JPH07171127A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance imaging device in which a metabolic activation changed image can be formed with high resolution, the metabolic activation changed part can be identified, and it can be judged whether the metabolic activation change is truly caused or not. CONSTITUTION:A high frequency pulse is repeatedly applied to a testee, and the repeating time is set to less than T1, T2, whereby a steady precession motion is caused in the spin. Paying attention to either signal of the FID signal generated just after the high frequency pulse and the Time-reversed FID signal generated just before the following high frequency pulse, the image based on the difference of the signals before and after the testee is stimulated, or a metabolic activation changed image 601 is provided. Further, the images by the FID signal and the Time-reversed FID signal before or after the stimulation is given, or a brain surface structural image 602 and a blood flow image 603 are superposed on the metabolic activation changed image to provide a composed image 604.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus, and more particularly to a magnetic resonance imaging apparatus suitable for obtaining an image showing changes in metabolic activation of a subject.

[0002]

2. Description of the Related Art A method for visualizing the function of the brain in magnetic resonance imaging is discussed in detail in the following references (1) and (2).

(1) Science, 1, Novenver,
1991, 254, 621 to 768 (Sci.
ence, 1 November 1991, Vol. 254, 621-768) (2) Magnetic Resonance in Medicine, 1992, No. 25, 390 to 397
Magnetic Resonance in Me-dicine, 1992, Vol.25,
390-397) It is known that when functions such as movement and sensation are activated, a large amount of blood collects in the region of the brain that controls them. In Reference (1), in order to visualize the metabolic process, a contrast agent is injected from a blood vessel, and the difference in signal intensity due to the contrast agent is measured and visualized by an echo planar method, which is one of the ultra-high-speed imaging methods. In reference (2), the oxidation phenomenon of blood accompanying activation is used to visualize the signal change at that time. The echo planar method is used as the method. In the case of blood, hemoglobin changes to oxyhemoglobin when oxygen is supplied with activation. Since oxyhemoglobin is diamagnetic, T ₂ * is extended and the signal strength is increased. After that, when it is reduced to reduced hemoglobin, it becomes paramagnetic and T ₂
* Shortens and signal strength weakens.

It is possible to image the brain function by measuring such changes by the echo planar method and comparing with normal times.

[0005]

However, the method of injecting a contrast medium from a blood vessel as in the literature (1) has a high risk to a subject and cannot be performed in the same manner as ordinary radiography. In addition, since the echo planner method, which is an ultra-high-speed imaging method, is used in the methods of Documents (1) and (2), the spatial resolution is poor due to its original property, and it is difficult to perform appropriate diagnosis. In addition, in order to determine which area of the brain the part where the signal change occurs corresponds to another method, for example, the spin echo method or the gradient field echo method, the brain surface structure must be imaged. Not only is it necessary to take a picture, but there is a problem of misalignment when combining two images. Further, there is a problem that it is impossible to determine whether the change in the signal amount is caused by the activation of the brain or the change in the blood flow amount in the vein.

An object of the present invention is to provide a magnetic resonance imaging apparatus which can obtain a change image of metabolic activation of a subject with high resolution and which is suitable for appropriate diagnosis. .

Another object of the present invention is to provide a magnetic resonance imaging apparatus suitable for identifying a place where a change in metabolic activation is occurring.

Still another object of the present invention is suitable for discriminating whether the change image of metabolic activation is due to a change in metabolic activation or a change in venous blood flow. Another object of the present invention is to provide a magnetic resonance imaging device.

[0009] Yet another object of the present invention is that it is necessary to make a measurement separate from the measurement for obtaining the change image of metabolic activation in order to identify the place where the change in metabolic activation is occurring. An object of the present invention is to provide a magnetic resonance imaging apparatus which does not have a magnetic resonance image.

Another object of the present invention is to identify the place where the change in metabolic activation is occurring, or whether the image of changes in metabolic activation is truly due to the change in metabolic activation. , Or to provide a magnetic resonance imaging apparatus which does not need to be separately measured from the measurement for obtaining a change image of metabolic activation in order to discriminate whether it is caused by a change in blood flow in a vein. is there.

[0011]

[Means for Solving the Problems] When a high frequency pulse is repeatedly applied to a subject and the repetition time is set to T ₁ or T ₂ or less, the spin is brought into a steady precession motion state (SSFP) and the first high frequency wave is generated. Immediately after the pulse, a magnetic resonance signal called the FID signal, and immediately before the second high-frequency pulse that follows it, Ti
It is known that magnetic resonance signals called me-reversed FID signals are generated respectively.

The present invention applies this phenomenon to obtain an image showing changes in metabolic activation of a subject. That is, according to the present invention, a stimulus is given to the subject, and a high frequency pulse is repeatedly applied to the subject so as to cause a steady precession motion in the spin of the subject, and the metabolic activity of the subject based on the stimulus is repeatedly applied. A signal is generated that is representative of the change in charge and an image of the subject is generated based on this signal.

According to another aspect of the present invention, a signal representing the surface structure of the subject is further generated, and an image of the subject generated based on this signal and a signal representing the change in the metabolic activation are added. The image originally generated is displayed in a superimposed manner.

According to yet another aspect of the present invention, a signal representing the blood flow of the subject is further generated, and based on the image generated based on this signal and the signal representing the change in metabolic activation. The generated image is superimposed and displayed.

According to still another aspect of the present invention, the first magnetic resonance signal generated immediately after the first high frequency pulse in the steady precession state and immediately before the subsequent second high frequency pulse. Focusing on one of the second magnetic resonance signals generated in the image, an image of the subject is generated and displayed based on the signal representing the difference between the signal before and after the stimulation is given to the subject. Further, an image generated based on the first or second magnetic resonance signal before or after the subject is stimulated is superimposed and displayed on the image.

[0016]

According to the present invention, the signal representing the change in metabolic activation of the subject is generated in the state where the spin is in the state of steady precession. An image based on a signal obtained in a steady precession state has a high spatial resolution unlike the above-mentioned eco-planar method, and therefore an appropriate diagnosis can be performed.

According to another aspect of the present invention, a signal representing the surface structure of the subject is further generated, and an image of the subject generated based on this signal and a signal representing the change in the metabolic activation are added. Since the image generated originally is displayed in an overlapping manner, the place where the change in metabolic activation is occurring can be identified from both the signal images.

According to yet another aspect of the present invention, a signal representing the blood flow of the subject is further generated, and based on the image generated based on this signal and the signal representing the change in metabolic activation. Since the generated image is displayed in an overlapping manner, it is possible to determine from these two signal images whether the change image of metabolic activation is truly due to the change in metabolic activation or whether it is due to the blood flow in the vein. Will be possible.

According to another aspect of the present invention, immediately before the first magnetic resonance signal and the subsequent second high frequency pulse generated immediately after the first high frequency pulse in the steady precession state. Focusing on one of the generated second magnetic resonance signals, an image of the subject is generated and displayed based on the signal representing the difference between the signal before and after the stimulation is given to the subject. Furthermore, since an image generated based on the first or second magnetic resonance signal before or after stimulation to the subject is superimposed and displayed on this image, a change in metabolic activation occurs. Metabolic activity to identify the location where the change is occurring, or to determine whether the image of changes in metabolic activation is truly due to changes in metabolic activation or due to changes in venous blood flow. To obtain the change image It is not necessary to separate measurement with.

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a block diagram showing an outline of the configuration of the MRI apparatus which is an embodiment of the present invention. 10 in the figure
Reference numeral 1 is a magnet for generating a uniform static magnetic field, 102 is an excitation system for generating a high-frequency magnetic field for causing nuclear magnetic resonance in the subject, and 103 is A / after receiving and detecting a signal generated from the subject. D-converting receiving system, 104
Is a gradient magnetic field generation system for independently imparting X, Y, Z magnetic field gradients to the static magnetic field, that is, for linearly changing the strength of the static magnetic field independently in the X, Y, Z directions.
Reference numeral 105 denotes an image processing system that performs various calculations necessary for image reconstruction based on measurement data from the measurement system,
Reference numeral 106 is a sequence control system for controlling the operation timing of each system in the above configuration,
Reference numeral 107 is a probe used for high-frequency transmission / reception, and reference numeral 108 is a console for performing operations.

FIG. 3 shows magnetic resonance signals generated in the steady precession state (SSFP). 201 is a FID signal generated immediately after the high frequency pulse, and 202 is a Time-reversed FID signal generated immediately before the high frequency pulse. An example of a gradient magnetic field pulse sequence for carrying out the present invention is shown in FIGS. FIG. 4 shows two signals in the SSFP state (signals that occur immediately after and immediately before a high frequency pulse) during a period 310,
Two-dimensional pulse that is sampled during 311 and draws the brain activation change from the signal immediately before or immediately before the high frequency pulse, and draws the brain surface structure by emphasizing the cerebrospinal fluid existing on the brain surface from the signal immediately before the high frequency pulse. It is a sequence.

There are two methods for measuring the noh function by changing the relaxation time. The method for measuring the functional function by T ₁ enhancement utilizes the fact that a large amount of unexcited magnetization flows in with an increase in blood flow and the apparent T ₁ becomes short.
In the method of measuring the functional function by T ₂ weighting, hemoglobin changes into oxyhemoglobin with activation, and apparent T ₂
It takes advantage of the lengthening.

A target region (slice) to be imaged is selectively excited by a gradient magnetic field 302 and a high frequency pulse 301 at an arbitrary angle. At this time, excitation is performed with an extremely short repetition time (TR) with respect to the relaxation time of the imaging region, signals generated immediately after the high frequency pulse are collected as echo signals by the gradient magnetic fields 307 and 308, and A / D sampling is performed during the period 310. Further, the signal generated immediately before the high frequency pulse is sampled through the gradient magnetic field 308 period 311. This process is the same as the phase encoding projection 305, 3
It is measured at 06. Although 303 and 304 are for returning the phase disturbed in the slice direction by the gradient magnetic field 302,
302, 303, 304 may be a phase insensitive gradient magnetic field application pattern. The gradient magnetic field 306 is applied as an amount having the same absolute value as the gradient magnetic field 305 but an opposite sign so as to restore it after A / D sampling around the phase by the gradient magnetic field 305. The gradient magnetic fields 307, 308, and 309 are applied to perform frequency encoding on the signal, but the gradient magnetic fields 307, 308, and 309 may have a phase insensitive gradient magnetic field application pattern. When the signal is measured while the phase-encoded projection 305 is changed before and after the brain function is activated with the imaging target near the head, especially near the parietal region, image reconstruction is performed, and subtraction processing is performed between these images, the period 310 or 311 is obtained. An image in which the change in brain function activation is drawn is obtained from the image of the signal sampled through, and an image in which the cerebrospinal fluid existing on the brain surface is emphasized is drawn from the signal sampled during the period 311. .

An image based on a signal in the SSFP state originally has a high spatial resolution, unlike an image based on the eco-planar method, and therefore an appropriate diagnosis can be performed.

FIG. 5 shows a three-dimensional measurement sequence. The gradient magnetic fields 401 and 402 are phase encoding gradient magnetic fields in the slice direction. The relationship between the gradient magnetic fields 401 and 402 is
Similar to the relationship between the gradient magnetic fields 305 and 306, the gradient magnetic field 402 is applied so that the absolute values are equal and the signs are opposite to each other so as to restore the original after the A / D sampling around the spin phase. In the case of this measurement, as in the case of FIG.
Signals are measured before and after brain function activation, image reconstruction is performed, and subtraction processing is performed between these images. An image in which changes in brain function activation are drawn can be obtained from the subtracted image. At this time, the brain surface structure can be drawn by extracting the brain region from one of the images and performing stereoscopic reproduction. Figure 6
Are two signals in the SSFP state (immediately after the high frequency pulse,
The signal that occurs immediately before) is sampled, the brain activation change is drawn from the signal immediately after or just before the high frequency pulse, and the blood flow is drawn as the high signal region from the signal immediately after the high frequency pulse,
This is a three-dimensional pulse sequence that draws the brain surface structure by emphasizing the cerebrospinal fluid existing on the brain surface from the signal immediately before the high frequency pulse. Gradient magnetic field 502 of the target region slice to be visualized
And a high frequency pulse 501 having an arbitrary angle is selectively excited.
At this time, excitation is performed with an extremely short repetition time (TR) with respect to the relaxation time of the imaging region, signals generated immediately after the high frequency pulse are collected as echo signals by the gradient magnetic fields 508, 509, and 510, and A / D sampling is performed through a period 512. To do. Further, the signal generated immediately before the high frequency pulse is collected as an echo signal by the gradient magnetic field 510 and is sampled during the period 513. This process is measured by the same phase encode projection 506. Gradient magnetic field 50
Reference numerals 3, 504, and 505 are for returning the phase of spins disturbed in the slice direction by the gradient magnetic field 502, but a phase-insensitive gradient magnetic field application that makes the phase rotation of the fluid part zero by the gradient magnetic fields 502, 503, and 504. Forming a pattern. Although the gradient magnetic fields 505 and 502 form the phase sensitive gradient magnetic field application pattern that causes the fluid portion to rotate around the phase, this may be a phase insensitive gradient magnetic field application pattern like the gradient magnetic fields 502, 503 and 504. The gradient magnetic field 507 is applied after A / D sampling around the spin phase caused by the gradient magnetic field 506 so that the gradient magnetic field 506 has the same absolute value as the gradient magnetic field 506 and an opposite sign. Gradient magnetic field 50
Reference numerals 8, 509, 510 and 511 apply a frequency encoding to a signal and apply it to collect it as an echo signal. The gradient magnetic fields 508, 509 and 510 form a phase insensitive gradient magnetic field application pattern. Gradient magnetic fields 510, 5
Although the phase sensitive gradient magnetic field application pattern is formed by 11, this may be a phase insensitive gradient magnetic field application pattern like 508, 509 and 510. The signal is measured while changing the phase-encoded projection 506 before and after the brain function activation with the imaging target as the head, especially near the crown.
When the image is reconstructed and the subtraction process is performed between the images, an image in which changes in brain function activation are drawn is obtained from the image of the signal sampled through the period 512 or 513.
An image in which the blood flow is drawn as a high signal region is obtained from the signal sampled through 12, and an image in which the cerebrospinal fluid existing on the brain surface is emphasized and the brain surface structure is drawn is simultaneously obtained from the signal sampled during the period 513. The gradient magnetic fields 514 and 515 are phase encoding gradient magnetic fields in the slice direction. The relationship between the gradient magnetic fields 514 and 515 is the same as the relationship between the gradient magnetic fields 506 and 507. After the A / D sampling around the phase, the absolute values are equal and the signs are opposite to each other so as to restore the original values. FIG. 1 is a diagram for explaining the synthesis of an image showing changes in functional activation, a brain surface image, and a blood flow image. Reference numeral 601 is an image showing changes in brain function activation, 602 is a brain surface image, and 603 is a blood flow image near the brain surface. Brain function activation change image (metabolic activation change image) 60
1. The composite image 604 is an image obtained by weighting addition of the brain surface image (brain surface structure image) 602 and the blood flow image 603, or coloring and adding different colors. When the three images are added, if the three images are added as they are, the three pieces of information may not be satisfactorily discriminated on one image because the respective signal intensities are different. Therefore, an image having a weak signal strength is multiplied by a constant value, amplified, and added. That is, weighting is performed as follows: pixel value of combined image = pixel value of brain surface image × A + pixel value of blood flow image × B + pixel value of brain function activation change image × C. For example, the value of A, B, C is A
= 1, B = 1.2, C = 1.5.

From the synthetic image 604, the brain function activation change site can be seen, and the reason why the brain function activation change image is obtained is due to the activation change or the change in the blood flow in the vein. You can judge whether it is something.

It is also understood that these images are obtained by simultaneous measurement using the same pulse sequence.

FIG. 7 shows the relationship between the stimulus source and the centers activated by the stimulus. Reference numeral 701 is a stimulus source, 702 is a sensory organ of a human body that receives the stimulus, and 703 is a center of the head activated by the stimulus. As the stimulation source 701, a flushing light source is used when stimulating the visual sense, a sound source that generates a sound is used when the auditory sense is stimulated, and an operation such as moving a finger is performed when the stimulation of the motion is given. The sensory organ 702 of the human body receives the stimulus emitted from the stimulus source 701, thereby activating the center 703 of the brain corresponding to the stimulus.

FIG. 8 is a flow chart showing the relationship between the stimulus and the signal source.
It is a chart. First, the human body is stimulated (801),
A first signal measurement is performed (802). After the completion of the first signal measurement, the stimulation is stopped (803) and the second signal measurement is performed (8
04). Here, steps 801 and 803 may be performed first. After the second signal measurement, image reconstruction of the measured signals 1 and 2 is performed. Further, in this portion, a brain surface structure image is created, a blood flow image is created, and a brain function activation portion is extracted by subtraction processing of the signals 1 and 2. The brain surface structure image and the blood flow image can be created using either of the signals 1 and 2. Next, the brain surface structure image created in step 805, the blood flow image, and the image in which the brain functional active area is extracted are combined (806). Finally, the image combined in this step is displayed.

[0030]

According to the present invention, the following effects can be obtained.

(1) There is provided a magnetic resonance imaging apparatus capable of obtaining a change image of metabolic activation of a subject with high resolution.

(2) A magnetic resonance imaging apparatus suitable for identifying a place where a change in metabolic activation is occurring is provided.

(3) Magnetic resonance imaging suitable for determining whether the change image of metabolic activation is due to the change in metabolic activation or the change in blood flow in the vein. A device is provided.

(4) A magnetic resonance imaging apparatus that does not require measurement separate from measurement for obtaining a change image of metabolic activation in order to identify the place where the change in metabolic activation occurs Provided.

(5) In order to identify the place where the change in metabolic activation is occurring, or whether the change image of metabolic activation is truly due to the change in metabolic activation, or the change in blood flow in the vein. There is provided a magnetic resonance imaging apparatus which does not need to be separately measured from the measurement for obtaining a change image of metabolic activation in order to discriminate whether or not it is caused by.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of synthesis of a brain function activation change image, a brain surface image, and a blood flow image according to the present invention,

FIG. 2 is a block diagram of a magnetic resonance imaging apparatus showing an embodiment of the present invention,

FIG. 3 is a diagram showing a magnetic resonance signal generated in a steady precession state;

FIG. 4 is a diagram showing an example of a pulse sequence according to the present invention,

FIG. 5 is a diagram showing another example of a pulse sequence according to the present invention,

FIG. 6 is a diagram showing still another example of the pulse sequence according to the present invention,

FIG. 7 is a schematic diagram showing a relationship between a stimulus source and a brain center for understanding the present invention,

FIG. 8 is a diagram showing an example of an operation flow for explaining the operation of the present invention.

[Explanation of symbols]

101 ... Magnet, 102 ... Excitation system, 103 ...
Reception system, 104 / gradient magnetic field generation system, 105
..Image processing system, 106..Sequence control system, 107..Probe, 108..Operating console, 201
..FID signal, 202..Time-reversed FID signal

Claims (13)

[Claims] 1. A means for generating a static magnetic field, a means for arranging a subject in the static magnetic field, a means for stimulating the subject, and a steady precession motion for the spin of the subject. And a means for generating a signal representing a change in metabolic activation of the subject based on the stimulation by repeatedly applying a high frequency pulse to the subject, and generating an image of the subject based on the signal. A magnetic resonance imaging device characterized in that 2. A means for generating a static magnetic field, a means for arranging a subject in the static magnetic field, a means for stimulating the subject, and a steady precession motion for the spin of the subject. To generate a signal representing a change in metabolic activation of the subject based on the stimulation by repeatedly applying a high frequency pulse to the subject and a signal representing the surface structure of the subject,
A magnetic resonance imaging apparatus comprising: means for generating respective images of the subject based on these signals and displaying the images in an overlapping manner. 3. A means for generating a static magnetic field, a means for arranging a subject in the static magnetic field, a means for stimulating the subject, and a steady precession motion for the spin of the subject. A signal representing a change in metabolic activation of the subject based on the stimulus by repeatedly applying a high frequency pulse to the subject, a signal representing the structure of the surface of the subject, and a signal representing blood flow in the vicinity of the surface. A magnetic resonance imaging apparatus comprising: a means for generating and generating an image of each of the subject based on these signals, and superimposing and displaying the images. 4. The image generating means is configured to perform weighted addition processing on the signal representing the change in metabolic activation, the signal representing the structure of the surface of the subject, and the signal representing blood flow in the vicinity of the surface. The magnetic resonance imaging apparatus according to claim 3, wherein the magnetic resonance imaging apparatus is a magnetic resonance imaging apparatus. 5. The image generating means displays the signal representing the change in metabolic activation, the image representing the structure of the surface of the subject and the image representing the blood flow in the vicinity of the surface in different colors. The magnetic resonance imaging apparatus according to claim 3, wherein the magnetic resonance imaging apparatus is configured to: 6. A means for generating a static magnetic field, a means for arranging a subject in the static magnetic field, a means for stimulating the subject, and spins in the subject before and after applying the stimulus. Based on the magnetic resonance signals generated before and after the stimulation, means for repeatedly applying a high frequency pulse to the subject to generate a steady precession and generating magnetic resonance signals from the subject. And a means for generating an image showing a change in metabolic activation of the subject. 7. The magnetic resonance imaging according to claim 1, wherein the image generating means is configured to take a difference between magnetic resonance signals generated before and after the stimulation is given. apparatus. 8. A means for generating a static magnetic field, a means for arranging a subject in the static magnetic field, a means for generating a gradient magnetic field for giving a magnetic field gradient to the static magnetic field, and a stimulus for the subject. Immediately after the first high-frequency pulse, a high-frequency pulse is repeatedly applied to the subject so as to cause steady precession motions in spins in the subject before and after applying the stimulus. And a means for generating a second magnetic resonance signal immediately before the subsequent second high-frequency pulse, and one of the first and second magnetic resonance signals before the stimulation is given. A magnetic field generating means for generating a signal representing a difference between the magnetic resonance signal and the corresponding magnetic resonance signal after the stimulation and generating and displaying the image of the subject based on the signal. Both Ime - Managing devices. 9. The image generating and displaying means generates an image of the subject based on one of the first and second magnetic resonance signals before or after applying the stimulus,
9. The magnetic resonance imaging apparatus according to claim 8, wherein the magnetic resonance imaging apparatus is configured to display the image based on the signal indicating the difference so as to be superimposed on the image. 10. The image generating and displaying means generates an image of the subject based on the other signal of the first and second magnetic resonance signals before or after the stimulation is given, and represents the difference. The magnetic resonance imaging apparatus according to claim 9, wherein the magnetic resonance imaging apparatus is configured so as to be superimposed and displayed on an image based on a signal. 11. The gradient magnetic field generating means is configured to exclude a phase rotation of a moving spin in the subject with respect to the first magnetic resonance signal.
The magnetic resonance imaging apparatus described in No. 0. 12. The magnetic resonance imaging apparatus according to claim 10, wherein the image generating and displaying means is configured to display the images in different colors. 13. The magnetic resonance imaging apparatus according to claim 10, wherein the image generating and displaying means is configured to perform weighted addition processing on the image.