JP2020075129A - Magnetic resonance imaging apparatus - Google Patents

Abstract

To determine an interlock value related to an SAR in accordance with a peripheral temperature.SOLUTION: A magnetic resonance imaging apparatus includes an acquisition unit and a determination unit. The acquisition unit acquires a peripheral temperature related to magnetic resonance imaging inspection. The determination unit determines an interlock value of an SAR (Specific Absorption Rate) in accordance with peripheral temperature.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a magnetic resonance imaging apparatus.

  A magnetic resonance imaging (MRI) apparatus irradiates an imaging site of a subject with an RF (Radio Frequency) pulse, which is a high-frequency magnetic field, in order to obtain a magnetic resonance image. The RF pulse is absorbed by the living tissue of the subject and raises the body temperature of the subject. The index of the energy of the RF pulse absorbed by the biological tissue of the subject is called SAR (Specific Absorption Rate).

  The value of SAR is limited as an upper limit value defined by a standard based on IEC (International Electrotechnical Commission). Therefore, in the conventional MRI apparatus, an interlock value that is sufficiently lower than the upper limit value of SAR is set regardless of the ambient temperature.

IEC 60601-2-33: Medical electrical equipment-Part 2-33: Partial requirement for the basics of the affirmation of the perfume ancessssssss.

  The problem to be solved by the present invention is to determine the interlock value for the SAR depending on the ambient temperature.

  The magnetic resonance imaging apparatus according to the embodiment includes an acquisition unit and a determination unit. The acquisition unit acquires the ambient temperature related to the magnetic resonance imaging examination. The determination unit determines the SAR interlock value according to the ambient temperature.

FIG. 1 is a diagram showing a configuration example of an MRI apparatus according to the first embodiment. FIG. 2 is a graph illustrating the relationship between temperature and interlock value in the first embodiment. FIG. 3 is a graph illustrating the relationship between the temperature and the interlock value in the first embodiment. FIG. 4 is a flowchart illustrating processing executed by the processing circuit according to the first embodiment. FIG. 5 is a flowchart illustrating another process executed by the processing circuit according to the first embodiment. FIG. 6 is a diagram showing a configuration example of a processing circuit of the MRI apparatus according to the second embodiment. FIG. 7 is a flowchart illustrating the processing executed by the processing circuit according to the second embodiment.

  Hereinafter, embodiments of a magnetic resonance imaging apparatus will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of the MRI apparatus according to the first embodiment. For example, as shown in FIG. 1, an MRI apparatus 100 according to an embodiment includes a static magnetic field magnet 101, a gradient magnetic field coil 103, a gradient magnetic field power supply 105, a bed 107, a bed control circuit 109, and a transmission circuit 113. The transmitter coil 115, the receiver coil 117, the receiver circuit 119, the imaging control circuit 121, the interface 123, the display 125, the storage device 127, the temperature sensor 129, and the processing circuit 131. The MRI apparatus 100 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, for example, a magnet formed in a hollow, substantially cylindrical shape. The static magnetic field magnet 101 generates a uniform static magnetic field in the bore 111 which is a space into which the subject P is inserted. As the static magnetic field magnet 101, for example, a superconducting magnet or the like is used.

  The gradient magnetic field coil 103 is, for example, a coil formed in a hollow and substantially 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 that are orthogonal to each other. The Z-axis direction is the same as the direction of the static magnetic field. The Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to the Z-axis and the Y-axis. The gradient magnetic field coil 103 generates a gradient magnetic field to be superimposed on the static magnetic field. Specifically, 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 magnetic field coil 103 form, for example, a frequency encoding gradient magnetic field (also referred to as 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 a magnetic resonance (Magnetic Resonance: MR) signal according to a spatial position. The phase-encoding gradient magnetic field is used to change the phase of the MR signal according to the spatial position. The slice selection gradient magnetic field is used to determine an 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 imaging control circuit 121.

  The bed 107 is a device including a top plate 107a on which the subject P is placed. Under the control of the bed control circuit 109, the bed 107 inserts the top 107a on which the subject P is placed into the bore 111. The bed 107 is installed, for example, in an examination room in which the MRI apparatus 100 is installed so that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 101. Since the examination room is provided with, for example, a radio wave shield or a magnetic shield, it is also called a shield room.

  The bed control circuit 109 is a circuit that controls the bed 107. The couch control circuit 109 drives the couch 107 according to a user's instruction via the interface 123, thereby moving the couchtop 107a in the longitudinal direction and the vertical direction, and in some cases, the lateral direction.

  The transmission circuit 113 supplies a high frequency pulse corresponding to the Larmor frequency or the like to the transmission coil 115 under the control of the imaging control circuit 121.

  The transmission coil 115 is an RF (Radio Frequency) coil arranged inside the gradient magnetic field coil 103. The transmission coil 115 receives the high frequency pulse supplied from the transmission circuit 113 and generates a high frequency magnetic field. The transmission coil is, for example, a whole body coil (WB coil). The WB coil may be used as a transmission / reception coil.

  The receiving coil 117 is an RF coil arranged inside the gradient magnetic field coil 103. The receiving coil 117 receives the MR signal emitted 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, one or more coils, and is typically a coil array having a plurality of coil elements. Although the transmission coil 115 and the reception coil 117 are described as separate RF coils in FIG. 1, the transmission coil 115 and the reception coil 117 may be implemented as an integrated transmission / reception coil. The transmit / receive coil is, for example, a local transmit / receive RF coil such as a head coil.

  Under the control of the imaging control circuit 121, the reception circuit 119 generates a digital MR signal that is digitized complex number data based on the MR signal output from the reception 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 / digital (A / D (Analog) on the data subjected to various signal processing. to Digital)) Perform the conversion. The receiving circuit 119 generates a digital MR signal (hereinafter referred to as MR data) by sampling (sampling) the A / D converted data. The reception circuit 119 outputs the generated MR data to the imaging control circuit 121.

  The imaging 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 imaging protocol output from the processing circuit 131, and performs imaging on the subject P. The imaging protocol has various pulse sequences according to the examination. The imaging protocol includes the magnitude of the current supplied by the gradient magnetic field power supply 105 to the gradient magnetic field coil 103, the timing at which the gradient magnetic field power supply 105 supplies the current to the gradient magnetic field coil 103, and the transmission circuit 113 supplies the current to the transmission coil 115. The magnitude of the high frequency pulse to be supplied, the timing at which the transmission circuit 113 supplies the high frequency pulse to the transmission coil 115, the timing at which the reception coil 117 receives the MR signal, and the like are set in advance. The imaging control circuit 121 is an example of an imaging unit.

  The interface 123 has a circuit that receives various instructions and information inputs from the user. The interface 123 has a circuit related to a pointing device such as a mouse or an input device such as a keyboard, for example. The circuit included in the interface 123 is not limited to the circuit related to physical operation parts such as a mouse and a keyboard. For example, the interface 123 receives an electric signal corresponding to an input operation from an external input device provided separately from the MRI apparatus 100, and outputs the received electric signal to various circuits. May have.

  The display 125 displays various MR images generated by the image generation function 131b, various information regarding imaging and image processing, etc. under the control of the system control function 131a in the processing circuit 131 described later. The display 125 is a display device such as, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the art, a monitor, or the like.

  The storage device 127 stores the MR data filled in the k space via the image generation function 131b, the image data generated by the image generation function 131b, and the like. The storage device 127 stores various imaging protocols, imaging conditions including a plurality of imaging parameters that define the imaging protocols, and the like. The imaging conditions include, for example, an imaging site and sequence type. The imaging site is, for example, the head, the heart, the spine (for example, the thoracolumbar spine and the whole spine), and the joints (shoulders, knees, hands and feet, etc.). The sequence species are, for example, a spin echo (Spin Echo) method, a gradient echo (Gradient Echo) method, a fast spin echo method, a fast gradient echo method, and Echo Planar Imaging (EPI). The storage device 127 stores programs corresponding to various functions executed by the processing circuit 131.

  Further, the storage device 127 stores a correspondence table showing a relationship between a temperature related to an MRI examination described later and an interlock value of the MRI apparatus 100. As the interlock value, for example, a SAR value (W / kg) is used. As the SAR value, for example, a value regarding the whole body SAR may be used, or a value regarding the SAR of any part of the human body such as the head and the body part may be used. Further, for example, a value relating to the SAR of a specific position or area where the value of the SAR tends to increase may be used. Further, as the interlock value, an upper limit value (hereinafter, referred to as a set upper limit value) for setting an imaging parameter related to SAR (for example, a parameter regarding an RF pulse based on the value of SAR) may be used. .. When the interlock value is the set upper limit value, the correspondence table associates the temperature with the set upper limit value. A lookup table (Look Up Table) may be used as the correspondence table. Further, the storage device 127 may store, instead of the correspondence table, a calculation formula indicating a function that determines the interlock value using temperature as a variable. Further, in the present specification, the “interlock value regarding SAR” may be replaced with the “interlock value of SAR”.

  Further, the SAR value may be either a predicted value or an actual measured value. The predicted value is a value calculated by the processing circuit 131 based on, for example, pulse sequence information. Specifically, there is a protocol average that averages the sum of SARs for each sequence in a certain protocol. The actual measurement value is, for example, a value calculated based on the reflected wave reflected at the output end of the WB coil among the high frequency pulses output from the transmission circuit 113 to the transmission coil 115 (for example, the WB coil). Specifically, an average value of 10 seconds, an average value of 6 minutes, and an average value of values calculated in real time over an arbitrary time length (for example, 10 seconds and 6 minutes) may be used.

FIG. 2 is a graph illustrating the relationship between the temperature and the interlock value in the first embodiment. As shown in FIG. 2, the horizontal axis of the graph 200 represents the temperature T [° C.], and the vertical axis of the graph 200 represents the interlock value IL [W / kg]. The graph 200 decreases substantially linearly from the interlock value IL ₃ to the interlock value IL ₁ between the temperature T ₀ and the temperature T ₂ , for example. Then, the graph 200 becomes constant at the interlock value IL ₁ when the temperature is equal to or higher than T ₂ . Incidentally, if the temperature _{T 1} of between a temperature _{T 0} to the temperature _{T 2} is set, the graph 200 includes a rate of change of interlock value between the temperature _{T 0} to the temperature _{T 1} of, from temperatures _{T 1} The rate of change in the interlock value up to the temperature T ₂ may be different.

  In other words, the graph 200 is a graph in which the interlock value changes depending on the temperature in the range below the arbitrary temperature. Specifically, in the graph 200, the interlock value increases as the temperature decreases in the range of an arbitrary temperature or lower.

The numerical values on the horizontal axis and the vertical axis of the graph 200 will be specifically described below. In the graph 200, for example, the values on the horizontal axis are {T ₀ , T ₁ , T ₂ } = {20, 25, 32} and the values on the vertical axis are {IL ₀ , IL ₁ , IL ₂ , IL ₃ } = {. 0, 2.0, 4.0, 5.4}. The graph 200 decreases substantially linearly from 5.4 W / kg to 2.0 W / kg between 20 ° C and 32 ° C. Specifically, the graph 200 shows a linear decrease from 5.4 W / kg to 4.0 W / kg between 20 ° C. and 25 ° C., and 4.0 W / kg between 25 ° C. and 32 ° C. It decreases linearly from kg to 2.0 W / kg. Then, the graph 200 is constant at 2.0 W / kg at 32 ° C. or higher. The graph 200 may be followed by a graph in which the linear relationship from T ₀ to T ₁ is maintained for T ₀ or less.

  In other words, the graph 200 is a graph in which the interlock value changes depending on the temperature in the range of 25 ° C. or lower. Alternatively, the graph 200 is a graph in which the interlock value increases as the temperature decreases in the range of 25 ° C. or lower. Alternatively, the graph 200 is a graph in which the interlock value increases in proportion to the temperature decrease in the range of 25 ° C. or less.

FIG. 3 is a graph illustrating the relationship between the temperature and the interlock value in the first embodiment. As shown in FIG. 3, the horizontal axis of the graph 300 represents temperature [° C.], and the vertical axis of the graph 300 represents interlock value [W / kg]. The graph 300 differs from the graph 200 in that the interlock value does not change linearly between the temperature T ₀ and the temperature T ₁ . The graph 300 is, for example, a curve that is convex upward from the interlock value IL ₄ to the interlock value IL ₂ between the temperature T ₀ and the temperature T ₁ .

  The correspondence table stored in the storage device 127 may be created based on the graph of FIG. 2 or the graph of FIG. 3, for example. Alternatively, the calculation formula stored in the storage device 127 may be formulated so as to satisfy the graph of FIG. 2 or the graph of FIG. 3, for example.

  The storage device 127 is, for example, a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk drive, a solid state drive, an optical disk, or the like. Further, the storage device 127 may be a drive device that reads and writes various information from and to a portable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory.

  The temperature sensor 129 is, for example, a thermometer that measures temperature. The temperature sensor 129 measures the temperature related to the MRI examination. The temperature sensor 129 outputs the measured temperature as temperature information to the processing circuit 131. The temperature sensor 129 may be a contact type thermometer such as a thermistor thermometer and a thermocouple thermometer, or may be a non-contact type thermometer such as an infrared radiation thermometer and an optical fiber thermometer. It should be noted that “related to MRI examination” includes at least the meaning of “before MRI examination” and may include the meaning of “during MRI examination”. Further, the measured temperature may be read as "ambient temperature".

  The temperature sensor 129 is arranged, for example, in a place where heat-generating components in the MRI apparatus 100 are gathered. The heat generating component is, for example, a balun and a decoupling switch included in the internal circuit of the transmission coil 115. The temperature sensor 129 is arranged inside the transmission coil 115, for example. When the transmission coil 115 is a WB coil, the temperature sensor 129 is arranged, for example, in the WB coil at a position close to the center of the vortex in the spiral coil pattern of the gradient magnetic field coil 103. Since the vortex center of the gradient magnetic field coil 103 has a large amount of heat generation and the temperature easily rises, the above position is suitable as a measurement point.

  Further, the temperature sensor 129 may be arranged, for example, in a space (patient space) in which the subject is placed during the MRI examination. Specifically, the temperature sensor 129 is arranged at an arbitrary position on the wall surface forming the bore 111. For example, the temperature sensor 129 is arranged below a rail that guides the top plate 107a. The temperature sensor 129 may be arranged near the opening end of the bore 111.

  Further, the temperature sensor 129 may be arranged, for example, in a shielded room for performing an MRI examination. Specifically, the temperature sensor 129 is arranged on an arbitrary surface of the MRI apparatus 100, around the MRI apparatus 100, or on the outer wall of the shield room.

  From the above, the temperature sensor 129 may be arranged in any place within the shield room for performing the MRI examination, as long as it is inside or outside the MRI apparatus 100, as long as the MRI examination is not hindered. Further, the temperature sensor 129 may be arranged at a plurality of positions. When the temperature sensors 129 are arranged at a plurality of positions, as the plurality of temperature sensors 129, thermometers of the same measurement method may be used, or thermometers of different measurement methods may be used. ..

  The processing circuit 131 has, as hardware resources, a processor (not shown), a memory such as a ROM (Read-Only Memory), a RAM, and the like, and controls the MRI apparatus 100. The processing circuit 131 has a system control function 131a, an image generation function 131b, a temperature acquisition function 131c, an interlock value determination function 131d, and a parameter adjustment function 131e. Functions such as the system control function 131a, the image generation function 131b, the temperature acquisition function 131c, the interlock value determination function 131d, and the parameter adjustment function 131e are stored in the storage device 127 in the form of a program executable by a computer. The processing circuit 131 is a processor that realizes a function corresponding to each program by reading a program corresponding to these various functions from the storage device 127 and executing the program. In other words, the processing circuit 131 in the state where each program is read out has the plurality of functions shown in the processing circuit 131 of FIG.

  In addition, in FIG. 1, the above-described various functions are realized by the single processing circuit 131, but the functions may be realized by a plurality of independent processors executing programs. In other words, the various functions described above 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. Good.

  The word "processor" used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application-specific integrated circuit (ASIC), a programmable logic device (for example, a simple logic device). A programmable programmable logic device (SPLD), a complex programmable logic device (Complex Programmable Logic Device: CPLD), and a field programmable gate array (Field Programmable Gate Array: FPGA), such as a circuit.

  The processor realizes various functions by reading and executing the program stored in the storage device 127. Instead of storing the program in the storage device 127, 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 incorporated in the circuit. Note that the bed control circuit 109, the transmission circuit 113, the reception circuit 119, the imaging control circuit 121, and the like are similarly configured by electronic circuits such as the processor. The system control function 131a, the image generation function 131b, the temperature acquisition function 131c, the interlock value determination function 131d, and the parameter adjustment function 131e included in the processing circuit 131 respectively include a system control unit, an image generation unit, an acquisition unit, a determination unit, and a It is an example of an adjustment unit.

  The processing circuit 131 controls the MRI apparatus by the system control function 131a. Specifically, the processing circuit 131 reads the system control program stored in the storage device 127, expands it on the memory, and controls each circuit of the MRI apparatus 100 according to the expanded system control program. For example, the processing circuit 131 reads the imaging protocol from the storage device 127 based on the imaging condition input by the user via the interface 123 by the system control function 131a. The processing circuit 131 may generate the imaging protocol based on the imaging conditions. The processing circuit 131 transmits the imaging protocol to the imaging control circuit 121 and controls the imaging of the subject P.

  The processing circuit 131 fills the k space with the MR data by the image generation function 131b. The processing circuit 131 generates an MR image by performing, for example, Fourier transform on the MR data filled in the k space. The MR image corresponds to, for example, a morphological image regarding the subject P. The processing circuit 131 outputs the MR image to the display 125 and the storage device 127.

  The processing circuit 131 uses the temperature acquisition function 131c to acquire the ambient temperature related to the magnetic resonance imaging examination. Specifically, the processing circuit 131 acquires the temperature information output from the temperature sensor 129. The processing circuit 131 may acquire the ambient temperature in real time when the temperature changes in real time during the MRI examination, the imaging of the MRI, or the like.

  The processing circuit 131 uses the interlock value determination function 131d to determine the SAR interlock value according to the acquired ambient temperature. Specifically, the processing circuit 131 uses the correspondence table read from the storage device 127 to determine the interlock value corresponding to the acquired temperature. Alternatively, the processing circuit 131 determines (calculates) the interlock value for the acquired temperature using the mathematical formula read from the storage device 127. When the ambient temperature is acquired in real time, the processing circuit 131 may determine the interlock value regarding the SAR in real time according to the ambient temperature acquired in real time.

For example, when the mathematical formula read from the storage device 127 is used in the determination of the interlock value, the processing circuit 131 uses the interlock value determination function 131d in the range where the ambient temperature is T ₂ (for example, 25 ° C.) or less, The interlock value may be determined using a function of the ambient temperature.

For example, when the correspondence table based on the graph of FIG. 2 or the like is used in the determination of the interlock value, the processing circuit 131 uses the interlock value determination function 131d in the range where the ambient temperature is T ₂ (for example, 25 ° C.) or less, The interlock value may be determined to increase as the ambient temperature decreases. Alternatively, the processing circuit 131 may determine that the interlock value increases in proportion to the decrease in the ambient temperature in the range where the ambient temperature is T ₂ (for example, 25 ° C.) or lower.

  The processing circuit 131 adjusts the upper limit value of the imaging parameter based on the determined interlock value by the parameter adjustment function 131e. Specifically, before the MRI examination, the processing circuit 131 adjusts the upper limit value of the imaging parameter related to the SAR based on the determined interlock value. Alternatively, during the MRI examination, the processing circuit 131 adjusts the upper limit value of the imaging parameter related to the SAR in real time based on the determined interlock value. Further, during the MRI examination, the processing circuit 131 forcibly adjusts the value of the parameter to the interlock value when the value of the set parameter exceeds the determined interlock value. Alternatively, the MRI examination itself may be forcibly terminated.

(First processing example)
FIG. 4 is a flowchart illustrating the processing executed by the processing circuit according to the first embodiment. The process of FIG. 4 is started, for example, before the MRI examination and before the imaging parameter is set from the interface 123 by the operator or the like, by the processing circuit 131 executing a program regarding determination of an interlock value regarding SAR. ..

(Step S410)
The processing circuit 131 uses the temperature acquisition function 131c to acquire the temperature related to the MRI examination. For example, the processing circuit 131 acquires the temperature information of the temperature T ₁ from the temperature sensor provided in the WB coil.

(Step S420)
The processing circuit 131 uses the interlock value determination function 131d to determine the SAR interlock value according to the acquired temperature. For example, the processing circuit 131 uses the correspondence table based on the graph of FIG. ₂ to determine the interlock value IL ₂ corresponding to the temperature T ₁ .

(Step S430)
The processing circuit 131 adjusts the upper limit value of the imaging parameter based on the determined interlock value by the parameter adjustment function 131e. For example, the processing circuit 131 adjusts the upper limit value of the parameter related to the RF pulse based on the interlock value IL ₂ .

(Second processing example)
FIG. 5 is a flowchart illustrating another process executed by the processing circuit according to the first embodiment. The process of FIG. 5 is started, for example, at the timing of the process of FIG. 4, and during the MRI examination, the processing circuit 131 continues to execute the program regarding the determination of the interlock value regarding the SAR until the end of imaging. Note that the processing of steps S510, S520, and S530 is the same as the processing of steps S410, S420, and S430, respectively, and thus description thereof will be omitted.

(Step S540)
If the image is being captured, the process returns to step S510. If not being photographed, the process ends.

  That is, in the process of FIG. 5, the temperature is always acquired during shooting, and the interlock value is determined according to the acquired temperature.

  As described above, according to the first embodiment, the MRI apparatus 100 acquires the ambient temperature and determines the SAR interlock value according to the acquired ambient temperature.

  Moreover, according to the first embodiment, the MRI apparatus 100 can determine different interlock values depending on the ambient temperature.

  Further, according to the first embodiment, the MRI apparatus 100 can determine the interlock value that changes depending on the temperature in the range of an arbitrary temperature or lower.

  Further, according to the first embodiment, the MRI apparatus 100 can acquire the ambient temperature in real time and determine the interlock value in real time according to the ambient temperature acquired in real time.

  Further, according to the first embodiment, the MRI apparatus 100 can determine the interlock value by using the function of the ambient temperature in the ambient temperature range of 25 ° C. or less.

  Further, according to the first embodiment, the MRI apparatus 100 can determine that the interlock value increases as the ambient temperature decreases in the ambient temperature range of 25 ° C. or less.

  Further, according to the first embodiment, the MRI apparatus 100 can determine that the interlock value increases in proportion to the decrease of the ambient temperature in the range of the ambient temperature of 25 ° C. or less.

  Therefore, the MRI apparatus 100 can determine the interlock value regarding the SAR according to the ambient temperature, so that it is possible to more flexibly determine the imaging condition while ensuring the safety according to the IEC standard. For example, if an RF pulse stronger than before can be used according to the determined interlock value, an image with higher contrast than before can be obtained. Further, when the determined interlock value is higher than the conventional interlock value, if the flip angle is the same, the imaging time can be shortened as compared with the conventional case. As a result, the TR time can be shortened as compared with the related art, so that the image quality (for example, contrast) of the T1 image can be improved. On the other hand, if the RF pulse has the same intensity as the conventional one and the imaging time is the same as the conventional one, the MRI apparatus 100 can emit more types of RF pulses and the number of RF pulses, and according to the conventional SAR standard. It is possible to use pulse sequences that were not available.

(Second embodiment)
FIG. 6 is a diagram showing a configuration example of a processing circuit of the magnetic resonance imaging apparatus according to the second embodiment. The magnetic resonance imaging apparatus according to the second embodiment has a processing circuit configuration different from that of the magnetic resonance imaging apparatus according to the first embodiment. Specifically, the processing circuit according to the second embodiment acquires a plurality of ambient temperatures and determines the interlock value according to the highest temperature among the plurality of acquired ambient temperatures.

  The processing circuit 600 of FIG. 6 has a processor (not shown), a memory such as a ROM (Read-Only Memory), a RAM, and the like as hardware resources, and controls the MRI apparatus 100. The processing circuit 600 has a system control function 600a, an image generation function 600b, a temperature acquisition function 600c, a temperature selection function 600d, an interlock value determination function 600e, and a parameter adjustment function 600f. Various functions performed by the system control function 600a, the image generation function 600b, the temperature acquisition function 600c, the temperature selection function 600d, the interlock value determination function 600e, and the parameter adjustment function 600f are storage devices in the form of programs executable by a computer. It is stored in 127. The processing circuit 600 is a processor that realizes a function corresponding to each program by reading a program corresponding to these various functions from the storage device 127 and executing the program. In other words, the processing circuit 600 in the state where each program is read out has the plurality of functions shown in the processing circuit 600 of FIG.

  The system control function 600a, the image generation function 600b, the temperature acquisition function 600c, the temperature selection function 600d, the interlock value determination function 600e, and the parameter adjustment function 600f included in the processing circuit 600 are respectively a system control unit, an image generation unit, and an acquisition unit. It is an example of a unit, a selection unit, a determination unit and an adjustment unit. Further, the system control function 600a, the image generation function 600b, and the parameter adjustment function 600f have the same functions as the system control function 131a, the image generation function 131b, and the parameter adjustment function 131e, respectively, and thus description thereof will be omitted.

  The processing circuit 600 acquires a plurality of ambient temperatures by the temperature acquisition function 600c. Specifically, the processing circuit 131 uses the temperature acquisition function 600c to acquire a plurality of pieces of temperature information respectively output from the plurality of temperature sensors 129.

  The processing circuit 600 uses the temperature selection function 600d to select the highest temperature among the plurality of acquired ambient temperatures as the selected temperature.

  The processing circuit 600 determines the interlock value regarding the SAR based on the selected temperature selected by the interlock value determination function 600e. The method for determining the interlock value is the same as that of the interlock value determining function 131d of the processing circuit 131, and the description thereof will be omitted.

  FIG. 7 is a flowchart illustrating a process executed by the processing circuit according to the second embodiment. The process of FIG. 7 is started, for example, before the MRI examination and before the imaging parameter is set from the interface 123 by the operator or the like, by the processing circuit 600 executing a program regarding determination of an interlock value regarding SAR. ..

  As a specific example of the process of FIG. 7, a description will be given assuming that a plurality of temperature sensors 129 are arranged inside the transmission coil, inside the bore 111, inside the shield room, and the like.

(Step S710)
The processing circuit 600 uses the temperature acquisition function 600c to acquire a plurality of temperatures related to the MRI examination. The plurality of temperature information is, for example, temperature information output from a plurality of temperature sensors 129 arranged inside the transmission coil, inside the bore 111, inside the shield room, and the like.

(Step S720)
The processing circuit 600 uses the temperature selection function 600d to select the highest temperature among the plurality of acquired temperatures. For example, the processing circuit 600 selects the temperature inside the transmitter coil as the highest temperature.

(Step S730)
The processing circuit 600 determines the interlock value of the SAR according to the selected temperature by the interlock value determination function 600e.

(Step S740)
The processing circuit 600 uses the parameter adjustment function 600f to adjust the upper limit value of the imaging parameter based on the determined interlock value.

  As described above, the MRI apparatus according to the second embodiment acquires a plurality of ambient temperatures, selects the highest temperature among the acquired plurality of ambient temperatures, and selects the SAR interface according to the selected temperature. The lock value can be determined.

  Therefore, the MRI apparatus according to the second embodiment can determine the interlock value in consideration of a plurality of ambient temperatures, and thus can further improve safety.

(Application example)
In the MRI apparatus according to the first embodiment and the second embodiment, the case where the temperature and the interlock value correspond to each other when the interlock value regarding the SAR is determined according to the ambient temperature has been described. On the other hand, in this application example, a case will be described in which the interlock value is determined by adding a correction value according to temperature to a preset reference value. In the following, the "processing circuit and interlock value determining function" corresponds to the "processing circuit 131 and interlock value determining function 131d" or the "processing circuit 600 and interlock value determining function 600e". The configuration other than the above is substantially the same as the MRI apparatus according to the first and second embodiments.

  In the application example, the processing circuit uses the interlock value determination function to determine the interlock value of the SAR according to the acquired ambient temperature. Specifically, the processing circuit determines the interlock value for the acquired temperature using the calculation formula read from the storage device 127. The calculation formula is, for example, the following formula (1).

IL _C = V _S + f (T _M ) ... (1)

IL _C is an interlock value, V _S is a preset reference value, T _M is an ambient temperature (obtained temperature), and f (T _M ) is a function that depends on the obtained temperature. The reference value set in advance is, for example, an upper limit value defined by the IEC standard. The function f (T _M ) is, for example, the following mathematical expression (2).

f (T _M ) = (T _B −T _M ) × α (2)

T _B represents the body temperature of the subject, and α represents an installation value (coefficient of the device) that can be calibrated for each device. The value of the function f (T _M ) may be called a correction value from the relationship between the reference value V _S and the interlock value IL _C in Expression (1). Note that, for T _B , for example, the average body temperature of the subject may be used as a fixed value (for example, 36 ° C.).

  Outlined above, the processing circuit determines the interlock value by adding a correction value based on the ambient temperature to a preset reference value.

  As described above, the MRI apparatus according to the application example can determine the interlock value by adding the correction value based on the ambient temperature to the preset reference value.

  Therefore, the MRI apparatus according to the application example can be applied to the existing system because it is only necessary to add the correction value to the reference value set in the interlock method of the existing system. Can be easily calibrated.

  According to at least one embodiment described above, the interlock value regarding the SAR can be determined according to the ambient temperature.

  Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the scope equivalent thereto.

100 Magnetic Resonance Imaging System (MRI System)
101 static magnetic field magnet 103 gradient magnetic field coil 107 bed 107a top plate 111 bore 115 transmission coil 117 reception coil 200, 300 graph

Claims (14)

An acquisition unit that acquires the ambient temperature related to the magnetic resonance imaging test,
A magnetic resonance imaging apparatus comprising: a determination unit that determines an interlock value of SAR (Specific Absorption Rate) according to the ambient temperature. The determination unit determines the interlock value that differs depending on the ambient temperature,
The magnetic resonance imaging apparatus according to claim 1. The interlock value changes depending on the temperature in a range below an arbitrary temperature,
The magnetic resonance imaging apparatus according to claim 1 or 2. The acquisition unit acquires the ambient temperature in real time,
The determining unit determines the interlock value in real time according to the ambient temperature acquired in real time,
The magnetic resonance imaging apparatus according to any one of claims 1 to 3. The determination unit determines the interlock value by adding a correction value based on the ambient temperature to a preset reference value,
The magnetic resonance imaging apparatus according to any one of claims 1 to 4. Further comprising a transmitter coil for transmitting an RF pulse,
The acquisition unit acquires the temperature inside the transmission coil as the ambient temperature,
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. The transmission coil is a whole body coil,
The magnetic resonance imaging apparatus according to claim 6. The acquisition unit acquires, as the ambient temperature, a temperature in a bore, which is a space into which a subject is inserted,
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. The acquisition unit acquires the temperature in the shielded room as the ambient temperature,
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. The ambient temperature is the highest temperature among the plurality of ambient temperatures of the temperature inside the transmission coil, the temperature inside the bore that is the space into which the subject is inserted, and the temperature inside the shield room.
The magnetic resonance imaging apparatus according to any one of claims 1 to 5. The acquisition unit acquires the plurality of ambient temperatures,
Further comprising a selection unit for selecting the highest temperature among the plurality of ambient temperatures as a selection temperature,
The determination unit determines the interlock value according to the selected temperature,
The magnetic resonance imaging apparatus according to claim 10. In the range where the ambient temperature is 25 ° C. or lower,
The determining unit determines the interlock value using a function of the ambient temperature,
The magnetic resonance imaging apparatus according to any one of claims 1 to 11. In the range where the ambient temperature is 25 ° C. or lower,
The determining unit determines so that the interlock value increases as the ambient temperature decreases.
The magnetic resonance imaging apparatus according to any one of claims 1 to 11. In the range where the ambient temperature is 25 ° C. or lower,
The determination unit determines to increase the interlock value in proportion to the decrease in the ambient temperature.
The magnetic resonance imaging apparatus according to any one of claims 1 to 11.