JP7114382B2 - Installation method of magnetic material and arithmetic device - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to a magnetic material installation method and an arithmetic device.

A magnetic resonance imaging apparatus includes a static magnetic field magnet that generates a static magnetic field and a gradient magnetic field coil that generates a gradient magnetic field. Also, the gradient coils are often integrated into a gradient coil unit that includes a shim tray containing shim members that compensate for static magnetic field inhomogeneities.

Since the gradient magnetic field coil generates a large amount of noise, noise countermeasures are important, and there are many points to be considered regarding the gradient magnetic field coil unit itself and its support structure. For example, the noise in the frequency band determined by the weight of the gradient magnetic field coil unit and the damping characteristics of the support structure, etc. is emphasized. It is difficult.

In addition, as a support structure for the gradient magnetic field coil unit, anti-vibration rubber is often laid under it. As a result, the homogeneity of the static magnetic field deteriorates over time due to relative positional variations (sinking) of the shim members in the gradient magnetic field coil unit.

JP 2013-154141 A

The problem to be solved by the present invention is to control the load exerted by the gradient coil unit on the support structure.

In a method for installing a magnetic body according to an embodiment, a magnetic resonance imaging apparatus including a static magnetic field magnet for generating a static magnetic field and a gradient magnetic field coil unit including a shim tray containing a shim member for correcting the static magnetic field is installed. A method for installing a magnetic body in an examination room in which the shim member is not accommodated in the shim tray so that a static magnetic field in the imaging space of the magnetic resonance imaging apparatus has a gradient. is provided in the examination room.

FIG. 1 is a diagram showing a configuration example around an examination room according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration example of a magnetic resonance imaging apparatus. FIG. 3 is a diagram showing a configuration example of a gradient magnetic field coil unit. FIG. 4 is a diagram showing a configuration example of a shim tray. FIG. 5 is a diagram illustrating a configuration example of an arithmetic unit. FIG. 6 is a flow chart showing an example of calculation processing for adjusting the environmental magnetic field. FIG. 7 is a diagram showing an example of laboratory design data. FIG. 8 is a diagram showing an example of static magnetic field characteristic data. FIG. 9 is a diagram showing an example of a coordinate system. FIG. 10 is a diagram showing an example of the magnetic field distribution in the imaging space. FIG. 11A is a diagram (1) showing an example of the orientation of the magnetic field gradient. FIG. 11B is a diagram (2) showing an example of the orientation of the magnetic field gradient. FIG. 11C is a diagram (3) showing an example of the orientation of the magnetic field gradient; FIG. 12A is a diagram (4) showing an example of the orientation of the magnetic field gradient. FIG. 12B is a diagram (5) showing an example of the orientation of the magnetic field gradient. FIG. 12C is a diagram (6) showing an example of the orientation of the magnetic field gradient. FIG. 13 is a diagram showing an example of harmonics. FIG. 14 is a flowchart illustrating a processing example of creating an arrangement example of magnetic bodies. FIG. 15A is a diagram (1) showing an example of magnetic field distribution. FIG. 15B is a diagram (2) showing an example of magnetic field distribution. FIG. 16 is a diagram showing an example of arrangement of magnetic bodies. FIG. 17 is a flowchart illustrating an example of processing of calculations for passive shimming.

Hereinafter, each embodiment of a method for installing a magnetic body and an arithmetic device will be described with reference to the drawings. In addition, embodiment is not restricted to the following contents. In principle, the contents described in one embodiment and modification are similarly applied to other embodiments and modifications.

(Configuration of embodiment)
FIG. 1 is a diagram showing a configuration example around an examination room 2 according to an embodiment of the present invention. In FIG. 1, a magnetic resonance imaging apparatus 3 is installed in an examination room 2 in a facility 1 such as a hospital. One or more magnetic bodies 4 for adjusting the environmental magnetic field of the magnetic resonance imaging apparatus 3 are arranged in the examination room 2 . The magnetic bodies 4 include those based on building steel frames, magnetic shields, etc., which are installed in advance from the structural point of view of the examination room 2, and those newly added to adjust the environmental magnetic field.

The environmental magnetic field is the magnetic field around the magnetic resonance imaging apparatus 3 . In this embodiment, the magnetic field distribution before passive shimming is performed in order to homogenize the static magnetic field in the imaging space (for example, a sphere with a diameter of about several tens of centimeters) of the magnetic resonance imaging apparatus 3 has a predetermined pattern. The environmental magnetic field is adjusted by the magnetic body 4 to the normal state. After the environmental magnetic field is adjusted to a predetermined pattern, passive shimming is performed by a normal method. are arranged, and the electromagnetic force acting on the shim member can exert a force in a predetermined direction on the gradient magnetic field coil unit of the magnetic resonance imaging apparatus 3 .

When the gradient magnetic field coil unit is caused to generate a vertically upward force, the load applied to the support structure of the gradient magnetic field coil unit can be reduced. Further, when the gradient magnetic field coil unit is caused to generate a vertically downward force, it is possible to increase the load applied to the support structure of the gradient magnetic field coil unit. By appropriately adjusting the vertically upward load and the vertically downward load, it becomes easier to control the load so as not to resonate with the noise frequency, and noise can be reduced. When generating a vertically upward force, the crushing of the anti-vibration rubber laid under the gradient magnetic field coil unit is reduced, and the uniformity of the magnetic field over time due to the relative positional fluctuation of the shim members in the gradient magnetic field coil unit. deterioration is reduced.

The computation device 5 is a computer device for performing computation for adjusting the environmental magnetic field and computation for passive shimming. The magnetic field measuring device 6 is a measuring device for measuring the static magnetic field in the imaging space of the magnetic resonance imaging apparatus 3 when passive shimming is performed. The computing device 5 and the magnetic field measuring device 6 are used when environmental magnetic field adjustment and passive shimming are performed, and are not required during normal inspection. By replacing the functions of the arithmetic unit 5 with a computer in the magnetic resonance imaging apparatus 3, the arithmetic unit 5 can be made unnecessary.

FIG. 2 is a diagram showing a configuration example of the magnetic resonance imaging apparatus 3. As shown in FIG. In FIG. 2, the magnetic resonance imaging apparatus 3 includes a magnet pedestal 301 and a bed 311 . In this embodiment, the longitudinal direction of the top plate 312 of the bed 311 is the Z-axis direction, the axial direction perpendicular to the Z-axis direction and horizontal to the floor surface is the X-axis direction, and the Z-axis direction is perpendicular to the floor surface. The direction of the axis perpendicular to it is defined as the Y-axis direction. The magnet mount 301 includes a static magnetic field magnet 302 , a gradient magnetic field coil unit 308 and an RF coil 309 . Note that the internal configuration of the magnet mount 301 is shown in a longitudinal sectional view.

The gradient magnetic field coil unit 308 includes a main coil 303 , a shield coil 304 , a shim tray 306 and a shim member 307 . The magnetic resonance imaging apparatus 3 also includes a gradient magnetic field power supply 322 , a transmission circuit 323 , a reception circuit 324 , a bed control circuit 325 , a sequence control circuit 326 and a computer 331 . Note that the magnetic resonance imaging apparatus 3 does not include the subject P (eg, human body). Also, the configuration shown in FIG. 2 is merely an example. For example, each part in the sequence control circuit 326 and the computer 331 may be integrated or separated as appropriate.

The static magnetic field magnet 302 has a substantially cylindrical shape, and generates a static magnetic field in a bore (a space inside the cylinder of the static magnetic field magnet 302) including an imaging region of the subject P. The static magnetic field magnet 302 may be a superconducting magnet or a permanent magnet.

The gradient magnetic field coil unit 308 also has a substantially cylindrical shape and is held inside the static magnetic field magnet 302 by a support structure such as anti-vibration rubber. The gradient magnetic field coil unit 308 applies a gradient magnetic field in directions of the X-axis, Y-axis, and Z-axis that are orthogonal to each other by the current supplied from the gradient magnetic field power supply 322, and cancels the leakage magnetic field of the main coil 303. and a shield coil 304 . A shim tray 306 is inserted between the main coil 303 and the shield coil 304 . The shim tray 306 houses shim members (also called iron shims, metal shims, etc.) 307 for correcting magnetic field inhomogeneities in the bore.

FIG. 3 is a diagram showing a configuration example of the gradient magnetic field coil unit 308. As shown in FIG. In FIG. 3, between the main coil 303 and the shield coil 304 of the gradient magnetic field coil unit 308, a plurality of slots 305 are provided at substantially equal intervals in the circumferential direction. Note that the number of slots 305 is not limited to that illustrated.

The slots 305 are through-holes that form openings on both end surfaces of the gradient magnetic field coil unit 308 and extend over the entire length of the gradient magnetic field coil unit 308 in the longitudinal direction (major axis direction). A shim tray 306 is inserted into each slot 305 , and each shim tray 306 is fixed approximately in the center of the gradient magnetic field coil unit 308 . The shim tray 306 is made of resin, which is a non-magnetic and non-conductive material, and has a substantially bar shape.

FIG. 4 is a diagram showing a configuration example of the shim tray 306. As shown in FIG. In FIG. 4, a plurality of continuously formed pockets 306a are formed in the longitudinal direction of the shim tray 306. As shown in FIG. The number of pockets 306a is not limited to that shown. Each pocket 306a accommodates a required number of shim members 307 at required locations for the purpose of homogenizing the static magnetic field in the imaging space in the intermediate portion of the bore. The shim member 307 is a thin metal plate about the size of a business card.

Returning to FIG. 2, the bed 311 has a table 312 on which the subject P is placed. It is inserted into the cavity (imaging aperture) of the coil unit 308 . The bed 311 is usually installed so that its longitudinal direction is parallel to the central axis of the static magnetic field magnet 302 . The bed control circuit 325 drives the bed 311 under the control of the computer 331 to move the top board 312 in the longitudinal direction and the vertical direction.

The RF coil 309 is arranged inside the gradient magnetic field coil unit 308, and is supplied with RF pulses (RF pulses corresponding to the Larmor frequency determined by the type of target atom and magnetic field strength) from the transmission circuit 323. It generates a high-frequency magnetic field, receives magnetic resonance signals emitted from the subject P under the influence of the high-frequency magnetic field, and outputs the received magnetic resonance signals to the receiving circuit 324 . Note that the RF coil 309 may be configured by being divided into a transmission coil and a reception coil.

The receiving circuit 324 detects magnetic resonance signals output from the RF coil 309 and generates magnetic resonance data based on the detected magnetic resonance signals. Specifically, the receiving circuit 324 generates magnetic resonance data by digitally converting the magnetic resonance signals received by the RF coil 309 . The receiving circuit 324 also transmits the generated magnetic resonance data to the sequence control circuit 326 . Note that the receiving circuit 324 may be provided on the magnet mount 301 side.

The sequence control circuit 326 images the subject P by driving the gradient magnetic field power supply 322 , the transmission circuit 323 and the reception circuit 324 based on the sequence information transmitted from the computer 331 . Here, the sequence information is information that defines the procedure for imaging. The sequence information includes the strength of the current supplied by the gradient magnetic field power supply 322 to the main coil 303 and the timing of supplying the current, the strength of the RF pulse supplied to the RF coil 309 by the transmission circuit 323, the timing of applying the RF pulse, and the reception circuit. 324 detects the magnetic resonance signal, etc. is defined. For example, sequence control circuit 326 is implemented by a processor.

Further, when the sequence control circuit 326 receives magnetic resonance data from the receiving circuit 324 as a result of imaging the subject P by driving the gradient magnetic field power supply 322, the transmitting circuit 323, and the receiving circuit 324, the received magnetic resonance data is transferred to the computer. 331.

The computer 331 performs overall control of the magnetic resonance imaging apparatus 3, image generation, and the like. Computer 331 includes memory 332 , input device 333 , display 334 and processing circuitry 335 . The processing circuitry 335 includes an interface function 336 , a control function 337 , an image generation function 338 , an environmental magnetic field calculation function 339 and a passive shimming calculation function 340 .

Each processing function performed by the interface function 336, the control function 337, the image generation function 338, the environmental magnetic field calculation function 339, and the passive shimming calculation function 340 is stored in the memory 332 in the form of a program executable by the computer 331. ing. The processing circuit 335 is a processor that reads a program from the memory 332 and executes it to realize a function corresponding to each program. In other words, the processing circuit 335 with each program read has each function shown in the processing circuit 335 of FIG. In FIG. 2, a single processing circuit 335 realizes processing functions performed by an interface function 336, a control function 337, an image generation function 338, an environmental magnetic field calculation function 339, and a passive shimming calculation function 340. However, the processing circuit 335 may be configured by combining a plurality of independent processors, and the functions may be realized by each processor executing a program. In other words, each function described above may be configured as a program, and one processing circuit 335 may execute each program. As another example, certain functions may be implemented in dedicated, separate program execution circuitry.

The term "processor" used in the above description is, for example, CPU (Central Processing Unit), GPU (Graphics Processing Unit), or application specific integrated circuit (ASIC), programmable logic device (for example , Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), or Field Programmable Gate Array (FPGA)). The processor implements its functions by reading and executing programs stored in the memory 332 . Note that instead of storing the program in the memory 332, the program may be configured to be directly embedded in the circuit of the processor. In this case, the processor implements its functions by reading and executing the program embedded in the circuit. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, and may be configured as one processor by combining a plurality of independent circuits to realize its function. good.

Similarly, the transmission circuit 323, the reception circuit 324, the bed control circuit 325, and the like are also configured by electronic circuits such as the processor.

Processing circuitry 335 transmits sequence information to sequence control circuitry 326 and receives magnetic resonance data from sequence control circuitry 326 via interface functions 336 . Also, upon receiving the magnetic resonance data, the processing circuit 335 having the interface function 336 stores the received magnetic resonance data in the memory 332 . The magnetic resonance data stored in memory 332 are arranged in k-space by control function 337 . As a result, memory 332 stores k-space data.

Memory 332 stores magnetic resonance data received by processing circuitry 335 having interface functionality 336 , k-space data arranged in k-space by processing circuitry 335 having control functionality 337 , and processing circuitry 335 having image generation functionality 338 . Stores image data and the like generated by For example, the memory 332 is a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk, an optical disk, or the like.

The input device 333 receives various instructions and information inputs from the operator. The input device 333 is, for example, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard. The input device 333 is an interface that receives input. A display 334 displays a GUI (Graphical User Interface) for accepting input of imaging conditions, an image generated by a processing circuit 335 having an image generating function 338, and the like under the control of a processing circuit 335 having a control function 337. do. The display 334 is, for example, a display device such as a liquid crystal display.

The processing circuit 335 performs overall control of the magnetic resonance imaging apparatus 3 by the control function 337, and controls imaging, image generation, image display, and the like. For example, a processing circuit 335 having a control function 337 receives input of imaging conditions (imaging parameters, etc.) on a GUI, and generates sequence information according to the received imaging conditions. Also, the processing circuit 335 having the control function 337 transmits the generated sequence information to the sequence control circuit 326 . The processing circuit 335 reads the k-space data from the memory 332 using the image generation function 338 and performs reconstruction processing such as Fourier transform on the read k-space data to generate an image.

The processing circuit 335 uses the environmental magnetic field calculation function 339 to perform calculations for adjusting the environmental magnetic field in order to control the load of the gradient magnetic field coil unit 308 . The environmental magnetic field calculation function 339 includes an electromagnetic field analysis function generally provided as electromagnetic field analysis software and a function generally provided as shimming software for passive shimming. The environmental magnetic field calculation function 339 is an example of an input section and an output section. It should be noted that the environmental magnetic field calculation function 339 can be omitted when the calculation for adjusting the environmental magnetic field is performed in the calculation device 5, so it is indicated by the dashed line.

The processing circuit 335 uses the passive shimming calculation function 340 to determine the position of the shim member 307 (circumferential position , Z-axis position) and numbers. The passive shimming calculation function 340 includes functions generally provided as shimming software for passive shimming. Note that when the passive shimming calculation is performed in the calculation device 5, the passive shimming calculation function 340 can be omitted, so it is indicated by a dashed line.

FIG. 5 is a diagram showing a configuration example of the arithmetic unit 5. As shown in FIG. In FIG. 5, the computing device 5 comprises a memory 51, an input device 52, a display 53 and a processing circuit . The processing circuit 54 has an environmental magnetic field calculation function 55 and a passive shimming calculation function 56 .

Each processing function performed by the environmental magnetic field calculation function 55 and the passive shimming calculation function 56 is stored in the memory 51 in the form of a program executable by the calculation device 5 . The processing circuit 54 is a processor that reads a program from the memory 51 and executes it to realize a function corresponding to each program. In other words, the processing circuit 54 with each program read has each function shown in the processing circuit 54 of FIG. In FIG. 5, it is assumed that the single processing circuit 54 implements the processing functions performed by the environmental magnetic field calculation function 55 and the passive shimming calculation function 56. The functions may be realized by configuring the processing circuit 54 and having each processor execute a program. In other words, each function described above may be configured as a program, and one processing circuit 54 may execute each program. As another example, certain functions may be implemented in dedicated, separate program execution circuitry. The meaning of the processor is as described above. The memory 51 is, for example, a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk, an optical disk, or the like.

Alternatively, instead of storing the program in the memory 51, the program may be directly incorporated into the circuit of the processor. In this case, the processor implements its functions by reading and executing the program embedded in the circuit. Further, each processor is not limited to being configured as a single circuit for each processor, but may be configured as one processor by combining a plurality of independent circuits to realize its function.

The input device 52 receives various instructions and information input from the operator. The input device 52 is, for example, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard. The input device 52 is an interface that receives input. The display 53 displays the calculation result for adjusting the environmental magnetic field and the calculation result of the position and number of shim members in passive shimming by GUI (Graphical User Interface) or the like. The display 53 is, for example, a display device such as a liquid crystal display.

The processing circuit 54 uses the environmental magnetic field calculation function 55 to perform calculations for adjusting the environmental magnetic field in order to control the load of the gradient magnetic field coil unit 308 of the magnetic resonance imaging apparatus 3 . The environmental magnetic field calculation function 55 includes an electromagnetic field analysis function generally provided as electromagnetic field analysis software and a function generally provided as shimming software for passive shimming. The environmental magnetic field calculation function 55 is an example of an input section and an output section. It should be noted that if the calculation for adjusting the environmental magnetic field is performed in the magnetic resonance imaging apparatus 3, the environmental magnetic field calculation function 55 can be omitted.

The processing circuit 54 uses the passive shimming calculation function 56 to determine the position of the shim member 307 (circumferential direction position , Z-axis position) and numbers. The passive shimming calculation function 56 includes functions generally provided as shimming software for passive shimming. Note that if the passive shimming calculation is performed in the magnetic resonance imaging apparatus 3, the passive shimming calculation function 56 can be omitted.

(Operation of embodiment)
FIG. 6 is a flow chart showing an example of calculation processing for adjusting the environmental magnetic field by the environmental magnetic field calculation function 55 of the calculation device 5 or the environmental magnetic field calculation function 339 of the magnetic resonance imaging apparatus 3 . Although the operation by the environmental magnetic field calculation function 55 of the arithmetic device 5 will be described below, the environmental magnetic field calculation function 55 is read as the environmental magnetic field calculation function 339 for the operation by the environmental magnetic field calculation function 339 of the magnetic resonance imaging apparatus 3 as well. can be applied by

In FIG. 6, the environmental magnetic field computing function 55 acquires examination room design data (step S11). The examination room design data is data indicating the details of the arrangement of magnetic bodies such as steel frames and magnetic shields when the examination room 2 (FIG. 1) is constructed and then repaired. FIG. 7 is a diagram showing an example of examination room design data, which includes the position (x, y, z) or position range where the magnetic material is arranged, the type of the magnetic material, and the mass of the magnetic material. there is

Returning to FIG. 6, the environmental magnetic field computing function 55 then acquires static magnetic field characteristic data (step S12). The static magnetic field characteristic data is data indicating the static magnetic field characteristic of the delivered product provided by the manufacturer of the static magnetic field magnet 302 (FIG. 2) of the magnetic resonance imaging apparatus 3 . The superconducting coils and the like that make up the static magnetic field magnet 302 contain errors even if they are manufactured based on the same standard, resulting in non-uniformity in the magnetic field. FIG. 8 is a diagram showing an example of static magnetic field characteristic data, which includes position (x, y, z or r, θ, φ) and magnetic flux density or magnetic flux density deviation. FIG. 9 is a diagram showing an example of the coordinate system, showing the correspondence between the orthogonal coordinate system X, Y, Z and the spherical coordinate system r, θ, φ.

Returning to FIG. 6, the environmental magnetic field calculation function 55 then inputs the designation of the direction in which the electromagnetic force acts on the gradient magnetic field coil unit 308 via the shim member 307 and the approximate value of the magnitude of the force. (Step S13). When the direction in which the electromagnetic force acts is vertically upward, the load applied to the support structure by the gradient magnetic field coil unit 308 is reduced. When the electromagnetic force acts vertically downward, the load applied to the support structure by the gradient magnetic field coil unit 308 increases.

Next, the environmental magnetic field calculation function 55 creates an arrangement example of magnetic bodies for creating an environmental magnetic field such that the imaging space before passive shimming has a target magnetic field gradient (step S14). There may be a plurality of arrangement examples of the magnetic bodies, or an optimum one may be selected. The target magnetic field gradient is as shown in FIG. 10, for example, when a vertically upward electromagnetic force is applied. FIG. 10 is a diagram showing an example of the magnetic field distribution in the imaging space, where the center is the origin, the horizontal axis is the Z axis, the left side is positive, and the vertical axis is the Y axis, and the upper side is positive. In FIG. 10, the upper left region R1 has a relatively weak static magnetic field in the Z-axis direction, and the lower right region R2 has a relatively strong static magnetic field in the Z-axis direction. FIG. 11A is a diagram showing an example of the direction of the magnetic field gradient, and the pattern of the direction of the magnetic field gradient is shown by an arrow pointing from the region R1 with the weak magnetic field to the region R2 with the strong magnetic field in FIG. In addition, in FIGS. 10 and 11A, the reason why the arrow points downward is assumed is that a magnetic body such as a magnetic shield exists on the right side. In other words, if there is a magnetic body such as a magnetic shield on the right side (generally, a magnetic shield is provided on the opposite wall of the bed), the magnetic field lines will be attracted to the magnetic body and the magnetic field on the right side will be strengthened. This is to utilize and reduce additional magnetic material.

From the viewpoint of applying a vertically upward electromagnetic force, a pattern in which an arrow points downward to the left as shown in FIG. It can be a facing pattern. 11B and 11C are diagrams showing examples of orientations of magnetic field gradients. Conversely, when a vertically downward electromagnetic force is applied, target magnetic field gradient patterns are as shown in FIGS. 12A to 12C. 12A-12C are diagrams showing examples of the orientation of magnetic field gradients. The target magnetic field gradient pattern is any one of FIGS. 11A to 11C when a vertically upward electromagnetic force is applied, and any one of FIGS. However, the operator may be allowed to specify the pattern.

Also, the target magnetic field gradient may be specified by each order component (harmonics) of the magnetic field strength (magnetic flux density) in the imaging space represented by spherical harmonics. FIG. 13 is a diagram showing an example of harmonics, in which the horizontal axis is the Z axis, the left side is the plus side, and the vertical axis is the normalized magnetic field strength. The first-order component a(1,0), which changes linearly with respect to the position in the Z-axis direction (first axis direction), is negative for the positive Z for the patterns of FIGS. 10 and 11A. is specified to be the value of As a result, the magnetic field on the left side (positive side of Z) is relatively weak and the magnetic field on the right side (negative side of Z) is relatively strong, and passive shimming has the effect of increasing the number of shim members at the end of the shim tray. Although not shown, the linear component b(1,1) that changes linearly in the Y-axis direction (second axis direction) is Y is specified to be a negative value for the positive of As a result, the magnetic field on the upper side (the positive side of Y) is relatively weak and the magnetic field on the lower side (the negative side of Y) is relatively strong, and passive shimming has the effect of increasing the number of shim members in the shim tray that is relatively on the upper side. .

Furthermore, as shown in FIG. 13, the quadratic component a(2,0), which varies with the square of the position in the Z-axis direction, is Z plus and Z for the patterns of FIGS. A negative value is specified to have a positive value, and passive shimming has the effect of increasing the number of shim members at both ends of the shim tray. Although not shown, the first-order component a(1,1), which varies linearly in the X-axis direction, affects the shim member in the X-axis direction and is appropriately adjusted. The plus/minus values of the harmonics values have been described for the patterns of FIGS. 10 and 11A, but in the case of FIG. 12A in which the direction of the force is reversed, the plus/minus values are reversed. Also, for other patterns, the directions of the values are appropriately changed.

FIG. 14 is a flow chart showing a processing example of creating an arrangement example of magnetic bodies (step S14 in FIG. 6). In FIG. 14, the environmental magnetic field calculation function 55 estimates the magnetic field distribution in the imaging space by electromagnetic field analysis from the examination room design data and the static magnetic field characteristic data (step S141).

Next, the environmental magnetic field calculation function 55 assumes a case where the estimated magnetic field distribution is homogenized by passive shimming (estimating the positions and numbers of the shim members 307), and estimates the total electromagnetic force acting on the shim members 307. (Step S142). 15A and 15B are diagrams showing examples of magnetic field distributions. FIG. 15A shows an example of magnetic field lines inside the static magnetic field magnet 302 and the gradient magnetic field coil unit 308 when no shim member exists, the circle indicates the imaging space, the magnetic field in the region R1 is relatively weak, and the magnetic field in the region R2 shows a case where the magnetic field of is relatively strong. In this case, as shown in FIG. 15B, the shim member 307-1 is virtually placed at a position close to the region where the magnetic field was weak, thereby attracting the magnetic lines of force upward (the drawn magnetic lines of force are indicated by dashed lines). , attempts to homogenize the magnetic field. Since there is also a portion where the magnetic field is weak right under the imaging space in FIG. 15B, the shim member 307-2 is virtually arranged near that portion. The virtually arranged shim members 307 - 1 and 307 - 2 receive electromagnetic force mainly due to the strong magnetic field of the superconducting coil that constitutes the static magnetic field magnet 302 . For example, the shim member 307-1 arranged on the upper side is mainly subjected to an upwardly attracted electromagnetic force. A vertically upward force acts on the unit 308 as a total.

Returning to FIG. 14, the environmental magnetic field calculation function 55 then determines whether or not the magnetic field distribution has a desired pattern and the electromagnetic force is sufficient (step S143). 11A to 11C ( If the pattern is specified, the specified pattern), and if the direction in which the electromagnetic force acts is vertically downward, one of FIGS. 12A to 12C (if the pattern is specified, pattern) and determines whether or not the total electromagnetic force acting on the shim member satisfies the specified approximate value.

If the determination condition is not satisfied (No in step S143), the environmental magnetic field calculation function 55 performs virtual placement of magnetic bodies (step S144). That is, the environmental magnetic field calculation function 55 virtually adds or changes the position, type, mass, etc. of the magnetic material so that the current magnetic field distribution in the imaging space approaches the target magnetic field distribution. When the magnetic body is placed, the magnetic lines of force are attracted to the magnetic body side, and there is an effect of strengthening the magnetic field of the part where the magnetic line of force is attracted.

Next, the environmental magnetic field calculation function 55 estimates the magnetic field distribution in the imaging space after the addition of the magnetic material by electromagnetic field analysis (step S145).

Next, the environmental magnetic field calculation function 55 assumes a case where the estimated magnetic field distribution is homogenized by passive shimming (estimating the positions and numbers of the shim members 307), and estimates the total electromagnetic force acting on the shim members 307. (Step S146). Then, the environmental magnetic field calculation function 55 again determines whether the magnetic field distribution has a desired pattern and the electromagnetic force is sufficient (step S143). If the judgment condition is not satisfied (No in step S143), steps S144 to S146 are repeated.

If the determination condition is satisfied (Yes in step S143), the creation of the magnetic body placement example is finished, and the magnetic body placement at that time becomes the created placement example. FIG. 16 is a diagram showing an example of the arrangement of magnetic bodies. A magnetic body 4-5 is provided behind the right inner wall, and magnetic bodies 4-6 and 4-7 are provided at the magnet ends of the magnetic resonance imaging apparatus 3. FIG. The magnetic bodies 4-6 and 4-7 provided at the ends of the magnets of the magnetic resonance imaging apparatus 3 are donut-shaped or the like so as not to block the opening of the magnetic resonance imaging apparatus 3. FIG. Further, the magnetic body may be provided under the legs supporting the static magnetic field magnet so as to sandwich the floor surface.

In FIG. 16, the magnetic body 4-1 is mainly for adjusting the component b(1,1), the magnetic body 4-2 is mainly for adjusting the component a(1,0) and the component b(1,1), The magnetic bodies 4-3 and 4-4 are mainly for adjusting the component b(1,1), the magnetic body 4-5 is mainly for adjusting the component a(1,0), and the magnetic bodies 4-6 and 4-7 are It is mainly for adjustment of component a(2,0). It should be noted that this does not mean that all of the illustrated magnetic bodies are always provided, and that they may be omitted or added as appropriate according to the characteristics of the static magnetic field magnet of the magnetic resonance imaging apparatus 3 .

Returning to FIG. 6, the environmental magnetic field calculation function 55 presents the operator with an arrangement example of the magnetic bodies (step S15). For example, the environmental magnetic field calculation function 55 presents the type and mass (size) of the magnetic material and the location (position) of the magnetic material. The operator actually arranges the magnetic bodies in the examination room 2 according to the presented arrangement example of the magnetic bodies.

The order of processing in the flowcharts described in FIGS. 6 and 14 may be changed within a range that does not essentially affect the results.

Steps S11 to S15 shown in FIG. 6 are steps corresponding to the environmental magnetic field calculation function 55 (or the environmental magnetic field calculation function 339). Steps S11 to S15 are performed by the processing circuit 54 (or the processing circuit 335) reading and executing a program corresponding to the environmental magnetic field calculation function 55 (or the environmental magnetic field calculation function 339) from the memory 51 (or the memory 332). This is the step in which the calculation function 55 (or the environmental magnetic field calculation function 339) is realized.

Steps S141 to S146 shown in FIG. 14 are steps corresponding to the environmental magnetic field calculation function 55 (or the environmental magnetic field calculation function 339). Steps S141 to S146 are performed by the processing circuit 54 (or the processing circuit 335) reading and executing a program corresponding to the environmental magnetic field calculation function 55 (or the environmental magnetic field calculation function 339) from the memory 51 (or the memory 332). This is the step in which the calculation function 55 (or the environmental magnetic field calculation function 339) is realized.

Next, FIG. 17 is a flow chart showing an example of calculation processing for passive shimming. Although the operation by the passive shimming arithmetic function 56 of the arithmetic device 5 will be described, it can also be applied to the operation by the passive shimming arithmetic function 340 of the magnetic resonance imaging apparatus 3 by replacing the passive shimming arithmetic function 56 with the passive shimming arithmetic function 340. can do.

In FIG. 17, the passive shimming calculation function 56 acquires measurement data of the static magnetic field in the imaging space (step S21). It is assumed that the measurement data of the static magnetic field in the imaging space is obtained in advance by the magnetic field measuring device 6 .

Next, the passive shimming calculation function 56 calculates the positions and the number of shim members 307 required to homogenize the static magnetic field in the imaging space based on the measured value of the static magnetic field in the imaging space (step S22 ).

Next, the passive shimming calculation function 56 presents the calculated positions and number of shim members 307 (step S23). The operator actually adjusts the number of shim members 307 on the shim tray 306 according to the presented position and number of shim members 307 .

The order of processing in the flow chart illustrated in FIG. 17 may be changed within a range that does not essentially affect the results. In addition, processing may be performed in parallel to the extent that the results are not essentially affected.

Steps S21 to S23 shown in FIG. 17 are steps corresponding to the passive shimming calculation function 56 (or the passive shimming calculation function 340). Steps S21 to S23 are performed by the processing circuit 54 (or the processing circuit 335) reading and executing a program corresponding to the passive shimming calculation function 56 (or the passive shimming calculation function 340) from the memory 51 (or the memory 332). This is the step in which the arithmetic function 56 (or the passive shimming arithmetic function 340) is implemented.

According to the embodiments described above, the load exerted by the gradient magnetic field coil unit on the support structure can be controlled.

For example, by controlling the load exerted on the support structure by the gradient magnetic field coil unit to an appropriate value, the frequency band of noise to be emphasized is changed, and noise reduction can be expected. For several types of sequences, when copper is used in the conductor part and when light aluminum is used, in many sequences a reduction in noise is observed in the case of light aluminum. In that respect, according to the embodiment, even if the conductor portion of the gradient magnetic field coil is not made lighter by replacing copper with aluminum, for example, by applying a vertically upward electromagnetic force to the gradient magnetic field coil unit, An effect equivalent to weight reduction can be obtained. For example, a weight reduction effect of 100 kgF to 500 kgF is expected. The load can be increased not only when the load applied to the support structure by the gradient magnetic field coil unit is reduced, but also when noise reduction is expected by increasing the load.

In addition, since the load exerted by the gradient magnetic field coil unit on the support structure is reduced, the crushing of the anti-vibration rubber laid under the gradient magnetic field coil unit is alleviated, and the shim members in the gradient magnetic field coil unit are placed relative to each other. Degradation of uniformity of the static magnetic field over time due to drastic positional fluctuations (sinking) is alleviated.

In addition, since the load exerted by the gradient magnetic field coil unit on the support structure can be controlled, the options for the support structure are increased and the design is facilitated.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention as well as the scope of the invention described in the claims and equivalents thereof.

1 facility 2 examination room 3 magnetic resonance imaging device 302 static magnetic field magnet 306 shim tray 307 shim member 308 gradient magnetic field coil unit 4 magnetic body 5 computing device 6 magnetic field measuring device

Claims (8)

A method of installing a magnetic body in an examination room in which a magnetic resonance imaging apparatus is installed, which includes a static magnetic field magnet that generates a static magnetic field and a gradient magnetic field coil unit that includes a shim tray containing a shim member that corrects the static magnetic field. There is
The magnetic body is provided in the examination room so that the static magnetic field in the imaging space of the magnetic resonance imaging apparatus has a gradient when the shim member is not stored in the shim tray.
Installation method of magnetic material. By virtually arranging the shim members so that the static magnetic field satisfies a predetermined uniformity , presenting an arrangement example of the magnetic body for exerting a vertically upward force on the shim members,
The installation method of the magnetic body according to claim 1. By virtually arranging the shim members so that the static magnetic field satisfies a predetermined uniformity , presenting an arrangement example of the magnetic body for exerting a vertically downward force on the shim members,
The installation method of the magnetic body according to claim 1. With the center of the imaging space as the origin, the moving direction of the table on which the subject is placed is the first axial direction, and the direction orthogonal to the first axial direction and perpendicular to the floor surface is the second axial direction. and when the static magnetic field is in the first axial direction,
Regarding the arrangement of the magnetic material, the magnetic flux density in the imaging space when the shim member is not stored in the shim tray is as follows:
The gradient is specified by the positive or negative value of the primary component in the direction of the first axis, the primary component in the direction of the second axis, or the secondary component in the direction of the first axis represented by a spherical harmonic function. Ru
The method for installing a magnetic body according to any one of claims 1 to 3. The magnetic body is provided on at least one of the ceiling, floor, or inner wall of the examination room,
The method for installing a magnetic body according to any one of claims 1 to 4. The magnetic body is provided on an end face having an opening in the static magnetic field magnet,
The method for installing a magnetic body according to any one of claims 1 to 5. The magnetic body is provided under the leg supporting the static magnetic field magnet so as to sandwich the floor surface,
The method for installing a magnetic body according to any one of claims 1 to 6. A static magnetic field magnet for generating a static magnetic field, and a gradient magnetic field coil unit including a shim tray containing a shim member for correcting the static magnetic field. A computing device for calculating information,
an input unit that receives information about magnetic field characteristics of the static magnetic field magnet;
an output unit that outputs information on the placement of the magnetic material in the examination room so that the static magnetic field in the imaging space of the magnetic resonance imaging apparatus has a gradient when the shim member is not stored in the shim tray;
Computing device with

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