JP3152690B2 - Magnetic resonance imaging - Google Patents

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 apparatus, and more particularly to a magnetic resonance imaging apparatus having a function of collecting a magnetic field intensity distribution in a subject at a high speed and adjusting magnetic field uniformity.

[0002]

2. Description of the Related Art In magnetic resonance imaging, when a group of nuclear spins having a unique magnetic moment is placed in a uniform static magnetic field, the energy of a high-frequency magnetic field rotating at a specific frequency is resonantly absorbed. This is a method of visualizing chemical and physical microscopic information of a substance using a phenomenon.

[0003] In this magnetic resonance imaging method, the magnetic field intensity distribution of the static magnetic field is uniform for the purpose of obtaining an image with less distortion and for obtaining a spectrum having a high frequency resolution in the spectroscopic imaging method. That is, magnetic field uniformity is required. In particular, high-speed imaging methods such as the echo planar method, ¹ H
In a spectroscopic imaging method for observing the spectrum of a specific nuclide such as (proton) and ³¹ P (phosphorus), a magnetic field uniformity of one part per million (ppm) or more is required. In order to obtain this magnetic field uniformity, it is necessary to adjust the magnetic field intensity distribution by some method. At this time, since the magnetic field uniformity is also affected by the magnetic susceptibility and shape of the subject, the magnetic field strength distribution in the subject is measured with the subject in a static magnetic field, and the magnetic field strength distribution is measured according to the measurement result. Is adjusted.

Conventionally, a chemical shift imaging method (AAMaudsley et al., "Rapid Measu
rement of Magnetic Field Distribution Using Nuclea
rMagnetic Resonance "Siemens R / D Report vol.8, pp326
331, 1979), or a so-called phase method for obtaining a magnetic field intensity distribution from two phase images obtained by performing a spin echo method sequence while changing the echo time (Japanese Patent Laid-Open No. 611-1).
No. 80130).

[0005] Among them, the chemical shift imaging method has a problem that the measurement is essentially time-consuming. The phase method has the advantage that measurement can be performed without being affected by errors due to uneven sensitivity of the high-frequency coil for irradiating a high-frequency magnetic field and detecting a magnetic resonance signal, and phase errors due to imperfections inherent to the device. In order to obtain a single phase image, it is necessary to repeat the pulse sequence of the spin echo method many times, so that there is a problem that the measurement also takes time.
In addition, the phase method is used when a plurality of substances having the same nuclide but different magnetic resonance frequencies due to chemical shift (for example, water and fat when paying attention to protons) are mixed in the subject, and the accurate magnetic field intensity distribution is obtained. There is also a problem that cannot be obtained.

[0006]

As described above, in the conventional magnetic field intensity distribution measuring techniques such as chemical shift imaging and the phase method, since the measurement takes a long time, the examination time becomes long and the pain given to the subject is increased. And a problem that an accurate magnetic field intensity distribution cannot be obtained due to the influence of the chemical shift of the nuclear spin of the target nuclide in the subject. An object of the present invention is to solve the above-mentioned problems and to provide a magnetic resonance imaging apparatus capable of accurately measuring a magnetic field intensity distribution in a subject and adjusting magnetic field uniformity in a short time.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a readout gradient magnetic field which is alternately inverted and applied to a region excited by the application of a high-frequency pulse and a slice gradient magnetic field, and a readout operation. A series of sequences for collecting an echo signal sequence by applying a phase encoding gradient magnetic field each time the gradient magnetic field was inverted was performed twice in succession, and excitation was performed from the obtained first and second echo signal sequences. Generating first and second phase images having a phase difference between the corresponding pixels that reflects the magnetic field intensity distribution in the region, and calculating the first and second phase image data and the time interval between the phase image data; The basic feature is to calculate the magnetic field intensity distribution in the subject.

In order to collect the first and second echo signal trains, according to one aspect of the present invention, a desired region is obtained by applying a high-frequency pulse having a predetermined flip angle and a slicing gradient magnetic field to a subject. After the first echo signal sequence is collected by exciting and applying a read gradient magnetic field to this area by inverting positive and negative alternately and applying a phase encode gradient magnetic field every time the read gradient magnetic field is inverted. Subsequently, the readout gradient magnetic field is alternately inverted and applied to the previously excited region and the phase encode gradient magnetic field is applied every time the readout gradient magnetic field is inverted, so that the second magnetic resonance signal is obtained. To collect the echo signal sequence.

According to another aspect, a desired region is excited by applying a high-frequency magnetic field pulse having a predetermined flip angle and a slicing gradient magnetic field to the subject, and this region is read out at a predetermined timing with respect to the excitation timing. After the first echo signal train is collected as a magnetic resonance signal by applying a gradient magnetic field for use alternately in the positive and negative directions and applying a gradient magnetic field for phase encoding each time the read gradient magnetic field is reversed, it is applied to the subject. By applying a high-frequency magnetic field pulse having a predetermined flip angle and a gradient magnetic field for slicing, the previously excited region is again excited, and the excited region is excited at a different timing from the first echo signal sequence with respect to the excitation timing. The gradient magnetic field for reading is reversed and applied alternately, and the gradient magnetic field for phase encoding is applied every time the gradient magnetic field for reading is reversed. By Rukoto, collecting the second echo signal train.

In these cases, the time interval between the two phase images, which is a time factor when calculating the magnetic field intensity distribution from the first and second phase images, is the zero encoding of the first and second echo signal sequences. Center-to-center spacing can be used.

Further, according to another aspect, the subject is 90 °
A desired region is excited by applying a high-frequency magnetic field pulse and a gradient magnetic field for slicing, and a gradient magnetic field for reading is alternately inverted and applied to this region, and a gradient magnetic field for phase encoding is applied every time the gradient magnetic field for reading is reversed. After the first echo signal train is collected by applying the above, a 180 ° high-frequency magnetic field pulse is applied to the excited region, and then the read gradient magnetic field is inverted and applied alternately. By applying a phase encoding gradient magnetic field for each inversion, the second
To collect the echo signal sequence.

In this case, 180 ° from the center of the 90 ° pulse.
The time interval from the center of the 90 ° pulse to the first echo signal is made equal to the time interval from the center of the 90 ° pulse to the center of the zero encode when the second echo signal train is collected. The time interval up to the center of zero encoding in column acquisition can be used as the time interval between the two phase images, which is the time factor when calculating the magnetic field intensity distribution from the first and second phase images.

On the other hand, when the nuclear spin of the nuclide to be imaged has a plurality of magnetic resonance frequencies in the subject due to chemical shift, it has a magnetic resonance frequency other than a predetermined magnetic resonance frequency in advance. First and second phase image data for suppressing a magnetic resonance signal from a nuclear spin, or particularly when the nuclear spin to be imaged has two magnetic resonance frequencies due to chemical shift in a subject. By controlling the pulse sequence so that the time factor when calculating the magnetic field intensity distribution from the magnetic field becomes the time when the phase difference between the two magnetic resonance frequencies of the nuclear spins of the imaging target becomes 360 °, the nuclear spin of the imaging target is obtained. Solves the problem that accurate magnetic field strength distribution cannot be obtained due to the influence of chemical shifts, and obtains accurate magnetic field strength distribution

In practicing the present invention, a three-dimensional magnetic field strength distribution is obtained by executing the above-described magnetic field strength distribution measurement a plurality of times while changing the slice plane, and the magnetic field strength distribution information is obtained from the three-dimensional magnetic field strength distribution information. A current correction value to be applied to each magnetic field uniformity adjusting coil for making the intensity distribution uniform is obtained, and a current applied to each magnetic field uniformity adjusting coil is controlled. When obtaining a current correction value to be applied to each magnetic field uniformity adjusting coil, it is desirable to use three-dimensional magnetic field strength distribution information of only a predetermined region in the subject.

[0015]

As described above, according to the present invention, two phase images in which the magnetic field intensity distribution in the subject is reflected in the phase difference by the two-dimensional imaging pulse sequence can be measured quickly and accurately. Become. Therefore, by adjusting the magnetic field uniformity using the information on the magnetic field intensity distribution thus measured, the magnetic field uniformity in the subject is improved.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a magnetic resonance imaging apparatus according to one embodiment of the present invention.

In FIG. 1, a static magnetic field magnet 1, a magnetic field uniformity adjusting coil 3 and a gradient magnetic field generating coil 5 are driven by power supplies 2, 4 and 6, respectively. As a result, a uniform static magnetic field and a gradient magnetic field having a linear gradient magnetic field distribution in three directions orthogonal to each other in the same direction as the static magnetic field are applied to the subject 7.

The high-frequency probe 9 is supplied with a high-frequency signal from the transmission unit 10 to apply a high-frequency magnetic field to the subject 7 and receive a magnetic resonance signal generated from the inside of the subject 7. Here, the high-frequency probe 9 is shared for transmission and reception, but a high-frequency probe may be separately provided for transmission and reception. The magnetic resonance signal received by the high-frequency probe 9 is subjected to quadrature phase detection by the receiving unit 11, transferred to the data collecting unit 13, and subjected to A / D conversion, so that digital data (hereinafter, referred to as image data) required for image reconstruction , Image reconstruction data) are collected.

The above-mentioned power supplies 2, 4 and 6 and the transmission unit 1
0, the receiving unit 11 and the data collecting unit 13 are controlled by the system controller 12. The system controller 12 and the computer 14 are controlled by commands from a console 15.

The electronic computer 14 performs an image reconstruction process by Fourier transform based on the image reconstruction data input from the data acquisition unit 13 to obtain image data of a subject 7 in a predetermined slice plane. This image data is sent to the image display 16 and displayed as an image.

A pulse sequence for acquiring image reconstruction data in a predetermined slice plane in the subject 7 and a pulse sequence for measuring a static magnetic field intensity distribution according to the present invention are controlled by the system controller 12. .

The procedure for measuring the magnetic field intensity distribution according to the present invention will be described below. FIG. 2 is a flowchart showing a schematic procedure of the magnetic field intensity distribution measurement according to the present invention. The excitation step S0, the first data collection step S1, the second data collection step S2, the image reconstruction step S3, It comprises a first and second phase image data generation step S4 and a magnetic field intensity distribution calculation step S5. As described later, a second excitation step may be inserted before the second data collection step S2.

3 to 5 show an embodiment of a pulse sequence for measuring a magnetic field intensity distribution. FIG. 3-
In FIG. 5, RF indicates a high-frequency magnetic field, Gs, Gr, and Ge indicate respective gradient magnetic fields for slicing, reading, and phase encoding, and signal indicates a magnetic resonance signal. Since the high-frequency magnetic field RF is applied in the form of a pulse, a high-frequency pulse that rotates the magnetization in the slice plane by 90 ° is referred to as a high-frequency pulse, and a high-frequency pulse that rotates 180 ° is 180 °. ° Pulses. The slice gradient magnetic field Gs is used to excite a desired region (slice plane) in the subject 7, the read gradient magnetic field Gr is used to read a magnetic resonance signal, and the phase encode gradient magnetic field Ge is used for slice. It is used to convert in-plane position information into magnetic resonance signal phase information.

In the pulse sequence according to the first embodiment shown in FIG. 3, a desired high-frequency pulse having an arbitrary flip angle α is applied at the same time as applying a slice gradient magnetic field Gs as an excitation step S0. Excitation of slice plane, FID as magnetic resonance signal signal
(Free induction decay) signal.

Subsequently, as a first data collection step S1, the read gradient magnetic field Gr is alternately inverted and applied, and a phase encoding gradient magnetic field Ge is applied every time the read gradient magnetic field Gr is inverted. By doing
The first echo signal sequence is collected as image reconstruction data (data collection I).

Next, following this data acquisition I, as a second data acquisition step S2, a read gradient magnetic field Gr
By applying the gradient magnetic field for phase encoding Ge in the same manner as described above, the second echo signal sequence is collected as image reconstruction data (data collection II).

Echo signal trains are collected by the data acquisitions I and II in that the desired nuclear magnetization in the slice plane excited by the application of the first high-frequency pulse of the flip angle α and the application of the slice gradient magnetic field Gs reduces the transverse magnetization. It takes place within a time that is alleviated by the phenomenon.

Next, as an image reconstruction step S3, the image reconstruction data based on the first and second echo signal trains collected as described above are respectively subjected to appropriate preprocessing,
Image reconstruction is performed by performing a complex Fourier transform to obtain image data.

Then, as first and second phase image generation steps S4, the first and second phase image data are obtained from the real and imaginary components of each pixel of the image data obtained by the complex Fourier transform in step S3. Generate each.

Next, as a magnetic field intensity distribution calculation step S5, a phase difference Φ (x, y) between each pixel between the first and second phase image data is obtained, and a time interval between these phase image data is determined. A time interval from the center of the zero encoding in the first data acquisition I shown in FIG. 1 to the center of the zero encoding in the second data acquisition II is represented by ΔT.
The phase difference Φ (x, y) for each pixel is converted into a magnetic field intensity distribution by the following equation (1).

ΔH (x, y) = Φ (x, y) / γ · ΔT γ: Magneto-rotation ratio of the target nuclear spin) (1) That is, the phase difference Φ (x, y) is converted to the angular frequency Φ. (X, y)
By converting to / ΔT, the non-uniformity ΔH (x, y) of Ho for each pixel is obtained from the relationship ωo = γHo. Here, the time interval ΔT is selected such that | γ · ΔHmax · ΔT | <π (2) where ΔHmax is the expected maximum value of the magnetic field inhomogeneity. In this way, the magnetic field inhomogeneity can be measured in a short time.

Next, a pulse sequence for measuring a magnetic field intensity distribution according to the second embodiment shown in FIG. 4 will be described. In this embodiment, first, a first echo signal sequence is acquired as image reconstruction data by a pulse sequence shown in FIG. 4A which is similar to the pulse sequence of data acquisition I in FIG. Next, a second echo signal sequence is collected as image reconstruction data by the same pulse sequence shown in FIG. Here, in the pulse sequences of FIGS. 4A and 4B, after the excitation of the slice surface by the application of the high-frequency pulse having the flip angle α and the slice gradient magnetic field Gs, the readout gradient magnetic field Gr and the phase encoding gradient magnetic field Ge are applied.
Are different by ΔT. Specifically, assuming that the time (echo time) from the application of the high-frequency pulse having the flip angle α and the slice gradient magnetic field Gs in FIG. It is TE + ΔT.

According to this embodiment, since the slice plane is excited by applying the high-frequency pulse and the slice gradient magnetic field Gs in FIGS. 4A and 4B, respectively, the magnetic field intensity is compared with the pulse sequence in FIG. Although it takes time to measure the distribution, compared to conventional chemical shift imaging or the phase method, the time required for measurement is much longer because all the image reconstruction data in the slice plane can be obtained by one pulse sequence. Short.

Further, according to the embodiment of FIG. 4, since the degree of freedom in setting the time interval ΔT is higher than that of the embodiment of FIG. 3, when the magnetic field inhomogeneity is large, ΔT is reduced. As a result, the phase difference Φ (x, y) can be reduced, and the measurement can be facilitated.

Next, a pulse sequence for measuring a magnetic field intensity distribution according to the third embodiment shown in FIG. 5 will be described. In this embodiment, first, a 90 ° pulse is applied as the high-frequency magnetic field RF, and at the same time, a slice surface is excited by applying the slice gradient magnetic field Gs to generate an FID signal.

Subsequently, the read gradient magnetic field Gr is alternately inverted and applied in the positive and negative directions, and the phase encode gradient magnetic field Ge is applied every time the read gradient magnetic field Gr is inverted, so that the first FID signal based on the FID signal is obtained. Are collected as data for image reconstruction (data collection I).

Next, following the data acquisition I, a 180 ° pulse is applied as a high-frequency magnetic field, and simultaneously a slice gradient magnetic field Gs is applied.
By applying r and the phase encoding gradient magnetic field Ge in the same manner as described above, a second echo signal sequence (spin echo signal sequence) is collected as image reconstruction data (data collection II).

The collection of echo signal trains by the data acquisitions I and II is performed by relaxing the desired nuclear magnetization in the slice plane excited by the application of the first 90 ° pulse and the slice gradient magnetic field Gs due to the transverse magnetization relaxation phenomenon. Will be done within the time you want.

Thereafter, similar to the first and second embodiments, the image reconstruction data obtained by the first and second echo signal trains thus collected are subjected to appropriate preprocessing, respectively.
Image reconstruction is performed by performing a complex Fourier transform, and first and second phase image data are respectively generated from the real component and the imaginary component of each pixel of the obtained image data. And a phase difference Φ for each pixel between the first and second phase image data.
(X, y) is obtained, and further converted into a magnetic field intensity distribution by the above equation (1).

In this case, 180 degrees from the center of the 90 ° pulse.
The time interval to the center of the 180 ° pulse and the time interval from the center of the 180 ° pulse to the center of the zero encoding in the second data acquisition II are equal to TE / 2. And 90
The calculation of (1) is performed with ΔT as the time interval from the center of the pulse to the center of zero encoding in the first data acquisition I.

Therefore, according to the present embodiment, the magnetic field intensity distribution can be measured in approximately the same measuring time as in the first embodiment, and the time factor ΔT for measuring the magnetic field intensity distribution as in the second embodiment. There is an advantage that can be set freely to some extent.

By the pulse sequence as in the first to third embodiments described above, a magnetic field intensity distribution on one slice plane, that is, a two-dimensional magnetic field intensity distribution can be obtained. If this pulse sequence is executed a plurality of times while changing the slice plane, a three-dimensional magnetic field intensity distribution ΔH (x, y, z) is obtained. Then, a current correction value applied to the magnetic field uniformity adjusting coil 3 in FIG. 1 for making the magnetic field intensity distribution uniform is obtained from the obtained information on the three-dimensional magnetic field intensity distribution using a method such as the least square method. By adjusting the power supply 4 for the magnetic field uniformity adjusting coil by the system controller 12 according to the correction value and controlling the current applied to each magnetic field uniformity adjusting coil 3, the magnetic field in the subject is made uniform. Can be.

In this case, when the imaging or inspection area is limited to a local area, each magnetic field uniformity for making the magnetic field intensity distribution uniform is obtained by using only information of a predetermined area in the magnetic field intensity distribution information. It is desirable to obtain a current correction value applied to the property adjusting coil 3 and to control the current applied to each magnetic field uniformity adjusting coil 3 accordingly.

In the magnetic field intensity distribution measuring method according to the present invention described above, it is necessary to consider image distortion due to the influence of magnetic field uniformity as in the case of the ultra-high-speed MRI pulse sequence as described in JP-A-64-56042. There is also. That is,
Strictly speaking, an error is included in the measurement result of the magnetic field strength distribution due to the influence of the inhomogeneous magnetic field. In order to eliminate this error, for example, the three-dimensional magnetic field intensity distribution ΔH obtained as described above is used.
From (x, y, z), position shift correction may be performed using the following equation (3). ΔH (x ′, y ′, z ′) = ΔH (x, y, z) x ′ = x + ΔH (x, y, z) / Gx y ′ = y + ΔH (x, y, z) / Gy

Z ′ = z + ΔH (x, y, z) / Gz (3) where Gx, Gy, and Gz are gradient magnetic field strengths in the x, y, and z directions, respectively. By performing such correction, more accurate information on the magnetic field strength distribution can be obtained.

In the magnetic field intensity distribution measurement described in the first to third embodiments, when a substance having a different magnetic resonance frequency of a target nuclear spin in a subject due to a chemical shift is mixed (for example, raw Water and fat when focusing on protons in the body) cannot obtain an accurate magnetic field intensity distribution. Thus, in the case where the subject is a substance having a plurality of magnetic resonance frequencies due to chemical shift or the like, before each measurement, each spin that produces magnetic resonance at a frequency other than the predetermined magnetic resonance frequency due to chemical shift or the like in the subject is performed. Is added and executed. As a specific example of such a pulse sequence, for example,

(A) CHESS method (A. Hasse et al. ¹ H
−NMR Chemical Shift Selective (CHESS) Imaging ”, Ph
ys. Med. Biol. vol. 30, pp. 341-344 (1985)) (b) 1-1 pulse method (CLDumoulin “A Method for Che
mical-Shift-Selective Imaging ”, Magn. Reso.Med.vo
l.2, pp583-585 (1985)) (c) 1-3-3-1 pulse method (PJHore “A New Method
for Water Suppression in the Proton NMR Spectra o
f Aqueous Solitions ", J.Magn.Reso.vol.54, pp539-542
(1983)), an appropriate method may be used depending on the case.

When the target nuclear spin has two magnetic resonance frequencies due to chemical shift in the subject, the magnetic field intensity distribution is calculated from the two phase image data in the pulse sequence. The pulse sequence may be controlled so that the time factor ΔT becomes Δωc · ΔT = 2π (4). Here, Δωc is 2 due to the chemical shift of the target nuclear spin.
Angular frequency difference between two magnetic resonance frequencies. By these methods, an accurate magnetic field intensity distribution can be obtained without being affected by the chemical shift of the target nuclear spin in the subject.

Further, according to the present invention, the magnetic field intensity distribution in the subject can be measured at high speed and the magnetic field uniformity can be improved. Therefore, when the subject is placed in a static magnetic field, or in a static magnetic field, When the position of the subject is moved or the like, it can be executed prior to a predetermined test. The present invention can be implemented with various other modifications. For example, the present invention can be applied to a known high-speed three-dimensional imaging method as shown in FIGS.

[0050]

According to the present invention, the magnetic field intensity distribution in the subject can be measured quickly and accurately. Therefore, when the subject is placed in the static magnetic field based on the measurement result or when the position of the subject is moved in the static magnetic field, the magnetic field uniformity in the subject is adjusted by adjusting the magnetic field uniformity. As a result, it is possible to obtain a good image without distortion and a spectrum with high frequency resolution, and it is possible to accurately and quickly obtain image information useful for diagnosing a disease. In addition, the pain given to the subject is reduced by shortening the examination time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is a flowchart for explaining a schematic procedure of a magnetic field intensity distribution measurement according to the present invention.

FIG. 3 is a diagram showing a pulse sequence for measuring a magnetic field intensity distribution according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a pulse sequence for measuring a magnetic field intensity distribution according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a pulse sequence for measuring a magnetic field intensity distribution according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a pulse sequence of high-speed three-dimensional imaging to which the present invention can be applied.

FIG. 7 is a diagram showing a pulse sequence of high-speed three-dimensional imaging to which the present invention can be applied.

[Description of Signs] 1 ... Static magnetic field magnet 2 ... Power supply for excitation 3 ... Magnetic field uniformity adjustment coil 4 ... Power supply for magnetic field uniformity adjustment coil 5 ... Gradient magnetic field generation coil 6 ... Power supply for gradient magnetic field generation coil 7 ... Subject 8 ... bed 9 ... probe 10 ... transmission unit 11 ... reception unit 12 ... system controller 13 ... data collection unit 14 ... computer 15 ... console 16 ... image display

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A high-frequency magnetic field and a gradient magnetic field for slicing, reading, and phase encoding are applied to a subject arranged in a uniform static magnetic field in accordance with a predetermined pulse sequence, so that a magnetic field from the subject is generated. In a magnetic resonance imaging apparatus for detecting and imaging a resonance signal, excitation means for exciting a desired area by applying a high-frequency pulse having a predetermined flip angle and a gradient magnetic field for slicing to a subject, and exciting by the excitation means A first echo signal train is collected as a magnetic resonance signal by applying a read gradient magnetic field to the read area in a manner that the read gradient magnetic field is alternately inverted and applied and a phase encode gradient magnetic field is applied every time the read gradient magnetic field is inverted. A first echo signal sequence collecting means, and a read-out operation in a region excited by the excitation means, following the collection of the first echo signal sequence. A second echo signal sequence for collecting a second echo signal sequence as a magnetic resonance signal by applying the distribution magnetic field by inverting the polarity alternately and applying the gradient magnetic field for phase encoding each time the gradient magnetic field for reading is reversed. Collecting means; and first and second echo signals from the first and second echo signal trains.
Phase image data generating means for generating the phase image data, and calculating means for calculating the magnetic field intensity distribution in the subject from the first and second phase image data and a time interval between the phase image data. A magnetic resonance imaging apparatus characterized in that: 2. A high-frequency magnetic field pulse and a gradient magnetic field for slicing, reading, and phase encoding are applied to a subject arranged in a uniform static magnetic field in accordance with a predetermined pulse sequence, so that a signal from the subject is generated. In a magnetic resonance imaging apparatus for detecting and imaging a magnetic resonance signal, a first excitation means for exciting a desired area by applying a high-frequency magnetic field pulse having a predetermined flip angle and a gradient magnetic field for slicing to a subject, A readout gradient magnetic field is alternately inverted and applied to the area excited by the first excitation means at a predetermined timing with respect to the excitation timing, and a phase encoding gradient magnetic field is applied every time the readout gradient magnetic field is inverted. A first echo signal sequence collecting means for collecting a first echo signal sequence as a magnetic resonance signal, and the first echo signal sequence And a second excitation unit that excites the region excited by the first excitation unit by applying a high-frequency magnetic field pulse having a predetermined flip angle and a gradient magnetic field for slicing to the subject, The readout gradient magnetic field is inverted and applied alternately to the area excited by the excitation means at a timing different from that of the first echo signal train collection means with respect to the excitation timing, and the phase encoding is performed every time the readout gradient magnetic field is inverted. A second echo signal sequence collecting means for collecting a second echo signal sequence as a magnetic resonance signal by applying a gradient magnetic field for use; a first and a second echo signal sequence from the first and second echo signal sequences;
Phase image data generating means for generating the phase image data, and calculating means for calculating a magnetic field intensity distribution in the subject from the first and second phase image data and a time interval between the phase image data. A magnetic resonance imaging apparatus characterized in that: 3. A high-frequency magnetic field and a gradient magnetic field for slicing, readout, and phase encoding are applied to a subject arranged in a uniform static magnetic field in accordance with a predetermined pulse sequence, so that a magnetic field from the subject is generated. In a magnetic resonance imaging apparatus for detecting and imaging a resonance signal, an excitation unit for exciting a desired region by applying a 90 ° high-frequency magnetic field pulse and a gradient magnetic field for slicing to a subject, and an area excited by the excitation unit A first echo signal train is collected as a magnetic resonance signal by applying a read gradient magnetic field to the positive and negative alternately and applying a phase encode gradient magnetic field every time the read gradient magnetic field is inverted. Echo signal train collecting means; and, following the collection of the first echo signal train, a 180 ° high-frequency magnetic field pulse is applied to an area excited by the exciting means. , The readout gradient magnetic field is reversed and applied alternately, and a phase encoding gradient magnetic field is applied every time the readout gradient magnetic field is inverted, so that a second echo signal sequence is collected as a magnetic resonance signal. A second echo signal train collecting means, and a first and second echo signal trains based on the first and second echo signal trains.
Phase image data generating means for generating phase image data of the following: a magnetic field in the subject based on a time interval between the first and second phase image data and the first echo signal sequence and the second echo signal sequence A magnetic resonance imaging apparatus comprising: a calculation unit for calculating an intensity distribution.