JP7286355B2 - Magnetic resonance imaging device - Google Patents

Description

Embodiments of the present invention relate to 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 transmission RF (Radio Frequency) coil, and receives magnetic resonance signals generated within the subject. It is received by the receiving coil in the RF coil device. A transmitting RF coil is installed in the frame of the magnetic resonance imaging apparatus. As an RF coil device for reception, there is a dedicated RF coil device corresponding to an imaging region in order to efficiently receive magnetic resonance signals. At this time, a dedicated RF coil device is installed near the subject. The receiving RF coil device is connected to the magnetic resonance imaging apparatus via a connector provided at the end of a cable in the receiving RF coil device and a port provided in the magnetic resonance imaging apparatus, and receives a magnetic resonance signal. Send to magnetic resonance imaging equipment. A port used for connection between the receiving RF coil device and the magnetic resonance imaging apparatus is provided, for example, on a pedestal, a top plate, or the like in the magnetic resonance imaging apparatus. The ports on the top plate are provided at various positions along the longitudinal direction of the top plate, such as the side of the bed, the central portion of the top plate, and the side opposite to the bed.

The RF pulse generated by the transmitting RF coil is applied not only to the subject but also to the receiving coil. In order to prevent the receiving RF coil device from being affected by the RF pulse, for example, a circuit for decoupling the effect of the RF pulse from the receiving coil (hereinafter referred to as a decoupling switch) or a balun: and a balance to unbalance transformer. In addition, the RF pulse transmitted from the transmitting RF coil has a SAR (Specific Absorption Rate), the amplitude of B ₁ (RF magnetic field), and the amplitude of B ₁ so that the subject and the receiving coil are not excessively irradiated. It is limited by the value of _{B_1rms} , which corresponds to the rms value and represents the root mean square of _B1 .

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

Restricting the value of B _1rms so as to suppress heat generation regardless of the position of the receiving coil device in the bore, routing of the cable, etc., leads to restrictions on the imaging conditions. For example, limiting the value of B _1rms leads to a decrease in the number of slices related to imaging per repetition time (TR), which causes a problem of extension of imaging time. Further, the guidebook prohibits the arrangement of the receiving RF coil device and the routing of the cables that cause the receiving RF coil device to overheat due to the influence of the RF pulse. However, if the operator misuses the receiving coil device, there is a problem that there is a risk of excessive heat generation or damage to the receiving RF coil device.

JP 2010-119744 A JP 2014-61176 A U.S. Pat. No. 4,806,867 U.S. Patent Application Publication No. 2016/0154074 U.S. 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 according to the position of the receiving coil device within the bore.

A magnetic resonance imaging apparatus according to this embodiment has a position information generator and a pulse intensity adjuster. The position information generator generates position information regarding the positional relationship between the transmission coil and the reception coil based on the magnetic resonance signals received from the subject. The pulse intensity adjustment unit adjusts the irradiation intensity of the RF pulse with which the subject is irradiated according to the position information.

FIG. 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus according to this embodiment. FIG. 2 is a diagram showing an example of a receiving coil device according to this embodiment. FIG. 3 is a view of the subject inserted into the bore as seen from the Z-axis direction in this embodiment. FIG. 4 is a view of the subject inserted into the bore as seen from the X-axis direction in this embodiment. FIG. 5 is a diagram showing 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 showing 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 showing an example of a procedure for adjusting the irradiation intensity of RF pulses in this embodiment. FIG. 8 is a diagram showing an example of a tolerance map in this embodiment. FIG. 9 is a diagram showing an example of the positional relationship among the top plate, the subject, and the receiving coil device in this embodiment. FIG. 10 is a diagram showing an example of an axial image in this embodiment. FIG. 11 is a diagram showing an example of a sagittal image in this embodiment. FIG. 12 is a diagram showing an example of a high-intensity region specified for the axial image in FIG. 10 in this embodiment. FIG. 13 is a diagram showing an example of a high-intensity region in the sagittal image in FIG. 11 in this embodiment. FIG. 14 is a diagram showing an example in which high intensity regions are applied to an allowable map using position information relating to high intensity regions in this embodiment. FIG. 15 is a diagram showing an example of a correspondence table of a plurality of tolerance coefficients with respect to a plurality of distances from the transmission coil in the first modified example of this embodiment. FIG. 16 is a diagram showing an example of the configuration of a processing circuit in a second modified example of this embodiment. FIG. 17 is a diagram showing an example of a processing procedure of pulse intensity adjustment processing in the second modified example of the present embodiment. FIG. 18 is a diagram showing an example of X-axis intensity distribution, Y-axis intensity distribution, and Z-axis intensity distribution for each of four coil elements in the second modification of this embodiment. FIG. 19 is a diagram showing an example of the configuration of a processing circuit in an application example of this embodiment. FIG. 20 is a view of the subject inserted into the bore as seen from the X-axis direction in an application example of this embodiment. FIG. 21 is a diagram showing an example of the positional relationship among the subject, receiving coils, cables, and connection ports in an application example of the present embodiment. FIG. 22 is a diagram illustrating an example of a processing procedure of pulse intensity adjustment processing in an 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 functions and configurations are denoted by the same reference numerals, and overlapping descriptions will be given when necessary.

(embodiment)
FIG. 1 is a block diagram showing the overall configuration of a magnetic resonance imaging (hereinafter referred to as MRI (magnetic resonance imaging)) apparatus 1 according to this embodiment. The MRI apparatus 1 includes a static magnetic field magnet 101, a gradient magnetic field coil 103, a gradient magnetic field power supply 105, a bed 107, a bed control circuit 109, a transmission circuit 113, a transmission coil 115, a reception coil device 117, and a reception It includes 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 . A pedestal 10 in the MRI apparatus 1 has a static magnetic field magnet 101 , a gradient magnetic field coil 103 and a transmission coil 115 . Note that the gantry 10 may be equipped with the gradient magnetic field power supply 105, the receiving circuit 119, the imaging control circuit 121, and the like. The MRI apparatus 1 may also 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 a bore 111, which is a space into which the subject P is inserted. A superconducting magnet, for example, 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 arranged inside the static magnetic field magnet 101 . The gradient magnetic field coil 103 is formed by combining three coils corresponding to the mutually orthogonal X, Y, and Z axes. It is assumed that the Z-axis direction is the same as the direction of the static magnetic field. The Y-axis direction is the vertical direction, and the X-axis direction is the 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 the 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 source 105 to generate gradient magnetic fields whose magnetic field strengths vary along the X, Y, and Z axes.

The X-, Y-, and Z-axis gradient magnetic fields 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-selecting gradient magnetic field. A frequency-encoding gradient magnetic field is used to change the frequency of a magnetic resonance (hereinafter referred to as MR (Magnetic Resonance)) signal according to a spatial position. A phase-encoding gradient magnetic field is used to change the phase of the MR signal depending on 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 current to the gradient magnetic field coil 103 under the control of the imaging control circuit 121 .

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

Top plate 1071 has a plurality of ports 1073 to which receiving coil device 117 can be connected. A subject P is placed on the top plate 1071 . A connector 1175 provided at one end of a cable 1173 in the receiving coil device 117 is connected to one of 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, the gantry 10, or the like. A signal line from the port 1073 is connected to the receiving circuit 119 . If the receiving coil device 117 has a high-frequency magnetic field transmitting function, the signal line from the port 1073 is connected to the transmitting circuit 113 in addition to the receiving circuit 119, although not shown in FIG.

The bed control circuit 109 is a circuit for controlling the bed 107. By driving the bed 107 according to an operator's instruction via the interface 125, the table 1071 can be moved in the longitudinal direction, the vertical direction, and in some cases the horizontal direction. Let

Under the control of the imaging control circuit 121 , 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 RF (Radio Frequency) pulse) corresponding to the Larmor frequency or the like.

The transmission coil 115 is an RF coil arranged inside the gradient magnetic field coil 103 . The transmission coil 115 receives supply of high frequency pulses from the transmission circuit 113 and generates RF pulses. The transmission coil is, for example, a coil for the whole body (hereinafter referred to as a WB (whole body) coil). A WB coil may be used as a transmit/receive coil.

The receiving coil device 117 includes a receiving coil 1171, an internal circuit 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 MR signals emitted from the subject P by RF pulses. Receiving coil device 117 outputs the received MR signal to receiving circuit 119 via cable 1173 and connector 1175 . Note that the receiving coil device 117 may wirelessly transmit the received MR signal to the receiving circuit 119 using a wireless transmission circuit (not shown). At this time, cable 1173 and connector 1175 in receiving coil device 117 become unnecessary.

The receiving coil 1171 has, for example, one or more, typically a plurality of coil elements. To make the description concrete, it is assumed that there are four coil elements. Four coil elements correspond, for example, to four receive channels. Each of the four coil elements is composed of loop coils. The 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 output order).

Although the transmit coil 115 and the receive coil device 117 are shown as separate RF coils in FIG. 1, the transmit coil 115 and the receive coil device 117 may be implemented as an integrated transmit and receive coil. The transmit/receive coil is, for example, a local transmit/receive RF coil, such as a head coil, corresponding to an imaging region.

FIG. 2 is a diagram showing an example of the receiving coil device 117. As shown in FIG. As shown in FIG. 2, a balun 1177 and a decoupling switch 1179 are provided for each of the four coil elements (ch1, ch2, ch3, ch4). A cable 1173 is connected to one side of the receiving coil 1171 that is adjacent to the coil element ch3 side and the coil element ch4 side. Note that the connection position CP between the receiving coil 1171 and the cable 1173 is not limited to the position shown in FIG.

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 MR signals generated from the subject P by application of RF pulses.

A balun 1177 is also provided on the cable 1173 in addition to each of the four coil elements. The balun 1177 is composed of, for example, a resonant circuit having a capacitor and an inductor. The balun 1177 absorbs the unbalanced current flowing through each of the plurality of coil elements and the cable 1173 due to the RF pulse with a resonant 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 RF pulses are 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 separated. Also, 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 MR signals forms a loop structure.

The receiving circuit 119 generates a digital MR signal, which is digitized complex number 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 analog/digital (A/D ( Perform Analog to Digital)) conversion. The receiving circuit 119 samples the A/D converted data to generate a digital MR signal (hereinafter referred to as MR data). The receiving 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, etc. according to the imaging protocol output from the processing circuit 131, and performs imaging of the subject P. FIG. The imaging protocol has various pulse sequences according to examinations. The imaging protocol includes the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing at which the current is supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, and the current supplied to the transmission coil 115 by the transmission circuit 113. The magnitude of the high-frequency pulse, the timing at which the transmission circuit 113 supplies the high-frequency pulse to the transmission coil 115, the timing at which the reception coil 1171 receives the MR signal, the ON/OFF timing of the decoupling switch 1179, etc. are set in advance. ing.

The interface 125 has a circuit for receiving various instructions and information input from the operator. The interface 125 has circuitry for, for example, a pointing device such as a mouse, or an input device such as a keyboard. Note that the circuits included in the interface 125 are not limited to circuits related to physical operation parts such as a mouse and keyboard. For example, the interface 125 receives electrical signals corresponding to input operations from an external input device provided separately from the MRI apparatus 1, and processes electrical signals such as outputting the received electrical signals to various circuits. You may have a circuit.

The display 127 displays various MR images generated by the image information generation function 1311 under the control of the system control function 1310 in the processing circuit 131, various information on imaging and image processing, and the like. 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 defining 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, an optical disk, or the like. Also, the storage device 129 may be a drive device that reads and writes various information from and to a portable storage medium such as a CD-ROM drive, a DVD drive, and a flash memory.

The processing circuit 131 has, as hardware resources, a processor (not shown), a memory such as a ROM (Read-Only Memory) and a RAM, and the like, and controls the MRI apparatus 1 . The processing circuit 131 has 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 computer-executable programs. there is The processing circuit 131 is a processor that reads out programs corresponding to these various functions from the storage device 129 and executes them, thereby implementing functions corresponding to each program. In other words, the processing circuit 131 in a state where each program is read has a plurality of functions shown in the processing circuit 131 of FIG.

In FIG. 1, the single processing circuit 131 has been described as realizing these various functions. It does not matter if the function is realized by 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

The term "processor" used in the above description refers to, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), or a programmable logic device (e.g., Circuits such as Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and Field Programmable Gate Arrays (FPGAs).

The processor implements various functions by reading and executing programs stored in the storage device 129 . Note that instead of storing the program in the storage device 129, the program may be configured to be directly installed in the circuit of the processor. In this case, the processor realizes its function by reading and executing the program embedded in the circuit. 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. 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 of 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 unit and a calculation unit.

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

The processing circuit 131 fills the k-space with MR data using the image information generating function 1311 . The processing circuit 131 generates an MR image by performing, for example, a 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 according to the present embodiment. In addition to such a configuration, the MRI apparatus 1 of this embodiment is configured to be able to adjust the irradiation intensity of the RF pulse according to the position of the receiving coil 1171 within the bore 111 .

FIG. 3 is a diagram of the subject P inserted into the bore 111 viewed from the Z-axis direction in this embodiment. FIG. 4 is a view of the subject P inserted into the bore 111 as seen from the X-axis direction in this embodiment. FIG. 5 is a diagram showing an example of a comparative example in which the subject P inserted into the bore 111 is viewed from the Z-axis direction. Moreover, FIG. 6 is a diagram showing 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, internal circuits are not shown.

The receive coil device 117 is approaching the transmit coil 115 . 3 and 4, the distance int between the receiving coil device 117 and the transmitting coil 115 is shorter than the distance between the receiving coil device 117 and the transmitting coil 115 in FIGS. On the other hand, in cases such as those shown in FIGS. 5 and 6, receive coil arrangement 117 is less susceptible to RF pulses applied by transmit coil 115 . From these things, when the receiving coil device 117 is provided in the subject P in the state shown in FIGS. stronger than the case. Therefore, the heat generation of the internal circuit in the receiving coil device 117 shown in FIGS. 3 and 4 is greater than that in FIGS.

The operation in this embodiment will be described below. FIG. 7 is a flow chart showing an example of the procedure of processing (hereinafter referred to as pulse intensity adjustment processing) relating to adjustment of the irradiation intensity of RF pulses in this embodiment. The pulse intensity adjustment process is executed with the receiving coil device 117 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 frame coordinate system). Storage device 129 stores tolerance maps 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 a region including the bore 111 in an axial section perpendicular to the Z-axis direction, ie, a plurality of coordinates in the frame coordinate system. Each of the plurality of allowable coefficients corresponds to, for example, the ratio of the allowable amount of irradiation intensity of the RF pulse in the main scan to the amount of irradiation intensity of the RF pulse. The allowable coefficient is set in advance for each receiving coil device corresponding to the imaging region according to the heat generation state of the internal circuit or the like based on experiments or simulations. The value obtained by subtracting the allowable coefficient from 1 indicates the rate at which the irradiation intensity is restricted with respect to the maximum allowable amount.

FIG. 8 is a diagram showing an example of a tolerance map. In FIG. 8, the transmit coil 115 is located outside the inner bore wall. In FIG. 8, "1" in the region including the center position of the bore 111 and the region near the center position indicates the maximum permissible amount of irradiation intensity of the RF pulse. As shown in FIG. 8, the closer to the inner wall of the bore, the smaller the allowable coefficient value. That is, the closer to the inner wall of the bore, the smaller the ratio of the permissible amount of irradiation intensity to the maximum permissible amount of RF pulse. In other words, the closer to the inner wall of the bore, the greater the limitation of irradiation intensity on the maximum allowable amount of RF pulses.

(Pulse intensity adjustment processing)
(Step Sa1)
The receiving coil device 117 is installed with respect to the subject P placed on the top plate 1071 . A connector 1175 at the tip of cable 1173 in receiving coil device 117 is connected to port 1073 in top plate 1071 . FIG. 9 is a diagram showing an example of the positional relationship among the top plate 1071, the subject P, and the receiving coil device 117. As shown in FIG. Various explanations will be given below based on the positional relationship as shown in FIG. The installation situation of the subject P and the receiving coil device 117 with respect to the tabletop 1071 shown in FIG. 9 is an example, and the installation situation is not limited to that shown in FIG. Note that the internal circuit is not shown in FIG.

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

(Step Sa2)
The processing circuit 131 uses an image information generation function 1311 to generate (reconstruct) image information based on the acquired MR signals. The image information has, for example, signal intensities corresponding to each of a plurality of frequency components in the MR signal as pixel values. Each of the plurality of frequency components corresponds to magnetic field strength in the gradient magnetic field on each of the X, Y, and Z axes. Therefore, the frequency components in the MR signal correspond to positions 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 the plurality of pixel values in the plurality of axial images based on the gradient magnetic fields of the X, Y, and Z axes.

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

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

As shown in FIGS. 10 and 11, the signal distributions for each of the multiple coil elements are separable in the gantry coordinate system. For this reason, the processing circuit 131 uses the image information generating function 1311 to attach coordinates in the gantry coordinate system to each of the plurality of signal distributions regarding the plurality of coil elements in each of the plurality of axial cross sections according to the position of the pixel.

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

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. do. That is, the processing circuitry 131 uses peak values in the signal distribution to identify high intensity regions for the signal distribution in each of the multiple axial images. A plurality of coordinates in the frame coordinate system are attached to the high-intensity region according to the position of the pixel by the processing in step Sa2.

FIG. 12 is a diagram showing an example of a high-intensity region identified with respect to the axial image AxI in FIG. 10; The axial section AxP shown in FIG. 12 shows a high intensity region HIR13 related to coil element ch1 or coil element ch3 and a high intensity region HIR24 related to coil element ch2 or coil element ch4.

FIG. 13 is a diagram showing an example of a high-intensity region in the sagittal image SgI in FIG. 11. FIG. The sagittal cross section SgP shown in FIG. 13 shows a high intensity region HIR34 related to coil element ch3 or coil element ch4, and a high intensity region HIR12 related to coil element ch1 or coil element ch2.

3, 4, 9, 12 and 13, the receiving coil 1171 or multiple coil elements are located near the high intensity region. Therefore, the high intensity region will be described as corresponding to the position of the receiving coil 1171, that is, the positions of the plurality of coil elements.

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

(Step Sa4)
The processing circuitry 131 uses the position information with the pulse strength adjustment function 1315 to fit the area for the receive coil 1171 in the image information to a tolerance map. Specifically, processing circuitry 131 fits the high intensity region to the tolerance map using a plurality of coordinates associated with the high intensity region in each of the plurality of axial cross-sections. That is, the processing circuitry 131 superimposes the high intensity regions onto the tolerance map using the positional information over the total number of axial slices.

FIG. 14 is a diagram showing an example of applying the high intensity region HIR13 and the high intensity region HIR24 to the allowable 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 the regions included in the high intensity region HIR13 and the high intensity region HIR24 indicate a plurality of allowable coefficients in the high intensity region HIR13 and a plurality of allowable coefficients in the high intensity region HIR24.

Note that the processing circuit 131 may superimpose all the high intensity regions over a plurality of axial cross sections on the tolerance map by the pulse intensity adjustment function 1315 . At this time, the high-intensity region HIR13 in FIG. 14 is an integrated region of all the high-intensity regions related to the coil elements ch1 and ch3, and the high-intensity region HIR24 is an integrated region of all the high-intensity regions related to the coil elements ch2 and ch4. area. Processing circuitry 131 may also fit the signal distribution to the tolerance map instead of the high intensity regions.

(Step Sa5)
The processing circuit 131 uses the pulse intensity adjustment function 1315 to determine the minimum allowable coefficient among the plurality of allowable coefficients included in the region related to the receiving coil 1171 in a tolerance map (hereinafter referred to as a region superposition map) to which the region related to the receiving coil 1171 is fitted. Identify the tolerance factor. Specifically, the processing circuitry 131 identifies the minimum allowable coefficient among the allowable coefficients included in the high-intensity regions in the multiple region superimposition maps respectively corresponding to the multiple axial cross-sections.

It should be noted that when all high intensity regions across multiple axial cross-sections are fitted to the tolerance map, processing circuitry 131 identifies the minimum tolerance coefficient among the plurality of tolerance coefficients included in the high intensity regions in the tolerance map. . For example, if an example of fitting all high intensity regions across multiple axial cross-sections to a tolerance map is FIG. 14, processing circuitry 131 identifies a tolerance factor of 0.5. It should be noted that when the specified allowable coefficient is "1", the present pulse intensity adjustment processing ends.

(Step Sa6)
The processing circuit 131 adjusts the irradiation intensity of the RF pulse for the main scan by using the specified tolerance factor with the pulse intensity adjustment function 1315 . Specifically, the processing circuitry 131 determines the RF pulse irradiation intensity for the main scan by multiplying the maximum allowable RF pulse irradiation intensity by the specified allowable coefficient. This reduces the permissible amount of irradiation intensity of the RF pulse.

The processing circuit 131 uses the irradiation intensity adjusted by the pulse intensity adjustment function 1315 to change the imaging condition preset by the operator or the like via the interface 125 or the like. 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, repetition time (TR), echo train length (ETL), flip angle of the refocusing RF pulse ( refocus flip angle), fat suppression pulse intensity, DE (Driven Equilibrium) pulse intensity, MTC (magnetization transfer contrast) pulse intensity, and the like. The processing circuit 131 changes the imaging conditions by changing the imaging parameters.

According to steps Sa4 to Sa6, the processing circuit 131 uses the pulse intensity adjustment function 1315 to adjust the irradiation intensity of the RF pulse with which the subject P is irradiated according to the position information. For example, processing circuit 131 adjusts the irradiation intensity so that the irradiation intensity decreases as the distance between transmitting coil 115 and receiving coil 1171 decreases.

(Step Sa7)
The processing circuit 131 calculates the extension time of the imaging time by the calculation function 1317 based on the change of the imaging conditions associated with the adjusted irradiation intensity. Specifically, the processing circuit 131 calculates the extension time of the imaging time based on the imaging conditions changed according to the adjustment of the irradiation intensity and the imaging conditions before the change. For example, the processing circuit 131 calculates the imaging time (hereinafter referred to as the pre-change time) when the main scan is executed using the imaging conditions before the change. Next, the processing circuit 131 calculates the imaging time (hereinafter referred to as post-change time) when the main scan is executed using the changed imaging conditions. The processing circuitry 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 by the pulse intensity adjusting function 1315 that the irradiation intensity is limited according to the position of the receiving coil 1171, that is, the position of the coil element. A display 127 displays messages output from the processing circuitry 131 . Processing circuit 131 outputs the calculated extension time to the display. Display 127 displays the message with an extended time.

Note that the processing circuit 131 may output to the display 127 the imaging conditions before and after the change, the 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, an image in which the high-intensity region is applied to the allowable map, and the like, along with the message and the extension time.

After this step, when an instruction to start the main scan is input via the interface 125 , the processing circuit 131 outputs the changed imaging conditions 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 conditions.

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

That is, according to the MRI apparatus 1, based on the MR signal received from the subject P, position information regarding the positional relationship between the transmitting coil 115 and the receiving coil 1171 is generated, and according to the position information, the subject The irradiation intensity of the RF pulse with which the specimen P is irradiated can be adjusted. Further, according to the MRI apparatus 1, the distance between the transmitting coil 115 and the receiving 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 MR signals. As a result, according to the MRI apparatus 1, the irradiation intensity can be adjusted so that the irradiation intensity decreases as the distance between the transmission coil 115 and the reception coil 1171 decreases.

More specifically, according to this MRI apparatus, image information having pixel values corresponding to signal intensities is generated based on the MR signal, and the receiving coil 1171 is detected using the coordinate system and the image information regarding the area including the bore 111. generating a plurality of coordinates relating to the position of the receiving coil as position information, and using the plurality of coordinates, 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, respectively. The region for 1171 is fitted and the smallest of the tolerance coefficients included in the region for receive coil 1171 can be used to adjust the illumination intensity.

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

For these reasons, according to the present MRI apparatus 1, according to the position of the receiving coil device 117 in the bore 111, the receiving coil 1171 and the internal circuit etc. are damaged without excessively limiting the irradiation intensity of the RF pulse. The optimum irradiation intensity can be determined in the main scan with reduced risk.

That is, according to the MRI apparatus 1, by considering various setting states of the receiving coil device 117 in the bore 111, it is expected that the heat generation in the receiving coil 1171 and the internal circuit is small. Since it is not necessary to protect the RF coil device 1117 excessively against magnetic fields, the main scan can be performed under imaging conditions with relaxed restrictions on high-frequency magnetic fields.

In addition, according to the MRI apparatus 1, in the arrangement of the receiving coil 1171 and the receiving coil 1171, which is expected to generate a large amount of heat in the internal circuit, the imaging condition is set to stricter restrictions on the high-frequency magnetic field, that is, the irradiation intensity of the RF pulse is lowered. The main scan can be executed under the imaging conditions in the state. Therefore, even if the operator makes a mistake in setting the receiving coil device 117, the main scan can be safely performed without damaging the receiving coil device 117. FIG.

Further, according to the MRI apparatus 1, it is possible to present the operator with a message that the reception coil device 117 is set to be 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 stricter restrictions on the imaging conditions due to the arrangement of the receiving coil device 117. FIG. That is, by providing the operator with such information as a guideline for resetting the receiving coil device 117 in the bore 111, the operator can select whether to edit the imaging conditions or reset the receiving coil device 117. It becomes possible to make a judgment, and the throughput of inspection can be improved.

(First modification)
The difference between this modification and the embodiment is that the distance from the transmission coil 115 to the reception coil 1171 is calculated as position information using image information, and a correspondence table ( lookup table) and the calculated distance to determine the minimum tolerance factor. The positional relationship is, for example, the distance between transmission coil 115 and 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 frame coordinate system. FIG. 15 is a diagram showing an example of the correspondence table. As shown in FIG. 15, the closer the receiving coil is to the transmitting coil 115, the smaller the tolerance factor. That is, the closer to the transmission coil 115, the tighter the limit on the maximum permissible amount of irradiation intensity of the RF pulse. The correspondence table shown in FIG. 15 corresponds to the tolerance map shown in FIG. 8 converted into the relationship of tolerance coefficients with respect to the distance from the transmission coil.

In the following, the pulse intensity adjustment processing in this modified example will be described with respect to the differences from the processing in steps Sa3 to Sa5 in the above-described embodiment.

(Pulse intensity adjustment processing)
(Step Sa3)
The processing circuit 131 uses the image information by the position information generation function 1313 to calculate the distance from the transmit coil 115 to the receive coil 1171 for each of a plurality of pixels in the image information. As shown in FIGS. 3 and 5, the transmit coil 115 is positioned surrounding the bore 111 on the outside of the bore inner wall. Thus, processing circuitry 131 calculates, for each of a plurality of pixels in the signal distribution, the shortest distance from the coordinates of transmit coil 115 to the coordinates of each of those pixels. Specifically, the processing circuit 131 calculates the shortest distance for each pixel by optimization processing using a formula for calculating the distance between two points from the transmission coil 115 to the pixel.

(Step Sa4)
Processing circuitry 131 determines a plurality of tolerance coefficients respectively corresponding to a plurality of pixels in the signal distribution by matching the distances calculated by pulse intensity adjustment function 1315 to a correspondence table.

(Step Sa5)
Processing circuitry 131 identifies the smallest tolerance factor among the plurality of determined tolerance factors through pulse strength adjustment function 1315 . The identified tolerance factor corresponds to the pixel closest to the transmit coil 115 .

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 of this modified example, image information having, as pixel values, signal intensities corresponding to each of a plurality of frequency components in the MR signal received from the subject P is generated based on the MR signal, and image information is generated. is used to calculate the distance from the transmitting coil 115 that irradiates the RF pulse to the subject P to the receiving coil 1171 as the positional information of the receiving coil 1171 in the bore 111 for each of a plurality of pixels in the image information, and transmit A plurality of tolerance coefficients respectively corresponding to a plurality of pixels are determined using a correspondence table of a plurality of tolerance coefficients indicating tolerance levels of irradiation intensity with respect to a plurality of distances from the coil 115 and the calculated distances. The irradiation intensity can be adjusted using the minimum tolerance factor among the plurality of tolerance factors. Other effects are the same as those of the embodiment, so description thereof is omitted.

(Second modification)
The difference between this modification and the embodiment is that based on MR signals corresponding to each of three gradient magnetic fields related to three different axes, a one-dimensional The object is to generate an intensity distribution for each of the three axes, and to generate position information based on the one-dimensional intensity distribution (one-dimensional profile) for each of the three axes. To make the description concrete, the three different axes are assumed to be the X-axis, the Y-axis, and the Z-axis. Note that the three different axes are not limited to the X-axis, Y-axis, and Z-axis.

Concerning the configuration and pulse intensity adjustment processing in this modified example, contents different from those of the above-described embodiment will be described. FIG. 16 is a diagram showing an example of the configuration of the processing circuit 131 in this modification. The processing circuitry 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 computer-executable program. The intensity distribution generation function 1319 of the processing circuit 131 is an example of an intensity distribution generation section. The processing contents of the intensity distribution generation function 1319 will be described in the processing procedure of the pulse intensity adjustment processing in this modified example.

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

(Pulse intensity adjustment processing)
(Step Sb1)
The receiving coil device 117 is installed with respect to the subject P placed on the tabletop 1071 before executing the prescan in this modified example. The installation situation of the receiving coil device 117 in this modified example is assumed to be the same as in FIG. 9 in order to avoid duplication of explanation.

The imaging control circuit 121 applies three gradient magnetic fields along the X-, Y-, and Z-axes to the subject P as a prescan, thereby obtaining MR images corresponding to the X-, Y-, and Z-axes. Collect signals. That is, the imaging control circuit 121 performs line scanning on each of the X-axis, Y-axis, and Z-axis. The prescan in this modified example corresponds to, for example, a scan that is used to select a coil element to be used for the main scan among a plurality of coil elements. Note that since the prescan in this modified example is intended to acquire MR signals, any imaging method may be used as long as the MR signals can be acquired in a short period of time regardless of the 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) as a readout gradient magnetic field to the subject P to generate an MR signal (hereinafter referred to as an X-axis gradient magnetic field). MR signals) are collected. The imaging control circuit 121 applies 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 generate an MR signal (hereinafter referred to as a Y-axis MR signal). to collect. The imaging control circuit 121 applies 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 generate an MR signal (hereinafter referred to as a Z-axis MR signal). to collect.

(Step Sb2)
The processing circuit 131 uses the intensity distribution generation function 1319 to generate a one-dimensional intensity distribution showing the distribution of signal intensity for each of a plurality of frequency components respectively corresponding to the X-axis, the Y-axis, and the Z-axis based on the MR signal. Generate for each axis, Y-axis, and Z-axis. Specifically, the processing circuit 131 performs a Fourier transform on the X-axis MR signal to obtain an intensity distribution ( hereinafter referred to as an X-axis intensity distribution). The processing circuit 131 performs a Fourier transform on the Y-axis MR signal to obtain a distribution of intensity of the Y-axis MR signal (hereinafter referred to as Y-axis intensity distribution). The processing circuit 131 performs a Fourier transform on the Z-axis MR signal to obtain a distribution of intensity of the Z-axis MR signal (hereinafter referred to as Z-axis intensity distribution). Each of the X-axis intensity distribution, Y-axis intensity distribution, and Z-axis intensity distribution corresponds to the one-dimensional intensity distribution. Also, 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 showing an example of X-axis intensity distribution, Y-axis intensity distribution, and Z-axis intensity distribution for each of four coil elements (ch1, ch2, ch3, ch4). Depending on the positions of the four coil elements in the bore 111, etc., the X-axis intensity distribution, Y-axis intensity distribution, and Z-axis intensity distribution differ for each coil element.

(Step Sb3)
Processing circuit 131 uses position information generating function 1313 to calculate the distance from transmitting coil 115 to receiving coil 1171 using three one-dimensional intensity distributions respectively corresponding to the X, Y and Z axes. Specifically, the processing circuit 131 identifies, for each coil element, the X-axis frequency corresponding to the peak of the signal intensity 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 identifies, for each coil element, the Y-axis frequency corresponding to the peak of the signal intensity in the Y-axis intensity distribution or the Y-axis frequency corresponding to the center of gravity in the Y-axis intensity distribution. The processing circuitry 131 identifies, for each coil element, the Z-axis frequency corresponding to the peak of the signal intensity 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 converts the specified X-axis frequency, specified Y-axis frequency, and specified Z-axis frequency to coordinates (hereinafter referred to as element coordinates) in the gantry coordinate system using the position information generation function 1313. Convert. Element coordinates corresponding to each of the plurality of coil elements correspond to positions of each of the plurality of coil elements. Processing circuitry 131 calculates the distance from the position of transmitting coil 115 to the position of each coil element using the coordinates of transmitting coil 115 and the element coordinates in the frame coordinate system. Since the calculated distance is the same as the shortest distance in the first modified example, the explanation is omitted. Through the above processing, the processing circuit 131 uses the X-axis intensity distribution, the Y-axis intensity distribution, and the Z-axis intensity distribution to obtain a plurality of shortest distances 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 by using the correspondence table for the allowable coefficient, 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 circuitry 131 checks the correspondence table against the plurality of shortest distances to determine a plurality of allowable coefficients respectively corresponding to the plurality of shortest distances. Processing circuitry 131 then identifies the smallest acceptable factor of the determined plurality of acceptable factors.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in this modified example, based on MR signals corresponding to each of three gradient magnetic fields related to three different axes, one-dimensional intensity showing distribution of signal intensity for each of a plurality of frequency components respectively corresponding to three axes 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 one-dimensional profiles of magnetic resonance signals in three axial directions formed by gradient magnetic fields. According to the MRI apparatus in this modified example, it is possible to determine the optimum irradiation intensity of the RF pulse even when line scanning is performed as prescanning. Other effects are the same as those of the embodiment, so description thereof is omitted.

(Application example)
The difference between this application example and the embodiment is position information of the receiving coil 1171 in the bore 111 , the direction in which the cable 1173 is led out from the receiving coil 1171 (hereinafter referred to as lead-out direction), and Based on the position of the port (hereinafter referred to as a connection port) to which the connector 1175 is connected, it is determined whether or not the routing of the cable 1173 in the bore 111 is U-shaped, and it is determined that the routing is U-shaped. If so, the object is to adjust the irradiation intensity of the RF pulse used in the main scan.

FIG. 19 is a diagram showing an example of the configuration of the processing circuit 131 in this application example. Processing circuitry 131 further comprises a decision function 1321 . The determination function 1321 is stored in the storage device 129 in the form of a computer-executable program. Details of processing related to the determination function 1321 will be described later. The determination function 1321 of the processing circuit 131 is an example of a determination unit.

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

The storage device 129 stores the lead-out direction for each of the plurality of receiving 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. The derivation direction is the direction set for the receiving coil device 117, regardless of the gantry coordinate system. The storage device 129 stores the positions of the multiple ports 1073 to which the connector 1175 is connected as the coordinates of the multiple ports 1073 in the gantry coordinate system. The storage device 129 also 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 is arranged in the bore 111 in a U-shape, 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 corresponding to the imaging region. Remember. The limiting factor is a positive decimal number less than 1, and corresponds to the imaged part according to the heat generation situation of the internal circuit, etc., according to experiments or simulations when the cable 1173 is routed in the bore 111 in a U shape. It is set in advance for each receiving coil device.

FIG. 22 is a diagram illustrating an example of a processing procedure of pulse intensity adjustment processing in this application example. The pulse intensity adjustment process in this application example is executed, for example, after step Sa6 in FIG. 7 in this embodiment. Note that the processing of steps Sc1 to Sc4 in FIG. 22 may be performed after step Sa3. Below, the pulse intensity adjustment processing in this application example will be described with the cables 1173 shown in FIGS. 20 and 21 being routed.

(Pulse intensity adjustment processing)
(Step Sc1)
The processing circuit 131 uses the determination function 1321 to determine whether or not the cable 1173 is routed in the bore 111 in a U shape based on the lead-out direction, the position information, and the position of the connection port 1073c to which the connector 1175 is connected. 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) is It is on the head side, and the coil element ch3 and the coil element ch4 are on the leg side of the subject P. On the other hand, the lead-out direction stored in the storage device 129 in association with the receiving coil device 117 is the direction from the coil elements ch1 and ch2 to the coil elements ch3 and ch4, as shown in FIG. Therefore, the processing circuit 131 determines whether or not there is a U-shape using the relative positional relationship between the plurality of coil elements and the connection port 1073c and the derivation direction.

20 and 21, the direction in which the cable 1173 extends from the receiving coil 1171 (hereinafter referred to as the cable direction) is the foot side of the subject P in the gantry coordinate system. direction. As shown in FIGS. 20 and 21, in the gantry coordinate system, 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 cable 1173 is routed in a U shape.

For example, the processing circuit 131 determines the cable direction by the determination function 1321 by using the position information of the receive coil 1171, eg, the coordinates of each coil element, to relate the derived direction to the gantry coordinate system. The processing circuit 131 also determines the coordinates of the receiving coil device 117 by averaging the coordinates corresponding to the coil elements. The coordinates of the receiving coil device 117 correspond to, for example, barycentric coordinates of a plurality of coil elements. Processing circuit 131 uses the coordinates of receive coil device 117 and the coordinates of connection port 1073c to calculate the port direction from receive coil device 117 to 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 calculates the inner product of the vector indicating the cable direction and the vector indicating the port direction by the decision function 1321 . Whether or not the inner product is negative corresponds to whether or not the cable direction is directed toward the connection port 1073c. If the calculated inner product is negative, processing circuitry 131 determines that the routing of cable 1173 within bore 111 is U-shaped. Processing circuitry 131 determines that the routing of cable 1173 within bore 111 is not U-shaped if the calculated inner product is non-negative. Note that the above description is only 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.

If it is determined that the cable 1173 is arranged in the bore 111 in a U shape, the processing circuit 131 causes the determination function 1321 to store the limit coefficient corresponding to the receiving coil device 117 connected to the connection port 1073c in the storage device. 129. If it is determined that the routing of cable 1173 in bore 111 is not U-shaped, this pulse intensity adjustment process ends.

(Step Sc2)
The processing circuitry 131 further adjusts the irradiation intensity with a pulse intensity adjustment function 1315 . Specifically, the processing circuit 131 further adjusts the irradiation intensity of the RF pulse for the main scan by multiplying the irradiation intensity adjusted in the processing of step Sa6 by the read limit coefficient. The processing circuitry 131 uses the adjusted irradiation intensity to change the imaging conditions.

(Step Sc3)
The processing circuit 131 uses the calculation function 1317 to calculate the extension time of the imaging time based on the change in the imaging conditions associated with the adjusted irradiation intensity. Since the processing contents in this step are the same as those in step Sa7, the description thereof is omitted.

(Step Sc4)
The processing circuit 131 outputs a message to the display 127 by the pulse intensity adjustment function 1315 that the irradiation intensity is limited according to the routing state of the cable 1173 . The display 127 displays a message indicating that the irradiation intensity is limited according to how the cable 1173 is routed. Processing circuit 131 outputs the calculated extension time to the display. Display 127 displays the message with an 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 device 117 having the receiving coil 1171, the cable 1173 connected to the receiving coil 1171 and transmitting the MR signal, and the connector 1175 provided at one end of the cable 1173, A plurality of ports 1073 connectable to the receiving coil device 117 and through which MR signals are input via connectors 1175 are provided. Based on the position of the port 1071c to which the cable 1175 is connected and the positional information, it is determined whether or not the routing of the cable 1173 in the bore 111 is U-shaped. Irradiation intensity can be adjusted.

As a result, according to the present MRI apparatus 1, according to the position of the receiving coil device 117 in the bore 111 and the routing of the cable in the bore, the risk of damaging the receiving coil 1171 and the internal circuit etc. is reduced, and the main scan is performed. , the optimum irradiation intensity can be determined. In other words, according to the MRI apparatus 1 of this application example, even if the routing of the cable 1173 in the bore 111 is not ideal, i. Also, by pulse intensity adjustment processing ( _B1 intensity adjustment processing), the main scan can be executed without resetting the arrangement of the receiving coil device 117 in the bore 111 and the routing of the cable 1173 . As a result, according to the MRI apparatus 1, it is possible to shorten the time required for the workflow before executing the main scan.

Further, according to the MRI apparatus 1, it is possible to display that the irradiation intensity is limited according to the routing state by adjusting the irradiation intensity. For example, according to the MRI apparatus of this application example, the irradiation intensity is limited according to the routing state 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. It can be displayed along with the extended time as a message that you are here. As a result, the operator can easily select determinations such as changing the imaging conditions, changing the installation of the receiving coil device 117, changing the routing of the cable 1173, and relaxing restrictions on the high-frequency magnetic field. For example, if the extension time displayed on the display 127 is five minutes or less, the operator can shorten the extension time by changing the imaging conditions. Further, if the extension time displayed on the display 127 is five minutes or longer, and at least one of the receiving coil device 117 and the routing of the cable 1173 can be reset, the operator can change the receiving coil device 117. Resetting of at least one of placement and routing of cables 1173 may be performed.

(Third modification)
The difference between this modification and the embodiment is that the irradiation intensity is adjusted using a set value (hereinafter referred to as a transmission set value) related to RF pulse transmission according to position information. The transmission setting 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. FIG. The transmission setting value is related to the spatial distribution of the transmission intensity of RF pulses (hereinafter referred to as transmission intensity distribution).

The storage device 129 stores a map (hereinafter referred to as correction map) for correcting the allowable map according to the transmission set value. The correction map is used to reflect the asymmetry of the transmission intensity distribution in the tolerance map when the transmission intensity distribution is asymmetric with respect to the center position of the bore 111 . For example, the correction map has coefficients (hereinafter referred to as correction coefficients) that are multiplied by the tolerance map at each of the plurality of coordinates. Note that the correction map may have coefficients subtracted from or added to the tolerance map at each of the plurality of coordinates instead of the correction coefficients. To make the description concrete, the correction map will be described below 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 composed of 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 of transmission setting values (hereinafter referred to as a "part setting value correspondence table") with respect to the shape of the imaged part (which varies depending on height, weight, imaged part, etc.).

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

The processing circuit 131 uses the pulse intensity adjustment function 1315 to determine the transmission setting value by comparing the imaged region with the region setting value correspondence table. Determination of the transmission set value in this modification is appropriately carried out in the process before step Sa4 in the pulse intensity adjustment process. Note that the processing circuit 131 uses the _B1 map generated by prescanning the subject P to make the transmission intensity distribution uniform within the subject (that is, by _B1 shimming) to determine the transmission set value. may At this time, the site setting value correspondence table is not required, and the determination of the transmission setting values is appropriately carried out in the process after the process of step Sa1 and before the process of step Sa4. The prescan for generating the _B1 map is executed by the imaging control circuit 121 using a sequence that does not affect the receiving coil 1171 .

The processing circuit 131 uses the pulse intensity adjustment function 1315 to adjust the irradiation intensity based on the position information regarding the positional relationship between the transmission coil 115 and the reception coil 1171 and the transmission set value. Specifically, processing circuit 131 identifies a correction map corresponding to the transmission setting value from a plurality of correction maps stored in storage device 129 . Next, the processing circuit 131 generates a modified tolerance map (hereinafter referred to as a modified tolerance map) by multiplying the tolerance map by the specified modification map. Processing circuitry 131 fits the regions (or high intensity regions) associated with receive coil 1171 to the modified tolerance map. The generation of the modified allowable map and the application of the area to the modified allowable map described above are performed instead of the process of step Sa4 in the pulse intensity adjustment process. In the pulse intensity adjustment processing in this modified example, the processing after step Sa5 is the same as the pulse intensity adjustment processing described in the embodiment, so the description is omitted.

Note that the processing circuit 131 may generate a transmission intensity distribution based on the transmission set value by the pulse intensity adjustment function 1315, and generate a correction map based on the generated transmission intensity distribution. Specifically, processing circuitry 131 calculates the transmit strength distribution by applying the transmit settings to the feed points in transmit 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 central position in the generated transmission intensity distribution is set to 1.

According to the configuration described above, the following effects can be obtained.
According to the MRI apparatus 1 in this modified example, it is possible to adjust the irradiation intensity using the setting value related to the transmission of the RF pulse. As a result, the irradiation intensity can be adjusted for each imaging site or for each result of _B1 shimming, without excessively limiting the irradiation intensity of the RF pulse and reducing the risk of damaging the receiving coil 1171 and internal circuits. Therefore, a more optimal irradiation intensity can be determined in the main scan. Since other effects are the same as those of the embodiment, etc., description thereof is omitted.

(Fourth modification)
The difference between this modified example and the embodiment is that the position information of the receiving coil 1171 in the bore 111 is generated without using the MR signal. The MRI apparatus 1 in this modified example 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. Different directions are, for example, three directions. The multiple cameras are, for example, optical cameras.

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

The storage device 129 stores the coordinates of each of the 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 receiving coil 1171 in the bore 111 based on the plurality of optical images. For example, the processing circuitry 131 extracts the region of the receive coil device 117 (hereinafter referred to as the coil device region) in the plurality of optical images by performing existing segmentation processing, recognition processing, etc. on each of the plurality of optical images. . Next, the processing circuit 131 generates positional information of the receiving coils 1171 within the bore 111 using the positions of the plurality of receiving coils 1171 in the receiving coil device 117, the coil device extraction regions, and the camera coordinates.

The imaging of the receiving coil device 117 inside the bore and the generation of the positional information of the receiving coil 1171 inside the bore 111 are performed in the pulse intensity adjustment process instead of the processes of steps Sa1 to Sa3. In the pulse intensity adjustment process related 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 this modified example, it is possible to generate the positional information of the receiving coil 1171 in the bore 111 and adjust the irradiation intensity of the RF pulse with which the subject P is irradiated based on the positional information. Other effects are the same as those of the first modified example, etc., so description thereof will be omitted.

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

While several embodiments of the invention have been described, these embodiments have been 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 modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

Reference Signs List 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 109 Bed control circuit 111 Bore 113 Transmission circuit 115 Transmission coil 117 Reception coil device 119 Receiver circuit 121 Imaging control circuit 125 Interface 127 Display 129 Storage device 131 Processing circuit 1071 Top board 1073 Port 1171 Receiving 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 Judgment function

Claims (10)

a position information generator that generates position information regarding the positional relationship between the transmission coil and the reception coil based on the magnetic resonance signals received from the subject;
a pulse intensity adjustment unit that adjusts the irradiation intensity of the RF pulse applied to the subject according to the position information;
and
the positional relationship is the distance between the transmitting coil and the receiving coil;
The pulse intensity adjustment unit adjusts the irradiation intensity so that the irradiation intensity decreases as the distance between the transmission coil and the reception coil decreases.
Magnetic resonance imaging equipment. 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 . The position information generating unit generates the position information based on an image obtained by reconstructing the magnetic resonance signal.
The magnetic resonance imaging apparatus according to claim 1 or 2 . an image information generator that generates image information having, as pixel values, signal intensities corresponding to each of the plurality of frequency components in the magnetic resonance signal, based on the magnetic resonance signal; Using image information, the distance from the transmission coil to the reception coil is calculated as the position information for each of a plurality of pixels in the image information, and the pulse intensity adjustment unit is configured to:
A plurality of tolerance coefficients corresponding to the plurality of pixels are calculated using a correspondence table of a plurality of tolerance coefficients indicating tolerance levels of the irradiation intensity with respect to the plurality of distances from the transmission coil and the calculated distances. decide and
Adjusting the irradiation intensity using the smallest allowable coefficient among the determined plurality of allowable coefficients;
4. The magnetic resonance imaging apparatus according to claim 1 . further comprising an image information generating unit that generates image information having pixel values corresponding to signal intensities corresponding to each of the plurality of frequency components in the magnetic resonance signal, based on the magnetic resonance signal;
The position information generating unit generates a plurality of coordinates regarding the position of the receiving coil as the position information using the coordinate system regarding the area including the bore and the image information,
The pulse intensity adjustment unit
Using the plurality of coordinates, applying the area related 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 a plurality of coordinates in the coordinate system,
Adjusting the irradiation intensity using the smallest allowable coefficient among a plurality of allowable coefficients included in the region related to the receive coil;
4. The magnetic resonance imaging apparatus according to claim 1 . The position information generating unit generates the position information by obtaining a one-dimensional profile of the magnetic resonance signal in three axial directions formed by the gradient magnetic field.
The magnetic resonance imaging apparatus according to claim 1 or 2 . a receiving coil device including the receiving coil, a cable connected to the receiving coil and transmitting the magnetic resonance signal, and a connector provided at one end of the cable;
a plurality of ports connectable to the receiving coil device and receiving the magnetic resonance signals through the connectors;
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 positional information, whether the cable is routed in the bore in a U shape or not. A determination unit that determines whether or not
further comprising
The pulse intensity adjustment unit
adjusting the irradiation intensity when it is determined that the handling is U-shaped;
7. The magnetic resonance imaging apparatus according to claim 1. Further comprising a display unit that displays that the irradiation intensity is limited according to the position of the receiving coil by adjusting the irradiation intensity,
8. The magnetic resonance imaging apparatus according to claim 1. further comprising a display unit that displays that the irradiation intensity is limited according to the routing state of the cable by adjusting the irradiation intensity;
The magnetic resonance imaging apparatus according to claim 7 . further comprising a calculation unit that calculates an extension 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 extension time;
The magnetic resonance imaging apparatus according to claim 8 or 9 .

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