JPH0856922A - Temperature adjusting device for mri - Google Patents

Abstract

PURPOSE: To provide a temperature adjusting device for MRI capable of performing the temperature control of a magnet without affecting on a magnetostatic field. CONSTITUTION: This temperature adjusting device for MRI is equipped with two or more heaters 31, 32 which generate magnetic field in the directions opposite to each other, a current supply means 23 which supplies a current to those two or more heaters, a sensor 22 which detects the temperature of the magnet, and a temperature control circuit 25 which controls a current value supplied to the heaters corresponding to the temperature detected by the sensor. The two or more heaters are arranged so as to adjust the temperature of the magnet in a state in which the magnetic fields generated in the heaters, respectively can be negated mutually.

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 (MRI) apparatus, and more particularly to an MRI temperature adjusting apparatus for adjusting the temperature of a magnet.

[0002]

2. Description of the Related Art An MRI apparatus measures the density distribution, relaxation time distribution, etc. of nuclear spins at a desired examination site in a subject by utilizing the nuclear magnetic resonance phenomenon, and the cross section of the subject is determined from the measured data. The image is displayed.

Nuclear spins of a subject placed in a uniform and strong static magnetic field generator perform precession around the direction of the static magnetic field at a frequency (Larmor frequency) determined by the strength of the static magnetic field. Therefore, when a high frequency pulse having a frequency equal to this Larmor frequency is irradiated from the outside, spins are excited and transition to a high energy state. This is called a nuclear magnetic resonance phenomenon. When the irradiation of the high frequency pulse is stopped, the spin returns to the original low energy state with a time constant corresponding to each state, and at this time, the electromagnetic wave is radiated to the outside. A high-frequency receiver coil (R
F coil) to detect. At this time, a triaxial gradient magnetic field is applied to the static magnetic field space for the purpose of adding position information to the space. As a result, position information in the space can be captured as frequency information.

An example of this MRI apparatus is shown in FIG. In FIG. 5, the magnet assembly 1 has a space portion (hole) for accommodating a subject therein, and a magnet for applying a constant static magnetic field to the subject and a gradient magnetic field are provided so as to surround the space portion. A gradient magnetic field coil to be generated (the gradient magnetic field coil is provided with coils of three axes of x, y, and z) and R for exciting spins of atomic nuclei in the subject.
An F pulse transmission coil and a reception coil (body coil or the like) for detecting an NMR signal from the subject are arranged.

Since the magnetic field strength of the magnet changes depending on the temperature, a temperature adjusting device 2 for adjusting the temperature is attached. The gradient magnetic field coil, the RF transmitting coil and the receiving coil are connected to the gradient magnetic field driving circuit 3, the RF power amplifier 4 and the preamplifier 5, respectively.

The sequence storage circuit 6 operates the gate modulation circuit 8 (modulates the RF output signal of the RF oscillating circuit 9 at a predetermined timing) in an arbitrary view in accordance with a command from the computer 7 to output an RF pulse signal to the RF power amplifier. 4 to RF
Apply to transmitter coil.

Further, the sequence storage circuit 6 operates the gradient magnetic field drive circuit 3 by a sequence signal based on the pulse sequence given from the operation console 12,
A gradient magnetic field is supplied to each of the three axes of x, y, and z.

The phase detector 10 phase-detects the received signal output of the preamplifier 5 using the output of the RF oscillation circuit 9 as a reference signal. The output signal of this phase detector 10 is A
It is converted into a digital signal in the D converter 11 and input to the computer 7. The result processed by the computer 7 is displayed as an image on the display device 13.

FIG. 6 shows the structure of the temperature adjusting device 2 of the MRI apparatus having the above-described structure, including a magnet 1a for static magnetic field,
It is a side view shown with 1b. Heater 21 (21a-2
1d) is a magnet 1a, 1 composed of a permanent magnet or the like.
A uniform magnetic field is generated by maintaining b at a constant temperature, and temperature control described later is performed. still,
Regarding the heater 21, in this example, 21a is provided on one side surface.
21d are arranged, and the same arrangement is made on the side not shown. In addition, although the magnet is often a permanent magnet whose temperature is to be adjusted, various other magnets (such as those using a coil) may be used. The sensor 22 detects the temperature of the magnet 1a, and is attached to the portion where the temperature adjustment is desired. Here, it is arranged on the magnet at an intermediate position between the heaters 21a and 21b. The power source 23 is the heater 2
In FIG. 6, an AC power source is assumed, but a DC power source may be used.
The current control unit 24 controls the current value from the power supply 23, and controls the current value by performing switching or the like according to an instruction from the temperature control circuit 25.

[0010]

In the temperature controller thus constructed, the temperature control circuit 25 controls the current control unit 24 according to the detection result of the sensor 22 to adjust the current from the power source 23, and the heater 21. The temperature is adjusted so that the temperature becomes constant.

By such temperature adjustment, the magnet composed of a permanent magnet or the like can maintain a constant temperature, and it is possible to generate a uniform magnetic field. Further, even if the magnet is composed of other than a permanent magnet, it is possible to generate a uniform magnetic field of constant strength by keeping the magnet at a constant temperature.

By the way, when a current flows through the heater 21, a weak magnetic field is generated, which may adversely affect the static magnetic field generated by the magnet. This heater 2
Although the magnetic field generated from No. 1 is weaker than the static magnetic field, the MRI apparatus requires a uniform static magnetic field.
It is not preferable that the magnetic field is generated from a place other than the desired magnetic field.

The present invention has been made in view of the above points, and an object thereof is to realize an MRI temperature adjusting device capable of controlling the temperature of a magnet without affecting the static magnetic field. That is.

[0014]

A first means for solving the above problems is a temperature adjusting means for adjusting the temperature of a magnet, and a control means for controlling the temperature adjusting means to keep the magnet at a predetermined temperature. And the temperature adjusting means is composed of a plurality of elements, and is arranged so as to cancel the magnetic fields generated from each of the plurality of elements with each other.

A second means for solving the above-mentioned problems is to provide two or more heaters which generate magnetic fields in mutually opposite directions, and these two heaters.
And a current supply means for supplying a current to the above heater,
In the MRI temperature adjusting device, the two or more heaters are arranged so as to adjust the temperature of the magnet in a state where the magnetic fields generated by the heaters cancel each other out.

A third means for solving the above-mentioned problems is to provide two or more heaters which generate magnetic fields in mutually opposite directions, and these two heaters.
The above-described two or more units are provided, which include a current supply unit that supplies a current to the heater, a sensor that detects the temperature of the magnet, and a temperature control circuit that controls the current value supplied to the heater according to the temperature detected by the sensor. Is a temperature adjusting device for MRI, which is arranged so as to adjust the temperature of the magnet in a state where the magnetic fields generated by the heaters cancel each other out.

[0017]

In the temperature adjusting device for MRI which is the first means for solving the problems, the temperature adjusting means is arranged so as to adjust the temperature of the magnet in a state where the magnetic fields generated by the plurality of elements cancel each other out. Therefore, the magnetic fields generated by the respective elements cancel each other and do not affect the static magnetic field.

In the temperature adjusting device for MRI which is the second means for solving the problem, two or more heaters which generate magnetic fields in mutually opposite directions adjust the temperature of the magnet while canceling the magnetic fields generated by each heater. Therefore, the magnetic fields generated by the heaters cancel each other out and do not affect the static magnetic field.

In the temperature adjusting device for MRI which is the third means for solving the problem, two or more heaters which generate magnetic fields in mutually opposite directions adjust the temperature of the magnet while canceling out the magnetic fields generated by each heater. Therefore, the magnetic fields generated from the heaters cancel each other out by the electric current supplied by the temperature control, and the static magnetic field is not affected.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a configuration of a main part of a temperature adjusting device for MRI according to an embodiment of the present invention. The same numbers are given to the same parts as those of the configuration of FIG. 6 which has already been described. The arrangement with respect to the magnet is the same as in the case of FIG.

In the temperature controller for MRI having the structure shown in FIG. 1, instead of a conventional single heater, two or more (2 in FIG. 1) heaters that generate magnetic fields in opposite directions are in close contact with each other. Is arranged so as to adjust the temperature of the magnet for the static magnetic field of MRI. As described above, in order to generate the magnetic fields in the opposite directions, the electric currents in the opposite directions are supplied from the power source 23 to the heaters having the same shape.

In the MRI temperature adjusting apparatus of this embodiment having the above-described structure, the temperature control circuit 25 controls the current control unit 24 according to the detection result of the sensor 22 to adjust the AC or DC current from the power supply 23. , The temperature is adjusted so that the magnet has a constant temperature.

By such temperature adjustment, the temperature of the magnet becomes constant, and it becomes possible to generate a uniform magnetic field. In this case, as shown in FIG.
A weak magnetic field is generated due to the right-handed screw's law when a current flows in each of them, but the opposite magnetic field is generated by flowing currents of the same value in opposite directions (an alternating phase if alternating current). In this configuration, since the heaters 31 and 32 are in close contact with each other, magnetic fields in opposite directions cancel each other out. For this reason,
The magnetic field hardly leaks to the outside of the heaters 31 and 32, and does not adversely affect the MRI magnet.

When the surfaces of the heaters 31 and 32 are electrically conductive, the heaters are arranged so as to be in close contact with each other while sandwiching the insulator 41, as shown in FIG. In such a case, an insulator made of a material as thin as possible is preferable so that the opposite magnetic fields generated by the heaters 31 and 32 can cancel each other out. Further, it is desirable that it does not affect the magnetic field.

Further, although the number of heaters is two in the embodiment shown in each of the above figures, four heaters 3 are provided as shown in FIG.
It is also possible to compose from 1 to 34. Also in this configuration, by flowing currents of the same value in opposite directions in each heater (opposite phases in the case of alternating current), magnetic fields in opposite directions are generated and cancel each other out. Therefore, the magnetic field of the MRI magnet is not adversely affected. Also in this case, the insulators 41 to 43 are used as necessary. Incidentally, it is also possible to combine six, eight, etc. heaters in the same manner.

Furthermore, it is possible to combine an odd number of heaters instead of an even number. In this case, it is necessary to set different current values to the heaters. Therefore, it is necessary to set current values that cancel the magnetic fields according to the distance between the heaters.

In the above embodiment, the current controller 24 directly controls the current value or the time for which the current flows, but the same operation can be performed by controlling the electric conductivity of the heater. It is possible. That is, a heater whose conductivity can be controlled is used in the same manner as in the above-described embodiment so that the electric current flows in the opposite direction, and the conductivity of these heaters that are in close contact is controlled in the same manner.
By controlling the conductivity in this way, the value of the current flowing through the heater changes and the temperature of the magnet is maintained at a specified value. At the same time, the current is passed in the opposite direction, and the heater is closely attached to the heater. The generated magnetic fields also cancel each other out.

In each of the above embodiments, a heater was used as a means for adjusting the temperature of the magnet.
For example, it is also possible to use an element (various temperature adjusting means, element) that cools or absorbs heat with an electric current. In this case as well, the temperature control and the cancellation of the generated magnetic field are realized by bringing the plurality of elements into close contact with each other so that the current flows in the opposite direction and controlling the temperature by the control means.

[0029]

As described in detail above, in the temperature adjusting apparatus for MRI having the temperature adjusting means arranged so as to adjust the temperature of the magnet in a state where the magnetic fields generated by the plurality of elements cancel each other out, The magnetic fields generated from the respective elements cancel each other out and do not affect the static magnetic field.

According to the temperature adjusting device for MRI that adjusts the temperature of the magnet in a state where two or more heaters that generate magnetic fields in opposite directions are closely attached to each other, the magnetic fields generated by the heaters cancel each other out, and the static magnetic field is eliminated. It has no effect.

Further, two or more heaters which generate magnetic fields in mutually opposite directions, a current supply means for supplying an electric current to these two or more heaters, a sensor for detecting the temperature of the magnet, and a temperature detected by this sensor. And a temperature control circuit that controls the current value supplied to the heater in accordance with the MR arranged in such a manner that the two or more heaters adjust the temperature of the magnet while canceling the magnetic fields generated by the heaters.
According to the temperature adjusting device for I, the magnetic fields generated from the heaters cancel each other out by the electric current supplied by the temperature control, and the static magnetic field is not affected.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram showing a configuration example of a temperature adjusting device for MRI according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of a magnetic field generated around a temperature adjusting unit or a heater.

FIG. 3 is a configuration diagram showing a configuration of a heater used in the temperature adjusting device for MRI according to an embodiment of the present invention.

FIG. 4 is a configuration diagram showing a configuration of a heater used in a temperature adjusting device for MRI according to an embodiment of the present invention.

FIG. 5 is a configuration diagram showing an example of the overall configuration of an MRI apparatus.

FIG. 6 is a side view showing a configuration of a conventional temperature adjusting device for MRI together with a magnet.

[Explanation of symbols]

 31-34 Heater 41-43 Insulator 22 Sensor 23 Power supply 24 Current control part 25 Temperature control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 9307-2G G01R 33/22

Claims (3)

[Claims] 1. A temperature adjusting means for adjusting the temperature of the magnet, and a control means for controlling the temperature adjusting means to keep the magnet at a predetermined temperature. The temperature adjusting means comprises a plurality of elements. A temperature adjusting device for MRI, wherein the temperature adjusting device is arranged so as to cancel out the magnetic fields generated from each of the plurality of elements. 2. A heater comprising: two or more heaters that generate magnetic fields in mutually opposite directions; and current supply means that supplies a current to the two or more heaters, wherein the two or more heaters cancel each other's magnetic fields. An MRI temperature adjusting device, which is arranged so as to adjust the temperature of a magnet in a fitted state. 3. Two or more heaters which generate magnetic fields in mutually opposite directions, a current supply means for supplying an electric current to these two or more heaters, a sensor for detecting the temperature of the magnet, and a temperature detected by this sensor. A temperature control circuit for controlling a current value supplied to the heater in accordance with the temperature control circuit, wherein the two or more heaters are arranged so as to adjust the temperature of the magnet in a state where the magnetic fields generated by the two or more heaters cancel each other out. MRI temperature controller.