JPH04367650A - Magnetoresonance imaging device - Google Patents

Abstract

PURPOSE:To obtain a cooling structure having high cooling efficiency by building a self-shielding type graded magnetic field coil (ASGC) constituted by providing a spacing between a primary coil and a screen coil, arranging cooling pipe in this spacing and packing an inert gas therein. CONSTITUTION:The ASGC 1 is constituted by providing the spacing between the primary coil 2 and the screen coil 3, winding and arranging the cooling pipe 4 in this spacing spirally along the outer peripheral surface of the primary coil 2 and packing an inert liquid 5 therein. The primary coil 2 consists of a winding frame 6 and a conductor 7 and the screen coil 3 consists of a winding frame 8 and a conductor 9. The conductors 7, 9 of the respective coils are connected in series. Water or oil flows as a medium in the cooling pipe 4 and the conductors 7, 9 of the primary coil 2 and the screen coil 3 are cooled by the inert liquid 5 to which the cold heat is transmitted thereto by this medium.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an "MRI apparatus") that obtains magnetic resonance images etc. using magnetic resonance phenomena, and in particular, the present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an "MRI apparatus") that obtains magnetic resonance images etc. using magnetic resonance phenomena. for phase encoding,
This invention relates to improvements in gradient magnetic field coils used to apply gradient magnetic fields for leads and the like.

0002

2. Description of the Related Art In recent years, gradient magnetic field coils, in other words, self-shielded gradient magnetic field coils (active shield type), have been developed in which a screen coil is coaxially arranged outside the primary coil to prevent leakage of magnetic fields to the outside.
d gradient coil is abbreviated as “AS” below.
GC) has been developed. This ASGC is said to be ideal because it does not cause "eddy current" as a magnetic interaction with the static magnetic field magnet, so it does not cause image quality deterioration or artifacts.

Conventionally, in this type of ASGC, since the strength of the gradient magnetic field required for an MRI apparatus is not very large, the current flowing through the coil is about 170 A at the maximum, and the resistance of the coil is 0.
It is designed to have a resistance of about 1Ω. In this case, at worst 2.8
Only about 9kW of energy becomes heat inside the ASGC, and in practical terms, it depends on the pulse sequence, but the energy is about 100kW.
Never used in % duty.

However, ultra-high-speed MRI equipment (echo p.
Lanar Imaging is abbreviated as “EPI” below.
Comparing the gradient magnetic field strength, it is necessary to increase the gradient magnetic field strength from 10 mT/m to about 50 mT/m, which results in a current of about 850 A flowing through the ASGC. This generates 25 energy that turns into heat.
It will double to 72.25kw. Therefore, ASGC
It is necessary to forcefully cool the

[0005] Therefore, as a method for cooling ASGC,
Various methods have been proposed, including forced air cooling of ASGCs and methods of cooling ASGCs with refrigerants such as water and oil.

[0006] However, forced air cooling has extremely poor cooling efficiency and is therefore inappropriate from the standpoint of equipment. On the other hand, for refrigerant cooling, we focused on the fact that in the simplest ASGC structure, the primary coil and the screen coil are connected in series so that they can be written in one stroke. It was thought that it would be possible to apply a method of flowing refrigerant through this hollow conductor using a straw-shaped hole (with holes drilled in it). However, ASG
Since the coil winding pattern in C was complicated, the refrigerant pressure would have to be raised considerably to prevent the refrigerant from flowing through the hollow conductor, making it impractical.

[0007] In another refrigerant cooling method, a cooling pipe is arranged between the primary coil and the screen coil,
The ASGC is provided with a cooling structure in which resin is impregnated between the periphery of the cooling pipe and the wall surfaces of the primary coil and screen coil. In this case, the refrigerant can be easily flowed through the cooling pipe.

[0008]

[Problems to be Solved by the Invention] However, when applied to an ASGC with a conventional cooling structure, a resin with low thermal conductivity (copper has a thermal conductivity of 0.941 cal) is used between the coil and the cooling pipe. /s/cm2 /(oc/c
m), whereas even high-density polyethylene, which has the highest thermal conductivity, has a thermal conductivity of 12.4 x 10-4 cal/s/cm2.
/(oc/cm)), the cooling efficiency is poor. Therefore, although it is useful for conventional MRI apparatuses that take a long imaging time, it cannot be applied to EPI.

[0009] The present invention has been made in view of this problem, and its object is to provide an MRI apparatus having an ASGC having a cooling structure with high cooling efficiency.

0010

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a gap between the primary coil and the screen coil, arranges a cooling pipe in the gap, and fills the gap with inert gas. It is characterized by comprising an ASGC.

[0011]

[Operation] With the configuration of the MRI apparatus according to the present invention, AS
In the GC, an inert liquid is filled between the periphery of the cooling pipe and the wall surfaces of the primary coil and the screen coil, so the thermal conductivity from the coil to the refrigerant in the cooling pipe is high and the cooling efficiency is high.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view schematically showing an ASGC 1 according to a first embodiment of an MRI apparatus to which the present invention is applied, and FIG. 2 is a diagram showing a cross-sectional structure of the ASGC 1.

As shown in FIGS. 1 and 2, the ASGC 1 of the first embodiment provides a gap between the primary coil 2 and the screen coil 3, and a spiral coil is formed in the gap along the outer peripheral surface of the primary coil 2. cooling pipe 4
are arranged in a wound manner and are filled with an inert liquid 5.

As shown in FIG. 2, the primary coil 2 consists of a winding frame 6 and a conducting wire 7. On the other hand, the screen coil 3 consists of a winding frame 8 and a conducting wire 9. The conductive wires 7 and 9 of each coil are connected in series so that writing can be done with one stroke.

Water or oil flows through the cooling pipe 4 as a refrigerant. The conductive wires 7 and 9 of the primary coil 2 and the screen coil 3 are cooled by the inert liquid 5 to which cold heat is transferred by the refrigerant. And in the inert liquid 5,
Since a liquid with excellent heat transfer properties such as CF4 or perfluorocarbon liquid is used, the cooling efficiency is greatly improved compared to the conventional cooling structure using resin interposed between the coils.

However, due to the heat generated by the conductors 7 and 9 of the primary coil 2 and the screen coil 3, natural convection occurs in the inert liquid 5 as shown by the arrows in FIG. Concentrate on the side. Therefore, the portion of the inert liquid 5 that exchanges heat with the cooling pipe 4 is reduced, making it impossible to further improve the cooling efficiency. In addition, since there is no part to mechanically fix the primary coil 2 and the screen coil 3, the AS
Noise due to bending during operation of the GC 1 is likely to occur, which is disadvantageous from the viewpoint of noise avoidance. This is improved by the ASGC of the second embodiment, which will be explained below using FIGS. 3 to 5.
It is 10.

FIG. 3 is a perspective view schematically showing an ASGC 10 of a second embodiment in an MRI apparatus to which the present invention is applied, FIG. 4 is a diagram showing a vertical cross-sectional structure of the ASGC 10, and FIG. 5 is a cross-sectional view of the ASGC 10. FIG. Note that in FIGS. 3 to 5, parts indicated by the same reference numerals as in FIGS. 1 and 2 indicate corresponding parts.

As shown in FIGS. 3 and 5, the ASGC 10 of the second embodiment divides the gap between the primary coil 2 and the screen coil 3 into a plurality of sections by a partition member 11 which also serves to fix the coils. Cooling pipes 4 are positioned vertically upward in each divided gap.
The piping is arranged so that it can be written with a single stroke, and the ASG
The refrigerant is arranged to be supplied and recovered at one end side of the C10, and an inert liquid 5 is provided in each divided gap.
is filled with.

In this configuration, the heat generated by the conductors 7 and 9 of each coil of the ASGC 10 is directly transferred to the inert liquid 5. The heat causes natural convection in the inert liquid 5. The inert liquid thus warmed gathers upward in the vertical direction within each divided gap. Since the cooling pipe 4 is installed above this, the heat of the warmed inert liquid 5 is transferred to the refrigerant flowing inside the cooling pipe 4. Since the refrigerant is flowing, it is carried outside the ASGC 10 and is cooled by a heat exchanger (not shown) installed outside the shield room of the MRI apparatus. The cooled refrigerant is guided to the cooling pipe 4 of the ASGC 10 and recirculated.

Through the above process, each conductor 7 of the primary coil 2 and screen coil 3 of the ASGC 10 is
, 9 is efficiently removed. Furthermore, since an inert liquid is used, electrical insulation properties do not deteriorate. Moreover, since the mechanical structure is such that the gap between the primary coil 2 and the screen coil 3 is divided into a plurality of parts by the partition member 11, the primary coil 2 and the screen coil 3
does not impair mechanical fixation.

The ASGC 10 of this second embodiment is used as a gradient magnetic field coil of a magnet assembly 20 as shown in FIG. In FIG. 6, 21 is a magnet for forming a static magnetic field space, 22 is a shim coil, 23 is a transmitting coil, and 24 is a receiving coil. Then, an excitation pulse is applied to the transmitting coil 23 to the subject P placed in the static magnetic field space created by the magnet 21, and
Each gradient magnetic field is applied from the ASGC 10, and the MR signal from the subject P is received by the receiving coil 24, and an MR image is constructed based on the collected data of this MR signal. On this occasion,
Even if the MIR device is an EPI, the ASGC of the second embodiment
10 can be used continuously because its cooling efficiency is significantly improved compared to conventional ASGC.

[0022]

[Effects of the Invention] As explained above, according to the present invention, A
without compromising the insulation between the SGC conductor and the cooling pipe.
Since highly efficient heat conduction is achieved, highly efficient cooling of the ASGC is possible. This allows EPI to use ASGC continuously.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing an ASGC of a first embodiment in an MRI apparatus to which the present invention is applied.

FIG. 2 is a diagram showing a cross-sectional structure of the ASGC shown in FIG. 1.

FIG. 3 is a perspective view schematically showing an ASGC of a second embodiment in an MRI apparatus to which the present invention is applied.

FIG. 4 is a diagram showing a vertical cross-sectional structure of the ASGC shown in FIG. 3;

FIG. 5 is a diagram showing a cross-sectional structure of the ASGC shown in FIG. 3;

FIG. 6 is a diagram showing a schematic configuration in which an MRI apparatus is provided with an ASGC.

[Explanation of symbols]

1 ASGC 2 Primary coil 3 Screen coil 4 Cooling pipe 5 Inert liquid 6 Winding frame 7 Conductor wire 8 Winding frame 9 Conductor wire 10 ASGC 11 Partition member

Claims (3)

[Claims] [Claim 1] A self-shielded gradient magnetic field coil comprising a gap provided between a primary coil and a screen coil, a cooling pipe disposed in the gap, and filled with an inert liquid. Magnetic resonance imaging device. 2. The self-shielded gradient magnetic field coil has a cooling pipe disposed within the gap in a positional relationship that allows uniform temperature distribution of the inert liquid by natural convection. Magnetic resonance imaging device. 3. The self-shielded gradient magnetic field coil is characterized in that the gap has a cross-sectional shape divided into a plurality of sections, and each section is provided with a cooling pipe and filled with an inert liquid. The magnetic resonance imaging apparatus according to claim 1 or claim 2.