JP2021087669A - Magnetic resonance imaging device and method for setting collection angle in k-space trajectory - Google Patents

Abstract

To provide a magnetic resonance imaging device capable of improving efficiency in data collection in non-cartesian collection.SOLUTION: A magnetic resonance imaging device 1 includes a setting unit and an imaging control unit. The setting unit sets a collection angle of a k-space trajectory for non-cartesian collection. The setting unit arranges a sample point in a first variable space defined by a variable different from the collection angle, and sets the collection angle by mapping the sample point arranged in the first variable space to a second variable space defined by the collection angle according to a value of the collection angle. The imaging control unit implements the non-cartesian collection according to the k-space trajectory.SELECTED DRAWING: Figure 1

Description

An embodiment of the present invention relates to a magnetic resonance imaging apparatus and a method for setting a collection angle of a k-space locus.

As one of the non-Cartesian collections, a radial method is known in which data is collected along a radial k-space locus set in the k-space. As one of the methods for setting the collection angle of the k-space locus in the radial method, the golden angle radial method, which repeatedly sets the collection angle of the k-space locus at an angle interval of the golden ratio (about 111.25 degrees), is used. Are known. According to the golden angle radial method, it is possible to set k-space loci at substantially equal intervals in k-space. This assumes that the value of the k-space locus is equal regardless of the collection angle. The golden angle radial method is not always appropriate when considering the value of the collection angle.

U.S. Patent Application Publication No. 2015/185301 Japanese Unexamined Patent Publication No. 2014-210209 U.S. Patent Application Publication No. 2019/0079154 JP-A-2018-42671

The problem to be solved by the present invention is to improve the efficiency of data collection for non-Cartesian collection.

The magnetic resonance imaging apparatus according to the embodiment includes a setting unit and an imaging control unit. The setting unit sets the collection angle of the k-space trajectory for non-Cartesian collection. The setting unit arranges sample points in a first variable space defined by a variable different from the collection angle, and the sample points arranged in the first variable space are defined by the collection angle. The collection angle is set by mapping to the variable space of 2 according to the value of the collection angle. The imaging control unit executes the non-Cartesian collection according to the k-space trajectory.

FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus according to the present embodiment. FIG. 2 is a diagram showing a k-space locus relating to radial collection in the k-space according to the present embodiment. FIG. 3 is an enlarged view around the origin of the k-space. FIG. 4 is a diagram showing an example of a sparse and dense k-space distribution of k-space loci. FIG. 5 is a diagram showing another example of the sparse and dense k-space distribution of the k-space locus. FIG. 6 is a diagram showing another example of the sparse and dense k-space distribution of the k-space locus. FIG. 7 is a diagram showing a typical flow of MR inspection using the GMA method by a magnetic resonance imaging apparatus. FIG. 8 is a diagram showing an example of mapping a k-space locus from the virtual variable axis to the collection angle axis. FIG. 9 is a diagram showing an example of a collection angle setting screen. FIG. 10 is a diagram showing a k-space locus and an imaging range related to radial collection in k-space. FIG. 11 is a diagram showing an example of a sparse and dense k-space distribution of k-space loci. FIG. 12 is a diagram showing a flow of MR inspection using the GMA method according to Application Example 1. FIG. 13 is a diagram showing a flow of MR inspection using the GMA method according to Application Example 2. FIG. 14 is a diagram showing an example of a GUI screen for adjusting the imaging range. FIG. 15 is a diagram showing a k-space locus and an imaging range related to radial collection in the k-space according to the modified example.

Hereinafter, the magnetic resonance imaging apparatus and the method for setting the collection angle of the k-space locus according to the present embodiment will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging device 1 according to the present embodiment. As shown in FIG. 1, the magnetic resonance imaging device 1 includes a gantry 11, a sleeper 13, a gradient magnetic field power supply 21, a transmission circuit 23, a reception circuit 25, a sleeper drive device 27, a sequence control circuit 29, and a host computer (Host Computer) 50. Has.

The gantry 11 has a static magnetic field magnet 41 and a gradient magnetic field coil 43. The static magnetic field magnet 41 and the gradient magnetic field coil 43 are housed in the housing of the gantry 11. A hollow bore is formed in the housing of the gantry 11. A transmission coil 45 and a reception coil 47 are arranged in the bore of the gantry 11.

The static magnetic field magnet 41 has a hollow substantially cylindrical shape, and generates a static magnetic field inside the substantially cylindrical shape. As the static magnetic field magnet 41, for example, a permanent magnet, a superconducting magnet, a normal conducting magnet, or the like is used. Here, the central axis of the static magnetic field magnet 41 is defined as the Z-axis, the axis perpendicular to the Z-axis is defined as the Y-axis, and the axis horizontally orthogonal to the Z-axis is defined as the X-axis. The X-axis, Y-axis and Z-axis form a Cartesian three-dimensional coordinate system.

The gradient magnetic field coil 43 is a coil unit attached to the inside of the static magnetic field magnet 41 and formed in a hollow substantially cylindrical shape. The gradient magnetic field coil 43 generates a gradient magnetic field by receiving a current supply from the gradient magnetic field power supply 21. More specifically, the gradient magnetic field coil 43 has three coils corresponding to the X-axis, Y-axis, and Z-axis that are orthogonal to each other. The three coils form a gradient magnetic field in which the magnetic field strength changes along each of the X-axis, Y-axis, and Z-axis. The gradient magnetic fields along the X-axis, Y-axis, and Z-axis are combined to form slice-selective gradient magnetic fields Gs, phase-encoded gradient magnetic fields Gp, and frequency-encoded gradient magnetic fields Gr that are orthogonal to each other in desired directions. The slice selection gradient magnetic field Gs is arbitrarily used to determine the imaging cross section (slice). The phase-encoded gradient magnetic field Gp is used to change the phase of a magnetic resonance signal (hereinafter referred to as an MR signal) according to a spatial position. The frequency-encoded gradient magnetic field Gr is used to change the frequency of the MR signal depending on the spatial position. In the following description, it is assumed that the inclination direction of the slice selection gradient magnetic field Gs is the Z axis, the inclination direction of the phase-encoded gradient magnetic field Gp is the Y-axis, and the inclination direction of the frequency-encoded gradient magnetic field Gr is the X-axis.

The gradient magnetic field power supply 21 supplies a current to the gradient magnetic field coil 43 according to the sequence control signal from the sequence control circuit 29. The gradient magnetic field power supply 21 supplies a current to the gradient magnetic field coil 43 to generate a gradient magnetic field along each of the X-axis, Y-axis, and Z-axis by the gradient magnetic field coil 43. The gradient magnetic field is superimposed on the static magnetic field formed by the static magnetic field magnet 41 and applied to the subject P.

The transmission coil 45 is arranged inside the gradient magnetic field coil 43, for example, and receives a current supply from the transmission circuit 23 to generate a high frequency pulse (hereinafter referred to as an RF pulse).

The transmission circuit 23 supplies a current to the transmission coil 45 in order to apply an RF pulse for exciting the target proton existing in the subject P to the subject P via the transmission coil 45. The RF pulse vibrates at a resonance frequency specific to the target proton to excite the target proton. An MR signal is generated from the excited target proton and detected by the receiving coil 47. The transmission coil 45 is, for example, a whole body coil (WB coil). The whole body coil may be used as a transmission / reception coil.

The receiving coil 47 receives the MR signal emitted from the target proton existing in the subject P under the action of the RF magnetic field pulse. The receiving coil 47 has a plurality of receiving coil elements capable of receiving MR signals. The received MR signal is supplied to the receiving circuit 25 via wire or wireless. Although not shown in FIG. 1, the receiving coil 47 has a plurality of receiving channels mounted in parallel. The receiving channel includes a receiving coil element that receives the MR signal, an amplifier that amplifies the MR signal, and the like. The MR signal is output for each reception channel. The total number of receiving channels and the total number of receiving coil elements may be the same, and the total number of receiving channels may be larger or smaller than the total number of receiving coil elements.

The receiving circuit 25 receives the MR signal generated from the excited target proton via the receiving coil 47. The receiving circuit 25 processes the received MR signal to generate a digital MR signal. The digital MR signal can be represented in the k-space defined by the spatial frequency. Therefore, hereinafter, the digital MR signal will be referred to as k-space data. The k-space data is a kind of raw data used for image reconstruction. The k-space data is supplied to the host computer 50 via wire or wireless.

The transmission coil 45 and the reception coil 47 are merely examples. Instead of the transmitting coil 45 and the receiving coil 47, a transmitting / receiving coil having a transmitting function and a receiving function may be used. Further, the transmission coil 45, the reception coil 47, and the transmission / reception coil may be combined.

A sleeper 13 is installed adjacent to the gantry 11. The sleeper 13 has a top plate 131 and a base 133. The subject P is placed on the top plate 131. The base 133 slidably supports the top plate 131 along each of the X-axis, Y-axis, and Z-axis. The sleeper drive device 27 is housed in the base 133. The sleeper drive device 27 moves the top plate 131 under the control of the sequence control circuit 29. The sleeper drive device 27 may include, for example, any motor such as a servo motor or a stepping motor.

The sequence control circuit 29 has a processor of a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory) as hardware resources. The sequence control circuit 29 synchronously controls the gradient magnetic field power supply 21, the transmission circuit 23, and the reception circuit 25 based on the imaging conditions set by the imaging condition setting function 512 of the processing circuit 51, and the pulse corresponding to the imaging conditions. MR imaging is performed on the subject P according to the sequence, and k-space data regarding the subject P is collected. The sequence control circuit 29 is an example of an image pickup control unit.

The sequence control circuit 29 according to the present embodiment executes non-Cartesian collection as a k-space filling method. Non-Cartesian collection is a k-space scanning method different from Cartesian collection, for example, two-dimensional or three-dimensional radial collection, spiral collection, or PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) collection. The k-space locus for non-Cartesian collection is characterized by the angle of the k-space locus in k-space (hereinafter referred to as the collection angle). For example, the k-space locus of radial collection, also called spokes, radiates through the origin of k-space. The collection angle of the k-space locus of radial collection is set to the angle around the k-space origin.

As shown in FIG. 1, the host computer 50 is a computer having a processing circuit 51, a memory 52, a display 53, an input interface 54, and a communication interface 55. The processing circuit 51 is an example of a processing unit, the memory 52 is an example of a storage unit, the display 53 is an example of a display unit, the input interface 54 is an example of an input unit, and the communication interface 55 is an example of a communication unit. Is.

The processing circuit 51 has a processor such as a CPU as a hardware resource. The processing circuit 51 functions as the center of the magnetic resonance imaging device 1. For example, the processing circuit 51 has an acquisition function 511, an imaging condition setting function 512, a reconstruction function 513, an image processing function 514, and a display control function 515 by executing various programs. The acquisition function 511 is an example of an acquisition unit, the imaging condition setting function 512 is an example of a setting unit, an adjustment unit, and a determination unit, the reconstruction function 513 is an example of a reconstruction unit, and the image processing function 514 is an image processing unit. The display control function 515 is an example of a display unit.

In the acquisition function 511, the processing circuit 51 acquires various data. For example, the processing circuit 51 acquires k-space data related to non-Cartesian collection collected by the sequence control circuit 29. The processing circuit 51 may directly acquire the k-space data from the sequence control circuit 29 or the receiving circuit 25, or may temporarily store the k-space data in the memory 52 and acquire the k-space data from the memory 52.

In the imaging condition setting function 512, the processing circuit 51 automatically or manually sets the imaging conditions. For example, the processing circuit 51 sets the collection angle of the k-space trajectory for non-Cartesian collection as one of the imaging conditions. Further, the processing circuit 51 may set or adjust an imaging range (FOV: Field Of View) as one of the imaging conditions. Further, the processing circuit 51 may determine the imaging time based on the shape of the imaging range. In addition to these imaging conditions, the processing circuit 51 can set any imaging conditions such as echo time TE and repetition time TR.

In the reconstruction function 513, the processing circuit 51 reconstructs the MR image relating to the subject P based on the k-space data acquired by the acquisition function 511. For example, the processing circuit 51 applies a Fourier transform or an inverse Fourier transform to the k-space data to generate an MR image. The reconstruction method is not limited to the Fourier transform or the inverse Fourier transform, and parallel imaging, compressed sensing, a machine learning model, or the like may be used.

In the image processing function 514, the processing circuit 51 performs various image processing on the MR image. For example, the processing circuit 51 performs image processing such as volume rendering, surface rendering, pixel value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing. Further, the processing circuit 51 can also perform various processes such as area extraction, image recognition, image analysis, and alignment as image processing.

In the display control function 515, the processing circuit 51 displays various information on the display 53. For example, the processing circuit 51 displays the MR image generated by the reconstruction function 513, the MR image generated by the image processing function 514, the collection angle setting screen, and the like on the display 53. The processing circuit 51 may appropriately perform display processing such as gradation processing, enlargement / reduction processing, and annotation processing on the MR image.

The memory 52 is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. Further, the memory 52 may be a drive device or the like that reads and writes various information to and from a portable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory. For example, the memory 52 stores imaging conditions, k-space data, MR images, control programs, and the like.

The display 53 displays various information by the display control function 515. For example, the display 53 displays an MR image generated by the reconstruction function 513, an MR image generated by the image processing function 514, a collection angle setting screen, and the like. As the display 53, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the art can be appropriately used.

The input interface 54 includes an input device that receives various commands from the user. As input devices, keyboards, mice, various switches, touch screens, touch pads, etc. can be used. The input device is not limited to one provided with physical operation parts such as a mouse and a keyboard. For example, an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the magnetic resonance imaging device 1 and outputs the received electric signal to various circuits is also input. It is included in the example of the interface 54. Further, the input interface 54 may be a voice recognition device that converts a voice signal collected by the microphone into an instruction signal.

The communication interface 55 connects the magnetic resonance imaging device 1 with a workstation, PACS (Picture Archiving and Communication System), HIS (Hospital Information System), RIS (Radiology Information System), etc. via a LAN (Local Area Network) or the like. It is an interface to connect. The network IF sends and receives various information to and from the workstation, PACS, HIS, and RIS to which it is connected.

The above configuration is an example and is not limited to this. For example, the sequence control circuit 29 may be incorporated in the host computer 50. Further, the sequence control circuit 29 and the processing circuit 51 may be mounted on the same board. Further, the imaging condition setting function 512 does not necessarily have to be mounted in the processing circuit 51 of the magnetic resonance imaging apparatus 1. For example, the imaging condition setting function 512 may be mounted on a computer for setting imaging conditions, which is separate from the magnetic resonance imaging device 1. In this case, the imaging conditions generated by the computer are supplied to the magnetic resonance imaging apparatus 1 via a network, a portable recording medium, or the like. Further, the storage area of the imaging condition in the memory 52 does not need to be mounted on the magnetic resonance imaging device 1, and may be mounted on a storage device connected to the magnetic resonance imaging device 1 via a network, for example. Good.

The processing circuit 51 according to the present embodiment sets the collection angle of the k-space locus related to the non-Cartesian collection by a method different from the golden angle radial method by the imaging condition setting function 512. More specifically, the processing circuit 51 first arranges the sample points in a first variable space defined by a variable different from the collection angle. Next, the processing circuit 51 sets the collection angle by mapping the sample points arranged in the first variable space to the second variable space defined by the collection angle according to the value of the collection angle. .. Hereinafter, the method of setting the collection angle according to the present embodiment will be referred to as a GMA (Golden Mapped Angle) method.

The GMA method focuses on the fact that the value of the collection angle of each k-space locus (hereinafter, simply referred to as the value) is not constant. Value means the usefulness of the collection angle, and more specifically, the contribution to the image quality of the reconstructed image. The density of the k-space locus is set higher in the collection angle range having a relatively high value, and the density of the k-space locus is set to be lower in the collection angle range having a relatively low value.

The value will be described in more detail below. In addition, in order to give a concrete explanation, two-dimensional radial collection will be described as an example of non-Cartesian collection.

FIG. 2 is a diagram showing a k-space locus KT set in the k-space 60 for radial collection. The k-space 60 is a space stretched by the spatial frequency ky and the spatial frequency kx. The size in the ky direction and the size in the kx direction of the k-space 60 are set to be the same. In the k-space 60, a circle 61 indicating the outer circumference of the scan range of the k-space locus KT is set. Further, a plurality of lattice points (also referred to as Cartesian lattice points) 62 defined by the Cartesian coordinate system are set in the k-space 60. For example, the center of the circle 61 is set to coincide with the origin 621 of the Cartesian coordinate system. In the k-space locus KT, the start point is set to one point on the circle 61, the end point is set to one point on the opposite side of the origin 621 from the start point, and the end point is set as a straight line passing through the origin 621. The angle around the origin 621 of the k-space locus KT is defined as the collection angle. A plurality of k-space loci KT for a plurality of different collection angles are set in the k-space 60. The collection angle of the k-space locus extending in the + kx direction is specified as 0 degrees, the collection angle of the k-space locus extending in the + ky direction is specified as 90 degrees, and the collection angle of the k-space locus extending in the -kx direction is specified as 180 degrees. Will be done. In the radial collection, the grid points 62 outside the circle 61 are ignored. Although four k-space locus KTs are set in FIG. 2, the number of k-space locus KTs set is not particularly limited.

An imaging range (FOV) indicating a range of k-space data used for the reconstructed image is set in the k-space 60. In this embodiment, it is assumed that the imaging range is set in the entire k-space 60. The circle 61 is set to be inscribed in the imaging range. In this case, the shape of the circle 61 is a perfect circle.

The k-space data of each k-space locus KT obtained by the radial collection is arranged in the Cartesian coordinate space shown in FIG. 2 through, for example, a pre-processing unit of grid processing. The pre-processing unit of the grid processing obtains the data values of the grid points 62 based on the k-space data of the plurality of k-space loci KT. The MR image represented by the Cartesian coordinate system is reconstructed by performing Fourier transform or inverse Fourier transform on the k-space data arranged in the Cartesian coordinate space and performing post-processing of grid processing on the obtained data. Will be done. That is, if there is a resolution equivalent to the grid points 62 of the Cartesian coordinate system, the number or density of k-space loci is sufficient.

FIG. 3 is an enlarged view around the origin 621 in the k-space. As shown in FIG. 3, each k-space locus KT passes through a plurality of grid points 62. The distance between two adjacent grid points 62 through which the k-space locus KT passes differs depending on the collection angle of the k-space locus KT. For example, when the distance between two adjacent grid points 62 through which the k-space locus KT (0 degree) of the collection angle "0 degree" passes is "1", the k-space locus KT (0 degree) of the collection angle "45 degrees" ( The distance between two adjacent grid points 62 through which 45 degrees) passes is “√2”. Since the k-space locus KT (0 degrees) and the KT (45 degrees) have the same length, the number of lattice points 62 that the k-space locus KT (0 degrees) passes through is the number of lattice points 62 that the k-space locus KT (45 degrees) passes through. This is more than the number of grid points 62. Therefore, in order to obtain the resolution corresponding to the grid points 62, it is not always necessary to set the k-space locus KT so that the collection angles are uniform. In this case, it can be said that the value of the collection angle is higher as the distance between the Cartesian lattice points through which the k-space locus passes is narrower.

FIG. 4 is a diagram showing an example of a sparse and dense k-space distribution of k-space loci. As shown in FIG. 4, the collection angle in which the distance between the Cartesian lattice points through which the k-space locus passes is short is high in value, and the k-space locus is densely set. For a collection angle with a long distance between the Cartesian lattice points through which the k-space locus passes, the value is low and the k-space locus is set sparsely. In the collection angle range where the k-space locus is densely set, the angular interval between adjacent k-space loci is set relatively narrow, and in the collection angle range where the k-space locus is sparsely set, the adjacent k-space is set. The angular spacing between the trajectories is set relatively wide. For example, the collection angle interval in the collection angle range near the collection angle "45 degrees" is set wider than the collection angle interval in the collection angle range near the collection angles "0 degrees" and "90 degrees".

In this way, data can be efficiently collected by arranging the k-space loci densely in the range where the value of the collection angle is high and sparsely arranging the k-space loci in the range where the value of the collection angle is low.

The collection angle interval corresponding to "dense" and the collection angle interval corresponding to "sparse" can be set to arbitrary values. The collection angle interval may be set in two stages of "dense" and "sparse", may be set in a plurality of stages of three or more, or may be set as a continuous value from the lower limit value to the upper limit value. You may. The lower limit value and the upper limit value can be set arbitrarily.

The value is not limited to being set based on the number of Cartesian lattice points through which the k-space locus passes, and can be set from various viewpoints (hereinafter referred to as value viewpoints). For example, an MR image may be generated based on the k-space data collected by the target imaging and the k-space data collected by the past imaging. In this case, the value may be set based on, for example, the proximity between the k-space locus of the imaging target (hereinafter referred to as the target imaging) for which the k-space locus is set and the collection angle of the k-space locus of the past imaging. .. The value perspective means how to define the value of the collection angle.

FIG. 5 is a diagram showing another example of the sparse and dense k-space distribution of the k-space locus. As shown in FIG. 5, the collection angle close to the k-space locus KTP of the past imaging has a low value, and the k-space locus of the target imaging is set sparsely. The collection angle far from the k-space locus KTP has high value, and the k-space locus of the target image is densely set.

The k-space locus of the past imaging may be several frames before the k-space locus of the target imaging. In addition, when setting the value of the collection angle of the target image, any number of k-space loci of the past image may be considered. For example, in FIG. 5, for the sake of simplicity, the value of the collection angle of the target imaging for one k-space locus of the past imaging is shown, but the same algorithm is used for two or more k-space trajectories of the past imaging. The value of the acquisition angle of the subject image may be set.

As described above, in FIG. 5, the value is set based on the locational proximity to the collection angle of the k-space locus of the past imaging. However, the value may be set based on the temporal proximity to the collection angle of the k-space trajectory of the past imaging.

FIG. 6 is a diagram showing another example of the sparse and dense k-space distribution of the k-space locus. In FIG. 6, the frame of the target imaging is expressed as “t”, and the frame of the past imaging before n (integer) frames with respect to “t” is expressed as “tn”. In FIG. 6, when setting the value of the collection angle of the target imaging, the k-space locus KT (t-1) of the past imaging 1 frame before the target imaging frame t and the k-space locus KT (t-1) of the past imaging 5 frames before. t-5) shall be taken into consideration.

As shown in FIG. 6, the collection angle range around the k-space locus KT (t-5) five frames before is compared with the collection angle range around the k-space locus KT (t-1) one frame before. The value is high, and the k-space trajectory of the target image is densely set. In this way, the closer the collection angle of the target image is to the k-space locus KT (tn) of the past image, which is separated in time, the higher the value is set, and the k-space locus becomes higher. Densely set. The value is set lower as the collection time of the k-space locus of the target image is farther from the collection time of the k-space locus KT (tn) of the past imaging.

The frame for past imaging may be any number of frames before the frame for target imaging. In addition, when setting the value of the collection angle of the target image, any number of k-space loci of the past image may be considered. For example, in FIG. 6, for the sake of simplicity, collection of object images for one k-space locus KT (t-1) one frame before and one k-space locus KT (t-5) five frames before. Although the value of the angle is shown, the k-space locus 2 to 4 frames before may be considered, or the k-space locus 6 or more frames before may be considered by the same algorithm.

Next, the flow of the MR inspection using the GMA method by the magnetic resonance imaging apparatus 1 according to the present embodiment will be described.

FIG. 7 is a diagram showing a typical flow of MR inspection using the GMA method by the magnetic resonance imaging apparatus 1. In FIG. 7, it is assumed that the k-space filling method is the radial method.

As shown in FIG. 7, first, the processing circuit 51 sets the collection angle of the k-space locus related to the radial collection by using the GMA method by realizing the imaging condition setting function 512 (steps SA1-SA3). Specifically, the processing circuit 51 sets the sample point in the first variable space (step SA1), maps the sample point to the second variable space (step SA2), and samples in the second variable space. The position of the point is set to the collection angle (step SA3).

The first variable space is a space defined by a virtual variable (hereinafter, referred to as a virtual variable) different from the collection angle. The second variable space is a space defined by the collection angle. The number of dimensions of the second variable space is one-dimensional in the case of the two-dimensional radial method and two-dimensional in the case of the three-dimensional radial method. The number of dimensions of the first variable space may be the same as or different from the number of dimensions of the second variable space. That is, the number of dimensions of the first variable space is, for example, 1 in the case of the two-dimensional radial method and 1 or 2 in the case of the three-dimensional radial method.

Hereinafter, steps SA1-SA3 will be described with reference to FIG. 8 by taking a two-dimensional radial method as an example. In this case, the first variable space is an axis defined by a one-dimensional virtual variable, and is referred to as a virtual variable axis. The second variable space is an axis defined by a one-dimensional collection angle, and will be referred to as a collection angle axis.

FIG. 8 is a diagram showing an example of mapping a sample point from the virtual variable axis 71 to the collection angle axis 72. The virtual variable axis 71 has a predetermined numerical range (length). The numerical range can be set to any value, but is set to a range from the lower limit "0" to the upper limit "1" as shown in FIG. 8, for example. The position on the virtual variable axis 71 represents a virtual variable. The collection angle axis 72 has a predetermined angle range. The angle range can be set to any value, but for example, as shown in FIG. 8, it is set to a range from the lower limit “0 degree” to the upper limit “180 degree”. The position on the collection angle axis 72 represents the collection angle. The virtual variable "0" corresponds to the collection angle "0 degrees".

As shown in FIG. 8, the processing circuit 51 arranges n sample points KT1k (1 ≦ k ≦ n) on the virtual variable axis 71 at the first distance interval D1k, and collects n sample points KT1k at a collection angle. By mapping to the axis 72, the positions of the n sample points KT2k arranged on the collection angle axis 72 are set to the collection angle by arranging them at the second distance interval D2k according to the value. Specifically, first, the numerical range of the virtual variable axis 71 and the distance interval D1k between two adjacent sample points KT1k on the virtual variable axis 71 are set. Each distance interval D1k is set, for example, at equal intervals. Next, the sample point KT1k is arranged as a point sequence on the virtual variable axis 71 according to the numerical range of the virtual variable axis 71 and the distance interval D1k. Each sample point KT1k is a symbol indicating the position of one k-space locus. Each sample point KT1k is mapped to the collection angle axis 72. By mapping, each sample point KT1k on the virtual variable axis 71 is converted into each sample point KT2k on the collection angle axis 72. The position of each sample point KT2k on the collection angle axis 72 is specified, and the specified position is set as the collection angle. As a result, the collection angle set is set. By mapping, for example, a set of n sample points KT1k arranged at equidistant D1k is transformed into a set of n collection angles KT2k arranged at non-equidistant D2k according to the value of the collection angle. It becomes. For example, the interval D21 is narrower than the interval D22, which means that the collection angle corresponding to the interval D21 is of high value.

Here, when the virtual variable is expressed by x and the collection angle is expressed by θ, the mapping from the virtual variable x to the collection angle θ is expressed as a function θ = f (x). The gradient df / dx of the mapping function f represents the value of the collection angle, in other words, the weight of the collection angle. When the distance interval D2 of the k-space locus KT2 on the collection angle axis 72 is uniform, the gradient df / dx corresponds to a constant that does not depend on x.

The mapping function f can be designed according to the above value viewpoints and parameters. As mentioned above, the value viewpoint is 1. The number of Cartesian lattice points that the k-space locus passes through, 2. 2. Locational proximity to the k-space trajectory of past imaging. It is roughly classified into three types: temporal proximity to the k-space trajectory of past imaging. In other words, the value viewpoint is one factor that determines the type of the mapping function f. The parameters are the gradient df / dx of the mapping function f, the bias, and the like.

In the case of the value viewpoint 1, the narrower the distance between the Cartesian lattice points through which the k-space locus passes, the higher the value of the collection angle of the k-space locus. In the case of the value viewpoint 1, the gradient df / dx is set so as to be larger as the number of collection angles through which the k-space locus passes is larger and smaller as the number of collection angles is smaller. Specifically, the gradient df / dx may be set to a value corresponding to the distance interval of the grid points. For example, the gradient df / dx is set in the range 1 / √2 to 1. At this time, the gradient df / dx is set to the minimum value = 1 / √2 for the collection angles θ = 45 degrees and 135 degrees, and the gradient df / dx is the maximum for the collection angles θ = 0 degrees, 90 degrees and 180 degrees. The value is set to 1.

In the case of the value viewpoint 2, the farther the collection angle of the k-space locus of the target imaging is from the collection angle of the other k-space loci of the past imaging, the higher the value of the collection angle of the k-space trajectory of the target imaging. In the case of the value viewpoint 2, the gradient df / dx is set so as to be larger as the collection angle is closer to the k-space trajectory of the past image and smaller as the collection angle is farther. Specifically, the gradient df / dx is set in the range from 1/2 to 1.

In the case of the value viewpoint 3, the closer the collection time of the k-space locus of the target image is to the collection time of the other k-space loci of the past imaging, the higher the value of the collection angle of the k-space trajectory of the target image. In the case of the value viewpoint 3, the gradient df / dx is set so as to be larger as the collection angle is closer in time to the k-space trajectory of the past image capture, and smaller as the collection angle is farther away. Specifically, the gradient df / dx is set in the range from 1/2 to 1.

For example, a method of deriving the mapping function f from the value viewpoint 1 will be briefly described. First, a circle set in k-space and a line passing through a Cartesian lattice point and parallel to the ky axis and the kx axis (hereinafter referred to as a lattice line) are set. Next, the angle at which the circle intersects each grid line is calculated, and the allowable sampling density at each grid point is determined based on the calculated angle. Then, the mapping function f can be obtained by interpolating the sampling density at each lattice point. The interpolation may be performed by, for example, a spline function, but is not limited to this, and may be interpolated by any linear function, quadratic function, or higher-order function.

The method for deriving the mapping function f is not limited to the above method. For example, the mapping function g from the collection angle θ to the virtual variable x may be determined, and the mapping function f may be calculated as an inverse function of the mapping function g. The mapping function g may be determined by any method. Further, the mapping function f may be a neural network trained to input a plurality of virtual variables and output a plurality of collection angles.

In the above explanation, the value viewpoint 1, the value viewpoint 2 and the value viewpoint 3 are explained independently, but the value viewpoint 1, the value viewpoint 2 and the value viewpoint 3 are not exclusive to each other and are compatible with each other. That is, two or all of the value viewpoint 1, the value viewpoint 2, and the value viewpoint 3 may be combined.

In the above description, the mapping has been described by taking two-dimensional radial collection as an example, but it can be extended to three-dimensional radial collection. Stack of Stars collection and Cushball collection are available as 3D radial collections. The stack of stars collection can use the method described as an example of two-dimensional radial collection. In the case of cush ball collection, the collection angle is defined by the combination of the first declination and the second declination. Therefore, the collection angle axis has a first collection angle axis with respect to the first declination and a second collection angle axis with respect to the second declination. Correspondingly, the virtual variable axis has a first virtual variable axis for the first virtual variable x1 corresponding to the first declination and a second virtual variable axis for the second virtual variable x2 corresponding to the second declination. It has a virtual variable axis. For example, in the case of the first declination "45 degrees" and the second declination "45 degrees", the distance interval between the Cartesian lattice points is the longest, the first declination "0 degrees" and the second declination. When the angle is "0 degree", the distance between the Cartesian lattice points is the shortest. Therefore, the gradient df / dx1 and the gradient df / dx2 may be set in the range of 1 / √3 to 1.

In the above description, the mapping has been described by taking radial collection as an example, but it can also be applied to two-dimensional spiral collection and three-dimensional spiral collection. As the three-dimensional spiral collection, cone collection using a cone-shaped k-space locus or the like is also possible. It can also be applied to two-dimensional PROPELLER collection and three-dimensional Stack-of-PROPELLERs collection.

The arrangement of the k-space locus KT1n on the virtual variable axis 71 is performed, for example, via a GUI (Graphical User Interface) screen (hereinafter, referred to as a setting screen) for setting the collection angle. The processing circuit 51 arranges the k-space locus KT1n on the virtual variable axis 71 according to the user's instruction via the setting screen.

FIG. 9 is a diagram showing an example of the collection angle setting screen I1. As shown in FIG. 9, the setting screen I1 has a display field I11, an evenly spaced button I12, a non-equidistantly spaced button I13, a GUI graphic element I14, and a GUI graphic element I16. In the display column I11, the number of k-space loci to be collected in the target imaging is displayed. The equidistant button I12 is a GUI button for arranging k-space loci at equal intervals on the virtual variable axis. The non-equidistant button I13 is a GUI button for arranging k-space loci at non-equal intervals on the virtual variable axis. The GUI graphic element I14 is a graphic element that imitates a virtual variable axis which is a first variable space. The graphic element I15 corresponding to the sample point before mapping is superimposed on the GUI graphic element I14. The GUI graphic element I16 is a graphic element that imitates the collection angle axis, which is a second variable space. The graphic element I17 corresponding to the sample point after mapping is superimposed on the GUI graphic element I16. Hereinafter, the GUI graphic element I14 is simply referred to as a virtual variable axis I14 because it is synonymous with the virtual variable axis, and the graphic element I15 is simply referred to as a sample point I15 because it is synonymous with the sample point before mapping. Since the element I16 is synonymous with the collection angle axis, it is simply called the collection angle axis I16, and the graphic element I17 is simply called the sample point I17 because it is synonymous with the sample point after mapping.

For example, the user sets the distance interval of the sample point I15 on the virtual variable axis I14, the type of mapping, and the parameters of mapping via the input interface 54. The distance interval of the sample point I15 is specified, for example, by a numerical value via the input interface 54. The length of the virtual variable axis I14 is set by selecting a mapping type and mapping parameters via the input interface 54. Then, when the equidistant button I12 is pressed, the processing circuit 51 arranges a plurality of sample points I15 on the virtual variable axis I14 according to the set distance interval, the type of mapping, and the parameters of the mapping. The number of sample points I15 arranged on the virtual variable axis I14 is displayed in the display column I11 as the number of k-space loci.

Further, a numerical value corresponding to the number may be input to the display field I11 via the input interface. When the number is input to the display field I11 and the equidistant button I12 is pressed, the processing circuit 51 arranges the input number of sample points I15 on the virtual variable axis I14 at equal intervals.

When the unequal interval button I13 is pressed, the processing circuit 51 arranges the sample points I15 on the virtual variable axis I14 at unequal intervals. For example, the processing circuit 51 arranges the sample point I15 at the position of the virtual variable axis I14 designated by the user via the input interface 54. Thereby, the sample point I15 can be arranged on the virtual variable axis I14 at the discretion of the user. Further, when the non-equidistant button I13 is pressed, the processing circuit 51 arranges the number of sample points I15 on the virtual variable axis I14 at non-equal intervals according to a predetermined rule. As a predetermined rule, for example, a method using bit reverse or a random number may be used.

When a plurality of sample points I15 are arranged on the virtual variable axis I14, the processing circuit 51 maps the arranged sample points I15 to the collection angle axis I16. Specifically, the processing circuit 51 specifies a virtual variable corresponding to the position of each sample point I15 on the virtual variable axis I14, and applies a mapping function to the specified virtual variable to calculate the collection angle. The mapping function is preset for each value viewpoint. The user specifies a desired value viewpoint from among a plurality of value viewpoints, for example, via the input interface 54. The processing circuit 51 performs mapping based on a mapping function corresponding to the designated value viewpoint. The processing circuit 51 arranges the sample point I17 after mapping at a position on the collection angle axis I16 corresponding to the calculated collection angle. The processing circuit 51 sets the position of the sample point I17 on the collection angle axis I16 as the collection angle. Typically, the position adjustment of the k-space locus I17 via the input interface 54 is limited.

When step SA3 is performed, the sequence control circuit 29 executes radial collection along the k-space locus of the collection angle set in step SA3 (step SA4).

When step SA4 is performed, the processing circuit 51 executes image reconstruction by executing the reconstruction function 513 (step SA5). In step SA5, the processing circuit 51 reconstructs an MR image of the subject P based on the k-space data collected in step SA4. The reconstructed MR image is displayed on the display 53 by realizing the display control function 515 by the processing circuit 51.

As a result, the MR inspection using the GMA method shown in FIG. 7 is completed.

As described above, the magnetic resonance imaging apparatus 1 according to the present embodiment includes a processing circuit 51 and a sequence control circuit 29. The processing circuit 51 sets the collection angle of the k-space locus for non-Cartesian collection. The processing circuit 51 arranges the sample points in the first variable space defined by the variable different from the collection angle, and the sample points arranged in the first variable space are the second sample points defined by the collection angle. The collection angle is set in the variable space by mapping according to the value of the collection angle. The sequence control circuit 29 executes non-Cartesian collection according to the k-space trajectory of the set collection angle.

According to the above configuration, the processing circuit 51 can set the collection angle of the k-space locus in consideration of the value of the collection angle. When the value of the collection angle is taken into consideration, it is possible to efficiently collect data having a resolution of the Cartesian lattice point or so with a smaller number of k-space loci as compared with the case where the value is not taken into consideration. In other words, when comparing the image quality of reconstructed images based on the same number of k-space trajectories, the collection angle with higher value is denser when the value of the collection angle is considered than when it is not considered. Image quality is improved because data can be collected.

Further, according to the above configuration, the processing circuit 51 does not directly set the k-space locus in consideration of the value of the collection angle in the second variable space. The processing circuit 51 first sets a sample point in the first variable space, and arranges the sample point in the second variable space by a mapping that reflects the value in the second variable space. The first variable space is defined by a virtual variable for setting the collection angle and does not reflect the value of the collection angle. Arranging the sample points at equal intervals in the first variable space means that the sample points are evenly spaced in the physical sense, the resolution sense, and the efficiency sense. The user may place the sample points in the first variable space in consideration of these meanings, and does not need to consider the value meanings. Therefore, according to the above configuration, it is possible to easily set a collection angle with good data collection efficiency.

(Application example 1)
In the above description, it is assumed that the imaging range is set in the entire k-space. However, this embodiment is not limited to this. The processing circuit 51 according to Application Example 1 sets an arbitrary imaging range in the k-space, and sets the collection angle of the k-space locus according to the shape of the imaging range. Hereinafter, the magnetic resonance imaging apparatus and the method for setting the collection angle of the k-space locus according to Application Example 1 will be described. In the following description, components having substantially the same functions as those of the present embodiment are designated by the same reference numerals and will be described in duplicate only when necessary.

FIG. 10 is a diagram showing a k-space locus and an imaging range related to radial collection set in the k-space. As shown in FIG. 10, an imaging range 65 is set in the k-space 60. The imaging range 65 indicates the output image range of the reconstructed image, and is also referred to as FOV (Field Of View). The size of the imaging range 65 corresponds to the size of the reconstructed image and is also referred to as the matrix size.

In Application Example 1, it is assumed that the size of the imaging range 65 in the ky direction is set shorter than the size of the k-space 60. In this case, the imaging range 65 has a horizontally long rectangular shape. When setting the k-space locus, the k-space locus KT is set so as to pass from one end of the circle 61 to another point through the origin, as in the above embodiment. That is, the k-space locus is set so that a part of the image extends beyond the imaging range 65. Radial collection is performed along the set k-space trajectory, and k-space data is collected. Of the collected k-space data, the portion outside the imaging range 65 may be discarded. In order to obtain an image, image reconstruction is performed on the collected k-space data.

FIG. 11 is a diagram showing an example of a sparse and dense k-space distribution of k-space loci. As shown in FIG. 11, when the imaging range 65 is shortened with respect to the spatial frequency ky direction, the imaging range 65 is rectangular. The flatter the imaging range 65, the more the value of the collection angle around the collection angles "0 degrees", "90 degrees" and "180 degrees" and the value of the collection angles around the collection angles "45 degrees" and "135 degrees". It will deviate from the value. The collection angle at which the k-space locus extends beyond the imaging range 65 is of low value, and the k-space locus is sparsely set. The collection angle at which the k-space locus falls within the imaging range 65 is of high value, and the k-space locus is densely set. From another point of view, a collection angle in which the number of grid points through which the k-space locus passes within the imaging range 65 is small has a low value, and the k-space locus is set sparsely. A collection angle having a large number of grid points through which the k-space locus passes within the imaging range 65 has a high value, and the k-space locus is densely set.

When the imaging range is set in the entire k-space, that is, when the imaging range is isotropic, all k-space loci fall within the imaging range. In this case, from the viewpoint of value according to Application Example 1, the value is uniform regardless of the collection angle. In this case, the value of the collection angle may be set according to one or more of the value viewpoints 1, the value viewpoint 2 and the value viewpoint 3 described above.

FIG. 12 is a diagram showing a flow of MR inspection using the GMA method according to Application Example 1. In FIG. 12, the k-space filling method is assumed to be the radial method.

As shown in FIG. 12, the processing circuit 51 sets the imaging range (FOV) by realizing the image pickup condition setting function 512 (step SB1).

When step SB1 is performed, the processing circuit 51 sets the sample point in the first variable space (step SB2), maps the sample point to the second variable space (step SB3), and sets the sample point in the second variable space. The position of the sample point is set to the collection angle (step SB4). Steps SB2, SB3 and SB4 are the same as steps SA1, SA2 and SA3 in FIG. 7, except that the value viewpoints are different.

When step SB4 is performed, the sequence control circuit 29 executes radial collection along the k-space locus of the collection angle set in step SB4 (step SB5). Regarding the collection angle at which the k-space locus extends beyond the imaging range, it is preferable that the application interval of the lead-out gradient magnetic field is set shorter than the collection angle at which the k-space locus falls within the imaging range. As a result, the collection angle at which the k-space locus extends beyond the imaging range is oversampled, and a sufficient amount of k-space data in the imaging range can be secured.

When step SB5 is performed, the processing circuit 51 executes image reconstruction by executing the reconstruction function 513 (step SB6). In step SB6, the processing circuit 51 removes a portion of the k-space data collected in step SA4 that extends beyond the imaging range set in step SB1. Then, the processing circuit 51 reconstructs the MR image regarding the imaging range based on the remaining k-space data. The reconstructed MR image is displayed on the display 53 by realizing the display control function 515 by the processing circuit 51.

As a result, the MR inspection shown in FIG. 12 is completed.

As described above, the processing circuit 51 according to Application Example 1 changes the value of the collection angle according to the shape of the imaging range. For example, when the imaging range is shortened with respect to the spatial frequency ky direction, the imaging range is rectangular. When the imaging range covers the entire k-space, the imaging range is isotropic. The flatter the imaging range, the more the value of the collection angle around the collection angles "0 degrees", "90 degrees" and "180 degrees" and the value of the collection angle around the collection angles "45 degrees" and "135 degrees". Will be separated. Therefore, the flatter the imaging range, the more the collection angle range around the collection angles "0 degrees", "90 degrees" and "180 degrees" and the collection angle range around the collection angles "45 degrees" and "135 degrees". Even if the difference in density of the k-space locus with respect to the angular direction in is large, it is acceptable. Therefore, the flatter the imaging range, the smaller the number of k-space trajectories, in other words, the number of read-encoding steps, so that the imaging time can be shortened. Further, when the number of k-space loci is not reduced, the k-space loci can be set more densely in the angular direction in a high-value collection angle range, so that the image quality can be improved. As described above, according to Application Example 1, the efficiency of data collection related to non-Cartesian collection can be improved.

(Application example 2)
Application example 2 is a development of application example 1. The processing circuit 51 according to Application Example 2 displays a GUI screen for adjusting the imaging range. Hereinafter, the magnetic resonance imaging apparatus and the method for setting the collection angle of the k-space locus according to Application Example 2 will be described. In the following description, components having substantially the same functions as in Application Example 1 will be designated by the same reference numerals, and will be described in duplicate only when necessary.

FIG. 13 is a diagram showing a flow of MR inspection using the GMA method according to Application Example 2. In FIG. 13, the k-space filling method is assumed to be the radial method.

As shown in FIG. 13, the processing circuit 51 sets the imaging range (FOV) by realizing the image pickup condition setting function 512 (step SC1). When step SC1 is performed, the processing circuit 51 sets the number of k-space loci and the collection angle by realizing the imaging condition setting function 512 (step SC2). When step SC2 is performed, the processing circuit 51 determines the imaging time by realizing the imaging condition setting function 512 (step SC3). When step SC3 is performed, the processing circuit 51 displays the imaging time by realizing the display control function 515 (step SC4).

Here, steps SC1-SC4 will be described in detail with reference to FIG. FIG. 14 is a diagram showing an example of a GUI screen (hereinafter, referred to as an adjustment screen) I2 for adjusting the imaging range. As shown in FIG. 14, the adjustment screen I2 has a graphic element I21 that imitates the k-space, a GUI graphic element I22 for adjusting the imaging range, an imaging time display column I23, and a display column I24 for the number of k-space loci. And has a confirm button I25. In step SC1, the processing circuit 51 displays the adjustment screen I2 on the display 53 by realizing the display control function 515. Since the graphic element I21 has the same meaning as the k-space, it is simply called the k-space I21, and the GUI graphic element I22 has the same meaning as the imaging range, so it is simply called the imaging range I22.

In step SC1, the processing circuit 51 adjusts the imaging range I22 via the adjustment screen I2. As shown in FIG. 14, the imaging range I22 is superimposed on the k-space I21 according to the actual positional relationship. The user adjusts the vertical size (size in the spatial frequency ky direction) and / or the horizontal size (size in the spatial frequency kx direction) of the imaging range I22 via the input interface 54. It is also possible to shift the imaging range I22 vertically or horizontally by adjusting the vertical size and / or the horizontal size. Typically, the vertical size of the imaging range I22 is adjusted, not the horizontal size. Adjusting the vertical size of the imaging range I22 is synonymous with adjusting the shape of the imaging range in k-space.

In step SC2, the processing circuit 51 sets the number of k-space loci and the collection angle in conjunction with the adjustment of the imaging range in step SC1. Specifically, the processing circuit 51 determines the mapping function f from the value viewpoint according to the application example 1 based on the adjusted imaging range. Then, the processing circuit 51 determines the collection angle set of the k-space locus according to the mapping function f. Specifically, first, using the setting screen I1 and the like in FIG. 9, a set of sample points is set on the virtual variable axis according to the type and parameter of the mapping function f and the sample point interval (first distance interval) on the virtual variable axis. Is placed. Next, the user adjusts the imaging range via the input interface 54 or the like. According to the method of Application Example 1, the mapping function f is determined in real time according to the shape of the imaged range after adjustment. According to the determined mapping function f, the set of sample points is mapped to the collection angle axis. The number of sample points arranged on the collection angle axis is counted as the number of k-space loci. If the type and parameter of the mapping function f and the sample point spacing on the virtual variable axis are not changed, the number of k-space loci will increase or decrease in conjunction with the adjustment of the imaging range.

In step SC3, the processing circuit 51 determines the imaging time based on the number of k-space loci. In step SC4, the processing circuit 51 displays the determined imaging time in the display column I23, and displays the number of k-space loci in the display column I24. That is, the imaging time displayed in the display column I23 and the number of k-space loci displayed in the display column I24 are updated in real time in conjunction with the adjustment of the imaging range.

As described above, there is a correlation between the shape of the imaging range and the imaging time. When the imaging range deviates from the isotropic shape, the k-space locus extends beyond the imaging range, so that the value of the collection angle is not isotropic. That is, the k-space locus can be reduced as the imaging range deviates from the isotropic shape. Since the number of k-space loci is small and the imaging time is shortened, the imaging time can be shortened as the imaging range deviates from the isotropic shape. In other words, the processing circuit 51 can change the imaging time according to the shape in the k-space of the imaging range.

When step SC4 is performed, the processing circuit 51 waits for the user to press the confirmation button I23 via the input interface 54 (step SC5). The user observes the GUI screen I2, confirms the imaging conditions such as the imaging range, the imaging time, and the number of k-space loci, and operates the imaging range figure to adjust the imaging range until he / she is satisfied. When the adjustment of the imaging range is completed, the user presses the confirmation button I23 via the input interface 54. When the confirmation button I23 is pressed, the processing circuit 51 determines the adjusted imaging range, the number of k-space loci, and the collection angle as the imaging conditions for the target imaging.

When confirmed (step SC5: Yes), the sequence control circuit 29 executes radial collection along the k-space locus of the collection angle included in the imaging conditions determined in step SC5 (step SC6).

When step SC6 is performed, the processing circuit 51 executes image reconstruction by executing the reconstruction function 513 (step SC7). In step SC7, the processing circuit 51 reconstructs the MR image relating to the imaging range based on the k-space data collected in step SC6. The reconstructed MR image is displayed on the display 53 by realizing the display control function 515 by the processing circuit 51.

As a result, the MR inspection shown in FIG. 13 is completed.

According to Application Example 2, the processing circuit 51 determines the imaging time in real time according to the shape of the imaging range in conjunction with the adjustment of the imaging range, and displays the imaging time on the display 53. Specifically, the number of k-space loci is increased or decreased according to the shape of the imaging range, and the imaging time depending on the number of k-space loci is also increased or decreased accordingly. As described above, according to Application Example 2, by considering the value of the collection angle, the optimum imaging time can be efficiently determined according to the shape of the imaging range.

(Modification example)
In Application Example 2, when the imaging range is not isotropic, the circle set in the k-space is a perfect circle, and data collection is also performed for the portion of the k-space locus that extends beyond the imaging range. However, this embodiment is not limited to this.

FIG. 15 is a diagram showing a k-space locus KT and an imaging range 65 related to radial collection set in the k-space 60 according to the modified example. As shown in FIG. 15, it is assumed that the k-space 60 is set with a rectangular imaging range 65 whose length in the ky direction is shorter than the length in the kx direction. A circle 66 indicating the scan range of the radial collection is set so as to be inscribed in the imaging range 65. In this case, the circle 66 is an ellipse.

Even when the circle 66 is an ellipse, it is possible to determine the collection angle of each k-space locus by the GMA method. Since the k-space locus KT is set in the ellipse 66, the length varies depending on the collection angle. That is, the number of Cartesian lattice points through which the k-space locus KT passes differs depending on the collection angle. As for the value of the collection angle, the smaller the number of Cartesian lattice points through which the k-space locus KT passes, the lower the value, and the larger the number of Cartesian grid points through which the k-space locus KT passes, the higher the value. In other words, the shorter the angle range of the k-space locus KT, the lower the value, and the longer the length of the k-space locus KT, the higher the value. The k-space locus is set sparsely for the low-value angle range, and the k-space locus is set densely for the high-value angle range.

Since the k-space locus KT is set in the ellipse 66, the length varies depending on the collection angle. The length of the k-space locus KT corresponds to the bandwidth of the lead-out gradient magnetic field in data acquisition. Therefore, at the time of data acquisition, the sequence control circuit 29 may perform radial collection while changing the bandwidth of the lead-out gradient magnetic field for each collection angle.

(Other variants)
In at least one embodiment described above, the k-space locus is assumed to be a straight line from one end of a circle set in the k-space to the other end through the center of the k-space. However, this embodiment is not limited to this. The k-space locus may be, for example, a straight line starting from the middle of a circle or ending at a point on the circle, as is often used in the collection of UTE (Ultrashort TE). As a result, the TE time can be shortened in the MR inspection using the GRA method.

According to at least one embodiment described above, the efficiency of data collection relating to non-Cartesian collection can be improved.

The term "processor" used in the above description refers to, for example, a CPU, a GPU, or an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device (Simple Programmable Logic Device)). : SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)). The processor realizes the function by reading and executing the program stored in the storage circuit. Instead of storing the program in the storage circuit, the program may be directly embedded in the circuit of the processor. In this case, the processor realizes the function by reading and executing the program embedded in the circuit. Further, instead of executing the program, the function corresponding to the program may be realized by a combination of logic circuits. It should be noted that each processor of the present embodiment is not limited to the case where each processor is configured as a single circuit, and a plurality of independent circuits may be combined to form one processor to realize its function. Good. Further, the plurality of components in FIG. 1 may be integrated into one processor to realize the function.

Although some 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 gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 Magnetic resonance imaging device 11 Stand 13 Sleeper 21 Tilt magnetic field power supply 23 Transmission circuit 25 Reception circuit 27 Sleeper drive device 29 Sequence control circuit 41 Static magnetic field magnet 43 Tilt magnetic field coil 45 Transmission coil 47 Reception coil 50 Host computer 51 Processing circuit 52 Memory 53 Display 54 Input interface 55 Communication interface 131 Top plate 133 Base 511 Acquisition function 512 Imaging condition setting function 513 Reconstruction function 514 Image processing function 515 Display control function

Claims (16)

A setting unit that sets the collection angle of the k-space trajectory for non-Cartesian collection,
An imaging control unit that executes the non-Cartesian acquisition according to the k-space locus, and the like.
The setting unit
Place the sample points in the first variable space defined by a variable different from the collection angle,
The collection angle is set by mapping the sample points arranged in the first variable space to the second variable space defined by the collection angle according to the value of the collection angle.
Magnetic resonance imaging device. The setting unit arranges the sample points in the first variable space at a first distance interval, and places the sample points in the second variable space by the mapping at a second distance interval according to the value. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is arranged and the position of the sample point arranged in the second variable space is set to the collection angle. The magnetic resonance imaging apparatus according to claim 2, wherein the first distance interval is an equal interval. The magnetic resonance imaging apparatus according to claim 2, wherein the second distance interval is narrower as the value of the collection angle increases. The magnetic resonance imaging apparatus according to claim 2, wherein the value is higher as the distance between the Cartesian lattice points through which the k-space locus corresponding to the collection angle passes is narrower. The magnetic resonance imaging apparatus according to claim 2, wherein the value is higher as the collection angle of the k-space locus is farther from the collection angle of another k-space locus of past imaging. The magnetic resonance imaging apparatus according to claim 2, wherein the value is higher as the collection time of the k-space trajectory is closer to the collection time of another k-space trajectory of past imaging. The value is higher as the number of Cartesian lattice points existing in the imaging range passes through the k-space locus corresponding to the collection angle, or the k-space of the k-space loci corresponding to the collection angle. The magnetic resonance imaging apparatus according to claim 2, wherein the more the portion protruding from the circle set in is, the higher the height is. An adjustment unit for adjusting the imaging range is further provided.
The setting unit sets the number of k-space loci and the collection angle in conjunction with the adjustment of the imaging range by the adjustment unit.
The magnetic resonance imaging apparatus according to claim 8. The magnetic resonance imaging apparatus according to claim 9, wherein the setting unit sets the collection angle according to a mapping based on the imaging range adjusted by the adjustment unit. A determination unit that determines the imaging time based on the number of k-space loci, and
A display unit for displaying the imaging time is further provided.
The magnetic resonance imaging apparatus according to claim 10. A display unit for displaying a setting screen for arranging the k-space locus in the first variable space is further provided.
The setting unit arranges the k-space locus in the first variable space according to a user's instruction via the setting screen.
The magnetic resonance imaging apparatus according to claim 1. The magnetic resonance imaging apparatus according to claim 12, wherein the setting screen includes a graphic element that imitates the first variable space and a graphic element that imitates the k-space locus. The magnetic resonance imaging apparatus according to claim 1, wherein the non-Cartesian collection is a two-dimensional or three-dimensional radial collection, a spiral collection, or a PROPELLER collection. Place the sample points in the first variable space defined by a variable different from the collection angle of the k-space locus for non-Cartesian collection.
By mapping the sample points arranged in the first variable space to the second variable space defined by the collection angle according to the value of the collection angle, the collection angle of the k-space locus can be obtained. Set,
A method of setting a collection angle of a k-space locus. A setting unit that sets the imaging range in k-space for non-Cartesian collection,
A determination unit that determines the imaging time based on the shape of the imaging range in k-space,
A display unit that displays the imaging time and
A magnetic resonance imaging apparatus comprising.

Images