JPH01145049A - Electromagnetic wave shield chamber for mri apparatus - Google Patents

Abstract

PURPOSE:To simultaneously, realize an RF electromagnetic shield, a shield of a static magnetic field, and a shield of a low frequency magnetic field, by constituting a wall panel and a ceiling panel of a good conductive metal panel on the indoor surface side and of a high permeability metal plate on the outdoor surface side. CONSTITUTION:Each of a wall panel 1 and a ceiling panel 2 is constituted of a metal plate 10 for an radio wave shield on an indoor side, a lightweight strength member 11 of an intermediate part and a metal plate 12 for a magnetic shield on an outdoor side. For example, the metal plate 10 for the radio wave shield is an aluminum plate and decorative painting is applied to the surface thereof. The metal plate 12 for the magnetic shield is formed of a high permeability metal. A floor surface 7 is constituted of the high permeability iron plate 16 for a floor on floor concrete 15, a copper foil sheet 17 for an RF shield, a composite panel material 18 for protecting the copper foil sheet 17 and the decorative vinyl chloride sheet 19 for the surface of the floor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the structure of an imaging room for a nuclear magnetic resonance imaging system, and in particular, to blocking external interfering electromagnetic waves and reducing leakage magnetic fields from magnets installed in the room. This invention relates to an electromagnetic shielding room suitable for shielding from the outside.

[Conventional technology]

Nuclear magnetic resonance imaging device (hereinafter referred to as MRI device)
has a magnet for generating a silent magnetic field, a high-frequency coil for irradiation provided in its internal space (into which the subject enters), a high-frequency coil for reception, and a gradient magnetic field coil. Here, while applying a uniform quiet magnetic field to the subject, an electromagnetic wave having a frequency that excites nuclear magnetic resonance is applied to the irradiation coil to obtain a nuclear magnetic resonance signal (NMR signal) from the subject. At this time, in order to further identify the emission part of the NMR signal from the subject,
A gradient magnetic field is provided by a gradient magnetic field coil.

In MRI machines, the magnetic field strength is typically +3. The nuclear magnetic resonance frequency of hydrogen nuclei is in the range of several MH2 to approximately 100 MHz. The excitation of nuclear magnetic resonance is pulsed R
It uses F (radio frequency) radio waves. Therefore, M
The purpose of RF shielding the RI imaging room is as follows.

1) Prevent radio wave interference to the surrounding area due to RF irradiation pulses.

2) Prevents high-frequency interference from the surroundings from being mixed into the signal of the receiving coil.

Furthermore, in addition to the above-mentioned RF shield, consideration must be given to magnetic fields in the MRI apparatus. In other words, since it has a magnet device that applies a strong silent magnetic field to the subject, l) the leakage magnetic field is
Adversely affects nearby equipment that is sensitive to magnetic fields. (Affected by X-ray LI, CRT, etc. at about 0.5 Gauss) 2) On the other hand, disturbance of magnetic field uniformity due to external magnetic material and
The alternating magnetic field emitted from an external transformer, etc. transforms into a silent magnetic field, causing M
R Both image quality deteriorates.

Problems such as these arise, and therefore magnetic field shield walls are required for quiet magnetic fields and low frequency magnetic fields.

Conventionally, in response to the above requirements, (a) built-in or (b) panel-type radio wave shield rooms were provided for RF 'E waves. A typical example of the construction method is copper foil (35μ
9) on the floor, wall, ceiling, etc. This will be finished with a decorative panel and will be carried out on site. The panel type is an RF
It was used as a shield room.

On the other hand, for the a-air shield, if necessary, a separate frame was assembled outside the RF7-led room and a metal plate with high magnetic permeability was installed during additional construction.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into account the simultaneous implementation of the cooled '1 field and the magnetic field, and has the problem of requiring separate work and υdouble work man-hours.

The aim of the invention is to overcome the above-mentioned drawbacks.

[Means for solving problems]

For the above purpose, the wall material of the shield room is made of a prefabricated panel structure, and the wall panel is made of a metal with good conductivity (such as aluminum) on the inner surface and a metal with high magnetic permeability on the outer surface.

This is accomplished by inserting a strength member into the intermediate portion and assembling it to form a chamber.

[Effect]

The photo booth is constructed using a good conductor metal on the inner surface of the wall panel (this is also done on the floor, but this will be explained in detail in the example).
, foreign US interference near the nuclear magnetic resonance frequency (high frequency near IOMHz)'4! Block the command wave.

It also suppresses leakage of the four waves of RF irradiation pulses generated indoors to the outside.

The high magnetic permeability metal attached to the outer surface of the wall panel shields the alternating current magnetic field near the commercial frequency from outside, and shields the leakage magnetic field from the quiet magnetic field generator installed indoors to the outside.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 schematically shows the configuration and arrangement of an MRI apparatus and an electromagnetic shielding chamber, which is one aspect of the present invention. First, the configuration of the MRI apparatus will be briefly described. 20 is a static magnetic field generating device (hereinafter abbreviated as magnet).

21 is a patient (subject) table; 22 is an MRI unit containing power sources for RF transmission/reception and gradient magnetic field coils;
23 is a central console, which contains an image processing device and a sequencer. Reference numeral 24 denotes a divisional photographing device for photographing both MR and MR image films.

An RF pulse is applied to the RF irradiation coil within the magnet 20 by an RF' power amplifier within the MRI unit 22 . The NMR signal from the object is detected by the receiving coil, amplified by the amplifier in the MRI unit 22, and after detection, converted into a digital quantity by the A/Di converter, and then sent to the image processing device 23.
sent to. Here, processing such as 7-lier transformation is performed to construct an image. The arrangement of the -i unit of the MRI apparatus is shown in FIG. 1. A magnet 20 and a patient table 21 are installed in the magnetic wave cooled multi-room imaging room, and an MRI unit 22 is installed in the operating room. It is common to arrange a central operation console 23° and a photographic device 24 divided by 23 degrees. Each unit is also connected by a cable.

Next, we will discuss the electromagnetic shield room. Electromagnetic shield room C, wall panel 1. Ceiling panel 2. Corner panel 3. Line filter box 4. Peephole 5. shield ig6
, made of flooring material 7. FIG. 2 shows a cross-sectional view of the wall, ceiling panel, and floor. The wall panel l consists of a shortwave shield metal plate 10 on the indoor side, a lightweight strength member 11 in the middle. A magnetic shielding metal plate 12 on the outside side f) is constructed. ceiling panel.

The configuration of the corner panel is the same as that of the copy panel.

In the embodiment, the metal plate 10 for radio wave shielding is an aluminum plate with a thickness of one layer, and one surface side is provided with decorative electrical equipment. And the metal plate 12 for magnetic shielding.

It is a high di-rate metal. (1) Permalloy (PC, iron.

(nickel alloy), (silicon steel sheet h (3) It is made of magnetic soft iron, etc. to 8I as required. Among these, permalloy has the highest magnetic permeability, so it is a thin sheet and has the same magnetic properties as thick sheets of other metals. Has shielding performance.

Radio wave shielding metal plate 101 strength member 11. The magnetic shielding metal plate 12 can be fixed together by bonding the metal plate 12 for radio wave shielding and the metal plate 10 for magnetic shielding, but the strength is The member 11 can also be made by foam injection of rigid polyurethane foam inside the frame.

The floor surface 7 has a high magnetic permeability iron plate 16 for flooring on top of a concrete floor 15. Steel foil sheet for RF shielding17. A panel material for protecting the copper foil sheet 17 (made of water-resistant veneer or the like, about 10 degrees thick) consists of a decorative vinyl chloride sheet 19 on the 18° floor surface. The floor iron plate 16 is
This is installed when other equipment is placed under the floor where the magnet is installed and magnetic field leakage becomes a problem, but as with walls, weight reduction is not as important, so electromagnetic soft iron plates are often laid down. . If the RF shielding copper foil 17 has a thickness of 35 μrn or more, it has a resistance of 60 MHz to radio waves around 10 MHz.
It has sufficient attenuation ability of dB or more.

Next, the assembly of the electromagnetic shielding room of the embodiment will be described. Fix the panel frame stand to the floor using bolts according to the required room dimensions (eX 4mX5mXz!m).

The above-mentioned corner panel 3. Insert and assemble wall panel 1. At this time, a shielding gasket 13 shown in FIG. 3 is inserted between the fitting portions that become the contact surfaces of the wall surface, and the shielding gaskets 13 are pressed into contact with each other to establish an electrical connection. The shielding gasket 13 is made by wrapping a hook mesh 31 around a rubber elastic body 30 (for example, silicone rubber), the other side of which has been plated to prevent rust. When the side surfaces are completed, as shown in FIG. 2, the ceiling panel is fixed with the shielding gasket 13 between them and the bolts 14 in the same way as for the 111th side.

Next, work on the floor. Place 16, 17, 18, 19 on top of the concrete floor 15. At this time, the steel foil 17 for RF shielding is usually a rolled product with a width of 1 m, and the seams thereof are continuously joined by soldering. In addition, the copper foil 17 can be connected to the side walls and corner panels 1 and 2 by soldering that can be used for aluminum, or by using conductive tape, all around the side in the lateral direction at position 33 shown in Figure 1. Make an electrical connection without any gaps. this is.

This is because, in practice, the effectiveness of the RF shield that is actually obtained is affected by the shielding effect of the material itself as well as by leakage from seams and seams. Furthermore, in practice, as shown in FIG. 1, a line filter box 4. Peephole 5. The shield door 6 is an essential component. Inside the line filter box 4, cables connecting the electromagnetic wave shielding room and the outdoors are collected, and all cables except the RF transmission/reception cable pass through a line filter for the purpose of cutting noise near the nuclear magnetic resonance frequency. Therefore, the outlet and lighting 8 in the photographing room are also provided with line filters. Additionally, for lighting, incandescent lights are used instead of fluorescent lights that generate noise. The viewing window 5 is for the operator to check the condition of the patient, and of course there is a need for radio wave shielding, so it is covered with a copper mesh. The shielding performance of copper mesh is determined by its wire warp and pitch, so select one according to the desired shielding performance.

Note that the line filter box 4 and the viewing window 5 are placed inside the wall panel 1 described above.

It goes without saying that the connecting portion is continuously joined to the radio wave shielding metal plate 10. The structure of the shield 6, which serves as the patient's entrance and exit, is similar to a wall panel and can be opened and closed with hinges.

Contact between the wall panel 1 and the shield 6 when the wall panel 1 is closed is achieved by placing the above-mentioned shielding gasket 13 on the outer periphery of the panel.

The requirements for RF shielding of MRI equipment are several MHz-
In the 100 MHz range, the RF shield is about 60 dB, but the RF shield of the embodiment described above is a negative shield, but the desired effect of 60 dB or more was achieved.

Regarding magnetic shielding, it is only necessary to assemble it in one room 1, and a high magnetic permeability metal plate 12t- is installed on the outer surface of the wall panel, and a magnetic shielding plate 16 is also provided on the floor. leakage can be reduced. For shielding of quiet magnetic fields and alternating magnetic fields near commercial frequencies, a slight gap is required.
It has little to do with performance, and is determined by the magnetic permeability and thickness of the material.

As in the embodiment, it is preferable to arrange it outside the room in relation to the RF shield.

〔Effect of the invention〕

As described in the above embodiments, RF radio wave shielding and shielding of silent magnetic fields and low frequency magnetic fields can be performed simultaneously.
The construction period for assembling the photography room can be reduced by about half, and it is also economical. In addition, we examine the installation environment in advance and predict the materials and orientation of the magnetic shield that will be required, based on this information on-site.

Wall panels can be arranged easily and in a short period of time.

[Brief explanation of the drawing]

Figure 1 shows an electromagnetic shielding room and MR according to an embodiment of the present invention.
2 is a sectional view of the electromagnetic shielding chamber, and FIG. 3 is an explanatory diagram of the gasket structure for 'liK shielding. -1...Wall panel, 2...Ceiling panel, 3...Corner panel, 4...Line filter box, end...
peephole. 6...Shield crime, 7...Flooring material, 8...Lighting lamp. DESCRIPTION OF SYMBOLS 10... Metal plate for radio wave shielding, 11... @ strength member, 12... Metal plate for magnetic shielding, 13... Gasket for shielding, 14... Fixing bolt, 16...
・Floor magnetic shield plate, 17... Copper foil for floor radio wave shield. 20... Silent magnetic field generating magnet.

Claims (3)

[Claims] 1. In an electromagnetic wave shielding room for nuclear magnetic resonance imaging equipment consisting of a wall panel, a ceiling panel, a floor, a line filter box, a sliding window, and a shield door, the wall panel and the ceiling panel are arranged such that the indoor side is a good conductive metal plate, and the outdoor side is An electromagnetic wave shielding chamber for an MRI apparatus, characterized in that the chamber is constructed of a high magnetic permeability metal plate. 2. 2. The electromagnetic wave shielding chamber for an MRI apparatus according to claim 1, wherein said metal plate with good conductivity is made of aluminum. 3. The electromagnetic wave shielding chamber for an MBI device according to claim 1, wherein the high magnetic permeability metal is an iron-nickel alloy.