JPS6373944A - Magnetic resonance imaging apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention (Industrial Application Field) The present invention relates to magnetic resonance (IR)
The present invention relates to a magnetic resonance imaging apparatus (MRI apparatus) that forms an MR image of a subject using a phenomenon (referred to as "sonance").

(Prior art) In an MRI apparatus, the echo time is
(on the order of ec) is shortened to (1) S /
' N can be improved.

(2) T1 contrast can be improved.

(3) Artifacts caused by movement of the subject can be reduced.

This results in advantages such as: Therefore, the shortening of TE is (*m).

By the way, in order to generate echoes in the neck of an MRI, π-
There are two methods: one uses a pulse (180' pulse) (this is called the pulse echo method), and the other uses only gradient (B 3p inversion) (this is called the gradient l-echo method). The pulse sequences are shown in FIGS. 2(0) and (b), respectively.

In the same figure, Gs.

GR and GE are gradient magnetic fields in the slice direction, readout direction, and two-phase encode direction, respectively.

In the pulse-echo method, the phase disturbance caused by the non-uniformity of the static magnetic field is canceled before and after the π-pulse.
There is only a difference in frequency (the same applies to chemical Schiff 1~)
On the other hand, it has the disadvantage that it is difficult to shorten the echo time TE, and the effects (1) to (3) above cannot be obtained.

On the other hand, in the gradient echo method, it is easy to shorten the echo time TE, but (1) phase disturbance occurs between excited spins due to non-uniformity of the static magnetic field (static magnetic field). ■In the chemical shift phenomenon, excited spins (
Since protons are assumed here, a phase disturbance occurs between the two main components (water and fat). There are drawbacks such as. Therefore, when adopting the gradient echo method with emphasis on shortening the echo time in the conventional device, the above-mentioned item ①.

The reality is that the phase disturbance described in (2) is unavoidable.

(Problems to be Solved by the Invention) As mentioned above, when the pulse echo method is adopted in the conventional device, it is difficult to shorten the echo time TE, and when the gradient echo method is adopted, the static magnetic field There are problems such as phase disturbance caused by chemical shift.

The present invention has been made in view of the above circumstances, and its purpose is to be able to ignore phase disturbances caused by static magnetic field particles and chemical shifts, even though it is a gradient echo method. An object of the present invention is to provide an MRI apparatus that can obtain magnetic resonance images with excellent diagnostic performance.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the gyromagnetic ratio is T, the chemical shift is δ,
When the static magnetic field strength is Ha, the echo time TE in the pulse sequence of the gradient pulse method is (γ
a system controller that controls magnetic resonance signal collection in a sequence that is an integer multiple of δHo)−1; and an imager that forms a magnetic resonance image of the subject by taking the absolute value of a complex image based on the collected magnetic resonance signals. and an image creation section.

(for production) The operation of the above configuration will be explained below.

As mentioned above, in the gradient echo method, there are effects of static magnetic field and chemical shift, and the repurchase-MR image is expressed as follows.

That is, f (x, V) = f ・N (X, V) + fF (x
, V): Proton distribution fw (X, V): Water fF (X, V): Fat γ: Magnetic rotation ratio Δl-1 (X, y): Distortion of static magnetic field δ: Chemical shift (3,5 ppm) Then, the reconstructed image f (x.

y) is f (x, y) = e ”π1γΔH(X', V)T
E fw (X・, Haya. 2 π i T (δ
t10 + ΔH(x″, V)) TE
f w (X”, V)
...It is expressed as (1).

However, X'0ΔH(x', V)=XX//+ΔH
X", V) 1 δHa =
X, V) TE(fw (x, y) +627r iγδ
” TEfr (x, V))...(2) If we create an absolute value image under the condition that TδHo'Tε is an integer (as a general rule, it is a non-negative value), it will be a normal image using the spin echo method. is obtained, because
Under this condition, l f(x, y)l= l e2π1γΔH(X, V
)TE ll fw (x, V)+fF(X, V)
l = l fw (X, V) + fF (X, V)
! = f w (x, V) + fF (X, V) =
This is because f (X, V) (3). Here, since HO is also a constant, TE
This indicates that the value of must be a multiple of 1/(γδ+10). Note that this value is as shown in the table below.

Therefore, under the control of the system controller, TE =
(γδH0)-1X (positive integer) ・By collecting data under the conditions of (4) and creating an absolute value image using the image creation unit, it is possible to obtain normal spin even though it is a gradient echo method. Similar to echo images, it is possible to obtain images with extremely little phase disturbance due to magnetostatic toothpicks or chemical shifts.

(Example) Examples of the present invention will be described below.

FIG. 1 is a block diagram of an MRI apparatus that is an embodiment of the present invention. This device uses a 1° excitation pulse (R
F pulse) transmitting section 2. Gradient magnetic field generator 3. System controller 4. It has a signal collection section 5, an image creation section 62, and an image display section 7.

The static magnetic field generator 1 generates a uniform static magnetic field,
The subject P is placed in this uniform magnetic field.

Further, the excitation pulse transmitter 2 transmits excitation pulses to the subject P, and the gradient @Yang generator 3 generates various gradient ta fields in the slice direction, the readout direction, and the two-phase encode direction. The signal collecting unit 5 collects magnetic resonance signals (MR signals) from the subject P, and the system controller 4 controls the static magnetic field generating unit 1. Excitation pulse transmitter 2, gradient magnetic field generator 3. It controls the operation of the signal collection section 5. The pulse sequence by the system controller 4 is basically the same as that shown in FIG. 2(b), but here the echo time TE is set so as to satisfy the following equation.

TE (γδH0)−1X (positive integer)−(5) where γ: gyromagnetic ratio δ: chemical shift (water and fat) Ho: static magnetic field strength.

Further, the image creation section 6 creates a magnetic resonance e (M configuration image) of the subject P by taking the absolute value of a complex image based on the MR multiplied signal collected by the signal collection section 5. (See equation (3)), the image display section 7 displays the magnetic resonance image created by the image creation section 6.

In the above configuration, under the control of the system controller 4, MR signal collection of the subject P (7) is performed using a pulse sequence using a gradient echo method that satisfies the previous equation (5), and the collected MR multiplied signal image creation unit 6 is sent out. Then, in the image creation section 6, an MR image of the subject P is formed by taking the absolute value of the complex image based on the MR multiplied signal, and this MR image is displayed on the image display section 7 and used for diagnosis.

In this way, in the present embodiment, the pulse sequence using the gradient echo method that satisfies the equation (1)
R signal'! 3. Since it is designed to obtain an MR image of the subject by performing acquisition control and taking the absolute value of the complex image, it is similar to the normal spin echo method, as it is a magnetostatic It is possible to obtain an image with extremely little phase shift due to toothpick or chemical shift].

Moreover, since it uses a gradient echo method,
Easily shortens echo time TE and improves S/N of MR images.

It is possible to easily improve T1 contrast 1 and reduce body motion arch 7 and so on.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above-mentioned embodiment and can be implemented in various modifications.

[Effects of the Invention] As detailed above, according to the present invention, phase disturbances caused by magnetostatic toothpicks and chemical shifts can be ignored despite the gradient echo method, resulting in excellent diagnostic performance. An MRI apparatus capable of obtaining magnetic resonance images can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, ff12
Figures (a> and (b) are explanatory diagrams of pulse sequences using a pulse echo method and a gradient erotic method, respectively. 4... System controller, 6... Image creation unit, P... Subject. Agent Patent Attorney Norihiro Chika Norio Ogo Figure 1

Claims (1)

[Claims] In a magnetic resonance imaging apparatus that forms a magnetic resonance image of a subject using magnetic resonance phenomena, when the gyromagnetic ratio is γ, the chemical shift is δ, and the static magnetic field strength is H_0, the pulse sequence of the gradient pulse method A system controller that controls magnetic resonance signal collection in a sequence in which the echo time T_E is an integer multiple of (γδH_0)^-^1, and a system controller that controls magnetic resonance signal collection in a sequence in which the echo time T_E is an integer multiple of (γδH_0)^-^1; What is claimed is: 1. A magnetic resonance imaging apparatus, comprising: an image creation unit that forms a magnetic resonance image of the image.