JP2004202043A - Magnetic resonance imaging equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging device which can image properly regardless of any change in breathing condition. <P>SOLUTION: The magnetic resonance imaging device obtains navigator echoes from an imaged object repeatedly (505) to produce profile of the object based on the navigator echoes (507), and determines whether the breathing phase matches the predetermined phase or not (511), based on the intensity of the signal from the profile at the predetermined point. The magnetic resonance imaging device alters the determined phase, when the breathing phase does not match the predetermined phase more frequent than the preset limit (537), and obtains an imaging echo (523) at the predetermined breathing phase from the object based on the phase decision to create an image based on the imaging echo (527). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus, and more particularly, to a magnetic resonance imaging apparatus using a navigator echo.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a magnetic resonance imaging apparatus acquires a navigator echo in the course of performing imaging and corrects an imaging result using the navigator echo (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP 2001-276017 A (pages 7-10, FIG. 3-7)
[0004]
[Problems to be solved by the invention]
When a profile of a subject to be photographed is created based on the navigator echo, the phase of the subject's respiration is determined based on the signal intensity of the profile at a predetermined determination point, and an image of a predetermined respiratory phase is taken, Due to a change over time in the state or the like, the initially set determination point may not be appropriate, and the photographing may be inaccurate.
[0005]
Therefore, an object of the present invention is to realize a magnetic resonance imaging apparatus that performs correct imaging irrespective of a change in respiratory state.
[0006]
[Means for Solving the Problems]
(1) According to one aspect of the present invention, there is provided a navigator echo acquiring unit that repeatedly acquires a navigator echo from a subject to be photographed, and a creating unit that creates a target profile based on the navigator echo. Determining means for determining whether or not the respiratory phase of the subject matches a predetermined phase based on the signal strength of the profile at a predetermined location, and the respiratory phase does not match the predetermined phase Correction means for correcting the determination point of the determination means when the frequency exceeds a predetermined limit, Imaging echo acquisition means for acquiring an imaging echo in a predetermined respiratory phase from the subject of imaging based on the determination Generating means for generating an image based on the imaging echo. It is a ringing imaging apparatus.
[0007]
(2) Another aspect of the present invention for solving the above-described problems is an acquisition unit that repeatedly acquires a navigator echo and an imaging echo, a creation unit that creates a target profile based on the navigator echo, Determining means for determining whether or not the respiratory phase matches a predetermined phase based on the signal intensity of the profile at a predetermined location, and a frequency at which the respiratory phase does not match the predetermined phase is determined in advance. Correction means for correcting the determination point of the determination means when exceeding a predetermined limit, adoption means for adopting an imaging echo in a predetermined respiratory phase among the imaging echoes based on the determination, Generating means for generating an image based on an imaged echo. It is a shadow system.
[0008]
In the invention in each of the above aspects, the correction unit corrects the determination point of the determination unit when the frequency at which the respiratory phase does not match the predetermined phase exceeds a predetermined limit, so that the correction unit is not affected by the change in the respiratory state. The correct shooting can be performed.
[0009]
It is preferable that the navigator echo is a spin echo in that a signal appropriate as the navigator echo is obtained. It is preferable that the imaging echo is a gradient echo from the viewpoint of obtaining a signal appropriate as the imaging echo. It is preferable that the profile is a one-dimensional profile in the body axis direction in that the determination of the respiratory phase is easy. It is preferable that the predetermined phase is an expiration phase from the viewpoint of taking an image of the expiration phase. It is preferable that the predetermined phase is an intake phase in that an image of the intake phase is taken. It is preferable that the frequency is the number of times or the time when the respiratory phase does not match the predetermined phase, in that the frequency appropriately corresponds to the change in the respiratory state.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the magnetic resonance imaging apparatus. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.
[0011]
As shown in the figure, the present apparatus has a magnet system (magnet system) 100. The magnet system 100 includes a main magnetic field coil unit 102, a gradient coil unit 106, and an RF (radio frequency) coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other. A subject 1 to be photographed is mounted on a cradle 500 and carried into and out of a generally cylindrical internal space (bore) of the magnet system 100 by a transport means (not shown).
[0012]
The main magnetic field coil unit 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is substantially parallel to the direction of the body axis of the subject 1. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. In addition, you may comprise using not only a superconducting coil but a normal conduction coil.
[0013]
The gradient coil unit 106 generates three gradient magnetic fields for giving a gradient to the static magnetic field strength in three directions perpendicular to each other, that is, in a slice axis, a phase axis, and a frequency axis.
[0014]
When coordinate axes perpendicular to each other in the static magnetic field space are x, y, and z, any of the axes can be a slice axis. In that case, one of the remaining two axes is a phase axis, and the other is a frequency axis. Further, the slice axis, the phase axis, and the frequency axis can have an arbitrary inclination with respect to the x, y, and z axes while maintaining the perpendicularity among them. This is also called oblique. In this apparatus, the direction of the body axis of the object 1 is defined as the z-axis direction.
[0015]
The gradient magnetic field in the slice axis direction is also called a slice gradient magnetic field. The gradient magnetic field in the phase axis direction is also referred to as a phase encode gradient magnetic field or a phase encode gradient magnetic field. The gradient magnetic field in the frequency axis direction is also referred to as a read out gradient magnetic field. The readout gradient magnetic field is synonymous with the frequency encoding gradient magnetic field. In order to enable generation of such a gradient magnetic field, the gradient coil section 106 has three gradient coils (not shown). Hereinafter, the gradient magnetic field is also simply referred to as a gradient.
[0016]
The RF coil unit 108 forms a high-frequency magnetic field for exciting a spin in the body of the subject 1 in the static magnetic field space. Hereinafter, forming a high-frequency magnetic field is also referred to as transmitting an RF excitation signal. The RF excitation signal is also called an RF pulse. An electromagnetic wave generated by the excited spin, that is, a magnetic resonance signal is received by the RF coil unit 108.
[0017]
The magnetic resonance signal is a signal in a frequency domain, that is, a Fourier space. Since the magnetic resonance signal is encoded in two axes by the gradients in the phase axis direction and the frequency axis direction, the magnetic resonance signal is obtained as a signal in a two-dimensional Fourier space. The phase encode gradient and the readout gradient determine the sampling position of the signal in two-dimensional Fourier space. Hereinafter, the two-dimensional Fourier space is also referred to as a k-space.
[0018]
The gradient driving unit 130 is connected to the gradient coil unit 106. The gradient driving unit 130 supplies a driving signal to the gradient coil unit 106 to generate a gradient magnetic field. The gradient drive unit 130 has three drive circuits (not shown) corresponding to the three gradient coils in the gradient coil unit 106.
[0019]
The RF driving section 140 is connected to the RF coil section 108. The RF driving unit 140 supplies a driving signal to the RF coil unit 108 to transmit an RF pulse to excite spins in the body of the subject 1.
[0020]
The data collection unit 150 is connected to the RF coil unit 108. The data collection unit 150 collects a reception signal received by the RF coil unit 108 as digital data.
[0021]
A sequence control unit 160 is connected to the gradient driving unit 130, the RF driving unit 140, and the data collection unit 150. The sequence controller 160 controls the gradient driver 130 to the data collector 150 to collect magnetic resonance signals.
[0022]
The sequence control unit 160 is configured using, for example, a computer. The sequence control unit 160 has a memory (not shown). The memory stores a program for the sequence control unit 160 and various data. The function of the sequence control unit 160 is realized by the computer executing a program stored in the memory.
[0023]
The output side of the data collection unit 150 is connected to the data processing unit 170. The data collected by the data collection unit 150 is input to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer or the like. The data processing unit 170 has a memory (not shown). The memory stores a program for the data processing unit 170 and various data.
[0024]
The data processing unit 170 is connected to the sequence control unit 160. The data processing unit 170 is above the sequence control unit 160 and controls it. The function of the present apparatus is realized by the data processing unit 170 executing a program stored in the memory.
[0025]
The data processing unit 170 stores the data collected by the data collection unit 150 in a memory. A data space is formed in the memory. This data space corresponds to k-space. The data processing unit 170 reconstructs an image by performing two-dimensional inverse Fourier transform on k-space data.
[0026]
The display section 180 and the operation section 190 are connected to the data processing section 170. The display unit 180 is configured by a graphic display or the like. The operation unit 190 includes a keyboard provided with a pointing device.
[0027]
The display unit 180 displays the reconstructed image output from the data processing unit 170 and various information. The operation unit 190 is operated by a user, and inputs various commands and information to the data processing unit 170. The user operates the present apparatus interactively through the display unit 180 and the operation unit 190.
[0028]
FIG. 2 shows a block diagram of another type of magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus shown in the figure is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.
[0029]
This apparatus has a magnet system 100 'that differs from the apparatus shown in FIG. Except for the magnet system 100 ', the configuration is the same as that of the apparatus shown in FIG. 1, and the same parts are denoted by the same reference numerals and description thereof will be omitted.
[0030]
The magnet system 100 'has a main magnetic field magnet unit 102', a gradient coil unit 106 ', and an RF coil unit 108'. Each of the main magnetic field magnet section 102 'and each coil section is composed of a pair of coils opposing each other across a space. Each of them has a substantially disk shape and is arranged so as to share a central axis. The target 1 is mounted on the cradle 500 and carried into and out of the internal space (bore) of the magnet system 100 ′ by a conveying means (not shown).
[0031]
The main magnetic field magnet unit 102 'forms a static magnetic field in the internal space of the magnet system 100'. The direction of the static magnetic field is substantially orthogonal to the direction of the body axis of the subject 1. That is, a so-called vertical magnetic field is formed. The main magnetic field magnet unit 102 'is configured using, for example, a permanent magnet. In addition, you may comprise using not only a permanent magnet but a superconducting electromagnet or a normal conducting electromagnet.
[0032]
The gradient coil unit 106 'generates three gradient magnetic fields for giving gradients to the static magnetic field strength in directions of three axes perpendicular to each other, namely, the slice axis, the phase axis, and the frequency axis.
[0033]
When coordinate axes perpendicular to each other in the static magnetic field space are x, y, and z, any of the axes can be a slice axis. In that case, one of the remaining two axes is a phase axis, and the other is a frequency axis. Further, the slice axis, the phase axis, and the frequency axis can have an arbitrary inclination with respect to the x, y, and z axes while maintaining perpendicularity between them, that is, oblique. Also in this apparatus, the direction of the body axis of the object 1 is defined as the z-axis direction. In order to enable the generation of a gradient magnetic field in three axial directions, the gradient coil unit 106 'has three gradient coils (not shown).
[0034]
The RF coil unit 108 'transmits an RF pulse for exciting spins in the body of the subject 1 to the static magnetic field space. An electromagnetic wave generated by the excited spin, that is, a magnetic resonance signal is received by the RF coil unit 108'. The reception signal of the RF coil unit 108 'is input to the data collection unit 150.
[0035]
FIG. 3 shows an example of a pulse sequence used for magnetic resonance imaging. This pulse sequence is a pulse sequence of a spin echo (SE: SpinEcho) method.
[0036]
That is, (1) is a sequence of 90 ° and 180 ° pulses for RF excitation in the SE method, and (2), (3), (4), and (5) are the slice gradient Gs and the read, respectively. This is a sequence of an out gradient Gr, a phase encoding gradient Gp, and a spin echo MR. Each of the 90 ° pulse and the 180 ° pulse is represented by a center signal. The pulse sequence proceeds from left to right along the time axis t.
[0037]
As shown in the figure, 90 ° excitation of spin is performed by a 90 ° pulse. At this time, a slice gradient Gs is applied, and selective excitation for a predetermined slice is performed. After a predetermined time from the 90 ° excitation, 180 ° excitation by a 180 ° pulse, that is, spin inversion is performed. Also at this time, the slice gradient Gs is applied, and selective inversion is performed for the same slice.
[0038]
During a period between the 90 ° excitation and the spin inversion, the readout gradient Gr and the phase encode gradient Gp are applied. Spin dephase is performed by the readout gradient Gr. The phase encoding of the spin is performed by the phase encoding gradient Gp.
[0039]
After the spin inversion, the spin is rephased by the readout gradient Gr to generate a spin echo MR. The spin echo MR is collected by the data collection unit 150 as view data. Such a pulse sequence is repeated 64 to 512 times in a cycle TR (repetition time). The phase encoding gradient Gp is changed for each repetition, and different phase encoding is performed each time. Thus, view data of 64 to 512 views is obtained.
[0040]
FIG. 4 shows another example of the pulse sequence for magnetic resonance imaging. This pulse sequence is a pulse sequence of a gradient echo (GRE) method.
[0041]
That is, (1) is a sequence of α ° pulses for RF excitation in the GRE method, and (2), (3), (4), and (5) are the slice gradient Gs, readout gradient Gr, It is a sequence of a phase encoding gradient Gp and a gradient echo MR. The α ° pulse is represented by the center signal. The pulse sequence proceeds from left to right along the time axis t.
[0042]
As shown in the figure, α ° excitation of spin is performed by an α ° pulse. α is 90 or less. At this time, a slice gradient Gs is applied, and selective excitation for a predetermined slice is performed.
[0043]
After α ° excitation, spin phase encoding is performed by the phase encoding gradient Gp. Next, the spin is first dephased by the readout gradient Gr, and then the spin is rephased to generate a gradient echo MR. The gradient echo MR is collected by the data collection unit 150 as view data. Such a pulse sequence is repeated 64 to 512 times in the period TR. The phase encoding gradient Gp is changed for each repetition, and different phase encoding is performed each time. Thus, view data of 64 to 512 views is obtained.
[0044]
View data obtained by the pulse sequence of FIG. 3 or 4 is collected in the memory of the data processing unit 170. Note that the pulse sequence is not limited to the SE method or the GRE method, and may be another appropriate technique such as a fast spin echo (FSE) method. The data processing unit 170 reconstructs an image based on the view data collected in the memory.
[0045]
Such imaging is performed for a predetermined phase of the respiration of the subject 1. That is, respiratory-gated imaging is performed. FIG. 5 shows a flow chart of the operation of the apparatus when performing respiratory-gated imaging.
[0046]
As shown in the figure, in step 501, phase designation is performed. FIG. 6 shows a flowchart of the phase designation. As shown in the figure, in step 601, navigator echo acquisition is performed. A pulse sequence as shown in FIG. 7 is used for acquiring the navigator echo. This pulse sequence corresponds to the pulse sequence of the spin echo method shown in FIG. 3 in which the phase encoding gradient Gp is set to 0.
[0047]
Using such a pulse sequence, as shown in FIG. 8, a 90 ° excitation is performed on the slice A of the target 1, a 180 ° excitation is performed on the slice B, and a spin echo generated from a straight line portion C where both slices intersect with each other. Read as navigator echo. The slices A and B are set such that the straight line portion C is substantially parallel to the body axis, deviates from the body axis, and extends from the lung field to the abdomen.
[0048]
Note that 90 ° excitation may be performed on slice B and 180 ° excitation may be performed on slice A. The slices A and B are basically set at positions where the navigator echo can be appropriately acquired irrespective of a slice for acquiring an imaging echo described later.
[0049]
Next, in step 603, a profile is created. Profile creation is performed by one-dimensional inverse Fourier transform of the navigator echo. As a result, a signal intensity distribution of spins on the straight line C, that is, a one-dimensional profile is obtained.
[0050]
Next, in step 605, a profile is displayed. As a result, the profile is displayed on the display unit 180. Since the straight line C is set from the lung field to the abdomen, for example, a profile as shown in FIG. 9 is obtained. This profile has a large difference in signal strength at the middle part. A portion where the signal intensity is low corresponds to the lung field, a portion where the signal intensity is high corresponds to the abdomen, and the middle portion corresponds to the diaphragm.
[0051]
The portion corresponding to the diaphragm reciprocates in the body axis direction with respiration. Hereinafter, a portion corresponding to the diaphragm is also simply referred to as a diaphragm. FIG. 10 shows the displacement of the diaphragm due to respiration. As shown in the figure, the diaphragm moves toward the abdomen during inspiration and moves toward the chest during expiration.
[0052]
Next, in step 607, a phase determination point is set on the profile. The setting of the phase determination point is performed by the user using the operation unit 190. Thereby, for example, one point on the body axis is set as the phase determination point P. The phase determination point P is set to a desired position between the maximum displacement position during inspiration of the diaphragm and the maximum displacement position during expiration.
[0053]
11 to 13 show three examples of the setting of the phase determination point P, respectively. FIG. 11 shows an example in which the setting is made closer to the exhalation side. With such settings, the expiration phase is designated as the imaging phase. FIG. 12 shows an example in which it is set closer to the intake side. By such setting, the intake phase is designated as the imaging phase. FIG. 13 shows an example in which the value is set between the expiration and the inspiration. Thus, an intermediate phase between the expiration and the inspiration is specified.
[0054]
The respiratory phase is determined based on whether or not the diaphragm is within a range of a predetermined distance ± α centering on the phase determination point P. Hereinafter, this range is also referred to as a determination area. In the setting as shown in FIG. 11, when the diaphragm is in the determination region, it is determined to be the expiratory phase, as indicated by the broken line.
[0055]
Detection of whether the diaphragm is in the determination area is performed based on the shape of the profile in the determination area. The profile is easy to detect because the signal intensity changes significantly at the diaphragm. In the setting shown in FIG. 12, when the diaphragm enters the determination area, it is determined that the phase is the expiration phase. In the setting shown in FIG. 13, it is determined that the phase is intermediate between expiration and inspiration.
[0056]
Returning to FIG. 5, in step 505, acquiring a navigator echo is performed. The acquisition of the navigator echo is performed in the same manner as in step 601 in FIG. That is, it is obtained as a spin echo. Since the spin echo is generated by 90 ° excitation and 180 ° excitation, it is suitable as a navigator echo for obtaining a profile.
[0057]
Next, in step 507, a profile is created. The profile creation is performed by using the navigator echo, similarly to step 601 in FIG. As a result, a profile similar to the profile shown in FIG. 9 is obtained.
[0058]
Next, in step 511, it is determined whether or not the phase is the designated phase. The determination of whether or not the phase is the designated phase is performed based on whether or not the diaphragm exists in the determination area, as described above.
[0059]
If the phase is the designated phase, in step 523, imaging echo acquisition is performed. The acquisition of the imaging echo is performed by, for example, the pulse sequence shown in FIG. 3 or the pulse sequence shown in FIG. The pulse sequence method of the gradient echo method shown in FIG. 4 is preferable in that an imaging echo, that is, a gradient echo can be obtained by one RF excitation. The imaging echo acquisition is performed for an appropriate number of views from one view to several views.
[0060]
Next, in step 525, it is determined whether or not all views have been acquired. If not, the process returns to step 505. Hereinafter, when the respiratory phase matches the designated phase and not all views have been adopted, the operations of steps 505 to 525 are repeated. By such an operation, imaging echoes in the respiratory phase coinciding with the designated phase are sequentially acquired.
[0061]
If it is determined in step 511 that the phase is not the designated phase, it is determined in step 535 whether the mismatch frequency has exceeded the limit. If not, the process returns to step 505. Hereinafter, when the respiratory phase does not match the designated phase and the frequency does not exceed the limit, the operations of steps 505 to 535 are repeated. Thus, during the phase mismatch, only the navigator echo is acquired and no imaging echo is acquired.
[0062]
Due to the periodicity of breathing, phase mismatches occur periodically. Therefore, an allowable limit is set for the frequency of mismatch. This limit is, for example, the number of mismatches within a certain time. Alternatively, the duration may be a mismatch.
[0063]
By repeating the operations of Steps 505 to 525 and the operations of Steps 505 to 535, an imaging echo during a period when the respiratory phase matches the designated phase is acquired. The number of times of mismatch or the measurement of time is reset each time the phases match.
[0064]
In the course of such an operation, the breathing state changes due to falling asleep or the like of the subject over time, and the profile may become as shown in FIG. 14 or FIG. 15, for example. FIG. 14 shows a state in which the movement range of the diaphragm has moved to the intake side, and the determination region has relatively deviated from the movement range of the diaphragm. FIG. 15 shows a state in which the movement range of the diaphragm has moved to the expiration side, and the determination region has relatively deviated from the movement range of the diaphragm.
[0065]
In such a case, since the diaphragm does not enter the determination area even though breathing is continued, it is always determined that the phases do not match. For this reason, the number of mismatches or the mismatch time eventually exceeds the limit.
[0066]
If the limit has been exceeded, in step 537, the phase determination point is corrected. The correction of the phase determination point is automatically performed by the data processing unit 170. That is, as shown in FIG. 16, for example, based on a threshold value TH having an intermediate value between the signal intensity of the abdomen and the signal intensity of the lung field, the maximum displacement position p1 of the diaphragm during inspiration and the maximum displacement position p2 during expiration are determined. A new phase determination point P 'is determined between the two positions. This makes it possible, for example, to restart the expiration phase determination. For the determination of the inspiratory phase and the intermediate phase between expiration and inspiration, a new phase determination point P ′ is defined as shown in FIGS.
[0067]
By such a phase determination point correction, the phase can be correctly determined irrespective of a change in the respiratory state, so that imaging echoes in the respiratory phase coinciding with the designated phase can be obtained for all views.
[0068]
If all views have been acquired, image reconstruction is performed in step 527. Since all imaging echoes were acquired at the designated phase, the reconstructed image is of high quality. The reconstructed image is displayed and stored at step 529.
[0069]
FIG. 19 shows a functional block diagram of the present apparatus. As shown in the figure, the present apparatus includes a navigator echo acquisition unit 702, a profile creation unit 704, a phase determination unit 706, an imaging echo acquisition unit 708, a determination point correction unit 710, and an image generation unit 712.
[0070]
The navigator echo acquisition unit 702 acquires a navigator echo and inputs it to the profile creation unit 704. The profile creation unit 704 creates a profile from the navigator echo and inputs the profile to the phase determination unit 706. The phase determination unit 706 determines the respiratory phase from the profile, and inputs the determination result to the imaging echo acquisition unit 708 and the determination point correction unit 710. The determination point correction unit 710 corrects the phase determination point of the phase determination unit 706 when the frequency of phase mismatch exceeds the limit.
[0071]
The imaging echo acquisition unit 708 acquires an imaging echo of a predetermined phase based on the phase determination result, and inputs the imaging echo to the image generation unit 712. The image generator 712 generates an image based on the input imaging echo.
[0072]
The navigator echo acquisition unit 702 corresponds to the function of step 505 in the flowchart of FIG. The navigator echo acquisition unit 702 is an example of an embodiment of the navigator echo acquisition means of the present invention. The profile creation unit 704 corresponds to the function of step 507 in the flowchart of FIG. The profile creation unit 704 is an example of an embodiment of a creation unit in the present invention.
[0073]
The phase determination unit 706 corresponds to the function of step 511 in the flowchart of FIG. The phase determination unit 706 is an example of an embodiment of a determination unit according to the present invention. The imaging echo acquisition unit 708 corresponds to the function of step 523 in the flowchart of FIG. The imaging echo acquisition unit 708 is an example of an embodiment of an imaging echo acquisition unit according to the present invention.
[0074]
The determination point correction unit 710 corresponds to the function of steps 535 and 537 in the flowchart of FIG. The judgment point correction unit 710 is an example of an embodiment of a correction unit in the present invention. The image generation unit 712 corresponds to the function of step 527 in the flowchart of FIG. The image generation unit 712 is an example of an embodiment of a generation unit according to the present invention.
[0075]
FIG. 20 shows a flowchart of another operation of the present apparatus. In the figure, the same operations as those shown in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. As shown in the figure, at step 505 ', acquisition of a navigator echo and an imaging echo is performed. The acquisition of the navigator echo is performed in the same manner as in step 601 in FIG. The acquisition of the imaging echo is performed by, for example, the pulse sequence shown in FIG. 3 or the pulse sequence shown in FIG.
[0076]
FIG. 21 shows a time chart for acquiring a navigator echo and an imaging echo. As shown in the figure, first, a navigator echo is obtained, and then an imaging echo is obtained. Such echo acquisition is repeated periodically. Thus, for example, imaging echoes of 64 to 512 views are sequentially acquired. Note that a plurality of imaging echoes may be obtained each time one navigator echo is obtained.
[0077]
In this manner, the imaging echo acquired as a pair with the navigator echo is used in step 523 ′ according to the phase determination in step 511 when it matches the designated phase, and in step 523 ′ when it does not match. At 533, imaging echo rejection is performed.
[0078]
By such an operation, among the imaging echoes acquired in step 505 ', those acquired at the respiratory phase that matches the designated phase are adopted as signals for image reconstruction, and acquired at the respiratory phase that does not match the designated phase. Things are not adopted. It should be noted that the imaging echo of the view not adopted is re-collected together with the navigator echo.
[0079]
If not adopted, that is, phase mismatch, it is determined in step 525 whether or not the mismatch frequency has exceeded the limit. If the limit has not been exceeded, the process returns to step 505 ′. , The phase determination point is corrected. The correction of the phase determination point is performed in the same manner as described above. This makes it possible to continue imaging at a predetermined phase irrespective of a change in the respiratory state, and together with re-taking of an imaging echo of a non-adopted view, data of all views can be acquired at a specified phase.
[0080]
FIG. 22 shows a functional block diagram of the present apparatus. As shown in the figure, the present apparatus includes a signal acquisition unit 702 ′, a profile creation unit 704, a phase determination unit 706, a signal adoption unit 708 ′, a determination point correction unit 710 ′, and an image generation unit 712. In this figure, the same parts as those shown in FIG. 19 are denoted by the same reference numerals, and description thereof will be omitted.
[0081]
The signal acquisition unit 702 ′ acquires the navigator echo and the imaging echo, inputs the navigator echo to the profile creation unit 704, and inputs the imaging echo to the signal adoption unit 708 ′.
[0082]
The profile creation unit 704 creates a profile from the navigator echo and inputs the profile to the phase determination unit 706. The phase determination unit 706 determines the respiratory phase from the profile, and inputs the determination result to the signal adoption unit 708 'and the determination point correction unit 710.
[0083]
The signal adoption unit 708 ′ determines the adoption / non-employment of the imaging echo according to the respiratory phase, and inputs the adopted imaging echo to the image generation unit 712. The determination point correction unit 710 ′ corrects the phase determination point of the phase determination unit 706 when the frequency of the phase mismatch exceeds the limit. The image generator 712 generates an image based on the adopted imaging echo.
[0084]
The signal acquisition unit 702 'corresponds to the function of step 505' in the flowchart of FIG. The signal acquisition unit 702 'is an example of an embodiment of an acquisition unit in the present invention. The profile creation unit 704 corresponds to the function of step 507 in the flowchart of FIG. The profile creation unit 704 is an example of an embodiment of a creation unit in the present invention.
[0085]
The phase determination unit 706 corresponds to the function of step 511 in the flowchart of FIG. The phase determination unit 706 is an example of an embodiment of a determination unit according to the present invention. The signal adoption unit 708 'corresponds to the function of steps 523' and 533 in the flowchart of FIG. The signal adoption unit 708 'is an example of an embodiment of the adoption means in the present invention.
[0086]
The judgment point correction unit 710 ′ corresponds to the function of Steps 525 and 537 in the flowchart of FIG. The judgment point correction unit 710 'is an example of an embodiment of a correction unit in the present invention. The image generation unit 712 corresponds to the function of Step 527 in the flowchart of FIG. The image generation unit 712 is an example of an embodiment of a generation unit according to the present invention.
[0087]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to realize a magnetic resonance imaging apparatus that performs correct imaging regardless of a change in respiratory state.
[Brief description of the drawings]
FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a pulse sequence executed by the device according to the example of the embodiment of the present invention;
FIG. 4 is a diagram illustrating an example of a pulse sequence executed by the device according to the example of the embodiment of the present invention;
FIG. 5 is a flowchart showing an operation of the apparatus according to the embodiment of the present invention;
FIG. 6 is a detailed view of a part of the flowchart of FIG. 5;
FIG. 7 is a diagram showing an example of a pulse sequence for acquiring a navigator echo.
FIG. 8 is a diagram illustrating an example of slice selection for acquiring a navigator echo.
FIG. 9 is a diagram showing a profile.
FIG. 10 is a diagram showing a profile.
FIG. 11 is a diagram illustrating an example of setting a phase determination point.
FIG. 12 is a diagram illustrating an example of setting a phase determination point.
FIG. 13 is a diagram illustrating an example of setting a phase determination point.
FIG. 14 is a diagram showing a relative shift of a phase determination point.
FIG. 15 is a diagram illustrating a relative shift of a phase determination point.
FIG. 16 is a diagram illustrating correction of a phase determination point.
FIG. 17 is a diagram illustrating correction of a phase determination point.
FIG. 18 is a diagram illustrating correction of a phase determination point.
FIG. 19 is a functional block diagram of a device according to an example of an embodiment of the present invention.
FIG. 20 is a flowchart of an operation of the apparatus according to the embodiment of the present invention;
FIG. 21 is a diagram showing a time chart of acquisition of a navigator echo and an imaging echo.
FIG. 22 is a functional block diagram of an apparatus according to an embodiment of the present invention.
[Explanation of symbols]
1 target
100,100 'magnet system
102 Main magnetic field coil
102 'Main magnetic field magnet
106, 106 'gradient coil section
108, 108 'RF coil section
130 Gradient drive
140 RF drive
150 Data collection unit
160 Sequence control unit
170 Data processing unit
180 Display
190 Operation unit
500 cradle
702 Navigator echo acquisition unit
704 Profile creation unit
706 Phase determination unit
708 Imaging echo acquisition unit
710, 710 'decision point correction unit
712 Image generation unit
702 'signal acquisition unit
708 'signal adoption unit

Claims (9)

A navigator echo acquiring means for repeatedly acquiring a navigator echo from an object to be photographed,
Creating means for creating a target profile based on the navigator echo, and determining whether or not the respiratory phase of the target matches a predetermined phase based on the signal intensity of the profile at a predetermined location Means,
Correction means for correcting the determination point of the determination means when the frequency at which the respiratory phase does not match the predetermined phase exceeds a predetermined limit,
Imaging echo acquisition means for acquiring an imaging echo in a predetermined respiratory phase from a subject of imaging based on the determination,
Generating means for generating an image based on the imaging echo,
A magnetic resonance imaging apparatus comprising: Acquisition means for repeatedly acquiring a navigator echo and an imaging echo;
Creating means for creating a target profile based on the navigator echo, and determining whether or not the respiratory phase of the target matches a predetermined phase based on the signal intensity of the profile at a predetermined location Means,
Correction means for correcting the determination point of the determination means when the frequency at which the respiratory phase does not match the predetermined phase exceeds a predetermined limit,
An adoption unit that employs an imaging echo in a predetermined respiratory phase among the imaging echoes based on the determination,
Generating means for generating an image based on the adopted imaging echo,
A magnetic resonance imaging apparatus comprising: The navigator echo is a spin echo,
The magnetic resonance imaging apparatus according to claim 1 or 2, wherein: The imaging echo is a gradient echo,
The magnetic resonance imaging apparatus according to any one of claims 1 to 3, wherein: The magnetic resonance imaging apparatus according to any one of claims 1 to 4, wherein the profile is a one-dimensional profile in a body axis direction. The predetermined phase is an expiration phase;
The magnetic resonance imaging apparatus according to any one of claims 1 to 5, wherein: The predetermined phase is an intake phase,
The magnetic resonance imaging apparatus according to any one of claims 1 to 5, wherein: The frequency is the number of times the respiratory phase does not match the predetermined phase,
The magnetic resonance imaging apparatus according to any one of claims 1 to 7, wherein: The frequency is a time when the respiratory phase does not match a predetermined phase,
The magnetic resonance imaging apparatus according to any one of claims 1 to 7, wherein:

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