JP2004329269A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus that can correct body motions while maintaining a satisfactory picture quality during the course of cardiac muscle perfusion. <P>SOLUTION: The control section of this magnetic resonance imaging (MRI) apparatus is provided with a saturation sequence for saturating the signals of a plurality of slices to be imaged except at least one slice, an image photographing sequence for acquiring image reconstituting signals with respect to the unsaturated slice, and a body motion navigating sequence for acquiring body motion navigating signals with respect to a slice which is equal to or different from the objective slice of the image photographing sequence as a photographing sequence. This imaging apparatus executes the saturation sequence, image photographing sequence, and body motion navigating sequence on the plurality of slices by changing the slicing positions of the slices. The control section non-saturates the plurality of slices in the saturation sequence and performs the body motion navigating sequence on one of the unsaturated slices and on another unsaturated slice. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus) having a perfusion imaging function, and more particularly to an MRI apparatus of this type having a body movement correction function by body movement navigation.
[0002]
[Prior art]
Perfusion imaging using an MRI apparatus, particularly myocardial perfusion imaging, is being clinically applied because an abnormal distribution of myocardial blood flow can be detected with high sensitivity. In the perfusion imaging, usually, under the administration of a contrast agent that shortens T1 of blood, an enhanced MR signal is acquired while the contrast agent passes through a myocardium as a target site. In this case, in order to increase the signal noise (SN) ratio in the perfusion region, there is a method using a presaturation sequence that saturates myocardial spins prior to a pulse sequence for image acquisition. For example, in Patent Literature 1, an RF saturation pulse having a cut-out profile excluding a predetermined slice is used to saturate a slice other than the slice, and then a pulse sequence for acquiring image data is performed on the slice. A technique for performing this is described.
[0003]
This method is schematically shown in FIG. In the drawing, the vertical axis represents a slice number, the horizontal axis represents alphabetical characters s and i, respectively, representing a saturation sequence and an image capturing sequence, and the numerals represent the sequence order. The black square in the saturation sequence indicates that the saturation sequence is saturated. In this method, first, the slices other than the second slice are saturated in s1, and then the image capturing sequence i1 of the second slice is executed. Next, after s2 saturates the slices other than the fourth slice, an image capturing sequence i2 of the fourth slice is executed. As described above, the image capturing sequence is executed while sequentially changing the slice for acquiring the image data without being saturated.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-120518
[0004]
This method has an advantage in that the number of imaging slices per section of the heartbeat can be increased and an image with a good SN can be obtained by combining with the heartbeat synchronization imaging.
[0005]
On the other hand, when imaging the abdomen such as myocardial perfusion, there is a problem that, in addition to the heart beat, a body motion artifact due to a respiratory motion occurs. In general, as a method of removing a body motion artifact, a method using a signal reflecting body motion information, that is, a body motion navigation echo is known, and a sequence for acquiring a body motion navigation echo signal and a body motion navigating method are known. Various body motion correction methods using echo have been proposed. For example, in the method described in Non-Patent Document 2, a body movement navigation signal is acquired prior to acquisition of an image reconstruction signal, and the position information (phase information) included in the body movement navigation signal is used to obtain a subsequent body movement navigation signal. Is performed to remove the body motion component of the image reconstruction signal acquired in this way. FIG. 12 shows an example of such a body movement navigating sequence. In the body movement navigating sequence shown in FIG. 3A, first, a slice to be imaged is selectively excited, and then a one-way gradient magnetic field (here, a read gradient magnetic field Gx) is applied without applying phase encoding. Then, a navigation signal is measured, and a signal for image reconstruction is acquired while applying phase encoding. In this sequence, body movement correction in the X direction can be performed. In the body movement navigating sequence shown in FIG. 2B, selection of an RF excitation pulse and a slice for detecting a body movement navigating echo and selection of an RF excitation pulse and a slice for detecting an image reconstruction signal are separately performed. At the same time, the amount of movement in the two directions is detected by using the two-direction gradient magnetic field (here, the readout direction gradient magnetic field Gx and the phase encoding direction gradient magnetic field Gy). As a result, body motion correction in the slice plane can be performed.
[Non-Patent Document 2] Magnetic Resonance of Medicine, 31, 195-503 (1994)
[0006]
[Problems to be solved by the invention]
Even in myocardial perfusion imaging with the above-mentioned presaturation sequence, in order to eliminate the influence of body motion and perform high-quality, high-precision measurement, it is desirable to apply a body movement navigation sequence, and to correct body movement. It is desirable that the body movement navigating sequence be performed consecutively with the image capturing sequence in order to perform the operation accurately.
[0007]
However, in the sequence shown in FIG. 12A, after the slice is selectively excited, the body reconstruction navigation signal is measured and then the image reconstruction signal is measured, so that the signal amount of the image reconstruction signal is reduced. In myocardial perfusion imaging, a perfusion site is measured using an extremely small difference in signal intensity, and such a decrease in the signal amount has a great effect on image quality and accuracy. In the sequence shown in FIG. 12B, since the RF excitation pulse and the slice selection are separately performed in the body movement navigation sequence and the image capturing sequence, the spin of the slice to be captured is saturated by the continuous excitation, resulting in a signal amount. And the effect of presaturation is hindered, and there is a problem that the SN of the image reconstruction signal decreases.
[0008]
Therefore, an object of the present invention is to provide an MRI apparatus which applies body motion navigation in perfusion imaging, has a good SN, and has high image quality and high accuracy with corrected body motion artifacts.
[0009]
[Means for Solving the Problems]
A control unit having a predetermined imaging sequence, respective magnetic field generating means for generating a gradient magnetic field and a high-frequency magnetic field in a static magnetic field space where the subject is placed under the control of the control unit, and measuring an NMR signal generated by the subject A magnetic resonance imaging apparatus comprising: a signal processing unit configured to perform imaging, wherein the control unit performs the imaging sequence so as to saturate a signal of a slice other than at least one slice among a plurality of slices to be imaged. A sequence, an image capturing sequence for obtaining an image reconstruction signal for a slice that has not been saturated, and a body motion navigating sequence for obtaining a body motion navigating signal for a slice that is the same as or different from the slice targeted by the image capturing sequence And the saturation sequence, image capture sequence And performing a body movement navigation sequence on the plurality of slices while changing a slice position, wherein the signal processing unit performs processing on the corresponding slice using the body movement navigation signal obtained by executing the body movement navigation sequence. The body motion correction of the acquired image reconstruction signal is performed.
[0010]
According to such an MRI apparatus of the present invention, body movement correction using a body movement navigation signal can be performed in myocardial perfusion imaging.
[0011]
In a preferred aspect of the MRI apparatus of the present invention, the control unit executes the body movement navigating sequence after the image capturing sequence on the same slice as that targeted by the image capturing sequence.
[0012]
According to this MRI apparatus, the body movement navigating sequence is performed after the image taking sequence, so that when the body movement navigating sequence and the image taking sequence are continuous with respect to the same slice, the image reconstruction signal is continuously excited. Even if a body movement navigating sequence is inserted, the image quality of myocardial perfusion imaging can be kept good, and body movement correction can reduce body movement artifacts.
[0013]
According to another preferred aspect of the MRI apparatus of the present invention, the saturation sequence suppresses a signal of a slice excluding a region including two or more slices (unsaturated region), and subsequently performs an image capturing sequence and body movement navigation. In the sequence, signals are acquired for different slices in the unsaturated region.
[0014]
According to this MRI apparatus, a signal for image reconstruction and a body movement navigation signal can be obtained from a slice that is not saturated after the saturation sequence and is different from the slice. Absent. In particular, when the body movement navigation sequence and the image capturing sequence are executed in order after the saturation sequence, the time interval from the saturation to the image acquisition is extended, so that the contrast of the contrast agent is enhanced in the perfusion imaging using the contrast agent. Thus, image quality can be improved.
[0015]
Particularly preferably, the unsaturated region of the saturation sequence partially overlaps with the unsaturated region of the next executed saturation sequence. In this case, after acquiring a body motion navigation signal for one slice in the unsaturated region after one saturation sequence, an image reconstruction signal can be acquired from the same slice that is not saturated after the next saturation sequence. Therefore, it is possible to prevent a decrease in the signal amount of the image reconstruction signal due to the body movement navigation sequence. As a result, body movement correction can be performed while maintaining good image quality, and higher accuracy of the image can be realized.
[0016]
In the preferred embodiment of the present invention, the unsaturated region in the saturation sequence may be composed of continuous slices, or may be divided into two or more regions separated in the slice direction. Even when the unsaturated region consists of two or more regions, similar to the MRI apparatus of the above embodiment, 1) since the image reconstruction signal and the body movement navigation signal can be obtained from different unsaturated regions, 2) If the body movement navigation sequence and the image capturing sequence are executed in this order after the saturation sequence, the time interval from the saturation to the image acquisition is extended. The contrast of the contrast agent is enhanced in the used perfusion imaging, and the image quality can be improved. 3) The unsaturated region of the saturation sequence partially overlaps with the unsaturated region of the next saturation sequence to be executed. This causes the motion navigation sequence to occur in the image reconstruction signal. Signal amount decreases to prevent the while maintaining good image quality, it is possible to perform motion compensation, can realize high accuracy of an image, the effect can be obtained as.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0018]
FIG. 1 is a diagram showing an overall outline of an MRI apparatus to which the present invention is applied. The MRI apparatus includes a magnet 101 for generating a uniform static magnetic field in a space where a test object 102 such as a patient is placed, a bed 103 for carrying the test object 102 into this space, and a high-frequency magnetic field applied to the test object. An RF coil 104 for irradiating and detecting a nuclear magnetic resonance signal (echo signal) generated from an inspection target, and gradient magnetic field generating coils 105 and 106 for generating a magnetic field gradient in the x, y, and z directions in a static magnetic field. , 107 and a control system for controlling these operations. Here, the horizontal magnetic field type MRI apparatus which employs a magnet which generates a static magnetic field in the body axis direction (horizontal direction) of the inspection object is shown, but the vertical magnetic field type which generates a static magnetic field in a direction orthogonal to the body axis direction. MRI apparatus may be used. Although the RF coil 104 has been described as having both the irradiation of the high-frequency magnetic field and the detection of the echo signal, these may be provided separately.
[0019]
The RF coil 104 is connected to a high-frequency magnetic field transmitting unit and a high-frequency magnetic field receiving unit via a switching circuit (not shown) in the case of a dual-purpose type as shown in the figure. The high-frequency magnetic field transmission unit mainly supplies power to the synthesizer 112 that generates a high-frequency signal of a predetermined frequency, a modulation circuit 113 that modulates the high-frequency signal generated by the synthesizer 112 into a signal of a predetermined envelope, and the RF coil 104. And a high frequency power supply 108. The high-frequency magnetic field receiving unit includes a receiver 115 including an amplifier 114, a quadrature detection circuit, an A / D converter, and the like.
[0020]
The gradient magnetic field generating coils 105, 106, and 107 in three directions are connected to power supplies 109, 110, and 111, respectively. The operations of the gradient magnetic field power supplies 109, 110, 111, the high-frequency magnetic field transmitting unit and the high-frequency magnetic field receiving unit are controlled by a control system according to a timing chart called a pulse sequence. The control system performs various calculations such as a correction calculation and a Fourier transform on the measured echo signal, and also controls a computer 118 that controls the entire apparatus, and an image and a spectrum that are the calculation results and input from a user. A display device 119 for displaying a GUI or the like, a storage device 117 for storing data necessary for calculation by the computer 118 and data after calculation, and a gradient magnetic field power supply 109, according to a pulse sequence selected in advance based on a command from the computer 118. And a sequencer 116 for controlling the high-frequency magnetic field transmitting unit and the high-frequency magnetic field receiving unit. The computer 118 includes an input device (not shown), and can register and call up an inspection target, select a pulse sequence according to an imaging method, input imaging parameters, and the like.
[0021]
In the MRI apparatus of the present invention, a pulse sequence for perfusion imaging is set in advance as an imaging method, and perfusion imaging can be started by selecting the pulse sequence via an input device. Details of these pulse sequences will be described later.
[0022]
Next, an embodiment of perfusion imaging employed by the MRI apparatus of the present invention will be described.
FIG. 2 is a diagram illustrating a first embodiment of perfusion imaging, and FIG. 3 is a diagram illustrating a flowchart illustrating a procedure of processing inside the computer 118. In FIG. 2, the vertical axis indicates a slice position, the horizontal axis indicates time (sequence of sequence execution), s1, s2, s3, and s4 are saturation sequences, i1, i2, i3, and i4 are image capturing sequences, respectively, and n1 , N2, n3, and n4 are diagrams each showing a body movement navigating sequence. Again, the black squares in the saturation sequence indicate that they are saturated (the same applies hereinafter). In FIG. 2, only four sequences are shown for each sequence. In this case, the processing is performed until signals are acquired for slices 1 to 8).
[0023]
In this embodiment, as shown in FIG. 2, after a saturation sequence sk (k represents 1, 2, 3,..., The same applies hereinafter), first, an image capturing sequence ik is performed to generate an image reconstruction signal. Acquisition is performed, and then the body movement navigation sequence nk is performed. When the perfusion shooting is selected, the conditions of these three sequences are derived (step 301). The conditions are the order of slices to be imaged and the frequency and phase of the high-frequency pulse according to the slice position. These conditions are stored in the storage device 117 as, for example, a table.
[0024]
Next, a first slice position is set (step 302), and a myocardial saturation sequence s1 is executed under conditions corresponding to the set slice position (step 303). For example, in the saturation sequence s1, a high-frequency pulse that excites the entire volume including the slice other than the slice 2 from which an image reconstruction signal is to be obtained is emitted, and the signals of the slices other than the slice 2 are suppressed. Next, a condition for selectively exciting only the slice 2 not saturated in the saturation sequence s1 is set, and the image capturing sequence i1 is executed for the slice 2 (step 304). The image reconstruction signal acquired in the image capturing sequence is stored at a predetermined address in the storage device 117 of the control system (signal processing system) (step 305). Following the image capturing sequence i1, the body movement navigating sequence n1 is executed for the same slice 2 (step 306). The body movement navigating signal acquired in the body movement navigating sequence is stored at a predetermined address in the storage device 117 of the signal processing system (control system) (step 307). Such a cycle from the saturation sequence (step 303) to the body movement navigating sequence (step 306) is repeated while updating the slice position (step 310), and is repeated until all the imaging target slices are photographed (step 309). .
[0025]
On the other hand, in the control system, the signals acquired in the image capturing sequence and the body movement navigating sequence in each cycle are stored at predetermined addresses in the storage device 117 as described above (steps 305 and 307). The body movement correction is performed on the use signal with the body movement navigation signal of the same slice obtained in the same cycle as the movement signal (step 308). There are several well-known methods for body movement correction using a body movement navigation signal, and any of them can be employed.Here, a reference position created in advance and a current position derived from the navigation signal are used. A method of comparing the position with the position and correcting the image reconstruction signal using the difference as a body motion component will be described.
[0026]
First, in order to create a phase map of the reference position, a body movement navigating sequence is executed for all slices to be imaged before the first saturation sequence. The body movement navigating signal obtained in this way is subjected to Fourier transformation to create a phase map reflecting the reference position, and stored at a predetermined address of the storage device. Thereafter, imaging is performed according to the procedure shown in FIG. 3, and a body movement navigation signal measured by the body movement navigation sequence executed in combination with the image imaging sequence is subjected to Fourier transform, and the position of the imaging target at the time of execution of the image imaging sequence Create a phase map reflecting the (current position). The difference between the phase map at the reference position and the phase map at the current position is obtained to obtain a body motion component. This phase difference map can be represented by a linear line with the axis from which the body movement navigation signal is acquired as the horizontal axis, and the inclination thereof becomes the body movement component. After Fourier transform is performed on the image reconstruction signal stored at the predetermined address, the body motion component is removed from the converted signal.
[0027]
As described above, by correcting the body motion components for the image reconstruction signals of all slices, three-dimensional myocardial perfusion image data can be finally obtained. According to this embodiment, by suppressing signals from slices other than the target slice in myocardial perfusion imaging, image data with excellent SN can be obtained, and the body movement navigation sequence can be executed after the image imaging sequence. By doing so, it is possible to prevent deterioration of the signal due to inserting the body movement navigation sequence, and to perform body movement correction of the image signal, and to achieve high precision and high image quality perfusion with reduced body movement artifacts Images can be obtained.
[0028]
Next, the details of the saturation sequence, the image capturing sequence, and the body movement navigating sequence employed in the perfusion photography of the present invention will be described.
[0029]
As described above, in the saturation sequence, in order to saturate a region excluding a specific region (unsaturated region), for example, a high-frequency pulse having an excitation profile excluding a specific region (slice) as shown in FIG. Used. As shown on the right side of FIG. 4C, this high-frequency pulse is a high-frequency pulse of a magnetic field waveform obtained by combining the sinc function shown in FIG. 4A and the impulse group shown in FIG. 4B (intensity modulation using the sinc function as the envelope). (A group of impulses), and excitation of a plurality of rectangular profiles as shown on the left side in FIG. 4C can be realized. At this time, by adjusting the width 2T1 of the sinc waveform and the interval T2 of the impulse group, a saturation pulse having a desired width in an unsaturated region and a saturated region can be obtained. That is, the number of slices that are not saturated and the number of slices that are saturated can be adjusted. Further, by changing the frequency or phase of the intensity-modulated impulse group, the position of the excitation profile shown on the left side in FIG. 4C can be moved. Therefore, when performing perfusion imaging as shown in FIG. 2, the frequency of the high frequency pulse used in each sequence should be tabulated, and the high frequency pulse of each sequence should be changed and applied according to the value of the frequency stored as a table. Can move the slice position. FIG. 5 shows an example of a saturation sequence frequency table. FIG. 6 shows an example of a saturation sequence using such a high-frequency pulse. As shown, by applying a high-frequency pulse RF having a specific excitation profile together with a selection gradient magnetic field Gz for selecting the entire slice to be imaged, for example, as shown in FIG. The excitation profile can be a saturation region.
[0030]
The image capturing sequence is, for example, high-speed imaging or ultra-high-speed imaging such as a gradient echo method or 2D-EPI (Echo Planar Imaging), and acquires image data of a slice selected in 50 ms to 150 ms. In the body movement navigation sequence, for example, after applying a rephasing gradient magnetic field for canceling the influence of the gradient magnetic field in the image capturing sequence, without applying the phase encoding gradient magnetic field, the readout gradient magnetic field is read in the direction of the body movement to be corrected for the body movement. The body movement navigation signal is measured.
[0031]
FIG. 7 shows an example of the image capturing sequence and the body movement navigating sequence. In FIG. 7, RF indicates a high-frequency excitation pulse, Gz indicates a slice selection gradient magnetic field, Gy indicates a phase encoding gradient magnetic field, Gx indicates a read gradient magnetic field, and A / D indicates a signal acquisition sampling time. As is clear from comparison with FIG. 12 showing a conventional body movement navigation sequence, in this embodiment, an image capturing sequence is executed before the body movement navigation sequence. That is, as shown in FIG. 7A, the slice selection gradient magnetic field 702 and the RF pulse 701 are simultaneously applied to selectively excite a slice that has not been excited in the preceding saturation sequence. Next, an echo signal for image reconstruction is measured while applying a phase encoding gradient magnetic field 703 and further applying a read gradient magnetic field 704. The process from the RF pulse 701 to the acquisition of the echo signal 705 is repeated while changing the intensity of the phase encoding gradient magnetic field 703 to acquire the echo signals of the number of phase encodings necessary for image reconstruction. Next, after applying the gradient magnetic field 704 of the opposite polarity to the phase encoding gradient magnetic field 703 applied in the last repetition time and performing rephasing, the body movement navigation signal is acquired while applying the gradient magnetic field 706 in the readout direction. Alternatively, as shown in FIG. 7B, after performing the same image capturing sequence as in FIG. 7A, a slice selection gradient magnetic field 711 and an RF pulse 712 are applied to selectively excite the same slice as in the image capturing sequence, and read out. Two body movement navigation signals are measured while applying gradient magnetic fields 713 and 714 in the direction and the phase encoding direction, respectively. When body motion information is obtained in two or more directions as described above, it is better to perform excitation using an excitation pulse separately from the image capturing sequence, so that the amount of the body movement navigation signal is less reduced and accurate body movement correction is performed. It can be performed. Here, a pulse sequence based on the gradient echo method is shown as the image capturing sequence, but an EPI or a sequence of divided EPI in which a plurality of echo signals are acquired by one excitation may be employed.
[0032]
As described above, as one embodiment of the present invention, an embodiment (FIGS. 2 and 3) in which an image capturing sequence and a body movement navigating sequence are executed in this order for one slice not saturated in the saturation sequence, Each sequence used for this myocardial perfusion imaging has been described.
[0033]
Next, as a second embodiment of the present invention, a shooting sequence with further improved image quality will be described. In this embodiment, a region (unsaturated region) that is not excited in the saturation sequence is composed of two or more slices, an image capturing sequence is executed for one of the two or more slices that are not saturated, and the other is performed. Execute the body movement navigation sequence. Here, a sequence using a high-frequency pulse as shown in FIG. 6 is adopted as the saturation sequence.
[0034]
FIG. 8 shows a second embodiment of the perfusion photography of the present invention. Also in FIG. 8, the vertical axis represents the slice position, and the horizontal axis represents time (sequence execution order). In this embodiment, the region that is not saturated in the saturation sequence includes three slices, and the other slices are saturated. In order to set a relatively wide area including a plurality of slices as the unsaturated area, the pulse width T1 and the impulse interval T2 of the envelope of the high-frequency pulse shown in FIG. 4C are adjusted. As a result, as shown in FIG. 8, for example, an excitation profile in which three slices (for example, slices 2 to 4) are unsaturated regions and both sides are saturated regions can be obtained. Also in this case, the slice position can be changed by adjusting the frequency or phase of the high-frequency pulse, as in the embodiment of FIG.
[0035]
Following such a saturation sequence, a body movement navigation sequence and an image capturing sequence are executed. The body movement navigating sequence and the image photographing sequence executed here are similar to those shown in FIG. 12B, but in this case, the slice and the image photographing sequence which are the object of the body movement These slices are slices that have not been saturated in the previous saturation sequence and are different from each other. For example, in the embodiment shown in FIG. 8, in the saturation sequence s1 executed first, slices 2 to 4 are unsaturated regions, and in the subsequent body movement navigation sequence n1, a body movement navigation echo is acquired for slice 4. In the image capturing sequence i1, an echo for image reconstruction is acquired for slice 2.
[0036]
In the next saturation sequence s2, an area overlapping with a part of the unsaturated area of the previously executed saturation sequence s1 is defined as an unsaturated area. In the illustrated example, slices 4 to 6 become unsaturated regions in the saturation sequence s2. In the image capturing sequence i2 following the saturation sequence s2, an echo for image reconstruction is acquired for the slice targeted in the first body movement navigating sequence n1, ie, slice 4. In this case, focusing on slice 4, this slice is in an unsaturated region that is not excited in the first and second saturation sequences, and the image is re-executed after the time to execute the saturation sequence s2 after acquiring the body movement navigation echo. Since the constituent echo is acquired, the signal amount of the image reconstruction echo does not decrease, and a signal with a good SN can be obtained. Further, since the time from the saturation sequence to the acquisition of the echo for image reconstruction is extended, the contrast of the contrast agent is enhanced in the myocardial perfusion using the contrast agent, and the image quality of the myocardial perfusion image can be improved. Further, since a signal is obtained from the unsaturated region for the body movement navigation echo, a decrease in the signal amount is prevented.
[0037]
As described above, in the present embodiment, a region including a plurality of slices is defined as an unsaturated region, body movement navigation echoes and image reconstruction echoes are obtained for different slices in the unsaturated region, and image capturing is performed based on the saturation sequence. The sequence up to the sequence is defined as one cycle, and is executed while sequentially shifting the unsaturated regions so as to partially overlap, and is repeated until image reconstruction echoes are obtained for all slices. Then, the image reconstruction echo is corrected for body motion using the body movement navigation echo acquired in the previous cycle, and the image is reconstructed using the corrected signal.
[0038]
In the present embodiment, the number of slices included in the unsaturated region may be two or more. However, in order to consider the overlap of the slices and to make the effect of saturation effective, the number of slices is set to three as illustrated. , It is preferable to acquire a body movement navigation signal on one of the two slices except for an intermediate slice and an image reconstruction signal on the other.
[0039]
According to the present embodiment, as compared with the embodiment of FIG. 2, it is possible to acquire a signal without a decrease in the signal amount for both the body movement navigation echo and the image reconstruction echo. Further, regarding the same slice, since the image capturing sequence and the body movement navigating sequence are not continuous, it is possible to prevent a decrease in the signal amount in any case. The above two effects can be obtained by preceding either the image capturing sequence or the body movement navigating sequence. In particular, when the body movement navigating is preceded as shown in FIG. Since the time until echo acquisition is prolonged, a myocardial perfusion image in which the contrast of the contrast agent is enhanced and the SN is good is obtained.
[0040]
Next, a third embodiment of myocardial perfusion imaging according to the present invention will be described. FIG. 9 is a diagram showing the third embodiment, in which reference numerals are the same as those in the embodiments shown in FIGS. 2 and 8. In this embodiment, two or more unsaturated regions separated in the slice direction are provided in the saturation sequence, and in the subsequent body movement navigation sequence and image capturing sequence, signals are acquired for slices in different unsaturated regions. That is, in the illustrated example, out of the twelve slices 1 to 12, the slices 2, 3, the slices 7, 8, and the slice 12 are unsaturated regions that are not saturated in the saturation sequence s1. A signal is acquired, and a signal is acquired from slice 2 in the image capturing sequence. Such selective excitation (setting of the unsaturated region) can also be realized by using the high-frequency pulse shown in FIG. 4C and changing the width of the envelope and the impulse interval.
[0041]
Also in the present embodiment, the saturation sequence, the body motion navigation sequence, and the image capturing sequence are defined as one cycle, and each cycle is executed while shifting the unsaturated region in the saturation sequence. At this time, the slice of the previous unsaturated region and the next unsaturated region are executed. The slices in the saturated region are partially overlapped. Then, in the next cycle, an echo for image reconstruction is acquired for the slice from which the body movement navigating echo was acquired in the previous cycle, and the body movement is corrected using the body movement navigating echo in the previous cycle.
[0042]
According to the present embodiment, similarly to the embodiment of FIG. 8, since the body movement navigation echo and the image reconstruction echo are obtained from different unsaturated regions, it is possible to obtain a signal without deterioration in both. It is possible to effectively perform the body motion correction. For the same slice, the image capturing sequence is executed after the saturation sequence after the body movement navigation sequence, so that the signal amount of the image reconstruction echo is prevented from being reduced. Further, by performing the body movement navigating sequence before the image capturing sequence, the time interval from saturation to image acquisition is extended, so that a high-quality perfusion image in which the contrast of the contrast agent is enhanced can be obtained.
[0043]
As described above, as the first embodiment, an imaging method in which one slice is set as an unsaturated region in a saturation sequence, and an image imaging sequence and a body movement navigating sequence are sequentially performed on the slice in this order, and second and third imaging methods are described. As an embodiment, an imaging method in which a region including a plurality of slices is set as an unsaturated region as a saturation sequence, and then a body movement navigating sequence and an imaging sequence are executed for different slices has been described. It is possible. Such an embodiment is shown in FIG.
[0044]
In this embodiment, as in the second embodiment shown in FIG. 8, the saturation sequence saturates except for an area including a plurality of slices (three slices in the figure). The gating sequence is executed in this order to obtain an image reconstruction signal and a body movement navigation signal for the same slice. In the next saturation sequence, the position of the unsaturated region is changed, but partially overlaps with the immediately preceding unsaturated region, and the other regions are saturated. The image capturing sequence and the body movement navigating sequence subsequent to the saturation sequence obtain an image reconstruction signal and a body movement navigating signal for slices that have not been overlapped and saturated. Hereinafter, each sequence is repeated while changing the position of the unsaturated region in the same manner, and finally, the image reconstruction signal and the body movement navigation signal for all slices are obtained.
[0045]
In this embodiment, a sequence as shown in FIGS. 7A and 7B is adopted, and it is not possible to correct a motion of an image reconstruction signal using a motion navigation signal obtained in the same slice. The same effect as that of the first embodiment can be obtained (for example, the signal amount of the image reconstruction signal does not decrease even if the body movement navigating sequence is inserted), but only one slice is examined. Since the time interval from the saturation by the saturation sequence to the image reconstruction signal is extended, a high-quality perfusion image in which the contrast by the contrast agent is enhanced can be obtained.
[0046]
As described above, each embodiment of the imaging sequence adopted by the MRI apparatus of the present invention has been described. However, the present invention is not limited to the above embodiment, and various changes can be made.
[0047]
【The invention's effect】
According to the MRI apparatus of the present invention, a body movement navigating sequence is incorporated into a perfusion imaging sequence in consideration of a combination of a slice order and a sequence to be imaged, thereby effectively correcting body movement in perfusion imaging. And a high-quality, high-precision perfusion image can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall outline of an MRI apparatus to which the present invention is applied;
FIG. 2 is a diagram showing an embodiment of an imaging sequence employed by the MRI apparatus of the present invention.
FIG. 3 is a flowchart showing a procedure of a photographing sequence in FIG. 2;
FIG. 4 is a diagram showing an example of a table storing shooting conditions of a shooting sequence.
FIG. 5 is a diagram illustrating a high-frequency magnetic field used in a saturation sequence.
FIG. 6 is a diagram showing a saturation sequence.
FIG. 7 is a timing chart showing an image capturing sequence and a body movement navigating sequence according to an embodiment of the present invention.
FIG. 8 is a diagram showing another embodiment of the imaging sequence employed by the MRI apparatus of the present invention.
FIG. 9 is a diagram showing another embodiment of the imaging sequence employed by the MRI apparatus of the present invention.
FIG. 10 is a diagram showing another embodiment of the imaging sequence employed by the MRI apparatus of the present invention.
FIG. 11 is a diagram showing conventional myocardial perfusion imaging.
FIG. 12 is a diagram showing a conventional body movement navigating sequence;
[Explanation of symbols]
101: Static magnetic field magnet, 104: RF coil, 105 to 107: Gradient magnetic field coil, 116: Sequencer, 117: Storage device, 118: Computer

Claims (5)

A control unit having a predetermined imaging sequence, respective magnetic field generating means for generating a gradient magnetic field and a high-frequency magnetic field in a static magnetic field space where the subject is placed under the control of the control unit, and measuring an NMR signal generated by the subject And a signal processing means for imaging, the magnetic resonance imaging apparatus comprising:
The control unit may include, as the imaging sequence, a saturation sequence that saturates a signal of a slice other than at least one of a plurality of slices to be imaged, and an image that obtains an image reconstruction signal for a non-saturated slice. An imaging sequence and a body movement navigating sequence for obtaining a body movement navigating signal for the same or a different slice as the slice targeted by the image imaging sequence.These saturation sequence, image imaging sequence and body navigating sequence Execute for the plurality of slices while changing the slice position,
Magnetic resonance imaging, wherein the signal processing means performs a motion correction of an image reconstruction signal obtained for a corresponding slice using the motion navigation signal obtained by executing the motion navigation sequence. apparatus. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the control unit executes the body movement navigating sequence on the same slice as a target slice of the image capturing sequence after the image capturing sequence. 3. The saturation sequence suppresses signals in slices excluding a region including two or more slices (unsaturated region), and in a subsequent image capturing sequence and body movement navigating sequence, signals for different slices in the unsaturated region are reduced. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus acquires the information. 4. The magnetic resonance imaging apparatus according to claim 1, wherein an unsaturated region of the saturation sequence partially overlaps with an unsaturated region of a saturation sequence to be executed next. The saturation sequence suppresses a signal of a slice excluding two or more unsaturated regions separated in a slice direction, and in a subsequent image capturing sequence and a body movement navigating sequence, signals of slices included in different unsaturated regions are different from each other. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus acquires the information.

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