JPH07124135A - MRI apparatus and coil positioning method - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a coil positioning method in an MRI apparatus capable of positioning a receiving coil with high accuracy. [Structure] A marker is attached to the center of the receiving coil, NMR signals from this marker are collected, and the position of the marker is determined from the collected result. Then, the position of the receiving coil is adjusted so that the marker position becomes a desired position. [Effect] The coil can be accurately and easily aligned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning method for setting a receiving coil used in an MRI apparatus (magnetic resonance imaging apparatus) at a predetermined position in an imaging area.

[0002]

2. Description of the Related Art In recent years, as medical diagnostic apparatuses have been developed, MRI apparatuses for noninvasively imaging the inside of a subject have come to be widely used. The MRI apparatus injects a subject into a static magnetic field, applies a gradient magnetic field and an RF pulse in a predetermined pulse sequence, and generates an NM.
An R image is received and the received signal is reconstructed to obtain an MR image (magnetic resonance image).

In such an MRI apparatus, NMR
It is necessary to position the receiving coil for receiving the signal and the center of the magnetic field which is the reference for applying the gradient magnetic field. That is, matching the center of the receiving coil with the center of the magnetic field is a condition for obtaining a highly accurate MR image.

In the conventional coil positioning, for example, in the case of a surface coil used as a receiving coil on the waist or the like, the affected part of the patient (the part to be imaged) is set at the position considered to be the center of the coil. Then, after adjusting the affected area to the projector for positioning,
The method of sending to the center of the magnetic field is used. However, in such a method, especially when photographing the lumbar region, the center of the surface coil is hidden by the patient's body, making it difficult for the operator to recognize, so it is necessary to determine where the coil position is with respect to the magnetic field center. Hard to do.

On the other hand, NMR signals are collected using a plurality of element coils such as a multi-coil, and then the collected signals are subjected to processing such as filtering and weighting to obtain a three-dimensional image or a plurality of tomographic images. When the method is adopted, it is essential to know the positional relationship between each element coil and the magnetic field center accurately and easily in order to obtain a highly accurate image quality.

However, in order to execute this by the conventional method, the procedure is such that the position of the coil is first adjusted by the light projector, and then the patient is put to a predetermined position, so that the patient cannot be arbitrarily placed anywhere. There was a drawback.

[0007]

As described above, in the conventional coil positioning method for the MRI apparatus, since accurate positioning cannot be performed, the burden on the patient increases, the operation time increases, the position accuracy decreases, and the like. There was a problem.

The present invention has been made to solve such a conventional problem, and an object thereof is to provide a positioning method capable of positioning a receiving coil with high accuracy.

[0009]

In order to achieve the above object, the present invention provides a receiving coil for receiving an NMR signal generated in an object to which an RF pulse is applied, at a predetermined position in an imaging region. In a coil positioning method for a matching MRI apparatus, an NMR signal from a marker, which is attached to a predetermined position of the receiving coil and is made of a substance that emits a strong NMR signal, is collected using a predetermined pulse sequence, It is characterized in that the marker position is obtained based on, and the position of the receiving coil is moved to a desired position based on the positional relationship between the marker position and the magnetic field center of the imaging region.

Further, a tabletop movable in a predetermined direction by a desired distance, receiving means arranged on the tabletop for receiving an NMR signal from a subject, and provided at a predetermined position of the receiving means. A marker composed of a substance that emits a strong NMR signal, a means for determining the position of the marker based on the NMR signal received by the receiving means, and the top plate based on the determined position of the marker. And a moving unit that moves to a desired position.

[0011]

According to the present invention constructed as described above, the marker is attached to the center of the receiving coil, and the NMR signal from the marker is collected by the pulse sequence such as the spin echo method. Then, the distance between the magnetic field center and the marker position is obtained by a predetermined calculation based on the frequency of the NMR signal. If the coil is moved based on this distance, the coil position can be easily and accurately adjusted to the desired position.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a diagram showing a state in which a patient is placed on a multi-coil composed of a plurality of element coils (three in the figure) in a sagittal section. That is, reference numeral 1 shown in the figure shows a human body, 2 is a mat, and 3a to 3c are element coils for receiving an NMR signal.
Reference numeral 7 denotes a top plate provided on the bed, and the top plate driving means 11
Can move a desired distance in the Z direction. The NMR signals received by the element coils 3a to 3c are input to the calculating means 10 via the receiving circuit 9. Calculation means 10
Calculates the position of the marker as described later. Further, the line indicated by the dotted line of H ₀ indicates the center of the magnetic field, and here, the line is G _Z = 0 (the gradient magnetic field in the Z direction is 0).

At the center of the coil 3c, there is provided a marker 4 which is made of a substance such as baby oil which emits a strong NMR signal. The marker 4 is placed at the center of the element coil 3c in the horizontal and vertical directions. What is placed at the center in the horizontal direction is a preliminary means for knowing the distance from the center of the element coil 3c to the center of the magnetic field, and what is placed at the center in the vertical direction obtains a stronger signal from the marker 4. This is because. Then, for such a setting, the read magnetic field G as shown in FIG.
_{When R} is applied and the projection data is collected and Fourier-transformed, a strong signal can be obtained from this data only in the region of the marker 4 as shown in FIG. 1 (c). That is, in the figure, portions 5a and 5b are signals obtained only from the human body 1, and reference numeral 6 is a signal from the marker 4 and the human body 1. Since only the signal of the marker 4 is the signal of interest in this operation, the other element coils 3a and 3b may be turned off by the switch 8 in the case of the multi-coil as in this embodiment.

The sequence for obtaining the projection data may be the spin echo method as shown in FIG. 2, for example. The slice gradient magnetic field G _R is applied in the X direction, and the read gradient magnetic field G _S is applied in the Z direction. Also, similar data can be obtained by using the field echo method. Here, the read gradient magnetic field G _R
The unit of is defined as [H _Z / cm], which is N
In the MR phenomenon, f ₀ [H _Z ] = (γ / 2π) · H
₀ (γ: gyromagnetic ratio, H ₀ : magnetic field strength), which is based on the fact that the magnetic field strength and frequency are uniquely determined when the target nuclide is determined.

Then, the frequency at the point where the signals from the human body 1 and the marker 4 are added as shown in FIG. 1 (c) can be easily obtained from the Fourier transform data by the calculating means 10, and the frequency is calculated. Is defined as f ₀ + Δf, the distance d from the magnetic field center H ₀ shown in FIG.
Can be calculated by the following equation (1).

[0016] _{d = (f 0 + Δf-} f 0) / G R [cm] ... (1) the positive side of the Z-axis direction when the value of the time d is plus, d
When the value of is negative, the marker 4 exists on the negative side in the Z-axis direction.

Information of the distance d from the magnetic field center H ₀ thus obtained to the marker 4 is input to the top driving means 11. When the table driving means 11 moves the table 7 by the distance d, the position of the marker 4 coincides with the center of the magnetic field, and the positioning of the coil is completed.

Further, in the multi-coil, since the relative positional relationship among the element coils 3a to 3c is usually fixed, other element coils can be obtained if the distance from the center of the element coil 3c to the magnetic field center H ₀ is known. 3a,
The distance from 3b to the magnetic field center H ₀ can be easily obtained. Therefore, it is possible to position the element coils 3a and 3b at the center of the magnetic field.

In this way, in this embodiment, the marker 4 is arranged at the center of the element coil 3c, and the marker 4
The signal from the element coil 3c is collected to obtain the distance between the element coil 3c and the magnetic field center H ₀ . Therefore, the coil can be positioned easily and accurately.

In this embodiment, the example of the multi-coil having a sagittal section is described, but the present invention is not limited to this, and it is obvious that other receiving coils and other sections can be applied. is there. In addition, the same procedure as in the above embodiment is used for other
If it is applied to a cross section, it is possible to obtain a three-dimensional position.

[0021]

As described above, according to the present invention,
Positioning of the receiving coil can be performed easily and accurately. As a result, problems such as a burden on the patient are solved, and an effect that the MRI image can be taken smoothly can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the method of the present invention.

FIG. 2 is an explanatory diagram showing a pulse sequence of a spin echo method.

[Explanation of symbols]

1 human body 2 mats 3a to 3c element coil 4 marker

Claims (2)

[Claims] 1. A coil positioning method in an MRI apparatus for aligning a receiving coil for receiving an NMR signal generated in a subject to which an RF pulse is applied, with a predetermined position in an imaging region, comprising: NM from a marker attached to a fixed position and composed of a substance emitting a strong NMR signal
Collecting an R signal using a predetermined pulse sequence, obtaining a marker position based on this, and moving the receiving coil position to a desired position based on the positional relationship between the marker position and the magnetic field center of the imaging region. A method for positioning a coil in an MRI apparatus characterized by the above. 2. A top plate movable in a predetermined direction by a desired distance, receiving means arranged on the top plate for receiving an NMR signal from a subject, and provided at a predetermined position of the receiving means. A marker composed of a substance that emits a strong NMR signal, a means for determining the position of the marker based on the NMR signal received by the receiving means, and the top plate based on the determined position of the marker. An MRI apparatus comprising: a moving unit that moves to a desired position.