JP2014213084A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus which appropriately sets a condition for calibration scanning such as preliminary scanning in MRI without requiring time and effort for setting operation from a user.SOLUTION: An MRI apparatus (10) includes a plan storing part (65), a calibration scan setting part (66), a calibration scan execution part and a condition determination part. The plan storing part stores an execution plan for main scanning. The calibration scan setting part calculates an acquisition region of MR signals in the calibration scanning used for determination of an image condition for the main scanning or a condition for correction processing for image data on the basis of the condition for the main scanning which is not executed even though included in the execution plan. The calibration scan execution part executes the calibration scanning in accordance with the acquisition region calculated by the calibration scan setting part. The condition determination part determines the image condition or the condition for the correction processing for the main scanning on the basis of the result of execution of the calibration scanning.

Description

  Embodiments of the invention relate to magnetic resonance imaging.

  MRI is an imaging method in which a nuclear spin of a subject placed in a static magnetic field is magnetically excited with an RF pulse having a Larmor frequency, and an image is reconstructed from MR signals generated by the excitation. The MRI means magnetic resonance imaging, the RF pulse means radio frequency pulse, and the MR signal means nuclear magnetic resonance signal. .

  In MRI, an RF coil device corresponding to an imaging region may be attached to a subject as a phased array coil, and MR signals may be received by the RF coil device. In general, the sensitivity of the whole body coil incorporated in the MRI apparatus is sufficiently uniform, but the sensitivity between the element coils in the RF coil apparatus for each imaging region is not so uniform as compared to the whole body coil. That is, even if the intensity of the MR signal emitted from the subject is uniform regardless of the position, the level of the received signal becomes non-uniform among the element coils of the phased array coil, thereby degrading the image quality.

  In addition, when a subject is placed in an imaging space in which a static magnetic field having a predetermined uniformity is formed, the uniformity of the static magnetic field is impaired due to the difference in magnetic permeability between the inside of the subject and its surroundings.

  Therefore, pre-scanning may be performed before the main scan, and imaging conditions for the main scan, conditions used for luminance correction after image reconstruction, and the like may be determined based on the execution result of the pre-scan. In this specification, scanning refers to MR signal acquisition operation and does not include image reconstruction.

  Examples of the pre-scan include the following sequences. Magnetic field measurement sequence for calculating an offset magnetic field (for example, see Patent Document 1), sensitivity distribution map sequence for generating a spatial sensitivity distribution map of each element coil in the RF coil device (for example, see Patent Document 2), A center frequency sequence for calculating a correction value of the center frequency of the RF pulse (for example, see Patent Document 3).

  The offset magnetic field is used as an index for correction to make the static magnetic field uniform in the main scan after the subject is placed in the imaging space. Further, the sensitivity distribution map is used for luminance correction processing for correcting an error in the luminance level of each pixel due to, for example, nonuniform sensitivity of the phased array coil after image reconstruction.

JP 2011-152348 A JP 2005-237703 A JP 2009-34152 A

  Since the execution result of the pre-scan greatly affects the image quality of the image obtained by the main scan, it is desired to perform the pre-scan under more appropriate conditions. However, the prescan conditions are automatically set uniformly regardless of the imaging conditions, or manually set by the user so as to be appropriate conditions.

  For this reason, in MRI, there has been a demand for a new technique for appropriately setting conditions for a calibration scan such as a pre-scan without requiring the user to perform a setting operation.

In one embodiment, the MRI apparatus includes a main scan execution unit, an image reconstruction unit, a plan storage unit, a calibration scan setting unit, a calibration scan execution unit, and a condition determination unit.
The main scan execution unit executes an actual scan that transmits an RF pulse according to the imaging conditions and collects MR signals from the subject in the imaging region.
The image reconstruction unit reconstructs image data of the imaging region based on the MR signal collected in the main scan.
The plan storage unit stores the execution plan of the main scan.
The calibration scan setting unit determines the MR signal collection area in the calibration scan used for determining the imaging condition of the main scan or the condition of the correction process of the image data based on the condition of the main scan that is included in the execution plan but has not been executed. calculate.
The calibration scan execution unit executes the calibration scan according to the collection area calculated by the calibration scan setting unit.
The condition determining unit determines an imaging condition or a correction process condition for the main scan based on the execution result of the calibration scan.

In the MRI apparatus, the calibration scan is, for example, a scan that adjusts conditions that are related to image quality and that does not accept manual input settings.
In the MRI apparatus, for example, the calibration scan setting unit may set the calibration scan acquisition area to the calculated condition after calculating the MR scan acquisition area of the calibration scan.
In the MRI apparatus, the calibration scan setting unit may calculate the MR scan acquisition area of the calibration scan and then present the calibration scan acquisition area on a display device, for example.

The block diagram which shows the whole structure of the MRI apparatus in this embodiment. The plane schematic diagram which shows an example of a structure of RF coil apparatus of FIG. The block diagram which shows an example of the detailed structure of RF receiver of FIG. Schematic explanatory drawing which shows an example of the setting method of the size of FOV in a magnetic field measurement sequence. Explanatory drawing which shows an example of the calculation method of the signal collection area | region of a sensitivity distribution map sequence in case a sensitivity distribution map exists with respect to a part of imaging range of this scan. Explanatory drawing which shows an example of the calculation method of the signal collection range of a sensitivity distribution map sequence in the case where a top-plate movement is accompanied by a sagittal section. The first half of the flowchart which shows an example of the flow of operation | movement of the MRI apparatus which concerns on this embodiment. The latter half of the flowchart which shows an example of the flow of operation | movement of the MRI apparatus which concerns on this embodiment. The flowchart which shows an example of the execution plan comprised from a 1st-6th group. The flowchart which shows an example of the determination algorithm of the necessity of the calibration scan insertion by a calibration scan setting part.

  Hereinafter, embodiments of an MRI apparatus and an MRI method will be described with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

<Configuration of this embodiment>
FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus 10 in the present embodiment. Here, as an example, the constituent elements of the MRI apparatus 10 will be described by dividing them into three parts: a bed unit 20, a gantry 30, and a control apparatus 40.

  First, the couch unit 20 includes a couch 21, a couchtop 22, and a couchtop moving mechanism 23 disposed in the couch 21. A subject P is placed on the top surface of the top plate 22. In addition, a reception RF coil 24 that detects an MR signal from the subject P is disposed in the top plate 22. Further, a plurality of connection ports 25 to which the wearable RF coil device 140 is connected are arranged on the top surface of the top plate 22.

  The bed 21 supports the top plate 22 so as to be movable in the horizontal direction (Z-axis direction of the apparatus coordinate system). The top plate moving mechanism 23 adjusts the vertical position of the top plate 22 by adjusting the height of the bed 21 when the top plate 22 is located outside the gantry 30. Further, the top plate moving mechanism 23 moves the top plate 22 in the horizontal direction to put the top plate 22 into the gantry 30 and takes the top plate 22 out of the gantry 30 after imaging.

  Second, the gantry 30 is configured in a cylindrical shape, for example, and is installed in the imaging room. The gantry 30 includes a static magnetic field magnet 31, a shim coil unit 32, a gradient magnetic field coil unit 33, and an RF coil unit 34.

  The static magnetic field magnet 31 is a superconducting coil, for example, and is configured in a cylindrical shape. The static magnetic field magnet 31 forms a static magnetic field in the imaging space by a current supplied from a static magnetic field power supply 42 of the control device 40 described later. The imaging space means, for example, a space in the gantry 30 where the subject P is placed and a static magnetic field is applied. In addition, you may comprise the static magnetic field magnet 31 with a permanent magnet, without providing the static magnetic field power supply 42. FIG.

  The shim coil unit 32 is configured, for example, in a cylindrical shape, and is arranged with the same axis as the static magnetic field magnet 31 inside the static magnetic field magnet 31. The shim coil unit 32 forms an offset magnetic field that makes the static magnetic field uniform by a current supplied from a shim coil power supply 44 of the control device 40 described later.

  The gradient coil unit 33 is configured in a cylindrical shape, for example, and is disposed inside the shim coil unit 32. The gradient coil unit 33 includes an X-axis gradient coil 33x, a Y-axis gradient coil 33y, and a Z-axis gradient coil 33z.

  In this specification, it is assumed that the X axis, the Y axis, and the Z axis are the apparatus coordinate system unless otherwise specified. Here, as an example, the X axis, Y axis, and Z axis of the apparatus coordinate system are defined as follows. First, the vertical direction is the Y-axis direction, and the top plate 22 is arranged so that the normal direction of the upper surface thereof is the Y-axis direction. The horizontal movement direction of the top plate 22 is taken as the Z-axis direction, and the gantry 30 is arranged so that the axial direction becomes the Z-axis direction. The X-axis direction is a direction orthogonal to the Y-axis direction and the Z-axis direction, and is the width direction of the top plate 22 in the example of FIG.

The X-axis gradient magnetic field coil 33x forms a gradient magnetic field Gx in the X-axis direction corresponding to a current supplied from an X-axis gradient magnetic field power supply 46x described later in the imaging region. Similarly, the Y-axis gradient magnetic field coil 33y forms in the imaging region a gradient magnetic field Gy in the Y-axis direction corresponding to a current supplied from a Y-axis gradient magnetic field power supply 46y described later. Similarly, the Z-axis gradient magnetic field coil 33z forms a gradient magnetic field Gz in the Z-axis direction corresponding to a current supplied from a Z-axis gradient magnetic field power supply 46z described later in the imaging region.
The slice selection direction gradient magnetic field Gss, the phase encode direction gradient magnetic field Gpe, and the readout direction (frequency encode direction) gradient magnetic field Gro can be arbitrarily determined by combining the gradient magnetic fields Gx, Gy, and Gz in the three-axis directions of the apparatus coordinate system. Can be set in the direction of.

The imaging region is, for example, at least a part of an MR signal collection range used for generating one image or one set of images and is an image region. For example, the imaging region is three-dimensionally defined in the apparatus coordinate system as a part of the imaging space. For example, in order to prevent aliasing artifacts, when MR signals are collected over a wider range than the region to be imaged, the imaging region is part of the MR signal collection range. On the other hand, the entire MR signal acquisition range may be an image, and the MR signal acquisition range may coincide with the imaging region.
The “one set of images” is a plurality of images when MR signals of a plurality of images are collected in a single pulse sequence, such as multi-slice imaging. Here, as an example, the imaging region is referred to as a slice if the region is thin, and is referred to as a slab if the region is thick to some extent.

  The RF coil unit 34 is configured in a cylindrical shape, for example, and is disposed inside the gradient magnetic field coil unit 33. The RF coil unit 34 includes, for example, a whole-body coil WB (see FIG. 3 to be described later) that combines RF pulse transmission and MR signal reception, and a transmission RF coil (not shown) that performs only RF pulse transmission. .

  Thirdly, the control device 40 includes a static magnetic field power supply 42, a shim coil power supply 44, a gradient magnetic field power supply 46, an RF transmitter 48, an RF receiver 50, a sequence controller 58, an arithmetic device 60, and an input device. 72, a display device 74, and a storage device 76.

  The gradient magnetic field power source 46 includes an X-axis gradient magnetic field power source 46x, a Y-axis gradient magnetic field power source 46y, and a Z-axis gradient magnetic field power source 46z. The X-axis gradient magnetic field power supply 46x, the Y-axis gradient magnetic field power supply 46y, and the Z-axis gradient magnetic field power supply 46z are used to generate currents for forming the gradient magnetic fields Gx, Gy, and Gz as X-axis gradient magnetic field coils 33x and Y-axis gradient magnetic field coils 33y. , And supplied to the Z-axis gradient coil 33z, respectively.

  The RF transmitter 48 generates an RF current pulse having a Larmor frequency that causes nuclear magnetic resonance based on the control information input from the sequence controller 58, and transmits this to the RF coil unit 34. An RF pulse corresponding to the RF current pulse is transmitted from the RF coil unit 34 to the subject P.

  The whole body coil WB and the reception RF coil 24 of the RF coil unit 34 detect the MR signal generated by the nuclear spin in the subject P being excited by the RF pulse, and the detected MR signal is RF Input to the receiver 50.

  The RF receiver 50 performs predetermined signal processing on the received MR signal and then performs A / D (analog to digital) conversion to generate raw data that is complex data of the digitized MR signal. . The RF receiver 50 inputs the raw data of the MR signal to the arithmetic device 60 (the image reconstruction unit 62 thereof).

  The sequence controller 58 stores control information necessary for driving the gradient magnetic field power supply 46, the RF transmitter 48, and the RF receiver 50 in accordance with a command from the arithmetic device 60. The control information here is, for example, sequence information describing operation control information such as the intensity, application time, and application timing of the pulse current to be applied to the gradient magnetic field power supply 46. The sequence controller 58 generates the gradient magnetic fields Gx, Gy, Gz, and RF pulses by driving the gradient magnetic field power supply 46, the RF transmitter 48, and the RF receiver 50 according to the stored predetermined sequence.

The sequence controller 58 moves the top plate 22 by controlling the top plate moving mechanism 23 in accordance with a command from the system control unit 61 of the arithmetic device 60 to be described later, so that, for example, imaging by the Moving Table method or the Stepping-Table method is performed. It is feasible.
The Moving Table method is a technique for obtaining a large field of view (FOV) in the moving direction by continuously moving the top plate 22 during imaging.
The Stepping-Table method is a technique for performing three-dimensional imaging by stepping the top plate 22 for each station. These techniques are used when imaging a wide area that cannot be captured at a time, such as whole body imaging. The arithmetic device 60 can also connect a plurality of images collected by moving the top plate 22 by combining processing.

  The arithmetic device 60 includes a system control unit 61, a system bus SB, an image reconstruction unit 62, an image database 63, an image processing unit 64, a plan storage unit 65, and a calibration scan setting unit 66.

The system control unit 61 performs system control of the entire MRI apparatus 10 via wiring such as the system bus SB in setting of imaging conditions for the main scan, imaging operation, and image display after imaging. The imaging condition means, for example, what kind of pulse sequence is used, what kind of condition is used to transmit an RF pulse or the like, and under what kind of condition the MR signal is collected from the subject P.
Examples of imaging conditions include the imaging area as positional information in the imaging space, the flip angle, the repetition time TR (Repetition Time), the number of slices, the imaging site, the type of pulse sequence such as spin echo method and parallel imaging, etc. Can be mentioned.
The imaging part means, for example, which part of the subject P such as the head, chest, and abdomen is imaged as an imaging region.

  The above-mentioned “main scan” is a scan for capturing a target diagnostic image such as a T1-weighted image, and does not include an MR signal acquisition scan for a positioning image or a correction scan. To do.

  The correction scan includes, for example, “undetermined conditions within the imaging conditions of the main scan” and “conditions and data for correction processing for image data reconstructed after the main scan”. Refers to a separate tuning scan. The pre-scan refers to a correction scan that is performed before the main scan.

  The calibration scan described below is a subordinate concept of the correction scan, and refers to a scan that adjusts “conditions related to image quality but not accepting manual input settings”.

  “Conditions related to image quality” include, for example, (A) a sensitivity distribution map of each element coil in the RF coil device used in luminance correction after image reconstruction, (B) the center frequency of the RF pulse, and (C ) Offset magnetic field intensity distribution for static magnetic field correction. These (A), (B), and (C) are also “conditions for not accepting manual input settings” in the input device 72 and the display device 74, that is, conditions where direct input settings by the user are not executed.

  It does not matter whether the calibration scan is executed before the main scan or after the main scan. Examples of the calibration scan include the following sequence.

First, a magnetic field measurement sequence for calculating an offset magnetic field for static magnetic field correction is performed before the main scan.
Second, a center frequency sequence for calculating the center frequency of the RF pulse in the main scan is performed before the main scan.
Third, there is a sensitivity distribution map sequence for generating a spatial sensitivity distribution map of each element coil in the wearable RF coil device, which can be performed before or after the main scan. Good.

Further, the system control unit 61 displays the imaging condition setting screen information on the display device 74, sets the imaging condition based on the instruction information from the input device 72, and inputs the set imaging condition to the sequence controller 58. Further, the system control unit 61 causes the display device 74 to display an image indicated by the generated display image data after imaging.
The input device 72 provides a user with a function of setting imaging conditions and image processing conditions.

  The image reconstruction unit 62 arranges and stores the raw data of the MR signal input from the RF receiver 50 as k-space data according to the number of phase encoding steps and the number of frequency encoding steps. The k space means a frequency space. The image reconstruction unit 62 generates image data of the subject P by performing image reconstruction processing including two-dimensional or three-dimensional Fourier transform on the k-space data. The image reconstruction unit 62 stores the generated image data in the image database 63.

  Note that the MRI image data is configured by, for example, each pixel having a pixel value. The pixel value indicates, for example, the luminance level (the intensity of the MR signal detected from the subject area corresponding to the pixel) when the pixel is displayed. In the case of a slice, the MRI image data has the number of vertical and horizontal pixels, for example, the number of phase encoding steps × the number of frequency encoding steps.

  The image processing unit 64 fetches image data from the image database 63, performs predetermined image processing on the image data, and stores the image data after the image processing in the storage device 76 as display image data.

The storage device 76 stores the imaging condition used for generating the display image data, information about the subject P (patient information), and the like as incidental information with respect to the display image data.
The plan storage unit 65 generates and stores an execution plan for the main scan based on the imaging conditions input via the input device 72.

The calibration scan setting unit 66 sets conditions for a calibration scan inserted in the middle of the execution plan for the main scan. A method for setting the conditions for the calibration scan will be described later with reference to FIG.
Note that the arithmetic device 60, the input device 72, the display device 74, and the storage device 76 may be configured as one computer and installed in a control room, for example.

  In the above description, the components of the MRI apparatus 10 are classified into the gantry 30, the couch unit 20, and the control apparatus 40, but this is only an example of interpretation. For example, the top plate moving mechanism 23 may be regarded as a part of the control device 40.

  Alternatively, the RF receiver 50 may be disposed inside the gantry 30 instead of outside the gantry 30. In this case, for example, an electronic circuit board corresponding to the RF receiver 50 is disposed in the gantry 30. Then, the MR signal converted from the electromagnetic wave to the analog electric signal by the receiving RF coil 24 or the like is amplified by a preamplifier in the electronic circuit board, outputted as a digital signal to the outside of the gantry 30, and inputted to the image reconstruction unit 62. Is done. For output to the outside of the gantry 30, for example, it is desirable to transmit it as an optical digital signal using an optical communication cable, because the influence of external noise is reduced.

In addition, “calculation and setting of undetermined imaging conditions” and “calculation (generation) of conditions and data used for image reconstruction processing and processing after image reconstruction” by each component in the arithmetic device 60 are: Automatically executed. For example, setting of a calibration scan condition by the calibration scan setting unit 66 and generation of a sensitivity distribution map by the system control unit 61 are automatically executed.
However, regarding the setting of conditions, data, and the like, the present embodiment is not limited to a form that is completely automatically executed by the arithmetic device 60. For example, the automatically calculated condition may be displayed on the display device 74, and after the user's confirmation input to the input device 72, the displayed condition may be determined (excluding only the user's final confirmation, automation is performed). The arithmetic device 60 may also be configured.

  FIG. 2 is a schematic plan view showing an example of the configuration of the RF coil device 140 of FIG. Here, as an example, the RF coil device 140 is an RF coil device that is worn on the upper body that receives MR signals. As shown in FIG. 2, the RF coil device 140 includes a cable 124, a connector 126, and a cover member 142.

  The cover member 142 is formed of a flexible material so that it can be bent or deformed. As the deformable material, for example, a flexible printed circuit (FPC) described in JP 2007-229004 A can be used.

  For example, 20 element coils 144 corresponding to the back side of the subject P are arranged in the upper half of the cover member 142 divided into two equal parts by a broken line in the horizontal direction in FIG. Here, as an example, on the back side, an element coil 144 smaller than the other element coils 144 is disposed near the body axis from the viewpoint of improving sensitivity in consideration of the spine of the subject P. The lower half of the cover member 142 is configured to cover the head, chest, and abdomen of the subject P, and, for example, 20 element coils 146 corresponding to the front side of the subject P are arranged therein. Established. In FIG. 2, the element coil 144 is indicated by a thick line, and the element coil 146 is indicated by a broken line.

  The RF coil device 140 includes a control circuit (not shown) and a storage element (not shown) that stores identification information of the RF coil device 140 in the cover member 142. When the connector 126 is connected to the connection port 25 in FIG. 1, the identification information of the RF coil device 140 is input from this control circuit to the system control unit 61 via the wiring in the MRI apparatus 10.

  FIG. 3 is a block diagram showing an example of a detailed configuration of the RF receiver 50 of FIG. Actually, it is possible to capture an image with a plurality of RF coil devices mounted on the subject P, but here, as an example, only the RF coil device 140 is mounted on the subject P.

  The RF coil unit 34 has the above-described whole body coil WB (corresponding to the thick square frame in FIG. 3). Element coils 144 and 146 function as phased array coils that receive MR signals.

  The RF receiver 50 includes a duplexer (transmission / reception switching device) 174, a plurality of amplifiers 176, a switching synthesizer 178, and a plurality of reception system circuits 180. The input side of the switching synthesizer 178 is individually connected to each of the element coils 144 and 146 via an amplifier 176 and is also individually connected to the whole body coil WB via the duplexer 174 and the amplifier 176. Each reception system circuit 180 is individually connected to the output side of the switching combiner 178.

  The duplexer 174 applies the RF pulse transmitted from the RF transmitter 48 to the whole body coil WB. Further, the duplexer 174 inputs the MR signal received by the whole body coil WB to the amplifier 176, and the MR signal is amplified by the amplifier 176 and given to the input side of the switching synthesizer 178. The MR signals received by the element coils 144 and 146 are amplified by the corresponding amplifiers 176 and supplied to the input side of the switching synthesizer 178.

  The switching synthesizer 178 performs synthesis processing and switching of MR signals detected from the element coils 144 and 146 and the whole body coil WB according to the number of the reception system circuits 180, and outputs the combined signal to the corresponding reception system circuit 180. . In this way, the MRI apparatus 10 forms a sensitivity distribution according to the imaging region using the whole body coil WB and the desired number of element coils 144 and 146.

  Here, as an example, it is assumed that the RF coil apparatus 140 is a part of the MRI apparatus 10, but the RF coil apparatus 140 may be separate from the MRI apparatus 10. In the present embodiment, in addition to the RF coil device 140, various wearable RF coil devices such as a lower limb RF coil device can be used for receiving MR signals. These wearable RF coil devices may also be regarded as a part of the MRI apparatus 10 or may be regarded as separate from the MRI apparatus 10.

  Next, a method for setting an MR signal collection area for a calibration scan by the calibration scan setting unit 66 will be described (hereinafter, the MR signal collection area is referred to as a “signal collection area”). In the following description, the terms “signal collection range” and “imaging range” are used in different meanings from the signal collection region and the imaging region.

  The signal collection range is assumed to be a minimum rectangular parallelepiped area including all signal collection areas in one sequence such as a magnetic field measurement sequence (however, it may not be a rectangular parallelepiped area). When MR signals are acquired by applying a phase encoding gradient magnetic field in the slice selection direction as in three-dimensional imaging, the signal acquisition range may be regarded as the signal acquisition region itself.

  On the other hand, when MR signals are collected from a plurality of slices as in two-dimensional imaging, the minimum rectangular parallelepiped region that includes all these slices is the signal collection range. In this case, the region between slices in the signal acquisition range is not strictly a signal acquisition region, and MR signals are not acquired. In this case, since the signal collection area is an area of each slice, for example, after the signal collection range is determined, each signal collection area can be precisely defined three-dimensionally by determining the slice interval, the slice thickness, and the number of slices.

  Similarly, the imaging range is, for example, synonymous with an imaging region in the case of three-dimensional imaging, and in the case of two-dimensional imaging that images a plurality of slices, the smallest (cubic) including all slices to be imaged It is assumed to be a region. In the case of two-dimensional imaging, the area between slices in the imaging range is not strictly an imaging area, and MR signals are not collected.

  If the signal acquisition range of the calibration scan does not include the imaging range of the main scan, that is, if it is too narrow, the image quality of the image obtained from the main scan may deteriorate. For example, if the sensitivity distribution map does not include the imaging range, the luminance correction process after image reconstruction cannot be executed properly.

  Alternatively, consider a case where a magnetic field measurement sequence is executed in a range narrower than the imaging range, and an offset magnetic field in a range narrower than the imaging range is calculated and superimposed on the static magnetic field. In this case, since the static magnetic field is made uniform only in a part of the imaging range, the effect of the RF pulse such as the fat suppression prepulse is lowered, and the image quality is deteriorated.

  On the contrary, when the signal acquisition range of the calibration scan is too wider than the imaging range of the main scan, the image quality deteriorates. For example, consider a case where a magnetic field measurement sequence is executed in a range that is too wider than the imaging range, an offset magnetic field is calculated in that range, and is superimposed on the static magnetic field. Usually, the imaging range is a part of the vicinity of the magnetic field center in the imaging space. Accordingly, when the offset magnetic field is calculated in a range that is too wide, the accuracy of the offset magnetic field becomes rough if attention is paid to the imaging range that is a part of the offset magnetic field. If the accuracy of the offset magnetic field in the imaging range decreases, the uniformity of the static magnetic field in the imaging range is impaired, and the image quality deteriorates.

  As described above, the image acquisition range of the calibration scan is deteriorated if it is too wide or too narrow. Therefore, the calibration scan setting unit 66 calculates the signal collection range of the calibration scan to be an appropriate range based on the imaging range of the main scan.

  Specifically, for example, in the case of a magnetic field measurement sequence and a sensitivity map sequence, the calibration scan setting unit 66 calculates a signal collection range that is a minimum size including an imaging range or a size obtained by enlarging the minimum size by a predetermined ratio. And set. For example, when each outer edge of the imaging range is a rectangular parallelepiped region along each axis of the apparatus coordinate system, the predetermined ratio is a range that is not too wide, and the vertical, horizontal, and depth sizes of the signal collection range are the minimum sizes. For example, it is increased by 5% or 10%.

  Further, when acquiring MR signals from a plurality of slices as in two-dimensional imaging, the calibration scan setting unit 66 sets the signal acquisition area of the calibration scan within an appropriate range based on the FOV and imaging position of the main scan. To calculate. The FOV is, for example, the vertical and horizontal sizes of the imaging region in the case of slice imaging, and the imaging position is the slice position in the Z-axis direction in the case of slice imaging of an axial cross section, for example. That is, the combination of the FOV and the imaging position defines the imaging area of each slice in the main scan (which range is imaged in the three-dimensional coordinates in the imaging space).

Specifically, for example, the calibration scan setting unit 66 expands the minimum size in the range satisfying the following two conditions in both the phase encoding direction and the reading direction, or the minimum size at a predetermined ratio similar to the above. Set the FOV of the calibration scan to be the size.
The first condition is that the calibration scan FOV includes the main scan FOV.
The second condition is that the FOV of the calibration scan does not become smaller than the initial setting value in both the phase encoding direction and the readout direction.

Next, the signal acquisition area is supplemented for each sequence of calibration scans.
First, in the case of the magnetic field measurement sequence, the calibration scan setting unit 66 does not reduce the number of slices relative to the width of the imaging range (in the normal direction of the slice), for example, and not too much. Set the number of slices.

  For example, when the head is an imaging region, the number of slices is 20 as an initial setting value, and when the chest and abdomen are imaging regions, the number of slices is 50 as an initial setting value. The calibration scan setting unit 66 stores the initial setting values of each parameter in advance as described above, and sets the conditions for the parameter based on this. Here, “preliminarily” means, for example, the power before the MRI apparatus 10 is turned on, and may be stored before the product of the MRI apparatus 10 is shipped. The above setting method is merely an example, and the present embodiment is not limited to the above setting method.

FIG. 4 is a schematic explanatory diagram illustrating an example of a method for setting the FOV size in the magnetic field measurement sequence. Here, as an example, a plurality of slices are assumed to be signal acquisition regions of the magnetic field measurement sequence.
The upper part of FIG. 4 shows the initial set value FOV. In this example, 30 cm is set as the initial setting value in the phase encoding direction (Phase Encode Direction) and 30 cm in the readout direction (Readout Direction).

  Next, it is assumed that the user sets an FOV of, for example, 20 cm in the phase encoding direction and 60 cm in the reading direction during the planning of the imaging conditions of the main scan. The middle part of FIG. 4 shows this state. In this case, the minimum size of the FOV satisfying the first condition and the second condition is 30 cm in the phase encoding direction and 60 cm in the reading direction. Therefore, the calibration scan setting unit 66 sets the FOV of the magnetic field measurement sequence as described above. The lower part of FIG. 4 shows this state.

  Further, the calibration scan setting unit 66 calculates the slice interval GAP based on the following equation (1), for example.

  GAP = {SSt− (Snu × Sth)} / (Snu−1) (1)

  In the equation (1), SSt is the width of the signal collection range of the magnetic field measurement sequence in the normal direction of the slice, Snu is the number of slices, and Sth is the slice thickness. For example, when the width of the signal collection range in the normal direction of the slice is 28 cm, the slice thickness Sth is 1 cm, and the number of slices Snu is 10, the slice interval GAP is calculated as 2 cm according to the equation (1).

  Second, in the case of the center frequency sequence, as an example, the calibration scan setting unit 66 sets the signal acquisition region so as to be the same region as the slice including the center of the imaging range of the main scan. For example, in the main scan, when 31 slices of an axial cross-section are imaged at predetermined intervals in the Z-axis direction, the slice including the center of the imaging range is the 16th slice from the minus side or the plus side in the Z-axis direction. It is.

  For example, under the assumption that the center frequency of the RF pulse is changed for each slice in the main scan, the calibration scan setting unit 66 may use a plurality of slices that are the same as all the slices in the main scan as each signal acquisition region. However, with respect to the center frequency of the RF pulse, sufficient image quality can be obtained even if it is calibrated with the representative slice as described above, and this is desirable from the viewpoints of SAR, imaging time, and power consumption. The SAR means the RF pulse energy (specific absorption ratio) absorbed by 1 kg of living tissue.

  Third, in the case of the sensitivity distribution map sequence, the calibration scan setting unit 66 calculates and sets a signal collection range and a signal collection region for each position of the top plate 22 (for each station) in principle. Here, “for each station” has the following meaning.

  For example, consider a case where the first main scan and the second main scan are sequentially executed at the first station, and then the third main scan and the fourth main scan are sequentially executed at the second station. In this case, the signal collection range of the sensitivity distribution map sequence at the first station is set so as to include the imaging ranges of the first and second main scans, and includes the imaging ranges of the third and fourth main scans. The signal collection range of the sensitivity distribution map sequence at the second station is set.

  That is, the sensitivity distribution map sequence is executed at least once at the first station and the second station. However, when the imaging area of the second main scan is changed after the sensitivity distribution map sequence and the first main scan are executed in the first station, the first distribution is performed for the area where the sensitivity distribution map becomes insufficient due to the change. A sensitivity distribution map sequence may additionally be performed at the station. The same applies to the second station.

  Here, as an example, the calibration scan setting unit 66 calculates and sets the number of matrices in the sensitivity distribution map sequence as follows. For example, when the number of element coils of the wearable RF coil device arranged in the imaging range is relatively large with respect to the volume of the imaging range, the calibration scan setting unit 66 sets the number of pixels as 256 × 256. This is because it is desirable to generate a more accurate sensitivity distribution map by detecting the distribution of the signal level of the received MR signal more finely as the number of element coils is relatively larger.

  Conversely, when the number of element coils arranged in the imaging range is relatively small with respect to the volume of the imaging range, the calibration scan setting unit 66 sets the number of pixels as 128 × 128. Whether the number of element coils arranged in the imaging range is relatively large or small relative to the volume of the imaging range depends on the number of element coils in the RF coil device based on the identification information of the RF coil device and the imaging region. Based on this, the calibration scan setting unit 66 determines.

When there is no sensitivity distribution map for any region in the total area of each imaging range of all the main scans in one station, the calibration scan setting unit 66 calculates the same area as the total area as an “insufficient range”. The shortage range is set as the signal collection range.
The “insufficient range” means a region where the sensitivity distribution map is insufficient for the same subject as compared with the imaging range of the main scan.
“With respect to the same subject” means that even if a sensitivity distribution map exists in the previous imaging of the subject, the sensitivity distribution map cannot be used as a sensitivity distribution map when imaging another subject. Means a restriction from

  FIG. 5 is an explanatory diagram showing an example of a method for calculating the signal collection region of the sensitivity distribution map sequence when a sensitivity distribution map exists for a part of the imaging range of the main scan.

  The upper part of FIG. 5 shows the imaging range Im1 (dotted line frame) of the main scan set in the sagittal section Sa1 of the patient coordinate system and the range 200 (dotted line frame) in which the sensitivity distribution map exists on the upper side. An imaging range Im1 in the axial section Ax1 which is a transverse section in the A1-A1 direction of Sa1 is shown on the lower side with a dotted frame. In this example, the right half of the imaging range Im1 in the sagittal section Sa1 is a range 200 where the sensitivity distribution map exists.

  In the lower part of FIG. 5, the signal collection range Ra1 (shaded portion) of the sensitivity distribution map sequence set by the calibration scan setting unit 66 in the sagittal section Sa1 and the range 200 (dotted line frame) where the sensitivity distribution map exists are on the upper side. The signal collection range Ra1 in the axial cross section Ax1 is shown below by a dotted frame.

  Here, as an example, the X axis, Y axis, and Z axis of the patient coordinate system are defined as follows. The left-right direction of the subject P is taken as the X-axis direction, and the front-rear direction of the subject P with the ventral side as the front and the back side as the back is taken as the Y-axis direction. In addition, the vertical direction of the subject P with the head up and the foot down in the spine extending direction is defined as the Z-axis direction. The XY plane of the patient coordinate system is an axial plane, the XZ plane of the patient coordinate system is a coronal plane, and the YZ plane of the patient coordinate system is a sagittal plane.

  In addition, here, as an example, it is assumed that the magnetic field center in the gantry 30, the origin of the patient coordinate system, and the origin of the apparatus coordinate system coincide with each other, and the subject P has its body axis direction in the Z axis direction of the apparatus coordinate system. It shall be mounted on the top plate 22 so as to match. That is, the plane directions of the XY plane (axial plane), the XZ plane (coronal plane), and the YZ plane (sagittal plane) are assumed to match in the patient coordinate system and the apparatus coordinate system, respectively. However, the above is only an example for simplification of description, and it is not necessary to match the directions and origins of the reference three axes with the apparatus coordinate system of the patient coordinate system.

  In the case of FIG. 5, the calibration scan setting unit 66 calculates, from the imaging range Im1, an area excluding the range 200 where the sensitivity distribution map exists as an insufficient range, and this insufficient range is used as the signal collection range Ra1 of the sensitivity distribution map sequence. Set. In the example of FIG. 5, the shortage range (signal collection range Ra1) in the sagittal section Sa1 is approximately the left half of the imaging range Im1.

  In the above example, the “insufficient range” is set as the signal collection range Ra1, but an “region where the insufficient range is slightly expanded” may be set as the signal collection range. Here, “slightly expanded” is within the range covered by the reception sensitivity of the element coils 144 and 146 used in the sensitivity distribution map sequence and includes the shortage range, and the region outside the subject is the sensitivity. It is preferable that it is wide enough to be included in the outer edge of the distribution map.

  The reason why the region outside the subject is preferably included is as follows. That is, the outside of the subject is air and the intensity of the MR signal is low, and information on the outer edge of the subject P can be obtained by including such a region outside the subject in the sensitivity distribution map. Information about whether the outer MR signal can be ignored in the main scan is obtained.

  In addition, the “range covered by the reception sensitivity” means, for example, a range in which an MR signal can be detected with a sensitivity sufficient to provide a diagnostic-free image quality if the MR signal is emitted from the range. is there.

  FIG. 6 is an explanatory diagram showing an example of a method for calculating the signal collection range of the sensitivity distribution map sequence in a sagittal section when the top plate is moved. In general, if an image is taken near the center of the magnetic field, the image is most beautiful. Therefore, it is desirable to set the imaging range of the main scan every time the top plate 22 moves so that the imaging range of each main scan includes the center of the magnetic field.

  In the upper part of FIG. 6, the imaging range Im2 of the main scan set before the top plate 22 is moved is indicated by a solid line frame. In the upper part of FIG. 6, the signal collection range Ra2 of the sensitivity distribution map sequence set for the imaging range Im2 is indicated by a dotted line frame by the method described in FIG. In the example of FIG. 6, the imaging range Im2 and the signal collection range Ra2 are the same.

  Here, as an example, the imaging range of the main scan and the signal collection area of the sensitivity distribution map sequence are rectangular parallelepiped areas, and the range (position information) is determined by the coordinates in the apparatus coordinate system of all eight vertices. Assuming that

  Under the above assumption, consider the case where the top 22 moves by ΔZ in the Z-axis direction of the apparatus coordinate system after the sensitivity distribution map sequence for the signal acquisition range Ra2 and the first main scan for the imaging range Im2 are completed. In this case, the calibration scan setting unit 66 corrects the stored position information of the signal collection range Ra2 of the sensitivity distribution map sequence in conjunction with the movement of the top board 22.

  Here, as an example, the calibration scan setting unit 66 shifts each Z coordinate value in the apparatus coordinate system of all vertices of the signal collection range Ra2 by ΔZ.

  In the lower part of FIG. 6, the signal collection range Ra2 corrected after the top plate 22 is moved as described above is indicated by a dotted frame. In the lower part of FIG. 6, the imaging range Im3 of another main scan newly set after the top plate 22 is moved is indicated by a one-dot chain line. In this case, the calibration scan setting unit 66 calculates and sets the signal collection range Ra3 of the sensitivity distribution map sequence for the imaging range Im3 in the same manner as the method described in FIG. In the example of FIG. 6, approximately 3/4 of the imaging range Im3 is the signal collection range Ra3.

  That is, the calibration scan setting unit 66 calculates an overlapping area between the imaging range Im3 of the main scan and the signal collection range Ra2 (the area where the sensitivity distribution map exists) for which the sensitivity distribution map sequence has been executed. Next, the calibration scan setting unit 66 calculates an area obtained by subtracting the overlapping area from the imaging range Im3 as an insufficient range, and sets the insufficient range as the signal collection range Ra3 of the sensitivity distribution map sequence. Thus, in this embodiment, when the top plate 22 moves, sensitivity distribution maps are made not to overlap.

  However, as described above, the method of correcting the position information of the generated sensitivity distribution map in conjunction with the movement of the top plate 22 and calculating the signal collection range of the sensitivity distribution map sequence while avoiding duplication is only an example. Absent.

As the sensitivity distribution map used for the MR signals collected in the main scan after the top plate 22 is moved, the sensitivity distribution map generated before the top plate 22 is moved may not be used.
That is, every time the top plate 22 moves, a sensitivity distribution map of the entire region necessary at the top plate position may be generated (in this case, the position information of the sensitivity distribution map linked to the movement of the top plate 22 is corrected Not)

  As the moving distance of the top plate 22 increases, the relative positional relationship between the phased array coil (element coils 144 and 146 in this example) and the magnetic field center changes, and the sensitivity distribution map of each element coil also changes. Therefore, especially when the moving distance of the top plate 22 is large, it is desirable to generate a sensitivity distribution map of the entire region necessary for the top plate position every time the top plate 22 moves.

  The above is the main description of the method for setting the signal acquisition area of the calibration scan. The optional function for setting the signal acquisition area of the calibration scan will be described. For the signal acquisition area of the calibration scan, it is possible to set the priority of which parameter should be changed first and which parameter should not be changed in the planning stage, for example. In addition to the FOV and the imaging position, parameters relating to the signal acquisition area of the calibration scan include the slice interval, the number of slices, the slice thickness, the number of matrices (the number of phase encoding steps and the number of frequency encoding steps), and the like.

  For example, consider a case where the signal acquisition area of the calibration scan is set so as to be compatible with the first and second main scans, and the FOV of the second main scan is changed after the execution of the calibration scan and the first main scan. In this case, the calibration scan setting unit 66 changes the signal acquisition area of the calibration scan executed before the first main scan as follows.

  As a first example, it is assumed that “the number of slices” is selected as the condition to be changed with the highest priority. Under this assumption, when the imaging area of the second main scan is reduced and the signal acquisition ranges of the magnetic field measurement sequence and the sensitivity distribution map sequence are reduced, for example, both ends of the signal acquisition range set in 31 slices. 2 slices are deleted. Thereby, the imaging time is shortened. Therefore, when priority is given to shortening the imaging time, the user can select the number of slices as a condition to be changed with the highest priority, for example.

  As a second example, it is assumed that “the number of matrices” is selected as the condition to be changed with the highest priority and that the spatial resolution is not changed. Under this assumption, if the FOV of the calibration scan becomes too narrow due to the expansion of the imaging area of the second main scan, and the signal acquisition range is expanded, the number of matrices is increased so that the spatial resolution is not changed. The In the case of priority on image quality, the user may select not to change the spatial resolution.

  As a third example, it is assumed that “slice interval” is selected as the condition to be changed with the highest priority. Under this assumption, when the imaging area of the second main scan is expanded and the depth of the signal acquisition range of the calibration scan is increased, the slice interval is increased so that other conditions are not changed.

  As a fourth example, it is assumed that “slice thickness” is selected as the condition to be changed with the highest priority. Under this assumption, when the imaging area of the second main scan is expanded and the depth of the signal acquisition range of the calibration scan is increased, the slice thickness is increased so that other conditions are not changed.

  In addition, as a condition to be changed with the highest priority for the signal acquisition area of the calibration scan, for example, a combination of two or more of the above-described four of the slice interval, the number of slices, the slice thickness, and the number of matrices may be used.

<Description of operation of this embodiment>
FIG. 7 is the first half of a flowchart showing an example of the operation flow of the MRI apparatus 10 in the present embodiment, and FIG. 8 is the second half thereof. Hereinafter, the operation of the MRI apparatus 10 will be described according to the step numbers shown in FIGS.

  [Step S1] The plan storage unit 65 (see FIG. 1) generates an execution plan for the main scan based on the imaging conditions input to the MRI apparatus 10 via the input device 72, and stores this. In the present embodiment, as an example, the execution plan is to execute the main scan twice in the following operation order in the first and second stations.

  That is, the calibration scan at the first station, the first scan of the T1-weighted image of the chest at the first station, the second scan of the T2-weighted image of the chest at the first station, the movement of the top plate 22, the second The calibration scan at the station, the third scan of the abdominal T1-weighted image at the second station, and the fourth scan of the abdominal T2-weighted image at the second station are executed in this order.

  Accordingly, the execution plan does not include executing a calibration scan (second time at the first station) after the first main scan and before the second main scan at the time of step S1. However, the second calibration scan can be inserted after the first main scan and before the second main scan in accordance with the FOV of the second main scan and the imaging position. The same applies to the second station.

  Here, for simplicity, the main scan at each station will be described with two examples. However, when the main scan is executed three times or more at each station, for example, an execution plan is configured as follows. In principle, a calibration scan is executed before the start of the first main scan (in this example, the first main scan). However, before the start of the second and subsequent main scans (in this example, the second main scan), the necessity of executing the calibration scan is determined each time, and the execution of the calibration scan is inserted according to the determination result And may not be inserted. Therefore, when the execution plan is generated, the execution of the calibration scan before the start of the second and subsequent main scans at each station is not included in the execution plan in principle.

  Further, the user can set, via the input device 72, the priority of which parameter may be changed first with respect to the signal acquisition region of the calibration scan and which parameter does not change the condition. However, this is only a priority of which one can be changed when the condition is automatically changed on the MRI apparatus 10 side, and the user cannot directly input and set the calibration scan condition. This is because the calibration scan is a scan that adjusts a condition that does not accept a manual manual input setting although it is a condition related to the image quality as described above.

  Thereafter, the subject P is placed on the top 22 and the RF coil device 140 is set on the subject P. Under the control of the system control unit 61, the top board moving mechanism 23 moves the top board 22 so that the imaging part (chest part) of the first station is located near the magnetic field center of the imaging space in the gantry 30.

  Further, for example, after the coil position measurement sequence described in Japanese Patent Application Laid-Open No. 2010-259777 is executed, an element coil is selected. Specifically, for example, after transmitting an RF pulse from the whole body coil WB, MR signals are collected from the element coils 144 and 146 in the RF coil device 140 attached to the subject P, and based on the collected MR signals. To generate profile data for coil positioning.

Next, the positions of the element coils 144 and 146 in the RF coil device 140 are calculated based on the profile data. Thereafter, based on the position of each element coil 144, 146, the system controller 61 automatically selects the element coil 144, 146 used for receiving the MR signal, or the position of each element coil 144, 146 is displayed on the display device. After being displayed on 74, the user selects element coils 144, 146 to be used for receiving MR signals.
Thereafter, the process proceeds to step S2.

  [Step S2] A locator image of the chest is captured at the first station by pilot scanning. The pilot scan is a scan that collects MR signals for the locator image separately from the main scan. Since the locator image is not a diagnostic image, the number of pilot scan matrices (the number of phase encoding steps and the number of frequency encoding steps) may be coarse.

  The locator image is a reference image (reference image) for positioning in the main scan. For example, the following two types are used as the locator image. First, for example, an image reconstructed from MR signals collected by a pilot scan in an axial section, a coronal section, a sagittal section, or the like. Second, when the pulse sequence of the main scan of the same subject has been executed, it is an image of the main scan obtained from the previous pulse sequence.

  In this example, only the image obtained by the pilot scan is used as the locator image before the first main scan of the T1-weighted image. On the other hand, before the second scan of the T2-weighted image executed thereafter, the image obtained by the pilot scan and the image obtained by the first scan of the T1-weighted image are used as the locator images.

The locator image capturing operation is as follows.
First, a static magnetic field is formed in the imaging space by the static magnetic field magnet 31 excited by the static magnetic field power source 42. Further, current is supplied from the shim coil power supply 44 to the shim coil unit 32, and the static magnetic field formed in the imaging space is made uniform.

  Next, the sequence controller 58 drives the gradient magnetic field power source 46, the RF transmitter 48, and the RF receiver 50 in accordance with the pulse sequence input from the system control unit 61, so that the imaging region including the imaging region of the subject P is included. A gradient magnetic field is formed in the RF coil unit 34 and an RF pulse is generated from the RF coil unit 34.

  Therefore, an MR signal generated by nuclear magnetic resonance in the subject P is detected by the RF coil unit 34 and the reception RF coil 24 and input to the RF receiver 50. The RF receiver 50 generates the raw data of the MR signal by performing the above-described processing on the MR signal, and inputs the raw data to the image reconstruction unit 62. The image reconstruction unit 62 arranges and stores the raw data of the MR signal as k-space data. The image reconstruction unit 62 reconstructs image data by performing image reconstruction processing including Fourier transform on the k-space data, and stores the obtained image data in the image database 63.

The image processing unit 64 takes in image data from the image database 63, performs predetermined image processing on the image data, generates two-dimensional display image data, and stores the display image data in the storage device 76. Thereafter, the system control unit 61 causes the display device 74 to display the image indicated by the display image data.
Thereafter, the process proceeds to step S3.

  [Step S3] The user selects the FOV and imaging position of the first and second main scans via the input device 72 based on the displayed locator image. However, it is sufficient to select the FOV and the imaging position in step S3 only for the next main scan (unexecuted and the first main scan), without selecting the FOV and the imaging position of the second main scan. May be.

In this example, since the first main scan is a T1-weighted image and the second main scan is a T2-weighted image, it may be easier to compare in terms of diagnosis if both FOVs and imaging positions are aligned. Accordingly, the system control unit 61 may automatically set the FOV and imaging position of the second main scan so as to match the FOV and imaging position of the first main scan selected by the user.
Thereafter, the process proceeds to step S4.

  [Step S4] The calibration scan setting unit 66 selects which one to perform as a calibration scan from the magnetic field measurement sequence, the center frequency sequence, and the sensitivity distribution map sequence as follows, for example.

  For example, when the pulse sequence of the main scan is parallel imaging, the calibration scan setting unit 66 sets the sensitivity distribution map sequence to be performed as a calibration scan. Note that parallel imaging is a high-speed imaging technique in which an RF coil is configured using a phased array coil having a plurality of element coils, and MR signals are collected using each element coil. In parallel imaging, the number of data acquisition times in the phase encoding direction is thinned out, and aliasing artifacts that occur at the number of thinned out phase encoding steps are compensated based on the sensitivity distribution map.

  In addition, when an RF coil device that cannot execute parallel imaging, such as a local RF coil device such as a shoulder RF coil device, is used for MR signal reception, the calibration scan setting unit 66 executes the sensitivity distribution map sequence. Set to not.

  Further, for example, when the uniformity of the static magnetic field is greatly disturbed or when the accuracy of the static magnetic field uniformity is particularly desired, the calibration scan setting unit 66 sets the magnetic field measurement sequence to be performed as a calibration scan. For example, when the top plate 22 moves as in multi-station imaging, the uniformity of the static magnetic field is disturbed. The case where the accuracy of the static magnetic field uniformity is particularly desired is, for example, a case where fat suppression is performed or a local shimming (see Japanese Patent Application Laid-Open No. 2007-209749) is desired in cardiac imaging.

  Further, for example, when there is no step movement of the top plate 22 and the main scan is executed many times on the same part of the subject P, the offset magnetic field obtained by the calibration scan performed before the first main scan is used. By using it, in the second and subsequent main scans, the static magnetic field can be corrected without performing the magnetic field measurement sequence. In such a case, the calibration scan setting unit 66 performs setting so that the magnetic field measurement sequence is not re-executed.

  For example, in breast imaging, since a lot of fat tissue is included, a fat suppression pre-pulse may be included in the pulse sequence of the main scan. When the fat suppression prepulse is included in the main scan, the calibration scan setting unit 66 sets the center frequency sequence to be performed as a calibration scan.

  Note that the above criteria are only examples. For example, the magnetic field measurement sequence and the center frequency sequence may be executed regardless of the imaging conditions of the main scan. Here, as an example, it is assumed that a sensitivity distribution map does not exist for the first main scan of the same subject P, and a sensitivity distribution map sequence, a magnetic field measurement sequence, and a center frequency sequence are executed as calibration scans.

Next, the calibration scan setting unit 66 calculates a signal collection area for each calibration scan based on the FOV and imaging position of the first main scan, and sets the signal collection area to the calculated area. The signal collection area calculation method has been described with reference to FIGS.
Thereafter, the process proceeds to step S5.

  [Step S5] Each calibration scan in which the signal acquisition area is set in Step S4 is executed in the first station. Although each calibration scan sequence is performed separately in time, the magnetic field measurement sequence and the center frequency sequence may be executed as one calibration scan.

  Here, it is desirable to perform the magnetic field measurement sequence before the center frequency sequence. This is because more accurate magnetic resonance spectrum data can be obtained by executing the center frequency sequence in a state where the static magnetic field is more uniformly corrected based on the offset magnetic field. Similarly, it is desirable to perform the magnetic field measurement sequence before the sensitivity distribution map sequence. If the uniformity of the static magnetic field is greatly disturbed by the size of the subject or the imaging site, the sensitivity distribution map sequence can be obtained more accurately if the sensitivity distribution map sequence is performed with the static magnetic field corrected more uniformly. is there.

  Therefore, here, as an example, the following description will be made in order, assuming that the magnetic field measurement sequence, the center frequency sequence, and the sensitivity distribution map sequence are performed in this order.

First, an example of a magnetic field measurement sequence will be described. This technique is described in, for example, Patent Document 1 and will be briefly described here.
Under the control of the sequence controller 58, a current is supplied from the static magnetic field power source 42 to the static magnetic field magnet 31, and a static magnetic field is applied in the imaging space. The supply current value to the static magnetic field magnet 31 here is controlled so that a uniform static magnetic field is generated if there is nothing in the imaging space. "Static magnetic field". Since the subject P is present in the imaging space, there is a region where the magnetic permeability is different from that of the surroundings, so that the actual static magnetic field intensity distribution in the imaging space is not uniform.

  Next, the sequence controller 58 selects a slice by applying a gradient magnetic field Gx, Gy, Gz or the like so as to obtain a magnetic field strength distribution in the imaging space based on a control signal from the system control unit 61, and an RF pulse. Send. Thereafter, the MR signal is detected by the RF receiver 50, and the detected MR signal is input to the system control unit 61 via the sequence controller 58.

  Since these MR signals are raw data in the k space, the system control unit 61 converts the input MR signals into real space data, calculates the magnetic field strength distribution in the imaging space based on the converted data, This is the magnetic field strength distribution Bm (x, y, z) of the measured value. (X, y, z) means a function of the coordinate position (x, y, z) in the apparatus coordinate system. Thereafter, the system control unit 61 calculates the intensity distribution Bo (x, y, z) of the offset magnetic field that makes the static magnetic field uniform by, for example, the following equation.

  Bo (x, y, z) = Bi (x, y, z) −Bm (x, y, z) (2)

  In equation (2), Bi (x, y, z) is a target distribution of the magnetic field strength of the static magnetic field, and is a uniform distribution over the imaging space. That is, if no offset magnetic field is applied, Bm (x, y, z) is generated as a static magnetic field distribution of the measured value, and in this scan, the offset magnetic field is superimposed on the reference static magnetic field. A static magnetic field with a target distribution can be obtained.

  Second, an example of the center frequency sequence will be described. The calibration scan is performed under the same conditions as the magnetic field measurement sequence, for example, except that the magnetic resonance spectroscopy is applied to the slice including the center of the FOV. The system control unit 61 controls each unit of the MRI apparatus 10 to collect and analyze frequency spectrum data by applying magnetic resonance spectroscopy to a slice including the center of the FOV, and based on the peak frequency and the like, the hydrogen nucleus The magnetic resonance frequency of the spin is detected.

  The system control unit 61 calculates and sets the center frequency of the RF pulse used in the first main scan based on the execution result of the sequence. Specifically, for example, the magnetic resonance frequency of the detected hydrogen nucleus spin is set as the center frequency of the RF pulse. For the sequence for detecting the center frequency, for example, a conventional method such as the technique described in Patent Document 3 may be used.

Third, an example of the sensitivity distribution map sequence will be described. This technique is described in, for example, Patent Document 2 and will be briefly described here.
First, MR signals are collected from the signal collection region set in step S4 using the RF coil device 140 mounted on the subject P and the whole body coil WB as a reception coil.

  Then, image data obtained from the MR signal detected by the whole body coil WB (hereinafter referred to as WB image data) and image data obtained from the MR signal detected by the RF coil device 140 (hereinafter referred to as main coil). Image data) is acquired as image data for estimating the sensitivity distribution of each of the element coils 144 and 146 in the RF coil device 140 and stored in the image database 63. Similar image data acquisition is performed over the entire signal collection range, and is stored in the image database 63 as volume data.

Based on the above execution results, the system control unit 61 generates sensitivity distributions of the element coils 144 and 146 in the signal collection range as three-dimensional sensitivity distribution map data, and stores them in the storage device 76.
Specifically, for example, the signal intensity distribution of the main coil image data is divided by the signal intensity distribution of the WB image data, and the signal intensity ratio between the two is estimated value of the sensitivity distribution of all the element coils 144 and 146 in the RF coil device 140. Calculate as If similar processing is performed on the image data of each cross section, three-dimensional sensitivity distribution map data can be generated. The three-dimensional sensitivity distribution map data is used for luminance correction processing after image data is reconstructed by the image reconstruction unit 62, for example.

Since the WB image data obtained from the whole body coil WB is used as a reference, the sensitivity distribution map can be obtained even if only the RF coil device 140 is used as a reception coil without using the whole body coil WB as a reception coil. Can be generated.
Thereafter, the process proceeds to step S6.

  [Step S6] Based on the imaging conditions set up to Step S3 and the center frequency and offset magnetic field of the RF pulse calculated and set in Step S5, the first main scan is executed in the first station. That is, as in the case of the pilot scan in step S2, each unit of the MRI apparatus 10 operates, and the MR signal collected in the first main scan is stored in the image reconstruction unit as k-space data.

  In parallel with the execution of the first main scan, image reconstruction and luminance correction are executed. That is, the image reconstruction unit 62 reconstructs image data by performing image reconstruction processing on the k-space data, and stores the obtained image data in the image database 63.

  The image processing unit 64 takes in the image data from the image database 63 and performs image processing such as luminance correction processing based on the sensitivity distribution map to generate two-dimensional display image data. The display image data is stored in the storage device. Save to 76.

[Step S7] The system control unit 61 displays on the display device 74 the image indicated by the display image data for the first main scan (T1-weighted image) generated in step S6 and the locator image generated in step S2. Let The user can reset (change) the FOV and imaging position of the second main scan to be executed next based on the locator image and the T1-weighted image. If not reset, for example, the FOV and imaging position of the second main scan are fixed under the conditions set in step S3.
After the FOV and imaging position of the second main scan are determined, the process proceeds to step S8.

  [Step S8] The calibration scan setting unit 66 determines whether or not to execute the magnetic field measurement sequence, the center frequency sequence, and the sensitivity distribution map sequence before the second main scan. Hereinafter, the determination method will be described.

  First, for the center frequency sequence, the calibration scan setting unit 66 determines whether or not it is necessary to execute it based on, for example, an imaging region and an elapsed time. For example, when the imaging area of the second main scan is changed in step S7, it is desirable to execute the center frequency sequence before the second main scan. This is because if the imaging region in the subject P changes, the center frequency of magnetic resonance may change greatly, for example, from a region with less fat to a region with more fat.

  In the case of a sequence in which the temperature of the gradient coil unit 33 is likely to rise, it is desirable to re-execute the center frequency sequence if the elapsed time from the previous execution of the center frequency sequence exceeds a predetermined value. The sequence in which the temperature is likely to rise is a sequence that consumes a large amount of power, such as echo planar imaging or dynamic imaging.

  When the temperature of the gradient magnetic field coil unit 33 rises, the temperature of an iron shim (not shown) in the vicinity thereof rises, the permeability of the iron shim changes, and the magnetic field in the imaging space changes. This is because the center frequency of magnetic resonance of hydrogen atoms changes. Note that a plurality of iron shims are arranged in the gantry 30 (not shown) in order to uniformize the magnetic field strength distribution of the static magnetic field in the imaging space.

  Secondly, for the magnetic field measurement sequence, the calibration scan setting unit 66 determines whether or not it is necessary to execute it based on the imaging region and the elapsed time, for example. For example, consider a case where the imaging region is not changed and the elapsed time from the previous execution of the magnetic field measurement sequence is less than a predetermined value.

  In this case, if it can be estimated that the subject P has not moved much since the previous execution of the magnetic field measurement sequence, the calibration scan setting unit 66 determines that the magnetic field measurement sequence is not required to be executed. In the present embodiment, the top plate 22 does not move, but if the top plate 22 has moved since the previous execution of the magnetic field measurement sequence, the calibration scan setting unit 66 determines that the magnetic field measurement sequence should be executed.

  Further, when the user resets the FOV in step S7, it is considered that the subject P is displaced, so that the calibration scan setting unit 66 determines that the magnetic field measurement sequence should be executed.

Thirdly, with respect to the sensitivity distribution map sequence, the calibration scan setting unit 66 determines the necessity of execution by comparing the already existing sensitivity distribution map with the imaging area of the second main scan. If the already existing sensitivity distribution map includes the imaging area of the second main scan, it is determined that the execution is not necessary, and if not, it is determined that the sensitivity distribution map should be executed.
If there is a calibration scan determined to be executed, the process proceeds to step S9.

  If there is no calibration scan determined to be executed, the system control unit 61 determines the conditions for the second main scan under the conditions set up to step S7, and then proceeds to step S11.

  [Step S9] The calibration scan setting unit 61 calculates the signal collection area of each calibration scan determined to be executed in step S8 based on the FOV of the second main scan and the imaging position in the same manner as in step S4. And set.

  Here, in step S1, when a condition that is preferentially changed or a condition that is not changed is selected for the signal acquisition region of the calibration scan, the calibration scan setting unit 61 is executed in step S5 according to the selection content. Change the signal acquisition area of the calibration scan.

For example, consider a case where the number of slices is selected as the condition to be changed with the highest priority, the imaging area of the second main scan is reduced, and the signal collection range of the sensitivity distribution map sequence is reduced. In this case, for example, two slices at both ends are deleted from the signal collection range of the sensitivity distribution map set at 31 slices (see the first to fourth examples described above).
Thereafter, the process proceeds to step S10.

  [Step S10] Each calibration scan determined to be executed in Step S8 is executed on the signal acquisition region set in Step S9 in the first station.

Thereafter, the system control unit 61 resets the center frequency of the RF pulse used in the second main scan, resets the offset magnetic field, and adds a sensitivity distribution map based on the execution result of the calibration scan in step S10. Perform at least one of the following: Further, the system control unit 61 determines the imaging conditions of the second main scan that are not related to the calibration scan under the conditions set up to step S7.
Thereafter, the process proceeds to step S11.

[Step S11] In accordance with the imaging conditions set up to Step S10, the second main scan is executed in the first station, and the MR signals collected in the second main scan are stored in the image reconstruction unit 62 as k-space data. The Then, as in steps S6 and S7, image reconstruction and luminance correction are executed, display image data is stored in the storage device 76, and the display image data for the second main scan (T2 weighted image) indicates. The image is displayed on the display device 74.
Thereafter, the process proceeds to step S12 in FIG.

  [Step S12] Under the control of the system control unit 61, the top plate moving mechanism 23 moves the top plate 22 so that the imaging region of the second station (the abdomen of the subject P) is located near the center of the magnetic field. The system control unit 61 corrects the coordinate position of the existing region of the sensitivity distribution map that has been generated up to step S10 as the top plate 22 moves. This correction method has already been described with reference to FIG.

Thereafter, an abdominal locator image is captured and displayed at the second station in the same manner as in step S2 by pilot scanning.
Thereafter, the process proceeds to step S13.

[Step S13] The user selects the FOV and imaging position of the third and fourth main scans via the input device 72 based on the displayed locator image. However, the FOV and imaging position of the fourth main scan may be automatically set so as to match the FOV and imaging position of the third main scan, regardless of the user's selection.
Thereafter, the process proceeds to step S14.

  [Step S14] The calibration scan setting unit 66 selects which one to perform as a calibration scan from the magnetic field measurement sequence, the center frequency sequence, and the sensitivity distribution map sequence in the same manner as in step S4. Since the imaging region changes after the top plate 22 is moved as in step S14, the magnetic field measurement sequence and the center frequency sequence are selected. In addition, it is usually difficult to think that a sensitivity distribution map of the abdomen, which is an imaging region of the second station, is generated in the first station whose chest is the magnetic field center. Accordingly, a sensitivity distribution map sequence is also selected.

Next, the calibration scan setting unit 66 calculates and sets the signal collection area of each calibration scan selected to be executed based on the FOV of the third main scan and the imaging position.
Thereafter, the process proceeds to step S15.

[Step S15] Similarly to step S5, each calibration scan in which the signal acquisition area is set in step S14 is executed in the second station. Thereby, the center frequency and the offset magnetic field of the RF pulse of the third main scan are set. In addition, a sensitivity distribution map that covers the confirmed imaging area of the third main scan and the imaging area of the fourth main scan that has been determined but has been set (added to the sensitivity distribution map of the first station) Automatically).
Thereafter, the process proceeds to step S16.

  [Step S16] Based on the imaging conditions set up to Step S13 and the center frequency and offset magnetic field of the RF pulse calculated and set in Step S15, the third main scan is executed in the second station. As a result, the display image data for the third main scan is stored in the storage device 76 as described above.

[Step S17] The system control unit 61 displays the image indicated by the display image data for the third main scan (T1-weighted image) generated in step S16 and the locator image generated in step S12 on the display device 74. Let Based on these, the user can reset the FOV and imaging position of the fourth main scan. When the resetting is not performed, for example, the FOV and the imaging position of the fourth main scan are determined under the conditions set in step S13.
After the FOV and imaging position of the fourth main scan are determined, the process proceeds to step S18.

[Step S18] The calibration scan setting unit 66 determines whether or not to execute the magnetic field measurement sequence, the center frequency sequence, and the sensitivity distribution map sequence before the fourth main scan, as in step S8.
If there is a calibration scan determined to be executed, the process proceeds to step S19.

  If there is no calibration scan determined to be executed, the system control unit 61 determines the conditions for the fourth main scan under the conditions set up to step S17, and then proceeds to step S21.

[Step S19] The calibration scan setting unit 61 calculates and sets the signal collection area of each calibration scan determined to be executed in Step S18 as described above. In step S1, when a condition that is changed preferentially or not to be changed is selected with respect to the signal acquisition area of the calibration scan, the calibration scan setting unit 61 follows the selection content in the same manner as in step S9. The signal acquisition area of the calibration scan executed in step S15 is changed.
Thereafter, the process proceeds to step S20.

  [Step S20] Each calibration scan determined to be executed in Step S18 is executed for the signal acquisition region set in Step S19. Thereafter, as in step S10, after the imaging conditions for the fourth main scan are determined, the process proceeds to step S21.

  [Step S21] In accordance with the imaging conditions set up to Step S20, the fourth main scan, image reconstruction, and the like are executed at the second station, and the image of the fourth main scan is displayed on the display device 74 as described above.

In this example, the number of stations is only two, but when the number of stations is three or more, locator image capturing and calibration scanning are executed for each station.
The above is the description of the operation of the MRI apparatus 10 of the present embodiment.

<Effect of this embodiment>
In the conventional technology, for example, in the case of a shaping region such as a limb joint, a signal acquisition region of one of the three cross sections of coronal, axial, and sagittal is used as the signal acquisition region of the calibration scan. For this reason, the signal collection areas of the sensitivity distribution map sequence, the center frequency sequence, and the magnetic field measurement sequence are too narrow with respect to the imaging area of the main scan to be performed thereafter, and the image quality may deteriorate.

  In the prior art, for example, in many cases, the imaging area of the pilot scan in breast imaging is set larger than the area of interest. In this case, the signal collection area of the sensitivity distribution map sequence, the center frequency sequence, and the magnetic field measurement sequence is too wide with respect to the imaging area of the main scan to be performed thereafter, and the image quality may be deteriorated.

  Therefore, in order to appropriately set the signal acquisition area for the calibration scan in the conventional technique, the user considers the imaging area of the main scan himself and adjusts the pilot scan FOV, imaging position, number of slices, etc. by manual operation. It took time to do. This is because the calibration scan is a scan that adjusts a condition that does not accept a manual input setting although it is a condition related to the image quality as defined above.

  Therefore, in the present embodiment, as described in FIGS. 4 to 6, the signal acquisition region of the calibration scan immediately before the first main scan at each station is included in the execution plan but is not yet executed. Appropriate automatic setting is made based on the imaging position (steps S4 and S14). For example, for the sensitivity distribution map sequence, the signal collection area is set so as not to overlap with the portion where the sensitivity distribution map exists.

  In each station, before the second and subsequent main scans are executed, the necessity of re-execution of the calibration scan is automatically determined appropriately (steps S8 and S18). In the case of re-execution, the signal collection area is automatically set appropriately as described above based on the FOV and the imaging position of the unexecuted main scan that is included in the execution plan (steps S9 and S19).

  Therefore, in the MRI apparatus 10 of the present embodiment, it is possible to automatically and appropriately set the necessity of executing the calibration scan and the signal acquisition area of the calibration scan without imposing a burden on the user. As a result, a calibration scan is properly executed, and an RF pulse having a center frequency appropriately corrected is transmitted under a static magnetic field uniformized by an appropriately calculated offset magnetic field, and MR signals are collected. Brightness correction is performed on the image data reconstructed from the MR signals collected under such favorable conditions using a sensitivity distribution map generated without shortage. As a result, good image quality can be obtained regardless of the skill of the user.

  When the top 22 moves, the imaging region changes, so execution of the center frequency sequence and magnetic field measurement sequence is selected (step S14), and the coordinates of the existing region of the sensitivity distribution map are corrected. Therefore, according to the MRI apparatus 10 of the present embodiment, it is possible to automatically and appropriately determine whether or not the calibration scan is necessary and the signal acquisition area of the calibration scan regardless of the movement of the top plate 22.

  Further, conditions that are preferentially changed or not changed with respect to the signal acquisition area of the calibration scan can be selected, and the calibration scan setting unit 61 collects the signal of the second calibration scan at each station according to the selected content. The area is changed from the first signal acquisition area. For example, when priority is given to shortening the imaging time, the user can select the number of slices as a condition to be changed with the highest priority, for example. When priority is given to image quality, the user can select not to change the spatial resolution. .

  That is, it is possible to automatically set the signal collection area for the calibration scan according to the user's request such as priority on image quality and priority on shortening the imaging time. If the configuration of the MRI apparatus 10 described above is combined, the signal collection area of the calibration scan can be optimized according to parameters such as the number of slices, slice thickness, slice interval, and number of matrices.

<Supplementary items of this embodiment>
[1] The execution plans described with reference to FIGS. 7 and 8 are only examples, and even with a more complicated execution plan, the signal acquisition area of the calibration scan can be set appropriately as described above.

  FIG. 9 is a flowchart showing an example of an execution plan composed of the first to sixth groups. In the execution plan of FIG. 9, after the top plate 22 moves so that the chest of the subject P is near the center of the magnetic field as the first station (step S41), it is divided into three sections: an axial section, a sagittal section, and a coronal section. T1-weighted images and T2-weighted images are captured as first to sixth main scans as the first to third groups (steps S42 to S44).

Here, the first imaging is a locator image of an axial section, a sagittal section, and a coronal section of the chest by a pilot scan in the first group.
After the locator image is captured, the FOV and imaging position of the first to sixth main scans are set by the user, but the FOV and imaging position are determined only by the first main scan by this setting.

  That is, after execution of the first main scan, the FOV or imaging position of the second main scan may be changed as in the embodiment of FIGS. 7 and 8, and a calibration scan may be inserted before the second main scan. However, when the execution plan is generated, the calibration scan is not included in the execution plan. The point that a calibration scan that is not included in the execution plan can be inserted is the same immediately before the third main scan, immediately before the fourth main scan, immediately before the fifth main scan, and immediately before the sixth main scan.

  After the sixth main scan, the top 22 moves so that the abdomen of the subject P is in the vicinity of the center of the magnetic field as the second station (step S45). Similarly, the top plate 22 is divided into three sections and T1 as the fourth to sixth groups. The enhanced image and the T2 enhanced image are captured as the seventh to twelfth main scans (steps S46 to S48).

  In the second station, first, after the locator images of the three abdominal sections are captured in the fourth group, the FOV and imaging position of the seventh to twelfth main scans are set. With this setting, the FOV and imaging position are set. Only the seventh main scan is determined. That is, as described above, a calibration scan not included in the execution plan can be inserted immediately before each of the eighth to twelfth main scans.

  For example, the following determination algorithm can be used for determining whether or not the calibration scan in the execution plan as described above needs to be inserted.

  FIG. 10 is a flowchart showing an example of an algorithm for determining whether or not the calibration scan setting unit 66 needs to insert a calibration scan. Hereinafter, the processing flow of the determination algorithm will be described according to the step numbers in the flowchart shown in FIG.

  [Step S51] The calibration scan setting unit 66 determines whether or not an unexecuted and unconfirmed imaging sequence remains in the execution plan. However, the normal execution plan is generated so that the calibration scan is inserted immediately before the first main scan (the first main scan in the example of FIG. 9). It is excluded. This is because it is an algorithm for setting the signal acquisition area of the calibration scan to be inserted after determining whether or not the calibration scan needs to be inserted.

  The imaging sequence here is a pulse sequence for image generation, and is, for example, a main scan or a pilot scan. The “unconfirmed” means that it has not been determined whether a calibration scan should be inserted immediately before the imaging sequence.

  If the determination result is affirmative, the first to be executed among the unexecuted and unconfirmed imaging sequences is selected as a determination target, and then the process proceeds to step S52. If the determination result is negative, the determination algorithm is finish.

[Step S52] If the imaging sequence determined in step S51 is a pilot scan (for locator images), the process returns to step S51. Otherwise, the process proceeds to step S53.
[Step S53] The calibration scan setting unit 66 acquires the imaging region of the imaging sequence that is the determination target in Step S51. Thereafter, the process proceeds to step S54.

  [Step S54] The calibration scan setting unit 66 determines whether or not the imaging region acquired in Step S53 is in the vicinity of the magnetic field center at the current position of the top plate 22. If the determination result is affirmative, the process proceeds to step S55. If the determination result is negative, even if a calibration scan is inserted, a good execution result is not desired at the current position of the top plate 22, so the process returns to step S51.

  [Step S55] A calibration scan setting unit determines whether or not the calibration scan should be re-executed before the imaging sequence determined in Step S51 by changing the signal acquisition area of the calibration scan executed immediately before. 66 determines. This criterion is the same as step S8 in FIG. If it is determined that the calibration scan should be performed again, the process proceeds to step S56. Otherwise, the process returns to step S51.

  [Step S56] The calibration scan setting unit 66 calculates the signal collection area of the calibration scan, as in step S9 of FIG. At this time, if a condition that is changed preferentially or a condition that is not changed is selected, the calibration scan setting unit 66 changes the signal acquisition area of the previous calibration scan in accordance with the selection contents as described above. Then, the signal acquisition area of the calibration scan to be inserted is calculated. Thereafter, the process proceeds to step S57.

  [Step S57] If the imaging sequence that is the current determination target is the last imaging sequence in the execution plan, the process proceeds to step S58. If not, the process returns to step S51. Here, as an example, it is determined whether or not it is the last imaging sequence in the execution plan. However, in the case of an execution plan consisting of a plurality of groups as shown in FIG. 9, it is determined whether or not it is the last imaging sequence in one group. You may do it.

[Step S58] The calibration scan setting unit 66 determines the signal collection area of the newly inserted calibration scan in the area calculated in Step S56. Thereafter, the process proceeds to step S59.
[Step S59] A calibration scan is performed on the signal acquisition region determined in Step S58. Thereafter, the process returns to step S51.

The determination algorithm of FIG. 10 can be applied to a desired execution plan including the execution plan of FIG. Therefore, the determination algorithm of FIG. 10 is merely an example, but is executed by the calibration scan setting unit 66 at the time when the execution plan is finalized or during the execution of the execution plan, for example.
[2] A correspondence relationship between the terms of the claims and the embodiment will be described. In addition, the correspondence shown below is one interpretation shown for reference, and does not limit the present invention.

  Each component in the gantry 30 and the whole of the control device 40 (see FIG. 1) are subjected to imaging of the subject P with application of a static magnetic field, a gradient magnetic field, and an RF pulse according to the imaging conditions of the main scan. The configuration for collecting MR signals from the imaging region including is an example of the main scan execution unit recited in the claims.

A configuration in which each component in the gantry 30 and the whole of the control device 40 collects MR signals with application of a gradient magnetic field and an RF pulse, and executes a calibration scan, includes a calibration scan execution unit according to claim. It is an example.
The set value of the center frequency of the RF pulse calculated from the execution result of the center frequency sequence that is one of the calibration scans is an example of the imaging condition of the main scan.

An offset magnetic field, which is calculated based on the execution result of the magnetic field measurement sequence that is one of the calibration scans and makes the static magnetic field uniform, is an example of imaging conditions for the main scan.
The sensitivity distribution map used in luminance correction is an example of the conditions for correction processing described in the claims.

  A function of the system control unit 61 that determines a part of imaging conditions (undefined) of the main scan and a condition of correction processing for the reconstructed image data based on the execution result of the calibration scan is as follows. It is an example of the condition determination part of description.

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

10: MRI apparatus,
20: Sleeper unit, 22: Top plate,
31: Static magnetic field magnet, 32: Shim coil unit, 33: Gradient magnetic field coil unit,
34: RF coil unit, 40: control device, 60: arithmetic device

Claims (6)

A main scan execution unit that transmits an RF pulse according to an imaging condition and executes a main scan for collecting a nuclear magnetic resonance signal from a subject in an imaging region, and the imaging based on the nuclear magnetic resonance signal collected in the main scan A magnetic resonance imaging apparatus comprising an image reconstruction unit that reconstructs image data of a region,
A plan storage unit for storing an execution plan of the main scan;
Collection region of the nuclear magnetic resonance signal in the calibration scan used for determining the imaging condition of the main scan or the condition of the correction process of the image data based on the condition of the main scan that is included in the execution plan but has not yet been executed A calibration scan setting unit for calculating
A calibration scan execution unit that executes the calibration scan according to the collection area calculated by the calibration scan setting unit;
A magnetic resonance imaging apparatus comprising: a condition determining unit that determines an imaging condition of the main scan or a condition of the correction process based on an execution result of the calibration scan. The magnetic resonance imaging apparatus according to claim 1.
The calibration scan setting unit calculates the collection region of the center frequency sequence for collecting the nuclear magnetic resonance signal used for calculating the center frequency of the RF pulse of the main scan,
The main scan execution unit executes the main scan while applying the RF pulse of the center frequency calculated based on the nuclear magnetic resonance signal collected in the center frequency sequence. Imaging device. The magnetic resonance imaging apparatus according to claim 1 or 2,
The calibration scan setting unit calculates the collection region of the magnetic field measurement sequence for measuring the magnetic field strength distribution in the imaging space where the subject is placed,
The calibration scan execution unit executes the magnetic field measurement sequence as the calibration scan,
The main scan execution unit executes the main scan while applying a static magnetic field corrected based on the magnetic field intensity distribution measured by the magnetic field measurement sequence to the imaging space. apparatus. The magnetic resonance imaging apparatus according to any one of claims 1 to 3,
An image processing unit for executing the correction process;
The calibration scan setting unit is attached to the subject and used to calculate a spatial sensitivity distribution map of a plurality of element coils in an RF coil device that detects the nuclear magnetic resonance signal in the main scan. Calculating the collection region of a sensitivity distribution map sequence for collecting magnetic resonance signals via the plurality of element coils;
The calibration scan execution unit executes the sensitivity distribution map sequence as the calibration scan,
The image processing unit executes, as the correction process, luminance correction corresponding to the sensitivity distribution map calculated based on the nuclear magnetic resonance signals collected in the sensitivity distribution map sequence with respect to the image data. A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to any one of claims 1 to 4,
A top plate moving mechanism for changing the imaging region by moving the top plate on which the subject is placed;
The magnetic resonance imaging apparatus, wherein the calibration scan setting unit calculates the collection region according to a position of the top board. The magnetic resonance imaging apparatus according to any one of claims 1 to 5,
The magnetic resonance imaging apparatus, wherein the calibration scan setting unit calculates the acquisition region according to a slice interval, the number of slices, a slice thickness, and a resolution in the unexecuted main scan.

Images