JPH08182661A - Magnetic resonance photographing method - Google Patents

Abstract

PURPOSE: To extract biological function with high time-resolving power, by exciting nuclear magnetization synchronized with heart beat or stimulation impression, generating echo signals of different time-lapses, and forming time series images by combination of echo signals whose time-lapse from the heart beat or the stimulatory impression are the same and gradient magnetic field impressed amount are different. CONSTITUTION: A high frequency magnetic field for nuclear magnetization excitation and plural kinds of gradient magnetic fields are impressed to a testee 2 in static magnetic field, in a MRI device provided with a static magnetic field generating magnet 1, and gradient magnetic field generating coils 8 to 10 of X to Z directions. An image is reconstituted based on the obtained echo signals, and on this occasion, high frequency magnetic field is impressed in synchronization with the heart beat of the testee 2. Plural echo signals whose time-lapse from the high frequency magnetic field impression are different are obtained by repeating polarity inversion of the signal reading gradient magnetic field. Then, the image is reconstituted by combination of plural echo signals whose time before aquisition are almost the same, and the time series images which are composed of plural images whose time from high frequency magnetic field impression are different are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging method for extracting the functions of the brain and heart using a magnetic resonance imaging apparatus (hereinafter referred to as MRI apparatus). More specifically, the present invention relates to an inspection method using MRI that can shorten the imaging interval of time-series images and extract the function of a living body with high time resolution.

[0002]

2. Description of the Related Art An MRI apparatus has a structure as shown in FIG. In FIG. 12, 1 is a magnet for generating a static magnetic field, 2 is an object to be imaged such as a subject, 3 is a bed on which the object to be imaged is placed, 4 is a high-frequency magnetic field, and at the same time, an echo signal generated from the object 2 is detected. Coil of
Reference numerals 8, 9 and 10 denote gradient magnetic field generating coils for generating gradient magnetic fields in the X, Y and Z directions, respectively. In this specification, the signal read gradient magnetic field Gr is generated by the X direction gradient magnetic field coil 8, the phase encode gradient magnetic field Gp is generated by the Y direction gradient magnetic field coil, and the slice selection gradient magnetic field Gs is generated by the Z direction gradient magnetic field coil. To do. Reference numerals 5, 6 and 7 are coil driving devices for supplying currents to the gradient magnetic field generating coils 8, 9 and 10, respectively. 15 is a computer for calculating the measured data, 16 is a computer 1
5 is a CRT display for displaying the calculation result in 5. Reference numeral 17 is a memory for storing data in the middle of calculation or final data.

The RF that excites the nuclear spins of the subject 2 is
The high frequency wave generated by the synthesizer 11 is modulated by the modulator 1.
Waveform shaping and power amplification are performed at 2, and a current is supplied to the coil 4 to generate it. The signal from the imaging target 2 is received by the coil 4, amplified by the amplifier 13, detected by the detector 14, and then input to the computer 15. After the calculation by the computer 15,
The calculation result is displayed on the CRT display 16.

In recent years, a technique for analyzing the functions of the brain and heart using an MRI device has been developed. Brain function measurement (hereinafter,
In the case of fMRI (functional MRI) as an example, an image when a stimulus such as light or sound is applied to a subject (stimulation application image)
And an image when no voltage is applied (rest image), respectively. Next, the difference in signal intensity is calculated for each pixel between the stimulus application image and the rest image. The region in which the difference in signal intensity is large can be regarded as a region in which nerve cells violently respond to the applied stimulus. This region is called an activation region, and in fMRI, attention is paid to the position of the activation region and the signal change in that region for analysis.

In such a method of extracting a biological function using an image, the time resolution of the image becomes important. For example,
When a stimulus is given by listening to and answering a question, the cerebral cortex receives the voice stimulus, judges the content, and responds. These reactions are triggered sequentially in different areas of the cerebral cortex. Therefore, it is necessary to perform imaging at intervals of about 10 ms in order to capture the time until activation of each region after applying a stimulus and the order of activation. At present, the EPI (Echo-planar imaging) method, which is the most excellent imaging method with time resolution, can capture one image in 100 ms or less. The EPI method is
P. Mansfield, "Multiple Image Formation Using NMR
Spin Echoes ", J. Phys. C: Solid State Phys., 10 , L5
5 (1977).

FIG. 11 (a) is a time chart (hereinafter referred to as a sequence) showing a magnetic field application procedure of a normal imaging method,
(B) is a sequence of the EPI method. The vertical axis of the sequence is magnetic field strength, and the horizontal axis is time. The value obtained by time-integrating the magnetic field strength is the magnetic field application amount. Here, the high-frequency magnetic field RF brings the nuclear magnetization into an excited state, and the signal reading gradient magnetic field G
The r and the phase encoding gradient magnetic field Gp give position information to the excited nuclear magnetization.

In the normal imaging method, one echo signal is acquired by one excitation. This is repeated a predetermined number of times by changing the Gp application amount, and echo signals of the number necessary for image creation are acquired. The repetition time is determined by the nuclear magnetization recovery time, and is usually several 100 ms to several seconds. Therefore, if the number of repetitions is 256, the photographing time will take several minutes.

Two methods are used as methods for shortening the photographing time. One is a method of shortening the recovery time of nuclear magnetization, and the other is a method of acquiring all echo signals necessary for image formation by one excitation. The former representative is F
It is a high-speed imaging method called a LASH (Fast Low Angle Shot) method, and the representative of the latter is the EPI method. FLASH
The method reduces the RF flip angle and shortens the recovery time, whereas the EPI method repeats the polarity inversion of Gr as shown in FIG. 11B to generate a plurality of echo signals. The time interval of echo signal generation can be set to 1 ms or less by increasing the polarity reversal frequency of Gr. Gp is applied during polarity reversal of Gr, and different position information is given to each echo signal. By acquiring all the echo signals necessary for image creation with one excitation, the waiting time for nuclear magnetization recovery is eliminated and the imaging time is shortened. In addition,
For details of the FLASH method, see P. Van der Me.
ulen, "Very fast MR Imaging by field echoes and sm
all angle excitation ", Magn. Reson. Imaging., 3, 2
97-299 (1985).

[0009]

When the EPI method is used for fMRI, several tens to several hundreds of images are photographed at a predetermined photographing interval. At that time, it is a general method to apply a stimulus for a certain period of time. This imaging interval is about several seconds, which is a nuclear magnetizing recovery waiting time. That is, even if the image capturing time of one image is 100 ms or less, the signal change caused by activation can be observed only with a time resolution (image capturing interval) of several seconds. Make the flip angle smaller,
If the nuclear magnetization recovery waiting time is shortened, the time resolution is improved to about 100 ms of the imaging time. In order to further improve the time resolution, it is necessary to increase the intensity of Gr. However, there is a limit due to the safety standard provided for the rate of change of the gradient magnetic field with time and the performance of the imaging apparatus. As described above, even if the EPI method is used, the time resolution of about 100 ms is the highest, and further improvement of the time resolution has been required. It is an object of the present invention to provide an inspection method using MRI that can shorten the imaging interval of time-series images and extract the function of a living body with high time resolution.

[0010]

According to the present invention, nuclear magnetization is excited in synchronization with application of a heartbeat or a stimulus to generate a plurality of echo signals having the same gradient magnetic field application amount and different time lapses.
A feature is that a time-series image is created by combining echo signals having the same time lapse from nuclear magnetization excitation and different gradient magnetic field application amounts.

That is, the present invention provides a subject in a static magnetic field with a high-frequency magnetic field for exciting nuclear magnetization, a slice gradient magnetic field for determining an excitation region, a signal reading gradient magnetic field for giving position information to the magnetization, and a phase encoding. In a magnetic resonance imaging method of applying a gradient magnetic field to acquire an echo signal and reconstructing an image based on the acquired echo signal, step 1 of applying a high-frequency magnetic field in synchronization with a heartbeat or a stimulus of a subject, By repeating the polarity reversal of the signal readout gradient magnetic field to obtain a plurality of echo signals with different times from the application of the high frequency magnetic field, and changing the application amount of the phase encoding gradient magnetic field, the steps 1 and 2 are performed in a predetermined manner. Step 3 which is repeated a number of times and a plurality of echo signals of the acquired echo signals from which the high-frequency magnetic field is applied to when the acquisition is almost the same. Performing image reconstruction by combining the result, the time from the application of the high frequency magnetic field, characterized in that it comprises the step 4 for creating a time-series images consisting of a plurality of different images.

At this time, among the echo signals, a signal strength correction value for making the signal strength of each echo signal the same is derived from the echo signal obtained without applying the phase encoding gradient magnetic field, and the image reconstruction At that time, it is preferable to correct the time-series image using the correction value. In the present invention, the high-frequency magnetic field is applied in synchronization with a heartbeat or stimulation of a subject and a first high-frequency magnetic field is applied at a constant time interval after the first high-frequency magnetic field. A second high-frequency magnetic field equal to the magnetic field, and the nuclear magnetization excited by the first high-frequency magnetic field and the nuclear magnetization excited by the second high-frequency magnetic field are made equal in phase encoding gradient magnetic field application amount. The step of acquiring the echo signal is repeated a predetermined number of times by changing the phase encode gradient magnetic field application amount,
A plurality of images having different times from the first high-frequency magnetic field application are obtained by performing image reconstruction by combining a plurality of echo signals of the acquired echo signals from which the first high-frequency magnetic field application is almost equal to the acquisition time. It is characterized by creating a time series image consisting of.

Acquiring the echo signal can include acquiring an echo signal for monitoring the body movement of the subject. The spatial resolution of the echo signal used to monitor the body movement and the spatial resolution of the echo signal used to create the image are different, and the spatial resolution of the echo signal used to monitor the body movement is better than the spatial resolution of the echo signal used to create the image. High resolution may be used.

The time series image may be created by using the half Fourier method, the specific area updating method, or both. The acquisition of the echo signal is preferably started from the echo signal having a small absolute value of the phase encode gradient magnetic field application amount. In addition, among the echo signals, the correction value of the phase distortion of each image is derived from the echo signal acquired without applying the phase encoding gradient magnetic field, and the correction value is used during image reconstruction to correct the time series image. Is preferably performed.

As the time-series images, a time-series image (still image) when no stimulus is applied to the subject and a time-series image (stimulation application image) when the stimulus is applied to the subject are photographed, and these two types are taken. If time-series images are used in combination with images that have the same elapsed time from the application of the high-frequency magnetic field, it is possible to extract the activated region in which the living body has reacted by the application of the stimulus, by creating a difference image or the like.

[0016]

[Function] By exciting nuclear magnetization in synchronization with the application of heartbeats and stimuli and generating a plurality of echo signals having the same gradient magnetic field application amount, a plurality of images with different time lapses from the application of heartbeats and stimuli are created. You can The echo signal acquisition interval can be set to 1 ms or less. Therefore, it becomes possible to perform the function extraction with the time resolution of 1 ms or less.

Half Fourier method or specific area updating method,
Alternatively, if both are used to create an image, it is possible to reduce the number of repeated acquisitions of echo signals required for image creation. Also, when a difference image between a still image and a stimulus-applied image with the same time lapse from heartbeat and stimulus application is created,
It is possible to eliminate the influence of the difference in blood flow velocity within one heartbeat on the activation region.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a photographing sequence, a signal processing method, and an activation area extracting method according to the present invention will be described below with reference to the drawings. The MRI apparatus shown in FIG. 12 is used for imaging. (1) Imaging Sequence FIG. 1A is a sequence showing an example of the present invention, and FIG. 1B is a sequence of the EPI method. In this example, the R wave of the electrocardiogram is used as the synchronizing signal.

The stimulus is applied at time t _d1 after the R wave. RF is applied after the time _td2 from the R wave. After that, in the present invention, the polarity inversion of Gr is repeated to generate a plurality of echo signals. However, Gp is not applied during the polarity reversal of Gr. In the sequence of the EPI method, as shown in FIG. 1B, Gp is applied during the polarity inversion of Gr and different position information is given to each echo signal, whereas in the present invention, all echoes are added. The signals have the same position information. That is, it is possible to obtain a plurality of echo signals having different time from the application of the stimulus and having the same position information. This sequence is repeated by changing the Gp application amount before Gr polarity inversion, and all echo signals necessary for image formation are acquired. The order of changing the Gp application amount is as shown in FIG.
It is desirable to first acquire an echo signal having a small absolute value of the p applied amount. This is because the correction value of each echo signal is derived using the echo signal with the Gp application amount of zero. The signal correction method will be described in detail in (2) below.

The image reconstruction is carried out by combining echo signals satisfying different conditions of Gp and the same time from the application of stimulus. This makes it possible to create a plurality of images with different times from RF application. Moreover, since the time interval of these images can be set to 1 ms or less, it becomes possible to perform function extraction with a time resolution of 1 ms or less. FIG.
While the sequence of (a) is based on the sequence of the EPI method, FIG. 13 is based on the sequence of the FLASH method. The stimulus is applied after time t _d1 from the R wave of the electrocardiogram. RF50 is the first RF that is applied in synchronization with the heartbeat, and RF51 is the second RF that is applied at a constant time interval TR after the first RF and the magnetic field application amount is equal to the first RF. . Here, the magnetic field application amounts of the echo signals excited by the first and second RF are made equal. This sequence is repeated by changing the Gp application amount, and all echo signals necessary for image creation are acquired. By performing image reconstruction by combining echo signals with the same time from the first RF application, the time from the first RF application is different,
Time series images can be created. This makes it possible to shorten the shooting interval of time-series images and perform function extraction with high time resolution.

The sequence which is the basis of the present invention has been described above with reference to FIGS. Since the following description is common to both sequences, the description will be given using the sequence of FIG. If there is a subject's body movement within the imaging time, fMRI causes erroneous extraction of the activation region. Therefore, it is necessary to monitor the subject's body movements and correct the positional deviation of the image. A photographing sequence for generating an echo signal for body movement monitoring (hereinafter referred to as a navigation echo) and a method for correcting the positional deviation of an image from the acquired data are described in, for example, Japanese Patent Application Laid-Open No. 5-154130. Also in the present invention, it is possible to generate a navigation echo during the imaging sequence and use the data to correct the body movement by a known method.

FIG. 3 shows an example of the photographing sequence.
In FIG. 3, the flip angle of RF22 is 90 ° (90
.Degree. Pulse) and the flip angle of RF23 is 180.degree. (180.degree. Pulse), but it is not necessarily limited to this value. Reference numeral 20 is an imaging sequence for acquiring a navigation echo, and 21 is an imaging sequence for fMRI. The echo signal generated in the sequence 20 is subjected to a one-dimensional Fourier transform in the kx direction to create a projection image on the X axis, and the amount of movement in the x direction can be measured from this projection image. If there is body movement, the data after the one-dimensional Fourier transform of the echo signal generated in sequence 20 in the kx direction is moved in the direction opposite to the movement amount measured by the echo signal in sequence 20, To correct. Also,
As shown in FIG. 4, the navigation echo acquisition sequence 20 may be inserted after the fMRI sequence 24. In FIG. 4, RF2 in sequence 24 of fMRI is shown.
2 shows an example in which after the nuclear magnetization is excited in 2, the navigation echo is generated by using the recovered nuclear magnetization component. As another method, there is a method of recovering nuclear magnetization by using a 180 ° pulse.

Even if the sequence 20 for generating such a navigation echo is added to the fMRI sequence, the entire imaging time does not change. The reason is as follows. In the present invention, since imaging is performed in synchronization with the electrocardiogram, the time for one heartbeat is the shortest repetition time. For this reason, when the image capturing for one time is repeated within one heartbeat time, the entire image capturing time does not change. Each of the sequence 21 and the sequence 20 can be photographed within 100 ms. FIG. 3 and FIG. 4 are combined sequences of these two sequences and can be performed within one heartbeat.
That is, the navigation echo acquisition sequence 20
The addition of does not extend the shooting time.

In order to accurately measure the amount of body movement, the spatial resolution of the echo signal of sequence 20 may be higher than the spatial resolution of the echo signal of sequence 21 or sequence 24. To obtain high spatial resolution data,
It is necessary to change the intensity of Gr, the number of sampling points of the echo signal, and the sampling rate. Even if the imaging time of the navigation echo acquisition sequence 20 becomes long due to the increase in the number of sampling points, the fMR
If the imaging time for one repetition combined with the sequence I is within one heartbeat time, a navigation echo with high spatial resolution can be obtained without extending the overall imaging time for the reason described above.

In the present invention, the interval between the time series images created is shortened to 1 ms or less. But on the other hand, 1
The image taking time becomes longer. The reason is that EPI method is 1
This is because one image is created with an imaging time of 00 ms or less, whereas in the sequence of the present invention, the Gp application amount is changed and echo signals are repeatedly acquired, which requires a waiting time for nuclear magnetization recovery. . There are two methods for reducing the shooting time. One is a method using a half Fourier method (hereinafter referred to as HF method), and the other is a method using a specific area updating method. The HF method is an imaging method that reduces the number of data acquired for image reconstruction to about half. For details of the HF method, for example,
DA Feinberg, "Halving MR imaging time by conju
gation: Demonstration at 3.5 KG ", Radiology, 161 ,
527-531 (1986). The specific area update method is an imaging method in which all echo signals necessary for image creation are acquired in advance, and then only the echo signals of a predetermined phase encoding gradient magnetic field application amount are sequentially updated. JJ Von Vaals, "Keyhole method for
accelerating imaging of contrast agent uptake ",
J. Magn. Reson. Imaging, 3 , 671-675 (1993). Hereinafter, a measurement space that is an array of acquired echo signals will be described, and then an application example of the HF method and the specific area updating method to the present invention will be described.

FIG. 5 shows a data array on the measurement space. Here, kx is a spatial angular frequency in the X direction, and ky is a spatial angular frequency in the Y direction. White circles in the figure are A / D sampling points. The distance between sampling points on the horizontal axis kx corresponds to the Gr application amount applied during one sampling time, and the distance between sampling points in the ky-axis direction corresponds to the Gp application amount from excitation. An example in which the HF method is applied to this is shown in FIG. In the measurement space shown in FIG. 6, data is acquired in the measurement area 2
5, the data of the estimation area 26 is not acquired. However, the data in the estimation area 26 is estimated and supplemented from the data in the measurement area 25 by using the property of the measurement space. By applying the HF method to the present invention, it is possible to reduce the number of repetitions and reduce the photographing time to about half.

FIG. 7 shows an example in which the specific area updating method is applied. (A) is an example in which all data in the measurement space is acquired, and (b) is a part in which the measurement space is not measured. , HF
In this example, the method and the specific area updating method are used at the same time. Figure 7
In (a), all data (high-frequency region 27, low-frequency region 28) in the measurement space is acquired in advance, then time series image capturing is started, and data is acquired again. However, the data acquired at this time is only the data in the same region as the low frequency region 28. The image 31 at time t ₁ shows the low frequency region 2
8 is updated with the newly acquired data 29, and the remaining high frequency region 27 is created using the data acquired before that. Then, the image 32 at time t ₂ has a low frequency region 29.
Is updated with the newly acquired data 30, and the remaining high frequency region 27 is created using the data acquired before that.

The same applies to the case of FIG. 7B in which the HF method is also used. However, in the case of FIG.
Is not acquired, but is estimated from the data of the high frequency region 34 and the data of the low frequency region using the property of the measurement space, and is compensated.
The data of the estimation region 33 may be estimated only once at first and compensated for, and the same data may be used thereafter, or the data of the low frequency region newly acquired at each image reconstruction is estimated. , May be supplemented.

FIG. 8 shows an example in which the specific area updating method of FIG. 7A is applied to the present invention. First, all data of the measurement space corresponding to times t ₁ , t ₂ , ... After applying a stimulus is acquired as a rest image (regions 40, 41). Next, a stimulus application image is taken. Here, as the data of the stimulus application image, only the data of the low frequency region (region 42, region 43) of the measurement space is acquired. Using the data of these low frequency regions, only the low frequency regions of the rest image where the time from excitation is the same are updated, and the stimulus application image is created. Thereby, the imaging time can be shortened as compared with the case where all the measurement spaces are updated every time.

(2) Signal Processing Method Here, a signal processing method performed after the echo signal is acquired will be described. When the polarity reversal of the gradient magnetic field is repeated as in the EPI method, the phase of the echo signal may be distorted due to the effect of the eddy current. This phase distortion causes deterioration of image quality. A method for correcting phase distortion is disclosed in, for example, Japanese Patent Laid-Open No. 5-68
No. 674 publication. This correction method is summarized below. First, the reference data is acquired without applying Gp, and the correction value of each echo signal is derived. Next, Gp is applied to acquire the main photographing data. When reconstructing the image of the main photographing data, the phase distortion is corrected using the correction value obtained previously. Also in the present invention, since the polarity reversal of the gradient magnetic field is repeated, it is necessary to correct the phase distortion, which can be corrected by the well-known correction method as described above. In the conventional method, when images are taken in time series, the correction value for phase distortion is the same for each image, but in the present invention, the correction value for phase distortion is different for time series images.

The intensity of the echo signal decreases exponentially with the lapse of time from the excitation. That is, compared with the signal intensity of the image created from the echo signal immediately after the excitation, the signal intensity of the image created from the echo signal with a long time elapsed from the excitation becomes small, so it is not necessary to observe the signal change in the activation region. It is also necessary to correct the signal strength. Table 1 shows the difference between the correction values of the phase distortion and the necessity of the signal strength correction when each imaging method is used for the functional measurement.

[0032]

[Table 1]

As for the phase distortion correction value of the present invention, for echo signals forming the same image, each echo signal is corrected with the same correction value. However, different correction values are used between the time series images. This is different from the EPI method and the normal imaging method. Further, in the present invention, it is necessary to correct the signal strength. FIG. 9 is an example of a processing procedure when shooting is performed using the sequence of FIG. First, echo signals are acquired at times t ₁ , t ₂ , ... Without applying Gp (S1). This data is zero-encoded data for each image, and at the same time is reference data for deriving a correction value for the phase distortion of each image. One-dimensional Fourier transform in the kx direction is applied to each reference data (S2), a correction value of the phase distortion of the reference data is derived by a known method (S3), and the phase distortion of the reference data is corrected using the correction value. (S4). Next, the one-dimensional inverse Fourier transform in the x direction is applied to the reference data with the phase distortion corrected (S5) to obtain a signal strength correction value for correcting the signal attenuation of the echo signal (S6), and the signal strength of the reference data is calculated. Correct (S7). What is the signal strength correction value?
It is a correction value (correction coefficient) for correcting the attenuation of each echo signal so that the signal strengths become the same.

Next, the Gp application amount is changed (S8), and Gp
Is applied to acquire an echo signal at times t ₁ , t ₂ , ... (S9). Subjected to one-dimensional Fourier transform of the kx direction acquired Gp applied data to each time (S10), using the correction value of the phase distortion obtained in step S3 before the time t _1, t
₂ , the phase distortion of Gp applied data is corrected (S11). The Gp applied data with the phase distortion corrected is subjected to the one-dimensional inverse Fourier transform in the x direction (S12), and each time t is calculated using the signal strength correction value obtained in step S6.
The signal strength of the Gp applied data at ₁ , t ₂ , ... Is corrected (S13). When the Gp application amount should be further changed and the data acquisition should be continued, the Gp application amount is changed and the Gp application data acquisition is repeated (S14). When the predetermined data acquisition is completed, the reference data for the same time t _i and the Gp application data are combined to create the main photographing data (S1).
5). Finally, _{2 is} added to the actual shooting data at each time t ₁ , t ₂ , ...
A three-dimensional Fourier transform is performed to create a time series image (S1
6).

When performing body movement correction, the body movement correction processing described in the sequence for generating the navigation echo in FIG. 3 is added between step S11 and step S12. This is the same when other imaging methods are used. In the case of the HF method, as shown in FIG.
Is changed to obtain Gp application data in step S8-
The number of times S14 is repeated is smaller than that in the case of the sequence of FIG. Therefore, the photographing time as a whole is shortened.
Instead, after step S15, a step of creating data of the estimation region 26 using the data of the measurement region 25 is added.

FIG. 10 shows an example of a processing procedure when a time series image is photographed by the specific area updating method. The data of the previously photographed area is subjected to the processing of steps S1 to S15 shown in FIG. 9 (S17), and then the newly photographed specific area is subjected to the processing of steps S1 to S15 shown in FIG. 9 (S1).
8). After that, a part of the previously photographed data is updated by using the newly photographed data of the specific area, and the actual photographing data is created (S19). Finally, two-dimensional Fourier transform is applied to the main photographing data to create an image (S20). HF
When the method and the specific area updating method are used together, in FIG. 10, a step of creating the data of the estimated area is added after the main imaging data is created in step S19.

(3) Activation Area Extraction Method FIG. 14 shows an example of the activation area extraction method in the conventional brain function measurement. FIG. 14A shows the measuring method,
A stationary period and a stimulus application period are provided during the time-series image capturing. FIG. 14B shows the activated area extraction method, in which the area in which the signal change is caused by the stimulus is extracted by creating the difference image from the averaged image of both periods.
Since this method processes the images by averaging, it is possible to obtain static information about the area that was activated during the measurement period due to stimulation, but it is expanded momentarily with the activity of the brain,
It is impossible to obtain dynamic information such as changes in the activation region that shrinks or moves, and temporal changes in the intensity of activity in the activation region.

FIG. 15 shows an example of the activated area extraction method according to the present invention. FIG. 15A shows a measuring method, in which a time-series image of a stationary period and a time-series image of a stimulus application period are captured. However, the time from the R wave of the electrocardiogram is the same between both time series images. FIG. 15B shows an activation area extraction method, in which a difference image is created using a still image and a stimulus application image with the same time elapsed from the R wave, and the activation area is extracted. As a result, it is possible to eliminate the effect of the difference in blood flow velocity within one heartbeat on the activation region. This is the most basic extraction method, but if there are many images with the same time elapsed from the R wave, the activation region may be extracted using statistical processing such as t-test. According to the method of the present invention, it is possible to obtain time-series information about an activation region, which could not be obtained conventionally, with high time resolution.

[0039]

As described above, according to the present invention, it is possible to shorten the photographing interval of time-series images and extract the function of the living body with high time resolution.

[Brief description of drawings]

FIG. 1A is a diagram showing an example of a sequence of the present invention based on the EPI method, and FIG. 1B is a diagram showing an example of a sequence of the EPI method.

FIG. 2 is a diagram showing an example of Gp application order in the sequence of the present invention.

FIG. 3 is a diagram showing an example in which a sequence for generating an echo signal for body movement correction is added to the sequence of the present invention based on the EPI method.

FIG. 4 is a diagram showing another example in which a sequence for generating an echo signal for body movement correction is added to the sequence of the present invention based on the EPI method.

FIG. 5 is a diagram showing a correspondence between a data array in a measurement space and a gradient magnetic field application amount.

FIG. 6 is a diagram showing a data acquisition region of the HF method.

FIG. 7A is an update data acquisition area when all data in the measurement space of the specific area update method is acquired, and FIG.
The figure which shows the update data acquisition area | region when using it simultaneously with F method.

FIG. 8 is a diagram showing an example in which a specific area updating method is applied to the present invention.

FIG. 9 is a flowchart showing an example of a signal processing procedure in the present invention.

FIG. 10 is a flowchart showing an example of a signal processing procedure in the specific area updating method.

FIG. 11 is a diagram showing a sequence of (a) normal imaging method and (b) EPI method.

FIG. 12 is a schematic explanatory diagram of a magnetic resonance imaging apparatus.

FIG. 13 is a diagram showing an example of a sequence using the FLASH method.

FIG. 14 is a diagram showing an example of (a) a measuring method and (b) an active area extracting method in the conventional brain function measurement.

FIG. 15 is a diagram showing (a) an example of a measuring method and (b) an example of an activated region extracting method in brain function measurement using the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Static magnetic field generating magnet, 2 ... Imaging target, 3 ... Bed on which an imaging target is placed, 4 ... High frequency magnetic field coil, 5 ... X direction gradient magnetic field power supply, 6 ... Y direction gradient magnetic field power supply, 7 ... Z direction gradient magnetic field power supply, 8 ... X-direction gradient magnetic field generating coil, 9 ... Y-direction gradient magnetic field generating coil, 10 ... Z-direction gradient magnetic field generating coil, 11 ... Synthesizer, 12 ... Modulator, 13 ... Amplifier, 14 ... Detector, 15 ... Calculator, 16 ... CRT display, 17 ... Memory, 20 ... Sequence for body movement correction, 21 ... Sequence for fMRI, 22 ... RF pulse (flip angle 90 °), 23 ... RF pulse (flip angle 180 °), 24 ... fMRI sequence, 25 ... HF method signal measurement area, 26 ... HF method signal estimation area, 27 ... high-frequency area that is not updated over time, 28 ... time elapsed Low-frequency region to update with, 29
... low-frequency region photographed at time t ₁ , 30 ... low-frequency region photographed at time t ₂ , 31 ... image at time t ₁ , 32 ... image at time t ₂ , 33 ... HF signal estimation region, 34 ... time High-frequency region not updated over time, 35 ... Low-frequency region updated over time, 36 ... Low-frequency region imaged at time t ₁ , 37 ... Low-frequency region imaged at time t ₂ , 38
... time t ₁ of the image, 39 ... time t ₂ of the image, 40 ... data acquisition area of the time t ₁ resting image, 41 ... data acquisition area of the time t ₂ of the rest image, 42 ... time t ₁ of the stimulus application image Data acquisition region of 43, ... Data acquisition region of stimulus application image at time t ₂ , 50 ... First RF, 51 ... Second RF

Claims (24)

[Claims] 1. A radio frequency magnetic field for exciting nuclear magnetization, a slice gradient magnetic field for determining an excitation region, a signal readout gradient magnetic field for giving position information to the magnetization, and a phase encoding gradient magnetic field for a subject in a static magnetic field. In the magnetic resonance imaging method of reconstructing an image on the basis of the acquired echo signal by applying a signal, a step 1 of applying a high-frequency magnetic field in synchronization with a heartbeat or stimulation of a subject, and a signal readout gradient Step 2 in which a plurality of echo signals with different times from high-frequency magnetic field application are obtained by repeating polarity reversal of the magnetic field, and step 1 and step 2 are repeated a predetermined number of times by changing the application amount of the phase encoding gradient magnetic field. 3 and a plurality of echo signals of the acquired echo signals, which have almost the same time from the application of the high-frequency magnetic field to the acquisition, are combined. By performing the image reconstruction, the magnetic resonance imaging method characterized by comprising the step 4 that the time from the application of the high frequency magnetic field to create a time-series images consisting of a plurality of different images. 2. The magnetic resonance imaging method according to claim 1, wherein the step 2 includes acquisition of an echo signal for monitoring the body movement of the subject. 3. The magnetic resonance imaging method according to claim 2, wherein the spatial resolution of the echo signal for monitoring the body movement is different from the spatial resolution of the echo signal used for image creation. 4. The magnetic resonance imaging method according to claim 3, wherein the spatial resolution of the echo signal for body movement monitoring is higher than the spatial resolution of the echo signal used for image creation. 5. The magnetic resonance imaging method according to claim 1, wherein the time-series images are created by using a half Fourier method. 6. The time-series image includes a step 1 in which all echo signals necessary for image creation are acquired and an image is created, and a step 2 in which only echo signals to which a predetermined amount of a phase-encoding gradient magnetic field is applied are sequentially acquired. 2. The magnetic resonance imaging according to claim 1, wherein the magnetic resonance imaging is performed by using the specific region updating method including the step 3 in which a part of the data in the step 1 is replaced with the echo signal acquired in the step 2 to create an image. Method. 7. The magnetic resonance imaging method according to claim 1, wherein the time series image is created by using a half Fourier method and a specific area updating method. 8. The magnetic resonance imaging method according to claim 1, wherein the acquisition of the echo signal is started from an echo signal having a small absolute value of a phase encode gradient magnetic field application amount. 9. A correction value of phase distortion of each image is derived from an echo signal obtained without applying a phase encoding gradient magnetic field among the echo signals, and the correction value of the phase distortion is calculated at the time of image reconstruction. The magnetic resonance imaging method according to claim 1, wherein the time-series image is corrected by using the time series image. 10. Of the echo signals, a signal strength correction value for making the signal strength of each echo signal the same is derived from the echo signal acquired without applying a phase encoding gradient magnetic field, and the image reconstruction The time series image is corrected by using the correction value of the signal strength at this time.
A method for magnetic resonance imaging as described. 11. The phase distortion correction value of each image is derived from the echo signal obtained without applying the phase encoding gradient magnetic field among the echo signals, and the phase encoding gradient magnetic field with the phase distortion corrected is not applied. From the acquired echo signal, derive a signal strength correction value for making the signal strength of each echo signal the same, and use the phase distortion correction value and the signal strength correction value when reconstructing an image. The magnetic resonance imaging method according to claim 1, wherein the series image is corrected. 12. The capturing of the time-series image includes capturing of a time-series image when a stimulus is not applied to the subject and capturing of a time-series image when a stimulus is applied to the subject. 2. The magnetic resonance imaging method according to claim 1, wherein among the series images, images having the same elapsed time from the application of the high-frequency magnetic field are used in combination to extract the activated region in which the living body has reacted by applying the stimulus. 13. The magnetic field according to claim 12, wherein a differential image is created by using an image of the two types of time-series images having the same elapsed time from the high-frequency magnetic field, and the activation region is extracted. Resonance imaging method. 14. A radio frequency magnetic field for exciting nuclear magnetization, a slice gradient magnetic field for determining an excitation region, a signal readout gradient magnetic field and a phase encoding gradient magnetic field for giving position information to the magnetization for a subject in a static magnetic field. In a magnetic resonance imaging method for reconstructing an image based on the acquired echo signal, wherein the high-frequency magnetic field is a first high-frequency magnetic field applied in synchronization with a heartbeat or a stimulus of a subject. , A second high-frequency magnetic field applied at a constant time interval after the first high-frequency magnetic field and having a magnetic field application amount equal to that of the first high-frequency magnetic field, and nuclear magnetization excited by the first high-frequency magnetic field; The step of acquiring multiple echo signals by equalizing the amount of applied phase encode gradient magnetic field with the nuclear magnetization excited by the high frequency magnetic field of By repeating a certain number of times, among the acquired echo signals, the time from the first high-frequency magnetic field application is performed by combining a plurality of echo signals having almost the same time from the first high-frequency magnetic field application to the acquisition. A magnetic resonance imaging method characterized by creating a time-series image composed of a plurality of images having different values. 15. The magnetic resonance imaging method according to claim 14, further comprising acquiring an echo signal for monitoring the body movement of the subject. 16. The magnetic resonance imaging method according to claim 15, wherein the spatial resolution of the echo signal for monitoring the body movement is different from the spatial resolution of the echo signal used for image creation. 17. The magnetic resonance imaging method according to claim 16, wherein the spatial resolution of the echo signal for body movement monitoring is higher than the spatial resolution of the echo signal used for image creation. 18. The magnetic resonance imaging method according to claim 14, wherein the time-series images are created by using a half Fourier method. 19. The time-series image includes a step 1 in which all echo signals necessary for image creation are acquired and an image is created, and a step 2 in which only echo signals to which a predetermined amount of phase-encoding gradient magnetic field is applied are sequentially acquired. 15. The magnetic resonance imaging according to claim 14, wherein the magnetic resonance imaging is performed by using the specific area updating method including the step 3 in which a part of the data in the step 1 is replaced with the echo signal acquired in the step 2 to create an image. Method. 20. The magnetic resonance imaging method according to claim 14, wherein the time-series image is created by using a half Fourier method and a specific area updating method. 21. The magnetic resonance imaging method according to claim 14, wherein the acquisition of the echo signal is started from an echo signal having a small absolute value of a phase encode gradient magnetic field application amount. 22. Among the echo signals, a correction value for the phase distortion of each image is derived from the echo signal acquired without applying a phase encoding gradient magnetic field, and the correction value for the phase distortion is calculated when the image is reconstructed. 15. The magnetic resonance imaging method according to claim 14, wherein the time-series images are corrected by using the time series images. 23. The capturing of the time-series images includes capturing of the time-series images when no stimulus is applied to the subject and capturing of the time-series images when the stimulus is applied to the subject. 15. The magnetic resonance imaging method according to claim 14, wherein among the series images, images having the same elapsed time from the application of the high-frequency magnetic field are used in combination to extract the activated region in which the living body has reacted by applying the stimulus. 24. The activation region is extracted by creating a difference image using an image of the two types of time-series images that has the same elapsed time from the application of the high-frequency magnetic field. Magnetic resonance imaging method.