JP5167556B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a tagging technique in a magnetic resonance imaging (MRI) apparatus.

  There is a technique called tagging in which a pre-saturation pulse is applied to modulate the nuclear magnetization of an object to be imaged and a striped or grid-like tag is added to the MRI image. A sequence for modulating the nuclear magnetization of the imaging target is called a tagging sequence. The tagging sequence is mainly applied as a pre-pulse sequence of the cine imaging sequence of the heart, and images the deformation behavior of the heart wall.

  A typical tagging sequence is a pulse sequence in which one gradient magnetic field pulse is applied in the phase encoding direction or the readout direction between two RF pulses having a flip angle of 90 degrees (for example, Non-Patent Document 1). reference.). When this tagging sequence is applied to a pre-pulse sequence, a region in which a signal is suppressed in a stripe shape in a direction orthogonal to the gradient magnetic field pulse application direction is generated in the obtained MRI image. This area is called a tag. In addition, there is a method of generating a lattice tag by continuously executing the pulse sequence in which the application direction of the gradient magnetic field pulse is in the phase encoding direction and in the readout direction. The deformation behavior of the heart wall can be grasped by detecting the transition of the position of a specific lattice point on the cine image provided with the lattice-like tag.

  Note that a pulse sequence in which a plurality of RF pulses are applied with the amplitude ratio being a binomial coefficient ratio is also used for the tagging sequence (see Non-Patent Document 2, for example). As the number of RF pulses is increased, the spatial distribution of nuclear magnetization becomes closer to a rectangular function from a sine function, and the blur of the edge of the tag is improved.

  There are a short-axis image, a long-axis image, and a four-chamber image as images acquired by cine imaging of the heart. In the short axis image, the left ventricle has a donut shape and expands and contracts in the radial direction with respect to the center of the left ventricle. Therefore, in general, a lattice-like tag is attached to examine deformation behavior such as twisting. On the other hand, in the long axis image and the four-chamber image, the deformation behavior in the long axis direction is emphasized and displayed rather than the expansion and contraction in the short axis direction. Therefore, in general, a striped tag is applied in the minor axis direction, and the deformation behavior in the major axis direction is examined.

Radiology, vol. 171, p841-845 (1989) Radiology, vol. 172, p349-350 (1989)

  In a conventional tagging sequence, tags are generated in the phase encoding direction or the readout direction. Therefore, for example, in long-axis / four-chamber imaging, in order to generate a tag in the short-axis direction, a series of imaging pulse sequences including a tagging sequence is performed with the phase encoding direction or readout direction coinciding with the short-axis. . That is, so-called in-plane rotation is performed in which the phase encoding direction is changed in accordance with the direction in which the tag is applied.

  However, since the heart is imaged on a double oblique surface, the phase encoding direction is determined so as not to cause aliasing artifacts. Therefore, changing the phase encoding direction to add tags in the desired direction can cause unexpected aliasing artifacts.

  Further, since the size of the heart varies from subject to subject, the interval and width of the tag must be changed each time. Conventionally, since the interval and width of a tag are designated numerically in advance, it is difficult to set a suitable one for each subject.

  The present invention has been made in view of the above circumstances, and allows specification of specifications such as direction, interval, and width of a tag in an easy-to-understand manner so that a desired tagged image can be obtained without unexpected artifacts. The purpose is to provide the technology to obtain.

  The present invention provides an interface for an operator to input at least one of tag direction, spacing, and width, and a gradient magnetic field pulse and / or a tagging sequence to generate a tag of the input direction, spacing, and width. Change the RF pulse.

  Specifically, a gradient magnetic field is generated and a static magnetic field is generated according to an imaging sequence for obtaining a tagged image by executing an imaging sequence for acquiring the image of the imaging target following a tagging sequence for modulating the nuclear magnetization of the imaging target. A magnetic resonance imaging apparatus comprising a control means for irradiating a subject in a magnetic field with a high-frequency magnetic field, the accepting means for accepting an instruction of the specification of the tag to be applied, and the tag with the specification accepted by the accepting means on the image There is provided a magnetic resonance imaging apparatus comprising tagging sequence changing means for changing the tagging sequence so as to be applied.

  According to the present invention, it is possible to specify the tag specifications such as direction, interval, and width in a form that is intuitively easy to grasp, and a desired tagged image can be obtained without any unexpected artifacts.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an MRI apparatus 700 of the present embodiment. As shown in the figure, an MRI apparatus 700 of the present embodiment includes a static magnetic field generator 702 that generates a static magnetic field in an imaging space, a bed 713 for mounting an imaging target 701 such as a patient and placing the imaging target in the imaging space, An RF coil 704 that applies a high-frequency magnetic field (RF) pulse to the imaging target 701, an RF probe 705 that detects a nuclear magnetic resonance (NMR) signal, and gradient magnetic fields in the X, Y, and Z directions are generated in the imaging space, respectively. A gradient magnetic field coil 703 is provided.

  Note that the gradient magnetic field coil 703 is composed of gradient magnetic field coils in three directions of X, Y, and Z, and each generates a gradient magnetic field in accordance with a signal from the gradient magnetic field power supply 709. An RF transmitter 710 that supplies a high-frequency current for generating an RF pulse is connected to the RF coil 704. A signal detector 706 that detects the received NMR signal is connected to the RF probe 705. The signal detected by the signal detection unit 706 is subjected to signal processing by the signal processing unit 707 and converted into an image signal. The image signal is displayed on the screen of the display unit 708 as an image. The gradient magnetic field power source 709, the RF transmission unit 710, and the signal detection unit 706 are controlled by the control unit 711. The control time chart is generally called a pulse sequence. The pulse sequence is stored in advance in a storage device (not shown) provided in the MRI apparatus 700. Various control information of the MRI apparatus 700 and control information of processing performed by the signal processing unit 707 are input from the operation unit 712. The operation unit 712 includes a mouse and a keyboard, and is disposed close to the display unit 708. The operator interactively controls various processes of the MRI apparatus through the operation unit 712 while viewing the screen. Note that the RF coil 704 and the RF probe 705 may be mounted for both transmission and reception.

  At present, what is widely used clinically as a subject of MRI imaging is the main constituent substance of the subject, proton. By imaging the spatial distribution of the proton density and the spatial distribution of the relaxation phenomenon in the excited state, the form or function of the human head, abdomen, limbs, etc. is photographed two-dimensionally or three-dimensionally.

  In the MRI apparatus 700, different phase encodings are given to protons by a gradient magnetic field, and echo signals obtained by the respective phase encodings are detected. As the number of phase encodings to be given, values such as 128, 256, and 512 are usually selected per image. Each echo signal is usually obtained as a time-series signal composed of 128, 256, 512, and 1024 sampling data. When acquiring the sampling data, the echo signal is frequency-encoded by the gradient magnetic field. These data are two-dimensionally Fourier transformed to create one MR image.

  In the present embodiment, a tagging sequence is executed as a pre-pulse sequence of the cine imaging sequence of the heart, and a striped tag orthogonal to the readout direction is given on the MRI image (cine image). In the present embodiment, the operator specifies the direction of the tag to be assigned on the image displayed on the display unit 708.

  In the present embodiment, in order to generate a tag in the direction input by the operator, the control unit 711 further generates an tag in the direction received by the input receiving unit that receives designation of the tag direction and in the direction received by the input receiving unit. A sequence changing unit for changing the tagging sequence. Further, in order to obtain an image in which the operator designates the tag direction, the image is acquired prior to the tagging sequence. In the present embodiment, as an example, a case where an image in which an operator designates a tag direction is a cine image will be described as an example. Therefore, in the present embodiment, a pulse sequence for cine imaging for acquiring a cine image and a tagging sequence are stored in the storage device. The tagging sequence stored in the storage device has a predetermined tag direction, and is hereinafter referred to as an initial tagging sequence. In this embodiment, in order to generate a tag in the direction input by the operator, this initial tagging sequence is changed by the sequence changing unit.

  First, the initial tagging sequence stored in the storage device will be described. In the present embodiment, a pulse sequence for generating a striped tag in a direction orthogonal to the gradient magnetic field pulse application direction is used as the initial tagging sequence. FIG. 2 is a diagram for explaining the basic configuration of the initial tagging sequence of the present embodiment and the tags obtained. The initial tagging sequence is the same as the conventional pulse sequence for generating a striped tag.

  As shown in FIG. 2A, the initial tagging sequence of the present embodiment includes two RF pulses 101 and 102 having a flip angle of 90 degrees and one gradient magnetic field pulse 111. In this figure, t0 is the application time of the gradient magnetic field pulse 111, and G0 is the intensity of the gradient magnetic field pulse 111. For example, when the gradient magnetic field pulse 111 is set to be applied in the readout direction, the obtained image has a direction orthogonal to the readout direction (phase encoding direction) as shown in FIG. A striped tag 121 is generated. Hereinafter, in this specification, the direction of the tag 121 is represented by an angle formed with the lead-out direction on the image, and the distance between the tags 121 is the distance between the centers of two adjacent tags (or two adjacent ones). (Distance between ends of matching tags on the same side) 122, and the tag width is represented by black line width 123. In the present embodiment, only a change in tag direction is accepted, and the interval and width are set as they are in the initial tagging sequence as they are. Hereinafter, processing for receiving an input from the operator and changing the initial tagging sequence will be described.

  FIG. 3A is an example of a screen for the operator to specify the tag direction. Here, a cine image 301 (hereinafter referred to as an image 301) acquired prior to the tagging sequence is displayed on the display unit 708. In the present embodiment, a case in which cine imaging is performed as a preceding sequence will be described as an example in order to finally add a tag to a cine image and observe changes in the imaging target such as the heart. However, since the operator only needs to know the direction and size of the target to which the tag is attached, the image acquired in advance is not limited to this. Reference numeral 304 denotes an image of an imaging region, here, a heart.

  The input receiving unit displays on the image 301 displayed on the display unit 708 an object for indicating the tag direction and receiving an instruction for the tag direction from the operator. In the present embodiment, a case where a line (hereinafter referred to as a tag line) 302 indicating a tag direction is used as an object will be described as an example. The direction of the tag displayed first is assumed to be the direction generated by the initial tagging sequence. Further, a determination button (not shown) is displayed in the display unit 708. Data displayed on the display unit 708 by the input receiving unit is stored in the storage device in advance.

  The operator inputs a desired tag direction by operating the tag line 302. Specifically, the operator translates the tag line 302 via the operation unit 712 such as a mouse and places the tag line 302 on the heart image 304. Thereafter, the image is rotated on the image 304, and when the desired direction is reached, the determination button is pressed. When the input accepting unit accepts pressing of the enter button, the input accepting unit reads an angle θ303 formed with the readout direction of the tag line 302 displayed on the display unit 708 at that time.

  In addition, you may provide the tag display function which displays a mode that the tag of the designated direction is provided on an image. The tag display function displays a tag display button (not shown) on the display unit 708. When an operator press is received, the angle θ 303 at that time is read, and the tags are displayed on the cine image of the display unit 708 at a predetermined tag interval and width. Further, the display unit 708 may have a function of displaying the angle θ303 as a numerical value.

As described above, the tag is generated in a direction orthogonal to the gradient magnetic field pulse application direction. Therefore, the tagging sequence may be changed so that the gradient magnetic field pulse is applied so as to be orthogonal to the direction in which the tag is to be generated. In other words, if the angle between the desired tag and the readout direction is θ, applying the gradient magnetic field pulse in the phase encoding direction and the readout direction so that the application direction of the synthesized gradient magnetic field pulse is perpendicular to θ. Good. If the gradient magnetic field pulse intensity in the phase encoding direction is Gp, the gradient magnetic field pulse intensity in the readout direction is Gr, and the gradient magnetic field pulse intensity in the initial tagging sequence is G0, Gp and Gr can be calculated by the following equations. Note that the gradient magnetic field pulse application time t0 is not changed.
Gp = G0 cos θ (Formula 1)
Gr = −G0sin θ (Formula 2)

  The sequence changing unit uses the angle θ303 of the tag line 302 read by the input receiving unit, and calculates application strengths Gp and Gr of the gradient magnetic field in the phase encoding direction and the readout direction according to (Equation 1) and (Equation 2). . Then, the sequence changing unit performs the initial tagging sequence so that the gradient magnetic field pulses 111p and 111r are applied between the two RF pulses 101 and 102 with the calculated gradient magnetic field pulse strengths Gp and Gr in each direction for t0 time. change. FIG. 4 shows the tagging sequence after the change. At this time, the phase encoding direction of the subsequent sequence is not changed.

  A flow of a tagging sequence creation process for creating a tagging sequence in the MRI apparatus 700 of the present embodiment using the above functions will be described. FIG. 5 is a processing flow of the tagging sequence creation processing of the present embodiment. In the present embodiment, it is assumed that cine imaging is performed prior to the tagging sequence creation process, and the cine image 301 obtained by cine imaging is displayed on the display unit 708.

The control unit 711 calculates the gradient magnetic field pulse intensity G0 of the initial tagging sequence using a predetermined tag interval x0 and gradient magnetic field pulse application time t0 (step 801). Note that the following relationship exists between the tag interval x0, the gradient magnetic field pulse intensity G0, and the gradient magnetic field pulse application time t0.
x0 = 1 / γ · G0 · t0 (Formula 3)
Here, γ is a magnetic rotation ratio.
Therefore,
G0 = γ · x0 / t0 (Formula 4)
It is. Here, the gradient magnetic field strength G0 of the initial tagging sequence is calculated using (Equation 4). Note that the processing in step 801 may be performed at any timing as long as it is before step 805.

  Next, the input receiving unit displays the image displayed on the display unit 708, and further displays the tag line 302 in the direction in which the tag is generated in the initial tagging sequence (step 802). At this time, the tag generated in the initial tagging sequence may be displayed with the tag interval and width set in advance.

  When receiving an instruction for the tag direction from the operator via the operation of the tag line 302 (step 803), the input receiving unit reads the angle θ303 formed with the lead-out direction (step 804) and transfers it to the sequence changing unit.

  The sequence changing unit substitutes the received angle θ303 and G0 and t0 into (Equation 1) and (Equation 2) to calculate the gradient magnetic field strengths Gp and Gr in the phase encoding direction and the readout direction (step 805). . Then, the tagging sequence is created by changing the initial tagging sequence using the calculated Gp and Gr (step 806).

  FIG. 3B shows an image obtained when the tagging sequence created by the above procedure is applied to the prepulse sequence. As shown in the figure, a tag is generated on the image 301 in the direction (θ) indicated by the tag line 302 by the operator.

  Although the case where the initial tagging sequence shown in FIG. 2A is used has been described as an example, the amplitude ratio of the RF pulse as shown in FIG. A thing may be used. Here, as an example, the case where the amplitude ratio of the RF pulses is 1: 4: 6: 4: 1 is shown. As described above, in such a tagging sequence, as the number of RF pulses is increased, the spatial distribution of nuclear magnetization becomes closer to a rectangular function from a sine function, and blurring of the tag edge is improved.

  Also in this case, the angle θ formed between the input tag line and the readout direction and the gradient magnetic field pulse intensity G0 for obtaining a tag having a preset interval x are used, and the phase encoding direction and the readout direction are used. Are calculated in accordance with (Equation 1) and (Equation 2), and the gradient magnetic field pulse intensity of the initial tagging sequence is replaced with it. The tagging sequence after the change is shown in FIG.

  In the present embodiment, the case where the tagging sequence shown in FIG. 2A is the initial tagging sequence and a striped tag is generated has been described as an example. The above processing procedure is basically the same even when a grid-like tag is generated. The procedure will be described below.

  First, an initial tagging sequence when generating a lattice tag will be described. FIG. 7 is a diagram for explaining a basic configuration of an initial tagging sequence and a tag to be obtained when a lattice tag is generated.

  As shown in FIG. 7A, the initial tagging sequence includes two RF pulses 201 and 202, one gradient magnetic field pulse 211 in the phase encoding direction, two RF pulses 203 and 204, and one read. And a gradient magnetic field pulse 212 in the out direction. Furthermore, in order to reduce the disturbance of nuclear magnetization, spoiler gradient magnetic fields 221 and 222 are applied in the slice direction. When this tagging sequence is applied to a pre-pulse sequence, the obtained image includes a striped tag orthogonal to the phase encoding direction and a striped tag orthogonal to the readout direction as shown in FIG. Generated. This initial tagging sequence is also the same as the conventional pulse sequence for generating a lattice-like tag. The application directions of the gradient magnetic field pulse 211 and the gradient magnetic field pulse 212 may be reversed. Hereinafter, a process for generating a grid-like tag according to the present embodiment will be described.

  FIGS. 8A and 8C are examples of a screen for instructing the operator of the direction of the grid-like tag. Here, FIG. 8A shows a case where the directions of the two-direction tags constituting the lattice can be set independently. FIG. 8C shows the case where the grid-like tags are orthogonal. Hereinafter, a description will be given with reference to FIG.

The input receiving unit displays tag lines 5021 and 5022 on the image 501 displayed on the display unit 708 in the direction of the tag generated by the initial tagging sequence. Here, the tag line 5021 indicates the direction of the tag by the gradient magnetic field pulse 211, and the tag line 5022 indicates the direction of the tag by the gradient magnetic field pulse 212. The operator rotates tag lines 5021 and 5022 via an operation unit 712 such as a mouse, and designates a desired tag direction. When the determination button 305 is pressed, the input receiving unit reads the angles θ1 (5031) and θ2 (5032) of the tag lines 5021 and 5022 displayed on the display unit 708 with respect to the readout direction. Reference numeral 504 denotes an imaged region, here, an image of the heart.

The sequence changing unit uses the angle θ1 (5031) read by the input receiving unit to calculate the intensity Gp1 and Gr1 of the gradient magnetic field pulse to be applied as the gradient magnetic field pulse 211 in FIG. Calculate using the following formula: G1 is the intensity of the gradient magnetic field pulse 211 in the initial tagging sequence.
Gp1 = G1 cos θ1 (Formula 5)
Gr1 = −G1sin θ1 (Formula 6)
Similarly, using the angle θ2 (5032) read by the input receiving unit, the intensity (Gp2, Gr2) of the gradient magnetic field pulse applied as the gradient magnetic field pulse 212 of FIG. Calculate using the following formula: G2 is the intensity of the gradient magnetic field pulse 211 in the initial tagging sequence.
Gp2 = G2cos θ2 (Formula 7)
Gr2 = −G2sin θ2 (Formula 8)
It becomes.

  The sequence changing unit changes the tagging sequence so that the gradient magnetic field pulses calculated according to the above (Expression 5) to (Expression 8) are applied as the gradient magnetic field pulses 211 and 212, respectively. FIG. 9 shows the tagging sequence after the change. FIG. 8B shows a part of an image tag obtained when photographing is performed by executing this tagging sequence as a pre-pulse sequence. As shown in the figure, tags are generated in the directions (θ1, θ2) indicated by the tag lines 5021 and 5022 on the image 501 by the operator.

As shown in FIG. 8C, when two tags are orthogonal, two tag lines are displayed, but when the operator operates one, the other remains orthogonal and follows its movement. The angle θ2 formed by the tag line 5022 with respect to the lead-out direction is π / 2 + θ1. Therefore, the gradient magnetic field pulse strengths Gp2 and Gr2 in the phase encoding direction and the readout direction of the second gradient magnetic field pulse 212 can be calculated by the following equations, respectively.
Gp2 = G2cos (π / 2 + θ1) = − G2sinθ1 (Formula 7 ′)
Gr2 = −G2sin (π / 2 + θ1) = G2cos θ1 (Formula 8 ′)
FIG. 8D shows a part of the tag of the photographing result in this case.

  In this embodiment, the angle θ 303 formed between the tag line 302 and the readout direction is read to calculate the gradient magnetic field pulse application intensity in each axial direction. However, the angle formed between the tag line 302 and the phase encoding direction is calculated. The reading and the gradient magnetic field pulse application intensity may be calculated. When the read angle is θ ′, when the tag is in one direction, the gradient magnetic field pulse intensity in the readout direction is −G cos θ ′, and the gradient magnetic field pulse intensity in the phase encoding direction is −G sin θ ′.

  As described above, in this embodiment, the operator can set the tag direction from the screen. That is, since the direction of the tag is designated on the image to be photographed to which the tag is actually attached, the desired direction can be easily set. The operator can specify the tag direction by means that are easy to grasp intuitively. Therefore, it is possible to easily obtain an image in which the deformation behavior of the imaging target part can be easily observed.

  In the present embodiment, the application direction of the gradient magnetic field pulse in the tagging sequence is adjusted so that the tag is generated in the direction specified by the operator. Therefore, it is possible to generate a tag in a desired direction without changing the phase encoding and readout direction in accordance with the tag generation direction. That is, since the tag direction can be changed independently of the lead-out direction and the phase encoding direction, there is no fear of unexpected artifacts that occur when the phase encoding direction is changed.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. In the first embodiment, the tag interval and width are set in advance, and an instruction is accepted from the operator only in the tag direction. In the present embodiment, in addition to the tag direction, an input of the tag interval is received from the operator, and the tag is assigned with the received direction and interval. The MRI apparatus of this embodiment basically has the same configuration as that of the first embodiment, but the processes performed by the input receiving unit and the sequence changing unit are different. Hereinafter, a description will be given focusing on the configuration different from the first embodiment.

  Hereinafter, also in this embodiment, the case where a striped tag is added will be described as an example. That is, the initial tagging sequence stored in the storage device is as shown in FIG. Also in this embodiment, it is assumed that a cine image is acquired prior to the tagging sequence, and the operator indicates the tag direction and interval on the cine image. The tag width is set in advance without changing it. Hereinafter, the process of setting the tag direction and interval according to the present embodiment will be described.

  FIG. 10A is an example of a screen for the operator to set the tag direction and interval. Here, a cine image 401 (hereinafter referred to as an image 401) is acquired and displayed prior to tagging photography. Reference numeral 404 denotes an imaged region, here, an image of the heart.

  The input receiving unit displays tag lines 402a and 402b and a determination button (not shown) as objects indicating the tag direction and the interval between the tags on the image 401 displayed on the display unit 708. Tag lines 402a and 402b are two parallel lines, the interval between them indicating the interval between the tags, and the direction indicating the direction of the tag to the operator. The operator inputs a tag direction instruction by rotating the tag lines 402a and 402b via the operation unit 712 such as a mouse. Also, the tag interval is input by translating either one of the tag lines 402a and 402b.

  Also in this embodiment, the operator presses the enter button when the desired direction and interval are reached. When the input accepting unit accepts pressing of the enter button, the angle θ403 formed between the tag lines 402a and 402b displayed on the display unit 708 at that time and the readout direction and the interval x405 between the tag lines 402a and 402b are set. read.

  Also in the present embodiment, a tag display function may be provided that displays a state in which tags having the designated direction and interval are provided on the image. When the tag display function displays a tag display button (not shown) on the display unit 708 and accepts pressing by the operator, the angle θ 403 and the interval x 405 at that time are read. Then, tags having a predetermined width are displayed on the cine image of the display unit 708 at the read angles and intervals. Further, the display unit 708 may have a function of displaying the angle θ403 and the interval x405 numerically.

The sequence changing unit calculates the strength of the gradient magnetic field applied in the phase encoding direction and the readout direction using the angle θ403 read by the input receiving unit and the interval x405. In this embodiment, first, the gradient magnetic field pulse intensity G0 to be applied when a tag is applied in the initial direction, that is, the phase encoding direction is calculated. The gradient magnetic field pulse intensity G0 is obtained as shown in (Expression 9) by substituting the read tag interval x405 into (Expression 3). In this embodiment, the gradient magnetic field pulse application time t0 is not changed.
G0 = (γ · x) / t0 (Formula 9)

  Then, the sequence changing unit uses the gradient magnetic field pulse strength G0 obtained in (Equation 9) to change the gradient magnetic field strengths Gp and Gr in the phase encoding direction and the readout direction into the first embodiment (Equation 1), It calculates | requires according to (Formula 2). Then, the initial tagging sequence is changed using the obtained gradient magnetic field pulse intensity in each axial direction.

  A tagging sequence creation process for creating a tagging sequence in the MRI apparatus 700 of the present embodiment using the above functions will be described. FIG. 11 is a process flow of the tagging sequence creation process of the present embodiment. In the present embodiment, it is assumed that cine imaging is performed prior to the tagging sequence creation process, and the cine image 401 obtained by cine imaging is displayed on the display unit 708.

  The input receiving unit includes an object (tag line) 402a that receives an instruction of the tag interval and direction from the operator at the tag interval and direction set as initial values on the image 401 displayed on the display unit 708. 402b is displayed (step 811).

  When the input receiving unit receives an instruction of the tag direction and interval from the operator through the operation of the tag lines 402a and 402b (step 812), the input receiving unit sets the angle θ403 formed with the readout direction and the interval x405 between the tag lines 402a and 402b. Read (step 813) and pass to the sequence changing unit.

  The sequence changing unit substitutes the received interval x405 and the gradient magnetic field pulse application time t0 set in advance into (Equation 9) to calculate the gradient magnetic field pulse intensity G0 (step 814). Then, the calculated gradient magnetic field pulse strength G0 and the received angle θ403 are substituted into (Equation 1) and (Equation 2) to calculate the gradient magnetic field strengths Gp and Gr in the phase encoding direction and the readout direction (step 815). ). Then, the tagging sequence is created by changing the initial tagging sequence using the calculated Gp and Gr (step 816).

  FIG. 10B shows an image obtained when the tagging sequence created by the above procedure is applied to the prepulse sequence. As shown in this figure, a tag with the specified interval (x) is generated in the direction (θ) indicated by the operator on the tag lines 402a and 402b on the image to be photographed.

  Next, in the present embodiment, processing when a lattice tag is added will be described. FIG. 12A shows an example of a screen for instructing the operator about the direction and interval of the grid-like tag. The same components as those in FIG.

  As shown in the figure, the input receiving unit displays tag lines 5121a, 5121b, 5122a, and 5122b on an image 511 displayed on the display unit 708. Here, the tag lines 5121a and 5121b and the tag lines 5122a and 5122b are always parallel. The operator operates the tag lines 5121a, 5121b, 5122a, and 5122b via the operation unit 712 such as a mouse to instruct the tag direction and interval.

  Other processes are the same as those in the case of setting the striped tag of this embodiment and the case of setting the grid-like tag of the first embodiment. A part of the tag of the obtained tagging image is shown in FIG. The same applies to the case where a grid-like tag is added and both are orthogonal to each other. The same applies to a tagging sequence in which the RF pulse amplitude ratio is a binomial coefficient ratio. Also in this embodiment, the angle read as the tag direction may be an angle formed with the phase encoding direction.

  As described above, in this embodiment, the operator can set the tag direction and interval from the screen. That is, since the tag direction and interval are specified on the image to be photographed to which the tag is actually attached, the desired direction and interval can be easily set. The operator can specify the tag direction and interval by means that are easy to grasp intuitively. Therefore, it is possible to easily obtain an image in which the deformation behavior of the imaging target part can be easily observed.

  Also in this embodiment, as in the first embodiment, the application direction of the gradient magnetic field pulse in the tagging sequence is adjusted so as to generate a tag in the direction specified by the operator. Therefore, there is no fear that unexpected artifacts generated by changing the phase encoding direction occur.

  In particular, in this embodiment, the tag interval can be designated on the image by the operator, so that the optimum tag interval for the imaging target can be easily set.

  In the present embodiment, the tag interval and direction are described as being input by the operator. However, the tag direction may be determined in advance, and the operator may input only the interval. In this case, the tag lines 402a and 402b displayed by the input receiving unit may be configured so that only translation is possible.

<< Third Embodiment >>
Next, a third embodiment to which the present invention is applied will be described. In the present embodiment, in addition to the second embodiment, the designation of the tag width is accepted from the operator, and the tag is given with the accepted width. The MRI apparatus of this embodiment basically has the same configuration as that of each of the above embodiments, but the processing performed by the input receiving unit and the sequence changing unit and the sequence used as the initial tagging sequence are different. Hereinafter, a description will be given focusing on the configuration different from the second embodiment.

  Hereinafter, also in this embodiment, the case where a striped tag is added will be described as an example. In the present embodiment, the tag width is also changed in accordance with the operator's instruction, so that the initial tagging sequence shown in FIG. 6A is used. It is assumed that the initial tagging sequence is initially set so as to add tags with an interval x0 and a width y0 in the phase encoding direction. Hereinafter, the process of setting the tag direction, interval, and width according to the present embodiment will be described.

  FIG. 13A is an example of a screen for the operator to set the tag direction, interval, and width. Here, a cine image 1001 (hereinafter referred to as an image 1001) is acquired and displayed prior to tagging photography. Reference numeral 1004 denotes an imaged region, here, an image of the heart.

  The input receiving unit displays tag lines 1002a, 1002b, 1002c and a determination button (not shown) as objects that support the direction, interval, and width of the tag on the image 1001 displayed on the display unit 708. The tag lines 1002a, 1002b, and 1002c are three parallel lines. The interval between the tag lines 1002a and 1002b indicates the interval between the tags, and the interval between the tag lines 1002a and 1002c indicates the width of the tag. The operator designates the tag direction by rotating the tag lines 1002a, 1002b, and 1002c via the operation unit 712 such as a mouse. Further, the tag line 1002b is translated to specify the tag interval, and the tag line 1002c is translated to specify the tag width.

Also in this embodiment, the operator presses the enter button when the desired direction and interval are reached. When the input accepting unit accepts pressing of the enter button, the angle θ1003 formed with the readout direction of the tag line 1002a displayed on the display unit 708 at that time, the interval x1005 between the tag lines 1002a and 1002b, and the tag line 1002a. And 1002c (hereinafter referred to as width) y1006.

  Also in the present embodiment, a tag display function may be provided that displays a state in which tags having the designated direction, interval, and width are provided on the image. When the tag display function displays a tag display button (not shown) on the display unit 708 and receives an operator's press, the tag display function reads the angle θ1003, the interval x1005, and the width y1006 at that time. Then, the tags of the read angle, interval, and width are displayed on the cine image 1001 of the display unit 708.

  The sequence changing unit uses the angle θ1003, the interval x1005, and the width y1006 read by the input receiving unit to calculate the strength of the gradient magnetic field applied in the phase encoding direction and the readout direction. First, as in the second embodiment, the interval x is substituted into (Equation 9) to calculate the gradient magnetic field pulse intensity G0. Then, using the obtained gradient magnetic field pulse strength G0, gradient magnetic field strengths Gp and Gr in the phase encoding direction and the readout direction are calculated according to (Equation 2) and (Equation 3). Also in this embodiment, the gradient magnetic field pulse application time t0 is not changed.

Next, the sequence changing unit of the present embodiment calculates the amplitude and pulse interval of the RF pulse to be applied in order to change the tag width. Here, as shown in FIG. 14A, assuming that the sync function for modulating the amplitude of the applied RF pulse is sinc (t / t1) and the interval between the applied RF pulses is t2, the applied gradient magnetic field pulse The following relationship exists between the intensity G0, the interval x, the width y, and t1 and t2.
y = γ · G0 · t1 (Formula 10)
x = γ · G0 · t2 (Formula 11)
Therefore, t1 and t2 are obtained from the following (Expression 10) and (Expression 11) as follows.
t1 = y / (γ · G0) (Formula 12)
t2 = x / (γ · G0) (Formula 13)

  The sequence changing unit changes the initial tagging sequence using the obtained gradient magnetic field pulse intensities Gp and Gr in the respective axial directions, the sink function for modulating the amplitude of the RF pulse, and the RF pulse interval. FIGS. 14B and 14C show the tagging sequence after the change. The gradient magnetic field pulse may be applied intermittently or continuously. FIG. 14B shows an example in which a gradient magnetic field pulse is applied intermittently, and FIG. 14C shows an example in which a gradient magnetic field pulse is applied continuously.

  FIG. 13B shows an image obtained when the tagging sequence created by the above procedure is applied to the prepulse sequence. As shown in the figure, the tag lines 1002a and 1002a and the interval (x) indicated by the tag lines 1002a and 1002b in the direction (θ) indicated by the operator on the tag line 1002a, 1002b and 1002c on the image 1004 to be photographed. A tag with the width (y) indicated in 1002c is generated.

  In the present embodiment, the case of setting a striped tag has been described as an example. Even when a grid-like tag is provided, it can be similarly realized by the method described in the first and second embodiments.

  As described above, in this embodiment, the operator can set the tag direction, interval, and width from the screen. That is, since the direction, interval, and width of the tag are designated on the image to be photographed to which the tag is actually attached, the desired direction, interval, and width can be easily set. The operator can specify the direction, interval, and width of the tag by means that are easy to grasp intuitively. Therefore, it is possible to easily obtain an image in which the deformation behavior of the imaging target part can be easily observed.

  Also in the present embodiment, the application direction of the gradient magnetic field pulse in the tagging sequence is adjusted so as to generate the tag in the direction specified by the operator, as in the above embodiments. Therefore, there is no fear that unexpected artifacts generated by changing the phase encoding direction occur.

  Particularly in this embodiment, since the operator can specify the interval and width of the tag on the image, it is possible to easily set the optimal tag interval for the imaging target.

  Also in this embodiment, it is not always necessary to accept the tag direction, interval, width, and all inputs, but only the width, width and direction, and width and interval may be accepted.

  In each of the above embodiments, a HARP (Harmonic Phase) image can be created as a post process of the tagging sequence.

  The HARP image is created by using a bandpass filter having a predetermined pass band with respect to the k space and extracting a signal of the first harmonic component in the k space. FIG. 15 is a diagram for explaining the appearance position of the harmonic component in the k space. In a normal tagging image, a tag is applied in the phase encoding direction and / or the readout direction, so that the harmonic component appears on the k-space axis as shown in FIG. Therefore, the band-pass filter 901 extracts the harmonic component in the k space on the axis. However, when the tagging sequence is changed by changing the tagging sequence using the methods of the above embodiments, the harmonic component does not appear on the axis. In other words, if the tag direction designated by the operator is θ, the harmonic component appears on the coordinate axis rotated by θ as shown in FIG. Therefore, the bandpass filter may be rotated by θ (902), the first harmonic component signal in the k space may be extracted, and a HARP image may be created.

It is a schematic block diagram of the MRI apparatus of 1st embodiment. It is a figure for demonstrating the tagging sequence which produces | generates the striped tag of 1st embodiment. It is a figure for demonstrating the method of designating the direction of the striped tag of 1st embodiment. It is a figure for demonstrating the tagging sequence which provides a striped tag in the designated direction of 1st embodiment. It is a processing flow of tagging sequence creation processing of the first embodiment. It is a figure for demonstrating another example of the tagging sequence which produces | generates the striped tag of 1st embodiment. It is a figure for demonstrating the tagging sequence which produces | generates the grid | lattice-like tag of 1st embodiment. It is a figure for demonstrating the method of designating the direction of the grid | lattice-like tag of 1st embodiment. It is a figure for demonstrating the tagging sequence which provides a grid | lattice-like tag in the designated direction of 1st embodiment. It is a figure for demonstrating the method of designating the direction and space | interval of the striped tag of 2nd embodiment. It is a processing flow of the tagging sequence creation processing of the second embodiment. It is a figure for demonstrating the method of designating the direction and space | interval of the grid | lattice-like tag of 2nd embodiment. It is a figure for demonstrating the method of designating the direction, space | interval, and width | variety of the striped tag of 3rd embodiment. It is a figure for demonstrating an example of the tagging sequence of 3rd embodiment. It is a figure for demonstrating the case where the tagging sequence of each embodiment is applied to HARP method.

Explanation of symbols

  700: MRI apparatus, 701: Subject, 702: Static magnetic field generator, 703: Gradient magnetic field coil, 704: RF coil, 705: RF probe, 706: Signal detection unit, 707: Signal processing unit, 708: Display unit, 709: Gradient magnetic field power supply, 710: RF transmission unit, 711: Control unit, 712: Operation unit, 713: Bed

Claims (11)

An object in a static magnetic field is generated and a gradient magnetic field is generated in accordance with an imaging sequence for obtaining a tagged image by executing an imaging sequence for acquiring an image of the imaging object following a tagging sequence for modulating nuclear magnetization of the imaging object A magnetic resonance imaging apparatus comprising a control means for irradiating a high frequency magnetic field to
The imaging sequence is HARP (Harmonic Phase) ,
Receiving means for receiving an instruction of the specification of the tag to be assigned;
Tagging sequence changing means for changing the tagging sequence so as to attach a tag to the image with the specification received by the receiving means;
Means for changing a measurement space region for acquiring harmonics in accordance with the set direction of the tag, and a magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1,
Display means;
And an input means,
The reception unit displays an image to be photographed and an object for inputting a tag specification on the display unit, and receives the instruction by an operation performed on the object by the user using the input unit. A magnetic resonance imaging apparatus characterized by the above. The magnetic resonance imaging apparatus according to claim 2,
The tag specification is the tag direction,
The accepting unit reads an angle formed by the object and a predetermined direction after a user operation,
The tagging sequence changing means calculates the gradient magnetic field strength in each axial direction applied during the tagging sequence using the angle read by the accepting means, and reflects the calculation result in the tagging sequence. Resonance imaging device. The magnetic resonance imaging apparatus according to claim 3,
The magnetic resonance imaging apparatus, wherein the object is a line indicating a direction of a tag on the image. A magnetic resonance imaging apparatus according to any one of claims 2 to 4,
The tag specification is tag spacing,
The reception unit reads an interval indicated by the object after a user operation,
The tagging sequence changing means calculates the gradient magnetic field strength applied during the tagging sequence using the interval read by the accepting means and reflects it in the tagging sequence. The magnetic resonance imaging apparatus according to claim 5,
The magnetic resonance imaging apparatus, wherein the object is two parallel lines indicating a distance between two tags on the image. The magnetic resonance imaging apparatus according to any one of claims 2 to 6,
The tag specification is the tag width,
The reception unit reads a width indicated by the object after a user operation,
The tagging sequence changing means calculates a function for modulating the pulse application interval and pulse amplitude of the high-frequency magnetic field applied during the tagging sequence using the width read by the accepting means, and reflects the function in the tagging sequence. A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 7,
The magnetic resonance imaging apparatus, wherein the object is a line having a width indicating a width of a tag on the image. The magnetic resonance imaging apparatus according to any one of claims 1 to 6,
The tagging sequence is for generating a striped tag on an image. The magnetic resonance imaging apparatus according to any one of claims 1 to 6,
The tagging sequence generates a grid-like tag on an image. A magnetic resonance imaging apparatus according to any one of claims 1 to 8,
In the magnetic resonance imaging apparatus, the tagging sequence applies a plurality of high-frequency magnetic field pulses with an amplitude ratio as a binomial coefficient ratio.

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