JP6694377B2 - Magnetic resonance imaging apparatus and pulse sequence calculation method - Google Patents

Description

  The present invention relates to a pulse sequence in a magnetic resonance imaging apparatus, and more particularly to a pulse sequence to which a velocity correction gradient magnetic field is added.

  In a magnetic resonance imaging (MRI) apparatus, a slice gradient magnetic field is applied to a subject placed in a static magnetic field, and at the same time, a high-frequency magnetic field having a specific frequency is applied to obtain nuclear magnetization in a section to be imaged. Excite. A phase encode gradient magnetic field and a read-out gradient magnetic field are applied to the excited nuclear magnetization to give a phase change depending on the position of the nuclear magnetization, and a nuclear magnetic resonance signal (echo) is measured. The high frequency magnetic field and each gradient magnetic field for generating the echo are applied based on a preset pulse sequence.

  As described above, the gradient magnetic field is applied to give positional information to nuclear magnetization, but in tissues with flow such as blood and cerebrospinal fluid, the phase changes depending on the position and velocity when the gradient magnetic field is applied. To do. Therefore, when an image is reconstructed by performing an inverse Fourier transform on the echo, a false image (artifact) such as a position shift or a ghost occurs. The artifacts caused by the flow are called flow artifacts. Flow artifacts can be dealt with by adjusting the imaging conditions. For example, in head imaging, there is a method of previously attenuating a signal of blood flowing into an imaging slice with a presaturation pulse. This is effective mainly in reducing flow artifacts due to arteries. Further, since the ghost of the flow artifact spreads in the phase encoding direction, there is also a method of reducing the flow artifact by appropriately selecting the phase encoding direction. For example, an artifact from the superior sagittal sinus of the head of the head can be captured by setting phase encoding in the left-right direction, so that a ghost from the superior sagittal sinus can be prevented from overlapping the brain parenchyma. However, even if these imaging conditions are devised, flow artifacts originating from the lateral sinus cannot be sufficiently reduced.

  On the other hand, as a flow artifact countermeasure by the pulse sequence, there is a method of correcting a phase change depending on the speed when a gradient magnetic field is applied by a speed correction gradient magnetic field (Non-Patent Document 1). This method is mainly used in MRA (MR Angiography) imaging for the purpose of suppressing signal loss and improving blood vessel signals, but is also an effective method for flow artifacts.

Jeong EK, Parker DL, Tsuruda JS, Won JY, Reduction of flow-related signal loss, flow-compensated 7 M, NR, anterior ed. 676 (2002)

  The velocity correction gradient magnetic field is a gradient magnetic field that is adjusted by the echo peak so that the phase change depending on the velocity when the gradient magnetic field is applied becomes zero at the echo peak time, and the application time and area are the adjustment parameters. .. If either of these adjustment parameters is fixed, waveform generation is facilitated, but the flexibility for changing the imaging conditions such as TE (time of echo) and the number of encodes is lost, and the degree of freedom in setting the imaging conditions is limited. In particular, since the SE (spin echo) sequence has more gradient magnetic field waveforms to be corrected than the GrE (gradient echo) sequence, the velocity gradient magnetic field waveform is taken into consideration in consideration of the constraints of imaging conditions and device constraints such as maximum gradient magnetic field strength. There is a problem in that the process of generating is complicated.

  The present invention provides a method for calculating a velocity correction gradient magnetic field that corrects a phase depending on a velocity at the time of applying a gradient magnetic field to zero under a set imaging condition constraint and a device constraint such as a maximum gradient magnetic field strength, and the like. The present invention provides an MRI apparatus having a function of realizing the method.

  Specifically, the MRI apparatus of the present invention includes a calculation unit that calculates a pulse sequence that determines the timing of application of a high-frequency magnetic field pulse, application of a gradient magnetic field pulse, and measurement of a nuclear magnetic resonance signal; A measuring unit that measures a nuclear magnetic resonance signal according to the pulse sequence, and the arithmetic unit refers to an imaging parameter that determines the pulse sequence, and as the gradient magnetic field pulse, a first gradient magnetic field waveform and A gradient magnetic field calculating section for calculating a bipolar gradient magnetic field having a first gradient magnetic field waveform and a second gradient magnetic field waveform having the same applied intensity and a reversed polarity, the gradient magnetic field calculating section comprising: The application time of the dipole gradient magnetic field determined by is a constraint condition, and the phase change of the moving nuclear magnetization before and after applying the first gradient magnetic field waveform and the second gradient magnetic field waveform. There calculates the switching time of said first gradient magnetic field waveform and the second gradient field waveform becomes zero, to generate the bipolar gradient waveform.

  According to the present invention, even when a plurality of gradient magnetic fields are applied to each axis, it is possible to easily create a velocity correction gradient magnetic field that takes into consideration the relaxation of the input limitation when setting the imaging condition, and it is expected that the operability will be improved. it can.

It is a block diagram which shows the typical structure of the MRI apparatus of 1st embodiment. It is a functional block diagram of a computer of a first embodiment. It is an example of a flow of a computer of the first embodiment. It is a figure which shows an example of SE sequence to which this invention is applied. FIG. 3 is a diagram showing an example of a bipolar magnetic field gradient of the phase encode axis according to the first embodiment. FIG. 3 is a diagram showing an example of a dipole gradient magnetic field of a slice selection gradient magnetic field axis according to the first embodiment. It is a figure which shows an example of the bipolar gradient magnetic field of the frequency encode axis by 1st embodiment. (A) And (b) is a figure explaining the effect of 1st embodiment. It is a figure which shows an example of the GrE sequence to which this invention is applied. It is a functional block diagram of a computer of a second embodiment. It is an example of a flow of a computer of the second embodiment. It is a figure which shows the example of a screen of recommendation parameter presentation in 2nd embodiment. It is a functional block diagram of a computer of a third embodiment. It is an example of a flow of a computer of the third embodiment. It is another example of the flow of the computer of the third embodiment. It is a figure which shows the example of a display screen common to each embodiment.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described. In all the drawings for explaining the embodiments of the present invention, unless otherwise specified, those having the same function are denoted by the same reference numeral, and the repeated description thereof will be omitted.

  As described above, the MRI apparatus 100 of the present embodiment applies a high-frequency magnetic field to the subject (imaging target) 103 placed in a static magnetic field to excite nuclear magnetization in the subject 103 and generate a nuclear magnetic field. A resonance signal (NMR signal, echo signal) is measured. At this time, position information is given to a magnetic resonance signal measured by applying a gradient magnetic field, and an image is taken (imaged).

  FIG. 1 is a block diagram showing a typical configuration of an MRI apparatus 100 of this embodiment that realizes this. The MRI apparatus 100 according to the present embodiment includes a magnet 101 that generates a static magnetic field, a gradient magnetic field coil 102 that generates a gradient magnetic field, an RF coil 107 that irradiates a subject 103 with a high frequency magnetic field pulse (hereinafter, RF pulse), An RF probe 108 that detects an echo signal generated from the subject 103, and a bed (table) 115 on which the subject (for example, a living body) 103 is placed in a static magnetic field space generated by the magnet 101 are provided.

  The gradient magnetic field coil 102 is composed of three sets of gradient magnetic field coils that generate a gradient magnetic field in three axial directions orthogonal to each other, and by appropriately combining them, position information can be given in any direction.

  Furthermore, the MRI apparatus 100 according to the present embodiment includes a gradient magnetic field power source 105 that drives each coil that constitutes the gradient magnetic field coil 102, a high-frequency magnetic field generator 106 that drives the RF coil 107, and an echo signal detected by the RF probe 108. To the receiver 109 for receiving the magnetic field, the gradient magnetic field power supply 105, and the high-frequency magnetic field generator 106 to generate a gradient magnetic field and a high-frequency magnetic field, respectively, and set the nuclear magnetic resonance frequency to be the reference for detection in the receiver 109. Sequencer 104, a computer 110 that performs signal processing on the detected signal, a display device 111 that displays the processing result of the computer 110, a storage device 112 that holds the processing result, and an instruction from the user. And an input device 116. In addition, the storage device 112 holds various data necessary for the processing in the computer 110.

  The MRI apparatus 100 may further include a shim coil 113 and a shim power supply 114 that drives the shim coil 113 when it is necessary to adjust the homogeneity of the static magnetic field. The shim coil 113 is composed of a plurality of channels and generates an additional magnetic field that corrects the static magnetic field inhomogeneity by the current supplied from the shim power supply 114. The sequencer 104 controls the current that flows in each channel of the shim coil 113 when the static magnetic field homogeneity is adjusted.

  In the MRI apparatus 100 having the above configuration, an RF pulse is applied to the subject 103 through the RF coil 107 under the control of the sequencer 104, and a gradient magnetic field for giving position information such as slice selection and phase encoding to the echo signal. The pulse is applied by the gradient coil 102. Further, the signal generated from the subject 103 is received by the RF probe 108, and the detected signal is sent to the computer 110, where signal processing such as image reconstruction is performed. Note that the storage device 112 may store not only the result of signal processing but also the detected signal itself, imaging conditions, and the like, if necessary.

  In addition, the computer 110 includes a CPU and a memory, and functions not only as a calculation unit that processes a received signal but also as a control system that controls the operation of the entire MRI apparatus 100. For example, the sequencer 104 is instructed to operate each part at a timing and intensity programmed in advance, the operation of each part constituting the MRI apparatus 100 is controlled, and measurement is performed. The pulse sequence describes the high frequency magnetic field, the gradient magnetic field, the timing and intensity of signal reception, among the above programs. There are various pulse sequences depending on the imaging method, and the basic pulse sequences thereof are stored in the storage device 112 in advance. In actual imaging, the basic pulse sequence is adjusted according to the imaging site, imaging purpose, and the like. The parameters for this adjustment are called imaging parameters and are input by the user via the input device 116. Imaging parameters include a repetition time (TR), an echo time (TE), a flip angle that determines the intensity of an RF pulse, a frequency encode number, a phase encode number, a slice thickness, a slice number, a slice interval, a reception bandwidth, and the like. The measurement is performed according to the pulse sequence and the imaging parameters required to control it.

  Furthermore, the MRI apparatus of the present embodiment performs adjustment so that the pulse sequence determined by the imaging parameter becomes a pulse sequence that corrects the phase depending on the velocity of nuclear magnetization when the gradient magnetic field is applied. That is, a pulse sequence including a gradient magnetic field (this is called a bipolar gradient magnetic field) composed of a pair of gradient magnetic field waveforms having opposite polarities and the same intensity is generated. This adjustment or calculation for it can be performed by the computer 110.

  FIG. 2 shows a function (function as a calculation unit) of the computer 110 that generates a pulse sequence including a bipolar gradient magnetic field. As illustrated, the computer 110 of the present embodiment includes a gradient magnetic field waveform calculation unit 200, and the gradient magnetic field waveform calculation unit 200 outputs a pulse sequence generated by the imaging parameter input by the user via the input device 116. A pulse sequence reference unit 210 to be referred to, and a switching time calculation unit that calculates a switching time between a first gradient magnetic field waveform and a second gradient magnetic field waveform forming a bipolar gradient magnetic field for the gradient magnetic field of each axis included in the pulse sequence. 220 and a bipolar gradient magnetic field waveform calculation unit 230 that generates a first gradient magnetic field waveform and a second gradient magnetic field waveform. The function shown in FIG. 2 is a function related to the function of generating a pulse sequence including a bipolar gradient magnetic field among the functions of the computer 110, and the computer 110 includes an unrepresented function such as an image reconstruction unit and a display control unit. Can be prepared.

  Each function of the computer 110 is realized by the CPU loading software (program) stored in the storage device 112 in advance into the memory and executing the software. It is not necessary to realize all of the above-mentioned functions by software, and some or all of them may be realized by hardware such as ASIC (Application Specific Integrated Circuit).

  Further, information necessary for executing the processing realized by each function, information obtained during the processing and finally obtained is stored in the storage device 112.

  Hereinafter, the flow of the bipolar magnetic field gradient waveform calculation by the gradient magnetic field waveform calculation unit 200 of the present embodiment will be described. FIG. 3 is a processing flow of the bipolar gradient magnetic field waveform calculation of the present embodiment.

  First, the pulse sequence reference unit 210 refers to the pulse sequence designated by the imaging parameter input by the operator via the input device 116, and determines the phase depending on the time to which the dipole gradient magnetic field can be applied and the velocity of nuclear magnetization. Information on the gradient magnetic field waveform that needs to be corrected for changes is acquired (step S301). Next, the switching time calculation unit 220 determines that the phase depending on the velocity of the nuclear magnetization generated by applying the gradient magnetic field is zero at the time of echo acquisition, and that the first gradient magnetic field waveform and the second gradient magnetic field waveform are calculated. The switching time between the first gradient magnetic field waveform and the second gradient magnetic field waveform that satisfies the condition that the absolute values of the applied strengths are equal is calculated (step S302). Next, the bipolar gradient magnetic field calculation unit 230 calculates the application center time and area of the first gradient magnetic field waveform and the second gradient magnetic field waveform from the calculated switching time (step S303), and generates the gradient magnetic field waveform. (Step S304).

The details of the processing of each unit will be described below.
As an example of the processing of this embodiment, a processing method for creating a dipole gradient magnetic field that corrects a phase change depending on the magnetization speed in the SE sequence will be described.

  FIG. 4 shows a typical 2D-SE sequence, in which RF, Gs, Gp, and Gf are an RF pulse axis, a slice selection gradient magnetic field axis (hereinafter also referred to as a slice axis), and a phase encode axis, respectively. , The frequency encoding axis. An echo is also shown on the RF axis. As shown in the figure, in the SE sequence, a 90-degree pulse 401 (also referred to as an excitation pulse) and a slice axis gradient magnetic field 501 are applied to excite nuclear magnetization spins in a slice determined by the applied intensity of the slice gradient magnetic field 501. Subsequently, the phase encode gradient magnetic field 601 is applied and the frequency encode gradient magnetic field 701 for dephase is applied. A refocus gradient magnetic field 502 is applied to the slice axis. After that, a 180-degree pulse (also referred to as an inversion pulse) 402 and a slice gradient magnetic field 503 are applied to invert the nuclear magnetic spins in the slice excited by the 90-degree pulse 401, from 90-degree pulse application to 180-degree pulse application. The spin echo 801 generated after the lapse of time is measured while applying the gradient magnetic field 702 in the frequency encoding direction. The time from the excitation pulse 401 (its center) to the echo (the center of the peak) is the echo time. Although not shown, a gradient magnetic field for returning the phase in the phase echo direction is applied after the echo signal measurement.

  Further, as indicated by a dotted line in the figure, crusher gradient magnetic fields 504, 505 and 704, 706 having relatively high strength may be added in order to reduce a free induction decay signal (FID). Here, the case where the crusher is added only to the slice axis and the frequency encode axis is shown, but the crusher may be added to any one axis, or may be added to all two axes or all three axes.

  Based on such a pulse sequence, a procedure for creating a bipolar gradient magnetic field for the phase encode axis will be described first with reference to FIG. In the present embodiment, the gradient magnetic field calculation unit generates a gradient magnetic field pulse composed of only a bipolar gradient magnetic field as the phase encoding gradient magnetic field pulse. FIG. 5 is a diagram in which the RF axis and the phase encode axis are extracted from the pulse sequence of FIG. 4, the upper phase encode axis Gp is the same basic pulse sequence as in FIG. 4, and the lower phase encode axis Gp. Indicates a phase encode gradient magnetic field composed of the created bipolar gradient magnetic field. The axis immediately below the phase encode axis Gp is a time axis Time for indicating the timing of each waveform. Further, FIG. 5 shows only one step of phase encoding.

  In step S301, the pulse sequence reference unit 210 reads the pulse sequence stored in the storage device 112, the SE sequence shown in FIG. 4 in the present embodiment, and the imaging parameter set by the user. Then, the end time of the 90-degree pulse 401 and the start time of the 180-degree pulse 402 are acquired and set as the start time t1 and the application end time t2 of the period T in which the bipolar gradient magnetic field can be applied, respectively. Further, the phase encode amount Sp is acquired from the phase encode gradient magnetic field waveform 601 on the phase encode axis Gp.

  Next, in step S302, the switching time calculation unit 220 assumes a dipole gradient magnetic field composed of the first gradient magnetic field waveform 611 and the second gradient magnetic field waveform 612 during the period T in which the dipole gradient magnetic field can be applied. As an example, the gradient magnetic field waveforms 611 and 612 are triangular waveforms. Next, a condition (condition 1) that the phase depending on the velocity of the nuclear magnetization generated when this dipole gradient magnetic field is applied becomes zero at the time of echo acquisition, and the first gradient magnetic field waveform 611 and the second gradient magnetic field waveform 612. The first gradient magnetic field waveform 611 and the second gradient magnetic field waveform 612 satisfying the condition (condition 2) that the absolute values of the applied intensities are equal are calculated.

Here, the switching time is tm, the central times of the gradient magnetic field waveforms 611 and 612 are ta and tb, and the areas of the gradient magnetic field waveforms are Sa and Sb. As a premise, in order to maintain the phase encoding amount Sp, the areas Sa and Sb of the dipole gradient magnetic field at the nuclear magnetization position x must satisfy the following expression (1).

Condition 1 can be expressed by the following expression (2), and condition 2 can be expressed by expression (3), where v is the nuclear magnetization speed.

  In these three formulas (1) to (3), since Sp and t1 and t2 are obtained by referring to the pulse sequence, three unknowns tm, Sa and Sb are expressed by simultaneous equations (1) to (3). It can be calculated by solving. That is, in step S302, the switching time tm is first calculated from the following equation (4) derived from the equations (1) to (3).

Next, in step S303, the bipolar gradient magnetic field calculation unit 230 calculates the application center time ta of the first gradient magnetic field waveform 611 and the application center time tb of the second gradient magnetic field waveform 612 by the following equation (5). ..

Further, the bipolar gradient magnetic field calculation unit 230 calculates the area Sa of the first gradient magnetic field waveform 611 and the area Sb of the second gradient magnetic field waveform 612 by the following equation (6).

  The bipolar gradient magnetic field waveform thus calculated maintains the same phase encoding amount as the original phase encoding gradient magnetic field 601 (Equation (1)) and two conditions, Condition 1 (Equation (2)) and Condition 2 (Equation 2). (3)) is satisfied. The above steps S301 to S303 are performed for all the set phase encoding steps, and the bipolar gradient magnetic field waveform of the phase encoding amount of each step is calculated.

  Finally, in step S304, the bipolar gradient magnetic field calculation unit 230 generates a gradient magnetic field waveform with the application center time and area calculated by the equations (5) and (6), and updates the pulse sequence.

Although FIG. 5 shows the case where the bipolar gradient magnetic field has a triangular waveform, the gradient magnetic field waveform is not limited to a triangular waveform. For example, in a trapezoidal waveform, if the trapezoidal rise time of each dipole gradient magnetic field waveform is t _SR , Condition 2 can be expressed by Equation (7).

ステップＳ３０３での計算処理は三角の波形と同様の処理にて双極傾斜磁場を生成することができる。また装置（傾斜磁場コイル）の特性による傾斜磁場波形の鈍化等を考慮して適宜補正係数などを導入してもよい。 At this time, in step S302, the switching time tm is first calculated from the following equation (8) derived from equations (1), (2) and (7).

The calculation process in step S303 can generate a bipolar gradient magnetic field by the same process as the triangular waveform. Further, a correction coefficient or the like may be appropriately introduced in consideration of the blunting of the gradient magnetic field waveform due to the characteristics of the device (gradient magnetic field coil).

  Next, a processing method for creating a bipolar gradient magnetic field that corrects a phase change depending on the velocity of magnetization in the slice gradient magnetic field axis of the SE sequence will be described with reference to FIG. Similar to FIG. 5, FIG. 6 is a diagram in which the RF pulse axis and the slice selection gradient magnetic field axis Gs are extracted from the SE sequence of FIG. 4, and the upper slice selection gradient magnetic field axis Gs is the same basic pulse sequence as in FIG. The lower slice selection gradient magnetic field axis Gs indicates the phase encode gradient magnetic field formed of the created bipolar gradient magnetic field. Further, here, a case where a crusher gradient magnetic field is added is shown.

  In step S301, the pulse sequence reference unit 210 refers to the RF pulse axis and the slice gradient magnetic field axis Gs, and determines the area Sc of the slice selection gradient magnetic field waveform 501 from the central time of the 90-degree pulse 401 to the application end time and its application center. The time t11, the application end time t12 of the 90-degree pulse 401 and the application end time t13 of the slice selection gradient magnetic field 501 and the area Sd of the slice selection gradient magnetic field waveform 501 between t12 and t13, and the 180-degree slice selection gradient magnetic field 503. Application start time t14, application start time t15 of the 180-degree pulse 402, area Se of the 180-degree slice selection gradient magnetic field waveform 503 from t14 to t15, and 180 from t15 to the central time of the 180-degree slice selection gradient magnetic field 503. Degree slice selection gradient magnetic field waveform 503 The area Sf and its application center time t16, the 180-degree pulse 402 end time t18, the application center time t17 of the 180-degree slice selection gradient magnetic field 503 from the center time of the 180-degree slice selection gradient magnetic field 503 to t18, and the 180-degree slice. The application end time t19 of the selective gradient magnetic field 503, the area Sg of the crusher gradient magnetic field waveform 505, and the central application time t20 are acquired.

Here, the slice selection gradient magnetic field waveform 501, the 180-degree slice selection gradient magnetic field waveform 503, and the crusher gradient magnetic field 505 applied after the 180-degree pulse application are not changed, and the application end time t13 of the slice selection gradient magnetic field waveform 501 is not changed. To the application start time t14 of the 180 ° slice selection gradient magnetic field 503 is set as a period in which the bipolar gradient magnetic field can be applied, and the first gradient magnetic field waveform 511 and the second gradient magnetic field waveform 512 applied during this period T are calculated. To do. As an example, the gradient magnetic field waveforms 511 and 512 are trapezoidal waveforms. Also in this calculation, the condition (condition 1) that the phase depending on the velocity of the nuclear magnetization generated by applying the gradient magnetic field becomes zero at the time of echo acquisition, and the first gradient magnetic field waveform 511 and the second gradient magnetic field waveform 512. The switching time tm of the gradient magnetic field waveforms 511 and 512, the rise time t _SR , the central times ta and tb, and the applied strengths Sa and Sb that satisfy the condition that the absolute values of the applied strengths of (2) are equal are calculated.

First, in step S302, the switching time calculation unit 220 calculates the switching time tm between the first gradient magnetic field waveform 512 and the second gradient magnetic field waveform 513 by the following formula.

When the waveform is triangular, the switching time tm is calculated by the following formula.

However, it does not depend on the waveform of the gradient magnetic field,

Next, in step S303, the bipolar gradient magnetic field calculator 230 calculates the application center time ta of the first gradient magnetic field waveform 511 and the application center time tb of the second gradient magnetic field waveform 512 by the following formula (12). ..

Further, the bipolar gradient magnetic field calculation unit 230 calculates the area Sa of the first gradient magnetic field waveform 511 and the area Sb of the second gradient magnetic field waveform 512 by the following formula.

  Finally, in step S304, the bipolar gradient magnetic field calculation unit 230 generates a gradient magnetic field waveform with the above-described application center time and area, and updates the pulse sequence.

  Next, a processing method for creating a dipole gradient magnetic field that corrects a phase change depending on the velocity of magnetization in the frequency encoding gradient magnetic field axis of the SE sequence will be described with reference to FIG. 7. Similar to FIG. 5, FIG. 7 is a diagram in which the RF pulse axis and the frequency encode axis Gf are extracted from the SE sequence of FIG. 4, and the upper frequency encode axis Gf is the same basic pulse sequence as in FIG. The side frequency encode axis Gf indicates the frequency encode gradient magnetic field formed of the created bipolar gradient magnetic field. Further, here, a case where a crusher gradient magnetic field is added is shown.

  In step S301, the pulse sequence reference unit 210 refers to the RF pulse axis and the frequency encoding gradient magnetic field axis Gf, and determines the end time t1 of the 90-degree pulse 401, the start time t2 of the 180-degree pulse, and the area of the crusher gradient magnetic field waveform 606. Sh and its application center time t3, application start time t4 and rising end time t5 of the frequency encode gradient magnetic field 702, area Sj of the frequency encode gradient magnetic field waveform 702 from t4 to t5, and t5 to the echo center time t10. The area Sk of the frequency encoding gradient magnetic field waveform 702 and the application center time t6 are acquired.

Here, the frequency encode gradient magnetic field waveform 702 applied after the 180-degree pulse 402 is not changed, and the interval between the end time t1 of the 90-degree pulse 401 and the start time t2 of the 180-degree pulse 402 is the bipolar magnetic field application period. , A first gradient magnetic field waveform 711 and a second gradient magnetic field waveform 712 constituting a bipolar gradient magnetic field, and a crusher gradient magnetic field 713 applied from the end time of the 180-degree pulse 402 to the start time of the frequency encode gradient magnetic field 702. To do. As an example, the gradient magnetic field waveforms 711 and 712 are trapezoidal waveforms. Also in this calculation, the condition in which the phase depending on the velocity of the nuclear magnetization generated by the gradient magnetic field application becomes zero at the time of echo acquisition, and the applied intensity of the first gradient magnetic field waveform 711 and the second gradient magnetic field waveform 712 The switching time tm of the gradient magnetic field waveforms 711 and 712, the rise time t _SR , the center times ta and tb, and the applied intensities Sa and Sb that satisfy the condition that the absolute values are equal are calculated.

First, in step S302, the switching time calculation unit 220 calculates the switching time tm between the first gradient magnetic field waveform 711 and the second gradient magnetic field waveform 712 by the following equation (14).

However,

Next, in step S303, the bipolar gradient magnetic field calculation unit 230 calculates the application center time ta of the first gradient magnetic field waveform 711 and the application center time tb of the second gradient magnetic field waveform 712 by the following formulas.

Further, the bipolar gradient magnetic field calculation unit 230 calculates the area Sa of the first gradient magnetic field waveform 711 and the area Sb of the second gradient magnetic field waveform 712 by the following formula.

  Next, in step S304, the bipolar gradient magnetic field calculation unit 230 generates a bipolar gradient magnetic field composed of the first gradient magnetic field waveform 711 and the second gradient magnetic field waveform 712 at the application center time and area described above, and further, A gradient magnetic field waveform 713 is generated by combining the crusher gradient magnetic field 704 and the dephase gradient magnetic field 701, and the pulse sequence is updated.

  As described above, the magnetic resonance imaging apparatus of the present embodiment generates a pulse sequence that corrects the phase depending on the velocity of nuclear magnetization when a gradient magnetic field is applied with a bipolar gradient magnetic field waveform having the same intensity. When generating this bipolar gradient magnetic field waveform, the constraint condition that the mutual intensities match within the applicable period is used. Therefore, when the user changes the echo time through the input device, by updating the dipole gradient magnetic field application start time t1 and the application end time t2, the phase depending on the velocity of nuclear magnetization at the time of applying the gradient magnetic field can be easily obtained. There is an advantage that a bipolar gradient magnetic field waveform to be corrected can be created.

  Further, according to this embodiment, even when there are a plurality of gradient magnetic fields to be velocity-corrected, the velocity correction can be performed only by the bipolar gradient magnetic field for a plurality of gradient magnetic fields including the crusher gradient magnetic field without extending the echo time. it can. Specifically, as shown in FIG. 8A, for example, a slice selection gradient magnetic field axis Gs, a slice selection gradient magnetic field 501, a slice refocusing gradient magnetic field 502, crusher gradient magnetic fields 504 and 505, and a 180-degree slice selection gradient are provided. In the case of the magnetic field 503, according to the conventional method, by applying the velocity correction gradient magnetic fields 511 to 513 to each, as shown in FIG. 8B, the interval between the 90-degree pulse 401 and the 180-degree pulse 402 is increased. Spread and extend echo time. Furthermore, in order to maintain the area of the crusher gradient magnetic field waveform, it is necessary to apply gradient magnetic field waveforms 514 and 515 having a larger area than the original crusher gradient magnetic field waveforms 504 and 505, and velocity correction is applied to the crusher gradient magnetic field. It becomes unrealistic to do. On the other hand, in the present embodiment, it is possible to realize the velocity correction of a plurality of gradient magnetic fields including the crusher gradient magnetic field only with the bipolar gradient magnetic field, and it is possible to shorten the echo time and perform the velocity correction including the crusher gradient magnetic field. There are advantages.

  In the present embodiment, the case where the dipole gradient magnetic field is generated for all the gradient magnetic field axes has been described. However, in the present embodiment, the dipole gradient magnetic field is generated only for one gradient magnetic field axis or for any two gradient magnetic field axes. You may change so that. The gradient magnetic field axis to which the bipolar gradient magnetic field is generated may be set automatically or by user selection depending on the imaging purpose or the imaging region.

<< Modified Example of First Embodiment >>
In the first embodiment, the case where the pulse sequence is the SE sequence has been described, but the present application is not limited to the pulse sequence. For example, a dipole gradient magnetic field can be similarly generated for the GrE sequence.

  FIG. 9 shows a typical GrE sequence. In the GrE sequence, the dephase frequency encode gradient magnetic field 701 and the rephase frequency encode gradient magnetic field 702 are applied so that the echo signal 910 reaches a peak (center time) after TE set after application of the RF pulse 901 (center time).

  In such a GrE sequence, when a bipolar gradient magnetic field is generated about the phase encode axis Gp, the application end time t1 of the RF pulse 901 is set as the application start time of the bipolar gradient magnetic field, and the application start time t4 of the frequency encode gradient magnetic field 702 is set. Is the end time of application of the bipolar gradient magnetic field. The other conditions are the same as those of the first embodiment, and the condition that the phase dependent on the velocity of nuclear magnetization generated when a dipole gradient magnetic field is applied becomes zero at the time of echo acquisition while maintaining the phase encoding amount (condition 1). And the switching time between the first gradient magnetic field waveform and the second gradient magnetic field waveform, which satisfies the condition (condition 2) that the absolute values of the applied intensities of the first gradient magnetic field waveform and the second gradient magnetic field waveform are equal, Calculate center time and area.

  When a bipolar gradient magnetic field is generated about the slice selection gradient magnetic field axis Gs, the period from the application end time t3 of the slice selection gradient magnetic field 501 applied at the same time as the RF pulse 901 to the application start time t4 of the frequency encoding gradient magnetic field 702 is set. The first gradient magnetic field waveform and the second gradient magnetic field waveform satisfying the above conditions 1 and 2 are calculated while maintaining the relationship with the application amount of the refocusing gradient magnetic field 502 by setting the dipolar gradient magnetic field as an applicable time.

Also in this modification, the velocity correction gradient magnetic field may be generated in all the axes, or the velocity correction gradient magnetic field may be generated in the uniaxial or biaxial gradient magnetic field axis.
Also in this modification, as in the first embodiment, the velocity correction gradient magnetic field can be easily created without imposing an excessive input restriction when setting the imaging condition (parameter).

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. The present embodiment is characterized by having a function of presenting recommended imaging parameters in the generation of the bipolar gradient magnetic field waveform. That is, the calculation unit of the MRI apparatus of the present embodiment includes a determination unit that determines whether or not the generated bipolar gradient magnetic field pulse satisfies the constraint of the device regarding the gradient magnetic field, and when the determination of the determination unit is negative, Among the parameters that determine the pulse sequence, a parameter that can change the restriction of the applicable time is displayed on the display device as a recommended parameter. The MRI apparatus of this embodiment basically has the same configuration as that of the first embodiment. Hereinafter, the configuration different from that of the first embodiment will be mainly described.

  In order to realize the function of presenting the recommended imaging parameters, the computer 110 of the present embodiment, in addition to the configuration of FIG. 2, shows whether or not the gradient magnetic field waveform in the pulse sequence satisfies the device constraint condition, as shown in FIG. A constraint condition determination unit 240, a recommended imaging parameter presentation unit 250 that presents recommended imaging parameters to the user when the constraint conditions are not satisfied, and an imaging parameter reception unit 260 that accepts a user's imaging parameter change.

  The processing flow in the computer 110 of this embodiment will be described below with reference to FIG. Steps S301 to S304 shown in FIG. 11 are substantially the same as steps S301 to S304 shown in FIG. That is, first, the pulse sequence reference unit 210 refers to the pulse sequence designated by the imaging parameter input by the operator via the input device 116, and depends on the time to which the bipolar gradient magnetic field can be applied and the nuclear magnetization speed. Information on the gradient magnetic field waveform that requires correction of the phase change is acquired (step S301). Next, the switching time calculation unit 220 determines that the phase depending on the velocity of nuclear magnetization generated by applying the gradient magnetic field becomes zero at the time of echo acquisition, and the first gradient magnetic field waveform and the second gradient magnetic field waveform The switching time between the first gradient magnetic field waveform and the second gradient magnetic field waveform that satisfies the condition that the absolute values of the applied strengths are equal is calculated (step S302). Next, the bipolar gradient magnetic field calculation unit 230 calculates the application center time and area of the first gradient magnetic field waveform and the second gradient magnetic field waveform from the calculated switching time (step S303), and generates the gradient magnetic field waveform. (Step S304).

  Next, the constraint condition determination unit 240 determines whether the generated bipolar gradient magnetic field waveform satisfies the device constraint (step S305). When the condition is satisfied, the process ends, and the pulse sequence is updated with the generated gradient magnetic field waveform. If not satisfied, the recommended parameter presentation unit 250 presents recommended parameters to the user (step S306). Next, when the imaging parameter reception unit 260 receives the parameter change of the user, the processing is repeated from step S301 (S307). If the user does not change the imaging parameter in step S307, the bipolar gradient magnetic field generation process ends (S308), and imaging is performed using the original pulse sequence.

  Based on the outline of the above processing, the details of the processing S305 and S306 characteristic of this embodiment will be described.

  The constraint condition determination unit 240 determines whether or not the range of the maximum gradient magnetic field intensity Gmax and the time change rate dB / dt of the gradient magnetic field intensity that can be applied by the device is satisfied, for example, as the device constraint of the bipolar gradient magnetic field waveform. ..

Specifically, a case will be described where it is determined whether the gradient magnetic field strengths of the first gradient magnetic field waveform 511 and the second gradient magnetic field waveform 512 of the slice axis in FIG. 6 exceed the maximum gradient magnetic field strength Gmax. Assuming that the rising time of the first gradient magnetic field waveform 511 and the second gradient magnetic field waveform 512 is t _SR , the respective gradient magnetic field strengths Ga and Gb are represented by the following equations.

Since the first gradient magnetic field waveform 511 and the second gradient magnetic field waveform 512 are created to have the same gradient magnetic field strength, Ga = Gb. The constraint condition that these are smaller than the maximum gradient magnetic field Gmax is expressed by the following equation.

  Since the value of the time change rate dB / dt is set according to the safety standard level, it is a device constraint that the dB / dt of the entire pulse sequence is equal to or less than the value set by the safety standard.

  If the device constraints are not satisfied in any case, the gradient can be adjusted by changing the imaging parameters such as echo time extension, frequency encode count reduction, phase encode count reduction, reception band increase, and crusher strength reduction. The magnetic field strengths Ga and Gb can be reduced. Therefore, the recommended imaging parameter presentation unit 250 presents the imaging parameters that can satisfy the device constraint as the recommended parameters to the user by changing the parameter values. Thereby, the user changes the parameter value of the desired imaging parameter in consideration of the priority of the imaging parameter.

  Further, when presenting the recommended parameters, the imaging parameters that have a particularly high effect of reducing the gradient magnetic field strengths Ga and Gb may be emphasized and displayed, and not only the recommended parameters are presented, but also the recommended parameter value and its increase / decrease value. May be calculated and presented. FIG. 12 shows an example of a display screen as a presentation example by the recommended imaging parameter presentation unit 250. This example is a screen for displaying imaging parameters for one of the plurality of measurements “measurement 1” defined as an inspection protocol, and can also be used as an imaging parameter setting screen. The “set value” block of the imaging parameter display unit 1200 displays the parameter value set in advance through the setting screen, and the “recommended value” column displays the calculated recommended parameter value. ..

  For example, when the echo time is presented as a recommended parameter for the bipolar gradient magnetic fields 511 and 512 in FIG. 6, the extension time Δt of the presented echo time can be calculated as follows. The applicable end time t14 of the second gradient magnetic field waveform 512 in FIG. 6 is extended by Δt, that is, Δt is added to the time t14 to t20 after t14, and the switching time tm of the bipolar gradient magnetic field and the application center times ta and tb. And the areas Sa and Sb are substituted into the above-described equations (9) and (11) to (13). In the obtained formula, Δt is an unknown number, but by using the formula (19), the minimum Δt or the range of Δt that satisfies the formula (19) can be calculated.

  Further, the strength Gc of the crusher gradient magnetic field 505 can be presented as a recommended parameter by calculating the gradient magnetic field strength that satisfies the equation (19) (Gc ≦ Gmax).

  The calculation of the parameter value in the case of extending the echo time has been described above. However, regarding the number of phase encodes, the number of frequency encodes, and the reception band, the first gradient magnetic field waveform and By calculating the second gradient magnetic field waveform and calculating the value satisfying the condition that the maximum gradient magnetic field strength is not exceeded, it is possible to calculate which value is the recommended value.

  As described above, according to the present embodiment, when the bipolar gradient magnetic field calculated by the set imaging parameter does not satisfy the device constraint, by presenting the recommended parameter or the recommended parameter value, the user is within the device constraint range. Has an advantage that the imaging parameter can be easily adjusted.

<< Third Embodiment >>
Next, a third embodiment to which the present invention is applied will be described. The calculation unit of the MRI apparatus of the present invention determines the dipole gradient magnetic field waveform based on the determination unit that determines whether the generated bipolar gradient magnetic field pulse satisfies the constraint of the apparatus regarding the gradient magnetic field and the determination result of the determination unit. And an adjusting unit for adjusting. Specifically, it has a function of adjusting the crusher strength when the generated dipole gradient magnetic field does not satisfy the apparatus constraint condition in the generation of the dipole gradient magnetic field waveform. The crusher strength can be adjusted by adjusting at least one of the application time and the area (strength). Here, an embodiment for adjusting the application time and the area to optimize the crusher strength will be described.

  The MRI apparatus of this embodiment basically has the same configuration as that of the first embodiment, but in order to realize the functions of this embodiment, the computer 110 of this embodiment has the configuration shown in FIG. 13, a constraint condition determination unit 240 that determines whether or not the gradient magnetic field waveform in the pulse sequence satisfies the device constraint condition, and an adjustment unit that adjusts the bipolar magnetic field gradient waveform, adjusts the application time of the gradient magnetic field waveform. And a gradient magnetic field waveform area adjustment unit 280 for adjusting the area of the gradient magnetic field waveform.

  Hereinafter, the bipolar gradient magnetic field generation processing of the present embodiment will be described with reference to the processing flow in the computer 110 of the present embodiment shown in FIG. Steps S301 to S304 shown in FIG. 14 are substantially the same as steps S301 to S304 shown in FIG. That is, first, the pulse sequence reference unit 210 refers to the pulse sequence designated by the imaging parameter input by the operator via the input device 116, and depends on the time during which the dipole gradient magnetic field can be applied and the nuclear magnetization speed. The information of the gradient magnetic field waveform that requires the correction of the phase change is acquired (step S301). Next, the switching time calculation unit 220 determines that the phase depending on the velocity of the nuclear magnetization generated by applying the gradient magnetic field becomes zero at the time of echo acquisition, and the first gradient magnetic field waveform and the second gradient magnetic field waveform. The switching time between the first gradient magnetic field waveform and the second gradient magnetic field waveform that satisfies the condition that the absolute values of the applied strengths are equal is calculated (step S302). Next, the gradient magnetic field waveform calculation unit 230 calculates the application center time and area of the first gradient magnetic field waveform and the second gradient magnetic field waveform from the calculated switching time (step S303), and generates the gradient magnetic field waveform. (Step S304).

  Next, the constraint condition determination unit 240 determines whether the generated bipolar gradient magnetic field waveform satisfies the device constraint (step S305). As described in the second embodiment, the device constraint is the maximum gradient magnetic field strength Gmax that can be applied by the device and the time change rate dB / dt of the gradient magnetic field. ).

  When the bipolar gradient magnetic field waveform satisfies the device constraint, the process ends, and the pulse sequence is updated with the generated gradient magnetic field waveform. If not, the recommended parameter for changing the imaging parameter is presented in the second embodiment, but the present embodiment changes the dipole gradient magnetic field waveform so as to satisfy the device constraint by adjusting the crusher strength. As shown in FIG. 6 (dipole gradient magnetic field of slice selection gradient magnetic field) and FIG. 7 (bipolar gradient magnetic field of frequency encode axis), the bipolar gradient magnetic field waveform generated by adding the crusher is the application of the crusher gradient magnetic field waveform. By shortening the central time, the areas of the first gradient magnetic field waveform and the second gradient magnetic field waveform to be generated are reduced without changing the area of the crusher gradient magnetic field waveform. For example, in the example of FIG. 6, by shortening the central time of the crusher 505, the areas of the first gradient magnetic field waveform 511 and the second gradient magnetic field waveform 512 are reduced.

  Therefore, the gradient magnetic field waveform application time adjusting unit 270 adjusts so as to shorten the application time while maintaining the area of the crusher gradient magnetic field waveform (step S311). That is, the gradient magnetic field waveform application time adjustment unit 270 does not change the application start time t19 of the crusher gradient magnetic field 505 but adjusts the application center time t20 to be short. This adjustment is performed within the range of the maximum gradient magnetic field strength Gmax that can be applied by the device and the time change rate dB / dt of the gradient magnetic field.

  After changing the central application time, steps S301 to S304 are repeated to recalculate the bipolar gradient magnetic field waveform (S312). Next, the constraint condition determination unit 240 determines again whether or not the generated bipolar gradient magnetic field waveform satisfies the device constraint (step S313). If it satisfies, it ends.

  If the result of recalculation after changing the center application time does not satisfy the apparatus constraint condition, the gradient magnetic field waveform area adjustment unit 280 adjusts so as to reduce the area of the crusher (S314). Next, steps S301 to S304 are repeated to recalculate the bipolar gradient magnetic field waveform (S315). After that, the process returns to S305, and the processes of S305 to S311 to S315 are repeated until it is determined in step S305 or S313 that the constraint condition range is not reached.

  In this case, the amount of change in the application time adjusted in step S311 and the area of the crusher adjusted in step S314 in this case can be set in advance in a single process.

  Further, in the processing flow shown in FIG. 14, processing S311 and S312 for changing the center application time of the crusher and recalculating the dipole gradient magnetic field, and processing S314 and S315 for changing the area of the crusher and recalculating the dipole gradient magnetic field. However, the area may be changed after the center application time of the crusher is changed to an allowable time.

  As described above, according to the present embodiment, it is possible to generate a bipolar gradient magnetic field waveform satisfying the device constraint by adjusting the crusher intensity without changing the set imaging parameter. Further, the crusher strength can be automatically adjusted without requiring complicated work.

<Modification of Third Embodiment>
In the third embodiment, an example is shown in which adjustment is performed to reduce the areas of the first gradient magnetic field waveform and the second gradient magnetic field waveform so as to satisfy the device constraint, but the first gradient so as to satisfy the device constraint. Adjustments may be made to increase the areas of the magnetic field waveform and the second gradient magnetic field waveform.

  FIG. 15 shows a flow of processing when the adjustment for maximizing the area is performed. Also in this process, steps S301 to S304 and S305 are the same as the process of FIG. When it is determined that the dipole gradient magnetic field generated in step S304 is out of the constraint condition range, the process proceeds to steps S311 to S315 in FIG. On the other hand, if it is determined in step S304 that it is within the constraint condition range, the generated gradient magnetic field waveform is stored in the storage device 112 and registered (S321). Next, in the pulse sequence including the registered gradient magnetic field waveform, while increasing the area of the crusher gradient magnetic field waveform (S322), the application time of the crusher gradient magnetic field waveform is set to the shortest under the condition of the increased area. , And calculates the bipolar gradient magnetic field waveform (S323). The amount of change in the area to be increased in step S322 can be set to a predetermined value in advance as in step S314 (adjustment to reduce the area) in FIG.

  Next, the constraint condition determination unit 240 determines whether or not the generated dipole gradient magnetic field waveform satisfies the device constraint condition (S324). If the constraint condition is satisfied, this bipolar gradient magnetic field is registered, and the bipolar gradient magnetic field registered in step S321 is updated (S325). Then, it returns to step S322 and repeats S322-S325. On the other hand, if it is determined in step S324 that the generated bipolar gradient magnetic field waveform does not satisfy the constraint condition, a pulse sequence is generated with the registered gradient magnetic field waveform.

  By such processing, there is an advantage that the pulse sequence can be adjusted to the maximum crusher intensity that can be applied, and artifacts due to the FID signal due to the 180-degree pulse can be suppressed.

  Although the embodiments of the pulse sequence calculation method realized by the MRI apparatus and the computer thereof according to the present invention have been described above, the present invention is not limited to the above embodiments and their modifications. For example, the above embodiment is premised on the calculation of the bipolar gradient magnetic field which is the velocity correction gradient magnetic field in the MRI apparatus, but when the measurement is performed according to the examination protocol including a plurality of measurements with different imaging methods. Depending on the purpose of imaging or the site of imaging, the bipolar gradient magnetic field that is the velocity correction gradient magnetic field may not be necessary. In such a case, for example, as shown in FIG. 16, it is possible to receive the input of the necessity of the velocity correction gradient magnetic field for each measurement included in the inspection protocol. Only when the input that the velocity correction gradient magnetic field is “necessary” is received, the bipolar gradient magnetic field waveform is calculated by any of the above-described embodiments.

  Further, although the embodiment in which the gradient magnetic field waveform is calculated by the computer of the MRI apparatus has been described, the function of calculating the gradient magnetic field waveform is realized not only by the computer integrated with the MRI apparatus but also by a computer independent of the MRI apparatus. It is possible. For example, when the pulse sequence and the imaging parameter are predetermined for each measurement of the examination protocol, the above-described gradient magnetic field waveform calculation is performed using a predetermined pulse sequence and the imaging parameter by a computer other than the MRI apparatus. Alternatively, the pulse sequence updated so as to include the bipolar gradient magnetic field may be registered in the storage device in the MRI apparatus or another storage device. The registered pulse sequence is read and executed when the measurement is performed according to the inspection protocol using the MRI apparatus.

  Further, the above-described embodiments and modified examples may be combined, or non-essential elements may be omitted or added unless technically contradictory.

100: MRI apparatus, 101: magnet, 102: gradient magnetic field coil, 103: subject (living body), 104: sequencer, 105: gradient magnetic field power supply, 106: high frequency magnetic field generator, 107: RF coil, 108: RF probe, 109: receiver, 110: calculator (calculation unit), 111: display device, 112: storage device, 113: shim coil, 114: shim power supply, 115: bed (table), 116: input device, 200: gradient magnetic field waveform calculation Part, 210: pulse sequence reference part, 220: switching time calculation part, 230: bipolar gradient magnetic field calculation part, 240: constraint condition determination part, 250: recommended imaging parameter presentation part, 260: imaging parameter reception part, 270: gradient magnetic field Waveform application time adjusting unit 280: gradient magnetic field waveform area adjusting unit.

Claims (13)

Performing application of the RF magnetic field pulse, application of the gradient magnetic field pulses, and a calculating unit for calculating a pulse sequence that defines the timing of measurement of the nuclear magnetic resonance signals, the measurement of the nuclear magnetic resonance signal in accordance with a pulse sequence in which the operation portion is calculated A magnetic resonance imaging apparatus comprising a measuring unit,
The calculation unit refers to an imaging parameter that determines the pulse sequence, and determines, as the gradient magnetic field pulse, a first gradient magnetic field waveform, the first gradient magnetic field waveform has the same waveform height, and the polarity is inverted. A gradient magnetic field calculation unit that calculates a bipolar gradient magnetic field having a second gradient magnetic field waveform,
The gradient magnetic field calculation unit,
As a constraint condition the applicable time of the bipolar gradient magnetic field determined by the imaging parameter,
The switching time between the first gradient magnetic field waveform and the second gradient magnetic field waveform in which the phase change of the moving nucleus magnetization due to the gradient magnetic field applied by the time of echo measurement becomes zero is calculated, and the dipole gradient magnetic field waveform is generated. A magnetic resonance imaging apparatus comprising: The magnetic resonance imaging apparatus according to claim 1, wherein
The gradient magnetic field pulse includes a phase encode gradient magnetic field pulse whose gradient magnetic field strength changes with each repetition,
The magnetic resonance imaging apparatus, wherein the gradient magnetic field calculation unit generates a gradient magnetic field pulse composed of only the bipolar gradient magnetic field as the phase encoding gradient magnetic field pulse. The magnetic resonance imaging apparatus according to claim 1, wherein
The pulse sequence is a spin echo system pulse sequence including an excitation pulse for exciting nuclear magnetization, and an inversion pulse for inverting nuclear magnetization excited by the excitation pulse,
The magnetic resonance imaging apparatus is characterized in that the gradient magnetic field calculation unit generates the dipolar gradient magnetic field with the application possible time being from a time point when the application of the excitation pulse is finished to a time point when the application of the inversion pulse is started. The magnetic resonance imaging apparatus according to claim 1, wherein
The pulse sequence is a gradient echo system pulse sequence including an excitation pulse for exciting nuclear magnetization, and a frequency encoding gradient magnetic field pulse applied after the excitation pulse,
The magnetic resonance imaging apparatus is characterized in that the gradient magnetic field calculating unit generates the bipolar gradient magnetic field with the application possible time being from a time point when the excitation pulse is applied to a time point when the frequency encode gradient magnetic field is applied. The magnetic resonance imaging apparatus according to claim 1, wherein
The pulse sequence is a spin echo system pulse sequence including an excitation pulse for exciting nuclear magnetization and an inversion pulse for inverting nuclear magnetization excited by the excitation pulse, wherein the excitation pulse and the inversion are used as the gradient magnetic field. A slice selection gradient magnetic field applied together with a pulse and a pair of crusher gradient magnetic fields applied before and after the inversion pulse,
The gradient magnetic field calculation unit, between the end time of application of the slice selection gradient magnetic field applied simultaneously with the excitation pulse and the start time of application of the slice selection gradient magnetic field applied simultaneously with the inversion pulse, the slice selection gradient magnetic field. Refocusing gradient magnetic field and a dipole gradient magnetic field that functions as one crusher gradient magnetic field. The magnetic resonance imaging apparatus according to claim 1, wherein
The pulse sequence is a spin echo system pulse sequence including an excitation pulse that excites nuclear magnetization and an inversion pulse that inverts nuclear magnetization excited by the excitation pulse, and is applied as the gradient magnetic field after the excitation pulse. A dephase frequency encoding gradient magnetic field, a rephase frequency encoding gradient magnetic field applied after the inversion pulse, and a pair of crusher gradient magnetic fields applied before and after the inversion pulse,
The gradient magnetic field calculation unit generates a dipole gradient magnetic field that functions as one crusher gradient magnetic field between the application end time of the excitation pulse and the application start time of the inversion pulse. .. The magnetic resonance imaging apparatus according to claim 1, wherein
The arithmetic unit has generated a bipolar gradient pulses comprises a determination section for determining whether or not satisfy the constraints of the apparatus relating to the gradient, when the determination of the determination unit is negative, the bipolar gradient pulse At least one of the echo time, the frequency encode number, the phase encode number, the reception band and the crusher intensity is determined from among the imaging parameters for determining the pulse sequence when it is determined that the restriction of the applicable time at the time of generation is necessary. A magnetic resonance imaging apparatus characterized in that a parameter capable of changing the constraint of the applicable time including is displayed as a recommended parameter on a display device. The magnetic resonance imaging apparatus according to claim 1 or 7, wherein
Further comprising a receiving unit for receiving the setting of the imaging parameter of the pulse sequence,
The magnetic resonance imaging apparatus, wherein the gradient magnetic field calculation unit repeats the generation of the bipolar gradient magnetic field waveform for the pulse sequence changed by the imaging parameter received by the reception unit. The magnetic resonance imaging apparatus according to claim 1, wherein
The calculation unit, the generated dipole gradient magnetic field pulse, a determination unit that determines whether or not the constraints of the apparatus regarding the gradient magnetic field,
The magnetic resonance imaging apparatus further comprising: an adjusting unit that adjusts the bipolar gradient magnetic field waveform according to the determination result of the determining unit. The magnetic resonance imaging apparatus according to claim 1, wherein
A storage unit that stores a pulse sequence including the bipolar gradient magnetic field calculated by the gradient magnetic field calculation unit,
A pulse sequence including the bipolar gradient magnetic field and a receiving unit that receives a selection of any one of the pulse sequences not including the bipolar polarity used to generate the bipolar gradient magnetic field, further comprising:
When the accepting unit accepts the selection of the pulse sequence including the dipole gradient magnetic field, the measuring unit measures the nuclear magnetic resonance signal according to the pulse sequence including the dipole gradient magnetic field stored in the storage unit. And a magnetic resonance imaging apparatus. A method of calculating a pulse sequence that determines the timing of application of a high-frequency magnetic field pulse in a magnetic resonance imaging apparatus, application of a gradient magnetic field pulse, and measurement of a nuclear magnetic resonance signal,
As the gradient magnetic field pulse, a step of calculating a velocity correction gradient magnetic field having a first gradient magnetic field waveform and a second gradient magnetic field waveform having a waveform height equal to that of the first gradient magnetic field waveform and polarity reversed. Including,
In the step of calculating, the phase change of the moving nucleus magnetization due to the gradient magnetic field applied until the echo measurement becomes zero, with the application possible time of the dipolar gradient magnetic field determined by the imaging parameter that determines the pulse sequence as a constraint condition. A pulse sequence calculation method comprising: calculating a switching time between a first gradient magnetic field waveform and a second gradient magnetic field waveform to generate the first gradient magnetic field waveform and the second gradient magnetic field waveform. The pulse sequence calculation method according to claim 11, wherein
The generated first gradient magnetic field waveform and the second gradient magnetic field waveform determines whether or not the constraint of the magnetic resonance imaging apparatus regarding the gradient magnetic field,
When the generated first gradient magnetic field waveform and the second gradient magnetic field waveform do not satisfy the constraint of the apparatus, the value of the imaging parameter is changed, and the constraint of the applicable time is changed in the changed pulse sequence. A pulse sequence calculation method characterized in that the calculation of the switching time between the first gradient magnetic field waveform and the second gradient magnetic field waveform used is repeated. The pulse sequence calculation method according to claim 11, wherein
The generated first gradient magnetic field waveform and the second gradient magnetic field waveform include a crusher gradient magnetic field,
The generated first gradient magnetic field waveform and the second gradient magnetic field waveform determines whether or not the constraint of the magnetic resonance imaging apparatus regarding the gradient magnetic field,
When the generated first gradient magnetic field waveform and the second gradient magnetic field waveform do not satisfy the constraint of the device, at least one of the center application time and the area of the crusher gradient magnetic field is adjusted, and the crusher gradient magnetic field after the adjustment is adjusted. A method of calculating a pulse sequence, characterized in that the calculation and generation of the switching time of the first gradient magnetic field waveform and the second gradient magnetic field waveform are repeated using the pulse sequence calculation method.

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