JP4301381B2 - Magnetic resonance imaging system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for magnetic resonance imaging (hereinafter referred to as “MRI”) that obtains a tomographic image of a subject using a nuclear magnetic resonance phenomenon, and in particular, obtains a plurality of signals by one excitation and obtains a tomographic image of the subject. The present invention relates to an MRI apparatus.
[0002]
[Prior art]
In MRI, a high-frequency (hereinafter referred to as “RF”) pulse and a gradient magnetic field are applied to a subject to select and excite a cross section of a specific part, and position information in one axial direction of the cross section is RF pulse. The position information in the other axis direction is encoded into the frequency of the RF pulse, and the obtained echo signal is decoded by Fourier transform to obtain a tomographic image representing the cross section of the part.
In this MRI, a plurality of echo signals can be obtained by one excitation such as Fast Spin Echo (hereinafter referred to as “FSE”) method, Fast Inversion Recovery (hereinafter referred to as “FIR”) method, Echo Planer Imaging (hereinafter referred to as “EPI”) method. There are known ways to obtain In these methods, the signal acquired by excitation attenuates according to an exponential function as time advances. Therefore, when the number of signals acquired by one excitation (Echo Train Length, hereinafter referred to as “ETL”) increases, The value of the acquired signal is extremely smaller than the value of the first signal. When the ETL is large, there is a common feature such that signal discontinuity occurs in the phase direction and artifacts due to the signal discontinuity occur.
Furthermore, when half scanning is used in combination with the above FSE method, FIR method, and EPI method, discontinuity of values occurs between the estimated portion and the acquired signal portion, and artifacts due to the discontinuity are particularly likely to occur.
[0003]
This artifact is generally generated in MRI, but in order to prevent this, data that is not subjected to phase encoding is obtained by prior measurement performed on the subject in advance, and each data in k-space is the inverse of its amplitude. Amplitude correction for multiplying is performed.
[0004]
[Problems to be solved by the invention]
However, in the amplitude correction described above, the signal intensity is attenuated by an exponential function. Therefore, when the ETL is large, the ratio of the signal intensity acquired first and the intensity of the subsequent signal becomes significantly smaller with time. Contrary to the significant decrease in the number of corrections, the correction amount extremely increases, so that the noise is increased at the same time, and the SN ratio is extremely deteriorated relatively.
SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic resonance imaging apparatus having a high rendering capability that reduces artifacts due to discontinuities in the phase direction of signals in k-space without lowering the signal-to-noise ratio in sequences with many ETLs. is there.
Another object of the present invention is to reduce artifacts derived from discontinuities in the phase direction of signals in k-space without reducing the signal-to-noise ratio in sequences with many ETLs while performing corrections that take into account the characteristics unique to the subject. An object of the present invention is to provide a magnetic resonance imaging apparatus with high imaging ability.
[0005]
[Means for Solving the Problems]
  In order to achieve the above object, a magnetic resonance imaging apparatus of the present invention comprises a static magnetic field generating means, a gradient magnetic field generating means for generating a gradient magnetic field in each direction of slice encoding, phase encoding, and frequency encoding, Using a transmission system that generates a high-frequency pulse that generates magnetic resonance by exciting the nuclei constituting the tissue, a reception system that detects an NMR signal from the subject by magnetic resonance, and an NMR signal detected by the reception system In a magnetic resonance imaging apparatus having a signal processing system for reconstructing an image and a sequencer that applies the gradient magnetic field and the high-frequency magnetic field in a predetermined sequence, the sequence encoding sequentially changes the phase-encoded gradient magnetic field by one excitation. A sequence for obtaining a plurality of NMR signals is executed, and the signal processing system applies a gradient magnetic field sign for the phase encoding. NMR signal from after the startMeasured valueIs the largest(The phase encoding is zero)BecomeOnly for measured data up toIt is characterized by performing a correction process.
  With such a configuration, according to the present invention, the data from the start of phase encoding in which the discontinuity of the signal leading to the artifact in the sequence with many ETLs is emphasized by the magnitude of the original signal intensity until the phase encoding 0 where the NMR signal is maximized. The correction is performed only for the value, and the value before the Fourier transform in the phase direction of the sharply decaying part is smoothed to effectively prevent the occurrence of artifacts, whereas the data after the value at which the signal becomes maximum is corrected. Is not performed, the data of the portion that attenuates relatively gently does not cause an increase in noise that deteriorates the SN ratio, and is derived from the discontinuity in the phase direction of the signal in the k space without decreasing the SN ratio. The present invention provides a magnetic resonance imaging apparatus with reduced imaging artifacts and high imaging performance.
[0006]
  The magnetic resonance imaging apparatus according to the present invention is aNoteThe positive processing is performed so that the measured values are symmetrical before and after the maximum point of the measured values.
  With this configuration, according to the present invention, the correction means performs a correction on the measurement value so that the NMR signal of the portion that rapidly attenuates according to the exponential function is symmetric with respect to a predetermined axis in the k space, and the discontinuity of the signal that leads to the artifact The data before the Fourier transformation in the phase direction is smoothed and the occurrence of artifacts is effectively prevented by correcting so that the data of the sharply decaying portion emphasized by the magnitude of the original signal is gently increased, Since the portion of the original signal that gently attenuates does not increase the noise that deteriorates the SN ratio, it is derived from the discontinuity in the phase direction of the signal in k-space without reducing the SN ratio in a sequence with many ETLs. Provided is a magnetic resonance imaging apparatus with high imaging performance with reduced artifacts.
[0007]
  The magnetic resonance imaging apparatus of the present invention isNoteThe positive processing is performed by correcting the signal intensity of the NMR signal detected by the receiving system.
  With such a configuration, data for correction is obtained directly from the subject. Therefore, the correction of the subject-specific characteristics is performed, and the signal in the k space is not reduced without reducing the SN ratio in a sequence with many ETLs. Provided is a magnetic resonance imaging apparatus with high rendering ability, in which artifacts due to discontinuities in the phase direction are reduced.
[0008]
  In the magnetic resonance imaging apparatus of the present invention, the correction processing is performed using correction data acquired without applying phase encoding to the NMR signal detected by the receiving system.
  With such a configuration, data for correction is obtained directly from the subject. Therefore, the correction of the subject-specific characteristics is performed, and the signal in the k space is not reduced without reducing the SN ratio in a sequence with many ETLs. Provided is a magnetic resonance imaging apparatus with high rendering ability, in which artifacts due to discontinuities in the phase direction are reduced.
  A correction function based on theoretical calculation can be used for the correction of the present invention.
  By doing so, the correction data is formed in the MRI apparatus in advance, and it is not necessary to perform a pre-measurement on the subject in order to obtain the correction data. Since tomographic image data can be obtained and the time required to bind the subject to the MRI apparatus is reduced without taking time for data acquisition, the SN ratio can be increased in a sequence with many ETLs without increasing the burden on the subject. Provided is a magnetic resonance imaging apparatus having a high rendering ability, in which artifacts derived from discontinuities in the phase direction of a signal on k-space are reduced without reduction.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a magnetic resonance imaging apparatus according to the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a block diagram showing a schematic overall configuration of an MRI apparatus to which the present invention is applied, FIG. 2 is a flowchart of the operation of the MRI apparatus of the present invention, and FIG. 3 is a diagram showing signals of a one-shot FSE sequence, 4 is a measurement value obtained by the MRI apparatus of the present invention, FIG. 5 is a diagram showing a signal before correction, FIG. 6 is a diagram showing correction data for correction, and FIG. 7 is a signal after correction. FIGS. 8 and 9 are trace diagrams of phase images obtained by the MRI apparatus of the present invention, and FIG. 10 is a diagram showing signals of a one-shot EPI sequence.
[0010]
FIG. 1 is a block diagram showing a schematic overall configuration of an MRI apparatus to which the present invention is applied. This MRI apparatus is for obtaining a tomographic image of a subject using a magnetic resonance phenomenon, and includes a static magnetic field generation means 1, a gradient magnetic field generation means 2, a transmission system 3, a reception system 4, a signal processing system 5, and a sequencer. 6, the central processing unit 7 and an operation unit (not shown).
The static magnetic field generating means 1 is composed of either a permanent magnet, a normal conducting magnet, or a superconducting magnet arranged in a wide space around the subject 8, and around the subject 8 in the direction of the body axis or the subject. A uniform static magnetic field is generated in a direction perpendicular to the body axis of the specimen.
The gradient magnetic field generating means 2 comprises a gradient magnetic field coil 9 wound in the X, Y and Z axis directions and a gradient magnetic field power source 10 for magnetizing each of these coils. By magnetizing each of the 10 coils, gradient magnetic fields Gs, Gp, and Gf in the three-axis directions of X, Y, and Z are applied to the subject 8. Depending on how the gradient magnetic field is applied, a cross-section for imaging and displaying the subject 8 is set.
[0011]
The transmission system 3 includes a high-frequency oscillator 11, a modulator 12, a high-frequency amplifier 13, and a high-frequency irradiation coil 14, and atomic nuclei constituting the biological tissue of the imaging section of the subject 8 set by the gradient magnetic field generating means 2. In order to excite and cause nuclear magnetic resonance, the high-frequency pulse output from the high-frequency oscillator 11 is amplified by the high-frequency amplifier 13 and then supplied to the high-frequency irradiation coil 14 installed in the vicinity of the subject 8. Irradiate.
The reception system 4 includes a high-frequency reception coil 15, a reception circuit 16, and an analog / digital (hereinafter referred to as “A / D”) converter 17, and the subject 8 caused by electromagnetic waves irradiated from the high-frequency irradiation coil 14 of the transmission system 3. NMR signals, which are echo signals generated by magnetic resonance of the nuclei of the living tissue, are detected by the high-frequency receiving coil 15 arranged close to the subject 8 and input to the A / D converter 17 via the receiving circuit 16. Then, the signal is converted into a digital signal, and the signal is sent to the signal processing system 5 as collected data sampled at a timing according to a command from the sequencer 6.
[0012]
The signal processing system 5 includes a CPU 7 that performs Fourier transformation and control of the sequencer 6 on the collected data, and a signal processing device that includes correction means of the present invention and performs processing necessary for reconstructing correction calculations and collected data into tomographic images. 18. Stores time-series image analysis processing and designated measurement sequence programs, parameters used for the execution, etc., and measurement parameters and reception system 4 obtained in advance measurement performed on the subject. A memory 19 for temporarily storing the collected data from the NMR signal detected in step 1 and an image used for setting the region of interest and storing parameters for setting the region of interest; a data storage unit for storing the reconstructed image data; The magnetic disk 20 and optical disk 21 and the image data read from these disks are visualized and displayed as tomographic images. Consists displaying 22. displays an image performs image reconstruction operation using the NMR signal detected by the receiving system 4.
The sequencer 6 operates under the control of the CPU 7 and repeatedly generates slice encoding, phase encoding, and frequency encoding gradient magnetic fields and high frequency magnetic field pulses in a predetermined pulse sequence, and obtains tomographic image data of the subject 8. Various commands necessary for the above are sent to the gradient magnetic field generating means 2, the transmission system 3, and the reception system 4.
The operation unit includes a trackball, a mouse, a keyboard, or the like, and inputs control information for processing performed by the signal processing system 5.
[0013]
The operation of the MRI apparatus of the present invention proceeds according to the flow shown in FIG. 2, and pulses of the sequence shown in FIG. 3 are applied to the subject in the case of the FSE method and FIG. 10 in the case of the EPI method. Since the data shown in FIG. 5-7 is acquired in order to compose the data in the k-space shown in FIG. 4, the operation for each step will be described based on the flow shown in FIG. Refer to the other drawings each time.
For the correction of the present invention, a correction function based on a theoretical calculation created in advance and stored in the memory 19 can be used. In this case, good tomographic image data of the subject can be obtained immediately from the first measurement.
It is also possible to use correction data acquired by prior measurement performed without applying a phase encoding gradient magnetic field to the subject. In this case, characteristics specific to the subject are added to the correction data. Either one of these methods can be installed in the MRI apparatus, or both can be installed and selected and designated each time. Hereinafter, two examples using the correction function by the FSE method and one example using the correction data acquired by the prior measurement by the EPI method will be described. In any case, the flow of operations related to correction is the same as shown in FIG. 2, and the pulse sequence for capturing a tomographic image and the method of creating data for correction calculation are different.
[0014]
FIG. 2 is a flowchart for explaining procedures of measurement and image processing in the MRI apparatus of the present invention.
When the MRI apparatus of the present invention is activated, first, in step 101, an imaging sequence with a large ETL is selected by the operation unit, and the FSE method is set in this embodiment. Imaging parameters necessary for this sequence are output from the memory 19. Next, the CPU 7 inquires whether correction is performed and whether the correction uses a function. In this embodiment, since a correction function created in advance is used, when such an input is made to the operation unit, the CPU 7 reads out a correction function, which will be described later, necessary for image processing created in advance, and stores it in the memory 19. If correction is not performed, the process proceeds to Steps 303 and 305, and the same image pickup as before is performed, and thus will not be described here. The case where the correction function is not used will be described in detail in another embodiment.
[0015]
Next, in step 103, a sequence of the FSE method with many ETLs is executed.
FIG. 3 shows a one-shot FSE sequence in which 128 data in half of the k-space are acquired by one excitation performed here and the remaining 128 data are estimated.
In this sequence, as shown in FIG. 3, a high-frequency 90-degree pulse RF is applied simultaneously with the gradient magnetic field pulse Gs for selecting a cross section, and then a high-frequency 180-degree pulse RF for generating a spin echo signal is applied simultaneously with the gradient magnetic field pulse Gs. The procedure of applying the gradient magnetic field Gp for phase encoding the readout gradient magnetic field pulse Gf and the echo signal and measuring the echo signal is repeated 128 times while the ETL is 128 here, and the phase encoding Gp is changed to a total of 128 ways. The k space is filled.
[0016]
Next, at step 105, the obtained data is stored in the memory 19.
FIG. 4 is a view showing measured values of tomographic images obtained by the MRI apparatus of the present invention. The CPU 7 processes the measurement values, calculates the estimation unit data from the actual measurement data and stores them in ky = 15 to 112 in the k space, and the obtained data is stored in ky = 113 to 241 in the k space.
[0017]
Next, since correction by the correction function is selected in this embodiment, at the time of reconstruction of the image, correction by the correction function is performed on the measured value in step 107. In this correction, the first measurement data after the start of phase encoding of the actual measurement data is set to ky = p + 1 (here, ky = 113 in FIG. 4), and the maximum measurement value is always monitored by monitoring the magnitude relationship with the previous measurement value. For n data (here, n = 16) ky = p + m data (here, ky = 112 + m) up to phase encode 0 data (here, ky = 128 in FIG. 4), Correction function
w (p + m) = exp (2 × echo interval × (mn) / time constant)
Is multiplied by the original measured value. Here, m is 1 to n, and no correction is performed for m> m. That is, correction is performed on n (16 here) data from ky = p + 1 (here ky = 113) to ky = p + n (here ky = 128). For data of ky = p + n, the correction coefficient is 1 because m = n. The time constant is an arbitrary value, and it is preferable to select the value from the TE of the sequence to the T2 value of the signal causing the artifact while observing the effect on the image. Here, the sequence TE of 248 ms is selected. is doing.
[0018]
As described above, in this embodiment, correction is performed so that the value of the signal in the k space is symmetric about the zero point of phase encoding until the measured value of the NMR signal becomes maximum after the phase encoding is started. ing.
FIG. 5 shows measured values before correction, FIG. 6 shows correction data obtained by the correction function, and FIG. 7 shows corrected data after multiplication. In FIG. 7, the data immediately after the start of phase encoding is gently corrected, and it can be read here that the data is symmetrically aligned in the ky direction with the 0 encoding point where ky = 128 as the axis.
Based on the data corrected in step 107 by the correction means in step 107, the image is reconstructed in step 109 to complete the MRI of the subject.
[0019]
Next, another embodiment will be described. This example differs from the above-described embodiment in that a correction coefficient α is further added to the correction function, and the use of other imaging sequences and correction functions is the same.
Here, as in the first embodiment, phase encoding 0 (here, ky in FIG. 4) that obtains the maximum value of the signal from the first ky = p + 1 (here, ky = 113) data after the start of phase encoding. = 128) up to n (here, n = 16) ky = p + m data, the correction function expressed below
w (p + m) = exp (α × 2 × echo interval × (mn) / time constant)
Correction is performed by multiplying. As in the first embodiment, m is 1 to n, and no correction is performed for m> m. The correction coefficient α is an arbitrary value between 0 and 1 and has an optimum value depending on the type of sequence. However, the correction coefficient α may be appropriately selected while checking the image so that the phase image of the actual acquired data of each sequence has the smallest artifact. .
[0020]
FIGS. 8 and 9 are trace diagrams of imaging results of phase images in which two types of test phantoms are imaged by changing the correction coefficient α using the FSE method sequence. FIGS. 8a and b are normal nickel chloride phantoms, FIGS. 9a and b are MRCP phantoms, FIGS. 8a and 9a are α = 1, FIGS. 8b and 9b are the results after correction coefficient multiplication, and FIG. α = 0.7, FIG. 9B shows α = 0.4, and these indicate that the time constants are all 248 ms, which is the TE of the sequence. In FIGS. 8b and 9b, it can be seen that the striped vortex of the artifact is eliminated and each phantom image is accurately displayed in a circle. By using this formula, it is not necessary to select the time constant in the formula of the first embodiment, and the work can be simplified by fixing it to TE of the sequence or an arbitrary value approximate thereto, and the result is confirmed by the phase image. However, the coefficient α may be determined in the range of 0-1.
[0021]
In the third embodiment, the first and second points are that the EPI method is set as a sequence with many ETLs in step 101, and the correction data unique to the subject obtained by the measurement performed in advance is used as the correction data. This is different from the embodiment.
FIG. 10 is a diagram showing a signal of a one-shot EPI sequence that takes in 128 pieces of data in half of k-space by one excitation performed in this embodiment and estimates the remaining 128 pieces of data.
In this sequence, as shown in FIG. 10, the cross-section selective gradient magnetic field Gs is applied simultaneously with the application of the high-frequency pulse RF to perform excitation by the RF pulse at a resonance frequency corresponding to a predetermined cross-section, and then simultaneously with the cross-section gradient magnetic field Gs. After applying the phase encoding gradient magnetic field Gp, a read magnetic field Gf and a phase encoding magnetic field Gp whose polarities are reversed are applied. In this example, since ETL is 128, 128 echo signals are detected every time the gradient magnetic field is inverted 128 times, and the k space is filled.
[0022]
In the third embodiment, since the subject-specific data is used as the correction data, in the step 201, the first data after the start of phase encoding is again applied without applying Gp in advance in the pulse sequence shown in FIG. If ky = p + 1 (here, ky = 113), the phase encode 0 data that always obtains the maximum measured value by monitoring the magnitude relationship with the immediately previous measured value is ky = p + n (here, ky = 128). ky = 113 to 113 + 2n data is acquired, and the following formula
mth correction data = (2n−m) th data / mth data
To obtain correction data.
Here, m = 1 to n and n = 16, and no correction is performed for data of m> n.
[0023]
In the above expression, ky = p + m that is the m-th data is divided by the value of the m-th data itself and multiplied by the value of ky = p + 2n-m that is the (2n−m) th data. m) It can be clearly understood that data of ky = p + n (here, ky = 128) having the same value as that of the ith data, that is, having a phase encoding of 0, is symmetrically distributed in the ky direction. After acquiring the correction data according to this rule and storing it in the memory 19, in step 203 this time Gp is applied and phase encoding is performed, and the subject is imaged in the same manner as in the first embodiment, and measured in step 205. In step 207, the correction means corrects the measured value of ky = p + m by multiplying the correction data by the correction data, and in step 109, the image data is reconstructed to display a tomographic image to display the MRI. finish.
As a result, even in this embodiment, the value of the NMR signal in the k space obtained from the start of phase encoding until the measured value of the NMR signal becomes maximum and without applying phase encoding is symmetrical about the zero point of phase encoding. The correction is performed.
[0024]
Although the above embodiment describes an example in which data correction is performed before Fourier transformation for image reconstruction, the correction of the present invention only needs to be performed before Fourier transformation in the phase direction. Even if the correction of the present invention is performed after the Fourier transform in the frequency direction, the same effect is obtained.
In the above embodiment, the one-shot half-scan sequence has been described. However, the apparatus of the present invention can perform an optional ETL for both a multi-shot sequence and a full-scan sequence by repeating correction of the number of shots. It is applicable to a sequence with many
[0025]
In the first and second embodiments, the correction value is assumed to be axially symmetric with respect to the phase encode 0 point after the correction calculation, but the phase encode that maximizes the measured value obtained as the NMR signal. If the correction is performed up to the zero point, the portion in which the discontinuity of the signal in the phase direction is emphasized by the intensity of the original signal is eliminated, so that a sufficient effect can be obtained even with the conventionally performed amplitude correction.
In this case, if the NMR signal obtained without applying phase encoding is corrected, the value of the NMR signal in the k-space becomes a straight line up to the zero point of phase encoding, and thereafter becomes a curve that attenuates smoothly with an exponential function. .
[0026]
In the above embodiment, the correction function based on the theoretical calculation is an exponential function. However, if the graph of the measured value is symmetrical with respect to the phase encode 0 point after correction, the correction function is approximated. Any function can be used.
Further, in the above-described embodiment, the example in which the correction unit is configured as hardware in the signal processing device 18 has been described. However, the correction function and the correction data may be stored in the memory 19 as a software program and executed by the CPU 7. It is.
[0027]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
According to the MRI apparatus of the present invention, from the start of phase encoding in which the discontinuity of the signal leading to the artifact is emphasized by the magnitude of the original signal intensity in the sequence with many ETLs, the phase encoding from 0 to the phase encoding 0 where the NMR signal becomes the maximum. The correction is performed only on the data, and the value before the Fourier transform in the phase direction of the sharply decaying part is smoothed to effectively prevent the occurrence of artifacts, whereas the data after the value where the signal becomes maximum Since no correction is performed, the data of the portion that attenuates relatively gently does not cause an increase in noise that deteriorates the SN ratio, and does not decrease the SN ratio, resulting in a discontinuity in the phase direction of the signal in the k space. Provided is a magnetic resonance imaging apparatus with high rendering ability, in which artifacts derived therefrom are reduced.
[0028]
Further, according to the MRI apparatus of the present invention, the correction means performs correction on the measurement value so that the NMR signal of the portion that rapidly attenuates according to the exponential function is symmetric with respect to a predetermined axis in the k space, and the signal that leads to the artifact is obtained. The data before the Fourier transform in the phase direction is smoothed by correcting the data so that the discontinuity is emphasized by the magnitude of the original signal, and the data in the abrupt decay is gradually increased, effectively preventing artifacts from occurring. In addition, since the noise that deteriorates the S / N ratio is not increased in the gently attenuated portion of the original signal, the discontinuity in the phase direction of the signal in the k space does not decrease without reducing the S / N ratio in a sequence with many ETLs. Provided is a magnetic resonance imaging apparatus with high rendering ability, in which artifacts derived therefrom are reduced.
Furthermore, according to the MRI apparatus of the present invention, data for correction is obtained directly from the subject, so that correction considering the subject-specific characteristics is performed and the SN ratio is not lowered in a sequence with many ETLs. Provided is a magnetic resonance imaging apparatus with high rendering ability, in which artifacts derived from discontinuities in the phase direction of signals in k space are reduced.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an MRI apparatus.
FIG. 2 is a flowchart of the operation of the MRI apparatus of the present invention.
FIG. 3 is a pulse diagram of a one-shot FSE sequence.
FIG. 4 is a cross-sectional measurement value obtained by the MRI apparatus of the present invention.
FIG. 5 is a diagram showing acquired data before correction.
FIG. 6 is a diagram showing correction data for correction.
FIG. 7 is a view showing a signal after correction.
FIG. 8 is a trace diagram of a phase image obtained by the MRI apparatus of the present invention.
FIG. 9 is a trace diagram of a phase image obtained by the MRI apparatus of the present invention.
FIG. 10 is a pulse diagram of a one-shot EPI sequence.
[Explanation of symbols]
1 ... Static magnetic field generation means
2 ... Gradient magnetic field generation means
3 ... Transmission system
4 ... Receiving system
5 .... Signal processing system
6: Sequencer
7 ……… CPU
8 ……… Subject

Claims (4)

Static magnetic field generation means, gradient magnetic field generation means for generating gradient magnetic fields in each direction of slice encoding, phase encoding, and frequency encoding, and high-frequency pulses that generate magnetic resonance by exciting nuclei constituting the tissue of the subject A transmission system, a reception system for detecting an NMR signal from a subject by magnetic resonance, a signal processing system for reconstructing an image using the NMR signal detected by the reception system, and the gradient magnetic field and the high-frequency magnetic field are predetermined. In a magnetic resonance imaging apparatus having a sequencer for applying in the sequence of
In the sequencer, a sequence for obtaining a plurality of NMR signals by sequentially changing the gradient magnetic field of phase encoding by one excitation is executed,
In the signal processing system, a correction process is performed only on actually measured data from when the application of the gradient magnetic field of the phase encoding is started until the measured value of the NMR signal becomes maximum (the phase encoding is zero). Resonance imaging device. Before Kiho positive process,
The magnetic resonance imaging apparatus according to claim 1, wherein the measurement is performed so that the measurement value is symmetric before and after the maximum point of the measurement value. Before Kiho positive process,
The magnetic resonance imaging apparatus according to claim 1, which is performed by correcting a signal intensity of an NMR signal detected by the receiving system. The correction process is as follows:
The magnetic resonance imaging apparatus according to claim 1, which is performed using correction data acquired without applying phase encoding to the NMR signal detected by the receiving system.

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