Magnetic resonance imaging apparatus and calibration method thereof

Abstract

The invention provides a magnetic resonance imaging device and a calibration method thereof. The present invention addresses the problem of improving the accuracy of automatic calibration without prolonging the examination time in MR examinations. A range of calibration performed prior to the formal imaging is determined with reference to the formal imaging range and other spatial information. The spatial information is composed of information capable of estimating an MR signal generation range, such as a subject region, a uniform magnetic field region, and limitations on the structure of the device, and the calibration range is determined so as to increase the ratio of the MR signal generation range included therein as much as possible.

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 implemented before imaging of the MRI apparatus. Background Art

[0002] The MRI device applies a high-frequency magnetic field to the subject in an imaging space that generates a uniform static magnetic field, obtains the nuclear magnetic resonance signal generated from the subject and images it. In order to obtain high-quality images in the MRI device, it is important to have high uniformity in the static magnetic field, the irradiated high-frequency magnetic field, and the receiving sensitivity distribution of the received nuclear magnetic resonance signal, but these contain various errors due to reasons on the subject or the device side. Therefore, in previous MRI devices, many calibration imagings were implemented before imaging to reduce various errors. The calibration items include, in addition to the above-mentioned static magnetic field distribution (B0 distribution), transmission sensitivity distribution (B1 distribution) and receiving sensitivity distribution, the subject shape, irradiation gain, receiving gain, center frequency, etc.

[0003] Calibration imaging is performed before formal imaging, and the results of the calibration imaging are used for imaging conditions of formal imaging and image reconstruction after imaging to obtain an image with reduced errors. For example, Patent Document 1 discloses a technique for obtaining the phase of the transmission magnetic field and the static magnetic field as calibration data and correcting the B0 map or B1 map in formal imaging. In addition, Patent Document 2 discloses a technique for obtaining a receiving sensitivity distribution through calibration imaging and using it for image reconstruction in formal imaging.

[0004] Conventionally, when the imaging position (formal imaging range) for formal imaging is determined, calibration imaging is automatically performed with reference to the formal imaging range. Figure 5 ) states that, for an inclined imaging section including an examination site, a region wider than the subject including the imaging section is used as a calibration range.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-153573

[0006] Patent Document 2: Japanese Patent Application Publication No. 2015-119866

[0007] However, depending on the configuration of the subject, etc., the accuracy of calibration is reduced, which sometimes leads to degradation of image quality. For example, in the case where the inspection part is a part away from the left and right center of the subject, such as the shoulder or limbs on either side, the formal imaging range becomes a prescribed range centered on the inspection part in a state where the inspection part is positioned at the center of the static magnetic field. In the case where the calibration range is set in a manner that includes the formal imaging range, the subject area may also exist at a position deviating from the calibration range. Since the calibration result of the subject existing outside the calibration range will not be reflected, if the imaging range is changed in the next formal imaging to include the area outside the calibration range in the formal imaging range, it is possible that the error will not be correctly corrected. Image. Specifically, when outside the calibration range of the receiving coil sensitivity distribution, the sensitivity distribution data cannot be correctly created, and therefore the signal cannot be reconstructed. Furthermore, when outside the calibration range of the static magnetic field distribution, the shim calculation data cannot be correctly created, and therefore the fat signal cannot be suppressed.

[0008] To prevent image quality degradation, if automatic calibration is re-executed or calibration imaging is performed with the calibration range expanded to include the entire width of the subject as disclosed in Patent Document 2, imaging time becomes longer, thereby prolonging the examination time. Summary of the invention

[0009] An object of the present invention is to improve the accuracy of automatic calibration without prolonging the inspection time.

[0010] In addition to the formal imaging range, the present invention also refers to the spatial information related to the various elements constituting the device or the subject to optimize the calibration imaging conditions, thereby avoiding lengthy calibration and improving the accuracy of automatic calibration.

[0011] That is, the MRI apparatus of the present invention comprises: an imaging unit that collects nuclear magnetic resonance signals generated from a subject placed in a static magnetic field space, performs formal imaging to obtain an image of the subject, and performs calibration imaging to collect calibration data required for the formal imaging; and a control unit that controls the operation of the imaging unit, the control unit having a calibration range setting unit that sets a range for calibration imaging. The calibration range setting unit sets the calibration range using a pre-set formal imaging range and spatial information outside the formal imaging range.

[0012] Furthermore, the calibration method of the present invention collects calibration data required for formal imaging before formal imaging of an image of a subject, and includes the step of setting a calibration range. In the step of setting the calibration range, the calibration range is set by combining a pre-set formal imaging range and spatial information outside the formal imaging range.

[0013] Effects of the Invention

[0014] According to the present invention, the calibration range is set and the calibration is performed in consideration of the spatial conditions of the device, its elements or the subject for the calibration object item, so that the calibration result in the originally required space can be efficiently obtained. As a result, the waste of re-calibration or setting an overly wide range, which leads to an extension of the inspection time, can be eliminated, and a high-precision calibration result can be obtained. As a result, a high-quality image can be obtained in a shorter inspection time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing the overall outline of an MRI apparatus to which the present invention is applied.

[0016] Figure 2 This is a functional block diagram of a control unit of an MRI apparatus according to an embodiment.

[0017] Figure 3 It is a diagram showing the flow of the calibration process according to the embodiment.

[0018] Figure 4 is a diagram illustrating the signal fill rate in the calibration range.

[0019] Figure 5 This is a diagram for explaining the setting of the calibration range in the first embodiment.

[0020] Figure 6 This is a diagram for explaining the setting of the calibration range in Modification 1 of Implementation Example 1.

[0021] Figure 7 This is a diagram for explaining the setting of the calibration range according to the second modification of the first embodiment.

[0022] Figure 8 This is a diagram for explaining the setting of the calibration range in a vertical magnetic field type MRI apparatus.

[0023] Fig. 9 This is a diagram for explaining the setting of the calibration range in the second embodiment.

[0024] Fig.10 This is a diagram for explaining the setting of the calibration range in the second embodiment.

[0025] Fig.11 This is a diagram for explaining the setting of the calibration range in the third embodiment.

[0026] Fig.12 This is a diagram for explaining the setting of the calibration range in the fourth embodiment.

[0027] Explanation of symbols

[0028] 1-MRI device, 10-imaging unit, 20-control unit, 30-UI unit, 40-external storage device, 50-subject, 210-imaging control unit, 220-imaging condition setting unit, 221-formal imaging range setting unit, 223-calibration range setting unit, 230-display control unit. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present invention will be described.

[0030] The MRI apparatus of the present invention generally includes: an imaging unit that causes a subject placed in a static magnetic field space to generate nuclear magnetic resonance, collects nuclear magnetic resonance signals (hereinafter referred to as MR signals) generated from the subject, and acquires an image of the subject; and a control unit that controls the operation of the imaging unit. The imaging performed by the imaging unit includes, in addition to imaging for acquiring an image of the subject (hereinafter referred to as formal imaging), calibration imaging for collecting calibration data used in formal imaging. The control unit controls the operation of the imaging unit including such calibration imaging.

[0031] The configuration of the MRI apparatus of the present invention is the same as that of a conventional MRI apparatus except for the function related to calibration. Figure 1 An example of an MRI apparatus to which the present invention is applied is shown.

[0032] like Figure 1 As shown, the MRI apparatus 1 comprises: an imaging unit 10 having a static magnetic field generating system 11, a gradient magnetic field generating system 12, a transmitting system 13, a receiving system 14 and a sequencer 15; a control unit 20 including a CPU 21; and a UI unit 30. Although not shown in the figure, the static magnetic field generating system 11 is composed of magnets that generate a static magnetic field, such as a superconducting magnet, a conventional electric magnet, or a permanent magnet, 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 generated static magnetic field, there are MRI apparatuses of a horizontal magnetic field type or a vertical magnetic field type. The present invention can be applied to MRI apparatuses of any type.

[0033] The gradient magnetic field generation system 12 applies gradients in three axial directions to the static magnetic field generated by the static magnetic field generation system 11, and includes gradient magnetic field coils 121 and gradient magnetic field power supplies 122 in three axial directions. The transmission system 13 includes a high-frequency transmitter 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 receiving system 14 includes a high-frequency coil 141, an amplifier 142, an orthogonal phase detector 143, and an A / D converter 144 for receiving MR signals generated from the subject 50. The sequencer 15 operates the gradient magnetic field generation system 12, the transmission system 13, and the receiving system 14 according to a predetermined pulse sequence. The operation of each element of the imaging unit 10 is the same as that of a general MRI apparatus, so a detailed description is omitted.

[0034] The control unit 20 controls the overall operation of the imaging unit 10, and performs image reconstruction using MR signals, various operations using the reconstructed images, and the like. The control unit 20 can be composed of a computer having a memory (ROM, RAM) 22 and a CPU 21. However, a part of the functions performed by the control unit 20 can be implemented by a programmable IC such as an ASIC or FPGA, and there is also a case where it is implemented by a processing device different from the MRI device. The control unit 20 is connected to a display device 31 having a GUI that displays images as processing results and performs interaction with the user, and a UI unit 30 having an input device 32 such as a mouse, a trackball, and a keyboard. The control unit (computer) 20 can also be connected to an external storage device 40.

[0035] Figure 2 An example of a functional block diagram of the control unit 20 is shown. As shown in the figure, the control unit 20 includes an imaging control unit 210, an imaging condition setting unit 220, and a display control unit 230 for controlling the imaging unit 10 via the sequencer 15. In addition to the function of setting the conditions for formal imaging (formal imaging range setting unit 221), the imaging condition setting unit 220 also has a function of setting the conditions for calibration imaging, for example, including a calibration range setting unit 223. The calibration range setting unit 223 determines an appropriate calibration range by referring to the formal imaging range determined based on the configuration of the subject for formal imaging and other spatial information, specifically spatial information related to the subject, magnetic field distribution information formed by the static magnetic field generation system 11 or the gradient magnetic field generation system 12, etc., position information of the high-frequency coils 134 and 141 for transmission and reception, and sets it as the condition for calibration imaging performed by the imaging unit 10.

[0036] The spatial information outside the formal imaging range referenced by the calibration range setting unit 223 includes information on images (including scans) obtained by pre-photographing of the subject, inspection conditions such as the inspection site, information on the specifications of the device, information on the magnetic field obtained by simulation, etc. The calibration range set by the calibration range setting unit 223 may vary depending on the object of calibration, or may be set to a range common to each item. The specific setting of the calibration range will be described in detail in the following embodiments.

[0037] Next, refer to Figure 3 , the flow of MRI examination including calibration imaging is described. In a general examination flow, multiple types of imaging (N imaging) are performed, so the description is based on this premise.

[0038] First, in order to determine the imaging position, positioning imaging of the whole body of the subject is performed (S1), and the imaging position of the first formal imaging is set (S2). For example, the user can make this setting via the UI unit 30. When the position of the formal imaging is set, the formal imaging range setting unit 221 determines the formal imaging range based on imaging conditions such as FOV (S3). In the past, automatic calibration imaging was performed by setting a prescribed calibration range determined based on the formal imaging range, but in the MRI device 1 of this embodiment, the calibration range setting unit 223 takes in spatial information outside the formal imaging range as spatial information required for setting the calibration range, and uses the formal imaging range and the taken-in spatial information to set the calibration range (S4).

[0039] If the calibration range is set, the imaging unit 10 performs calibration imaging (S5) under the control of the imaging control unit 210. The content of the calibration imaging varies depending on the calibration items, such as static magnetic field distribution, irradiation / reception sensitivity distribution, etc., but generally a high-speed sequence such as FSE and FGR is used. In addition, there is also a case where multiple items are acquired through one calibration imaging.

[0040] Next, the calibration result is reflected and the main imaging is performed (S6). The method of reflecting the calibration result varies depending on the project, but for example, when B1 distribution, receiving sensitivity distribution, etc. are obtained as calibration data, the distribution is used to correct the collected MR signals or the image reconstructed therefrom. Also, when B0 distribution, irradiation gain, receiving gain, center frequency, etc. are obtained as calibration data, these values ​​are adjusted during imaging to perform imaging.

[0041] For the second and subsequent photography, after the formal photography range is determined (S7), if there is no need to change the calibration range (S8), the formal photography is directly performed (S9). If any of the formal photography range and other spatial information changes and the calibration range needs to be changed, return to S4, reset the calibration range, perform calibration photography again (S5), and perform formal photography (S6). Repeat the above steps until the predetermined number of formal photographys (N times) are completed. In addition, based on the spatial information referenced in S4, the initially set calibration range can be used in subsequent formal photography. In this case, S8 is not required.

[0042] According to this embodiment, as the spatial information required for determining the calibration range, not only the formal imaging range is referenced, but also the spatial information on the device side, such as the subject, the spatial restrictions on the device side, and the magnetic field distribution generated by the device, can be referenced. This can effectively obtain the calibration data required and sufficient for improving the image quality, can shorten the time required for calibration imaging, and can take into account both the efficiency of the inspection and the improvement of the image quality. In addition, by setting an appropriate calibration range, the re-execution of the calibration can be reduced, and the extension of the inspection time can be prevented.

[0043] Specific embodiments of setting the calibration range will be described below. The basic feature of these embodiments is that the calibration range is set in such a way that the signal filling rate in the calibration range is maximized.

[0044] like Figure 4 As shown, the signal filling rate refers to the ratio of the calibration range covering the range for generating MR signals (signal generating range) and / or the range for receiving MR signals (the two are collectively referred to as MR signal range).

[0045] When the signal filling rate R is defined three-dimensionally, it can be expressed by the following equation, for example.

[0046] R = MR signal range (X) / calibration range (X)

[0047] ×MR signal range (Y) / calibration range (Y)

[0048] ×MR signal range (Z) / calibration range (Z)

[0049] In addition, when it is difficult to estimate the MR signal range in all directions, it is also possible to simply use only the range in a specific direction for calculation. For example, the following formula is used.

[0050] R = MR signal range (X) / calibration range (X)

[0051] Furthermore, based on the premise that the calibration range covers the MR signal range, the MR signal range is preferably smaller than the calibration range.

[0052] The calibration range setting unit 223 refers to the spatial information (the function of estimating the signal generation range) in order to determine the MR signal range. Specifically, as the spatial information used to estimate the MR signal range, there are the subject area, the uniform magnetic field area of ​​the static magnetic field, the restricted area based on the structure of the bed or the gantry, the gradient magnetic field range, the transmission and reception sensitivity range, etc. The subject area can be roughly determined by taking low spatial resolution images by ultra-high-speed imaging sequence, or a positioning image can be used. The uniform magnetic field area can be obtained from the output of the magnetic field lines measured when designing the static magnetic field magnet. It can also be estimated by simulation. Regarding the bed or gantry, the position in the device coordinates (imaging space coordinates) can be determined as an area where no MR signal is generated based on the three-dimensional design data. The gradient magnetic field range or the transmission sensitivity range can be obtained by simulation. The receiving sensitivity distribution can be obtained by associating the sensitivity distribution of the receiving coil itself calculated by simulation and the image of the receiving coil installed on the subject (camera image or MR image) with the device coordinates.

[0053] The calibration range setting unit 223 sets the calibration range in a manner to maximize the signal filling rate estimated based on the spatial information. By increasing the signal filling rate, the range irrelevant to the image quality can be excluded as much as possible, and the efficiency of the calibration can be improved, that is, the time required for calibration photography can be reduced and the image quality can be improved. The following is a specific implementation method for improving the signal filling rate.

[0054] In the following embodiments, Figure 2 The structure of the control unit shown in FIG. Figure 3 The processes shown are common, so reference is made to these drawings as appropriate.

[0055] <Implementation Method 1>

[0056] In the present embodiment, the calibration range is set with reference to the subject position as spatial information outside the actual imaging range.

[0057] As an example, Figure 5 The figure shows the case where the imaging part deviates from the left-right center of the subject. In the figure, the inside of the rack represented by the outermost ellipse is the imaging space (hereinafter the same). The formal imaging range setting unit 221 sets the formal imaging range 501 in such a way that the imaging part P specified by the user based on the positioning image (scanogram) becomes the center. Figure 5 As shown in the figure above, when the imaging part P is arranged at the approximate center of the magnetic field, as shown in the figure, it is set to a predetermined range (for example, a three-dimensional area) pre-set around the imaging part P. At this time, the subject 50 is arranged at a position further to the left than the center of the bed 60.

[0058] like Figure 5As shown in the upper side of , when the calibration range 502 is set to cover the regular imaging range 501, a part of the subject may be out of 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).

[0059] The calibration range setting unit 223 obtains the position of the subject from the scan image, such as Figure 5 As shown in the lower side of , a calibration range 503 is set to be consistent with the width of the subject in the left-right direction. By setting the calibration range 503 in this way, the signal filling rate can be improved, and the required calibration data can be effectively acquired. In the calibration range 503, the area where the subject 50 does not exist in the formal imaging range 501 is removed, but this area is an area where no MR signal is generated, and it is an area that does not require correction based on calibration data, and it is not necessary to acquire calibration data.

[0060] According to this embodiment, by using the position information of the subject as the spatial information for determining the calibration range, even when the configuration of the subject is biased toward the center of the magnetic field, calibration data can be reliably acquired for the area where data leakage may occur within the range based on the formal imaging range, and acquisition of useless calibration data can be reduced. As a result, the effectiveness of image quality improvement using calibration data can be improved, and the extension of inspection time can be suppressed.

[0061] <Variation 1 of Implementation Example 1>

[0062] In the first embodiment, the position information of the subject is used as the spatial information outside the formal imaging range, but other spatial information can be further added to set the calibration range. For example, the spatial information of the magnetic field uniformity (static magnetic field map) and the information of the space where the MR signal is not generated due to the limitation of the device are used as other spatial information.

[0063] Regarding the static magnetic field map, data obtained by measuring the static magnetic field distribution of the device (information included in the specifications of the device) can be stored in advance in the external storage device 40, etc., and the calibration range setting unit 223 can read the data for use, or information obtained by other calibration imaging can be used. Information about the space where no MR signal is generated includes, for example, position information of a bed on which a subject is placed, position information of a fixture or a restrainer attached to a subject, etc.

[0064] Figure 6 FIG. 1 shows the case where a calibration range is set using a static magnetic field distribution in a horizontal magnetic field type MRI apparatus. Figure 5In the embodiment, the calibration range 503 is set to cover the left and right width of the subject arranged away from the center of the magnetic field, but in this modification, the information of the area determined as the uniform magnetic field area 700 based on the static magnetic field measurement data is referred to. Figure 5 The calibration range 503 excludes the area deviating from the uniform magnetic field area 700 (inside the area indicated by a circle in the figure) as the calibration range 504. The area deviating from the uniform magnetic field area 700 does not generate MR signals under the same conditions as the uniform magnetic field area 700, so by excluding it, the signal filling rate can be further improved.

[0065] <Variation 2 of Implementation Example 1>

[0066] This modification example is a modification example in which the calibration range 503 is narrowed in order to further improve the signal filling rate in the vertical direction of the subject. Figure 7 As shown, the calibration range 505 is determined with reference to the vertical position information of the subject and the position information of the bed. As in Embodiment 1, the vertical position information of the subject can be obtained from a pre-measured image such as a scanogram. The bed information can be obtained from the bed geometry information and bed drive information on the device side.

[0067] The calibration range setting unit 223 uses these spatial information and Figure 6 The same uniform magnetic field region 700 information, from Figure 5 The calibration range 505 is determined by excluding the area above the subject 50 area and the area where the bed 60 exists from the calibration range 503, and excluding the uniform magnetic field area 700. This can further improve the signal filling rate.

[0068] <Other Modifications>

[0069] In Modifications 1 and 2, the use of information about a uniform magnetic field region as spatial information related to the magnetic field is described, but information about a region where the irradiation sensitivity distribution is uniform or a region where the primary gradient magnetic field can be obtained can be further used to exclude regions outside the MR signal range. Furthermore, as spatial information related to the device, in addition to the bed, information about a gantry that accommodates a static magnetic field generating magnet and provides an imaging space can also be used. That is, when the calibration range includes the gantry (structure), this range is outside the MR signal range and is therefore excluded.

[0070] and, Figure 6 , Figure 7 is based on Figure 5The calibration range 503 shown in the figure is an example of a modified calibration range setting, but in addition to the subject area, the reference spatial information can be a combination of multiple or separate information. In addition, although it is not a modified example of embodiment 1, an embodiment of setting the calibration range using the information of the formal imaging range and the spatial information other than the subject area is also included in the present invention.

[0071] In embodiment 1 and its variations, a horizontal magnetic field type MRI apparatus in which a subject is placed in a tunnel-shaped imaging space is used as an example for explanation, but the calibration range can also be set with the same idea for a vertical magnetic field type MRI apparatus that generates a static magnetic field in a direction orthogonal to the subject's body axis.

[0072] Figure 8 The outline of the MRI apparatus of the vertical magnetic field method is shown. The MRI apparatus of the vertical magnetic field method has a structure in which magnets are arranged vertically up and down across the imaging space, and generates a static magnetic field in the up and down directions. In this MRI apparatus, a subject 50 lying on a bed 60 is placed between an upper frame and a lower frame that respectively accommodate the upper and lower magnets, and imaging is performed. In the vertical magnetic field method, the uniform magnetic field region 800 (inside the region represented by a circle in the figure) is also a spherical region with a predetermined radius from the center of the imaging space, and the region deviating from the uniform magnetic field region 800 does not generate MR signals. Therefore, even if there is a subject region in the region deviating from the uniform magnetic field region 800, the portion is excluded from the calibration range to set the calibration range 506. As in the first embodiment, the region of the formal imaging range 501 where the subject 50 does not exist is excluded from the calibration range 506. In this way, even in the vertical magnetic field method, as in the horizontal magnetic field method, calibration imaging with a high signal filling rate and high efficiency can be achieved.

[0073] <Implementation Method 2>

[0074] The present embodiment is applicable to the case where the imaging ranges are different in a plurality of formal imaging included in an MR examination. In MR examinations, for example, in hip joint imaging, there are many cases where local imaging and imaging with a wider range are performed in the same examination. In the present embodiment, the subject information (information of the imaging part) in a plurality of formal imaging is used to set a calibration range applicable to a plurality of formal imaging. In addition, the case where the inspection process includes a plurality of formal imaging with different imaging ranges can be understood based on the data of the inspection process or the imaging conditions (imaging part), and it can be obtained as preliminary information to perform the processing of the present embodiment.

[0075] Fig. 9The upper and lower figures are figures showing two imaging ranges 501-1 and 501-2 of formal imaging with different imaging ranges. As shown in the figure, the imaging range of formal imaging 1 is smaller than the imaging range of formal imaging 2, and the positional relationship between the center of the imaging range and the center of the magnetic field is also different. When the calibration ranges 502-1 and 502-2 are determined based on the imaging range, the ranges of formal imaging 1 and formal imaging 2 are different.

[0076] In this embodiment, the two imaging ranges 501-1 and 501-2 of the actual imaging and the position of the subject are used to determine the calibration range applicable to both. Fig.10 As shown, the calibration range 502-3 is determined as a range excluding the area outside the MR signal range from the sum of the calibration range 502-1 of the narrower one (in this example, the formal imaging 1) and the calibration range 502-2 of the wider one (in this example, the formal imaging 2).

[0077] By setting the calibration range in this way, data obtained by one calibration imaging can be used in both the formal imaging 1 and the formal imaging 2. Figure 2 The S8 step is omitted in the process, and there is no need to re-perform calibration, which can reduce inspection time.

[0078] in addition, Fig. 9 and Fig.10 This is an example of using information from multiple formal imaging ranges and subject positions to set a calibration range, but like the modified example of implementation mode 1, spatial information other than the subject position, such as spatial information outside the uniform magnetic field region or the MR signal range, can also be added to achieve the same effect.

[0079] <Implementation Method 3>

[0080] In embodiment 1, the calibration range is set with reference to the position of the subject, in particular, the position of the subject configured to be offset from the center of the static magnetic field. However, in the present embodiment, when the set formal imaging range is set to a range that is inappropriate for the subject, etc., the calibration range is set using spatial information on the subject's external shape.

[0081] Based on the set examination part, the formal imaging range is set to include the examination part. However, if the user mistakenly sets the part that should be set to "shoulder joint" to "wrist joint", for example, the formal imaging range becomes a small range centered on the wrist. If the calibration range is automatically set based on this, it becomes an inappropriate calibration range. Fig.11As shown in the upper side of FIG. 5 , the calibration range 501A is set inside the subject region, not the original formal imaging range 501. Such inappropriate setting of the calibration range 502 may also occur when the subject is unexpectedly large.

[0082] In this embodiment, information on the region where the subject is located is acquired, and the calibration range 506 is set so as to cover the region of the subject.

[0083] Fig.11 An example is shown in which the originally required calibration range cannot be covered only by the formal imaging range. However, when the subject is smaller than expected and the signal filling rate of the calibration range is greatly reduced, the calibration range is set in a manner that takes in the spatial information of the subject, covers the subject and improves the signal filling rate.

[0084] According to this embodiment, it is possible to prevent the calibration range determined based on the formal imaging range from becoming inappropriate due to the relationship with the subject, thereby preventing the required calibration data from being obtained, or preventing the calibration imaging time from being prolonged due to unnecessary calibration data, and to set an appropriate calibration range.

[0085] <Implementation Method 4>

[0086] In Embodiments 1 to 3 and their modifications, the case where the device automatically reads the spatial information and sets an appropriate calibration range is described. However, the present embodiment realizes user adjustment via the UI unit 30 .

[0087] The user adjustment is realized by displaying the calibration range set by the display control unit 230 to the display device 31 of the UI unit 30 and accepting the user's adjustment. The display method on the display device is not particularly limited, but the calibration range 503 set by the calibration range setting unit 223 is displayed on the pre-measurement image of the subject by a line graph or the like. Fig.12 As shown, it can also be displayed together with the inspection part P or the formal imaging range 501. The line graph representing the calibration range constitutes a GUI that can be moved, enlarged or reduced by operating the mouse of the input device, etc., and accepts user changes. The image can be a three-dimensional image or an image of three cross sections.

[0088] The user can make the following adjustments: confirm the calibration range indicated, exclude areas outside the MR signal range ( Fig.12 For example: adjusting from 503-1 to 503-2), or judging whether wide-range data is needed to expand the range even if it takes a certain amount of time. In addition, when multiple formal imaging with different ranges or parts is performed, the range of the calibration performed before can be prompted for each formal imaging, and a button (GUI) can be prompted to accept whether re-calibration is required.

[0089] According to the present embodiment, by providing the user with an adjustment mechanism, the user's freedom can be improved, and errors such as inappropriate designation of an examination site as described in the third embodiment can be noticed before the actual imaging.

[0090] As mentioned above, each embodiment and modification of the present invention have been described. However, these embodiments and modification thereof can be appropriately combined as long as there is no technical contradiction, and such combination is also included in the present invention.

Claims

1. A magnetic resonance imaging device, characterized in that: have: an imaging unit that collects nuclear magnetic resonance signals generated from a subject placed in a static magnetic field space, performs formal imaging to obtain an image of the subject, and performs calibration imaging to collect calibration data required for the formal imaging; and a control unit that controls the operation of the imaging unit, The control unit includes a calibration range setting unit that sets the range of the calibration imaging, and the calibration range setting unit sets the calibration range using a predetermined formal imaging range and spatial information other than the formal imaging range.

2. The magnetic resonance imaging apparatus according to claim 1, characterized in that The calibration range setting unit uses at least one of a static magnetic field uniformity range, a gradient magnetic field range, a transmission / reception sensitivity range, gantry space information, and a subject range as the space information outside the regular imaging range.

3. The magnetic resonance imaging apparatus according to claim 1, characterized in that: The calibration range setting unit estimates a signal generation range in which a nuclear magnetic resonance signal is generated using spatial information outside the formal imaging range, and sets a calibration range using the signal generation range.

4. The magnetic resonance imaging apparatus according to claim 3, characterized in that: The spatial information outside the formal imaging range includes at least one of the subject range, static magnetic field uniformity range, gradient magnetic field range, transceiver sensitivity range and gantry space information. The calibration range setting unit estimates the signal generation range using the subject range and other spatial information.

5. The magnetic resonance imaging apparatus according to claim 3, characterized in that: The calibration range setting unit sets the calibration range so as to maximize a signal filling rate, that is, a ratio of the signal generation range to the calibration range.

6. The magnetic resonance imaging apparatus according to claim 2, characterized in that: When the center of the formal imaging range is offset from the center of the subject range, the calibration range setting unit sets the calibration range excluding a portion of the formal imaging range that does not overlap with the subject range.

7. The magnetic resonance imaging apparatus according to claim 1, characterized in that: The camera unit sets different main camera ranges to perform multiple main camera shots. The control unit determines, after one main imaging, whether a calibration range of a calibration imaging performed for the one main imaging is applicable to a calibration imaging for a next main imaging, and does not perform the calibration imaging for the next main imaging if the calibration range is applicable.

8. The magnetic resonance imaging apparatus according to claim 1, characterized in that: Also available: The UI unit displays the calibration range set by the calibration range setting unit and accepts a change in the calibration range.

9. A calibration method for collecting calibration data required for actual imaging before actual imaging of an image of a subject, the calibration method comprising the steps of setting a calibration range, In the step of setting the calibration range, The calibration range is set by combining a preset official imaging range and spatial information outside the official imaging range.

10. The calibration method according to claim 9, characterized in that: Also includes: The step of estimating a signal generation range where a nuclear magnetic resonance signal is generated using spatial information outside the formal imaging range, In the step of setting the calibration range, the calibration range is set using the signal generation range.

11. The calibration method according to claim 10, characterized in that: In the step of setting the calibration range, the calibration range is set in such a way that the ratio of the signal generation range to the calibration range, ie, the signal filling rate, is maximized.

12. The calibration method according to claim 9, characterized in that: The spatial information outside the formal imaging range includes any one of a static magnetic field uniformity range, a gradient magnetic field range, a transceiver sensitivity range, a gantry space information, and a subject range.

13. The calibration method according to claim 12, characterized in that: In the step of setting the calibration range, When the center of the regular imaging range deviates from the center of the subject range, a calibration range is set including the subject range.

14. The calibration method according to claim 12, characterized in that: The calibration range is set by removing a portion of the subject range that is not included in the static magnetic field uniform range from the calibration range.

15. The calibration method according to claim 12, characterized in that: In the step of setting the calibration range, The calibration range is set by excluding the area where the arrangement of the subject is restricted from the regular imaging range using the gantry space information.

16. The calibration method according to claim 12, characterized in that: The formal filming includes multiple formal films with different formal filming ranges. The step of setting the calibration range includes, when there is a calibration range set for a previous main imaging, a step of determining whether to use the set calibration range.

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