD (Quadrature Detection) method is known as a method for improving the irradiation efficiency and reception sensitivity of the RF coil. The QD method is a method for detecting a magnetic resonance signal using two RF coils arranged with their axes orthogonal to each other. When a magnetic resonance signal is detected by this method, a signal whose phase is shifted by 90 degrees is detected from each RF coil. By combining these detection signals, the SN ratio is theoretically improved by a factor of √2 compared to the case where the signals are received by one RF coil. Further, since the circularly polarized light is irradiated when the high frequency magnetic field is irradiated, the electric power is halved, and the high frequency heat generation of the subject can be reduced. Furthermore, the sensitivity uniformity of the xy plane can be improved. The birdcage type RF coil can be easily applied with the QD method because of the symmetry of its structure. That is, by arranging two power feeding ports for transmitting and receiving signals at positions orthogonal to each other, transmission and reception by the QD method can be performed with one birdcage type RF coil. FIG. 23 shows an RF coil 100A which is an example in which the QD method is applied to the RF coil 100 shown in FIG. FIG. 23A is an explanatory diagram for explaining the appearance, and FIG. 23B is an explanatory diagram viewed from the z-axis direction. In the RF coil 100A, the two

power supply ports

151 and 152 are arranged at positions orthogonal to each other.

Furthermore, the birdcage RF coil can also be used as a multi-channel array coil by connecting a capacitor to the rung (for example, Non-Patent Document 1). FIG. 24 shows an example in which the RF coil 100 shown in FIG. 22 is used as a multi-channel array coil 100C. Here, a case where the RF coil 100 having eight rungs 130 is used as the 8-channel array coil 100C is illustrated. In the array coil 100 </ b> C, the electromagnetic interference with the adjacent channel can be reduced by adjusting the capacitance of the capacitor Cr connected to the

rings

110 and 120 and the capacitance of the capacitor CL connected to the rung 130. For this reason, each channel can receive or transmit independently. Further, during irradiation with a high-frequency magnetic field, it is possible to generate circularly polarized waves inside the coil by shifting the phase of each channel by 360 degrees ÷ run number (8) = 45 degrees.

In addition, the birdcage type RF coil has a semi-cylindrical shape or a partial cylindrical shape (for example, Non-Patent Document 2) and a planar shape (for example, Patent Document 2).

U.S. Pat. No. 4,916,418 Japanese Patent Laid-Open No. 8-280652

As a recent trend of improving the examination environment in MRI, there is a demand for a spacious and open examination space where fat people and claustrophobic people can take MRI examinations with peace of mind. In particular, there is a strong demand for a tunnel-type MRI apparatus having a tunnel-type inspection space as described above. In addition, contrast medium injector devices and non-magnetic treatment devices are installed inside the MRI apparatus, and they have been used for precise diagnosis and treatment, ensuring a space for installing various devices in the vicinity of the subject. Therefore, an MRI apparatus having a wide examination space is required.

In a tunnel type MRI apparatus, a magnet that generates a static magnetic field, a gradient coil that generates a gradient magnetic field, and an RF coil are arranged in this order from the outside to the inside of the tunnel. When the above-described RF coil 100 is used as the RF coil, the inside of the cylinder formed by the RF coil is an examination space in which the subject enters.

For example, the inspection space can be expanded by increasing the inner diameter of the magnet. However, this significantly increases manufacturing costs. Further, since the magnetic field generation efficiency is improved when the magnet is closer to the subject, it cannot be easily increased. Further, an RF shield is disposed between the RF coil and the gradient coil at a certain distance from the conductor of the RF coil. The RF shield is for reducing noise emitted from the gradient coil and blocking electromagnetic coupling between the gradient coil and the RF coil. Therefore, a predetermined distance is required between the RF shield and the RF coil in order to maintain the magnetic field and avoid abrupt changes in its distribution. Therefore, the examination space is compressed accordingly.

FIG. 25 is an explanatory diagram when the RF coil is viewed from the z-axis direction when the subject is inserted when the subject is a human. When the human lies on the table on which the subject is placed, the body portion has an approximate elliptic cylinder shape that is long in the x direction and short in the y direction. When the size of the magnet is determined so that the subject is accommodated with priority given to the manufacturing cost and the efficiency of magnetic field generation, in the examination space, generally both shoulders of the subject are approaching the tunnel inner wall formed by the RF coil, I feel cramped.

The present invention has been made in view of the above circumstances, and in a tunnel-type MRI apparatus, a technique for ensuring a comfortable inspection space without increasing the manufacturing cost of the MRI apparatus and without sacrificing performance. The purpose is to provide.

In the present invention, in a tunnel type MRI apparatus, two partial cylindrical loop type RF coils having a prospective angle of less than 180 degrees are arranged in opposing positions in a gradient magnetic field coil having a cylindrical inner wall. At this time, the arrangement positions of the two loop type RF coils are determined according to the purpose of use.

Specifically, an annular magnet unit that generates a static magnetic field, an annular gradient coil disposed coaxially with the magnet unit in an inspection region surrounded by the magnet unit, and an inner side of the gradient coil. A high-frequency magnetic field coil, wherein the high-frequency magnetic field coil is an annular ring disposed coaxially with the gradient magnetic field coil along an inner wall of the gradient magnetic field coil inside the gradient magnetic field coil. A high frequency magnetic field shield, and a partial cylindrical loop coil having two partial cylindrical shapes disposed opposite to each other inside the high frequency magnetic field shield, wherein the partial cylindrical loop coils are spaced apart from each other by a predetermined distance. A plurality of linear conductors arranged in parallel with each other in the axial direction and two partial arc-shaped conductors connecting the plurality of linear conductors at both ends of the partial cylindrical shape in the axial direction. When the equipped, visual angle in the circumferential direction of both ends of the respective partial cylindrical shape to provide a magnetic resonance measurement apparatus and less than 180 degrees.

According to the present invention, in a tunnel type MRI apparatus, a comfortable inspection space can be secured without increasing the manufacturing cost of the MRI apparatus and without sacrificing performance.

It is an external view of the MRI apparatus of 1st embodiment. It is a block diagram which shows the whole structure of the MRI apparatus of 1st embodiment. (A) is explanatory drawing which shows yz cross section for demonstrating the transmission coil arrange | positioned in the gradient magnetic field coil of 1st embodiment, (b) is xy sectional drawing. (A), (b) is xy sectional drawing for demonstrating the structure of the transmission coil of 1st embodiment, and the fixing method of RF base. (A) is a graph which shows the irradiation intensity distribution of the x-axis direction of the transmission coil of 1st embodiment, (b) is a graph which shows the irradiation intensity distribution of the same y-axis direction. It is explanatory drawing for demonstrating the mode inside the test | inspection space seen from the z direction at the time of the test | inspection of 1st embodiment. (A) is explanatory drawing which shows yz cross section for demonstrating the other example of the transmission coil arrange | positioned in the gradient magnetic field coil of 1st embodiment, (b) is the xy cross section. . It is explanatory drawing for demonstrating the usage example of the transmission coil of 1st embodiment. It is explanatory drawing for demonstrating the usage example of the transmission coil of 1st embodiment. (A) is explanatory drawing which shows yz cross section for demonstrating the transmission coil arrange | positioned in the gradient magnetic field coil of 2nd embodiment, (b) is xy sectional drawing. (A) is a graph which shows the irradiation intensity distribution of the x-axis direction of the transmission coil of 2nd embodiment, (b) is a graph which shows the irradiation intensity distribution of the same y-axis direction. (A), (b) is xy sectional drawing for demonstrating the fixing method of RF base of 2nd embodiment. (A) is explanatory drawing for demonstrating the mode inside the test | inspection space seen from the z direction at the time of the test | inspection of 2nd embodiment, (b) is other of the transmission coil of 2nd embodiment. It is xy sectional drawing of an example. (A) is explanatory drawing which shows xz cross section for demonstrating the other example of the transmission coil arrange | positioned in the gradient magnetic field coil of 2nd embodiment, (b) is the xy cross section. (C) is explanatory drawing for demonstrating the mode inside the test | inspection space seen from the z direction at the time of a test | inspection. (A) is a graph which shows the irradiation intensity distribution of the x-axis direction of the other example of the transmission coil of 2nd embodiment, (b) is a graph which shows the irradiation intensity distribution of the same y-axis direction. (A) is explanatory drawing which shows xz cross section for demonstrating the transmission coil arrange | positioned in the gradient magnetic field coil of 3rd embodiment, (b) is xy sectional drawing. (A) is a graph which shows the irradiation intensity distribution of the x-axis direction of the transmission coil of 3rd embodiment, (b) is a graph which shows the irradiation intensity distribution of the same y-axis direction. (A) is explanatory drawing which shows xz cross section for demonstrating the transmission coil of the comparative example of 3rd embodiment, (b) is xy sectional drawing, (c), (d) is the same. It is explanatory drawing for demonstrating the electric current which flows into the transmission coil. It is xy sectional drawing of the other example of the transmission coil arrange | positioned in the gradient magnetic field coil of 3rd embodiment. (A) is explanatory drawing which shows xz cross section for demonstrating the other example of the transmission coil arrange | positioned in the gradient magnetic field coil of 3rd embodiment, (b) is the xy cross section. . (A)-(d) is xy sectional drawing of the modification of the transmission coil respectively arrange | positioned in the gradient magnetic field coil of 3rd Embodiment. (A), (b) is explanatory drawing of the conventional birdcage type | mold RF coil. (A), (b) is explanatory drawing at the time of applying a QD system to the conventional birdcage type | mold RF coil. It is explanatory drawing at the time of using the conventional birdcage type | mold RF coil as an array coil. It is explanatory drawing for demonstrating the mode at the time of the test | inspection of the conventional birdcage type | mold RF coil.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described. In all the drawings for explaining the embodiments of the present invention, those having the same function are denoted by the same reference numerals, and repeated explanation thereof is omitted.

First, the magnetic resonance imaging apparatus (MRI apparatus) of this embodiment will be described. The MRI apparatus images information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, thereby imaging the form or function of the human head, abdomen, limbs, etc. two-dimensionally or three-dimensionally. To do. At present, the nuclide to be imaged by the MRI apparatus, which is widely used clinically, is a hydrogen nucleus (proton) which is a main constituent material of the subject.

The MRI apparatus 10 of the present embodiment that realizes this will be described. FIG. 1 is an external view of the MRI apparatus 10 of the present embodiment. The MRI apparatus 10 of the present embodiment includes a cylindrical magnet 21 constituting a horizontal magnetic field type static magnetic field generation system and a table 11 on which the subject 1 is placed. The subject 1 laid on the table 11 is inserted into the examination space 22 in the bore formed by the cylindrical magnet 21 and photographed. Hereinafter, in the present specification, in the MRI apparatus 10 of the present embodiment, a coordinate system (stationary coordinates) in which the center of the bore is the origin and the center axis (cylindrical axis) of the cylindrical magnet 21 that is the static magnetic field direction is the z axis. System). The table 11 is arranged so that the body axis direction of the subject 1 to be placed coincides with the z-axis direction. Of the two axes orthogonal to the z-axis, the direction parallel to the surface of the table 11 is defined as the x-axis direction, and the direction orthogonal to the surface of the table 11 is defined as the y-axis direction.

Next, the overall configuration of the MRI apparatus 10 of the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram showing the overall configuration of the MRI apparatus 10 of the present embodiment. The MRI apparatus 10 of the present embodiment obtains a tomographic image of the subject 1 using a nuclear magnetic resonance (NMR) phenomenon, and includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, A reception system 6, a sequencer 4, an information processing device 7, and a table 11 on which the subject 1 is placed are provided.

In the static magnetic field generation system 2 of the present embodiment, a magnet 21 which is a permanent magnet type, normal conduction type or superconducting type static magnetic field generation source is provided around the subject 1 in order to generate a uniform static magnetic field in the body axis direction. Be placed.

The gradient magnetic field generation system 3 includes a gradient magnetic field coil 31 wound in the three axes of x, y, and z in the coordinate system of the MRI apparatus 10 and a gradient magnetic field power source 32 that drives each gradient magnetic field coil. By driving the gradient magnetic field power supply 32 of each coil in accordance with the command from the sequencer 4, gradient magnetic field pulses Gx, Gy, Gz are applied in the three axial directions of x, y, z. At the time of imaging, a slice direction gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 1, and the remaining two orthogonal to the slice plane and orthogonal to each other. A phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied in one direction, and position information in each direction is encoded in the echo signal.

The transmission system 5 irradiates the subject 1 with a high-frequency magnetic field pulse (RF pulse) in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the living tissue of the subject 1. And a transmission-side high-frequency coil (transmission coil) 51. The RF pulse output from the high-frequency oscillator 52 is amplitude-modulated by the modulator 53 at a timing according to a command from the sequencer 4, and the amplitude-modulated RF pulse is amplified by the high-frequency amplifier 54 and then placed close to the subject 1. By supplying to the transmitting coil 51, the subject 1 is irradiated with the RF pulse.

The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and includes a receiving-side high-frequency coil (receiving coil) 61 and a signal amplifier 62. And a quadrature phase detector 63 and an A / D converter 64. An NMR signal from a nuclear spin in the subject 1 induced by the electromagnetic wave irradiated from the transmitting coil 51 is detected by a receiving coil 61 arranged close to the subject 1. The detected NMR signal is amplified by the signal amplifier 62 and then divided into two orthogonal signals by the quadrature phase detector 63 at a timing according to a command from the sequencer 4 described later, and each of them is an A / D converter. 64 is converted into a digital quantity and sent to the information processing apparatus 7.

Sequencer 4 repeatedly applies an RF pulse and a gradient magnetic field pulse according to a predetermined pulse sequence. The sequencer 4 operates under the control of the information processing apparatus 7, and sends various commands necessary for collecting tomographic image data of the subject 1 to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6. Note that the pulse sequence is held in advance in a storage device or the like provided in the information processing apparatus 7 to be described later.

The information processing apparatus 7 controls the overall operation of the MRI apparatus 10 and performs various data processing and display and storage of processing results. The CPU 71, a storage device 72 such as a ROM and a RAM, an optical disk, and a magnetic disk An external storage device 73 such as a display, a display device 74 such as a display, and an input device 75 such as a trackball, a mouse, and a keyboard. When data is input from the reception system 6, the CPU 71 executes processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 1 as a result on the display device 74, and the storage device 72 or the external device. Record in the storage device 73. Also, input of various control information of the MRI apparatus 10 is accepted via the input device 75. A command is given to the sequencer 4 according to the received control information and a pulse sequence stored in the storage device 72 in advance. The input device 75 is disposed in the vicinity of the display device 74, and the operator interactively controls various processes of the MRI apparatus 10 through the input device 75 while looking at the display device 74. The information processing device 7 may be a general-purpose information processing device.

In this embodiment, the transmission coil 51 and the gradient magnetic field coil 31 are arranged so as to surround the subject 1 in the static magnetic field space formed by the static magnetic field generation system 2 into which the subject 1 is inserted. Further, the transmission coil 51 and the gradient magnetic field coil 31 are arranged and arranged coaxially with the magnet 21 in this order from the inside. The receiving coil 61 is installed so as to face or surround the subject 1.

In the present embodiment, a wide inspection space 22 is secured by devising the shape of the transmission coil 51 without changing the sizes of the magnet 21 and the gradient coil 31. Hereinafter, the transmission coil 51 of this embodiment which implement | achieves this is demonstrated using FIG. 3 and FIG. 3 and 4 are diagrams for explaining the configuration of the transmission coil 51 of the present embodiment. FIG. 3A is an explanatory view showing a yz section of the transmission coil 51 arranged in the gradient magnetic field coil 31, and FIG. 3B is an xy section view thereof.

As shown in these drawings, the transmitting coil 51 of the present embodiment includes a cylindrical RF shield 510, two partially cylindrical RF bases 520 (not shown in FIG. 3), and two RF bases 520. A partially cylindrical RF coil 540 formed respectively.

The RF shield 510 has a cylindrical shape coaxial with the gradient magnetic field coil 31, and is disposed inside the gradient magnetic field coil 31 at a certain distance from the gradient magnetic field coil 31. The RF shield 510 is configured by appropriately laminating a nonmagnetic metal foil or a net, and is disposed on the surface of the resin support member or the gradient coil 31. Hereinafter, in this embodiment, the case where it affixes on a resin shield bobbin (not shown in FIG. 3) will be described as an example.

Each of the two RF bases 520 has a partial cylindrical shape in which a part of a side surface of the cylinder is cut off in the cylindrical axis direction, and has a partial cylindrical shape with a prospective angle 740 of a cross section of less than 180 degrees. As shown in FIG. 4, the two RF bases 520 are arranged in the examination space 22 so as to face each other around the z axis at a certain distance from the RF shield 510. At this time, as shown in FIG. 3B, straight lines 580 connecting the centers M in the circumferential direction of the partial cylindrical RF coils 540 respectively formed on the two RF bases 520 are parallel to the x-axis. Are arranged in the examination space 22. That is, in the present embodiment, the partial cylindrical RF coil 540 is arranged in the examination space 22 so as to be plane-symmetric with respect to the xz plane determined by the x axis and the z axis. Note that the RF base is formed of a nonmagnetic resin such as acrylic or FRP.

The partial cylindrical RF coil 540 includes a plurality of linear conductors (rungs) 541 extending in the z-axis direction, and two partial arc-shaped conductors (partial rings) 542 and 543 connecting the ends of the plurality of rungs. And formed on the RF base 520 along the shape of the RF base 520. The rungs 541 are arranged at equal intervals, and each end of the partial ring 542 is connected to each end of the corresponding partial ring 543 to constitute a loop type coil. Each

partial ring

542 and 543 includes a capacitor 544 between the connection points with the rung 541. Each rung 541 includes a capacitor 545. The partial cylindrical RF coil 540 configured as described above has a shape obtained by cutting a part of a cylindrical birdcage RF coil in the rung direction, and the prospective angles at both ends in the cross section orthogonal to the z-axis are: It is substantially the same as the prospective angle 740 of the RF base 520 and is less than 180 degrees.

Here, the RF shield 510 has two functions: a) reducing noise emitted from the gradient coil 31 and b) shielding electromagnetic coupling between the conductor of the gradient coil 31 and the partial cylindrical RF coil 540. And a predetermined distance (typically 10 mm to 40 mm) is required between it and the partially cylindrical RF coil 540. This is because when both are brought close to each other, the high-frequency eddy current increases, the magnetic field is canceled, and the magnetic field distribution in the vicinity of the partial cylindrical RF coil 540 changes abruptly. Hereinafter, a method of fixing the RF base 520 forming the partial cylindrical RF coil 540 at a predetermined distance inside the RF shield 510 in the examination space 22 will be described with reference to FIG.

As shown in the figure, a plurality of protrusions 512 are formed on a shield bobbin 511 to which the RF shield 510 is attached, and the RF base 520 is fixed to the protrusions 512 with nonmagnetic bolts 513. Note that the optimal shape and number of protrusions 512 formed on the shield bobbin 511 are determined by the number of rungs 541, the diameter of the transmission coil 51, and the like. However, the protrusion 512 is not necessarily provided at the end of the RF base 520, but at least one protrusion 512 is provided at a distance capable of maintaining mechanical strength from both ends of the RF base 520. The partial cylindrical RF coil 540 may be arranged on the inspection space 22 side (inside) of the RF base 520 as shown in FIG. 4A, or as shown in FIG. The base 520 may be disposed on the RF shield 510 side (outside).

According to the transmission coil 51 of the present embodiment, the RF base 520 and the partial cylindrical RF coil 540 are arranged as described above. Therefore, as shown in FIGS. 3B, 4A, and 4B, the partial cylindrical RF is provided at both ends in the y-axis direction in the inspection space 22 over the entire z-axis direction of the inspection space 22. It is possible to obtain the space 560 in which the coil 540 and the RF base 520 that supports the coil 540 and the protrusions 512 do not exist. Therefore, as compared with the case where the transmission coil 51 using the conventional birdcage type RF coil is used, a wider inspection space 22 can be secured.

Generally, it is desirable that the irradiation intensity of the transmission coil 51 in the imaging region is within a predetermined range in order to accurately capture the imaging region when exciting the nuclear spin in the subject 1. This is because if the irradiation intensity is very uneven, the nuclear spin excitation state varies depending on the site in the subject 1, resulting in unevenness in the contrast of the obtained image and artifacts. A region where the irradiation intensity is within a predetermined range is referred to as a uniform irradiation intensity region.

In the transmission coil 51 of the present embodiment, the conductor constituting the partial cylindrical RF coil 540 does not exist in the vicinity of the RF shield 510 at both ends in the y-axis direction in the examination space 22 on the cross section perpendicular to the z-axis. Therefore, the region with uniform irradiation intensity in the y-axis direction is narrower in the examination space 22 than in the x-axis direction because there is no magnetic field generated in this region. The irradiation intensity uniform region becomes narrower as the prospective angle 740 becomes smaller. Therefore, in this embodiment, in order to ensure the required performance, the prospective angle 740 is determined so that the irradiation intensity uniform region includes the examination region of the subject 1.

Here, in the transmission coil 51 of the present embodiment having the above configuration, it is shown that the imaging region is actually within the irradiation intensity uniform region. First, FIG. 5 shows an irradiation intensity (sensitivity) distribution of the transmission coil 51 of the present embodiment manufactured with a size close to the size actually used. FIG. 5A is a graph showing the sensitivity distribution in the x-axis direction, and FIG. 5B is a graph showing the sensitivity distribution in the y-axis direction. Here, the diameter of the cross section perpendicular to the z-axis of the RF shield 510 is 710 mm, and the conductors (the rung 541 and the partial rings 542 and 543) constituting the partial cylindrical RF coil 540 are arranged at a distance of 40 mm from the RF shield 510. The transmission coil 51 is used. The prospective angle 740 was set to 124 degrees.

Here, the uniform irradiation intensity region is defined as a region where the irradiation intensity is within ± 30% with reference to the central irradiation intensity of the transmission coil 51. According to the transmission coil 51 of the above size, the uniform irradiation intensity region in the x-axis direction is about 50 cm from FIG. 5A, and the uniform irradiation intensity region in the y-axis direction is about 36 cm from FIG. Hereinafter, in the present specification, the above definition is used for the irradiation intensity uniform region.

The relationship among the subject 1, the table 11, and the transmission coil 51 at the time of examination will be described. FIG. 6 shows these relationships at the time of inspection. Here, the RF base 520, the shield bobbin 511, the projection 512, and the nonmagnetic bolt 513 are omitted. As shown in this figure, the cross-sectional shape in the xy plane of the subject 1 (here, a human) when placed on the table 11 during the examination is an approximate ellipse that is long in the x-axis direction and short in the y-axis direction. Shape. A typical example of an adult male who is the main subject 1 has a shoulder width that is the length in the x-axis direction is 50 cm and a trunk thickness that is the length in the y-axis direction is about 35 cm.

5A and 5B show the lengths of the subject 1 in the respective axial directions as Subject. From this figure, it can be seen that in the case of the transmission coil 51 under the above conditions, the range indicated as Subject, that is, the region where the subject 1 exists is within the irradiation intensity uniform region in both the x-axis direction and the y-axis direction.

As described above, according to the transmission coil 51 of the present embodiment, a uniform irradiation intensity distribution can be actually obtained in a necessary region in the examination space 22 as described above. That is, it can be seen that necessary performance can be obtained while ensuring a wide inspection space 22.

Furthermore, according to the transmission coil 51 of the present embodiment, since the partial cylindrical RF coil 540 does not exist in the vicinity of the RF shield 510 at both ends in the y-axis direction, a spatial margin is created above the subject 1. For this reason, as shown in FIG. 6, it is possible to secure an installation space for various devices 13 such as a contrast medium injector device and a non-magnetic treatment device in the examination space 22.

In the above embodiment, the case where the gradient coil 31 is configured coaxially with the magnet 21 and the inner wall thereof is cylindrical is described as an example. However, the shape of the inner wall of the gradient coil 31 is not limited to this. I can't. For example, as shown in FIG. 7, the cross section perpendicular to the z-axis may be an elliptical shape having a long-axis direction in the y-axis direction or a shape similar to the elliptical shape. With this configuration, the spatial margin in the y-axis direction is further increased. FIG. 7A is an explanatory view showing a yz section of a transmission coil 51A arranged in an elliptical cylindrical gradient magnetic field coil, and FIG. 7B is an xy section view thereof.

For example, inside the gradient coil 31A, the RF shield 510A is an oval cylinder whose cross section perpendicular to the z-axis is an ellipse having a major axis of 790 mm and a minor axis of 630 mm, and the RF base 520A is separated from the RF shield 510A. A transmitting coil 51A is disposed with a distance of 40 mm. In this case, compared to the transmission coil 51, the RF shield 510A is 8 cm wider in the y-axis direction.

In this modification, only the inner wall of the gradient magnetic field coil 31 </ b> A is configured in an elliptical cylinder shape, and the outer wall is formed in a cylindrical shape along the inner wall of the magnet 21. Therefore, since the shape of the magnet 21 does not change, the manufacturing cost of the magnet 21 does not increase. Since the cross-sectional area of the inner wall of the gradient magnetic field coil 31A is substantially the same as that of the cylindrical gradient magnetic field coil 31 of the above embodiment, the magnetic field generation efficiency of the gradient magnetic field coil 31A is substantially the same as that of the gradient magnetic field coil 31.

Further, according to the transmission coil 51A of the present modification example, in the examination space 22, there is a further spatial margin in the y-axis direction over the entire z-axis direction. For example, as shown in FIG. It can be rotated and tilted around a predetermined axis. By configuring in this manner, the subject 1 can be examined in an oblique sitting position. For example, when the inclination angle (angle) of the table 11 is 18 degrees or more, the subject 1 can naturally look outside the magnet 21 while being placed on the table 11. According to the present modification, this configuration can be realized without increasing the inner wall of the magnet 21, which cannot be realized without increasing the inner wall of the magnet 21 in the conventional MRI apparatus. Therefore, it is possible to provide the MRI apparatus 10 that is excellent in visual openness without increasing the manufacturing cost.

In recent years, molecular imaging research by MRI has progressed, and brain function measurement experiments using monkeys have been actively conducted. Also in this case, the transmission coil 51A of this modification is effective. Since monkeys have the habit of sleeping when lying on a bed, it has been difficult to obtain data in the awake state with a conventional MRI apparatus. However, when the MRI apparatus 10 having the examination space 22 having a spatial margin in the y-axis direction over the entire z-axis direction as in this modification is used, a chair-type table 12 is used as shown in FIG. It is possible to position the monkey head at the center of the magnet 21 (center of the static magnetic field) by sitting on the chair table 12. As a result, brain function measurement experiments can be performed on awake monkeys.

Further, when photographing in the posture shown in FIG. 9, a highly sensitive solenoid coil 610 can be used as the receiving coil 61. In general, an RF coil used in MRI needs to be arranged so as to have sensitivity in a direction orthogonal to the static magnetic field direction (z-axis direction). Accordingly, the solenoid coil 610 cannot be used when the examination is performed with the subject 1 lying on the table 11 as in the prior art. However, in the case of the posture shown in FIG. 9, since the static magnetic field direction is perpendicular to the body axis direction of the monkey head, the sensitivity of the solenoid coil 610 provided in the monkey head is orthogonal to the static magnetic field direction. 61 can be used. Thereby, the detection sensitivity of the MRI signal can be increased, and as a result, a highly accurate brain function measurement experiment can be performed.

As described above, according to the present embodiment, the inspection space 22 can be widened while ensuring the uniformity of irradiation intensity in a necessary region without increasing the inner diameter of the magnet 21. Therefore, the tunnel-type MRI apparatus 10 can provide a test space 22 that is comfortable for the subject 1 without increasing the manufacturing cost of the entire MRI apparatus 10 and without sacrificing performance. Furthermore, an installation space for various devices can be secured in the inspection space 22.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. Also in the present embodiment, a wide inspection space 22 is secured by the transmission coil without changing the sizes of the magnet 21 and the gradient magnetic field coil 31. However, in the transmission coil of this embodiment, two partial cylindrical RF coils are arranged at positions facing each other in the y-axis direction. Other configurations of the present embodiment are basically the same as those of the first embodiment. Hereinafter, the present embodiment will be described focusing on a transmission coil having a configuration different from that of the first embodiment. In this embodiment, the x, y, and z axes are the same as those in the first embodiment.

FIG. 10 is a view for explaining the appearance of the transmission coil 51B of the present embodiment. FIG. 10A is an explanatory view showing a yz section, and FIG. 10B is an xy section view. As in the first embodiment, the transmission coil 51B of the present embodiment includes a cylindrical RF shield 510, a first cylindrical RF base 520 (not shown in FIG. 10), and an RF base 520. A partially cylindrical RF coil 540 to be formed.

The configuration, shape, and material of each part are the same as those in the first embodiment. That is, the prospective angle 740 at both ends of the RF base 520 is set to less than 180 degrees. The partial cylindrical RF coil 540 is formed on the RF base 520 along the shape of the RF base 520. Similar to the first embodiment, the two RF bases 520 are arranged in the examination space 22 so as to face each other around the z axis at a certain distance from the RF shield 510. However, in this embodiment, the partial cylindrical RF coil 540 has a circumferential center M of the partial cylindrical RF coils 540 respectively formed on the two RF bases 520 as shown in FIG. A connecting straight line 590 is arranged in the examination space 22 so as to be parallel to the y-axis. That is, in the present embodiment, the partial cylindrical RF coil 540 is disposed in the examination space 22 so as to be plane-symmetric with respect to the yz plane determined by the y axis and the z axis.

Since the partial cylindrical RF coil 540 is arranged as described above, in the transmission coil 51B of the present embodiment, the partial cylindrical type is provided in the vicinity of the RF shields 510 at both ends in the x-axis direction on the cross section orthogonal to the z-axis. There is no conductor constituting the RF coil 540. Therefore, the irradiation uniform region in the x-axis direction becomes narrower in the examination space 22 than in the y-axis direction because there is no magnetic field generated in this region. Similar to the first embodiment, the smaller the prospective angle 740, the narrower it becomes. Therefore, also in the present embodiment, the prospective angle 740 is determined so that the uniform irradiation intensity region includes the examination region of the subject 1.

Here, in the transmission coil 51B of the present embodiment having the above-described configuration, it is shown that the imaging region is actually within the irradiation intensity uniform region. First, FIG. 11 shows an irradiation intensity (sensitivity) distribution of the transmission coil 51B of the present embodiment having a specific size. FIG. 11A is a graph showing the sensitivity distribution in the x-axis direction, and FIG. 11B is a graph showing the sensitivity distribution in the y-axis direction. Here, the same size as that of the transmission coil 51 of the first embodiment, that is, the diameter of the cross section perpendicular to the z-axis of the RF shield 510 is 710 mm, and the conductor (the rung 541 and the partial ring) constituting the partial cylindrical RF coil 540. 542, 543) used the transmission coil 51B disposed at a distance of 40 mm from the RF shield 510. The prospective angle 740 was set to 124 degrees.

As shown in the figure, according to the transmission coil 51B of the above size, the irradiation intensity uniform region in the x-axis direction is about 36 cm, and the irradiation intensity uniform region in the y-axis direction is about 50 cm. The typical size of an adult male is 35 cm torso width and 35 cm torso thickness. Therefore, when photographing the trunk, the region where the subject 1 exists is within the uniform irradiation intensity region of the transmission coil 51B of the above size. I understand that. That is, according to the transmission coil 51 </ b> B of the present embodiment, a uniform irradiation intensity distribution can be obtained in a necessary region in the inspection space 22 while ensuring a wide inspection space 22.

In the transmission coil 51B of the present embodiment, the technique for fixing these RF bases 520 inside the RF shield 510 is basically the same as that of the first embodiment as shown in FIG. Also in this embodiment, the partial cylindrical RF coil 540 may be formed inside the RF base 520 as shown in FIG. 12A, or the RF base 520 as shown in FIG. You may form in the outer side.

As described above, according to the transmission coil 51B of the present embodiment, the RF base 520 and the partial cylindrical RF coil 540 are arranged as described above. For this reason, as shown in FIG. 10B, the partial cylindrical RF coil 540 and the RF base 520 that supports the partial cylindrical RF coil 540 are provided at both ends in the x-axis direction in the examination space 22 over the entire z-axis direction of the examination space 22. A space portion 560 in which no protrusion 512 or the like exists can be obtained. Therefore, as compared with the transmission coil using the conventional birdcage type RF coil, a wider inspection space 22 can be secured.

FIG. 13 (a) shows the relationship among the subject 1, the table 11, and the transmission coil 51B at the time of examination. Here, the RF base 520, the shield bobbin 511, the projection 512, and the nonmagnetic bolt 513 are omitted. As described above, the cross-sectional shape in the xy plane of the subject 1 (here, a human) when placed on the table 11 during the examination is an approximate elliptical shape that is long in the x-axis direction and short in the y-axis direction. is there. According to the transmission coil 51B of the present embodiment, the partial cylindrical RF coil 540 or the like does not exist in the examination space 22 in the vicinity of the RF shield 510 in the x-axis direction. Spatial room is created in the axial direction. Therefore, according to the transmission coil 51B of the present embodiment, particularly when the subject 1 is a human, as shown in FIG. 13A, a margin is created in the shoulder width direction, and a comfortable examination space 22 is provided. Can do.

In this embodiment as well, the inner wall of the gradient magnetic field coil arranged outside the transmission coil 51B may be an elliptic cylinder. The gradient magnetic field coil 31C and the transmission coil 51C in this case are illustrated in FIG. FIG. 14A is an explanatory view showing an xz section of a transmission coil 51C arranged in the gradient coil 31C, and FIG. 14B is an xy section view thereof. FIG. 14C is an explanatory diagram showing an xy cross-section for explaining a state when the subject 1 is inserted into the examination space 22. Thus, when the gradient magnetic field coil 31C is an ellipse whose cross section perpendicular to the z-axis direction of the inner wall is the long axis in the x-axis direction, the RF shield 510C is arranged along the inner wall of the gradient magnetic field coil 31C. As described above, the RF base 520C (not shown in FIG. 14) is disposed at a certain distance from the RF shield 510C, and the partial cylindrical RF coil 540 is formed thereon. Therefore, in the transmission coil 51C, as compared with the transmission coil 51B, it is possible to obtain a wider examination space 22 in the x-axis direction because the inner wall of the gradient magnetic field coil 31C is wider.

Here, in the transmission coil 51C of the present embodiment having the above-described configuration, it is shown that the imaging region is actually within the irradiation intensity uniform region. FIG. 15 shows an irradiation intensity (sensitivity) distribution of the transmission coil 51C having a specific size. FIG. 15A is a graph showing the sensitivity distribution in the x-axis direction, and FIG. 15B is a graph showing the sensitivity distribution in the y-axis direction. Here, the RF shield 510C is an elliptical cylinder whose cross section perpendicular to the z-axis is an ellipse having a major axis of 790 mm and a minor axis of 630 mm, and the RF base 520C is disposed with a distance of 40 mm from the RF shield 511 being disposed. 51C was used. The prospective angle 740 was set to 126 degrees. In the transmission coil 51C, the RF shield 510C is 8 cm wider in the x-axis direction than the transmission coil 51B.

15A and 15B, according to the transmission coil 51C of the above size, the irradiation intensity uniform region in the y-axis direction is approximately 42 cm, and the irradiation intensity uniform region in the x-axis direction is approximately 44 cm. According to the transmission coil 51C of the present modification, a region wider in the shoulder width direction than the transmission coil 51B can be within the irradiation intensity uniform region.

In addition, in the transmission coil 51C of the modified example, the distance between the RF base 520C forming the partial cylindrical RF coil 540 and the RF shield 510C may be changed. For example, as shown in FIG. 14C, on the xy plane, the central portion in the x-axis direction is set to 40 mm, and gradually narrows toward both ends in the x-axis direction, and the end portion is set to 20 mm. You may comprise. By configuring in this way, a spatial margin is created not only in the left-right (x-axis) direction but also in the vertical (y-axis) direction at the end in the x-axis direction in the examination space 22, thereby providing a more comfortable examination space 22. can do.

The transmission coil 51C also has a small increase in manufacturing cost for the same reason as the transmission coil 51A of the first embodiment.

As described above, according to the present embodiment, the inspection space 22 can be expanded without increasing the inner diameter of the magnet 21. Therefore, the tunnel-type MRI apparatus 10 can provide a test space 22 that is comfortable for the subject 1 without increasing the manufacturing cost of the entire MRI apparatus 10 and without sacrificing performance.

In this embodiment, the two partial cylindrical RF coils 540 and the RF base 520 that supports the two partial cylindrical RF coils 540 have the same shape, the same size, and are opposed to each other as an example. Not limited to. For example, if the centers in the circumferential direction of the two partial cylindrical RF coils 540 are on the y-axis, the sizes of the two may be different as shown in FIG. In particular, when the partial cylindrical RF coil 540 and the RF base 520 that supports the part cylindrical RF coil 540 disposed on the upper side (opposite to the table 11) of the subject 1 in the examination space 22 are made smaller, the upper part of the subject 1 is wider. Space can be secured and a more comfortable inspection space 22 can be provided.

<< Third Embodiment >>
Next, a third embodiment to which the present invention is applied will be described. This embodiment basically has the same configuration as that of the second embodiment, and secures a wider inspection space for the transmission coil without changing the sizes of the magnet 21 and the gradient magnetic field coil 31. However, the transmission coil of this embodiment expands the irradiation intensity uniform region in the x-axis direction. Hereinafter, the present embodiment will be described focusing on a transmission coil having a configuration different from that of the second embodiment. In this embodiment, the x, y, and z axes are the same as those in the first embodiment.

FIG. 16 is a diagram for explaining the external appearance of the transmission coil 51D of the present embodiment. FIG. 16A is an explanatory view showing an xz section of a transmission coil 51D arranged in the gradient coil 31, and FIG. 16B is an xy section view thereof.

As shown in the figure, the transmission coil 51D of the present embodiment is formed on a cylindrical RF shield 510, two partial cylindrical RF bases 520D (not shown in FIG. 16), and the RF base 520, respectively. A partial cylindrical RF coil 540D. The configuration, arrangement, shape, and material of each part are the same as those in the second embodiment. However, in the present embodiment, the partial cylindrical RF coil 540D is not necessarily plane-symmetric with respect to the yz plane.

Each partial cylindrical RF coil 540D of the present embodiment includes a plurality of (2 or 3) rectangular loop coils 710 having substantially the same length in the z-axis direction. Each loop type coil 710 includes a capacitor on each side. Each loop type coil 710 is arranged in the circumferential direction so that two sides are parallel to the z-axis direction at substantially the same position in the z-axis direction. At this time, each loop type coil 710 is arranged so as not to be in contact with the adjacent loop type coil 710, and the adjacent loop type coil 710 overlaps with a predetermined area in the circumferential direction. This overlapping area is adjusted so that the electromagnetic interference with each other is most reduced. The optimum overlap area is an area that measures the input impedance of each coil and is closest to the input impedance when the coil is alone.

Further, the loop type coil 710 disposed at both ends in the circumferential direction forms a current loop with the conductor constituting the RF shield 510 as a part of the loop. The RF shield 510 is connected via a capacitor 730. The loop-type coil 710 includes one or more conductors (rungs) connected in the loop between the two sides in the circumferential direction and substantially parallel to the z-axis direction, each including a capacitor. You may comprise so that a capacitor may be provided between the connection points with each rung of a side. Further, the RF base 520 is provided so as to be associated with and support each loop type coil 710.

In this embodiment, the prospective angle 740D of the RF base 520D and the partial cylindrical RF coil 540D formed thereon is less than 180 degrees. That is, in this embodiment, the prospective angle 740D in the cross section orthogonal to the z axis at the connection position of the loop type coil 710 at both ends with the RF shield 510 is less than 180 degrees. Within this range, the prospective angle 740D is determined so that the uniform irradiation intensity region includes the examination region of the subject 1 as in the above embodiments.

According to the transmission coil 51 </ b> D of the present embodiment, a current is induced on the RF shield 510 at the end in the x-axis direction in the inspection space 22 by connecting the loop type coil 710 at both ends and the RF shield 510. A magnetic field is generated in the vicinity of the RF shield 510 at the end in the x-axis direction (side surface of the RF shield 510). Thereby, the uniform irradiation intensity region in the x-axis direction is widened. Accordingly, if the size of the prospective angle 740D is the same as the prospective angle 740 of the second embodiment, the uniform irradiation intensity region in the x-axis direction is widened accordingly.

Here, FIG. 17 shows an irradiation intensity (sensitivity) distribution of the transmission coil 51D of the present embodiment having the above-described configuration and having a specific size. FIG. 17A is a graph showing the sensitivity distribution in the x-axis direction, and FIG. 17B is a graph showing the sensitivity distribution in the y-axis direction. Here, similarly to the transmission coil 51B of the second embodiment, the diameter of the cross section orthogonal to the z-axis of the RF shield 510 is 710 mm, and the conductor constituting the partial cylindrical RF coil 540D is on the y-axis. A transmission coil 51D disposed at a position 40 mm from the RF shield 510 was used. The prospective angle 740D was 150 degrees.

According to the transmission coil 51D of the above size, the irradiation intensity uniform region in the x-axis direction is about 50 cm, and the irradiation intensity uniform region in the y-axis direction is about 50 cm. Compared with the irradiation intensity (sensitivity) distribution by the transmission coil 51B of the second embodiment shown in FIG. 11, it can be seen that the irradiation intensity uniformity in the x-axis direction is greatly improved. In addition, as described above, since the shoulder width is about 50 cm in a typical size of an adult male, even if the region over the entire shoulder width is a photographing region, it can be sufficiently handled.

Here, in the transmission coil 51D of this embodiment, the reason why the partial cylindrical RF coil 540D is arranged with a plurality of loop coils 710 arranged in a non-contact manner and provided with an overlap portion will be described. FIG. 18 shows an example of the transmission coil 51E in the case where the partial cylindrical RF coil 540 shown in each of the above embodiments is connected to the RF shield 510 as it is. FIG. 18A shows a transmission arranged in the gradient magnetic field coil 31. It is explanatory drawing which shows xz cross section of the coil 51E, FIG.18 (b) is the xy cross section. Further, FIGS. 18C and 18D are explanatory diagrams for explaining the current flowing through the transmission coil 51E.

As shown in FIG. 18, when the non-contact loop type coil 710 is not configured, the conductor of the partial cylindrical RF coil 540 and the conductor of the RF shield 510 are continuous. Alternatively,

currents

810 and 820 shown in (d) flow. For example, as described in Non-Patent Document 1, the birdcage type RF coil adjusts the capacitance of the capacitor connected to the ring and the capacitance of the capacitor connected to the rung so as to electromagnetically connect the adjacent channel. Interference can be reduced and it can be easily used as a multi-channel array coil. However, when such a current flows, electrical coupling with adjacent channels increases, and even if the above method is used, a sufficient electromagnetic interference reduction effect cannot be obtained. Therefore, when used as a multi-channel array coil, each channel cannot be driven independently.

On the other hand, according to the transmission coil 51D of the present embodiment, the partial cylindrical RF coil 540D is composed of a plurality of loop coils 710 arranged in a non-contact manner, and therefore, shown in FIGS. 18 (c) and 18 (d). A current passing through the conductor of the RF shield 510 does not flow through the partial cylindrical RF coil 540D. Therefore, it can be easily used as a multi-channel array coil.

Note that, in the transmission coil 51D, the loop coil 710 constituting one partial cylindrical RF coil 540D has a prospective angle 740D of less than 180 degrees at the connection position of the loop coil 710 disposed at both ends. If so, it does not matter. As the prospective angle increases, the openness decreases, but the magnetic field generated at the end in the x-axis direction in the examination space 22 increases, so the irradiation intensity uniformity in the x-axis direction improves. For example, as shown in FIG. 19, when the connection positions of the loop type coils 710 at both ends are set so that the prospective angle 740D is close to 180 degrees, the prospective angle 740 is set smaller than this. Compared to the above, the openness is reduced, but the irradiation intensity uniformity in the x-axis direction is further improved.

As described above, according to the transmission coil 51D of the present embodiment, the partial cylindrical RF coil is disposed in the vicinity of the RF shields 510 at both ends in the x-axis direction of the examination space 22 over the entire z-axis direction of the examination space 22. It is possible to obtain a space 560 in which the 540D and the RF base 520D that supports the 540D do not exist. Therefore, a wider examination space 22 can be ensured compared to the case where the transmission coil 51 using a conventional birdcage RF coil is used, and the subject 1 can be given a sense of openness.

It should be noted that the size, overlap position, and number of each loop type coil 710 constituting the partial cylindrical RF coil 540D are not limited to those shown in FIGS. For example, as shown in FIGS. 20A and 20B, the two overlap positions may be closer to the yz plane than that shown in FIG.

In the case of the transmission coil 51E shown in FIG. 20, the overlap position of the loop type coil 710 is closer to the yz plane. Therefore, when the subject 1 is a person compared to the transmission coil 51D shown in FIG. A wider space can be secured. As described above, the closer the overlap position is to the yz plane, the more comfortable examination space 22 can be provided. On the other hand, the transmission coil 51D shown in FIG. 16 is close to the xz plane where the overlap position is determined by the x-axis and the z-axis, so that the circumferential length of the loop coil 710 disposed at both ends can be shortened. And the configuration can be simplified. Therefore, manufacture and adjustment are easy.

Further, as shown in FIGS. 21A, 21B, and 21C, in the transmission coil 51D, each partial cylindrical RF coil 540D may be configured by two loop coils 710. In this case, with respect to one partial cylindrical RF coil 540D, since there is one overlap portion in the circumferential direction, device mounting is simplified.

In this case, the overlap location is not specified. For example, as shown to Fig.21 (a), you may provide in the intersection vicinity of partial cylindrical RF coil 540D and yz plane. Further, as shown in FIG. 21B, each partial cylindrical RF coil 540D may be provided at an arbitrary position on the z axis. Furthermore, as shown in FIG. 21C, the position may not be a target position on the z axis. Further, as shown in FIG. 21 (d), each of the two partial cylindrical RF coils 540D may include a different number of loop coils 710. The number of loop coils 710 and the overlap position may be set at optimum locations according to the type of the subject 1 and the examination site.

As described above, in this embodiment, the rungs 541 are removed from both ends in the circumferential direction of the partial cylindrical RF coil 540D, and instead connected to the RF shield 510 via a capacitor. Thus, by configuring the conductor of the RF shield 510 as a part of the loop, a magnetic field is generated in the vicinity of both ends of the RF shield 510 in the x-axis direction, and the region of uniform irradiation intensity in the x-axis direction is expanded. Furthermore, in order to cut off the current passing through the RF shield 510 on the partial cylindrical RF coil 540D, the loop coil 710 is constituted by a plurality of loop coils 710 arranged in a non-contact manner. On the other hand, an overlap portion is provided to electromagnetically couple the loop type coils 710 constituting the partial cylindrical RF coil 540D to function as one partial cylindrical RF coil 540D as a whole.

According to the transmission coil 51D of the present embodiment having the above configuration, it is possible to obtain the transmission coil 51D having a wide irradiation intensity uniform region in the examination space 22 and a wide use range. Further, since the size of the magnet 21 is not changed, there is no increase in manufacturing cost. Therefore, the comfort of the examination space 22 can be enhanced while having substantially the same performance as the conventional birdcage RF coil. Therefore, according to the transmission coil 51D of the present embodiment, a comfortable examination space 22 can be secured in the tunnel type MRI apparatus without increasing the manufacturing cost of the MRI apparatus 10 and without sacrificing performance.

Also in this embodiment, the shape of the inner wall of the gradient magnetic field coil 31 disposed outside the transmission coil 51D is not limited to a cylindrical shape, and may be an elliptical cylindrical shape as in the above embodiments. Further, as in the first embodiment, the examination space 22 may be configured to have a margin in both end portions in the y-axis direction.

In each of the above embodiments, the case where the transmitter coil 51 is used has been described as an example. However, the RF coil having the configuration described in the above embodiment may be used as a receiver coil. Moreover, you may use as a coil for transmission / reception.

Furthermore, the transmission coil of each of the above embodiments can be used in any device that uses an electromagnetic wave having a frequency of several MHz to several GHz in addition to being used as a part of the MRI apparatus.

1: subject, 2: static magnetic field generation system, 3: gradient magnetic field generation system, 4: sequencer, 5: transmission system, 6: reception system, 7: information processing system, 10: MRI apparatus, 11: table, 12: Chair table, 13: various devices, 21: magnet, 22: inspection space, 31: gradient magnetic field coil, 31A: gradient magnetic field coil, 31C: gradient magnetic field coil, 32: gradient magnetic field power supply, 51: transmission coil, 51A: transmission Coil, 51B: Transmitting coil, 51C: Transmitting coil, 51D: Transmitting coil, 51E: Transmitting coil, 52: High frequency oscillator, 53: Modulator, 54: High frequency amplifier, 61: Reception coil, 62: Signal amplifier, 63: Quadrature Phase detector, 64: A / D converter, 71: CPU, 72: storage device, 73: external storage device, 74: display device, 75: input device, 100: RF coil, 100A: R Coil, 100C: Array coil, 110: Ring, 120: Ring, 130: Lang, 140: Direction of static magnetic field, 150: Feed point, 151: Feed port, 152: Feed port, 160: Tunnel inner wall, 510: RF shield , 510A: RF shield, 510C: RF shield, 511: shield bobbin, 512: protrusion, 513: non-magnetic bolt, 520: RF base, 520A: RF base, 520C: RF base, 520D: RF base, 540: part Cylindrical RF coil, 540C: Partial cylindrical RF coil, 540D: Partial cylindrical RF coil, 541: Lang, 542: Partial ring, 543: Partial ring, 544: Capacitor, 545: Capacitor, 560: Space part, 580: Straight line, 590: Straight line, 610: Solenoid coil, 710 Loop coil, 730: capacitor, 740: apparent angle, 740D: apparent angle, 810: current, 820: Current

Claims

An annular magnet unit for generating a static magnetic field, an annular gradient coil disposed coaxially with the magnet unit in an inspection region surrounded by the magnet unit, and a high-frequency magnetic coil disposed inside the gradient coil A magnetic resonance measuring apparatus comprising:
The high frequency magnetic field coil is:
An annular high-frequency magnetic field shield disposed coaxially with the gradient magnetic field coil along the inner wall of the gradient magnetic field coil inside the gradient magnetic field coil,
A partial cylindrical loop coil having two partial cylindrical shapes arranged facing the inside of the high-frequency magnetic field shield,
Each of the partial cylindrical loop coils is
A plurality of linear conductors arranged in parallel with each other at a predetermined distance from each other in the axial direction;
Two partial arcuate conductors connecting the plurality of linear conductors at both axial ends of the partial cylindrical shape,
The magnetic resonance measuring apparatus according to claim 1, wherein a prospective angle at each circumferential end of each partial cylindrical shape is less than 180 degrees.
A magnetic resonance measuring apparatus according to claim 1,
The magnetic resonance measuring apparatus, wherein an inner wall of the gradient magnetic field coil is cylindrical.
The magnetic resonance measuring apparatus according to claim 1,
An inner wall of the gradient magnetic field coil has an elliptical cylindrical shape.
The magnetic resonance measuring apparatus according to claim 1,
Further comprising a table for holding the subject in parallel with the central axis of the magnet section in the examination region, the body axis of the subject,
In the two partial cylindrical loop coils, a straight line connecting the circumferential center positions of the partial cylindrical loop coils on one virtual cross section orthogonal to the central axis mounts the subject of the table. The magnetic resonance measuring apparatus is arranged so as to be parallel to a surface to be placed.
The magnetic resonance measuring apparatus according to claim 1,
Further comprising a table for holding the subject in parallel with the central axis of the magnet section in the examination region, the body axis of the subject,
In the two partial cylindrical loop coils, a straight line connecting the circumferential center positions of the partial cylindrical loop coils on one virtual cross section orthogonal to the central axis mounts the subject of the table. A magnetic resonance measuring apparatus, wherein the magnetic resonance measuring apparatus is arranged so as to be orthogonal to a surface to be placed.
The magnetic resonance measuring apparatus according to claim 1,
The two partial cylindrical loop coils have the same shape.
The magnetic resonance measuring apparatus according to claim 1,
The magnetic resonance measuring apparatus, wherein the two partial cylindrical loop coils are arranged at a certain distance from the high-frequency magnetic field shield.
The magnetic resonance measuring apparatus according to claim 1,
Each of the two partial cylindrical loop coils is a loop coil having substantially the same length in the central axis direction, and is overlapped by a predetermined area in the circumferential direction of the partial cylindrical loop coil without contact with each other. A magnetic resonance measuring apparatus comprising three or less loop coils arranged and connected to the high-frequency magnetic field shield at both ends in a circumferential direction.
The magnetic resonance measuring apparatus according to claim 8,
The number of the loop coils is 3, and the two loop coils arranged at both ends in the circumferential direction do not include the linear conductor.
The magnetic resonance measuring apparatus according to claim 8,
Each of the loop coils includes the linear conductor. A magnetic resonance measuring apparatus.
The magnetic resonance measuring apparatus according to claim 1,
The magnetic resonance measurement apparatus characterized in that the prospective angles at both ends in the circumferential direction of each partial cylinder shape are determined such that a predetermined range in the inspection region falls within a predetermined irradiation intensity range.