JP2019181201A - Magnetic resonance imaging apparatus, RF coil, and magnetic resonance imaging method - Google Patents

Abstract

To perform parallel imaging with the consistency of an RF magnetic field ensured without using an array coil.SOLUTION: An MRI apparatus according to the embodiment includes a whole body RF coil housed in a gantry, the whole body RF coil including: a first element unit used for transmitting a radio frequency magnetic field; and a second element unit used for receiving magnetic resonance signals generated from a subject upon reception of the radio frequency magnetic field. The first element unit is a birdcage-type RF coil having two end rings and a plurality of rungs spaced apart from each other along a circumferential direction of the end rings. The second element unit is a microstrip antenna.SELECTED DRAWING: Figure 3

Description

  Embodiments described herein relate generally to a magnetic resonance imaging apparatus, an RF coil, and a magnetic resonance imaging method.

  2. Description of the Related Art Conventionally, a magnetic resonance imaging (MRI) apparatus applies a high frequency magnetic field to a subject placed in a static magnetic field, and subjects the subject based on a magnetic resonance signal generated from the subject due to the influence of the high frequency magnetic field. It is an apparatus which produces | generates the image inside.

  In such a magnetic resonance imaging apparatus, parallel imaging is known as a technique for shortening the imaging time. Parallel imaging is an imaging method using an array coil having a plurality of coil elements, and speeds up imaging by using the sensitivity distribution of each coil element included in the array coil.

JP 2007-275164 A Japanese Patent Laying-Open No. 2005-270674 JP 2005-523094 A

  The problem to be solved by the present invention is to perform parallel imaging while ensuring the uniformity of the RF magnetic field without using an array coil.

  The MRI apparatus according to the embodiment includes a first element unit used for transmitting a high-frequency magnetic field and a second element unit used for receiving a magnetic resonance signal generated from a subject by receiving the high-frequency magnetic field. A whole body RF coil housed in a gantry is provided. The first element part is a birdcage type RF coil having two end rings and a plurality of rungs arranged at intervals along the circumferential direction of the end ring. The second element part is a microstrip antenna.

FIG. 1 is a diagram illustrating a configuration example of an MRI apparatus according to the present embodiment. FIG. 2 is a perspective view illustrating a configuration example of a first element portion included in the WB coil according to the first embodiment. FIG. 3 is a side view showing a configuration example of a second element part included in the WB coil according to the first embodiment. FIG. 4 is a diagram illustrating a configuration example of a transmission / reception switching circuit included in the WB coil according to the first embodiment. FIG. 5 is a side view showing a configuration example of the WB coil according to the second embodiment. FIG. 6 is a side view showing a configuration example of the WB coil according to the third embodiment. FIG. 7 is a side view showing a configuration example of the WB coil according to the fourth embodiment. FIG. 8 is a flowchart illustrating an example of parallel imaging executed by the MRI apparatus according to the fifth embodiment. FIG. 9 is a flowchart illustrating another example of parallel imaging executed by the MRI apparatus according to the fifth embodiment.

  Hereinafter, embodiments of an MRI apparatus, an RF coil, and an MRI method will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of an MRI apparatus according to the first embodiment.

  For example, as shown in FIG. 1, the MRI apparatus 100 according to this embodiment includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power source 3, a whole body (WB) coil 4, a bed 5, and a transmission circuit 6. A receiving circuit 7, a radio frequency (RF) shield 8, a gantry 9, an interface 10, a display 11, a memory circuit 12, and processing circuits 13 to 16.

  The static magnetic field magnet 1 generates a static magnetic field in the imaging space where the subject S is arranged. Specifically, the static magnetic field magnet 1 is formed in a hollow, substantially cylindrical shape (including a shape in which a cross-sectional shape orthogonal to the central axis of the cylinder is elliptical), and is an imaging space disposed in the cylinder. A static magnetic field is generated. For example, the static magnetic field magnet 1 includes a cooling container formed in a substantially cylindrical shape, and a magnet such as a superconducting magnet immersed in a coolant (for example, liquid helium) filled in the cooling container. Here, for example, the static magnetic field magnet 1 may generate a static magnetic field using a permanent magnet.

  The gradient magnetic field coil 2 is disposed inside the static magnetic field magnet 1 and generates a gradient magnetic field along a plurality of axial directions in an imaging space in which the subject S is disposed. Specifically, the gradient magnetic field coil 2 is formed in a hollow substantially cylindrical shape (including a shape in which a cross-sectional shape perpendicular to the central axis of the cylinder is elliptical), and is an imaging space disposed in the cylinder. In addition, gradient magnetic fields are generated along the X-axis, Y-axis, and Z-axis directions orthogonal to each other. Here, the X axis, the Y axis, and the Z axis constitute an apparatus coordinate system unique to the MRI apparatus 100. For example, the Z axis coincides with the cylinder axis of the gradient magnetic field coil 2 and is set along the magnetic flux of the static magnetic field generated by the static magnetic field magnet 1. Further, the X axis is set along a horizontal direction orthogonal to the Z axis, and the Y axis is set along a vertical direction orthogonal to the Z axis and the X axis.

  The gradient magnetic field power source 3 supplies a current to the gradient magnetic field coil 2 to generate a gradient magnetic field along the X-axis, Y-axis, and Z-axis directions in the space inside the gradient magnetic field coil 2. In this way, the gradient magnetic field power supply 3 generates gradient magnetic fields along the X-axis, Y-axis, and Z-axis directions, so that the gradient magnetic fields along the readout direction, the phase encoding direction, and the slice direction, respectively. Can be generated. Here, each axis along the lead-out direction, the phase encoding direction, and the slice direction constitutes a logical coordinate system for defining a slice area or volume area to be imaged. Hereinafter, the gradient magnetic field along the readout direction is referred to as a readout gradient magnetic field, the gradient magnetic field along the phase encoding direction is referred to as a phase encoding gradient magnetic field, and the gradient magnetic field along the slice direction is referred to as a slice gradient magnetic field. .

  Each gradient magnetic field of the readout gradient magnetic field, the phase encoding gradient magnetic field, and the slice gradient magnetic field is superimposed on the static magnetic field generated by the static magnetic field magnet 1 and is spaced in the magnetic resonance (MR) signal generated from the subject S. Location information. The lead-out gradient magnetic field changes the frequency of the MR signal in accordance with the position in the lead-out direction, thereby giving positional information along the lead-out direction to the MR signal. The phase encoding gradient magnetic field changes the phase of the MR signal along the phase encoding direction, thereby giving position information in the phase encoding direction to the MR signal. The slice gradient magnetic field gives positional information along the slice direction to the MR signal. For example, the slice gradient magnetic field is used to determine the direction, thickness, and number of slice areas when the imaging area is a slice area, and according to the position in the slice direction when the imaging area is a volume area. And used to change the phase of the MR signal.

  The WB coil 4 is disposed inside the gradient magnetic field coil 2 and is generated from the subject S due to the function of the transmission coil that applies the RF magnetic field to the imaging space in which the subject S is disposed and the influence of the RF magnetic field. It is a whole body RF coil having the function of a receiving coil for receiving MR signals. Specifically, the WB coil 4 is formed in a hollow, substantially cylindrical shape (including one having a cross-sectional shape orthogonal to the central axis of the cylinder is elliptical), and is supplied with an RF pulse supplied from the transmission circuit 6. Based on the signal, an RF magnetic field is applied to the imaging space arranged in the cylinder. The WB coil 4 receives an MR signal generated from the subject S due to the influence of the RF magnetic field, and outputs the received MR signal to the receiving circuit 7.

  The bed 5 includes a top plate 51 on which the subject S is placed, and when the subject S is imaged, the top plate 51 on which the subject S is placed moves to the imaging space. For example, the bed 5 is installed such that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 1.

  The transmission circuit 6 outputs an RF pulse signal corresponding to the Larmor frequency specific to the target nucleus placed in the static magnetic field to the WB coil 4. Specifically, the transmission circuit 6 includes a pulse generator, an RF generator, a modulator, and an RF amplifier. The pulse generator generates an RF pulse signal waveform. The RF generator generates an RF signal having a resonance frequency. The modulator generates an RF pulse signal by modulating the amplitude of the RF signal generated by the RF generator with the waveform generated by the pulse generator. The RF amplifier amplifies the RF pulse signal generated by the modulator and outputs it to the WB coil 4.

  The receiving circuit 7 generates MR signal data based on the MR signal received by the WB coil 4 and outputs the generated MR signal data to the processing circuit 14. Specifically, the receiving circuit 7 includes a preamplifier, a detector, and an A / D (Analog / Digital) converter. The preamplifier amplifies the MR signal output from the WB coil 4. The detector detects an analog signal obtained by subtracting the resonance frequency component from the MR signal amplified by the preamplifier. The A / D converter generates MR signal data by converting the analog signal detected by the detector into a digital signal, and outputs the generated MR signal data to the processing circuit 14.

  The RF shield 8 is disposed between the gradient magnetic field coil 2 and the WB coil 4 and shields the gradient magnetic field coil 2 from the RF magnetic field generated by the WB coil 4. Specifically, the RF shield 8 is formed in a hollow substantially cylindrical shape (including a shape in which a cross-sectional shape orthogonal to the central axis of the cylinder is elliptical), and on the inner peripheral side of the gradient coil 2. It arrange | positions so that the outer peripheral surface of WB coil 4 may be covered in space.

  The gantry 9 accommodates the static magnetic field magnet 1, the gradient magnetic field coil 2, the WB coil 4, and the RF shield 8. Specifically, the gantry 9 has a hollow bore B formed in a cylindrical shape, and the static magnetic field magnet 1, the gradient magnetic field coil 2, the WB coil 4, and the RF shield 8 are arranged so as to surround the bore B. Each is accommodated. Here, the space inside the bore B of the gantry 9 is an imaging space in which the subject S is arranged when the subject S is imaged.

  Here, an example in which the MRI apparatus 100 has a so-called tunnel type configuration in which the static magnetic field magnet 1, the gradient magnetic field coil 2, and the WB coil 4 are each formed in a substantially cylindrical shape will be described. Is not limited to this. For example, the MRI apparatus 100 has a so-called open type configuration in which a pair of static magnetic field magnets, a pair of gradient magnetic field coils, and a pair of RF coils are disposed so as to face each other with an imaging space in which the subject S is disposed. You may do it.

  The interface 10 receives various instructions and various information input operations from the operator. Specifically, the interface 10 is connected to the processing circuit 16, converts an input operation received from the operator into an electrical signal, and outputs the electrical signal to the processing circuit 16. For example, the interface 10 includes a trackball, a switch button, a mouse, a keyboard, a touch pad for performing an input operation by touching an operation surface, and a display screen for setting an imaging condition, a region of interest (ROI), and the like. And a touch pad integrated with each other, a non-contact input circuit using an optical sensor, a voice input circuit, and the like. In the present specification, the interface 10 is not limited to one having physical operation components such as a mouse and a keyboard. For example, an example of the interface 10 includes an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the apparatus and outputs the electric signal to the control circuit.

  The display 11 displays various information and various images. Specifically, the display 11 is connected to the processing circuit 16, converts various information and various image data sent from the processing circuit 16 into electrical signals for display, and outputs them. For example, the display 11 is realized by a liquid crystal monitor, a CRT (Cathode Ray Tube) monitor, a touch panel, or the like.

  The storage circuit 12 stores various data. Specifically, the storage circuit 12 stores MR signal data and image data. For example, the storage circuit 12 is realized by a semiconductor memory device such as a RAM (Random Access Memory) or a flash memory, a hard disk, an optical disk, or the like.

  The processing circuit 13 has a bed control function 131. The bed control function 131 controls the operation of the bed 5 by outputting a control electric signal to the bed 5. For example, the bed control function 131 receives an instruction to move the table 51 in the longitudinal direction, the vertical direction, or the horizontal direction from the operator via the interface 10 and moves the table 51 so as to move the table 51 according to the received instruction. 5 is operated.

  The processing circuit 14 has a data collection function 141. The data collection function 141 collects MR signal data of the subject S by driving the gradient magnetic field power supply 3, the transmission circuit 6 and the reception circuit 7. Specifically, the data collection function 141 collects MR signal data by executing various pulse sequences based on the sequence execution data output from the processing circuit 16. Here, the sequence execution data includes the timing at which the gradient magnetic field power supply 3 supplies current to the gradient magnetic field coil 2 and the intensity of the supplied current, the strength and supply timing of the RF pulse signal that the transmission circuit 6 supplies to the WB coil 4, This is information defining detection timing and the like at which the receiving circuit 7 detects MR signals. The data collection function 141 receives MR signal data from the receiving circuit 7 as a result of executing various pulse sequences, and stores the received MR signal data in the storage circuit 12. The set of MR signal data received by the data collection function 141 is arranged two-dimensionally or three-dimensionally according to the positional information given by the readout gradient magnetic field, phase encoding gradient magnetic field, and slice gradient magnetic field. Thus, the data is stored in the storage circuit 12 as data constituting the k space.

  The processing circuit 15 has an image generation function 151. The image generation function 151 generates an image based on the MR signal data stored in the storage circuit 12. Specifically, the image generation function 151 reads the MR signal data stored in the storage circuit 12 by the data collection function 141, and performs post-processing, that is, reconstruction processing such as Fourier transform on the read MR signal data. To generate an image. Further, the image generation function 151 causes the storage circuit 12 to store the image data of the generated image.

  The processing circuit 16 has a main control function 161. The main control function 161 performs overall control of the MRI apparatus 100 by controlling each component included in the MRI apparatus 100. Specifically, the main control function 161 displays on the display 11 a GUI (Graphical User Interface) for accepting various instructions and various information input operations from the operator. The main control function 161 controls each component included in the MRI apparatus 100 in accordance with an input operation received via the interface 10. For example, the main control function 161 receives input of imaging conditions from the operator via the interface 10. The main control function 161 generates sequence execution data based on the accepted imaging conditions, and transmits the sequence execution data to the processing circuit 14 to execute various pulse sequences. For example, the main control function 161 reads out image data from the storage circuit 12 and outputs it to the display 11 in response to a request from the operator.

  Here, the processing circuits 13 to 16 described above are realized by, for example, a processor. In this case, the processing function of each processing circuit is stored in the storage circuit 12 in the form of a program that can be executed by a computer, for example. Each processing circuit implements a function corresponding to each program by reading each program from the storage circuit 12 and executing it. Here, each processing circuit may be constituted by a plurality of processors, and each processing function may be realized by each processor executing a program. In addition, the processing functions of each processing circuit may be realized by being appropriately distributed or integrated into a single or a plurality of processing circuits. Also, here, a single storage circuit 12 has been described as storing a program corresponding to each processing function. However, a plurality of storage circuits are arranged in a distributed manner, and the processing circuits correspond to individual storage circuits. It may be configured to read the program.

  The overall configuration of the MRI apparatus 100 according to the present embodiment has been described above. Under such a configuration, the MRI apparatus 100 according to the present embodiment has a function of performing parallel imaging.

  In general, in an MRI apparatus, an array coil having a plurality of coil elements is attached to a patient (subject), and imaging is performed. However, the setting operation of the array coil tends to be complicated and takes time. The patient may feel uncomfortable because it is in close contact with the body. On the other hand, when only the birdcage type WB coil built in the MRI apparatus is used, this problem does not occur, but parallel imaging cannot be performed. On the other hand, for example, when a plurality of coil elements are arranged for parallel imaging, an RF magnetic field is transmitted for each coil element, and thus the uniformity of the RF magnetic field cannot be ensured. In order to make these compatible, for example, a coil element arranged to generate a uniform RF magnetic field and a coil element for parallel imaging may be used in combination, but if a coil element is simply arranged, It becomes difficult to perform decoupling between elements.

  For this reason, the MRI apparatus 100 according to the present embodiment is configured to perform parallel imaging while ensuring the uniformity of the RF magnetic field without using an array coil.

  Specifically, in the present embodiment, the WB coil 4 includes a first element unit for transmission or transmission / reception, and a plurality of second element units for reception or transmission / reception. Here, in the present embodiment, the first element portion is a birdcage type RF coil having two end rings and a plurality of rungs arranged at intervals along the circumferential direction of the end rings. The second element part is a plurality of microstrip antennas (also referred to as microstrip patch antennas or patch antennas) each configured by using a part of the first element part as a ground conductor.

  That is, the WB coil 4 according to the present embodiment is an RF coil obtained by combining a birdcage type RF coil and a plurality of microstrip antennas. According to such a WB coil 4, parallel imaging can be performed by using a birdcage type RF coil at the time of transmission to ensure the uniformity of the RF magnetic field and using a plurality of microstrip antennas at the time of reception. Will be able to do. Thereby, in this embodiment, it becomes possible to perform parallel imaging while ensuring the uniformity of the RF magnetic field without using an array coil.

  Hereinafter, the configuration of the MRI apparatus 100 according to the above-described embodiment will be described in detail.

  FIG. 2 is a perspective view illustrating a configuration example of the first element portion included in the WB coil 4 according to the first embodiment.

  For example, as shown in FIG. 2, the WB coil 4 includes a base material 41, two end rings 42, a plurality of capacitors 43, and a plurality of rungs 44.

  The base material 41 is a dielectric member (also called a bobbin) formed in a cylindrical shape, and supports the end ring 42, the rung 44, the capacitor 43, and the like.

  Each of the end rings 42 is a ring-shaped conductor disposed along the circumferential direction on the outer peripheral surface of the base material 41, and is disposed one by one at both ends in the axial direction of the base material 41. Each end ring 42 is composed of a plurality of conductors arranged side by side along the circumferential direction of the base material 41, and each conductor is connected by a capacitor 43.

  The capacitors 43 are fixed capacitors each having a predetermined amount of capacitance, and are disposed at a plurality of positions along the circumferential direction in the end ring 42. Each capacitor 43 is arranged on both sides of each of a plurality of connection portions where the end ring 42 and the rung 44 are connected along the circumferential direction of the end ring 42.

  Each of the rungs 44 is an elongated rectangular conductor disposed along the axial direction on the outer peripheral surface of the base material 41, and a plurality of the rungs 44 are disposed at regular intervals along the circumferential direction of the end ring 42. . Specifically, the rungs 44 are provided every other conductor constituting the end ring 42 along the circumferential direction of the end ring 42. Each rung 44 has one end in the longitudinal direction connected to one of the two end rings 42, and the other end in the longitudinal direction connected to the other of the two end rings 42.

  In this embodiment, each microstrip antenna included in the second element portion is disposed along the rung 44 included in the first element portion, and the rung is configured as a ground conductor.

  FIG. 3 is a side view showing a configuration example of the second element portion included in the WB coil 4 according to the first embodiment. In FIG. 3, illustration of the base material 41 and the capacitor 43 is omitted for convenience of explanation.

  For example, as shown in FIG. 3, the WB coil 4 has a plurality of antenna conductors 45.

  Each of the antenna conductors 45 is a conductor formed in an elongated flat plate shape, and is disposed at a position inside the rung 44 on the inner peripheral surface of the base material 41. Here, the antenna conductor 45 is formed so that the length in the longitudinal direction is substantially the same as that of the rung 44, and is arranged along the rung 44 throughout the longitudinal direction of the rung 44.

  Thus, in this embodiment, the dielectric base material 41 is disposed between the antenna conductor 45 and the rung 44 so that the rung 44 can be used as the ground conductor of the microstrip antenna. .

  In this embodiment, the WB coil 4 uses one of the first element part and the second element part during transmission, and uses one of the first element part and the second element part during reception. .

  For example, the WB coil 4 uses the first element part at the time of transmission and uses one of the first element part and the second element part at the time of reception.

  Here, in the WB coil 4, when the first element portion is used, the second element portion and the first element portion are short-circuited. On the other hand, in the WB coil 4, the rung 44 is used as the ground conductor of the microstrip antenna when the second element portion is used.

  Specifically, the WB coil 4 has a transmission / reception switching circuit for switching between a transmission state and a reception state.

  FIG. 4 is a diagram illustrating a configuration example of a transmission / reception switching circuit included in the WB coil 4 according to the first embodiment. In FIG. 4, one of a plurality of connection portions where the end ring 42 and the rung 44 are connected is illustrated, but the other connection portions are configured in the same manner.

  For example, as illustrated in FIG. 4, the WB coil 4 includes first to fourth diodes 461 to 464, first to fourth trap circuits 465 to 468, and a capacitor 469 as transmission / reception switching circuits. In addition, a balun 47 and an amplifier 48 are provided.

  Here, one end of the first diode 461 is connected to the end ring 42 via the capacitor 469, and in parallel to that, is connected to the processing circuit 14 via the first trap circuit 465. The end is connected to ground.

  The second diode 462 has one end connected to the antenna conductor 45 and the other end connected to the processing circuit 14 via the end ring 42 and the second trap circuit 466.

  The third diode 463 has one end connected to the ground and the other end connected to the antenna conductor 45.

  The fourth diode 464 is provided in a conductor to which the rung 44 of the plurality of conductors constituting the end ring 42 is not connected, and a gap that divides the conductor into two in the circumferential direction is provided. It is provided so as to be bridged at both ends. The fourth diode 464 has one end connected to the processing circuit 14 via the third trap circuit 467 and the other end connected to the ground via the fourth trap circuit 468.

  Here, the first to fourth trap circuits 465 to 468 are tuning circuits tuned so as to cut off the high frequency of the resonance frequency.

  The balun 47 has an input end connected to each of a path connecting the capacitor 469 and the end ring 42 and a path connecting the third diode 463 and the antenna conductor 45, and an output end connecting the amplifier 48. To the receiving circuit 7 (Rx). The end ring 42 is connected to the transmission circuit 6 (Tx).

  Here, the path between the end ring 42 and the ground via the first diode 461 and the path between the antenna conductor 45 and the ground via the third diode 463 are respectively transmitted from the transmission circuit 6. When the wavelength of the supplied RF pulse signal is λ, the electrical path length is λ / 4.

  In this embodiment, when the data collection function 141 of the processing circuit 14 executes the pulse sequence, the state of the transmission / reception switching circuit described above is switched between transmission and reception.

  Here, an example will be described in which the first element unit is used during transmission and the second coil element is used during reception.

  For example, the data collection function 141 supplies the control current (direct current) DC1 to the first diode 461 via the first trap circuit 465 when the first element unit is used during transmission, and the second The control current (DC current) DC2 is supplied to the second diode 462 and the third diode 463 via the trap circuit 466, and the control current (DC current) is supplied to the fourth diode 464 via the third trap circuit 467. ) Turn on each diode by supplying DC3.

  Here, when the fourth diode 464 is turned on, the entire end ring 42 and the rung 44 are electrically connected. Further, when the first diode 461 is turned on, the end ring 42 and the ground are electrically connected. In addition, when the second diode 462 is turned on, the antenna conductor 45 and the end ring 42 and the rung 44 are electrically connected. Further, when the third diode 463 is turned on, the antenna conductor 45 and the ground are electrically connected.

  Thus, when an RF pulse signal is supplied from the transmission circuit 6 to the WB coil 4, the current of the RF pal signal flows through a birdcage type coil composed of two end rings 42 and a plurality of rungs 44. Become. That is, an RF magnetic field is applied to the imaging space by the first element unit.

  At this time, as described above, the path between the end ring 42 and the ground via the first diode 461 and the path between the antenna conductor 45 and the ground via the third diode 463 are as follows. Since the electrical path length is configured to be λ / 4, the input ends from the end ring 42 and the rung 44 to the receiving system are opened. Therefore, neither the current of the RF pulse signal flowing through the end ring 42 and the rung 44 nor the current of the RF pulse signal flowing through the antenna conductor 45 short-circuited to the end ring 42 and the rung 44 flows through the receiving circuit 7. It becomes like this.

  On the other hand, the data collection function 141 turns off each diode by not supplying the control current to the first to fourth diodes 461 to 464 when the second element unit is used during reception. .

  Here, when the fourth diode 464 is turned off, the rungs 44 are electrically disconnected from each other. Further, when the first diode 461 is turned off, the end ring 42 and the rung 44 and the receiving system are electrically connected. Further, when the second diode 462 is turned off, the antenna conductor 45 and the end ring 42 and the rung 44 are electrically disconnected. Further, when the third diode 463 is turned off, the antenna conductor 45 and the receiving system are electrically connected.

  Thus, when an MR signal is generated from the subject S, the rung 44 becomes a ground conductor, and the MR signal is received by the microstrip antenna constituted by the antenna conductor 45 and the rung 44 and is output to the receiving circuit 7. It becomes like this. That is, the MR signal is received by the second element unit.

  The configuration of the transmission / reception switching circuit provided in the WB coil 4 is not limited to that described above, and can be realized using various circuit elements.

  Thus, in the present embodiment, when the first element portion is used, the second element portion and the first element portion are short-circuited, so that decoupling becomes unnecessary. On the other hand, when the second element portion is used, the rung 44 is used as the ground conductor of the microstrip antenna, so that decoupling is not necessary.

  In this embodiment, the main control function 161 of the processing circuit 16 has a function of performing parallel imaging using the sensitivity distribution of each microstrip antenna included in the second element portion. Here, as the parallel imaging performed by the main control function 161, for example, various known methods such as SENSE (Sensitivity Encoding), SMASH (Simultaneous Acquisition of Spatial Harmonics), and GRAPPA (Generalized Autocalibrating Partially Parallel Acquisitions) may be used. it can.

  Further, in the present embodiment, for example, the image generation function 151 of the processing circuit 15 includes each image included in the second element unit with reference to an image generated based on the MR signal collected by the first element unit. It has a function of performing sensitivity correction for correcting non-uniformity in an image generated based on the MR signal received by the microstrip antenna. For example, the image generation function 151 performs a first scan using the first element unit and a second scan using the second element unit as reference scans. The image generation function 151 generates a first image based on the MR signal collected by the first scan, generates a second image based on the MR signal collected by the second scan, A sensitivity map is generated by comparing both images. Then, the image generation function 151 corrects non-uniformity in the generated image based on the MR signal collected by the main scan using the second element unit, using the generated sensitivity map.

  When performing such image sensitivity correction, the image used as a reference is required to have uniform sensitivity. In this regard, in the present embodiment, since the first element portion is a birdcage type coil, a reference image with uniform sensitivity can be obtained.

  In the above-described example, the case where the first element unit is used at the time of transmission and the second coil element is used at the time of reception has been described assuming that parallel imaging is performed. The usage of the coil element is not limited to this. For example, when imaging other than parallel imaging is performed, the first element unit may be used for both transmission and reception, and the second element unit is used for both transmission and reception. May be.

  As described above, in the present embodiment, the WB coil 4 has a birdcage type coil as the first element portion, and the birdcage type coil rung 44 is grounded as the second element portion. It has a plurality of microstrip antennas as conductors. According to such a configuration, by using a birdcage type coil, a uniform RF magnetic field can be generated, and parallel imaging can be performed using the sensitivity distribution of each microstrip antenna. become. Therefore, according to the present embodiment, parallel imaging can be performed while ensuring the uniformity of the RF magnetic field without using an array coil.

  Further, in the present embodiment, when image sensitivity correction is performed, a reference image with uniform sensitivity can be obtained by using the first element portion. Therefore, according to this embodiment, an image having a sufficient SNR can be obtained by parallel imaging using only the WB coil 4 without using an array coil.

  In the first embodiment described above, the antenna conductor 45 included in the second element portion has been described as being disposed along the rung 44 over the entire length in the longitudinal direction of the rung 44. The embodiment is not limited to this.

  For example, in the configuration described above, in the second element portion, the direction along the magnetic flux of the static magnetic field is the Z direction, the horizontal direction orthogonal to the Z direction is the X direction, and the vertical direction is orthogonal to each of the Z direction and the X direction. Where Y is the Y direction, the in-plane sensitivity distribution along the X and Y directions is the same at each position in the Z direction. That is, according to the configuration described above, parallel imaging using in-plane sensitivity distribution along the X direction and the Y direction can be performed.

  On the other hand, for example, the second element portion may be configured by arranging a plurality of microstrip antennas so that the in-plane sensitivity distribution along the X direction and the Y direction differs depending on the position in the Z direction. . According to this configuration, parallel imaging can be performed using the sensitivity distribution along the Z direction in addition to the in-plane sensitivity distribution along the X and Y directions.

  Therefore, in the following, another embodiment related to the WB coil in such a case will be described. Note that, in the embodiment described below, the description will focus on points that are different from the first embodiment, and description of the contents common to the first embodiment will be omitted.

(Second Embodiment)
For example, in the WB coil, the second element portion may include a plurality of microstrip antennas that are shorter in the Z direction than the first element portion and are arranged at different positions in the first direction. .

  FIG. 5 is a side view showing a configuration example of the WB coil 104 according to the second embodiment. In FIG. 5, illustration of the base material 41 and the capacitor 43 is omitted for convenience of explanation.

  For example, as shown in FIG. 5, in this embodiment, the antenna conductor 1045 is formed so that the length in the Z direction is shorter than the rung 44. In the present embodiment, each antenna conductor 1045 is arranged close to either one of both ends of the rung 44 in the Z direction on the inner peripheral surface of the base material 41, and each Z direction. Are arranged so as to be alternately switched one by one along the circumferential direction of the WB coil 104.

  Note that the positions of the antenna conductors 1045 in the Z direction are not changed one by one along the circumferential direction of the WB coil 104, but for example, every two or three, such as every two or more. It may be replaced.

  In the present embodiment, each antenna conductor 1045 is formed to be longer than ½ of the length of the rung 44. Thereby, in this embodiment, all the antenna conductors 1045 are arranged in the plane along the X direction and the Y direction near the center of the WB coil 104 in the axial direction.

  According to such a configuration, in the second element portion, in the X direction in the vicinity of the center in the Z direction, the range close to one end side at both ends in the Z direction, and the range close to the other end side in both ends in the Z direction. And the in-plane sensitivity distribution along the Y direction becomes different.

(Third embodiment)
For example, in the WB coil, the second element portion may include a plurality of microstrip antennas having different lengths in the Z direction.

  FIG. 6 is a side view showing a configuration example of the WB coil 204 according to the third embodiment. In FIG. 6, the base material 41 and the capacitor 43 are not shown for convenience of explanation.

  For example, as shown in FIG. 6, in this embodiment, the antenna conductors 2045 are formed such that the lengths in the Z direction are shorter than the rungs 44, and the lengths are different from each other. Has been. Also in the present embodiment, each antenna conductor 2045 is arranged close to either one of both ends in the Z direction of the rung 44 on the inner peripheral surface of the base material 41 and the WB coil 104 Along the circumferential direction, the Z-direction positions are alternately switched one by one.

  Also in this embodiment, the position of each antenna conductor 1045 in the Z direction is not changed one by one along the circumferential direction of the WB coil 104, but, for example, every two or every three, You may change every several numbers.

  According to such a configuration, in the second element portion, the in-plane sensitivity distribution along the X direction and the Y direction at each position in the Z direction is different.

(Fourth embodiment)
For example, in the WB coil, each rung 44 included in the first element portion may be arranged obliquely with respect to the Z direction.

  FIG. 7 is a side view showing a configuration example of the WB coil 304 according to the fourth embodiment. In FIG. 7, illustration of the base material 41 and the capacitor 43 is omitted for convenience of explanation.

  For example, as shown in FIG. 7, in the present embodiment, each rung 3044 is arranged obliquely with respect to the Z direction. That is, each rung 3044 is disposed obliquely with respect to the circumferential direction of the two end rings 42 along the outer peripheral surface of the base material 41. In this embodiment, each antenna conductor 3045 is arranged along the rung 3044 over the entire length of the rung 3044.

  According to such a configuration, in the second element portion, the in-plane sensitivity distribution along the X direction and the Y direction changes while rotating in the circumferential direction of the WB coil 304 as the position in the Z direction shifts. It becomes like this.

  In the second and third embodiments described above, each microstrip antenna included in the second element portion includes a distance between the antenna conductor and the rung, a dielectric material of the base material 41, and an antenna. The length of the antenna conductor in the Z direction is determined based on at least one of the conductor widths.

  According to the second to fourth embodiments described above, in the second element portion, the plurality of microstrip antennas are arranged so that the in-plane sensitivity distribution along the X direction and the Y direction differs depending on the position in the Z direction. As a result, in addition to the in-plane sensitivity distribution along the X and Y directions, parallel imaging can be performed using the sensitivity distribution along the Z direction.

  In the first to fourth embodiments described above, the example in which each microstrip antenna is configured by disposing the dielectric base material 41 between the antenna conductor and the rung has been described. The embodiment is not limited to this. For example, each microstrip antenna may be configured by disposing a dielectric different from the base material 41 between the antenna conductor and the rung, and each microstrip may be disposed on the outer peripheral surface of the base material 41. .

(Fifth embodiment)
The MRI apparatus 100 according to the first to fourth embodiments has been described above. As described above, the MRI apparatus 100 according to each embodiment can perform parallel imaging with the above-described configuration while ensuring the uniformity of the RF magnetic field without using an array coil. Hereinafter, parallel imaging executed by the MRI apparatus 100 according to each embodiment described above will be described in detail as a fifth embodiment.

  Specifically, as described in each embodiment, the MRI apparatus 100 is used for receiving a first element unit used for transmitting an RF magnetic field and an MR signal generated from a subject by receiving the RF magnetic field. And a whole body RF coil 4 housed in a gantry having a second element portion. Here, the first element portion is a birdcage-type RF coil having two end rings and a plurality of rungs arranged at intervals along the circumferential direction of the end ring. The second element portion is a microstrip antenna.

  When parallel imaging is performed, the data collection function 141 of the processing circuit 14 transmits an RF magnetic field using the first element unit based on the parallel imaging pulse sequence, and receives the RF magnetic field. By receiving the MR signal generated from the subject using the second element unit, the first k-space data thinned out in the phase encoding direction is collected for each microstrip antenna. Thereafter, the image generation function 151 of the processing circuit 15 generates an image by developing the aliasing in the first k-space data using the sensitivity difference between the microstrip antennas.

  FIG. 8 is a flowchart illustrating an example of parallel imaging executed by the MRI apparatus 100 according to the fifth embodiment. Here, an example in which SENSE is executed will be described as an example of parallel imaging.

  For example, as shown in FIG. 8, first, the data collection function 141 transmits an RF magnetic field using the first element unit based on a preset pulse sequence for sensitivity distribution measurement, and the RF magnetic field is By receiving the MR signal generated from the subject using the second element unit, the second k-space data is collected for each microstrip antenna (step S11).

  Thereafter, the image generation function 151 generates, for each microstrip antenna, a first sensitivity map indicating the sensitivity distribution of the microstrip antenna based on the collected second k-space data (step S12).

  Subsequently, the data collection function 141 transmits an RF magnetic field using the first element unit based on a preset pulse sequence for sensitivity correction (also referred to as luminance correction), receives the RF magnetic field, and receives the RF magnetic field. The third k-space data is collected by receiving the MR signal generated from the sample using the first element unit (step S13).

  Thereafter, the image generation function 151 generates a second sensitivity map indicating the sensitivity distribution of the first element portion based on the collected third k-space data (step S14).

  Subsequently, the data acquisition function 141 transmits an RF magnetic field using the first element unit based on a preset SENSE pulse sequence, and receives an MR signal generated from the subject in response to the RF magnetic field. By receiving using the second element unit, the first k-space data thinned out in the phase encoding direction is collected for each microstrip antenna (step S15).

  Thereafter, the image generation function 151 expands the aliasing on the image data generated from the first k-space data using the first sensitivity map for each microstrip antenna to generate an image (step S16). ). Here, the method for the image generation function 151 to generate the image by expanding the aliasing on the image data is the same as the method performed in the conventional SENSE.

  Further, the image generation function 151 performs sensitivity correction for correcting non-uniformity in the generated image using the second sensitivity map (step S17). For example, the image generation function 151 compares the second sensitivity map obtained using the first element unit with the first sensitivity map obtained for each microstrip for each pixel, and according to the ratio. Then, the non-uniformity in the image is corrected by correcting the signal value of each pixel.

  Here, among the processes described above, the processes of steps S11, S13, and S15 are realized by, for example, the processing circuit 14 reading out and executing a predetermined program corresponding to the data collection function 141 from the storage circuit 12. Further, the processing of steps S12, S14, S16, and S17 is realized by the processing circuit 15 reading out and executing a predetermined program corresponding to the image generation function 151 from the storage circuit 12, for example.

  If image sensitivity correction is not required, the processes of steps S13 (sensitivity correction data collection), S14 (sensitivity correction sensitivity map generation), and S17 (image sensitivity correction) need not be executed. .

  Moreover, the process of step S11-S14 mentioned above does not necessarily need to be performed in the order mentioned above. For example, even after the processing of steps S13 and S14 (sensitivity correction data collection and sensitivity map generation) is executed, the processing of steps S11 and S12 (sensitivity distribution measurement data collection and sensitivity map generation) is executed. Good. Alternatively, for example, after the processing of steps S11 and S13 (data collection for sensitivity distribution measurement and sensitivity correction) is executed, the processing of steps S12 and S14 (sensitivity map generation for sensitivity distribution measurement and sensitivity correction) is performed. May be executed.

  FIG. 9 is a flowchart showing another example of parallel imaging executed by the MRI apparatus 100 according to the fifth embodiment. Here, an example in which GRAPPA is executed will be described as another example of parallel imaging.

  For example, as shown in FIG. 9, first, the data collection function 141 transmits an RF magnetic field using the first element unit based on a preset pulse sequence for sensitivity correction (also referred to as luminance correction). The third k-space data is collected by receiving the MR signal generated from the subject by receiving the RF magnetic field using the first element unit (step S21).

  Thereafter, the image generation function 151 generates a second sensitivity map indicating the sensitivity distribution of the first element portion based on the collected third k-space data (step S22).

  Subsequently, the data collection function 141 transmits an RF magnetic field using the first element unit based on a preset pulse sequence for GRAPPA, and receives an MR signal generated from the subject in response to the RF magnetic field. By receiving using the second element unit, the first k-space data thinned out in the phase encoding direction is collected for each microstrip antenna (step S23). At this time, the data collection function 141 collects the first k-space data so as to include the data of the central portion of the k-space for each microstrip antenna.

  Thereafter, the image generation function 151 generates an image by expanding the first k-space data by performing weighted addition of signal values between the first k-space data collected for each microstrip antenna. (Step S24). Here, the method for the image generation function 151 to generate the image by expanding the aliasing on the first k-space data is the same as the method performed in the conventional GRAPPA.

  Further, the image generation function 151 performs sensitivity correction for correcting non-uniformity in the generated image using the second sensitivity map (step S25). For example, the image generation function 151 displays, for each pixel, the second sensitivity map obtained by using the first element unit and the image generated from the first k-space data obtained by developing the folding for each microstrip. The nonuniformity in the image is corrected by comparing and correcting the signal value of each pixel in accordance with the ratio.

  Here, among the processes described above, the processes of steps S21 and S23 are realized by, for example, the processing circuit 14 reading out and executing a predetermined program corresponding to the data collection function 141 from the storage circuit 12. Further, the processing of steps S22, S24, and S25 is realized by, for example, the processing circuit 15 reading a predetermined program corresponding to the image generation function 151 from the storage circuit 12 and executing it.

  If image sensitivity correction is not required, the processes in steps S13, S14, and S17 may not be executed.

  The case where SENSE and GRAPPA are executed has been described above as an example, but the embodiment is not limited thereto. The MRI apparatus 100 according to each embodiment described above can execute various other parallel imaging by using the first element unit and the second element unit included in the WB coil 4 in the same manner. .

  As described above, when performing parallel imaging, the MRI apparatus 100 according to the present embodiment uses the first element unit, which is a birdcage type RF coil, to transmit an RF magnetic field, and to receive an MR signal. A second element portion including a plurality of microstrip antennas is used. Thereby, in this embodiment, while being able to generate a uniform RF magnetic field, parallel imaging can be performed using the sensitivity difference between microstrip antennas. Therefore, according to the present embodiment, parallel imaging can be performed while ensuring the uniformity of the RF magnetic field without using an array coil.

  The MRI apparatus 100 according to the present embodiment uses the first element unit, which is a birdcage type RF coil, to transmit an RF magnetic field and receive an MR signal when performing sensitivity correction of an image. A correction sensitivity map (second sensitivity map) is collected. Thereby, in this embodiment, the sensitivity correction of an image can be performed on the basis of a sensitivity map with uniform sensitivity, and an image with a good SNR can be obtained.

  The term “processor” used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), or a programmable logic device. (For example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). Instead of storing the program in the storage circuit, the program may be directly incorporated in the processor circuit. In this case, the processor realizes the function by reading and executing the program incorporated in the circuit. In addition, each processor of the present embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining a plurality of independent circuits to realize its function. Good. Furthermore, a plurality of components in FIG. 1 may be integrated into one processor to realize the function.

  Here, the program executed by the processor is provided by being incorporated in advance in a ROM (Read Only Memory), a storage circuit, or the like, for example. This program is a file in a format installable or executable in these devices, and is a computer such as a CD (Compact Disk) -ROM, FD (Flexible Disk), CD-R (Recordable), DVD (Digital Versatile Disk), etc. And may be provided by being recorded on a storage medium readable by the computer. The program may be provided or distributed by being stored on a computer connected to a network such as the Internet and downloaded via the network. For example, this program is composed of modules including the above-described functional units. As actual hardware, the CPU reads a program from a storage medium such as a ROM and executes it, whereby each module is loaded on the main storage device and generated on the main storage device.

  According to at least one embodiment described above, parallel imaging can be performed while ensuring the uniformity of the RF magnetic field without using an array coil.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

DESCRIPTION OF SYMBOLS 100 Magnetic Resonance Imaging (MRI) apparatus 4 WB coil 42 End ring 44 Lang 45 Antenna conductor

Claims (17)

Whole body RF housed in a gantry having a first element portion used for transmitting a high-frequency magnetic field and a second element portion used for receiving a magnetic resonance signal generated from the subject by receiving the high-frequency magnetic field With a coil,
The first element part is a birdcage type RF coil having two end rings and a plurality of rungs arranged at intervals along the circumferential direction of the end ring,
The second element part is a microstrip antenna.
Magnetic resonance imaging device. The second element portion has a direction along the magnetic flux of the static magnetic field as a first direction, a direction orthogonal to the first direction as a second direction, the first direction and the second direction. The microstrip antenna so that the in-plane sensitivity distribution along the second direction and the third direction differs depending on the position in the first direction when the direction orthogonal to each is the third direction. Are arranged and configured,
The magnetic resonance imaging apparatus according to claim 1. The microstrip antenna is disposed along a rung included in the first element portion, and the rung is configured as a ground conductor.
The magnetic resonance imaging apparatus according to claim 1 or 2. The first element unit is further used for receiving the high-frequency magnetic field.
The magnetic resonance imaging apparatus according to claim 1. The second element portion is further used for transmitting the high-frequency magnetic field.
The magnetic resonance imaging apparatus according to claim 1. The RF coil for whole body is short-circuited between the second element part and the first element part when the first element part is used.
The magnetic resonance imaging apparatus according to claim 1. The second element portion includes a plurality of microstrip antennas that are shorter in the first direction than the first element portion and are arranged at different positions in the first direction.
The magnetic resonance imaging apparatus according to claim 2. The second element portion includes a plurality of microstrip antennas having different lengths in the first direction.
The magnetic resonance imaging apparatus according to claim 2. Each rung included in the first element portion is disposed obliquely with respect to the first direction,
Each microstrip antenna included in the second element portion is disposed along a rung included in the first element portion, and the rung is configured as a ground conductor.
The magnetic resonance imaging apparatus according to claim 2. Each of the microstrip antennas included in the second element portion includes a part of the first element portion as a ground conductor, and a dielectric disposed between the antenna conductor and the antenna conductor and the ground conductor. A first direction of the antenna conductor based on at least one of a distance between the antenna conductor and the ground conductor, a material of the dielectric, and a width of the antenna conductor The length of
The magnetic resonance imaging apparatus according to claim 7 or 8. A control unit that performs parallel imaging using sensitivity distribution of each microstrip antenna included in the second element unit;
The magnetic resonance imaging apparatus according to any one of claims 2 and 7 to 10. The control unit performs the parallel imaging using a sensitivity distribution along the first direction of each microstrip antenna.
The magnetic resonance imaging apparatus according to claim 11. An RF coil having a first element portion used for transmitting a high-frequency magnetic field and a second element portion used for receiving a magnetic resonance signal generated from a subject by receiving the high-frequency magnetic field,
The first element part is a birdcage type RF coil having two end rings and a plurality of rungs arranged at intervals along the circumferential direction of the end ring,
The second element part is a microstrip antenna.
RF coil. Birdcage type comprising a whole body RF coil housed in a gantry, the whole body RF coil having two end rings and a plurality of rungs arranged at intervals along the circumferential direction of the end ring A magnetic resonance imaging method executed by a magnetic resonance imaging apparatus having a first element portion that is an RF coil of the first coil portion and a second element portion that includes a plurality of microstrip antennas,
Based on a pulse sequence for parallel imaging, a high-frequency magnetic field is transmitted using the first element unit, and a magnetic resonance signal generated from a subject is received using the second element unit in response to the high-frequency magnetic field. Collecting the first k-space data thinned out in the phase encoding direction for each of the microstrip antennas,
A magnetic resonance imaging method comprising: generating an image by developing a fold in the first k-space data using a sensitivity difference between the microstrip antennas. Based on a pulse sequence for sensitivity distribution measurement, a high-frequency magnetic field is transmitted using the first element unit, and a magnetic resonance signal generated from the subject in response to the high-frequency magnetic field is transmitted using the second element unit. Collecting second k-space data for each microstrip antenna by receiving,
Generating, for each microstrip antenna, a first sensitivity map indicating a sensitivity distribution of the microstrip antenna based on the second k-space data;
For each of the microstrip antennas, using the first sensitivity map, unfolding is performed on the image data generated from the first k-space data to generate the image.
The magnetic resonance imaging method according to claim 14. Collecting the first k-space data for each microstrip antenna to include data for a central portion of k-space;
15. The image is generated by expanding a fold on the first k-space data by performing weighted addition of signal values between the first k-space data collected for each microstrip antenna. A magnetic resonance imaging method according to claim 1. Based on a pulse sequence for sensitivity correction, a high-frequency magnetic field is transmitted using the first element unit, and a magnetic resonance signal generated from a subject by receiving the high-frequency magnetic field is received using the first element unit. To collect the third k-space data,
Generating a second sensitivity map indicating a sensitivity distribution of the first element portion based on the third k-space data;
Further comprising performing a sensitivity correction for correcting non-uniformity in the image using the second sensitivity map.
The magnetic resonance imaging method according to any one of claims 14 to 16.

Images