Magnetic resonance imaging apparatus and method of calibration for the same

Abstract

To improve accuracy of automatic calibration without causing any extension of examination time on MR examination.SOLUTION: A magnetic resonance imaging apparatus determines a range of calibration that is conducted before regular imaging by referring to a regular imaging range and space information other than that, where the space information comprises information capable of estimating an MR signal generation range such as a subject region, a uniform magnetic field region, and a structural limit of the apparatus and the range of calibration is determined such that a ratio of the MR signal generation range included therein becomes as high as possible.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a calibration technique that is performed before imaging by the MRI apparatus. [Background technology]

[0002] An MRI system applies a high-frequency magnetic field to an object to be imaged and acquires the nuclear magnetic resonance signals generated by the object. To obtain high image quality with an MRI system, it is important that the static magnetic field, the irradiated high-frequency magnetic field, and the reception sensitivity distribution for receiving the nuclear magnetic resonance signals are highly uniform. However, these contain various errors due to factors on the object and the device. For this reason, conventional MRI systems perform many calibration scans before imaging to reduce various errors. Calibration items include the static magnetic field distribution (B0 distribution), transmission sensitivity distribution (B1 distribution), and reception sensitivity distribution mentioned above, as well as the object's external shape, irradiation gain, reception gain, center frequency, etc.

[0003] The calibration imaging is performed prior to the actual imaging, and the results of the calibration imaging are used for the imaging conditions of the actual imaging and for image reconstruction after the imaging, so as to obtain an image with reduced errors. For example, Patent Document 1 discloses that the phases of the transmission magnetic field and the static magnetic field are obtained as calibration data, and the B0 map and the B1 map in the actual imaging are corrected. Patent Document 2 discloses that the reception sensitivity distribution is obtained by the calibration imaging and used for image reconstruction in the actual imaging.

[0004] Conventionally, when the imaging position (main imaging range) of the main imaging is determined, the calibration imaging is automatically performed by referring to the main imaging range. For example, Patent Document 2 (FIG. 5) describes that for an oblique imaging section including an examination site, a region wider than the subject including the examination site is set as the calibration range. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-153573 A [Patent Document 2] JP 2015-119866 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, depending on the subject's position, the accuracy of the calibration may decrease, leading to deterioration of image quality. For example, when the subject is examined at a location away from the center of the subject's left and right sides, such as the left or right shoulder or limb, the actual imaging range is a predetermined range centered on the examined part with the examined part positioned at the center of the static magnetic field. If the calibration range is set to include the actual imaging range, the subject area may exist at a position outside the calibration range. Since the calibration result is not reflected in the subject that exists outside the calibration range, if the imaging range is changed in the next actual imaging and the area outside the calibration range is included in the actual imaging range, there is a risk that the image will not be correctly corrected for errors. Specifically, when the sensitivity distribution of the receiving coil is outside the calibration range, the sensitivity distribution data is not correctly created, and the signal cannot be reconstructed. Also, when the sensitivity distribution is outside the calibration range of the static magnetic field distribution, the shimming calculation data is not correctly created, and the fat signal cannot be suppressed.

[0007] In order to prevent deterioration in image quality, if automatic calibration is performed again or the calibration range is expanded to include the entire width of the subject and calibration imaging is performed as disclosed in Patent Document 2, the imaging time becomes longer and the examination time is extended.

[0008] An object of the present invention is to improve the accuracy of automatic calibration without extending the inspection time. [Means for solving the problem]

[0009] The present invention optimizes calibration imaging conditions by referring to spatial information related to each element of the apparatus or the subject in addition to the actual imaging range, thereby avoiding redundant calibration and improving the accuracy of automatic calibration.

[0010] That is, the MRI apparatus of the present invention includes an imaging unit that collects nuclear magnetic resonance signals generated from a subject placed in a static magnetic field space and performs main imaging to obtain an image of the subject and calibration imaging to collect calibration data required for the main imaging, and a control unit that controls the operation of the imaging unit, and the control unit has a calibration range setting unit that sets the range of the calibration imaging. The calibration range setting unit sets the calibration range using a preset main imaging range and spatial information other than the main imaging range.

[0011] A calibration method of the present invention is a calibration method for collecting calibration data required for main imaging prior to main imaging for acquiring an image of a subject, and includes a step of setting a calibration range. The step of setting the calibration range combines a preset main imaging range with spatial information other than the main imaging range to set the calibration range. Effect of the Invention

[0012] According to the present invention, the calibration range is set for the calibration target item taking into consideration the spatial conditions of the device, its elements, or the subject, and calibration is then performed, so that calibration results can be obtained efficiently in the space that is originally required. This eliminates wasteful actions that would lead to extended examination times, such as re-executing calibration or setting an excessively wide range, and allows for accurate calibration results to be obtained. As a result, images with good quality can be obtained in a short examination time. [Brief description of the drawings]

[0013] [Figure 1]FIG. 1 is a diagram showing an overall outline of an MRI apparatus to which the present invention is applied. [Diagram 2] A functional block diagram of a control unit of the MRI apparatus according to the embodiment. [Diagram 3] FIG. 1 is a diagram showing a flow of a calibration process according to an embodiment; [Figure 4] Diagram explaining the signal filling rate in the calibration range [Diagram 5] FIG. 1 is a diagram for explaining the setting of a calibration range in the first embodiment; [Figure 6] FIG. 13 is a diagram for explaining the setting of a calibration range in a first modified example of the first embodiment. [Figure 7] FIG. 13 is a diagram for explaining the setting of a calibration range in a second modified example of the first embodiment. [Figure 8] A diagram explaining the setting of the calibration range in a vertical magnetic field MRI scanner. [Figure 9] FIG. 13 is a diagram for explaining the setting of a calibration range in the second embodiment. [Figure 10] FIG. 13 is a diagram for explaining the setting of a calibration range in the second embodiment. [Figure 11] FIG. 13 is a diagram for explaining the setting of a calibration range in the third embodiment. [Figure 12] FIG. 13 is a diagram for explaining the setting of a calibration range in the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described.

[0015] The MRI apparatus of the present invention is broadly composed of an imaging section that generates nuclear magnetic resonance in a subject placed in a static magnetic field space, collects nuclear magnetic resonance signals (hereinafter referred to as MR signals) generated from the subject, and obtains an image of the subject, and a control section that controls the operation of the imaging section. The imaging performed by the imaging section includes imaging for obtaining an image of the subject (hereinafter referred to as main imaging), as well as calibration imaging for collecting calibration data used in main imaging. The control section controls the operation of the imaging section, including such calibration imaging.

[0016] The MRI apparatus of the present invention has the same configuration as a conventional MRI apparatus, except for the function related to calibration. The outline of the apparatus will be described below. Figure 1 shows an example of an MRI apparatus to which the present invention is applied.

[0017] As shown in Fig. 1, the MRI apparatus 1 includes an imaging section 10 having a static magnetic field generating system 11, a gradient magnetic field generating system 12, a transmission system 13, a reception system 14, and a sequencer 15, a control section 20 including a CPU 21, and a UI section 30. The static magnetic field generating system 11 is made of a magnet that generates a static magnetic field, such as a superconducting magnet, a resistive magnet, or a permanent magnet (not shown), and provides a static magnetic field space (imaging space) in which a subject 50 is placed. The subject 50 is inserted into the static magnetic field space while being placed on a bed 60. Depending on the direction of the static magnetic field generated, there are MRI apparatuses of a horizontal magnetic field type and a vertical magnetic field type. The present invention is applicable to either type of MRI apparatus.

[0018] The gradient magnetic field generating system 12 provides a three-axis gradient to the static magnetic field generated by the static magnetic field generating system 11, and includes a three-axis gradient coil 121 and a power supply 121 for the three-axis. The transmission system 13 includes a high-frequency oscillator 131, a modulator 132, a high-frequency amplifier 133, and a high-frequency coil 134, and applies a pulsed high-frequency magnetic field to the subject 50. The reception system 134 includes a high-frequency coil 141, an amplifier 142, a quadrature phase detector 143, and an A / D converter 144 for receiving an MR signal generated from the subject 50. The sequencer 15 operates the gradient magnetic field generating system 12, the transmission system 13, and the reception system 14 according to a predetermined pulse sequence. The operation of each element of the imaging unit 10 is similar to that of a general MRI device, and therefore a detailed description thereof will be omitted.

[0019] The control unit 20 controls the overall operation of the imaging unit 10, and performs image reconstruction using MR signals and various calculations using the reconstructed images. The control unit 20 can be configured as a computer equipped with a memory (ROM, RAM) 22 and a CPU 21. However, some of the functions performed by the control unit 20 may be realized by a programmable IC such as an ASIC or FPGA, or may be realized by a processing device other than the MRI device. A UI unit 30 equipped with a display device 31 that displays images resulting from processing and a GUI for user interaction, and an input device 32 such as a mouse, a trackball, and a keyboard is connected to the control unit 20. An external storage device 40 may be connected to the control unit (computer) 20.

[0020] 2 shows an example of a functional block diagram of the control unit 20. As shown in the figure, the control unit 20 has an imaging control unit 210 that controls the imaging unit 10 via a sequencer 15, an imaging condition setting unit 220, and a display control unit 230. The imaging condition setting unit 220 has a function of setting conditions for calibration imaging in addition to a function of setting conditions for main imaging (main imaging range setting unit 221), and includes, for example, a calibration range setting unit 223. The calibration range setting unit 223 determines an appropriate calibration range by referring to the main imaging range determined based on the subject placement in the main imaging as well as other spatial information, specifically, spatial information on the subject, magnetic field distribution information formed by the static magnetic field generating system 11 and the gradient magnetic field generating system 12, position information of the transmitting and receiving high frequency coils 134, 141, and the like, and sets the calibration range as a condition for calibration imaging performed by the imaging unit 10.

[0021] The spatial information other than the actual imaging range referred to by the calibration range setting unit 223 includes information on images (including scanograms) obtained by pre-imaging of the subject, examination conditions such as the examination site, information possessed as the specifications of the device, magnetic field information obtained by simulation, etc. The calibration range set by the calibration range setting unit 223 may be different depending on the item to be calibrated, or may be set as a range common to each item. Specific settings of the calibration range will be described in detail in a later embodiment.

[0022] Next, the flow of an MRI examination including calibration imaging will be described with reference to Fig. 3. In a general examination flow, multiple types of imaging (N imaging) are performed, so the description will be based on this premise.

[0023] First, in order to determine the imaging position, positioning imaging is performed to scan the entire body of the subject (S1), and the imaging position for the first main imaging is set (S2). This setting can be performed by the user via the UI unit 30, for example. When the position for the main imaging is set, the main imaging setting unit 221 determines the main imaging range based on imaging conditions such as FOV (S3). Conventionally, a predetermined calibration range determined based on the main imaging range is set and automatic calibration imaging is performed, but in the MRI apparatus 1 of this embodiment, the calibration range setting unit 223 imports spatial information other than the main imaging range as spatial information required to set the calibration range, and sets the calibration range using the main imaging range and the imported spatial information (S4).

[0024] Once the calibration range has been set, the imaging unit 10 executes calibration imaging under the control of the imaging control unit 210 (S5). The content of the calibration imaging varies depending on the calibration items, such as static magnetic field distribution, irradiation / reception sensitivity distribution, etc., but typically, high-speed sequences such as FSE and FGR are used. In addition, multiple items may be acquired in one calibration imaging.

[0025] Next, the actual imaging is performed reflecting the calibration results (S6). The method of reflecting the calibration results differs depending on the item, but for example, when B1 distribution, reception sensitivity distribution, etc. are obtained as calibration data, they are used to correct the acquired MR signal or the image reconstructed from it. Also, when B0 distribution, irradiation gain, reception gain, center frequency, etc. are obtained as calibration data, these values ​​are adjusted during imaging.

[0026] For the second and subsequent imaging, after the main imaging range is determined (S7), if there is no need to change the calibration range (S8), main imaging is performed as is (S9). If there is a change in either the main imaging range or other spatial information and it is necessary to change the calibration range, the process returns to S4, the calibration range is reset, calibration imaging is performed again (S5), and main imaging is performed (S6). The above steps are repeated until the scheduled number of main imaging (N times) is completed. Depending on the spatial information referenced in S4, it is possible to reuse the initially set calibration range in subsequent main imaging, in which case S8 is unnecessary.

[0027] According to this embodiment, by referring to not only the actual imaging range but also other subject and device-side spatial information such as spatial constraints on the device and magnetic field distribution generated by the device as spatial information required for determining the calibration range, it is possible to efficiently acquire calibration data necessary and sufficient for improving image quality, shorten the time required for calibration imaging, and achieve both improved examination efficiency and improved image quality. Furthermore, by setting an appropriate calibration range, it is possible to reduce the number of times calibration is performed again, and prevent an extension of the examination time.

[0028] Specific embodiments of the calibration range setting will be described below, but these embodiments are basically characterized in that the calibration range is set so as to maximize the signal filling rate in the calibration range.

[0029] As shown in FIG. 4, the signal filling rate is the rate at which the calibration range covers the range where MR signals are generated (signal generation range) and / or the range where MR signals can be received (both collectively referred to as the MR signal range). If the signal filling rate R is defined three-dimensionally, it can be expressed, for example, by the following equation. R = MR signal range (X) / calibration range (X) × MR signal range (Y) / calibration range (Y) × MR signal range (Z) / calibration range (Z)

[0030] If it is difficult to estimate the MR signal range in all directions, it may be calculated simply by using the range in a specific direction. For example, the following formula is used. R = MR signal range (X) / calibration range (X)

[0031] Also, based on the premise that the calibration range covers the MR signal range, it is desirable that the MR signal range be smaller than the calibration range.

[0032] The calibration range setting unit 223 refers to spatial information to determine this MR signal range (signal generation range estimation function). The spatial information used to estimate the MR signal range specifically includes the subject region, the homogeneous magnetic field region of the static magnetic field, the restricted region due to the structure of the bed or gantry, the gradient magnetic field range, and the transmission / reception sensitivity range. The subject region may be roughly determined by capturing an image with low spatial resolution using an ultra-high speed imaging sequence, or a positioning image may be used. The homogeneous magnetic field region can be obtained from the output of the magnetic field lines measured at the time of designing the static magnetic field magnet. It may also be estimated by a separate simulation. The position of the bed or gantry in the device coordinates (imaging space coordinates) can be determined as a region where no MR signal is generated from three-dimensional design data. The gradient magnetic field range and the transmission sensitivity range can be obtained by simulation. The reception sensitivity distribution can be obtained by associating the sensitivity distribution of the receiving coil itself calculated by simulation or the like and the image (camera image or MR image) of the receiving coil attached to the subject with the device coordinates.

[0033] The calibration range setting unit 223 sets the calibration range so as to maximize the signal filling rate estimated based on the spatial information. By increasing the signal filling rate, it is possible to eliminate as much of the range that does not affect the image quality as possible, and it is possible to improve the efficiency of the calibration, i.e., to reduce the time required for calibration imaging while improving the image quality. Specific embodiments for increasing the signal filling rate are described below.

[0034] In the embodiments described below, the configuration of the control unit shown in FIG. 2 and the flow shown in FIG. 3 are common, so these drawings will also be referred to as appropriate.

[0035] <Embodiment 1> In this embodiment, the calibration range is set by referring to the subject position as spatial information other than the actual imaging range.

[0036] As an example, a case where the imaging region is offset from the center of the subject in the left-right direction is shown in FIG. 5. In the figure, the inside of the gantry indicated by the outermost ellipse is the imaging space (similar below). The actual imaging range setting unit 221 sets the actual imaging range 501 so that the imaging region P specified by the user based on the positioning image (scanogram) is at the center. As shown in the upper diagram of FIG. 5, when the imaging region P is placed approximately at the center of the magnetic field, a predetermined range (e.g., a three-dimensional region) is set in advance with the imaging region P at the center, as shown in the figure. At this time, the subject 50 is placed at a position offset to the left of the center of the bed 60.

[0037] 5, when a calibration range 502 is set so as to cover a main imaging range 501, a part of the subject may fall outside the calibration range. On the other hand, most of the calibration range 502 is a region where no MR signal is generated (outside the MR signal range).

[0038] The calibration range setting unit 223 acquires the subject position from the scanogram, and sets a calibration range 503 that matches the left-right width of the subject, as shown in the lower part of Fig. 5. By setting the calibration range 503 in this way, the signal filling rate can be increased, and necessary calibration data can be acquired efficiently. In the calibration range 503, a region in the main imaging range 501 where the subject 50 does not exist is excluded, but this region is a region where no MR signal is generated, and does not require correction by calibration data, and therefore does not require acquisition of calibration data.

[0039] According to this embodiment, by using the position information of the subject as spatial information for determining the calibration range, even if the subject is positioned offset from the center of the magnetic field, calibration data can be reliably acquired from an area where data leakage may occur when the imaging range is used as a reference, and the acquisition of unnecessary calibration data can be reduced. As a result, the effectiveness of image quality improvement using the calibration data can be improved and the extension of the examination time can be suppressed.

[0040] <Modification 1 of the First Embodiment> In the first embodiment, the position information of the subject is used as the spatial information other than the main imaging range, but it is possible to set the calibration range by adding other spatial information. For example, spatial information of magnetic field homogeneity (static magnetic field map) and information of the space where MR signals are not generated due to device limitations are used as the other spatial information.

[0041] The static magnetic field map may be obtained by previously measuring the static magnetic field distribution of the apparatus (information owned as the apparatus specifications) and storing it in the storage device 40 or the like, and the calibration range setting unit 223 may read and use the data, or information obtained by other calibration imaging may be used. Information on the space where no MR signal is generated includes, for example, position information of the bed on which the subject is placed, and position information of fixing devices and restraining devices attached to the subject.

[0042] Fig. 6 shows a case where a calibration range is set using a static magnetic field distribution in a horizontal magnetic field type MRI apparatus. In Fig. 5, the calibration range 503 is set so as to cover the left and right width of the subject placed at a position shifted from the center of the magnetic field, but in this modification, information on the area determined to be a homogeneous magnetic field area 700 from the static magnetic field measurement data is referred to, and the area outside the homogeneous magnetic field area 700 (inside the area indicated by the circle in the figure) is excluded from the calibration range 503 in Fig. 5 and set as a calibration range 504. Since the MR signal is not generated in the area outside the homogeneous magnetic field area 700 under the same conditions as the homogeneous magnetic field area 700, the signal filling rate can be further increased by excluding the area.

[0043] <Modification 2 of the First Embodiment> In this modification, the calibration range 503 is narrowed to increase the signal filling rate also in the vertical direction of the subject, and a calibration range 505 is determined by referring to the vertical position information of the subject and the position information of the bed, as shown in Fig. 7. The vertical position information of the subject can be acquired from a pre-measurement image such as a scanogram, as in the first embodiment. The bed information can be acquired from the geometric information of the bed and the driving information of the bed held by the apparatus.

[0044] 6, the calibration range setting unit 223 excludes the region above the subject 50 region and the region where the bed 60 exists from the calibration range 503 in Fig. 5, and also excludes the homogeneous magnetic field region 700 to determine the calibration range 505. This can further improve the signal filling rate.

[0045] <Other Modifications> In the first and second modified examples, the information on the uniform magnetic field region is used as the spatial information on the magnetic field, but the information on the region with uniform irradiation sensitivity distribution or the region where the primary gradient magnetic field is obtained may be used, and the region outside the MR signal range is excluded using this information. In addition to the bed, the information on the gantry that houses the static magnetic field generating magnet and provides the imaging space may be used as the spatial information on the device. In other words, if the calibration range includes the gantry (structure), that range is outside the MR signal range and is excluded.

[0046] 6 and 7 show an example of a calibration range setting modified based on the calibration range 503 shown in Fig. 5, but the spatial information to be referred to in addition to the subject region may be a combination of multiple pieces of information or may be a single piece of information. Although not a modification of the first embodiment, an embodiment in which the calibration range is set using information on the main imaging range and spatial information other than the subject region is also included in the present invention.

[0047] In the first embodiment and its modified example, a horizontal magnetic field type MRI apparatus in which a subject is placed in a tunnel-shaped imaging space has been described as an example, but the calibration range can also be set in a similar manner for a vertical magnetic field type MRI apparatus that generates a static magnetic field in a direction perpendicular to the body axis of the subject.

[0048] FIG. 8 shows an overview of a vertical magnetic field type MRI apparatus. The vertical magnetic field type MRI apparatus has a structure in which magnets are arranged vertically above and below an imaging space, and a static magnetic field is generated in the vertical direction. In this MRI apparatus, an object 50 lying on a bed 60 is placed between an upper gantry and a lower gantry that respectively house the upper and lower magnets, and imaging is performed. Even in the vertical magnetic field type, a uniform magnetic field region 800 (inside the region indicated by a circle in the figure) is a spherical region of a predetermined radius from the center of the imaging space, and an MR signal is not generated in the region outside the uniform magnetic field region 800. Therefore, even if the object region exists in the region outside the uniform magnetic field region 800, this part is excluded from the calibration range to set the calibration range 506. The region of the main imaging range 501 where the object 50 does not exist is excluded from the calibration range 506, as in the first embodiment. In this way, even with the vertical magnetic field type, as with the horizontal magnetic field type, efficient calibration imaging with a high signal filling rate can be realized.

[0049] <Embodiment 2> This embodiment is applied when the imaging ranges are different in multiple main imaging included in an MR examination. In an MR examination, for example, in hip joint imaging, local imaging and imaging of a wider range are often performed in the same examination. In this embodiment, a calibration range that can be applied to the subject information (information on the imaging site) and multiple main imaging in multiple main imaging is set. Note that the fact that an examination flow includes multiple main imaging with different imaging ranges can be understood from the data of the examination flow and imaging conditions (imaging site), and this information can be obtained as advance information to perform the processing of this embodiment.

[0050] The upper and lower diagrams in Fig. 9 are diagrams showing imaging ranges 501-1 and 501-2 of two actual imagings with different imaging ranges. As shown in the figure, the imaging range of actual imaging 1 is smaller than that of actual imaging 2, and the positional relationship between the center of the imaging range and the center of the magnetic field is also different. If the calibration ranges 502-1 and 502-2 are determined based on the imaging range, the ranges will be different between actual imaging 1 and actual imaging 2.

[0051] In this embodiment, a calibration range applicable to both imaging ranges 501-1 and 501-2 of two actual imagings and a subject position are used to determine a calibration range applicable to both imaging ranges. Specifically, as shown in Fig. 10, a calibration range 502-3 is determined as a range obtained by excluding an area other than the MR signal range from the sum of a narrower calibration range 502-1 (in this example, actual imaging 1) and a wider calibration range 502-2 (in this example, actual imaging 2).

[0052] By setting the calibration range in this manner, data obtained from one calibration imaging can be used in both actual imaging 1 and actual imaging 2. The inspection flow of this embodiment is the same as that of Fig. 2 except that step S8 is omitted, making it unnecessary to perform calibration again and reducing the inspection time.

[0053] 9 and 10 show an example in which the calibration range is set using information on a plurality of main imaging ranges and the subject position. However, as in the modified example of the first embodiment, spatial information other than the subject position, such as a homogeneous magnetic field region or spatial information outside the MR signal range, may be taken into account, and the same effect can be obtained.

[0054] <Embodiment 3> In the first embodiment, the calibration range is set by referring to the position of the subject, particularly the position of the subject positioned away from the center of the static magnetic field. However, in the present embodiment, in cases where the set actual imaging range is set to a range that is inappropriate for the subject, for example, the calibration range is set using spatial information on the outer shape of the subject.

[0055] The actual imaging range is set to a range including the set examination region, but if the user mistakenly sets "wrist joint" instead of "shoulder joint," the actual imaging range becomes a small range centered on the wrist, and if the calibration range is automatically set based on that, it will be an inappropriate calibration range. For example, as shown in the upper part of Fig. 11, a calibration range 501A is set inside the subject region instead of the original actual imaging range 501. Such an inappropriate setting of the calibration range 502 can also occur when the subject's physique is unexpectedly large.

[0056] In this embodiment, information on the area where the object is present is acquired, and the calibration range 506 is set so as to cover the area of ​​the object.

[0057] FIG. 11 shows an example in which the actual imaging range alone is not enough to cover the calibration range that is actually required. Even if the object is smaller than expected and the signal filling rate of the calibration range is significantly reduced, the calibration range is set so as to capture spatial information of the object, cover the object, and increase the signal filling rate.

[0058] According to the present embodiment, it is possible to prevent a situation in which the calibration range determined from the actual imaging range becomes inappropriate in relation to the subject, and the necessary calibration data cannot be obtained, or the calibration imaging time becomes long due to calibration data that is not actually required, and it is possible to set an appropriate calibration range.

[0059] <Embodiment 4> In the first to third embodiments and their modified examples, the device automatically reads spatial information and sets an appropriate calibration range. However, the present embodiment allows user adjustment via the UI unit 30.

[0060] The user adjustment is realized by presenting the calibration range set by the display control unit 230 on the display device 31 of the UI unit 30 and accepting the adjustment by the user. The method of displaying on the display device is not particularly limited, but the calibration range 503 set by the calibration range setting unit 223 is displayed as a line diagram or the like on a pre-measurement image of the subject. At this time, it may be displayed together with the examination site P and the actual imaging range 501 as shown in FIG. 12. The line diagram showing the calibration range constitutes a GUI that can be moved and enlarged / reduced by operating the mouse of the input device, and accepts changes by the user. The image may be a three-dimensional image or an image of three cross sections.

[0061] The user can check the presented calibration range, exclude areas outside the MR signal range (example in FIG. 12: adjustment from 503-1 to 503-2), or widen or adjust the range by judging whether data of a wider range is necessary even if it takes some time. When performing multiple main imaging with different ranges or parts, the range of the calibration performed before each main imaging may be presented, and a button (GUI) for accepting the need for re-execution of the calibration may be presented.

[0062] According to this embodiment, by providing the user with a means for adjustment, the user's freedom can be increased, and errors such as specifying an inappropriate examination area as described in embodiment 3 can be noticed before the actual imaging.

[0063] Although the embodiments and modifications of the present invention have been described above, these embodiments and their modifications can be combined as appropriate as long as there is no technical contradiction, and such combinations are also encompassed by the present invention. [Explanation of symbols]

[0064] 1: MRI device, 10: imaging section, 20: control section, 30: UI section, 40: external storage device, 50: subject, 210: imaging control section, 220: imaging range setting section, 221: actual imaging range setting section, 223: calibration range setting section, 230: display control section

Claims

1. an imaging unit that collects nuclear magnetic resonance signals generated from a subject placed in a static magnetic field space, performs main imaging to obtain an image of the subject, and performs calibration imaging to collect calibration data required for the main imaging, and a control unit that controls the operation of the imaging unit; The control unit has a calibration range setting unit that sets a range of the calibration imaging, and the calibration range setting unit sets the calibration range by using a preset main imaging range and spatial information other than the main imaging range.

2. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus characterized in that the calibration range setting unit uses one or more of a static magnetic field homogeneous range, a gradient magnetic field range, a transmission / reception sensitivity range, gantry spatial information, and a subject range as spatial information other than the main imaging range.

3. 2. The magnetic resonance imaging apparatus according to claim 1, a calibration range setting unit that uses spatial information other than the main imaging range to estimate a signal generation range in which a nuclear magnetic resonance signal is generated, and sets a calibration range using the signal generation range.

4. 4. The magnetic resonance imaging apparatus according to claim 3, the spatial information other than the main imaging range includes at least one of a subject range, a static magnetic field homogeneous range, a gradient magnetic field range, a transmission / reception sensitivity range, and gantry spatial information; The magnetic resonance imaging apparatus according to claim 1, wherein the calibration range setting unit estimates the signal generation range by using the subject range and other spatial information.

5. 4. The magnetic resonance imaging apparatus according to claim 3, A magnetic resonance imaging apparatus, wherein the calibration range setting unit sets the calibration range so as to maximize a proportion (signal filling factor) of the signal generation range that occupies the calibration range.

6. 3. The magnetic resonance imaging apparatus according to claim 2, a calibration range setting unit that sets the calibration range by excluding a portion of the main imaging range that does not overlap with the subject range when the center of the main imaging range and the center of the subject range are misaligned.

7. 2. The magnetic resonance imaging apparatus according to claim 1, The imaging unit sets different main imaging ranges and performs a plurality of main imaging operations, a control unit that determines, after one main imaging, whether a calibration range of the calibration imaging performed for the one main imaging is applicable to calibration imaging for a next main imaging, and if applicable, does not perform calibration imaging for the next main imaging.

8. 2. The magnetic resonance imaging apparatus according to claim 1, 4. A magnetic resonance imaging apparatus comprising: a UI unit that displays the calibration range set by the calibration range setting unit and accepts changes to the calibration range.

9. A calibration method for collecting calibration data required for actual imaging prior to actual imaging for acquiring an image of a subject, the method comprising the steps of: setting a calibration range; The step of setting the calibration range includes: A calibration method comprising the steps of: setting a calibration range by combining a preset main imaging range with spatial information other than the main imaging range.

10. A calibration method according to claim 9, comprising: The method further includes estimating a signal generation range in which a nuclear magnetic resonance signal is generated by using spatial information other than the main imaging range, A calibration method, wherein the step of setting the calibration range sets the calibration range using the signal generation range.

11. A calibration method according to claim 10, comprising: A calibration method, characterized in that the step of setting the calibration range sets the calibration range so as to maximize a ratio (signal filling factor) of the signal generation range occupying the calibration range.

12. A calibration method according to claim 9, comprising: A calibration method, wherein the spatial information other than the main imaging range includes any one of a static magnetic field homogeneous range, a gradient magnetic field range, a transmission / reception sensitivity range, gantry spatial information, and a subject range.

13. A calibration method according to claim 12, comprising the steps of: The step of setting the calibration range includes: A calibration method comprising the steps of: when a center of the main imaging range and a center of the subject range are misaligned, setting a calibration range including the subject range.

14. A calibration method according to claim 12, comprising the steps of: A calibration method comprising the steps of: setting a calibration range by excluding, from the calibration range, a portion of the subject range that is not included in a static magnetic field homogeneous range.

15. A calibration method according to claim 12, comprising the steps of: The step of setting the calibration range includes: a calibration range is set by excluding an area in which a position of a subject is restricted from the main imaging range, using the gantry space information.

16. A calibration method according to claim 12, comprising the steps of: The main imaging includes a plurality of main imagings having different main imaging ranges, A calibration method characterized in that the step of setting the calibration range includes a step of determining whether to reuse a calibration range that has already been set for a previous actual imaging, if the calibration range has already been set for the previous actual imaging.

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