JP2014068990A - Magnetic resonance imaging apparatus and abnormality detection method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus effectively detecting miswiring and oscillation of an output current of a gradient magnetic field coil.SOLUTION: A magnetic resonance imaging apparatus comprises: an inverter circuit 51x that is connected to a direct-current voltage source; a current sensor 44x that detects a current to be supplied to an Xch coil 22x as an output of the inverter circuit 51x; a switching control circuit 52x that calculates a switching waveform on the basis of an input signal and an error signal output from the current sensor 44x, and performs pulse width modulation control of the inverter circuit 51x on the basis of the switching waveform; an Xch comparator 46x that obtains a difference between a predicted switching waveform and the actual switching waveform which is calculated by the switching control circuit 52x on the basis of the switching waveform whose duty factor is 50%, and generates an output pulse waveform; and a sequencer 30 that detects abnormality when an integral value of the output pulse waveform in a time width corresponding to a natural number multiple of a pulse interval of the predicted switching waveform is not equal to 0.

Description

  The present embodiment as one aspect of the present invention relates to a magnetic resonance imaging (MRI) apparatus including a gradient magnetic field power supply apparatus and an abnormality detection method thereof.

  An MRI apparatus measures an NMR signal (echo signal) generated by a nuclear spin that constitutes a subject, particularly a tissue of a human body, and forms the shape and function of the head, abdomen, and extremities in a two-dimensional or three-dimensional manner. It is a device that images. In imaging, the echo signal is given different phase encoding and frequency encoding depending on the gradient magnetic field. The measured echo signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  The MRI apparatus includes each gradient magnetic field coil that receives a current supply individually from the gradient magnetic field power supply device and generates a gradient magnetic field in which the magnetic field intensity changes along each of the X, Y, and Z axes. Each gradient coil is designed to have a low resistance value in order to reduce heat generation. However, if the output cable of the gradient magnetic field power supply device is not connected to an appropriate gradient magnetic field coil, the resistance value of the connecting portion of the gradient magnetic field coil rises to generate heat. This can lead to damage to the connection. Such damage is likely to occur during system installation.

  Therefore, in the conventional MRI apparatus, the abnormality is detected before the connection portion is damaged by monitoring the output current and output voltage of the gradient magnetic field amplifier.

  As a conventional technique related to the present invention, a power supply apparatus suitable for various power supplies required for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field of an MRI apparatus that requires a high voltage and a large current, and an MRI using the power supply apparatus An apparatus is disclosed (for example, refer to Patent Document 1).

International Publication No. 2007/004565

  However, in the method of monitoring the output current and output voltage of the gradient magnetic field amplifier, an abnormality can be detected only at the time of output of the gradient magnetic field amplifier. Therefore, there is a possibility that the connection portion is damaged during the time from the abnormality detection to the system stop. Further, when detecting an abnormality by monitoring the output current or output voltage, hardware for detecting an abnormality is required.

  Furthermore, if an incorrect wiring is generated inside the gradient magnetic field power supply apparatus when the MRI apparatus is installed, it takes time for the confirmation work. Accidents may occur depending on the method of confirmation work.

  Further, if the load condition changes unexpectedly or the gradient magnetic field amplifier runs away, the output current of the gradient magnetic field amplifier may oscillate, but there is no means for detecting it.

  In order to solve the above-described problem, the magnetic resonance imaging apparatus of the present embodiment has an inverter circuit connected to a DC voltage source, and an output of the inverter circuit is supplied to a gradient magnetic field coil as a load. Switching that calculates a switching waveform based on a current sensor that detects a current flowing in the magnetic field coil, an input signal and an error signal that is an output of the current sensor, and performs pulse width modulation control on the inverter circuit based on the switching waveform The difference between the control circuit, the actual switching waveform calculated by the switching control circuit based on the switching waveform with a duty ratio of 50%, and the predicted switching waveform as the switching waveform with the duty ratio of 50% is used as an output pulse waveform. Comparing means to be generated and the pulse of the predicted switching waveform Having an abnormality detecting means integral value of the output pulse waveform in the natural number multiple of the duration of the interval is abnormally detected if other than 0, the.

  In order to solve the above-described problems, the abnormality detection method for a gradient magnetic field power supply apparatus according to the present embodiment supplies an inverter circuit connected to a DC voltage source, and an output of the inverter circuit to a gradient coil that is a load. A switching waveform is calculated based on an input signal and an error signal that is an output of the current sensor, and a pulse width of the inverter circuit is calculated based on the switching waveform. An abnormality detection method for a magnetic resonance imaging apparatus, comprising: a switching control circuit that performs modulation control; an actual switching waveform calculated by the switching control circuit based on a switching waveform having a duty ratio of 50%; and the duty ratio of 50% Outputs the difference from the predicted switching waveform as the switching waveform of Generating a pulse waveform, the integral value of the output pulse waveform in the natural number multiple of the duration of the pulse interval of the prediction switching waveform is abnormal detected when non-zero.

Schematic which shows the hardware constitutions of the MRI apparatus of this embodiment. The figure which shows the structure of the gradient magnetic field power supply device with which the MRI apparatus of this embodiment is equipped. The figure which shows a structure in case the wiring between a switching control circuit and a multilevel inverter circuit (control signal line) is miswired between Xch and Ych. The figure which shows the input pulse waveform and output pulse waveform ((phi) = 0) of the Xch comparator in process (1-2) when there is no miswiring. The figure which shows the input pulse waveform and output pulse waveform ((phi) = Tx / 4) of an Xch comparator in process (1-2) when there is no miswiring. The figure which shows the input pulse waveform and output pulse waveform ((phi) = Tx / 2) of an Xch comparator in process (1-2) when there is no miswiring. The figure which shows the input pulse waveform and output pulse waveform of the Xch comparator in the process (1-2) at the time of miswiring between Xch and Ych between a switching control circuit and a multilevel inverter circuit. The figure which shows the input pulse waveform and output pulse waveform of a Ych comparator in process (1-2) at the time of miswiring between Xch and Ych between a switching control circuit and a multilevel inverter circuit. The figure which shows a structure when the wiring between a gradient magnetic field amplifier and a gradient magnetic field coil is miswired. The figure which shows the input pulse waveform and output pulse waveform of an Xch comparator in the process (2-3) at the time of miswiring between a gradient magnetic field amplifier and a gradient magnetic field coil. The figure which shows the input pulse waveform and output pulse waveform of an Xch comparator in the process (2-3) at the time of miswiring between a gradient magnetic field amplifier and a gradient magnetic field coil. The figure which shows the input pulse waveform and output pulse waveform of a comparator in the process (2-3) when the output current of a gradient magnetic field amplifier oscillates. The figure which shows the input pulse waveform and output pulse waveform of a comparator in the process (2-3) when the output current of a gradient magnetic field amplifier oscillates.

  A magnetic resonance imaging (MRI) apparatus and an abnormality detection method thereof according to this embodiment will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a hardware configuration of the MRI apparatus of the present embodiment.

  FIG. 1 shows an MRI apparatus 10 of the present embodiment that performs imaging of a subject (patient) P. The MRI apparatus 10 mainly includes an imaging system 11 and a control system 12.

  The imaging system 11 includes a static magnetic field magnet 21, a gradient magnetic field coil 22, a gradient magnetic field power supply device 23, a bed 24, a bed control unit 25, a transmission coil 26, a transmission unit 27, reception coils 28a to 28e, a reception unit 29, and a sequencer 30. Is provided.

  The static magnetic field magnet 21 is formed in a hollow cylindrical shape at the outermost part of a gantry (not shown), and generates a uniform static magnetic field in the internal space. As the static magnetic field magnet 21, for example, a permanent magnet or a superconducting magnet is used.

  The gradient magnetic field coil 22 is formed in a hollow cylindrical shape, and is disposed inside the static magnetic field magnet 21. The gradient magnetic field coil 22 is formed by combining an Xch coil 22x, a Ych coil 22y, and a Zch coil 22z (shown in FIG. 2) respectively corresponding to the X, Y, and Z axes orthogonal to each other. The three coils 22x, 22y, and 22z are individually supplied with current from a gradient magnetic field power supply device 23, which will be described later, and generate a gradient magnetic field in which the 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 coil 22 respectively correspond to, for example, the readout gradient magnetic field Gr, the phase encoding gradient magnetic field Ge, and the slice selection gradient magnetic field Gs. . The readout gradient magnetic field Gr is used to change the frequency of an NMR (nuclear magnetic resonance) signal in accordance with the spatial position. The phase encoding gradient magnetic field Ge is used to change the phase of the NMR signal in accordance with the spatial position. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section.

  The gradient magnetic field power supply device 23 supplies current to the gradient magnetic field coil 22 based on the pulse sequence execution data sent from the sequencer 30.

  FIG. 2 is a diagram illustrating a configuration of the gradient magnetic field power supply device 23 provided in the MRI apparatus 10 of the present embodiment.

  The gradient magnetic field power supply device 23 includes an AC-DC converter 41, a smoothing capacitor 42, gradient magnetic field amplifiers 43x, 43y, 43z, current sensors 44x, 44y, 44z, a conversion module 45, and comparators (comparators) 46x, 46y, 46z. Is provided. The gradient magnetic field power supply device 23 is configured to be supplied with electric power from the three-phase AC power supply S and to connect to the gradient magnetic field coil 22 that is a load to supply current.

  The AC-DC converter 41 has a function of boosting the three-phase AC voltage connected to the three-phase AC power source S to a DC voltage of, for example, 2000V.

  The smoothing capacitor 42 is connected to the output side of the AC-DC converter 41 and smoothes the DC voltage.

  The gradient magnetic field amplifiers 43x, 43y, and 43z are respectively connected to the smoothing capacitor 42 and receive a smoothed DC voltage. The gradient magnetic field amplifiers 43x, 43y, and 43z supply currents to the Xch coil 22x, the Ych coil 22y, and the Zch coil 22z, respectively.

  The gradient magnetic field amplifiers 43x, 43y, 43z are provided with multi-level inverter circuits 51x, 51y, 51z and switching control circuits 52x, 52y, 52z, respectively.

  The multilevel inverter circuits 51x, 51y, 51z are full bridge circuits respectively connected in parallel to the smoothing capacitor 42 constituting the input DC voltage source. The outputs of the multilevel inverter circuits 51x, 51y, 51z are supplied to the coils 22x, 22y, 22z, which are loads, respectively.

  The current sensors 44x, 44y, 44z detect the currents flowing through the coils 22x, 22y, 22z, respectively, when the outputs of the multilevel inverter circuits 51x, 51y, 51z are supplied to the coils 22x, 22y, 22z, respectively.

  The switching control circuits 52x, 52y, 52z receive input signals (command currents) Rx, Ry, Rz from the sequencer 30 and error signals (detected currents) Sx, Sy, Sz that are outputs of the current sensors 44x, 44y, 44z. Each is input, and the switching waveform is calculated so that the difference between them is zero. Then, the switching control circuits 52x, 52y, and 52z respectively perform pulse width modulation (PWM: pulse) on the multilevel inverter circuits 51x, 51y, and 51z via the control signal lines Lx, Ly, and Lz based on the switching waveform of each channel. width modulation).

  The conversion module 45 generates a predicted Xch predicted switching waveform, a Ych predicted switching waveform, and a Zch predicted switching waveform based on the input signals Rx, Ry, and Rz from the sequencer 30, respectively.

  The comparators 46x, 46y, and 46z have a first input connected to the control signal lines Lx, Ly, and Lz, and a second input (reference) connected to the conversion module 45, respectively. The comparators 46x, 46y, and 46z are the predicted switching waveforms of the respective channels based on the input signals Rx, Ry, and Rz to the gradient magnetic field amplifiers 43x, 43y, and 43z, and the actual respective channels from the control signal lines Lx, Ly, and Lz. Are compared (differed) with each other and output to the sequencer 30.

  Returning to the description of FIG. 1, the bed 24 includes a top 24 a on which the subject P is placed. The couch 24 inserts the couchtop 24a into the cavity (imaging port) of the gradient magnetic field coil 22 with the subject P placed under the control of the couch controller 25 described later. Usually, the bed 24 is installed such that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 21.

  The couch controller 25 drives the couch 24 under the control of the sequencer 30 to move the couchtop 24a in the longitudinal direction and the vertical direction.

  The transmission coil 26 is disposed inside the gradient magnetic field coil 22 and receives a high frequency pulse from the transmission unit 27 to generate a high frequency magnetic field.

  The transmission unit 27 transmits a high frequency pulse corresponding to the Larmor frequency to the transmission coil 26 based on the pulse sequence execution data transmitted from the sequencer 30.

  The receiving coils 28a to 28e are arranged inside the gradient magnetic field coil 22 and receive NMR signals emitted from the subject P due to the influence of the high-frequency magnetic field. Here, each of the reception coils 28a to 28e is an array coil having a plurality of element coils that respectively receive magnetic resonance signals emitted from the subject P. When the NMR signal is received by each element coil, the reception coils 28a to 28e receive The NMR signal thus output is output to the receiving unit 29.

  The receiving coil 28a is a head coil that is attached to the head of the subject P. The reception coils 28b and 28c are spinal coils disposed between the back of the subject P and the top plate 24a. The receiving coils 28d and 28e are abdominal coils that are attached to the ventral side of the subject P, respectively.

  The receiving unit 29 generates NMR signal data based on the NMR signals output from the receiving coils 28 a to 28 e based on the pulse sequence execution data sent from the sequencer 30. Further, when generating the NMR signal data, the receiving unit 29 transmits the NMR signal data to the control system 12 via the sequencer 30.

  The receiving unit 29 has a plurality of receiving channels for receiving NMR signals output from a plurality of element coils included in the receiving coils 28a to 28e. And when the element coil used for imaging is notified from the control system 12, the receiving unit 29 receives the notified element coil so that the NMR signal output from the notified element coil is received. Assign a receive channel.

  The sequencer 30 is connected to the gradient magnetic field power supply device 23, the bed control unit 25, the transmission unit 27, the reception unit 29, and the control system 12. The sequencer 30 includes a processor (not shown) such as a CPU (central processing unit) and a memory, and control information necessary for driving the gradient magnetic field power supply device 23, the bed control unit 25, the transmission unit 27, and the reception unit 29. For example, sequence information describing operation control information such as the intensity, application time, and application timing of the pulse current to be applied to the gradient magnetic field power supply device 23 is stored.

  In addition, the sequencer 30 drives the bed control unit 25 according to the stored predetermined sequence, thereby moving the table 24a forward and backward in the Z direction with respect to the gantry. Further, the sequencer 30 drives the gradient magnetic field power supply device 23, the transmission unit 27, and the reception unit 29 in accordance with the stored predetermined sequence, so that the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, and the Z-axis gradient are placed in the gantry. A magnetic field Gz and an RF signal are generated.

  The control system 12 performs overall control of the MRI apparatus 10, data collection, image reconstruction, and the like. The control system 12 includes an interface unit 31, a data collection unit 32, a data processing unit 33, a storage unit 34, a display unit 35, an input unit 36, and a control unit 37.

  The interface unit 31 is connected to the gradient magnetic field power supply device 23, the bed control unit 25, the transmission unit 27, and the reception unit 29 of the imaging system 11 through the sequencer 30, and these connected units and the control system 12 Controls input and output of signals exchanged between the two.

  The data collection unit 32 collects NMR signal data transmitted from the reception unit 29 via the interface unit 31. When collecting the NMR signal data, the data collecting unit 32 stores the collected NMR signal data in the storage unit 34.

  The data processing unit 33 performs post-processing, that is, reconstruction processing such as Fourier transform, on the NMR signal data stored in the storage unit 34, so that spectrum data or image data of the desired nuclear spin in the subject P is obtained. Is generated. Further, when the positioning image is captured, the data processing unit 33, based on the NMR signal received by each of the plurality of element coils included in the reception coils 28a to 28e, the NMR signal in the arrangement direction of the element coils. Profile data indicating the distribution is generated for each element coil. Then, the data processing unit 33 stores the generated various data in the storage unit 34.

  The storage unit 34 stores the NMR signal data collected by the data collection unit 32, the image data generated by the data processing unit 33, and the like for each subject P.

  The display unit 35 displays various information such as spectrum data or image data generated by the data processing unit 33. As the display unit 35, a display device such as a liquid crystal display can be used.

  The input unit 36 receives various operations and information inputs from the operator. As the input unit 36, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard can be used as appropriate.

  The control unit 37 has a CPU (central processing unit), a memory, and the like (not shown), and controls the MRI apparatus 10 by controlling each of the above-described units.

  Next, an abnormality detection method for the MRI apparatus 10 according to the present embodiment will be described.

(First abnormality detection method)
FIG. 3 is a diagram illustrating a configuration in a case where the wiring between the switching control circuit and the multilevel inverter circuit (control signal line) is miswired between Xch and Ych.

  As shown in FIG. 3, the control signal line Lx erroneously connects the multilevel inverter circuit 51x to the switching control circuit 52y. In addition, the control signal line Ly mistakenly connects the multilevel inverter circuit 51y to the switching control circuit 52x. On the other hand, the control signal line Lz correctly connects the multilevel inverter circuit 51z to the switching control circuit 52z.

  The first abnormality detection method is a method for confirming the wiring inside the gradient magnetic field power supply device 23 before imaging of the subject P by the MRI apparatus 10, that is, the multilevel inverter circuits 51x, 51y, and 51z perform appropriate amplifier switching. This is to confirm whether it is connected to the control circuit.

  Before imaging, a switching waveform is transmitted to the comparators 46x, 46y, and 46z in accordance with the following steps for wiring confirmation. In addition, the output of gradient magnetic field amplifier 43x, 43y, 43z can be set to 0 by making the duty ratio (duty ratio) of the switching waveform transmitted 50%.

(1-1) Non-transmission of Xch, Ych, and Zch switching waveforms (initial state)
(1-2) Transmit only Xch switching waveform (duty ratio 50%) at pulse interval Tx (1-3) Transmit only Ych switching waveform (duty ratio 50%) at pulse interval Ty (1-4) Zch at pulse interval Tz Send only switching waveform (duty ratio 50%)

  First, the input pulse waveform and the output pulse waveform of the comparator when there is no erroneous wiring will be described with reference to FIGS.

  4 to 6 are diagrams showing an input pulse waveform and an output pulse waveform of the Xch comparator 46x in the step (1-2) when there is no erroneous wiring. 4 shows the case where the phase difference φ = 0, FIG. 5 shows the case where the phase difference φ = Tx / 4, and FIG. 6 shows the case where the phase difference φ = Tx / 2.

  “In1” shown in FIGS. 4 to 6 is the first input pulse waveform of the Xch comparator 46x in the step (1-2) in the case shown in FIG. 2 where there is no miswiring, and in the step (1-2). It is an actual Xch actual switching waveform calculated by the switching control circuit 52x based on the transmitted Xch switching waveform with a duty ratio of 50%. Similarly, “In2” is the second input pulse waveform of the Xch comparator 46x in step (1-2) in the case shown in FIG. 2 where there is no miswiring, and the duty ratio 50 transmitted in step (1-2). It is an Xch prediction switching waveform as a% Xch switching waveform. Similarly, “Out” is the output pulse waveform of the Xch comparator 46x in the step (1-2) in the case shown in FIG. 2 where there is no erroneous wiring, and the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are differentiated. It is a differential pulse waveform.

  The Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIG. 4 are synchronized (φ = 0), while the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIGS. 5 and 6 are not synchronized. (Φ ≠ 0).

  As shown in FIGS. 4 to 6, regardless of whether the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are synchronized, a natural number multiple (Tx, 2Tx,...) Of the pulse interval (rising period) Tx. The integrated value of the output pulse waveform Out of the Xch comparator 46x in the time width is zero.

  Note that the input pulse waveform and output pulse waveform of the comparator in steps (1-3) and (1-4) when there is no erroneous wiring are the same as those shown in FIGS. Therefore, when there is no miswiring, the integral value of the output pulse waveform of the Ych comparator 46y and the time that is a natural number times the pulse interval of the Zch predictive switching waveform in the time width that is a natural number times the pulse interval of the Ych predictive switching waveform. The integrated value of the output pulse waveform of the Zch comparator 46z in the width is also zero.

  Next, as shown in FIG. 3, the input pulse waveform and the output pulse waveform of the comparator when there is an incorrect wiring between the switching control circuit and the multilevel inverter circuit (control signal line) will be described with reference to FIGS. explain.

  FIG. 7 is a diagram showing an input pulse waveform and an output pulse waveform of the Xch comparator 46x in the step (1-2) when the wiring between the switching control circuit and the multilevel inverter circuit is miswired between the Xch and Ych. is there. That is, FIG. 7 is a diagram showing an input pulse waveform and an output pulse waveform of the Xch comparator 46x in the step (1-2) in the case of the incorrect wiring shown in FIG.

  “In1” shown in FIG. 7 is the first input pulse waveform of the Xch comparator 46x in the step (1-2) in the case shown in FIG. 3 where there is an erroneous wiring between Xch and Ych, and the step (1-2) ) Is the actual Ych actual switching waveform “0” calculated by the switching control circuit 52y based on the Ych switching waveform with a duty ratio of 50% that is not transmitted. Similarly, “In2” is the second input pulse waveform of the Xch comparator 46x in the step (1-2) in the case shown in FIG. 3 where there is an incorrect wiring between the Xch and Ych, and is transmitted in the step (1-2). It is an Xch prediction switching waveform as an Xch switching waveform with a duty ratio of 50%. Similarly, “Out” is an output pulse waveform of the Xch comparator 46x in the step (1-2) in the case of FIG. 3 where there is an erroneous wiring, and the Ych actual switching waveform In1 and the Xch predicted switching waveform In2 are differentiated. It is a differential pulse waveform.

  As shown in FIG. 7, the integral value of the output pulse waveform Out of the Xch comparator 46x in a time width that is a natural number multiple of the pulse interval Tx is other than zero. Therefore, the sequencer 30 (shown in FIG. 3) can detect an abnormality (interlock) when the integral value of the output pulse waveform Out in a time width that is a natural number multiple of the pulse interval Tx is other than zero.

  Further, as shown in FIG. 7, the integrated value of the output pulse waveform Out of the Xch comparator 46x corresponding to one pulse interval Tx is a constant value regardless of the passage of time. Therefore, the sequencer 30 (shown in FIG. 3) has an integration value of the output pulse waveform Out corresponding to one pulse interval Tx and the integration value of the output pulse waveform Out in a time width that is a natural number multiple of the pulse interval Tx is other than zero. When the value is a constant value regardless of the passage of time, it is possible to detect an abnormality as the multilevel inverter circuit 51x is not connected to an appropriate switching control circuit.

  Although the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIG. 7 are synchronized, even if they are not synchronized, the integral value of the output pulse waveform Out in the time width that is a natural number multiple of the pulse interval Tx is It will be other than zero. Furthermore, even if not synchronized, the integrated value of the output pulse waveform Out corresponding to one pulse interval Tx is a constant value regardless of the passage of time.

  FIG. 8 is a diagram showing an input pulse waveform and an output pulse waveform of the Ych comparator 46y in the step (1-2) when the wiring between the switching control circuit and the multilevel inverter circuit is miswired between the Xch and Ych. is there. That is, FIG. 8 is a diagram showing an input pulse waveform and an output pulse waveform of the Ych comparator 46y in the step (1-2) in the case of erroneous wiring shown in FIG.

  “In1” shown in FIG. 8 is the first input pulse waveform of the Ych comparator 46y in the step (1-2) in the case shown in FIG. 3 where there is an incorrect wiring between Xch and Ych, and the step (1-2) ) Is an actual Xch actual switching waveform calculated by the switching control circuit 52x based on the Xch switching waveform with a duty ratio of 50% transmitted in (1). Similarly, “In2” is the second input pulse waveform of the Ych comparator 46y in the step (1-2) in the case shown in FIG. 3 where there is an incorrect wiring between the Xch and Ych, and is transmitted in the step (1-2). This is a Ych predicted switching waveform “0” as a Ych switching waveform with a duty ratio of 50%. Similarly, “Out” is an output pulse waveform of the Ych comparator 46y in the step (1-2) in the case of FIG. 3 where there is an erroneous wiring, and the Xch actual switching waveform In1 and the Ych predicted switching waveform In2 are differentiated. It is a differential pulse waveform.

  As shown in FIG. 8, the integral value of the output pulse waveform Out of the Ych comparator 46y is other than 0 in a time width that is a natural number times the pulse interval Tx (shown in FIG. 7). Therefore, the sequencer 30 (shown in FIG. 3) can detect an abnormality when the integral value of the output pulse waveform Out in a time width that is a natural number times the pulse interval Tx is other than zero.

  Further, as shown in FIG. 8, the integrated value of the output pulse waveform Out of the Ych comparator 46y corresponding to one pulse interval Tx (shown in FIG. 7) is a constant value regardless of the passage of time. Therefore, the sequencer 30 (shown in FIG. 3) has an integration value of the output pulse waveform Out corresponding to one pulse interval Tx and the integration value of the output pulse waveform Out in a time width that is a natural number multiple of the pulse interval Tx is other than zero. When the value is a constant value regardless of the passage of time, it is possible to detect an abnormality as the multilevel inverter circuit 51y is not connected to an appropriate switching control circuit.

  Although the Xch actual switching waveform In1 and the Ych predicted switching waveform In2 shown in FIG. 8 are synchronized, the integrated value of the output pulse waveform Out in a time width that is a natural number multiple of the pulse interval Tx is not 0 even if not synchronized. It becomes. Furthermore, even if not synchronized, the integrated value of the output pulse waveform Out corresponding to one pulse interval Tx of the Ych predicted switching waveform In2 is a constant value regardless of the passage of time.

  Note that the input pulse waveform and output pulse waveform of the Xch comparator 46x in the step (1-3) in the case of erroneous wiring shown in FIG. 3 are the same as those shown in FIG. The input pulse waveform and output pulse waveform of the Ych comparator 46y in the step (1-3) in the case of erroneous wiring shown in FIG. 3 are the same as those shown in FIG.

  According to the MRI apparatus 10 of this embodiment, before the output of the gradient magnetic field amplifiers 43x, 43y, and 43z, erroneous wiring inside the gradient magnetic field power supply device 23 is effectively detected based on the predicted switching waveform and the actual switching waveform. it can.

(Second abnormality detection method)
FIG. 9 is a diagram illustrating a configuration in a case where the wiring between the gradient magnetic field amplifier and the gradient magnetic field coil is erroneously wired.

  As shown in FIG. 9, the Xch gradient magnetic field amplifier 43x is erroneously connected to the Ych coil 22y. The Ych gradient magnetic field amplifier 43y is erroneously connected to the Xch coil 22x. On the other hand, the Zch gradient magnetic field amplifier 43z is correctly connected to the Zch coil 22z.

  The second abnormality detection method is to confirm whether the gradient magnetic field power supply device 23 is connected to an appropriate gradient magnetic field coil when the MRI apparatus 10 is installed. When a constant current is output from the gradient magnetic field power supply device 23 and the output voltage of the gradient magnetic field power supply device 23 is PWM-controlled, the duty ratio of the pulse of the switching waveform is proportional to the resistance value of the output unit. That is, since the load resistance value can be estimated from the pulse width of the switching waveform based on the output of a constant current, the second abnormality detection method checks the connection of the load depending on whether or not the approximate resistance value is larger than the specified value. To do.

  At the time of installation, a switching waveform is transmitted to the comparators 46x, 46y, and 46z according to the following steps for wiring confirmation. Note that the output of the gradient magnetic field amplifiers 43x, 43y, and 43z can be set to 0 by setting the duty ratio of the transmitted switching waveform to 50%.

(2-1) Non-transmission of Xch, Ych, and Zch switching waveforms (initial state)
(2-2) Transmit only the Xch switching waveform (duty ratio 50%) at the pulse interval Tx. (2-3) Input the input signal (ramp signal with a small slope) only to the Xch. (2-4) Ych switching at the pulse interval Ty. Transmit only waveform (duty ratio 50%) (2-5) Input signal (ramp signal with small slope) only to Ych (2-6) Transmit only Zch switching waveform (duty ratio 50%) at pulse interval Tz (2 -7) Input signal (ramp signal with a small slope) input to Zch only

  Steps (2-2), (2-4), and (2-6) are processes for creating a standby state before the ramp signal is input, and are not essential steps in the present embodiment.

  Next, the input pulse waveform and the output pulse waveform of the comparator when there is an incorrect wiring between the gradient magnetic field amplifier and the gradient magnetic field coil as shown in FIG. 9 will be described with reference to FIGS.

  FIGS. 10 and 11 are diagrams showing an input pulse waveform and an output pulse waveform of the Xch comparator 46x in the step (2-3) when the wiring between the gradient magnetic field amplifier and the gradient magnetic field coil is erroneously wired. 10 and 11 are diagrams showing the input pulse waveform and the output pulse waveform of the Xch comparator 46x in the step (2-3) in the case of the incorrect wiring shown in FIG.

  “In1” shown in FIGS. 10 and 11 is an Xch actual switching waveform, and is calculated based on a difference value obtained by subtracting the actual output from the input signal. Here, since the actual output is always 0, the Xch actual switching waveform In1 increases as the input signal increases. Incidentally, when the difference value obtained by subtracting the actual output from the input signal is 0, the duty ratio is 50%. Similarly, since “In2” is a ramp signal, the duty ratio gradually increases. When the duty ratio of the Xch actual switching waveform In1 and the duty ratio of the Xch predicted switching waveform In2 are compared, the former always increases. Therefore, the output pulse waveform Out of the Xch comparator 46x always outputs a positive value. Similarly, “Out” is an output pulse waveform of the Xch comparator 46x in the step (2-3) in the case of FIG. 9 where there is an erroneous wiring, and the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are differentiated. It is a differential pulse waveform.

  While the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIG. 10 are synchronized, the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIG. 11 are not synchronized.

  As shown in FIGS. 10 and 11, the output of the Xch comparator 46x in a time width that is a natural number times the pulse interval Tx, regardless of whether the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are synchronized. The integrated value of the pulse waveform Out is other than zero. Therefore, the sequencer 30 (shown in FIG. 9) can detect an abnormality when the integrated value of the output pulse waveform Out in a time width that is a natural number multiple of the pulse interval Tx is other than zero.

  As shown in FIGS. 10 and 11, the output pulse waveform of the Xch comparator 46x corresponding to one pulse interval Tx regardless of whether or not the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are synchronized. The integrated value of Out has an increasing tendency as time passes (decreasing tendency when the input to the comparator 46x is opposite). Therefore, the sequencer 30 (shown in FIG. 9) integrates the output pulse waveform Out corresponding to the one-pulse interval Tx, and the integrated value of the output pulse waveform Out in a time width that is a natural number multiple of the pulse interval Tx is other than zero. When the value tends to increase with time, the multilevel inverter circuit 51x can be detected as abnormal if it is not connected to an appropriate gradient coil.

  According to the MRI apparatus 10 of the present embodiment, incorrect wiring between the gradient magnetic field power supply device 23 and the gradient magnetic field coil 22 is performed based on the predicted switching waveform and the actual switching waveform before the output of the gradient magnetic field amplifiers 43x, 43y, and 43z. It can be detected effectively.

  (Third abnormality detection method)

  In the configuration shown in FIG. 2, the output currents of the gradient magnetic field amplifiers 43x, 43y, and 43z are switched to the comparators 46x, 46y, and 46z according to the above steps (2-1) to (2-7) in order to confirm oscillation. Duty ratio 50%) is transmitted. When the load condition changes unexpectedly or the gradient magnetic field amplifiers 43x, 43y, 43z run away, the output currents of the gradient magnetic field amplifiers 43x, 43y, 43z oscillate.

  Next, the input pulse waveform and the output pulse waveform of the comparator when the output current of the gradient magnetic field amplifier oscillates in the configuration shown in FIG. 2 will be described with reference to FIGS.

  12 and 13 are diagrams showing an input pulse waveform and an output pulse waveform of the comparator in step (2-3) when the output current of the gradient magnetic field amplifier oscillates.

  “In1” shown in FIGS. 12 and 13 is an input pulse waveform of the Xch comparator 46x in the step (2-3) when the output current of the Xch gradient magnetic field amplifier 43x oscillates in the configuration shown in FIG. This is an actual Xch actual switching waveform calculated by the switching control circuit 52x based on the Xch switching waveform with a duty ratio of 50% transmitted in (2-3). Similarly, “In2” is an input pulse waveform of the Xch comparator 46x in the step (2-3) when the output current of the Xch gradient magnetic field amplifier 43x oscillates in the configuration shown in FIG. 2, and in the step (2-3). It is an Xch prediction switching waveform as an Xch switching waveform with a duty ratio of 50% to be transmitted. Similarly, “Out” is an output pulse waveform of the Xch comparator 46x in the step (2-3) when the output current of the Xch gradient magnetic field amplifier 43x oscillates in the configuration shown in FIG. It is a differential pulse waveform obtained by subtracting the Xch predicted switching waveform In2.

  While the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIG. 12 are synchronized, the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 shown in FIG. 13 are not synchronized.

  As shown in FIGS. 12 and 13, the output of the Xch comparator 46x in a time width that is a natural number times the pulse interval Tx, regardless of whether the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are synchronized. The integrated value of the pulse waveform Out is other than zero. Therefore, the sequencer 30 (shown in FIG. 2) can detect an abnormality when the integral value of the output pulse waveform Out in a time width that is a natural number times the pulse interval Tx is other than zero.

  As shown in FIGS. 12 and 13, the output pulse waveform of the Xch comparator 46x corresponding to one pulse interval Tx regardless of whether the Xch actual switching waveform In1 and the Xch predicted switching waveform In2 are synchronized. The integrated value of Out repeats increasing and decreasing over time. Therefore, the sequencer 30 (shown in FIG. 2) corresponds to the one-pulse interval Tx of the Xch predicted switching waveform In2 whose integration value of the output pulse waveform Out is other than 0 in a time width that is a natural number multiple of the pulse interval Tx. When the integrated value of the output pulse waveform Out repeatedly increases and decreases with time, an abnormality can be detected as the output current of the Xch gradient magnetic field amplifier 43x oscillates.

  In the present embodiment, the configuration in which the actual switching waveform and the predicted switching waveform are compared using the comparators 46x, 46y, and 46z has been described. However, the configuration is not limited to this case. For example, the sequencer 30 may compare the actual switching waveform and the predicted switching waveform in terms of software.

  According to the MRI apparatus 10 of this embodiment, before the output of the gradient magnetic field amplifiers 43x, 43y, and 43z, the output current of the gradient magnetic field amplifiers 43x, 43y, and 43z is effectively oscillated based on the predicted switching waveform and the actual switching waveform. Can be detected automatically.

  Further, according to the MRI apparatus 10 of the present embodiment, before the output of the gradient magnetic field amplifiers 43x, 43y, 43z, detection of erroneous wiring inside the gradient magnetic field power supply device 23, and the connection between the gradient magnetic field power supply device 23 and the gradient magnetic field coil 22 are performed. Detection of erroneous wiring and detection of oscillation of the output current of the gradient magnetic field amplifiers 43x, 43y, and 43z can be realized with a common configuration.

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

DESCRIPTION OF SYMBOLS 10 MRI apparatus 22 Gradient magnetic field coil 23 Gradient magnetic field power supply apparatus 30 Sequencer 41 AC-DC converter 42 Smoothing capacitor 43x, 43y, 43z Gradient magnetic field amplifier 44x, 44y, 44z Current sensor 45 Conversion module 46x, 46y, 46z Comparator 51x, 51y, 51z multi-level inverter circuits 52x, 52y, 52z switching control circuit

Claims (6)

An inverter circuit connected to a DC voltage source;
When the output of the inverter circuit is supplied to a gradient coil that is a load, a current sensor that detects a current flowing through the gradient coil;
A switching control circuit that calculates a switching waveform based on an input signal and an error signal that is an output of the current sensor, and that performs pulse width modulation control on the inverter circuit based on the switching waveform;
Comparing means for generating an output pulse waveform by subtracting an actual switching waveform calculated by the switching control circuit based on a switching waveform having a duty ratio of 50% and a predicted switching waveform as the switching waveform having a duty ratio of 50% When,
An anomaly detecting means for detecting an anomaly when the integral value of the output pulse waveform in a time width that is a natural number times the pulse interval of the predicted switching waveform is other than 0;
A magnetic resonance imaging apparatus.   When the integral value is other than 0 and the integral value of the output pulse waveform corresponding to one pulse interval of the predicted switching waveform repeatedly increases and decreases as time passes, the abnormality detection means determines that the output current of the inverter circuit is The magnetic resonance imaging apparatus according to claim 1, wherein an abnormality is detected as an oscillation.   When the integral value is other than 0, the anomaly detection means is configured such that when the integral value of the output pulse waveform corresponding to one pulse interval of the predicted switching waveform tends to increase or decrease over time, the inverter circuit and the gradient magnetic field The magnetic resonance imaging apparatus according to claim 1, wherein an abnormality is detected as a miswiring between the coil and the coil.   When the integral value is other than 0, the abnormality detection means is configured such that when the integral value of the output pulse waveform corresponding to one pulse interval of the predicted switching waveform is a constant value regardless of the passage of time, the switching control circuit and the inverter The magnetic resonance imaging apparatus according to claim 1, wherein an abnormality is detected as an incorrect wiring between the circuit and the circuit.   The magnetic resonance imaging apparatus according to claim 1, wherein the comparison unit includes a comparator. An inverter circuit connected to a DC voltage source;
When the output of the inverter circuit is supplied to a gradient coil that is a load, a current sensor that detects a current flowing through the gradient coil;
A switching control circuit that calculates a switching waveform based on an input signal and an error signal that is an output of the current sensor, and performs pulse width modulation control on the inverter circuit based on the switching waveform. In the abnormality detection method,
A difference between an actual switching waveform calculated by the switching control circuit based on a switching waveform having a duty ratio of 50% and a predicted switching waveform as the switching waveform having a duty ratio of 50%, and generating an output pulse waveform,
An abnormality detection method for a magnetic resonance imaging apparatus, wherein abnormality detection is performed when an integrated value of the output pulse waveform in a time width that is a natural number times the pulse interval of the predicted switching waveform is other than zero.

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