JPH06319714A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To provide an MRI apparatus wherein an opening part is provided to the side surface of a gantry without impairing thermostatic control for stabilizing image quality and an RF shield in a permanent magnet type MRI apparatus. CONSTITUTION:A gantry is constituted of a permanent magnet type magnetic circuit 10, the covers 70a, 70b, 70c, 70d covering the circuit 10, a heat insulating material, an RF cover 13a and copper shields 14a, 14b. Openings 20 are formed to both side surface covers 70c of the gantry and the yoke 3 of the magnetic circuit 10 is covered with the heat insulating material. Holes are formed to both side surfaces of the RF cover and an RF shield is divided into side surface shields 14a, 14b. By this constitution, the state of a patient during scanning can be observed in a side surface direction and the approach to the patient in the gantry can be performed from a side surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus, and more particularly to a magnetic resonance imaging apparatus in which an opening in a permanent magnet type magnetic circuit is provided not only before and after a patient enters but also on a side surface.

[0002]

2. Description of the Related Art As described in Japanese Patent Publication No. 1-28931, since the magnetic circuit of the conventional permanent magnet system has temperature dependence, it is possible to always maintain the resonance frequency by actively controlling the heat retention (constant temperature control) in the system. Is stable and a good image can be obtained. on the other hand,
Since it generally takes several minutes or more to take an MRI,
In the meantime, if you look at the condition of the subject, or if you perform simple treatment with the subject inside the gantry opening, if there is an opening in the lateral direction of the gantry, you can observe and treat the subject. Although it can be easily performed, it is difficult to realize due to the above limitation of the heat insulating structure or the necessity of the RF shield.

As one of the countermeasures against these problems, there has been one in which the RF shield on the side surface is made of a transparent member so that the subject can be observed from the outside. However, this could not access the inside. In addition, some magnetic circuits do not have thermal control and have an opening on the side to allow access to the subject, but this system requires constant temperature control of the entire imaging room, which stabilizes the resonance frequency. There was a problem of lacking.

[0004]

As described above, the permanent magnet system M is used in which the heat insulation control of the magnetic circuit and the RF shield are carried out.
In the RI apparatus, it was difficult to provide the side opening portion, so that none of them was realized. The present invention solves this problem.

[0005]

In order to stabilize the resonance frequency of a permanent magnet type magnetic circuit, a heat insulating material should be placed around the magnetic circuit as usual. In particular, the yoke is heat-insulated independently, and a heater is provided inside to control the heat retention. The side cover of the gantry is provided with an opening, and the side surface of the RF coil is also provided with an opening. Also, R
For the F shield (Faraday shield) as well, in order to provide the opening, the portion corresponding to the opening is divided into front and rear parts and separated.

[0006]

The heat insulating material on the side surface is conventionally sandwiched from both sides so that an opening is provided, and the four pillars, which are vertical yokes, are surrounded by the surrounding pillars. The upper and lower yokes were covered with independent heat insulating materials. This prevents the insulation of the vertical yoke from interfering with the opening. RF
The shield was conventionally provided at the center of the side surface, but since it is arranged separately in the front-rear direction, it does not interfere with the opening.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an external view of an MRI apparatus according to an embodiment of the present invention. 1 (a) is a side view thereof, and FIG. 1 (b) is a front view thereof,
Reference numeral 21 in the figure denotes a gantry, which has a magnetic circuit inside.
22 is a patient table. Here, reference numeral 20 denotes an opening on the side surface which is a feature of the present invention.

A detailed perspective view showing the inside of the gantry 21 is shown in FIG. The permanent magnet type magnetic circuit 10 includes permanent magnets 1a and 1b (1b is not shown) arranged above and below and magnetic pole pieces (pole pieces) 5a to achieve magnetic field homogeneity.
5b (5b is not shown), upper and lower yokes 2a and 2b fixing these, and a vertical yoke (4 cylinders in the embodiment) 3 for maintaining a gap between the upper and lower sides. Further, in the gantry 21, a gradient magnetic field coil (not shown) necessary for MR imaging, an irradiation coil (indicated by 11 in FIG. 3) that causes a magnetic resonance phenomenon, and a receiving coil (see FIG. 3) for receiving a signal from a patient. (Not shown). In the magnetic circuit 10, the permanent magnets 1a and 1b have temperature dependence.
(About -1000ppm / ℃)
It is covered with and is controlled to a constant temperature by the heater provided in it. Regarding this constant temperature control, for example, Japanese Patent Publication No. 3-2
Since it is described in Japanese Patent Publication No. 8931, detailed description will be omitted.

In FIG. 2, 70a and 70b are front and rear covers of the gantry 21. It is provided with a generally rectangular (oblong) opening for patient entry. 70d shows a top cover and 70c shows a side cover. The side cover 70c is also provided with a rectangular opening so that the doctor or the operator can perform a simple treatment on the patient from the side and can see the state of the patient during scanning from the side. In the embodiment, the height is about 40 cm and the width is about 60 cm.

As for the side heat insulating material, conventionally, two vertical yokes 3 are sandwiched from both sides, but in the present embodiment, the heat insulating material is wrapped around each pillar to cover it.
This prevents the insulation from blocking the side openings.

FIG. 3 shows an RF coil (trans-emitter coil) consisting of the irradiation coil 11 and the RF cover 12. The RF cover 12 is provided with a hole 50 for opening the side surface, as indicated by the hatched lines in FIG. Since this hole 50 is provided just between the copper plates of the irradiation coil, there is no performance problem.

Further, FIG. 4 shows a vertical copper shield (for the purpose of providing a shield for blocking the coupling between the irradiation coil and the magnetic circuit) 13a, 13b (13b is not shown).
And an RF shield including side shields 14a and 14b. By electrically and mechanically connecting the upper and lower shields 13a and 13b and the side shields 14a and 14b, a Faraday shield surrounded by four sides is realized, and the coupling between the magnetic circuit and the irradiation coil is eliminated. . In this embodiment, since the side surface shield is provided with the side surface opening 20, the conventional shields 15a and 15b (shown by broken lines) are formed in the front-rear direction as described above.
Separated as a and 14b, the performance of the Faraday shield is maintained.

[0013]

As described above, according to the present invention, in addition to the patient's opening (front and back), openings are provided on the left and right sides. Therefore, (1) the appearance of the patient during the scan is better seen. (2) The doctor can approach the subject from the side while still in the gantry, so simple treatment is possible. Therefore, MR images before and after the treatment can be rapidly obtained, and a new medical application field is expanded.

[Brief description of drawings]

FIG. 1 is a front view and a side view of an embodiment of an MRI apparatus of the present invention.

FIG. 2 is a perspective view showing details of the structure of a gantry.

FIG. 3 is a perspective view of an RF coil according to the present invention, which is slanted.

FIG. 4 is a perspective view showing an RF shield of the present invention.

[Explanation of symbols]

 10 Permanent Magnet Type Magnetic Circuit 12 RF Cover 13a Lower Copper Shield 14a Side Copper Shield 14b Side Copper Shield 20 Side Opening 70c Side Cover

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location 9219-2J G01N 24/04 Z 9219-2J 24/06 A 8203-2G G01R 33/22 S 8203- 2G N

Claims (1)

[Claims] 1. A first and a second laminated body composed of magnetic pole pieces for generating a uniform magnetic field and a permanent magnet, which are opposed to each other through a measurement space, and respective magnetic poles of the first and second laminated bodies. A static magnetic field magnetic circuit including first and second magnetic paths provided in contact with the surface of the permanent magnet on the opposite side to the one piece, and a third magnetic path connecting the first and second magnetic paths, A gradient magnetic field coil that generates a gradient magnetic field that is added to the uniform magnetic field, a trans-emitter coil that applies an electromagnetic wave having a frequency that causes nuclear magnetic resonance to the subject in the measurement space, an RF shield, and a nucleus from the subject. A receiver coil for receiving a magnetic resonance signal; and a magnetic field comprising a magnetic field for static magnetic field, a heat insulating material surrounding the magnetic circuit to form a heat insulating portion, and a temperature adjusting heater provided inside the heat insulating portion. Before entering the subject in the resonance imaging system In addition to the opening direction, the magnetic resonance imaging apparatus characterized by also having an opening in the side surface direction.