JPWO2015093222A1 - Magnetic resonance imaging apparatus and imaging condition setting support method in magnetic resonance imaging apparatus - Google Patents

Abstract

Provided is a technique that appropriately supports setting of an application region of an RF prepulse so that a desired effect can be obtained and a high-quality image can be obtained regardless of the magnetic field strength of the apparatus. For this purpose, the present invention assists in setting the RF prepulse application region so that the shift of the RF prepulse application region due to chemical shift does not affect the imaging region. Support is performed by indicating to the user the direction in which the excitation region of the fat signal shifts due to a chemical shift when the imaging region and the RF prepulse application region are set on the positioning image.

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as “MRI”) technique, and more particularly to a technique for suppressing artifacts caused by moving substances such as blood flow.

  The MRI device measures NMR signals generated by the spins of the subject, especially the tissues of the human body, and visualizes the form and function of the head, abdomen, limbs, etc. in two or three dimensions Device. In imaging, the NMR signal is phase-encoded and frequency-encoded by a gradient magnetic field, is added with position information, and is measured as time-series data. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  In such magnetic resonance imaging, prior to the application of excitation RF pulses for collecting echo signals, RF pulses may be applied for purposes such as image contrast decoration and unnecessary signal removal. Such an RF pulse is generally called an RF prepulse (hereinafter simply referred to as a prepulse in this specification), and a plurality of different prepulses may be applied depending on the purpose.

  For example, if there is a fluid in the imaging area or there is a part that moves at a specific period, the excitation area is excited with the excitation RF pulse and the slice selective gradient magnetic field pulse, and the position information is given. In the meantime, the state of the imaging region changes. There are pre-saturation pulses and IR (inversion recovery) pulses as pre-pulses that use this to remove unnecessary signals.

  The pre-saturation pulse is used in a pre-saturation technique that suppresses blood flowing into the imaging region with a pre-pulse before the main imaging. This technique excites nuclear spins at sites that generate artifacts before the main imaging and makes the phases different, thereby reducing the signal obtained from the site during main imaging and suppressing the artifacts.

  In addition, the IR pulse is applied to make the magnetization in the imaging region longitudinal magnetization before the main imaging.

  These pre-pulse application areas are set while confirming the positional relationship with the imaging area on the positioning image (see, for example, Patent Document 1). Then, according to the setting, the region of the desired position is excited by combining the frequency of the RF pulse and the slice selective gradient magnetic field pulse.

Japanese Patent No. 3519794

In an MRI apparatus, a nuclear spin of proton ( ¹ H) contained in a subject tissue is excited by a radio frequency (RF) magnetic field having the same frequency as the resonance frequency, and a generated NMR signal is measured. Among substances containing protons, water and fat have extremely large signal values. However, water and fat have different resonance frequencies (chemical shift). For this reason, when a prepulse is applied to a region where water and fat are mixed, a difference in resonance frequency due to chemical shift appears as a difference in excitation region.

  In particular, the presaturation pulse that suppresses the signal of the part that generates the artifact has a higher suppression effect when the application region is set as close to the imaging region as possible. However, if the positions are set close to each other, the fat excitation area is shifted into the imaging area due to chemical shift, and the fat signal in the imaging area is suppressed, and the image quality may be deteriorated. In particular, in a recent high magnetic field MRI apparatus such as 3T (Tesla), this positional deviation is remarkable.

  The direction in which the fat excitation region shifts with respect to water due to chemical shift is determined by the polarity of the slice selective gradient magnetic field pulse that is simultaneously applied when the prepulse is applied. However, in the method described in Patent Document 1, the operator cannot know the polarity of the slice selective gradient magnetic field pulse.

  The present invention has been made in view of the above circumstances, and is a technique that appropriately supports setting of a prepulse application region so that a desired effect can be obtained and a high-quality image can be obtained regardless of the magnetic field strength of the apparatus. The purpose is to provide.

  The present invention assists in setting the pre-pulse application region so that the shift of the pre-pulse application region due to chemical shift does not affect the imaging region. Support is performed by indicating to the user the direction in which the fat signal excitation region is shifted by the chemical shift when the imaging region and the pre-pulse application region are set on the positioning image. When the shift direction of the excitation region is on the imaging region side, the polarity of the slice selection gradient magnetic field applied together with the pre-pulse may be reversed. In this case, the frequency of the RF pulse applied as the pre-pulse may be changed so as to change the excitation region.

  Regardless of the magnetic field strength of the apparatus, it is possible to support appropriate setting of the prepulse application region so that a desired effect can be obtained, and as a result, a high-quality image can be obtained.

The block diagram which shows the whole structure of the MRI apparatus of 1st embodiment Functional block diagram of the control processing system of the first embodiment Explanatory diagram for explaining pre-saturation pulse sequence (a) is an explanatory diagram for explaining an example of the region setting screen of the first embodiment (b) is an explanatory diagram for explaining a display example of the shift direction on the region setting screen of the first embodiment. Explanatory drawing for demonstrating the polarity inversion instruction | indication of a slice selection gradient magnetic field pulse of 1st embodiment Explanatory drawing for demonstrating the display aspect of the area | region setting screen after polarity inversion of the slice selection gradient magnetic field pulse of 1st embodiment Flowchart of the imaging condition setting process of the first embodiment The flowchart of the modification of the imaging condition setting process of 1st embodiment Functional block diagram of the control processing system of the second embodiment Explanatory drawing for demonstrating the display example of the excitation area | region display in the area | region setting screen of 2nd embodiment. Explanatory drawing for demonstrating the display example of the excitation area | region display in the excitation area | region setting screen after the prepulse sequence change of 2nd embodiment Flowchart of imaging condition setting process of the second embodiment Explanatory drawing for demonstrating the example which sets a presaturation pulse application area | region perpendicularly | vertically with respect to an imaging slice in 1st and 2nd embodiment.

<< First Embodiment >>
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that in all the drawings for explaining the embodiments of the invention, the same reference numerals are given to components having the same function unless otherwise specified, and the repeated description thereof is omitted.

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

  The MRI apparatus 100 of the present embodiment obtains a tomographic image of a subject using an NMR phenomenon, and as shown in FIG. 1, a static magnetic field generation system 120, a gradient magnetic field generation system 130, and a high-frequency magnetic field generation system (Hereinafter referred to as a transmission system) 150, a high-frequency magnetic field detection system (hereinafter referred to as a reception system) 160, a control processing system 170, and a sequencer 140.

  The static magnetic field generation system 120 generates a uniform static magnetic field in the direction perpendicular to the body axis in the space around the subject 101 if the vertical magnetic field method is used, and in the body axis direction if the horizontal magnetic field method is used. The apparatus includes a permanent magnet type, normal conducting type or superconducting type static magnetic field generating source disposed around the subject 101.

  The gradient magnetic field generation system 130 includes a gradient magnetic field coil 131 wound in the three-axis directions of X, Y, and Z, which is a coordinate system (device coordinate system) of the MRI apparatus 100, and a gradient magnetic field power source that drives each gradient magnetic field coil 132, and by applying the gradient magnetic field power supply 132 of each gradient coil 131 in accordance with a command from the sequencer 140 described later, gradient magnetic fields Gx, Gy, and Gz are applied in the X, Y, and Z axis directions. .

  At the time of imaging, a slice direction gradient magnetic field pulse is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 101, and the remaining two directions orthogonal to the slice plane and orthogonal to each other A phase encoding direction gradient magnetic field pulse and a frequency encoding direction gradient magnetic field pulse are applied to the echo signal, and position information in each direction is encoded in the echo signal.

  The transmission system 150 irradiates the subject 101 with a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the biological tissue of the subject 101. And a high-frequency oscillator (synthesizer) 152, a modulator 153, a high-frequency amplifier 154, and a high-frequency coil (transmission coil) 151 on the transmission side. The high frequency oscillator 152 generates and outputs an RF pulse. The modulator 153 amplitude-modulates the output RF pulse at a timing according to a command from the sequencer 140, and the high-frequency amplifier 154 amplifies the amplitude-modulated RF pulse and transmits the RF pulse that is arranged close to the subject 101. The coil 151 is supplied. The transmission coil 151 irradiates the subject 101 with the supplied RF pulse.

  The receiving system 160 detects a nuclear magnetic resonance signal (echo signal, NMR signal) emitted by nuclear magnetic resonance of the nuclear spin constituting the living tissue of the subject 101, and receives a high-frequency coil (receiving coil) on the receiving side. 161, a signal amplifier 162, a quadrature detector 163, and an A / D converter 164. The reception coil 161 is disposed in the vicinity of the subject 101 and detects an NMR signal in response to the subject 101 induced by the electromagnetic wave irradiated from the transmission coil 151. The detected NMR signal is amplified by the signal amplifier 162 and then divided into two orthogonal signals by the quadrature phase detector 163 at the timing according to the command from the sequencer 140, and each is digitally converted by the A / D converter 164. It is converted into a quantity and sent to the control processing system 170.

  The sequencer 140 applies an RF pulse and a gradient magnetic field pulse in accordance with an instruction from the control processing system 170. Specifically, in accordance with an instruction from the control processing system 170, various commands necessary for collecting tomographic image data of the subject 101 are transmitted to the transmission system 150, the gradient magnetic field generation system 130, and the reception system 160.

  The control processing system 170 controls the entire MRI apparatus 100, performs various data processing operations, displays and stores processing results, and includes a CPU 171, a storage device 172, a display device 173, and an input device 174. The storage device 172 includes an internal storage device such as a hard disk and an external storage device such as an external hard disk, an optical disk, and a magnetic disk. The display device 173 is a display device such as a CRT or a liquid crystal. The input device 174 is an interface for inputting various control information of the MRI apparatus 100 and control information of processing performed by the control processing system 170, and includes, for example, a trackball or a mouse and a keyboard. The input device 174 is disposed in the vicinity of the display device 173. The operator interactively inputs instructions and data necessary for various processes of the MRI apparatus 100 through the input device 174 while looking at the display device 173.

  The CPU 171 implements each process of the control processing system 170 such as control of operations of the MRI apparatus 100 and various data processes by executing a program stored in advance in the storage device 172 in accordance with an instruction input by the operator. The above-described instruction to the sequencer 140 is made in accordance with a pulse sequence held in advance in the storage device. When data from the reception system 160 is input to the control processing system 170, the CPU 171 executes signal processing, image reconstruction processing, and the like, and displays the tomographic image of the subject 101 as a result on the display device 173. At the same time, it is stored in the storage device 172.

  In the static magnetic field space of the static magnetic field generation system 120 into which the subject 101 is inserted, the transmission coil 151 and the gradient magnetic field coil 131 are opposed to the subject 101 in the vertical magnetic field method, and in the horizontal magnetic field method. It is installed so as to surround the subject 101. Further, the receiving coil 161 is installed so as to face or surround the subject 101.

  Currently, the nuclide to be imaged by the MRI apparatus, which is widely used clinically, is a hydrogen nucleus (proton) that is a main constituent material of the subject 101. In the MRI apparatus 100, 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. can be expressed two-dimensionally or three-dimensionally. Take an image.

  In the present embodiment, a pre-pulse sequence for applying a pre-pulse is executed prior to execution of a sequence for acquiring an image (main imaging). The pre-pulse applied in the pre-pulse sequence of the present embodiment is a nuclear spin that flows into the imaging region at the time of main imaging, and is a pulse that acts on the nuclear spin that exists in a region close to the imaging region. Such a pre-pulse is, for example, a pre-saturation pulse or an IR pulse. Hereinafter, in the present embodiment, a case where a presaturation pulse (hereinafter referred to as a presaturation pulse) is applied as a prepulse will be described as an example.

  In the present embodiment, when a user sets an imaging region determined by one or more imaging slices and a region to be excited by applying a presatisfaction pulse (hereinafter referred to as a presatisfaction region) on the positioning image, the chemical by prepulses is set. The shift direction of the fat excitation region due to the shift is presented to the user. In the present embodiment, the shift amount of the fat excitation region from the presati region set by the user is not reflected in the display, and only the shift direction is shown.

<Functional configuration of control processing system>
As shown in FIG. 2, the control processing system 170 according to the present embodiment receives imaging conditions such as various parameters necessary for imaging from the user, and sets the imaging conditions that are set in advance, and the imaging conditions that are set in advance. And an imaging unit 210 that performs imaging according to the pulse sequence. In the present embodiment, the imaging unit 210 executes an imaging sequence for imaging an imaging region and a prepulse sequence for applying a prepulse to an excitation region different from the imaging region before the imaging sequence. The imaging condition setting unit sets these imaging conditions.

  In order to realize that the change of the fat excitation region due to the chemical shift is presented to the user when the imaging condition is set, the imaging condition setting unit 220 of the present embodiment performs an imaging region and a prepulse ( A receiving unit 221 that accepts the setting of the excitation region (pre-sachi region) of the pre-saturation pulse), and a direction specifying unit 222 that identifies the direction in which the excitation region due to the fat pre-pulse is shifted by a chemical shift as a shift direction with respect to the pre-sachi region, A display unit 223 indicating the identified shift direction to the user, a changing unit 224 for changing the pulses constituting the pre-pulse sequence, and a parameter corresponding to the accepted imaging region and the accepted pre-saturation region. And a setting unit 225 for setting as an imaging parameter.

  Each function of the control processing system 170 is realized by the CPU 171 loading a program stored in the storage device 172 or the like into the memory and executing it.

<Prepulse sequence>
Prior to description of each function, a pre-pulse sequence (pre-saturation sequence) for applying a pre-saturation pulse according to the present embodiment will be described. FIG. 3 is a diagram for explaining the pre-saturation sequence 300. In this figure, RF, Gs, Gp, and Gf indicate application axes of the RF pulse, slice selection gradient magnetic field pulse, phase encode gradient magnetic field pulse, and frequency encode gradient magnetic field pulse, respectively.

  As shown in the figure, in the presati sequence 300, a slice selection gradient magnetic field pulse 302 and an excitation RF pulse 301 are applied, and subsequently, a gradient magnetic field pulse 304 in an arbitrary direction is applied. The slice selective gradient magnetic field pulse 302 and the excitation RF pulse 301 are applied so as to excite a predetermined region (presati region) upstream of the blood flow with respect to the slice region of the imaging region.

  In the pre-saturation sequence 300, at least a blood flow portion upstream from the imaging region is excited, and a gradient magnetic field is applied to the nuclear spin generated thereby, thereby causing the phase of the nuclear spin to fall apart. In this way, before blood flows into the imaging region, artifacts are suppressed by saturating and suppressing NMR signals related to blood flow. That is, if the phases of the nuclear spins are separated and randomized, a signal obtained by synthesizing the nuclear spins becomes a sufficiently small signal. As a result, artifacts caused by the blood flow portion flowing into the imaging region can be suppressed.

  As described above, the shift direction of the fat excitation region with respect to water is determined by the polarity of the slice selective gradient magnetic field pulse 302 applied together with the excitation RF pulse 301 in the presati sequence 300. As shown by the solid line in FIG. 3, when applying a positive gradient magnetic field (302) to the device coordinate system as a slice selection gradient magnetic field pulse, the fat excitation region is shifted in the positive direction of the device coordinate system. To do. As shown by the dotted line in FIG. 3, when the polarity of the slice gradient magnetic field pulse is reversed (303), the fat excitation region shifts in the negative direction of the apparatus coordinate system.

<Reception Department>
The accepting unit 221 of the present embodiment displays a positioning image acquired in advance on a GUI (graphical user interface) screen on the display device 173, and accepts an imaging region and a presaturation region on the positioning image.

  FIG. 4A shows an example of the area setting screen 400 displayed as a GUI screen at this time. On the area setting screen 400, a positioning image 410 is displayed. On the positioning image 410, the user sets the imaging region 420 and the presatis region 430. The user sets these positions using, for example, a pointing device prepared as the input device 174.

  Furthermore, the receiving unit 221 of the present embodiment receives an instruction to invert the polarity of the slice selection gradient magnetic field pulse 302 of the pre-saturation sequence 300, as will be described later. There is no limitation on the method of accepting an instruction to reverse the polarity. For example, it may be accepted by a technique of double-clicking on the presatis region 430 on the region setting screen 400, a rotation operation for the display of the presachi region 430, that is, rotating the presachi region 430 on the region setting screen 400 by 180 degrees. . Further, a button dedicated to the instruction may be displayed on the area setting screen 400 and an instruction to press the button may be given.

<Direction specific part>
The direction specifying unit 222 of the present embodiment specifies the shift direction of the fat excitation region by chemical shift in the presati region 430. As mentioned above, fat protons have a lower frequency of precession than water protons. Accordingly, the resonance frequencies of the two are different. This difference in resonance frequency appears as a shift in the excitation region. This shift direction is determined by the polarity of the slice selective gradient magnetic field pulse 302 as described above. The direction specifying unit 222 of this embodiment specifies the shift direction according to the polarity of the slice selection gradient magnetic field pulse 302 of the pre-sachi sequence 300.

<Change section>
The changing unit 224 changes the pulses that make up the pre-saturation sequence 300. For example, when an instruction is received from the user to change the polarity of the slice selection gradient magnetic field pulse 302 of the presati sequence 300, the polarity of the slice selection gradient magnetic field pulse 302 of the presati sequence 300 is changed.

<Display section>
The display unit 223 performs a display (direction display) indicating the direction specified by the direction specifying unit 222 on the positioning image 410. The direction is displayed by displaying a predetermined graphic on the shift direction side of the presatis 430.

  A display example at this time is shown in FIG. Here, as a direction display 440 indicating the shift direction, a case where a dotted line is displayed along the presachi region 430 on the shift direction side of the presatis region 430 is shown as an example.

  The user can grasp the shift direction of the excitation region of the fat signal by looking at this direction display 440. Then, the user can change the prepulse sequence so that this shift does not affect the imaging region. For example, when the shift direction is the imaging region 420 side, an instruction to invert the polarity of the slice selection gradient magnetic field pulse 302 is performed by the above-described method.

  The instruction at this time is received by a method of rotating the pre-satisfied region 430 on the region setting screen 400 as described above. The state of rotation at this time is shown in FIG.

  Upon receiving an instruction from the user, the changing unit 224 changes the polarity of the slice selection gradient magnetic field pulse 302 in the pre-saturation sequence 300. When the configuration of the presaturation sequence 300 is changed, the direction specifying unit 222 specifies the shift direction each time, and the display unit 223 updates the display in response to the change.

  FIG. 6 shows a display example displayed on the region setting screen 400 after the user gives an instruction to reverse the polarity of the slice selection gradient magnetic field pulse 302. As shown in this figure, since the polarity of the slice selective gradient magnetic field pulse 302 is inverted, the shift direction is on the opposite side of the presatis region 430. Accordingly, the direction display 440 is displayed on the opposite side to the direction display 440 shown in FIG.

  As a result, the shift direction is on the opposite side of the presachi region 430, and even if the fat signal excitation region is shifted by chemical shift, the imaging region 420 is not affected.

<Setting section>
The setting unit 225 sets various imaging conditions including the imaging area 420 and the pre-saturation area 430 set by the user as imaging parameters and a pulse sequence during imaging. Furthermore, when the user finishes setting the imaging conditions, the imaging parameters and pulse sequence used at the time of imaging are determined according to the settings.

  When setting of the imaging region and the pre-satisfaction region is received from the user, the imaging parameter is set so that the position according to the user's setting is imaged and excited.

  Further, when accepting the intention of setting confirmation from the user, the imaging conditions and pulse sequence set at that time are determined as imaging parameters and pulse sequences used for imaging. The intention to confirm is received, for example, by pressing a confirmation button provided on the imaging condition setting screen displayed on the display device 173 when the imaging conditions are set. The area setting screen 400 is included in the imaging condition setting screen.

<Imaging condition setting process>
Hereinafter, the flow of the imaging condition setting process performed by the imaging condition setting unit 220 according to the present embodiment will be described with a focus on pre-sachi region setting. FIG. 7 is a process flow of the imaging condition setting process of the present embodiment.

  The imaging condition setting unit 220 displays the area setting screen 400 on the display device 173 (step S1001). The user sets the imaging area 420 and the presatis 430 on the area setting screen 400. Accordingly, the accepting unit 221 accepts these settings by the user (step S1002).

  The direction identifying unit 222 refers to a predetermined pre-pulse sequence (pre-saturated sequence 300) and identifies the shift direction (step S1003). The display unit 223 displays the direction display 440 indicating the shift direction on the positioning image 410 together with the imaging region 420 and the pre-saturation region 430 (step S1004).

  Thereafter, the imaging condition setting unit 220 waits for an instruction to reverse the polarity of the slice selection gradient magnetic field pulse 302 from the user.

  Here, when the receiving unit 221 receives the instruction (step S1005), the direction specifying unit 222 changes (inverts) the shift direction to the opposite side, and accordingly, the display unit 223 changes the display position of the direction display 440. change. Further, the changing unit 224 inverts the polarity of the slice selection gradient magnetic field pulse in the presati sequence 300 (step S1006).

  When receiving an instruction from the user that the imaging condition setting has been confirmed including other imaging conditions, the setting unit 225 uses the imaging parameters used for imaging to accept various imaging conditions and pulse sequence change instructions received at that time. And it reflects and confirms in a pulse sequence (step S1007), and an imaging condition setting process is complete | finished.

  Thereafter, when receiving an instruction to start imaging from the user, the imaging unit 210 starts imaging according to the determined imaging parameter and pulse sequence.

  As described above, the MRI apparatus 100 according to the present embodiment includes an imaging sequence that performs imaging of an imaging region, and a prepulse sequence that applies a prepulse to an excitation region (presatis region) that is different from the imaging region before the imaging sequence. An imaging condition setting unit 220 for setting an imaging condition for executing (pre-saturation sequence 300), and the imaging condition setting unit 220 sets the imaging region 420 and the excitation region 430 on the positioning image 410. Receiving direction unit 221 for receiving, a direction specifying unit 222 for specifying a direction in which the fat excitation region by the prepulse is shifted by a chemical shift as a shift direction with respect to the received excitation region 430, and the specified shift direction. A display unit 223 that is shown to a user, and the direction specifying unit 222 includes poles of a slice selection gradient magnetic field pulse 302 constituting the pre-pulse sequence 300. The shift direction is specified according to the sex.

  The display unit 223 displays a predetermined graphic 440 on the shift direction side of the received excitation region 430 along with the received imaging region 420 and the received excitation region 430 on the positioning image 410. , Indicate the specified shift direction to the user.

  As described above, according to the present embodiment, when a prepulse application region such as a presaturation pulse is set, the shift direction of the fat excitation region by the chemical shift with respect to the prepulse application region is presented to the user. Thereby, the user can grasp the direction in which the fat excitation region shifts.

  Therefore, for example, if the shift direction is the imaging region direction, the user can reverse the polarity of the pre-slice slice selection gradient magnetic field pulse so that the influence of the fat excitation region shift does not affect the imaging region. In particular, even in a high magnetic field MRI apparatus, even if the fat excitation region is greatly shifted due to chemical shift, the prepulse sequence can be changed so as not to affect the imaging region.

  As described above, according to the present embodiment, it is possible to prevent the fat signal in the imaging region from being erroneously suppressed by the pre-pulse chemical shift. That is, regardless of the magnetic field intensity of the MRI apparatus 100, it is possible to assist in appropriately setting the prepulse application region so that a desired effect is obtained and the imaging region is not adversely affected.

  In particular, when the pre-pulse is a pre-saturation pulse that suppresses a signal of a part that generates an artifact, it is more effective to set the pre-saturation pulse application region at a position close to the imaging region. In such a case, the present embodiment is useful.

  In the present embodiment, the direction (direction display 440) in which a chemical shift occurs is indicated by a dotted line, but the present invention is not limited to this. As long as the direction in which the chemical shift occurs is known, any display form may be used. For example, a predetermined figure may be displayed on the shift direction side of the application region of the presaturation pulse. Examples of the graphic to be displayed include a solid line, a line such as a wavy line, a polygon such as a triangle and a quadrangle, an arrow, and the like.

  In the present embodiment, after the shift direction is presented to the user, the shift direction of the presaturation pulse is reversed according to the user's instruction. However, the shift direction may be automatically reversed. That is, in the control processing system 170, after specifying the shift direction, it is determined whether or not the direction is the imaging region side. Then, in the case of the imaging region side, the polarity of the slice selection gradient magnetic field pulse 302 of the presati sequence 300 is reversed.

  In this case, after specifying the shift direction, the direction specifying unit 222 determines whether or not the shift direction is on the imaging region side. Then, the result is notified to the changing unit 224. The change unit 224 receives the notification and inverts the polarity of the slice selection gradient magnetic field pulse 302 when the shift direction is the imaging region 420 side of the pre-sachi region 430. At the same time, the display unit 223 receives the fact that the polarity is inverted, and indicates the shift direction after the polarity is inverted to the user. Here, the display position of the direction display 440 is changed to the opposite side of the presatis region 430 accordingly.

<Modification of imaging condition setting process>
FIG. 8 shows a processing flow of the imaging condition setting process by the imaging condition setting unit 220 in this case.

  The imaging condition setting unit 220 displays the area setting screen 400 on the display device 173 (step S1101). The user sets the imaging area 420 and the presatis 430 on the area setting screen 400. In response to this, the receiving unit 221 receives these settings by the user (step S1102).

  The direction specifying unit 222 refers to a predetermined pre-pulse sequence (pre-saturation sequence 300), specifies the shift direction, and determines whether or not the specified shift direction is the imaging region 420 side. (Step S1103). The display unit 223 displays a direction display 440 indicating the shift direction on the positioning image 410 together with the imaging region 420 and the pre-saturation region 430 (step S1104).

  When the determination result by the direction specifying unit 222 is on the imaging region 420 side (step S1105), the changing unit 224 changes the pre-saturation sequence 300 so that the shift direction is reversed (step S1106). Here, the polarity of the slice selection gradient magnetic field pulse 302 of the pre-sachi sequence 300 is inverted. Accordingly, the display unit 223 changes the display position of the direction display 440.

  When receiving an instruction from the user that the imaging condition setting including other imaging conditions has been confirmed, the setting unit 225 sets the imaging parameters and pulse sequence used for imaging to the various imaging conditions and pulse sequences received at that time. (Step S1107), and the imaging condition setting process ends.

  Thereafter, when receiving an instruction to start imaging from the user, the imaging unit 210 starts imaging according to the determined imaging parameter and pulse sequence.

  In this embodiment, the shift direction may be changed according to an instruction from the user or automatically. In this case, buttons, switches and the like for receiving instructions for switching between the two methods are arranged.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. In the first embodiment, what is presented to the user is only the shift direction of the presachi region due to chemical shift, but in this embodiment, the shift amount is also presented to the user. Furthermore, in the present embodiment, the pre-satisfactory region is adjusted so that the imaging region is not affected by this shift in consideration of the calculated shift amount.

  The MRI apparatus 100 of this embodiment basically has the same configuration as that of the first embodiment. Also in the present embodiment, the control processing system 170 includes an imaging unit 210 and an imaging condition setting unit 220, as shown in FIG. The imaging condition setting unit 220 includes a receiving unit 221, a direction specifying unit 222, a display unit 223, a changing unit 224, and a setting unit 225. In the present embodiment, the imaging condition setting unit 220 further includes a displacement amount calculation unit 226 that calculates a shift amount. Then, the changing unit 224 changes the pre-saturation sequence 300 in order to adjust the pre-sachi region according to the calculated shift amount. In addition, the display unit 223 shows the end of the excited region after the shift to the user.

Each function of the control processing system 170 is basically the same as that of the same name in the first embodiment.
However, the functions of the changing unit 224 and the display unit 223 are different. Hereinafter, the present embodiment will be described focusing on the configuration different from the first embodiment.

<Displacement amount calculation unit>
The displacement amount calculation unit 226 calculates the shift amount of the excitation region due to the chemical shift of the fat signal with respect to the set presachi region based on the information of the presachi region received by the reception unit 221. The calculation is performed when the shift direction specified by the direction specifying unit 222 is on the imaging region 420 side. The shift amount is calculated by the following method as the shift amount of the excitation region between water and fat.

  Fat protons have a precession frequency about 3.5 ppm lower than water protons. Therefore, the difference Δf [Hz] between the resonance frequency fw [Hz] of water and the resonance frequency fs [Hz] of fat is expressed by the following equation (1) using the resonance frequency fw of water.

Δf = (3.5 / 1,000,000) × fw (1)
Using this resonance frequency difference Δf, the frequency band BW [Hz] of the RF pulse applied as the pre-saturation pulse, and the thickness Th [cm] of the excitation region, the deviation δ [cm] of the excitation region between water and fat is Is calculated according to the following equation (2).

δ = Δf × Th / BW (2)
<Display section>
As shown in FIG. 10, the display unit 223 of the present embodiment, on the positioning image 410, along with the received imaging region 420 and the received presati region 430, the fat excitation by the presatis pulse at a position shifted by the calculated shift amount. Displays information that identifies the area.

  In the present embodiment, the excitation region display 450 is performed at the position of the end of the fat excitation region due to the presatis pulse on the imaging region 420 side as information for specifying the fat excitation region due to the presatisfaction pulse. The display mode of the excitation area display 450 is a predetermined figure such as a dotted line, similar to the direction display 440 of the first embodiment.

<Change section>
The changing unit 224 of the present embodiment determines whether or not the fat excitation region shifted by the calculated shift amount overlaps the imaging region 420, and if so, the prepulse sequence so that the fat excitation region is outside the imaging region 420. Change (Presati sequence 300).

  In the present embodiment, the changing unit 224 changes the frequency of the RF pulse 301 of the prepulse sequence (presaturation sequence 300) so that the presaturation region 430 moves by the shift amount δ in the direction opposite to the imaging region 420.

  Note that the position of the presatis region 430 moves in response to the frequency change of the RF pulse 301 of the changing unit 224. In response to this, the display unit 223 changes the display of the presati region 430 and the excitation region display 450 to the position after movement. The state after the change is shown in FIG. In this figure, a region surrounded by a dotted line is a pre-satis region 430 before movement, and a region surrounded by a solid line is a pre-sachi region 430 after movement.

  Note that the change unit 224 may reverse the polarity of the slice selection gradient magnetic field pulse 302 as in the first embodiment. The state after the change in this case is the same as in FIG.

<Imaging condition setting process>
Hereinafter, the flow of the imaging region setting process performed by the imaging condition setting unit 220 according to the present embodiment will be described until imaging starts. FIG. 12 is a processing flow of the imaging area setting process of the present embodiment. This process starts according to a user instruction.

  The imaging condition setting unit 220 displays the area setting screen 400 on the display device 173 (step S2001). The user sets the imaging area 420 and the presatis 430 on the area setting screen 400. Accordingly, the accepting unit 221 accepts these settings by the user (step S2002).

  The direction specifying unit 222 refers to a predetermined pre-pulse sequence (pre-saturation sequence 300), specifies the shift direction, and determines whether or not the specified shift direction is the imaging region 420 side. (Step S2003).

  Then, when the calculated shift direction is the imaging region 420 side, the displacement amount calculation unit 226 calculates the shift amount δ (step S2004). The display unit 223 displays the excitation region display 450 on the positioning image 410 at the position shifted by the shift amount δ in the shift direction together with the imaging region 420 and the presati region 430 (step S2005).

  When the determination result by the direction specifying unit 222 is on the imaging region 420 side (step S2006), the changing unit 224 determines whether or not the fat excitation position shifted by the calculated shift amount δ overlaps the imaging region 420. It discriminate | determines (step S2007).

  If they overlap at step S2007, the changing unit 224 changes the pre-saturation sequence 300 (step S2008). In the present embodiment, the frequency of the RF pulse of the presati sequence 300 is changed. Accordingly, the display unit 223 changes the display position of the presati region 430 to the changed position.

  When receiving an instruction from the user that the imaging condition setting including other imaging conditions has been confirmed, the setting unit 225 sets the imaging parameters and pulse sequence used for imaging to the various imaging conditions and pulse sequences received at that time. (Step S2009), and the imaging condition setting process ends.

  Thereafter, when receiving an instruction to start imaging from the user, the imaging unit 210 starts imaging according to the determined imaging parameter and pulse sequence.

  As described above, the MRI apparatus 100 according to the present embodiment includes an imaging sequence that performs imaging of an imaging region, and a prepulse sequence that applies a prepulse to an excitation region (presatis region) that is different from the imaging region before the imaging sequence. An imaging condition setting unit 220 for setting an imaging condition for executing (pre-saturation sequence 300), and the imaging condition setting unit 220 sets the imaging region 420 and the excitation region 430 on the positioning image 410. Receiving direction unit 221 for receiving, a direction specifying unit 222 for specifying a direction in which the fat excitation region by the prepulse is shifted by a chemical shift as a shift direction with respect to the received excitation region 430, and the specified shift direction. A display unit 223 that is shown to a user, and the direction specifying unit 222 includes poles of a slice selection gradient magnetic field pulse 302 constituting the pre-pulse sequence 300. The shift direction is specified according to the sex.

  The imaging condition setting unit 220 further includes a displacement amount calculation unit 226 that calculates a shift amount due to the chemical shift when the shift direction is the imaging region 420 side of the received excitation region 430, and the display unit 223 displays on the positioning image 410, together with the accepted imaging region and the accepted excitation region, the fat excitation region shifted by the calculated shift amount.

  The imaging condition setting unit 220 further includes a changing unit 224 that changes the pulses constituting the pre-pulse sequence 300, and the changing unit 224 has the fat excitation region shifted by the calculated shift amount as the imaging region 420. The prepulse sequence 300 is changed so that the fat excitation region is outside the imaging region 420.

  As described above, according to the present embodiment, when a pre-pulse application region such as a pre-saturation pulse is set, the actual application region is adjusted in consideration of the shift direction of the fat excitation region due to chemical shift with respect to the application region. Is done. Therefore, according to the present embodiment, even if a shift occurs in the application region of the presaturation pulse due to chemical shift, it does not overlap the imaging region. In addition, since adjustment is performed automatically, it does not take time and effort for the user.

  Therefore, according to this embodiment, it is possible to prevent the fat signal in the imaging region from being erroneously suppressed by the chemical shift of the prepulse. Regardless of the magnetic field intensity of the MRI apparatus, a desired effect can be obtained, and a pre-pulse application area can be appropriately set so that a desired image can be obtained so as not to adversely affect the imaging area.

  Similar to the first embodiment, this embodiment is also useful particularly when the pre-pulse is a pre-saturation pulse.

  In this embodiment, after the shift direction and the shift amount are calculated, the pre-saturation sequence 300 is adjusted so that these shifts do not affect the imaging region automatically, but the present invention is not limited to this. As in the first embodiment, the display may be limited to the display of the excitation region 450. Then, in response to an instruction from the user, adjustments such as reversing the polarity of the slice selection gradient magnetic field pulse 302 and changing the frequency of the RF pulse 301 may be performed.

  Further, in the present embodiment, the display on the positioning image 410 may be the direction display 440, and the calculated shift amount may be used only for adjustment of the pre-satch sequence 300 inside.

  Further, in the present embodiment, it may be configured to select whether the adjustment is performed in response to an instruction from the user or automatically. In this case, buttons, switches and the like for receiving instructions for switching between the two methods are arranged.

  As described above, the prepulse targeted by the present embodiment is not limited to the presaturation pulse. For example, an IR pulse may be used.

  The IR pulse is applied to make the magnetization in the imaging plane longitudinal magnetization before executing the pulse sequence of the main imaging. This is a pulse that gives contrast by utilizing the difference in relaxation time of spins contained in the tissue by using longitudinal magnetization.

  When the blood flow velocity is slow and the blood moves only within a shift amount δ within the imaging time, the effect of shifting the presatis region 430 by the shift amount δ is high. However, when the blood flow rate is high and the blood flow moves larger than the shift amount δ within the imaging time, the effect of shifting the excitation region is low. For this reason, the method of this embodiment may be applied only when the blood flow velocity is measured and the effect is high.

  Further, in each of the above-described embodiments, the case where the pre-saturation region is set in parallel to the imaging slice has been described as an example, but the present invention is not limited to this. The angle between the pre-sachi region and the imaging region to be set does not matter. For example, as shown in FIG. 13, it may be set perpendicular to the imaging slice.

  100 MRI system, 101 subject, 120 static magnetic field generation system, 130 gradient magnetic field generation system, 131 gradient magnetic field coil, 132 gradient magnetic field power supply, 140 sequencer, 150 transmission system, 151 transmission coil, 152 high-frequency oscillator, 153 modulator, 154 High-frequency amplifier, 160 reception system, 161 reception coil, 162 signal amplifier, 163 quadrature detector, 164 A / D converter, 170 control processing system, 171 CPU, 172 storage device, 173 display device, 174 input device, 210 imaging , 220 Imaging condition setting unit, 221 Accepting unit, 222 Direction specifying unit, 223 Display unit, 224 Changing unit, 225 Setting unit, 226 Displacement amount calculating unit, 300 Presati sequence, 301 Excitation RF pulse, 302 Slice selection tilt Magnetic field pulse, 303 slice selection gradient magnetic field pulse, 304 gradient magnetic field pulse, 400 area setting screen, 410 positioning image, 420 imaging area, 430 pre-sachi area, 440 direction display, 450 excitation area display

As described above, the shift direction of the fat excitation region with respect to water is determined by the polarity of the slice selective gradient magnetic field pulse 302 applied together with the excitation RF pulse 301 in the presati sequence 300. As indicated by a solid line in FIG. 3, when a slice selective gradient magnetic field pulse (302) in the positive direction is applied to the apparatus coordinate system as a slice selective gradient magnetic field pulse , the fat excitation region is the positive of the apparatus coordinate system. Shift in direction. As shown by the dotted line in FIG. 3, when the polarity of the slice gradient magnetic field pulse is reversed (303), the fat excitation region shifts in the negative direction of the apparatus coordinate system.

As described above, the MRI apparatus 100 according to the present embodiment includes an imaging sequence that performs imaging of an imaging region, and a prepulse sequence that applies a prepulse to an excitation region (presatis region) that is different from the imaging region before the imaging sequence. An imaging condition setting unit 220 for setting an imaging condition for executing (pre-saturation sequence 300), and the imaging condition setting unit 220 sets the imaging region 420 and the excitation region 430 on the positioning image 410. Receiving direction unit 221 for receiving, a direction specifying unit 222 for specifying a direction in which the fat excitation region by the prepulse is shifted by a chemical shift as a shift direction with respect to the received excitation region 430, and the specified shift direction. A display unit 223 shown to a user, and the direction specifying unit 222 has a polarity of a slice selection gradient magnetic field pulse 302 that constitutes the pre-saturation sequence 300 The shift direction is specified according to

The display unit 223 displays, on the positioning image 410, a figure (direction display) 440 predetermined on the shift direction side of the received excitation area 430 together with the received imaging area 420 and the received excitation area 430. By displaying, the specified shift direction is shown to the user.

Claims (14)

An imaging condition setting unit configured to set imaging conditions for performing an imaging sequence for imaging an imaging area and a prepulse sequence for applying an RF prepulse to an excitation area different from the imaging area before the imaging sequence;
The imaging condition setting unit
On the positioning image, a reception unit that receives settings of the imaging region and the excitation region;
A direction specifying unit that specifies the direction in which the fat excitation region by the RF prepulse is shifted by a chemical shift as the shift direction with respect to the received excitation region,
A display unit indicating the specified shift direction to the user,
The magnetic resonance imaging apparatus, wherein the direction specifying unit specifies the shift direction according to a polarity of a slice selective gradient magnetic field pulse constituting the pre-pulse sequence. The magnetic resonance imaging apparatus according to claim 1,
The display unit displays the predetermined figure on the positioning image together with the received imaging region and the received excitation region along with a predetermined figure on the shift direction side of the received excitation region. A magnetic resonance imaging apparatus characterized by showing a direction to a user. The magnetic resonance imaging apparatus according to claim 1,
The imaging condition setting unit further includes a changing unit that changes a pulse constituting the pre-pulse sequence,
The receiving unit further receives an instruction to reverse the polarity of the slice selection gradient magnetic field pulse;
The changing unit reverses the polarity of the slice selective gradient magnetic field pulse in accordance with the instruction. The magnetic resonance imaging apparatus according to claim 1,
The imaging condition setting unit further includes a changing unit that changes a pulse constituting the pre-pulse sequence,
When the shift direction is the imaging region side of the accepted excitation region, the changing unit reverses the polarity of the slice selection gradient magnetic field pulse,
The magnetic resonance imaging apparatus, wherein the display unit indicates to the user the shift direction after the polarity is inverted. The magnetic resonance imaging apparatus according to claim 1,
The imaging condition setting unit further includes a displacement amount calculation unit that calculates a shift amount due to the chemical shift when the shift direction is on the imaging region side of the received excitation region, and the display unit includes the positioning The magnetic resonance imaging apparatus, wherein the fat excitation region shifted in the shift direction by the calculated shift amount is displayed on the image together with the accepted imaging region and the accepted excitation region. The magnetic resonance imaging apparatus according to claim 5,
The imaging condition setting unit further includes a changing unit that changes a pulse constituting the pre-pulse sequence,
When the fat excitation region shifted by the calculated shift amount overlaps the imaging region, the changing unit changes the prepulse sequence so that the fat excitation region is outside the imaging region. Magnetic resonance imaging device. The magnetic resonance imaging apparatus according to claim 6,
The magnetic resonance imaging apparatus, wherein the changing unit changes the frequency of the RF pulse of the pre-pulse sequence so that the received excitation region moves in the opposite direction to the imaging region by the shift amount. The magnetic resonance imaging apparatus according to claim 6,
The magnetic resonance imaging apparatus, wherein the changing unit inverts the polarity of the slice selective gradient magnetic field pulse. The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus, wherein the predetermined figure is one of a line, an arrow, and a polygon along the received excitation region. The magnetic resonance imaging apparatus according to claim 3,
The display unit displays the positioning image and the received excitation region on a graphical user interface (GUI) screen,
The magnetic resonance imaging apparatus, wherein the reception unit receives an instruction to invert the polarity by a rotation operation with respect to the display of the received excitation region. The magnetic resonance imaging apparatus according to claim 1,
The magnetic resonance imaging apparatus, wherein the RF prepulse is a presaturation pulse that suppresses blood flowing into the imaging region before main imaging. The magnetic resonance imaging apparatus according to claim 1,
The RF resonance pulse is an IR (inversion recovery) pulse, and is a magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1,
The imaging target is a blood vessel,
The imaging condition setting unit
When the shift direction is on the imaging region side of the accepted excitation region, a displacement amount calculation unit that calculates a shift amount due to the chemical shift;
A change unit that sets and changes the pulses constituting the pre-pulse sequence, and
When the fat excitation region shifted by the calculated shift amount overlaps the imaging region, the changing unit calculates a blood movement amount within an imaging time based on a blood flow velocity, and the movement amount is If the shift amount is less than or equal to the shift amount, changing the prepulse sequence so that the received excitation region moves to the opposite side of the imaging region by the shift amount;
A magnetic resonance imaging apparatus. Imaging in a magnetic resonance imaging apparatus that supports setting of imaging conditions for executing an imaging sequence for imaging an imaging area and a prepulse sequence for applying an RF prepulse to an excitation area different from the imaging area before the imaging sequence A condition setting support method that accepts settings of the imaging region and the excitation region on a positioning image,
For the accepted excitation region, the direction in which the fat excitation region by the RF prepulse is shifted by a chemical shift is specified as the shift direction,
An imaging condition setting support method in a magnetic resonance imaging apparatus, wherein the specified shift direction is indicated to a user.

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