JP2022076262A - Magnetic resonance imaging apparatus, temperature measurement apparatus, and temperature measurement method - Google Patents

Abstract

To provide a magnetic resonance imaging apparatus capable of improving estimation accuracy of the temperature of a superconducting coil which forms a magnet generating a magnetostatic field.SOLUTION: A magnetic resonance imaging apparatus comprises a temperature sensor and a sensor control part 21. The temperature sensor measures the temperature of a superconducting coil which forms a magnet generating a magnetostatic field. The sensor control part excludes an output from the temperature sensor or stops the function of the temperature sensor, in an object period including at least a period in which a high frequency magnetic field is applied.SELECTED DRAWING: Figure 1

Description

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

In the superconducting magnetic resonance imaging device (superconducting MRI device), for example, helium is used as the refrigerant of the superconducting coil. However, the soaring price of helium in recent years has put pressure on the lifetime cost of MRI equipment.
Therefore, it is desired to use a low-capacity refrigerant having a helium capacity as small as possible. However, in an MRI device with a large capacity of helium, that is, a sufficient amount of refrigerant, there is a high possibility that heat generation can be absorbed by the evaporation of the refrigerant even if the temperature of the superconducting coil rises. If the amount is small, the possibility of quenching due to the intrusion of heat from the outside world increases.
Therefore, in an MRI apparatus using a low-capacity refrigerant, it is important to control the temperature of the superconducting coil in order to maintain the superconducting state inside the magnet.

Japanese Unexamined Patent Publication No. 2009-183472 Japanese Unexamined Patent Publication No. 01-24252

One of the problems to be solved by the embodiment disclosed in the specification and the like is to improve the accuracy of temperature estimation. However, the problems to be solved by the embodiments disclosed in the present specification and the drawings are not limited to the above problems. The problem corresponding to each effect by each configuration shown in the embodiment described later can be positioned as another problem.

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

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

Hereinafter, the magnetic resonance imaging apparatus (MRI apparatus), the temperature measuring apparatus, and the temperature measuring method according to the present embodiment will be described with reference to the drawings. In the following embodiments, the parts with the same reference numerals perform the same operation, and duplicate description will be omitted as appropriate.

(First Embodiment)
FIG. 1 is a conceptual diagram showing an MRI apparatus according to the first embodiment.
As shown in FIG. 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 sleeper 107, a sleeper control circuit 109, and a transmission circuit 113. The transmitter coil 115, the receiver coil 117, the receiver circuit 119, the sequence control circuit 121, the bus 123, the interface 125, the display 127, the storage device 129, and the processing circuit 131 are provided. The MRI apparatus 1 may have 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 substantially cylindrical shape. The static magnetic field magnet 101 is not limited to a substantially 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. As the static magnetic field magnet 101, in the present embodiment, a superconducting magnet using a superconducting coil is assumed.

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

The gradient magnetic fields of the X, Y, and Z axes generated by the gradient magnetic field coil 103 form, for example, a gradient magnetic field for frequency encoding (also referred to as a lead-out gradient magnetic field), a gradient magnetic field for phase encoding, and a gradient magnetic field for slice selection. The gradient magnetic field for frequency encoding is used to change the frequency of the MR signal according to the spatial position. The gradient magnetic field for phase encoding is used to change the phase of the MR signal according to the spatial position. The gradient gradient magnetic field for slice selection is used to determine the imaging cross section.

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

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

The sleeper control circuit 109 is a circuit that controls the sleeper 107, and moves the top plate 1071 in the longitudinal direction and the vertical direction by driving the sleeper 107 according to the instruction of the operator via the interface 125.

The transmission coil 115 is an RF coil arranged inside the gradient magnetic field coil 103. The transmission coil 115 receives an RF (Radio Frequency) pulse from the transmission circuit 113 to generate a transmission RF wave corresponding to a high frequency magnetic field. The transmission coil 115 is, for example, a whole body coil. The whole body coil may be used as a transmit / receive 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 RF pulses (RF pulses corresponding to the Larmor frequency and the like) 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 the MR signal radiated from the subject P by the high frequency magnetic field. The receiving coil 117 outputs the received MR signal to the receiving circuit 119. The receiving coil 117 is, for example, a coil array having one or more, typically a plurality of coil elements. The receiving coil 117 is, for example, a phased array coil.

The receiving circuit 119 generates a digital MR signal, which is digitized complex number data, based on the MR signal output from the receiving coil 117 under the control of the sequence control circuit 121. Specifically, the receiving circuit 119 performs various signal processing on the MR signal output from the receiving coil 117, and then performs analog / digital (A / D) conversion on the data subjected to various signal processing. To execute. 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, and the like according to the inspection protocol output from the processing circuit 131, and performs imaging on the subject P. The inspection protocol has various pulse sequences (also referred to as imaging sequences) according to the inspection. The inspection protocol includes the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing of supply of the current to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, and the supply to the transmission coil 115 by the transmission circuit 113. The magnitude of the RF pulse, 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, and the like are defined.

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

The interface 125 has a circuit that receives various instructions and information inputs from the operator. The interface 125 has, for example, a circuit related to a pointing device such as a mouse or an input device such as a keyboard. The circuit of the interface 125 is not limited to the circuit related to physical operating parts such as a mouse and a keyboard. For example, the interface 125 is an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the MRI device 1 and outputs the received electric signal to various circuits. May have.

The display 127 displays various magnetic resonance images (MR images) generated by the image generation function 1313, various information related to image pickup and image processing, and the like under the control of the system control function 1311 in the processing circuit 131. The display 127 is, for example, a display device such as 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 MR data filled in the k-space via the image generation function 1313, image data generated by the image generation function 1313, and the like. The storage device 129 stores various inspection protocols, imaging conditions including a plurality of imaging parameters defining the inspection protocol, and the like. The storage device 129 stores programs corresponding to various functions executed by the processing circuit 131. The storage device 129 is, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk drive, a solid state drive, an optical disk, or the like. Further, the storage device 129 may be a drive device or the like that reads and writes various information to and from a portable storage medium such as a CD-ROM drive, a DVD drive, and a flash memory.

The magnet management unit 2 includes a temperature measurement circuit 20, a sensor control unit 21, and a calculation unit 22. As will be described later, the same configuration may be realized by the temperature measurement circuit 20, the system control function 1311 and the calculation function 1315 of the processing circuit 131.

The temperature measuring circuit 20 has a circuit configuration for measuring the temperature of one or more superconducting coils forming the static magnetic field magnet 101 that generates a static magnetic field by a temperature sensor. The temperature measuring circuit 20 is also referred to as a temperature measuring device.

The sensor control unit 21 excludes the output from the temperature sensor or stops the function of the temperature sensor in the target period including at least the period in 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 the temperature data measured in a period other than the target period.

The processing circuit 131 has a processor (not shown) as a hardware resource, a memory such as a ROM (Read-Only Memory) or a RAM, and the like, and controls the MRI apparatus 1 in an integrated manner. The processing circuit 131 has a system control function 1311, an image generation function 1313, and a calculation function 1315.

Various functions of the processing circuit 131 are stored in the storage device 129 in the form of a program that can be executed by a computer. The processing circuit 131 is a processor that realizes the functions corresponding to each program by reading the programs corresponding to these various functions from the storage device 129 and executing the programs. In other words, the processing circuit 131 in the state where each program is read out has a plurality of functions and the like shown in the processing circuit 131 of FIG.

Although it has been described in FIG. 1 that these various functions are realized by a single processing circuit 131, a processing circuit 131 is configured by combining a plurality of independent processors, and each processor executes a program. It does not matter if the function is realized by. 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. You may.

The word "processor" used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an integrated circuit for a specific application (Application Specific Integrated Circuit: ASIC), or a programmable logic device (for example,). , Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA).

The processor realizes various functions by reading and executing a program stored in the storage device 129. Instead of storing the program in the storage device 129, the program may be directly incorporated in the circuit of the processor. In this case, the processor realizes the function by reading and executing the program embedded in the circuit. The sleeper control circuit 109, the transmission circuit 113, the reception circuit 119, the sequence control circuit 121, and the like are also configured by electronic circuits such as the processor.

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

The processing circuit 131 is controlled by the system control function 1311 to apply an excitation pulse according to an excitation pulse sequence and apply a gradient magnetic field. The processing circuit 131 collects MR signals from the subject P and generates MR data according to the data collection sequence, which is a pulse sequence for collecting various data, after executing the excitation pulse sequence by the system control function 1311. The system control function 1311 may have a function of performing the same processing as the sensor control unit 21.

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

When the processing circuit 131 can acquire the temperature data from the magnet management unit 2, the calculation function 1315 calculates the 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 seen from the Z-axis direction, and shows cross sections of the static magnetic field magnet 101, the gradient magnetic field coil 103, and the transmission coil 115, respectively. Further, FIG. 2 also illustrates the concept of an equivalent circuit of the temperature measuring circuit 20, which is partially arranged adjacent to the static magnetic field magnet 101.

The static magnetic field magnet 101 is formed by a superconducting coil 1011 to which a plurality of coil blocks arranged in a gantry are connected. 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) so as not to be vaporized, so that the superconducting state of the superconducting coil 1011 is maintained.

In the case of a low-capacity refrigerant, the refrigerant may be contained in a closed-loop structure called a thermosiphon, and heat transfer may be cooled by a closed-loop flow path. Alternatively, a conduction cooling method in which heat is absorbed from the cold head of the refrigerator using only the heat transfer material may be realized without using a refrigerant.

The temperature measurement circuit 20 includes a temperature sensor 201 which is a resistance type sensor having a resistance value R and a reference resistance 202 having a resistance value R0. The temperature sensor 201 is arranged in the static magnetic field magnet 101 in the vicinity of the superconducting coil 1011. Although the example of FIG. 2 shows an example in which one temperature sensor 201 is arranged, a plurality of temperature sensors 201 may be arranged. By arranging a plurality of temperature sensors 201, it is possible to detect a local temperature rise of the superconducting coil 1011.

The temperature of the superconducting coil 1011 may be measured by measuring the voltage between the temperature sensor 201 and the reference resistance 202 and calculating the temperature from the fluctuation of the voltage value. Since the resistance value of the temperature sensor 201 changes according to the temperature, the measured voltage value also changes. Therefore, the temperature and temperature change of the superconducting coil 1011 can be determined by referring to the measured voltage Vm obtained by measuring the voltage applied to the temperature sensor 201 and the reference resistance 202 with the reference voltage V0 as a reference, and the correspondence between the resistance value and the temperature. Can be measured.

The method for measuring the temperature by the temperature measuring circuit 20 is as described above, but in reality, during the imaging of the MRI apparatus 1, electromagnetic induction (induced voltage) due to 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. Noise caused by such a high-frequency magnetic field is superimposed on the measured value as noise having a voltage several tens of times higher than the measured voltage for temperature measurement depending on the conditions, which greatly deteriorates the temperature measurement accuracy. Therefore, in the MRI apparatus according to the present embodiment, control for removing such noise is executed.

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, shooting is started according to the imaging sequence.
In step S302, the temperature sensor 201 measures the temperature of the superconducting coil 1011 to acquire temperature data. Further, when the temperature measurement circuit 20 can acquire the time information when the temperature is measured, the temperature measurement circuit 20 acquires the temperature data including the measured value of the temperature sensor 201 and the time information indicating the time when the measured value is obtained. You may.

In step S303, the sensor control unit 21 acquires image pickup sequence information from, for example, the sequence control circuit 121.
In step S304, the sensor control unit 21 determines the non-use period based on the imaging sequence information. Specifically, the sensor control unit 21 determines at least a period in which the RF pulse is applied as a non-use period. As a method for determining the non-use period, for example, the period during which the RF pulse is applied can be calculated by referring to the width and timing of the application of the RF pulse from the imaging sequence information, so that the period is the non-use period. It may be decided as.

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 obtained by removing the temperature data during the non-use period from the acquired temperature data to the calculation unit 22.
In step S306, the calculation unit 22 calculates the estimated temperature of the superconducting coil 1011 from the remaining temperature data from which the temperature data during the unused period has been removed 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. 4A is time-series data showing the application period 401 of the RF pulse, FIG. 4B is time-series data of the voltage measured by the temperature measurement circuit 20, and FIG. 4C is not. The time series data of the measured voltage when the usage period is set is shown.

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 becomes an approximately constant value, so that the time-series data of the measured voltage should show an approximately constant value. However, in the RF pulse application period 401, the noise caused by the high frequency magnetic field of the RF pulse is superimposed on the measured value by the temperature measuring circuit 20, so that an error occurs in the measured value.

Therefore, the period in which the RF pulse is applied is set as the non-use period 402, and the temperature data measured in the non-use period 402 is removed, that is, the temperature data measured in the non-use period 402 is masked. Thereby, the estimated temperature of the superconducting coil 1011 can be calculated from the temperature data measured during the period without the influence of noise without using the temperature data measured during the period with the influence of noise.

In the temperature data measured after applying the RF pulse, a transient response occurs until the influence of noise caused by the RF pulse returns to the true value due to the inductance component or resistance component of the signal line and cable of the temperature measurement circuit 20. there's a possibility that. Therefore, the period of the transient response may be considered.

A second specific example of the temperature measurement process of the MRI apparatus 1 in consideration of the transient response will be described with reference to FIG.
FIG. 5 shows the case where (a) time-series data indicating the application period of the RF pulse, (b) time-series data of the measured voltage, and (c) non-use period are set in order from the top, as in FIG. It is time series data of the measured voltage.

Unlike FIG. 4, even after the RF pulse application period 401, there is a period in which the measured value fluctuates due to the transient response. Since the period is the transient response period 501, the total period of the RF pulse application period 401 and the transient response period 501 may be determined as the non-use period 502.

The transient response period 501 may be determined by a type test or the like. In addition, based on the temperature data (or measured voltage) acquired in the past, the transient response period is the period from the end of the application of the RF pulse to the return of the temperature (or the measured voltage) to the constant value before the application of the RF pulse. It may be determined as 501.

Since the RF pulse generates a high-frequency magnetic field, a large amount of noise superimposed on the temperature measurement circuit 20 may be generated, but even if the gradient magnetic field is not a high-frequency magnetic field, a large amount of energy is generated by applying the gradient magnetic field. Therefore, there is a possibility that the S / N ratio may deteriorate, such as raising the bottom of the entire signal measured by the temperature measuring circuit 20. Further, noise may be generated due to the vibration of the device when the gradient magnetic field is applied, and the generated noise may be superimposed on the measured value of the temperature sensor 201.

Therefore, in addition to the RF pulse, the period in which the gradient magnetic field is applied may be set as the unused period. A third specific example of the temperature measurement process of the MRI apparatus 1 in consideration of the gradient magnetic field will be described with reference to FIG.
6 (a), (c), and (d) are the same as those of FIGS. 4 (a), (b), and (c), respectively. FIG. 6B is time series data showing the application period 601 of the gradient magnetic field.

As shown in FIG. 6, the period in which at least one of the RF pulse and the gradient magnetic field is applied may be set as the non-use period 602.
In an imaging sequence in which an RF pulse and a gradient magnetic field are applied for a long period of time, such as long-time imaging such as functional MRI (fMRI), if the temperature data in the unused period 602 is removed, the superconducting coil 1011 There is also the possibility that the number of remaining temperature data for calculating the estimated temperature of will be small. In such a case, a blank period for temperature measurement may be provided in the imaging sequence. The temperature measurement circuit 20 can secure the number of temperature data data for calculating the estimated temperature by measuring the temperature of the superconducting coil 1011 and acquiring the temperature data in the blank period in which the RF pulse and the gradient magnetic field are not applied. .. Further, the temperature sensor 201 may measure the temperature of the superconducting coil 1011 and the temperature measuring circuit 20 may acquire the temperature data between the inspection protocol and the next inspection protocol, not during the imaging sequence.

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

According to the first embodiment shown above, the sensor control unit removes the temperature data acquired during the non-use period from the data group for calculating the estimated temperature of the superconducting coil. As a result, the estimated temperature of the superconducting coil can be calculated based on the temperature data that is not affected by the noise generated by the application of the RF pulse or the gradient magnetic field, and the estimation accuracy of the temperature of the superconducting coil can be improved. ..

(Second embodiment)
The second embodiment is different from the first embodiment in that the temperature measuring circuit 20 is provided with a switch so that the temperature data during the non-use period is not physically acquired.

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

The switch 701 is connected between the temperature sensor 201 and the reference resistance 202. By controlling the switch 701 on and off by the switch control circuit 702, the conduction or disconnection of the current to the temperature sensor 201 is realized. The switch 701 is assumed to be formed by using, for example, a mercury relay, but the switch 701 is not limited to this, and may be configured so as to be able to conduct a weak current when the switch is turned on.

The switch control circuit 702 receives the imaging sequence information from, for example, the sequence control circuit 121 or the sensor control unit 21, refers to the information regarding the application period of the RF pulse and / or the gradient magnetic field included in the imaging sequence information, and turns the switch 701 on and off. Control. When receiving information from the sensor control unit 21, information regarding the application period of the RF pulse and / or the gradient magnetic field extracted by the sensor control unit 21 from the image pickup sequence information may be received instead of the entire image pickup sequence information.

Although the switch control circuit 702 is assumed to be included in the temperature measurement circuit 20 here, it may exist in the magnet management unit 2 or may exist separately from the magnet management unit 2. That is, the switch 701 may be present anywhere as long as it can be turned on and off based on the imaging sequence information. Further, instead of the switch control circuit 702, the sensor control unit 21 may be configured to execute the function 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 of FIG. The flowchart of FIG. 8 shows the temperature measurement process in one imaging sequence.

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

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

In step S805, since the RF pulse or the gradient magnetic field is being applied, the switch control circuit 702 turns off the switch 701 so that the measurement is not performed by the temperature measuring circuit 20. If the switch is already off, it is not necessary to switch the switch as it is.

In step S806, since the period during which the RF pulse or the gradient magnetic field is not applied, the switch control circuit 702 turns on the switch 701 so that the measurement is not performed by the temperature measuring circuit 20. If the switch is already on, it is not necessary to switch the switch as it is.

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 the 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.
9 (a) is time-series data showing the application period 401 of the RF pulse, FIG. 9 (b) is time-series data showing the control state of the switch 701, and FIG. 9 (c) is the measured voltage. It is the time series data of.

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

The switch control circuit 702 is not limited to the RF pulse, and the switch 701 may be turned off during the transient response period 501 and the gradient magnetic field application period 601 shown in the first embodiment.
As a result, the temperature measuring circuit 20 can measure the temperature without being affected by the noise caused by the RF pulse or the gradient magnetic field, so that the accuracy of the measured temperature can be improved.

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

The first switch 1001 may have the same configuration as the switch 701, and is connected between the temperature sensor 201 and the reference resistance 202. The switch 701 is on / off controlled by the switch control circuit 702 to realize current conduction or interruption.

The second switch 1002 is connected in parallel with 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 the same configuration as the switch 701. Since the voltage source V0 is connected to GND by switches 1002 and 1003, it is desirable to provide an appropriate current limiting mechanism on the power supply side.

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

Next, an example of the temperature measurement process according to the second configuration example of the temperature measurement circuit 20 according to the second embodiment will be described with reference to FIG.
11 (a) is time-series data showing the application period 401 of the RF pulse, FIG. 11 (b) is time-series data showing the control state of the first switch 1001, and FIG. 11 (c) is. It is the time series data which shows the control state of the 2nd switch 1002 and the 3rd switch 1003, and FIG. 11D is the 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. As a result, the temperature is not measured. On the other hand, in the period 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. As a result, the temperature is measured by the temperature sensor 201.

The switch control circuit 1004 is not limited to the RF pulse, and the transient response period 501 and the gradient magnetic field are applied so that the temperature is not measured during the transient response period 501 and the gradient magnetic field application period 601 shown in the first embodiment. During the period 601 the first switch 1001 may be turned off and the second and third switches may be turned on.

According to the second embodiment shown above, the switch is arranged in the temperature measurement circuit, the switch is controlled on and off during the period when the RF pulse or the gradient magnetic field is applied, and the temperature sensor is set so that no current flows. .. As a result, the temperature sensor can measure the temperature without being affected by the noise caused by the RF pulse or the gradient magnetic field, so that the accuracy of the measured temperature can be improved.

(Third embodiment)
Next, the temperature measurement circuit 20 according to the third embodiment will be described with reference to FIG.
FIG. 12 is a cross-sectional view of the gantry seen from the Z-axis direction as in FIG. 7. The temperature measurement circuit 20 according to the third embodiment includes a temperature sensor 201, a reference resistance 202, a first diode block 1201, and a second diode block 1202.

The first diode block 1201 includes a capacitor and two diodes having different polarities and connected in parallel (hereinafter, also referred to as a cross diode). 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.

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

In each of the first diode block 1201 and the second diode block 1202, when the energy of noise equal to or higher than the forward voltage of the diode is generated in the temperature measuring circuit 20, a current flows to the ground side (flows to the GND side). On the other hand, when the energy of noise 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 the element behaves as a non-operating element.

That is, when noise caused by the high frequency magnetic field and the gradient magnetic field due to the RF pulse is generated in the temperature measuring circuit 20, the cross diode serves as a switch by releasing the current to the ground side so that the current does not flow in the temperature sensor 201. Can be fulfilled. Therefore, since the current to the temperature sensor 201 can be cut off, the temperature is not measured by the temperature measuring circuit 20.

On the other hand, in the normal state where noise is not generated in the temperature measurement circuit 20, no current flows in the first diode block 1201 and the second diode block 1202, so that a current flows in the temperature sensor 201 and the temperature in the temperature measurement circuit 20. Is measured.

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

According to the third embodiment shown above, when noise energy equal to or higher than the forward voltage of the diode is generated in the temperature measurement circuit, a cross diode block is arranged in the temperature measurement circuit so that the current flows to the ground side. do. This makes it possible to prevent energy from flowing into the temperature sensor when noise exceeding the threshold value is generated without using the switch and the switch control circuit as in the second embodiment. Therefore, as in the second embodiment, the temperature is not measured during the period affected by the high frequency magnetic field and the gradient magnetic field of the RF pulse, and the temperature can be measured only during the period not affected by the high frequency magnetic field and the gradient magnetic field. Therefore, the accuracy of estimating the temperature of the superconducting coil can be improved. In this embodiment, it is difficult to reduce the noise of the gradient magnetic field having a low frequency, but if the noise caused by the gradient magnetic field is sufficiently small or the frequency of the noise caused by the gradient magnetic field is sufficiently high, no special control circuit is required. The influence of noise caused by a high frequency magnetic field can be reduced.

According to at least one embodiment described above, the accuracy of temperature estimation can be improved.

In addition, each function according to the embodiment can also be realized by installing a program for executing the process on a computer such as a workstation and expanding these on a memory. At this time, the program that allows the computer to execute the method is stored in a storage medium such as a magnetic disk (hard disk, etc.), an optical disk (CD-ROM, DVD, Blu-ray (registered trademark) disk, etc.), or a semiconductor memory. It is also possible to distribute it.

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

Regarding the above embodiments, the following appendices are disclosed as one aspect and selective features of the invention.

(Appendix 1)
A temperature sensor that measures the temperature of the superconducting coil that forms the static magnetic field magnet,
A sensor control unit that excludes the output from the temperature sensor or stops the function of the temperature sensor during a target period including at least a period in which a high-frequency magnetic field is applied.
A magnetic resonance imaging device comprising.

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

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

(Appendix 4)
A calculation unit for calculating the estimated temperature of the superconducting coil may be further included using the temperature data measured in a period other than the target period.

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

(Appendix 6)
The magnetic resonance imaging device 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 device includes a second switch connected to one end of the temperature sensor and a second switch.
A third switch connected to the other end of the temperature sensor may be further included.
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.
One end of the third switch may be connected to one end of the second switch, and the other end may be grounded.
The sensor control unit may turn on the second switch and the third switch during the target period.

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

(Appendix 10)
A temperature sensor that measures the temperature of a superconducting coil that forms a magnet that generates a static magnetic field,
A first diode block formed of a capacitor and a diode, one end connected to one end of the temperature sensor and the other end grounded.
Includes a second diode block formed of a capacitor and a diode, one end connected to the other end of the temperature sensor and the other end grounded.
In the first diode block and the second diode block, when at least one of the potential fluctuation and the electromagnetic induction caused by at least one of the high frequency magnetic field and the gradient magnetic field exceeds the forward voltage of the diode, no current flows through the temperature sensor. A temperature measuring device arranged so as to be.

(Appendix 11)
The first diode block and the second diode block may be arranged so that the distance between the connection point of the temperature sensor with the signal line and the ground is such that the distance does not resonate 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 measuring method that excludes temperature data measured during a target period including a period in which a high-frequency magnetic field is applied, or stops the temperature measuring function.

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

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

(Appendix 15)
The first diode block and the second diode block are arranged so that the distance between the connection point with the signal line of the temperature sensor and the ground is shorter than a quarter wavelength of the resonance frequency of the high frequency magnetic field. May be done.

1 MRI device 2 Magnet management unit 20 Temperature measurement circuit 21 Sensor control unit 22 Calculation unit 101 Static magnetic field magnet 103 Diagonal magnetic field coil 105 Diagonal magnetic field power supply 107 Sleeper 109 Sleeper control circuit 111 Bore 113 Transmit circuit 115 Transmit coil 117 Receive coil 119 Receive circuit 121 Sequence control circuit 123 Bus 125 Interface 127 Display 129 Storage device 131 Processing circuit 201 Temperature sensor 202 Reference resistance 401,601 Application period 402,502,602 Non-use period 501 Transient response period 701 Switch 702,1004 Switch control circuit 1001 1st Switch 1002 2nd switch 1003 3rd switch 1011 Superconducting coil 1071 Top plate 1201 1st diode block 1202 2nd diode block 1311 System control function 1313 Image generation function 1315 Calculation function

Claims (12)

A temperature sensor that measures the temperature of a superconducting coil that forms a magnet that generates a static magnetic field,
A sensor control unit that excludes the output from the temperature sensor or stops the function of the temperature sensor during a target period including at least a period in which a high-frequency magnetic field is applied.
A magnetic resonance imaging device comprising. The magnetic resonance imaging apparatus according to claim 1, wherein the target period includes a period in 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 due to the application of the high frequency magnetic field is generated. The magnetic resonance imaging according to any one of claims 1 to 3, further comprising a calculation unit for calculating an estimated temperature of the superconducting coil using temperature data measured in a period other than the target period. Device. The magnetic resonance imaging device according to any one of claims 1 to 4, wherein the sensor control unit excludes the temperature data of the target period from the temperature data measured by the temperature sensor. Further equipped with a first switch connected to the temperature sensor,
The magnetic resonance imaging apparatus according to any one of claims 1 to 5, 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,
A third switch connected to the other end of the temperature sensor is further provided.
The magnetic resonance imaging device according to claim 6, wherein the sensor control unit controls the second switch and the third switch so that a current does not flow through the temperature sensor during the target period. The second switch is connected in parallel with the temperature sensor and is connected.
One end of the third switch is connected to one end of the second switch, and the other end is grounded.
The magnetic resonance imaging device according to claim 7, wherein the sensor control unit turns on the second switch and the third switch during the target period. One end of the second switch is connected to one end of the temperature sensor, and the other end is grounded.
One end of the third switch is connected to the other end of the temperature sensor, and the other end is grounded.
The magnetic resonance imaging device according to claim 7, wherein the sensor control unit turns on the second switch and the third switch during the target period. A temperature sensor that measures the temperature of a superconducting coil that forms a magnet that generates a static magnetic field,
A first diode block formed of a capacitor and a diode, one end connected to one end of the temperature sensor and the other end grounded.
It comprises a second diode block formed of a capacitor and a diode, one end connected to the other end of the temperature sensor and the other end grounded.
The first diode block and the second diode block prevent current from flowing through the temperature sensor when the induced voltage that causes noise due to at least one of the high frequency magnetic field and the gradient magnetic field exceeds the forward voltage of the diode. A temperature measuring device to be placed. 10. The first diode block and the second diode block are arranged so that the distance between the connection point of the temperature sensor with the signal line and the ground is such that the distance does not resonate with the high frequency magnetic field. The temperature measuring device according to. Measure the temperature of the superconducting coil that forms the magnet that generates the static magnetic field,
A temperature measuring method that excludes temperature data measured during a target period including a period in which a high-frequency magnetic field is applied, or stops the temperature measuring function.

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