JP2011098093A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus, suitably protecting a receiving coil from a high-frequency magnetic field applied by a transmitting coil. <P>SOLUTION: In this MRI apparatus 100, a computer system 70 detects the magnitude of electric load generated in the receiving coil 14 based on the magnitude of induced electromotive pressure generated in a search coil 15 due to application of a high-frequency magnetic field by the transmitting coil 13. The computer system 70 controls imaging to protect the receiving coil 14 based on the magnitude of the detected electric load. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus.

  A magnetic resonance imaging apparatus is an apparatus that images a subject using a magnetic resonance phenomenon. Such a magnetic resonance imaging apparatus includes a static magnetic field magnet that generates a static magnetic field in an imaging region, a transmission coil that applies a high-frequency magnetic field to a subject placed in the static magnetic field, and a magnetic resonance emitted from the subject by applying a high-frequency magnetic field. A receiving coil for receiving signals is provided.

  In such a magnetic resonance imaging apparatus, the receiving coil is generally disposed inside the transmitting coil. Therefore, when a high-frequency magnetic field is applied by the transmission coil, an induced electromotive force is generated in the reception coil by the high-frequency magnetic field. When an unexpectedly large induced electromotive force is generated in the reception coil, the circuit included in the reception coil The element may be damaged. For example, Patent Document 1 proposes a technique for setting imaging conditions so as not to exceed a threshold related to the strength of a high-frequency magnetic field.

JP 2006-95278 A

  However, the electrical load generated in the receiving coil has not been actually measured. Therefore, for example, all of the energy supplied to the transmission coil is calculated as a load generated in the reception coil, and control is performed so that the calculated load does not exceed the upper limit value. That is, the load of the receiving coil is calculated under the worst condition. As a result, excessive protection was performed on the receiving coil.

  The present invention has been made in view of the above, and an object thereof is to provide a magnetic resonance imaging apparatus capable of appropriately protecting a receiving coil from a high-frequency magnetic field applied by a transmitting coil.

  In order to solve the above-described problems and achieve the object, according to the present invention, a magnetic resonance imaging apparatus includes a transmission coil for applying a high-frequency magnetic field to a subject placed in a static magnetic field, and the transmission A receiving coil that is disposed inside the coil and receives a magnetic resonance signal emitted from the subject by application of the high-frequency magnetic field, and the reception by the high-frequency magnetic field based on the strength of the high-frequency magnetic field applied by the transmission coil Coil load detection means for detecting the magnitude of the electrical load generated in the coil, and imaging so that the receiving coil is protected based on the magnitude of the electrical load detected by the coil load detection means And an imaging control means for controlling the camera.

  According to the first aspect of the present invention, there is an effect that the receiving coil can be appropriately protected from the high frequency magnetic field applied by the transmitting coil.

FIG. 1 is a diagram illustrating an overall configuration of the MRI apparatus according to the present embodiment. FIG. 2 is a diagram for explaining the arrangement of the search coils. FIG. 3 is a functional block diagram showing a detailed configuration of the computer system. FIG. 4 is a diagram illustrating an example of threshold values stored by the threshold value table. FIG. 5 is a diagram for explaining an example of calculation of an average value of induced electromotive force by the imaging control unit. FIG. 6 is a flowchart illustrating a flow of imaging control by the MRI apparatus according to the present embodiment. FIG. 7 is a diagram for explaining the arrangement of search coils when a plurality of search coils are used.

  Embodiments of an image processing apparatus, a magnetic resonance imaging apparatus, and an image management system according to the present invention will be described below in detail with reference to the drawings. Hereinafter, the magnetic resonance imaging apparatus is referred to as “MRI (Magnetic Resonance Imaging) apparatus”, and the magnetic resonance signal is referred to as “MR (Magnetic Resonance) signal”.

  First, the overall configuration of the MRI apparatus according to the present embodiment will be described. FIG. 1 is a diagram illustrating an overall configuration of the MRI apparatus according to the present embodiment. As shown in FIG. 1, the MRI apparatus 100 according to the present embodiment includes a gantry unit 10, a gradient magnetic field power supply 20, a transmission unit 30, a reception unit 40, a bed 50, a bed control unit 60, and a computer system 70.

  The gantry 10 applies a high-frequency magnetic field to the subject placed in the static magnetic field, and detects an MR signal emitted from the subject by the application of the high-frequency magnetic field. The gantry 10 is formed in a substantially cylindrical shape, and includes a static magnetic field magnet 11, a gradient magnetic field coil 12, a transmission coil 13, a reception coil 14, and a search coil 15 inside.

  The static magnetic field magnet 11 is formed in a hollow cylindrical shape and generates a uniform static magnetic field in the internal space. The static magnetic field magnet 11 is formed using, for example, a superconducting magnet.

  The gradient coil 12 is formed in a hollow cylindrical shape and is disposed inside the static magnetic field magnet 11. The gradient coil 12 is formed by combining three coils corresponding to the X, Y, and Z axes orthogonal to each other. These three coils are individually supplied with a current from a gradient magnetic field power supply 20 to be described later, and generate a gradient magnetic field whose magnetic field strength changes along the X, Y, and Z axes. The Z-axis direction is the same direction as the static magnetic field.

  Here, the gradient magnetic fields of the X, Y, and Z axes generated by the gradient magnetic field coil 12 correspond to, for example, the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr, respectively. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to change the phase of the MR signal in accordance with the spatial position. The readout gradient magnetic field Gr is used to change the frequency of the MR signal in accordance with the spatial position.

  The transmission coil 13 is arranged inside the gradient magnetic field coil 12 and generates a high frequency magnetic field upon receiving a high frequency pulse from a transmission unit 30 described later. In this embodiment, the transmission coil 13 is a WB (Whole Body) coil formed in a cylindrical shape.

  The reception coil 14 is disposed inside the transmission coil 13 and receives MR signals emitted from the subject due to the influence of the high-frequency magnetic field generated by the transmission coil 13. And the receiving coil 14 outputs the received MR signal to the receiving part 40 mentioned later.

  The search coil 15 is a coil installed inside the transmission coil 13. When a high frequency magnetic field is applied by the transmission coil 13, the search coil 15 generates a dielectric electromotive voltage having a magnitude corresponding to the strength of the applied high frequency magnetic field. The arrangement of the search coil 15 will be described later in detail.

  The gradient magnetic field power supply 20 supplies a current to the gradient magnetic field coil 12 under the control of a computer system 70 described later.

  The bed 50 includes a top plate 51 on which the subject P is placed, and the gradient magnetic field coil 12 is moved by moving the top plate 51 in the vertical direction or the longitudinal direction under the control of a bed control unit 60 described later. The subject P is moved in and out of the imaging region inside the. Normally, the bed 50 is installed such that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 11.

  The bed control unit 60 drives the bed 50 so as to move the table 51 in the longitudinal direction or the vertical direction under the control of the computer system 70 described later.

  The transmission unit 30 transmits high-frequency pulses corresponding to the Larmor frequency to the transmission coil 13 under the control of the computer system 70 described later.

  The receiving unit 40 generates MR signal data based on the MR signal output from the receiving coil 14 under the control of the computer system 70 described later, and transmits the generated MR signal data to the computer system 70.

  The computer system 70 performs overall control of the MRI apparatus 100, data collection, image reconstruction, and the like. The computer system 70 includes an interface unit 71, a data collection unit 72, an image reconstruction unit 73, a storage unit 74, a display unit 75, an input unit 76, and a control unit 77.

  The interface unit 71 is connected to the gradient magnetic field power supply 20, the transmission unit 30, the reception unit 40, and the bed control unit 60, and controls input / output of signals transmitted / received between these units and the computer system 70.

  The data collection unit 72 collects MR signal data transmitted from the reception unit 40 via the interface unit 71. Then, the data collection unit 72 stores the collected MR signal data in the storage unit 74.

  The image reconstruction unit 73 performs an reconstruction process such as Fourier transform on the MR signal data stored in the storage unit 74 to generate an image relating to the body of the subject P. Then, the image reconstruction unit 73 stores the generated image in the storage unit 74.

  The storage unit 74 stores the MR signal data collected by the data collection unit 72 and the image generated by the image reconstruction unit 73 for each subject P. For example, the storage unit 74 is a hard disk drive, a DVD (Digital Versatile Disc) drive, or the like.

  The display unit 75 displays various information such as an image stored in the storage unit 74 and a GUI (Graphical User Interface) for receiving an imaging condition from the operator under the control of the control unit 77. For example, the display unit 75 is a CRT (Cathode Ray Tube) monitor or a liquid crystal monitor.

  The input unit 76 receives various information such as imaging conditions and various operation inputs from the operator. For example, the input unit 76 includes, as imaging conditions, the type of imaging sequence, repetition time (TR), inversion recovery time (TI), flip angle (FA: Flip Angle) of the excitation high-frequency magnetic field pulse, Accepts inputs such as the number of slices and slice thickness.

  The control unit 77 includes a CPU (Central Processing Unit), a memory, and the like (not shown), and controls the MRI apparatus 100 overall. For example, the control unit 77 generates various pulse sequences based on the imaging conditions received from the operator, and controls the gradient magnetic field power source 20, the transmission unit 30, and the reception unit 40 according to the generated pulse sequences, thereby The imaging is executed.

  Here, the “pulse sequence” refers to the strength of the power supplied from the gradient magnetic field power supply 20 to the gradient magnetic field coil 12 and the timing of supplying the power, the strength of the high frequency pulse transmitted from the transmission unit 30 to the transmission coil 13, This is information defining a procedure for performing imaging, such as a timing for transmitting a pulse and a timing for detecting the MR signal by the receiving unit 40.

  The overall configuration of the MRI apparatus 100 according to the present embodiment has been described above. Under such a configuration, in the MRI apparatus 100 according to the present embodiment, the computer system 70 receives the receiving coil based on the magnitude of the induced electromotive voltage generated in the search coil 15 by the application of the high-frequency magnetic field by the transmitting coil 13. The magnitude of the electrical load generated at 14 is detected. Then, the computer system 70 controls the imaging so that the receiving coil 14 is protected based on the detected magnitude of the electrical load.

  That is, in this embodiment, when a high-frequency magnetic field is applied by the transmission coil 13, the receiving coil 14 is protected based on the strength of the high-frequency magnetic field that is actually measured as an induced electromotive voltage generated in the search coil 15. In this way, the imaging is controlled. For this reason, even when information such as weight and height presented by the patient at the time of diagnosis is incorrect, or when an operator inputs information incorrectly, imaging is controlled based on the actual measurement value. Therefore, according to the present embodiment, the receiving coil 14 can be appropriately protected from the high frequency magnetic field applied by the transmitting coil 13.

  Hereinafter, the MRI apparatus 100 according to the present embodiment will be described in detail with a focus on the search coil 15 and the computer system 70 described above. In the present embodiment, a case where a power value is used as a value indicating the magnitude of an electrical load generated in the receiving coil 14 by a high-frequency magnetic field will be described.

  First, the arrangement of the search coil 15 will be described. FIG. 2 is a diagram for explaining the arrangement of the search coil 15. As shown in FIG. 2, for example, the search coil 15 is provided on the lower surface of the top plate rail 16 attached to the inside of the static magnetic field magnet 11, the gradient magnetic field coil 12, and the transmission coil 13 in the gantry 10. Accordingly, the search coil 15 does not prevent the top plate 51 from moving.

  Further, the search coil 15 is provided so as to be positioned at the center in the axial direction of the transmission coil 13. Thereby, the strength of the high-frequency magnetic field is measured at a position close to the magnetic field center, that is, at a position where an imaging region is set and the reception coil 14 is likely to be installed. Therefore, the receiving coil 14 can be protected more reliably.

  Next, details of the computer system 70 will be described. FIG. 3 is a functional block diagram showing a detailed configuration of the computer system 70. As shown in FIG. 3, in the computer system 70, the storage unit 74 has a threshold value table 74a. The threshold value table 74a stores a threshold value indicating the magnitude of the electrical load allowed to occur in the receiving coil 14.

  Specifically, the threshold value table 74a stores a threshold value indicating the magnitude of the electrical load for each of the plurality of receiving coils. FIG. 4 is a diagram illustrating an example of threshold values stored by the threshold value table 74a. As shown in FIG. 4, for example, the threshold value table 74a stores coil identification information, an average power threshold value, and a maximum power threshold value in association with each other.

  Here, the “coil identification information” is identification information for uniquely identifying the receiving coil. The “maximum power threshold” is the maximum value of the induced electromotive force that is allowed to be generated in the receiving coil by one application of the high-frequency magnetic field. The “average power threshold” is an average value of induced electromotive force that is allowed to be generated in the receiving coil within a predetermined period. Note that the maximum power threshold value and the average power threshold value stored in the threshold value table 74a are determined in advance based on the specifications of the elements, circuits, circuit elements, etc. of each receiving coil.

  Returning to FIG. 3, in the computer system 70, the control unit 77 includes a coil load detection unit 77a and an imaging control unit 77b.

  The coil load detection unit 77a detects the magnitude of the electrical load generated in the receiving coil 14 by the high frequency magnetic field based on the strength of the high frequency magnetic field applied by the transmission coil 13. The coil load detection unit 77a is connected to the search coil 15 via the interface unit 71.

  In the present embodiment, the coil load detection unit 77a determines the magnitude of the induced electromotive force generated in the receiving coil 14 based on the magnitude of the induced electromotive voltage generated in the search coil 15 due to the application of the high-frequency magnetic field by the transmission coil 13. calculate. For example, the coil load detecting unit 77a sets the induced electromotive voltage generated in the search coil 15 to E, the pulse length of the high frequency magnetic field T, and the induced electromotive voltage generated in the search coil 15 to the receiving coil 14. When the correction coefficient for conversion into electric power is α, the induced electromotive force P generated in the receiving coil is calculated by the following equation (1). The correction coefficient α used here is determined according to the size of the coil for each receiving coil.

      P = E × T × α (1)

  In the present embodiment, the case where the induced electromotive force generated in the receiving coil 14 is calculated using the correction coefficient α will be described, but the present invention is not limited to this. For example, a conversion table in which the induced electromotive voltage generated in the search coil 15 and the induced electromotive force generated in the receiving coil 14 are associated with each other based on the actually measured value is created and stored in the storage unit 74. The coil load detection unit 77a may convert the induced electromotive voltage generated in the search coil 15 as the induced electromotive force generated in the receiving coil 14 with reference to the conversion table.

  The imaging control unit 77b controls imaging by driving the gradient magnetic field power source 20, the transmission unit 30, and the reception unit 40 based on the imaging conditions input from the operator. Further, the imaging control unit 77b controls the imaging so that the receiving coil 14 is protected based on the magnitude of the electrical load detected by the coil load detection unit 77a.

  Specifically, the imaging control unit 77b first acquires a threshold value corresponding to the receiving coil used for imaging from the threshold values stored in the threshold value table 74a. Then, the imaging control unit 77b stops imaging when the magnitude of the electrical load detected by the coil load detection unit 77a exceeds the threshold acquired from the threshold table 74a.

  For example, the imaging controller 77b stops imaging when the maximum value of the induced electromotive force calculated by the coil load detector 77a exceeds the maximum power threshold stored in the threshold table 74a within a predetermined period.

  For example, the imaging control unit 77b stops imaging when the average value of the induced electromotive force detected by the coil load detection unit 77a within the predetermined period exceeds the average power threshold stored in the threshold table 74a. .

  Here, an example of calculating the average value of the induced electromotive force by the imaging control unit 77b will be described. Here, a case where the repetition time set as the imaging condition is a predetermined period will be described. FIG. 5 is a diagram for explaining an example of calculation of an average value of induced electromotive force by the imaging control unit 77b. FIG. 5 shows the timing at which an induced electromotive voltage is generated in the search coil 15 when four slices are imaged in one inspection. In FIG. 5, a rectangle R indicates an induced electromotive voltage generated in the search coil 15. Specifically, the width of the rectangle R indicates the pulse length T of the high-frequency magnetic field, and the height of the rectangle R indicates the magnitude of the induced electromotive voltage E generated in the search coil 15.

  In such a case, for example, when the repetition time is TR and the number of slices is S, the imaging control unit 77b calculates the average value AP of the induced electromotive force by the following equation (2).

      AP = (E × T / TR) × S × α (2)

  Next, the flow of imaging control by the MRI apparatus 100 according to the present embodiment will be described. FIG. 6 is a flowchart illustrating the flow of imaging control by the MRI apparatus 100 according to the present embodiment. Here, a case will be described in which the pre-scan and the main scan are each performed by one imaging.

  As illustrated in FIG. 6, first, the imaging control unit 77b drives the gradient magnetic field power source 20, the transmission unit 30, and the reception unit 40 to execute pre-scanning (Step S101).

  Then, during the pre-scan, the coil load detector 77a measures the strength of the high-frequency magnetic field applied by the transmission coil 13 (step S102). Specifically, the coil load detection unit 77a measures the magnitude of the induced electromotive voltage generated in the search coil 15 as a value indicating the strength of the high frequency magnetic field.

  Subsequently, the imaging control unit 77b receives an input of imaging conditions from the operator via the input unit 76 (step S103). Specifically, the imaging control unit 77b receives inputs such as the type of imaging sequence, the pulse length of the high-frequency magnetic field, the flip angle, and the number of slices.

  Thereafter, the coil load detector 77a detects the magnitude of the electrical load generated in the receiving coil 14 based on the magnitude of the induced electromotive voltage generated in the search coil 15 (step S104). Specifically, the coil load detection unit 77a calculates the magnitude of the induced electromotive force generated in the receiving coil 14 based on the magnitude of the induced electromotive voltage generated in the search coil 15.

  Subsequently, the imaging control unit 77b acquires a threshold value corresponding to the reception coil 14 from the threshold values stored in the threshold value table 74a, and the magnitude of the electrical load detected by the coil load detection unit 77a corresponds to the threshold value. It is determined whether or not the threshold value is exceeded (step S105).

  Specifically, the imaging control unit 77b calculates the maximum value and the average value of the induced electromotive force calculated by the coil load detection unit 77a during the prescan. Then, when the calculated maximum value exceeds the maximum power threshold value of the threshold value table 74a or the calculated average value exceeds the average power threshold value of the threshold value table 74a, the imaging control unit 77b Is determined to exceed the threshold. On the other hand, when the calculated maximum value does not exceed the maximum power threshold value of the threshold value table 74a and the calculated average value does not exceed the average power threshold value of the threshold value table 74a, the imaging control unit 77b It determines with the magnitude | size of load not exceeding the threshold value.

  Here, when the magnitude of the load exceeds the threshold (step S105, Yes), the imaging control unit 77b stops imaging (step S106) and returns to step S103. At this time, for example, the imaging control unit 77b may output a warning message for prompting re-input of imaging conditions to the display unit 75. On the other hand, when the magnitude of the load does not exceed the threshold (No at Step S105), the imaging control unit 77b starts the main scan (Step S107).

  Then, during the execution of the main scan, the coil load detector 77a measures the strength of the high-frequency magnetic field applied by the transmission coil 13 (step S108). Specifically, the coil load detection unit 77a measures the magnitude of the induced electromotive voltage generated in the search coil 15 as a value indicating the strength of the high frequency magnetic field.

  Thereafter, the coil load detector 77a detects the magnitude of the electrical load generated in the receiving coil 14 based on the magnitude of the induced electromotive voltage generated in the search coil 15 (step S109). Specifically, the coil load detection unit 77a calculates the magnitude of the induced electromotive force generated in the receiving coil 14 based on the magnitude of the induced electromotive voltage generated in the search coil 15.

  Subsequently, the imaging control unit 77b acquires a threshold value corresponding to the reception coil 14 from the threshold values stored in the threshold value table 74a, and the magnitude of the electrical load detected by the coil load detection unit 77a corresponds to the threshold value. It is determined whether or not the threshold value is exceeded (step S110).

  Specifically, the imaging control unit 77b calculates the maximum value and the average value of the induced electromotive force calculated by the coil load detection unit 77a within a predetermined period during execution of the main scan. Then, when the calculated maximum value exceeds the maximum power threshold value of the threshold value table 74a or the calculated average value exceeds the average power threshold value of the threshold value table 74a, the imaging control unit 77b Is determined to exceed the threshold. On the other hand, when the calculated maximum value does not exceed the maximum power threshold value of the threshold value table 74a and the calculated average value does not exceed the average power threshold value of the threshold value table 74a, the imaging control unit 77b It determines with the magnitude | size of load not exceeding the threshold value.

  If the magnitude of the load exceeds the threshold (step S110, Yes), the imaging control unit 77b stops imaging (step S111) and returns to step S103. On the other hand, when the magnitude of the load does not exceed the threshold (No at Step S110), the imaging control unit 77b continues imaging (Step S112). Note that the imaging control unit 77b may periodically execute the processes of steps S108 to S110 at regular intervals, or may be performed at equal intervals as many times as specified by the operator.

  The imaging control unit 77b repeats the processing in steps S108 to S110 until imaging is completed (No in step S113). And the imaging control part 77b complete | finishes a process, when imaging is completed (step S113, Yes).

  Here, the case where the imaging control is performed by measuring the intensity of the high-frequency magnetic field in each of the pre-scan and the main scan has been described. However, for example, only one of the pre-scan and the main scan may be performed. Good.

  As described above, in this embodiment, the coil load detector 77a detects the magnitude of the electrical load generated in the receiving coil 14 by the high frequency magnetic field based on the strength of the high frequency magnetic field applied by the transmission coil 13. To do. Then, the imaging control unit 77b controls the imaging so that the reception coil 14 is protected based on the magnitude of the electrical load detected by the coil load detection unit 77a.

  That is, in this embodiment, when a high-frequency magnetic field is applied by the transmission coil 13, the receiving coil 14 is protected based on the strength of the high-frequency magnetic field that is actually measured as an induced electromotive voltage generated in the search coil 15. In this way, the imaging is controlled. For this reason, even when information such as weight and height presented by the patient at the time of diagnosis is incorrect, or when an operator inputs information incorrectly, imaging is controlled based on the actual measurement value. Therefore, according to the present embodiment, the receiving coil 14 can be appropriately protected from the high frequency magnetic field applied by the transmitting coil 13.

  In the present embodiment, the search coil 15 is installed inside the transmission coil 13, and the coil load detection unit 77 a is based on the magnitude of the induced electromotive voltage generated in the search coil 15 by the application of the high-frequency magnetic field by the transmission coil 13. Thus, the magnitude of the electrical load generated in the receiving coil 14 is detected. Therefore, according to the present embodiment, the receiving coil 14 can be appropriately protected with a simple configuration using the search coil 15.

  In this embodiment, the threshold value table 74a stores a threshold value indicating the magnitude of an electrical load that is allowed to occur in the receiving coil 14. Then, the imaging control unit 77b stops imaging when the magnitude of the electrical load detected by the coil load detection unit 77a exceeds the threshold value stored in the threshold value table 74a. Therefore, according to the present embodiment, the reception coil 14 can be easily protected by registering in the table the threshold value of the electrical load determined based on the specification of the reception coil in advance.

  In the present embodiment, the threshold value table 74a stores a threshold value for each of the plurality of receiving coils. Then, the imaging control unit 77b acquires the threshold value corresponding to the reception coil used for imaging from the threshold values stored in the threshold value table 74a, and the magnitude of the electrical load detected by the coil load detection unit 77a. If the value exceeds the threshold, the imaging is stopped. Therefore, according to the present embodiment, each receiving coil can be appropriately protected even when a plurality of receiving coils are used for imaging.

  In this embodiment, the threshold table 74a stores the maximum value of the electrical load that is allowed to be generated in the receiving coil 14 by one application of the high-frequency magnetic field as the maximum power threshold. The imaging control unit 77b captures an image when the maximum value of the electrical load detected by the coil load detection unit 77a within a predetermined period exceeds the maximum power threshold stored in the threshold table 74a during the imaging. Cancel. Therefore, according to the present embodiment, it is possible to appropriately protect the receiving coil 14 even when the intensity of the high-frequency magnetic field changes instantaneously due to the movement of the subject P or the like.

  In the present embodiment, the threshold value table 74a stores an average value of electrical loads allowed to occur in the reception coil 14 within a predetermined period as an average power threshold value. Then, the imaging control unit 77b performs imaging when the average value of the electrical load detected by the coil load detection unit 77a within the predetermined period exceeds the average power threshold stored in the threshold table 74a during imaging. Cancel. According to the present embodiment, the receiving coil 14 can be appropriately protected even when the intensity of the high-frequency magnetic field continuously changes.

In the present embodiment, as a result of the pre-scan performed by the imaging control unit 77b, the maximum value of the electrical load detected by the coil load detection unit 77a exceeds the maximum power threshold stored in the threshold table 74a. In this case, the imaging is stopped without executing the main scan.
Therefore, according to the present embodiment, even when the intensity of the high-frequency magnetic field instantaneously changes due to the movement of the subject P, the receiving coil 14 can be appropriately protected before the main scan is executed.

  In the present embodiment, the average power stored in the threshold value table 74a is the average value of the electrical load detected by the coil load detection unit 77a within a predetermined period as a result of the prescan being performed by the imaging control unit 77b. If the threshold value is exceeded, the imaging is stopped without executing the main scan. Therefore, according to the present embodiment, even when the intensity of the high-frequency magnetic field continuously changes, it is possible to appropriately protect the receiving coil 14 before executing the main scan.

  In the present embodiment, the case where only one search coil 15 is used has been described. However, the present invention is not limited to this, and a plurality of search coils may be used. FIG. 7 is a diagram for explaining the arrangement of search coils when a plurality of search coils are used. FIG. 7 shows an example in which three search coils 15a, 15b and 15c are used.

  As shown in FIG. 7, when three search coils 15 a, 15 b and 15 c are used, for example, each search coil is provided inside the static magnetic field magnet 11, the gradient magnetic field coil 12 and the transmission coil 13 in the gantry 10. It is provided on the lower surface of the top plate rail 16.

  Here, for example, the search coil 15a is provided so as to be positioned at the center of the transmission coil 13 in the axial direction, similarly to the search coil 15 shown in FIG. Further, the search coils 15b and 15c are provided so as to be positioned at both ends of the transmission coil 13, respectively. Thereby, since the intensity | strength of a high frequency magnetic field can be measured in several places where the receiving coil 14 may be installed, the receiving coil 14 can be protected more reliably.

  In general, both ends of the transmission coil 13 are provided with end rings made of copper foil. Therefore, the electric field generated between the coils can be measured using the search coils 15b and 15c. Thereby, it becomes possible to detect the load generated in the reception coil 14 by the electric field generated by the transmission coil 13 and to control the imaging, so that the reception coil 14 can be protected more strictly.

  Moreover, although the present Example demonstrated the case where the one receiving coil 14 was used for an imaging, this invention is not limited to this. For example, the present invention can be similarly applied when a plurality of receiving coils are used for imaging. In that case, for example, the coil load detection unit 77a calculates the induced electromotive force generated in the reception coil from the magnitude of the induced electromotive voltage generated in the search coil 15 for each reception coil. The imaging control unit 77b stops imaging when any one of the induced electromotive forces calculated for each receiving coil exceeds the threshold value.

  Moreover, although the present Example demonstrated the case where the intensity | strength of a high frequency magnetic field was measured using the search coil 15, this invention is not limited to this. For example, other devices or instruments that can measure the intensity of the high-frequency magnetic field, such as a magnetic field sensor, may be used instead of the search coil 15.

  In the present embodiment, the case where the power value is used as the value indicating the magnitude of the electrical load generated in the receiving coil 14 by the high-frequency magnetic field has been described, but the present invention is not limited to this. For example, other electrical values such as a voltage value and a current value may be used.

100 MRI system (magnetic resonance imaging system)
DESCRIPTION OF SYMBOLS 13 Transmission coil 14 Reception coil 15 Search coil 70 Computer system 74 Storage part 74a Threshold table 77 Control part 77a Coil load detection part 77b Imaging control part

Claims (8)

A transmission coil for applying a high-frequency magnetic field to a subject placed in a static magnetic field;
A receiving coil arranged inside the transmitting coil and receiving a magnetic resonance signal emitted from the subject by application of the high-frequency magnetic field;
Coil load detection means for detecting the magnitude of the electrical load generated in the receiving coil by the high frequency magnetic field based on the intensity of the high frequency magnetic field applied by the transmission coil;
Magnetic resonance imaging apparatus, comprising: imaging control means for controlling imaging so that the receiving coil is protected based on the magnitude of the electrical load detected by the coil load detection means . A search coil installed inside the transmission coil;
The coil load detecting means detects a magnitude of an electrical load generated in the receiving coil based on a magnitude of an induced electromotive voltage generated in the search coil by application of the high-frequency magnetic field by the transmitting coil. The magnetic resonance imaging apparatus according to claim 1. Threshold value storage means for storing a threshold value indicating the magnitude of an electrical load allowed to occur in the receiving coil;
The imaging control unit stops the imaging when the magnitude of the electrical load detected by the coil load detection unit exceeds the threshold stored by the threshold storage unit. The magnetic resonance imaging apparatus according to claim 1 or 2. The threshold storage means stores the threshold for each of a plurality of receiving coils,
The imaging control means obtains a threshold value corresponding to a receiving coil used for imaging from the threshold values stored by the threshold value storage means, and the magnitude of the electrical load detected by the coil load detection means. The magnetic resonance imaging apparatus according to claim 3, wherein the imaging is stopped when the value exceeds the threshold value. The threshold storage means stores, as the threshold, the maximum value of the electrical load that is allowed to occur in the reception coil by one application of the high-frequency magnetic field,
When the maximum value of the electrical load detected by the coil load detection means within the predetermined period exceeds the threshold stored by the threshold storage means during imaging, the imaging control means The magnetic resonance imaging apparatus according to claim 3 or 4, wherein imaging is stopped. The threshold storage means stores, as the threshold, an average value of the electrical load that is allowed to occur in the receiving coil within a predetermined period.
When the average value of the electrical load detected by the coil load detection unit within the predetermined period exceeds the threshold stored by the threshold storage unit during imaging, the imaging control unit The magnetic resonance imaging apparatus according to claim 3 or 4, wherein imaging is stopped.   The imaging control unit performs the main scan when the maximum value of the electrical load detected by the coil load detection unit exceeds the threshold stored by the threshold storage unit as a result of performing the pre-scan. The magnetic resonance imaging apparatus according to claim 5, wherein the imaging is stopped without executing.   When the imaging control means has performed pre-scanning, the average value of the electrical load detected by the coil load detection means within the predetermined period exceeds the threshold stored by the threshold storage means The magnetic resonance imaging apparatus according to claim 6, wherein the imaging is stopped without executing the main scan.

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