JP2003000567A - Magnetic resonance imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To deal with a pulse sequence for outputting the RF pulses for long time or with high duty ratio. SOLUTION: In the magnetic resonance imaging system having a high frequency coil 14 for impressing the RF pulse (RFout) to a reagent placed within a photographing area according to the prescribed sequence, a plurality of high frequency amplifiers 24b for amplifying the RF pulse to be supplied to the high frequency coil are operated while being successively switched by a sequence control part 31. Thus, heating of the high frequency amplifiers is suppressed, the RF pulses of long pulse width or high duty ratio can be outputted and the pulse sequence of high grade can be dealt with.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus, which realizes output of an RF pulse for a long time and can execute a pulse sequence having a high duty factor. Regarding

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus (hereinafter referred to as MR
I device. ) Is for a subject placed in a static magnetic field,
By applying a high-frequency magnetic field, the nuclear spins that make up the biological tissue are excited, and the magnetic resonance signals (hereinafter referred to as MR signals) generated by the nuclear spins are measured, and the spatial distribution and spectrum of the nuclear spins are measured. It is to be visualized. At this time, a gradient magnetic field is applied to add position information to the MR signal. Since such an MRI apparatus has been introduced, it has been an important issue to shorten the imaging time and improve the image quality, and various pulse sequences have been proposed as countermeasures against these issues. For example, a series of sequences for collecting a plurality of MR signals by an RF pulse in which a refocusing RF pulse (180 ° pulse) is repeatedly applied after magnetization excitation with a 90 ° pulse is performed at a constant repetition period (repetition time TR ) Repeated fast spin echo method (fast SE method), or after excitation of magnetization, instead of a refocusing RF pulse, a series of sequences for collecting a plurality of echoes by gradient magnetic field reversal is repeated at a constant repetition time TR for an echo planar imaging Method (EPI method).

In order to execute these pulse sequences, a high frequency amplifier capable of withstanding a high pulse output of several KW in a frequency band of several 10 MHz was required. Of course, there is also a strong demand for miniaturization, so for example,
A high frequency amplifier using a semiconductor element such as a FET element has been proposed. A schematic configuration of this high frequency amplifier is shown in FIG.
However, since the high frequency power that can be extracted from one semiconductor element is about several hundred W at most, it is intended to obtain a large output by connecting a plurality of semiconductor elements in a tree shape. is there. That is,
In the high frequency amplifier shown in FIG. 8, the output of the preamplifier 1 is
The gain / phase adjuster 2 is branched and supplied to a pair of amplifiers A11 and A12 composed of FET elements, and the output of the amplifier A11 is further supplied to the amplifiers A21 and A22 of the next stage.
The output of the amplifier A12 is branched and supplied to the amplifiers A23 and A24 in the next stage.
The outputs of the final stage amplifiers (A21 to A24 in this case) are combined by the combiner 3 into one output. Therefore, the input pulse RFin of several tens of MHz band is supplied to the preamplifier 1 from a high frequency control unit (not shown), and has a level required for the amplifiers A11 and A12 in the next stage to be supplied to the amplifiers A21 to A24 in the final stage. Is amplified up to. And
The output pulse of the preamplifier 1 is introduced into the gain / phase adjuster 2, and the gain and the phase are adjusted appropriately in consideration of the arrangement of the amplifiers in the subsequent stage. Then, the pulse signals whose gain and phase have been adjusted are sequentially amplified by the amplifiers A11, A12 and the amplifiers A21 to A24. Finally, the output of each amplifier in the final stage is combined by the combiner 3 and, for example, several K
One high-frequency output pulse RFou of W to several tens of kW
The output pulse RFout is output as t and is supplied to a high-frequency coil (not shown).

The preamplifier 1 and each of the amplifiers A11, A
The operation timings of 12, A21 to A24, etc. are controlled by a gate signal Gate supplied to each gate from a sequence controller (not shown). That is, basically, depending on the responsivity of the FET or the like that constitutes the amplifier, several μs to
The gate signal Gate is applied (ON) several ten μs ago, and cut off (OFF) at the same time as the end of the high frequency pulse. Therefore, each amplifier amplifies the input signal only while the gate signal Gate is being applied. The purpose of controlling the operation of each amplifier by this gate signal Gate is to reduce noise generated by switching between transmission and reception and to stop the amplification operation when there is no signal. Further, the configurations of the amplifiers A11 to A24 are appropriately changed to supply the necessary electric power. That is, in FIG. 8, the amplifier has a two-stage configuration of a middle stage and a final stage, but in order to obtain a larger output, the number of stages is added to add three stages.
It is possible to change the configuration such that the number of stages is equal to or more than one, the number of the two middle stage amplifiers is three, and the number of the final stage four amplifiers is six.

[0005]

It is possible to obtain a high frequency output of about several KW to several tens of KW by combining a plurality of amplifiers composed of semiconductor elements in a tree structure as described above. Due to the characteristics of a semiconductor element, it is difficult to continue the operation of outputting a pulse train for a long time due to factors such as heat generation and driving form, and the continuous operation time is limited to several tens of ms at most. Fast spin echo pulse sequence (fastSE method)
Then, as an RF pulse for collecting data for one slice, the pulse width is usually 2 m after the 90 ° pulse.
A 180 ° pulse of about s is applied for 8 to 16 pulses. However, as a new pulse sequence that improves the pumping characteristics, such as by increasing the speed of data collection and suppressing unnecessary signals for improving image quality, 256
The pulsed 180 ° pulse continues for a long time (for example,
For the purpose of applying the signal for several hundred ms and suppressing an unnecessary signal, a device using a pulse having a long pulse width of 60 ms has been proposed. However, it is difficult for the conventional high frequency amplifier having the above tree structure to cope with such a new pulse sequence. Therefore, in order to cope with a new pulse sequence, there has been a demand for a high frequency amplifier capable of outputting an RF pulse composed of a pulse train having a long duration or a high duty ratio. The present invention has been made to solve the above problems and meet new demands.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 is for applying a high-frequency excitation signal to a subject placed in an imaging region according to a predetermined sequence. A magnetic resonance imaging apparatus having a high frequency coil, comprising: a plurality of high frequency amplification means for amplifying the excitation signal supplied to the high frequency coil; and a switching control means for sequentially operating the plurality of high frequency amplification means. Is characterized by. The invention according to claim 2 is the magnetic resonance imaging apparatus according to claim 1, further comprising a combining means for combining the outputs of the plurality of high frequency amplifying means controlled by the switching control means. And The invention according to claim 3 is the magnetic resonance imaging apparatus according to any one of claims 1 and 2, wherein the switching control means temporally connects the plurality of high-frequency amplification means. It is characterized by sequentially switching. According to a fourth aspect of the present invention, in the magnetic resonance imaging apparatus according to the third aspect, the switching control means, when sequentially switching the plurality of high frequency amplification means, switches both high frequency amplification means to be switched for a predetermined time. It is characterized in that the two high-frequency amplifiers are simultaneously and transiently operated simultaneously, and the outputs are controlled to be substantially constant while the both high-frequency amplifiers are transiently and simultaneously operated.

As a result, even if the excitation signal has a long pulse width, it is possible to suppress the heat generation of the high frequency amplifying means and stabilize its operation to obtain a high output, and to cope with a high level pulse sequence. Will also be possible.

Further, the invention according to claim 5 is the magnetic resonance imaging apparatus according to claim 1, wherein the switching control means is configured to perform the plurality of excitation signals for each excitation signal for at least one slice according to the predetermined sequence. It is characterized in that the high frequency amplification means of (1) is sequentially switched. With this, one high-frequency amplifying unit is intermittently operated for each slice, so that a down time is secured, and heat generation of the high-frequency amplifying unit can be suppressed to obtain a high output. Therefore,
Data acquisition can be performed continuously, and it is possible to support advanced pulse sequences. Further, the invention according to claim 6 is the magnetic resonance imaging apparatus according to claim 1, wherein the switching control means is for each one or a plurality of excitation signals in the series of the excitation signals in the predetermined sequence. The plurality of high frequency amplifying means are sequentially switched. As a result, one high-frequency amplifying means is intermittently operated in a shorter time, so that a down time is secured and heat generation of the high-frequency amplifying means is suppressed even if the excitation signal has a high duty ratio. It is possible to obtain high output, and it is also possible to support advanced pulse sequences.

Further, the invention according to claim 7 is the magnetic resonance imaging apparatus according to any one of claims 1 to 6, wherein the switching control means controls the operating time of the high frequency amplification means. It is characterized by controlling. The invention according to claim 8 is the magnetic resonance imaging apparatus according to claim 7, wherein the switching control means controls the operating time of the high frequency amplification means according to the amplitude of the high frequency excitation signal. Is characterized by. Thereby, the operating time of the high frequency amplifying means is made to correspond to the output of the excitation signal for each pulse sequence, so that the duty of the pulse train forming the excitation signal can be improved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Various embodiments of a magnetic resonance imaging apparatus according to the present invention will be described in detail below with reference to FIGS. FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention. In the coil assembly indicated by reference numeral 10 in the figure, a static magnetic field magnet 11, a shim coil 12, a gradient magnetic field coil 13, and a high frequency coil 14 are sequentially installed around a cylindrical space 5 for accommodating a subject. ing. The static magnetic field magnet 11 is usually composed of a normal conducting coil or a superconducting coil, and receives a current supply from the static magnetic field controller 21 to form a static magnetic field in the cylindrical space 5 along the Z-axis direction. . The shim coil 12 is provided to further enhance the homogeneity of the static magnetic field formed by the static magnetic field magnet 11, and is supplied with current from the shim coil power supply 22 under the control of the sequence control unit 31 described later. The gradient magnetic field coil 13 is composed of three sets of coils that generate gradient magnetic fields of X, Y, and Z axes.
A gradient magnetic field current is supplied to a gradient magnetic field coil 13 of each axis from a gradient magnetic field power source 23 including an X-axis gradient magnetic field power source, a Y-axis gradient magnetic field power source, and a Z-axis gradient magnetic field power source, under the control of a sequence controller 31 described later. It

The high frequency coil 14 transmits an RF pulse to the subject under the control of the sequence control section 31 described later,
It is for receiving a magnetic resonance signal (MR signal) from a subject, and is composed of a coil itself and a tuning / matching portion for tuning the resonance frequency of the coil. The frequency to be tuned depends on the target nuclide, and is usually tuned to the resonance frequency of the proton. For example, the static magnetic field strength is 1.0T.
That at (Tesla) is 42.5 MHz. And
The high frequency coil 14 is connected to the transmitter 24 at the time of transmission and to the receiver 25 at the time of reception by a duplexer (not shown). The high frequency coil 14 is shown in FIG.
In the above description, the transmission / reception function is used, but the transmission-only function and the reception-only function may be independently configured. Here, by combining the gradient magnetic field coils 13, for example, the X-axis gradient magnetic field coil serves as a read gradient magnetic field, the Y-axis gradient magnetic field coil serves as a phase encode gradient magnetic field, and further, Z The axial gradient magnetic field coil can be used as a slice select gradient magnetic field (hereinafter, described as having such a combination). An area in which the magnetic field strengths in the three axial directions all change linearly is set as an imaging area, and echoes (MR signals) from the subject can be collected in this imaging area. Therefore, the subject is inserted into the imaging region as the top plate slides while being placed on a bed top plate (not shown).

Now, a sequence control unit 31 for executing a pulse sequence for collecting MR signals from a subject.
Is provided. This pulse sequence has an X axis,
The intensity and timing of each gradient magnetic field pulse applied from the Y-axis and Z-axis gradient magnetic field power supply 23 to the corresponding gradient magnetic field coil 13 (read gradient magnetic field coil, phase encoding gradient magnetic field coil, slice selection gradient magnetic field coil), and The frequency, phase, intensity, timing, etc. of the RF pulse applied from the transmitter 24 to the high-frequency coil 14 are further included in the receiver 2.
5 and the sampling width and sampling period of data collection in the data collection unit 26 are finely defined,
These are stored in the computer system 32 for each pulse sequence. Therefore, the sequence control unit 31 follows the pulse sequence selected on the computer system 32 and the shim coil power supply 22 and the gradient magnetic field power supply 23 (X axis,
(Y-axis and Z-axis gradient magnetic field power source), transmitter 24, receiver 25
Then, the data acquisition unit 26 is controlled to execute the pulse sequence. With the execution of the pulse sequence, the MR signal from the subject is received by the high frequency coil 14. This MR signal is an analog signal, and the receiving unit 25
Receives this signal and amplifies and detects it. Further, the detected MR signal is introduced into the data acquisition unit 26, converted into a digital signal, and transferred to the computer system 32 for each acquisition unit or collectively. This computer system 3
2 has a central function of controlling the entire system of the magnetic resonance imaging apparatus, a function of generating an MR image of a subject based on an MR signal and an interface function for setting a cross section, and the like. Images and data are displayed on the display 33.

A console 34 having input devices such as a keyboard and a mouse is connected to the computer system 32. Therefore, the data necessary for the operator to capture the image is transferred to the computer system 32 via the console 34.
, And the computer system 32 supplies the data to the sequence control unit 31, so that imaging in a desired pulse sequence is executed. Now, when executing the pulse sequence, a predetermined RF pulse is transmitted from the transmission unit 24 to the high frequency coil 1 under the control of the sequence control unit 31.
4 is applied to the transmitter 24, the transmitter 24, as shown in FIG.
It is composed of a high frequency control unit 24a and a high frequency amplifier 24b. Under the control of the sequence control unit 31, the high frequency control unit 24a generates a signal of a frequency necessary to excite a target target nuclide (for example, proton), and makes this signal have a desired phase. The input signal RFin is supplied to the high frequency amplifier 24b. Then, the high frequency amplifier 24b, based on the gate signal Gate given from the sequence control unit 31,
The signal supplied from the high frequency control unit 24a is amplified to a desired level, and its output signal RFout is supplied to the high frequency coil 14 as an RF pulse.

The high frequency amplifier 24 of the transmitter 24 as described above
Conventionally, b has a configuration in which a plurality of amplifiers as shown in FIG. 8 are connected in a tree structure, but as described above, the conventional configuration cannot withstand a long-time operation. Therefore, in the present invention, a plurality of high-frequency amplifiers 24b having the same configuration as the conventional one is provided as a unit, and each unit is appropriately switched and operated in accordance with the RF pulse generated according to the pulse sequence to be executed. Is. Therefore, one embodiment of the transmission unit 24 employed in the magnetic resonance imaging apparatus of the present invention is shown in FIG. 3, so the details of the transmission unit 24 will be described next. That is, the transmitter 24 includes the high frequency control unit 24a and a plurality of high frequency amplifiers 24b1 and 24b.
24bn and a high frequency input signal RFin supplied from the high frequency control unit 24a are supplied to each high frequency amplifier 24b.
24bn that adjusts and distributes to 1, 24b2, ... 24bn an appropriate impedance, and high-frequency signals obtained from the respective high-frequency amplifiers 24b1, 24b2, ... 24bn to the load (high-frequency coil 14). And a combiner 24d for adjusting and combining so that the optimum power can be supplied. In addition, in FIG.
RFout indicates an RF pulse supplied from the combiner 24d to the high frequency coil 14.

Next, the operation of the transmitting section 24 thus constructed will be described. When executing the pulse sequence, the high frequency control unit 2 is controlled under the control of the sequence control unit 31.
From 4a, a 90 ° pulse followed by a 180 ° pulse is emitted as an input signal RFin and introduced into the distributor 24c.
Therefore, the distributor 24c distributes the input signal RFin to the plurality of high frequency amplifiers 24b1, 24b2, ... 24bn is supplied to the high-frequency amplifiers 24b1, 24b2, ... 24bn from the sequence control unit 31, and the high-frequency amplifiers 24b1, 24b2, ... 24bn perform an amplifying operation only while the gate signal Gate is being supplied. It will be. However, the gate signal Gate from the sequence control unit 31 is supplied to all the high frequency amplifiers 24b1, 24b2,
24bn are not supplied simultaneously, but by individually controlling the application timing of the gate signal Gate, the amplification operation of each high-frequency amplifier 24b1, 24b2, ... 24bn is switched so as to be appropriately shifted in time. Therefore, for example, from the high frequency amplifier 24b1 to the high frequency amplifier 2
The high-frequency amplifier 24b which operates by sequentially supplying the gate signals Gate to 4b2, ...
24bn are switched one after another so that the amplification operation is continuously continued in total.

Therefore, by appropriately controlling the application timing of the gate signal Gate, each high-frequency amplifier 24b.
Details of various embodiments in which the amplification operation of 1, 24b2, ..., 24bn is switched will be described with reference to FIGS. 4 to 7. First, the embodiment shown in FIG. 4 will be described. In this embodiment, three high frequency amplifiers 24b1, 24b2, 24b3 are used for convenience, and each high frequency amplifier 24b1, 24b is used.
The amplifying operations of 2 and 24b3 are sequentially switched so as not to be interrupted, and the amplifiers are operated as if they were one high-frequency amplifier 24b. In addition, in FIG. 4, (a)
Is a schematic representation of the high frequency output RFout from the transmitter 24 supplied to the high frequency coil 14, which is
For example, in a certain pulse sequence, the high frequency coil 14
It is assumed that the RF pulse is a single RF pulse having a long pulse width. Furthermore, the magnitude of the waveform of the RF pulse RFout represents the magnitude of power. And (b)
When obtaining one RF pulse RFout, all the high frequency amplifiers 24b1, 24b2,
Total time width of gate signal given to 24b3
And (c), (d), and (e) show the individual gate signals Gate1, Gate2, and Gate3 supplied to the high-frequency amplifiers 24b1, 24b2, and 24b3, respectively.

As is apparent from FIG. 4, in the present invention, for example, three high frequency amplifiers 24b1, 24b2, 24b3 are used.
When using a high frequency amplifier 24b1, 2
The gate signals Gate1, Gate2, and Gate3 are sequentially supplied from the sequence controller 31 to 4b2 and 24b3.
The gate signals Gate1, Gate2, and Gate3 may have the same time width, but when the amplitude (power) of the RF pulse RFout changes extremely with time, a high frequency signal that amplifies a signal with a small amplitude is amplified. In order to increase the operating time of the amplifier and shorten the operating time of the high-frequency amplifier that amplifies a signal with a large amplitude, the gate signal Ga
It is good to adjust the time width of te1, Gate2, Gate3 as appropriate.
Therefore, the high-frequency amplifier to which the gate signal is supplied performs an amplifying operation only during that time, and the high-frequency amplifier to which the gate signal is not supplied does not operate during that time and is not loaded. Therefore, even if the RF pulse RFout is a pulse train having a long duty cycle or a high duty ratio, the load is distributed to the high-frequency amplifiers 24b1, 24b2, and 24b3 to generate heat even in the amplifier configured by the semiconductor element. A high output can be obtained by suppressing and stabilizing the operation. That is, it becomes possible to endure high load and long-time operation. Also, RF pulse RFout
By controlling the operating time of each high-frequency amplifier 24b according to the amplitude of the RF pulse RFou
The duty of the pulse train forming t can be improved.

It is to be noted that, ideally, in a portion where a continuous gate signal is connected, that is, in a portion where the gate signal Gate1 is switched to the gate signal Gate2, such as a portion surrounded by a circle in FIGS. 4C and 4D, It is desired that the output of the high-frequency amplifier 24b1 instantaneously become zero and that the high-frequency amplifier 24b2 subsequently output all desired pulse signals. However, because of the response characteristic of the high frequency amplifier 24b,
When the gate signal Gate is turned ON / OFF, the RF pulse cannot be momentarily turned ON / OFF, and the response time is delayed by, for example, several μs to several tens of μs. Therefore, the gate signal is set so that the operation of the high frequency amplifier 24b1 is stopped and the next high frequency amplifier 24b2 is operated.
At the moment of switching the gate signal when switching from Gate1 to Gate2, the high frequency amplifier 24b1 and the high frequency amplifier 24
The RF pulse RFout is output from both b2. In such a transient situation, the amplitude and phase of the RF pulse RFout change every moment, so this characteristic is shown in FIG.
The gains of the high frequency amplifiers 24b1 and 24b2 are adjusted and corrected by the gate signals Gate1 and Gate2 as shown in FIG.

That is, FIG. 5A shows the gate signal Gate1 applied to the high frequency amplifier 24b1.
(B) is a gate signal applied to the high frequency amplifier 24b2
Gate2 is shown, and (c) shows the gain of the high frequency amplifier 24b in the switching range T of the gate signal Gate. As is clear from these, the rising portion and the falling portion of the gate signal Gate have a gentle slope, and in the switching range T of the gate signal Gate, the falling portion of the gate signal Gate1 and the rising portion of the gate signal Gate2 Adjust so that they overlap. Therefore, in the switching range T of the gate signal Gate, when the outputs of the high-frequency amplifiers 24b1 and 24b2 that are operated at the same time are combined, the combined outputs can be made substantially constant so that discontinuity does not occur. Since this transient characteristic can be measured in advance, each high-frequency amplifier 24b1,
24bn, ..., 24bn transient characteristics are stored in the sequence control unit 31, and when the gate signal Gate is switched,
The high frequency amplifiers 24b1 and 24b according to the transient characteristics.
By controlling the gain / phase adjuster 2 included in b2, ..., 24bn, the amplitude and the phase can be appropriately adjusted so as not to cause discontinuity in the RF pulse RFout in the switching range T of the gate signal Gate. it can.

In the above embodiment, one RF pulse having a long pulse width is output by driving the plurality of high frequency amplifiers 24b in a time division manner. With respect to a series of RF pulses in a multi-slice sequence for obtaining MR signals from a plurality of slice planes, a plurality of high-frequency amplifiers are appropriately switched and driven for each pulse train for collecting information for each slice plane. The form will be described with reference to FIG. FIG. 6A shows a typical pulse train RFout in the fast spin echo pulse sequence, in which an α ° pulse for excitation and a number of subsequent 180 ° inversion pulses are repeatedly transmitted for each slice. Is shown. Then, (b) shows a plurality of high-frequency amplifiers 24b1 for the pulse train RFout for each slice plane,
In order to selectively operate 24b2, ..., 24bn, all the high frequency amplifiers 24b1,
24b2, ... All the gate signals To given to 24bn
talgate, and (c), (d), and (e) show gate signals Gate1, Gate2, and Gaten supplied to the high-frequency amplifiers 24b1, 24b2, and 24bn, respectively.

In this embodiment, the slice plane 1 (Slic
In order to obtain the MR signal from e # 1), as shown in FIG. 6C, first, only the high frequency amplifier 24b1 is made to correspond to each RF pulse, and the sequence control unit 31 outputs the gate signal.
Supply Gate1. Therefore, only the high-frequency amplifier 24b1 operates in response to the supply of the gate signal Gate1, and the distributor 24c
The input signal RFin supplied from the high frequency amplifier 24b1
The output pulse train RFout is amplified by the transmitter 24 and applied to the high-frequency coil 14. Therefore, the receiving unit 25
Thus, the MR signal from the slice plane 1 is received. Next, MR from slice plane 2 (Slice # 2)
In order to obtain the signal, as shown in FIG. 6D, the sequence control unit 31 supplies the gate signal Gate2 to only the high frequency amplifier 24b2 in association with each RF pulse. Similarly, in order to obtain the MR signal from the slice plane N (Slice # N), as shown in FIG. 6E, the high frequency amplifier 24bn
The gate signal Gaten is supplied from the sequence control unit 31 only to. In this way, by executing the pulse sequence,
When collecting a series of MR signals, the high frequency coil 14
RF amplifiers 2 for amplifying RF pulses supplied to
Since 4b is switched and operated so as to obtain the MR signal for each slice plane, each high-frequency amplifier 24b is operated intermittently to secure the down time. Therefore, the load on each high-frequency amplifier 24b is reduced, and the RF with a high duty ratio is used.
A pulse output can be realized. The number n of the high frequency amplifiers 24b does not have to be equivalent to the number N of slice planes. It goes without saying that MR signals can be sequentially acquired from four or more slice planes. Further, when executing this embodiment, the combiner 2 shown in FIG.
4d may be omitted.

The interval between 180 ° inversion pulses in the above high-speed spin echo pulse sequence is about several ms, and several to several tens of such pulses per one slice, or several hundreds in some cases. Individually applied. If the repetition time is shortened to shorten the inspection time, the duty ratio becomes higher, and there is a possibility that the number of pulses that can be output must be limited. Such a situation can be dealt with by the embodiment shown in FIG. Therefore, the embodiment will be described with reference to FIG. Note that FIG.
In the embodiment shown in FIG. 7, the high-frequency amplifier 24b to be operated is switched for each slice, but in the embodiment shown in FIG. 7, one or a plurality of R's in the RF pulse train RFout are switched.
The high frequency amplifier 24b to be operated is switched every F pulse. 7A and 7B are similar to FIGS. 6A and 6B,
The pulse train RFout and all gate signals Totalgate are shown respectively. In addition, (c) of FIG.
Under the control of the sequence control unit 31, (d) and (e) show each high-frequency amplifier 24b for each RF pulse.
Gate signal Gate supplied to 1, 24b2, 24bn
1, Gate2, Gaten are shown, but this gate signal Gat
The method of supplying e1, Gate2, ... Gaten is different from that in the embodiment shown in FIG.

That is, in this embodiment, for a series of pulse trains RFout, gate signals Gate1 and
Gate2, ..., Gaten are switched, and the high-frequency amplifier 24b is sequentially switched to operate. Therefore, for example, for the α ° pulse of the first slice, the sequence control unit 31 gives the gate signal Gate1 to the high-frequency amplifier 24b1 to operate it, and for the first 180 ° inversion pulse following the α ° pulse, the gate control is performed. Signal Gate2 as high frequency amplifier 24b2
To operate the high-frequency amplifier 24b2, and the gate signal Gatem is supplied to the high-frequency amplifier 24bm to operate the high-frequency amplifier 24bm with respect to the m−1th 180 ° inversion pulse. The gate signal Gaten-1 is applied to the high frequency amplifier 24 with respect to the last 180 ° inversion pulse of the first slice.
If it is given to bn−1, α of the next second slice
° High frequency amplifier 2 for gate signal Gaten for pulse
4bn to operate the high frequency amplifier 24bn, and in the same manner, under the control of the sequence control unit 31, the individual R
The operation of the high frequency amplifier 24b is sequentially switched for each F pulse. In this case as well, the number of high frequency amplifiers 24b is set to 1
It does not have to be the same as the number of RF pulses applied to obtain the MR signal from the slice plane.

According to such an embodiment, when attention is paid to one high frequency amplifier 24b, the high frequency amplifier 24b is intermittently operated in a shorter time. In other words, the pulse interval of the RF pulse output from the high frequency amplifier 24b becomes long. Therefore, the high-frequency amplifier 24b can be freed from problems such as heat generation and can obtain high output, and can cope with a pulse train having a higher duty ratio.

The present invention is not limited to the above-mentioned embodiment, but can be implemented in various forms.
For example, the gate signals Gate having the same timing are supplied to the two high frequency amplifiers 24b1 and 24b2 to operate them simultaneously, and then the other two high frequency amplifiers 24b3 and 2b2
4b4, gate signals of the same timing in sequence
The Gate may be supplied to a plurality of high frequency amplifiers, in which case the output power can be doubled.
Further, the combination of the two high frequency amplifiers may be such that the high frequency amplifiers 24b1 and 24b2 are first shifted, and then the high frequency amplifiers 24b2 and 24b3 are shifted one by one.

[0026]

As described above in detail, according to the present invention, a plurality of high-frequency amplifiers are appropriately switched and operated according to the RF pulse output in accordance with a predetermined sequence, so that the high-frequency amplifier generates heat. It can be suppressed and its operation can be stabilized. Therefore, a magnetic resonance imaging apparatus that can output a pulse train for a long time or a high duty ratio is provided. As a result, it becomes possible to support advanced pulse sequences.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a schematic configuration of a transmission unit in a magnetic resonance imaging apparatus.

FIG. 3 is a system diagram showing an embodiment of the transmitting unit shown in FIG.

FIG. 4 is a timing chart shown for explaining one embodiment of the operation of the high-frequency amplifier according to the present invention.

FIG. 5 is an explanatory diagram in which the timing chart shown in FIG. 4 is partially enlarged.

FIG. 6 is a timing chart shown for explaining the operation of another embodiment of the present invention.

FIG. 7 is a timing chart shown for explaining the operation of still another embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a schematic configuration of a conventional high frequency amplifier.

[Explanation of symbols]

10 Coil assembly 11 Static magnetic field magnet 12 shim coils 13 gradient coil 14 RF coil 21 Static magnetic field controller 22 shim coil power supply 23 Gradient magnetic field power supply 24 Transmitter 24a High frequency control unit 24b high frequency amplifier 25 Receiver 26 Data Collection Department 31 Sequence control unit 32 Computer system 33 display 34 consoles

Claims (8)

[Claims] 1. A magnetic resonance imaging apparatus having a radio frequency coil for applying an RF pulse to a subject placed in an imaging region according to a predetermined sequence, wherein a plurality of the RF pulses supplied to the radio frequency coil are amplified. 2. A magnetic resonance imaging apparatus comprising: the high-frequency amplification means and the switching control means for sequentially switching and operating the plurality of high-frequency amplification means. 2. The magnetic resonance imaging apparatus according to claim 1, further comprising a synthesizing unit that synthesizes outputs of the plurality of high frequency amplifying units controlled by the switching control unit. 3. The magnetic resonance imaging according to claim 1, wherein the switching control unit sequentially switches the plurality of high frequency amplification units so as to be temporally continuous. apparatus. 4. The switching control means, when sequentially switching the plurality of high-frequency amplification means, both the high-frequency amplification means to be switched are transiently and simultaneously operated for a predetermined time, and the both high-frequency amplification means are transiently operated. 4. The magnetic resonance imaging apparatus according to claim 3, wherein the outputs synthesized by the simultaneous operation are controlled so that discontinuity does not occur. 5. The switching control means sequentially switches the plurality of high frequency amplification means for each RF pulse of at least one slice under a sequence in which RF pulses of a plurality of slices are continuously applied. The magnetic resonance imaging apparatus according to claim 1, wherein: 6. The switching control means sequentially switches the plurality of high frequency amplification means for each one or a plurality of RF pulses in the series of the RF pulses in the predetermined sequence. 1. The magnetic resonance imaging apparatus according to 1. 7. The magnetic resonance imaging apparatus according to claim 1, wherein the switching control means controls an operating time of the high frequency amplification means. 8. The magnetic resonance imaging apparatus according to claim 7, wherein the switching control means controls the operating time of the high frequency amplification means according to the amplitude of the RF pulse.