JP3316264B2 - Magnetic resonance imaging equipment - Google Patents

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 having a presaturation function.

[0002]

2. Description of the Related Art When displaying a tomographic image at an arbitrary position of a subject by a magnetic resonance imaging apparatus, a moving part, for example, a blood flow part or an abdomen moving by breathing is displayed in a display area of the tomographic image. Usually, an artifact occurs in the portion.

For this reason, in recent years, a magnetic resonance imaging apparatus having a so-called presaturation function for displaying images without such artifacts has been known.

[0004] A setting for applying the presaturation function to only a predetermined area of the displayed cross-sectional image can be made. In this setting, a display that clearly shows the predetermined area of the tomographic image is enlarged. Alternatively, it is performed together with the tomographic image in a state where the image can be reduced.

[0005] Thus, presaturation is performed in a predetermined area in a state where the area where the blissaturation is performed and the area where the blissaturation is not performed are sufficiently recognized by the display.

[0006]

However, the display device using the magnetic resonance imaging apparatus having such a configuration has a display that defines an area where presaturation is performed and an area where presaturation is not performed, depending on whether or not the function can be achieved. There is no problem in particular when the boundary of the display is clear, but usually, even within the region where presaturation is performed, a region where the effect is gradually increased from the boundary with the region where presaturation is not performed. Existing.

For this reason, presaturation is performed (in this case, the effect is sufficiently achieved).
There is a possibility that the region may be recognized as it is by the display, and a region where sufficient presaturation is not performed as described above may be recognized as being completely presaturated.

Therefore, it has been pointed out that the presaturation function cannot be sufficiently operated in a moving part, and that the artifact cannot be completely removed.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetic resonance imaging apparatus capable of completely removing artifacts.

[0010]

SUMMARY OF THE INVENTION In order to achieve such an object, the present invention relates to an area including a moving part of a subject.
Presaturation to remove area artifacts
Control means for executing the presaturation,
Display means for displaying a tomographic image obtained by the
The magnetic resonance imaging apparatus having the display
The device superimposes the presaturation area on the tomographic image
The presaturation area is displayed
At least two based on the effects of resaturation
Formed from a region and representing a boundary of the at least two regions.
It is characterized by showing .

[0011]

According to the magnetic resonance imaging apparatus configured as described above, the image is superimposed on the tomographic image displayed on the display device.
To display the presaturation area.
Presaturation area of presaturation
Formed from at least two regions based on the effect,
Presaturation by displaying area boundaries
Area can be divided according to its effect.

[0012] The at least two regions, for example, shows a high portion and a lower portion of the effect of the pre-saturation
And identify such presaturation effects.
In a state where easily the, it becomes possible to freely set the pre-saturating rate sucrose emission area.

[0013] Therefore, the lower part of the effect of Purisa trituration function, without thereby recognized as high as in the prior art, it is possible to accurately set the range to have a presaturation effect.

Therefore, the artifact can be completely removed from the displayed tomographic image.

[0015]

FIG. 3 is an overall block diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention.

The magnetic resonance imaging apparatus shown in FIG.
Broadly speaking, a central processing unit (CPU) 8, a sequencer 7, a transmission system 4, a static magnetic field generating magnetic circuit 2, and a reception system 5
And a signal processing system 6.

The central processing unit (CPU) 8 controls each of the sequencer 7, the transmission system 4, the reception system 5, and the signal processing system 6 according to a predetermined program. The sequencer 7 operates based on a control command from the central processing unit 8, and sends various commands necessary for data collection of tomographic images of the subject 1 to the transmission system 4 and the gradient magnetic field generation system 3 of the static magnetic field generation magnetic circuit 2. , To the receiving system 5.

The transmission system 4 includes a high-frequency oscillator 11 and a modulator 1
2 and an irradiation coil as a high-frequency coil 14a. The high-frequency pulse from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 in accordance with a command from the sequencer 7, and the amplitude-modulated high-frequency pulse is amplified via the high-frequency amplifier 13. By supplying the high-frequency coil 14a, the subject 1 is irradiated with a predetermined pulsed electromagnetic wave.

The static magnetic field generating magnetic circuit 2 generates a uniform static magnetic field around the subject 1 in an arbitrary direction. Inside the static magnetic field generating magnetic circuit 2, a high frequency coil 14a, gradient magnetic field coil groups 9a and 9b for generating a gradient magnetic field, and a high frequency coil 14b as a receiving coil of the receiving system 5 are arranged. Static magnetic field generation magnetic circuit 2
Is a gradient magnetic field coil group 9a, 9b having a configuration capable of independently applying a gradient magnetic field in the Cartesian coordinate axis direction orthogonal to each other, a gradient magnetic field power supply 10 for supplying a current to the gradient magnetic field coil groups 9a, 9b, Magnetic field power supply 10
Is controlled by a sequencer 7 for controlling

The receiving system 5 includes a high-frequency coil 14b as a receiving coil, an amplifier 15 connected to the high-frequency coil 14b, a quadrature phase detector 16, and an A / D converter 17
It is composed of When the high frequency coil 14b detects the NMR signal from the subject 1, the signal is amplified by the amplifier 1.
5. The digital data is converted into a digital value via the quadrature phase detector 16 and the A / D converter 17, and is converted into two series of collected data sampled by the quadrature phase detector 16 at the timing specified by the sequencer 7 to be centralized. The data is sent to the processing device 8.

The signal processing system 6 has an external storage device such as a magnetic disk 18 and a magnetic tape device 19 and a display device 20 such as a CRT. Data from the receiving system 5 is input to the central processing unit 8. Then, the central processing unit 8 executes processing such as signal processing and image reconstruction, and displays a desired cross-sectional image of the subject 1 on the display device 20 and the magnetic disk device 18 of the external storage device. Etc. are recorded.

FIG. 4 is an explanatory diagram showing an embodiment of a pulse sequence incorporated in the sequencer 2.

In the figure, sections I and II are sections where presaturation is performed, and sections III to VI are used.
Is a section for obtaining tomographic image information.

At this point, predetermined tomographic image information is obtained by first driving the sequence in the sections III to VI.
When the image is displayed on the display device 20, an area to be provided with a presaturation function is specified through the display device 20 as described later in detail. Then, the sequence of the sections I to VI is driven based on the designation.

That is, the sequence driving in the sections I and II is performed by the NM from the moving part of the designated subject.
The purpose is to invalidate the R signal.

The sequence in sections III to VI is
This is a pulse sequence showing a typical spin echo method among so-called two-dimensional Fourier imaging methods. In this pulse sequence, first, after applying a 90 ° pulse 30, a 180 ° pulse 31 is applied after the time of Te / 2, where the echo time is Te. After the 90 ° pulse 30 is applied, each spin starts to rotate in the XY plane at a unique speed, and a phase difference occurs between the spins with the passage of time. Here, when the 180 ° pulse 31 is applied, each spin is inverted symmetrically to the X axis as shown in FIG. 5D, and thereafter the spin is continued at the same speed for a time T.
At e, the spins refocus and form an echo signal 34.

Here, as described above, the echo signal 34
Is measured, but the spatial distribution of the signal must be obtained in order to form a tomographic image. For this purpose, a linear gradient magnetic field is used. By superimposing a gradient magnetic field on a uniform static magnetic field, a spatial magnetic field gradient can be created. Since the spin rotation frequency is proportional to the magnetic intensity, the spin frequency of each spin is spatially different when a gradient magnetic field is applied.
Therefore, by examining this frequency, the position of each spin can be known. For this purpose, the phase encoding gradient 35, the frequency encoding gradient 3
6, 37 are used.

Here, each section III to VI in FIG.
The behaviors of the respective spins in FIG. 5 are shown in association with (b) to (e) of FIG. FIG. 3A shows a thermal equilibrium state immediately before the application of a 90 ° pulse.

Next, sections I and II will be described.

In section I, a presaturation pulse 29 and a gradient magnetic field 32 are applied. Thus, the presaturation pulse 2
As shown in FIG. 16B, the spins of the presaturation region 43 selectively excited by 9 and the gradient magnetic field 32 immediately before the application of the first 90 ° pulse 30 for obtaining tomographic image information, No vertical component is generated at all.

Therefore, the NMR signal 34 generated after the application of the 90 ° pulse 30 and the 180 ° pulse 31 for obtaining tomographic image information does not include any signal from the presaturation area 43. .

In the section II, the gradient magnetic field applied to each axis is called a spoil gradient magnetic field, and performs spoiling of spins.

In this case, as shown in FIG. 7A, the tomographic image 1A obtained without the presaturation function has an artifact 42 in the phase encoding direction 41 due to the movement 40 of the abdomen. Will happen. However, as shown in FIG. 7B, a region surrounding the abdomen is designated as a presaturation region 43, and the designated region is provided with a presaturation function.
Can be obtained.

Next, the specification of the presaturation area 43 will be described with reference to FIG. In the figure,
A tomographic image 1A is displayed on a display surface 20A of the display device 20. Then, a display 50 for defining a presaturation area is provided on the display surface 20A. The display 50 includes, for example, a line segment (solid line) display 50B extending in the direction of the abdomen and the line segment (solid line) display 5
A line segment (solid line) display 50A extending crossing both ends of OB.

The display 50 can be moved to a predetermined position on the display surface 20, and the length of a line (solid line) display 50A can be arbitrarily changed. Such an operation can be performed using, for example, a keyboard on a console (not shown).

This makes it possible to designate a region between the respective line segment (solid line) displays 50B as a presaturation region.

In this embodiment, particularly, in the presaturation area, each line segment (solid line) display 50B
A line segment (dotted line) display 50C is also made in parallel with the above.

The line segment (dotted line) display 50C is shown in FIG.
As shown in FIG. 2A, the presaturation area in the line segment (solid line) display 50B is divided into a high effect area A and a low effect area a.
(B).

That is, in FIG. 2B, the horizontal axis indicates the width of the presaturation function, and the vertical axis indicates the degree of the presaturation function.

In the figure, the region A where the presaturation effect is high is a region where an effect of almost 100% can be expected as compared with the region where the presaturation effect is low.

Then, a line segment (solid line) display 50B and a line segment (dotted line) display 5 adjacent to the line segment (solid line) display 50B
The distance from 0C is determined by the characteristics of the magnetic resonance imaging apparatus. Therefore, if the length of the line segment (solid line) display 50A changes, the distance changes accordingly.

According to such an embodiment, a new display 50C is further added to the display 50 defining the presaturation area in the tomographic image 1A together with the tomographic image 1A on the display surface 20A of the display device 20. This new display 50C is
It defines the high and low effects of the tulation function.

This means that a high presaturation effect portion and a low presaturation effect portion can be distinguished by using the new display 50C as a guide, and an area where presaturation is to be performed in a state where the discrimination is easily recognized. It can be set freely.

[0044] Therefore, the lower part of the effect of Purisa trituration function, without thereby recognized as high as in the prior art, it is possible to accurately set the range to have a presaturation effect.

Therefore, artifacts can be completely removed from the displayed tomographic image 1A.

In the above-described embodiment, the presaturation for removing so-called respiratory motion artifacts has been described. However, the present invention is not limited to this. For example, in the case of presaturation for removing blood flow artifacts, Needless to say, it can be applied to

[0047]

As is apparent from the above description,
According to the magnetic resonance imaging apparatus of the present invention, it is possible to completely remove artifacts from a displayed tomographic image.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a main part of an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is an explanatory view of a main part of an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 3 is a schematic configuration diagram of one embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing one embodiment of a sequence used in the magnetic resonance imaging apparatus according to the present invention.

FIG. 5 is an explanatory diagram showing a principle of obtaining a tomographic image in the magnetic resonance imaging apparatus according to the present invention.

FIG. 6 is a principle explanatory diagram in which presaturation is performed in the magnetic resonance imaging apparatus according to the present invention.

FIG. 7 is an explanatory diagram for explaining presaturation of the magnetic resonance imaging apparatus according to the present invention.

[Explanation of symbols]

1A tomographic image 20 display device 20A display surface 50 line segment display (display indicating presaturation area) 60C line segment display (newly added in the present invention)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 G01R 33/20

Claims (1)

(57) [Claims] An object including a moving part of an object;
Pre-saturation to eliminate artifacts
Control means for performing and the presaturation
Display means for displaying a tomographic image obtained by the function
In the magnetic resonance imaging apparatus, the display device includes a pre-saturation area, the
The image is displayed superimposed on the image and the presaturation
The area is at least based on the effect of presaturation
Is also formed from two regions, of which at least two regions
A magnetic resonance imaging apparatus for displaying a boundary .