JPH03264048A - Mri device - Google Patents

Abstract

PURPOSE:To obtain an MRI device which uses an RF shielding member in a sanitary manner by installing the RF shielding member free from the contact with an inspected body in an RF magnetic field. CONSTITUTION:An RF shielding member 6 is constituted of a mesh type shielding member 6a made of the nonmagnetic and electric-conductive material such as copper and carbon, and a supporting frame 6b which is made of the insulating material such as resin and supports the shielding member 6a. A projecting handle 6c is installed at one edge part of the supporting frame 6b. Further, the shielding member 6a is supported from the above and below through a screw 8 by a pair of supporting frame 6b. The RF shielding member 6 is installed on a ceiling plate 5 and supported by a flexible supporting member 7, and installed so as not to contact an inspected body 3. The RF shielding member 6 can be installed so as to approach an arbitrary nonrelated region of the inspected body through the deformation of the flexible supporting member 7. Since the inspected body 3 is installed in an RF magnetic field free from the contact with the RF shielding member 6, the MR signal supplied from the nonrelated region can be suppressed in a sanitary manner. Accordingly, the inspected body is prevented from being given with the discomfortable feeling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an MRI apparatus that suppresses detection of MR multiplied signals from regions of no interest in a subject.

(Prior Art) As shown in FIG. 17, an MRI (magnetic resonance imaging) apparatus includes a static magnetic field formed by a main magnet 1 and a gradient magnetic field formed by a gradient magnetic field coil 2 for detecting position information. The subject 3 is placed in a superimposed magnetic field, and the transmitter/receiver coil 4 applies an RF magnetic field H to the subject 3 to excite the target nuclide, and when the application of the RF magnetic field is stopped, the target nuclide generates An MR (magnetic resonance) signal is detected by a transmitting/receiving coil 4, and an image of a desired region is reconstructed based on the signal to obtain diagnostic information.

The transmitting/receiving coil 4 may be provided independently for transmitting and receiving. 5 is a top plate for supporting the subject.

Here, M detected from the subject by the transmitting/receiving coil 4
The R-fold signal distribution is determined by the sensitivity distribution of the transmitting/receiving coil 4. On the other hand, depending on the region to be diagnosed, unnecessary MR multiplied signals may be detected from a region adjacent to the region (non-interest region), and in this case, there is a risk of obtaining erroneous diagnostic information. Therefore, in such a case, the shape of the transmitting/receiving coil 4 must be devised to change the sensitivity distribution so as to prevent or suppress unnecessary MR multiplied signal detection from the non-interest region. However, depending on the requirements, it is necessary to prepare transmitter/receiver coils with complicated shapes, so there is a drawback that it takes time and effort to form them.

In order to eliminate these drawbacks, the shape of the transmitter/receiver coil remains the same, but an RF shield member is attached near the area of non-interest of the subject to absorb unnecessary MR multiplied signals.
I device is shown in Japanese Patent Application Laid-Open No. 1-146532. As shown in Fig. 18, this MRI apparatus has a non-magnetic
An RF shielding member 2 is obtained by wrapping a strip 21 made of a flexible and conductive material with a soft material 22 that is an electrical insulator.
3, and this RF shield member 23 is attached to a non-interest area such as the arm of the subject. According to such an MHI device, the MR multiplied signal from the arm, which is a region of no interest, is absorbed by the RF shield member 23, so it is controlled, and only the MR multiplied signal from the necessary diagnosis target region is absorbed. be able to be detected.

(Problems to be Solved by the Invention) However, in conventional MHI devices, the RF shield member is attached to a non-interest area of the subject, which results in unsanitary conditions and causes discomfort to the subject. . Also R
When the F shield member is attached, it is likely to fall off or shift laterally, making it difficult to accurately suppress the MR multiplied signal from the region of no interest.

The present invention has been made in response to the above-mentioned problems.
MHI that uses RF shielding materials for sanitary purposes
The purpose is to provide a device.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for locating a subject in a magnetic field in which a gradient magnetic field is superimposed on a static magnetic field, and applying an RF magnetic field to a desired region. The MRI apparatus detects an MR multiplied signal from the RF magnetic field, and is characterized in that an RF shield member is installed within the RF magnetic field without contacting the subject.

(Function) The RF shield member is placed within the RF magnetic field without coming into contact with the subject. As a result, the MR multiplied signal RF shield member from the region of non-interest is not placed in contact with the subject (
Furthermore, since the RF shield member does not fall off or shift laterally, it is possible to obtain diagnostic information hygienically and accurately. Further, by configuring the impedance characteristics of the RF shielding member to be controllable as necessary, the shielding effect can be varied.

(Example) The present invention will be described in detail below with reference to the drawings.

FIGS. 1(a) and 1(b) are a cross-sectional view and a vertical cross-sectional view showing an embodiment of the MRI apparatus of the present invention, in which 1 is a main magnet that forms a static magnetic field, and 2 is an inclined part for detecting position information. A gradient magnetic field coil that forms a magnetic field, 3 is a subject placed in a magnetic field in which a gradient magnetic field is superimposed on these static magnetic fields, and 4 is placed around the subject 3 to apply an RF magnetic field to the subject 3. In addition, a transmitting/receiving coil 5 detects the MR multiplied signal from the subject 3.
is the top plate.

Reference numeral 6 denotes an RF shielding member, which is installed in a direction interlinking with the RF magnetic field H formed by the transmitting/receiving coil 4, and this RF shielding member 6 is attached to the top plate 5 and supported by a flexible support member 7. and is installed so as not to come into contact with the subject 3.

By deforming the flexible support member 7, the RF shield member 7 can be placed close to any non-interest area of the subject.

FIG. 2 shows details of the RF shielding member 6, including a mesh-shaped shielding material 6a made of a non-magnetic and conductive material such as copper or carbon, and an insulating material such as various resins supporting this shielding material 6a. The support frame 6b is made of a material, and a protruding handle 6c is provided at one end of the support frame 6b. As is clear from the cross-sectional view in Figure 3,
The shield material 6a has a structure in which it is supported from above and below by a pair of support frames 6b via screws 8.

5(a), (b), and (c) show details of the flexible support member 7, which is shown in (a).
), it is composed of, for example, a pair of flexible pipes 7a, a holder 7b as shown in (b) provided at its upper end, and a support 7c shown in (C) provided at its lower end. As shown in (C), a rail 9 is provided in advance in the center of the top plate 5, and this rail 9 supports) 7
By guiding and fixing c, the flexible support member 7 is movable in the length direction of the top plate 5. Holder 7b
By positioning the RF shield member 6, it is possible to firmly support it.

According to this embodiment, since the RF shielding member 6 is placed in the RF magnetic field without contacting the subject 3, it is possible to hygienically suppress the MR multiplied signal from the region of no interest. Therefore, the subject will not feel uncomfortable. In addition, since the RF shield member 6 is firmly attached to the top plate 5 by the flexible support member 7, it does not fall off or shift laterally as in the conventional case, so it is possible to accurately detect MR from non-interest areas.
The signal can be suppressed twice. The position of the flexible support member 7 can be moved to any desired position by moving on the rail 9 or by deforming the flexible pipe 7a, so the RF shield member 6 can be easily optimized depending on the area of non-concern. installed in position. The embodiment shown in FIG. 1 shows an example in which the RF shield member 6 is installed close to the chest.

FIG. 4 shows that the shield material 6a is attached to the support frame 6 by adhesive 10.
An example is shown in which it is supported by b. Further, FIG. 6 shows a modification of the RF shield member 6, in which the entire structure is curved to match the surface shape of the subject 3. As shown in FIG. For finely curved parts such as arms and legs, it is also possible to further curve them into a saddle-like shape.

FIG. 7 shows a second embodiment of the present invention, in which 1 is a main magnet, 2 is a gradient magnetic field coil, 3 is a subject, 4 is a transmitting/receiving coil, and 5 is a top plate. Reference numeral 11 denotes an RF shielding member, which is installed in a direction that is slightly inclined to and interlinks with the RF magnetic field H formed by the transmitting/receiving coil 4. As in the previous embodiment, this RF shield member 11 is supported by a flexible support member (not shown) and is installed so as not to come into contact with the subject 3. As shown in FIGS. 8 and 9, the RF shielding member 11 includes a loop-shaped shielding material 11a made of a non-magnetic and conductive material such as copper, covered with a flexible insulator 11b such as silicone resin,
Furthermore, this flexible insulator 11b is covered with a heat insulating material 11c. A protruding handle lid is provided at one end of the heat insulating material 11C. These loop-shaped shield materials 1
1a and the flexible insulator 11b are configured to be deformable and are supported by a flexible support member via the handle lid.

According to this embodiment, when the RF magnetic field H is transmitted from the transmitting/receiving coil 4 to the subject with the RF shielding member 11 installed so as not to come into contact with the subject 3, a loop shape is generated as shown in FIG. When the magnetic flux passing through the shielding material 11a changes, the loop-shaped shielding material 11 changes according to the electromagnetic induction side.
A current is induced in a. This current generates a demagnetizing field H' that generates a magnetic flux that cancels out the magnetic flux. That is, by this, the loop-shaped shield material 1
A shielding effect against the RF magnetic field H due to 1a is produced. When the RF magnetic field is applied to the subject 3 in this way, a current is induced in the loop-shaped shield material 11a, so that the shield material 11a generates heat. However, this heat can be dissipated through the flexible insulator 11b and the heat insulating material 11c to avoid the risk that the subject may come into contact with the high temperature part.

As shown in FIG. 7, a pair of RF
When the shielding member 11 is installed, the above-mentioned shielding effect occurs in these loop-shaped shielding members 11a, so that the RF magnetic field H cannot sufficiently pass through. However, as a result of the passing RF magnetic field exciting the target nuclide within the object 3, this nuclide generates an MR multiplied signal, and the magnetic field based on this MR multiplied signal is transmitted again to the loop-shaped shield material 1.
Trying to pass through 1a. However, due to the above-mentioned shielding effect, the magnetic field hardly passes through, and the MR multiplied signal from the abdomen 3b, which is the so-called non-interest region, is suppressed.

FIG. 11 shows both MR images obtained by such an imaging method, and the shaded area 16 indicates the abdomen 3a which is darkened due to suppression of the detected MR multiplied signal. By suppressing unnecessary MR multiplied signals from regions of non-interest in this way, the signals that are the source of artifacts also become weak (as a result, artifacts can also be suppressed and the image quality of the entire abdomen can be improved. become able to.

Such an imaging method can also be applied to other parts. For example, if the right knee is selected as the area to be diagnosed, if there is a weak signal from the left knee, the MRI machine will not be able to distinguish whether it is a signal from the right or left knee. The image is constructed by overlapping the necessary right knee signal, resulting in aliasing artifacts. In this case, by placing the RF shield member 11 close to the left knee, which is an area of non-interest, it is possible to suppress the occurrence of aliasing artifacts.

FIGS. 12(a) and 12(b) show a modification of the second embodiment, in which a variable resistor 13 is connected to the end of the loop-shaped shield material 11a as shown in FIG. 12(a). be. Note that the structure is shown with the flexible insulator and breaking material omitted.

According to such a modification, as shown in the equivalent circuit shown in FIG. 3(b), by rotating the shaft 13a of the variable resistor 13 and adjusting its resistance value R, it is possible to control the induced current flowing through the shield material 11a. This allows you to vary the shielding effect.

That is, if for some reason it is desired to change the shielding effect of the RF shielding member, this can be easily done by adjusting the variable resistor 13. In principle, it is not limited to a resistor, but may be an impedance element such as an inductance, and in short, any circuit element that can vary the induced current may be used. Furthermore, by connecting a plurality of variable resistors 13A, 13B, 13C, etc. so as to form an equivalent circuit as shown in Fig. 13, and switching each variable resistor with switches 14A, 14B, 14C, etc., the shielding effect can be made more finely. It becomes possible to select.

FIG. 14 shows another modification of the second embodiment.
This figure shows a structure in which loop-shaped shielding materials 11A and IIB are provided concentrically. By providing the two loop-shaped shielding materials 11A and 11B in this way, the induced current is reduced by each shielding material 11A.

11B, the shielding effect can be almost doubled compared to the case of one shielding material. Furthermore, by increasing the number of shielding materials, the shielding effect can be further increased. When providing a plurality of loop-shaped shield materials in this way, as shown in FIG.
It is more advantageous in terms of weight to directly cover A and 11B with the heat insulating material ie. Note that, as shown in FIG. 16, the loop-shaped shielding material may be a flat conductor 15 instead of a pipe-shaped one.

According to the embodiment of the present invention, the RF shielding member is placed in the RF magnetic field without coming into contact with the subject, so when performing imaging, it is possible to move away from the area of non-interest without causing discomfort to the subject. The MR signal can be suppressed twice. Furthermore, since the RF shield member does not fall off or shift laterally, it is possible to accurately suppress the MR multiplied signal from the region of no interest. Furthermore, according to the second embodiment, the RF shielding member is formed into a loop shape, and the shielding effect can be arbitrarily varied by adjusting the resistance value of this loop-shaped shielding material, thereby expanding the range of application. be able to.

[Effects of the Invention] As described above, according to the present invention, since the RF shielding member is installed within the RF magnetic field without coming into contact with the subject, MR multiplied signals from areas of non-interest can be hygienically suppressed. You can take pictures that you can.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) show the first part of the MRI apparatus of the present invention.
FIG. 2 is a perspective view showing the RF shield member used in this embodiment, FIG. 3 is a sectional view taken along the line ■-■ in FIG. The figure is a cross-sectional view showing a modification of the cross-sectional structure in Figure 3, Figures 5 (a), (b),
(c) is a perspective view showing an RF shield member used in the present invention, FIG. 6 is a perspective view showing a modification of the RF shield member used in this embodiment, and FIG. 7 is a second embodiment of the present invention. 8 is a perspective view showing the RF shield member used in the second embodiment, and FIG. 9 is a sectional view showing the RF shield member used in the second embodiment.
- A cross-sectional view taken along the line IX, FIG. 10 is an explanatory diagram of the operating principle of the second embodiment, FIG. 11 is a schematic diagram of an image obtained by the second embodiment, FIG. 12 (a), ( b) is a schematic diagram and equivalent circuit of the main parts of the RF shield member used in the second embodiment, FIG. 13 is an equivalent circuit showing a modification of FIG. 12(b), and FIG. 14 is a diagram of the second embodiment. RF used in the example
A perspective view showing a modified example of the shield member, FIG.
16 is a cross-sectional view showing a modification of the cross-sectional structure of FIG. 15, and FIG. 17 is a conventional MR
FIG. 18 is a cross-sectional view showing the I device, and a perspective view showing an RF shield member used in a conventional MHI device. 3... Subject, 4... Transmitting/receiving coil, 6.11.
...RF shield member, 7...Flexible support member, 11a, IIA, IIB...Loop-shaped shield material, 13...Variable resistor. 1a56 / (0) 1st Fig. 7b nail plate (C) fig.

Claims (5)

[Claims] (1) In an MRI apparatus that detects MR signals from a desired region by placing a subject in a magnetic field in which a gradient magnetic field is superimposed on a static magnetic field and applying an RF magnetic field, the subject does not come into contact with the subject within the RF magnetic field. An MRI apparatus characterized by installing an RF shield member. (2) The MRI apparatus according to claim 1, wherein the RF shield member is supported by a flexible support member. (3) The MRI apparatus according to claim 1, wherein the RF shield member includes a shield portion made of a nonmagnetic and conductive material, and an insulating portion that supports the shield portion. (4) The MRI apparatus according to claim 3, wherein the shield portion of the RF shield member has a loop shape. (5) The MRI apparatus according to claim 4, wherein an impedance element is connected to the loop-shaped shield portion.