JP5646145B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a method for homogenizing a static magnetic field in a magnetic resonance imaging (hereinafter referred to as MRI) apparatus, and more particularly to a technique for automatically setting an optimum region for homogenization.

  The MRI apparatus measures a nuclear magnetic resonance (hereinafter referred to as NMR) signal generated by a nuclear spin that constitutes a subject, particularly a human tissue, and two-dimensionally describes the shape and function of the head, abdomen, limbs, etc. Alternatively, it is an apparatus for imaging three-dimensionally. In the 2D or 3D Fourier transform method, which is a typical MRI image construction method, an object is placed in a static magnetic field that is spatially uniform and directed in a certain direction, and the nuclear spin of the object is applied to a horizontal plane by applying a high-frequency pulse. Then, by applying a gradient magnetic field of a predetermined combination, a distribution corresponding to the spatial position is generated in the phase of the nuclear spin, and the signal is measured.

  For this reason, when the static magnetic field is not uniform, phase rotation occurs due to this non-uniformity, thereby generating a false image, positional distortion, etc., and degrading image quality. In order to correct this non-uniformity of the static magnetic field, the MRI apparatus performs shimming to make the static magnetic field uniform before the main imaging. Shimming is performed by adjusting the amount of current flowing through the magnetic field correction coil (shim coil). The amount of current to be applied is adjusted in advance based on the result of static magnetic field distribution measurement.

  Static magnetic field inhomogeneity is caused by, for example, the device limitations of a magnet that generates a static magnetic field, and the permeability of a living body that is a subject is slightly different for each tissue. When correcting the static magnetic field inhomogeneity caused by the living body, since it is performed after the subject is placed in the static magnetic field, it is necessary to perform in a short time.

  Since it is difficult to homogenize the entire area where the static magnetic field distribution measurement has been performed in a short time, generally, the static magnetic field is corrected and uniformed only in the imaging area. This shortens the shimming time and improves the magnetic field uniformity within the region. If the region to be corrected is limited, particularly in the living body shimming, when a region such as the heart that reduces the uniformity of the static magnetic field is included in the imaging region, such a region can be excluded and useful.

Japanese Patent Laid-Open No. 11-113880

  Conventionally, a user designates an area to be corrected through a GUI provided in the MRI apparatus. However, since the user needs to set the area to be corrected in addition to the setting of the shooting area, the burden on the user increases.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for easily determining an appropriate static magnetic field correction region without increasing the burden on the user.

  In the present invention, a correction area for correcting the static magnetic field uniformity is automatically set based on the imaging area.

Specifically, a control means for processing the signals obtained with performing a static magnetic field generating means for applying a static magnetic field to the subject, the photographing and controls the entire apparatus, an input means for inputting an instruction to the control means The control means includes a static magnetic field correction means for correcting non-uniformity of the static magnetic field distribution, and a correction for correcting the non-uniformity of the static magnetic field distribution by the static magnetic field correction means. and a correction region determination means for determining a region, the correction area determining means, according to imaging parameters inputted through said input means, characterized in that to determine the correction region in a predetermined measurement region A magnetic resonance imaging apparatus is provided.

  According to the present invention, an appropriate static magnetic field correction region can be easily determined without increasing the burden on the user.

It is a block diagram which shows the whole structure of the MRI apparatus of 1st embodiment. It is a functional block diagram of the information processing system of 1st embodiment. It is a figure for demonstrating the correction | amendment area | region bottom face determination method of 1st embodiment. It is a figure for demonstrating the correction | amendment area | region bottom face determination method of 1st embodiment. It is a figure for demonstrating the 1st correction area | region height determination method of 1st embodiment. It is a figure for demonstrating the 2nd correction | amendment area | region height determination method of 1st embodiment. It is a processing flow of the correction area | region determination process of 1st embodiment. It is a processing flow of the correction area | region determination process of 2nd embodiment. It is a figure for demonstrating another example of the correction | amendment area | region bottom face determination method of each embodiment.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described. Hereinafter, in all the drawings for explaining the embodiments of the present invention, those having the same function are denoted by the same reference numerals, and repeated explanation thereof is omitted.

  First, the overall configuration of the MRI apparatus of this embodiment will be described. FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus 100 of the present embodiment. The MRI apparatus 100 of the present embodiment obtains a tomographic image of a subject using an NMR phenomenon, and includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a sequencer 4, a transmission system 5, and a reception system. 6 and an information processing system 7.

  If the static magnetic field generation system 2 is a vertical magnetic field system, the static magnetic field is uniform in the direction perpendicular to the body axis in the space around the subject 1 and if it is a horizontal magnetic field system, the static magnetic field is uniform in the body axis direction of the subject 1. To generate a static magnetic field generation source (not shown) of a permanent magnet system, a normal conduction system, or a superconductivity system disposed around the subject 1, and a plurality of corrections for non-uniformity of the static magnetic field due to the static magnetic field generation source. A shim coil 21 having a plurality of channels, and a shim power source 22 that is driven by supplying current to each channel of the shim coil 21.

  The shim coil 21 includes three or more channels of static magnetic field generating coils that generate magnetic fields orthogonal to each other. The adjustment (shimming) of the static magnetic field by the shim coils 21 is performed by superimposing the static magnetic field generated by the static magnetic field generation source and the additional static magnetic field generated by passing a current through each shim coil 21.

  The gradient magnetic field generation system 3 supplies a gradient magnetic field coil 31 that generates gradient magnetic field pulses Gx, Gy, and Gz whose magnetic field strengths linearly change in three orthogonal directions, a current to the gradient magnetic field coil 31, and the gradient magnetic field coil 31. And a gradient magnetic field power source 33 for driving.

  The transmission system 5 includes a high-frequency coil (transmission coil) 51 that irradiates the subject 1 with a high-frequency magnetic field (RF) pulse in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the living tissue of the subject 1. A synthesizer 52 that generates a high-frequency signal to be applied to the high-frequency coil 51, a modulator 53 that modulates the high-frequency signal under the control of the sequencer 7, and an amplifier 54 that amplifies the modulated signal.

The receiving system 6 is a high-frequency coil (receiving coil) 61 that detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of atomic nuclear spins constituting the biological tissue of the subject 1 and amplifies the detected echo signal. And an A / D converter 64 for converting the analog output from the quadrature detector 63 into a digital signal. The digital signal converted by the A / D converter 64 is sent to the information processing system 7 as measurement data.

  In FIG. 1, a transmission coil 51 and a gradient magnetic field coil 31 are opposed to the subject 1 in the static magnetic field space of the static magnetic field generation system 2 into which the subject 1 is inserted. If it is a horizontal magnetic field system, it is installed so as to surround the subject 1. The receiving coil 61 is installed so as to face the subject 1 or surround the subject 1. Moreover, although the case where the transmission coil 51 and the reception coil 61 are provided separately is illustrated here, it is not limited thereto. For example, one high frequency coil may be configured to share both functions.

  The sequencer 4 controls to repeatedly apply the RF pulse and the gradient magnetic field pulse in accordance with a predetermined pulse sequence. The sequencer 4 operates according to the control of the information processing system 7 and data for reconstructing a tomographic image of the subject 1. Various commands necessary for collection are sent to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6. The transmission system 5 and the gradient magnetic field generation system 3 respectively control the application timing, period and intensity of the RF pulse, and the application timing, period and intensity of the gradient magnetic field pulse in accordance with instructions from the sequencer 4. Further, the receiving system 6 detects an echo signal in accordance with an instruction from the sequencer 4. The pulse sequence is created in advance according to the purpose of measurement, and stored as a program and data in a storage device 72 or the like to be described later in the information processing system 7.

  The information processing system 7 controls the overall operation of the MRI apparatus 100 according to the imaging conditions input by the user, executes imaging, and processes the obtained measurement data. The information processing system 7 includes a CPU 71, a storage device 72 such as a ROM and a RAM, an external storage device 73 such as an optical disk and a magnetic disk, a display device 74 such as a display, and an input device 75 such as a trackball or a mouse and a keyboard. With. The input device 75 is disposed close to the display device 74, and the user interactively inputs information necessary for various processes of the MRI apparatus 100 through the input device 75 while looking at the display device 74.

  FIG. 2 shows a functional configuration diagram of the information processing system 7 of the present embodiment. In order to realize the above functions, the information processing system 7 of the present embodiment adjusts the static magnetic field distribution, an imaging unit 710 that controls imaging, a signal processing unit 720 that processes measurement data, as shown in FIG. A static magnetic field adjustment unit 730. These functions are realized by the CPU 71 executing a program stored in the storage device 72.

The imaging unit 710 gives an instruction to the sequencer 4 in accordance with imaging conditions input from the user via the input device 75 and a pulse sequence stored in advance in the storage device 72 or the like, and captures an imaging area determined by the imaging conditions. Execute. At present, the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is a main constituent material of the subject as widely used clinically. Information on the spatial distribution of the proton density and the spatial distribution of the relaxation time of the excited state is imaged, thereby imaging the form or function of the human head, abdomen, limbs, etc. two-dimensionally or three-dimensionally.

  When receiving the measurement data from the receiving system 6, the signal processing unit 720 executes processing such as signal processing and image reconstruction, displays the result on the display device 74, and displays the result on the storage device 72 or the external storage device 73. Record.

  The static magnetic field adjustment unit 730 measures the static magnetic field distribution measurement unit 731 that measures the distribution of the static magnetic field by the static magnetic field generation system 2, the measurement result by the static magnetic field distribution measurement unit 731, and the imaging conditions set through the input device 75. Based on this, in order to improve the uniformity of the static magnetic field, a correction area determination unit 732 that determines a correction area for correcting the static magnetic field strength (to perform shimming), and shimming with respect to the correction area determined by the correction area determination unit 732 And a static magnetic field correction unit 733.

  The static magnetic field distribution measurement unit 731 calculates the static magnetic field strength of each of a plurality of predetermined lattice points for a predetermined static magnetic field distribution measurement region. The static magnetic field distribution measurement region is a region inside a quadrangular prism (a rectangular parallelepiped) whose axial direction is one axial direction of three orthogonal directions determined in advance according to the inclination of the subject 1 or the like. For example, a region that substantially includes the entire region in which the static magnetic field is generated by the static magnetic field generation source is designated as the static magnetic field distribution measurement region and measured. The measurement is performed using, for example, a pulse sequence described in Patent Document 1. Further, the obtained static magnetic field strength of each lattice point is stored in the storage device 72 or the like in association with the coordinates of each lattice point specified in the coordinate system unique to the MRI apparatus 100.

  The static magnetic field correction unit 733 performs shimming on the correction region determined by the correction region determination unit 732. In accordance with the static magnetic field distribution measured by the static magnetic field distribution measuring unit 731, the amount of current applied to each shim coil 21 is determined by a known method so that the uniformity of the static magnetic field in the region determined by the correction region determining unit 732 is improved.

The correction area determination unit 732 determines an area for shimming as a correction area in the static magnetic field distribution measurement area. In the present embodiment, the correction area is obtained as a quadrangular prism (a rectangular parallelepiped) whose centroid coincides with the imaging area and whose static magnetic field distribution measurement area and the bottom face are parallel. The determination of the correction area by the correction area determination unit 732 is performed every time the imaging parameter for specifying the imaging area is changed among the imaging parameters input as the imaging conditions. Hereinafter, details of the correction region determination unit 732 according to the present embodiment will be described.

  First, a method for determining the bottom surface of the correction region (correction region bottom surface determination method) by the correction region determination unit 732 will be described. 3 and 4 are diagrams for explaining a correction area bottom surface determination method by the correction area determination unit 732 of the present embodiment. Here, the imaging region specified by the imaging parameter input by the user is projected onto a predetermined surface of the static magnetic field distribution region. Here, the center of the imaging region is the origin, and the three axes parallel to each side of the rectangular column (cuboid) in the static magnetic field distribution measurement region are the Sx axis, Sy axis, and Sz axis, respectively. The bottom surface of the quadrangular prism (cuboid) is the Sxy plane determined by the Sx axis and the Sy axis, and the axial direction of the quadrangular prism (cuboid) is the Sz axis. Therefore, the surface to be projected to determine the bottom surface of the correction area is the Sxy plane. FIG. 3 is a diagram for explaining a bottom surface determination method on the Sxy plane, and FIG. 4 is a diagram for explaining a bottom surface determination method on a surface determined by the Sx axis and the Sy axis. .

  As shown in these drawings, the correction area determination unit 732 is a rectangle surrounded by sides parallel to the Sx axis and the Sy axis on the Sxy plane, and the minimum rectangle including the entire projection plane is determined as a uniform area. The bottom. Specifically, as shown in this figure, the Sx coordinates and Sy coordinates of the projection points 431, 432, 433, 434, 435, 436, 437, 438 corresponding to the eight vertices of the rectangular parallelepiped constituting the imaging region 420, respectively. The rectangle on the Sxy plane determined by the maximum values Sxmax and Symax in both axial directions and the minimum values Sxmin and Symin is determined as the bottom surface 430 of the correction region. The determination result is held in the storage device 72 or the like. The coordinates of the four vertices of the bottom surface 430 of the correction area are (Sxmax, Symax), (Sxmax, Symin), (Sxmin, Symax), and (Sxmin, Symin).

  Next, a method for determining the height of the correction region by the correction region determination unit 732 will be described. In the present embodiment, two types of height determination methods are prepared according to the part of the imaging region. Hereinafter, they are referred to as a first correction area height determination method and a second correction area height determination method. As described above, the height of the correction region is the same direction as the height (axial direction) of the static magnetic field distribution measurement region, that is, the Sz axis direction.

  FIG. 5 is a diagram for explaining the first correction area height determination method of the present embodiment. In the first correction area height determination method, the same length as the height 429 of the imaging area 420 is determined as the correction area height (first correction area height) 440. Specifically, as shown in FIG. 5, both end portions on the Sz axis when the height 429 of the imaging region 420 is rotated to the Sz axis around the origin of coordinates determined by the Sx axis, the Sy axis, and the Sz axis. The length between them is the first correction area height 440. The determination result is held in the storage device 72 or the like. In the present embodiment, the length of the longest side projected onto the Sz axis among the three orthogonal sides of the rectangular parallelepiped constituting the photographing region 420 is the height 429 of the photographing region 420.

  According to the first correction area height determination method, the end area of the imaging area 420 can be excluded from the area determined as the correction area. For example, when the imaging target region is the head, there is a nasal cavity at the end of the imaging region. Such a part that adversely affects the current amount calculation in the static magnetic field uniformity correction can be removed.

  FIG. 6 is a diagram for explaining a second correction area height determination method according to the present embodiment. In the second correction area height determination method, a length obtained by projecting the height 429 of the imaging area 420 on the Sz axis is determined as a height (second correction area height) 450. Specifically, as shown in FIG. 6, the maximum value and the minimum value of the Sz coordinates of the projection points (451, 453, 454, 454, 456, 458) obtained by projecting the vertices of the imaging region 420 on the Sz axis, The length determined in step 2 is set as a second correction area height 450. The determination result is held in the storage device 72 or the like.

  The correction area whose height is determined by the second correction area height determination method includes the entire imaging area 420. Therefore, the static magnetic field uniformity of the entire imaging region 420 can be corrected.

  In determining the height of the correction area, it is determined in advance which of the first correction area height determination method and the second correction area height determination method is used, and is stored in the storage device 72 or the like. The In the present embodiment, which determination method is used in advance is associated with an imaging region, and the determination method database is stored in the storage device 72 or the like. That is, the correction area determination unit 732 according to the present embodiment determines which determination method is to be used by referring to the determination method database based on the imaging parameters for specifying the imaging region in the input imaging conditions.

Hereinafter, the flow of the correction area determination process performed by the correction area determination unit 732 according to this embodiment will be described. FIG. 7 is a process flow of the correction area determination process of the present embodiment. The correction area determination unit 732 according to the present embodiment corrects information in response to a change in information for specifying the shooting area 420 in the shooting conditions, for example, shooting parameters such as tilt, position, and shooting plane size. The area determination process is started.

The correction area determination unit 732 receives the change of the imaging parameter, and first determines the bottom surface 430 of the correction area using the correction area bottom surface determination method (step S201). Next, the correction area determination unit 732 refers to the determination method database and determines which height determination method to use in accordance with the imaging region specified by the imaging parameters (step S202).

  When it is determined that the first correction area height determination method is to be used, the correction area determination unit 732 determines the correction area height 440 according to the above-described first correction area height determination method (step S203). When it is determined that the second correction area height determination method is used, the correction area determination unit 732 determines the correction area height 450 in accordance with the second correction area height determination method described above (step S204).

  The correction area determination unit 732 is a rectangular parallelepiped area specified by the bottom surface 430 and the height 440 or 450 determined in the above procedure, and has a rectangular parallelepiped area having the same center of gravity as the imaging area 420 as a correction area. And is displayed on the display device 74 as a region for correcting the uniformity (step S205), and the process ends.

  Note that the static magnetic field correction unit 733 performs the shimming before the main photographing based on the information on the correction area held in the storage device 72.

  As described above, according to the present embodiment, an area for automatically correcting the static magnetic field uniformity is determined according to the imaging area. The region for correcting the static magnetic field uniformity is performed every time the user changes the imaging region by changing the imaging parameter. Therefore, the user can automatically determine the optimum region for correcting the static magnetic field uniformity by simply setting the photographing parameters and specifying the photographing region as usual.

  Further, as described above, an appropriate range is set in the correction area according to the imaging region. Therefore, according to the present embodiment, the optimum static magnetic field correction region can be easily and quickly specified according to the imaging region and the imaging region without increasing the burden on the user.

  In the above-described embodiment, the static magnetic field correction unit 733 is configured to use the correction region determined in the above process as it is, but is not limited thereto. For example, after the display in step S205, the adjustment from the user may be accepted. The user performs fine adjustment of the correction area using the input device 75 while viewing the correction area displayed on the display device 74. A technique in which the user finely adjusts the correction area uses a conventional technique in which the user inputs the correction area via the GUI.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. The MRI apparatus of this embodiment basically has the same configuration as that of the first embodiment. In the first embodiment, the method for determining the height of the imaging region is changed according to the part to be imaged. However, in this embodiment, the method for determining the height is changed according to the size of the correction area. Hereinafter, the present embodiment will be described focusing on the configuration different from the first embodiment.

  The correction for improving the static magnetic field uniformity can be more improved if it is performed in the minimum necessary region. However, if the number of grid points that have obtained the static magnetic field intensity in the static magnetic field distribution measurement and the number of grid points included in the area extracted as the correction area is small, the correction accuracy increases because the number of data is small. There may not be. In order to avoid this, the correction area determination unit 732 according to this embodiment uses either the first correction area height determination method or the second correction area height determination method to determine the height of the correction area. This is determined by the size of the correction area. The determination is performed by comparison with a threshold value stored in advance in the storage device 72. Hereinafter, the correction area determination process by the correction area determination unit 732 of the present embodiment will be described.

  FIG. 8 is a processing flow of correction area determination processing by the correction area determination unit 732 of the present embodiment. Also in the present embodiment, the correction area determination process is started in response to a change in the shooting parameters for specifying the shooting area in the shooting conditions, as in the first embodiment.

  The correction area determination unit 732 first determines the bottom surface 430 of the correction area using the correction area bottom surface determination method described in the first embodiment in response to the change of the imaging parameter (step S301). Next, the correction area determination unit 732 determines the correction area height 440 using the first correction area height determination method described in the first embodiment (step S302), and determines the entire correction area. .

  Next, the correction area determination unit 732 counts the number of lattice points obtained by the static magnetic field distribution measurement unit 731 in the determined correction area (step S303). The number of grid points in the correction area is calculated from, for example, the interval between the grid points obtained at the time of measuring the static magnetic field distribution and the volume of the correction area. And it is discriminate | determined whether the number of obtained grid points is more than the threshold value previously hold | maintained at the memory | storage device 72 (step S304).

  If it is less than the threshold value in step S304, the correction area determination unit 732 calculates the correction area height 450 by the second correction area height determination method described in the first embodiment, and the height calculated in step S702. 440 is replaced (step S305). On the other hand, if it is equal to or greater than the threshold value in step S704, the obtained height 440 is used as the height of the correction area.

  The correction area determination unit 732 is a rectangular parallelepiped area specified by the bottom surface 430 and the height 440 or 450 determined in the above procedure, and has a rectangular parallelepiped area having the same center of gravity as the imaging area 420 as a correction area. In addition, the image is displayed on the display device 74 as a region where the uniformity is corrected (step S306), and the process is terminated. In the present embodiment, the adjustment from the user may be accepted after the display in step S306.

  Also in the present embodiment, the static magnetic field correction unit 733 performs the shimming before the main photographing based on the information on the correction area held in the storage device 72.

  As described above, according to this embodiment, similarly to the first embodiment, a region for automatically correcting the static magnetic field uniformity is determined according to the imaging region. The region for correcting the static magnetic field uniformity is performed every time the user changes the imaging region by changing the imaging parameter. Therefore, the user can automatically determine the optimum region for correcting the static magnetic field uniformity by simply setting the photographing parameters and specifying the photographing region as usual.

  In addition, according to the present embodiment, the minimum area necessary for improving the uniformity of the static magnetic field by correction can be selected as the correction area.

  Note that the first embodiment and the second embodiment may be combined. That is, after determining the bottom surface 430 of the correction area, the correction area determination unit 732 determines which one of the first correction area height determination method and the second correction area height determination method is used depending on the imaging region. It discriminate | determines by the discrimination method similar to a form. If it is determined that the first correction area height determination method is used, the processing after step S302 in the second embodiment is performed.

  By configuring in this way, it is possible to determine an optimum correction area according to the part and to secure a necessary minimum area. Therefore, the optimal correction area can be determined more efficiently.

  Furthermore, in each of the above-described embodiments, the bottom surface of the correction area is determined as a rectangle defined by a straight line parallel to the Sx axis and the Sy axis, which is obtained by projecting the imaging area onto the Sxy plane. Not limited to. For example, as shown in FIG. 9, the area obtained by projecting the imaging area 420 onto the Sxy plane may be used as it is. Specifically, a hexagon that connects the coordinates of the six vertices of the imaging region when the imaging region is projected onto the Sxy plane is defined as the bottom surface 460.

  By determining the bottom surface 460 in this way, a region having a higher degree of coincidence with the imaging region 420 can be determined as a correction region, and the accuracy of correcting the static magnetic field uniformity in the imaging region 420 can be improved. it can.

  Which method is used to determine the bottom surface is determined in advance. Or you may determine according to an imaging | photography site | part similarly to 1st embodiment. In this case, as in the first embodiment, which bottom surface determination method is used in association with the imaging region is stored in the database. Further, the bottom surface determination method may be determined by comparing with a threshold value. That is, first, the bottom surface 460 of the correction area is determined by the above method, the height is determined according to the imaging region, and the correction area is determined by the same method as in the first embodiment. Thereafter, the number of data points in the correction area is compared with a threshold value stored in advance, and if it is less than the threshold value, the bottom surface determination method may be changed to that shown in each of the above embodiments.

  Further, when determining the height of the correction area, the determination method is stored in the storage device 72 in association with the part of the imaging parameter, but the present invention is not limited to this. For example, the determination method may be held in association with the type of receiving coil 61 to be used. This is because the receiving coil 61 to be used differs depending on the part, and thus the imaging part can be specified if the type of the receiving coil 61 is known. Moreover, you may hold | maintain by matching both information of a site | part and the receiving coil 61 classification.

  In each of the above embodiments, in order to correct the non-uniformity of the static magnetic field distribution, the shim coil 21 and the shim power source 22 are provided and the correction is performed by driving them. However, the invention is not limited to this. For example, the gradient magnetic field coil 31 may be used to correct the nonuniformity of the static magnetic field distribution.

1: subject, 2: static magnetic field generation system, 3: gradient magnetic field generation system, 4: sequencer, 5: transmission system, 6: reception system, 7: information processing system, 21: shim coil, 22: shim power supply, 31: Gradient magnetic field coil, 33: Gradient magnetic field power supply, 51: Transmitting coil, 52: Synthesizer, 53: Modulator, 54: Amplifier, 61: Receiving coil, 62: Amplifier, 63: Quadrature phase detector, 64: A / D conversion 71: CPU, 72: storage device, 73: external storage device, 74: display device, 75: input device, 100: MRI device, 420: imaging area, 429: height of imaging area, 430: correction area Bottom, 431: Projection point, 432: Projection point, 433: Projection point, 434: Projection point, 435: Projection point, 436: Projection point, 437: Projection point, 438: Projection point, 440: First correction area height 450: Second correction area Height, 451: Projection point, 453: Projection point, 454: Projection point, 455: Projection point, 456: Projection point, 458: Projection point, 460: Bottom surface of correction region, 710: Imaging unit, 720: Signal processing unit 730: Static magnetic field adjustment unit, 731: Static magnetic field distribution measurement unit, 732: Correction region determination unit, 733: Static magnetic field correction unit

Claims (9)

Magnetism comprising: a static magnetic field generating means for applying a static magnetic field to a subject; a control means for executing imaging by controlling the entire apparatus; and processing an obtained signal; and an input means for inputting an instruction to the control means. A resonance imaging apparatus comprising:
The control means includes
Static magnetic field correction means for correcting non-uniformity of the static magnetic field distribution;
Correction area determination means for determining a correction area in which the static magnetic field correction means corrects the non-uniformity of the static magnetic field distribution within a predetermined measurement area according to the imaging parameter input via the input means; Prepared,
The measurement region is an internal region of a quadrangular prism whose axial direction is one axial direction of three predetermined orthogonal axes,
The correction region, said an internal region of the measurement region and polygonal for the axially same, Ri region der determined according to the imaging region specified by the imaging parameters,
The correction area determining means includes
A bottom surface shape determining unit that has a shape including at least a projection shape obtained by projecting the imaging region on a surface orthogonal to the axial direction, and a bottom surface shape of the polygonal column;
Rukoto and a height determining means for the height and the same length and one of the length of the height length projected in the axial direction of the imaging area to the height of the polygonal prism of said imaging area A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1 ,
A magnetic resonance imaging apparatus characterized in that, for each imaging target region specified by the imaging parameters, it is predetermined which of the two types of lengths is determined as the height of the polygonal column. The magnetic resonance imaging apparatus according to claim 1 ,
A static magnetic field distribution measuring means for measuring the static magnetic field distribution in the measurement region;
The static magnetic field distribution measuring means measures the static magnetic field strength of a plurality of predetermined lattice points in the measurement region as the static magnetic field distribution,
When the number of the lattice points included in the correction area when the length equal to the height of the imaging area is the height of the polygonal prism is a predetermined value or more, the height determining means A magnetic resonance imaging apparatus, wherein the height of the polygonal column is the same length as the height of the polygonal column. The magnetic resonance imaging apparatus according to any one of claims 1 to 3 ,
The magnetic resonance imaging apparatus characterized in that the bottom surface shape is a rectangle that includes the projection shape and is a rectangle that is parallel to two axes orthogonal to the axial direction and has the smallest area. The magnetic resonance imaging apparatus according to any one of claims 1 to 3 ,
The magnetic resonance imaging apparatus, wherein the bottom surface shape is the projected shape. The magnetic resonance imaging apparatus according to claim 2 ,
A static magnetic field distribution measuring means for measuring the static magnetic field distribution in the measurement region;
The static magnetic field distribution measuring means measures the static magnetic field strength of a plurality of predetermined lattice points in the measurement region as the static magnetic field distribution,
When the number of the grid points included in the correction area when the length equal to the height of the imaging area is the height of the polygonal prism is less than a predetermined value, the height determining means Even when the part is determined to have the same length as the height of the imaging region as the height of the polygonal prism, the length of the height of the imaging region projected in the axial direction is the polygonal prism. A magnetic resonance imaging apparatus characterized by having a height of. The magnetic resonance imaging apparatus according to any one of claims 1 to 6 ,
The magnetic resonance imaging apparatus characterized in that the correction area determination means determines the correction area every time the imaging area is changed by changing the imaging parameter. The magnetic resonance imaging apparatus according to any one of claims 1 to 7 ,
The magnetic resonance imaging apparatus, wherein the correction area is an internal area of a polygonal cylinder having the same center as the imaging area specified by the imaging parameters. Static magnetic field generating means for applying a static magnetic field to the subject, control means for controlling the entire apparatus to execute imaging, processing signals obtained, input means for inputting instructions to the control means, and the static magnetic field In a magnetic resonance imaging apparatus comprising a static magnetic field homogeneity correction unit that corrects the homogeneity of the static magnetic field, the static magnetic field homogeneity correction unit determines a correction region for correcting the static magnetic field homogeneity. A decision method,
A bottom surface calculating step for calculating a bottom surface of the correction region;
A height calculating step of calculating the height of the correction area according to the imaging region specified by the imaging parameter input via the input means;
A correction area determining step for determining, as the correction area, an area having the same center of gravity as the imaging area determined by the imaging parameters, using the bottom surface calculated in the bottom surface calculating step and the height calculated in the height calculating step; With
In the bottom surface calculating step, a shape including at least a projection shape obtained by projecting the imaging region onto a surface parallel to the bottom surface of the measurement region is calculated as the bottom surface.
In the height calculation step, either one of the same length as the height of the imaging region and the length obtained by projecting the height of the imaging region in the axial direction perpendicular to the bottom surface of the measurement region according to the imaging region A method for determining a static magnetic field homogeneity correction region, wherein the length is calculated as the height.

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