JP2002094333A - Temperature compensation method, amplifier and magnetic resonance imaging equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for correcting temperature changes in an operating characteristic of an amplifier element, an amplifier provided with a temperature compensating means and magnetic resonance imaging equipment provided with the amplifier. SOLUTION: A compensated signal, on the basis of a temperature of an amplifier element, is added (412) to the bias signal of the amplifier element, and the gain of an input signal to the amplifier element is adjusted on the basis of the temperature of the amplifier element (416, 414).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensating method, an amplifying apparatus and a magnetic resonance imaging apparatus, and more particularly to a method for compensating a change in characteristics of an amplifying element due to temperature, and an amplifying apparatus having such a temperature compensating means. And a magnetic resonance imaging apparatus having such an amplification device.

[0002]

2. Description of the Related Art Magnetic resonance imaging (MRI: Magneti)
c Resonance Imaging) device
A subject to be imaged is carried into an internal space of a magnet system, that is, a space in which a static magnetic field is formed, a gradient magnetic field and a high-frequency magnetic field are applied, a magnetic resonance signal is generated in the subject, and based on the received signal, To generate (reconstruct) a tomographic image.

In order to supply RF power for generating a high-frequency magnetic field, an RF power amplifier, that is, an RF amplifier (RF amp) is used.
modifier) is used. The RF amplifier has a plurality of amplifying elements connected in multiple stages. As an amplification element at the output stage, a MOSFET (Metal Oxide Semi) is used.
conductor Field Effect Tr
ansistor) is used.

[0004]

The input / output characteristics of the MOSFET, that is, the so-called gm characteristics, change due to the self-heating of the MOSFET. Therefore, even if the RF input signal is constant, the output signal changes and a stable high-frequency magnetic field is generated. Can not get.

Accordingly, an object of the present invention is to provide a method for correcting a temperature change in the operating characteristics of an amplification element, an amplification apparatus provided with a temperature compensating means, and a magnetic resonance imaging apparatus provided with such an amplification apparatus. That is.

[0006]

Means for Solving the Problems (1) According to one aspect of the invention for solving the above problems, a compensation signal based on the temperature of the amplifying element is added to a bias signal of the amplifying element. Temperature compensation method.

In the invention according to this aspect, since the compensation signal based on the temperature of the amplifier is added to the bias signal of the amplifier, it is possible to prevent a change in the temperature of the output signal of the amplifier.

(2) According to another aspect of the present invention, there is provided a temperature compensation method comprising: adjusting a gain of an input signal of an amplifier based on a temperature of the amplifier. is there.

In the invention according to this aspect, the gain of the input signal of the amplifier is adjusted based on the temperature of the amplifier.
It is possible to prevent a change in the temperature of the output signal of the amplification element. (3) According to another aspect of the invention for solving the above-described problem, a compensation signal based on the temperature of the amplifying element is added to a bias signal of the amplifying element, and a gain of an input signal of the amplifying element is adjusted by the amplifying element. The temperature is compensated based on the temperature of the temperature.

In the invention according to this aspect, a compensation signal based on the temperature of the amplification element is added to the bias signal of the amplification element, and the gain of the input signal of the amplification element is adjusted based on the temperature of the amplification element. Thus, it is possible to prevent a change in the temperature of the output signal of the amplification element.

(4) According to another aspect of the invention for solving the above-mentioned problem, the invention is characterized in that a compensation signal based on an ambient temperature is added to the bias signal. Temperature compensation method.

In the invention according to this aspect, in addition to (1) or (3), the compensation signal based on the ambient temperature is added to the bias signal, so that the temperature change of the output signal of the amplifying element including the ambient temperature is included. Can be prevented.

(5) The invention according to another aspect for solving the above problem is characterized in that the gain of the input signal of the amplifying element is adjusted based on the ambient temperature. ).

In the invention according to this aspect, in addition to (2) or (3), the gain of the input signal is adjusted based on the ambient temperature. Can be prevented.

(6) According to another aspect of the invention for solving the above-described problem, a compensation signal based on an ambient temperature is added to the bias signal, and a gain of an input signal of the amplifying element is adjusted based on an ambient temperature. The temperature compensation method according to (3), wherein the temperature compensation is performed.

In the invention from this viewpoint, in addition to (3),
Since the compensation signal based on the ambient temperature is added to the bias signal and the gain of the input signal is adjusted based on the ambient temperature, it is possible to prevent a change in the temperature of the output signal of the amplifier element including the ambient temperature.

(7) According to another aspect of the invention for solving the above-mentioned problem, in the adjustment of the gain of the input signal, the temperature characteristic of the amplification factor of the amplifying element is first-order approximated in a predetermined temperature range. A temperature compensation method according to (2), (3), (5) or (6), wherein the temperature compensation is performed on an object.

According to the invention in this respect, the temperature compensation is performed on the temperature characteristic of the amplification factor of the amplification element which is first-order approximated in a predetermined temperature range, so that the temperature compensation signal can be easily generated. .

(8) According to another aspect of the invention for solving the above-mentioned problem, the invention is characterized in that the amplifying element is a MOSFET. It is a temperature compensation method described.

According to the invention in this respect, the temperature characteristics of the MOSFET can be effectively compensated. (9) According to another aspect of the present invention, there is provided an amplifying apparatus having an amplifying element to which a bias signal is applied, wherein a compensation signal based on a temperature of the amplifying element is added to the bias signal. An amplifying device comprising a compensation signal adding means.

In the invention according to this aspect, since a compensation signal based on the temperature of the amplifier is added to the bias signal of the amplifier, it is possible to prevent a change in the temperature of the output signal of the amplifier.

(10) According to another aspect of the present invention, there is provided an amplifying apparatus having an amplifying element to which an input signal is applied, wherein the gain of the input signal is based on the temperature of the amplifying element. And a gain adjusting means for adjusting the gain.

In the invention according to this aspect, the gain of the input signal of the amplifier is adjusted based on the temperature of the amplifier.
It is possible to prevent a change in the temperature of the output signal of the amplification element. (11) According to another aspect of the present invention, there is provided an amplifying apparatus having an amplifying element to which a bias signal and an input signal are provided, wherein the bias signal includes a compensation signal based on a temperature of the amplifying element. And a gain adjusting means for adjusting the gain of the input signal based on the temperature of the amplifying element.

In the invention according to this aspect, a compensation signal based on the temperature of the amplification element is added to the bias signal of the amplification element, and the gain of the input signal of the amplification element is adjusted based on the temperature of the amplification element. Thus, it is possible to prevent a change in the temperature of the output signal of the amplification element.

(12) According to another aspect of the present invention, there is provided a compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal. An amplifier according to (9) or (11).

In the invention from this viewpoint, (9) or (1)
Since the compensation signal based on the ambient temperature is added to the bias signal in addition to 1), it is possible to prevent a change in the temperature of the output signal of the amplifier element including the ambient temperature.

(13) According to another aspect of the present invention, there is provided another gain adjusting means for adjusting a gain of an input signal of the amplifying element based on an ambient temperature. (10) or (11).

In the invention according to this aspect, in addition to (10) or (11), the gain of the input signal is adjusted based on the ambient temperature. Can be prevented.

(14) According to another aspect of the present invention, there is provided another compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal, and an input signal of the amplifying element. (11) The amplification device according to (11), further including another gain adjustment unit that adjusts a gain based on an ambient temperature.

In the invention according to this aspect, in addition to (11), a compensation signal based on the ambient temperature is added to the bias signal, and the gain of the input signal is adjusted based on the ambient temperature. In addition, it is possible to prevent a change in the temperature of the output signal of the amplification element.

(15) According to another aspect of the invention for solving the above-mentioned problem, in the adjustment of the gain of the input signal, the temperature characteristic of the amplification factor of the amplifying element is first-order approximated in a predetermined temperature range. The amplifying device according to (10), (11), (13) or (14), wherein the amplifying device is performed on a device.

In the invention according to this aspect, the temperature compensation is performed on the temperature characteristic of the amplification factor of the amplification element which is first-order approximated in a predetermined temperature range, so that the temperature compensation signal can be easily generated. .

(16) According to another aspect of the invention for solving the above-mentioned problems, the amplifying element is a MOSFET.
An amplifier according to any one of (9) to (15), characterized in that:

According to the invention from this viewpoint, the temperature characteristics of the MOSFET can be effectively compensated. (17) According to another aspect of the present invention, there is provided a magnetic resonance imaging apparatus that forms an image based on a magnetic resonance signal generated inside a target using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field. An amplifying device having an amplifying element to which a bias signal is applied, wherein the amplifying device outputs RF power for forming the high-frequency magnetic field,
A magnetic resonance imaging apparatus, comprising: an amplification device having compensation signal addition means for adding a compensation signal based on the temperature of the amplification element to the bias signal.

In the invention according to this aspect, since the compensation signal based on the temperature of the amplifier is added to the bias signal of the amplifier that outputs the RF power, it is possible to prevent a change in the temperature of the output signal of the amplifier. Thus, high-quality imaging can be performed with a stable high-frequency magnetic field.

(18) According to another aspect of the invention for solving the above-described problem, an image is formed based on a magnetic resonance signal generated inside a target using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field. What is claimed is: 1. A magnetic resonance imaging apparatus, comprising: an amplifying device that outputs an RF power for forming the high-frequency magnetic field, the amplifying device having an amplifying element to which an RF input signal is given, wherein the gain of the RF input signal is amplified. A magnetic resonance imaging apparatus, comprising: an amplification device having gain adjustment means for adjusting based on the temperature of an element.

In the invention according to this aspect, since the gain of the input signal of the amplifying element that outputs RF power is adjusted based on the temperature of the amplifying element, it is possible to prevent a change in the temperature of the output signal of the amplifying element. Thus, high-quality imaging can be performed with a stable high-frequency magnetic field.

(19) According to another aspect of the invention for solving the above-described problem, an image is formed based on a magnetic resonance signal generated inside a target using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field. A magnetic resonance imaging apparatus, comprising: an amplifying device that supplies a bias signal and an RF input signal as an amplifying device that outputs RF power for forming the high-frequency magnetic field. An amplification device having compensation signal addition means for adding a compensation signal based on the temperature of the element, and gain adjustment means for adjusting the gain of the RF input signal based on the temperature of the amplification element. Magnetic resonance imaging apparatus.

In the invention according to this aspect, a compensation signal based on the temperature of the amplifier is added to the bias signal of the amplifier that outputs RF power, and the gain of the input signal of the amplifier is adjusted based on the temperature of the amplifier. Therefore, it is possible to more thoroughly prevent a change in the temperature of the output signal of the amplification element.
Thus, high-quality imaging can be performed with a stable high-frequency magnetic field.

(20) According to another aspect of the present invention, there is provided a compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal. A magnetic resonance imaging apparatus according to (17) or (19).

According to the invention in this respect, in addition to (17) or (19), a compensation signal based on the ambient temperature is added to the bias signal, so that the temperature change of the output signal of the amplifying element also includes the ambient temperature. Can be prevented.

(21) According to another aspect of the present invention, there is provided another gain adjusting means for adjusting a gain of the RF input signal based on an ambient temperature. A magnetic resonance imaging apparatus according to (18) or (19).

In the invention according to this aspect, in addition to (18) or (19), the gain of the input signal is adjusted based on the ambient temperature. Can be prevented.

(22) According to another aspect of the present invention, there is provided a compensation signal adding unit for adding a compensation signal based on an ambient temperature to the bias signal, and the RF signal.
(19) Another gain adjusting means for adjusting the gain of the input signal based on the ambient temperature.
2. A magnetic resonance imaging apparatus according to item 1.

In the invention according to this aspect, in addition to (19), a compensation signal based on the ambient temperature is added to the bias signal, and the gain of the input signal is adjusted based on the ambient temperature. In addition, it is possible to prevent a change in the temperature of the output signal of the amplification element.

(23) According to another aspect of the invention for solving the above-mentioned problem, the gain of the RF input signal is adjusted by first-order approximation of a temperature characteristic of an amplification factor of the amplifying element in a predetermined temperature range. (18), (19), (21) or (22).

In the invention according to this aspect, the temperature compensation is performed for the temperature characteristic of the amplification factor of the amplification element which is first-order approximated in a predetermined temperature range, so that the temperature compensation signal can be easily generated. .

(24) According to another aspect of the invention for solving the above-mentioned problem, the amplifying element is a MOSFET.
The magnetic resonance imaging apparatus according to any one of (17) to (23), wherein:

According to the invention in this respect, the temperature characteristics of the MOSFET can be effectively compensated.

[0050]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the magnetic resonance imaging apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

As shown in FIG. 1, the present apparatus has a magnet system 100. The magnet system 100 includes a main magnetic field coil unit 102 and a gradient coil unit 106
And an RF (radio frequency) coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other. A generally cylindrical internal space of the magnet system 100 (bore: bor)
e), the subject 300 to be photographed is a cradle
e) loaded and unloaded by transport means (not shown) mounted on the 500;

The main magnetic field coil section 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is substantially parallel to the direction of the body axis of the object 300. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. It is needless to say that not only the superconducting coil but also a normal conducting coil may be used.

The gradient coil section 106 generates a gradient magnetic field for giving a gradient to the static magnetic field strength. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field. The gradient coil unit 1 corresponds to these three types of gradient magnetic fields.
Reference numeral 06 has three gradient coils (not shown).

The RF coil unit 108 controls the object 3 in the static magnetic field space.
A high-frequency magnetic field for exciting spins in the body of 00 is formed. Hereinafter, forming a high-frequency magnetic field is also referred to as transmitting an RF excitation signal. The RF coil unit 108 also receives an electromagnetic wave generated by the excited spin, that is, a magnetic resonance signal.

The RF coil unit 108 has a transmitting coil and a receiving coil (not shown). The same coil is used for the transmitting coil and the receiving coil, or a dedicated coil is used for each.

The gradient coil unit 106 includes a gradient driving unit 130
Is connected. The gradient driving unit 130 is a gradient coil unit 1
A drive signal is given to 06 to generate a gradient magnetic field. The gradient drive unit 130 has three drive circuits (not shown) corresponding to the three gradient coils in the gradient coil unit 106.

The RF coil unit 108 includes an RF driving unit 140
Is connected. The RF driving unit 140 is the RF coil unit 1
08, a drive signal is given, an RF excitation signal is transmitted, and the target 3
Excite the spins in the body of 00. The RF drive unit 140
It is an example of an embodiment of an amplifying device of the present invention. An example of an embodiment of the amplifying device according to the present invention is shown by the configuration of the RF driver 140. The operation of the RF driver 140 indicates an example of an embodiment relating to the method of the present invention. The RF driver 140 will be described later.

The RF coil unit 108 includes the data collection unit 15
0 is connected. The data collection unit 150 captures a received signal received by the RF coil unit 108 and collects the received signal as view data.

A control unit 160 is connected to the gradient driving unit 130, the RF driving unit 140, and the data collection unit 150. The control unit 160 controls the gradient driving unit 130 to the data collection unit 150 to perform photographing.

The output side of the data collection unit 150 is connected to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer. The data processing unit 170 includes a memory (me
(money). The memory stores a program for the data processing unit 170 and various data. The function of the present apparatus is realized by the data processing unit 170 executing a program stored in the memory.

The data processing unit 170 is provided with the data collection unit 15
The data taken from 0 is stored in the memory. A data space is formed in the memory. The data space is two-dimensional
It constitutes a Fourier space. The data processing unit 170 performs two-dimensional inverse Fourier transform on the data in the two-dimensional Fourier space to generate an image of the target 300 (reconstruction).
I do. Hereinafter, the two-dimensional Fourier space is referred to as a k-space (k-s
space).

The data processing section 170 is connected to the control section 160. The data processing unit 170 is at a higher level than the control unit 160 and controls it. The display section 180 and the operation section 190 are connected to the data processing section 170. The display unit 180 includes a graphic display (graphic).
display). The operation unit 190 is a pointing device.
e) is composed of a keyboard provided with e).

The display section 180 displays the reconstructed image output from the data processing section 170 and various kinds of information. The operation unit 190 is operated by an operator, and inputs various commands and information to the data processing unit 170. The operator operates the present apparatus interactively through the display unit 180 and the operation unit 190.

FIG. 2 shows a block diagram of another type of magnetic resonance imaging apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

The apparatus shown in FIG. 2 has a magnet system 100 ′ which is different from the apparatus shown in FIG.
Except for the magnet system 100 ', the configuration is the same as that of the apparatus shown in FIG. 1, and the same parts are denoted by the same reference numerals and description thereof will be omitted.

The magnet system 100 'has a main magnetic field magnet unit 102', a gradient coil unit 106 ', and an RF coil unit 108'. These main magnetic field magnet units 1
02 ′ and each of the coil portions are formed of a pair of coils opposing each other across a space. Each of them has a substantially disk shape and is arranged so as to share a central axis. The object 300 is mounted on the cradle 500 and is carried in and out of the internal space (bore) of the magnet system 100 ′ by carrying means (not shown).

The main magnetic field magnet section 102 'forms a static magnetic field in the internal space of the magnet system 100'. The direction of the static magnetic field is substantially perpendicular to the body axis direction of the object 300. That is, a so-called vertical magnetic field is formed. The main magnetic field magnet unit 102 'is configured using, for example, a permanent magnet. It is needless to say that the present invention is not limited to the permanent magnet and may be configured using a superconducting electromagnet or a normal conducting electromagnet.

The gradient coil section 106 'generates a gradient magnetic field for giving a gradient to the static magnetic field strength. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field, and the gradient coil unit 106 'has three types of gradient coils (not shown) corresponding to these three types of gradient magnetic fields. .

The RF coil unit 108 ′ transmits an RF excitation signal for exciting spins in the body of the subject 300 to the static magnetic field space. The RF coil unit 108 'also receives a magnetic resonance signal generated by the excited spin. The RF coil unit 108 'has a transmitting coil and a receiving coil (not shown). The same coil is used for the transmitting coil and the receiving coil, or a dedicated coil is used for each.

FIG. 3 shows an example of a pulse sequence used for magnetic resonance imaging. This pulse sequence is a pulse sequence based on a gradient echo (GRE) method.

That is, (1) is the RF in the GRE method.
A sequence of α ° pulses for excitation, (2)
(3), (4) and (5) are the sequences of the slice gradient Gs, readout gradient Gr, phase encode gradient Gp and gradient echo MR, respectively. The α ° pulse is represented by the center signal.
The pulse sequence proceeds from left to right along the time axis t.

As shown in the figure, α ° excitation of spin is performed by an α ° pulse. Flip angle (flip
angle) α ° is 90 ° or less. At this time, a slice gradient Gs is applied, and selective excitation for a predetermined slice is performed.

After the α ° excitation, the phase encode gradient Gp
Performs phase encoding of the spin. next,
The spin is first dephased by the readout gradient Gr, and then the spin is rephased (r
ephase) to generate a gradient echo MR. The signal strength of the gradient echo MR is α °
It becomes maximum at the time point after the echo time (echo time) TE from the excitation. The gradient echo MR is collected by the data collection unit 150 as view data.

Such a pulse sequence has a period TR
(Repetition time) is repeated 64 to 512 times. The phase encoding gradient Gp is changed for each repetition, and a different phase encoding is performed each time. As a result, view data of 64 to 512 views filling the k space is obtained.

FIG. 4 shows another example of the pulse sequence for magnetic resonance imaging. This pulse sequence is a pulse sequence of a spin echo (SE: Spin Echo) method.

That is, (1) is a sequence of 90 ° and 180 ° pulses for RF excitation in the SE method, and (2), (3), (4) and (5) are slice gradients, respectively. Gs, readout gradient G
r, phase encoding gradient Gp and spin echo M
This is a sequence of R. Note that a 90 ° pulse and 18
Each 0 ° pulse is represented by a center signal. The pulse sequence proceeds from left to right along the time axis t.

As shown in the figure, 90 ° excitation of spin is performed by a 90 ° pulse. At this time, the slice gradient G
s is applied to perform selective excitation for a predetermined slice. After a predetermined time from the 90 ° excitation, 180 ° excitation by a 180 ° pulse, that is, spin inversion is performed. Also at this time, the slice gradient Gs is applied, and selective inversion is performed for the same slice.

During the period between the 90 ° excitation and the spin inversion, the readout gradient Gr and the phase encode gradient Gp
Is applied. The spin dephase is performed by the readout gradient Gr. The phase encoding of the spin is performed by the phase encoding gradient Gp.

After the spin inversion, the spin is rephased by the readout gradient Gr to generate a spin echo MR.
The signal intensity of the spin echo MR becomes maximum at a point after TE from the 90 ° excitation. The spin echo MR is collected by the data collection unit 150 as view data. Such a pulse sequence is repeated 64 to 512 times in the period TR. Phase encoding gradient Gp for each iteration
And perform different phase encoding each time. As a result, view data of 64 to 512 views filling the k space is obtained.

The pulse sequence used for photographing is G
The method is not limited to the RE method or the SE method.
E (Fast Spin Echo) method, Fast Recovery FSE (Fast Recovery Fast)
Spin Echo method, Echo Planar Imaging (EPI: Echo Planar Imaging)
g) or any other suitable technique.

The data processing unit 170 reconstructs a tomographic image of the object 300 by performing two-dimensional inverse Fourier transform on the view data in the k space. The reconstructed image is stored in the memory and displayed on the display unit 180.

FIG. 5 is a block diagram of a basic form of the RF drive section 140. As shown in the figure, in the RF drive section 140, the output signal (gate signal) of the gate signal generation circuit 402 and the output signal (RF signal) of the RF signal generation circuit 404 are provided.
Are added by the addition circuit 406 and input to the RF output circuit 408. The RF output circuit 408 power-amplifies the input RF signal and supplies the amplified RF signal to the RF coil unit 108.

The gate signal generation circuit 402 includes a gate signal generation source and an amplification circuit for amplifying the output signal. The gate signal is a rectangular wave signal as shown in FIG. The RF signal generation circuit 404 includes an RF signal generation source and an amplification circuit for amplifying the output signal. The RF signal is, for example, an RF signal having a sinc waveform as an envelope as shown in FIG.

The amplification element at the input stage of the RF output circuit 408 is an enhancement type (enhancement type).
type) MOSFET (Metal Oxide)
Semiconductor Field Effect
t Transistor).

A heat sink for heat radiation is attached to the MOSFET. MODFE
The relationship between T and the heat sink is, for example, as shown in FIG. That is, the package of the MOSFET 502 (pa
The surface of the heat sink 586 is coupled to the heat sink 586 via the heat conductive plate 504, and M
A lead 506 of the OSFET 502 is connected to a circuit pattern on the circuit board 582 by soldering or the like.

A temperature sensor 410 is mounted on the surface of the package of the MOSFET 502. As the temperature sensor 410, for example, a voltage output type is used.
The voltage output type temperature sensor is preferable in that it generates a linear temperature detection signal. The temperature sensor is not limited to the voltage output type.

In the figure, the temperature sensor is a MOSFET 5
An example is shown in which the package is mounted on the side of the package 02, but the package is not limited to the side and may be anywhere on the surface of the package. Alternatively, it may be attached to the heat conduction plate 504 or the heat sink 586. In short, MOSFET502
It is only necessary to be thermally coupled to

The MOSFET 502 has, for example, input / output characteristics as shown in FIG. This input / output characteristic is also called gm characteristic. The gate signal gives a bias voltage Eb for this input / output characteristic.

The MOSFET 502 has the bias voltage E
b is converted to a predetermined amplification factor (gain: ga).
Amplify in). MOSFET 502 amplifies the RF signal by class A operation. The amplification gain is determined by the slope of the gm characteristic curve at the operating point. MOSFET5
02 is an example of an embodiment of the amplifying element of the present invention.

The MOSFET 502 generates heat by consuming power internally, and its temperature rises. The gm characteristic changes due to the temperature rise, and the output signal changes. gm
The characteristic temperature change is as shown in FIG. 9, for example. As shown in the figure, the gm characteristic at the temperature T0 changes to the gm characteristic at the temperature T1 as the temperature increases. That is, the position of the gm characteristic curve changes in the direction of the origin with an increase in temperature, and the inclination decreases.

Therefore, under the bias voltage Eb, the operating point changes from a to b, and the output signal changes accordingly. In order to prevent such a change in the output signal, the following temperature compensation is performed.

One temperature compensation is the adjustment of the bias voltage. That is, the operating point is set to c by changing the bias voltage from Eb to Eb 'according to the temperature change, and the change of the level of the output signal is prevented.

FIG. 10 is a block diagram showing an example of the RF driving section 140 having the bias voltage adjusting means. As shown in FIG.
8, the temperature of the MOSFET 502 is detected and input to the bias adjustment circuit 412.

The bias adjustment circuit 412 forms a temperature compensation voltage Ec based on the temperature detection signal, and generates the temperature compensation voltage Ec.
To enter. In the addition circuit 406, the bias voltage E
The temperature compensation voltage Ec is added to b. The temperature compensation voltage Ec is set so that the algebraic sum of the two becomes the above-described bias voltage Eb ′.
Is adjusted. When the input signal is a linear voltage signal, the bias adjustment circuit 412 may multiply the input signal by a predetermined coefficient. A portion including the temperature sensor 410, the bias adjustment circuit 412, and the addition circuit 406
5 is an example of an embodiment of a compensation signal adding unit according to the present invention.

Another temperature compensation is a gain adjustment of the RF signal. That is, the amplitude of the RF signal input to the MOSFET 502 is changed in accordance with the temperature change, thereby canceling the influence of the change in the slope of the gm characteristic due to the temperature change, and preventing the amplitude change of the RF output signal.

FIG. 11 is a block diagram showing an example of the RF drive section 140 having gain adjusting means. As shown in the figure, the output signal of the RF signal generation circuit 404 is input to the addition circuit 406 through the variable gain circuit 414,
The gain of the variable gain circuit 414 is
The adjustment is made based on the temperature detection signal of the temperature sensor 410 by the step 6. When the input signal is a linear voltage signal, the gain adjustment circuit 416 may multiply the input signal by a predetermined coefficient.

The variable gain circuit 414 is, for example, a voltage input type variable attenuator. A specific example of such a variable attenuator is, for example, a PIN diode attenuator (PIN Diode).
de Attenuator).

The gain adjustment circuit 416 changes the gain of the variable gain circuit 414 in the same direction and in the opposite direction as the change in the gain due to the change in the gm characteristic. This allows MOSF
In the ET 502, the influence of the temperature change of the gm characteristic is canceled, and the amplitude change of the RF output signal is prevented. The portion including the temperature sensor 410, the gain adjustment circuit 416, and the variable gain circuit 414 is an example of the embodiment of the gain adjustment means in the present invention.

FIG. 12 is a block diagram showing an example of the RF driver 140 having the bias adjusting means and the gain adjusting means. This corresponds to a combination of the configurations shown in FIGS. With such a configuration, the bias adjustment and the gain adjustment corresponding to the temperature change of the gm characteristic can be performed at the same time, and a more stable RF output can be obtained.

When the temperature of the MOSFET 502 is detected on the surface of the package as shown in FIG. 7, the temperature of the internal chip is not directly detected.
When the ambient temperature fluctuates due to a change in room temperature or the like, an error may occur in temperature compensation.

In order to prevent this, as shown in FIG. 13, for example, the ambient temperature is detected by a temperature sensor 420, a bias adjustment signal is formed by a bias adjustment circuit 422 based on the detected signal, and a bias adjustment signal is formed by an addition circuit 424. It is added to the output signal of the adjustment circuit 412 to compensate for the influence of the ambient temperature. Temperature sensor 420, bias adjustment circuit 422,
The adding circuits 424 and 406 are an example of an embodiment of another compensation signal adding means in the present invention.

When removing the influence of the ambient temperature on the gain adjustment, as shown in FIG. 14, the ambient temperature is detected by a temperature sensor 420, and a gain adjustment signal is formed by a gain adjustment circuit 432 based on the detected signal. , Addition circuit 4
At 34, the sum is added to the output signal of the gain adjustment circuit 416 to compensate for the influence of the ambient temperature. The temperature sensor 420, the gain adjustment circuit 432, and the addition circuits 434, 406 are an example of an embodiment of another gain adjustment unit in the present invention.

In order to eliminate the influence of the ambient temperature on both the bias and the gain, the configuration shown in FIG. 15 is used. This corresponds to a combination of the configurations shown in FIGS. Thereby, stable RF that is not affected by both the temperature of MOSFET 502 and the ambient temperature
You can get the output.

The change characteristic of the gain of the MOSFET according to the temperature change includes a strictly quadratic term of the temperature, and is, for example, as shown by a solid line in FIG. Such a temperature characteristic of the gain can be approximated by a first-order characteristic as shown by a constant chain line in the operating temperature range of the MOSFET 502.

The approximate primary characteristic is obtained by calculation by, for example, the least square method, and minimizes the secondary error. Such approximate primary characteristics intersect actual temperature characteristics at two points A and B inside the operating temperature range. Therefore, the temperature changes Ta and Tb at the two intersections A and B are obtained, and the gain adjustment circuit 416 having the primary temperature compensation characteristic is calibrated at these two points A and B. Thereby, the compensation characteristic of the gain adjustment circuit 416 can be adapted to the approximate primary characteristic.

As described above, since the gain adjustment circuit 416 can have only the primary temperature compensation characteristic, the configuration can be simplified. Gain adjustment circuit 4
The same applies to 32.

In the above, an example in which the amplifying element is a MOSFET has been described. However, the amplifying element is not limited to the MOSFET, and may be an amplifying element that amplifies an input signal superimposed on a bias. According to the present invention, it is possible to effectively perform temperature compensation on such an amplification element.

[0108]

As described above in detail, according to the present invention, there is provided a method for correcting a temperature change in the operating characteristics of an amplifier element,
It is possible to realize an amplification device provided with a temperature compensating means and a magnetic resonance imaging apparatus provided with such an amplification device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a pulse sequence executed by the device shown in FIG. 1 or FIG. 2;

FIG. 4 is a diagram showing an example of a pulse sequence executed by the device shown in FIG. 1 or 2;

FIG. 5 is a block diagram of an example of an RF drive unit in the device shown in FIG. 1 or FIG.

FIG. 6 is a waveform diagram of signals in the RF drive unit shown in FIG.

FIG. 7 is a diagram showing a relationship between a MOSFET and a temperature sensor.

FIG. 8 is a diagram illustrating an example of input / output characteristics of a MOSFET.

FIG. 9 is a diagram showing a temperature change of input / output characteristics of a MOSFET.

FIG. 10 is a block diagram of an example of an RF drive unit in the device shown in FIG. 1 or FIG.

FIG. 11 is a block diagram of an example of an RF driving unit in the device shown in FIG. 1 or FIG.

FIG. 12 is a block diagram of an example of an RF drive unit in the device shown in FIG. 1 or FIG.

FIG. 13 is a block diagram of an example of an RF drive unit in the device shown in FIG. 1 or FIG.

FIG. 14 is a block diagram of an example of an RF driver in the device shown in FIG. 1 or FIG.

FIG. 15 is a block diagram of an example of an RF driving unit in the device shown in FIG. 1 or FIG.

FIG. 16 is a diagram showing a change in temperature of a gain of a MOSFET.

[Explanation of symbols]

 100, 100 'Magnet system 102 Main magnetic field coil unit 102' Main magnetic field magnet unit 106, 106 'Gradient coil unit 108, 108' RF coil unit 130 Gradient drive unit 140 RF drive unit 150 Data collection unit 160 Control unit 170 Data processing unit 180 display section 190 operation section 300 object 402 gate signal generation circuit 404 RF signal generation circuit 406, 424, 434 addition circuit 408 RF output circuit 410, 420 temperature sensor 412, 422 bias adjustment circuit 416, 432 gain adjustment circuit 414 variable gain circuit 500 cradle 502 MOSFET

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Kono 127 G-Yokogawa Medical System Co., Ltd., 4-7 Asahigaoka, Hino-shi, Tokyo F-term (reference) 4C096 AB34 AB50 AD10 CC32 CC40 5J090 AA04 AA41 AA54 CA02 CA86 CN04 FA10 FN06 FN08 FN14 HA10 HA39 HA43 HN15 HN20 KA12 KA26 KA65 QA04 SA15 TA01 TA04 TA06

Claims (24)

[Claims] 1. A temperature compensation method comprising: adding a compensation signal based on a temperature of an amplification element to a bias signal of the amplification element. 2. A temperature compensation method, comprising: adjusting a gain of an input signal of an amplification element based on a temperature of the amplification element. 3. The method according to claim 1, further comprising adding a compensation signal based on a temperature of the amplification element to a bias signal of the amplification element, and adjusting a gain of an input signal of the amplification element based on the temperature of the amplification element. Compensation method. 4. The temperature compensation method according to claim 1, wherein a compensation signal based on an ambient temperature is added to the bias signal. 5. The temperature compensation method according to claim 2, wherein a gain of an input signal of the amplification element is adjusted based on an ambient temperature. 6. The temperature compensation method according to claim 3, wherein a compensation signal based on an ambient temperature is added to the bias signal, and a gain of an input signal of the amplification element is adjusted based on an ambient temperature. . 7. The method according to claim 2, wherein the gain of the input signal is adjusted for a first-order approximation of the temperature characteristic of the amplification factor of the amplification element in a predetermined temperature range. 3. The temperature compensation method according to claim 5 or claim 6. 8. The temperature compensation method according to claim 1, wherein the amplification element is a MOSFET. 9. An amplifying device having an amplifying element to which a bias signal is applied, comprising: a compensating signal adding means for adding a compensating signal based on a temperature of the amplifying element to the bias signal. apparatus. 10. An amplifying apparatus having an amplifying element to which an input signal is applied, comprising: gain adjusting means for adjusting a gain of the input signal based on a temperature of the amplifying element. . 11. An amplifying device having an amplifying element to which a bias signal and an input signal are provided, wherein: a compensating signal adding means for adding a compensating signal based on a temperature of the amplifying element to the bias signal; And a gain adjusting means for adjusting the temperature based on the temperature of the amplifying element. 12. The amplifying device according to claim 9, further comprising another compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal. 13. The amplifying device according to claim 10, further comprising another gain adjusting means for adjusting a gain of an input signal of the amplifying element based on an ambient temperature. 14. A compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal, and another gain adjusting means for adjusting a gain of an input signal of the amplifying element based on an ambient temperature. The amplifying device according to claim 11, wherein the amplifying device is provided. 15. The apparatus according to claim 10, wherein the gain of the input signal is adjusted for a temperature characteristic of an amplification factor of the amplifying element which is first-order approximated in a predetermined temperature range. The amplifying device according to claim 11, 13 or 14. 16. The amplifying element is a MOSFET.
The amplifying device according to any one of claims 9 to 15, wherein: 17. A magnetic resonance imaging apparatus configured to form an image based on a magnetic resonance signal generated inside a subject using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, wherein: an RF for forming the high-frequency magnetic field As an amplifying device for outputting power, an amplifying device having an amplifying element to which a bias signal is applied, comprising: an amplifying device having compensation signal adding means for adding a compensation signal based on a temperature of the amplifying element to the bias signal. A magnetic resonance imaging apparatus. 18. A magnetic resonance imaging apparatus configured to form an image based on a magnetic resonance signal generated inside a subject using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, wherein an RF for forming the high-frequency magnetic field is provided. An amplifying device having an amplifying element to which an RF input signal is supplied, as an amplifying device for outputting power, wherein the amplifying device includes gain adjusting means for adjusting a gain of the RF input signal based on a temperature of the amplifying element. A magnetic resonance imaging apparatus comprising: 19. A magnetic resonance imaging apparatus configured to form an image based on a magnetic resonance signal generated inside a subject using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, wherein: an RF for forming the high-frequency magnetic field An amplifying device that outputs an electric power, the amplifying device having an amplifying element to which a bias signal and an RF input signal are provided, wherein a compensation signal adding unit that adds a compensation signal based on a temperature of the amplifying element to the bias signal; A magnetic resonance imaging apparatus, comprising: an amplifying device having gain control means for adjusting a gain of an RF input signal based on a temperature of the amplifying element. 20. The magnetic resonance imaging apparatus according to claim 17, further comprising another compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal. 21. The magnetic resonance imaging apparatus according to claim 18, further comprising another gain adjusting means for adjusting a gain of the RF input signal based on an ambient temperature. 22. Other compensation signal adding means for adding a compensation signal based on an ambient temperature to the bias signal, and another gain adjusting means for adjusting a gain of the RF input signal based on an ambient temperature. 20. The magnetic resonance imaging apparatus according to claim 19, wherein: 23. The apparatus according to claim 18, wherein the adjustment of the gain of the RF input signal is performed for a temperature characteristic of an amplification factor of the amplification element which is first-order approximated in a predetermined temperature range. Claim 19, Claim 21 or Claim 2
3. The magnetic resonance imaging apparatus according to 2. 24. The amplification device is a MOSFET.
The magnetic resonance imaging apparatus according to any one of claims 17 to 23, characterized in that: