JP2000079104A - Magnetic resonance imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent overlapping of false images generated by signals from unnecessary area spin excited by RF pulse for pre-saturation on the necessary area in an MRI. SOLUTION: The impressing phase is controlled while impressing RF pulse for pre-saturation. More concretely, control of the impressing phase is the manners as follows. Phase of the false signals relative to the image constitution signals changes π every phase encoding, or phase of the false signals relative to the image constitution signals random changes every phase encoding, or the impressing phase ϕ of the RF pulse for pre-saturation changes every encoding according to the formula as ϕk=ϕk-1+k×Δϕ(in the formula, k is the impressing time of the RF pulse for pre-saturation, Δϕ is an arbitrary angle.). By this manner, the false signals generated by spin in unnecessary area excited by RF pulse for pre-saturation are not overlapped on the images of necessary area. Therefore, the invention results in no obstacles on diagnosis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging (hereinafter abbreviated as "MRI") for obtaining a tomographic image of a desired part of a subject by utilizing a nuclear magnetic resonance (hereinafter abbreviated as "NMR") phenomenon. Prior to the implementation of a pulse sequence for obtaining an image composition signal, a predetermined high-frequency magnetic field pulse (hereinafter, referred to as an RF pulse) and a gradient magnetic field pulse are applied to generate a signal in a region that is an obstacle for diagnosis. In the suppression method (presaturation method), the present invention relates to a method suitable for favorably suppressing a signal in the unnecessary area.

[0002]

2. Description of the Related Art As is generally known, MRI is susceptible to movements and flows during measurement, and it is known that such effects cause false images. Since such false images hinder the diagnosis, methods for reducing or suppressing them have been proposed.

One method for suppressing such false images is a method called pre-saturation. In this method, as shown in FIG. 2 (a), when there is a region (unnecessary region) 22 where an artifact causing a diagnosis is generated in a part of the human body 21 in the region of interest 20, a signal from the region is suppressed. Before performing a pulse sequence (main measurement) for acquiring a signal for image construction, a slice or slab 23 (FIG. 2B) including the region 22 is selected and RF pulses (presaturation) are performed. RF pulse)
Is applied. After the application of the RF pulse, the spins in the region 23 begin to relax (recover) from the excited state to the initial state. When the spin excitation RF pulse is applied in the main measurement, the longitudinal magnetization component of the spin in the area 23 during the recovery is set to 0.
The spin excitation angle of the RF pulse for presaturation is set so that As a result, in the main measurement, the spin in the region 23 does not generate a transverse magnetization component, does not generate a signal,
An image in which the signal of the region 23 is suppressed can be obtained.

[0004]

In such a presaturation method, a signal from the region 23 should not originally be generated, but the spin in the region 23 is also applied by the gradient magnetic field pulse applied in the pulse sequence of the main measurement. Depending on the pattern, a phase change occurs in the application direction of the gradient magnetic field (three-axis direction). When this phase change causes diffusion and convergence in the three axial directions, a signal from the region 23 (hereinafter referred to as a false signal) is mixed during the signal measurement of the main measurement, and a false image is formed on the image obtained by the main measurement. May occur.

For example, FIG. 9 shows the phase change in the gradient magnetic field direction of the region 23 when the pulse sequence ((a) to (d)) of the presaturation and the main measurement is repeated while changing the phase encoding amount (e). ) To (g). As can be seen from the figure, in the first repetition, the spin in region 23 is the RF pulse for presaturation.
After being excited by 4101, the following gradient magnetic field pulses 4103 to 4112 in the Gx, Gy, and Gz directions cause respective phase changes according to the applied amount, and the spin is inverted by the RF pulse 4201 for presaturation in the next repetition. Thereafter, gradient magnetic field pulses 4203 to 4212 in the Gx, Gy, and Gz directions are further provided.
As a result, the phase changes according to the applied amount. as a result,
As shown in the figure, when the gradient magnetic field 4211 in the second readout direction is applied, the phase change of spin in almost three axial directions is 0 or one encode step in the phase encode direction (Gy direction). At the same time, a signal from the area 23, that is, a false signal is measured.

As described above, when each signal is measured, the signal excited by the RF pulse for presaturation in the immediately preceding pulse sequence cycle is superimposed, and the superimposed signal has the same amount of phase encoding (Gy) for all phase encodings. Direction phase rotation amount does not change). As shown in FIG. 2 (b), an image in which a false signal generated by such a mechanism is superimposed is located inside the presaturation application area 23 and at a location corresponding to a DC component (or a center frequency) in the phase encoding direction. A linear false image 24 is superimposed on.

It is an object of the present invention to provide a presaturation method capable of suppressing a false signal generated by the above-mentioned mechanism and favorably reducing a false image on an image.

[0008]

To achieve the above object, the present invention provides a presaturation RF pulse by controlling an application phase of a presaturation RF pulse.
The signal from the spin excited by the pulse is suppressed from being superimposed in the image. That is, the MRI method of the present invention comprises the steps of: applying a presaturation RF pulse that selects and excites a specific region (unnecessary region) of a subject to suppress a signal from the region; Applying a high-frequency pulse for selectively exciting nuclear spins in a region to be converted (imaging region), applying a gradient magnetic field for phase-encoding the nuclear spins, and nuclear magnetic resonance generated from the nuclei of the subject Measuring the signal is repeated while changing the magnitude of the phase encoding gradient magnetic field, and in the magnetic resonance imaging method for reconstructing the image of the imaging region, the application phase of the RF pulse for presaturation is changed for each application. Is controlled.

According to the first aspect of the method for controlling an applied phase according to the present invention, the nuclear magnetic resonance signals measured in the i-th phase encoding and the (i + 1) -th phase encoding are included.
Signal from the imaging area (hereinafter referred to as a main measurement signal)
The phase difference between the signals S1 (i) and S1 (i + 1) is φ1 (i), and the phase difference between the signals (false signals) S2 (i) and S2 (i + 1) from the specific area is When φ2 (i) is set, the application phase of the RF pulse for presaturation is controlled so as to maintain the relationship of the following equation (1).

Φ1 (i) −φ2 (i) = φ1 (i + 1) −φ2 (i + 1) + π (1) According to the second aspect of the method for controlling the applied phase according to the present invention, the main measurement is performed. Phase difference φ1 (i) between signals S1 (i) and S1 (i + 1)
And the pre-saturation RF such that the phase difference φ2 (i) between the false signals S2 (i) and S2 (i + 1) maintains the relationship of the following equation (2).
Controls the pulse application phase.

Φ1 (i) −φ2 (i) = φrnd (i) (2) (where φrnd (i) is a random value for i and 0 ≦ φr
nd (i) represents an angle satisfying <2π) Further, according to the third aspect of the applied phase control method of the present invention, the k-th and (k +
1) Of the nuclear magnetic resonance signals measured at the repetition,
When the phase difference between the false signals S2 (k) and S2 (k + 1) is φ2 (k), φ2 (k) = φ2 (k-1) + k × Δφ (3) (where Δφ is (Representing an arbitrary angle).

By performing such phase control, even if a signal from a spin existing in an unnecessary region excited by the RF pulse for presaturation is mixed into the signal of the main measurement, a false signal of a high signal is included in the image. An image is not formed as an image, or appears in a place where the image does not affect the image even if the image is formed. As a result, it is possible to remove a failure in diagnosis due to a false signal.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 4 is a view showing an outline of an MRI apparatus to which the present invention is applied. This MRI apparatus generates a static magnetic field having an electromagnet or a permanent magnet for generating a uniform static magnetic field in a space where a subject 401 is placed. The magnetic circuit 402 and 3
A gradient magnetic field generation system 403 that generates an axial gradient magnetic field, a transmission system 404 that generates a high-frequency magnetic field that excites nuclear spins of nuclei constituting the tissue of the subject, and a nucleus generated in the subject by application of the high-frequency magnetic field A detection system 405 for detecting a magnetic resonance signal, a control system (sequencer 407, computer 408) for controlling these gradient magnetic field generation system 403, transmission system 404 and detection system 405 according to a predetermined pulse sequence, and detection system 405 A computer 408 and a signal processing system 406 that perform calculations for image reconstruction based on the obtained signals,
A display unit (display) 428 for displaying an image as a calculated result.

The gradient magnetic field generation system 403 includes a gradient magnetic field coil 409 for generating a gradient magnetic field in three orthogonal directions, and a power supply 410 for the gradient magnetic field coil.

The transmission system 404 includes a synthesizer (high-frequency generation circuit) 411 for generating a constant high-frequency signal, and a modulator 412.
And a preamplifier 413 and an irradiation coil 414a, and modulates a high-frequency signal generated from the synthesizer 411 by a modulator 412 at a timing controlled by a control system.
It is sent to the irradiation coil 414a via 13. As a result, a high frequency magnetic field (RF) pulse having a predetermined envelope is applied to the subject from the irradiation coil.

Here, the synthesizer 411 includes an oscillator and a delay circuit for transmitting the high frequency generated by the oscillator at a predetermined timing, and the delay amount of the delay circuit is controlled by a control system. Accordingly, the phase of the high-frequency signal generated from synthesizer 411 can be controlled, and as a result, an RF pulse having an arbitrary phase can be generated from the irradiation coil.

The detection system 405 includes a receiving coil 414b and an amplifier 4
15, a quadrature detector 416, and an A / D converter 417,
A nuclear magnetic resonance signal (high-frequency magnetic field) from the subject detected by the receiving coil 414b is transmitted via the amplifier 415 to the quadrature phase detector 416.
Are detected as two-series signals, converted into digital signals by the A / D converter 417, and sent to the computer 408.

The computer 408 performs an operation such as Fourier transform on the two series of signals, reconstructs an image of the subject, and displays the image on the display 428. The data in the middle of the calculation and the calculation result are stored in the storage devices 424 to 427 of the signal processing system 406.

The computer 408 also functions as a control system for controlling the gradient magnetic field generation system 403, the transmission system 404, and the detection system 405, sends commands to the sequencer 407, and drives the gradient magnetic field generation system, the transmission system, and the detection system. The timing is controlled according to a predetermined pulse sequence, and imaging is performed by a desired imaging method. In the present invention, imaging using a presaturation method is performed, and at this time, the false image is suppressed by controlling the phase of the RF pulse.

Hereinafter, a photographing method according to the present invention will be described with reference to FIGS.

The pulse sequence of the presaturation method employed in the imaging method of the present invention is the same as the pulse sequence of the conventional presaturation method. For example, as shown in FIG. Pulse 31 and gradient magnetic field to suppress the signal of
Apply 35 and 32. Here, the gradient magnetic field 35 is a gradient magnetic field for selecting an unnecessary area 22 shown in FIG.
By applying a gradient magnetic field in the Gy and Gz directions, a slab (region) 23 in a direction perpendicular to the paper including the region 22 (FIG. 2B)
Can be selectively excited. The gradient magnetic field 32 applied after the irradiation of the RF pulse 31 is a spoil gradient magnetic field that spreads the phase of the excited spin and further suppresses a signal from the spin.

Although the sequence of the main measurement 33 is not particularly limited, a sequence of a gradient echo (GrE) system is exemplified here. First, an RF pulse 34 is applied together with a gradient magnetic field Gx36 for selecting a section to be imaged. Then, after applying the gradient magnetic field Gy37 for phase encoding and the gradient magnetic field Gz38 in the reading direction, the echo signal is measured while applying the gradient magnetic field Gz39 in the reading direction for signal measurement. The gradient magnetic field Gz38 in the reading direction is a preliminary pulse for adjusting the peak position of the echo signal.

The number of echo signals necessary for reconstructing one image is repeatedly measured by changing the intensity of the gradient magnetic field Gy37 in the phase encoding direction in units of a pulse sequence as shown in FIG. .

In the imaging method according to the present invention, when imaging is performed in accordance with such a pulse sequence, the phases of the RF pulse 31, the RF pulse 34 and the measured echo signal are controlled every repetition, and the main measurement is performed. Control is performed so that the phase of the signal (false signal) from the unnecessary area has a specific relationship with the phase of the signal from the excited area (hereinafter, simply referred to as the signal of the main measurement).

That is, as shown in the flowchart of FIG. 1, first, the application phase of the presaturation RF pulse 31 is set to a specific phase Ph1 (11) and applied (12). Next, main measurement 33
Set the applied phase of the RF pulse 34 to a specific phase Ph2 (1
3) Apply (14). The setting of the phase of these RF pulses can be controlled by controlling the timing of generating a high frequency in the synthesizer as described above. Also, the phase of the signal measurement is set to Ph3 (15), and the signal is measured (16). The phase of signal measurement can be set by controlling the phase of the reference signal for detection in the quadrature detector. Step 11 of such phase control
Steps 16 to 16 are repeated until the necessary addition in the same phase encoding is completed (17), and then the phase encoding amount is changed, and steps 11 to 17 are repeated until the measurement of all the phase encodings is completed (18), and the shooting is completed I do.

In this case, the phases Ph1, Ph2, and Ph3 have an effect on the image even if a false signal is mixed when the signal of the main measurement is measured, or the false signal does not form an image. Not controlled.

A specific embodiment of the method for controlling the application phase of the RF pulse for presaturation will be described below.

FIGS. 5 and 6 are views showing a method of controlling the application phase of the RF pulse for presaturation in the first embodiment of the present invention. FIGS. 9 shows a phase control flow.

First, as shown in FIG. 5, the application phase of the RF pulse 31 for presaturation is set to Φ1 (601). This phase Φ1 can be any value. An RF pulse is applied at the set phase (602). Next, R for actual measurement
Set the applied phase Φ of F pulse 34 to 0 (603),
An RF pulse is applied (604). The phase φ of the signal measurement is set to 0 (605), and the signal is measured (606). This 601-606
Is repeated until the signal addition required for the same phase encoding is completed (607). After the signal addition is completed, if the signal measurement corresponding to all the phase encodings required for the image configuration has been completed, the processing is terminated. (608). If the signal measurement in all the phase encodings has not been completed, the next phase encoding amount (i + 1) is set (609), and the process 61 in FIG.
Proceed to 1.

In the next phase encoding measurement, the application phase of the presaturation RF pulse 31 is set to (Φ1 + π) (611), and the RF pulse is applied at the set phase (6).
12). In the following steps 613 to 617, setting the applied phase Φ of the main measurement RF pulse to 0 and applying the same, and setting the signal measurement phase Φ to 0 and performing the measurement are the same as the previous measurement (FIG. 5). The same is true. Also in this measurement, steps 611 to 616 are repeated until the necessary addition is completed. After the addition is completed, if the signal measurement in all phase encodings has not been completed (61).
8), the next phase encoding amount is set (619), and the process proceeds to processing 601 in FIG. In the next cycle, the applied phase Φ1 of the RF pulse for presaturation set in process 601
Is the same as the initially set value.

As described above, both the applied phase of the main measurement RF pulse and the phase of signal measurement are always set to 0,
By changing the applied phase of the presaturation RF pulse by π between adjacent phase encodings, the signal of this measurement has a constant phase for all phase encodings, but is excited by the RF pulse for presaturation. The phase of the false signal is 18 per adjacent phase encoding.
Invert 0 °.

That is, the i-th phase encoding and the (i + 1) -th encoding
When the phase difference between two adjacent image forming signals measured in the phase encoding is φ1 (i), and the phase difference between two adjacent false signals is φ2 (i), the following expression ( 1) The relationship of φ1 (i) −φ2 (i) = φ1 (i + 1) −φ2 (i + 1) + π (1) is maintained.

As a result, on the reconstructed image, the false signal is located at the highest frequency, that is, at the end of the image. Since the false signal always receives the same amount of phase rotation for all phase encoding amounts as described above, the false image due to the false signal appears linearly at the extreme end position of the image due to image reconstruction. . Therefore, the false image due to the false signal does not overlap inside the image and does not hinder the diagnosis.

In the above embodiment, the case where both the applied phase Ph2 of the main measurement RF pulse and the signal measurement phase Ph3 are set to 0 has been described. However, in the MRI, the applied phase Ph2 of the RF pulse and the signal measurement phase Ph2 are set. Can be variously combined, for example, one is set to 0 and the other is set to π, and this embodiment can be implemented with any combination. That is, in the present embodiment, the change in the phase of the main measurement RF pulse and the change in the phase of the pre-saturation RF pulse in the measurement of two adjacent different phase encodes should satisfy the relationship of Expression (1). Therefore, by setting the application phase Ph1 of the RF pulse for presaturation so as to satisfy the relationship of Expression (1) with respect to the application phase Ph2 of the RF pulse, the same effect as that of the present embodiment can be obtained.

In the flow charts of FIGS. 5 and 6, the case where the applied phase of the RF pulse for presaturation is constant (Φ1 or Φ1 + π) in the same phase encoding has been described. Control of the application phase of the RF pulse for presaturation may be added so as to cancel the false signals measured continuously. That is, for example, when measuring by adding twice,
The application phase of the RF pulse for presaturation can be controlled so that the phase of the false signal in the first measurement and the phase of the false signal in the next measurement are inverted. Also in this case, the relationship between the phase difference of the main measurement signal and the phase difference of the false signal in the measurement of the adjacent phase encodes is to maintain the relationship of Expression (1). Thereby, in addition to the effect of causing the false image to appear at the end of the image, the effect of reducing the false image itself can be obtained.

Next, a second embodiment of the present invention will be described. In this embodiment, the application phase of the RF pulse for presaturation is controlled so that imaging by a false signal does not occur in the image of the main measurement. FIG. 7 is a diagram showing a method for controlling the application phase of the RF pulse for presaturation in the second embodiment.

After the start of the measurement, first, the application phase of the RF pulse for the presaturation pulse is set to a random value Φrnd (71). An RF pulse is applied at the set phase (72). In the following steps 73 to 77, the application phase Φ of the main measurement RF pulse is set to 0 and applied, and the signal measurement is performed by setting the signal measurement phase Φ to 0 according to the embodiment shown in FIG. The same is true. The steps from the application of the RF pulse for presaturation pulse (72) to the signal measurement (76) are repeated until necessary signal addition is completed. After the signal addition is completed, the next phase encoding is set (79), the application phase of the RF pulse for presaturation pulse is newly set to a random value Φrnd (71), and steps 72 to 72 are performed until the necessary signal addition is completed. Repeat 77. The above measurement is repeated until all the phase encodings necessary for the image configuration are completed (78).

By measuring the signal by performing such phase control, the signal of this measurement has a constant phase every phase encoding, but the phase of the false signal excited by the RF pulse for presaturation is It becomes a random value for each phase encoding. That is, the phase difference φ2 (i) between the false signal in the measurement of the i-th phase encoding and the false signal in the measurement of the (i + 1) -th phase encoding is the same as the phase difference φ1 (i) of the corresponding signal in the main measurement. Control is performed so as to satisfy the relationship of Expression (2).

Φ1 (i) −φ2 (i) = φrnd (i) (2) (where φrnd (i) is a random value with respect to i, and 0 ≦
(φrnd (i) <2π is satisfied) As a result, on the reconstructed image, the false signal is randomly scattered in the phase encoding direction. Therefore, the false signal is not superimposed as a false image of a high signal gathered inside the image,
It does not interfere with diagnosis.

In this embodiment, the case where both the applied phase of the signal for the main measurement and the phase of the signal measurement are set to 0 has been described. And the same effect can be obtained.

The flow chart shown in FIG. 7 shows a case where the applied phase of the RF pulse for presaturation is constant in the measurement of the same phase encoding (in the addition loop).
Return the signal addition (77) feedback loop to before step 71,
Control may be performed so that the application phase of the RF pulse for presaturation has a random value Φrnd for each excitation. Even when the application phase is controlled in this manner, the same effect as that of the embodiment shown in FIG. 7 can be obtained.

Alternatively, also in this embodiment, in the repetition of the pulse sequence by the addition, the RF signal for presaturation is canceled so that the false signals continuously measured are canceled each other.
The application phase of the pulse may be controlled. For example, when measurement is performed by adding twice, the application phase of the RF pulse for presaturation is controlled so that the phase of the false signal in the first measurement and the phase of the false signal in the next measurement are inverted. In this case, such an application phase control step is added immediately before the presaturation RF pulse application step (72), and the feedback loop of the addition (77) returns to before this added step. . Accordingly, in addition to the effect of dispersing the false image based on the relationship of Expression (2), the effect of reducing the false signal can be further obtained.

FIG. 8 is a diagram showing a method of controlling the application phase of the RF pulse for presaturation in the third embodiment. In this embodiment, a signal from a region excited by the RF pulse for presaturation is excited. The application phase of the RF pulse for presaturation is controlled so as to gradually change (increase or decrease gradually) every time, thereby preventing a false signal from being superimposed as a false image of a high signal combined in the image of the main measurement.

That is, after the start of the measurement, first, in step 801, the number of excitations k is initialized to 0, and at the same time, the application phase Φ2 of the RF pulse for presaturation is set to the initial value Φ1. This Φ1 may be arbitrary. Next, the application phase Φ2 of the RF pulse for presaturation pulse is set according to the following equation (3 ′) (802).

Φ2 = Φ2 + k × φ (3 ′) (where φ represents an arbitrary angle) After applying an RF pulse at the set phase (803),
The number of excitations k is set to (k + 1) (804). In the subsequent steps 805 to 808, the application phase Φ of the main measurement RF pulse is set to 0 and applied, and the measurement of the signal measurement phase is set to Φ0 to perform the measurement, as in the first and second embodiments. The same is true.

Also in this case, steps 802 to 808 are repeated until the signal addition is completed (809). In this embodiment, the applied phase Φ2 of the RF pulse for the presaturation pulse changes for each excitation, and the number of excitations k Increases by φ each time.

After the necessary signal addition is completed, if signal measurement in all phase encodings has not been completed (810), the next phase encoding amount is set (811), and steps 802 to 80 are performed.
Repeat 9. If the signal measurement corresponding to all the phase encodings necessary for the image configuration has been completed, the process ends.

By controlling the phase in this way, the phase of the signal of the main measurement is constant, while the measurement of the false signal is performed after the k-th excitation as shown in the following equation (3).
1) The phase difference φ2 (k) between two adjacent false signals obtained in the measurement after the first excitation always changes by k × Δφ, and φ2 (k) = φ2 (k-1) + K × Δφ (3) (where, Δφ represents an arbitrary angle) The false signal whose phase has been controlled in this manner does not form a false image on the reconstructed image. Therefore, there is no obstacle to diagnosis.

Also in this embodiment, the applied phase of the signal for the main measurement and the phase of the signal measurement can be any combination that can be taken in MRI, and the same effect can be obtained.

In the three embodiments described above, the case where the phase encoding is changed by one encoding step at each repetition of the pulse sequence has been described, but the present invention is not limited to this. In addition, the pulse sequence of the main measurement can be similarly executed by a pulse sequence other than the gradient echo method shown in 33 of FIG. 3, and the same effect can be obtained.

[0052]

According to the magnetic resonance imaging method of the present invention, by controlling the phase of the RF pulse for presaturation, the spurious signal generated from the spin in the unnecessary region excited by the RF pulse for presaturation is formed. Even if the image is formed, it is located at the end of the image or is not formed as a high-signal false image on the image, so that accurate diagnosis can be performed efficiently without hindering the diagnosis.

[Brief description of the drawings]

FIG. 1 is a diagram showing a procedure of a phase control of an RF pulse for presaturation according to the present invention.

FIG. 2A is a diagram illustrating an image of a subject and an unnecessary portion existing inside the image, and FIG. 2B is a diagram illustrating an unnecessary region suppressed by presaturation;

FIG. 3 is a diagram showing an example of a pulse sequence including presaturation.

FIG. 4 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied;

FIG. 5 is a flowchart showing a part of a procedure according to the first embodiment of the MRI method of the present invention.

FIG. 6 is a flowchart showing another part of the procedure according to the first embodiment of the MRI method of the present invention.

FIG. 7 is a flowchart showing a procedure according to a second embodiment of the MRI method of the present invention.

FIG. 8 is a flowchart showing a procedure according to a third embodiment of the MRI method of the present invention.

FIG. 9 is a view for explaining generation of a false image in the presaturation method.

[Explanation of symbols]

 23: Signal suppression area by presaturation 24: False image 31: RF pulse for presaturation 34: RF pulse for main measurement

Claims (4)

[Claims] 1. A step of applying a high frequency pulse for presaturation to select and excite a specific region of a subject to suppress a signal from the specific region of the subject, and select a nuclear spin of a region of the subject to be imaged. Applying a high-frequency pulse for exciting the magnetic field, applying a gradient magnetic field for phase-encoding the nuclear spin, and measuring a nuclear magnetic resonance signal generated from the nucleus of the subject, A magnetic resonance imaging method for reconstructing an image of a region to be imaged repeatedly while changing the size, wherein an application phase of the high frequency pulse for presaturation is controlled for each application. . 2. The method according to claim 1, wherein the control of the application phase of the presaturation high-frequency pulse includes the i-th phase encoding and the (i +
1) Among nuclear magnetic resonance signals measured in phase encoding, signals S1 (i) and S1 (i + 1) from the region to be imaged.
Φ1 (i), the signal S2 from the specific area
When the phase difference between the signals (i) and S2 (i + 1) is φ2 (i), the relationship φ1 (i) −φ2 (i) = φ1 (i + 1) −φ2 (i + 1) + π 2. The magnetic resonance imaging method according to claim 1, wherein the method is performed so as to maintain the following. 3. The control of the application phase of the pre-saturation high-frequency pulse includes the i-th phase encoding and the (i +
1) Among nuclear magnetic resonance signals measured in phase encoding, signals S1 (i) and S1 (i + 1) from the region to be imaged.
Φ1 (i), the signal S2 from the specific area
(i), when the phase difference between signals of S2 (i + 1) is φ2 (i), φ1 (i) −φ2 (i) = φrnd (i) (where φrnd (i) is And random value and 0 ≦ φr
2. The magnetic resonance imaging method according to claim 1, wherein the relationship is maintained such that nd (i) <represents an angle satisfying <2π). 4. The method according to claim 1, wherein the control of the application phase of the high frequency pulse for presaturation is performed in the specific region of the nuclear magnetic resonance signals measured at the k-th and (k + 1) -th repetitions of the respective steps. S2 (k), S2 (k + 1)
Where φ2 (k) is the phase difference between the signals, φ2 (k) = φ2 (k-1) + k × Δφ (where Δφ represents an arbitrary angle). The magnetic resonance imaging method according to claim 1, wherein