Magnetic resonance imaging device and operation method of magnetic resonance imaging device

Abstract

To accurately detect magnetic materials present in an imaging space and its vicinity with a simple configuration.SOLUTION: A magnetic resonance imaging device according to one aspect of the present invention is the magnetic resonance imaging device for capturing a magnetic resonance image of a subject and includes: a high-frequency coil; a gradient magnetic field generation coil; and a static magnetic field generation coil being a superconducting coil which has inductance larger than the inductance of the high-frequency coil and the inductance of the gradient magnetic field generation coil; an electric conduction control unit which supplies the current to the static magnetic field generation coil; a voltage measurement unit which measures the voltage between the current lead terminals of the static magnetic field generation coil; and a magnetic material detection unit which detects magnetic materials present in the imaging space of the magnetic resonance imaging device and its vicinity on the basis of the first voltage being the voltage measured in such a state that the first current smaller than the rated current used in imaging is supplied to the static magnetic field generation coil.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a magnetic resonance imaging apparatus and a method for operating the magnetic resonance imaging apparatus, and more particularly to a technique for detecting magnetic objects present in an imaging space of the magnetic resonance imaging apparatus and its surroundings. [Background technology]

[0002] Magnetic resonance imaging devices (MRI devices, MRI: Magnetic Resonance Imaging) have the property that images are distorted by the presence of magnetic materials. For this reason, technology is used to detect or sense magnetic materials present near the MRI device. For example, Patent Document 1 describes detecting metal by detecting changes in electrical data of a gradient magnetic field coil equipped in the MRI device, and Patent Document 2 describes detecting metal using a radio frequency antenna device (high frequency coil) equipped in the MRI device. Patent Document 3 describes generating a magnetic field using a coil for detecting magnetic materials provided separately from the MRI device to determine whether a magnetic material is approaching. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2017-536864 [Patent Document 2] Patent No. 6684832 [Patent Document 3] JP2007-289670A Summary of the Invention [Problem to be solved by the invention]

[0004] When detecting a magnetic body by a change in electrical data (for example, voltage) of a coil, the voltage change of the coil is proportional to the inductance, but since the gradient magnetic field coil and high frequency coil of an MRI device have a small inductance and the voltage change caused by a magnetic body is small, the magnetic body cannot be detected with high accuracy by the techniques such as those in Patent Documents 1 and 2. Furthermore, providing a magnetic body detection device separately from the MRI device as in Patent Document 3 causes the system configuration to become complicated or large.

[0005] As described above, conventional techniques have not been able to accurately detect magnetic objects present in the imaging space of an MRI device or in its vicinity using a simple configuration.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide a magnetic resonance imaging apparatus and an operating method of a magnetic resonance imaging apparatus that can accurately detect magnetic objects present in an imaging space and its vicinity with a simple configuration. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, a magnetic resonance imaging apparatus according to a first aspect of the present invention is a magnetic resonance imaging apparatus for capturing a magnetic resonance image of a subject, and includes a radio frequency coil, a gradient magnetic field generating coil, a static magnetic field generating coil which is a superconducting coil and has an inductance larger than the inductance of the radio frequency coil and the inductance of the gradient magnetic field generating coil, a current control unit which passes current through the static magnetic field generating coil, a voltage measurement unit which measures the voltage between the current lead terminals of the static magnetic field generating coil, and a magnetic material detection unit which detects magnetic materials present in the imaging space of the magnetic resonance imaging apparatus and magnetic materials present in the vicinity of the imaging space based on a first voltage which is a voltage measured when a first current smaller than a rated current when performing imaging is passed through the static magnetic field generating coil.

[0008] According to the first aspect, the static magnetic field generating coil has an inductance larger than the inductance of the high frequency coil and the inductance of the gradient magnetic field generating coil, and is a superconducting coil. Therefore, even when a first current smaller than the rated current is applied, the voltage change due to the presence of the magnetic body is large, and the magnetic body present in the imaging space and the magnetic body present in the vicinity of the imaging space can be detected with high accuracy. The superconducting coil is also called a superconducting coil. Furthermore, since the static magnetic field generating coil provided in the magnetic resonance imaging device is used, there is no need to provide a device other than the imaging device for magnetic body detection, and the configuration of the device can be simplified. The "presence" of the magnetic body includes the case where the magnetic body or the subject having the magnetic body moves and enters the imaging space or its periphery (the same applies to the following aspects). The "imaging space" is the space in which the subject is located when the magnetic resonance image is captured, and in the case of a tunnel bore type device, for example, it is the inside of the tunnel. In the first aspect, "energization" refers to giving energy to the superconducting coil in a cooled state (superconducting state) by electromagnetic induction or connecting a power source from the outside. High frequency coils are also called RF coils (RF: radio frequency).

[0009] In the first aspect and each of the following aspects, the magnetic objects to be detected may be, for example, instruments or machines used in the vicinity of a magnetic resonance imaging device, or objects worn by a subject or user (including pacemakers or artificial joints inside the subject or user's body).

[0010] In the magnetic resonance imaging device according to the second aspect, in the first aspect, the magnetic material detection unit determines that a magnetic material has been detected when at least one of the first voltage being equal to or greater than a threshold value and the time rate of change of the first voltage being equal to or greater than a reference value is satisfied. The second aspect specifies that, in a predetermined case, it is determined that "a magnetic material affecting imaging is present."

[0011] In the magnetic resonance imaging device according to the third aspect, in the second aspect, the current control unit applies a rated current to the static magnetic field generating coil when at least one of the following conditions is met: the first voltage does not meet a threshold value, and the time rate of change of the first voltage does not meet a reference value. In the third aspect, when at least one of the following conditions is met: the first voltage does not meet a threshold value, and the time rate of change of the first voltage does not meet a reference value, it can be determined that "no magnetic body that affects imaging is present in the imaging space or its periphery," and the current control unit applies a rated current to the static magnetic field generating coil to enable imaging of a magnetic resonance image.

[0012] The magnetic resonance imaging device according to the fourth aspect is any one of the first to third aspects, and when the magnetic body detector detects a magnetic body, it performs one or more of the following: stopping the power supply to the static magnetic field generating coil, stopping the movement of the subject into the imaging space, and notifying the detection of the magnetic body. The fourth aspect specifies the response when it is determined that "a magnetic body that affects imaging is present", and these responses can prevent the image from being distorted due to the influence of the magnetic body. The notification can be made by displaying on a display device, issuing a sound, etc.

[0013] A magnetic resonance imaging apparatus according to a fifth aspect is any one of the first to fourth aspects, in which the current supply control unit starts supplying the first current before the subject is moved into the imaging space. According to the fifth aspect, it is possible to detect a magnetic body before the subject is moved into the imaging space.

[0014] The magnetic resonance imaging apparatus according to a sixth aspect is any one of the first to fifth aspects, further comprising an information output unit that outputs information indicating whether or not a magnetic body is present. The information output unit may directly output "whether or not a magnetic body is present" using characters or sound, or may output information indirectly indicating "whether or not a magnetic body is present" (the applied current or the measured voltage) using characters, numbers, graphs, etc.

[0015] A magnetic resonance imaging apparatus according to a seventh aspect is any one of the first to sixth aspects, further comprising an operation unit that receives an operation to instruct the current control unit to apply the first current.

[0016] The magnetic resonance imaging apparatus according to an eighth aspect is the magnetic resonance imaging apparatus according to any one of the first to seventh aspects, wherein the magnetic body is a metal.

[0017] In order to achieve the above object, a method of operating a magnetic resonance imaging apparatus according to a ninth aspect of the present invention is a method of operating a magnetic resonance imaging apparatus that includes a high-frequency coil, a gradient magnetic field generating coil, a static magnetic field generating coil that has an inductance larger than the inductance of the high-frequency coil and the inductance of the gradient magnetic field generating coil and is a superconducting coil, and a processor, and that captures a magnetic resonance image of a subject, in which the processor applies a current to the static magnetic field generating coil, measures a voltage between current lead terminals of the static magnetic field generating coil, and detects a magnetic body that exists in an imaging space of the magnetic resonance imaging apparatus and a magnetic body that exists near the imaging space based on a first voltage that is a voltage measured in a state in which a first current smaller than a rated current for performing the imaging is applied to the static magnetic field generating coil. According to the tenth aspect, as in the first aspect, magnetic bodies that exist in the imaging space and its periphery can be detected with high accuracy with a simple configuration. The method of operating according to the ninth aspect may further include a configuration corresponding to the second to eighth aspects. Effect of the Invention

[0018] As described above, according to the magnetic resonance imaging apparatus and the method of operating the magnetic resonance imaging apparatus of the present invention, it is possible to accurately detect magnetic bodies present in the imaging space and in its vicinity with a simple configuration. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing the configuration of a magnetic resonance imaging system. [Diagram 2] FIG. 2 is a diagram showing the configuration of a magnetic resonance imaging apparatus. [Diagram 3]FIG. 3 is a diagram showing the configuration of a static magnetic field generating source. [Figure 4] FIG. 4 is a diagram illustrating a functional configuration of the processor. [Diagram 5] FIG. 5 is a schematic diagram showing how a magnetic material is detected. [Figure 6] FIG. 6 is a diagram showing the current and voltage of the static magnetic field generating coil (when no magnetic body is present). [Figure 7] FIG. 7 is a diagram showing the current and voltage of the static magnetic field generating coil (when a magnetic body is present). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, preferred embodiments of a magnetic resonance imaging apparatus and a method for operating a magnetic resonance imaging apparatus according to the present invention will be described with reference to the accompanying drawings. Note that in the accompanying drawings, some components may be omitted for convenience of explanation. Also, the accompanying drawings do not show the exact shape or dimensions of the magnetic resonance imaging apparatus.

[0021] [First embodiment] [Configuration of magnetic resonance imaging device] First, the configuration of the magnetic resonance imaging apparatus will be described. As shown in FIG.

[0022] The magnetic resonance imaging apparatus 100 is an apparatus for obtaining a tomographic image of a subject 110 (see FIG. 2), and in this embodiment, it is an MRI apparatus (Magnetic Resonance Imaging) that utilizes the nuclear magnetic resonance (NMR) phenomenon. FIG. 1 shows a tunnel bore type MRI apparatus equipped with a cylindrical gantry as an example of the magnetic resonance imaging apparatus 100 and the apparatus main body 101. The apparatus main body 101 has a cylindrical tunnel 102 with the axial direction horizontal, and generates a static magnetic field in the tunnel 102 to create an imaging space. The apparatus main body 101 is placed in an electromagnetically shielded room, and the gradient magnetic field power supply 132, the sequencer 140, the high frequency oscillator 151, the modulator 152, the high frequency amplifier 153, the signal amplifier 162, the quadrature phase detector 163, the A / D converter 164, the control unit 170, and the like (see FIG. 2) are placed outside the electromagnetically shielded room and are electrically connected to the apparatus main body 101 by cables.

[0023] [Configuration of magnetic resonance imaging device] Fig. 2 is a diagram showing the configuration of the magnetic resonance imaging apparatus 100. As shown in Fig. 2, the magnetic resonance imaging apparatus 100 includes a static magnetic field generating source 120, a gradient magnetic field generating unit 130, a sequencer 140, a radio frequency irradiation unit 150, a signal detection unit 160, and a control unit 170.

[0024] 3, the static magnetic field generating source 120 includes a power supply 122 and a superconducting coil 124 (static magnetic field generating coil), and generates a uniform static magnetic field in a static magnetic field space accommodating the subject 110 in a direction perpendicular to the body axis of the subject 110 in the case of a vertical magnetic field type, or in the direction of the body axis of the subject 110 in the case of a horizontal magnetic field type. The static magnetic field generating source 120 is disposed around the subject 110. The current and voltage of the superconducting coil 124 are measured by an ammeter 126 and a voltmeter 128, and are input to a processor 171 (control unit 170). The static magnetic field generating coil may be a normal conducting coil instead of a superconducting coil.

[0025] Returning to FIG. 2, the gradient magnetic field generating unit 130 has gradient magnetic field coils 131 (coils for generating gradient magnetic fields) that are superimposed on the static magnetic field space and generate gradient magnetic fields in three axial directions of X, Y, and Z, which are the coordinate system (stationary coordinate system) of the magnetic resonance imaging apparatus 100, and gradient magnetic field power supplies 132 that drive the respective gradient magnetic field coils 131. The gradient magnetic field power supplies 132 of the respective coils are driven according to commands, i.e., control, from a sequencer 140 described later, to generate gradient magnetic fields Gx, Gy, and Gz in the three axial directions of X, Y, and Z. During imaging, a slice direction gradient magnetic field pulse (Gs) is applied in a direction perpendicular to the slice plane (imaging cross section) to set a slice plane for the subject 110, and a phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied in the remaining two directions perpendicular to the slice plane and perpendicular to each other, to encode position information in each direction in an echo signal.

[0026] The sequencer 140 repeatedly applies radio frequency magnetic field pulses (RF pulses) and gradient magnetic field pulses in a predetermined pulse sequence. The sequencer 140 operates under the control of the processor 171, and sends various commands, i.e., controls, required for data collection of tomographic images of the subject 110 to the gradient magnetic field generating unit 130, the radio frequency irradiation unit 150, and the signal detecting unit 160.

[0027] The radio-frequency irradiation unit 150 irradiates the subject 110 with an RF pulse in order to cause nuclear magnetic resonance in the nuclear spins of atoms constituting the biological tissue of the subject 110. The radio-frequency irradiation unit 150 includes a radio-frequency oscillator 151, a modulator 152, a radio-frequency amplifier 153, and an irradiation coil 154 (radio-frequency coil) which is a radio-frequency coil on the transmitting side. The RF pulse output from the radio-frequency oscillator 151 is amplitude-modulated by the modulator 152 at a timing according to a command from the sequencer 140, and the amplitude-modulated RF pulse is amplified by the radio-frequency amplifier 153, and then supplied to the irradiation coil 154 arranged close to the subject 110, whereby the subject 110 is irradiated with an electromagnetic wave.

[0028] The signal detection unit 160 detects an echo signal, which is an NMR signal emitted by nuclear magnetic resonance of atomic spins constituting the biological tissue of the subject 110. The signal detection unit 160 includes a receiving coil 161 (radio frequency coil) which is a radio frequency coil on the receiving side, a signal amplifier 162, a quadrature phase detector 163, and an A / D converter 164 (analog / digital converter). An NMR signal of a response induced in the subject 110 by an electromagnetic wave irradiated from the irradiation coil 154 is detected by the receiving coil 161 arranged close to the subject 110, amplified by the signal amplifier 162, and then split into two orthogonal systems of signals by the quadrature phase detector 163 at a timing according to a command from the sequencer 140, each of which is converted into a digital quantity by the A / D converter 164 and sent to the control unit 170.

[0029] The control unit 170 (processor) performs various data processing, and displays and stores the processing results. The control unit 170 includes a processor 171 (processor), storage devices such as a RAM 172A (RAM: random access memory) and a ROM 172B (ROM: read only memory), an external storage device 180 such as an optical disk 181 and a magnetic disk 182, and an input / output unit 190. When the signal detection unit 160 receives a signal or data, the processor 171 uses the RAM 172A as a working area to execute signal processing, image reconstruction, and other processing, and displays the resultant tomographic image of the subject 110 on the output device 200 and records it in the external storage device 180. When executing these processes, the processor 171 can refer to the programs and data recorded in the ROM 172B.

[0030] Furthermore, under the control of processor 171, control unit 170 can cause power source 122 to supply current to superconducting coil 124 (coil for generating a static magnetic field), and can measure the current being supplied and the voltage between current lead terminals of superconducting coil 124 using ammeter 126 and voltmeter 128. Control unit 170 (processor 171) also detects a magnetic body based on these measurement results, and outputs the results.

[0031] In this manner, the processor 171 operates as an imaging control unit 171A, an energization control unit 171B (energization control unit), a voltage measurement unit 171C (voltage measurement unit), a magnetic material detection unit 171D (magnetic material detection unit), and an information output unit 171E (information output unit) (FIG. 1). The detection of a magnetic material by each of these units will be described in detail below.

[0032] The input / output unit 190 inputs and outputs various control information of the magnetic resonance imaging apparatus 100 and control information of processing performed by the control unit 170, specifically, accepts input and displays imaging parameters of a pulse sequence. The input / output unit 190 also accepts an operation to instruct energization (first current, etc.) to the static magnetic field generating coil, and outputs information indicating an energization state and a measured voltage. The input / output unit 190 includes an input device 210 (operation unit) including a pointing device 211 such as a trackball, mouse, pad, touch panel, etc., and a keyboard 212, and an output device 200 (information output unit) including a display 201 such as a cathode-ray tube (CRT) or a liquid crystal display (LCD), etc., and a printer 202. The input device 210 may be disposed close to the output device 200, and an operator may interactively control the magnetic resonance imaging apparatus 100 by, for example, instructing the magnetic resonance imaging apparatus 100 to execute various processes through the pointing device 211 while looking at the display 201. Also, a touch panel that operates as the input device 210 may be disposed on the display surface of the display 201, and input operations may be performed by selecting or operating the contents displayed on the display 201.

[0033] In addition, the input / output unit 190 may be equipped with audio input / output devices such as a microphone and a speaker, and these devices may allow the operator to perform operations by voice via the microphone, or to provide audio notification such as information indicating the current flow state and measured voltage, or notification when a magnetic body is detected (for example, a notification regarding one or more of stopping the flow of current to the static magnetic field generating coil, stopping the movement of the subject into the imaging space, and detection of a magnetic body).

[0034] The subject 110 is placed on a top board 310 of the bed device 300, and is accommodated in a static magnetic field space, which is an imaging space, by a bed moving device 220 (see FIG. 2). The transmission side irradiation coil 154 and gradient magnetic field coil 131 are installed in the static magnetic field space in which the subject 110 is accommodated, facing the subject 110 in the case of a vertical magnetic field type, or surrounding the subject 110 in the case of a horizontal magnetic field type. The reception side receiving coil 161 is installed facing the part of the subject 110 to be imaged, or surrounding the part to be imaged.

[0035] The nuclide currently being imaged by MRI devices, which is widely used in clinical practice, is hydrogen nuclei (protons), which are the main constituent of the subject 110. By imaging information on the spatial distribution of proton density and the spatial distribution of the relaxation time of the excited state, the morphology or function of the human head, abdomen, limbs, etc. can be imaged two-dimensionally or three-dimensionally.

[0036] [Example of coil inductance and generated voltage] As described above, the magnetic resonance imaging apparatus 100 includes the irradiation coil 154 and the receiving coil 161 (high frequency coil), the gradient magnetic field coil 131 (gradient magnetic field generating coil), and the superconducting coil 124 (static magnetic field generating coil). As an example of the inductance of these coils and the voltage generated in the coils when the magnetic body moves, the inductance of the high frequency coil, the gradient magnetic field generating coil, and the static magnetic field generating coil is 1 μH (H: Henry), 1 mH, and 30 H, respectively, and the generated voltages (relative values) are 0.001, 1, and 30000, respectively. When the static magnetic field generating coil is a superconducting coil, the superconducting coil has a superconducting wire wound, for example, several thousand turns, so that the inductance is large. Thus, the static magnetic field generating coil has a large inductance, and therefore the voltage generated by the magnetic body is also high, so that it is suitable for detecting the magnetic body.

[0037] [Couch system configuration] The bed device 300 includes a top board 310 and a top board holder 311 on which the subject 110 is placed, and a main body 340. In the first embodiment, the bed device 300 is fixed to the device main body 101. However, the bed device 300 may be configured separately from the magnetic resonance imaging device 100 so as to be connectable and detachable to the device main body 101. The top board 310 is held by the top board holder 311 and can slide into or out of the imaging space by a bed moving device 220 (see FIG. 2) in the magnetic resonance imaging device 100. The bed device 300 also includes a top board locking mechanism (not shown), which can lock the top board 310 to prevent it from sliding, or unlock the top board 310 to allow it to slide. The bed device 300 includes a tabletop lifting mechanism (not shown) (which may be constituted by, for example, a hydraulic jack or a pantograph arm) and is capable of lifting and lowering the tabletop 310 and the tabletop holder 311.

[0038] [Detection of magnetic objects] Next, detection of a magnetic body in the imaging space of the magnetic resonance imaging device 100 and its vicinity will be described. Fig. 5 is a schematic diagram (only some components are shown) showing the manner of detection of a magnetic body, Fig. 6 is a diagram showing the current and voltage of the superconducting coil 124 (static magnetic field generating coil) when no magnetic body is present in the imaging space or its vicinity, and Fig. 7 is a diagram showing the current and voltage of the superconducting coil 124 when a magnetic body is present in the imaging space or its vicinity. Note that the information output unit 171E (processor 171; information output unit) can display on the display 201 the graphs shown in Figs. 6 and 7, the current and voltage values, whether or not a magnetic body is present, etc.

[0039] First, a case where no magnetic body exists in the imaging space or in the vicinity thereof will be described. Part (a) of FIG. 5 shows a state where the subject 110 enters the space (examination room, etc.) in which the magnetic resonance imaging apparatus 100 is installed. The current control unit 171B (processor 171; current control unit) starts to pass a first current (current A1 in part (a) of FIG. 6) smaller than the rated current for imaging to the superconducting coil 124 in accordance with this timing (t=t0). The subject 110 does not have to enter the room and start passing current at the same time. The voltmeter 176 (voltage measurement unit) measures the voltage V, and the information output unit 171E outputs information indicating the measured voltage to the display 201 (output device), etc. These measurements and outputs are continued until the imaging is completed. The first current can be, for example, half or less of the rated current, but may be a different value depending on the detection accuracy of the magnetic body and other conditions. Furthermore, the magnitude of the first current may be variable, and the energization control unit 171B may energize the first current having a value according to the user's operation.

[0040] Part (b) of Fig. 5 shows a state in which the subject 110 approaches the magnetic resonance imaging apparatus 100 (time t = t1 to t2), and part (c) of the same figure shows a state in which the subject 110 lies on the top board 310 and is able to move into the imaging space (time t = t2). Since Fig. 6 shows an example in which no magnetic body exists in the imaging space or in its vicinity, the voltage V of the superconducting coil 124 does not increase even when the first current is applied (see part (b) of Fig. 6; the period from time t1 to t2).

[0041] In a state where the subject 110 can be moved to the imaging space (part (a) of FIG. 5; time t=t2), the voltage V (first voltage) is less than the threshold value, and the time rate of change of the voltage V does not reach the reference value. Therefore, the current supply control unit 171B increases the current (period of time t=t2 to t3) and supplies a rated current (current A2 in part (a) of FIG. 6) to the superconducting coil 124 (static magnetic field generating coil). In addition, the bed moving device 220 slides the top board 310 to move the subject 110 to the imaging space (state shown in part (d) of FIG. 5). This makes it possible to pick up a magnetic resonance image of the subject 110. Note that it is preferable that the information output unit 171E outputs information indicating that no magnetic body is present or is not detected (one aspect of information indicating whether or not a magnetic body is present) to the display 201 or the like before supplying the rated current to the superconducting coil 124.

[0042] Next, a case where a magnetic body is present in the imaging space or in its vicinity (for example, in an examination room in which the apparatus main body 101 is installed, or in the vicinity of the bed apparatus 300) will be described. Here, the magnetic body is an object (for example, a pacemaker, an artificial joint, etc.) possessed by the subject 110, but may be an article such as a machine or an instrument used in the vicinity of the magnetic resonance imaging apparatus 100. In addition, the magnetic body is, for example, a metal such as iron, but magnetic bodies other than metals can also be detected. When such a magnetic body is present in the imaging space or in its vicinity, a voltage (first voltage) according to inductance is generated between the current lead terminals of the superconducting coil 124 when a first current is applied to the superconducting coil 124 (static magnetic field generating coil) (time t=t0 to t1; part (a) of FIG. 7). This first voltage increases (times t1 to t4; parts (a) to (c) of FIG. 5 and part (b) of FIG. 7) as the subject 110 approaches the magnetic resonance imaging apparatus 100 (i.e., as the magnetic body approaches the magnetic resonance imaging apparatus 100). In the example shown in FIG. 7, since the first voltage becomes equal to or greater than the threshold value V0 at time t=t4, the magnetic body detection unit 171D can determine that "a magnetic body that affects (interferes with) imaging is present in the imaging space or in its vicinity." In this case, it is preferable that the information output unit 171E outputs information indicating the presence of a magnetic body (one aspect of information indicating whether or not a magnetic body is present) to the display 201 or the like.

[0043] The magnetic body detection unit 171D may determine that a "magnetic body has been detected" when at least one of the following is satisfied: the first voltage is equal to or greater than a threshold value; and the time rate of change of the first voltage (change in the first voltage during the period from time t=t1 to t4 in the example of FIG. 7) is equal to or greater than a reference value. In response to this determination (detection of a magnetic body), the magnetic body detection unit 171D (processor 171) can perform one or more of the following: stopping the application of electricity to the superconducting coil 124 (static magnetic field generating coil), stopping the movement of the subject 110 into the imaging space, and notifying that a magnetic body has been detected, thereby preventing imaging from being disturbed due to the presence of a magnetic body. The magnetic body detection unit 171D (processor 171, control unit 170) may perform a plurality of the above-mentioned actions, or may perform all of them. In the example of FIG. 7, the first voltage becomes equal to or greater than the threshold voltage V0 at time t=t4 (part (b) of the figure), and in response, the control unit 170 (current control unit) stops supplying current to the superconducting coil 124 (current is zero at time t=t5; part (a) of the figure).

[0044] As described above, in the magnetic resonance imaging apparatus 100, it is preferable to start passing a current (passing a first current) through the superconducting coil 124 before moving the subject 110 into the imaging space, so that a prompt response can be made if a magnetic body is detected.

[0045] If the conditions for the magnitude and time rate of change of the first voltage are not met (if the first voltage does not meet the threshold value and the time rate of change of the first voltage does not meet the reference value), the processor 171 (control unit 170) determines that "a magnetic body is not present" or "a magnetic body is present but does not affect (interfere with) imaging", and can pass a rated current through the superconducting coil 124 and proceed to imaging.

[0046] As described above, the magnetic resonance imaging apparatus 100 can accurately detect magnetic objects present in the imaging space and magnetic objects present in the vicinity of the imaging space with a simple configuration.

[0047] [others] In the magnetic resonance imaging apparatus 100 of this embodiment, the processor 171 may include, in terms of hardware, various processors such as those shown below. The "various processors" include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and functions as various processing units, a programmable logic device (PLD), which is a processor whose circuit configuration can be changed after manufacture such as an FPGA (Field Programmable Gate Array), and a dedicated electric circuit, which is a processor having a circuit configuration designed exclusively for executing specific processing such as an ASIC (Application Specific Integrated Circuit).

[0048] The processor 171 may be configured with one of these various processors, or may be configured with two or more processors of the same or different types (for example, multiple FPGAs, or a combination of a CPU and an FPGA). Also, multiple processing units may be configured with one processor. As an example of configuring multiple processing units with one processor, first, as represented by a computer such as a client or server, there is a form in which one processor is configured with a combination of one or more CPUs and software, and this processor functions as multiple processing units. Second, as represented by a system on chip (SoC), there is a form in which a processor is used that realizes the functions of the entire system including multiple processing units with one IC (Integrated Circuit) chip. In this way, the various processing units can be configured using one or more of the above various processors as a hardware structure.

[0049] More specifically, the hardware structure of these various processors is an electric circuit that combines circuit elements such as semiconductor elements. When the various processors operate, they can refer to programs and data recorded in non-transient and tangible recording media such as ROM 172B, and can use recording media such as RAM 172A as a temporary working area during operation.

[0050] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible. [Explanation of symbols]

[0051] A1 1st current A2 Rated current V0 Threshold

Claims

1. A magnetic resonance imaging apparatus for capturing a magnetic resonance image of a subject, comprising: A high frequency coil; A gradient magnetic field generating coil; a static magnetic field generating coil which is a superconducting coil and has an inductance larger than the inductance of the high frequency coil and the inductance of the gradient magnetic field generating coil; A current control unit that applies current to the static magnetic field generating coil; A voltage measurement unit that measures a voltage between current lead terminals of the static magnetic field generating coil; a magnetic body detection unit that detects a magnetic body present in an imaging space of the magnetic resonance imaging device and a magnetic body present in the vicinity of the imaging space based on a first voltage that is a voltage measured in a state in which a first current that is smaller than a rated current for performing the imaging is passed through the static magnetic field generating coil; A magnetic resonance imaging apparatus comprising:

2. 2. The magnetic resonance imaging device according to claim 1, wherein the magnetic material detection unit determines that the magnetic material has been detected when at least one of the following conditions is satisfied: the first voltage is equal to or greater than a threshold value; and a time rate of change of the first voltage is equal to or greater than a reference value.

3. 3. The magnetic resonance imaging apparatus of claim 2, wherein the current control unit supplies the rated current to the static magnetic field generating coil when the first voltage does not satisfy the threshold value and the time rate of change of the first voltage does not satisfy the reference value.

4. 4. The magnetic resonance imaging device according to claim 1, wherein, when the magnetic material detection unit detects the magnetic material, it performs one or more of the following: stopping the flow of current to the static magnetic field generating coil, stopping movement of the subject into the imaging space, and notifying the user that the magnetic material has been detected.

5. The magnetic resonance imaging apparatus according to claim 1 , wherein the current control unit starts the application of the first current before the subject is moved into the imaging space.

6. The magnetic resonance imaging apparatus according to claim 1 , further comprising an information output unit that outputs information indicating whether or not the magnetic body is present.

7. The magnetic resonance imaging apparatus according to claim 1 , further comprising an operation unit configured to receive an operation for instructing the current control unit to apply the first current.

8. 4. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic material is a metal.

9. 1. A method for operating a magnetic resonance imaging apparatus for capturing a magnetic resonance image of a subject, the method comprising: a radio frequency coil; a gradient magnetic field generating coil; a static magnetic field generating coil which is a superconducting coil and has an inductance larger than an inductance of the radio frequency coil and an inductance of the gradient magnetic field generating coil; and a processor, the method comprising the steps of: The processor, energizing the static magnetic field generating coil; Measure the voltage between the current lead terminals of the static magnetic field generating coil; detecting a magnetic body present in an imaging space of the magnetic resonance imaging device and a magnetic body present in the vicinity of the imaging space based on a first voltage, the first voltage being a voltage measured in a state in which a first current smaller than a rated current for performing the imaging is passed through the static magnetic field generating coil; A method for operating a magnetic resonance imaging device.

Images