JP6013324B2 - Magnetic resonance imaging apparatus and radial sampling method - Google Patents

Description

  The present invention relates to radial sampling using an FSE sequence in a magnetic resonance imaging (hereinafter referred to as MRI) apparatus, and more particularly to a measurement order of echo data in a blade.

  The MRI device measures NMR signals (echo signals) generated by the spins of the subject, especially the tissues of the human body, and forms the shape and function of the head, abdomen, limbs, etc. in two or three dimensions. It is a device that images. In imaging, the echo signal is given different phase encoding depending on the gradient magnetic field and is frequency-encoded and measured as time-series data. The measured echo signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  In the MRI apparatus, imaging of a subject is performed using a high-speed spin echo (hereinafter referred to as FSE) sequence. In the FSE sequence, the mixture of echo signals with different echo times (TE) affects the image contrast.Therefore, the echo time of echo data measured by the TE set by the operator is treated as effective TE instead of true TE. Is called. In the orthogonal sampling method using the FSE sequence, the echo data corresponding to the effective TE is arranged at the center of the k space, so that the contrast of the echo data of the effective TE is reflected in the contrast of the image. That is, the effective TE echo data determines the contrast of the image.

  On the other hand, radial sampling has been put to practical use as one of non-orthogonal sampling methods. In the case of radial sampling using an FSE sequence (hereinafter also referred to as radial scan), a plurality of echo data having different TEs acquired in one repetition time (TR) are arranged in the blade. At this time, the echo data of the effective TE is arranged on a locus passing through the center of the k space in the blade. However, since the echo data of TE different from the effective TE is mixed in the blade, and all the blades are arranged near the center of k-space, the echo data of different TE is compared with the orthogonal sampling method. There is a case where an image having a desired contrast specified by the effective TE cannot be obtained.

  In Patent Document 1, each echo data is sequentially measured from the end within the blade, and then the measurement order is reversed to measure twice in total, and the obtained echo data is added for each blade to obtain an image of the subject. As a result, the image quality is improved.

JP 2006-304955 A

  However, in the invention described in Patent Document 1, since the measurement order of each echo data is reversed and measured twice, the imaging time is doubled, thus leaving an unsolved problem that the imaging time is extended. .

  Therefore, the object of the present invention is that the contrast of the echo data of the effective TE is clearly reflected by the image contrast in the radial scan without extending the imaging time, and the contrast closer to the contrast expected by the designation of the effective TE is obtained. An MRI apparatus and a radial sampling method capable of obtaining an image having the same are provided.

In order to achieve the above object, the present invention measures echo data along each parallel trajectory in a blade having a plurality of parallel trajectories in k space in one repetition time, and Is a radial sampling method for performing radial sampling that repeats measurement of echo data of each blade by rotating the blades around the blade, and the measurement order of echo data with one blade and the other blade, The phase encoding direction of the blade is set to be opposite to each other, and the measurement of echo data from the subject is controlled based on radial sampling .

  The MRI apparatus and the radial sampling method of the present invention invert the echo data measurement order in the selected blade around the effective TE echo data, thereby affecting the effect of different TE echo data on image contrast in k-space. Disperse isotropically. As a result, the contrast of the effective TE echo data is clearly reflected by the image contrast without extending the imaging time, and it is possible to obtain an image having a contrast close to the TE specified by the effective TE.

The block diagram which shows the whole structure of one Example of the MRI apparatus which concerns on this invention A diagram showing an example of a radial sampling measurement trajectory in a two-dimensional k-space having a (kx-ky) axis is a diagram of the entire configuration of the k-space, and (b) shows details of the blade 201 parallel to the kx-axis. Schematic illustration Sequence chart showing an example of a 2D FSE sequence for 2D radial sampling The figure (a) showing the case where the first embodiment is applied to the k space representing the radial sampling shown in FIG. 2 is a bell showing a case where the measurement order of echo data is reversed every three blades. b) shows an example of reversing the measurement order of blade echo data every other blade FIG. 6 shows a data distribution diagram in the k space when only echo data of TE different from effective TE is extracted in the radial scan using the FSE sequence according to the present invention. (a) is an overall view of the k-space distribution map, and (b) is an enlarged view of the central part of k-space. The data distribution figure in k space at the time of extracting only the echo data of TE different from effective TE in the radial scan using the conventional FSE sequence is shown. (a) is an overall view of the k-space distribution map, and (b) is an enlarged view of the central part of k-space. FIG. 2A is a diagram illustrating a case where the second embodiment is applied to the k-space representing the radial sampling illustrated in FIG. 2, and illustrates a case where the measurement order of echo data is reversed every three blades. b) shows an example of reversing the measurement order of blade echo data every other blade Functional block diagram showing each function of arithmetic processing unit 114 according to an embodiment of the present invention The flowchart which shows the processing flow based on the Example of this invention. Diagram showing an example of the imaging parameter setting GUI

  Hereinafter, preferred embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings. In all the drawings for explaining the embodiments of the invention, those having the same function are given the same reference numerals, and their repeated explanation is omitted.

  First, an MRI apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of an embodiment of an MRI apparatus according to the present invention.

  This MRI apparatus uses a NMR phenomenon to obtain a tomographic image of a subject 101. As shown in FIG. 1, a static magnetic field generating magnet 102, a gradient magnetic field coil 103, a gradient magnetic field power supply 109, and an RF transmission coil 104, an RF transmitter 110, an RF receiver coil 105, a signal detector 106, a signal processor 107, a measurement controller 111, an overall controller 108, a display / operation unit 113, and a subject 101 are mounted. And a bed 112 for taking the top plate into and out of the static magnetic field generating magnet 102.

  The static magnetic field generating magnet 102 generates a uniform static magnetic field in the direction perpendicular to the body axis of the subject 101 in the vertical magnetic field method and in the body axis direction in the horizontal magnetic field method. A permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the.

  The gradient magnetic field coil 103 is a coil wound in the three-axis directions of X, Y, and Z that are the real space coordinate system (stationary coordinate system) of the MRI apparatus, and each gradient magnetic field coil is a gradient magnetic field that drives it. A current is supplied to the power source 109. Specifically, the gradient magnetic field power supply 109 of each gradient coil is driven according to a command from the measurement control unit 111 described later, and supplies a current to each gradient coil. Thereby, gradient magnetic fields Gx, Gy, and Gz are generated in the three-axis directions of X, Y, and Z.

  When imaging a two-dimensional slice plane, a slice gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 101, orthogonal to the slice plane and orthogonal to each other. Phase encoding gradient magnetic field pulse (Gp) and frequency encoding (leadout) gradient magnetic field pulse (Gf) are applied in the remaining two directions, and position information in each direction is encoded in the NMR signal (echo signal). .

  The RF transmission coil 104 is a coil that irradiates the subject 101 with an RF pulse, and is connected to the RF transmission unit 110 and supplied with a high-frequency pulse current. As a result, an NMR phenomenon is induced in the spins of atoms constituting the living tissue of the subject 101. Specifically, the RF transmission unit 110 is driven in accordance with a command from the measurement control unit 111 described later, and the RF transmission coil 104 is disposed in the vicinity of the subject 101 after the high frequency pulse is amplitude-modulated and amplified. , The subject 101 is irradiated with an RF pulse.

  The RF receiving coil 105 is a coil that receives an echo signal emitted by the NMR phenomenon of spin that constitutes the living tissue of the subject 101. The received echo signal is connected to the signal detecting unit 106 and is received by the signal detecting unit 106. Sent.

  The signal detection unit 106 performs processing for detecting an echo signal received by the RF receiving coil 105. Specifically, in accordance with a command from the measurement control unit 111 described later, the signal detection unit 106 amplifies the received echo signal, divides the signal into two orthogonal signals by quadrature detection, For example, 128, 256, 512, etc.) are sampled, each sampling signal is A / D converted into a digital quantity, and sent to a signal processing unit 107 described later. Therefore, the echo signal is obtained as time-series digital data (hereinafter referred to as echo data) composed of a predetermined number of sampling data.

  The signal processing unit 107 performs various processes on the echo data, and sends the processed echo data to the measurement control unit 111.

  The measurement control unit 111 mainly transmits various commands for collecting echo data necessary for reconstruction of the tomographic image of the subject 101 to the gradient magnetic field power source 109, the RF transmission unit 110, and the signal detection unit 106. And a control unit for controlling them. Specifically, the measurement control unit 111 operates under the control of the overall control unit 108, which will be described later, and controls the gradient magnetic field power source 109, the RF transmission unit 110, and the signal detection unit 106 based on a predetermined sequence of control data. Then, it is necessary to reconstruct the image of the imaging region of the subject 101 by repeatedly performing the irradiation of the RF pulse and the application of the gradient magnetic field pulse to the subject 101 and the detection of the echo signal from the subject 101. Control the collection of accurate echo data. In the repetition, the application amount of the phase encoding gradient magnetic field is changed in the case of two-dimensional imaging, and the application amount of the slice encoding gradient magnetic field is further changed in the case of three-dimensional imaging. Values such as 128, 256, and 512 are normally selected as the number of phase encodings, and values such as 16, 32, and 64 are normally selected as the number of slice encodings. With these controls, echo data from the signal processing unit 107 is output to the overall control unit 108.

  The overall control unit 108 controls the measurement control unit 111 and controls various data processing and processing result display and storage, and includes an arithmetic processing unit 114 having a CPU and a memory, an optical disc, And a storage unit 115 such as a magnetic disk. Specifically, the measurement control unit 111 is controlled to execute the collection of echo data, and when the echo data is input from the measurement control unit 111, the arithmetic processing unit 114 converts the encoded information applied to the echo data. Based on this, it is stored in an area corresponding to the k space in the memory. Hereinafter, the description that the echo data is arranged in the k space means that the echo data is stored in an area corresponding to the k space in the memory. A group of echo data stored in an area corresponding to the k space in the memory is also referred to as k space data. The arithmetic processing unit 114 performs processing such as signal processing and image reconstruction by Fourier transform on the k-space data, and displays the resulting image of the subject 101 on the display / operation unit 113 described later. And is recorded in the storage unit 115.

  The display / operation unit 113 includes a display unit for displaying the reconstructed image of the subject 101, a trackball or a mouse and a keyboard for inputting various control information of the MRI apparatus and control information for processing performed by the overall control unit 108. Etc., and an operation unit. The operation unit is disposed in the vicinity of the display unit, and an operator interactively controls various processes of the MRI apparatus through the operation unit while looking at the display unit.

  At present, the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is a main constituent material of the subject as being widely used clinically. By imaging information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

(Radial scan measurement trajectory in k-space)
First, the radial scan according to the present invention will be described.

  In radial sampling, a blade having a plurality of parallel loci in k space is used as a unit region, and a plurality of blades are arranged around the origin at different rotation angles to sample substantially the entire k space. The angle between the blades is preferably equal, but may not be equal. Since each blade has a plurality of parallel trajectories, the direction perpendicular to the parallel trajectories is taken as the phase encoding direction, and the echo data of each parallel trajectory is added with phase encoding and measured. Since each blade is arranged so as to overlap each other in the low spatial frequency region near the center of the k space, the echo data in the low spatial frequency region near the center of the k space is measured a plurality of times or densely. Become.

  In one blade, in the sequential order measurement order, the echo data of each parallel locus is sequentially measured from one end to the other end in the blade phase encoding direction. On the other hand, in the measurement order of the centric order, the echo data of each parallel locus is sequentially measured while alternately reversing the polarity of the phase encoding from the center toward both ends with respect to the phase encoding direction of the blade.

  FIG. 2 shows an example of a radial sampling measurement locus in a two-dimensional k-space having a (kx-ky) axis. FIG. 2 (a) shows the entire configuration of the k space, and FIG. 2 (b) schematically shows details of the blade 201 parallel to the kx axis. One rectangle means one measurement trajectory and echo data corresponding to the trajectory. The radial sampling measurement trajectory is an example in which six blades having five parallel trajectories (in the example of FIG. 2 (b), five rectangles) are arranged around the k-space origin every 30 °. In particular, the blade 201 parallel to the kx axis indicates that echo data of parallel trajectories 201-1 to 201-5 is measured. In the blade 201 shown in FIG. 2 (b), if the measurement order is a sequential order, (201-1-> 201-2-> 201-3-> 201-4-> 201-5) 212-1 or ( 201-5-> 201-4-> 201-3-> 201-2-> 201-1) The echo data of each locus is measured in the order of 212-2. If it is a centric order, (201-3-> 201-4-> 201-2-> 201-5-> 201-1) 213-1 or (201-3-> 201-2-> 201-4 -> 201-1-> 201-5) The echo data of each locus is measured in the order of 213-2. The same applies to the other blades.

  In the example shown in FIG. 2, since five (odd number) echo data are measured for each blade, the echo data arranged at the center of the blade is echo data measured at the time of effective TE. In the case of the blade 201, the echo data 201-3 arranged at the center thereof is the effective TE echo data. When an even number of echo data is measured by each blade, there is no echo data measured at the effective TE time, and two echo data measured before and after the effective TE sandwich the center of the blade. Will be placed.

(FSE sequence with radial sampling)
Next, the FSE sequence when performing a radial scan will be described with reference to FIG. Figure 3 shows an example of a two-dimensional FSE sequence for performing two-dimensional radial sampling, with one excitation, that is, within one repetition time (TR), echoes along each parallel trajectory that constitutes one blade. It is a sequence chart which shows the case where each data is measured. Therefore, the number of echo data (ETL; Echo Train Length) measured within one repetition time (TR) and the number of parallel trajectories constituting one blade are the same value.

  In FIG. 3, RF, Gs, Gkx, Gky, and Echo represent the axes of the RF pulse, slice gradient magnetic field, kx direction encode gradient magnetic field, ky direction encode gradient magnetic field, and echo signal, respectively. The main difference between the FSE sequence in radial sampling and the FSE sequence in the orthogonal sampling method is that there is no distinction between the phase encoding direction Gp and the frequency encoding direction Gf. Therefore, in FIG. 3, the gradient magnetic field in two directions perpendicular to the slice direction is used as the kx direction encoded gradient magnetic field Gkx and the ky direction encoded gradient magnetic field Gky without representing the phase encode gradient magnetic field axis Gp and the frequency encode gradient magnetic field axis Gf. It represents the direction.

  In the FSE sequence 300, a refocus RF pulse 302 is sequentially applied after one excitation RF pulse 301, and each echo signal 341 is measured between the refocus RF pulses 302, for a total of five echo signals (ETL = 5). This is an example of measuring (341-1 to 341-5). Specifically, the excitation RF pulse 301 is applied to the spin in the imaging surface, and the slice selection gradient magnetic field pulse 311 is applied.

  Thereafter, a refocus RF pulse 302 for reversing the spin in the slice plane is repeatedly applied. Here, as described above, in order to measure five echo signal groups (341-1 to 341-5) for one excitation RF pulse 301, the refocus RF pulse 302 is performed five times (302-1 to 302). -5) Apply. Then, each time the refocus RF pulse 302 is applied, a slice selection gradient magnetic field pulse 312 for selecting a slice is applied, and a phase encoding gradient magnetic field pulse 321, a read gradient magnetic field pulse 322, and a rephase gradient magnetic field pulse 323 are applied in the kx direction. The echo signal 341 is measured by applying the phase encode gradient magnetic field pulse 331, the read gradient magnetic field pulse 332, and the rephase gradient magnetic field pulse 333 in the ky direction.

  In order to give different phase encodings to the echo signals (341-1 to 341-5), the application amounts of the phase encoding gradient magnetic field pulses 321 and 331 are different for each echo signal. Since the rephase gradient magnetic field pulse 323 is a gradient magnetic field pulse for canceling the application amount of the phase encode gradient magnetic field pulse 321 and returning it to zero, the rephase gradient magnetic field pulse 323 and the phase encode gradient magnetic field pulse 321 are absolute in reverse polarity. The value is the same applied amount. That is, as shown by the arrows, the application order is reversed. Similarly, the rephase gradient magnetic field pulse 333 and the phase encode gradient magnetic field pulse 323 have opposite polarities and the same absolute application amount, and the application order is reversed as indicated by arrows.

  In addition, in order to measure each of a plurality of blades having different rotation angles, for each time interval (TR) 351 between adjacent excitation RF pulses 301, the amplitude and applied amount of each gradient magnetic field pulse in the Gkx direction and the Gky direction (= The FSE sequence 300 is repeated while changing the area surrounded by the waveform and the axis according to the rotation angle, and echo signals 341 of all blades necessary for image reconstruction are measured. Depending on the rotation angle of the blade to be measured, the amplitude and applied amount of each gradient magnetic field pulse distributed in the Gkx direction and the Gky direction change, so the horizontal stripe pattern of Gkx and Gky in FIG. It shows that the gradient magnetic field pulse changes.

  One excitation by the excitation RF pulse 301, that is, one execution of the FSE sequence 300 is also called a shot. Therefore, the FSE sequence 300 that performs radial sampling is also a multi-shot FSE sequence.

  The k space shown in FIG. 2 and the FSE sequence shown in FIG. 3 show the case of two-dimensional imaging, but in the case of three-dimensional imaging, a three-dimensional k-space (kx, ky, ks) Data is acquired. In the 3D FSE sequence, in order to perform slice encoding (ks) on the echo signal, slice encoding gradient magnetic field pulses are applied in the slice direction Gs, and 3D k-space (kx, ky, ks) data is acquired. become. Since the 3D k-space data is configured by stacking the 2D k-space data shown in FIG. 2 in the ks direction, the 3D imaging is performed with the slice encoding set to a predetermined value as described above. This process is performed by repeating the process of acquiring k-space data while changing the slice encoding.

(Outline of the present invention)
In the radial scan method, the present invention is characterized in that the measurement order of echo data in at least one blade is different from the measurement order of echo data in other blades. Specifically, the measurement order of the echo data in the phase encoding direction of the blades is opposite to each other with respect to the echo data of the center of the blade or the effective TE in one blade and the other blade. That is, one blade is reversed with respect to the other blade with respect to the measurement order of the echo data in the phase encoding direction of the blade. This inversion of the measurement order is performed on the center of the blade or the echo data of the effective TE. In other words, the measurement order of echo data in one blade is reversed in the phase encoding direction of the blade with respect to the echo data of the center of the blade or effective TE with respect to the measurement order of echo data in the other blade.

  Hereinafter, some embodiments of how to change the measurement order of the echo data of the blade will be described.

(First embodiment: In the case of sequential order)
Next, a first embodiment of the MRI apparatus and radial sampling method of the present invention will be described. In the present embodiment, the measurement order of each echo data in the blade is a sequential order that is sequentially performed from one end to the other end with respect to the phase encoding direction of the blade. Then, the measurement order of echo data between one blade and the other blade is opposite to each other with respect to the phase encoding direction of the blade. Specifically, one blade has a measurement order in which echo data is measured in a direction in which phase encoding increases, and the other one blade has a measurement order in which echo data is measured in a direction in which phase encoding decreases. As a result, the measurement order of the echo data in the blade phase encoding direction is opposite to each other with respect to the center of the blade or the effective TE echo data in one blade and the other blade. Hereinafter, this embodiment will be described in detail based on FIG.

  FIG. 4 shows a case where the present embodiment is applied to the k-space representing the radial sampling shown in FIG. The blades 201 to 206 are assigned the same numbers 1 to 5 to the echo data at the same position. In this case, the echo data 3 is effective TE echo data and is arranged at the center of the blade. FIG. 4 (a) shows a case where the measurement order of echo data is reversed every three blades as an example of reversing the measurement order of the echo data of the blade every plural blades. Specifically, the blades 201 to 203 measure the echo data in the order of 1, 2, 3, 4, 5 in which the phase encoding increases, and the other blades 204 to 206 perform the echo data in the reverse direction. This is an example of measurement in the order of 5, 4, 3, 2, 1 in which the encoding decreases. FIG. 4B is an example in which the measurement order of the echo data of the blade is reversed every other blade. Specifically, in the blades 201, 203, and 205, echo data is measured in the order of 1, 2, 3, 4, and 5 in which the phase encoding increases, and in the other blades 202, 204, and 206, as the reverse direction, In this example, echo data is measured in the order of 5, 4, 3, 2, 1 in which the phase encoding decreases.

  In the example of FIG. 4 (a), all blades are divided into two groups of blades 201 to 203 and blades 204 to 206, and the groups of blades 204 to 206 are echoed to the blades 201 to 203. It can be regarded as a case where the data measurement order is reversed.

  The selection and combination of blades that change the measurement order may be performed directly by the operator, or may be selected by the operator from a plurality of predetermined blade patterns, or performed automatically. May be. Details will be described later.

  The effect of this embodiment will be described with reference to FIGS. FIGS. 5 and 6 show data distribution diagrams in the k-space (hereinafter referred to as k-space distribution diagrams) when only the echo data of the TE different from the effective TE is extracted in the radial scan using the FSE sequence. The portions where the echo data with different TEs overlap have different contribution ratios to the image contrast. Therefore, the display mode is changed based on the contribution ratios.

  501 in FIG. 5 (a) is an overall view of the k-space distribution diagram, and shows a case where the measurement order of the echo data of the blade shown in FIG. 4 (b) is reversed every other blade. Reference numeral 502 in FIG. 5 (b) is an enlarged view of the center portion of the k space 501. As indicated by 501, it is understood that the contribution ratio is isotropically distributed throughout the k-space. Further, as indicated by 502, it is understood that there is no portion showing a high contribution rate in the vicinity of the center of the k space. In other words, when measuring the echo data of the blade in sequential order, by reversing the measurement order every other blade, echo data other than the effective TE in the vicinity of the center of the k space is dispersed, and the image The contrast is close to that expected with effective TE. The same applies when the measurement order of the echo data of the blade shown in FIG. 4 (a) is reversed every three blades, and the measurement order of the echo data is the same for at least one blade and the other blade. A similar effect can be obtained by setting the direction opposite to the phase encoding direction.

  As a comparative example, FIG. 6 shows a case where the measurement order of echo data is the same for all blades. 601 corresponds to 501, and 602 corresponds to 502. As indicated by 601, it can be understood that the contribution ratio is concentrated on one side as compared with 501. Further, as indicated by 602, it can be understood that there is a portion showing a high contribution rate in the vicinity of the center of the k space as compared with 502. That is, in the vicinity of the center of the k space, many echo data of TE different from the effective TE are mixed, and the image contrast does not become the contrast expected by the effective TE. Therefore, an image obtained by reconstructing 501 k-space data has an image contrast closer to that expected by effective TE than an image obtained by reconstructing 601 k-space data. In addition, since the measurement order of echo data is only reversed with respect to the phase encoding direction of the blades with at least one blade and the other blade, the imaging time is not extended.

(Second embodiment: Centric order)
Next, a second embodiment of the MRI apparatus and radial sampling method of the present invention will be described. In the present embodiment, the measurement order of each echo data in the blade is a centric order in which the polarity of the phase encoding is alternately reversed from the center toward both ends with respect to the phase encoding direction of the blade. Then, at least one blade and the other blade are opposite to each other in the manner of alternating inversion. Specifically, the measurement order is such that the phase encode polarity is (0 + − + −...) For one blade, and the phase encode polarity is (0− +) for the other blade. The measurement order is such that − +. Here, the sign of 0 or + − in () indicates the polarity of phase encoding. As a result, the measurement order of the echo data in the blade phase encoding direction is opposite to each other with respect to the center of the blade or the effective TE echo data in one blade and the other blade. Hereinafter, the present embodiment will be described in detail based on FIG.

  FIG. 7 shows a case where the present embodiment is applied to the k-space representing the radial sampling shown in FIG. The blades 201 to 206 are assigned the same numbers 1 to 5 to the echo data at the same position. Also in this case, the echo data 3 is effective TE echo data and is arranged at the center of the blade. FIG. 7 (a) shows a case where the measurement order of the echo data is reversed every three blades as an example of reversing the measurement order of the echo data of the blade every plural blades. Specifically, the blades 201 to 203 measure echo data in the order of phase encoding 3 (0), 2 (+), 4 (−), 1 (+), 5 (−), and other blades. 204 to 206 are examples in which the echo data is measured in the order of phase encoding 3 (0), 4 (−), 2 (+), 5 (−), and 1 (+). FIG. 7B is an example in which the measurement order of the echo data of the blade is reversed every other blade. Specifically, the blades 201, 203, and 205 measure the echo data in the order of phase encoding 3 (0), 2 (+), 4 (-), 1 (+), 5 (-), etc. In the blades 202, 204, and 206, the echo data is measured in the order of phase encoding 3 (0), 4 (−), 2 (+), 5 (−), and 1 (+).

  In the example of FIG. 7 (a), as in the case of FIG. 4 (a), all blades are divided into two groups of blades 201 to 203 and blades 204 to 206. The group can be regarded as a case where the measurement order of the echo data is reversed with respect to the blades 201 to 203.

  The selection and combination of blades that change the measurement order are the same as in the first embodiment.

  The effect of this embodiment is the same as that of FIG. 5 described in the first embodiment. That is, 501 indicates that the measurement order of the echo data of the blade shown in FIG. 7 (a) is reversed every three blades, or the measurement order of the echo data of the blade shown in FIG. Corresponds to the case of inverting. Also in the second embodiment, as in the first embodiment described above, the contribution rate is isotropically distributed over the entire k space, and there is no portion showing a high contribution rate near the center of the k space. Therefore, when measuring the echo data of a blade in centric order, it is effective in the vicinity of the center of k-space by reversing the inversion of at least one blade and the other blade. Echo data other than TE is distributed. As a result, compared with the case where the measurement order of echo data is the same for all the blades shown in FIG. 6, the image contrast of the present embodiment is closer to the contrast expected in the effective TE.

(Selecting the blade to reverse the measurement order)
If at least one of the blades for reversing the echo data measurement order is present, the effects of the present invention can be exhibited. Preferably, if the number of blades that reverse the measurement order of echo data is half that of all blades, a balance is achieved with a blade that does not reverse the measurement order of echo data, and the contribution ratio is isotropically distributed throughout the k-space.

  There can be a plurality of combinations of blades that reverse the echo data measurement order. As shown in FIGS. 4 and 7, the echo data measurement order may be reversed every other blade or every other blade. Further, all the blades may be divided into a plurality of groups, and the measurement order of echo data of the blade group belonging to the selected group may be reversed.

  Further, the selection of the blade that reverses the measurement order of the echo data may be made by the operator directly selecting the blade, or by the operator selecting from a plurality of predetermined blade patterns. As described above, the blade pattern includes a plurality of blades, every other blade, or a blade group.

  Further, when the same blade is measured a plurality of times, addition / averaging may be performed by switching whether or not the echo data measurement order is reversed with the same blade.

(Example)
Based on the outline of each embodiment of the present invention described above, specific examples according to the present invention will be described.

  First, each function of the arithmetic processing unit 114 according to the radial sampling of the present embodiment will be described based on the functional block diagram shown in FIG. The arithmetic processing unit 114 according to this embodiment includes an imaging parameter display control unit 801, a radial sampling setting unit 802, a measurement order inversion blade selection unit 803, an echo data measurement order setting unit 804, a phase encoding gradient magnetic field setting unit 805, and imaging activation. Part 806. The outline of each function will be described below.

  The imaging parameter display control unit 801 generates an imaging parameter setting GUI (details will be described later) as shown in FIG. 9 and displays it on the display unit. And the setting or change of the imaging parameter from an operator is received. In particular, regarding the measurement order, selection of a sequential order or a centric order is accepted. Then, the value of the imaging parameter set or changed is notified to the radial sampling setting unit 802.

  The radial sampling setting unit 802 receives the imaging parameter value set by the imaging parameter display control unit 801. Based on the value of the imaging parameter, regarding the FSE sequence for radial sampling, specific control data necessary for the execution of the FSE sequence including the application timing and application amount of the RF pulse and gradient magnetic field pulse is generated. To do. In particular, the measurement order in the phase encoding direction of the echo data of the blade (that is, the phase encoding order for each echo data) is provisionally set according to whether the measurement order is a sequential order or a centric order.

  The measurement order reversal blade selection unit 803 accepts selection by the operator of the blade that reverses the measurement order of echo data on the imaging parameter setting GUI in the radial scan, and receives the selected blade information as the echo data measurement order setting unit 804. Notify Alternatively, a blade that reverses the measurement order of echo data may be automatically selected, and the selected blade information may be notified to the echo data measurement order setting unit 804. The selection of the blade that reverses the measurement order of the echo data is as described above.

  The echo data measurement order setting unit 804 includes information on the blade that reverses the measurement order of the echo data selected by the measurement order inversion blade selection unit 803, and phase encoding of the echo data of the blade temporarily set by the radial sampling setting unit 802. The direction measurement order is input. For the blades not selected, the measurement order of the echo data temporarily set by the radial sampling setting unit 802 is set (determined) as it is. On the other hand, for the selected blade, the echo data measurement order temporarily set by the radial sampling setting unit 802 is inverted to set (determine) the echo data measurement order of the blade. Specifically, when the measurement order is a sequential order, the echo data measurement order described in the first embodiment is reversed on the selected blade. When the measurement order is a centric order, the measurement order of the echo data described in the second embodiment is reversed on the selected blade. Then, the phase encoding order for each echo data of each blade is set so that the measurement order of the echo data of each blade is set.

  The phase encoding gradient magnetic field setting unit 805 receives the phase encoding order for each blade set by the echo data measurement order setting unit 804. Based on this phase encoding order, the application amount of the phase encoding gradient magnetic field pulse applied at the time of measuring each echo data in each blade is set for each echo data. Specifically, with respect to a blade whose echo data measurement order is not reversed, the phase encoding applied at the time of measurement of each echo data in the blade so as to be the echo data measurement order temporarily set by the radial sampling setting unit 802 The application amount of the gradient magnetic field pulse is set for each echo data. On the other hand, in the blade in which the measurement order of the echo data is reversed, the phase encoding gradient applied at the time of measuring each echo data in the blade so that the measurement order of the echo data reversed by the echo data measurement order setting unit 804 is obtained. The application amount of the magnetic field pulse is set for each echo data. Then, control data is generated so that the application amount of the phase encoding gradient magnetic field pulse set for each echo data is obtained.

  The imaging activation unit 806 receives control data generated by the radial sampling setting unit 802 and control data on the application amount of the phase encoding gradient magnetic field for each echo data set by the phase encoding gradient magnetic field setting unit 805. . The measurement control unit 111 is notified of specific control data necessary for executing the FSE sequence for performing radial sampling. Then, imaging by the radial scan is activated via the measurement control unit 111.

  Next, a processing flow of the present embodiment, which is performed in cooperation with each functional unit of the arithmetic processing unit 114, will be described based on a flowchart shown in FIG. This flowchart is stored in advance in the storage unit 115 as a radial sampling program, and is loaded into the memory of the arithmetic processing unit 114 and executed by the CPU or the like as necessary. Hereinafter, the processing of each step will be described.

  In step 901, a specific value is set for the imaging parameter. For example, the imaging parameter display control unit 801 generates an imaging parameter setting GUI as illustrated in FIG. 9 and causes the display unit to display the GUI. The operator sets, changes, or selects a specific value for each imaging parameter on the imaging parameter setting GUI.

  In step 902, the operator selects whether to perform a radial scan as an imaging sequence. For example, when the operator selects an FSE sequence as an imaging sequence on the imaging parameter setting GUI and designates radial sampling to be ON, a radial scan is selected, and the process proceeds to step 903. If it is not selected, imaging using another pulse sequence is executed, and the process proceeds to step 907 and imaging using the pulse sequence is executed.

  In step 903, since the radial scan is selected in step 902, the radial sampling setting unit 802 generates specific control data necessary for the execution of the radial scan. The radial scan in step 903 is a conventional radial scan before the echo data measurement order is reversed according to the present invention.

  In step 904, the operator sets whether or not to reverse the echo data measurement order on the imaging parameter setting GUI. This setting can also be determined based on whether or not a blade that reverses the echo data measurement order in step 905 is selected. When the measurement order is reversed, the process proceeds to step 905. If the measurement order is not reversed, the process proceeds to step 907 and the conventional radial scan set in step 902 is performed.

  In step 905, a blade that reverses the measurement order of echo data is selected. The measurement order reversing blade selection unit 803 displays a GUI for accepting selection of a blade for reversing the measurement order of echo data by the operator on the display unit, and accepts the operator's selection. For example, the measurement order reversal blade selection unit 803 displays the imaging parameter setting GUI on the display unit and accepts the operator's selection. Then, the operator selects a blade that reverses the measurement order of echo data on the imaging parameter setting GUI. The measurement order reversal blade selection unit 803 notifies the selected blade information to the echo data measurement order setting unit 804. Alternatively, the measurement order reversal blade selection unit 803 may automatically select a blade whose echo data measurement order is reversed and notify the echo data measurement order setting unit 804 of the selected blade information. The selection of the blade that reverses the measurement order of the echo data is as described above.

  In step 906, the phase encoding gradient magnetic field setting unit 805 sets the application sequence of the phase encoding gradient magnetic field used when measuring the echo data of the blade so that the measurement order of the echo data is reversed in the blade selected in step 905. To do. Specifically, when the measurement order is a sequential order, the application order of the phase encoding gradient magnetic field is set so that the measurement order described in the first embodiment is reversed in the selected blade, Control data for that purpose is generated. When the measurement order is a centric order, the application order of the phase encoding gradient magnetic field is set so that the measurement order described in the second embodiment is reversed in the selected blade, and control data for that is set. Is generated.

  In Step 907, the imaging activation unit 806 includes the radial scan generated in Step 903 including the control data of the application amount of the phase encoding gradient magnetic field in the blade that reverses the measurement order of the echo data generated in Step 906. The measurement control unit 111 is notified of other control data necessary for the execution of the above, and imaging by the radial scan is activated. Then, the measurement control unit 111 performs a radial scan by inverting the measurement order of echo data in the blade selected in step 905. Thereby, the measurement control unit 111 executes the radial scan by changing the measurement order of the echo data in at least one blade to be different from the measurement order of the echo data in the other blades.

  The above is the description of the processing flow of the present embodiment.

  Next, an example of the imaging parameter setting GUI in step 901 will be described based on FIG. An imaging parameter setting GUI 1001 shown in FIG. 10 includes a patient information display area 1001, an imaging parameter setting input area 1002 by graphic operation, an imaging parameter setting input area 1003 by value input, and an imaging control area 1004.

  In the imaging parameter setting input area 1002 by graphic operation, the operator can set / change imaging parameter values such as rotation of a slice section by operating the parameter value input auxiliary graphic displayed on the area. The imaging parameter setting input area 1003 is an area for accepting setting / changing of parameter values by direct input of values by the operator.

As an imaging parameter and its value related to the radial scan of the present invention, the imaging parameter setting input area 1003 includes:
1) Value: FSE sequence (FSE in the figure) is set to the sequence parameter (Sequence in the figure)
2) Value: ON is set to the parameter for specifying radial scan (RadialScan in the figure)
3) Value: Sequential order (Sequential in the figure) is set in the parameter (EchoAlloc. In the figure) that specifies the echo data arrangement method in the blade,
4) Each blade (Type 1 in the figure) is set in the parameter (BladeType in the figure) that determines the selection method of the blade that reverses the measurement order of the echo data. In this example of the imaging parameter setting GUI 1000, regarding the parameter 4) that determines the selection method of the blade that reverses the measurement order of echo data, several blade patterns that reverse the measurement order are prepared in advance (Type1, Type2, ...・), An example of selecting from among them is shown.

  As described above, the MRI apparatus and the radial sampling method of the present embodiment are configured so that the measurement order of the echo data of the blade is sequential order or centric order in the blade selected by the operator or automatically selected in the radial scan. Accordingly, the measurement order of echo data in at least one blade is reversed to make it different from the measurement order of echo data in other blades. Accordingly, echo data other than the effective TE in the vicinity of the center of the k space can be dispersed without extending the imaging time, and as a result, the image contrast can be brought close to the contrast expected by the effective TE.

  As mentioned above, although the Example of this invention was described, this invention is not limited to these. For example, in the above-described embodiment, the measurement order of the echo data of the blade is a sequential order or a centric order. However, the present invention is not limited to these two measurement orders, and any other measurement order is possible. It is also applicable to. In other words, the measurement order of the echo data in the phase encoding direction can be reversed with respect to the center of the blade or the effective TE echo data with at least one blade and the other blade. Good.

  101 Subject, 102 Static magnetic field generating magnet, 103 Gradient magnetic field coil, 104 Transmitting RF coil, 105 RF receiving coil, 106 Signal detection unit 106, 107 Signal processing unit, 108 Overall control unit, 109 Gradient magnetic field power source, 110 RF transmission unit , 111 Measurement control unit, 112 beds, 113 Display / operation unit, 114 Arithmetic processing unit, 115 Storage unit

Claims (13)

In k space, echo data is measured in one repetition time along each parallel trajectory in a blade having a plurality of parallel trajectories, and the blade is rotated around the center of the k space, A magnetic resonance imaging apparatus for performing radial sampling that repeats measurement of blade echo data at an angle ,
Echo data measurement order setting unit that sets the measurement order of echo data in one blade and the other one blade in opposite directions with respect to the phase encoding direction of the blade,
Based on the radial sampling, a measurement control unit that controls measurement of echo data from the subject; and
A measurement order reversal blade selector for selecting a blade for reversing the measurement order of the echo data;
A magnetic resonance imaging apparatus comprising: In the magnetic resonance imaging apparatus according to claim 1,
The echo data measurement order setting unit sets the echo data measurement order in one blade with respect to the echo data measurement order in the other blade with respect to the center of the blade or the effective TE echo data. A magnetic resonance imaging apparatus characterized in that the direction is reversed. In the magnetic resonance imaging apparatus according to claim 1 or 2,
The echo data measurement order setting unit sets a measurement order in which echo data is measured in a direction in which phase encoding increases in one blade with respect to a phase encoding direction of the blade, and phase encoding decreases in the other one blade. A magnetic resonance imaging apparatus having a measurement order in which echo data is measured in a direction to be performed. In the magnetic resonance imaging apparatus according to claim 1 or 2,
The measurement order of each echo data in the blade is a centric order in which the polarity of the phase encoding is alternately reversed from the center toward both ends with respect to the phase encoding direction of the blade,
The magnetic resonance imaging apparatus characterized in that the echo data measurement order setting unit reverses the alternating inversion method between the one blade and the other blade. In the magnetic resonance imaging apparatus according to any one of claims 1 to 4 ,
The measurement order reversing blade selection unit selects a blade that reverses the measurement order of the echo data so that the number of blades that reverses the measurement order of the echo data is half of the total number of blades. Magnetic resonance imaging device. In the magnetic resonance imaging apparatus according to any one of claims 1 to 4 ,
The magnetic resonance imaging apparatus, wherein the measurement order reversing blade selection unit selects a blade that reverses the measurement order of the echo data every plural blades . In the magnetic resonance imaging apparatus according to any one of claims 1 to 4 ,
The magnetic resonance imaging apparatus, wherein the measurement order reversing blade selection unit selects a blade that reverses the measurement order of the echo data every other blade . In k space, echo data is measured in one repetition time along each parallel trajectory in a blade having a plurality of parallel trajectories, and the blade is rotated around the center of the k space, A magnetic resonance imaging apparatus for performing radial sampling that repeats measurement of blade echo data at an angle,
Echo data measurement order setting unit that sets the measurement order of echo data in one blade and the other one blade in opposite directions with respect to the phase encoding direction of the blade,
Based on the radial sampling, a measurement control unit that controls measurement of echo data from the subject; and
With
The echo data measurement order setting unit divides all blades into a plurality of groups, and selects a blade group belonging to at least one group as a blade that reverses the measurement order of the echo data. Imaging device. In k space, echo data is measured in one repetition time along each parallel trajectory in a blade having a plurality of parallel trajectories, and the blade is rotated around the center of the k space, A magnetic resonance imaging apparatus for performing radial sampling that repeats measurement of blade echo data at an angle,
Echo data measurement order setting unit that sets the measurement order of echo data in one blade and the other one blade in opposite directions with respect to the phase encoding direction of the blade,
Based on the radial sampling, a measurement control unit that controls measurement of echo data from the subject; and
An input unit for selecting a blade for reversing the measurement order of the echo data;
With
The echo data measurement order setting unit selects a blade selected via the input unit as a blade that reverses the measurement order of the echo data . In a magnetic resonance imaging apparatus, echo data is measured in one repetition time along each parallel locus in a blade having a plurality of parallel loci in k space, and the blade is arranged around the center of the k space. Is a radial sampling method for performing radial sampling that repeats the measurement of the echo data of the blade at each angle,
An echo data measurement order setting step for setting the measurement order of echo data in one blade and the other one blade in opposite directions with respect to the phase encoding direction of the blade;
A measurement control step for controlling the measurement of echo data from the subject based on the radial sampling;
Dividing all the blades into a plurality of groups, and selecting a blade group belonging to at least one group as a blade that reverses the measurement order of the echo data; and
A radial sampling method comprising: The radial sampling method according to claim 10, wherein
The step of setting the echo data measurement order includes the phase encoding of the blade with respect to the echo data of the center of the blade or the effective TE with respect to the measurement order of the echo data in one blade. A radial sampling method characterized by inverting in the direction . In the radial sampling method according to claim 10 or 11 ,
The measurement order of each echo data in the blade is a sequential order sequentially performed from one end to the other end with respect to the phase encoding direction of the blade,
The echo data measurement order setting step includes a radial sampling method in which the measurement order of echo data is opposite to each other with respect to the phase encoding direction of the blades in the one blade and the other one blade. . In the radial sampling method according to claim 10 or 11,
The measurement order of each echo data in the blade is a centric order in which the polarity of the phase encoding is alternately reversed from the center toward both ends with respect to the phase encoding direction of the blade,
In the radial sampling method, the echo data measurement order setting step reverses the alternate inversion method between the one blade and the other blade .

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