JP5268287B2 - Array coil and magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to an array coil suitable for use as a reception RF coil of a magnetic resonance imaging apparatus, and a magnetic resonance imaging apparatus including the array coil.

  An array coil is widely used as a reception RF (radio frequency) coil of a magnetic resonance imaging apparatus (MRI apparatus). The array coil is configured by arranging a plurality of element coils.

  Among the array coils, there is a type that includes a large number of element coils and can cope with a wide imaging range. In this type of array coil, when the field of view (FOV) is narrower than the sensitivity area of the entire array coil, the actual sensitivity area (actual sensitivity area) can be obtained by enabling a part of many element coils. Can be set to a size according to the FOV.

As a technique similar to this, Patent Document 1 discloses a magnetic resonance imaging apparatus that selects and activates only a plurality of coil assemblies that are involved in imaging.
JP-A-4-212329

  Now, when the sensitivity area required according to the FOV (hereinafter referred to as “required sensitivity area”) can be achieved by only a part of the element coils, the effective element coils can be selected from all the element coils included in the array coil. Will choose. At this time, it is necessary that all of the necessary sensitivity regions overlap with any one of the individual sensitivity regions (hereinafter referred to as individual sensitivity regions) of the selected element coil. For this reason, depending on the positional relationship between the FOV and each element coil, it may be necessary to select more element coils than the minimum number necessary to form an actual sensitivity region having the same size as the FOV. In this case, since the actual sensitivity region becomes larger than the FOV, there is a possibility that aliasing artifacts (aliasing) may occur.

  In order to keep the number of element coils to be selected closer to the above minimum number, the width of the element coils in the arrangement direction of the element coils can be reduced, or the overlapping amount of adjacent element coils can be increased. Can be considered. However, in the former method, the sensitivity related to the area away from the array coil is lowered. In the latter method, since the interference between the element coils increases, the SN characteristic is deteriorated.

  The present invention has been made in consideration of such circumstances, and its object is to make it possible to increase the degree of freedom in setting the sensitivity region without relying on the above-described method. is there.

Each of the array coils according to the first aspect of the present invention has a loop shape, three or more odd-numbered conductive elements arranged at a predetermined interval and so that adjacent ones partially overlap each other , and A connection that connects two conductive elements located at one end of the odd number of conductive elements is arranged so as to switch connection / disconnection of the overlapping conductive elements at a portion where the conductive elements overlap. A plurality of connection patterns that can connect the three or more conductive elements with a plurality of types of connection patterns including a pattern and a connection pattern that connects two conductive elements located at the other end of the odd number of conductive elements. comprising of a first switch, a second switch ends of the two conductive elements located in a loop of the connection / disconnection of the two switching each of said three or more conductive elements .

The magnetic resonance imaging apparatus according to the second aspect of the present invention includes three or more odd-numbered conductive elements each having a loop shape and arranged such that adjacent ones partially overlap each other at a predetermined interval. And in a portion where the conductive elements overlap each other, it is arranged to switch connection / disconnection of the overlapping conductive elements, and two conductive elements located at one end of the odd number of conductive elements are connected. The three or more conductive elements can be connected by a plurality of types of connection patterns including a connection pattern that connects two of the odd-numbered conductive elements and a connection pattern that connects two conductive elements at the other end. a plurality of first switches, and said three or more conductive two second Sui switching both ends of the two located on the conductive element loop connection / disconnection of the of the element An array coil with a switch, and a pattern selector for selecting one of said plurality of kinds connecting patterns, so as to connect the three or more conductive elements by a connecting pattern selected by the pattern selection unit Magnetic resonance in which a control unit that controls the plurality of first switches and the two second switches , and a conductive element group connected by the connection pattern selected by the pattern selection unit are emitted from a subject. A reconstruction unit configured to reconstruct an image related to the subject based on a signal received and output.

  According to the present invention, it is possible to increase the degree of freedom in setting the sensitivity region.

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

  FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (MRI apparatus) according to the present embodiment. The MRI apparatus shown in FIG. 1 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, a bed 4, a bed control unit 5, RF coil units 6a, 6b and 6c, a transmission unit 7, a selection circuit 8, and a reception. A section 9 and a computer system 10.

  The static magnetic field magnet 1 has a hollow cylindrical shape and generates a uniform static magnetic field in an internal space. As the static magnetic field magnet 1, for example, a permanent magnet, a superconducting magnet or the like is used.

  The gradient magnetic field coil 2 has a hollow cylindrical shape and is disposed inside the static magnetic field magnet 1. The gradient magnetic field coil 2 is a combination of three types of coils corresponding to the X, Y, and Z axes orthogonal to each other. The gradient magnetic field coil 2 generates a gradient magnetic field in which the above three types of coils are individually supplied with current from the gradient magnetic field power supply 3 and the magnetic field strength is inclined along the X, Y, and Z axes. The Z-axis direction is the same as the static magnetic field direction, for example. 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 slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to change the phase of the magnetic resonance signal in accordance with the spatial position. The readout gradient magnetic field Gr is used for changing the frequency of the magnetic resonance signal in accordance with the spatial position.

  The subject 100 is inserted into the space (imaging space) inside the gradient magnetic field coil 2 while being placed on the top 4 a of the bed 4. Under the control of the bed control unit 5, the bed 4 moves the top 4a in the longitudinal direction (left and right direction in FIG. 1) and in the vertical direction. Usually, the bed 4 is installed such that the longitudinal direction thereof is parallel to the central axis of the static magnetic field magnet 1.

  The RF coil unit 6a is configured by housing one or more coils in a cylindrical case. The RF coil unit 6 a is disposed inside the gradient magnetic field coil 2. The RF coil unit 6a receives a high frequency pulse (RF pulse) from the transmitter 7 and generates a high frequency magnetic field.

  The RF coil units 6 b and 6 c are placed on the top plate 4 a, built in the top plate 4 a, or attached to the subject 100. At the time of imaging, the object 100 is inserted into the imaging space. Array coils are used as the RF coil units 6b and 6c. That is, each of the RF coil units 6b and 6c includes a plurality of element coils. The element coils provided in the RF coil units 6b and 6c each receive a magnetic resonance signal radiated from the subject 100. The output signals of the element coils are individually input to the selection circuit 8. The receiving RF coil unit is not limited to the RF coil units 6b and 6c, and various types of RF coil units can be arbitrarily attached. One or three or more RF coil units for reception may be attached.

  The transmitter 7 supplies an RF pulse corresponding to the Larmor frequency to the RF coil unit 6a.

  The selection circuit 8 selects some of a number of magnetic resonance signals output from the RF coil units 6b and 6c. Then, the selection circuit 8 gives the selected magnetic resonance signal to the reception unit 9. Which channel is selected is instructed from the computer system 10.

  The receiving unit 9 includes a plurality of processing systems including an amplifier, a phase detector, and an analog / digital converter. Magnetic resonance signals selected by the selection circuit 8 are respectively input to the processing systems of these multiple channels. The amplifier amplifies the magnetic resonance signal. The phase detector detects the phase of the magnetic resonance signal output from the amplifier. The analog-digital converter converts the signal output from the phase detector into a digital signal. The receiving unit 9 outputs a digital signal obtained by each processing system.

  The computer system 10 includes an interface unit 11, a data collection unit 12, a reconstruction unit 13, a storage unit 14, a display unit 15, an input unit 16, and a main control unit 17.

  The interface unit 11 is connected to the gradient magnetic field power source 3, the bed control unit 5, the RF coil unit 6b, the transmission unit 7, the reception unit 9, the selection circuit 8, and the like. The interface unit 11 inputs and outputs signals exchanged between these connected units and the computer system 10.

  The data collection unit 12 collects digital signals output from the reception unit 9. The data collection unit 12 stores the collected digital signal, that is, magnetic resonance signal data in the storage unit 14.

  The reconstruction unit 13 performs post-processing, that is, Fourier transform, on the magnetic resonance signal data stored in the storage unit 14 to obtain spectrum data or image data of the desired nuclear spin in the subject 100.

  The storage unit 14 stores magnetic resonance signal data and spectrum data or image data for each subject.

  The display unit 15 displays various information such as spectrum data or image data under the control of the main control unit 17. As the display unit 15, a display device such as a liquid crystal display can be used.

  The input unit 16 receives various commands and information input from the operator. As the input unit 16, a pointing device such as a mouse or a trackball, a selection device such as a mode change switch, or an input device such as a keyboard can be used as appropriate.

  The main control unit 17 includes a CPU, a memory, and the like (not shown), and comprehensively controls the MRI apparatus of the present embodiment. The main control unit 17 has the following two functions in addition to the function of performing control for realizing a known operation in the MRI apparatus. One of these functions automatically selects the operation mode of the RF coil unit 6b. Another of the above functions is to automatically select an effective element coil among the element coils included in the RF coil unit 6b.

  The above is the overall configuration of the MRI apparatus according to the present embodiment. A feature of the present embodiment is an array coil that can be used as the RF coil units 6b and 6c. Therefore, the array coils that can be used as the RF coil units 6b and 6c will be described in detail below.

(First embodiment)
FIG. 2 is a diagram showing a circuit configuration of the array coil 200 according to the first embodiment.

  The array coil 200 includes a coil group G1 including four element coils 21-1, 21-2, 21-3, 21-4, and four element coils 22-1, 22-2, 22-3, 22-. And a coil group G2 including four.

  In addition to this, the array coil 200 includes capacitors 23-1, 23-2, 23-3, 23-4, matching circuits 24-1, 24-2, 24-3, 24-4, capacitors 25-1, 25- 2, 25-3, 25-4, coils 26-1, 26-2, 26-3, 26-4, PIN diodes 27-1, 27-2, 27-3, 27-4, 28-1, 28 -2, 28-3, 28-4, choke coils 29, 30, capacitors 31-1, 31-2, 31-3, 31-4, matching circuits 32-1, 32-2, 32-3, 32- 4, capacitors 33-1, 33-2, 33-3, 33-4, coils 34-1, 34-2, 34-3, 34-4, PIN diodes 35-1, 35-2, 35-3, 35-4, 36-1, 36-2, 36-3, 36-4, choke coils 37, 38 and preamplifiers 39-1, 39-2, 39-3, 39-4 are included.

  Among these, capacitors 23-1 to 23-4, matching circuits 24-1 to 24-4, capacitors 25-1 to 25-4, coils 26-1 to 26-4, and PIN diodes 27-1 to 27-4, 28 For -1 to 28-4, the one with the code ending in "-1" is in the element coil 21-1, the one with the code ending in "-2" is in the element coil 21-2, and the code ending is Those with “−3” are attached to the element coil 21-3, and those with the suffix “−4” are attached to the element coil 21-4. Capacitors 31-1 to 31-4, matching circuits 32-1 to 32-4, capacitors 33-1 to 33-4, coils 34-1 to 34-4, and PIN diodes 35-1 to 35-4, 36-1 ~ 36-4, the one with the end of the sign "-1" is the element coil 22-1, the one with the end of the sign "-2" is the element coil 22-2, and the end of the sign is "- Those with “3” are attached to the element coil 22-3, and those with the suffix “-4” are attached to the element coil 22-4.

  Element coil 21-1 receives a magnetic resonance signal. The magnetic resonance signal received by the element coil 21-1 is input to the preamplifier 39-1 via the matching circuit 24-1 and the capacitor 25-1. The matching circuit 24-1 performs impedance matching between the element coil 21-1 and the preamplifier 39-1. Capacitor 25-1 cuts the DC component from the signal input to preamplifier 39-1.

  The capacitor 23-1 is inserted in the middle of the element coil 21-1. One end of the coil 26-1 and the cathode of the PIN diode 27-1 are connected. The coil 26-1 and the PIN diode 27-1 are connected in parallel to the capacitor 23-1. One end of the choke coil 29 is connected to a connection point between the coil 26-1 and the PIN diode 27-1. The cathode of the PIN diode 28-1 is connected to the connection point between the matching circuit 24-1 and the capacitor 25-1. The anode of the PIN diode 28-1 is grounded and connected to one end of the choke coil 30. A first control signal is supplied from the computer system 10 between the other end of the choke coil 29 and the other end of the choke coil 30. The computer system 10 grounds the signal line connected to the choke coil 29 and sets the potential of the signal line connected to the choke coil 30 to be positive or negative, thereby setting the positive bias or the negative bias to the first control signal. To the array coil 200.

  As can be seen from FIG. 2, the circuits related to the element coils 21-2 to 21-4 have the same configuration as the above-described circuit related to the element coil 21-1 by the respective elements associated therewith. However, the capacitors 25-2, 25-3, and 25-4 are connected to the preamplifiers 39-2 to 39-4, respectively. That is, the magnetic resonance signals received by the element coils 21-2 to 21-4 are input to the preamplifiers 39-2 to 39-4, respectively. The connection point between coil 26-2 and PIN diode 27-2, the connection point between coil 26-3 and PIN diode 27-3, and the connection point between coil 26-4 and PIN diode 27-4 are all included. A choke coil 29 is connected. The anodes of the PIN diodes 28-2, 28-3, and 28-4 are all grounded and connected to the choke coil 30.

  The circuit related to the element coil 22-1 is a circuit related to the element coil 21-1 by the capacitor 31-1, the matching circuit 32-1, the capacitor 33-1, the coil 34-1 and the PIN diodes 35-1 and 36-1. It is configured in the same way. The circuits related to the element coils 22-2 to 22-4 also have the same configuration as that of the element coil 22-1, depending on the elements associated therewith. However, the capacitors 33-1 to 33-4 are connected to the preamplifiers 39-1 to 39-4, respectively. That is, the magnetic resonance signals received by the element coils 22-2 to 22-4 are input to the preamplifiers 39-2 to 39-4, respectively. Connection point between coil 34-1 and PIN diode 35-1, connection point between coil 34-2 and PIN diode 35-2, connection point between coil 34-3 and PIN diode 35-3, and coil 34-4 One end of the choke coil 37 is connected to the connection point between the PIN diode 35-4 and the PIN diode 35-4. Each of the anodes of the PIN diodes 36-1 to 36-4 is grounded and connected to one end of the choke coil 38.

  A second control signal is supplied from the computer system 10 between the other end of the choke coil 37 and the other end of the choke coil 38. The computer system 10 grounds the signal line connected to the choke coil 38 and sets the potential of the signal line connected to the choke coil 37 to be positive or negative, thereby setting the positive bias or the negative bias to the second control signal. To the array coil 200.

  In this way, the capacitor 25-1 and the capacitor 33-1 are connected to the input terminal of the preamplifier 39-1. The length of the transmission line from the connection point C1 of the preamplifier 39-1, the capacitor 25-1 and the capacitor 33-1 to the connection point C2 of the capacitor 25-1 and the diode 28-1 is λ / 4 + (λ / 2 ) × r (r is an integer). The length of the transmission line from the connection point C1 to the connection point C3 between the capacitor 33-1 and the diode 36-1 is also preferably λ / 4 + (λ / 2) × r. The same applies to the input terminals of the preamplifiers 39-2 to 39-4. Note that λ is the wavelength of the magnetic resonance signal.

  The preamplifiers 39-1 to 39-4 amplify and output the signal input to the input terminal. The outputs of the preamplifiers 39-1 to 39-4 are given to the selection circuit 8 as magnetic resonance signals of the first channel ch1 to the fourth channel ch4, respectively.

  FIG. 3 is a diagram schematically showing the arrangement of the element coils 21-1 to 21-4 and 22-1 to 22-4. The upper side shows a plan view and the lower side shows a side view. In the plan view, the element coils 22-1 to 22-4 are indicated by broken lines in order to clearly indicate the difference in position between the element coils 21-1 to 21-4 and the element coils 22-1 to 22-4. ing.

  The element coils 21-1 to 21-4 are arranged along the first direction at a constant interval P1. In the element coils 21-1 to 21-4, end portions of adjacent elements are overlapped with each other. The element coils 22-1 to 22-4 are arranged along the first direction at a constant interval P1. In the element coils 22-1 to 22-4, end portions of adjacent elements are overlapped with each other. With such an arrangement, coil groups G1 and G2 are formed. The coil group G1 and the coil group G2 are arranged along a second direction orthogonal to the first direction. The positions of the coil group G1 and the coil group G2 coincide with each other in the third direction orthogonal to the first and second directions. The coil group G1 and the coil group G2 are different from each other in the position in the first direction. The amount of deviation between the coil group G1 and the coil group G2 is ½ of the interval P1. Thus, each of the element coils 21-1 to 21-4 and each of the element coils 22-1 to 22-4 do not face each other. The directions and positions of the element coils 21-1 to 21-4 and 22-1 to 22-4 do not have to strictly satisfy the above-described conditions, and may be slightly shifted.

  Next, the operation of the array coil 200 configured as described above will be described.

  When the positive bias is input as the first control signal, the PIN diodes 27-1 to 27-4 and 28-1 to 28-4 are all turned to reverse because they are reverse biases. Thereby, the element coils 21-1 to 21-4 are in a state where they can receive magnetic resonance signals.

  When a negative bias is input as the first control signal, the PIN diodes 27-1 to 27-4 and 28-1 to 28-4 are all turned on because they are forward biased. As a result, the element coils 21-1 to 21-4 are in a state where they cannot receive the magnetic resonance signal.

  When the positive bias is input as the second control signal, the PIN diodes 35-1 to 35-4 and 36-1 to 36-4 are all reversely biased and are turned off. As a result, the element coils 22-1 to 22-4 are in a state where they can receive magnetic resonance signals.

  When a negative bias is input as the second control signal, the PIN diodes 35-1 to 35-4 and 36-1 to 36-4 are all turned on because they are forward biased. As a result, the element coils 22-1 to 22-4 cannot receive the magnetic resonance signal.

  Thus, when the positive bias is input as the first control signal and the negative bias is input as the second control signal, the coil group G1 is enabled. When the negative bias is input as the first control signal and the positive bias is input as the second control signal, the coil group G2 is enabled. Only the magnetic resonance signals received by the element coils included in the valid coil group are input to the preamplifiers 39-1 to 39-4, respectively. At this time, for example, if all the element coils of each of the coil groups G1 and G2 are selected by the selection circuit 8, for example, when the coil group G1 is enabled and when the coil group G2 is enabled, The position of the actual sensitivity region is shifted by P1 / 2. That is, the position of the actual sensitivity region can be changed by an amount smaller than the interval between the element coils in one coil group.

  The selection between the first mode in which the coil group G1 is enabled and the second mode in which the coil group G2 is enabled may be performed by the user. Further, the user may select a valid channel among the four channels of magnetic resonance signals output from the preamplifiers 39-1 to 39-4. In this case, the main control unit 17 validates the coil group G1 when the user designates the first mode using the input unit 16, and validates the coil group G2 when the second mode is designated. . The main control unit 17 also controls the selection circuit 8 so as to select the magnetic resonance signal of the effective channel designated by the user using the input unit 16. However, the main control unit 17 can also automatically select a mode and an effective channel as described below.

  FIG. 4 is a flowchart of processing of the main control unit 17.

  In the processing described here, the various coordinates relate to a one-dimensional coordinate system along the Z-axis direction with one end of the top 4a as a reference point.

  In step Sa1, the main control unit 17 determines the end coordinate A0. The end coordinate A0 is a coordinate where the element coil 21-1 is located as shown in FIG. The end coordinate A0 may be input by the user, or may be determined based on the mounting position of the array coil 200 on the top plate 4a. The mounting position of the array coil 200 on the top plate 4a may be detected by a sensor provided on the top plate 4a or the like, or received by each of the element coils 21-1 to 21-4 and 22-1 to 22-4. Detection may be performed based on a signal to be transmitted.

  In step Sa2, the main control unit 17 determines the center coordinate C0 of the FOV and the width k in the Z-axis direction. The FOV is determined in a known manner based on various shooting conditions designated by the user.

In step Sa3, the main control unit 17 obtains the minimum j that satisfies the following expression (1), and substitutes the value for the variable j1.
C0 + k / 2 ≦ A0 + P1 / 2 × j (1)
The variable j1 obtained as a result of the first block B1 to the ninth block B9 as shown in FIG. 5 is at least partly located at the coordinates where the FOV exists and is far from the reference point. This is the number of the block located at the same coordinates as the end portion (hereinafter referred to as the far end portion). That is, in the example shown in FIG. 5, the variable j1 is obtained as “7”, and from this variable j1, at least a part is located in the coordinate range in which the FOV exists (hereinafter referred to as the FOV range), and is far away. It can be seen that the block located at the same coordinates as the end is the seventh block B7. Note that the first block B1 to the ninth block B9 are determined by dividing each of the P1 / 2 widths from the end of the element coil 21-1.

In step Sa4, the main control unit 17 obtains the maximum j that satisfies the following expression (2), and substitutes the value for the variable j2.
C0−k / 2 ≧ A0 + P1 / 2 × j (2)
The variable j2 obtained as a result represents the number of blocks that completely protrude from the FOV range to the reference point side from the end portion of the FOV closer to the reference point (hereinafter referred to as the adjacent end portion). In the example shown in FIG. 5, the variable j2 is obtained as “1”, and it can be seen that only one block, that is, the first block B1 protrudes as described above.

  In step Sa5, the main controller 17 checks whether or not the value obtained as “j1-j2” is an odd number. The value obtained as “j1-j2” corresponds to the number of blocks that are at least partially located in the FOV range. Therefore, if the value obtained as “j1-j2” is an even number, the FOV can be covered by the number of element coils corresponding to ½ of the value. Therefore, in this case, the main control unit 17 proceeds from step Sa5 to step Sa6, and checks whether or not the variable j1 is an odd number. One of the element coils 21-1 to 21-4 belonging to the coil group G1 and one of the element coils 22-1 to 22-4 belonging to the coil group G2 are located at the same coordinates as the far end of the FOV. In this case, when the variable j1 is an even number, the former element coil has a smaller amount of protrusion from the FOV range than the latter element coil, and when the variable j1 is an odd number, the former element coil is the former element coil. The amount of protrusion from the FOV range is smaller than that of the element coil. Therefore, the main control unit 17 proceeds from step Sa6 to step Sa9 if the variable j1 is not an odd number, and proceeds from step Sa6 to step Sa11 if the variable j1 is an odd number.

If the value obtained as “j1-j2” is an odd number, the main control unit 17 proceeds from step Sa5 to step Sa7. In step Sa7, the main control unit 17 compares the amount L1 of the block located at the same coordinate as the far end portion and the amount L2 of the block located at the same coordinate as the neighboring end portion and the amount L2 of the block located outside the FOV range. L1 and L2 are obtained by the following equations (3) and (4), respectively.
L1 = (A0 + P1 / 2 × j1) − (C0 + k / 2) (3)
L2 = (C0−k / 2) − (A0 + P1 / 2 × j2) (4)
When L1 is smaller than L2, it is preferable to use an element coil having a small amount of protrusion from the FOV range among element coils located at the same coordinates as the far end. Therefore, the main control unit 17 proceeds from step Sa7 to step Sa6, and performs the processing as described above.

  On the other hand, when L1 is not smaller than L2, it is desirable to use an element coil having a small amount of protrusion from the FOV range among element coils located at the same coordinates as the neighboring end. Therefore, the main control unit 17 proceeds from step Sa7 to step Sa8, and checks whether or not the variable j1 is an odd number. The main control unit 17 proceeds from step Sa8 to step Sa9 if the variable j1 is an odd number, and proceeds from step Sa8 to step Sa11 if the variable j1 is not an odd number.

  When the process proceeds from step Sa6 or step Sa8 to step Sa9, the main control unit 17 selects the first mode. In step Sa10, the main control unit 17 selects an effective channel according to the first setting table shown in FIG.

  When the process proceeds from step Sa6 or step Sa8 to step Sa11, the main control unit 17 selects the second mode. In step Sa10, the main control unit 17 selects an effective channel according to the second setting table shown in FIG.

  In the example shown in FIG. 5, since j1 is “7” and j2 is “1”, the value obtained as “j1-j2” is an even number, and j1 is an odd number. For this reason, the main controller 17 selects the second mode. Then, according to the second setting table shown in FIG. 7, channels ch1 to ch3 are selected as effective channels. As a result, the element coils 22-1 to 22-3 are made effective. If the first mode is selected in the example shown in FIG. 5, the FOV range cannot be covered unless the element coils 21-1 to 21-4 are enabled, so that the above selection is appropriate. It is clear that there is.

  As described above, according to the present embodiment, in consideration of the positional relationship between each element coil and the FOV, the selection of the coil group and the selection of the element coil are performed so that the amount of the selected element coil protruding from the FOV range is minimized. Is automatically performed, it is possible to collect magnetic resonance signals in a state in which the sensitivity other than the FOV is minimized.

(Second Embodiment)
FIG. 8 is a diagram illustrating a configuration of an array coil 300 according to the second embodiment.

  The array coil 300 includes conductive elements 41, 42, 43, 44, 45, 46, 47, 48, 49, switch circuits 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, a matching circuit. 60, 61, 62, 63 and preamplifiers 64, 65, 66, 67 are included.

  The conductive elements 41 to 49 each have a loop shape, and are arranged in a line at regular intervals. Adjacent conductive elements partially overlap each other.

  Each of the switch circuits 51 to 58 is provided between two adjacent conductive elements. The switch circuits 50 and 59 are attached to the conductive elements 41 and 49, respectively. The switch circuits 51 to 58 connect or disconnect two adjacent conductive elements to each other based on the first or second control signal. The first control signal is input to the switch circuits 50, 52, 54, 56, and 58, and the second control signal is input to the switch circuits 51, 53, 55, 57, and 59.

  The matching circuits 60 to 63 are attached to the conductive elements 42, 44, 46, and 48, respectively. The matching circuits 60 to 63 perform impedance matching between the element coils formed as described later and the preamplifiers 64 to 67 by the conductive elements 42, 44, 46, and 48 and the conductive elements adjacent to the conductive elements 42, 44, 46, and 48.

  The preamplifiers 64 to 67 receive the output signals of the matching circuits 60 to 63, respectively, and amplify these signals. The outputs of the preamplifiers 64 to 67 are given to the selection circuit 8 as magnetic resonance signals of the first channel ch1 to the fourth channel ch4, respectively.

  FIG. 9 is a circuit diagram showing a detailed configuration of the switch circuits 50-59. Since the switch circuits 50 to 59 have the same configuration, FIG. 9 shows the configuration of one switch circuit. However, the switch circuits 50 to 59 are referred to as the first conductive element 91 and the second conductive element 92 here, although the conductive elements to be connected / disconnected differ from one another. The first conductive element 91 corresponds to the conductive elements 41, 42, 43, 44, 45, 46, 47, and 48 in the switch circuits 51 to 58, respectively. The second conductive element 92 corresponds to the conductive elements 42, 43, 44, 45, 46, 47, 48, and 49 in the switch circuits 51 to 58, respectively. In the switch circuit 50, the conductive element 41 corresponds to the second conductive element 92, but there is no conductive element corresponding to the first conductive element 91. In the switch circuit 59, the conductive element 49 corresponds to the first conductive element 91, but there is no conductive element corresponding to the second conductive element 92.

  As shown in FIG. 9, the switch circuits 50 to 59 include capacitors 71, 72, 73, 74, coils 75, 76, 77, 78, PIN diodes 79, 80, 81, 82, and choke coils 83, 84, 85, respectively. 86.

  The capacitor 71 is inserted in the middle of the first conductive element 91. One end of the coil 75 and the cathode of the PIN diode 79 are connected. The coil 75 and the PIN diode 79 are connected to the capacitor 71 in parallel.

  The capacitor 72 is inserted in the middle of the second conductive element 92. One end of the coil 76 and the cathode of the PIN diode 80 are connected. The coil 76 and the PIN diode 80 are connected to the capacitor 72 in parallel.

  Capacitors 73 and 74 are respectively inserted between the first conductive element 91 and the second conductive element 92. A connection point of the capacitor 73 to the first conductive element 91 and a connection point of the capacitor 74 to the first conductive element 91 are located with the capacitor 71 interposed therebetween. A connection point of the capacitor 73 to the second conductive element 92 and a connection point of the capacitor 74 to the second conductive element 92 are located with the capacitor 72 interposed therebetween. One end of the coil 77 and the cathode of the PIN diode 81 are connected. The coil 77 and the PIN diode 81 are connected to the capacitor 73 in parallel. One end of the coil 78 and the cathode of the PIN diode 82 are connected. The coil 78 and the PIN diode 82 are connected in parallel with the capacitor 74.

  When one PIN diode is turned on, one coil connected to the cathode of the PIN diode and one capacitor connected in parallel to the PIN diode and the coil form a closed circuit. The inductance of the coil and the capacitance of the capacitor are set so that the closed circuit resonates at the frequency of the magnetic resonance signal.

  One end of the choke coil 83 is connected to a connection point of the capacitor 73 to the second conductive element 92. One end of the choke coil 84 is connected to a connection point of the capacitor 74 to the first conductive element 91. One end of the choke coil 85 is connected to a connection point of the capacitor 74 to the second conductive element 92. One end of the choke coil 86 is connected to a connection point of the capacitor 73 to the first conductive element 91. The other end of the choke coil 83 is connected to the other end of the choke coil 84. The other end of the choke coil 85 is connected to the other end of the choke coil 86.

  A control signal is supplied from the computer system 10 between the connection point of the choke coils 83 and 84 and the connection point of the choke coils 85 and 86. The computer system 10 controls the positive bias or the negative bias by grounding the signal line connected to the choke coils 85 and 86 and making the potential of the signal line connected to the choke coils 83 and 84 positive or negative. The signal is supplied to the array coil 300 as a signal. This control signal is a first control signal in the switch circuits 50, 52, 54, 56, and 58, and a second control signal in the switch circuits 51, 53, 55, 57, and 59.

  Next, the operation of the array coil 300 configured as described above will be described.

  The computer system 10 outputs a positive bias as one of the first and second control signals and a negative bias as the other. That is, the main control unit 17 controls the interface unit 11 to output a positive bias as the first control signal and to output a negative bias as the second control signal in the first mode. Further, the main control unit 17 controls the interface unit 11 to output a negative bias as the first control signal and to output a positive bias as the second control signal in the second mode. When the positive bias is input as the first or second control signal, the PIN diodes 79 and 80 are forward biased, and the PIN diodes 81 and 82 are respectively reverse biased. As a result, the PIN diodes 79 and 80 are both turned on, and the PIN diodes 81 and 82 are both turned off. Thereby, a signal can be sent through the paths Pc and Pd shown in FIG. Thereby, the first conductive element 91 and the second conductive element 92 are connected to each other.

  On the other hand, when a negative bias is input as the first or second control signal, the PIN diodes 79 and 80 are respectively reverse biased, and the PIN diodes 81 and 82 are respectively forward biased. As a result, the PIN diodes 79 and 80 are both turned off, and the PIN diodes 81 and 82 are both turned on. Thereby, a signal can be sent through the paths Pa and Pb shown in FIG. Thereby, the first conductive element 91 and the second conductive element 92 are separated from each other.

  Thus, in the second mode, as shown in FIG. 10A, the switch circuits 51, 53, 55, and 57 connect adjacent conductive elements to each other, and the switch circuits 52, 54, 56, and 58 Separate the elements from each other. That is, the conducting element 41 and the conducting element 42, the conducting element 43 and the conducting element 44, the conducting element 45 and the conducting element 46, the conducting element 47 and the conducting element 48 are coupled to each other. The magnetic resonance signals received by the conduction element 41 and the conduction element 42, the conduction element 43 and the conduction element 44, the conduction element 45 and the conduction element 46, the conduction element 47 and the conduction element 48, respectively, are matched circuits 60, 61, 62, 63 and preamplifiers 64, 65, 66, and 67, respectively, are sent to the selection circuit 8. That is, the conducting element 41 and the conducting element 42 are element coils of the first channel, the conducting element 43 and the conducting element 44 are element coils of the second channel, and the conducting element 45 and the conducting element 46 are elements of the third channel. The conductive element 47 and the conductive element 48 function as the coil and the element coil of the fourth channel, respectively.

  On the other hand, in the first mode, as shown in FIG. 10B, the switch circuits 51, 53, 55, and 57 separate adjacent conductive elements from each other, and the switch circuits 52, 54, 56, and 58 are adjacent conductive elements. Are connected to each other. That is, the conducting element 42 and the conducting element 43, the conducting element 44 and the conducting element 45, the conducting element 46 and the conducting element 47, the conducting element 48 and the conducting element 49 are connected to each other. The magnetic resonance signals received by the conduction element 42 and the conduction element 43, the conduction element 44 and the conduction element 45, the conduction element 46 and the conduction element 47, the conduction element 48 and the conduction element 49, respectively, are matched circuits 60, 61, 62, 63 and preamplifiers 64, 65, 66, and 67, respectively, are sent to the selection circuit 8. That is, the conducting element 42 and the conducting element 43 are element coils of the first channel, the conducting element 44 and the conducting element 45 are element coils of the second channel, and the conducting element 46 and the conducting element 47 are elements of the third channel. The conductive element 48 and the conductive element 49 function as the coil and the element coil of the fourth channel, respectively.

  Now, the arrangement interval of the element coils with respect to the arrangement direction of the element coils (the arrangement direction of the conductive elements 41 to 49) is as follows when either of the first and second control signals is input, as indicated by P2 in FIG. Is also constant. The shift amount of the position of the element coil of the same channel when the first control signal is input and when the second control signal is input is 1/2 of P2 as shown in FIG. . That is, the position of the actual sensitivity region can be changed by an amount smaller than the interval between the element coils.

  The selection between the first mode and the second mode may be performed by the user. In addition, the effective channel selection among the four-channel magnetic resonance signals may be performed by the user. In this case, the main control unit 17 sets a mode specified by the user using the input unit 16. The main control unit 17 also controls the selection circuit 8 so as to select the magnetic resonance signal of the effective channel designated by the user using the input unit 16. However, the main control unit 17 can also automatically select a mode and an effective channel in the same manner as in the first embodiment. However, in the second embodiment, “P2” is used instead of “P1” in the expressions (1) to (4).

  This embodiment can be variously modified as follows.

  In the first embodiment, the number of element coils included in each of the coil groups G1 and G2 may be an arbitrary number of 2 or more.

  In the first embodiment, the number of coil groups may be three or more. The amount of deviation between the coil groups is preferably 1 / p of the interval between two adjacent element coils in one coil group, where p is the number of coil groups. However, this is not essential, and the amount of deviation between the coil groups may be determined arbitrarily.

  In the first embodiment, the coil group may be a two-dimensional array of element coils.

  In the second embodiment, the number of channels may be any number greater than or equal to two.

  In the second embodiment, one element coil may be configured by connecting three or more conductive elements.

  In the second embodiment, the conductive elements 41 and 49 at both ends are not necessarily cut. That is, the switch circuits 50 and 59 can be omitted.

  A two-dimensional array coil can also be configured by arranging a plurality of sets of internal structures of the array coils 200 and 300 as shown in the first or second embodiment. FIG. 11 is a diagram showing a configuration of a two-dimensional array coil 400 configured by arranging three sets of the internal structure of the array coil 300 shown in the second embodiment. In FIG. 11, elements corresponding to the elements illustrated in FIG. 8 are denoted by reference numerals obtained by adding “−1”, “−2”, or “−3” to the end of the reference numerals illustrated in FIG. 8. The elements having the same “-1”, “−2” or “−3” added to the end in the reference numerals shown in FIG. 11 belong to the same set.

  In the two-dimensional array coil 400, the element coils belonging to the same group are arranged in the same direction in each group. That is, the arrangement direction of the element coils 41-1, 42-1, 43-1, the arrangement direction of the element coils 41-2, 42-2, 43-2, and the element coils 41-3, 42-3, 43 -3... Are arranged in the same direction. This direction generally coincides with the body axis direction (Z-axis direction) of the subject 100.

  Element coils belonging to different groups are in a direction orthogonal to the arrangement direction of element coils belonging to the same group. That is, for example, the element coils 41-1, 41-2, 41-3 are in a direction orthogonal to the arrangement direction of the element coils 41-3, 42-3, 43-3. This direction is generally coincident with the X-axis direction.

  Mode selection and effective channel selection are performed for each group in the same manner as in the second embodiment. However, in a normal use state, it is desirable that the mode and the effective channel are matched for each set.

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

1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (MRI apparatus) according to an embodiment of the present invention. The figure which shows the circuit structure of the array coil 200 which concerns on 1st Embodiment. The figure which shows typically arrangement | positioning of the element coils 21-1 to 21-4 and 22-1 to 22-4 in FIG. The flowchart of the process of the main control part 17 in FIG. The figure which shows an example of the mounting position on the top plate 4a of the array coil 200 in FIG. The figure which shows an example of the 1st setting table for selecting an effective channel in 1st mode. The figure which shows an example of the 2nd setting table for selecting an effective channel in 2nd mode. The figure which shows the structure of the array coil 300 which concerns on 2nd Embodiment. FIG. 9 is a circuit diagram showing a detailed configuration of switch circuits 50 to 59 in FIG. 8. The figure which shows the operation state of the array coil 300 which concerns on 2nd Embodiment. The figure which shows the structural example of a two-dimensional array coil.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... Gradient magnetic field power supply, 4 ... Bed, 5 ... Bed control part, 6a, 6b, 6c ... RF coil unit, 7 ... Transmission part, 8 ... Selection circuit, 9 ... Receiving unit, 10: computer system, 21-1 to 21-4, 22-1 to 22-4 ... element coil, 23-1 to 23-4, 25-1 to 25-4, 31-1 to 31-4 , 33-1 to 33-4, 71, 72, 73, 74 ... capacitors, 24-1 to 24-4, 32-1 to 32-4, 60, 61, 62, 63 ... matching circuits, 26-1 to 26-4, 34-1 to 34-4, 75, 76, 77, 78 ... coil, 27-1 to 27-4, 28-1 to 28-4, 35-1 to 35-4, 36-1 to 36-4, 79, 80, 81, 82 ... PIN diode, 29, 30, 37, 38, 83, 84, 85, 86 ... Choke coil, 39-1 to 39-4, 64, 65, 66, 67 ... Preamplifiers, 41 to 49, conductive elements, 50 to 59, switch circuits, 91, first conductive elements, 92, second conductive elements. Child, 200, 300, 400 ... array coils, G1, G2 ... group coil.

Claims (6)

Three or more odd-numbered conductive elements, each of which is in the form of a loop, arranged at a predetermined interval and so that adjacent ones partially overlap each other ;
A connection that connects two conductive elements located at one end of the odd number of conductive elements is arranged so as to switch connection / disconnection of the overlapping conductive elements at a portion where the conductive elements overlap. A plurality of connection patterns that can connect the three or more conductive elements with a plurality of types of connection patterns including a pattern and a connection pattern that connects two conductive elements located at the other end of the odd number of conductive elements. a first switch,
An array coil comprising: two second switches for switching connection / disconnection of a loop of two conductive elements located at both ends of the three or more conductive elements . Each overlaps at a portion where three or more , odd-numbered conductive elements arranged in a loop shape, with a predetermined interval , and adjacent elements partially overlap each other , and the conductive elements overlap each other. A connection pattern connecting two conductive elements located at one end of the odd number of conductive elements, and a connection pattern arranged to switch connection / non-connection of the conductive elements; a plurality of first switches and with more connection patterns can be connected to the three or more conductive elements of conductive elements and a connection pattern for connecting two by two located at the other end, the three or more An array coil comprising two second switches for respectively switching connection / disconnection of a loop of two conductive elements located at both ends of the conductive elements ;
A pattern selection unit for selecting one of the plurality of types of connection patterns;
A control unit for controlling the plurality of first switches and the two second switches so as to connect the three or more conductive elements in a connection pattern selected by the pattern selection unit;
A reconstructing unit that reconstructs an image related to the subject based on a signal received and output from a magnetic resonance signal emitted from the subject by the conductive element group coupled by the coupling pattern selected by the pattern selection unit. A magnetic resonance imaging apparatus comprising: The magnetic resonance according to claim 2 , wherein the pattern selection unit selects one of the plurality of types of connection patterns based on a positional relationship between an imaging range and the three or more conductive elements. Imaging device. 4. The magnetism according to claim 3 , wherein the pattern selection unit selects the connection pattern capable of performing reception of the magnetic resonance signal from the entire imaging range by a smaller number of the conductive elements. 5. Resonance imaging device. The position of the imaging range and the three or more conductive elements at least part of the magnetic resonance signals output from the conductive element sets connected by the connection pattern selected by the pattern selection unit. A signal selection unit that selects based on the relationship;
The magnetic resonance imaging apparatus according to claim 2 , wherein the reconstruction unit reconstructs the image based on the magnetic resonance signal selected by the signal selection unit. The magnetic resonance imaging apparatus according to claim 5 , wherein the signal selection unit selects a smaller number of the magnetic resonance signals that can collect the magnetic resonance signals from the entire imaging range.

Images