JP7480026B2 - Magnetic resonance imaging apparatus, temperature measuring apparatus and temperature measuring method - Google Patents

Description

The embodiments disclosed in the specification relate to a magnetic resonance imaging device, a temperature measurement device, and a temperature measurement method.

In a superconducting magnetic resonance imaging apparatus (superconducting MRI apparatus), for example, helium is used as a coolant for a superconducting coil. However, due to the recent increase in the price of helium, the lifetime cost of the MRI apparatus is being put under pressure.
For this reason, it is desirable to use a low-capacity refrigerant with as little helium as possible. However, in an MRI device with a large helium capacity, that is, with a sufficient amount of refrigerant, even if the temperature of the superconducting coil rises, there is a high possibility that the heat can be absorbed by evaporation of the refrigerant, but if the amount of refrigerant is small, such as in a low-capacity refrigerant, there is a high possibility that quenching will occur due to the intrusion of heat from the outside.
Therefore, in an MRI apparatus using a low-volume refrigerant, it is important to control the temperature of the superconducting coil in order to maintain the superconducting state inside the magnet.

JP 2009-183472 A Japanese Patent Application Laid-Open No. 01-242052

One of the problems that the embodiments disclosed in the specification and drawings aim to solve is to improve the accuracy of estimating temperature. However, the problems that the embodiments disclosed in the 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 below can also be positioned as other problems.

The magnetic resonance imaging apparatus according to this embodiment includes a temperature sensor and a sensor control unit. The temperature sensor measures the temperature of a superconducting coil that forms a magnet that generates a static magnetic field. The sensor control unit excludes output from the temperature sensor or stops the function of the temperature sensor during a target period that includes at least the period during which a high-frequency magnetic field is applied.

FIG. 1 is a conceptual diagram showing an MRI apparatus according to this embodiment. FIG. 2 is a conceptual diagram of the temperature measurement circuit according to the first embodiment. FIG. 3 is a flowchart showing the temperature measurement process in the MRI apparatus according to the first embodiment. FIG. 4 is a diagram illustrating a first example of the temperature measurement process according to the first embodiment. FIG. 5 is a diagram illustrating a second example of the temperature measurement process according to the first embodiment. FIG. 6 is a diagram illustrating a third example of the temperature measurement process according to the first embodiment. FIG. 7 is a diagram showing a first configuration example of the temperature measurement circuit according to the second embodiment. FIG. 8 is a flowchart showing a temperature measurement process in the MRI apparatus according to the second embodiment. FIG. 9 is a diagram illustrating an example of a temperature measurement process in the first configuration example of the temperature measurement circuit according to the second embodiment. FIG. 10 is a diagram showing a second configuration example of the temperature measurement circuit according to the second embodiment. FIG. 11 is a diagram illustrating an example of a temperature measurement process in the second configuration example of the temperature measurement circuit according to the second embodiment. FIG. 12 is a diagram showing an example of the configuration of a temperature measurement circuit according to the third embodiment.

The magnetic resonance imaging apparatus (MRI apparatus), temperature measurement apparatus, and temperature measurement method according to this embodiment will be described below with reference to the drawings. In the following embodiment, parts with the same reference numerals perform similar operations, and duplicated descriptions will be omitted as appropriate.

First Embodiment
FIG. 1 is a conceptual diagram showing an MRI apparatus according to the first embodiment.
1, the MRI apparatus 1 includes a static magnetic field magnet 101, a magnet management unit 2, a gradient magnetic field coil 103, a gradient magnetic field power supply 105, a bed 107, a bed control circuit 109, a transmission circuit 113, a transmission coil 115, a reception coil 117, a reception circuit 119, a sequence control circuit 121, a bus 123, an interface 125, a display 127, a storage device 129, and a processing circuit 131. The MRI apparatus 1 may include a hollow cylindrical shim coil between the static magnetic field magnet 101 and the gradient magnetic field coil 103.

The static magnetic field magnet 101 is a magnet formed in a hollow, approximately cylindrical shape. Note that the static magnetic field magnet 101 is not limited to an approximately cylindrical shape, and may be configured in an open shape. The static magnetic field magnet 101 generates a uniform static magnetic field in the internal space. In this embodiment, the static magnetic field magnet 101 is assumed to be a superconducting magnet using a superconducting coil.

The gradient magnetic field coil 103 is a coil formed in a hollow cylindrical shape. The gradient magnetic field coil 103 is placed inside the static magnetic field magnet 101. The gradient magnetic field coil 103 is formed by combining three coils corresponding to the mutually orthogonal X, Y, and Z axes. The Z-axis direction is the same direction as the static magnetic field direction. The Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to the Z and Y axes. The three coils in the gradient magnetic field coil 103 are individually supplied with current from the gradient magnetic field power supply 105 to generate a gradient magnetic field whose magnetic field strength changes along each of the X, Y, and Z axes.

The X-, Y-, and Z-axis gradient magnetic fields generated by the gradient coil 103 form, for example, a frequency encoding gradient magnetic field (also called a readout gradient magnetic field), a phase encoding gradient magnetic field, and a slice selection gradient magnetic field. The frequency encoding gradient magnetic field is used to change the frequency of the MR signal depending on the spatial position. The phase encoding gradient magnetic field is used to change the phase of the MR signal depending on the spatial position. The slice selection gradient magnetic field is used to determine the imaging cross-section.

The gradient magnetic field power supply 105 is a power supply device that supplies current to the gradient magnetic field coil 103 under the control of the sequence control circuit 121.

The bed 107 is a device equipped with a tabletop 1071 on which the subject P is placed. Under the control of a bed control circuit 109, the bed 107 inserts the tabletop 1071 on which the subject P is placed into the bore 111. The bed 107 is installed in the examination room in which the MRI apparatus 1 is installed, for example, so that its longitudinal direction is parallel to the central axis of the static magnetic field magnet 101.

The bed control circuit 109 is a circuit that controls the bed 107, and drives the bed 107 in response to instructions from the operator via the interface 125, thereby moving the tabletop 1071 in the longitudinal and vertical directions.

The transmitting coil 115 is an RF coil arranged inside the gradient magnetic field coil 103. The transmitting coil 115 receives RF (Radio Frequency) pulses from the transmitting circuit 113 and generates a transmitting RF wave equivalent to a high frequency magnetic field. The transmitting coil 115 is, for example, a whole-body coil. The whole-body coil may be used as a transmitting/receiving coil. A cylindrical RF shield is installed between the whole-body coil and the gradient magnetic field coil 103 to magnetically separate these coils.

The transmission circuit 113 supplies an RF pulse (corresponding to the Larmor frequency, etc.) to the transmission coil 115 under the control of the sequence control circuit 121.

The receiving coil 117 is an RF coil arranged inside the gradient magnetic field coil 103. The receiving coil 117 receives an MR signal emitted from the subject P by a high frequency magnetic field. The receiving coil 117 outputs the received MR signal to a receiving circuit 119. The receiving coil 117 is, for example, a coil array having one or more, typically multiple coil elements. The receiving coil 117 is, for example, a phased array coil.

Under the control of the sequence control circuit 121, the receiving circuit 119 generates a digital MR signal, which is digitized complex data, based on the MR signal output from the receiving coil 117. Specifically, the receiving circuit 119 performs various signal processing on the MR signal output from the receiving coil 117, and then performs analog-to-digital (A/D) conversion on the data that has been subjected to various signal processing. The receiving circuit 119 samples the A/D converted data. As a result, the receiving circuit 119 generates a digital MR signal (hereinafter referred to as MR data). The receiving circuit 119 outputs the generated MR data to the sequence control circuit 121.

The sequence control circuit 121 controls the gradient magnetic field power supply 105, the transmission circuit 113, the reception circuit 119, etc. according to the examination protocol output from the processing circuit 131, and performs imaging of the subject P. The examination protocol has various pulse sequences (also called imaging sequences) according to the examination. The examination protocol defines the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing at which the gradient magnetic field power supply 105 supplies the current to the gradient magnetic field coil 103, the magnitude of the RF pulse supplied to the transmission coil 115 by the transmission circuit 113, the timing at which the RF pulse is supplied to the transmission coil 115 by the transmission circuit 113, the timing at which the MR signal is received by the reception coil 117, etc.

The bus 123 is a transmission path for transmitting data between the interface 125, the display 127, the storage device 129, and the processing circuit 131. Various biosignal measuring devices, external storage devices, various modalities, etc. may be appropriately connected to the bus 123 via a network or the like. For example, an electrocardiograph (not shown) is connected to the bus as a biosignal measuring device.

The interface 125 has circuits that accept various instructions and information input from an operator. The interface 125 has circuits related to input devices such as a pointing device such as a mouse, or a keyboard. Note that the circuits of the interface 125 are not limited to circuits related to physical operating parts such as a mouse and a keyboard. For example, the interface 125 may have an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device provided separately from the MRI apparatus 1, and outputs the received electrical signals to various circuits.

Under the control of the system control function 1311 in the processing circuit 131, the display 127 displays various magnetic resonance images (MR images) generated by the image generation function 1313, various information related to imaging and image processing, and the like. The display 127 is, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display or monitor known in the art.

The storage device 129 stores the MR data filled in the k-space via the image generation function 1313, the image data generated by the image generation function 1313, etc. The storage device 129 stores various examination protocols, imaging conditions including a plurality of imaging parameters that define the examination protocols, etc. The storage device 129 stores programs corresponding to various functions executed by the processing circuitry 131. The storage device 129 is, for example, a semiconductor memory element such as a random access memory (RAM), a flash memory, a hard disk drive, a solid state drive, an optical disk, etc. The storage device 129 may also be a drive device that reads and writes various information to and from a portable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory.

The magnet management unit 2 includes a temperature measurement circuit 20, a sensor control unit 21, and a calculation unit 22. Note that, as described below, a similar configuration may be realized by the temperature measurement circuit 20 and the system control function 1311 and calculation function 1315 of the processing circuit 131.

The temperature measurement circuit 20 has a circuit configuration that uses a temperature sensor to measure the temperature of one or more superconducting coils that form the static magnetic field magnet 101 that generates a static magnetic field. The temperature measurement circuit 20 is also called a temperature measurement device.

The sensor control unit 21 excludes output from the temperature sensor or stops the function of the temperature sensor during a target period that includes at least the period during which the high-frequency magnetic field is applied. In the following, the target period is also referred to as a non-use period.

The calculation unit 22 calculates the estimated temperature of the superconducting coil using temperature data measured during a period other than the target period.

The processing circuitry 131 has hardware resources such as a processor (not shown), memory such as a ROM (Read-Only Memory) and a RAM, and generally controls the MRI apparatus 1. The processing circuitry 131 has a system control function 1311, an image generation function 1313, and a calculation function 1315.

The various functions of the processing circuit 131 are stored in the storage device 129 in the form of programs executable by a computer. The processing circuit 131 is a processor that realizes the functions corresponding to these various functions by reading the programs corresponding to these various functions from the storage device 129 and executing them. In other words, the processing circuit 131 in a state in which each program has been read out has multiple functions, etc., as shown in the processing circuit 131 in Figure 1.

In FIG. 1, it has been described that these various functions are realized by a single processing circuit 131, but the processing circuit 131 may be configured by combining multiple independent processors, and each processor may execute a program to realize the functions. In other words, each of the above-mentioned functions may be configured as a program and one processing circuit may execute each program, or a specific function may be implemented in a dedicated, independent program execution circuit.

The term "processor" used in the above description refers to circuits such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)).

The processor realizes various functions by reading and executing programs stored in the memory device 129. Note that instead of storing the programs in the memory device 129, the programs may be directly built into the processor's circuitry. In this case, the processor realizes functions by reading and executing the programs built into the circuitry. Note that the bed control circuitry 109, transmission circuitry 113, reception circuitry 119, sequence control circuitry 121, etc. are also similarly configured from electronic circuits such as the above-mentioned processor.

The processing circuitry 131 controls the MRI apparatus 1 by the system control function 1311. Specifically, the processing circuitry 131 reads out a system control program stored in the storage device 129, expands it in memory, and controls each circuit of the MRI apparatus 1 according to the expanded system control program. For example, the processing circuitry 131 reads out an examination protocol from the storage device 129 by the system control function 1311 based on the imaging conditions input by the operator via the interface 125. The processing circuitry 131 may generate an examination protocol based on the imaging conditions. The processing circuitry 131 transmits the examination protocol to the sequence control circuitry 121 and controls imaging of the subject P.

The processing circuitry 131 uses the system control function 1311 to apply excitation pulses and apply gradient magnetic fields according to the excitation pulse sequence. After executing the excitation pulse sequence using the system control function 1311, the processing circuitry 131 collects MR signals from the subject P according to a data collection sequence, which is a pulse sequence for collecting various types of data, and generates MR data. The system control function 1311 may have a function to perform processing similar to that of the sensor control unit 21.

The processing circuitry 131 fills the MR data along the readout direction of the k-space according to the strength of the readout gradient magnetic field using the image generation function 1313. The processing circuitry 131 generates an MR image by performing a Fourier transform on the MR data filled in the k-space. For example, the processing circuitry 131 can generate an absolute value (magnitude) image from complex MR data. The processing circuitry 131 can also generate a phase image using real and imaginary data in the complex MR data. The processing circuitry 131 outputs MR images such as the absolute value image and the phase image to the display 127 or the storage device 129.

When the processing circuit 131 is able to acquire temperature data from the magnet management unit 2, the calculation function 1315 calculates an estimated temperature of the superconducting coil in the same manner as the calculation unit 22 included in the magnet management unit 2.

Next, a conceptual diagram of the temperature measurement circuit 20 according to the first embodiment will be described with reference to FIG.
Fig. 2 is a cross-sectional view of the gantry as viewed from the Z-axis direction, showing cross sections of the static magnetic field magnet 101, the gradient magnetic field coil 103, and the transmission coil 115. Fig. 2 also shows the concept of an equivalent circuit of the temperature measurement circuit 20, a part of which is disposed adjacent to the static magnetic field magnet 101.

The static magnetic field magnet 101 is formed by a superconducting coil 1011 connected to multiple coil blocks arranged in a pedestal. The superconducting coil 1011 is immersed in a refrigerant container (not shown) containing liquid helium. The liquid helium is cooled by a cryogenic refrigerator (not shown) to prevent it from evaporating, thereby maintaining the superconducting state of the superconducting coil 1011.

For low-volume refrigerants, the refrigerant can be sealed in a closed loop structure called a thermosiphon and cooled by heat transfer through the closed loop flow path. Alternatively, it can be achieved without using a refrigerant by using a conduction cooling method that absorbs heat from the cold head of the refrigerator using only a heat transfer material.

The temperature measurement circuit 20 includes a temperature sensor 201, which is a resistive sensor having a resistance value R, and a reference resistor 202 having a resistance value R0. The temperature sensor 201 is placed close to the superconducting coil 1011 within the static magnetic field magnet 101. Note that while the example in FIG. 2 shows an example in which one temperature sensor 201 is placed, multiple temperature sensors 201 may be placed. By placing multiple temperature sensors 201, local temperature increases in the superconducting coil 1011 can also be detected.

The temperature of the superconducting coil 1011 can be measured by measuring the voltage between the temperature sensor 201 and the reference resistor 202 and calculating the temperature from the fluctuation in the voltage value. Because the resistance value of the temperature sensor 201 changes depending on the temperature, the measured voltage value also changes. Therefore, the temperature and temperature change of the superconducting coil 1011 can be measured by referring to the measurement voltage Vm, which measures the voltage applied to the temperature sensor 201 and the reference resistor 202 based on the reference voltage V0, and the correspondence between the resistance value and the temperature.

The method of measuring temperature by the temperature measurement circuit 20 is as described above, but in reality, during imaging by the MRI apparatus 1, electromagnetic induction (induced voltage) caused by the application of an RF pulse, which is a high-frequency magnetic field, to the subject is generated as noise in the temperature sensor 201. Such noise caused by the high-frequency magnetic field is superimposed on the measured value as noise of a voltage several tens of times higher than the measurement voltage for temperature measurement depending on the conditions, greatly degrading the accuracy of the temperature measurement. Therefore, in the MRI apparatus according to this embodiment, control is executed to remove such noise.

Specifically, the temperature estimation process in the MRI apparatus according to the first embodiment will be described with reference to the flowchart of FIG.
In step S301, imaging is started according to the imaging sequence.
In step S302, temperature data is acquired by the temperature sensor 201 measuring the temperature of the superconducting coil 1011. In addition, when time information at which the temperature was measured can be acquired in the temperature measurement circuit 20, the temperature measurement circuit 20 may acquire temperature data including the measurement value of the temperature sensor 201 and time information indicating the time at which the measurement value was obtained.

In step S303, the sensor control unit 21 acquires imaging sequence information from the sequence control circuit 121, for example.
In step S304, the sensor control unit 21 determines the unused period based on the imaging sequence information. Specifically, the sensor control unit 21 determines the period during which at least the RF pulse is applied as the unused period. As a method for determining the unused period, for example, the width and timing of the application of the RF pulse are referred to from the imaging sequence information, so that the period during which the RF pulse is applied can be calculated, and the period may be determined as the unused period.

In step S305, the sensor control unit 21 removes the temperature data acquired during the non-use period. The sensor control unit 21 sends the remaining data, after removing the temperature data acquired during the non-use period, to the calculation unit 22.
In step S306, calculation unit 22 calculates an estimated temperature of superconducting coil 1011 from the remaining temperature data after removing the temperature data during the non-use period in step S305.

Next, a first specific example of the temperature measurement process according to the first embodiment will be described with reference to FIG.
FIG. 4(a) is time series data showing the application period 401 of the RF pulse, FIG. 4(b) is time series data of the voltage measured by the temperature measurement circuit 20, and FIG. 4(c) shows time series data of the voltage measured when a non-use period is set.

Since the superconducting coil 1011 is cooled to a constant temperature, the resistance value of the temperature sensor 201 of the temperature measurement circuit 20 is approximately constant, and the time series data of the measured voltage should therefore show approximately constant values. However, during the application period 401 of the RF pulse, noise caused by the high-frequency magnetic field of the RF pulse is superimposed on the measured value in the temperature measurement circuit 20, causing an error in the measured value.

Therefore, the period during which the RF pulse is applied is set as the non-use period 402, and the temperature data measured during the non-use period 402 is removed, that is, the temperature data measured during the non-use period 402 is masked. This makes it possible to calculate the estimated temperature of the superconducting coil 1011 from the temperature data measured during a period not affected by noise, without using the temperature data measured during a period affected by noise.

Note that the temperature data measured after application of the RF pulse may experience a transient response due to the inductance or resistance of the signal line and cable of the temperature measurement circuit 20 before the noise caused by the RF pulse returns to the true value. Therefore, the period of this transient response may be taken into consideration.

A second specific example of the temperature measurement process of the MRI apparatus 1 taking into consideration the transient response will be described with reference to FIG.
FIG. 5, like FIG. 4, shows, from top to bottom, (a) time series data indicating the application period of an RF pulse, (b) time series data of the measured voltage, and (c) time series data of the measured voltage when a non-use period is set.

Unlike FIG. 4, there is a period after the RF pulse application period 401 during which the measurement value fluctuates due to a transient response. This period is the transient response period 501, so the sum of the RF pulse application period 401 and the transient response period 501 can be determined as the non-use period 502.

The transient response period 501 may be determined by a type test or the like. Also, based on previously acquired temperature data (or measured voltage), the transient response period 501 may be determined as the period from when the application of the RF pulse ends until the temperature (or measured voltage) returns to the constant value before the application of the RF pulse.

Since an RF pulse generates a high-frequency magnetic field, a lot of noise can be generated that is superimposed on the temperature measurement circuit 20. However, even if the gradient magnetic field is not a high-frequency magnetic field, applying the gradient magnetic field generates a large amount of energy. This can result in a deterioration of the S/N ratio, such as raising the overall signal measured by the temperature measurement circuit 20. Furthermore, noise can be generated due to vibrations of the device when applying a gradient magnetic field, and the generated noise can be superimposed on the measurement value of the temperature sensor 201.

Therefore, in addition to the RF pulse, the period during which the gradient magnetic field is applied may also be set as the non-use period. A third specific example of the temperature measurement process of the MRI apparatus 1 taking the gradient magnetic field into consideration will be described with reference to FIG.
Figures 6(a), 6(c), and 6(d) are similar to Figures 4(a), 4(b), and 4(c), respectively. Figure 6(b) is time-series data showing a period 601 during which a gradient magnetic field is applied.

As shown in FIG. 6, a period during which at least one of an RF pulse and a gradient magnetic field is applied may be set as a non-use period 602 .
In addition, in an imaging sequence in which the period during which the RF pulse and the gradient magnetic field are applied is long, such as in a long-term imaging such as functional MRI (fMRI), if the temperature data in the unused period 602 is removed, the number of remaining temperature data for calculating the estimated temperature of the superconducting coil 1011 may be reduced. In such a case, a blank period for temperature measurement may be provided during the imaging sequence. The temperature measurement circuit 20 measures the temperature of the superconducting coil 1011 during the blank period during which the RF pulse and the gradient magnetic field are not applied, and acquires the temperature data, thereby ensuring the number of temperature data for calculating the estimated temperature. Furthermore, the temperature sensor 201 may measure the temperature of the superconducting coil 1011 and the temperature measurement circuit 20 may acquire the temperature data between the examination protocol and the next examination protocol, rather than during the imaging sequence.

In addition, regardless of the application period 401 of the RF pulse and the application period 601 of the gradient magnetic field, if the number of data for calculating the estimated temperature is insufficient and the S/N ratio of the measured value cannot be ensured, the calculation unit 22 may also improve the S/N ratio by calculating the time average of the temperature data acquired outside the non-use period.

According to the first embodiment described above, the sensor control unit removes the temperature data acquired during the non-use period from the data group used to calculate the estimated temperature of the superconducting coil. This makes it possible to calculate the estimated temperature of the superconducting coil based on temperature data that is not affected by noise generated by application of an RF pulse or a gradient magnetic field, thereby improving the accuracy of estimating the temperature of the superconducting coil.

Second Embodiment
The second embodiment differs from the first embodiment in that a switch is provided in the temperature measurement circuit 20 to prevent physical acquisition of temperature data during periods of non-use.

A first configuration example of the temperature measuring circuit 20 according to the second embodiment will be described with reference to FIG.
Fig. 7 is a cross-sectional view of the stand as viewed from the Z-axis direction, similar to Fig. 2. The temperature measuring circuit 20 according to the second embodiment includes a temperature sensor 201, a reference resistor 202, a switch 701, and a switch control circuit 702.

The switch 701 is connected between the temperature sensor 201 and the reference resistor 202. The switch 701 is controlled to be turned on and off by the switch control circuit 702, thereby conducting or blocking the current to the temperature sensor 201. The switch 701 is assumed to be formed using a mercury relay, for example, but is not limited to this, and may be configured to conduct a weak current when the switch is on.

The switch control circuit 702 receives imaging sequence information from, for example, the sequence control circuit 121 or the sensor control unit 21, and controls the on/off of the switch 701 by referring to information on the application period of the RF pulse and/or gradient magnetic field contained in the imaging sequence information. Note that when receiving information from the sensor control unit 21, it may receive information on the application period of the RF pulse and/or gradient magnetic field extracted from the imaging sequence information by the sensor control unit 21, rather than the entire imaging sequence information.

Here, it is assumed that the switch control circuit 702 is included in the temperature measurement circuit 20, but it may be present in the magnet management unit 2 or may be present separately from the magnet management unit 2. In other words, it may be present anywhere as long as the switch 701 can be controlled to be turned on and off based on the imaging sequence information. Also, instead of the switch control circuit 702, the sensor control unit 21 may be configured to perform the functions of the switch control circuit 702.

Next, the temperature measurement process of the MRI apparatus 1 according to the second embodiment will be described with reference to the flowchart in FIG. 8. The flowchart in FIG. 8 shows the temperature measurement process in one imaging sequence.

In step S801, the switch control circuit 702 acquires imaging sequence information before starting imaging.
In step S802, shooting is started according to the imaging sequence.

In step S803, the temperature measurement circuit 20 acquires temperature data.
In step S804, the switch control circuit 702 determines whether or not the period corresponds to a period during which an RF pulse or a gradient magnetic field is being applied based on the imaging sequence information. If the period corresponds to a period during which an RF pulse or a gradient magnetic field is being applied, the process proceeds to step S805, and if the period corresponds to a period during which an RF pulse or a gradient magnetic field is not being applied, the process proceeds to step S806.

In step S805, since an RF pulse or a gradient magnetic field is being applied, the switch control circuit 702 turns off the switch 701 so that the temperature measurement circuit 20 does not perform measurements. Note that if the switch is already off, there is no need to switch it on.

In step S806, since this is a period in which no RF pulse or gradient magnetic field is being applied, the switch control circuit 702 turns on the switch 701 so that the temperature measurement circuit 20 does not perform measurements. Note that if the switch is already on, there is no need to switch it on.

In step S807, the calculation unit 22 calculates the estimated temperature of the superconducting coil 1011 from the temperature data acquired by the temperature measurement circuit 20.

Next, an example of a temperature measurement process in the first configuration example of the temperature measurement circuit 20 according to the second embodiment will be described with reference to FIG.
9A is time series data showing the application period 401 of an RF pulse, FIG. 9B is time series data showing the control state of the switch 701, and FIG. 9C is time series data of the measured voltage.

As shown in FIG. 9, the switch control circuit 702 turns off the switch 701 during the application period 401 of the RF pulse, and no current flows through the temperature sensor 201, so the temperature is not measured. On the other hand, the switch 701 turns on during the application period 401 of the RF pulse, so that a current flows through the temperature sensor 201 and the temperature is measured.

The switch control circuit 702 may turn off the switch 701 during the transient response period 501 and the gradient magnetic field application period 601 shown in the first embodiment, without being limited to the application of an RF pulse.
This allows the temperature measurement circuit 20 to measure the temperature without being affected by noise caused by the RF pulse or the gradient magnetic field, thereby improving the accuracy of the measured temperature.

Next, a second configuration example of the temperature measuring circuit 20 according to the second embodiment will be described with reference to FIG.
Fig. 10 is a cross-sectional view of the stand as viewed from the Z-axis direction, similar to Fig. 7. The temperature measurement circuit 20 according to the modified example of the second embodiment includes a temperature sensor 201, a reference resistor 202, a first switch 1001, a second switch 1002, a third switch 1003, and a switch control circuit 1004.

The first switch 1001 may have a configuration similar to that of the switch 701, and is connected between the temperature sensor 201 and the reference resistor 202. The switch 701 is controlled to be turned on and off by the switch control circuit 702, thereby realizing the conduction or interruption of the current.

The second switch 1002 is connected in parallel to the temperature sensor 201 .
One end of the third switch 1003 is connected to one end of the second switch 1002 on the first switch 1001 side, and the other end is grounded (connected to GND). The second switch 1002 and the third switch 1003 may be realized with a configuration similar to that of the switch 701. Since the voltage source V0 is connected to GND by the switches 1002 and 1003, it is desirable to provide an appropriate current limiting mechanism on the power source side.

The switch control circuit 1004 is similar to the switch control circuit 702, receives imaging sequence information, refers to information on the application period of an RF pulse and/or a gradient magnetic field included in the imaging sequence information, and when measuring temperature, controls so as to turn on the first switch 1001 and turn off the second switch 1002 and the third switch 1003. As a result, a current flows through the temperature sensor 201, and no current flows to the ground side.
On the other hand, when the temperature is not being measured, the switch control circuit 1004 controls the first switch 1001 to be turned off and the second switch 1002 and the third switch 1003 to be turned on. As a result, no current flows through the temperature sensor 201, and a current flows to the ground side via the second switch 1002 and the third switch 1003.
One end of the second switch 1002 may be connected to a signal line on the reference voltage V0 side, and the other end may be grounded.

Next, an example of a temperature measurement process in the second configuration example of the temperature measurement circuit 20 according to the second embodiment will be described with reference to FIG.
Figure 11(a) is time series data showing the application period 401 of the RF pulse, Figure 11(b) is time series data showing the control state of the first switch 1001, Figure 11(c) is time series data showing the control states of the second switch 1002 and the third switch 1003, and Figure 11(d) is time series data of the measured voltage.

As shown in FIG. 11, the switch control circuit 1004 turns off the first switch 1001 during the RF pulse application period 401, while turning on the second switch 1002 and the third switch 1003. This prevents the temperature from being measured. On the other hand, during periods other than the RF pulse application period 401, the switch 1001 is turned on, and the second switch 1002 and the third switch 1003 are turned off. This allows the temperature sensor 201 to measure the temperature.

The switch control circuit 1004 may turn off the first switch 1001 and turn on the second switch and the third switch during the transient response period 501 and the application period 601 of the gradient magnetic field shown in the first embodiment, so as not to measure the temperature during the transient response period 501 and the application period 601 of the gradient magnetic field, not limited to the RF pulse.

According to the second embodiment described above, a switch is placed in the temperature measurement circuit, and the switch is controlled to be turned on and off during the period when the RF pulse or gradient magnetic field is applied, so that no current flows through the temperature sensor. This allows the temperature sensor to measure the temperature without being affected by noise caused by the RF pulse or gradient magnetic field, thereby improving the accuracy of the measured temperature.

Third Embodiment
Next, a temperature measuring circuit 20 according to a third embodiment will be described with reference to FIG.
Fig. 12 is a cross-sectional view of the stand as viewed from the Z-axis direction, similar to Fig. 7. The temperature measurement circuit 20 according to the third embodiment includes a temperature sensor 201, a reference resistor 202, a first diode block 1201, and a second diode block 1202.

The first diode block 1201 includes a capacitor and two diodes of opposite polarity connected in parallel (hereinafter also referred to as cross diodes). One end of the first diode block 1201 is connected to one end of the temperature sensor 201, and the other end is grounded.

The second diode block 1202 has the same configuration as the first diode block 1201. One end of the second diode block 1202 is connected to the other end of the temperature sensor 201, and the other end is grounded.

In addition, similar to the second switch 1002 and the third switch 1003 shown in FIG. 10, the first diode block 1201 may be connected in parallel with the temperature sensor 201, one end of the second diode block 1202 may be connected to one end of the first diode block 1201, and the other end may be grounded.

When noise energy equal to or greater than the forward voltage of the diode occurs in the temperature measurement circuit 20, the first diode block 1201 and the second diode block 1202 each cause a current to flow to the ground side (to the GND side). On the other hand, when the noise energy is less than the forward voltage of the diode, no current flows through the first diode block 1201 and the second diode block 1202, and they behave as elements that do not operate in particular.

In other words, when noise caused by the high-frequency magnetic field and gradient magnetic field due to the RF pulse occurs in the temperature measurement circuit 20, the cross diode can act as a switch by diverting the current to the ground side so that the current does not flow to the temperature sensor 201. Therefore, the current to the temperature sensor 201 can be cut off, and the temperature is not measured by the temperature measurement circuit 20.

On the other hand, under normal circumstances when noise is not occurring in the temperature measurement circuit 20, no current flows through the first diode block 1201 and the second diode block 1202, so that a current flows through the temperature sensor 201 and the temperature is measured by the temperature measurement circuit 20.

The first diode block 1201 and the second diode block 1202 are each arranged so that the distance from the connection point of the signal line of the temperature sensor 201 to the ground is a distance that does not resonate with the RF pulse. For example, they are arranged so that the distance between the connection point of the signal line drawn from the temperature sensor 201 and the ground is not half or a quarter of the wavelength of the resonant frequency of the RF pulse. More specifically, they may be arranged so that the distance is shorter than a quarter of the wavelength of the resonant frequency, for example.

According to the third embodiment described above, a cross diode block is arranged in the temperature measurement circuit so that when noise energy equal to or greater than the forward voltage of the diode occurs in the temperature measurement circuit, a current flows to the ground side. This makes it possible to prevent energy from flowing into the temperature sensor when noise equal to or greater than a threshold occurs without using a switch and a switch control circuit as in the second embodiment. Therefore, as in the second embodiment, the temperature is not measured during the period when the temperature is affected by the high-frequency magnetic field and gradient magnetic field of the RF pulse, and the temperature can be measured only during the period when the temperature is not affected by the high-frequency magnetic field and gradient magnetic field, thereby improving the accuracy of estimating the temperature of the superconducting coil. In this embodiment, it is difficult to reduce noise from a low-frequency gradient magnetic field, but when the noise caused by the gradient magnetic field is sufficiently small or when the frequency of the noise caused by the gradient magnetic field is sufficiently high, the effect of the noise caused by the high-frequency magnetic field can be reduced without a special control circuit.

According to at least one of the embodiments described above, it is possible to improve the accuracy of temperature estimation.

In addition, each function according to the embodiment can be realized by installing a program that executes the relevant process in a computer such as a workstation and expanding the program in memory. In this case, the program that can cause the computer to execute the relevant method can be stored and distributed on a storage medium such as a magnetic disk (such as a hard disk), an optical disk (such as a CD-ROM, DVD, Blu-ray (registered trademark) disk), or a semiconductor memory.

Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

With regard to the above embodiment, the following notes are disclosed as one aspect and optional feature of the invention.

(Appendix 1)
A temperature sensor for measuring the temperature of a superconducting coil forming a static magnetic field magnet;
a sensor control unit that excludes an output from the temperature sensor or stops a function of the temperature sensor during a target period that includes at least a period during which a high-frequency magnetic field is applied;
A magnetic resonance imaging apparatus comprising:

(Appendix 2)
The target period may include a period during which a gradient magnetic field is applied.

(Appendix 3)
The target period may include a period during which a transient response occurs due to application of the high frequency magnetic field.

(Appendix 4)
The temperature control device may further include a calculation unit that calculates an estimated temperature of the superconducting coil by using temperature data measured in a period other than the target period.

(Appendix 5)
The sensor control unit may exclude temperature data for the target period from the temperature data measured by the temperature sensor.

(Appendix 6)
The magnetic resonance imaging apparatus may further include a first switch connected to the temperature sensor.
The sensor control unit may turn off the first switch during the target period.

(Appendix 7)
The magnetic resonance imaging apparatus includes a second switch connected to one end of the temperature sensor;
The temperature sensor may further include a third switch connected to the other end of the temperature sensor.
The sensor control unit may control the second switch and the third switch so that no current flows through the temperature sensor during the target period.

(Appendix 8)
The second switch may be connected in parallel with the temperature sensor.
The third switch may have one end connected to one end of the second switch and the other end grounded.
The sensor control unit may turn on the second switch and the third switch during the target period.

(Appendix 9)
The second switch may have one end connected to one end of the temperature sensor and the other end grounded.
The third switch may have one end connected to the other end of the temperature sensor and the other end grounded.
The sensor control unit may turn on the second switch and the third switch during the target period.

(Appendix 10)
A temperature sensor for measuring the temperature of a superconducting coil forming a magnet that generates a static magnetic field;
a first diode block including a capacitor and a diode, one end of which is connected to one end of the temperature sensor and the other end of which is grounded;
a second diode block including a capacitor and a diode, the second diode block having one end connected to the other end of the temperature sensor and the other end grounded;
A temperature measuring device, wherein the first diode block and the second diode block are arranged so that no current flows through the temperature sensor when at least one of potential fluctuations and electromagnetic induction caused by at least one of a high-frequency magnetic field and a gradient magnetic field exceeds a forward voltage of a diode.

(Appendix 11)
The first diode block and the second diode block may be arranged such that a distance between a connection point of the temperature sensor to a signal line and ground is such that no resonance occurs with the high frequency magnetic field.

(Appendix 12)
Measure the temperature of the superconducting coil that forms the magnet that generates the static magnetic field,
A temperature measurement method, comprising excluding temperature data measured during a target period that includes at least a period during which a high-frequency magnetic field is applied, or stopping a temperature measurement function.

(Appendix 13)
The first diode block may be connected in parallel with the temperature sensor.
The second diode block may have one end connected to one end of the temperature sensor and the other end grounded.

(Appendix 14)
The first diode block and the second diode block may include cross diodes.

(Appendix 15)
The first diode block and the second diode block may be arranged such that a distance between a connection point of the temperature sensor to a signal line and ground is shorter than a quarter wavelength of a resonant frequency of the high frequency magnetic field.

REFERENCE SIGNS LIST 1 MRI apparatus 2 Magnet management unit 20 Temperature measurement circuit 21 Sensor control unit 22 Calculation unit 101 Static magnetic field magnet 103 Gradient magnetic field coil 105 Gradient magnetic field power supply 107 Bed 109 Bed control circuit 111 Bore 113 Transmitting circuit 115 Transmitting coil 117 Receiving coil 119 Receiving circuit 121 Sequence control circuit 123 Bus 125 Interface 127 Display 129 Storage device 131 Processing circuit 201 Temperature sensor 202 Reference resistor 401, 601 Application period 402, 502, 602 Non-use period 501 Transient response period 701 Switch 702, 1004 Switch control circuit 1001 First switch 1002 Second switch 1003 Third switch 1011 Superconducting coil 1071 Top plate 1201 First diode block 1202 Second diode block 1311 System control function 1313 Image generation function 1315 Calculation function

Claims (11)

A temperature sensor for measuring the temperature of a superconducting coil forming a magnet that generates a static magnetic field;
a sensor control unit that excludes an output from the temperature sensor or stops a function of the temperature sensor during a target period that includes at least a period during which a high-frequency magnetic field is applied;
Equipped with
The sensor control unit excludes temperature data for the target period from the temperature data measured by the temperature sensor . The magnetic resonance imaging apparatus of claim 1, wherein the target period includes a period during which a gradient magnetic field is applied. The magnetic resonance imaging apparatus according to claim 1 or 2, wherein the target period includes a period during which a transient response occurs due to application of the high frequency magnetic field. The magnetic resonance imaging apparatus according to any one of claims 1 to 3, further comprising a calculation unit that calculates an estimated temperature of the superconducting coil using temperature data measured during a period other than the target period. a first switch connected to the temperature sensor;
The magnetic resonance imaging apparatus according to claim 1 , wherein the sensor control unit turns off the first switch during the target period. A second switch connected to one end of the temperature sensor;
and a third switch connected to the other end of the temperature sensor.
The magnetic resonance imaging apparatus according to claim 5 , wherein the sensor control unit controls the second switch and the third switch so that no current flows through the temperature sensor during the target period. the second switch is connected in parallel with the temperature sensor;
The third switch has one end connected to one end of the second switch and the other end grounded,
The magnetic resonance imaging apparatus according to claim 6 , wherein the sensor control unit turns on the second switch and the third switch during the target period. The second switch has one end connected to one end of the temperature sensor and the other end grounded,
the third switch has one end connected to the other end of the temperature sensor and the other end grounded;
The magnetic resonance imaging apparatus according to claim 6 , wherein the sensor control unit turns on the second switch and the third switch during the target period. A temperature sensor for measuring the temperature of a superconducting coil forming a magnet that generates a static magnetic field;
a first diode block including a capacitor and a diode, one end of which is connected to one end of the temperature sensor and the other end of which is grounded;
a second diode block including a capacitor and a diode, the second diode block having one end connected to the other end of the temperature sensor and the other end grounded;
A temperature measuring device, wherein the first diode block and the second diode block are positioned so that no current flows through the temperature sensor when an induced voltage that becomes noise due to at least one of a high-frequency magnetic field and a gradient magnetic field exceeds a forward voltage of the diode. The temperature measuring device according to claim 9 , wherein the first diode block and the second diode block are arranged such that a distance between a connection point of the temperature sensor to a signal line and ground is such that they do not resonate with the high-frequency magnetic field. Measure the temperature of the superconducting coil that forms the magnet that generates the static magnetic field,
Exclude temperature data measured during the target period that includes at least the period during which the high-frequency magnetic field is applied, or stop the temperature measurement function ;
A temperature measuring method comprising excluding temperature data for the target period from the measured temperature data of the superconducting coil .