Magnetic resonance imaging apparatus and control method thereof

Abstract

To optimize a sampling pattern and achieve improvement in image quality and acceleration of imaging in the blade type radial measurement using an MRI apparatus.SOLUTION: In performing blade-type radial measurement for sampling a k space radially by making angles of blades composed of a plurality of parallel sampling lines different, intervals between lines of the plurality of parallel sampling lines are made irregular about at least one blade of the plurality of blades with different angles. The sampling with irregular intervals is evaluated, and the line intervals can be adjusted further on the basis of the evaluation result.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a technique for controlling a data sampling pattern of an MRI apparatus. [Background technology]

[0002] MRI devices collect nuclear magnetic resonance signals while applying gradient magnetic fields of different magnitudes to the static magnetic field, thereby encoding the nuclear magnetic resonance signals and adding position information to the nuclear magnetic resonance signals, which are the sum of spatially distributed atomic spins. The encoded nuclear magnetic resonance signals are collected as k-space data in the frequency domain, and this k-space data is visualized by calculations such as FFT.

[0003] K-space data is 2D or 3D data with axes corresponding to the gradient magnetic fields in the three axial directions in real space, and in general imaging, Cartesian sampling is used to collect this k-space data along the axial direction. There is also radial sampling, which samples radially from the center of k-space.

[0004] Radial sampling is a method of sampling the central region of k-space, i.e., the low-frequency region that contributes to image contrast, at a high frequency, so it is an imaging method that is resistant to motion and can suppress blood flow artifacts. However, there are also sampling methods in which the angle changes for each radial line, and methods in which multiple sampling lines are used for each angle (blade-type radial measurement). Multiple lines at the same angle are called blades.

[0005] General problems with MRI include reducing artifacts and shortening imaging time, and various methods for solving these problems have been proposed. For example, Non-Patent Document 1 discloses a technology for reducing artifacts in radial sampling MRI that rotates one line by performing iterative reconstruction to minimize the difference between each channel data and the channel data after sensitivity correction. Patent Document 1 also discloses a technology for controlling k-space sampling to reduce motion artifacts by full sampling in the central region and thinning sampling in the peripheral region. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Magnetic Resonance in Medicine 57:1086-1098(2007), “Undersampled Radial MRI with Multipel Coils. Iterative Image Reconstruction Using a Total Variation Constraint.” [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-029777 Summary of the Invention [Problem to be solved by the invention]

[0008] For blade-type radial measurements, it is also necessary to reduce artifacts while shortening the imaging time.

[0009] In blade-type radial measurements, measurements are repeated for each blade with different blade angles to measure a circular area centered on the origin of k-space, and the sampling pattern is determined by the number of blades, i.e., the number of shots, and the number of lines that make up the blade, ETL (Echo Train Length).In order to speed up imaging here, it is necessary to set the ELT and number of shots small and reduce the number of radial sampling lines, but reducing the number of sampling lines creates gaps (areas where data cannot be collected) in the high-frequency region, resulting in streak artifacts.

[0010] To address such issues with blade-type radial measurement, the technology described in Non-Patent Document 1 aims to reduce artifacts by adopting iterative reconstruction, but the image quality varies depending on the sampling pattern, and there is a possibility that artifacts cannot be reduced. In addition, the technology described in Patent Document 1 is based on Cartesian sampling, and cannot be applied to optimize the sampling pattern in blade-type radial measurement, which has a different sampling pattern.

[0011] An object of the present invention is to provide an MRI apparatus capable of performing optimal sampling from the standpoint of improving image quality and reducing artifacts when performing blade-type radial measurement. [Means for solving the problem]

[0012] In order to solve the above problem, the present invention makes it possible to suppress artifacts while reducing the number of blades by controlling the sampling pattern within a blade in blade-type radial measurement.

[0013] That is, the MRI apparatus of the present invention includes an imaging unit that measures nuclear magnetic resonance signals generated by a subject and collects k-space data according to a predetermined pulse sequence, and a control unit that controls sampling of the nuclear magnetic resonance signals. The control unit controls the radial sampling of k-space by varying the angles of blades composed of multiple parallel sampling lines, and at that time, the intervals between the multiple parallel sampling lines are made unequal for at least one of the multiple blades with different angles.

[0014] Furthermore, the control method for an MRI apparatus of the present invention is a control method for an MRI apparatus having an imaging unit that measures nuclear magnetic resonance signals generated by a subject according to a predetermined pulse sequence and collects k-space data, and is characterized in that the angles of blades consisting of multiple parallel sampling lines are varied to control radial sampling of k-space, and in that, for at least one of the multiple blades having different angles, the spacing between the lines of the multiple parallel sampling lines is made unequal. Effect of the Invention

[0015] According to the present invention, by making the spacing between lines in a blade unequal, it is possible to mitigate the large difference in sampling density between the high-frequency region and the low-frequency region of k-space, and optimize the overall sampling density, thereby reducing streak artifacts caused by sparse high-frequency regions even when the number of blades is reduced. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an overview of an MRI apparatus to which the present invention is applied. [Diagram 2] Functional block diagram of a control unit according to the first embodiment [Diagram 3] FIG. 1 shows an example of a pulse sequence. [Figure 4] Diagram explaining radial sampling [Diagram 5] FIG. 1 shows an example of a sampling pattern according to the first embodiment. [Figure 6] FIG. 13 is a diagram showing another example of the sampling pattern according to the first embodiment; [Figure 7] FIG. 1 is a diagram showing a control flow of the first embodiment. [Figure 8] Functional block diagram of a control unit according to the second embodiment [Figure 9] Diagram showing sampling pattern [Figure 10] Diagram explaining the evaluation of sampling patterns [Figure 11] FIG. 13 is a diagram showing the control flow of the second embodiment. [Figure 12] A diagram showing an example of the display screen of the UI section DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of an MRI apparatus of the present invention will be described with reference to the drawings.

[0018] The MRI apparatus is roughly divided into an imaging section that measures the nuclear magnetic resonance signals generated from the subject and collects data to reconstruct an image of the subject, and a computer that controls the operation of the imaging section and performs various calculations using the data collected by the imaging section. The MRI apparatus of the present invention has an imaging section similar to that of a general MRI apparatus, but is characterized in that it has a function of controlling and optimizing the sampling of k-space when the imaging section performs blade-type radial measurement, as a main function of the computer.

[0019] <Embodiment 1> (Embodiment that does not involve the evaluation unit) First, an outline of the configuration of the MRI apparatus will be described. As shown in Fig. 1, the MRI apparatus 1 includes an imaging section 10 and a computer 30, and a subject 50 is placed in an imaging space of the imaging section 10 while lying on a bed device 20. A UI section 40 including a display device and an input device for interfacing with an operator (user) is connected to the computer 30.

[0020] The configuration of the imaging unit 10 is similar to that of a general MRI device, and includes a static magnetic field magnet 101 that forms a uniform static magnetic field in the imaging space, a gradient magnetic field coil 102 that provides a magnetic field gradient in three axial directions perpendicular to the static magnetic field, an RF transmitting coil 103 for irradiating a high frequency magnetic field to the subject 50, an RF receiving coil 104 for receiving a nuclear magnetic resonance signal generated from the subject 50, and a sequencer 108.

[0021] The three-axis gradient magnetic field coils 102 are each connected to a gradient magnetic field power supply 105, and generate a gradient magnetic field according to the power supplied from the gradient magnetic field power supply 105. In addition, by combining the gradient magnetic fields in the three axis directions, a gradient magnetic field of any magnitude can be generated in any direction.

[0022] The RF transmission coil 103 is connected to a transmitter 106 equipped with a high-frequency magnetic field generator, a high-frequency amplifier, etc., and irradiates the subject with a high-frequency magnetic field of a predetermined frequency as an RF pulse in response to the output from the transmitter 106 .

[0023] The RF receiving coil 104 is connected to a receiver 107 equipped with an amplifier, a quadrature detector, an A / D converter, etc. The receiver 107 samples the nuclear magnetic resonance signal using an A / D converter and passes it to a signal processing system (computer 30) as digital data. The RF receiving coil 104 may be a multi-channel coil made up of multiple small coils, in which case data is collected for each channel of each small coil.

[0024] The sequencer 108 operates the gradient magnetic field power supply 105, the transmitter 106, and the receiver 107 according to a predetermined pulse sequence. Various pulse sequences are stored in the device, and when imaging, the sequencer 108 calculates a pulse sequence to be used for imaging using imaging conditions and imaging parameters set via the UI unit 40, etc., and imaging is performed based on the calculated pulse sequence. In this embodiment, imaging is performed based on blade-type radial measurement.

[0025] The computer 30 can be configured with a computer having a CPU and a memory, and realizes functions as a control unit such as an imaging control unit 310 and a display control unit 320, and functions as a calculation unit such as an image reconstruction unit 330. The imaging control unit 310 controls the operation of the imaging unit 10 via the sequencer 108. In the MRI apparatus 1 of this embodiment, the imaging control unit 310 controls the sampling pattern of each blade in the case of blade-type radial measurement. FIG. 2 shows an example of a functional block diagram of the computer 30 related to the control of blade-type radial measurement.

[0026] As shown in the figure, the imaging control unit 310 is provided with a sampling pattern setting unit 340. In blade-type radial measurement, the sampling pattern setting unit 340 determines the number of blades (number of shots), rotation angle, blade width, and number of measurement lines within the blade from the imaging conditions input by the user, and sets a sampling pattern with unequal intervals between lines.

[0027] The image reconstruction unit 330 performs image reconstruction using an appropriate image reconstruction method for the k-space data obtained by the blade-type radial measurement. For example, image reconstruction using fast Fourier transform or sequential calculation such as compressed sensing is performed. In addition, when the RF receiving coil is a multi-channel coil, it performs synthesis of data collected for each channel, parallel imaging reconstruction using the sensitivity distribution of each small coil, etc.

[0028] Furthermore, the calculator 30 may have a function (evaluation unit 350) for evaluating the sampling pattern of the blade-type radial measurement. The evaluation unit 350, for example, calculates an evaluation value based on a predetermined evaluation criterion for the sampling pattern, and generates a preliminary image such as a simulation image when the sampling pattern is used.

[0029] The display control unit 320 causes the UI unit 40 to display a GUI for accepting user settings for the imaging conditions of the blade-type radial measurement, particularly the sampling pattern, and also accepts the user settings through the GUI and passes them to the imaging control unit 310. When the evaluation unit 350 is provided, the display control unit 320 causes the UI unit 40 to display the evaluation results by the evaluation unit 350 and the preliminary images generated by the preliminary image generation unit 353.

[0030] The functions of the computer 30 as the control unit and the calculation unit described above are stored in memory as programs in advance, and are realized by the CPU uploading and executing the programs for each function. However, some of the functions of the computer 30 can also be executed by a programmable IC.

[0031] Next, the blade-type radial measurement and its sampling pattern will be explained. First, the pulse sequence of the blade-type radial measurement and the k-space data acquired by the blade-type radial measurement will be described.

[0032] The pulse sequence used for imaging of the blade-type radial measurement is not limited, but a pulse sequence is executed to continuously acquire multiple nuclear magnetic resonance signals after applying one excitation RF pulse (hereinafter referred to as excitation pulse). Examples of such pulse sequences include a sequence of the FSE (Fast Spin Echo) method and a pulse sequence of the gradient echo system. FIG. 3 shows an example of an FSE pulse sequence. In this FSE sequence, a nuclear magnetic resonance signal is generated as a spin echo 205 by applying an inversion RF pulse 201 and measured. The application of the inversion RF pulse 201 is repeated while changing the magnitude of the phase encoding gradient magnetic field (Gp) 203 for each inversion RF pulse, and data for one blade is collected. One echo 205 corresponds to one line in the blade. Although six echoes are shown in FIG. 3, the number of echoes is arbitrary.

[0033] By executing a similar pulse sequence with different axes (combination of two axes) of the readout gradient magnetic field (Gp) and the phase encoding gradient magnetic field (Gp), data with different blade angles can be collected on the same slice surface. Note that, although Fig. 3 shows a 2D pulse sequence that applies a slice gradient magnetic field (Gs) 202 that selects a slice surface together with an excitation pulse 200 and an inversion RF pulse 201, a 3D pulse sequence using a slice encoding gradient magnetic field may also be used.

[0034] The k-space arrangement of data obtained by such blade-type radial measurement, i.e., the sampling pattern, is shown in FIG. 4. The upper part of FIG. 4 shows an example of k-space data obtained by general blade-type radial measurement, with one blade 410A shown on the left and all k-space data 400A obtained by rotating the blade and measuring it on the right. In a general sampling pattern, the lines within the blade are arranged at equal intervals. If the lines within the blade are evenly spaced, the effect of thinning out will be a coherent signal, which will cause artifacts. The MRI apparatus of this embodiment employs a sampling pattern 400B in which the lines within the blade 410B are unevenly spaced.

[0035] The line spacing within the blade is determined by how the encoding step of the phase encoding gradient magnetic field pulse 203 is changed. In a typical sampling pattern, the encoding step changes linearly as shown by the dotted line in Figure 3, whereas in this embodiment, the change is non-linear, thereby controlling the spacing to be unequal.

[0036] The uneven spacing is not limited to this embodiment, and the lower part of Figure 4 shows an example of uneven spacing in which the central region of the blade is dense and the data in the peripheral region is thinned out, but there are also other embodiments in which the line spacing is random.

[0037] Fig. 5 shows the details of an unevenly spaced sampling pattern in which the intervals increase from the center to the periphery. The left side of Fig. 5 shows an example of a geometric series interval, and the right side shows an example of a Fibonacci series interval. If the width between the center line of the blade and the nth line at the very edge is wb, then in the case of a geometric series interval, Δ=wb / n 2 Let the distance between the center line of the blade and the nth line (n=1, 2,...) be n 2 Let Δ be the Fibonacci interval. Δ is calculated so that the line interval is the Fibonacci sequence (excluding the first 0 and 1) × Δ. As for unequal intervals that increase in interval from the center to the periphery, intervals that change according to a quadratic function, etc., can be used.

[0038] In the case of sequential calculations involving conversion to a sparse space such as compressed sensing for image reconstruction, it is preferable for the data to be random, so random sampling is suitable. In that case, the uneven spacing pattern is not limited to a pattern in which the line spacing gradually increases / decreases as shown in Figure 5, but may be a pattern in which the spacing changes randomly within the blade, or the pattern may differ depending on the blade (randomness between blades) as shown in Figure 6. In the example of Figure 6, the line spacing differs for each blade.

[0039] The sampling pattern may be unevenly spaced for all blades, or may be evenly spaced for some blades and unevenly spaced for others. If there are multiple blades that are unevenly spaced, the patterns may be the same for the multiple blades, or may be different.

[0040] Of the above-mentioned sampling patterns, which sampling pattern is to be used may be preset, or may be set by accepting a user setting or user adjustment via the UI unit 40.

[0041] The flow of imaging control in the MRI apparatus configured as above will be described below. As shown in Fig. 7, first, when blade-type radial measurement is set as an imaging condition (S1), the sampling pattern setting unit 340 determines imaging parameters (number of blades, blade width, number of measurement lines in the blade (echo train length): ETL) and sets a sampling pattern (S2). Specifically, a blade-shaped sampling region is set in the k-space at a position rotated around the origin, and measurement lines are set in parallel to each other in the longitudinal direction of the blade in each blade. At that time, the measurement lines are set at unequal intervals in the lateral direction of the blade. The encoding step of the phase encoding gradient magnetic field pulse is determined based on the set sampling pattern.

[0042] If there is no user designation (S3), the imaging control unit 310 controls the imaging unit 10 at the determined encoding step and performs blade-type radial measurement (S4). That is, for example, echoes are measured according to the FSE pulse sequence shown in Fig. 3, and k-space data as shown in Fig. 4(B) is collected.

[0043] The image reconstruction unit 330 reconstructs an image by calculation using the collected k-space data (S5). The image reconstruction method is the same as that of a typical radial scan, and reconstruction is performed by fast Fourier transform (FFT) after gridding (data rearrangement to the grid points of k-space) or sequential calculation. At that time, sensitivity correction of the receiving coil and channel synthesis are performed as necessary. The optimal reconstruction method may be automatically selected according to the set sampling pattern.

[0044] When the sampling pattern set by the sampling pattern setting unit 340 is to be adjusted or specified by the user (S3), the sampling pattern setting unit 340 determines the sampling pattern again based on the conditions specified by the user, and the process proceeds to step S4.

[0045] According to this embodiment, in blade-type radial measurement in which k-space data is collected by varying the blade angle, the intervals between lines in the blade are controlled to be unequal, thereby suppressing the occurrence of artifacts that tend to occur when the intervals are equal. In addition, even when the k-space is thinned out and measured, the sampling pattern can be optimized, and the imaging speed can be increased while suppressing the deterioration of image quality.

[0046] <Embodiment 2> In this embodiment, a function of evaluating a sampling pattern and an adjustment function based on the evaluation result are added to the control unit of embodiment 1. The configuration of the computer of this embodiment is shown in Fig. 8. In Fig. 8, the same elements as in Fig. 2 are indicated by the same reference numerals, and duplicated explanations will be omitted.

[0047] As shown in Fig. 8, the MRI apparatus of this embodiment includes an evaluation unit 350 in the computer 30 that calculates an index of whether the sampling pattern set by the sampling pattern setting unit 340 is appropriate. In this embodiment, the evaluation unit 350 includes an evaluation value calculation unit 351 and a preliminary image generation unit 353, and the evaluation unit 350 calculates an evaluation value based on a predetermined criterion and generates a predicted image (hereinafter referred to as a preliminary image) obtained when a blade-shaped radial measurement is performed using the set sampling pattern. However, the evaluation index may be either the evaluation value or the preliminary image, and in that case, one of the evaluation value calculation unit 351 and the preliminary image generation unit 353 can be omitted.

[0048] In this embodiment, a line spacing adjustment unit 341 that adjusts the line spacing within the blade may be provided as a function of the imaging control unit 310. The function of adjusting the line spacing will be described later.

[0049] The evaluation of a sampling pattern evaluates how the sampling pattern affects the point spread function (PSF). Indices for evaluating the effect on the PSF include, for example, the maximum value of the side lobe of the PSF in the sampling pattern and the sampling density.

[0050] The PSF in the sampling pattern can be created by gridding simulated data in which the sampling positions are set to 1 and other positions to 0, and then performing an inverse Fourier transform. The maximum value of the side lobe is calculated from the side lobe shape of this PSF, and this value is used as the evaluation value.

[0051] The side lobe and its maximum value will be described in detail with reference to Figs. 9 and 10. Fig. 9 shows the sampling patterns of a typical blade-type radial measurement (Type A) in which the line intervals within the blade are uniform, and the blade-type radial measurement of the embodiment of the present invention (Types B and C), and Fig. 10 shows the PSF results for these three sampling patterns. The upper side of Fig. 10 is a PSF image, where (A) is a speed ratio of 2 and (B) is a speed ratio of 4. The lower side of Fig. 10 shows a horizontal line profile passing through the origin of the upper image, where (C) is a speed ratio of 2 and (D) is a speed ratio of 4. Note that the blade-type radial measurement is for 10 shots (number of blades = 10). Type B is sampling at geometric series intervals, and Type C is sampling at Fibonacci intervals.

[0052] As shown in Figure 10(A), in the radial measurement of the blade type of Type A, the side lobes of the PSF are scattered in a ring shape around the origin. On the other hand, in Types B and C, the side lobes of the PSF show a radial spread. As shown in Figure 10(C), the profile shows that in Type A, the scattered signal state is clearly visible as a side lobe peak, while in Types B and C, the side lobes are leveled and no large peaks appear.

[0053] As shown in FIG. 10D, when the thinning rate is increased (thinning rate = 4), the size of the side lobes is larger in all cases than when the thinning rate = 2. However, the tendency is the same as when the thinning rate = 2, and the side lobes that were clear in Type A are leveled out in Types B and C.

[0054] When the side lobes are clearly separated, the maximum value is large, which causes artifacts. Therefore, by knowing the size of the maximum value, it is possible to evaluate the degree to which artifacts are suppressed.

[0055] Regarding the sampling density, the sampling pattern is divided into regions, the density of the sampling points is calculated for each region, and it is evaluated whether the sampling density of each region is within an appropriate range. For example, predetermined thresholds (Th1, Th2) are set for the peripheral region and the central region, and the evaluation value of the density is calculated based on criteria such as (1) the peripheral region is not completely sparse (for example, the sampling density of the peripheral region is equal to or greater than the threshold Th1) and (2) the central region is relatively dense (for example, the sampling density of the central region is equal to the threshold Th2).

[0056] The preliminary image can be generated in advance, for example, by performing blade-type radial measurement for each sampling pattern using a digital phantom. When a sampling pattern is set, the preliminary image generated for that pattern is displayed. Note that since the image differs depending on the number of lines in the blade and the thinning rate, preliminary images are generated with these conditions changed for each sampling pattern, and a preliminary image is selected and displayed according to the conditions of the set sampling pattern.

[0057] The display control unit 320 may be configured to display the preview images generated by the preview image generation unit 353 in sequential order in thumbnail format each time the sampling pattern to be processed by the evaluation unit 350 and its conditions are changed.

[0058] By referring to the above-mentioned evaluation values ​​and preview images, the user can determine whether or not to proceed with measurement using the set sampling pattern, and can also change the pattern or conditions and select the pattern again, adjust the number of lines or the speed ratio, etc.

[0059] Next, the flow of processing for blade-type radial measurement in this embodiment will be described with reference to Fig. 11. In Fig. 11, the same processes as those in Fig. 7 are designated by the same reference numerals, and overlapping descriptions will be omitted.

[0060] When the imaging control unit 310 selects blade-type radial measurement as the imaging method and sets the imaging conditions (S1), the sampling pattern setting unit 340 sets a sampling pattern based on the imaging conditions (S2). The evaluation unit 350 evaluates the sampling pattern set by the sampling pattern setting unit 340 (S21). Note that, although the process of user specification or change of the sampling pattern (FIG. 7: S3) is omitted in FIG. 11, user adjustment may be accepted prior to the evaluation by the evaluation unit 350. In that case, the sampling pattern after the user adjustment is evaluated.

[0061] As described above, the evaluation involves at least one of the calculation of an evaluation value based on the maximum value of the side lobe and the sampling density, and the generation of a preliminary image. The display control unit 320 displays the evaluation result of the evaluation unit 350 (S22). Depending on the displayed result, the user decides whether or not to make a new designation. If there is no user designation (S3), the process proceeds to step S4, where a blade-shaped radial measurement is performed using the set sampling pattern (S4), and a reconstructed image is displayed (S5).

[0062] Based on the results of the evaluation, the line spacing of the sampling pattern may be automatically adjusted by the device.

[0063] In this case, as shown in FIG. 8, the imaging control unit 310 is provided with a line spacing adjustment unit 341 that is associated with the sampling pattern setting unit 340 and realizes a function of adjusting the line spacing. When the line spacing adjustment unit 341 receives the evaluation result (evaluation value) of the evaluation unit 350, if the evaluation value is lower than a preset reference value, the line spacing adjustment unit 341 changes the line spacing. The reference value is, for example, an evaluation value of equal-interval sampling in a typical blade-type radial measurement, or an evaluation value that is several percent or more better than the evaluation value. Alternatively, if the sampling density does not satisfy the reference value in either the peripheral region or the central region, it is determined that the sampling density is lower than the reference value. If the sampling density is the evaluation value, the line spacing is adjusted so that the sampling density is appropriate. In the case of the maximum value of the side lobe, the line spacing that minimizes the maximum value may be searched for by repeating fine adjustment and evaluation by the evaluation unit 350. The processing by the line spacing adjustment unit 341 includes or replaces the user designation / change in step S3 in the flow of FIG. 10.

[0064] Even when the line spacing adjustment is performed automatically within the device, the display control unit 320 may cause the UI unit 40 to display the evaluation results during and after the adjustment, the sampling pattern and its conditions, or preview images at that time.

[0065] By automatically adjusting the line spacing in this way, the user can avoid the troublesome task of resetting the imaging conditions, etc. Furthermore, the results are displayed, allowing the user to confirm that the sampling pattern is as desired.

[0066] According to this embodiment, in addition to the same effects as those of the first embodiment, by evaluating the sampling pattern and setting the sampling pattern reflecting the results, it is possible to optimize sampling with greater precision, thereby suppressing artifacts while increasing speed.

[0067] In addition, by presenting the set sampling to the user and displaying a GUI that accepts conditions for setting the sampling pattern, the user's freedom in setting the sampling pattern can be increased, enabling appropriate settings. In particular, by providing parameters for the user to adjust the set uneven intervals as imaging conditions, the user can clearly understand what is to be adjusted.

[0068] <Display embodiment> FIG. 12 shows an example of a GUI that enables the user to make the above-mentioned adjustments. 12 is a diagram showing an example of a display screen 1200 of the display device of the UI unit 40. Broadly speaking, the screen displays a block 1201 for inputting imaging conditions, an image display block 1202, and an operation button block 1203. This screen is switched and displayed, for example, when blade-type radial measurement is selected on the upper imaging condition setting screen.

[0069] The imaging condition block 1201 displays conditions specialized for blade-type radial measurement, such as the number of blades (number of shots), ETL (number of lines in a blade), and selection of even or uneven sampling intervals (uneven). Default values ​​set in advance are displayed and can be changed by the user. When uneven sampling intervals are selected, for example, a new window 1204 may be opened, allowing selection of an uneven sampling pattern (Type B, Type C, etc.), setting of sampling density, degree of uneven intervals, etc. to be set.

[0070] When the function of the evaluation unit 350 is included, the user operates each button of the operation button block 1203 to perform evaluation such as calculation of an evaluation value and generation of a preview image, and display of the evaluation result. The preview image is displayed in the image display block 1202. The evaluation value may be displayed together with the image.

[0071] The set sampling pattern and conditions are determined by the user pressing the enter button.

[0072] The GUI in FIG. 12 and the above description are merely examples, and various modifications are possible depending on the functions of the imaging control unit, such as omitting or modifying some of the GUI, providing additional instruction buttons, or providing a display block for the automatic adjustment results.

[0073] Providing such a user interface improves the convenience of the sampling pattern design involving the user. [Explanation of symbols]

[0074] 10: imaging unit, 30: computer (control unit), 310: imaging control unit, 320: display control unit, 330: image reconstruction unit, 340: sampling pattern setting unit, 350: evaluation unit

Claims

1. an imaging unit that measures a nuclear magnetic resonance signal generated by a subject in accordance with a predetermined pulse sequence and collects k-space data; and a control unit that controls sampling of the nuclear magnetic resonance signal; The control unit controls the angle of blades consisting of multiple parallel sampling lines to sample k-space radially, and in this case, the spacing between the multiple parallel sampling lines is made unequal for at least one of the multiple blades having different angles.

2. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus according to claim 1, wherein the control unit controls the intervals between the lines so that the intervals become wider from the center to the outside.

3. 3. The magnetic resonance imaging apparatus according to claim 2, A magnetic resonance imaging apparatus, wherein the intervals between the lines are at least one of geometric series intervals, Fibonacci intervals, and intervals that vary according to a quadratic function.

4. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus according to claim 1, wherein the control unit performs control so that a sampling pattern is different depending on the blade.

5. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus according to claim 1, wherein the control unit includes an evaluation unit for evaluating sampling of the k-space.

6. 6. The magnetic resonance imaging apparatus according to claim 5, The magnetic resonance imaging apparatus according to claim 1, wherein the evaluation unit evaluates sampling by using a sampling density of k-space as an evaluation value.

7. 6. The magnetic resonance imaging apparatus according to claim 5, The magnetic resonance imaging apparatus according to claim 1, wherein the evaluation unit evaluates the sampling by using as an evaluation value a maximum value of a side lobe of a PFS (point spread function) generated by a sampling pattern.

8. 6. The magnetic resonance imaging apparatus according to claim 5, The magnetic resonance imaging apparatus according to claim 1, wherein the control unit adjusts the interval between the lines based on the evaluation value of the evaluation unit.

9. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus further comprising a UI unit that presents to a user at least one of a k-space sampling pattern and a predicted image reconstructed from k-space data of the sampling pattern.

10. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus further comprising a UI unit that accepts user selection or user adjustment of a sampling pattern of k-space.

11. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus further comprises an image reconstruction unit that reconstructs an image of the subject by Fourier transform or iterative reconstruction calculation using the k-space data.

12. 12. The magnetic resonance imaging apparatus according to claim 11, The control unit sets the intervals between the lines to random intervals, The magnetic resonance imaging apparatus according to claim 1, wherein the image reconstruction unit generates an image by a sequential reconstruction calculation.

13. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus, wherein the pulse sequence is an FSE sequence or a GrE multi-echo sequence, and one blade is sampled by one excitation pulse.

14. A method for controlling a magnetic resonance imaging apparatus having an imaging unit that measures nuclear magnetic resonance signals generated by a subject and collects k-space data in accordance with a predetermined pulse sequence, comprising the steps of: A control method comprising: controlling the radial sampling of k-space by varying the angles of blades consisting of multiple parallel sampling lines; and, in so doing, making the spacing between the parallel sampling lines unequal for at least one of the multiple blades having different angles.

15. A method for controlling a magnetic resonance imaging apparatus according to claim 14, comprising the steps of: evaluating a sampling pattern; A control method comprising adjusting the unequal intervals based on an evaluation result of the sampling pattern.

Images