Magnetic resonance imaging apparatus and method for detecting abnormalities

Abstract

In a magnetic resonance imaging system, the state of insulation degradation of the wires in the gradient coils is determined. [Solution] The magnetic resonance imaging apparatus according to the embodiment comprises a gradient coil assembly, a detection coil, and a determination unit. The gradient coil assembly is a gradient coil constructed by winding a conductor multiple times, and has at least one gradient coil that applies a gradient magnetic field to a subject by passing a predetermined current through the conductor. The detection coil is provided inside or on the outer circumference of the gradient coil and detects the current flowing through the conductor. The determination unit determines the insulation degradation state of the conductor based on the current value detected by the detection coil.

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to a magnetic resonance imaging apparatus and a method for detecting abnormal locations.

Background Art

[0002] A magnetic resonance imaging apparatus is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with a high-frequency (RF: Radio Frequency) signal at the Larmor frequency, and reconstructs the magnetic resonance (MR: Magnetic Resonance) signal generated from the subject upon excitation to generate an image.

[0003] In a magnetic resonance imaging apparatus, the subject is imaged by executing a predetermined pulse sequence. When the pulse sequence is executed, a large current flows through the gradient magnetic field coil, and insulation degradation occurs due to heat load caused by Joule heat and eddy current heat, and a short circuit may occur between the windings or channels constituting the gradient magnetic field coil. In addition, mechanical stress is applied to the conductor of the gradient magnetic field coil by the Lorentz force, which may cause a load at the fastening part of the conductor and result in a short circuit. Conventionally, the insulation performance is confirmed by performing a partial discharge test during the manufacturing process, and the presence or absence of internal discharge is confirmed by inspection during installation. However, these confirmations and inspections alone cannot detect insulation degradation and short circuits between channels caused by aging heat cycles.

[0004] Also, the soundness of each channel can be confirmed by measuring the impedance of each channel using a gradient magnetic field power supply. However, it is impossible to detect a short circuit caused by a current within the threshold value or a short circuit between channels when the pulse sequence is being executed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] One of the problems that the embodiments disclosed in this specification and drawings aim to solve is determining the insulation degradation state of the wires of a gradient magnetic field coil in a magnetic resonance imaging apparatus. However, the problems that the embodiments disclosed in this specification and drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0007] The magnetic resonance imaging apparatus according to this embodiment comprises a gradient coil assembly, a detection coil, and a determination unit. The gradient coil assembly is a gradient coil constructed by winding a wire multiple times, and has at least one gradient coil that applies a gradient magnetic field to a subject by passing a predetermined current through the wire. The detection coil is provided inside or on the outer circumference of the gradient coil and detects the current flowing through the wire. The determination unit determines the insulation degradation state of the wire based on the current value detected by the detection coil. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus according to the first embodiment. [Figure 2] Figure 2 is a block diagram showing a configuration for determining the insulation degradation state of the wires of a gradient magnetic field coil according to the first embodiment. [Figure 3] Figure 3 is a schematic diagram showing an example of current flow in the conductor of a gradient magnetic field coil according to the first embodiment. [Figure 4] Figure 4 shows the detection of current and determination of the wire condition by the detection coil according to the first embodiment. [Figure 5] Figure 5 is a perspective view showing the structure of a gradient coil according to the first embodiment. [Figure 6] Figure 6 is a perspective view showing the structure of the ASGC according to the first embodiment. [Figure 7] Figure 7 is a flowchart showing the anomaly detection process according to the first embodiment. [Figure 8] Figure 8 is a flowchart showing the inspection scan process according to the second embodiment. [Figure 9] Figure 9 is a perspective view showing how to use the inspection coil according to the third embodiment. [Modes for carrying out the invention]

[0009] A magnetic resonance imaging apparatus and anomaly detection method according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the following embodiments, parts with the same reference numerals perform the same operation, and redundant explanations will be omitted as appropriate.

[0010] [First Embodiment] In the first embodiment, a detection coil is used to detect the magnetic field generated in an abnormal current path in the conductor of the gradient magnetic field coil, thereby determining that a short circuit has occurred between the conductors and that the insulation of the conductors has deteriorated.

[0011] Figure 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus 1 according to the first embodiment. The magnetic resonance imaging apparatus 1 comprises a magnet stand 100, a control cabinet 300, a console 400, a bed 500, and an RF (Radio Frequency) coil 20.

[0012] The magnet base 100 includes a static magnetic field magnet 10, a gradient magnetic field coil assembly 110, and a WB (Whole Body) coil 12. These components are housed in a cylindrical casing. The bed 500 includes a bed body 50 and a top plate 51.

[0013] The control cabinet 300 includes a gradient magnetic field power supply 31 (31x for the X-axis, 31y for the Y-axis, 31z for the Z-axis), a coil selection circuit 36, an RF receiver 32, an RF transmitter 33, and a sequence controller 34.

[0014] The console 400 includes a processing circuit 40, a memory circuit 41, a display 42, and an input device 43. The console 400 functions as a host computer.

[0015] The static magnetic field magnet 10 of the magnet gantry 100 has a generally cylindrical shape and generates a static magnetic field within a bore in which a subject, for example a patient, is transported. The bore is the space inside the cylinder of the magnet gantry 100. The static magnetic field magnet 10 incorporates a 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 supply (not shown) to the superconducting coil in the excitation mode. Thereafter, when the static magnetic field magnet 10 transitions to the persistent current mode, the static magnetic field power supply is disconnected from the static magnetic field magnet 10. Once it transitions to the persistent current mode, the static magnetic field magnet 10 continues to generate a large static magnetic field for a long time, for example, for more than one year.

[0016] The gradient magnetic field coil assembly 110 has at least one gradient magnetic field coil 11. The gradient magnetic field coil 11 has a generally cylindrical shape and is fixed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 applies a gradient magnetic field to the subject in the directions of the X-axis, Y-axis, and Z-axis, respectively, by currents supplied from the gradient magnetic field power supplies 31x, 31y, and 31z. Specifically, the gradient magnetic field coil 11 is formed by winding a conductor multiple times, and a gradient magnetic field is applied to the subject by flowing a predetermined current through the conductor. The gradient magnetic field power supply 31 applies a gradient magnetic field current to the gradient magnetic field coil 11.

[0017] Furthermore, the detection coil 71 is provided inside or on the outer periphery of the gradient magnetic field coil 11. The detection coil 71 detects the current flowing through the conductor of the gradient magnetic field coil 11 and outputs the current value to the processing circuit 40. Details will be described later.

[0018] The bed body 50 of the bed 500 can move the top plate 51 in the vertical and horizontal directions. The bed body 50 moves the subject placed on the top plate 51 before imaging to a predetermined height. Then, during imaging, the bed body 50 moves the top plate 51 in the horizontal direction to move the subject into the bore.

[0019] The WB coil 12 is also called a whole-body coil and is fixed in a substantially cylindrical shape so as to surround the subject inside the gradient magnetic field coil 11. The WB coil 12 transmits the RF pulse transmitted from the RF transmitter 33 toward the subject. Further, the WB coil 12 receives the magnetic resonance signal, that is, the MR signal, emitted from the subject due to the excitation of hydrogen nuclei.

[0020] The magnetic resonance imaging apparatus 1 includes, in addition to the WB coil 12, an RF coil 20 as shown in FIG. 1. The RF coil 20 is a coil placed close to the body surface of the subject. The RF coil 20 includes a plurality of element coils. Since these plurality of element coils are arranged in an array inside the RF coil 20, it is sometimes called a PAC (Phased Array Coil). There are several types of the RF coil 20. For example, as the RF coil 20, there are types such as a body coil installed on the chest, abdomen, or leg of the subject as shown in FIG. 1, and a spine coil installed on the back of the subject.

[0021] The RF transmitter 33 generates an RF pulse based on an instruction from the sequence controller 34. The generated RF pulse is transmitted to the WB coil 12 or the RF coil 20 and applied to the subject. An MR signal is generated from the subject by the application of the RF pulse. This MR signal is received by the WB coil 12 or the RF coil 20.

[0022] The MR signal received by the RF coil 20, more specifically, the MR signal received by each element coil within the RF coil 20, is transmitted to the coil selection circuit 36 ​​via cables provided on the top plate 51 and the bed body 50. The coil selection circuit 36 ​​selects the signal output from the RF coil 20 or the signal output from the WB coil 12 according to the control signal output from the sequence controller 34 or console 400.

[0023] The selected signal is output to the RF receiver 32. The RF receiver 32 performs an analog-to-digital (AD) conversion on the channel signal, i.e., the MR signal, and outputs it to the sequence controller 34. The MR signal converted to digital is sometimes called raw data. Note that the AD conversion may also be performed inside the RF coil 20 or in the coil selection circuit 36.

[0024] The sequence controller 34 performs a scan of the subject by driving the gradient power supply 31, RF transmitter 33, and RF receiver 32, respectively, under the control of the console 400. When raw data is received from the RF receiver 32 during the scan, the sequence controller 34 transmits that raw data to the console 400.

[0025] The sequence controller 34 includes a processing circuit (not shown in the diagram). This processing circuit consists of, for example, a processor that executes a predetermined program, or hardware such as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0026] The console 400 comprises a memory circuit 41, an input device 43, a display 42, and a processing circuit 40. The memory circuit 41 is a storage medium that includes ROM (Read Only Memory), RAM (Random Access Memory), and external storage devices such as HDDs (Hard Disk Drives) and optical disc drives. The memory circuit 41 stores various information and data, as well as various programs executed by the processor in the processing circuit 40.

[0027] The input device 43 includes, for example, a mouse, keyboard, trackball, touch panel, etc., and includes various devices for the operator to input various types of information and data. The display 42 is a display device such as a liquid crystal display panel, plasma display panel, or organic EL panel.

[0028] The processing circuit 40 is, for example, a circuit equipped with a CPU or a dedicated or general-purpose processor. The processor realizes various functions described later by executing various programs stored in the memory circuit 41. The processing circuit 40 may also be composed of hardware such as an FPGA or ASIC. Various functions described later can also be realized by this hardware. Furthermore, the processing circuit 40 can realize various functions by combining software processing by the processor and programs with hardware processing.

[0029] Figure 2 is a block diagram showing the configuration for determining the insulation degradation state of the wires of the gradient coils 11 that constitute the gradient coil assembly 110 in the magnetic resonance imaging apparatus 1 according to the first embodiment. As shown in Figure 2, a detection coil 71 is placed near the wires of the gradient coils 11. An A / D converter 72 is connected between the detection coil 71 and the processing circuit 40. The detection coil 71 detects the magnetic field generated by the current flowing through the wires of the gradient power supply 31 and outputs a current value corresponding to the magnetic field to the A / D converter 72. The A / D converter 72 acquires the current value from the detection coil 71, converts the current value from analog to digital, and outputs the converted current value to the processing circuit 40.

[0030] The memory circuit 41 stores the background data 411. The background data 411 is data of the signal waveform obtained by the specific sequence of magnetic resonance imaging under normal conditions. In other words, the memory circuit 41 stores the current value detected by the detection coil 71 when the pulse sequence of magnetic resonance imaging is executed normally as a reference value. The memory circuit 41 is an example of a memory unit. The background data 411 is an example of a reference value.

[0031] As shown in Figure 2, the processing circuit 40 of the console 400 implements a wire condition determination function 401 and a system control function 402. Each of these functions is realized, for example, by the processor provided in the processing circuit 40 executing a predetermined program stored in the memory circuit 41.

[0032] The wire condition determination function 401 includes a function to determine the insulation degradation state of the wires constituting the gradient magnetic field coil 11 based on the current value detected by the detection coil 71. The system control function 402 includes a function to control the entire magnetic resonance imaging apparatus 1.

[0033] Figure 3 is a schematic diagram showing an example of current flow in the conductor of the gradient magnetic field coil 11 according to the first embodiment. As shown in Figure 3, in both cases, the two conductors A and B are in close proximity to each other. "Conductors in close proximity to each other" means that "multiple conductors are wound adjacent to each other." Figures 3(a) and 3(b) show examples of normal wire configurations. In the example in Figure 3(a), current flows in the same direction (from left to right) through wires A and B. In the example in Figure 3(b), current flows in opposite directions through wires A and B. That is, current flows through wire A from right to left, while current flows through wire B from left to right.

[0034] Figures 3(c) and 3(d) show examples of abnormal conductors. In the example in Figure 3(c), current was flowing as in Figure 3(a), but a break occurred in the middle of conductor A, causing a short circuit from conductor A to conductor B. As a result, no current flows on the right side of conductor A. On the right side of conductor B, a current flows that is the sum of the current originally flowing through conductor B and the current flowing through conductor A. Figure 3(c) shows an example of insulation degradation occurring between conductor A and conductor B.

[0035] In the example in Figure 3(d), as in Figure 3(b), current was flowing, but a break occurred in the middle of conductors A and B, causing a short circuit from conductor B to conductor A. As a result, current no longer flows to the right of conductors A and B. On the left side of conductor A, the current flowing to the left of conductor B continues to flow. Figure 3(d) also shows an example of insulation degradation occurring between conductors A and B.

[0036] Figure 4 shows the detection of current and determination of the wire state by the detection coil 71 according to the first embodiment. Figures 4(a) to 4(c) show the detection of current flowing through the wire by the detection coil 71. As shown in Figures 4(a) to 4(c), the detection coil 71 is placed, for example, between wires A and B.

[0037] As shown in Figure 4(a), when both conductors A and B are functioning normally, the current flows in the same direction. Therefore, between conductors A and B, the magnetic field caused by the current flowing through conductor A and the magnetic field caused by the current flowing through conductor B are in opposite directions and cancel each other out. For example, if the magnetic field due to conductor B is greater than the magnetic field due to conductor A, the detection coil 71 outputs a waveform image of a normal value, such as the one shown in Figure 4(d), as a current value corresponding to the difference between the magnetic fields. The memory circuit 41 stores this normal value waveform image as a reference value. More specifically, the memory circuit 41 stores the peak value of the current value when the pulse sequence of magnetic resonance imaging is executed normally as a reference value.

[0038] Subsequently, as shown in Figure 4(b), if a break occurs in the middle of conductor A, a short circuit occurs from conductor A to conductor B. At this time, a magnetic field is generated by the short-circuit current from conductor A to conductor B. As a result, the magnetic field passing through the detection coil 71 becomes even larger, and the detection coil 71 outputs, for example, the waveform image of the upper abnormal value shown in Figure 4(d).

[0039] On the other hand, as shown in Figure 4(c), if a break occurs in the middle of conductor B, a short circuit occurs from conductor B to conductor A. At this time, a magnetic field is generated by the short-circuit current from conductor B to conductor A (a magnetic field in the opposite direction to that in Figure 4(b)). As a result, the magnetic fields passing through the detection coil 71 cancel each other out, and the detection coil 71 outputs, for example, the waveform image of the lower abnormal value shown in Figure 4(d).

[0040] Figure 4(d) shows how the insulation degradation state of the wires constituting the gradient magnetic field coil 11 is determined. Specifically, Figure 4(d) shows the waveform image output by the detection coil 71. The wire condition determination function 401 determines that wire A or B is abnormal when the pulse sequence of magnetic resonance imaging is executed and the peak value of the current detected by the detection coil 71 deviates from the normal value by a predetermined threshold. If the wire condition determination function 401 determines that a wire is abnormal, it may estimate the position of the detection coil 71 as the approximate discharge location.

[0041] In Figure 4(d), the upper abnormal values ​​are greater than the normal values ​​by a predetermined threshold. The lower abnormal values ​​are less than the normal values ​​by a predetermined threshold. The normal values ​​are examples of reference values. The predetermined thresholds are calculated from the back data 411 of the memory circuit 41.

[0042] Figure 5 is a perspective view showing the structure of the gradient magnetic field coil 11 according to the first embodiment. The detection coil 71 is placed between conductors that are in close proximity to each other. This allows the detection coil 71 to be placed in a location among the conductors of the gradient magnetic field coil 11 that is relatively prone to short circuits.

[0043] Figure 5(a) shows a gradient coil 11x that generates a magnetic field in the X direction. As shown in Figure 5(a), the detection coil 71x1 is placed in the narrow gap between the upper end of the wire constituting the gradient coil 11x1 and the upper end of the wire constituting the gradient coil 11x2. The detection coil 71x1 detects the magnetic field caused by the current flowing through these two wires and outputs a current corresponding to that magnetic field. The detection coil 71x2 is placed in the narrow gap between adjacent wires in the center of the wires constituting the gradient coil 11x1. The detection coil 71x2 detects the magnetic field caused by the current flowing through these two wires and outputs a current corresponding to that magnetic field.

[0044] Figure 5(b) shows a gradient coil 11y that generates a magnetic field in the Y direction. As shown in Figure 5(b), the detection coil 71y1 is placed in the narrow gap between the right end of the wire constituting the gradient coil 11y1 and the right end of the wire constituting the gradient coil 11y2. The detection coil 71y1 detects the magnetic field caused by the current flowing through these two wires and outputs a current corresponding to that magnetic field. The detection coil 71y2 is placed in the narrow gap between adjacent wires in the center of the wires constituting the gradient coil 11y1. The detection coil 71y2 detects the magnetic field caused by the current flowing through these two wires and outputs a current corresponding to that magnetic field.

[0045] Figure 5(c) shows a gradient coil 11z that generates a magnetic field in the Z direction. The gradient coil 11z is wound around a cylindrical resin. The resin and the gradient coil 11z are then stacked on top of each other so as to cover the gradient coil 11y shown in Figure 5(b). In this case, if the cylindrical resin is thin, the wires of the gradient coil 11y and the wires of the gradient coil 11z may be close together, potentially causing a short circuit between the two wires. Therefore, a detection coil 71z is placed between the gradient coil 11y and the resin around which the gradient coil 11z is wound. The detection coil 71z detects the magnetic field caused by the current flowing through the two wires and outputs a current corresponding to that magnetic field.

[0046] The gradient coil 11y is wound around a cylindrical resin. The resin and the gradient coil 11y are then superimposed so as to cover the gradient coil 11x shown in Figure 5(a). Therefore, similarly to the above, the detection coil 71z may be placed between the gradient coil 11x and the resin on which the gradient coil 11y is wound. The configuration in which the gradient coil 11x in Figure 5(a), the gradient coil 11y in Figure 5(b), and the gradient coil 11z in Figure 5(c) overlap is applied to the main coil 111 and shield coil 112 of the ASGC described later.

[0047] Figure 6 is a perspective view showing the structure of an ASGC according to the first embodiment. The gradient coil assembly 110 may be an ASGC (Active Shield Gradient Coil). In an ASGC, the gradient coil 11 consists of a main coil 111 and a shield coil 112. The main coil 111 applies a gradient magnetic field to the test subject. The shield coil 112 applies a gradient magnetic field in the opposite direction to the main coil 111 by passing current in the opposite direction to the main coil 111. This suppresses the generation of eddy currents due to unwanted leakage magnetic fields from the main coil 111.

[0048] The main coil 111 consists of a pattern of wires through which current flows to apply a gradient magnetic field in the X direction, a pattern of wires through which current flows to apply a gradient magnetic field in the Y direction, and a pattern of wires through which current flows to apply a gradient magnetic field in the Z direction.

[0049] The shield coil 112 is located outside the main coil 111 and consists of a wire pattern in which current flows in the opposite direction to the current of the wire corresponding to the X direction, a wire pattern in which current flows in the opposite direction to the current of the wire corresponding to the Y direction, and a wire pattern in which current flows in the opposite direction to the current of the wire corresponding to the Z direction.

[0050] As shown in Figure 6, a first connection terminal C1, a second connection terminal C2, and a third connection terminal C3 are installed at the end of the gradient coil assembly 110, which is an ASGC. The first connection terminal C1 connects one end of the wire corresponding to the X direction of the main coil 111 and one end of the wire corresponding to the X direction of the shield coil 112 at the side of the end of the ASGC. The first connection terminal C1 is an example of a first connector. Similarly, the second connection terminal C2 connects one end of the wire corresponding to the Y direction of the main coil 111 and one end of the wire corresponding to the Y direction of the shield coil 112 at the side of the end of the ASGC. The second connection terminal C2 is an example of a second connector. Similarly, the third connection terminal C3 connects one end of the wire corresponding to the Z direction of the main coil 111 and one end of the wire corresponding to the Z direction of the shield coil 112 at the side of the end of the ASGC. The third connection terminal C3 is an example of a third connector. The side of the end of the ASGC is an example of the exterior.

[0051] The detection coil 71 is positioned adjacent to the point where the wires of the gradient coil 11 bend. More specifically, the detection coil 71 is positioned on both sides adjacent to the first connection terminal C1, on both sides adjacent to the second connection terminal C2, and adjacent to the third connection terminal C3. The detection coil 71 may be positioned at least one of the three positions. Note that in Figure 6, the detection coil 71 extending along the central axis direction of the gradient coil assembly 110 is the same as the detection coil 71x1 in Figure 5(a) and the detection coil 71y1 in Figure 5(b).

[0052] In other words, the main coil 111 has layers on its substantially cylindrical surface, each consisting of a wire pattern that applies a gradient magnetic field in the X direction, a wire pattern that applies a gradient magnetic field in the Y direction, and a wire pattern that applies a gradient magnetic field in the Z direction. The shield coil 112 is located outside the main coil 111, and has layers on its substantially cylindrical surface, each consisting of a wire pattern that applies a gradient magnetic field in the opposite direction to the X direction, a wire pattern that applies a gradient magnetic field in the opposite direction to the Y direction, and a wire pattern that applies a gradient magnetic field in the opposite direction to the Z direction.

[0053] The detection coil 71 is positioned between the layers formed in the main coil 111 and between the layers formed in the shield coil 112, at least one of the two. More specifically, the detection coil 71 is positioned between the layer in the X direction and the layer in the Y direction that overlaps it, and between the layer in the Y direction and the layer in the Z direction that overlaps it. Since there is a distance between the main coil 111 and the shield coil 112, it is considered that a short circuit due to discharge will not occur.

[0054] According to the above, the detection coil 71 is embedded and positioned inside the ASGC. This avoids magnetic coupling between the detection coil 71 and the ASGC, magnet, or other coils. Furthermore, by embedding the detection coil 71 in the ASGC, the insulation degradation trend can be measured continuously without affecting the image.

[0055] Furthermore, the detection coil 71 is positioned adjacent to the end of the ASGC, that is, the connection terminal where the main coil 111 and the shield coil 112 are externally connected. Near the connection terminal (i.e., the fastening point of the conductors), mechanical stress is applied to the conductors of the gradient magnetic field coil 11 by the Lorentz force, which may cause a load on the fastening point of the conductors and lead to a short circuit. By positioning the detection coil 71 near the connection terminal, the detection coil 71 can be positioned to cover the area near the fastening point, which is relatively prone to disconnection and has a high risk of discharge.

[0056] Figure 7 is a flowchart showing the anomaly detection process according to the first embodiment. This flowchart shows the process for detecting anomalies in the wires of the gradient coil 11 during a normal scan of a subject.

[0057] In step ST1, the system control function 402 in the processing circuit 40 of the console 400 starts a normal scan. The sequence controller 34 performs a scan of the subject under the control of the console 400.

[0058] In step ST2, the gradient power supply 31 applies a gradient current to the gradient coil 11. This causes current to flow through the gradient coil 11.

[0059] In step ST3, a short circuit occurs between the conductors inside the gradient coil 11. If the two conductors are close together and one conductor breaks, and the insulation between the two conductors deteriorates, a short circuit may occur from one conductor to the other.

[0060] In step ST4, the short circuit that occurred in step ST3 generates an unintended abnormal magnetic field from the conductor near the short circuit. This is explained in Figures 3 and 4.

[0061] In step ST5, the detection coil 71 detects the abnormal magnetic field generated in step ST4 and outputs a current corresponding to the magnetic field to the processing circuit 40. The wire condition determination function 401 of the processing circuit 40 determines the insulation degradation state of the wire based on the current value obtained from the detection coil 71.

[0062] In step ST6, if the wire condition determination function 401 determines that there is a wire abnormality, the system control function 402 stops the normal scan.

[0063] As described above, by detecting abnormal magnetic fields generated by unexpected current paths due to short circuits between conductors, the cause of abnormal image display can be clearly identified, thereby improving serviceability. Furthermore, when the output current of the detection coil 71 exceeds a minor threshold, the risk of fire in the magnetic resonance imaging apparatus 1, caused by abnormal heat generation due to short-circuit currents between conductors, can be avoided.

[0064] [Second Embodiment] The second embodiment relates to a process that restricts the pulse sequence of magnetic resonance imaging when an abnormality is detected in the wires of the gradient coil 11. The system control function 402 includes a function to identify the parameters of a degenerate pulse sequence that can operate in degenerate mode when the wire condition determination function 401 determines that the wires are abnormal. The system control function 402 further includes a function to execute the identified degenerate pulse sequence.

[0065] The degenerate mode referred to here is a mode in which, when an abnormality is detected in the wires of the gradient coil 11, the current value flowing through the wire is suppressed, thereby limiting the normal scanning function for the subject while continuing functions that are possible even with the current value suppressed. The degenerate pulse sequence is a pulse sequence for magnetic resonance imaging that can operate in degenerate mode. Note that the current value is just one example of a parameter.

[0066] Figure 8 is a flowchart showing the inspection scan process for setting the current value that can be applied when there is a conductor abnormality according to the second embodiment. This process is executed when the conductor condition determination function 401 determines that there is a conductor abnormality.

[0067] In step ST11, the system control function 402 starts an inspection scan. The purpose of the inspection scan is to set the current value that can be applied to the gradient coil 11, so a subject is not required. At this time, the system control function 402 initializes the current value to be applied to the gradient coil 11. The initial value of the current is, for example, the current value obtained by subtracting a predetermined value from the current value that was applied to the gradient coil 11 when there was a wire abnormality, and is the current value at which it is expected that the wire will be judged to be normal.

[0068] In step ST12, the system control function 402 applies current to the gradient magnetic field coil 11. As a result, the detection coil 71 outputs a current corresponding to the magnetic field generated by the current flowing through the conductor.

[0069] In step ST13, the wire condition determination function 401 determines whether the wire adjacent to the detection coil 71 is normal or not based on the current value output by the detection coil 71. The determination method is as described above in the explanation of Figure 4. If it is determined that the wire is normal (YES in step ST13), the system control function 402 executes the process in step ST14. If it is determined that the wire is not normal (NO in step ST13), the system control function 402 executes the process in step ST15.

[0070] In step ST14, the system control function 402 increases the current value applied to the gradient coil 11. The amount of the current value increase is set appropriately, taking into account the accuracy and efficiency when setting the current value that can be applied to the gradient coil 11. After that, the system control function 402 returns to the process of step ST12.

[0071] In step ST15, the system control function 402 sets the current value that can be applied to the gradient coil 11. That is, the system control function 402 identifies the parameters of a degenerate pulse sequence that can operate in degenerate mode, and by executing the identified degenerate pulse sequence, it transitions from the normal operating mode to the degenerate mode. The current value that can be applied is set to, for example, the current value that was applied to the gradient coil 11 when the last result in step ST13 was determined to be YES, i.e., when the condition of the conductor was determined to be normal.

[0072] In step ST16, the system control function 402 terminates the inspection scan. Subsequently, the system control function 402 executes a sequence of actions by applying the current value set in step ST15 to the gradient magnetic field coil 11.

[0073] According to the above, when an abnormality is detected in the conductor of the gradient coil 11, an applied current is identified that prevents the generation of an abnormal magnetic field at a location adjacent to the conductor. Then, by limiting the pulse sequence of magnetic resonance imaging that can be performed with this applied current, a normal scan of the subject can be resumed. This minimizes the downtime of the magnetic resonance imaging system.

[0074] [Third Embodiment] The third embodiment relates to a process for identifying the location of an abnormality in the conductors of the gradient magnetic field coil 11 using a separate jig. The location of the abnormality is the location that caused the conductor abnormality, for example, the location where a short circuit has occurred due to discharge between the conductors.

[0075] Figure 9 is a perspective view showing how to use the inspection coil 73 according to the third embodiment. As shown in Figure 9, position P is where both conductors A and B are normal. Position Q is where a short circuit from conductor A to B has occurred due to a break in conductor A and deterioration of insulation between conductors A and B. Position R is where conductor B is normal, but conductor A is not conducting current, and the detection coil 71 has detected an abnormality in either conductor A or B. The inspection coil 73 is a jig for detecting the magnetic field caused by the conductors from outside the gradient magnetic field coil 11. The inspection coil 73 is an example of a detection coil that is moved.

[0076] The procedure for identifying the location of the abnormality is described below. First, the wire condition determination function 401 determines the abnormality of the wire based on the current value output from the detection coil 71 installed at position R. Then, the inspection coil 73 is moved, for example, to the left from position R, along the extension direction of wires A and B. The movement of the inspection coil 73 may be automatically controlled or manually performed by a person.

[0077] While moving the inspection coil 73, the wire condition determination function 401 determines the insulation degradation state of wires A and B based on the current value detected by the inspection coil 73. While the inspection coil 73 is between positions R and Q, the wire condition determination function 401 determines that wires A and B are abnormal. Then, when the inspection coil 73 reaches position P, the wire condition determination function 401 determines that wires A and B are normal. At this point, the wire condition determination function 401 detects position Q of the inspection coil 73, which was determined to be abnormal just before wires A and B were determined to be normal, as the location where the wire abnormality occurred, i.e., the location where a short circuit due to discharge caused by insulation degradation has occurred.

[0078] According to at least one embodiment described above, the insulation degradation state of the wires of the gradient magnetic field coil can be determined in a magnetic resonance imaging apparatus.

[0079] The wire condition determination function 401 is an example of a determination unit. The system control function 402 is an example of a control unit.

[0080] Although several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0081] 1. Magnetic Resonance Imaging System 11. Gradient field coil 110 Gradient Magnetic Field Coil Assembly 111 Main coil 112 Shielded Coil 40 Processing Circuits 401 Wire condition detection function 402 System Control Function 41 Memory circuit 411 Back data 71 Detection coil 73 Inspection Coil A, B conductors C1 First connection terminal C2 Second connection terminal C3 Third connection terminal

Claims

1. A gradient magnetic field coil assembly comprising a gradient magnetic field coil formed by winding a wire multiple times, wherein a gradient magnetic field coil applies a gradient magnetic field to a subject by passing a predetermined current through the wire, A detection coil provided inside or on the outer circumference of the gradient magnetic field coil, which detects the current flowing through the conductor, A determination unit that determines the insulation degradation state of the conductor based on the current value detected by the detection coil, A magnetic resonance imaging system equipped with the following features.

2. The detection coil is positioned between the conductors that are in close proximity to each other. The magnetic resonance imaging apparatus according to claim 1.

3. The gradient magnetic field coil assembly consists of a main coil and a shield coil. The main coil has layers on its substantially cylindrical circumferential surface, each consisting of a pattern of wires that applies a gradient magnetic field in the X direction, a pattern of wires that applies a gradient magnetic field in the Y direction, and a pattern of wires that applies a gradient magnetic field in the Z direction. The shield coil is located outside the main coil, and has layers on its substantially cylindrical circumferential surface, each consisting of a wire pattern that applies a gradient magnetic field in the opposite direction to the X direction, a wire pattern that applies a gradient magnetic field in the opposite direction to the Y direction, and a wire pattern that applies a gradient magnetic field in the opposite direction to the Z direction. The detection coil is positioned between the layers formed in the main coil and between the layers formed in the shield coil, The magnetic resonance imaging apparatus according to claim 2.

4. The detection coil is positioned adjacent to the point where the conductor bends. The magnetic resonance imaging apparatus according to claim 1.

5. The gradient magnetic field coil assembly consists of a main coil and a shield coil. The main coil is composed of a pattern of wires through which current flows to apply a gradient magnetic field in the X direction, a pattern of wires through which current flows to apply a gradient magnetic field in the Y direction, and a pattern of wires through which current flows to apply a gradient magnetic field in the Z direction. The shield coil is located outside the main coil and consists of a wire pattern through which current flows in the opposite direction to the current in the wire corresponding to the X direction, a wire pattern through which current flows in the opposite direction to the current in the wire corresponding to the Y direction, and a wire pattern through which current flows in the opposite direction to the current in the wire corresponding to the Z direction. A first connector externally connects the conductor corresponding to the X direction of the main coil and the conductor corresponding to the X direction of the shield coil, A second connector externally connects the conductor corresponding to the Y direction of the main coil and the conductor corresponding to the Y direction of the shield coil, A third connector externally connects the conductor corresponding to the Z direction of the main coil and the conductor corresponding to the Z direction of the shield coil, Furthermore, The detection coil is positioned at least one of the following locations: adjacent to the first connector, adjacent to the second connector, and adjacent to the third connector. The magnetic resonance imaging apparatus according to claim 4.

6. The system further includes a storage unit that stores the current value detected by the detection coil as a reference value when the pulse sequence of magnetic resonance imaging is executed successfully. The determination unit determines that the conductor is abnormal when the pulse sequence is executed and the current value detected by the detection coil deviates from the reference value by a predetermined threshold or more. The magnetic resonance imaging apparatus according to claim 1.

7. The memory unit stores the peak value of the current as the reference value. The determination unit determines that the conductor is abnormal when the pulse sequence is executed and the peak value of the current value deviates from the reference value by a predetermined threshold or more. The magnetic resonance imaging apparatus according to claim 6.

8. If the determination unit determines that the conductor is abnormal, the control unit identifies the parameters of a degenerate pulse sequence that can operate in degenerate mode. The magnetic resonance imaging apparatus according to claim 6, further comprising:

9. The control unit executes the identified degenerate pulse sequence. The magnetic resonance imaging apparatus according to claim 8.

10. A method for detecting an abnormality in a gradient magnetic field coil, which is constructed by winding a wire multiple times, and which applies a gradient magnetic field to a subject by passing a predetermined current through the wire, While moving a detection coil that detects the current flowing through the aforementioned conductor, the state of insulation deterioration of the conductor is determined based on the current value detected by the detection coil. The position of the detection coil when the aforementioned conductor is determined to be abnormal is detected as the location of the abnormality in the conductor. Method for detecting abnormal areas.

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