JP6991793B2 - Magnetic resonance imaging device - Google Patents

Description

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

The MRI apparatus is an apparatus that captures an image of a subject on a top plate and acquires internal information of the subject as image data.

The MRI apparatus includes a gradient magnetic field coil and a transmission coil that transmits a high frequency pulse, that is, an RF (Radio Frequency) pulse, for example, a WB (Whole Body) coil. The WB coil receives an RF pulse signal from the RF transmitter and excites the nuclear spin of the imaging site placed in a static magnetic field with a high frequency pulse of Larmor frequency, that is, an RF pulse. Then, the MRI apparatus receives a magnetic resonance signal generated from the imaging site in association with the excitation, that is, an MR (Magnetic Resonance) signal with a receiving coil, for example, a local coil, and generates image data based on the MR signal.

The gradient magnetic field coil includes a plurality of channels that generate gradient magnetic fields in different directions. If there is an unintended potential difference between channels during execution of a pulse sequence by the MRI apparatus, there is a possibility that discharge between channels or space discharge has occurred. The effect of electric discharge may not be a problem in use at all, but if noise is generated on the image, dielectric breakdown occurs and it becomes impossible to generate a gradient magnetic field, in the worst case, the gradient magnetic field coil is damaged and MRI. The device may not function, and the greater the degree of discharge, the greater the problem.

Japanese Patent No. 5972742

An object to be solved by the present invention is to provide an MRI apparatus capable of recognizing an abnormality of a gradient magnetic field coil before it deteriorates to a level that affects the apparatus.

The MRI apparatus according to the present embodiment includes a gradient magnetic field coil, a sensor that detects output information to the gradient magnetic field coil, and sequence output information and the output information to the gradient magnetic field coil during execution of a specific sequence. It has means for determining that there is an abnormality when a plurality of difference values are obtained by performing a difference, the plurality of difference values are integrated to obtain an integrated value, and the integrated value exceeds a predetermined threshold value.

The schematic diagram which shows the whole structure of the MRI apparatus which concerns on this embodiment. The figure which shows the detailed structure of the power source for the gradient magnetic field provided in the MRI apparatus which concerns on this embodiment. The figure which shows an example of the transition of the current detected by the current sensor in the MRI apparatus which concerns on this embodiment. The figure which shows an example of the time transition of the difference value in the gradient magnetic field coil provided in the MRI apparatus which concerns on this embodiment as a graph. The figure which shows the detailed structure of the power source for the gradient magnetic field of the MRI apparatus which concerns on the prior art. The figure which shows the detailed structure of the modification of the power source for gradient magnetic fields provided in the MRI apparatus which concerns on this embodiment. (A) and (B) are diagrams showing an example of the transition of the integrated value in the gradient magnetic field coil provided in the MRI apparatus according to the present embodiment as a graph.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic view showing the overall configuration of the MRI apparatus according to the present embodiment.

FIG. 1 shows an MRI apparatus 1 according to the present embodiment. The MRI apparatus 1 includes a magnet mount 100, a control cabinet 300, a console 400, and a bed apparatus 500. The magnet stand 100, the control cabinet 300, and the bed device 500 are generally provided in the examination room. The examination room is also called a photography room. The console 400 is provided in the control room. The control room is also called the operation room.

The magnet mount 100 has a static magnetic field magnet 10, a gradient magnetic field coil 11, and a WB coil 12. These members are housed in a cylindrical housing. The bed device 500 has a bed body 50 and a top plate 51.

The control cabinet 300 includes a gradient magnetic field power supply 31 (X-axis 31x, Y-axis 31y, Z-axis 31z), an RF transmitter 32, an RF receiver 33, and a sequence controller 34.

The console 400 includes a processing unit (for example, a processing circuit) 40, a storage unit (for example, a storage circuit) 41, a display unit (for example, a display) 42, and an input unit (for example, an input circuit) 43. The console 400 functions as a host computer.

The static magnetic field magnet 10 of the magnet mount 100 is roughly classified into a tunnel type in which the magnet has a cylindrical magnet structure and an open type (open type) in which a pair of magnets are arranged above and below the image pickup space. Here, the case where the static magnetic field magnet 10 is a tunnel type will be described, but the case is not limited to that case.

The static magnetic field magnet 10 has a substantially cylindrical shape, and generates a static magnetic field in a bore in which a subject, for example, a patient U, is carried. The bore is the space inside the cylinder of the magnet mount 100. The static magnetic field magnet 10 is composed of, for example, a housing for holding liquid helium, a refrigerator for cooling the liquid helium to an extremely low temperature, and a superconducting coil inside the housing. The static magnetic field magnet 10 may be composed of a permanent magnet. Hereinafter, a case where the static magnetic field magnet 10 has a superconducting coil will be described.

The static magnetic field magnet 10 has a built-in superconducting coil, and the superconducting coil is cooled to an extremely low temperature by liquid helium. The static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power source to the superconducting coil in the excitation mode. After that, when the mode shifts to the permanent current mode, the static magnetic field power supply is disconnected. Once transitioned to the permanent current mode, the static magnetic field magnet 10 continues to generate a static magnetic field for a long period of time, for example, one year or more.

The gradient magnetic field coil 11 has a substantially cylindrical shape like the static magnetic field magnet 10, and is installed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 applies a gradient magnetic field to the patient U by the electric power supplied from the gradient magnetic field power supply 31.

Here, since the eddy current generated by the generation of the gradient magnetic field hinders the imaging, for example, ASGC (Actively Shielded Gradient Coil) for the purpose of reducing the eddy current is used as the gradient magnetic field coil 11. May be good. The ASGC is a gradient magnetic field coil provided with a shield coil for suppressing a leakage magnetic field on the outside of a main coil for forming each gradient magnetic field in the X-axis, Y-axis, and Z-axis directions.

The WB coil 12, also called a whole-body coil, is installed inside the gradient magnetic field coil 11 in a substantially cylindrical shape so as to surround the patient U. The WB coil 12 functions as a transmission coil. That is, the WB coil 12 transmits the RF pulse toward the patient U according to the RF pulse signal transmitted from the RF transmitter 32. On the other hand, the WB coil 12 may have a function as a receiving coil in addition to the function as a transmitting coil for transmitting RF pulses. In that case, the WB coil 12 receives the MR signal emitted from the patient U by the excitation of the atomic nucleus as the receiving coil.

The MRI apparatus 1 may include a local coil 20 in addition to the WB coil 12. The local coil 20 is placed close to the body surface of the patient U. The local coil 20 may include a plurality of coil elements. Since these plurality of coil elements are arranged in an array inside the local coil 20, they are sometimes called a PAC (Phased Array Coil).

There are several types of local coil 20. For example, the local coil 20 includes a body coil (Body Coil) installed on the chest, abdomen, or leg of the patient U as shown in FIG. 1, and a spine coil (Spine Coil) installed on the dorsal side of the patient U. ). In addition, the local coil 20 has a type such as a head coil for imaging the head of the patient U and a foot coil for imaging the foot. The local coil 20 also includes a wrist coil (Wrist Coil) for imaging the wrist, a knee coil (Knee Coil) for imaging the knee, and a shoulder coil (Shoulder Coil) for imaging the shoulder.

The local coil 20 functions as a receiving coil. That is, the local coil 20 receives the MR signal described above. However, the local coil 20 may be a transmission / reception coil having a function as a transmission coil for transmitting RF pulses in addition to the function as a reception coil for receiving MR signals. For example, the transmission / reception coil also exists in the head coil and knee coil as the local coil 20. That is, the local coil 20 may be of any type of transmission-only, reception-only, or transmission / reception-only.

The gradient magnetic field power supply 31 includes gradient magnetic field power supplies 31x, 31y, 31z for each channel that drives coils that generate gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions. The gradient magnetic field power supplies 31x, 31y, and 31z output the required current independently for each channel according to the command of the sequence controller 34. Thereby, the gradient magnetic field coil 11 can apply a gradient magnetic field in the X-axis, Y-axis, and Z-axis directions to the patient U. The detailed configuration of the gradient magnetic field power supply 31 will be described later with reference to FIGS. 2 and 6.

The RF transmitter 32 generates an RF pulse signal based on an instruction from the sequence controller 34. The RF transmitter 32 transmits the generated RF pulse signal to the WB coil 12. The detailed configuration of the RF transmitter 32 will be described later with reference to FIG.

The MR signal received by the local coil 20, more specifically, the MR signal received by each coil element in the local coil 20 is transmitted to the RF receiver 33. The output line of each coil element and the output line of the WB coil 12 are called channels. Therefore, each MR signal output from each coil element or the WB coil 12 may be referred to as a channel signal. The channel signal received by the WB coil 12 is also transmitted to the RF receiver 33.

The RF receiver 33 AD (Analog to Digital) converts a channel signal from the local coil 20 or the WB coil 12, that is, an MR signal, and outputs the channel signal to the sequence controller 34. The digitally converted MR signal is sometimes called raw data.

The sequence controller 34 takes an image of the patient U by driving the gradient magnetic field power supply 31, the RF transmitter 32, and the RF receiver 33, respectively, under the control of the console 400. Upon receiving the raw data from the RF receiver 33 by imaging, the sequence controller 34 transmits the raw data to the console 400.

The sequence controller 34 includes a processing circuit (not shown). This processing circuit is composed of, for example, a processor that executes a predetermined program and hardware such as FPGA (Field Programmable Gate Array) and ASIC (Application Specific Integrated Circuit).

The console 400 includes a processing circuit 40, a storage circuit 41, a display 42, and an input circuit 43.

The processing circuit 40 means a processing circuit such as an integrated circuit (ASIC) for a specific application, a programmable logic device, or the like, in addition to a dedicated or general-purpose CPU (Central Processing Unit) or MPU (Micro Processor Unit). Examples of the programmable logic device include circuits such as a simple programmable logic device (SPLD: Simple Programmable Logic Device), a compound programmable logic device (CPLD: Complex Programmable Logic Device), and a field programmable gate array (FPGA). The processing circuit 40 controls the operation of the sequence controller 34 by reading and executing a program stored in the storage circuit 41 or directly incorporated in the processing circuit 40, and a pulse sequence (simply in the present specification). It realizes a function to generate an MR image by performing imaging according to (referred to as "sequence").

Further, the processing circuit 40 may be composed of a single processing circuit or a combination of a plurality of independent processing circuits. In the latter case, the plurality of storage circuits 41 may store programs corresponding to the functions of the plurality of processing circuits, respectively, or one storage circuit 41 may store a program corresponding to the functions of the plurality of processing circuits. It may be something to remember.

The storage circuit 41 includes a semiconductor memory element such as a RAM (Random Access Memory) and a flash memory (Flash Memory), a hard disk, an optical disk, and the like. The storage circuit 41 may include a portable medium such as a USB (Universal Serial bus) memory and a DVD (Digital Video Disk). The storage circuit 41 stores various processing programs (including an OS (Operating System) as well as an application program) used in the processing circuit 40, data necessary for executing the program, and medical images. Further, the OS may include a GUI (Graphical User Interface) that makes extensive use of graphics for displaying information on the display 42 to the operator and allows basic operations to be performed by the input circuit 43.

The display 42 is a display device such as a liquid crystal display panel, a plasma display panel, and an organic EL (Electro Luminescence) panel.

The input circuit 43 is a circuit for inputting a signal from an input device that can be operated by an operator, and here, the input device itself is also included in the input circuit 43. Input devices include pointing devices (eg, mice), keyboards, and various buttons. When the input device is operated by the operator, the input circuit 43 generates an input signal corresponding to the operation and outputs the input signal to the processing circuit 40. The MRI apparatus 1 may include a touch panel in which the input device is integrally configured with the display 42.

The console 400 collects MR signals transmitted from the sequence controller 34 under the control of the processing circuit 40, and stores the collected MR signals in the storage circuit 41. The console 400 generates a desired MR image in the patient U by performing post-processing, that is, reconstruction processing such as Fourier transform on the MR signal stored in the storage circuit 41 under the control of the processing circuit 40. do. Then, the console 400 stores the generated various MR images in the storage circuit 41 under the control of the processing circuit 40.

The bed device 500 includes a bed body 50 and a top plate 51. The bed body 50 is arranged so that the top plate 51 can be moved in, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. The movement of the top plate 51 in the X-axis direction is a movement in the left-right direction of the top plate 51, that is, a movement in the lateral direction of the top plate 51. The movement of the top plate 51 in the Y-axis direction is a movement in the vertical direction of the top plate 51, that is, a movement in the thickness direction of the top plate 51. The movement of the top plate 51 in the Z-axis direction is a movement in the front-rear direction of the top plate 51, that is, a movement in the longitudinal direction of the top plate 51. Before imaging, the patient U placed on the top plate 51 is moved to a predetermined height in the Y-axis direction. After that, the bed body 50 causes the top plate 51 to travel in the Z-axis direction to move the patient U inside the magnet stand 100.

FIG. 2 is a diagram showing a detailed configuration of a gradient magnetic field power supply 31 provided in the MRI apparatus 1.

FIG. 2 shows a gradient magnetic field power supply 31, a sequence controller 34 that controls the gradient magnetic field power supply 31, and a gradient magnetic field coil 11 that applies a gradient magnetic field to the patient U by power supplied from the gradient magnetic field power supply 31. .. Here, the gradient magnetic field coil 11 includes an X channel 11x that generates a gradient magnetic field in the X-axis direction, a Y channel 11y that generates a gradient magnetic field in the Y-axis direction, and a Z channel 11z that generates a gradient magnetic field in the Z-axis direction. To be equipped.

The gradient magnetic field power supply 31 includes an AC-DC converter 61, a smoothing capacitor 62, a gradient magnetic field amplifier 63x, 63y, 63z, a current sensor 64x, 64y, 64z, and a determination means according to the present embodiment. In the configuration shown in FIG. 2, the determination means include a difference circuit 65x, 65y, 65z, an integration circuit 66x, 66y, 66z, an A / D (Analog to Digital) conversion circuit 67x, 67y, 67z, and a determination circuit 68. ,including. The gradient magnetic field power supply 31 is configured to be supplied with electric power from the three-phase AC power supply S and connected to the gradient magnetic field coil 11 which is a load to supply a current.

The AC-DC converter 61 has a function of boosting the three-phase AC voltage connected to the three-phase AC power supply S to, for example, a DC voltage of 2000 V.

The smoothing capacitor 62 is connected to the output side of the AC-DC converter 61 to smooth the DC voltage.

The gradient magnetic field amplifiers 63x, 63y, 63z correspond to the channels 11x, 11y, 11z, respectively. The gradient magnetic field amplifiers 63x, 63y, and 63z are connected to the smoothing capacitor 62, respectively, and receive a smoothed DC voltage. The gradient magnetic field amplifiers 63x, 63y, 63z supply currents to the channels 11x, 11y, 11z, respectively.

The gradient magnetic field amplifier 63x, 63y, 63z is provided with a multi-level inverter circuit 71x, 71y, 71z. The multi-level inverter circuits 71x, 71y, 71z correspond to channels 11x, 11y, 11z, respectively. The multi-level inverter circuits 71x, 71y, and 71z are full-bridge circuits connected in parallel to the smoothing capacitor 62 constituting the input DC voltage source. The outputs of the multi-level inverter circuits 71x, 71y, 71z are supplied to the channels 11x, 11y, 11z, which are loads, respectively.

The current sensors 64x, 64y, 64z correspond to the channels 11x, 11y, 11z, respectively. The current sensors 64x, 64y, 64z detect the currents flowing through the channels 11x, 11y, and 11z when the outputs of the multi-level inverter circuits 71x, 71y, and 71z are supplied to the channels 11x, 11y, and 11z, respectively.

FIG. 3 is a diagram showing an example of the transition of the current detected by the current sensors 64x, 64y, 64z in the MRI apparatus 1.

FIG. 3 shows the transition of the detected current Px by the current sensor 64x, the transition of the detected current Py by the current sensor 64y, and the transition of the detected current Pz by the current sensor 64z. As shown in FIG. 3, currents having different waveforms are supplied to the channels 11x, 11y, and 11z according to the sequence output information Rx, Ry, and Rz (shown in FIG. 2) from the sequence controller 34. In the example shown in FIG. 3, the discharge output is observed in the current Px detected by the current sensor 64x due to the potential difference between the channels 11x and 11z.

Returning to the description of FIG. 2, the difference circuits 65x, 65y, 65z correspond to the channels 11x, 11y, 11z, respectively. The difference circuits 65x, 65y, 65z and the sequence output information (for example, command current) Rx, Ry, Rz according to the type of sequence during the execution of the pulse sequence (referred to simply as "sequence" in the present specification). , The difference from the actual output information (for example, the detected current) Sx, Sy, Sz is performed, and a plurality of difference values are obtained for each channel.

FIG. 4 is a graph showing an example of the time transition of the difference value in the gradient magnetic field coil 11 provided in the MRI apparatus 1.

As shown in FIG. 4, the time transition of the difference value corresponding to the X channel 11x is shown when a plurality of, for example, two sequences are executed in one inspection.

As shown in FIG. 4, the degree of increase in the difference value in the X channel 11x is small during the execution of the first sequence. On the other hand, during the execution of the second sequence, the degree of increase in the difference value in the X channel 11x is large. As a second sequence in which the degree of increase in the difference value is large, for example, a sequence classified into echoplanar imaging (EPI) in which k-space data is collected while repeatedly reversing the polarity of the gradient magnetic field can be mentioned. The sequence for acquiring a diffusion-weighted image (DWI) is an example of the second sequence. This is because such a specific sequence has a large fluctuation in the voltage applied to the channel and is likely to be accompanied by discharge of the channel.

Returning to the description of FIG. 2, the integrating circuits 66x, 66y, 66z correspond to the channels 11x, 11y, 11z, respectively. The integration circuit 66x, 66y, 66z integrates a plurality of difference values obtained by the difference circuits 65x, 65y, 65z, and obtains an integrated value for each channel. The integrated value of each channel is estimated as the discharge amount of the channel. Further, by taking the difference value, only the discharge noise component can be extracted. The integrated value is defined as an area of a diagonal line, that is, a closed curve, sandwiched between the graph showing the transition of the difference value shown in FIG. 4 and the horizontal axis.

The A / D conversion circuits 67x, 67y, 67z correspond to the channels 11x, 11y, 11z, respectively. The A / D conversion circuit 67x, 67y, 67z digitally converts the integrated value by the integrating circuit 66x, 66y, 66z.

The determination circuit 68 determines that there is an abnormality when the integrated value for each channel output from the A / D conversion circuits 67x, 67y, 67z exceeds a predetermined threshold value. It should be noted that three determination circuits 68 may be provided so as to correspond to the channels 11x, 11y, and 11z, respectively.

Explaining the operation of the determination circuit 68 using the first and second sequences shown in FIG. 4, the determination circuit 68 may be used substantially continuously or intermittently (for example, the repetition time TR) during the execution of the second sequence. The integral value with respect to the X channel 11x is compared with a predetermined threshold value in a cycle (a cycle of several times the natural number of the natural number). Then, the determination circuit 68 determines that there is an abnormality when the integrated value exceeds a predetermined threshold value during the execution of the second sequence, that is, the discharge amount is excessive, and operates via the sequence controller 34. Notify the person (for example, a warning display).

Alternatively, the determination circuit 68 compares the integrated value with respect to the X channel 11x with a predetermined threshold value substantially continuously or intermittently during the execution of the second sequence. Then, when the integrated value exceeds a predetermined threshold value during the execution of the second sequence, the determination circuit 68 determines that there is an abnormality after the inspection including the first and second sequences is completed, and determines that there is an abnormality, and the sequence controller. Notify the operator via 34.

Although the case where the integrated value for the X channel 11x and the predetermined threshold value are compared with each other is described with reference to FIG. 4, the integrated value and the predetermined threshold value can be similarly compared for the channels 11y and 11z, respectively. can. When comparing the integrated value for a plurality of channels with a predetermined threshold value, the determination circuit 68 may determine that there is an abnormality when the integrated value exceeds the predetermined threshold value even for one channel, or all of them. When the integral value of the channel exceeds a predetermined threshold value, it may be determined that there is an abnormality.

As described above, the MRI apparatus 1 obtains an integrated value for each channel based on the detection signals Sx, Sy, and Sz without pulse width modulation control, and compares the integrated value with a predetermined threshold value during execution of the sequence.

FIG. 5 is a diagram showing a detailed configuration of a power supply for a gradient magnetic field of the MRI apparatus according to the prior art.

FIG. 5 shows a gradient magnetic field power supply 131, a sequence controller 134 that controls the gradient magnetic field power supply 131, and a gradient magnetic field coil 111 that applies a gradient magnetic field to a patient by power supplied from the gradient magnetic field power supply 131. The configuration and function of the gradient magnetic field coil 111 are the same as those of the gradient magnetic field coil 11 shown in FIG. 2, and thus the description thereof will be omitted.

The gradient magnetic field power supply 131 includes an AC-DC converter 161, a smoothing capacitor 162, a gradient magnetic field amplifier 163x, 163y, 163z, and a current sensor 164x, 164y, 164z. The gradient magnetic field power supply 131 is configured to be supplied with electric power from the three-phase AC power supply S and connected to the gradient magnetic field coil 111, which is a load, to supply a current. Regarding the configuration and function of the AC-DC converter 161, the smoothing capacitor 162, and the current sensors 164x, 164y, 164z, the AC-DC converter 61, the smoothing capacitor 62, and the current sensor 64x, 64y shown in FIG. Since it is equivalent to 64z, the description thereof will be omitted.

The gradient magnetic field amplifiers 163x, 163y, 163z are provided with switching control circuits 172x, 172y, 172z in addition to the multi-level inverter circuits 171x, 171y, 171z.

The switching control circuits 172x, 172y, 172z correspond to channels 111x, 111y, 111z, respectively. The switching control circuits 172x, 172y, 172z input the command currents Rx, Ry, Rz from the sequence controller 134 and the detection currents Tx, Ty, Tz of the current sensors 164x, 164y, 164z, respectively, and the difference between the two becomes 0. The switching waveforms are calculated so as to be. Then, the switching control circuits 172x, 172y, 172z pulse width modulation (PWM: Pulse) of the multi-level inverter circuits 171x, 171y, 171z via the control signal lines Lx, Ly, Lz based on the switching waveform in each channel. Width Modulation) Control.

The conventional MRI apparatus shown in FIG. 5 is provided with switching control circuits 172x, 172y, 172z, and obtains a plurality of difference values based on the detected currents Tx, Ty, Tz after the pulse width change after the pulse width modulation control. be. Therefore, according to the MRI apparatus of the prior art, in addition to requiring the input of the command currents Rx, Ry, Rz to the switching control circuits 172x, 172y, 172z, the variation in manufacturing quality of the gradient magnetic field coil 111 is taken into consideration. The state of the gradient magnetic field coil 111 cannot be determined.

According to the MRI apparatus 1, by estimating the discharge amount of the channels 11x, 11y, 11z based on the detection signals Sx, Sy, Sz without pulse width modulation control, the manufacturing quality of the gradient magnetic field coil 11 varies. It is possible to recognize in advance the abnormality of the gradient magnetic field coil 11 caused by the abnormality.

(Modification example)
In the MRI apparatus 1 shown in FIGS. 1 and 2, the integration circuit 66x, 66y, 66z as an analog circuit has been described as integrating a plurality of difference values. However, it is not limited to that case. For example, the MRI apparatus 1 may be configured such that a processing circuit, for example, a sequence controller 34, integrates a plurality of difference values by executing a program.

FIG. 6 is a diagram showing a detailed configuration of a modified example of the gradient magnetic field power supply 31 provided in the MRI apparatus 1. Since the overall configuration of the MRI apparatus 1 has been described with reference to FIG. 1, the description thereof will be omitted.

FIG. 6 shows a gradient magnetic field power supply 31, a sequence controller 34 that controls the gradient magnetic field power supply 31, and a gradient magnetic field coil 11 that applies a gradient magnetic field to the patient U by the power supplied from the gradient magnetic field power supply 31. .. The gradient magnetic field power supply 31 includes an AC-DC converter 61, a smoothing capacitor 62, a gradient magnetic field amplifier 63x, 63y, 63z, a current sensor 64x, 64y, 64z, and a determination means. In the configuration shown in FIG. 6, the determination means includes a difference circuit 65x, 65y, 65z, an A / D conversion circuit 69x, 69y, 69z, an integration function 34A, and a determination function 34B. In FIG. 6, the same members as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

The A / D conversion circuits 69x, 69y, 69z correspond to the channels 11x, 11y, 11z, respectively. The A / D conversion circuit 69x, 69y, 69z digitally converts a plurality of difference values obtained by the difference circuit 65x, 65y, 65z.

The processing circuit of the sequence controller functions as the integration function 34A and the determination function 34B by executing the program.

The integration function 34A integrates a plurality of difference values output from the A / D conversion circuits 69x, 69y, and 69z, and obtains an integrated value for each channel. When the integration function 34A cannot express the transition of the difference value as a function, the integration function 34A can obtain the integration value by adopting an integration calculation such as the Monte Carlo method.

The determination function 34B determines that there is an abnormality when the integrated value for each channel obtained by the integration function 34A exceeds a predetermined threshold value.

Explaining the operation of the determination function 34B using the first and second sequences shown in FIG. 4, the determination function 34B relates to the X channel 11x substantially continuously or intermittently during the execution of the second sequence. A comparison is made between the integrated value and a predetermined threshold value. Then, the determination function 34B determines that there is an abnormality when the integrated value exceeds a predetermined threshold value during the execution of the second sequence, that is, the discharge amount is excessive, and notifies the operator to that effect. ..

Alternatively, the determination function 34B compares the integrated value with respect to the X channel 11x with a predetermined threshold value substantially continuously or intermittently during the execution of the second sequence. Then, when the integrated value exceeds a predetermined threshold value during the execution of the second sequence, the determination function 34B determines that there is an abnormality after the completion of the inspection including the first and second sequences, and informs the operator. Notify that.

7 (A) and 7 (B) are diagrams showing an example of the transition of the integrated value in the gradient magnetic field coil 11 provided in the MRI apparatus 1 as a graph. That is, FIGS. 7A and 7B show the transition of the estimated value of the discharge amount in the gradient magnetic field coil 11 as a graph.

Each point in FIG. 7A shows an integral value related to the specific sequence on the execution date of the specific sequence. In this way, the integral function 34A obtains the integral value based on the plurality of difference values related to the specific sequence and plots it on the graph, whereby the integral value of the main execution date (9/9) of the specific sequence and the specific sequence are obtained. Since the upward tendency of the discharge amount of the gradient magnetic field coil 11 is clarified by comparison with the integrated value in the past execution date, it is possible to easily determine the abnormality of the gradient magnetic field coil 11.

The specific sequence may be executed n (n: 2,3, ..., N) times on the execution date of the specific sequence. In that case, the integration function 34A obtains representative values of n integrated values corresponding to n specific sequences as integrated values on the execution date of the specific sequence. Here, the representative value is the maximum value, the average value, or the integrated value related to the specific sequence executed at the last Nth time of the n integrated values.

Further, each point in FIG. 7B shows an integrated value related to the specific sequence. In this way, the integral function 34A obtains the integral value based on the plurality of difference values related to the specific sequence and plots it on the graph, whereby the integral value of the number of main executions (30th time) of the specific sequence and the integral value of the specific sequence are obtained. Since the tendency of the discharge amount of the gradient magnetic field coil 11 to increase becomes clear by comparison with the integrated value in the past number of executions, it is possible to easily determine the abnormality of the gradient magnetic field coil 11.

According to a modification of the MRI apparatus 1, the manufacturing quality of the gradient magnetic field coil 11 is estimated by estimating the discharge amount of the channels 11x, 11y, 11z based on the detection signals Sx, Sy, Sz without pulse width modulation control. It is possible to recognize in advance the abnormality of the gradient magnetic field coil 11 due to the variation in the above.

According to the MRI apparatus of at least one embodiment described above, the abnormality of the gradient magnetic field coil can be recognized before it deteriorates to a level that affects the apparatus.

Although some 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 embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Magnetic resonance imaging (MRI) device 11 ... Diagonal magnetic circuit coil 11x, 11y, 11z ... Channel 31 ... Power supply for gradient magnetic field 34 ... Sequence controller 61 ... AC-DC converter 62 ... Smoothing capacitor 63x, 63y, 63z ... Diagonal magnetic field Amplifier 64x, 64y, 64z ... Current sensor 65x, 65y, 65z ... Difference circuit 66x, 66y, 66z ... Integration circuit 67x, 67y, 67z ... A / D conversion circuit 68 ... Judgment circuit 69x, 69y, 69z ... A / D conversion Circuit 34A ... Integration function 34B ... Judgment function

Claims (6)

With a gradient magnetic field coil,
A sensor that detects output information to the gradient magnetic field coil and
During the execution of the specific sequence, the difference between the sequence output information and the output information to the gradient magnetic field coil is performed to obtain a plurality of difference values, and the plurality of difference values are integrated to obtain an integrated value, and the integrated value is obtained. A determination means for determining that there is an abnormality when the value exceeds a predetermined threshold, and
Magnetic resonance imaging device with. The determination means is a sequence in which the specific sequence is collected while repeating the polarity reversal of the gradient magnetic field in the k-space data.
The magnetic resonance imaging apparatus according to claim 1. The determination means uses the specific sequence as a pulse sequence by the echo-planar method.
The magnetic resonance imaging apparatus according to claim 2. The determination means obtains the integral value for each channel of the gradient magnetic field coil, and determines that there is an abnormality when at least one of the plurality of integral values corresponding to the plurality of channels exceeds the predetermined threshold value.
The magnetic resonance imaging apparatus according to any one of claims 1 to 3. The determination means is
The difference circuit that obtains the plurality of difference values and
The integrator circuit for obtaining the integral value and
A digital conversion circuit that digitally converts the integrated value, and
A determination circuit that determines that there is an abnormality when the digitally converted integral value exceeds a predetermined threshold value, and
The magnetic resonance imaging apparatus according to any one of claims 1 to 4. The determination means is
The difference circuit that obtains the plurality of difference values and
A digital conversion circuit that digitally converts the plurality of difference values, and
A determination circuit that integrates a plurality of digitally converted difference values to obtain an integrated value, and determines that there is an abnormality when the integrated value exceeds a predetermined threshold value.
The magnetic resonance imaging apparatus according to any one of claims 1 to 4.

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