Magnetic resonance imaging apparatus
The MRI apparatus accurately determines pulse sequence execution by calculating power consumption and capacitor voltage using resistance tables and Fourier transforms, addressing voltage drop issues in gradient coils, ensuring stable power supply and image quality.
Patent Information
- Application Number
- JP2024024867
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-02-21
- Publication Date
- 2025-09-02
AI Technical Summary
Conventional magnetic resonance imaging (MRI) systems face challenges in accurately determining whether a pulse sequence can be executed due to voltage drops in electrolytic capacitors, especially during high-frequency sequences, leading to potential errors in power calculations and inefficient power supply to gradient magnetic field coils.
The MRI apparatus includes a gradient magnetic field coil, power supply with capacitors, and an analyzer to calculate current and voltage values, using resistance tables and Fourier transforms to determine power consumption and capacitor voltage, ensuring accurate execution of pulse sequences.
This approach allows for precise determination of whether a pulse sequence can be executed, reducing errors and ensuring stable power supply to gradient coils, thereby maintaining image quality and avoiding inconvenient system shutdowns.
Smart Images
Figure 2025127880000001_ABST
Abstract
Description
[Technical Field]
[0001] The embodiments disclosed in this specification and drawings relate to a magnetic resonance imaging apparatus. [Background technology]
[0002] A magnetic resonance imaging device is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with radio frequency (RF) signals at the Larmor frequency, and generates images by reconstructing magnetic resonance (MR) signals generated from the subject as a result of the excitation.
[0003] As a conventional technology, in a magnetic resonance imaging apparatus, an equivalent circuit model of a gradient coil (ASGC: Active Shield Gradient Coil) shown in FIG. 8 is used to calculate the power consumption of the gradient coil, predict the voltage drop of an electrolytic capacitor in a gradient power supply, and determine whether or not a pulse sequence can be executed.
[0004] A gradient magnetic field power supply supplies a gradient magnetic field coil with an arbitrary output current waveform according to the pulse sequence conditions. The gradient magnetic field power supply is equipped with an electrolytic capacitor to assist in the power supply to the gradient magnetic field coil. However, if the power supplied to the gradient magnetic field coil increases, the voltage of the electrolytic capacitor may drop. In this case, the gradient magnetic field power supply cannot output the target current waveform. In particular, since the resistance value of the gradient magnetic field coil has a frequency characteristic, pulse sequences with high frequency components, such as EPI (Echo Planar Imaging), increase the power consumption of the gradient magnetic field coil and significantly decrease the voltage of the electrolytic capacitor. Therefore, in order to support a wide variety of pulse sequences, it is necessary to predict the voltage drop of the electrolytic capacitor and determine whether the pulse sequence can be executed.
[0005] In the conventional technology, it is necessary to set the parameter values of coils 1, 2, and 3 in Fig. 8, such as the self-inductances L1i to L3i and the mutual inductances M12i and M13i, so that the frequency characteristics of the equivalent circuit model are equal to the measured values of the gradient coil. However, there are problems such as the time-consuming process of adjusting the parameter values and the occurrence of errors with the measured values. In addition, because the resistance value of the gradient coil changes with temperature, there is a problem that the error in the conventional calculation method becomes even larger when the temperature of the gradient coil rises, such as immediately after a high-load sequence is output. [Prior art documents] [Patent documents]
[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-35305 Summary of the Invention [Problem to be solved by the invention]
[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to accurately determine whether a pulse sequence can be executed in a magnetic resonance imaging apparatus. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]
[0008] A magnetic resonance imaging apparatus according to an embodiment includes a gradient magnetic field coil, a gradient magnetic field power supply, an analyzer, a power calculation unit, and a voltage calculation unit. The gradient magnetic field coil applies a gradient magnetic field to a subject. The gradient magnetic field power supply is a power supply that applies a gradient magnetic field current to the gradient magnetic field coil and has a capacitor therein for power supplementation. The analyzer determines, for each frequency, the current value of the gradient magnetic field current to be output to the gradient magnetic field coil when a pulse sequence is executed. The power calculation unit calculates the power consumption in the gradient magnetic field coil based on the resistance value and current value of the gradient magnetic field coil for each frequency. The voltage calculation unit calculates the voltage value of the capacitor based on the power consumption. [Brief explanation of the drawings]
[0009] [Figure 1] FIG. 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of a gradient magnetic field power supply according to the first embodiment. [Figure 3] FIG. 3 is a block diagram showing a configuration for determining whether or not a pulse sequence can be executed in the magnetic resonance imaging apparatus according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of an output current waveform of a pulse sequence according to the first embodiment. [Figure 5] FIG. 5 is a diagram showing an example of frequency characteristics of the resistance value of the gradient magnetic field coil according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing an example of a result of Fourier transform of a current value according to the first embodiment. [Figure 7] FIG. 7 is a block diagram showing a configuration for determining whether or not a pulse sequence can be executed in a magnetic resonance imaging apparatus according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing an equivalent circuit model of a gradient magnetic field coil according to the prior art. DETAILED DESCRIPTION OF THE INVENTION
[0010] A magnetic resonance imaging apparatus according to an embodiment will be described with reference to the accompanying drawings. In the following embodiments, parts with the same reference numerals operate in the same manner, and redundant description will be omitted as appropriate.
[0011] [First embodiment] 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 includes a magnet gantry 100, a control cabinet 300, a console 400, a bed 500, and an RF (Radio Frequency) coil 20.
[0012] The magnetic gantry 100 has a static magnetic field magnet 10, a gradient magnetic field coil 11, and a WB (Whole Body) coil 12. These components are housed in a cylindrical housing. The bed 500 has a bed body 50 and a tabletop 51.
[0013] The control cabinet 300 includes gradient magnetic field power supplies 31 (for the X axis 31x, for the Y axis 31y, and for the Z axis 31z), a coil selection circuit , an RF receiver 32, an RF transmitter 33, and a sequence controller .
[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 magnetic gantry 100 has a roughly cylindrical shape and generates a static magnetic field within a bore into which a subject, e.g., a patient, is transported. The bore is the space inside the cylinder of the magnetic gantry 100. The static magnetic field magnet 10 incorporates a superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, 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. 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 transitioned to the persistent current mode, the static magnetic field magnet 10 continues to generate a large static magnetic field for a long period of time, e.g., for more than one year.
[0016] The gradient magnetic field coil 11 also has a roughly cylindrical shape and is fixed inside the static magnetic field magnet 10. This gradient magnetic field coil 11 applies gradient magnetic fields to the subject in the X-axis, Y-axis, and Z-axis directions, respectively, by currents supplied from gradient magnetic field power supplies 31x, 31y, and 31z. The gradient magnetic field power supply 31 is a gradient magnetic field power supply that applies gradient magnetic field current to the gradient magnetic field coil 11, and has a capacitor bank CB (see FIG. 2) therein for power supplementation. The capacitor bank CBx is an example of a capacitor.
[0017] The bed body 50 of the bed 500 can move the top plate 51 in the vertical and horizontal directions. Before imaging, the subject placed on the top plate 51 is moved to a predetermined height. Then, during imaging, the top plate 51 is moved horizontally to move the subject into the bore.
[0018] The WB coil 12, also called a whole-body coil, is fixed in a roughly cylindrical shape so as to surround the subject inside the gradient coil 11. The WB coil 12 transmits RF pulses transmitted from an RF transmitter 33 toward the subject. It also receives magnetic resonance signals, i.e., MR (Magnetic Resonance) signals, emitted from the subject due to excitation of hydrogen nuclei.
[0019] In addition to the WB coil 12, the magnetic resonance imaging apparatus 1 also includes an RF coil 20 as shown in FIG. 1. The RF coil 20 is a coil that is placed close to the body surface of the subject. The RF coil 20 includes a plurality of element coils. These element coils are arranged in an array inside the RF coil 20, and are therefore sometimes called PAC (Phased Array Coil). There are several types of RF coils. For example, the RF coil 20 includes a body coil that is placed on the chest, abdomen, or legs of the subject as shown in FIG. 1, and a spine coil that is placed on the back of the subject.
[0020] 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. The application of the RF pulse generates an MR signal from the subject. The RF coil 20 or the WB coil 11 receives this MR signal.
[0021] The MR signals received by the RF coil 20, more specifically, the MR signals received by each element coil in the RF coil 20, are transmitted to the coil selection circuit 36 via cables provided on the tabletop 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 in accordance with a control signal output from the sequence controller 34 or the console 400.
[0022] The selected signal is output to the RF receiver 32. The RF receiver 32 converts the channel signal, i.e., the MR signal, from analog to digital (AD) and outputs it to a sequence controller 34. The digitalized MR signal is also called raw data. The AD conversion may be performed inside the RF coil 20 or in the coil selection circuit 36.
[0023] The sequence controller 34 scans the subject by driving the gradient magnetic field power supply 31, the RF transmitter 33, and the RF receiver 32 under the control of the console 400. When raw data is received from the RF receiver 32 by the scan, the sequence controller 34 transmits the raw data to the console 400.
[0024] The sequence controller 34 includes a processing circuit (not shown). This processing circuit is configured with hardware such as a processor that executes a predetermined program, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit). The console 400 includes a memory circuitry 41, an input device 43, a display 42, and a processing circuitry 40. The memory circuitry 41 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), and an external storage device such as an HDD (Hard Disk Drive) or an optical disk device. The memory circuitry 41 stores various types of information and data, as well as various programs executed by a processor included in the processing circuitry 40.
[0025] The input device 43 includes various devices such as a mouse, keyboard, trackball, touch panel, etc., which are used by the operator to input various information and data. The display 42 is a display device such as a liquid crystal display panel, a plasma display panel, an organic EL panel, etc.
[0026] The processing circuit 40 is a circuit including, for example, a CPU or a dedicated or general-purpose processor. The processor executes various programs stored in the storage circuit 41 to realize various functions described below. The processing circuit 40 may be configured with hardware such as an FPGA or an ASIC. The various functions described below can also be realized by such hardware. The processing circuit 40 can also realize various functions by combining software processing by a processor and a program with hardware processing.
[0027] Fig. 2 is a block diagram showing the configuration of the gradient magnetic field power supply 31 according to the first embodiment. As shown in Fig. 2, the gradient magnetic field power supply 31 is made up of gradient magnetic field power supplies 31x, 31y, and 31z. The gradient magnetic field power supply 31x includes a DC power supply PSx, a capacitor bank CBx, and a pulse modulation circuit PMCx. The gradient magnetic field power supply 31y includes a DC power supply PSy, a capacitor bank CBy, and a pulse modulation circuit PMCy. The gradient magnetic field power supply 31z includes a DC power supply PSz, a capacitor bank CBz, and a pulse modulation circuit PMCz.
[0028] In the gradient magnetic field power supply 31x, the DC power supply PSx is a power supply that supplies energy to the pulse modulation circuit PWCx. The DC power supply PSx outputs a constant voltage when the load of the downstream stage is small, but switches to a constant current mode when the load of the downstream stage increases. For example, the DC power supply PSx is a 400V voltage source when the supply power is 10 kW or less, but when the supply power exceeds 10 kW, the voltage is reduced and a current flows while maintaining the supply power of 10 kW. Note that the DC power supplies PSx, PSy, and PSz may be integrated.
[0029] The capacitor bank CBx is a capacitor that supplements the power supply that is insufficient from the DC power supply PSx, and is configured to include, for example, a plurality of electrolytic capacitors.
[0030] The pulse modulation circuit PMCx is a pulse amplifier that converts the waveform of the pulse sequence output from the sequence controller 34 into a large current pulse and outputs it to the gradient magnetic field coil 11x. For example, a PWM (Pulse Width Modulation) class D amplifier or the like is used as the pulse modulation circuit PMCx.
[0031] The above description of the components of the gradient power supply 31x also applies to the components of the gradient power supplies 31y and 31z. Gradient magnetic field currents as large current pulses generated by the gradient magnetic field power supplies 31x, 31y, and 31z are applied to the gradient magnetic field coils 11x, 11y, and 11z, respectively. Furthermore, in the magnetic resonance imaging apparatus 1 according to the first embodiment, current detectors 71x, 71y, and 71z are provided between the gradient magnetic field power supplies 31x, 31y, and 31z and the gradient magnetic field coils 11x, 11y, and 11z, respectively. As will be described later, the current detectors 71x, 71y, and 71z measure gradient magnetic field currents supplied from the gradient magnetic field power supplies 31x, 31y, and 31z to the gradient magnetic field coils 11x, 11y, and 11z. The current detectors 71x, 71y, and 71z may be provided inside the gradient magnetic field power supplies 31x, 31y, and 31z, respectively.
[0032] When it becomes necessary to pass a large current through the gradient magnetic field coils 11x-11z of all axes in a short period of time, the required power supply may temporarily exceed the power that the DC power supplies PSx-PSz can supply. Even in such a case, the existence of the capacitor banks CBx-CBz allows stable power supply to the gradient magnetic field coils 11x-11z. In other words, by supplementing the power of the DC power supplies PSx-PSz with the power of the capacitor banks CBx-CBz, the power supply to the gradient magnetic field coils 11x-11z can be maintained for as long as possible.
[0033] However, depending on the pulse sequence conditions, the power consumption of the gradient coils 11x to 11z may increase more than expected, and even if the capacitor banks CBx to CBz supplement the power, sufficient power may still not be supplied. For example, when the frequency of the gradient current used in the pulse sequence increases, the effective cross-sectional area of the conductors of the gradient coils 11x to 11z decreases due to the skin effect. As a result, the resistance value of the gradient coils 11x to 11z (i.e., the pure resistance component other than the reactance component of the gradient coils 11x to 11z) increases, resulting in a large amount of energy consumption. In particular, an EPI (Echo Planar Imaging) sequence consumes more energy than an SE (Spin Echo) sequence because of its higher frequency. Therefore, even if the capacitor banks CBx to CBz supplement the power of the DC power supplies PSx to PSz, sufficient power may still not be supplied to the gradient coils 11x to 11z. As a result, the intended gradient magnetic field cannot be applied to the subject by the gradient coils 11x to 11z, and normal magnetic resonance images cannot be generated. On the other hand, there is a negative correlation between the power consumption of the gradient magnetic field coils 11x to 11z and the output voltage values of the capacitors in the capacitor banks CBx to CBz (hereinafter simply referred to as the voltage values of the capacitor banks CBx to CBz).
[0034] Therefore, by monitoring the voltage values of the capacitor banks CBx-CBz, it is possible to estimate the power consumption of the gradient magnetic field coils 11x-11z. For this reason, for example, in a conventional magnetic resonance imaging apparatus 1, when the voltage of the capacitor banks CBx-CBz drops below a predetermined value, the gradient magnetic field power supplies 31x-31z determine that it has become difficult to operate as power supplies for supplying power to the gradient magnetic field coils 11x-11z, and are shut down as an error. However, if the apparatus shuts down during a diagnosis of a subject, it is necessary to reset the imaging conditions, such as a pulse sequence, by partially changing them, and then redo the imaging, which is inconvenient.
[0035] Therefore, the magnetic resonance imaging apparatus 1 according to the first embodiment has a configuration for calculating the voltage values of the capacitor banks CBx to CBz in advance and determining whether or not the pulse sequence can be executed.
[0036] FIG. 3 is a block diagram showing a configuration for determining whether a pulse sequence can be executed in the magnetic resonance imaging apparatus 1 according to the first embodiment. As shown in FIG. 3, a current detector 71 is connected between the gradient magnetic field power supply 31 and the gradient magnetic field coil 11 (similar to FIG. 2). An A / D converter 72 is connected between the current detector 71 and the processing circuit 40. The current detector 71 detects a current value of the pulse sequence applied from the gradient magnetic field power supply 31 to the gradient magnetic field coil 11 and outputs the current value to the A / D converter 72. The A / D converter 72 acquires the current value of the pulse sequence from the current detector 71, performs analog-to-digital conversion on the current value, and outputs the converted current value to the processing circuit 40. FIG. 4 is a diagram showing an example of an output current waveform of the pulse sequence according to the first embodiment. FIG. 4 shows an output current waveform for one period (TR, repetition pulse).
[0037] The memory circuit 41 stores a resistance value table 411. The resistance value table 411 is a lookup table in which frequencies are associated with the resistance values of the gradient magnetic field coil 11. The resistance values of the gradient magnetic field coil 11 for each frequency are measured in advance and recorded in the resistance value table 411. FIG. 5 is a diagram showing an example of the frequency characteristics of the resistance value of the gradient magnetic field coil 11 according to the first embodiment. For example, as shown in FIG. 5, the resistance value table 411 associates frequencies f1, f2, and f3 with resistance values R1, R2, and R3, respectively.
[0038] 3, the processing circuitry 40 of the console 400 realizes a current analysis function 401, a power calculation function 402, a voltage calculation function 403, and an execution determination function 404. Each of these functions is realized, for example, by a processor included in the processing circuitry 40 executing a predetermined program stored in the memory circuitry 41.
[0039] The current analysis function 401 includes a function for calculating, for each frequency, the current value of the gradient magnetic field current output to the gradient magnetic field coil 11 when a pulse sequence is executed. Specifically, the current analysis function 401 acquires the digital value of the gradient magnetic field current from the A / D converter 72. The current analysis function 401 then performs a Fourier transform on the digital current value to calculate the current value for each frequency. FIG. 6 is a diagram showing an example of the result of the Fourier transform of the current value according to the first embodiment. Assume that a spectrum density having peaks is obtained when the output current waveform of the pulse sequence is Fourier transformed. As shown in FIG. 6, the frequencies at which the current value peaks are defined as f1, f2, and f3, and the effective values Irms (root mean square) of the current at these frequencies are defined as I1, I2, and I3, respectively.
[0040] The power calculation function 402 includes a function for calculating the power consumed by the gradient magnetic field coil 11 from the current value of the gradient magnetic field current output to the gradient magnetic field coil 11 and the resistance value of the gradient magnetic field coil 11. In detail, the power calculation function 402 acquires the resistance value for each frequency of the gradient magnetic field coil 11 from the resistance value table 411 in the memory circuitry 41. Next, the power calculation function 402 acquires the current value for each frequency from the current analysis function 401. Then, the power calculation function 402 calculates the power value for each frequency from the resistance value for each frequency and the current value for each frequency, and sums up the power values. This sum becomes the power consumption P of the gradient magnetic field coil 11. For example, the power consumption P can be calculated using the following (Equation 1). P = R1*I1 2 +R2*I2 2 +R3*I3 2 (Formula 1)
[0041] The voltage calculation function 403 includes a function of calculating the voltage value V of the capacitor bank CB of the gradient magnetic field power supply 31 based on the power consumption P, using the following (Equation 2). V = F(P) (Equation 2) Here, F() is a function F relating the power consumption P of the gradient magnetic field coil 11 to the voltage value V of the capacitor bank CB. The function F may be an approximation of a fitting curve obtained from the relationship between the power consumption P of the gradient magnetic field coil 11 measured in advance and the voltage value V of the capacitor bank CB, or may be defined by an arithmetic expression based on the law of conservation of energy, as described in Patent Document 1. Here, the energy consumption E of the gradient magnetic field coil 11 is calculated by the product of (Equation 1) and the time t of one cycle of the pulse sequence. TR This can be expressed as the following (Equation 3) using E = (R1*I1 2 +R2*I2 2 +R3*I3 2 )*t TR (Formula 3) Alternatively, the function F may be defined as a look-up table obtained from the relationship between the power consumption P of the gradient magnetic field coil 11 measured in advance and the voltage value V of the capacitor bank CB.
[0042] The execution determination function 404 includes a function for determining whether or not a pulse sequence can be executed based on the voltage value V of the capacitor bank CB. For example, the execution determination function 404 compares the voltage value V with a predetermined threshold value, and determines that the pulse sequence cannot be executed if the voltage value V is smaller than the predetermined threshold value. The threshold value may be a threshold value related to an interlock of the magnetic resonance imaging apparatus 1, a threshold value related to the image quality standard of an MRI image, or the like.
[0043] According to the first embodiment, the power consumption P of the gradient magnetic field coil 11 is calculated using the actual measured value of the gradient magnetic field current, which eliminates the need to adjust the parameter values of the equivalent circuit model and reduces errors that occur when using the equivalent circuit model. Furthermore, according to the first embodiment, the power consumption P of the gradient magnetic field coil 11 is calculated using the resistance value of the gradient magnetic field coil 11, which may differ for each frequency, and the frequency component of the gradient magnetic field current, so that the power consumption P of the gradient magnetic field coil 11, which reflects the frequency component of the pulse sequence, can be calculated with high accuracy depending on the type of pulse sequence.
[0044] Second Embodiment In the first embodiment, the resistance value table 411 in the memory circuit 41 was used to obtain the resistance value of the gradient magnetic field coil 11, but in the second embodiment, the current applied to the gradient magnetic field coil 11 and the voltage of the gradient magnetic field coil 11 are obtained, and the resistance value of the gradient magnetic field coil 11 is calculated from the current and voltage.
[0045] 7 is a block diagram showing a configuration for determining whether a pulse sequence can be executed in a magnetic resonance imaging apparatus 1a according to the second embodiment. Hereinafter, a description of the same components as those in the magnetic resonance imaging apparatus 1 will be omitted. As shown in FIG. 7, the magnetic resonance imaging apparatus 1a further includes a resistance measurement function 8, a first switch SW1, and a second switch SW2.
[0046] The resistance measurement function 8 includes a function for measuring the resistance value for each frequency of the gradient magnetic field coil 11. For example, an impedance meter, an impedance analyzer, or the like is used as the resistance measurement function 8. The resistance measurement function 8 includes a sine wave generator 73, a voltage / current measuring device 74, and a resistance calculation function 405. The resistance calculation function 405 is realized by the processing circuit 40a. The processing circuit 40a has a configuration equivalent to that of the above-mentioned processing circuit 40, and realizes a current analysis function 401, a power calculation function 402, a voltage calculation function 403, and an execution determination function 404 in addition to the resistance calculation function 405.
[0047] The sine wave generator 73 applies a sine wave signal with a variable frequency to the gradient magnetic field coil 11, independently of the application of the gradient magnetic field current. The voltage / current measuring device 74 measures the voltage and current of the sine wave signal applied to the gradient magnetic field coil 11. The resistance calculation function 405 includes a function for calculating the resistance value for each frequency of the gradient magnetic field coil 11 from the measured voltage and current of the sine wave signal. The resistance calculation function 405 outputs the resistance value to the power calculation function 402a. At this time, the power calculation function 402a obtains the resistance value for each frequency of the gradient magnetic field coil 11 from the resistance calculation function 405.
[0048] The first switch SW1 turns on and off the connection between the gradient magnetic field power supply 31 and the gradient magnetic field coil 11. When measuring the resistance value of the gradient magnetic field coil 11, the first switch SW1 cuts off the application of the gradient magnetic field current to the gradient magnetic field coil 11, and when not measuring the resistance value, the first switch SW1 applies the gradient magnetic field current to the gradient magnetic field coil 11.
[0049] The second switch SW2 turns on and off the connection between the sine wave generator 73 and the gradient magnetic field coil 11. The second switch SW2 applies a sine wave signal to the gradient magnetic field coil 11 when measuring the resistance value of the gradient magnetic field coil 11, and cuts off the application of the sine wave signal to the gradient magnetic field coil 11 when not measuring the resistance value.
[0050] The resistance calculation function 405 may calculate the resistance value of the gradient magnetic field coil 11 as a pure resistance component not including the inductance component of the gradient magnetic field coil 11 from a current component of the voltage and the current that is in phase with the voltage, or from a voltage component of the current and the voltage that is in phase with the current. For example, if the sine wave generator 73 is a constant voltage source, the resistance value of the gradient magnetic field coil 11 is calculated from the voltage applied by the sine wave generator 73 and a current component that is in phase with the voltage. On the other hand, if the sine wave generator 73 is a constant current source, the resistance value of the gradient magnetic field coil 11 is calculated from the current applied by the sine wave generator 73 and a voltage component that is in phase with the current.
[0051] In addition, when a second pulse sequence is executed following the execution of a first pulse sequence (i.e., scanning of the subject), the resistance measurement function 8 may measure the resistance value of the gradient magnetic field coil 11 after the first pulse sequence is completed and before the second pulse sequence is started.
[0052] According to the second embodiment, by measuring the frequency characteristics of the resistance value of the gradient magnetic field coil 11 between scans of the subject, it is possible to calculate the power consumption of the gradient magnetic field coil 11 that reflects changes in the resistance value of the gradient magnetic field coil 11 due to temperature changes. As a result, it is possible to estimate the voltage value V of the capacitor bank CB with high accuracy, and it is possible to determine with high reliability whether or not a pulse sequence can be executed.
[0053] According to at least one of the embodiments described above, it is possible to accurately determine whether or not a pulse sequence can be executed in a magnetic resonance imaging apparatus.
[0054] The current analysis function 401 is an example of an analysis unit. The power calculation functions 402 and 402a are an example of a power calculation unit. The voltage calculation function 403 is an example of a voltage calculation unit. The execution determination function 404 is an example of a determination unit. The resistance calculation function 405 is an example of a resistance calculation unit. The resistance measurement function 8 is an example of a measurement unit.
[0055] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied 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 modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the inventions and their equivalents as set forth in the claims. [Explanation of symbols]
[0056] 1, 1a Magnetic resonance imaging device 11 Gradient magnetic field coil 31 Gradient magnetic field power supply 40, 40a Processing circuit 41 Memory circuit 401 Current analysis function 402, 402a power calculation function 403 Voltage Calculator 404 Execution Judgment Function 405 Resistance calculation function 411 Resistance Value Table 8 Resistance measurement function CB Capacitor Bank
Claims
1. a gradient magnetic field coil for applying a gradient magnetic field to the subject; a gradient magnetic field power supply that applies a gradient magnetic field current to the gradient magnetic field coil, the gradient magnetic field power supply having a capacitor for power supplementation therein; an analysis unit that calculates, for each frequency, a current value of a gradient magnetic field current to be output to the gradient magnetic field coil when a pulse sequence is executed; a power calculation unit that calculates the power consumption in the gradient magnetic field coil based on a resistance value for each frequency of the gradient magnetic field coil and the current value; a voltage calculation unit that calculates a voltage value of the capacitor based on the power consumption; A magnetic resonance imaging apparatus comprising:
2. a determination unit that determines whether or not the pulse sequence is executable based on a voltage value of the capacitor; The magnetic resonance imaging apparatus according to claim 1 , further comprising:
3. The analysis unit performs a Fourier transform of the current value and calculates the current value for each frequency.
2. The magnetic resonance imaging apparatus according to claim 1.
4. The resistance value of the gradient magnetic field coil for each frequency is measured in advance and recorded in a look-up table.
2. The magnetic resonance imaging apparatus according to claim 1.
5. a measurement unit for measuring a resistance value for each frequency of the gradient magnetic field coil; The magnetic resonance imaging apparatus according to claim 1 , further comprising:
6. The measurement unit a sine wave generator that applies a variable frequency sine wave signal to the gradient coil independently of the application of the gradient current; a voltage / current measuring device for measuring the voltage and current of the sinusoidal signal applied to the gradient magnetic field coil; a resistance calculation unit that calculates a resistance value for each frequency of the gradient magnetic field coil from the measured voltage and current; 6. The magnetic resonance imaging apparatus according to claim 5, comprising:
7. a first switch that cuts off application of the gradient magnetic field current to the gradient magnetic field coil when measuring the resistance value, and applies the gradient magnetic field current to the gradient magnetic field coil when not measuring the resistance value; a second switch that applies the sine wave signal to the gradient coil when the resistance value is being measured, and cuts off application of the sine wave signal to the gradient coil when the resistance value is not being measured; The magnetic resonance imaging apparatus according to claim 6 , further comprising:
8. the resistance calculation unit calculates the resistance value as a pure resistance component not including an inductance component of the gradient magnetic field coil from a current component of the voltage and the current that is in phase with the voltage, or from a voltage component of the current and the voltage that is in phase with the current.
7. The magnetic resonance imaging apparatus according to claim 6.
9. the measurement unit measures the resistance value of the gradient magnetic field coil after the first pulse sequence is completed and before the second pulse sequence is started, in a case where a second pulse sequence is executed following the execution of a first pulse sequence.
9. A magnetic resonance imaging apparatus according to claim 5.
Citation Information
Patent Citations
Magnetic resonance imaging apparatus
JP2017035305A