WO2003037183A1

WO2003037183A1 - Magnetic resonance imaging device

Info

Publication number: WO2003037183A1
Application number: PCT/JP2002/009631
Authority: WO
Inventors: Yoshinori Togasawa
Original assignee: Hitachi Medical Corporation
Priority date: 2001-10-30
Filing date: 2002-09-19
Publication date: 2003-05-08
Also published as: JP4319035B2; JPWO2003037183A1

Abstract

An MRI device has an imaging pulse sequence for measuring echo signals by applying 90° excitation pulse (21) and an inverting 180° high-frequency magnetic field pulse (22) a plurality of times. In performing this pulse sequence, prepulses (25-27) for keeping constant the gradient magnetic field error component entering during the immediately previous slice measurement before the application of the 90° excitation pulse (21) are applied a predetermined time before the application of the 90° excitation pulse (21). In this way, the fluctuation gradient magnetic field error component caused by the gradient magnetic field applied during the immediately previous slice measurement is made ineffective, and the residual gradient magnetic field component during the application of the 90° excitation pulse (21) is always kept uniform, thus making the spin phase rotation error caused later a constant error component that can be eliminated by later correction. Thus an MRI device by an imaging method using a pulse train by the CPMG method is provided from which the gradient magnetic field error component varying depending on the imaging condition and the influence of the spin phase error caused by the error component are eliminated and which creates an image for which the artifact due to the spin phase error is suppressed.

Description

Magnetic resonance imaging equipment

Technical field

The present invention relates to a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus) for imaging nuclear distribution and spectrum information in a subject by utilizing a nuclear magnetic resonance phenomenon.

A multi-shot based on the Carr-Purcel l-Meiboom-Gill (CPMG) method was used to reduce the eddy currents and artifacts generated by the residual gradient magnetic field due to the influence of the gradient magnetic field for the previous shot or slice measurement. The present invention relates to an improvement of an MRI apparatus having a single-slice slice and a multi-shot multi-slice imaging pulse sequence. Background technology

An MRI apparatus applies a high-frequency magnetic field to a subject placed in a uniform static magnetic field, causing nuclear magnetic resonance to occur in nuclei (usually protons) existing in an arbitrary region of the subject, thereby generating the nuclear magnetic resonance. The tomographic image of the area is obtained from the nuclear magnetic resonance signal (echo signal). Normally, an MRI apparatus applies a slice gradient magnetic field that specifies a plane on which a tomographic image of a subject is to be obtained, and simultaneously applies an excitation pulse (high-frequency pulse) that excites spins in the plane, and is excited by this. Obtain the echo signal generated when the spin converges. In order to give positional information to the echo signal, a phase encoding gradient magnetic field and a readout (frequency encoding) gradient magnetic field are applied in directions orthogonal to each other in the tomographic plane during the period from excitation to obtaining the echo signal. The echoes thus obtained are arranged in k-space with the phase encoding direction as the ordinate and the readout direction as the abscissa, and an image is reconstructed by performing an inverse Fourier transform on the data arranged in the k-space. You. A high-frequency pulse for generating an echo signal and each gradient magnetic field are applied based on a preset pulse sequence. Various pulse sequences are known according to the purpose of imaging. In the fast spin echo method, 180 ° inversion pulses equal to the number of set echo numbers are applied after the 90 ° excitation pulse, and at that time, echo signals are collected by giving a different phase encoding amount for each echo number. It is a high-speed imaging method that acquires multiple echo signals with a short repetition time (TR).

In this fast spin echo method, it is common to use a pulse train based on the CPMG method in which the application axis of the 180 ° inversion pulse is different from the application axis of the 90 ° excitation pulse. This CPMG method has an excellent effect of compensating for imperfections of the 180 ° pulse (the nuclear spin does not become perfect 180 °), but it is necessary to control the phase of the excitation pulse and the gradient magnetic field with high precision. Yes, distortion and incompleteness of the gradient magnetic field due to eddy current and magnetic hysteresis cause artifacts in the image. This tendency often occurs in MRI devices that use a permanent magnet method as a static magnetic field generating magnet. For the pulse train of the CPMG method, see, for example, US Pat. No. 4,818,940.

This will be described with reference to FIGS. 5A and 5B. Fig. 5A shows the pulse sequence by the fast spin echo method based on the CPMG method, and Fig. 5B shows the behavior of the spin due to it. Here, for the sake of simplicity, the high-frequency pulse and the frequency code ( Readout) Only the gradient magnetic field in the direction is shown. As shown in the figure, by applying a 90 ° excitation pulse 51, a specific spin tilted to the x′-y ′ plane is rotated from the position 1 to 2 by the gradient magnetic field 53. The amount of phase rotation at this time is defined as Next, the position is changed from 2 to 3 by the 180 ° inversion pulse 52, and further moved from 3 to 4 by the gradient magnetic field 54. Here, the gradient magnetic field 53 and the gradient magnetic field 54 have an applied intensity X application time of 1: 2, and thus the phase rotation amount at this time is 2. After that, the same repetition occurs at the position of 5 to 6 by the next inversion pulse 52 and gradient magnetic field 54, but when the first 1: 2 relationship is broken, multiple echo signals are generated. At the same time, spin rotation errors occur in the spins and accumulate, causing signal loss and the like, and artifacts occur. Generally, as a method of suppressing artifacts due to gradient magnetic field distortion and imperfection, for example, Japanese Patent Application Laid-Open No. H11-89817 discloses a magnetic detection method that generates a correction magnetic field waveform for correcting a gradient field distortion due to eddy current. It has been proposed to introduce a digital eddy current correction circuit including a circuit.

Eddy current correction by adding a hardware circuit as described above is extremely effective in correcting gradient magnetic field distortion due to eddy currents with little fluctuation, but fluctuations occur in pulse sequences with different conditions such as the number of slices and repetition time. It is not possible to deal with the residual magnetic field. For example, in the multi-slice measurement shown in Fig. 6, in which a plurality of slices (three in this case, S1 to S3) are measured adjacent or very close within a given repetition time TR, Imaging is repeated by equally distributing the time for each slice. However, the time interval between slices (the time from the end of measurement of one slice to the measurement of the next slice) is not always the same, so that a certain time due to eddy currents generated in the magnet's conductive members, etc. The gradient magnetic field error component that attenuates with a constant is different for each slice, and this error component affects the slice to be measured next, so that the spin is affected by a different phase error for each slice. Similarly, the residual gradient magnetic field component due to the magnetic hysteresis will also be different if the time interval between each slice is different. Therefore, the resulting phase error component of the spin which differs for each slice cannot be completely removed by the zero-order or first-order phase error correction. Therefore, it was difficult to remove the artifacts caused by these phase errors, especially in a multi-shot multi-slice using the fast spin echo method based on the CPMG method that requires the accuracy of the spin phase.

Therefore, an object of the present invention is to provide a gradient magnetic field applied at the time of the immediately preceding shot or slice measurement in an MRI apparatus having an imaging function using a multi-shot single slice and a multi-shot multi-slice pulse sequence based on the CPMG method. The gradient magnetic field error component that fluctuates for each shot or slice due to eddy current or residual magnetic field due to The purpose is to suppress the artifacts caused by the phase rotation error of the spins generated for each shot or slice. Disclosure of the invention

The present invention provides an MRI apparatus having an imaging function based on a multi-slice method pulse sequence, in which a different residual gradient magnetic field component for each slice, which is mixed in a slice measurement to be measured next from a slice measurement completed immediately before, is used for each slice measurement. A predetermined amount of gradient magnetic field pre-pulse is applied prior to application of the excitation pulse in each slice measurement so that the same value is applied when the excitation pulse (first high-frequency magnetic field pulse) is applied. Further, in order to cancel the phase rotation error generated in the nuclear spin excited by the residual component of the gradient magnetic field pre-pulse, the residual component of the gradient magnetic field pre-pulse is canceled by the time of applying the second high frequency magnetic field pulse after the excitation. A gradient magnetic field component is applied.

According to this MRI system, the imperfections of the gradient magnetic field applied in the immediately preceding shot or slice measurement at the time of applying the 90 ° excitation high-frequency pulse for spin excitation can be obtained by adding a gradient magnetic field pre-pulse. The error component due to the gradient magnetic field is substantially nullified. Only the known and constant gradient magnetic field error component due to the gradient magnetic field pre-pulse can be artificially introduced. The phase rotation error component that is uniform over each shot or slice of the spin caused by such a constant residual gradient magnetic field error component that does not fluctuate can be easily removed by zero-order or first-order correction, and the Can be controlled.

Further, in the MRI apparatus of the present invention, the gradient magnetic field pre-pulse is applied a predetermined time before the application of the 90 ° excitation high-frequency magnetic field pulse.

The MRI apparatus of the present invention is suitable for an MRI apparatus having a multi-shot multi-slice type pulse sequence based on the CPMG method. That is, in a preferred embodiment of the present invention, the 90 ° excitation high-frequency magnetic field pulse and the 180 ° inverted high-frequency magnetic field pulse are applied such that their applied axes are orthogonal to each other in the rotating coordinate system. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing an overall outline of an MRI apparatus to which the present invention is applied.

FIG. 2 is a diagram showing an imaging sequence by the high-speed spin echo method based on the CPMG method provided in the MRI apparatus of the present invention.

Figure 3 illustrates the incompleteness of the gradient magnetic field due to eddy currents.

FIG. 4 is a diagram illustrating a residual gradient magnetic field due to magnetic hysteresis.

FIG. 5A is a diagram illustrating a conventional high-speed spin echo method based on the CPMG method.

FIG. 5B is a diagram for explaining the behavior of the spin in the sequence of FIG. 5A.

FIG. 6 is a diagram for explaining a change in a gradient magnetic field error component in multi-slice imaging. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described.

FIG. 1 is a block diagram showing the overall configuration of an MRI device to which the present invention is applied. This MRI apparatus mainly includes a static magnetic field generating magnet 2 for generating a uniform static magnetic field in a space where the subject 1 is placed, a gradient magnetic field generating system 3 for applying a magnetic field gradient to the static magnetic field, and a tissue of the subject 1. A transmission system 5 that generates a high-frequency magnetic field that causes nuclear magnetic resonance in the nuclei (usually, protons) of the atoms that make up the target, a reception system 6 that receives an echo signal generated from the subject 1 by nuclear magnetic resonance, The signal processing system 7 processes the echo signal received by the receiving system 6 and creates an image representing the spatial density and spectrum of the nucleus.The signal processing system 7 performs various operations and controls the entire device. A central processing unit (CPU) 8 is provided.

The static magnetic field generating magnet 2 is composed of a permanent magnet, a normal conducting type or a superconducting type magnet, and generates a uniform static magnetic field around the subject 1 in the body axis direction or in a direction orthogonal to the body axis. The gradient magnetic field generation system 3 includes a gradient magnetic field coil 9 wound in three directions of x, y, and z, and a gradient magnetic field power supply 10 for driving each gradient magnetic field coil. Drives the gradient power supply 10 for each coil according to Thereby, gradient magnetic fields Gx, Gy, Gz in the three axes of x, y, z are applied to the subject 1. By applying the gradient magnetic field, an imaging target region (slice, slab) of the subject 1 can be set, and position information such as phase encoding and frequency encoding can be added to the echo signal. The triaxial gradient magnetic fields Gx, Gy, and Gz can be any of the slice gradient magnetic field Gs, the phase encode gradient magnetic field Gp, and the frequency encode gradient magnetic field Gf according to the set cross section of the MRI apparatus. Can correspond.

The transmission system 5 irradiates a high-frequency magnetic field to cause nuclear magnetic resonance in the nuclei of the atoms constituting the biological tissue of the subject 1 by the high-frequency pulse sent from the sequencer 4, and includes a high-frequency oscillator 11; It comprises a modulator 12, a high-frequency amplifier 13, and a high-frequency coil 14a on the transmission side. In the transmission system 5, the high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1. The subject 1 is irradiated with a high-frequency magnetic field (electromagnetic wave) by supplying it to the high-frequency coil 14a. The receiving system 6 detects an echo signal (NMR signal) emitted from the subject 1 by nuclear magnetic resonance, and includes a high-frequency coil 14b on the receiving side, an amplifier 15, a quadrature phase detector 16, A / D converter 17. In the receiving system 6, the echo signal detected by the high-frequency coil 14b is input to the A / D converter 17 via the amplifier 15 and the quadrature detector 16 to convert the echo signal into a digital signal. And sent to the signal processing system 7 as two series of collected data.

The signal processing system 7 includes a CFU 8, a recording device 18 such as a magnetic disk and a magnetic tape, and a display 19 such as a CRT.The CPU 8 performs processing such as Fourier transform, correction coefficient calculation, and image reconstruction operation. The obtained image and image are displayed on the display 19. Further, the CPU 8 sends various commands necessary for data collection of tomographic images of the subject 1 to the gradient magnetic field generation system 3, the transmission system 5, and the reception system 6 via the sequencer 4. The sequencer 4 generates a gradient magnetic field so as to collect data necessary for image reconstruction according to a pulse sequence which is a time chart of a predetermined control determined by an imaging method. Controls raw 3, transmitting 5 and receiving 6. In the MRI apparatus of the present invention, the pulse sequence includes a pulse sequence based on the CPMG method, for example, a pulse sequence based on the high-speed spin echo method. Such a pulse sequence is incorporated in the CPU 8 as a program.

Next, the imaging by the high-speed spin echo method based on the CPMG method executed by the MRI apparatus having such a configuration will be described. FIG. 2 is a diagram showing a pulse sequence for one slice in the whole pulse sequence by the multi-shot multi-slice type fast spin echo method shown in FIG. In this pulse sequence, a gradient magnetic field 25 to 27 as a pre-pulse is added to the pulse sequence based on the conventional high-speed spin echo method based on the CPMG method, and the subsequent pulse trains are almost the same as the conventional pulse sequence.

That is, after a certain period of time has elapsed after applying the pre-pulses 25 to 27, a 90 ° excitation pulse 21 is applied simultaneously with the first slice selection gradient magnetic field 20 for selecting a predetermined cross section to excite spins in the cross section . Next, a plurality of 180 ° inversion pulses 22 are sequentially applied simultaneously with the slice selection gradient magnetic field 20 to generate an echo signal. Each time an echo signal is generated, a phase encoding gradient magnetic field 23, 23 'having a different polarity and strength is applied to give a different amount of phase encoding to each echo signal, and a gradient magnetic field 24 in the frequency direction is applied to generate an echo signal. measure. Regarding the gradient magnetic field in the frequency direction, a dephasing gradient magnetic field 24 'is applied prior to the generation of the echo signal. The illustrated pulse sequence is based on the CPMG method. The applied axis y ′ of the 180 ° inversion pulse 22 is orthogonal to the applied axis x ′ of the 90 ° excitation pulse 21 and the 180 ° inverted pulse. The application interval is set to be exactly twice the interval between the 90 ° excitation pulse and the first 180 ° inversion pulse. The pulse sequence of the high-speed spin echo method based on the CPMG method is repeatedly executed by setting a plurality of slices within the repetition time TR to acquire the necessary number of echo signals to reconstruct an image for each slice You.

Prepulse gradient applied before the 90 ° excitation pulse in the pulse sequence Nos. 25 to 27 give a constant gradient magnetic field error component which does not fluctuate when a 90 ° excitation pulse is applied. By applying such a pre-pulse, the imperfections of the gradient magnetic field caused by the eddy current generated in the slice measurement immediately before and the influence of the variable residual magnetic field error component generated by the residual gradient magnetic field due to the magnetic hysteresis are removed. The induced phase error of the spin is made constant, ie, a phase error that can be subsequently removed by zero-order and first-order correction.

This will be further explained with reference to FIG. Figure 3 is a diagram showing a case where the gradient magnetic field has imperfections due to eddy currents. The amount of phase rotation given to spins by the gradient magnetic field that attenuates with this time constant <If the slice direction is taken as an example, as shown in equation (1), the amount is proportional to the gradient magnetic field strength Gs and the application time t .

0 == J r G s-S d t = r G s-S-t (1)

γ: magnetic rotation ratio

S: distance from the center of the measurement space to the slice Here, the time from the application of the prepulse gradient magnetic field 25 to the application of the 90 ° excitation pulse 21 is made constant in the pulse sequence for each slice, so that the residual gradient magnetic field of the prepulse 25 becomes 90 ° The amount of phase rotation given to the excited spin (^ can always be set to the 0th and ぴ 1st order correctable constant value iS later. Such a constant phase rotation amount] 8 In the case of a slice gradient magnetic field, by adjusting the intensity of the refresh gradient magnetic field 20 ′ applied immediately after the 90 ° excitation pulse, the correction can be made so as to maintain the CPMG effect.

The same applies to the case where the residual gradient magnetic field is generated due to the magnetic hysteresis as shown in FIG. 4, and the area indicated by the hatched area in the figure is the error component. The error component due to the residual gradient magnetic field can be kept constant by keeping the time from the application of the pre-pulse gradient magnetic field to the application of the 90 ° excitation pulse constant. Is also removed by correction in the same manner as above. You can leave.

As described above, since the pre-pulse is for keeping the residual gradient magnetic field constant, its intensity does not require a strong gradient magnetic field intensity such as a spoil gradient magnetic field, and the gradient applied in the pulse sequence is not required. It is sufficient to use the same strength and application time as the magnetic field.

Specifically, assuming that the excitation pulse bandwidth is constant in the slice direction, the intensity of the slice selection gradient magnetic field changes depending on the set slice thickness, so that the phase error component in the slice direction is inversely proportional to the slice thickness. Become a relationship. Therefore, it is preferable to change the applied intensity of the prepulse gradient magnetic field 25 in inverse proportion to the slice thickness. As a result, a linear phase error component can be generated with respect to the applied intensity of the slice selection gradient magnetic field. Therefore, the rephase gradient magnetic field immediately after the first slice selection gradient magnetic field 20 can be easily added or subtracted at the time of application. Can be corrected.

Similarly, in the frequency direction, in order to take advantage of the CPMG effect, the applied intensity and application time of the pre-pulse 27 are set to be the same as the applied intensity and application time of the phase gradient magnetic field 24 ', and the application of the 90 ° excitation pulse 21 is repeated. The amount of application of the phase gradient magnetic field 24 'is adjusted in order to correct the phase rotation of the spin due to the residual gradient magnetic field due to the prepulse 27 applied to the spins before the start of the application of the phase gradient magnetic field 24'. When the applied amount of the phase gradient magnetic field 24 'is adjusted, the applied amount of the read gradient magnetic field 24 applied thereafter must be changed accordingly.

As for the phase encoding direction, in order to prevent the accumulation of the amount of phase rotation, it is preferable to use bipolar pre-pulses 26 and 26 'which are applied with close timing as shown in the figure. Further, it is preferable that the intensity of the pre-pulse in the phase encoding direction is changed depending on the number of phase encodings. That is, in the pulse sequence by the high-speed spin echo method, the intensity of the phase encoding gradient magnetic field 23, 23 'changes at each repetition. The pre-pulses 26 and 26 are applied in the same manner as the applied intensity and application time of the phase-encoding gradient magnetic field applied at the beginning of this repetition. By applying the phase rotation error canceling gradient magnetic field pulse 26 "to correct the phase rotation of the spin due to the residual gradient magnetic field due to the pre-pulses 26, 26 applied to the spin later, as in the case of the gradient magnetic field in other directions, Correction can be performed and the CPMG effect is maintained. In this way, image reconstruction using echo signals acquired by repeating the pulse sequence to which the pre-pulse is applied is the same as that of a conventional MRI apparatus. The resulting image is an image in which the artifact caused by the imperfect gradient magnetic field is suppressed.

As described above, one embodiment of the present invention has been described with reference to FIG. 2, but the present invention is not limited to the above embodiment, and various modifications can be made. For example, FIG. 2 shows a case in which pre-pulses 25 to 27 are applied in three directions, ie, a slice direction, a phase encoder direction, and a frequency direction. However, the effect can be obtained by performing at least one in one direction.

FIG. 2 shows the case of sequential ordering as the measurement order in the k-space, but the measurement order can be arbitrary.

In addition, Fig. 2 shows an imaging method using the fast spin echo method as a pulse sequence based on the CPMG method.However, in the present invention, a sequence of a 90 ° excitation pulse and a plurality of 180 ° inversion pulses is repeated several times and multiple It can be applied as long as it is an imaging method that measures the echo of an object. For example, a gradient echo and spin echo imaging method in which a gradient magnetic field in the frequency direction is repeatedly inverted and a plurality of echo signals are measured after applying a 180 ° inversion pulse ( GRASE) can also be applied. That is, in the above embodiment, the multishot multislice imaging method has been described as an example, but it is easy to see that the concept of the present invention is also effective in a multishot single slice imaging method with a shortened TR. Could be understood.

According to the present invention, in the multi-slice imaging by the CPMG method that requires high-precision control of the phase and the gradient magnetic field, the gradient magnetic field error component that fluctuates according to the set TR, the number of multi-slices, and the like, and the phase error of the spin due to the gradient magnetic field error component. Reduce the impact Artifacts due to phase errors can be effectively suppressed. Industrial applicability

As described above, an MRI apparatus having a multi-shot single slice and a multi-shot multi-slice pulse sequence that requires high speed and high image quality based on the CPMG method according to the present invention is useful as a medical image diagnostic apparatus. .

Claims

The scope of the claims

1. Magnetic field generating means for generating a static magnetic field and a gradient magnetic field in a space where the subject is placed, and a transmission system for generating a high-frequency magnetic field for exciting spins to nuclei of atoms constituting the tissue of the subject; A receiving system that detects an echo signal generated from the subject by a high-frequency magnetic field; a signal processing system that reconstructs a tomographic image of the subject using the detected echo signal; And a control means for controlling a signal processing system and a signal processing system according to a predetermined pulse sequence.

The control means includes a multi-shot pulse sequence for measuring a plurality of echo signals by applying a first high-frequency magnetic field pulse and a subsequent second high-frequency magnetic field pulse, and prior to the application of the first high-frequency magnetic field pulse A magnetic resonance imaging system that applies a gradient magnetic field pre-pulse at a certain time before.

2. The gradient magnetic field pre-pulse is applied by a predetermined amount before a certain time before the application of the first high frequency magnetic field pulse, and a constant gradient by the gradient magnetic field pre-pulse after the application of the first high frequency magnetic field pulse in each shot. 2. The magnetic resonance imaging apparatus according to claim 1, wherein an amount of spin phase rotation caused by a magnetic field error component is the same.

3. The first or second claim, wherein the first high-frequency magnetic field pulse and the inverted second high-frequency magnetic field pulse are CPMG pulse sequences that are applied so that applied axes are orthogonal to each other in a rotating coordinate system. The magnetic resonance imaging apparatus according to item 2,

4. The magnetic resonance according to claim 3, wherein the multi-shot pulse sequence based on the CPMG method is a multi-shot pulse slice sequence. Imaging device.

5. The magnetic resonance imaging apparatus according to claim 3, wherein the multi-shot pulse sequence based on the CPMG method is a multi-shot multi-slice pulse sequence.

6. The control means strikes a constant phase rotation error of the spin caused by the predetermined gradient magnetic field pre-pulse after the application of the first high-frequency magnetic field pulse and before the application of the first inverted second high-frequency magnetic field pulse. 3. The magnetic resonance imaging apparatus according to claim 1, wherein a gradient magnetic field component to be eliminated is applied.

7. The magnetic resonance imaging apparatus according to claim 6, wherein the predetermined gradient magnetic field pre-pulse is applied in at least one of a slice direction, a phase encoding direction, and a lead direction.

8. The magnetic resonance imaging apparatus according to claim 7, wherein a predetermined application amount of the gradient magnetic field pre-pulse in the slice direction is the same as a slice selection gradient magnetic field pulse applied simultaneously with the first high frequency magnetic field pulse.

9. The gradient magnetic field component that cancels out a certain phase rotation error of the spin caused by the gradient magnetic field pre-pulse in the slice direction is applied immediately after the slice selection gradient magnetic field pulse applied simultaneously with the first high frequency magnetic field pulse. 9. The magnetic resonance imaging apparatus according to claim 8, wherein the magnetic resonance imaging apparatus is included in a rephase gradient magnetic field pulse.

10. The gradient magnetic field pre-pulse in the phase encoding direction is a bipolar pre-pulse whose application timing is close, and the applied amount is the same as the first phase encode gradient magnetic field pulse of the subsequent measurement. Magnetic resonance imagers Device.

1 1. A gradient component that counteracts a constant phase rotation error of the spin caused by the gradient pre-pulse in the phase encoder direction is applied before the application of the first inverted second high-frequency magnetic field pulse. 10. The magnetic resonance imaging apparatus according to claim 10, wherein the magnetic field pulse is a phase rotation error canceling gradient magnetic field pulse in a phase encoding direction.

12. The predetermined gradient magnetic field pre-pulse applied in the readout direction is the same as a diffuse gradient magnetic field pulse applied immediately after the application of the first high-frequency magnetic field pulse. Magnetic resonance imaging device.

13. The magnetic resonance according to claim 12, wherein a gradient magnetic field component for canceling a constant phase rotation error of spin caused by the gradient magnetic field pre-pulse in the readout direction is included in the dephase gradient magnetic field pulse. Imaging device.