JP2019084162A - Magnetic resonance imaging apparatus - Google Patents

Abstract

To control allocation of output current from a power supply device by using software.SOLUTION: A magnetic resonance imaging apparatus comprises: a plurality of gradient magnetic field coils 103 that, upon reception of power supply, generates gradient magnetic fields each having a different axis; and a gradient magnetic field power source 105 for supplying power. The gradient magnetic field power source 105 includes: a plurality of amplifiers 20 connected to the plurality of gradient magnetic field coils 103 respectively; a power supply device 11 for supplying current to the plurality of amplifiers 20; a measuring instrument 12 for measuring voltages applied to the plurality of amplifiers 20; and power control circuitry 13 for controlling current supplied to the amplifiers from the power supply device based on the voltages. The power control circuitry 13 comprises: a comparison unit for comparing the voltages applied to the plurality of amplifiers with threshold voltages; and a memory having associated information that associates a comparison result of the comparison unit with the ratio of current respectively supplied to the plurality of amplifiers 20 corresponding to the plurality of gradient magnetic field coils 103, to the total sum of the current supplied to the plurality of amplifiers 20.SELECTED DRAWING: Figure 2

Description

  Embodiments of the present invention relate to a magnetic resonance imaging apparatus.

  The gradient power supply of the Magnetic Resonance Imaging (MRI) device is based on the number of output channels used to supply power from the amplifier to the gradient coil, the number of outputs from the power supply used as the power supply of the amplifier. Set At this time, the conventional gradient magnetic field power supply performs the allocation of the output current from the power supply device by hardware control.

  However, since the gradient magnetic field power source performing hardware control has many analog signals to be controlled, it has a complicated configuration.

JP, 2013-173, A JP, 2017-35305, A

  The problem to be solved by the present invention is to control the allocation of the output current from the power supply using software.

  A magnetic resonance imaging apparatus according to an embodiment includes a plurality of gradient magnetic field coils that receive power supply to generate gradient magnetic fields of multiple axes, and a gradient magnetic field power supply that supplies power. The gradient magnetic field power supply includes a plurality of amplifiers respectively connected to the plurality of gradient magnetic field coils, a power supply supplying current to the plurality of amplifiers, a measuring instrument measuring the voltage applied to the plurality of amplifiers, and a voltage And a power control circuit for controlling the current supplied from the power supply to the amplifier. The power control circuit compares a voltage applied to the plurality of amplifiers with a threshold voltage, a comparison result by the comparison unit, and current supplied to each of the plurality of amplifiers corresponding to the plurality of gradient magnetic field coils. And a memory having corresponding information for correlating the ratio to the sum of currents supplied to the plurality of amplifiers.

FIG. 1 is a diagram showing the configuration of an MRI apparatus according to an embodiment. FIG. 2 is a diagram showing the configuration of a gradient magnetic field power supply and the like in one embodiment. FIG. 3 is a diagram showing a circuit configuration of a gradient magnetic field power supply in one embodiment. FIG. 4 illustrates a software configuration associated with the power control circuit in one embodiment. FIG. 5 is a flow chart illustrating a process performed by the power control circuit in one embodiment. FIG. 6 shows a look-up table in one embodiment.

  Hereinafter, embodiments of the MRI apparatus will be described in detail with reference to the drawings.

  FIG. 1 is a view showing a configuration example of an MRI apparatus according to an embodiment. For example, as shown in FIG. 1, the MRI apparatus 100 according to an embodiment 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, and a transmission circuit 113. A transmission coil 115, a reception coil 117, a reception circuit 119, an imaging control circuit 121, an interface 123, a display 125, a storage device 127, and a processing circuit 129.

  The static magnetic field magnet 101 is, for example, a magnet formed in a hollow substantially cylindrical shape. The static magnetic field magnet 101 generates a uniform static magnetic field in the internal space. For example, a superconducting magnet or the like is used as the static magnetic field magnet 101. The static magnetic field magnet 101 may be configured in an open type.

  The gradient magnetic field coil 103 is a coil formed in a hollow cylindrical shape. The gradient magnetic field coil 103 is disposed inside the static magnetic field magnet 101. The gradient coil 103 is formed by combining three coils corresponding to X, Y, and Z axes orthogonal to one another. The Z-axis direction is assumed to be the same as the direction of the static magnetic field. The Y-axis direction is a vertical direction, and the X-axis direction is a direction perpendicular to the Z-axis and the Y-axis. The three coils in the gradient magnetic field coil 103 receive power supply individually from the gradient magnetic field power supply 105 to generate a gradient magnetic field whose magnetic field intensity changes along the X, Y, Z axes.

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

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

  The bed 107 is a device provided with a top 107 a on which the subject P is placed. The bed 107 inserts the top plate 107 a 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, for example, in an examination room in which the present MRI apparatus 100 is installed so that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 101.

  The bed control circuit 109 is a circuit that controls the bed 107, and moves the top plate 107a in the longitudinal direction and the up-down direction by driving the bed 107 in accordance with an instruction from the operator via the interface 123. The bed control circuit 109 is an example of implementation means of the bed control unit.

  The transmission circuit 113 supplies a high frequency pulse (RF (Radio Frequency) pulse) corresponding to the Larmor frequency or the like to the transmission coil 115 under the control of the imaging control circuit 121. The transmission circuit 113 is an example of an implementation unit of the transmission unit.

  The transmission coil 115 is an RF coil disposed inside the gradient coil 103. The transmission coil 115 receives supply of the RF pulse from the transmission circuit 113 and generates a transmission RF wave corresponding to a high frequency magnetic field. The transmission coil is, for example, a whole body coil (whole body coil: WB coil). The WB coil may be used as a transmit and receive coil.

  The receiving coil 117 is an RF coil disposed inside the gradient coil 103. The receiving coil 117 receives the MR signal emitted from the subject P by the high frequency magnetic field. The receiving coil 117 outputs the received MR signal to the receiving circuit 119. The receiving coil 117 is, for example, a coil array having one or more, typically a plurality of coil elements. Although the transmission coil 115 and the reception coil 117 are described as separate RF coils in FIG. 1, the transmission coil 115 and the reception coil 117 may be implemented as an integrated transmission / reception coil. The transmission / reception coil corresponds to the imaging target of the subject P, and is, for example, a local transmission / reception RF coil such as a head coil.

  Under the control of the imaging control circuit 121, the receiving circuit 119 generates a digital MR signal, which is digitized complex data, based on the MR signal output from the receiving coil 117. Specifically, the receiving circuit 119 subjects the MR signal output from the receiving coil 117 to various signal processing, and then performs analog / digital (A / D (Analog (Analog to Digital)) perform the conversion. The receiving circuit 119 samples (samples) A / D converted data. Thereby, a digital MR signal (hereinafter referred to as MR data) is generated. The receiving circuit 119 outputs the generated MR data to the imaging control circuit 121. The receiving circuit 119 is an example of implementation means of the receiving unit.

  The imaging control circuit 121 controls the gradient magnetic field power supply 105, the transmitting circuit 113, the receiving circuit 119, and the like in accordance with the imaging protocol output from the processing circuit 129, and performs imaging on the subject P. The imaging protocol has various pulse sequences depending on the examination. In the imaging protocol, a gradient magnetic field waveform indicating the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing when the current is supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, and transmission by the transmission circuit 113 The magnitude of the RF pulse supplied to the coil 115, the timing when the transmission circuit 113 supplies the RF pulse to the transmission coil 115, the timing when the MR signal is received by the reception coil 117, and the like are defined. The imaging control circuit 121 is an example of an implementation unit of the imaging control unit.

  The interface 123 has a circuit that receives various instructions and information input from the operator. The interface 123 includes, for example, a circuit related to a pointing device such as a mouse or an input device such as a keyboard. The circuit included in the interface 123 is not limited to the circuit related to physical operation parts such as a mouse and a keyboard. For example, the interface 123 receives an electrical signal corresponding to an input operation from an external input device provided separately from the MRI apparatus 100, and processes the electrical signal to output the received electrical signal to various circuits. It may have a circuit.

  The display 125 displays various MR images generated by the image generation function and various information related to imaging and image processing under the control of the system control function 129 a of the processing circuit 129. The display 125 is, for example, a display device such as a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display, monitor or the like known in the art.

  The storage device 127 stores MR data filled in the k space via the image generation function 129b, image data generated by the image generation function 129b, and the like. The storage device 127 stores various imaging protocols, imaging conditions including a plurality of imaging parameters that define the imaging protocol, and the like. The storage device 127 stores programs corresponding to various functions executed by the processing circuit 129. The storage device 127 is, for example, a random access memory (RAM), a semiconductor memory device such as a flash memory, a hard disk drive, a solid state drive, an optical disk, or the like. In addition, the storage device 127 may be a drive device or the like that reads and writes various information from and to a portable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory. The storage device 127 is an example of an implementation unit of the storage unit.

  The processing circuit 129 includes, 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 100. The processing circuit 129 has a system control function 129a and an image generation function 129b. The various functions performed by the system control function 129 a and the image generation function 129 b are stored in the storage device 127 in the form of a computer-executable program. The processing circuit 129 is a processor that reads out programs corresponding to these various functions from the storage device 127 and executes the programs to realize the functions corresponding to the respective programs. In other words, the processing circuit 129 in the state of reading out each program has a plurality of functions and the like shown in the processing circuit 129 of FIG. The processing circuit 129 is an example of an implementation unit of the processing unit.

  Although FIG. 1 describes that these various functions are realized by a single processing circuit 129, a plurality of independent processors are combined to form the processing circuit 129, and each processor executes a program. The function may be 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 be

  The word “processor” used in the above description may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple logic circuit). Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), Field Programmable Gate Arrays (FPGAs), etc. It means the road.

  The processor implements various functions by reading and executing the program stored in the storage device 127. Note that instead of storing the program in the storage device 127, the program may be directly incorporated in the circuit of the processor. In this case, the processor implements the function by reading and executing a 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 processing circuit 129 controls the MRI apparatus 100 by the system control function 129a. Specifically, the processing circuit 129 reads out the system control program stored in the storage device 127, expands it on the memory, and controls each circuit of the MRI apparatus 100 according to the expanded system control program. For example, the processing circuit 129 reads an imaging protocol from the storage device 127 by the system control function 129 a based on the imaging condition input from the operator via the interface 123. The processing circuit 129 may generate an imaging protocol based on the imaging conditions. The processing circuit 129 transmits an imaging protocol to the imaging control circuit 121 and controls imaging on the subject P. The processing circuit 129 that executes the system control function 129a is an example of an implementation unit of the system control unit.

  The processing circuit 129 fills the MR data along the readout direction of the k space according to the strength of the readout gradient magnetic field by the image generation function 129 b. The processing circuit 129 generates an MR image by performing Fourier transform on the MR data filled in the k space. The processing circuit 129 outputs the MR image to the display 125 or the storage device 127. The processing circuit 129 that executes the image generation function 129 b is an example of an implementation unit of the image generation unit.

  The above is the description of the overall configuration of the MRI apparatus 100 according to an embodiment. Next, the configuration of the gradient magnetic field power supply 105 will be described in detail with reference to FIG.

  FIG. 2 is a diagram showing a configuration of a gradient magnetic field power supply and the like in one embodiment. For example, as shown in FIG. 2, the gradient power supply 105 in one embodiment includes an internal power supply unit 10 and an amplifier 20. The internal power supply unit 10 includes a power supply 11, a measuring instrument 12, and a power control circuit 13. The amplifier 20 includes a capacitor bank for X-axis gradient magnetic field coils (hereinafter referred to as X-axis capacitor bank) 21x, a capacitor bank for Y-axis gradient magnetic field coils (hereinafter referred to as Y-axis capacitor bank) 21y, and a Z-axis gradient magnetic field. Capacitor bank for coil (hereinafter referred to as Z-axis capacitor bank) 21z, amplifier for X-axis gradient magnetic field coil (hereinafter referred to as X-axis amplifier) 22x, amplifier for Y-axis gradient magnetic field coil (hereinafter referred to as Y-axis amplifier) And a Z-axis gradient magnetic field coil amplifier (hereinafter referred to as a Z-axis amplifier) 22z.

  The power supply 11 is a device having a role of a power supply for supplying energy to each of the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z. Under the control of the power control circuit 13, the power supply 11 supplies the first current, the second current, and the third current to the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z. Supply each one. The power supply unit 11 is configured by, for example, an AC / DC converter (not shown), a full bridge circuit, and a pulse width modulation (PWM) control circuit. The AC / DC converter rectifies alternating current output from an alternating current power supply. The full bridge circuit supplies power to the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z, respectively. The PWM control circuit controls the plurality of switching elements in each of the plurality of full bridge circuits using the correction amount received from the power control circuit 13 as a drive signal.

  The power supply 11 is, for example, a DC power supply having a CV (Constant Voltage) / CC (Constant Current) characteristic. In the case of a DC power supply having CV / CC characteristics, the power supply 11 functions as a constant current source when the load at the rear stage is large, and functions as a constant voltage source when the load at the rear stage is small. However, in the situation described in the following embodiment, the power supply 11 functions as a constant current source because the load on the subsequent stage is large.

  The measuring instrument 12 is a measuring instrument that measures the current supplied to each of the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z and the voltage corresponding to the current. The measuring instrument 12 has a first voltage corresponding to the first current supplied to the X-axis amplifier 22x, a second voltage corresponding to the second current supplied to the Y-axis amplifier 22y, and a Z-axis amplifier The third voltage corresponding to the third current supplied to 22z is measured respectively.

  Specifically, the measuring instrument 12 has an X-axis measuring instrument 12x, a Y-axis measuring instrument 12y, and a Z-axis measuring instrument 12z. The X-axis measuring instrument 12x measures a first current supplied to the X-axis amplifier 22x and a first voltage corresponding to the first current. The Y-axis measuring instrument 12y measures a second current supplied to the Y-axis amplifier 22y and a second voltage corresponding to the second current. The Z-axis measuring instrument 12z measures a third current supplied to the Z-axis amplifier 22z and a third voltage corresponding to the third current. The X-axis measuring instrument 12x, the Y-axis measuring instrument 12y, and the Z-axis measuring instrument 12z output the values of the measured current and voltage to the power control circuit 13.

  The power control circuit 13 has a processor (not shown), a memory such as a ROM or a RAM, and the like as hardware resources, and controls the power supply unit 11. The power control circuit 13 receives the values of the measured current and voltage from the X-axis meter 12x, the Y-axis meter 12y, and the Z-axis meter 12z. The power control circuit 13 uses the received current and voltage values to calculate the ratio of the amount of current output from the power supply 11 to the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z (hereinafter referred to as the current ratio). (Hereinafter referred to as current ratio control function). The current ratio is the ratio of the target current to the total amount of current supplied by the power supply 11 (hereinafter referred to as the total current amount). In other words, the power control circuit 13 uses the current ratio control function to use the first voltage, the second voltage, and the third voltage measured by the measuring instrument 12 to set the X-axis amplifier 22x, the Y-axis. The first current supplied to the amplifier 22y and the Z-axis amplifier 22z, the second current, and the third current are controlled.

  The current ratio control function is stored in the memory (or storage device 127) in the form of a computer-executable program. The power control circuit 13 is a processor that realizes a current ratio control function by reading a program corresponding to the current ratio control function from a memory or the like and executing the program. The power control circuit 13 is an example of an implementation means of the power control unit.

  Generally speaking, the power control circuit 13 compares the measured voltage with the threshold voltage to determine whether charging of the X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z is completed. Determine The power control circuit 13 determines the current ratio corresponding to the combination of the aforementioned determination results. The power control circuit 13 controls the full bridge circuit in the power supply unit 11 using feedback control such as PI (Proportional Integral) control or PID (Proportional Integral Differential) control for the current amount according to the current ratio. Determine the amount of correction to The power control circuit 13 controls the power supply 11 using the determined correction amount.

  When current is preferentially supplied to the X-axis amplifier 22x, for example, the power control circuit 13 supplies a current having a current ratio of 92% to the X-axis amplifier 22x, and the Y-axis amplifier 22y and the Z-axis amplifier 22z. Supply a current ratio of 4% to each. The current supplied to the Y-axis amplifier 22y and the Z-axis amplifier 22z (here, a current ratio of 4%) is a current for operating the amplifier itself (hereinafter referred to as an idling current). It is set to an appropriate amount of current.

  The X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z are connected between the power supply 11 and the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z. The X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z supply power to the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z together with the power supply 11. That is, the X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z are capacitors serving as batteries that bear power supply that can not be compensated by the power supply device 11. Specifically, the X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z temporarily store the power flowing in from the power supply 11, and the stored power may be X as necessary. It outputs to the axis amplifier 22x, the Y axis amplifier 22y, and the Z axis amplifier 22z.

  Here, the roles of the X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z are as follows. For example, when it is necessary to flow a large current to all of the X-axis gradient magnetic field coil 103x, the Y-axis gradient magnetic field coil 103y, and the Z-axis gradient magnetic field coil 103z in a short time, the power supply 11 temporarily supplies The required power supply may exceed the available power. Even in such a case, by storing power in the X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z, the gradient magnetic field power supply 105 is configured to have the X-axis gradient coil 103x, the Y-axis gradient. Stable power can be supplied to the magnetic field coil 103y and the Z-axis gradient magnetic field coil 103z.

  The X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z amplify the gradient magnetic field waveform into a large current pulse. The X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z output the amplified large current pulse to the gradient coil 103.

  As described above, the gradient magnetic field power supply 105 supplies the current necessary for imaging to the gradient magnetic field coil 103. The gradient magnetic field power supply 105 will be described in more detail below.

  FIG. 3 is a diagram showing a circuit configuration of a gradient magnetic field power supply according to an embodiment. FIG. 3 shows the configuration of the X-axis gradient magnetic field coil 103x, and the configuration of the Y-axis gradient magnetic field coil 103y and the configuration of the Z-axis gradient magnetic field coil 103z are omitted to simplify the description. For example, as shown in FIG. 3, the gradient magnetic field power source 105 corresponding to the X axis gradient magnetic field coil 103x includes a power supply 11, an X axis measuring instrument 12x, a power control circuit 13, and an X axis capacitor bank 21x. And an X-axis amplifier 22x.

  The X-axis measuring instrument 12x measures the value of the current output from the power supply 11 to the X-axis amplifier 22x and the value of the voltage corresponding to the current. For example, the X-axis measuring instrument 12x includes a voltmeter 12xa and an ammeter 12xb. The voltmeter 12xa measures the value of the voltage. The voltmeter 12xa outputs the measured voltage value to the power control circuit 13. The ammeter 12xb measures the value of the current. The ammeter 12xb outputs the measured current value to the power control circuit 13.

The power control circuit 13 receives the value of the voltage _{(V OUT_X)} values and current _{(I OUT_X)} from the X-axis instrument 12x. The power control circuit 13 controls the power supply 11 by software control described later using the value of the voltage and the value of the current.

  The X-axis capacitor bank 21x is provided between the power supply 11 and the X-axis amplifier 22x. The X-axis capacitor bank 21 x is connected in parallel to the output from the power supply 11. The X-axis capacitor bank 21 x supplies power to the gradient coil 103 together with the power supply 11.

  The X-axis amplifier 22x amplifies the gradient magnetic field waveform received from the imaging control circuit 121 into a large current pulse. The X-axis amplifier 22x outputs the amplified large current pulse to the X-axis gradient coil 103x. The power supply voltage applied to the X-axis amplifier 22 x is a DC voltage generated by the power supply 11.

  FIG. 4 is a diagram showing the software configuration associated with the power control circuit 13 in one embodiment. For example, as shown in FIG. 4, the power control circuit 13 in one embodiment performs the first comparison function 210 x, the second comparison function 210 y, and the third comparison function in order to realize the current ratio control function. 210z, a decision function 220, and a feedback control function 230.

The memory of the power control circuit 13 includes a look-up table (LUT) in which values generated by the comparison function are associated with the current ratio, a threshold voltage (V _th ), and a reference voltage (V _ref ). Remember. The threshold voltage is set lower than the reference voltage in consideration of ripple noise. The LUT will be described in detail later.

  The various functions performed in the first comparison function 210x, the second comparison function 210y, the third comparison function 210z, the determination function 220, and the feedback control function 230 are power control circuits in the form of computer-executable programs. 13 is stored in the memory (or storage device 127). The power control circuit 13 is a processor that reads out programs corresponding to these various functions from the memory and executes the programs to realize the functions corresponding to the respective programs. In other words, the power control circuit 13 in the state where each program is read has a plurality of functions and the like shown in the power control circuit 13 of FIG.

  Although FIG. 4 is described on the assumption that these various functions are realized by a single power control circuit 13, a plurality of independent processors are combined to form the power control circuit 13, and each processor executes a program. It does not matter if the function is realized by doing this. In other words, each function described above may be configured as a program, and one processing circuit may execute each program, or a specific function may be implemented in a dedicated independent program execution circuit. May be

The power control circuit 13 receives the first voltage (V out — _x ) from the X-axis measuring instrument 12 x by the first comparison function 210 x. The power control circuit 13 generates a first comparison result (V _x ) by comparing the first voltage with the threshold voltage. The first comparison result is, for example, a signal whose truth value corresponds to 1 (V _x = 1) when the first voltage is equal to or higher than the threshold voltage, and the truth value when the first voltage is lower than the threshold voltage. Is a signal corresponding to 0 (V _x = 0). Note that “the first voltage is equal to or higher than the threshold voltage” corresponds to “a state where charging of the X-axis capacitor bank 21x is completed (charging completion mode)”, and “first voltage is lower than the threshold voltage” is This corresponds to "a state in which charging of the X-axis capacitor bank 21x is required (charging mode)". The power control circuit 13 that executes the first comparison function 210x is an example of an implementation means of the first comparison unit.

The power control circuit 13 receives the second voltage (V out — _y ) from the Y-axis measuring instrument 12 y by the second comparison function 210 y. The power control circuit 13 generates a second comparison result (V _y ) by comparing the second voltage with the threshold voltage. The second comparison result is, for example, a signal whose truth value corresponds to 1 (V _y = 1) when the second voltage is greater than or equal to the threshold voltage, and a truth value when the second voltage is less than the threshold voltage. Is a signal corresponding to 0 (V _y = 0). Note that "the second voltage is equal to or higher than the threshold voltage" corresponds to "the state where the charging of the Y-axis capacitor bank 21y is completed (charging completion mode)", and "the second voltage is lower than the threshold voltage" This corresponds to "a state where charging of the Y-axis capacitor bank 21y is required (charging mode)". The power control circuit 13 that executes the second comparison function 210y is an example of an implementation means of the second comparison unit.

The power control circuit 13 receives the third voltage (V out — _z ) from the Z-axis measuring instrument 12 z by the third comparison function 210 z. The power control circuit 13 generates a third comparison result (V _z ) by comparing the third voltage with the threshold voltage. The third comparison result is, for example, a signal whose truth value corresponds to 1 (V _z = 1) when the third voltage is greater than or equal to the threshold voltage, and a truth value when the third voltage is less than the threshold voltage. Is a signal corresponding to 0 (V _z = 0). “The third voltage is equal to or higher than the threshold voltage” corresponds to “a state where charging of the Z-axis capacitor bank 21 z is completed (charging completion mode)”, and “third voltage is lower than the threshold voltage” is This corresponds to "a state in which charging of the Z-axis capacitor bank 21z is required (charging mode)". The power control circuit 13 that executes the third comparison function 210z is an example of an implementation means of the third comparison unit.

The power control circuit 13 determines the current ratio based on the combination of the first comparison result, the second comparison result, the third comparison result, and the LUT by the determination function 220. The power control circuit 13 generates three target currents (I _{limit — x} , I _{limit — y} and I _{limit — z} ) according to the determined current ratio. The power control circuit 13 which executes the determination function 220 is an example of an implementation means of the determination unit.

  The LUT is a correspondence table that associates the first combination with the second combination. The first combination is three output values (signals corresponding to each truth value) generated by the first comparison function 210x, the second comparison function 210y, and the third comparison function 210z. The second combination includes a first ratio of the first current to the sum of the first current, the second current, and the third current output from the power supply 11, and a second ratio of the second current to the sum. It is a combination of two ratios and a third ratio of the third current to the sum. Note that, as an alternative to the LUT, the memory includes the comparison result by the comparison unit (the first comparison unit, the second comparison unit, and the third comparison unit), and for each of the plurality of amplifiers corresponding to the plurality of gradient magnetic field coils. Correspondence information may be stored that associates the ratio of the supplied current to the sum of the currents supplied to the plurality of amplifiers.

The power control circuit 13 uses the feedback control function 230 to use the three target currents (I _{limit — x} , I _{limit — y} and I _{limit — z} ) to generate the first current and the second current output from the power supply 11. , Feedback control is performed on the third current. The power control circuit 13 which executes the feedback control function 230 is an example of an implementation means of the feedback control unit.

  The feedback control function 230 includes a first PID control function 231x, a second PID control function 231y, a third PID control function 231z, a fourth comparison function 232x, a fifth comparison function 232y, and a fifth comparison function 232y. It has the comparison function 232z of 6, the fourth PID control function 233x, the fifth PID control function 233y, and the sixth PID control function 233z.

  Hereinafter, feedback processing on the output to the X-axis amplifier 22x (X-axis feedback processing), feedback processing on the output to the Y-axis amplifier 22y (Y-axis feedback processing), and output to the Z-axis amplifier 22z in the power supply 11 Feedback processing (Z-axis feedback processing) will be described.

(X-axis feedback processing)
The power control circuit 13 receives the first voltage (V out — _x ) from the X-axis measuring instrument 12 x by the first PID control function 231 x. The power control circuit 13 performs feedback control on the first voltage using the reference voltage and the first voltage. The power control circuit 13 generates a first correction current (I _{ref — x} ) as a result of feedback control.

The power control circuit 13 generates a first reference current (i _{ref — x} ) by comparing the first correction current with the first target current (I _{limit — x} ) by the fourth comparison function 232 x. The first reference current is, for example, the first correction current (ie, i _ref — _x = I _ref — _x fourth PID control function 233 x) when the first correction current is equal to or less than the first target current, and the first reference current is If the correction current is larger than the first target current, the first target current (i.e., i _ref — _x = I _limit — _x ) is obtained.

The power control circuit 13 receives the first current (I out — _x ) from the X-axis measuring instrument 12 x by the fourth PID control function 233 x. The power control circuit 13 performs feedback control on the first current using the first reference current and the first current. The power control circuit 13 generates a first correction amount for controlling the full bridge circuit as a result of feedback control. The first correction amount is, for example, a drive signal to each of the plurality of switching elements in the full bridge circuit for supplying power to the X-axis amplifier 22x.

(Y-axis feedback processing)
The power control circuit 13 receives a second voltage (V out — _y ) from the Y-axis measuring instrument 12 y as a second PID control function 231 y. The power control circuit 13 performs feedback control on the second voltage using the reference voltage and the second voltage. The power control circuit 13 generates a second correction current (I _{ref — y} ) as a result of feedback control.

The power control circuit 13 generates a second reference current (i _{ref — y} ) by comparing the second correction current with the second target current (I _{limit — y} ) as the fifth comparison function 232 y. The second reference current is, for example, the second correction current (ie, i _ref — _y = I _ref — _y ) when the second correction current is less than or equal to the second target current, and the second correction current is the second target If it is larger than the current, the second target current (i.e., i _ref — _y = I _limit — _y ) is obtained.

The power control circuit 13 receives the second current (I out — _y ) from the Y-axis measuring instrument 12 y by the fifth PID control function 233 y. The power control circuit 13 performs feedback control on the second current using the second reference current and the second current. The power control circuit 13 generates a second correction amount for controlling the full bridge circuit as a result of feedback control. The second correction amount is, for example, a drive signal to each of the plurality of switching elements in the full bridge circuit for supplying power to the Y-axis amplifier 22y.

(Z-axis feedback processing)
The power control circuit 13 receives the third voltage (V out — _z ) from the Z-axis measuring instrument 12 z as the third PID control function 231 z. The power control circuit 13 performs feedback control on the third voltage using the reference voltage and the third voltage. The power control circuit 13 generates a third correction current (I _{ref — z} ) as a result of feedback control.

The power control circuit 13 generates a third reference current (i _{ref — z} ) by comparing the third correction current with the third target current (I _{limit — z} ) as the sixth comparison function 232 z. The third reference current is, for example, the third correction current (that is, i _ref — _z = I _ref — _z ) when the third correction current is less than or equal to the third target current, and the third correction current is the third target If it is larger than the current, the third target current (i.e., i _ref — _z = I _limit — _z ) is obtained.

The power control circuit 13 receives the third current (I out — _z ) from the Z-axis measuring instrument 12 z by the sixth PID control function 233 z. The power control circuit 13 performs feedback control on the third current using the third reference current and the third current. The power control circuit 13 generates a third correction amount for controlling the full bridge circuit as a result of feedback control. The third correction amount is, for example, a drive signal to each of the plurality of switching elements in the full bridge circuit for supplying power to the Z-axis amplifier 22z.

  The power supply 11 controls the full bridge circuit corresponding to the X-axis amplifier 22x by using the first correction amount by the PWM control circuit. Further, the power supply device 11 controls the full bridge circuit corresponding to the Y-axis amplifier 22y by using the second correction amount by the PWM control circuit. Furthermore, the power supply device 11 controls the full bridge circuit corresponding to the Z-axis amplifier 22z using the third correction amount by the PWM control circuit. The power supply 11 supplies current to the X-axis amplifier 22x, the Y-axis amplifier 22y, and the Z-axis amplifier 22z, respectively, under the control described above.

  FIG. 5 is a flowchart illustrating the process performed by the power control circuit in one embodiment. Hereinafter, processing of the current ratio control function by the power control circuit 13 will be described.

  First, the magnetic resonance imaging apparatus 100 reads an imaging protocol from the storage device 127 based on an imaging condition input from the operator by the system control function 129a. The magnetic resonance imaging apparatus 100 transmits an imaging protocol to the imaging control circuit 121 and controls imaging of the subject P. At this time, the power control circuit 13 of the gradient magnetic field power source 105 starts the operation of step S501 simultaneously with the start of imaging of the subject P.

(Step S501)
The power control circuit 13 acquires the value of the first voltage (V out _{_ x} ) from the X-axis measuring instrument 12 x, and acquires the value of the second voltage (V out _{_ y} ) from the Y-axis measuring instrument 12 y. Obtain the value of the third voltage (V out — _z ) from _12z .

(Step S502)
The power control circuit 13 determines whether or not a value is inputted to the first comparison result (V _x ) (V _x = null?). If no value is input to V _x , the process proceeds to step S 503. If a value is input to V _x , the process proceeds to step S507.

(Step S503)
The power control circuit 13 substitutes x into the variable j, and the process proceeds to step S504. This assignment, during the subsequent step S504～S506, the power control circuit 13 _performs processing as _V out_j ₌ V out_x and _V j = _{V x.}

(Step S504)
The power control circuit 13 determines whether the first voltage (V out — _x ) is equal to or higher than the threshold voltage (V _th ) by the first comparison function 210 x. If the first voltage is equal to or higher than the threshold voltage, the process proceeds to step S505. If the first voltage is less than the threshold voltage, the process proceeds to step S506.

When y is substituted for the variable j, the power control circuit 13 determines whether the second voltage (V out — _y ) is equal to or higher than the threshold voltage (V _th ) by the second comparison function 210 y. If the second voltage is equal to or higher than the threshold voltage, the process proceeds to step S505. If the second voltage is less than the threshold voltage, the process proceeds to step S506.

When z is substituted for the variable j, the power control circuit 13 determines whether or not the third voltage (V out — _z ) is equal to or higher than the threshold voltage (V _th ) by the third comparison function 210 z. If the third voltage is equal to or higher than the threshold voltage, the process proceeds to step S505. If the third voltage is less than the threshold voltage, the process proceeds to step S506.

(Step S505)
Since the first voltage is equal to or higher than the threshold voltage, the power control circuit 13 generates the first comparison result (V _x ) as “1”.

When y is substituted for the variable j, the second voltage is equal to or higher than the threshold voltage, and the power control circuit 13 generates the second comparison result (V _y ) as “1”.

When z is substituted into the variable j, the third voltage is equal to or higher than the threshold voltage, and the power control circuit 13 generates the third comparison result (V _z ) as “1”. After step S505, the process returns to step S502.

(Step S506)
Since the first voltage is less than the threshold voltage, the power control circuit 13 generates the first comparison result (V _x ) as “0”.

When y is substituted for the variable j, the second voltage is less than the threshold voltage, and the power control circuit 13 generates the second comparison result (V _y ) as “0”.

When z is substituted into the variable j, the power control circuit 13 generates the third comparison result (V _z ) as “0” because the third voltage is less than the threshold voltage. After step S506, the process returns to step S502.

(Step S507)
The power control circuit 13 determines whether a value is input to the second comparison result (V _y ) (V _y = null?). If a value is not input to V _y , the process proceeds to step S508. If a value is input to V _y , the process proceeds to step S509.

(Step S508)
The power control circuit 13 substitutes y for the variable j, and the process proceeds to step S504. This assignment, during the subsequent step S504～S506, the power control circuit _{13, V out_j =} V _{out_y,} the process as V j = _{V y} performed.

(Step S509)
The power control circuit 13 determines whether a value is input to the third comparison result (V _z ) (V _z = null?). If no value is input to V _z , the process proceeds to step S510. _If a value is input to Vz, the process proceeds to step S511.

(Step S510)
The power control circuit 13 substitutes z into the variable j, and the process proceeds to step S504. This assignment, during the subsequent step S504～S506, the power control circuit _{13, V out_j =} V _{out_z,} the process as V j = _{V z} performed.

(Step S511)
The power control circuit 13 outputs an output corresponding to the first combination of the first comparison result (V _x ), the second comparison result (V _y ), and the third comparison result (V _z ) by the determination function 220. _Read the mode (I _{limit — x} , I _{limit — y} and I _{limit — z} ) from the LUT.

After step S511, the values of the first comparison result (V _x ), the second comparison result (V _y ), and the third comparison result (V _z ) are reset, and the process ends. "The value of the first comparison result is reset" corresponds to "V _x = null", and "the value of the second comparison result is reset" corresponds to "V _y = null", “The value of the third comparison result is reset” corresponds to “V _z = null”. The above processing is repeatedly performed until all of the X-axis capacitor bank 21x, the Y-axis capacitor bank 21y, and the Z-axis capacitor bank 21z are in the charge completion mode.

The processes from step S502 to step S510 may be performed in parallel. Step S511 is executed by the determination function 220 when the first combination of the first comparison result (V _x ), the second comparison result (V _y ), and the third comparison result (V _z ) is completed. Processing is performed.

FIG. 6 is a diagram showing a LUT in one embodiment. For example, as shown in FIG. 6, in the LUT 600 according to an embodiment, the first combination of V _x , V _y and V _z corresponds to the second combination of I _{limit — x} , I _{limit — y} and I _{limit — z} . It is attached. The first combination is three output values (signals corresponding to the truth values) generated by the first comparison function 210x, the second comparison function 210y, and the third comparison function 210z. The second combination is the first ratio of the first current to the sum (total current amount) of the first current, the second current, and the third current output from the power supply 11, and the first to the transmission flow rate. The second ratio of the current of 2 and the third ratio of the third current to the transmission flow rate are each represented by an integer percentage (%).

Since the combination 601 is (V _x , V _y , V _z ) = (1, 1, 1), the X axis capacitor bank 21 x, the Y axis capacitor bank 21 y, and the Z axis capacitor bank 21 z are all in the charge completion mode. It means that there is. Since the combination 602 corresponding to the combination 601 is (I _{limit — x} , I _{limit — y} , I _limit — _z ) = (33, ₃₃ , ₃₃ ), the X axis capacitor bank 21 x, the Y axis capacitor bank 21 y, and the Z axis capacitor bank 21 z It means that current amounts substantially equal to each other are allocated.

Since the combination 603 is (V _x , V _y , V _z ) = (1, 1, 0), this means that the X axis capacitor bank 21 x and the Y axis capacitor bank 21 y are in the charge completion mode, and the Z axis It means that the capacitor bank 21z is in the charge mode. The combination 604 corresponding to the combination 603 is (I _{limit — x} , I _{limit — y} , I _limit — _z ) = (4, 4, 92), which means that the current amount is preferentially allocated to the Z-axis capacitor bank 21 z.

The combination 605 is (V _x , V _y , V _z ) = (1, 0, 1), which means that the X axis capacitor bank 21 _x and the Z axis capacitor bank 21 z are in the charge completion mode, and the Y axis is It means that the capacitor bank 21y is in the charge mode. The combination 606 corresponding to the combination 605 is (I _{limit — x} , I _{limit — y} , I _limit — _z ) = (4, 92, 4), which means that the current amount is preferentially allocated to the Y-axis capacitor bank 21 y.

The combination 607 is (V _x , V _y , V _z ) = (1, 0, 0), which means that the X axis capacitor bank 21 x is in the charge completion mode, and the Y axis capacitor bank 21 y and the Z axis It means that the capacitor bank 21z is in the charge mode. The combination 608 corresponding to the combination 607 is (I _{limit — x} , I _{limit — y} , I _limit — _z ) = (4, 48, 48), and the current amount is preferentially given to the Y axis capacitor bank 21 y and the Z axis capacitor bank 21 z. It means to allocate.

Since the combination 609 is (V _x , V _y , V _z ) = (0, 0, 0), the X axis capacitor bank 21 x, the Y axis capacitor bank 21 y, and the Z axis capacitor bank 21 z are all in the charge mode. It means that. Since the combination 610 corresponding to the combination 609 is (I _{limit — x} , I _{limit — y} , I _limit — _z ) = (33, ₃₃ , ₃₃ ), the X axis capacitor bank 21 x, the Y axis capacitor bank 21 y, and the Z axis capacitor bank 21 z It means that current amounts substantially equal to each other are allocated.

  As described above, the magnetic resonance imaging apparatus 100 according to an embodiment includes a plurality of gradient magnetic field coils that receive power supply to generate gradient magnetic fields of multiple axes, and a gradient magnetic field power supply that supplies power. The gradient magnetic field power supply includes a plurality of amplifiers respectively connected to the plurality of gradient magnetic field coils, a power supply supplying current to the plurality of amplifiers, a measuring instrument measuring the voltage applied to the plurality of amplifiers, and a voltage And a power control circuit for controlling the current supplied from the power supply to the amplifier. The power control circuit compares a voltage applied to the plurality of amplifiers with a threshold voltage, a comparison result by the comparison unit, and current supplied to each of the plurality of amplifiers corresponding to the plurality of gradient magnetic field coils. And a memory having corresponding information for correlating the ratio to the sum of currents supplied to the plurality of amplifiers. Thus, the magnetic resonance imaging apparatus 100 can control the allocation of the output current from the power supply using software.

  Further, the magnetic resonance imaging apparatus 100 according to the present embodiment includes an X-axis gradient magnetic field coil, a Y-axis gradient magnetic field coil, a Z-axis gradient magnetic field coil, and a gradient magnetic field power supply. The gradient magnetic field power supply has a power supply, a measuring instrument, and a power control circuit. The power supply includes three amplifiers connected respectively to the X-axis gradient coil, the Y-axis gradient coil, and the Z-axis gradient coil, the first current, the second current, and the third current. Supply current and respectively. The measuring device measures a first voltage corresponding to the first current, a second voltage corresponding to the second current, and a third voltage corresponding to the third current. The power control circuit controls the first current, the second current, and the third current using the first voltage, the second voltage, and the third voltage. The power control circuit includes a first comparison unit, a second comparison unit, a third comparison unit, a memory, and a determination unit. The first comparing unit generates a first comparison result by comparing the first voltage with the threshold voltage. The second comparing unit generates a second comparison result by comparing the second voltage with the threshold voltage. The third comparing unit generates a third comparison result by comparing the third voltage with the threshold voltage. The memory includes a first combination of three comparison results generated by the first comparison unit, the second comparison unit, and the third comparison unit, a first current, a second current, and a third, respectively. A look-up table in which the first ratio of the first current to the sum of the currents, the second ratio of the second current to the sum, and the second combination of the third ratio of the third current to the sum are associated Remember. The determination unit determines a second combination based on the combination of the first comparison result, the second comparison result, and the third comparison result, and the lookup table. The power control circuit controls the power supply according to the determined second combination. Thus, the magnetic resonance imaging apparatus 100 can control the allocation of the output current from the power supply using software.

  In addition, the magnetic resonance imaging apparatus 100 performs feedback control on the first current, the second current, and the third current using the determined second combination in the power control circuit. And a feedback control unit. Thus, the magnetic resonance imaging apparatus 100 can control the allocation of the output current from the power supply using software.

  According to at least one embodiment described above, the distribution of the output current from the power supply can be controlled using software.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various 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 invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

12 measuring instrument 100 magnetic resonance imaging apparatus 101 static magnetic field magnet 103 gradient magnetic field coil 105 gradient magnetic field power source 107 bed 115 transmitting coil 117 receiving coil 210 x first comparison function 210 y second comparison function 210 z third comparison function 230 feedback control function 232x fourth comparison function 232y fifth comparison function 232z sixth comparison function 600 LUT

Claims (3)

A plurality of gradient magnetic field coils receiving power supply to generate gradient magnetic fields of multiple axes;
A gradient magnetic field power supply for supplying the power;
The gradient magnetic field power supply is
A plurality of amplifiers respectively connected to the plurality of gradient magnetic field coils;
A power supply for supplying current to the plurality of amplifiers;
A measuring device for measuring a voltage applied to the amplifier;
And power control circuit for controlling the current supplied from the power supply to the amplifier based on the voltage.
The power control circuit
A comparison unit that compares a voltage applied to the amplifier with a threshold voltage;
A memory having correspondence information that associates the comparison result by the comparison unit with the ratio of the current supplied to each of the plurality of amplifiers corresponding to the plurality of gradient magnetic field coils to the sum of the currents supplied to the plurality of amplifiers When,
Magnetic resonance imaging device equipped with An X-axis gradient magnetic field coil, a Y-axis gradient magnetic field coil, a Z-axis gradient magnetic field coil, and a gradient magnetic field power supply,
The gradient magnetic field power supply is
The first current, the second current, and the third current to three amplifiers respectively connected to the X-axis gradient coil, the Y-axis gradient coil, and the Z-axis gradient coil. A power supply for supplying
A measuring instrument that measures a first voltage corresponding to the first current, a second voltage corresponding to the second current, and a third voltage corresponding to the third current;
Power control circuit for controlling the first current, the second current, and the third current using the first voltage, the second voltage, and the third voltage Have and
The power control circuit
A first comparison unit that generates a first comparison result by comparing the first voltage with a threshold voltage;
A second comparison unit that generates a second comparison result by comparing the second voltage with the threshold voltage;
A third comparison unit that generates a third comparison result by comparing the third voltage with the threshold voltage;
A first combination of three comparison results respectively generated by the first comparing unit, the second comparing unit, and the third comparing unit, the first current, the second current, and And a second combination of a first ratio of the first current to the sum of the third currents, a second ratio of the second current to the sum, and a third ratio of the third current to the sum. A memory storing a lookup table in which
A determination unit that determines the second combination based on the combination of the first comparison result, the second comparison result, the third comparison result, and the look-up table;
The magnetic resonance imaging apparatus, wherein the power control circuit controls the power supply according to the determined second combination. The power control circuit performs feedback control on the first current, the second current, and the third current using the determined second combination. The magnetic resonance imaging apparatus according to claim 2, further comprising: