JPH011211A - Static magnetic field coil device for MRI - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a static magnetic field coil for MRI (magnetic resonance imaging), which is a modified static magnetic field coil that forms a static magnetic lift for MRI (magnetic resonance imaging) by supplying current. Regarding equipment.

(Prior art) Conventionally, in normal-current 39 MRI, once the current supply to the normal-conducting static magnetic field coil is cut off (when the power is turned off), it is possible to perform imaging after turning on the power supply. It took a long time (about 30 minutes). This time is usually referred to as the preheating period, but due to the existence of this time, when using a static 4MRI system, the static magnetic field coil is always supplied with the rated current ( A current (current) was flowing to generate the static magnetic field necessary for enemy shadows. For this reason, in the past, running costs related to electricity charges were high.

Therefore, the inventor of the present application has previously proposed a magnetic resonance imaging apparatus that uses an idling system to reduce running costs (Japanese Patent Application No. 61-266561).

This method reduces the current flowing through the static magnetic field coil to a fraction of the rated current (for example, L/4) during non-operating conditions, and also reduces the current flowing through the static magnetic field coil from the water cooling system P1 for current detection inside the power supply to the resistor and the static magnetic field coil. The objective is to reduce and control the flow rate of cold water that cools the water so that it does not change from each temperature.

According to this Detling method, if the current is increased to the rated current when shading is required, it becomes possible to immediately shading the knee even though a long preheating time is required. In addition, when there is no dark shadow, the power consumption is - (for example, 1/16) the power consumption when there is enemy shadow, so running costs are significantly reduced compared to the previous method (continuous energization method). It can be realized.

(Problem to be solved by the invention) However, in the above idling method, although the coil supply current is reduced during non-operation, it is necessary to keep a certain amount of current flowing, so the power consumption in the static magnetic field coil is reduced. cannot be made zero.

Therefore, the present invention aims to further reduce the running cost compared to the above-mentioned idling method, and eliminates the need for power consumption in the static magnetic field coil when there is no dark shadow, and moreover, when there is enemy shadow, the static magnetic field coil that is required immediately MRI that creates and clears the ia field
The purpose of this project is to provide a static magnetic field coil device for use.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a magnetostatic lift for MRI, which is equipped with a coil that forms a static magnetic field for MRI by supplying electric power. A heat insulating layer is provided to block heat radiation from the coil.

(Function) In the conventional method (continuous energization method), after the power is turned off and then turned on again, a long preheating time is required before decoy shadowing is possible due to the following two characteristics.

That is, ■Static magnetic field strength drifts.

In MRI, the magnetic field strength drift 1 that occurs during the dark shadow time is required to be several ppm or less.

■The distribution of static magnetic field strength changes.

In MRI, it is required that the distribution of magnetic field strength be highly uniform (approximately 10 ppm).

Both of the above two problems are caused by the performance of the static magnetic field coil. In other words, when current is no longer supplied to the static magnetic field coil, the heat of the static magnetic field coil is dissipated into the atmosphere even if the supply of cooling water is stopped, the temperature of the static magnetic field coil itself decreases, and the temperature of the static magnetic field coil decreases. Dimensions/normal changes occur. When a current is supplied to the static magnetic field coil again, the above-mentioned changes in size and shape do not immediately return to their original state, but require a long time to stabilize.

Therefore, as mentioned above, between the static magnetic field coil and the atmosphere,
If an IJT thermal layer is provided to block the heat from the static magnetic field coil, even if no current is supplied to the static magnetic field coil at all, the temperature drop in the static magnetic field coil itself will be small and small, and the coil's temperature will be small. The dimensions and shape also hardly change. Therefore, when a current is supplied to the static magnetic field coil again, the static magnetic field formed by the coil stabilizes immediately.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 1 shows an embodiment of the present invention.

2 is a static magnetic field coil device for MRI, and this device 2 is:
A static magnetic field coil 3 is provided, and a heat insulating layer 4 is provided between the static magnetic field coil 3 and the magnet. A predetermined current is supplied from the power supply 1 to the static magnetic field coil 3, and by supplying this current, the static magnetic field coil 3 forms a predetermined static magnetic field for MRI. In addition, cooling water is circulated between the main parts in the power supply 1 (for example, a water-cooled shunt resistor for output current detection, etc.) and the static pump 3, and the cooling unit 5. Power supply 1 by cooling water
The main parts inside and the static Ia field coil 3 are appropriately cooled.

Here, the heat insulating layer 4 in the static magnetic field coil device 2 for MRI has a function of blocking heat radiation from the static magnetic field coil 3, that is, a function of keeping the static magnetic field coil 3 warm.

Various methods can be considered as the specific structure of this heat insulating layer 4. For example, as shown in FIG. 2, the outside of the coil winding may be covered with a heat insulating section vI4A at the 3A angle of a plurality of static magnetic field coils, or as shown in FIG. A heat insulating member 4Δ may be provided inside the coil case body 6 that houses the coil 3A. In short,
It is only necessary to have a configuration that can block heat radiation from the static magnetic field coil, and the type of heat insulating member and its mounting location can be determined as appropriate.

In the above configuration, at the time of imaging, a predetermined current is supplied from the power source 1 to the static magnetic field coil 3 as in the conventional apparatus, thereby forming a magnetostatic field for MRI.

Furthermore, during non-operation, the current supply to the static magnetic field coil 3 is completely stopped, and at the same time, the circulation of cooling water by the cooling units 1 to 5 is stopped.

FIG. 4 shows the timing of this embodiment.

In the same figure, ■ indicates the current supplied from the power source 1 to the static magnetic field coil 3, and the king indicates the temperature of the static magnetic field coil 3.
-1 indicates the strength of the static magnetic field formed by the static magnetic field coil 3. Furthermore, in the characteristic curves, the solid line indicates this embodiment, and the broken line indicates the conventional example.

As is clear from the figure, in the past, when the power supply 1 was turned off and the current supply to the static magnetic field coil 3 was stopped (tl), the coil temperature dropped rapidly. Therefore, when the power is turned on again (Code 2), the temperature of the coil has dropped significantly (
ΔT), the dimensions of the static magnetic field coil were smaller. Therefore, the static magnetic field that is generated at this point will be larger than Δ even though the coil current value ■ is the same as before it was turned off.
1”). Incidentally, the following equation generally holds between the temperature change T of the coil and the fluctuation ΔH of the generated magnetic field.

Δ11', 2αΔd...(1)
Here, Δ11: Amount of change in magnetic field strength α: Coefficient of linear expansion of coil material (ppm/'C) ΔT: Change in temperature of coil (°C) On the other hand, according to this embodiment, the heat insulating layer 4 is provided. Therefore, even if the power supply 1 is turned off, the heat dissipated into the atmosphere can be extremely reduced, so that the temperature drop of the static magnetic field coil 3 is significantly reduced (Δd'). Therefore, the change in the dimensions of the static magnetic field coil 3 becomes small, and the amount of change in the static magnetic field when the power supply 1 is turned on again becomes small (Δl''').

If the amount of change in the static magnetic field strength 1-1 can be reduced in this manner, the time required for the change in the static magnetic field strength and distribution to fall within the allowable value during imaging can be significantly shortened. Furthermore, in this embodiment, since the coil current can be reduced to zero (power consumption is also zero) during non-imaging times, running costs are significantly reduced.

[Effect of the invention 1] As detailed above, according to the present invention, the static magnetic field coil for MRI does not require power consumption during non-imaging periods, and the necessary static magnetic field is immediately generated during imaging. A magnetic field coil device can be provided.

[Brief explanation of drawings]

Figure 1 is a block diagram of one embodiment of the present invention, Figures 2 and 3 are block diagrams of one embodiment of the present invention.
This figure is a sectional view showing the detailed structure of the main part of FIG. 1, and FIG. 4 is a timing chart for explaining the operation of this embodiment. 1... Power supply, 2... Static magnetic field coil device for MRI,
3... Static VIi field coil, 4... Heat insulation layer. Agent Patent Attorney Norihiro Kondo Takeshi Kondo A/' 3, A/Condolence 3 Figure 1 Off On Figure 4

Claims (1)

[Claims] A static magnetic field coil device for MRI comprising a static magnetic field coil that forms a static magnetic field for MRI by supplying current, characterized in that a heat insulating layer is provided between the static magnetic field coil and the atmosphere to block heat radiation from the coil. A static magnetic field coil device for MRI.