JP2009254583A - Magnetic resonance imaging apparatus and controlling method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove affection of vortex resulting from a gradient magnetic field in a phase encode direction. <P>SOLUTION: A zero-th component of a phase encode in which affection of vortex resulting from a gradient magnetic field G<SB>PE</SB>for the phase encode in a phase encode (PE) direction is dominant is measured by two prescannings, for example first and second prescannings A and B. On the basis of the zero-th component of the phase encode, affection of vortex resulting from a gradient magnetic field G<SB>PE</SB>for the phase encodein a phase encode (PE) direction is corrected in the present scan. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus using a fast spin echo (FSE) method and a control method thereof.

  A magnetic resonance imaging (MRI) apparatus utilizes the magnetic resonance phenomenon of nuclear spins, and can obtain an image in a subject non-invasively. As a result, MRI apparatuses are being implemented more and more actively in the field of medical technology, and with the advancement and advancement of techniques such as image processing, the quality requirements for MR images and the degree of high-speed imaging have increased greatly. Yes. In such an MRI apparatus, various pulse sequences for magnetic resonance imaging are implemented or proposed, and the FSE method is one of them.

  In an MRI apparatus using the fast spin echo (FSE) method, for example, a phase shift of a spin echo is detected when performing a prescan, and a phase shift detected by the prescan in the main scan is corrected. For example, Patent Document 1 collects spin echoes from which phase encoding (PE) has been removed, measures 0th-order and first-order phase differences between the first and second echoes, and mainly uses the 0th-order phase difference. It is disclosed that correction is performed using an RF phase, and a primary phase difference is corrected by adding a correction pulse to a gradient magnetic field pulse in a readout direction.

  In addition, a pulse for spoiling −1, +1, −2, +2,... And a STE (stimulated echo) component (hereinafter referred to as sub-echo) is applied to the phase encode (PE). By collecting the same shot twice and appropriately controlling the RF, the side echo can be removed. Thereby, if the pre-scan of the FSE method is used, it is possible to completely remove the phase shift caused by the vortex between the gradient magnetic field in the slice direction and the gradient magnetic field in the read direction.

  The sub-echo is as follows. The MRI apparatus performs the main scan by the FSE method. This main scan is a scan for collecting k-space data for imaging. In the FSE method, a plurality of flop pulses are given after one flip pulse to create a spin echo (SE) train. At this time, each spin echo (SE) is made to correspond to a different line in k-space by giving each spin echo (SE) a phase encoding (PE) of a different magnitude. Thereby, the fast spin echo (FSE) method collects a plurality of different views in one excitation.

  In the fast spin echo (FSE) method, if the waveform of the RF pulse and the gradient magnetic field signal repeated after the flop pulse are symmetric, the first type spin echo α and the first type spin echo of the MR signal are provided. Two series of echo components in which β appears alternately are included. These two series of echo components will be referred to as a main echo component and a sub-echo component, respectively.

However, the fast spin echo (FSE) method has large vortices and vibrations and high resolution in the phase encoding (PE) direction. In such a fast spin echo (FSE) method, the influence of a vortex due to a gradient magnetic field in the phase encoding (PE) direction cannot be ignored. Conventionally, in a magnetic resonance imaging apparatus, the phase shift due to the vortex between the gradient magnetic field in the slice direction and the gradient magnetic field in the read direction can be removed, but the influence of the vortex due to the gradient magnetic field in the phase encoding (PE) direction should be removed. I can't. For this reason, in the main scan in which phase encoding (PE) is applied, interference fringes may occur in the MR image.
US Pat. No. 6,369,568

  An object of the present invention is to provide a magnetic resonance imaging apparatus and a control method thereof that can eliminate the influence of vortices caused by a gradient magnetic field in the phase encoding direction.

  The magnetic resonance imaging apparatus according to claim 1 of the present invention has a high-frequency excitation pulse and a plurality of high-frequency inversion pulses and a plurality of high-frequency inversion pulses before the main scan for obtaining an MR image of the subject. A first pre-scan of a pulse sequence in which the application phase is set to a reference phase value, and application of an even-numbered high-frequency inversion pulse having a high-frequency excitation pulse and a plurality of high-frequency inversion pulses A plurality of echo signals obtained by the first prescan in the magnetic resonance imaging apparatus that respectively performs the second prescan of the pulse sequence in which the phase is set to a value having a phase difference of 180 ° with respect to the reference phase value And a second echo data group consisting of a plurality of echo signals obtained by the second pre-scan. At least determine the 0-order component of phase encoding, to correct the phase encoding gradient magnetic field in the direction of the phase encoding in the main scan based on the zero-order components of the phase-encoding.

  The method of controlling a magnetic resonance imaging apparatus according to claim 6 of the present invention includes a high frequency excitation pulse and a plurality of high frequency inversion pulses before a main scan for obtaining an MR image of a subject, A first pre-scan of a pulse sequence in which the application phase of the high-frequency inversion pulse is set to a reference phase value is performed, and then a high-frequency excitation pulse and a plurality of high-frequency inversion pulses are included. A second pre-scan of a pulse sequence in which the application phase of the even-numbered high frequency inversion pulse was set to a value having a phase difference of 180 ° with respect to the reference phase value was performed, and then obtained by the first pre-scan. At least a phase based on a first echo data group composed of a plurality of echo signals and a second echo data group composed of a plurality of echo signals obtained by the second prescan. Calculated zero-order component of Nkodo, correcting the phase encoding gradient field in the direction of the phase encoding in the main scan based on the zero-order components of the phase-encoding.

  ADVANTAGE OF THE INVENTION According to this invention, the magnetic resonance imaging apparatus which can remove the influence of the eddy by the gradient magnetic field of a phase encoding direction, and its control method can be provided.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration diagram of a magnetic resonance imaging (MRI) apparatus. This MRI apparatus takes charge of system control and image reconstruction, a magnet part for generating a static magnetic field, a gradient magnetic field part for adding position information to the static magnetic field, a transmitting / receiving part for selective excitation and MR signal reception. And a control / arithmetic unit.
The magnet unit includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 that supplies current to the magnet 1. This magnet unit generates a static magnetic field H ₀ in the Z-axis direction (longitudinal direction) of the cylindrical diagnostic space into which the subject P to be imaged is inserted.

  The gradient magnetic field unit includes three sets of gradient magnetic field coils 3x to 3z in the X-axis direction, the Y-axis direction, and the Z-axis direction incorporated in the magnet 1, and a gradient magnetic field power source 4 that supplies current to the gradient magnetic field coils 3x to 3z. And a gradient magnetic field sequencer 5 a included in the sequencer 5 that controls the power source 4. The gradient magnetic field coil 3x in the X-axis direction generates a gradient magnetic field in the X-axis direction. The gradient magnetic field coil 3y in the Y-axis direction generates a gradient magnetic field in the Y-axis direction.

The gradient magnetic field coil 3z in the Z-axis direction generates a gradient magnetic field in the Z-axis direction. The gradient magnetic field in the X-axis direction, the gradient magnetic field in the Y-axis direction, and the gradient magnetic field in the Z-axis direction are orthogonal to each other.

  When the gradient magnetic field sequencer 5a includes a computer and receives a signal for instructing a collection sequence such as the FSE method for performing pre-scan and main scan from the controller 6 (equipped with the computer) of the entire apparatus, the gradient magnetic field sequencer 5a responds to this command Then, the pre-scan and main scan processes are executed.

Thus, the gradient sequencer 5a is, X-axis direction according to a sequence which is commanded from the controller 6, Y-axis direction, and controls the application and its intensity of each gradient magnetic field in the Z axis direction, these gradient magnetic fields on the static magnetic field H ₀ Superposition is possible. Incidentally, the Z-axis direction of the tilting slice gradient magnetic field G _SS of the three mutually perpendicular axes. The gradient magnetic field in the X-axis direction is defined as a read gradient magnetic field _GRO . The gradient magnetic field in the Y-axis direction is a phase encoding gradient magnetic field _GPE .

  The transmission / reception unit includes a high-frequency coil (RF coil) 7 disposed in the vicinity of the subject P in the imaging space in the magnet 1, a transmitter 8T and a receiver 8R connected to the RF coil 7, and these transmissions. And an RF sequencer 5b (equipped with a computer) for controlling the operation timing of the machine 8T and receiver 8R. The RF sequencer 5b forms the sequencer 5 together with the gradient magnetic field sequencer 5a.

  The RF sequencer 5b instructs the transmitter 8T and the receiver 8R to apply RF pulses in a state synchronized with the gradient magnetic field sequencer 5a. The transmitter 8T and the receiver 8R supply an RF current pulse having a Larmor frequency for exciting nuclear magnetic resonance (NMR) to the RF coil 7 and received by the RF coil 7 under the control of the RF sequencer 5b. Various signal processes are performed on the high frequency signal (MR signal) to form an echo signal.

In addition to the controller 6, the control / arithmetic unit includes a multiplexer 11 that receives a digital echo signal formed by the receiver 8R. The multiplexer 11 selectively switches the output path between the controller side and the reconstruction unit side in response to a control signal from the controller 6.
Further, on one output side of the multiplexer 11, a reconstruction unit 12 that performs image reconstruction by a Fourier transform method, a storage unit 13 that stores the reconstructed image data, a display device 14 that displays an image, and an input And a container 15. The controller 6 incorporates a computer as described above, and controls the operation content and operation timing of the entire system.

The controller 6 performs two pre-scans, for example, first and second pre-scans, of the zero-order component of the phase encode in which the influence of the vortex due to the phase encode gradient magnetic field G _PE in the phase encode (PE) direction is dominant. a, measured in B, and corrects the influence of the eddy due to the phase encoding gradient field G _PE direction the phase encoding (PE) in the main scan based on the zero-order components of the phase-encoding. In this case, the zero-order component of the phase encoding gradient magnetic field _GPE is corrected by the phase of the 90 ° or 180 ° RF pulse from the RF coil 7.

That is, the controller 6 executes the fast spin echo (FSE) method, and when the waveforms of the RF pulse and the gradient magnetic field signal repeated after the flop pulse in the fast spin echo (FSE) method are symmetric, the MR signal is converted into an MR signal. In this scan, the phase of the main echo component (first type spin echo α) and sub echo component (second type spin echo β) that appear alternately is extracted from the two echo components. The same PE sequence as the shot for collecting the encoding (PE = 0) is applied in the PE direction, that is, a PE sequence that eliminates the phase difference between the main echo component α and the secondary echo β is applied in the PE direction in the main scan. In other words, on the k space where the plurality of echo signals are arranged, the first echo data group composed of the plurality of echo signals obtained by the first prescan A across the center position on the k space and the second seeking the difference between the plurality of echo signals obtained by prescan B, and equivalent when obtaining the pulse PE series of correcting gradient field G _PE phase encoding direction of phase encoding (PE) on the basis of this difference .

Next, vortex removal by the phase encoding gradient magnetic field Gpe in the phase encoding (PE) direction in the apparatus configured as described above will be described with reference to a control flowchart shown in FIG. Here, the controller 6 executes a CPMG pulse sequence of fast spin echo (FSE) as a pulse sequence.
In step S1, the controller 6 causes the sequencer 5 to execute the first pre-scan A of the pulse sequence shown in FIG. 3 with the switch path of the multiplexer 11 switched to the controller 6 side. input.

In the first pre-scan A, first, a slice gradient magnetic field pulse Gss is applied, and a high-frequency excitation pulse RFex (application phase φ = 0 °, flip angle θ = α (here 90 °)) is applied. Next, the first pre-scan A includes the first high-frequency inversion pulse RFrel (application phase φ = 90 °) together with the slicing gradient magnetic field pulse Gss after the elapse of time τ / 2 from the application of the high-frequency excitation pulse RFex. Flip angle θ = β1 (180 ° here)) is applied.
Next, after τ time from the application of the first high-frequency excitation pulse RFex, in the first prescan A, the echo signal E (1) is read while applying the read gradient magnetic field pulse Gro.

  Thereafter, in the first pre-scan A, the second and subsequent high-frequency inversion pulses RFre2, RFre3,..., Together with the slicing gradient magnetic field pulse Gss, every time τ has elapsed since the application of the first high-frequency inversion pulse RFrel. And echo signals E (2), E (3),... Are read out in the same manner. In the first print scan A, as shown in the figure, the phase encoding gradient magnetic field pulse Gpe is always zero.

  In the first pudding spin A, if there is a phase shift in the nuclear spin due to some cause, each of the echo signals E (2), E (3),... Other than the first echo signal E (1) Is divided into two echo components, that is, a main echo component Emain (2) (Emain (3),...) And a sub-echo component Esub (2) (Esub (3),...) As shown in FIG. When there is no cause of phase shift, the phase arg {Emain (n)} of the main echo component Emain (n) and the phase arg {Esub (n)} of the sub-echo component Esub (n) are equal (n = 2, 3 ...).

Next, in step S2, the controller 6 causes the sequencer 5 to execute the second pre-scan B as shown in FIG. 4, and inputs an echo signal obtained as a result.
In the second pre-scan B, first, a high-frequency excitation pulse RFex (application phase φ = 0 °, flip angle θ = α (90 ° in this case)) is applied together with the slice gradient magnetic field pulse Gss. After elapse of time τ / 2 from the time of application of the high frequency excitation pulse RFex, the second pre-scan B is combined with the slice gradient magnetic field pulse Gss and the high frequency inversion pulse RFrel (application phase φ = 90 °, flip angle θ = α ( Here, 180 °)) is applied.
Next, in the second pre-scan B, the echo signal E (1) is read out while applying the read gradient magnetic field pulse Gro after τ time from the application of the first high-frequency excitation pulse RFex.

  Thereafter, the second pre-scan B applies the second and subsequent high-frequency inversion pulses RFre2, RFre3,... Together with the slicing gradient magnetic field pulse Gss every τ time from the application of the first high-frequency inversion pulse RFrel. , Echo signals E (2), E (3),.

  In the second pre-scan B, the application phase φ of the even-numbered high-frequency inversion pulses RFre2, RFre4,... Is further 180 ° from the odd-numbered high-frequency inversion pulses RFre3, REre5,. The rotated value (φ = 270 °) is set. The phase encoding gradient magnetic field pulse Gpe is always zero as in the first prescan A.

  If there is a phase shift in the nuclear spin due to some cause, each of the echo signals E (2), E (3),. Echo components, that is, main echo components Emain (2) (Emain (3),...) And sub-echo components Esub (2) (Esub (3),. Since the applied phase φ of... Is further rotated by 180 °, only the phase arg {Esub (n)} of the sub-echo components Esub (2), Esub (3),. Rotate 180 ° relative to the corresponding phase at time A.

The reason for this will be described with reference to FIG. The phase of the nth echo signal is θn, and the phases of the (n + 1) th and n + 2nd high frequency inversion pulses are φn + 1 and φn + 2, respectively. The phase θ _{n + 2, SE of the} main echo component generated by the (n + 2) th high frequency inversion pulse, and the phase θ _{n + 2, STE} of the substimulated echo component are:
θ _{n + 2, SE} = 2φn + 2−φn + 1 + θn (1)
θ _{n + 2, STE} = φn + 2 + φn + 1−θn (2)
It is represented by.

In the case of the first prescan A shown in FIG. 3, φn = 90 °, θn for all integers n of 1 or more. = 90 °, θ _{n + 2, SE} = 90 °, θ _{n + 2, STE} = 90 °. Therefore, the phases of the main echo component Emain (n) and the sub-echo component Esub (n), which are a combination of a plurality of echo paths on the phase diagram, are also equal to each other and become 90 °.

In the case of the second pre-scan B shown in FIG.
When n = 2m (m is an integer of 1 or more)

  The sub-echo component generated from the nth main echo component Emain (n) due to φn + 1 and φn + 2 is Esub (n + 2). As a result, the phase of the sub-echo component Esub (n) in the second pre-scan B shown in FIG. 4 is 270 ° for all n of n = 2 or more, that is, the state of the first pre-scan A shown in FIG. It can be seen that 180 ° is inverted.

As a result of the above prescan, if the echo signal obtained in the first prescan A is Ea (n) and the echo signal obtained in the second prescan B is Eb (n) (n = 2, 3). , ...),
Ea (n) = Emain (n) + Esub (n) (3)
Eb (n) = Emain (n) −Esub (n) (4)
The relationship is established.

Next, in step S3, the controller 6 performs an averaging process between the echo signals obtained by the first and second pre-scans A and B. That is, the controller 6
{Ea (n) + Eb (n)} / 2 (5)
n = 1, 2,...
Perform the operation.
The concept of this averaging operation is shown in the schematic diagrams of FIGS. 6 (a) and 6 (b) and FIG. As shown in these figures, in the second and subsequent echo signals E (2), E (3),..., The sub-echo components Esub (2), Esub (3),. Since A and B differ from each other by 180 °, they are canceled as appropriate, and only the main echo component Emain (n) (n = 1, 2,...) Is extracted.
In addition, FIG.7 (b)
{Ea (n) -Eb (n)} / 2 (6)
FIG. 6 schematically shows how only the sub-echo component Esub (n) (n = 2, 3,...) Is extracted when the above calculation is performed.

  Next, in step S4, the controller 6 performs pure phase shifts φmain (1), φmain (2) and position shift pmain (1) of the peak of the main echo component based on the first and second echo signals. pmain (2) is calculated. The zero-order component φ of the phase shift is proportional to the difference between the phase of the first echo signal and the phase of the second echo signal. That is, obtaining the zero-order component φ of the phase shift is equivalent to measuring the phase difference between the peak of the first echo and the peak of the second echo.

Then, the controller 6, in step S5, PE series for correcting the influence of the eddy due to the gradient magnetic field G _PE phase encoding direction of phase encoding (PE) in the main scan based on the 0-order component of the phase shift φ PE1, PE2, PE3, and PE4 are obtained. That is, the controller 6 applies the same PE series pulses PE1, PE2, PE3, and PE4 in the PE direction as the shot that collects the phase encode (PE = 0) in the main scan based on the pulse sequence shown in FIG. A PE sequence that eliminates the phase difference between the echo component α and the sub-echo component β is applied in the PE direction in the main scan.

Next, in step S6, the controller 6 switches the switch path of the multiplexer 11 to the reconstruction unit 12 side, and causes the sequencer 5 to execute the main scan based on the pulse sequence shown in FIG.
In this scan, after lapse of τ / 2 from the first excitation, the first high-frequency inversion pulse RFrel (application phase φ = 90 °, flip angle θ = β1 (here, 180 °)) together with the slice gradient magnetic field pulse Gss. Is applied, and the phase of the spin is reversed.
Then, for each main scan execution of the sequence, the pulse PE1 of PE sequence is applied for correcting the influence of the eddy due to the phase encoding gradient field G _PE direction the phase encoding (PE), followed by PE series Pulse PE2 is applied.

  Next, in the main scan, the read gradient magnetic field pulse Gro is applied with the elapse of τ time from the first selective excitation, and the first echo signal E (1) is collected in parallel with this.

Next, in this scan, the sliced gradient magnetic field pulse Gss and the high-frequency inversion pulses RFre2, RFre3,... (Applied phase φ = 90 °, flip angles θ = β2, β3,... (Here, 180 °)) are sequentially provided. Applied.
After a lapse of 3τ time from the first selective excitation, in this scan, PE series of pulses PE3 for correcting the influence of the eddy due to the phase encoding gradient field G _PE direction the phase encoding (PE) is applied Subsequently, a PE series pulse PE4 is applied.
The zero-order component of the correction of the phase encoding gradient magnetic field _GPE is matched with the phase of the 90 ° or 180 ° RF pulse from the RF coil 7. In the main scan, the zero-order component of the phase encoding gradient magnetic field _GPE is corrected by the phase of the RF pulse. Each time high frequency inversion pulses RFre2, RFre3,... (Applied phase φ = 90 °, flip angles θ = β2, β3,... (180 ° in this case)) are sequentially applied, the phase of the RF pulse is 0 °, 180 °. , 180 °, 180 °,..., Phase 0, 90 + Δφ, 90 + Δφ, 90 + Δφ,. Δφ = 0 order phase difference / 2.

  Similarly, the high-frequency inversion pulses RFre2, RFre3,... (Application phase φ = 90 °, flip angles θ = β2, β3,... (Here 180 °) are sequentially applied together with the slicing gradient magnetic field pulse Gss. Meanwhile, echo signals E (2), E (3),... Accompanying the spin phase inversion are sequentially collected.

  The echo signal E (n) collected by the main scan is sequentially received by the receiver 8R and converted into echo data. This processing includes quadrature detection and A / D conversion of the echo signal E (n). The reconstruction unit 12 arranges the echo data on a memory forming a k (Fourier) space according to the encoding amount, and reconstructs the MR image data by a Fourier transform method.

Thus, according to the above embodiment, two pre-scans the 0-order component of the phase encoding influence of the eddy due to the phase encoding gradient field G _PE is dominant in the direction of the phase encoding (PE), e.g. first and second pre-scan a, measured in B, and corrects the influence of the eddy due to the phase encoding gradient field G _PE direction the phase encoding in the main scan based on the zero-order component of the phase-encoding (PE) . In this case, the zero-order component of the correction of the phase encoding gradient magnetic field _GPE is controlled by the phase of the 90 ° or 180 ° RF pulse. Thereby, in the fast spin echo (FSE) method with high resolution in the phase encoding (PE) direction, the influence of the vortex due to the gradient magnetic field in the phase encoding (PE) direction can be removed, and the phase encoding (PE) is applied. With this scan, high-accuracy MR image data with little variation in sensitivity without interference fringes can be acquired. Then, the phase difference between the peak of the first echo and the peak of the second echo, that is, the zero-order component φ of the phase shift incorporates the influence of phase encoding (PE) into the zero-order component to be corrected. Since the echo of phase encode (PE) = 0 has a large amplitude, it can be corrected with high reliability.

By performing the first and second pre-scans A and B in the fast spin echo (FSE) method, a gradient magnetic field in the slice direction, a gradient magnetic field in the read direction, and a gradient magnetic field in the phase encoding (PE) direction are obtained. It is possible to determine the phase shift of the zero-order component due to the vortex. Further, the primary component of the phase shift of the gradient magnetic field in the lead direction can be obtained by obtaining the primary gradient by performing Fourier transform (FT) on the echo signal arranged in the k space. Thus it is possible to correct the influence of the eddy due to the phase encoding gradient field G _PE direction the phase encoding (PE) in the main scan based on the phase shift of the zero-order component determined.

  Further, pre-scanning is performed to apply a magnetic field by a sensitivity pulse to the gradient magnetic field in the read direction, and the phase shift of the primary component due to the vortex between the gradient magnetic field in the slice direction and the gradient magnetic field in the read direction is obtained. Next, a magnetic field by a correction pulse for correcting a gradient magnetic field in the lead direction to be corrected by performing a new pre-scan is applied, and in this state, the above-described embodiment is carried out. Thereby, the phase shift of the primary component due to the vortex of the gradient magnetic field in the lead direction can be completely corrected. However, this is effective for an apparatus using an unshielded gradient coil.

Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
In the above-described embodiment, the combination of the application phases of the CPMG pulse series is basically changed. However, the present invention is not limited to this, and the application phases of the first and second high frequency pulses of the prescans A and B are not limited thereto. If the combination satisfies the above equations (1) and (2) and the main echo component Emain (n) or the sub-echo component Esub (n) has a phase difference of 180 ° in two pre-scans, Any combination of phases may be used.

1 is a configuration diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. The control flowchart in the same apparatus. The figure which shows the pre-scan A of the pulse sequence in the same apparatus. The figure which shows the pre-scan B of the pulse sequence in the same apparatus. The figure for demonstrating 180 degree phase rotation of the subecho signal in the same apparatus. Explanatory drawing which shows isolation | separation extraction of the main echo component in the same apparatus. Explanatory drawing which shows isolation | separation extraction of the main echo component and a subecho component in the same apparatus. The figure which shows the main scan of the pulse sequence in the same apparatus.

Explanation of symbols

  1: superconducting magnet, 2: static magnetic field power supply, 3x: gradient magnetic field coil in X axis direction, 3y: gradient magnetic field coil in Y axis direction, 3z: gradient magnetic field coil in Z axis direction, 4: gradient magnetic field power supply, 5 : Sequencer, 5a: Gradient magnetic field sequencer, 5b: RF sequencer, 6: Controller, 7: High frequency coil (RF coil), 8T: Transmitter, 8R: Receiver, 11: Multiplexer, 12: Reconfiguration unit, 13: Memory Unit, 14: indicator, 15: input device.

Claims (9)

Before the main scan for obtaining the MR image of the subject, a first pulse sequence having a high-frequency excitation pulse and a plurality of high-frequency inversion pulses and the application phase of the plurality of high-frequency inversion pulses set as a reference phase value One pre-scan, a high-frequency excitation pulse and a plurality of high-frequency inversion pulses, and the application phase of an even-numbered high-frequency inversion pulse among the plurality of high-frequency inversion pulses is 180 ° relative to the reference phase value. In the magnetic resonance imaging apparatus for performing the second pre-scan of the pulse sequence set to a value having a phase difference, respectively
At least phase encoding based on a first echo data group consisting of a plurality of echo signals obtained by the first prescan and a second echo data group consisting of a plurality of echo signals obtained by the second prescan. And correcting the gradient magnetic field for phase encoding in the phase encoding direction in the main scan based on the zeroth order component of the phase encoding.
A magnetic resonance imaging apparatus.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the first pre-scan pulse sequence and the second pre-scan pulse sequence are at least a CPMG pulse sequence.   The magnetic resonance imaging apparatus according to claim 1, wherein a phase encoding gradient magnetic field of the first and second pre-scan pulse sequences is always zero.   2. The magnetic component according to claim 1, wherein the zero-order component of the phase shift is obtained from a phase difference between a peak of the first echo and a peak of the second echo appearing when the fast spin echo is performed. Resonance imaging device.   A first echo data group composed of a plurality of echo signals obtained by the first pre-scan and a second pre-scan on a k-space where the plurality of echo signals are arranged with a center position in the k-space interposed therebetween. The magnetic resonance imaging apparatus according to claim 1, wherein a difference from a plurality of echo signals obtained by scanning is obtained, and the phase encoding gradient magnetic field in the phase encoding direction is corrected based on the difference. Before the main scan for obtaining the MR image of the subject, a first pulse sequence having a high-frequency excitation pulse and a plurality of high-frequency inversion pulses and the application phase of the plurality of high-frequency inversion pulses set as a reference phase value 1 pre-scan,
Next, it has a high-frequency excitation pulse and a plurality of high-frequency inversion pulses, and the application phase of an even-numbered high-frequency inversion pulse among the plurality of high-frequency inversion pulses has a phase difference of 180 ° with respect to the reference phase value Perform a second prescan of the pulse sequence set to the value,
Next, based on a first echo data group composed of a plurality of echo signals obtained by the first prescan and a second echo data group composed of a plurality of echo signals obtained by the second prescan. Find at least the zeroth-order component of phase encoding,
Correcting the gradient magnetic field for phase encoding in the phase encoding direction in the main scan based on the zeroth-order component of the phase encoding;
A method of controlling a magnetic resonance imaging apparatus.   7. The method of controlling a magnetic resonance imaging apparatus according to claim 6, wherein a phase encoding gradient magnetic field of the first and second pre-scanning pulse sequences is always zero.   7. The magnetic component according to claim 6, wherein the zero-order component of the phase shift is obtained from a phase difference between a peak of the first echo and a peak of the second echo that appears when the fast spin echo is performed. A method for controlling a resonance imaging apparatus.   2. The method of controlling a magnetic resonance imaging apparatus according to claim 1, wherein the zero-order component of the correction of the phase encoding gradient magnetic field is controlled by a phase of a 90 ° or 180 ° RF pulse.

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