JP7433871B2 - Magnetic resonance imaging device and method for setting collection angle of k-space trajectory - Google Patents

Description

Embodiments of the present invention relate to a magnetic resonance imaging apparatus and a method for setting a collection angle of a k-space trajectory.

A radial method is known as one of the non-Cartesian collection methods in which data is collected along radial k-space trajectories set in k-space. One method for setting the collection angle of the k-space trajectory in the radial method is the golden angle radial method, which repeatedly sets the collection angle of the k-space trajectory at angular intervals of the golden ratio (approximately 111.25 degrees). Are known. According to the golden angle radial method, it is possible to set k-space trajectories at approximately equal intervals in k-space. This assumes that the value of the k-space trajectory is the same regardless of the acquisition angle. When considering the value of the collection angle, the golden angle radial method is not necessarily appropriate.

US Patent Application Publication No. 2015/185301 Japanese Patent Application Publication No. 2014-210209 US Patent Application Publication No. 2019/0079154 JP2018-42671A

The problem that the present invention seeks to solve is to improve the efficiency of data collection for non-Cartesian collections.

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

FIG. 1 is a diagram showing the configuration of a magnetic resonance imaging apparatus according to this embodiment. FIG. 2 is a diagram showing a k-space trajectory regarding radial acquisition in k-space according to the present embodiment. FIG. 3 is an enlarged view of the vicinity of the origin of k-space. FIG. 4 is a diagram showing an example of a sparse and dense k-space distribution of a k-space trajectory. 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 an MR examination using the GMA method using a magnetic resonance imaging apparatus. FIG. 8 is a diagram illustrating an example of mapping a k-space trajectory from a virtual variable axis to a 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 trajectory and imaging range for radial acquisition in k-space. FIG. 11 is a diagram showing an example of a sparse and dense k-space distribution of a k-space trajectory. FIG. 12 is a diagram showing the flow of an MR examination using the GMA method according to application example 1. FIG. 13 is a diagram showing the flow of an MR examination 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 trajectory and an imaging range regarding radial acquisition in k-space according to a modified example.

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

FIG. 1 is a diagram showing the configuration of a magnetic resonance imaging apparatus 1 according to this embodiment. As shown in FIG. 1, the magnetic resonance imaging apparatus 1 includes a gantry 11, a bed 13, a gradient magnetic field power supply 21, a transmitting circuit 23, a receiving circuit 25, a bed driving device 27, a sequence control circuit 29, and a host computer 50. has.

The pedestal 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 casing of the pedestal 11. A hollow bore is formed in the casing of the pedestal 11 . A transmitting coil 45 and a receiving coil 47 are arranged within the bore of the pedestal 11.

The static magnetic field magnet 41 has a hollow, substantially cylindrical shape, and generates a static magnetic field substantially inside the cylinder. As the static 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 vertically orthogonal 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 constitute an orthogonal three-dimensional coordinate system.

The gradient magnetic field coil 43 is a coil unit that is attached inside the static magnetic field magnet 41 and formed in a hollow, substantially cylindrical shape. The gradient magnetic field coil 43 receives current from the gradient magnetic field power supply 21 and generates a gradient magnetic field. 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 whose magnetic field strength changes along each of the X-axis, Y-axis, and Z-axis. The gradient magnetic fields along the X, Y, and Z axes are combined to form a mutually orthogonal slice selection gradient magnetic field Gs, phase encode gradient magnetic field Gp, and frequency encode gradient magnetic field Gr in a desired direction. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section (slice). The phase encoding gradient magnetic field Gp is used to change the phase of a magnetic resonance signal (hereinafter referred to as an MR signal) depending on the spatial position. The frequency encode 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 gradient direction of the slice selection gradient magnetic field Gs is the Z axis, the gradient direction of the phase encode gradient magnetic field Gp is the Y axis, and the gradient direction of the frequency encode gradient magnetic field Gr is the X axis.

The gradient magnetic field power supply 21 supplies current to the gradient magnetic field coil 43 according to a sequence control signal from the sequence control circuit 29 . The gradient magnetic field power supply 21 supplies current to the gradient magnetic field coils 43, thereby causing the gradient magnetic field coils 43 to generate gradient magnetic fields along the X, Y, and Z axes. The gradient magnetic field is applied to the subject P while being superimposed on the static magnetic field formed by the static magnetic field magnet 41.

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

The transmitting circuit 23 supplies current to the transmitting coil 45 in order to apply an RF pulse for exciting target protons present in the subject P to the subject P via the transmitting coil 45. The RF pulse oscillates at a resonant frequency specific to the target proton and excites the target proton. An MR signal is generated from the excited target protons and detected by the receiving coil 47. The transmitting coil 45 is, for example, a whole body coil (WB coil). Whole body coils may be used as transmit and receive coils.

The receiving coil 47 receives the MR signal emitted from the target protons present 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 wirelessly. Although not shown in FIG. 1, the receiving coil 47 has a plurality of receiving channels implemented in parallel. The reception channel includes a reception coil element that receives the MR signal, an amplifier that amplifies the MR signal, and the like. The MR signal is output for each receiving channel. The total number of reception channels and the total number of reception coil elements may be the same, or the total number of reception channels may be greater or less than the total number of reception coil elements.

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

Note that the above-mentioned transmitting coil 45 and receiving 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. Moreover, the transmitting coil 45, the receiving coil 47, and the transmitting/receiving coil may be combined.

A bed 13 is installed adjacent to the pedestal 11. The bed 13 has a top plate 131 and a base 133. A subject P is placed on the top plate 131. The base 133 supports the top plate 131 so as to be slidable along each of the X-axis, Y-axis, and Z-axis. The bed driving device 27 is accommodated in the base 133. The bed driving device 27 moves the top plate 131 under control from the sequence control circuit 29. The bed driving device 27 may include any motor such as a servo motor or a stepping motor.

The sequence control circuit 29 has, as hardware resources, a processor such as 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). The sequence control circuit 29 synchronously controls the gradient magnetic field power supply 21, the transmitting circuit 23, and the receiving circuit 25 based on the imaging conditions set by the imaging condition setting function 512 of the processing circuit 51, and generates pulses according 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 imaging control section.

The sequence control circuit 29 according to this embodiment executes non-Cartesian acquisition as a k-space filling method. Non-Cartesian acquisition is a k-space scanning method that is different from Cartesian acquisition, such as 2-dimensional or 3-dimensional radial acquisition, spiral acquisition, or PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) acquisition. The k-space trajectory for non-Cartesian acquisitions is characterized by the angle of the k-space trajectory in k-space (hereinafter referred to as acquisition angle). For example, a radial acquisition k-space trajectory, also called a spoke, passes radially through the origin of k-space. The acquisition angle of the k-space trajectory for radial acquisition is set to an 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 section, the memory 52 is an example of a storage section, the display 53 is an example of a display section, the input interface 54 is an example of an input section, and the communication interface 55 is an example of a communication section. It is.

The processing circuit 51 has a processor such as a CPU as a hardware resource. The processing circuit 51 functions as the core of the magnetic resonance imaging apparatus 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 example of an image processing unit. The display control function 515 is an example of a display section.

In the acquisition function 511, the processing circuit 51 acquires various data. For example, processing circuit 51 obtains k-space data for non-Cartesian acquisitions acquired by 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 it from the memory 52.

In the imaging condition setting function 512, the processing circuit 51 automatically or manually sets imaging conditions. For example, the processing circuit 51 sets the acquisition angle of the k-space trajectory regarding non-Cartesian acquisition 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. Furthermore, 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 also set any imaging conditions such as echo time TE and repetition time TR.

In the reconstruction function 513, the processing circuit 51 reconstructs an MR image regarding the subject P based on the k-space data acquired by the acquisition function 511. For example, the processing circuit 51 generates an MR image by subjecting the k-space data to Fourier transform or inverse Fourier transform. Note that the reconstruction method is not limited to Fourier transform or inverse Fourier transform, and parallel imaging, compressed sensing, machine learning models, etc. may also 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. Furthermore, the processing circuit 51 is also capable of performing various types of image processing such as area extraction, image recognition, image analysis, and alignment.

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

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

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

Note that the above configuration is an example and is not limited thereto. For example, the sequence control circuit 29 may be incorporated into the host computer 50. Furthermore, the sequence control circuit 29 and the processing circuit 51 may be mounted on the same substrate. Further, the imaging condition setting function 512 does not necessarily need to be implemented in the processing circuit 51 of the magnetic resonance imaging apparatus 1. For example, the imaging condition setting function 512 may be implemented in a computer separate from the magnetic resonance imaging apparatus 1 for setting imaging conditions. 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 conditions in the memory 52 does not need to be installed in the magnetic resonance imaging apparatus 1, and may be installed in a storage device connected to the magnetic resonance imaging apparatus 1 via a network, for example. good.

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

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

Value will be explained in more detail below. Note that, in order to provide a concrete explanation, two-dimensional radial acquisition will be described as an example of non-Cartesian acquisition.

FIG. 2 is a diagram showing a k-space trajectory KT set in k-space 60 regarding radial acquisition. The k space 60 is a space defined by a spatial frequency ky and a spatial frequency kx. The size of the k-space 60 in the ky direction and the size in the kx direction are set to be the same. A circle 61 indicating the outer circumference of the scan range of the k-space locus KT is set in the k-space 60. Further, a plurality of lattice points (also referred to as Cartesian lattice points) 62 defined by a 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. The k-space trajectory KT has a starting point set at a point on the circle 61, an ending point set at a point on the opposite side of the origin 621 from the starting point, and is set as a straight line passing through the origin 621. The angle around the origin 621 of the k-space trajectory KT is defined as the collection angle. A plurality of k-space trajectories KT for different acquisition angles are set in k-space 60. The collection angle of the k-space trajectory extending in the +kx direction is defined as 0 degrees, the collection angle of the k-space trajectory extending in the +ky direction is defined as 90 degrees, and the collection angle of the k-space trajectory extending in the -kx direction is defined as 180 degrees. be done. In radial collection, grid points 62 outside the circle 61 are ignored. Although four k-space trajectories KT are set in FIG. 2, the number of k-space trajectories KT is not particularly limited.

An imaging range (FOV) is set in the k-space 60, which indicates the range of k-space data used in the reconstructed image. In this embodiment, it is assumed that the imaging range is set to 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 becomes a perfect circle.

The k-space data of each k-space trajectory KT obtained by radial acquisition is arranged in the Cartesian coordinate space shown in FIG. 2, for example, through a pre-processing section of grid processing. A preprocessing unit for grid processing obtains data values for each grid point 62 based on k-space data of a plurality of k-space trajectories KT. The MR image expressed in 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 post-processing grid processing on the obtained data. be done. That is, if the resolution is equivalent to 62 grid points in the Cartesian coordinate system, the number or density of k-space trajectories is sufficient.

FIG. 3 is an enlarged view of the vicinity of the origin 621 of k-space. As shown in FIG. 3, each k-space trajectory KT passes through a plurality of grid points 62. The distance between two adjacent grid points 62 through which the k-space trajectory KT passes varies depending on the acquisition angle of the k-space trajectory KT. For example, if the distance between two adjacent grid points 62 through which the k-space trajectory KT (0 degrees) with a collection angle of "0 degrees" passes is "1", then the k-space trajectory KT (0 degrees) with a collection angle of "45 degrees" passes through the distance between two adjacent grid points 62 is "1". The distance between two adjacent grid points 62 through which the angle (45 degrees) passes is "√2". Since the k-space trajectory KT (0 degrees) and KT (45 degrees) have the same length, the number of grid points 62 that the k-space trajectory KT (0 degrees) passes through is equal to the number of lattice points 62 that the k-space trajectory KT (45 degrees) passes through. The number of lattice points 62 is greater than the number of lattice points 62. Therefore, it can be seen that in order to obtain a resolution equivalent to 62 lattice points, it is not 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 grid points through which the k-space trajectory passes is narrower.

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

In this way, data can be collected efficiently by arranging k-space trajectories densely for the valuable range of collection angles and sparsely arranging the k-space trajectories for the angular range of low value.

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

The value is not limited to being set based on the number of Cartesian grid points through which the k-space trajectory passes, but can be set from various viewpoints (hereinafter referred to as value viewpoints). For example, an MR image may be generated based on k-space data collected by object imaging and k-space data collected by past imaging. In this case, the value may be set, for example, based on the proximity of the k-space trajectory of the imaging target (hereinafter referred to as target imaging) and the collection angle of the k-space trajectory of the past imaging. . Value perspective means how to define the value of a 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, acquisition angles close to the k-space trajectory KTP of past imaging have low value, and the k-space trajectory of target imaging is set sparsely. Acquisition angles far from the k-space trajectory KTP are of high value, and the k-space trajectory of object imaging is set densely.

Note that the k-space locus of past imaging may be any number of frames temporally earlier than the k-space locus of target imaging. Further, when setting the value of the acquisition angle of object imaging, any number of k-space trajectories of past imaging may be considered. For example, in Fig. 5, for the sake of simplicity, the value of the acquisition angle of the target image for one k-space trajectory of past imaging is shown, but using a similar algorithm, The value of the acquisition angle of object imaging may be set.

As mentioned above, in FIG. 5, the value is set based on the locational proximity to the acquisition angle of the k-space trajectory of past imaging. However, the value may be set based on the temporal proximity to the acquisition angle of the k-space trajectory of a 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 image is expressed as "t", and the frame of the past image captured n (integer) frames before "t" is expressed as "tn". In FIG. 6, when setting the value of the acquisition angle of target imaging, the k-space trajectory KT(t-1) of the past imaging one frame before the target imaging frame t and the k-space trajectory KT(t-1) of the past imaging 5 frames before the target imaging frame t. t-5) shall be taken into consideration.

As shown in FIG. 6, the collection angle range around the k-space trajectory KT(t-5) five frames ago is compared to the collection angle range around the k-space trajectory KT(t-1) one frame before. The value is high, and the k-space trajectory of object imaging is set densely. In this way, the closer the collection angle of the target image is to the k-space locus KT(tn) of the temporally distant past image, the higher the value is set, and the more the k-space locus is Closely 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 image.

Note that the past imaged frame may be any number of frames earlier than the target imaged frame. Further, when setting the value of the acquisition angle of object imaging, any number of k-space trajectories of past imaging may be considered. For example, in FIG. 6, for simplicity, object imaging is collected for one k-space trajectory KT (t-1) one frame before and one k-space trajectory KT (t-5) five frames ago. Although angular values are shown, a similar algorithm may consider k-space trajectories from 2 to 4 frames ago, or k-space trajectories from 6 or more frames ago.

Next, the flow of an MR examination using the GMA method by the magnetic resonance imaging apparatus 1 according to this embodiment will be explained.

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

As shown in FIG. 7, the processing circuit 51 first sets the acquisition angle of the k-space locus regarding radial acquisition by implementing the imaging condition setting function 512 using the GMA method (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 sets the sample point 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 virtual variables (hereinafter referred to as virtual variables) different from the acquisition angle. The second variable space is the space defined by the acquisition 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 the number of dimensions of the second variable space, or may be different. That is, the number of dimensions of the first variable space is, for example, 1 in the case of a two-dimensional radial method, and 1 or 2 in the case of a three-dimensional radial method.

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

FIG. 8 is a diagram showing an example of mapping sample points 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 for example, as shown in FIG. 8, it is set to a range from a lower limit of "0" to an upper limit of "1". Positions on the virtual variable axis 71 represent virtual variables. Collection angle axis 72 has a predetermined angular range. Although the angle range can be set to any value, for example, as shown in FIG. 8, it is set to a range from a lower limit of "0 degrees" to an upper limit of "180 degrees." The position on the collection angle axis 72 represents the collection angle. The virtual variable "0" corresponds to the acquisition 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 a first distance interval D1k, and arranges the n sample points KT1k at a collection angle. By mapping to the axis 72, the position of each of the n sample points KT2k arranged at the second distance interval D2k according to the value and arranged on the collection angle axis 72 is set to the collection angle. 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, sample points KT1k are 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 onto a 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, a collection angle set is set. By mapping, for example, a set of n sample points KT1k arranged at equal intervals D1k is converted into a set of n collection angles KT2k arranged at non-equal intervals D2k according to the values of the collection angles. 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 higher value.

Here, when the virtual variable is expressed as x and the collection angle is expressed as θ, the mapping from the virtual variable x to the acquisition angle θ is expressed as a function θ=f(x). The gradient df/dx of the mapping function f represents the value of the acquisition angle, in other words, the weight of the acquisition angle. Note that when the distance interval D2 of the k-space locus KT2 on the collection angle axis 72 is equal, the gradient df/dx corresponds to a constant independent of x.

The mapping function f can be designed according to the above values and parameters. As mentioned above, the value perspective is 1. The number of Cartesian grid points through which the k-space trajectory passes, 2. Locational proximity to the k-space trajectory of past imaging; 3. It can be broadly classified into three types: temporal proximity to the k-space locus of past imaging. In other words, the value viewpoint is one element that determines the type of mapping function f. The parameters include the gradient df/dx of the mapping function f, the bias, and the like.

In the case of value viewpoint 1, the narrower the distance between the Cartesian grid points through which the k-space trajectory passes, the higher the value of the collection angle of the k-space trajectory. In the case of value viewpoint 1, the gradient df/dx is set such that it increases as the number of Cartesian grid points through which the k-space trajectory passes increases, and decreases as the acquisition angle decreases. Specifically, the gradient df/dx may be set to a value that corresponds to the distance interval between the grid points. For example, the gradient df/dx is set in a range from 1/√2 to 1. At this time, for collection angles θ = 45 degrees and 135 degrees, the slope df/dx is set to the minimum value = 1/√2, and for collection angles θ = 0 degrees, 90 degrees and 180 degrees, the slope df/dx is set to the maximum Value=1.

In the case of value viewpoint 2, the farther the collection angle of the k-space locus of the target imaging is from the collection angle of other k-space trajectories of past imaging, the higher the value of the collection angle of the k-space trajectory of the target imaging. In the case of value viewpoint 2, the gradient df/dx is set such that the gradient df/dx becomes larger as the acquisition angle is closer to the k-space locus of past imaging, and becomes smaller as the acquisition angle is farther away. Specifically, the gradient df/dx is set in a range from 1/2 to 1.

In the case of value viewpoint 3, the closer the collection time of the k-space locus of the object imaging is to the collection time of other k-space trajectories of past imaging, the higher the value of the collection angle of the k-space trajectory of the target image. In the case of value viewpoint 3, the gradient df/dx is set such that the gradient df/dx becomes larger as the acquisition angle is temporally closer to the k-space locus of past imaging, and becomes smaller as the acquisition angle is farther away. Specifically, the gradient df/dx is set in a range from 1/2 to 1.

For example, a method for deriving the mapping function f in value viewpoint 1 will be briefly explained. First, a circle is set in k-space and lines passing through Cartesian grid points and parallel to the ky and kx axes (hereinafter referred to as grid lines) are set. Next, the angle at which the circle intersects each grid line is calculated, and based on the calculated angle, an allowable sampling density at each grid point is determined. Then, the mapping function f is determined by interpolating the sampling density at each grid point. For example, a spline function is appropriate for the interpolation, but the interpolation is not limited to this, and may be performed using 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, a mapping function g from the acquisition 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. The mapping function f may also be a neural network trained to input a plurality of virtual variables and output a plurality of acquisition angles.

In the above explanation, value perspective 1, value perspective 2, and value perspective 3 were explained independently, but value perspective 1, value perspective 2, and value perspective 3 are not mutually exclusive and are compatible. That is, two or all three of value viewpoint 1, value viewpoint 2, and value viewpoint 3 may be combined.

In the above description, mapping has been explained using two-dimensional radial acquisition as an example, but it can be extended to three-dimensional radial acquisition as well. Stack of Stars collection and Kush Ball collection can be used as three-dimensional radial collection. Stack of Stars collection can use the method described as an example of two-dimensional radial collection. For Kush ball collection, the collection angle is defined by a combination of a first argument and a second argument. Accordingly, the collection angle axes have a first collection angle axis for a first argument and a second collection angle axis for a second argument. Correspondingly, the virtual variable axes include a first virtual variable axis regarding the first virtual variable x1 corresponding to the first argument, and a second virtual variable axis regarding the second virtual variable x2 corresponding to the second argument. It has a virtual variable axis. For example, when the first declination angle is "45 degrees" and the second declination angle is "45 degrees," the distance interval between Cartesian lattice points is the longest, and when the first declination angle is "0 degrees" and the second declination angle is When the angle is "0 degrees", the distance interval between Cartesian lattice points is the shortest. Therefore, the gradient df/dx1 and the gradient df/dx2 are preferably set in the range of 1/√3 to 1.

In the above description, mapping has been explained using radial collection as an example, but it is also applicable to two-dimensional spiral collection and three-dimensional spiral collection. As the three-dimensional spiral collection, cone collection based on a cone-shaped k-space trajectory is also possible. It is also applicable to two-dimensional PROPELLER collection and three-dimensional stack-of-PROPELLER 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 acquisition angle. The processing circuit 51 places the k-space locus KT1n on the virtual variable axis 71 according to the user's instructions 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 includes a display field I11, equally spaced buttons I12, non-equally spaced buttons I13, a GUI graphic element I14, and a GUI graphic element I16. In the display field I11, the number of k-space trajectories scheduled for data collection in object imaging is displayed. The equal interval button I12 is a GUI button for arranging k-space trajectories at equal intervals on the virtual variable axis. The non-uniform interval button I13 is a GUI button for arranging the k-space trajectory at non-uniform intervals on the virtual variable axis. The GUI graphic element I14 is a graphic element imitating a virtual variable axis that is a first variable space. A 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 simulates the collection angle axis that is the second variable space. A 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 synonymous with the virtual variable axis, so it will be simply referred to as the virtual variable axis I14, and the graphic element I15 is synonymous with the sample point before mapping, so it will simply be referred to as the sample point I15. The element I16 has the same meaning as the acquisition angle axis, so it is simply called the acquisition angle axis I16, and the graphic element I17 has the same meaning as the sample point after mapping, so it is simply called the sample point I17.

For example, the user sets the distance interval of the sample points I15 on the virtual variable axis I14, the type of mapping, and the parameters of the mapping via the input interface 54. The distance interval between the sample points I15 is specified by a numerical value via the input interface 54, for example. The length of the virtual variable axis I14 is set by selecting the mapping type and mapping parameters via the input interface 54. When the equal interval 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, mapping type, and mapping parameter. 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 trajectories.

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

When the irregular interval button I13 is pressed, the processing circuit 51 arranges sample points I15 at irregular intervals on the virtual variable axis I14. For example, the processing circuit 51 places the sample point I15 at a position on the virtual variable axis I14 designated by the user via the input interface 54. This allows the sample point I15 to be placed on the virtual variable axis I14 at the user's discretion. Further, when the non-uniform interval button I13 is pressed, the processing circuit 51 arranges the number of sample points I15 at non-uniform intervals on the virtual variable axis I14 according to a predetermined rule. As the predetermined rule, for example, a method using bit reverse or random numbers 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 onto 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, applies a mapping function to the specified virtual variable, and calculates the acquisition angle. The mapping function is set in advance for each value viewpoint. For example, the user specifies a desired value viewpoint from among a plurality of value viewpoints via the input interface 54. The processing circuit 51 performs mapping based on a mapping function corresponding to the specified value viewpoint. The processing circuit 51 arranges the mapped sample point I17 at a position on the acquisition angle axis I16 that corresponds to the calculated acquisition angle. The processing circuit 51 sets the position of the sample point I17 on the collection angle axis I16 as the collection angle. Typically, position adjustment of k-space trajectory I17 via input interface 54 is limited.

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

After step SA4 is performed, the processing circuit 51 performs image reconstruction by executing the reconstruction function 513 (step SA5). In step SA5, the processing circuit 51 reconstructs an MR image regarding 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.

With the above steps, the MR examination using the GMA method shown in FIG. 7 is completed.

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

According to the above configuration, the processing circuit 51 can set the acquisition angle of the k-space trajectory in consideration of the value of the acquisition angle. When the value of the collection angle is taken into account, data collection can be efficiently performed with a smaller number of k-space trajectories than when the value of the collection angle is not taken into account. In other words, if you compare the image quality of reconstructed images based on the same number of k-space trajectories, taking the value of the acquisition angle into consideration is better than not taking the value of the acquisition angle into consideration. Image quality improves because data can be collected.

Further, according to the above configuration, the processing circuit 51 does not directly set the k-space trajectory in which the value of the acquisition angle is taken into consideration 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 mapping the value to the second variable space. The first variable space is defined by virtual variables for setting the acquisition angle, and does not reflect the value of the acquisition angle. Arranging the sample points at equal intervals in the first variable space means that they are equally spaced in a physical sense, a resolution sense, and an efficiency sense. The user only has to consider these meanings when placing the sample points in the first variable space, and there is no need to consider the value meaning. 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. It is assumed that the processing circuit 51 according to Application Example 1 sets an arbitrary imaging range in k-space and sets a collection angle of a k-space trajectory according to the shape of the imaging range. Hereinafter, a magnetic resonance imaging apparatus and a method for setting a collection angle of a k-space trajectory according to Application Example 1 will be described. In the following description, components having substantially the same functions as those in this embodiment are denoted by the same reference numerals, and will be described repeatedly only when necessary.

FIG. 10 is a diagram showing a k-space trajectory and an imaging range for radial acquisition, which are set in k-space. As shown in FIG. 10, an imaging range 65 is set in 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 matrix size.

In application example 1, it is assumed that the size of the imaging range 65 in the ky direction is set to be 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 trajectory, the k-space trajectory KT is set from one end of the circle 61 through the origin to another point, similar to the above embodiment. That is, the k-space locus is set so that a part of it protrudes from the imaging range 65. Radial acquisition is performed along the set k-space trajectory to collect k-space data. Of the collected k-space data, portions that extend outside the imaging range 65 may be discarded. 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 a k-space trajectory. As shown in FIG. 11, when the imaging range 65 is shortened in the spatial frequency ky direction, the imaging range 65 has a rectangular shape. The flatter the imaging range 65 is, the more valuable the collection angles around the collection angles "0 degrees," "90 degrees," and "180 degrees," and the values around the collection angles "45 degrees" and "135 degrees." The value will diverge. Acquisition angles where the k-space trajectory falls outside the imaging range 65 are of low value and the k-space trajectory is set to be sparse. Acquisition angles whose k-space trajectory falls within the imaging range 65 are of high value, and the k-space trajectory is set densely. From another point of view, acquisition angles in which the number of grid points through which the k-space trajectory passes within the imaging range 65 are small are of low value, and the k-space trajectory is set sparsely. An acquisition angle with a large number of grid points through which the k-space trajectory passes within the imaging range 65 has a high value, and the k-space trajectory is set densely.

Note that if the imaging range is set to cover the entire k-space, that is, if the imaging range is isotropic, all k-space trajectories will fall within the imaging range. In this case, in terms 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 above value viewpoints 1, 2, and 3.

FIG. 12 is a diagram showing the flow of an MR examination using the GMA method according to application example 1. Note that in FIG. 12, it is assumed that the k-space filling method is the radial method.

As shown in FIG. 12, the processing circuit 51 sets an imaging range (FOV) by realizing the imaging 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 first variable space (step SB3). 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, respectively, except that the values are different.

When step SB4 is performed, the sequence control circuit 29 executes radial acquisition along the k-space locus of the acquisition angle set in step SB4 (step SB5). Note that for acquisition angles where the k-space locus falls outside the imaging range, the application interval of the readout gradient magnetic field may be set to be shorter than at acquisition angles where the k-space locus falls within the imaging range. As a result, oversampling is performed for acquisition angles where the k-space locus protrudes from the imaging range, making it possible to secure a sufficient amount of k-space data in the imaging range.

After step SB5 is performed, the processing circuit 51 performs image reconstruction by executing the reconstruction function 513 (step SB6). In step SB6, the processing circuit 51 removes the portion that protrudes from the imaging range set in step SB1 from the k-space data collected in step SA4. The processing circuit 51 then reconstructs an 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.

With the above steps, the MR examination shown in FIG. 12 is completed.

As explained above, the processing circuit 51 according to Application Example 1 changes the value of the acquisition angle depending on the shape of the imaging range. For example, when the imaging range is shortened in the spatial frequency ky direction, the imaging range is rectangular. If the imaging range spans the entire k-space, the imaging range is isotropic. The flatter the imaging range, the more valuable the collection angles around the collection angles "0 degrees," "90 degrees," and "180 degrees," and the values around the collection angles "45 degrees" and "135 degrees." This results in a divergence between the two. Therefore, the flatter the imaging range, the smaller the collection angle range around collection angles "0 degrees," "90 degrees," and "180 degrees," and the collection angle ranges around collection angles "45 degrees" and "135 degrees." A large difference in the density of k-space trajectories with respect to the angular direction is allowed. Therefore, as the imaging range becomes flatter, the number of k-space trajectories, in other words, the number of readout encoding steps can be reduced, and the imaging time can be shortened. In addition, if the number of k-space trajectories is not reduced, the k-space trajectories can be set more densely in the angular direction in a valuable collection angle range, so that image quality can be improved. As described above, according to Application Example 1, the efficiency of data collection regarding 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, a magnetic resonance imaging apparatus and a method for setting a collection angle of a k-space trajectory according to Application Example 2 will be described. In the following description, components having substantially the same functions as those in Application Example 1 are denoted by the same reference numerals, and will be described repeatedly only when necessary.

FIG. 13 is a diagram showing the flow of an MR examination using the GMA method according to application example 2. Note that in FIG. 13, it is assumed that the k-space filling method is the radial method.

As shown in FIG. 13, the processing circuit 51 sets an imaging range (FOV) by realizing the imaging condition setting function 512 (step SC1). When step SC1 is performed, the processing circuit 51 sets the number of k-space trajectories and the acquisition 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 implementing 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 explained 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 includes a graphical element I21 simulating k-space, a GUI graphical element I22 for adjusting the imaging range, a display column I23 for imaging time, and a display column I24 for the number of k-space trajectories. and a confirmation 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. Note that the graphical element I21 has the same meaning as k-space, so it will simply be called k-space I21, and the GUI graphical element I22 has the same meaning as imaging range, so it will simply be called 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, but the horizontal size is not adjusted. 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 trajectories and the acquisition angle in conjunction with the adjustment of the imaging range in step SC1. Specifically, the processing circuit 51 determines the mapping function f based on the value perspective according to Application Example 1 based on the adjusted imaging range. Then, the processing circuit 51 determines a collection angle set of the k-space trajectory according to the mapping function f. Specifically, first, using the setting screen I1 in FIG. is located. Next, the user adjusts the imaging range via the input interface 54 or the like. By the method of application example 1, the mapping function f is determined in real time according to the shape of the imaging range after adjustment. The sample point set is mapped onto the collection angle axis according to the determined mapping function f. The number of sample points placed on the acquisition angle axis is counted as the number of k-space trajectories. If the type and parameters of the mapping function f and the sample point interval on the virtual variable axis are not changed, the number of k-space trajectories will increase or decrease in conjunction with adjustment of the imaging range.

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

As mentioned above, there is a correlation between the shape of the imaging range and the imaging time. If the imaging range deviates from the isotropic shape, the value of the acquisition angle is no longer isotropic as the k-space trajectory extends beyond the imaging range. That is, the more the imaging range deviates from the isotropic shape, the more the k-space locus can be reduced. Since the imaging time becomes shorter when the number of k-space trajectories is small, 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 depending on the shape of the imaging range in k-space.

After step SC4 is performed, the processing circuit 51 waits for the user to press the confirm 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, imaging time, and number of k-space trajectories, and adjusts the imaging range by operating the imaging range figure until satisfied. When the adjustment of the imaging range is completed, the user presses the confirm button I23 via the input interface 54. When the confirm button I23 is pressed, the processing circuit 51 confirms the adjusted imaging range, the number of k-space trajectories, and the acquisition angle as the imaging conditions for object imaging.

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

After step SC6 is performed, the processing circuit 51 performs image reconstruction by executing the reconstruction function 513 (step SC7). In step SC7, the processing circuit 51 reconstructs an MR image regarding 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.

With the above steps, the MR examination 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 trajectories is increased or decreased depending on the shape of the imaging range, and the imaging time, which depends on the number of k-space trajectories, is also increased or decreased accordingly. As described above, according to Application Example 2, by considering the value of the acquisition angle, it is possible to determine the optimal imaging time for acquisition efficiency according to the shape of the imaging range.

(Modified example)
In application example 2, when the imaging range is not isotropic, the circle set in k-space is a perfect circle, and data collection is also performed on the portion of the k-space locus that protrudes from the imaging range. However, this embodiment is not limited to this.

FIG. 15 is a diagram showing a k-space trajectory KT and an imaging range 65 regarding radial acquisition, which are set in the k-space 60 according to a modification. As shown in FIG. 15, it is assumed that a rectangular imaging range 65 whose length in the ky direction is shorter than the length in the kx direction is set in the k space 60. A circle 66 indicating a scan range for radial acquisition is set so as to be inscribed in the imaging range 65 . In this case, the circle 66 becomes an ellipse.

Even if the circle 66 is an ellipse, it is possible to determine the collection angle of each k-space trajectory using the GMA method. Since the k-space trajectory KT is set within an ellipse 66, its length varies depending on the acquisition angle. That is, the number of Cartesian grid points through which the k-space trajectory KT passes differs depending on the acquisition angle. Regarding the value of the collection angle, the value of the angle range is lower as the number of Cartesian lattice points through which the k-space trajectory KT passes is lower, and the value is higher as the angular range has a larger number of Cartesian lattice points through which the k-space trajectory KT passes. In other words, the shorter the length of the k-space trajectory KT is, the lower the value is, and the longer the length of the k-space trajectory KT is, the higher the value. For angular ranges of low value, the k-space trajectory is set sparsely, and for angular ranges of high value, the k-space trajectory is set densely.

Since the k-space trajectory KT is set within an ellipse 66, its length varies depending on the acquisition angle. The length of the k-space trajectory KT corresponds to the bandwidth of the readout gradient field in data acquisition. Therefore, during data acquisition, the sequence control circuit 29 may perform radial acquisition while changing the bandwidth of the readout gradient magnetic field for each acquisition angle.

(Other variations)
In at least one embodiment described above, the k-space locus is a straight line from one end of a circle set in k-space to the other end passing through the center of k-space. However, this embodiment is not limited to this. The k-space trajectory may be, for example, a straight line starting from the middle of a circle or the center of the k-space and ending at a point on the circle, as is often used in UTE (Ultrashort TE) collection. This makes it possible to shorten the TE time in MR examinations using the GRA method.

According to at least one embodiment described above, it is possible to improve the efficiency of data collection regarding non-Cartesian collection.

The term "processor" used in the above description refers to, for example, a CPU, GPU, or Application Specific Integrated Circuit (ASIC), or a programmable logic device (for example, a Simple Programmable Logic Device). :SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA). A processor realizes its functions by reading and executing a program stored in a memory circuit. Note that instead of storing the program in the memory circuit, the program may be directly incorporated into the circuit of the processor. In this case, the processor realizes its functions by reading and executing a program built into the circuit. Furthermore, instead of executing a program, functions corresponding to the program may be realized by combining logic circuits. Note that each processor of this embodiment is not limited to being configured as a single circuit for each processor, but may also be configured as a single processor by combining multiple independent circuits to realize its functions. good. Furthermore, a plurality of components in FIG. 1 may be integrated into one processor to realize its functions.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

1 Magnetic resonance imaging apparatus 11 Mount 13 Bed 21 Gradient magnetic field power supply 23 Transmission circuit 25 Receiving circuit 27 Bed driving device 29 Sequence control circuit 41 Static magnetic field magnet 43 Gradient magnetic field coil 45 Transmitting coil 47 Receiving 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 (18)

a setting unit that sets a collection angle of a k-space trajectory regarding non-Cartesian collection;
an imaging control unit that executes the non-Cartesian acquisition according to the k-space trajectory,
The setting section includes:
placing a sample point in a first variable space defined by a variable different from the collection angle;
setting the collection angle by mapping the sample points located in the first variable space to a 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 arranges the sample points in the second variable space by the mapping at a second distance interval according to the value. 2. The magnetic resonance imaging apparatus according to claim 1, wherein a position of the sample point arranged in the second variable space is set to the acquisition angle. The magnetic resonance imaging apparatus according to claim 2, wherein the first distance intervals are equal intervals. 3. The magnetic resonance imaging apparatus of claim 2, wherein the second distance interval is narrower as the value of the acquisition angle is higher. 3. The magnetic resonance imaging apparatus according to claim 2, wherein the value is higher as the distance between Cartesian lattice points through which the k-space trajectory corresponding to the acquisition angle is narrower. 3. The magnetic resonance imaging apparatus according to claim 2, wherein the value increases as the acquisition angle of the k-space trajectory is farther from acquisition angles of other k-space trajectories of past imaging. 3. The magnetic resonance imaging apparatus according to claim 2, wherein the value is higher as the acquisition time of the k-space trajectory is closer to the acquisition time of other k-space trajectories of past imaging. The value increases as the number of Cartesian grid points that the k-space locus corresponding to the acquisition angle passes through and exists in the imaging range increases, or the k-space trajectory of the k-space locus corresponding to the acquisition angle increases. 3. The magnetic resonance imaging apparatus according to claim 2, wherein the magnetic resonance imaging apparatus according to claim 2, wherein the larger the portion protrudes from the circle set at . further comprising an adjustment unit that adjusts the imaging range,
The setting unit sets the number of k-space trajectories 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 section sets the acquisition angle according to mapping based on the imaging range adjusted by the adjustment section. a determining unit that determines an imaging time based on the number of the k-space trajectories;
further comprising a display unit that displays the imaging time;
The magnetic resonance imaging apparatus according to claim 10. further comprising a display unit that displays a setting screen for arranging the k-space trajectory in the first variable space,
The setting unit places the k-space trajectory in the first variable space according to a user's instruction via the setting screen.
The magnetic resonance imaging apparatus according to claim 1. 13. The magnetic resonance imaging apparatus according to claim 12, wherein the setting screen includes a graphical element simulating the first variable space and a graphical element simulating the k-space locus. 2. The magnetic resonance imaging apparatus of claim 1, wherein the non-Cartesian acquisition is a two-dimensional or three-dimensional radial acquisition, spiral acquisition, or PROPELLER acquisition. placing the sample points in a first variable space defined by a variable different from the collection angle of the k-space trajectory for non-Cartesian collection;
The collection angle of the k-space trajectory is determined by mapping the sample points placed in the first variable space into a second variable space defined by the collection angle according to the value of the collection angle. set,
A method for setting a collection angle of a k-space trajectory, comprising: a setting unit that sets an imaging range in k-space regarding non-Cartesian acquisition;
a determining unit that determines an imaging time based on the shape of the imaging range in k-space;
a display unit that displays the imaging time;
Equipped with
The setting unit sets the number of k-space trajectories based on the shape of the imaging range in k-space,
the display unit displays the number of the k-space trajectories;
Magnetic resonance imaging device. a setting unit that sets an imaging range in k-space regarding non-Cartesian acquisition;
a determining unit that determines an imaging time based on the shape of the imaging range in k-space;
a display unit that displays the imaging time;
Equipped with
The display unit displays a first graphical element simulating k-space and a second graphical element for adjusting the imaging range.
Magnetic resonance imaging device. The magnetic resonance imaging apparatus according to claim 17 , wherein the display section displays Cartesian lattice points on the first graphical element and/or the second graphical element.