JP2019171036A - Magnetic resonance imaging device - Google Patents

Abstract

To adjust irradiation intensity of an RF pulse depending of a position of a receiving coil in a bore.SOLUTION: A magnetic resonance imaging device 1 according to an embodiment comprises a position information generating unit and a pulse intensity adjusting unit. The position information generating unit generates position information related to a positional relation between a transmitting coil and a receiving coil on the basis of a magnetic resonance signal received from a subject. The pulse intensity adjusting unit adjusts irradiation intensity of an RF pulse with which the subject is irradiated, depending on the position information.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a magnetic resonance imaging apparatus.

  Conventionally, a magnetic resonance imaging apparatus irradiates a subject with a high-frequency magnetic field (hereinafter referred to as an RF pulse) generated by a transmitting RF (Radio Frequency) coil, and receives a magnetic resonance signal generated in the subject. The signal is received by the receiving coil in the RF coil device for use. The transmitting RF coil is installed in the gantry of the magnetic resonance imaging apparatus. As a receiving RF coil device, there is a dedicated RF coil device corresponding to an imaging region in order to efficiently receive a magnetic resonance signal. At this time, the dedicated RF coil device is installed near the subject. The receiving RF coil apparatus is connected to the magnetic resonance imaging apparatus via a connector provided at the end of the cable in the receiving RF coil apparatus and a port provided in the magnetic resonance imaging apparatus, and receives the received magnetic resonance signal. Transmit to the magnetic resonance imaging apparatus. A port used for connection between the receiving RF coil device and the magnetic resonance imaging apparatus is provided, for example, on a frame, a top plate, or the like in the magnetic resonance imaging apparatus. Ports on the top plate are provided at various positions along the long axis direction of the top plate, such as a bed side, a central portion of the top plate, and a side opposite to the bed.

The RF pulse generated by the transmitting RF coil is irradiated on the subject and also on the receiving coil. In order to prevent the reception RF coil device from being affected by the RF pulse, for example, a circuit for decoupling the influence of the RF pulse from the reception coil (hereinafter referred to as a decoupling switch) or a balun: balance to unbalance transformer (balance-unbalance converter)). In addition, the RF pulse transmitted from the transmitting RF coil is not subjected to excessive irradiation to the subject and the receiving coil. SAR (Specific Absorption Rate), B ₁ (RF magnetic field) amplitude, and B ₁ It is limited by the equivalent to the value of B _1Rms showing the square root of the mean square of B ₁ to the effective value.

  As a receiving RF coil device, for example, there is a receiving RF coil device in which the position in the bore is not fixed and the position can be changed according to the size of the subject. In such a receiving RF coil device, when the receiving coil is close to the transmitting coil, the receiving RF coil device may be greatly affected by the RF pulse. Also, the receiving RF coil device may be greatly affected by the RF pulse depending on the state of the cable from the receiving coil to the port. At this time, heat may increase in an internal circuit such as a decoupling switch or a balun mounted on the receiving RF coil device. In addition, when a cylindrical magnet is used as a static magnetic field magnet in the magnetic resonance imaging apparatus, if the cable is arranged along the static magnetic field direction, the receiving RF coil device is not easily affected by the RF pulse. On the other hand, when the cable is bent in a U shape in the bore with respect to the direction of the static magnetic field, heat generation in the internal circuit in the receiving RF coil device may increase.

_Limiting the value of B 1 _rms so as to suppress heat generation regardless of the position of the receiving coil device in the bore, the handling of the cable, and the like leads to a limitation of imaging conditions. For example, the limitation of the value of B 1 _rms leads to a decrease in the number of slices related to imaging per repetition time (TR: Repetition time), and there is a problem that the imaging time is extended. In addition, the placement of the receiving RF coil device and the routing of the cable that cause the receiving RF coil device to generate excessive heat due to the influence of the RF pulse are prohibited in the manual. However, when the operator misuses the receiving coil device, there is a problem in that there is a risk of excessive heat generation or damage in the receiving RF coil device.

JP 2010-119744 A JP 2014-61176 A U.S. Pat. No. 4,806,867 US Patent Application Publication No. 2016/0154074 US Patent Application Publication No. 2017/0097396

  The problem to be solved by the present invention is to adjust the irradiation intensity of the RF pulse in accordance with the position of the receiving coil device in the bore.

  The magnetic resonance imaging apparatus according to the present embodiment includes a position information generation unit and a pulse intensity adjustment unit. The position information generation unit generates position information related to the positional relationship between the transmission coil and the reception coil based on the magnetic resonance signal received from the subject. The pulse intensity adjustment unit adjusts the irradiation intensity of the RF pulse irradiated to the subject according to the position information.

FIG. 1 is a block diagram showing the overall configuration of the magnetic resonance imaging apparatus in the present embodiment. FIG. 2 is a diagram illustrating an example of the receiving coil device according to the present embodiment. FIG. 3 is a view of the subject inserted into the bore as viewed from the Z-axis direction in the present embodiment. FIG. 4 is a view of the subject inserted into the bore as viewed from the X-axis direction in the present embodiment. FIG. 5 is a diagram illustrating an example of a comparative example in which the subject inserted into the bore is viewed from the Z-axis direction. FIG. 6 is a diagram illustrating an example of a comparative example in which the subject inserted into the bore is viewed from the X-axis direction. FIG. 7 is a flowchart illustrating an example of a processing procedure relating to adjustment of the irradiation intensity of the RF pulse in the present embodiment. FIG. 8 is a diagram illustrating an example of an allowance map in the present embodiment. FIG. 9 is a diagram illustrating an example of a positional relationship among the top plate, the subject, and the receiving coil device in the present embodiment. FIG. 10 is a diagram illustrating an example of an axial image in the present embodiment. FIG. 11 is a diagram illustrating an example of a sagittal image in the present embodiment. FIG. 12 is a diagram illustrating an example of a high-intensity region specified for the axial image in FIG. 10 in the present embodiment. FIG. 13 is a diagram illustrating an example of a high intensity region in the sagittal image in FIG. 11 in the present embodiment. FIG. 14 is a diagram illustrating an example in which a high-intensity region is applied to an allowance map using position information regarding the high-intensity region in the present embodiment. FIG. 15 is a diagram illustrating an example of a correspondence table of a plurality of allowable coefficients with respect to a plurality of distances from the transmission coil in the first modification of the present embodiment. FIG. 16 is a diagram illustrating an example of a configuration of a processing circuit in the second modification example of the present embodiment. FIG. 17 is a diagram illustrating an example of a processing procedure of a pulse intensity adjustment process in the second modification example of the present embodiment. FIG. 18 is a diagram illustrating an example of the X-axis intensity distribution, the Y-axis intensity distribution, and the Z-axis intensity distribution for each of the four coil elements in the second modification example of the present embodiment. FIG. 19 is a diagram illustrating an example of a configuration of a processing circuit in an application example of the present embodiment. FIG. 20 is a view of the subject inserted into the bore as viewed from the X-axis direction in the application example of the present embodiment. FIG. 21 is a diagram illustrating an example of a positional relationship among the subject, the reception coil, the cable, and the connection port in the application example of the present embodiment. FIG. 22 is a diagram illustrating an example of a processing procedure of pulse intensity adjustment processing in the application example of the present embodiment.

  Hereinafter, this embodiment of the magnetic resonance imaging apparatus will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given when necessary.

(Embodiment)
FIG. 1 is a block diagram showing an overall configuration of a magnetic resonance imaging (hereinafter, referred to as MRI (magnetic resonance imaging)) apparatus 1 according to the present embodiment. The MRI apparatus 1 includes a static magnetic field magnet 101, a gradient magnetic field coil 103, a gradient magnetic field power source 105, a bed 107, a bed control circuit 109, a transmission circuit 113, a transmission coil 115, a reception coil apparatus 117, and a reception A circuit 119, an imaging control circuit (imaging unit) 121, an interface (input unit) 125, a display (display unit) 127, a storage device (storage unit) 129, and a processing circuit (processing unit) 131 are provided. The gantry 10 in the MRI apparatus 1 includes a static magnetic field magnet 101, a gradient magnetic field coil 103, and a transmission coil 115. The gantry 10 may be equipped with a gradient magnetic field power source 105, a receiving circuit 119, an imaging control circuit 121, and the like. The MRI apparatus 1 may have a hollow cylindrical shim coil between the static magnetic field magnet 101 and the gradient magnetic field coil 103.

  The static magnetic field magnet 101 is, for example, a magnet formed in a hollow, substantially cylindrical shape. The static magnetic field magnet 101 generates a uniform static magnetic field in the bore 111 that is a space in which the subject P is inserted. For example, a superconducting magnet is used as the static magnetic field magnet 101.

  The gradient magnetic field coil 103 is, for example, a coil formed in a hollow, substantially cylindrical shape. The gradient magnetic field coil 103 is disposed inside the static magnetic field magnet 101. The gradient coil 103 is formed by combining three coils corresponding to the X, Y, and Z axes orthogonal to each other. The Z-axis direction is assumed to be the same as the direction of the static magnetic field. The Y-axis direction is a vertical direction, and the X-axis direction is a direction perpendicular to the Z-axis direction and the Y-axis direction. The gradient magnetic field coil 103 generates a gradient magnetic field to be superimposed on a static magnetic field. Specifically, the three coils in the gradient magnetic field coil 103 are individually supplied with current from the gradient magnetic field power supply 105 and generate gradient magnetic fields whose magnetic field strengths change along the X, Y, and Z axes.

  The gradient magnetic fields of the X, Y, and Z axes generated by the gradient magnetic field coil 103 form, for example, a frequency encoding gradient magnetic field (also referred to as a readout gradient magnetic field), a phase encoding gradient magnetic field, and a slice selection gradient magnetic field. The frequency encoding gradient magnetic field is used to change the frequency of a magnetic resonance (hereinafter referred to as MR (Magnetic Resonance)) signal in accordance with the spatial position. The phase encoding gradient magnetic field is used to change the phase of the MR signal in accordance with the spatial position. The slice selection gradient magnetic field is used to determine the imaging section.

  The gradient magnetic field power supply 105 is a power supply device that supplies a current to the gradient magnetic field coil 103 under the control of the imaging control circuit 121.

  The bed 107 is an apparatus including a top plate 1071 on which the subject P is placed. Under the control of the bed control circuit 109, the bed 107 inserts the top plate 1071 on which the subject P is placed into the bore 111. For example, the bed 107 is installed in the examination room so that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 101.

  The top plate 1071 has a plurality of ports 1073 to which the receiving coil device 117 can be connected. A subject P is disposed on the top plate 1071. A connector 1175 provided at one end of the cable 1173 in the receiving coil device 117 is connected to one port among the plurality of ports. Note that the installation location of the port 1073 is not limited to the top plate 1071, and the port 1073 may be provided on the bed 107 or the gantry 10 or the like. A signal line from the port 1073 is connected to the reception circuit 119. When the reception coil device 117 has a high-frequency magnetic field transmission function, the signal line from the port 1073 is connected to the transmission circuit 113 in addition to the reception circuit 119, although not shown in FIG.

  The couch control circuit 109 is a circuit that controls the couch 107. By driving the couch 107 according to an instruction from the operator via the interface 125, the couch 1071 is moved in the longitudinal direction, the up-down direction, and in some cases, the left-right direction. Let

  The transmission circuit 113 supplies the transmission coil 115 with a high-frequency pulse for generating a high-frequency magnetic field (hereinafter referred to as an RF (Radio Frequency) pulse) corresponding to the Larmor frequency or the like under the control of the imaging control circuit 121.

  The transmission coil 115 is an RF coil disposed inside the gradient magnetic field coil 103. The transmission coil 115 is supplied with a high frequency pulse from the transmission circuit 113 and generates an RF pulse. The transmission coil is, for example, a whole-body coil (hereinafter referred to as a WB (whole body) coil). The WB coil may be used as a transmission / reception coil.

  The receiving coil device 117 includes a receiving coil 1171, internal circuits such as a balun (balance to unbalance transformer) and a decoupling switch, and a cable 1173 connected to the receiving coil 1171 at one end. And a connector 1175 provided at the other end of the cable 1173. The receiving coil device 117 receives the MR signal radiated from the subject P by the RF pulse. The reception coil device 117 outputs the received MR signal to the reception circuit 119 via the cable 1173 and the connector 1175. The reception coil device 117 may wirelessly transmit the received MR signal to the reception circuit 119 using a wireless transmission circuit (not shown). At this time, the cable 1173 and the connector 1175 in the receiving coil device 117 are not necessary.

  The reception coil 1171 has, for example, one or more, typically a plurality of coil elements. Hereinafter, for the sake of specific explanation, it is assumed that there are four coil elements. The four coil elements correspond to, for example, four reception channels. Each of the four coil elements is constituted by a loop coil. MR signals received by each of the four coil elements are output to the receiving circuit 119 in the order set for each of the four coil elements (hereinafter referred to as the output order).

  In FIG. 1, the transmission coil 115 and the reception coil device 117 are described as separate RF coils, but the transmission coil 115 and the reception coil device 117 may be implemented as an integrated transmission / reception coil. The transmission / reception coil is, for example, a local transmission / reception RF coil corresponding to an imaging region such as a head coil.

  FIG. 2 is a diagram illustrating an example of the receiving coil device 117. As shown in FIG. 2, each of the four coil elements (ch1, ch2, ch3, ch4) is provided with a balun 1177 and a decoupling switch 1179. In the receiving coil 1171, a cable 1173 is connected to one side close to the coil element ch3 side and the coil element ch4 side. Note that the connection position CP between the reception coil 1171 and the cable 1173 is not limited to the position shown in FIG. 2 and can be set to an arbitrary position with respect to the reception coil 1171.

  Each of the four coil elements (ch1, ch2, ch3, ch4) forms a loop structure when the decoupling switch 1179 is in the OFF state. Each of the four coil elements receives an MR signal generated from the subject P by applying an RF pulse.

  A balun 1177 is provided on the cable 1173 in addition to each of the four coil elements. The balun 1177 is configured by a resonant circuit having a capacitor and an inductor, for example. The balun 1177 absorbs an unbalanced current flowing in each of the plurality of coil elements and the cable 1173 by the RF pulse by the resonance circuit, and suppresses the unbalanced current in each of the four coil elements and the cable 1173.

  The decoupling switch 1179 is turned on under the control of the imaging control circuit 121 when an RF pulse is applied to each of the plurality of coil elements, that is, in the RF transmission mode. At this time, the loop structure is cut in each of the plurality of coil elements, and the electrical coupling in each of the plurality of coil elements is cut off. Further, the decoupling switch 1179 is turned off under the control of the imaging control circuit 121 in the reception mode for receiving the MR signal. At this time, each of the plurality of coil elements used for receiving the MR signal forms a loop structure.

  The receiving circuit 119 generates a digital MR signal that is digitized complex data based on the MR signal output from the receiving coil device 117 under the control of the imaging control circuit 121. Specifically, the receiving circuit 119 performs various signal processing on the MR signal output from the receiving coil device 117, and then performs analog / digital (A / D (A / D () on the data subjected to the various signal processing). Analog to Digital)) Perform the conversion. The receiving circuit 119 generates a digital MR signal (hereinafter referred to as MR data) by sampling the A / D converted data. The reception circuit 119 outputs the generated MR data to the imaging control circuit 121.

  The imaging control circuit 121 controls the gradient magnetic field power supply 105, the transmission circuit 113, the reception circuit 119, and the like according to the imaging protocol output from the processing circuit 131, and performs imaging on the subject P. The imaging protocol has various pulse sequences according to the examination. The imaging protocol includes the magnitude of the current supplied from the gradient magnetic field power source 105 to the gradient magnetic field coil 103, the timing at which the current is supplied from the gradient magnetic field power source 105 to the gradient magnetic field coil 103, and the transmission circuit 113 supplied to the transmission coil 115. The timing of the high frequency pulse to be transmitted, the timing at which the transmission circuit 113 supplies the high frequency pulse to the transmission coil 115, the timing at which the MR signal is received by the reception coil 1171, the ON / OFF timing of the decoupling switch 1179, etc. are preset. ing.

  The interface 125 includes a circuit that receives various instructions and information input from the operator. The interface 125 includes a circuit related to a pointing device such as a mouse or an input device such as a keyboard. The circuit included in the interface 125 is not limited to a circuit related to physical operation components such as a mouse and a keyboard. For example, the interface 125 receives an electrical signal corresponding to an input operation from an external input device provided separately from the MRI apparatus 1, and processes the electrical signal so as to output the received electrical signal to various circuits. You may have a circuit.

  The display 127 displays various MR images generated by the image information generation function 1311 and various types of information related to imaging and image processing under the control of the system control function 1310 in the processing circuit 131. The display 127 is, for example, a display device such as a CRT display, liquid crystal display, organic EL display, LED display, plasma display, or any other display or monitor known in the art.

  The storage device 129 stores MR data filled in the k space via the image information generation function 1311, image data generated by the image information generation function 1311, and the like. The storage device 129 stores various imaging protocols, imaging conditions including a plurality of imaging parameters that define the imaging protocols, and the like. The storage device 129 stores programs corresponding to various functions executed by the processing circuit 131. The storage device 129 is, for example, a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk drive, a solid state drive, or an optical disk. The storage device 129 may be a drive device that reads / writes various information from / to a portable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory.

  The processing circuit 131 includes, as hardware resources, a processor (not shown), a memory such as a ROM (Read-Only Memory), a RAM, and the like, and controls the MRI apparatus 1. The processing circuit 131 includes a system control function 1310, an image information generation function 1311, a position information generation function 1313, a pulse intensity adjustment function 1315, and a calculation function 1317. Various functions performed by the system control function 1310, the image information generation function 1311, the position information generation function 1313, the pulse intensity adjustment function 1315, and the calculation function 1317 are stored in the storage device 129 in the form of a program executable by a computer. Yes. The processing circuit 131 is a processor that realizes a function corresponding to each program by reading a program corresponding to these various functions from the storage device 129 and executing the program. In other words, the processing circuit 131 in a state where each program is read has a plurality of functions and the like shown in the processing circuit 131 of FIG.

  In FIG. 1, it has been described that these various functions are realized by a single processing circuit 131. However, the processing circuit 131 is configured by combining a plurality of independent processors, and each processor executes a program. The function may be realized by the above. In other words, each function described above may be configured as a program, and one processing circuit may execute each program, or a specific function may be implemented in a dedicated independent program execution circuit. May be.

  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). Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (Complex Programmable Logic Device: CPLD), and Field Programmable Gate Array (FPGA), etc. It means circuit.

  The processor implements various functions by reading and executing a program stored in the storage device 129. Instead of storing the program in the storage device 129, the program may be directly incorporated into the processor circuit. In this case, the processor realizes the function by reading and executing the program incorporated in the circuit. Note that the bed control circuit 109, the transmission circuit 113, the reception circuit 119, the imaging control circuit 121, and the like are similarly configured by electronic circuits such as the processor. Further, the system control function 1310, the image information generation function 1311, the position information generation function 1313, the pulse intensity adjustment function 1315, and the calculation function 1317 included in the processing circuit 131 are respectively a system control unit, an image information generation unit, a position information generation unit, It is an example of a pulse intensity adjustment part and a calculation part.

  The processing circuit 131 controls various circuits in the MRI apparatus 1 by the system control function 1310. Specifically, the processing circuit 131 reads out the system control program stored in the storage device 129, expands it on the memory, and controls each circuit of the MRI apparatus 1 according to the expanded system control program. For example, the processing circuit 131 reads the imaging protocol from the storage device 129 based on the imaging conditions input from the operator via the interface 125 by the system control function 1310. Note that the processing circuit 131 may generate an imaging protocol based on the imaging conditions. The processing circuit 131 transmits an imaging protocol to the imaging control circuit 121 and controls various imaging for the subject P.

  The processing circuit 131 fills the MR data in the k space by the image information generation function 1311. The processing circuit 131 generates an MR image by performing, for example, Fourier transform on the MR data filled in the k space. The image information generation function 1311, the position information generation function 1313, the pulse intensity adjustment function 1315, and the calculation function 1317 will be described later in the operation.

  The above is a schematic description of the overall configuration of the MRI apparatus 1 in the present embodiment. In addition to such a configuration, the MRI apparatus 1 in the present embodiment is configured to be able to adjust the irradiation intensity of the RF pulse according to the position of the receiving coil 1171 in the bore 111.

  FIG. 3 is a diagram of the subject P inserted into the bore 111 as viewed from the Z-axis direction in the present embodiment. FIG. 4 is a view of the subject P inserted into the bore 111 as viewed from the X-axis direction in the present embodiment. FIG. 5 is a diagram illustrating an example of a comparative example in which the subject P inserted into the bore 111 is viewed from the Z-axis direction. FIG. 6 is a diagram illustrating an example of a comparative example in which the subject P inserted into the bore 111 is viewed from the X-axis direction. 3 to 6, the internal circuit is not shown.

  The reception coil device 117 is approaching the transmission coil 115. 3 and 4, the distance int between the reception coil device 117 and the transmission coil 115 is shorter than the distance between the reception coil device 117 and the transmission coil 115 in FIGS. On the other hand, in the case shown in FIGS. 5 and 6, the reception coil device 117 is not easily affected by the RF pulse applied by the transmission coil 115. For these reasons, when the receiving coil device 117 is provided on the subject P in the state shown in FIGS. 3 and 4, the influence of the RF pulse on the receiving coil device 117 is as shown in FIGS. It becomes stronger than the case. For this reason, the heat generation of the internal circuit in the receiving coil device 117 shown in FIGS. 3 and 4 is larger than that in FIGS. 5 and 6.

  The operation in this embodiment will be described below. FIG. 7 is a flowchart illustrating an example of a procedure of processing relating to adjustment of irradiation intensity of RF pulses (hereinafter referred to as pulse intensity adjustment processing) in the present embodiment. The pulse intensity adjustment processing is executed in a state where the receiving coil device 117 is installed on the subject P as shown in FIGS.

  The storage device 129 stores the position of the inner wall of the bore 111 as coordinates in a coordinate system of an area including the transmission coil 115 and the bore 111 (hereinafter referred to as a pedestal coordinate system). The storage device 129 stores an allowable map used by the pulse intensity adjustment process. The tolerance map corresponds to, for example, a map in which a plurality of tolerance coefficients are assigned to a plurality of positions in an area including the bore 111 in the axial section perpendicular to the Z-axis direction, that is, a plurality of coordinates in the gantry coordinate system. Each of the plurality of allowable coefficients corresponds to, for example, the ratio of the allowable amount in which the irradiation intensity of the RF pulse is allowed in the main scan to the irradiation intensity amount of the RF pulse. The allowable coefficient is set in advance for each receiving coil device corresponding to the imaging region in accordance with the heat generation state of the internal circuit or the like by experiments or simulations. Note that the value obtained by subtracting the allowable coefficient from 1 indicates the rate at which the irradiation intensity is limited with respect to the maximum allowable amount.

  FIG. 8 is a diagram illustrating an example of an allowance map. In FIG. 8, the transmission coil 115 is located outside the bore inner wall. In FIG. 8, “1” in a region including the center position of the bore 111 and a region near the center position indicates the maximum allowable amount of irradiation intensity of the RF pulse. As shown in FIG. 8, the closer to the bore inner wall, the smaller the allowable coefficient value. That is, the closer to the bore inner wall, the smaller the ratio of the allowable amount of irradiation intensity to the maximum allowable amount of RF pulse. In other words, the closer to the bore inner wall, the greater the limit of irradiation intensity with respect to the maximum allowable amount of RF pulses.

(Pulse intensity adjustment processing)
(Step Sa1)
A receiving coil device 117 is installed for the subject P placed on the top plate 1071. The connector 1175 at the end of the cable 1173 in the receiving coil device 117 is connected to the port 1073 in the top plate 1071. FIG. 9 is a diagram illustrating an example of a positional relationship among the top plate 1071, the subject P, and the reception coil device 117. Hereinafter, various descriptions will be given based on the positional relationship shown in FIG. The installation situation of the subject P and the reception coil device 117 with respect to the top plate 1071 shown in FIG. 9 is an example, and is not limited to the installation situation in FIG. In FIG. 9, the internal circuit is not shown.

  The imaging control circuit 121 collects MR signals by executing a pre-scan prior to the execution of the main scan. The pre-scan corresponds to pre-imaging such as positioning imaging (locator) for obtaining a positioning image in which an imaging region related to the main scan is set, and imaging for obtaining a sensitivity map used in parallel imaging. The pre-scan is a scan related to volume imaging on the subject P such as two-dimensional multi-slice imaging or three-dimensional imaging. Note that since prescan is intended to collect MR signals, any imaging method may be used as long as MR signals can be collected in a short time without depending on image quality. The imaging control circuit 121 attaches information for discriminating the coil elements to the MR signals collected in the respective coil elements using the output order.

(Step Sa2)
The processing circuit 131 uses the image information generation function 1311 to generate (reconstruct) image information based on the collected MR signals. The image information has, for example, a signal intensity corresponding to each of a plurality of frequency components in the MR signal as a pixel value. Each of the plurality of frequency components corresponds to the magnetic field strength in the gradient magnetic field of each axis of X, Y, and Z. Therefore, the frequency component in the MR signal corresponds to the position in the gantry coordinate system.

  Specifically, the processing circuit 131 uses the image information generation function 1311 to generate a plurality of cross-sectional images (hereinafter referred to as axial images) corresponding to a plurality of slices perpendicular to the Z-axis direction based on the MR signal. . The processing circuit 131 attaches coordinates in the gantry coordinate system to each of a plurality of pixel values in a plurality of axial images based on the gradient magnetic fields of the X, Y, and Z axes.

  FIG. 10 is a diagram illustrating an example of the axial image AxI. In the axial section AxP of the subject P shown in FIG. 10, the MR signal intensity distribution (hereinafter referred to as signal distribution) sid13 related to the coil element ch1 or the coil element ch3, and the signal distribution sid24 related to the coil element ch2 or the coil element ch4. Is shown.

  FIG. 11 is a diagram illustrating an example of the sagittal image SgI. A sagittal cross section SgP of the subject P shown in FIG. 11 shows a signal distribution sid12 related to the coil element ch1 or the coil element ch2 and a signal distribution sid34 related to the coil element ch3 or the coil element ch4.

  As shown in FIGS. 10 and 11, the signal distribution relating to each of the plurality of coil elements can be separated in the gantry coordinate system. For this reason, the processing circuit 131 attaches coordinates in the gantry coordinate system to each of the plurality of signal distributions related to the plurality of coil elements in each of the plurality of axial sections by the image information generation function 1311 according to the position of the pixel.

(Step Sa3)
The processing circuit 131 generates position information related to the positional relationship between the transmission coil 115 and the reception coil 1171 based on the MR signal received from the subject P by the position information generation function 1313. In other words, the processing circuit 131 generates position information of the receiving coil 1171 in the bore 111 based on the signal strength corresponding to each of a plurality of frequency components in the MR signal received from the subject P. That is, the processing circuit 131 generates position information of a plurality of coil elements in the bore 111 based on the image information. In other words, the processing circuit 131 generates position information based on the image obtained by reconstructing the MR signal. Hereinafter, the generation of position information will be specifically described.

  The processing circuit 131 uses the position information generation function 1313 to identify a region (hereinafter referred to as a high intensity region) that includes a value from the peak value in the signal distribution to 70% to 80% of the peak value in the image information. To do. That is, the processing circuit 131 specifies a high intensity region for the signal distribution in each of the plurality of axial images using the peak value in the signal distribution. In the high intensity region, a plurality of coordinates in the gantry coordinate system are attached according to the position of the pixel by the processing in step Sa2.

  FIG. 12 is a diagram illustrating an example of a high-intensity region specified for the axial image AxI in FIG. The axial section AxP shown in FIG. 12 shows a high strength region HIR13 related to the coil element ch1 or the coil element ch3 and a high strength region HIR24 related to the coil element ch2 or the coil element ch4.

  FIG. 13 is a diagram illustrating an example of a high intensity region in the sagittal image SgI in FIG. The sagittal section SgP shown in FIG. 13 shows a high strength region HIR34 related to the coil element ch3 or the coil element ch4 and a high strength region HIR12 related to the coil element ch1 or the coil element ch2.

  According to FIGS. 3, 4, 9, 12, and 13, the receiving coil 1171, that is, the plurality of coil elements are located in the vicinity of the high-strength region. Therefore, the description will be made assuming that the high-strength region corresponds to the position of the receiving coil 1171, that is, the position of a plurality of coil elements.

  The processing circuit 131 uses the position information generation function 1313 to obtain a plurality of coordinates corresponding to a plurality of pixels included in the high-intensity region in each of the plurality of axial images. It is generated as position information for each coil element. Note that the processing circuit 131 may generate position information assuming that the signal distribution corresponds to the position of the reception coil 1171 without specifying a high-intensity region. At this time, as illustrated in FIG. 9, the processing circuit 131 generates, as position information of the receiving coil 1171, a plurality of coordinates corresponding to a plurality of pixels included in the signal distribution in each of the plurality of axial images.

(Step Sa4)
Using the position information, the processing circuit 131 applies the region related to the reception coil 1171 in the image information to the tolerance map by using the pulse intensity adjustment function 1315. Specifically, the processing circuit 131 assigns the high-intensity region to the allowable map using a plurality of coordinates attached to the high-intensity region in each of the plurality of axial cross sections. That is, the processing circuit 131 performs superimposition of the high-intensity region on the tolerance map using the position information over the total number of the plurality of axial cross sections.

  FIG. 14 is a diagram illustrating an example in which the high-intensity region HIR13 and the high-intensity region HIR24 are applied to the tolerance map using the position information regarding the high-intensity region HIR13 and the position information regarding the high-intensity region HIR24. A plurality of numerical values in a region included in the high-intensity region HIR13 and the high-intensity region HIR24 indicate a plurality of tolerance coefficients in the high-intensity region HIR13 and a plurality of tolerance coefficients in the high-intensity region HIR24.

  Note that the processing circuit 131 may superimpose all high-intensity regions over a plurality of axial sections on the tolerance map by the pulse intensity adjustment function 1315. At this time, the high strength region HIR13 in FIG. 14 is a region where all the high strength regions related to the coil element ch1 and the coil element ch3 are integrated, and the high strength region HIR24 is a region where all the high strength regions related to the coil element ch2 and the coil element ch4 are integrated. It becomes the area. Further, the processing circuit 131 may apply the signal distribution to the tolerance map instead of the high intensity region.

(Step Sa5)
The processing circuit 131 is the smallest of a plurality of allowable coefficients included in the region related to the receiving coil 1171 in the allowable map (hereinafter referred to as a region superposition map) in which the region related to the receiving coil 1171 is applied by the pulse intensity adjustment function 1315. Specify the tolerance factor. Specifically, the processing circuit 131 specifies the minimum allowable coefficient among the plurality of allowable coefficients included in the plurality of high-intensity areas in the plurality of area superimposition maps respectively corresponding to the plurality of axial cross sections.

  When all the high-intensity areas over a plurality of axial sections are applied to the tolerance map, the processing circuit 131 specifies the minimum tolerance coefficient among the plurality of tolerance coefficients included in the high-intensity area in the tolerance map. . For example, when FIG. 14 shows an example in which all high-intensity regions over a plurality of axial cross sections are applied to the tolerance map, the processing circuit 131 specifies a tolerance coefficient of 0.5. If the specified allowable coefficient is “1”, the pulse intensity adjustment process ends.

(Step Sa6)
The processing circuit 131 adjusts the irradiation intensity of the RF pulse related to the main scan using the specified tolerance coefficient by the pulse intensity adjustment function 1315. Specifically, the processing circuit 131 determines the irradiation intensity of the RF pulse related to the main scan by multiplying the maximum allowable amount of irradiation intensity of the RF pulse by the specified allowable coefficient. Thereby, the allowable amount of irradiation intensity of the RF pulse is reduced.

  The processing circuit 131 changes imaging conditions preset by an operator or the like via the interface 125 or the like using the irradiation intensity adjusted by the pulse intensity adjustment function 1315. Specifically, the processing circuit 131 changes the imaging parameters in the imaging conditions according to the adjustment of the irradiation intensity. The imaging parameters to be changed are parameters related to the irradiation intensity of the RF pulse. For example, the repetition time (TR: repetition time), the echo train length (ETL), the flip angle of the refocusing RF pulse ( For example, the intensity of the feedback fringe angle, the intensity of the fat suppression pulse, the intensity of the DE (Driven Equilibrium) pulse, the intensity of the MTC (Magnetization Transfer Contrast) pulse. The processing circuit 131 changes the imaging condition by changing the imaging parameter.

  In step Sa4 to step Sa6, the processing circuit 131 adjusts the irradiation intensity of the RF pulse irradiated to the subject P according to the position information by the pulse intensity adjustment function 1315. For example, the processing circuit 131 adjusts the irradiation intensity so that the irradiation intensity decreases as the distance between the transmission coil 115 and the reception coil 1171 decreases.

(Step Sa7)
The processing circuit 131 uses the calculation function 1317 to calculate an extension time of the imaging time based on the change of the imaging condition according to the adjusted irradiation intensity. Specifically, the processing circuit 131 calculates the extended time of the imaging time based on the imaging condition changed according to the adjustment of the irradiation intensity and the imaging condition before the change. For example, the processing circuit 131 calculates the imaging time when the main scan is executed using the imaging conditions before the change (hereinafter referred to as the pre-change time). Next, the processing circuit 131 calculates an imaging time (hereinafter referred to as a changed time) when the main scan is executed using the changed imaging condition. The processing circuit 131 calculates the extension time by subtracting the pre-change time from the post-change time.

(Step Sa8)
The processing circuit 131 outputs a message to the display 127 that the irradiation intensity is limited according to the position of the receiving coil 1171, that is, the position of the coil element, by the pulse intensity adjustment function 1315. The display 127 displays the message output from the processing circuit 131. The processing circuit 131 outputs the calculated extension time to the display. The display 127 displays the message together with the extended time.

  Note that the processing circuit 131 may output, to the display 127, imaging conditions before and after the change, imaging parameters before and after the change, an image in which the high intensity region is applied to the allowable map, and the like by the pulse intensity adjustment function 1315. At this time, the display 127 displays the imaging conditions before and after the change, the imaging parameters before and after the change, the image in which the high-intensity area is applied to the allowable map, and the like together with the message and the extension time.

  When a main scan start instruction is input via the interface 125 after this step, the processing circuit 131 outputs the changed imaging condition to the imaging control circuit 121 by the system control function 1310. The imaging control circuit 121 executes the main scan according to the changed imaging condition.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in the present embodiment, the position information of the receiving coil 1171 in the bore 111 is generated based on the signal intensity corresponding to each of a plurality of frequency components in the MR signal received from the subject P, and the position The irradiation intensity of the RF pulse irradiated to the subject P can be adjusted based on the information.

  That is, according to the MRI apparatus 1, position information related to the positional relationship between the transmission coil 115 and the reception coil 1171 is generated based on the MR signal received from the subject P, and the object is detected according to the position information. The irradiation intensity of the RF pulse applied to the specimen P can be adjusted. Further, according to the MRI apparatus 1, the distance between the transmission coil 115 and the reception coil 1171 can be used as the positional relationship. Further, according to the MRI apparatus 1, position information can be generated based on an image obtained by reconstructing an MR signal. Thus, according to the present MRI apparatus 1, it is possible to adjust the irradiation intensity so that the irradiation intensity decreases as the distance between the transmission coil 115 and the reception coil 1171 approaches.

  More specifically, according to the present MRI apparatus, image information having a pixel value corresponding to the signal intensity is generated based on the MR signal, and the receiving coil 1171 is generated using the coordinate system and the image information regarding the region including the bore 111. A plurality of coordinates relating to the position of the position is generated as position information, and a plurality of tolerance coefficients indicating the degree of tolerance of the irradiation intensity are associated with the plurality of coordinates in the coordinate system using the plurality of coordinates. It is possible to adjust the irradiation intensity using the minimum allowable coefficient among a plurality of allowable coefficients included in the area related to the reception coil 1171 by fitting the area related to 1171.

  Further, according to the MRI apparatus 1, it is possible to display that the irradiation intensity is limited according to the position of the receiving coil by adjusting the irradiation intensity. In addition, according to the present MRI apparatus 1, the extension time of the imaging time is calculated based on the imaging condition changed according to the adjustment of the irradiation intensity and the imaging condition before the change, and the calculated extension time is displayed. be able to.

  Therefore, according to the present MRI apparatus 1, the receiving coil 1171 and the internal circuit are damaged without excessively limiting the irradiation intensity of the RF pulse according to the position of the receiving coil apparatus 117 in the bore 111. It is possible to reduce the risk and determine the optimum irradiation intensity in the main scan.

  That is, according to the present MRI apparatus 1, by considering various setting states of the receiving coil apparatus 117 in the bore 111, the arrangement of the receiving coil 1171 and the receiving coil 1171 expected to generate small heat in the internal circuit is high frequency. Since it is not necessary to excessively protect the RF coil device 1117 against the magnetic field, the main scan can be executed under an imaging condition in which the restriction on the high-frequency magnetic field is relaxed.

  Further, according to the MRI apparatus 1, in the arrangement of the receiving coil 1171 and the receiving coil 1171 expected to generate a large amount of heat in the internal circuit, the imaging conditions in which the restriction on the high frequency magnetic field is severe, that is, the irradiation intensity of the RF pulse is lowered. The main scan can be executed under the imaging conditions in the state. For this reason, even if the operator makes a mistake in the setting method of the reception coil device 117, the main scan can be executed safely without damaging the reception coil device 117.

  Further, according to the present MRI apparatus 1, it is possible to present to the operator by a message that the receiving coil apparatus 117 is a setting that is greatly affected by the high frequency magnetic field. In addition, according to the MRI apparatus 1, it is possible to present to the operator that the imaging time is extended due to the strict limitation of the imaging conditions due to the arrangement of the receiving coil device 117. That is, by providing the operator with such information as an indication of resetting the receiving coil device 117 in the bore 111, the operator can select whether to edit the imaging condition or reset the receiving coil device 117. Judgment can be made and the inspection throughput can be improved.

(First modification)
The difference between the present modification and the embodiment is that a distance from the transmission coil 115 to the reception coil 1171 is calculated as position information using image information, and a correspondence table of a plurality of allowable coefficients for a plurality of distances from the transmission coil 115 ( The minimum allowable coefficient is determined using a lookup table) and the calculated distance. The positional relationship is, for example, the distance between the transmission coil 115 and the reception coil 1171.

  The storage device 129 stores the correspondence table. The storage device 129 stores the position of the transmission coil 115 as coordinates in the gantry coordinate system. FIG. 15 is a diagram showing an example of the correspondence table. As shown in FIG. 15, the closer the position of the receiving coil is to the transmitting coil 115, the smaller the allowable coefficient. That is, the closer to the transmission coil 115, the stronger the limit on the maximum allowable amount of irradiation intensity of the RF pulse. The correspondence table shown in FIG. 15 corresponds to a table obtained by converting the tolerance map shown in FIG.

  Hereinafter, the difference in the pulse intensity adjustment processing in the present modification from the processing in steps Sa3 to Sa5 in the above embodiment will be described.

(Pulse intensity adjustment processing)
(Step Sa3)
The processing circuit 131 uses the position information generation function 1313 to calculate the distance from the transmission coil 115 to the reception coil 1171 for each of a plurality of pixels in the image information using the image information. As shown in FIGS. 3 and 5, the transmission coil 115 is disposed outside the bore inner wall so as to surround the bore 111. For this reason, the processing circuit 131 calculates, for each of a plurality of pixels in the signal distribution, the shortest distance from the coordinates of the transmission coil 115 to the coordinates of these pixels. Specifically, the processing circuit 131 calculates the shortest distance for each pixel by an optimization process using a calculation formula for obtaining a distance between two points from the transmission coil 115 to the pixel.

(Step Sa4)
The processing circuit 131 uses the pulse intensity adjustment function 1315 to collate the calculated distance with the correspondence table, thereby determining a plurality of allowable coefficients corresponding to a plurality of pixels in the signal distribution.

(Step Sa5)
The processing circuit 131 uses the pulse intensity adjustment function 1315 to specify the minimum allowable coefficient among the plurality of determined allowable coefficients. The specified tolerance coefficient corresponds to the pixel closest to the transmission coil 115.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in the present modification, image information having signal intensities corresponding to each of a plurality of frequency components in the MR signal received from the subject P as pixel values is generated based on the MR signal, and the image information is generated. The distance from the transmission coil 115 that irradiates the subject P with the RF pulse to the reception coil 1171 is calculated as position information of the reception coil 1171 in the bore 111 for each of a plurality of pixels in the image information and transmitted. A plurality of tolerance coefficients corresponding to a plurality of pixels are determined using a correspondence table of a plurality of tolerance coefficients indicating a degree of tolerance of irradiation intensity with respect to a plurality of distances from the coil 115 and the calculated distance. Further, the irradiation intensity can be adjusted by using the minimum allowable coefficient among the plurality of allowable coefficients. Since other effects are the same as those of the embodiment, description thereof is omitted.

(Second modification)
The difference between the present modification and the embodiment is a one-dimensional distribution indicating signal intensity distributions for a plurality of frequency components respectively corresponding to the three axes based on MR signals corresponding to the three gradient magnetic fields with respect to the three different axes. An intensity distribution is generated for each of the three axes, and position information is generated based on a one-dimensional intensity distribution (one-dimensional profile) for each of the three axes. Hereinafter, for the sake of specific explanation, it is assumed that the three different axes are the X axis, the Y axis, and the Z axis. The three different axes are not limited to the X axis, the Y axis, and the Z axis.

  Regarding the configuration and pulse intensity adjustment processing in this modification, the contents different from those of the above embodiment will be described. FIG. 16 is a diagram illustrating an example of the configuration of the processing circuit 131 in the present modification. The processing circuit 131 further has an intensity distribution generation function 1319. The intensity distribution generation function 1319 is stored in the storage device 129 in the form of a program that can be executed by a computer. The intensity distribution generation function 1319 included in the processing circuit 131 is an example of an intensity distribution generation unit. The processing content related to the intensity distribution generation function 1319 will be described in the processing procedure of the pulse intensity adjustment processing in this modification.

  FIG. 17 is a diagram illustrating an example of a processing procedure of pulse intensity adjustment processing in the present modification. In the pulse intensity adjustment process, steps Sb1 to Sb4 in FIG. 17 are replaced with steps Sa1 to Sa5 in FIG. 7 in the present embodiment. That is, in FIG. 17, the processing following step Sb4 is processing after step Sa6 in FIG.

(Pulse intensity adjustment processing)
(Step Sb1)
The reception coil device 117 is installed for the subject P placed on the top board 1071 before the pre-scan in this modification is executed. The installation situation of the receiving coil device 117 in this modification is assumed to be the same as that in FIG. 9 in order to avoid redundant description.

  The imaging control circuit 121 applies three gradient magnetic fields along the X-axis, Y-axis, and Z-axis to the subject P as pre-scans, respectively, so that MR corresponding to the X-axis, Y-axis, and Z-axis respectively. Collect signals. That is, the imaging control circuit 121 performs a line scan for each of the X axis, the Y axis, and the Z axis. The pre-scan in this modification corresponds to, for example, a scan used to select a coil element used for the main scan among a plurality of coil elements. Note that the pre-scan in this modification is intended to collect MR signals, so any imaging method may be used as long as MR signals can be collected in a short time regardless of image quality.

  Specifically, the imaging control circuit 121 applies a gradient magnetic field along the X axis (hereinafter referred to as an X axis gradient magnetic field) to the subject P as a readout gradient magnetic field, thereby causing an MR signal (hereinafter referred to as the X axis). (Referred to as MR signals). The imaging control circuit 121 applies an MR magnetic field (hereinafter referred to as a Y-axis MR signal) by applying a gradient magnetic field along the Y axis (hereinafter referred to as a Y-axis gradient magnetic field) to the subject P as a readout gradient magnetic field. To collect. The imaging control circuit 121 applies an MR magnetic field (hereinafter referred to as a Z-axis MR signal) by applying a gradient magnetic field along the Z-axis (hereinafter referred to as a Z-axis gradient magnetic field) to the subject P as a readout gradient magnetic field. To collect.

(Step Sb2)
Based on the MR signal, the processing circuit 131 uses the intensity distribution generation function 1319 to generate a one-dimensional intensity distribution indicating a signal intensity distribution for each of a plurality of frequency components respectively corresponding to the X axis, the Y axis, and the Z axis. Generated for each axis, Y axis, and Z axis. Specifically, the processing circuit 131 performs Fourier transformation on the X-axis MR signal, thereby distributing the intensity of the X-axis MR signal with respect to the frequency related to the X-axis gradient magnetic field (hereinafter referred to as the X-axis frequency) ( Hereinafter, this is referred to as an X-axis intensity distribution. The processing circuit 131 performs a Fourier transform on the Y-axis MR signal to thereby distribute the intensity of the Y-axis MR signal (hereinafter referred to as the Y-axis intensity) with respect to the frequency related to the Y-axis gradient magnetic field (hereinafter referred to as the Y-axis frequency). Called distribution). The processing circuit 131 performs a Fourier transform on the Z-axis MR signal to thereby distribute the intensity of the Z-axis MR signal (hereinafter referred to as the Z-axis intensity) with respect to the frequency related to the Z-axis gradient magnetic field (hereinafter referred to as the Z-axis frequency). Called distribution). Each of the X-axis intensity distribution, the Y-axis intensity distribution, and the Z-axis intensity distribution corresponds to the one-dimensional intensity distribution. The X-axis frequency, the Y-axis frequency, and the Z-axis frequency correspond to the X-axis position, the Y-axis position, and the Z-axis position, respectively.

  FIG. 18 is a diagram illustrating an example of the X-axis intensity distribution, the Y-axis intensity distribution, and the Z-axis intensity distribution for each of the four coil elements (ch1, ch2, ch3, ch4). Depending on the position of the four coil elements in the bore 111, the X-axis intensity distribution, the Y-axis intensity distribution, and the Z-axis intensity distribution differ for each coil element.

(Step Sb3)
The processing circuit 131 calculates the distance from the transmission coil 115 to the reception coil 1171 by using the three one-dimensional intensity distributions respectively corresponding to the X axis, the Y axis, and the Z axis by the position information generation function 1313. Specifically, the processing circuit 131 specifies, for each coil element, the X-axis frequency corresponding to the signal intensity peak in the X-axis intensity distribution or the X-axis frequency corresponding to the center of gravity in the X-axis intensity distribution. The processing circuit 131 specifies, for each coil element, a Y-axis frequency corresponding to a signal intensity peak in the Y-axis intensity distribution or a Y-axis frequency corresponding to the center of gravity in the Y-axis intensity distribution. The processing circuit 131 specifies, for each coil element, the Z-axis frequency corresponding to the signal intensity peak in the Z-axis intensity distribution or the Z-axis frequency corresponding to the center of gravity in the Z-axis intensity distribution.

  The processing circuit 131 uses the position information generation function 1313 to specify the specified X-axis frequency, the specified Y-axis frequency, and the specified Z-axis frequency as coordinates in the gantry coordinate system (hereinafter referred to as element coordinates), respectively. Convert. The element coordinates corresponding to each of the plurality of coil elements corresponds to the position of each of the plurality of coil elements. The processing circuit 131 calculates the distance from the position of the transmission coil 115 to the position of each coil element using the coordinates of the transmission coil 115 and the element coordinates in the gantry coordinate system. Since the calculated distance is the same as the shortest distance in the first modification, description thereof is omitted. With the above processing, the processing circuit 131 uses the X-axis intensity distribution, the Y-axis intensity distribution, and the Z-axis intensity distribution as a plurality of shortest distances respectively corresponding to the plurality of coil elements as position information of the receiving coil 1171. Generate.

(Step Sb4)
The processing circuit 131 uses the pulse intensity adjustment function 1315 to specify the minimum allowable coefficient using the allowable coefficient correspondence table, that is, the correspondence table shown in FIG. 15 and the plurality of shortest distances calculated for each of the plurality of coil elements. . Specifically, the processing circuit 131 collates the correspondence table with a plurality of shortest distances to determine a plurality of allowable coefficients respectively corresponding to the plurality of shortest distances. Next, the processing circuit 131 specifies the minimum allowable coefficient among the plurality of determined allowable coefficients.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in the present modification, based on MR signals corresponding to three gradient magnetic fields with respect to three different axes, a one-dimensional intensity indicating a signal intensity distribution for each of a plurality of frequency components corresponding to the three axes, respectively. A distribution can be generated for each of the three axes, and position information can be generated based on the one-dimensional intensity distribution for each of the three axes. That is, according to the MRI apparatus 1, position information can be generated by obtaining a one-dimensional profile of the magnetic resonance signal in the three-axis directions formed by the gradient magnetic field. According to the MRI apparatus in the present modification, the optimum irradiation intensity of the RF pulse can be determined even when a line scan is executed as a prescan. Since other effects are the same as those of the embodiment, description thereof is omitted.

(Application examples)
The difference between this application example and the embodiment is that the position information of the receiving coil 1171 in the bore 111, the direction in which the cable 1173 is derived from the receiving coil 1171 (hereinafter referred to as the derivation direction), and the plurality of ports 1073 Based on the position of the port to which the connector 1175 is connected (hereinafter referred to as a connection port), it is determined whether or not the cable 1173 in the bore 111 is U-shaped, and it is determined that the routing is U-shaped. In this case, the irradiation intensity of the RF pulse used in the main scan is adjusted.

  FIG. 19 is a diagram illustrating an example of the configuration of the processing circuit 131 in this application example. The processing circuit 131 further has a determination function 1321. The determination function 1321 is stored in the storage device 129 in the form of a program that can be executed by a computer. The processing contents regarding the determination function 1321 will be described later. The determination function 1321 included in the processing circuit 131 is an example of a determination unit.

  FIG. 20 is a view of the subject P inserted into the bore 111 as viewed from the X-axis direction in this application example. FIG. 21 is a view of the positional relationship among the subject P, the reception coil 1171, the cable 1173, and the connection port 1073c as viewed from the Y-axis direction in this application example. As shown in FIGS. 20 and 21, the cable 1173 in the bore 111 is U-shaped. In FIG. 20 and FIG. 21, the internal circuit is not shown.

  The storage device 129 stores the derivation direction in each of the plurality of reception coil devices corresponding to the imaging region. The lead-out direction corresponds to, for example, the direction in which the cable 1173 is led out from the connection position CP in FIG. 2, that is, the direction away from the receiving coil 1171 in the tangential direction of the cable 1173 at the connection position CP. The derivation direction is irrelevant to the gantry coordinate system, and is a direction set for the receiving coil device 117. The storage device 129 stores the positions of the plurality of ports 1073 to which the connector 1175 is connected as the coordinates of the plurality of ports 1073 in the gantry coordinate system. The storage device 129 stores the position of the connection port 1073c, that is, the coordinates in the gantry coordinate system. When the top plate 1071 is inserted into the bore, the storage device 129 updates and stores the coordinates of the connection port 1073c according to the position of the top plate 1071.

  When the cable 1173 in the bore 111 is U-shaped, the storage device 129 associates a limiting coefficient for limiting the irradiation intensity of the RF pulse with each of the plurality of receiving coil devices according to the imaging region. Remember. The limiting coefficient is a positive decimal number less than 1, and corresponds to the imaging region depending on the state of heat generation in the internal circuit or the like by experiments or simulations when the cable 1173 in the bore 111 is U-shaped. It is preset for each receiving coil device.

  FIG. 22 is a diagram illustrating an example of a processing procedure of a pulse intensity adjustment process in this application example. For example, the pulse intensity adjustment process in this application example is executed after step Sa6 in FIG. Note that the processing of step Sc1 to step Sc4 in FIG. 22 may be executed after step Sa3. Hereinafter, the pulse intensity adjustment processing in this application example will be described with reference to the cable 1173 shown in FIGS.

(Pulse intensity adjustment processing)
(Step Sc1)
Based on the derivation direction, the position information, and the position of the connection port 1073c to which the connector 1175 is connected, the processing circuit 131 determines whether the cable 1173 in the bore 111 is U-shaped based on the determination function 1321. judge. When the positions of the four coil elements with respect to the subject P are as shown in FIG. 21, the positional relationship of the signal distribution along the Z-axis direction (static magnetic field direction) indicates that the coil element ch1 and the coil element ch2 are The head side is the coil element ch3 and the coil element ch4 are the foot side of the subject P. On the other hand, the derivation direction stored in the storage device 129 in association with the reception coil device 117 is a direction from the coil elements ch1 and ch2 toward the coil elements ch3 and ch4 as shown in FIG. For this reason, the processing circuit 131 determines the presence or absence of the U shape using the relative positional relationship and the derivation direction of the plurality of coil elements and the connection port 1073c.

  20 and 21, the direction in which the cable 1173 protrudes from the receiving coil 1171 (hereinafter referred to as the cable direction) in FIG. 20 and FIG. 21 is the foot side of the subject P in the gantry coordinate system. Direction. 20 and 21, in the gantry coordinate system, since the connection port 1073c is on the head side of the subject P and the cable direction is on the foot side of the subject P, the processing circuit 131 is provided in the bore 111. It is determined that the cable 1173 is U-shaped.

  For example, the processing circuit 131 uses the determination function 1321 to determine the cable direction by associating the derived direction with the gantry coordinate system using the position information of the receiving coil 1171, for example, the coordinates of each coil element. Further, the processing circuit 131 determines the coordinates of the reception coil device 117 by averaging a plurality of coordinates respectively corresponding to the plurality of coil elements. The coordinates of the receiving coil device 117 correspond to, for example, barycentric coordinates by a plurality of coil elements. The processing circuit 131 uses the coordinates of the reception coil device 117 and the coordinates of the connection port 1073c to calculate the port direction from the reception coil device 117 toward the connection port 1073c. The cable direction corresponds to the arrow cdd shown in FIG. 21, and the port direction corresponds to the arrow ctp shown in FIG.

  The processing circuit 131 uses the determination function 1321 to calculate the inner product of the vector indicating the cable direction and the vector indicating the port direction. Whether the inner product is negative corresponds to whether the cable direction does not face the connection port 1073c. If the calculated inner product is negative, the processing circuit 131 determines that the routing of the cable 1173 in the bore 111 is U-shaped. If the calculated inner product is not negative, the processing circuit 131 determines that the routing of the cable 1173 in the bore 111 is not U-shaped. Note that the above description is an example, and the present invention is not limited to the above description as long as it can be determined whether or not the cable direction is facing the connection port 1073c.

  When it is determined that the routing of the cable 1173 in the bore 111 is U-shaped, the processing circuit 131 uses the determination function 1321 to store the limiting coefficient corresponding to the reception coil device 117 connected to the connection port 1073c as a storage device. Read from 129. If it is determined that the routing of the cable 1173 in the bore 111 is not U-shaped, this pulse intensity adjustment process ends.

(Step Sc2)
The processing circuit 131 further adjusts the irradiation intensity by the pulse intensity adjustment function 1315. Specifically, the processing circuit 131 further adjusts the irradiation intensity of the RF pulse related to the main scan by multiplying the irradiation intensity adjusted in the process of step Sa6 by the read limiting coefficient. The processing circuit 131 changes the imaging condition using the adjusted irradiation intensity.

(Step Sc3)
The processing circuit 131 uses the calculation function 1317 to calculate an extension time of the imaging time based on the change of the imaging condition according to the further adjusted irradiation intensity. Since the processing content in this step is the same as that in step Sa7, description thereof is omitted.

(Step Sc4)
The processing circuit 131 outputs a message to the display 127 that the irradiation intensity is limited by the pulse intensity adjustment function 1315 according to the state of the cable 1173. The display 127 displays a message whose irradiation intensity is limited according to the state of the cable 1173. The processing circuit 131 outputs the calculated extension time to the display. The display 127 displays the message together with the extended time.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in this application example, the receiving coil apparatus 117 includes a receiving coil 1171, a cable 1173 that is connected to the receiving coil 1171 and transmits an MR signal, and a connector 1175 provided at one end of the cable 1173; A plurality of ports 1073 that can be connected to the receiving coil device 117 and receive MR signals via the connector 1175; the direction in which the cable 1173 is led out from the receiving coil 1171; and the connector of the plurality of ports 1073 Based on the position of the port 1071c to which 1175 is connected and the position information, it is determined whether or not the routing of the cable 1173 in the bore 111 is U-shaped, and if it is determined that the routing is U-shaped, Irradiation intensity can be adjusted.

Thereby, according to this MRI apparatus 1, the risk of damaging the receiving coil 1171 and the internal circuit is reduced according to the position of the receiving coil apparatus 117 in the bore 111 and the routing of the cable in the bore, and the main scanning is performed. The optimum irradiation intensity can be determined at. In other words, according to the MRI apparatus 1 in this application example, it is assumed that the cable 1173 in the bore 111 is not ideally arranged, that is, the arrangement of the cable 1173 having the lowest risk of heat generation in the internal circuit or the like. In addition, the main scan can be executed without resetting the arrangement of the receiving coil device 117 in the bore 111 and the handling of the cable 1173 by the pulse intensity adjustment process (B ₁ intensity adjustment process). Thereby, according to the present MRI apparatus 1, it is possible to reduce the time required for the workflow before the actual scan is executed.

  Further, according to the MRI apparatus 1, it is possible to display that the irradiation intensity is limited according to the handling state by adjusting the irradiation intensity. For example, according to the present MRI apparatus in this application example, the irradiation intensity is limited according to the state of handling of the cable 1173, and the irradiation intensity is limited according to the position of the receiving coil 1171, that is, the position of the coil element. Can be displayed as a message along with the extended time. Thereby, the operator can easily select judgments such as changing the imaging conditions, changing the installation of the receiving coil device 117, changing the routing of the cable 1173, and relaxing the restriction on the high-frequency magnetic field. For example, when the extended time displayed on the display 127 is within 5 minutes, the operator can shorten the extended time by changing the imaging condition. Further, if the extension time displayed on the display 127 is 5 minutes or longer and at least one of the reception coil device 117 and the cable 1173 can be set again, the operator can change the reception coil device 117. A resetting of at least one of placement and routing of the cable 1173 can be performed.

(Third Modification)
The difference between the present modification and the embodiment is that the irradiation intensity is adjusted using a setting value (hereinafter referred to as a transmission setting value) related to the transmission of the RF pulse in accordance with the position information. The transmission set value corresponds to, for example, the phase of the RF pulse and the amplitude of the RF pulse determined according to the imaging region of the subject P. The transmission set value is related to the spatial distribution of RF pulse transmission intensity (hereinafter referred to as transmission intensity distribution).

  The storage device 129 stores a map for correcting the allowable map according to the transmission setting value (hereinafter referred to as a correction map). When the transmission strength distribution is asymmetric with respect to the center position of the bore 111, the correction map is used to reflect the asymmetry of the transmission strength distribution in the tolerance map. For example, the correction map has a coefficient (hereinafter referred to as a correction coefficient) that is multiplied by the tolerance map at each of a plurality of coordinates. Note that the correction map may have a coefficient that is different from the allowable map or a coefficient that is added to the allowable map in each of the plurality of coordinates instead of the correction coefficient. Hereinafter, for the sake of specific description, the correction map will be described as having a correction coefficient at each of a plurality of coordinates.

  Specifically, the storage device 129 stores a plurality of correction maps respectively corresponding to a plurality of transmission setting values. For example, when the transmission coil 115 is configured by a plurality of coil elements, the storage device 129 stores a plurality of correction maps corresponding to combinations of a plurality of transmission setting values respectively corresponding to the plurality of coil elements. The storage device 129 stores a correspondence table (hereinafter referred to as a part setting value correspondence table) of transmission setting values with respect to the shape of the imaging part (which varies depending on the height, weight, imaging part, and the like).

  The interface 125 inputs an imaging part for the subject P. The input of the imaging region in this modification is performed before the step Sa1 in the pulse intensity adjustment process.

The processing circuit 131 determines the transmission setting value by collating the imaging region with the region setting value correspondence table by the pulse intensity adjustment function 1315. The determination of the transmission set value in the present modification is appropriately performed in a process preceding step Sa4 in the pulse intensity adjustment process. The processing circuit 131 (by i.e. B ₁ shimming) so as to equalize the transmission intensity distribution within the object by using the B ₁ map generated by the pre-scan of the subject P, and determines the transmission setting value May be. At this time, the part set value correspondence table is not necessary, and the transmission set value is determined appropriately after the process of step Sa1 and before the process of step Sa4. The pre-scan relating to the generation of the B ₁ map is executed by the imaging control circuit 121 using a sequence that does not affect the reception coil 1171.

  The processing circuit 131 uses the pulse intensity adjustment function 1315 to adjust the irradiation intensity on the basis of the position information regarding the positional relationship between the transmission coil 115 and the reception coil 1171 and the transmission set value. Specifically, the processing circuit 131 specifies a correction map corresponding to the transmission setting value from a plurality of correction maps stored in the storage device 129. Next, the processing circuit 131 generates a corrected tolerance map (hereinafter referred to as a correction tolerance map) by multiplying the tolerance map by the identified correction map. The processing circuit 131 assigns the region (or high intensity region) related to the reception coil 1171 to the correction allowable map. The generation of the correction allowance map and the fitting of the area to the correction allowance map described above are performed instead of the process of step Sa4 in the pulse intensity adjustment process. In the pulse intensity adjustment process in the present modification, the processes after step Sa5 are the same as the pulse intensity adjustment process described in the embodiment, and thus the description thereof is omitted.

  Note that the processing circuit 131 may generate a transmission intensity distribution based on the transmission setting value by the pulse intensity adjustment function 1315 and generate a correction map based on the generated transmission intensity distribution. Specifically, the processing circuit 131 calculates the transmission intensity distribution by applying the transmission set value to the feeding point in the transmission coil 115. Next, the processing circuit 131 generates a correction map by normalizing the values of the entire transmission intensity distribution so that the value of the center position in the generated transmission intensity distribution is 1.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in the present modification, the irradiation intensity can be adjusted using the set value related to the transmission of the RF pulse. As a result, the irradiation intensity can be adjusted for each imaging region or for each B ₁ shimming result, and the risk of damaging the receiving coil 1171 and the internal circuit is reduced without excessively limiting the irradiation intensity of the RF pulse. Thus, it is possible to determine a more optimal irradiation intensity in the main scan. Since other effects are the same as those of the embodiment, the description thereof is omitted.

(Fourth modification)
The difference between this modification and the embodiment is that position information of the receiving coil 1171 in the bore 111 is generated without using the MR signal. The MRI apparatus 1 in this modification has, for example, a plurality of cameras (not shown). Each of the plurality of cameras is provided, for example, at a position where the inside of the bore 111 can be photographed from different directions. The different directions are, for example, three directions. The plurality of cameras are, for example, optical cameras.

  Each of the plurality of cameras images the receiving coil device 117 provided on the subject P inserted into the bore 111 prior to the main scan. For example, the plurality of cameras generate a plurality of images (hereinafter referred to as optical images) including the receiving coil device 117 in the bore 111, respectively. The plurality of cameras output a plurality of optical images to the processing circuit 131, respectively.

  The storage device 129 stores the coordinates of each of a plurality of cameras in the gantry coordinate system (hereinafter referred to as camera coordinates).

  The processing circuit 131 uses the position information generation function 1313 to generate position information of the reception coil 1171 in the bore 111 based on the plurality of optical images. For example, the processing circuit 131 extracts a region of the receiving coil device 117 (hereinafter referred to as a coil device region) in the plurality of optical images by executing existing segmentation processing and recognition processing in each of the plurality of optical images. . Next, the processing circuit 131 generates position information of the reception coil 1171 in the bore 111 by using the positions of the plurality of reception coils 1171 in the reception coil device 117, the coil device extraction region, and the camera coordinates.

  Imaging of the receiving coil device 117 in the bore and generation of position information of the receiving coil 1171 in the bore 111 are executed in the pulse intensity adjustment process instead of the processes of Step Sa1 to Step Sa3. In the pulse intensity adjustment process according to this modification, the processes after step Sa4 are the same as the pulse intensity adjustment process described in the first modification, and thus description thereof is omitted.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 of the present modification, position information of the receiving coil 1171 in the bore 111 can be generated, and the irradiation intensity of the RF pulse irradiated to the subject P can be adjusted based on the position information. Since other effects are the same as those of the first modification, description thereof will be omitted.

  According to the magnetic resonance imaging apparatus 1 such as the embodiment described above, the irradiation intensity of the RF pulse can be adjusted according to the position of the receiving coil apparatus 117 in the bore 111.

  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 novel 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 scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Magnetic resonance imaging apparatus 10 ... Base 101 ... Static magnetic field magnet 103 ... Gradient magnetic field coil 105 ... Gradient magnetic field power supply 107 ... Bed bed 109 ... Bed control circuit 111 ... Bore 113 ... Transmission circuit 115 ... Transmission coil 117 ... Reception coil device 119 ... Reception circuit 121 ... Imaging control circuit 125 ... Interface 127 ... Display 129 ... Storage device 131 ... Processing circuit 1071 ... Top plate 1073 ... Port 1171 ... Reception coil 1173 ... Cable 1175 ... Connector 1177 ... Balun 1179 ... Decoupling switch 1310 ... System control Function 1311 ... Image information generation function 1313 ... Position information generation function 1315 ... Pulse intensity adjustment function 1317 ... Calculation function 1319 ... Intensity distribution generation function 1321 ... Determination function

Claims (13)

A position information generation unit that generates position information related to the positional relationship between the transmission coil and the reception coil based on the magnetic resonance signal received from the subject;
A pulse intensity adjusting unit that adjusts the irradiation intensity of the RF pulse irradiated to the subject according to the position information;
A magnetic resonance imaging apparatus comprising: The positional relationship is a distance between the transmission coil and the reception coil.
The magnetic resonance imaging apparatus according to claim 1. The pulse intensity adjustment unit adjusts the irradiation intensity using a setting value related to transmission of the RF pulse,
The magnetic resonance imaging apparatus according to claim 1 or 2. The pulse intensity adjustment unit adjusts the irradiation intensity so as to decrease the irradiation intensity as the distance between the transmission coil and the reception coil decreases.
The magnetic resonance imaging apparatus according to claim 1. The position information generation unit generates the position information based on an image obtained by reconstructing the magnetic resonance signal.
The magnetic resonance imaging apparatus according to any one of claims 1 to 4. Based on the magnetic resonance signal, further comprising an image information generation unit that generates image information having a signal intensity corresponding to each of a plurality of frequency components in the magnetic resonance signal as a pixel value;
The position information generation unit uses the image information to calculate the distance from the transmission coil to the reception coil as the position information for each of a plurality of pixels in the image information,
The pulse intensity adjustment unit
A plurality of tolerance coefficients corresponding to the plurality of pixels are obtained using a correspondence table of a plurality of tolerance coefficients indicating a degree of tolerance of the irradiation intensity with respect to a plurality of distances from the transmission coil and the calculated distance. Decide
Adjusting the irradiation intensity using a minimum tolerance coefficient among the plurality of tolerance coefficients determined;
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. An image information generation unit that generates image information having pixel values corresponding to signal intensities corresponding to a plurality of frequency components in the magnetic resonance signal based on the magnetic resonance signal;
The position information generation unit generates, as the position information, a plurality of coordinates related to the position of the receiving coil using a coordinate system related to an area including a bore and the image information.
The pulse intensity adjustment unit
Using the plurality of coordinates, fit a region relating to the receiving coil to a tolerance map in which a plurality of tolerance coefficients indicating the degree of tolerance of the irradiation intensity are associated with the plurality of coordinates in the coordinate system,
Adjusting the irradiation intensity using a minimum allowable coefficient among a plurality of allowable coefficients included in the region related to the receiving coil,
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. The position information generation unit generates the position information by obtaining a one-dimensional profile of the magnetic resonance signal in three axial directions formed by a gradient magnetic field.
The magnetic resonance imaging apparatus according to claim 1. A receiving coil device comprising: the receiving coil; a cable connected to the receiving coil for transmitting the magnetic resonance signal; and a connector provided at one end of the cable;
A plurality of ports that can be connected to the receiving coil device and to which the magnetic resonance signal is input via the connector;
Based on the direction in which the cable is led out from the receiving coil, the position of the port to which the connector is connected among the plurality of ports, and the position information, whether the routing of the cable in the bore is U-shaped. A determination unit for determining whether or not,
Further comprising
The pulse intensity adjustment unit
When the handling is determined to be the U-shape, the irradiation intensity is adjusted.
The magnetic resonance imaging apparatus according to claim 1. A display unit for displaying that the irradiation intensity is limited according to the position of the receiving coil by adjusting the irradiation intensity;
The magnetic resonance imaging apparatus according to claim 1. A display unit for displaying that the irradiation intensity is limited according to the state of the routing of the cable by adjusting the irradiation intensity;
The magnetic resonance imaging apparatus according to claim 9. Further comprising a calculation unit that calculates an extended time of the imaging time based on the imaging condition changed according to the adjustment of the irradiation intensity and the imaging condition before the change,
The display unit displays the extended time.
The magnetic resonance imaging apparatus according to claim 10 or 11. A position information generator for generating position information of the receiving coil in the bore;
A pulse intensity adjusting unit that adjusts the irradiation intensity of the RF pulse applied to the subject based on the position information;
A magnetic resonance imaging apparatus comprising: