JP2001112735A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stable images free of linear artifacts and image distortion through EPI imaging. SOLUTION: Phase changes between pre-measurement echo signals which are adjacent to each other in time are calculated by use of a pre-measurement echo signal which is measured, separately from a main measurement echo signal for image capturing, within each period of a readout gradient magnetic field which is reversed without application of a phase encoding inclined pulse, and a map of phase differences is originated by use of each phase change (107, 108). In this case, elimination of and averaging of the phase differences, etc., are effected to enhance the accuracy of the phase differences (109, 110). The lag of sampling times when the main measurement echo signal is obtained by use of the map of the phase differences is calculated (112). The sampling times of a main measurement sequence are adjusted so that the lags match among odd-numbered echoes and even-numbered echoes in EPI (114).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures a nuclear magnetic resonance (hereinafter, referred to as "NMR") signal from hydrogen, phosphorus, or the like in a subject, and visualizes a nuclear density distribution, a relaxation time distribution, and the like. The present invention relates to a magnetic resonance imaging (MRI) apparatus, and more particularly to an MRI apparatus capable of effectively suppressing an artifact caused by a phase change between echo signals.

[0002]

2. Description of the Related Art In an imaging method using MRI, a method of measuring an NMR signal as an echo by using inversion of a readout gradient magnetic field is generally used. The echo signal is measured for a fixed sampling time to obtain time-series data of a predetermined sampling number. An echo signal is generated when, for example, the product (integral value) of the application time and the applied intensity of the read gradient magnetic field of the positive polarity and the product of the applied time and the applied intensity of the read gradient magnetic field of the negative polarity coincide with each other. Since the echo becomes a peak at the time of the coincidence, the sampling time is set around the time of the peak.

[0003] However, in the MRI apparatus, the echo signal thus measured may be shifted from the center of the measurement space. This is because even if a high static magnetic field uniformity is maintained by a static magnetic field generator such as a permanent magnet or a superconducting magnet, the magnetic field offset changes due to the magnetic susceptibility of the object to be measured, This is due to imperfections or errors in output response.

[0004] One or several times of RF irradiation as an imaging method
There is a single-shot or multi-shot echo planar imaging (EPI) method for acquiring an echo signal necessary for reconstructing one image. In this imaging method, a plurality of echo signals are acquired in time series while reversing the readout gradient magnetic field. Therefore, when these plurality of echoes are arranged in the measurement space, the peaks of the echoes differ between the even-numbered echo and the odd-numbered echo. Position.

FIG. 9 (a) schematically shows this state. For example, if time series data of odd echoes are arranged in order from the left of the illustrated measurement space 901, even-numbered echoes are located on the right of the measurement space. Will be arranged from. Therefore, when the peak positions 9021, 9022... Of the odd echoes are shifted to the left from the center 904 of the measurement space, the peak positions 9031, 903 of the even echoes are shifted.
2 ... are shifted to the right with respect to the center 904 of the measurement space.

When such data is Fourier-transformed in the readout direction, the phase change is reversed between the even-numbered echo and the odd-numbered echo, so that an artifact 905 as shown in FIG. This is commonly referred to as N / 2 artifact.

A method for removing such N / 2 artifacts by signal processing has been proposed (JP-A-8-21517).
4, JP-A-5-68674). In these methods, prior to imaging (main measurement) for forming an image of a subject, static magnetic field correction data is acquired in advance without applying a phase encoding gradient magnetic field, and this correction data is obtained. The echo signal (main measurement data) measured by using this is corrected.

For example, in the method described in Japanese Patent Application Laid-Open No. 8-215174, a set of even-numbered echoes and odd-numbered echoes is acquired as correction data, and these echoes are subjected to Fourier transform, and then the phase difference between the echoes is determined. Then, the main measurement data is corrected. In the method described in Japanese Patent Application Laid-Open No. 5-68674, correction data and main measurement data are each subjected to one-dimensional Fourier transform in the readout direction, and correction is performed by subtracting the phase of the correction data from the main measurement data. .

[0009]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 8-215174
In the correction method described in Japanese Patent Application Laid-Open Publication No. H10-265, the phase change in the phase encoding direction in the measurement space is not considered. In other words, the phase difference may differ due to the eddy current of the gradient magnetic field in the echo train (a plurality of echoes continuously measured in one excitation), and such a change is considered in the above-described correction method. It has not been. In the method described in JP-A-5-68674, when the offset in the phase encoding direction is not optimally adjusted, the correction data obtained by performing one-dimensional Fourier transform on the correction echo signal as shown in FIG. Noise-like change in the phase of 1001,1002 ...
012 may be mixed. The image 1020 corrected using such correction data has linear artifacts (streak artifacts) 1031 and 1032 as shown in (b).
Occurs. Also, since a secondary change may be mixed in the phase of the correction data, the corrected image is shown in FIG.
In some cases, distortion as shown by 41 and 1042 occurs.

Accordingly, an object of the present invention is to obtain an MR image which can be corrected including an offset in a phase encoding direction and a secondary mixed phase noise, and has high accuracy and reduced N / 2 artifacts.

[0011]

In order to achieve the above object, according to the present invention, a number of pre-measurement echoes corresponding to the main measurement echo measured within at least one repetition time is obtained.
The phase change is calculated for each of the pre-measurement echoes that are temporally adjacent to each other, and a correction phase map reflecting the phase change of the main measurement echo in the phase encoding direction is created. Further, the obtained phase difference (phase change) is subjected to a process for improving its accuracy. By correcting the main measurement echo or adjusting the pulse sequence using such a correction phase map, N / 2 artifacts can be removed with high accuracy.

That is, the MRI apparatus of the present invention comprises a means for irradiating a subject with a high-frequency pulse, a means for applying a readout gradient magnetic field pulse, a means for applying a phase encoding gradient magnetic field pulse, and at least one repetition time. Means for detecting an echo signal generated in the apparatus in time series, means for creating and displaying an image from the echo signal, and control means for controlling the respective means according to a predetermined pulse sequence.
In the MRI apparatus, the control means, apart from the main measurement echo signal for image acquisition, using a pre-measurement echo signal measured within at least one repetition time without applying a phase encoding gradient magnetic field pulse, A phase change between each pre-measurement echo signal is calculated, and a phase map for correction is created using each phase change, and a pulse sequence for acquiring the main measurement echo signal using the phase map for correction is calculated. It has means for adjusting the echo measurement time.

In the MRI apparatus according to the present invention, the control means may perform a measurement before and after the measurement within at least one repetition time without applying a phase encoding gradient magnetic field pulse separately from the main measurement echo signal for acquiring an image. Using the measurement echo signal, calculate the phase change between each pre-measurement echo signal, create a correction phase map using each phase change, and measure the main measurement echo within at least one repetition time. Means for correcting the signals using the corresponding correction data of the correction phase map.

In the MRI apparatus of the present invention, a phase change is calculated for each of a plurality of continuously measured echo signals, and a correction phase map is created. Can be corrected.

Further, the MRI apparatus of the present invention comprises a static magnetic field generating means for generating a static magnetic field for forming a uniform magnetic field space, and a high frequency pulse generating means for irradiating a subject placed in the uniform magnetic field space with a high frequency pulse. Gradient magnetic field generating means for applying a gradient magnetic field in the slice direction, phase encoding direction, and readout direction to the subject; detecting means for detecting an echo signal from the subject; The image processing means to be constituted, the image display means for displaying the obtained image, the high-frequency pulse generation means according to a predetermined sequence, controlling the generation timing of the gradient magnetic field generation means and the detection means, the image processing means, the image display means In an MRI apparatus having control means for controlling each, the control means is provided after a pre-measurement sequence in which phase encoding is not applied. The main measurement sequence to which phase encoding is added is controlled to be executed, and in the sequence, a phase change between each pre-measurement echo signal is measured using pre-measurement echo signals continuously measured within at least one repetition time. Based on the phase change information corresponding to the main measurement echo signals arranged in time series on the measurement space, the phase of the even measurement acquisition main measurement echo signal is changed to the odd measurement acquisition measurement signal. The phase of the main measurement echo signal of the odd-number acquisition is adjusted to the phase of the main measurement echo signal of the even-number acquisition, or the phase of the measurement center is adjusted. It is characterized by having.

The MRI apparatus according to a preferred embodiment of the present invention includes a process for improving the accuracy of the calculated phase change in creating a correction phase map. More specifically, these processes include main value rotation correction and phase difference averaging.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an MRI apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 8 is a diagram showing the overall configuration of an MRI apparatus to which the present invention is applied. This MRI apparatus includes a magnet 802 for generating a static magnetic field in a predetermined space surrounding a subject 801 and a gradient magnetic field in the space. , A RF coil 804 for generating a high-frequency magnetic field in this space, and an MR coil for generating a subject 801.
An RF probe 805 for detecting a signal is provided. Bed 8
Numeral 12 is for the subject to lie down.

The gradient magnetic field coil 803 is composed of gradient magnetic field coils in three directions of X, Y and Z, and generates a gradient magnetic field in accordance with a signal from a gradient magnetic field power supply 809. The gradient magnetic field includes a slice selection gradient magnetic field applied to select a predetermined slice of the subject, a phase encoding gradient magnetic field applied to phase-encode the echo signal, and frequency encoding of the echo signal and gradient echo. There is a read-out gradient magnetic field to generate
In the present invention, a read gradient magnetic field whose polarity is inverted is used.

The RF coil 804 generates a high-frequency magnetic field according to a signal from the RF transmitting unit 810. The signal of the RF probe 805 is detected by the signal detection unit 806, and the signal is processed by the signal processing unit 807.
It is converted into an image signal by calculation. The image is displayed on the display unit 80
Displayed as 8.

The gradient magnetic field power supply 809, the RF transmitter 810, and the signal detector 806 are controlled by a controller 811 according to a time chart generally called a pulse sequence.

The control unit 811 performs various operations on the echo signal, which is a digital signal processed by the signal processing unit 807, and uses the echo signal generated in each cycle of the inverted read-out gradient magnetic field to perform phase calculation. It has a function of calculating a change, creating a correction phase map, adjusting a pulse sequence using the correction phase map, and / or correcting a main measurement echo using the correction phase map. Each function of the control unit 811 is constructed as a computer program constituting the control unit 811.

Next, a first embodiment of the present invention having such a configuration will be described. In this embodiment, as shown in FIG. 1, the pre-measurement sequence 100 is executed prior to the main measurement 200, and the sampling time of the main measurement sequence is adjusted using the correction echo 101 obtained in the pre-measurement sequence.

This measurement sequence is a single-shot or multi-shot EPI sequence in which a predetermined area of the subject is excited by a high-frequency pulse, and then a read-out gradient magnetic field that is continuously inverted is applied while simultaneously performing phase encoding. A gradient magnetic field is applied to measure a plurality of echo signals having different phase encodings. As the number of phase encodings, values such as 64, 128, 256, and 512 are usually selected for one image. In the single shot EPI, these signals having different phase encodings are measured by one excitation, and in the multi shot EPI, the signals are divided and measured. Each echo signal is usually 12
It is obtained as a time-series signal composed of 8, 256, 512, and 1024 sampling data.

In the following, this measurement sequence is a multi-shot
The case of EPI will be described as an example. FIG. 2 is a diagram showing a main measurement sequence before correction. In this pulse sequence, a pulse for applying a phase encoding offset after applying a high-frequency pulse 201 and a slice selection gradient magnetic field pulse 202.
203 and pulse 204 giving read gradient magnetic field offset
The echo signal 102 of each phase encoding is generated within each period of the readout gradient magnetic field 206 which is inverted while discretely applying the phase encoding gradient magnetic field pulse 205, and this is sampled for each sampling time 207. Time series data 102 is obtained. The sampling time 207 is typically about 1 ms each.

This sequence 208 is repeated a plurality of times (N times), and all the actual measurement echo signals h required for image reconstruction are obtained.
(n, m, t) 102 is acquired. Note that n is a repetition number (1 ≦ n ≦
N) and m are echo numbers (1 ≦ m ≦ M), and t is time. As an example, the number of main measurement echo signals measured by one high-frequency pulse application is 16 (M = 16), and the number of data in the readout direction is
128 (x = 128), the number of encodes in the phase encode direction is 128
, The number of repetitions necessary to obtain one image is 8 (N = 8).

As described above, the main measurement echo measured in this manner has a peak position of the echo corresponding to the sampling time.
Since it does not coincide with the center of 207, the peak position of the odd-numbered echo (m is an odd number) and the peak position of the even-numbered echo (m is an even number) in the measurement space are respectively shifted in opposite directions with respect to the center of the measurement space. (FIG. 9 (a)).

The peak shift of the echo signal in the measurement space corresponds to a phase change in the space after the Fourier transform. Therefore, first, the phase change between the odd-numbered echo and the even-numbered echo is obtained by the previous measurement, the shift of the peak position is obtained from this phase change, and the sampling time in the main measurement sequence is adjusted so that the peak positions of the odd-numbered echo and the even-numbered echo coincide. .

FIG. 3 is a diagram showing an example of a pre-measurement pulse sequence for detecting such a phase, which is based on a multi-shot EPI sequence corresponding to the main measurement sequence. However, the pulse sequence of FIG. 3 is different from the EPI sequence of this measurement in that the phase encoding gradient magnetic field is not applied.

That is, first, a high-frequency pulse 201 is applied to a subject including a magnetization to be detected, and at the same time, a gradient magnetic field pulse 202 for selecting a slice is applied to select a slice to be imaged. Next, after applying a pulse 204 for giving an offset of the read gradient magnetic field, a read gradient magnetic field pulse 206 for continuously inverting is applied, and a read gradient magnetic field
Since the echo signal 101 is generated in time series in each cycle of 06, the echo signal 101 is sampled for each time range 207 to obtain the time series data 101. The intensity, application timing, and time range 207 of the read gradient magnetic field 206 to be reversed are the same as those in the main measurement sequence.

A phase difference map is created using the time series data 101 acquired in the sequence 208, that is, the previously measured echo signal p (m, t) 101. M is the echo number (1
≦ m ≦ M), and t represents time. For this reason, first, the pre-measurement echo signal p (m, t) 101 is Fourier-transformed in the readout direction to obtain correction data p (m, x) 105 (step 103). Here, x represents a position in the reading direction, and 1 ≦ x ≦ X.

Next, a phase difference s (k, x) 108 between the correction data for the even-numbered echo and the correction data for the odd-numbered echo is calculated (step 107). Specifically, the following calculation is performed.

[0033]

(Equation 1) Here, k is 1 ≦ k ≦ M / 2, re [] and im [] represent the real and imaginary parts of the signal, respectively, and || represents the absolute value of the signal. In this calculation, the phase difference between the odd-numbered echo (2k-1th echo) and two even-numbered echoes (2k-2nd and 2kth) that are adjacent in time series is calculated, and the average is calculated. s (k, x).

Next, processing (109, 110) for improving the accuracy of the phase difference s (k, x) is performed. As can be seen from the above equation, since this calculation is performed in the range of -π to + π, those exceeding -π are folded back toward + π, and those exceeding + π are folded close to -π The values each change discretely (this is called around the main value, and when the phase locally turns around the main value, it is called the main value jump). Since the main value jump noise is mixed in the phase difference s (k, x) obtained as described above, it is removed by the following calculation (step 109).

[0035]

(Equation 2) Here, i and j represent points in the filter range, and -X /
2 ≦ i ≦ X / 2 and −X / 2 ≦ j ≦ X / 2.

Further, in order to remove noise mixed into the phase difference other than the main value jump noise, the phase difference is averaged by the following equation (step 110).

[0037]

(Equation 3) Here, i and j represent points in the filter range, and X / 2
≦ i ≦ X / 2, X / 2 ≦ j ≦ X / 2.

The accuracy of peak shift detection can be improved by these processes 109 and 110.

Next, the sampling time 207 in the main measurement sequence is set using the phase difference map obtained in this manner. FIG. 4 shows the relationship between the shift of the peak of the echo signal from the center of the measurement space and the phase change. As shown in FIG.
When it is at 01, the change in phase in the space obtained by one-dimensional Fourier transform of the echo is 0 as shown by a straight line 405,
When the peak of the echo signal 403 deviates from the center 401
(Shift amount 404), in a space obtained by one-dimensional Fourier transform of the echo signal, the phase changes like a straight line 406 in a linear function. Therefore, the shift amount (time) can be obtained by obtaining the inclination of the phase change.

For this reason, the phase difference s ′ (k, x) created in step 110 is subjected to fitting processing to calculate the slope of the phase change.
(First order component) is calculated (step 111). As the fitting, for example, the least square method can be adopted. Such fitting is performed for all k of the phase difference s ′ (k, x).

In step 111, a deviation Δt (k) 112 of the sampling time 207 is calculated from the gradient a (k) obtained for each k of s ′ (k, x) by the following equation.

[0042]

(Equation 4) Here, Sp is the pitch of sampling 207 (sampling time of one point), and At is the time of sampling 207. Since the phase difference of one pixel is 2π, it can be seen from this calculation that the peak shift can be detected with high accuracy in subpixel units. For example, a peak difference of 0.1 pixel unit is known for each echo.

Next, the echo measurement time of the main measurement sequence is calculated from the obtained Δt (k) (step 113). Specifically, the sampling time of the even-numbered echo is shifted by Δt (k) while the sampling time of the odd-numbered echo is kept as it is in the main measurement sequence of FIG. FIG. 5 shows the main measurement sequence adjusted in this manner. Here, only the readout gradient magnetic field (Gr), sampling (A / D), and the generated echo signal (echo) are shown during the main measurement sequence.

As shown, the peak position of the echo signal 102 is shifted from the center of the measurement space by 501 (5011, 5012...). This shift 501 corresponds to Δt (k) / 2 obtained by the above calculation. Therefore, the sampling time 207 of the even-numbered echo is shifted by Δt (k) (502). As a result, the peak positions of the echo signals in the measurement space are aligned.

As described above, the main measurement sequence calculated in the pre-measurement processing 114 from steps 103 to 113 is executed, and the main measurement echo signal 102 is obtained. FIG. 6 shows an arrangement of the measurement space 601 of the main measurement echo 102 acquired. As shown
The peaks 6021, 6022,... Of the even-numbered echoes 602 are changed by shifting the sampling time.
The same position as 6032 ... These are the measurement space as a whole
Although it is shifted from the center 604 of the 601, the peaks of the respective echoes are aligned. Therefore, in the image 118 created by performing the two-dimensional Fourier transform and performing the image reconstruction 119, the N / 2 artifact is greatly reduced.

FIG. 6 shows a case where the deviation from the center of the measurement space is the same regardless of the echo number. However, as described above, in the present invention, the phase difference is a function of the echo number (k). Since it is required, even if the phase difference changes within the echo train, the peaks can be accurately aligned.

As described above, the first embodiment of the present invention has been described. In this embodiment, the case where the sampling time of the even-numbered echo is adjusted has been described. However, the odd-numbered echo may be adjusted, or both may be adjusted. The processing of the present invention can be applied not only to multi-shot sequences but also to one-shot type sequences, multi-slices, 3D measurement, and the like.

According to the MRI apparatus of the first embodiment, the phase change between echoes is calculated from the correction data, and the main measurement sequence is optimally adjusted in subpixel units for each echo. High quality image capturing can be realized without causing artifacts.

Further, since the main measurement sequence is adjusted without performing the correction processing at the time of image reconstruction using the correction data, the main measurement can be performed without extending the reconstruction time.

Next, a second embodiment of the present invention will be described. In this embodiment as well, the pre-measurement sequence is executed prior to the main measurement to create correction data for each echo as in the first embodiment, but in the second embodiment, the correction data p The phase of each echo measured in the main measurement sequence is corrected using (m, x) 101.

FIG. 7 shows a processing procedure according to this embodiment. The same processes as those in FIG. 1 are denoted by the same reference numerals as those in FIG. Here, the multi-shot EPI will be described as an example.
First, the pre-measurement sequence shown in FIG. 2 is executed to measure the correction echo p (m, t) (step 101). Here, m is an echo number, and t is time, and the same number of echoes as those measured in one repetition time of the main measurement sequence are measured. This correction echo is Fourier-transformed in the readout direction for each echo to obtain correction data p (m, x) (step 103).

The phase difference s (k, x) between the odd echo and the even echo is calculated from the correction data (step 107).
This calculation is the same as the calculation for obtaining the phase difference s (k, x) in the first embodiment. Therefore, also in this case, the process of removing the main value jump noise (step 109) and the process of obtaining the average of the phase difference (step 110) are performed. The phase difference s ′ (k, x) with improved accuracy is stored in the memory of the control unit as a correction phase map.

On the other hand, the main measurement sequence shown in FIG. 2 is executed, and the main measurement echo h (n, m, t) is measured (step 10).
2). Here, n is a repetition number, m is an echo number, and t is time. Next, the main measurement echo h (n, m, t) is Fourier-transformed in the readout direction to obtain main measurement data h (n, m, x) (step 106).

The main measurement data is corrected using the correction phase map s' (k, x) obtained in the previous measurement (step 111).
The calculation of the correction is performed by, for example, the following equation.

[0055]

(Equation 5) As can be seen from the above equation, in this example, the odd-numbered echo uses the measured data as it is, and corrects only the even-numbered echo. .., The peaks 6011, 6012,... Of the even-numbered echoes 602 are in the same positions as the peaks 6031, 6032,. In this case, odd-numbered echoes may be corrected and aligned with even-numbered echoes, or both may be corrected and their peaks may be aligned with the center of the measurement space.

After the phases of the odd-numbered echo and the even-numbered echo are aligned in this manner, the image is reconstructed by subjecting the main measurement data to Fourier transform in the phase encoding direction (step 112). In the reconstructed image 113, N / 2 artifacts are significantly reduced.

Also in this embodiment, the phase difference is obtained as a function of the echo number (k), and the main measurement echoes having different echo numbers m are corrected using the corresponding phase difference data. Even when there is a fluctuation, that is, even when the phase difference changes within the echo train, it is possible to correct accurately. As a result, it is possible to realize high quality image capturing without causing image distortion and linear artifacts.

Although the second embodiment of the present invention has been described above, this embodiment can also be applied to one-shot sequence, multi-slice measurement, and 3D measurement as in the first embodiment.

[0059]

The present invention has been configured as described above.
The following effects are obtained. For all echoes, the phase difference between the even-numbered echo and the odd-numbered echo signal is calculated, so even if the difference is different for each echo due to the eddy current of the gradient magnetic field in the echo train, the actual measurement echo can be accurately corrected. . Alternatively, the main measurement sequence can be adjusted. Performs processing to improve the accuracy of the correction data after the Fourier transform in the readout direction, so that streak artifacts such as the lower brain that could not be removed by conventional correction can be removed, and MR images with good image quality can be obtained. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a processing procedure in a first embodiment of the MRI apparatus of the present invention.

FIG. 2 is a diagram showing an example of a main measurement pulse sequence executed by the MRI apparatus of the present invention.

FIG. 3 is a diagram showing an example of a pulse sequence of pre-measurement executed by the MRI apparatus of the present invention.

FIG. 4 is a view for explaining a relationship between a shift of a peak position of an echo and a phase change.

FIG. 5 is a view showing an example of a main measurement pulse sequence after adjustment, which is executed by the MRI apparatus of the first embodiment.

FIG. 6 is a diagram showing a measurement space arrangement of echoes measured by the pulse sequence of FIG. 5;

FIG. 7 is a diagram showing a processing procedure in a second embodiment of the MRI apparatus of the present invention.

FIG. 8 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied.

FIG. 9 is a view for explaining the principle of generation of N / 2 artifacts.

FIG. 10 is a view for explaining other artifacts.

[Explanation of symbols]

803 means for applying a read gradient magnetic field, means for applying a phase encoding gradient magnetic field 804 means for detecting an echo signal 805 means for applying a high-frequency pulse 811 means for controlling

Claims (3)

[Claims] A means for irradiating a subject with a high-frequency pulse;
Means for applying a read gradient magnetic field pulse, means for applying a phase encoding gradient magnetic field pulse, means for detecting an echo signal generated within at least one repetition time in time series, and creating an image from the echo signal. A magnetic resonance imaging apparatus comprising: a display unit; and a control unit that controls each of the units in accordance with a predetermined pulse sequence. The control unit, apart from the main measurement echo signal for acquiring an image, Using a pre-measurement echo signal measured within at least one repetition time without applying a pulse, a phase change between each pre-measurement echo signal is calculated, and a phase map for correction is calculated using each phase change. A pulse sequence echometer for creating and obtaining a main measurement echo signal using the correction phase map Magnetic resonance imaging apparatus characterized by comprising means for adjusting the time. 2. A means for irradiating a subject with a high-frequency pulse,
Means for applying a read gradient magnetic field pulse, means for applying a phase encoding gradient magnetic field pulse, means for detecting an echo signal generated within at least one repetition time in time series, and creating an image from the echo signal. A magnetic resonance imaging apparatus comprising: a display unit; and a control unit that controls each of the units in accordance with a predetermined pulse sequence. The control unit, apart from the main measurement echo signal for acquiring an image, Using a pre-measurement echo signal measured within at least one repetition time without applying a pulse, a phase change between each pre-measurement echo signal is calculated, and a phase map for correction is calculated using each phase change. While creating, the main measurement echo signal measured within at least one repetition time of each of the correction phase map A magnetic resonance imaging apparatus having means for performing correction using corresponding correction data. 3. A static magnetic field generating means for generating a static magnetic field for forming a uniform magnetic field space; a high frequency pulse generating means for irradiating a subject placed in the uniform magnetic field space with a high frequency pulse; On the other hand, gradient magnetic field generating means for applying each gradient magnetic field in the slice direction, phase encoding direction and readout direction, detecting means for detecting an echo signal from the subject, and image processing means for reconstructing an image from the echo signal Image display means for displaying the obtained image, high-frequency pulse generation means according to a predetermined sequence, control means for controlling the generation timing of the gradient magnetic field generation means and control means for detecting means, image processing means, image display means, respectively In the magnetic resonance imaging apparatus provided with, the control means, the phase after the pre-measurement sequence without applying the phase encode Controlling to execute the main measurement sequence to which encoding is added, and in the sequence, using the pre-measurement echo signals continuously measured within at least one repetition time, the phase change between each pre-measurement echo signal is respectively While calculating, based on the information on the phase change corresponding to the main measurement echo signal arranged in time series on the measurement space, the phase of the even measurement acquisition main measurement echo signal is changed to the odd measurement acquisition main measurement echo signal. Phase correction means for performing one of the following processes: aligning the phase of the main measurement echo signal of the odd-number acquisition with the phase of the main measurement echo signal of the even-number acquisition, or aligning the phase with the phase of the measurement center. A magnetic resonance imaging apparatus, characterized in that: