JPH0578342B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention is directed to magnetic resonance (MR).
Magnetic resonance imaging equipment that uses the resonance phenomenon to obtain morphological information such as slice images of a subject (living body) and qualitative information such as spectroscopy, and is particularly capable of imaging blood flow velocity. The present invention relates to an imaging device.

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs only electromagnetic waves of a specific frequency. It resonates at the angular frequency ω ₀ (ω ₀ =2πν, ν ₀ : Larmor frequency).

ω ₀ =γH ₀ where γ is the gyromagnetic ratio specific to the type of atomic nucleus, and H ₀ is the static magnetic field strength.

The device that performs biological diagnosis using the above principles is
The electromagnetic waves of the same frequency as above that are induced after the above-mentioned resonance absorption are signal-processed to generate diagnostic information that reflects information such as nuclear density, longitudinal relaxation time T ₁ , transverse relaxation time T ₂ , flow, chemical shift, etc. Slice images of the subject are obtained non-invasively.

Collecting diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical requirements for imaging images. from,
The actual device excites a specific region and collects its signals.

There is a method that applies blood flow velocity as a target of this non-invasive imaging. In other words, in principle,
When a blood vessel to be imaged in a subject runs along the Z-axis, if a certain slice plane along the Z-axis is selectively excited and only the blood within this slice plane is excited, after the echo time T _E Since this blood is extracted from the slice surface by a distance d, the velocity V=d/T _E can be determined by measuring this distance d. Conventional blood flow velocity imaging methods that utilize this principle perform frequency encoding in the Z-axis direction after excitation of the slice plane to obtain blood position information in the Z-axis direction, and phase information in the X and Y axes. There is a method of performing encoding to obtain position information of blood in the X and Y axis directions.

In this method, after selectively exciting the slice plane,
Since signals are collected by identifying only the flow velocity direction from the excitation area of the blood to be imaged, although the blood flow is visualized, it is difficult to identify the positional relationship of how the blood flows in the blood vessels. It is not possible. For this reason, in clinical settings, different images are displayed in parallel in order to identify the positional relationship of blood flow.
Therefore, there has been a problem that clinically usable diagnostic information cannot be obtained unless blood flow velocity imaging and tomographic imaging are performed, making it impractical.

(Problems to be Solved by the Invention) As described above, in the conventional technology, the obtained blood flow velocity information can only identify the direction of flow velocity from the excitation region of the blood to be imaged, and is not clinically useful. There was a problem that it could not be used as

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that obtains blood flow velocity information that can identify the direction of flow velocity from an excitation site of blood to be imaged and its positional relationship.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized by taking the following measures in order to solve the above problems and achieve the object. That is, a static magnetic field generating means for generating a static magnetic field to be applied to the subject; a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the subject together with the static magnetic field; A high-frequency pulse generating means for generating a selective excitation pulse related to the excitation of protons, which is applied together with a gradient magnetic field; a coil, which applies the gradient magnetic field and selective excitation pulse under predetermined conditions to the subject placed in the static magnetic field, selectively exciting a first region orthogonal to a specific blood vessel within the subject; a control means for executing a pulse sequence for selectively exciting a second region along the direction in which the specific blood vessel runs; and when the control means is driven, the second region
Reconstruction processing means for obtaining tomographic image information of the second region by reconstructing an echo signal as a magnetic resonance signal induced from the region and obtained from the receiving coil.

(Function) According to such a configuration, the first region and the excited blood existing in the region move due to the blood flow velocity and appear in the second region, and this blood is selectively excited in the second region. Since the signal is saturated and becomes a low signal level, the positional relationship of the blood vessel on the second region can be recognized.

(Example) An example of a magnetic resonance imaging apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the magnetic resonance imaging apparatus of this embodiment.

As shown in FIG. 1, the magnetic resonance imaging apparatus in this embodiment includes a bed 1 having a movable top plate 1a on which a subject P is placed, and a static magnetic field coil (a shim coil for static magnetic field correction is added). ) 2. A probe 4 consisting of a gradient magnetic field generating coil 3 for generating a gradient magnetic field, and a coil as a transmitting/receiving system for transmitting a rotating high-frequency magnetic field and detecting the induced magnetic resonance signal (MR signal). The main body part 5 is configured by a static magnetic field power supply 6, an X axis, a Y axis, and
axis, Z-axis gradient magnetic field power supplies 7, 8, 9, transmitter 10,
It is comprised of a sequencer 12 that drives the receiver 11 with a desired pulse sequence, and a computer system 13 that controls these and performs signal processing of detection signals and display thereof.

In such a configuration, the subject P is placed by moving the top plate 1a of the bed 1 in the static magnetic field generated by the static magnetic field coil 2, and the pulse sequence shown in FIG. 2 or 3 is performed by the operation of the sequencer 12. For example, the transmitter 10 is driven to apply a rotating magnetic field from the transmitting coil of the probe 4, and the gradient magnetic field power supplies 7, 8, and 9 are driven to apply a gradient magnetic field from the gradient magnetic field generating coil 3.

That is, in the pulse sequence shown in FIG. 2, when a blood vessel along the Z-axis direction is to be imaged, a Z-axis gradient magnetic field Gz is applied as a slicing gradient magnetic field (Z
The axis is perpendicular to the target vessel. ) Then, as shown in FIG. 2a, a 90° RF pulse is applied to selectively excite the first slice plane _S1 shown in FIG. 4. Then the first
In order to selectively excite the second slice plane S ₂ that includes the slice plane S ₁ and is along the imaging target blood vessel, a Y-axis gradient magnetic field Gy is applied as a slicing gradient magnetic field as shown in FIG. ), and as shown in FIG. 2a, a 90° RF pulse is applied to selectively excite the second slice plane _S2 shown in FIG. 4.

Then, as shown in Figure 2d, the second slice plane
Apply a Z-axis gradient magnetic field Gz to encode the signal collection at S ₂ , as shown in Figure 2a.
Normal encoding by applying 180° RF pulse, Y-axis gradient magnetic field Gy in read gradient magnetic field application method,
An echo signal due to magnetic resonance is generated by applying the X-axis gradient magnetic field Gx as shown in FIG. By performing signal processing such as processing, tomographic image information of the second slice plane is obtained, and an image is displayed as shown in FIG.

As shown in FIG. 5, on the second slice plane _S2 ,
The blood in the blood vessels BV ₁ and BV ₂ excited at the first slice plane S ₁ moves by distances d ₁ and d ₂ from the first slice plane S ₁ due to the blood flow velocity, resulting in a low signal level.

Here, since the slice thickness h of the first slice plane S ₁ , the excitation time difference T between the first slice plane S ₁ and the second slice plane S ₂ , and the echo time T _E can be known, the blood vessel BV ₁ ,
The blood flow velocities V ₁ and V ₂ of BV ₂ can be calculated using the following formulas.

V ₁ = d ₁ /T _E , V ₂ = d ₂ /T _E Also, based on the above data and _the displayed image in FIG. and quantitative information can be clearly recognized visually.

The present invention is not limited to the above embodiments, and the pulse sequences shown in Fig. 3a, b,
The gradient echo method sequences shown in c, d, and e may also be implemented. Furthermore, in the above embodiment, the first slice plane _S1 is set perpendicular to the Z-axis to be perpendicular to the blood vessel, and the second slice plane _S2 is set to be perpendicular to the blood vessel, on the premise that the blood vessel to be imaged is along the Z-axis. Although the X-axis is set perpendicular to the 1-slice plane S ₁ , slice planes with various inclinations are set depending on the morphology of the blood vessel to be imaged within the subject, and are not limited to this, to obtain the desired blood flow velocity. It is capable of performing imaging. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus that can recognize the positional relationship of blood vessels using images.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the magnetic resonance imaging apparatus according to the present invention, FIG.
4 is a diagram showing a pulse sequence, FIG. 4 is a diagram showing setting of a slice plane, and FIG. 5 is a diagram showing an example of display by imaging. 1... Bed, 2... Static magnetic field coil, 3... Gradient magnetic field generating coil, 4... Probe, 5... Main body, 6... Static magnetic field power supply, 7... X-axis gradient magnetic field power supply, 8... Y-axis gradient magnetic field power supply, 9... Z Axial gradient magnetic field power supply, 10... Transmitter, 1
1...Receiver, 12...Sequencer, 13...Computer system.

Claims (1)

[Scope of Claims] 1. A static magnetic field generating means for generating a static magnetic field to be applied to the subject; a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the subject together with the static magnetic field; a high-frequency pulse generating means for generating a selective excitation pulse related to the excitation of protons, which is applied together with the static magnetic field and the gradient magnetic field; a receiving coil disposed in the static magnetic field; the gradient magnetic field and the selective excitation pulse being applied under predetermined conditions to the subject placed in the static magnetic field; a control means for executing a pulse sequence for selectively exciting one region and then selectively exciting a second region along a direction running toward the specific blood vessel; and when this control means is driven, the second region
A magnetic resonance imaging apparatus comprising: reconstruction processing means for obtaining tomographic image information of the second region by reconstructing an echo signal as a magnetic resonance signal induced from the region and obtained from the receiving coil.