JPH04194767A - Oscillating device for rf pulse - Google Patents

Abstract

PURPOSE:To obtain an RF pulse containing little harmonic component by a construction wherein an RF amplifier is of a push-pull type and LPF has an attenuation pole at a frequency being equivalent to a tertiary harmonic generated from the RF amplifier. CONSTITUTION:In an output of an oscillator 1, i.e. an output signal at a point P1, only an RF signal of a frequency (f) exists. When the output passes through an RF amplifier 4 and is amplified thereby, thereafter, harmonic components are generated. Since the amplifier 4 employed herein is of a push-pull type, on the occasion, an odd-number-order harmonic component is large and an even-number-order harmonic component is small due to the characteristics of the amplifier. In an output of the amplifier 4, i.e. an output signal at a point P2, accordingly, the component of a tertiary harmonic 3f is large. LPF 5 is so set as to have an attenuation pole at the harmonic 3f, and therefore the harmonic components of the tertiary harmonic and around it can be removed. Accordingly, the RF signal hardly containing the harmonic components can be obtained for an output of the LPF 5, i.e. an output signal at a point P3.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an RF pulse oscillation device used in an MHI device, and particularly relates to a technique for removing harmonic components generated from an RF amplifier. .

(Prior Art) Generally, an MRI apparatus (magnetic resonance imaging apparatus) is provided with an RF coil for applying a high frequency wave at a resonance frequency to a subject, and an RF pulse is provided for applying an RF pulse to the RF coil. Equipped with an oscillator.

As shown in FIG. 4, a conventional RF pulse oscillation device is composed of an oscillator 1, an all-solid-state RF amplifier 2, and a low-pass filter 3 (hereinafter referred to as LPF), and the RF pulse oscillator output from the oscillator 1 After being amplified by the double signal RF amplifier 2, harmonic components are removed by the LPF 3, and the signal is output to the RF coil.

(Problem to be solved by the invention) However, in such conventional RF pulse oscillation devices, a broadband all-solid-state type is used as the RF amplifier 2, so there is a lot of harmonic distortion and the waveform The drawback was that it was very inconvenient to monitor. In addition, since the LPF 3 that removes harmonic components must have a steep attenuation characteristic, the LPF 3 circuit configuration is not only complicated, but also the adjustment operation becomes complicated. Ta.

This invention was made in order to solve such conventional problems, and its purpose is to provide an RF pulse that can obtain RF pulses with few harmonic components using an LPF configured with a simple circuit. An object of the present invention is to provide a pulse oscillation device.

[Structure of the invention] (Means for solving the problem) In order to achieve the above object, the present invention amplifies the RF multiplied signal output from an oscillator with an RF amplifier, and removes harmonic components with a low-pass filter. After that, RF is supplied to the RF coil.
In the pulse oscillator, the RF amplifier is of a push-pull type, and the low-pass filter has an attenuation pole at a frequency corresponding to a third harmonic generated from the RF amplifier.

(Function) With the configuration as described above, the RF pulse output from the oscillator is amplified by the push-pull type RF amplifier. The amplified signal contains many odd-numbered harmonic components and few even-numbered harmonic components. Therefore, if a low-pass filter having an attenuation pole for the third harmonic is used, most of the harmonic components can be removed and an RF pulse with less harmonic distortion can be obtained.

(Embodiment) FIG. 1 is a configuration diagram showing an embodiment of the present invention. The RF pulse oscillator shown in the figure includes an oscillator 1 that oscillates an RF multiplied signal, a push-pull type RF amplifier 4 that amplifies the RF multiplied signal, and a low-pass filter 5 that removes harmonic components.
(hereinafter referred to as LPF).

As shown in FIG. 2, the LPF 5 has a characteristic of having an attenuation pole at the third harmonic 3f of the RF frequency f.

In such a configuration, the output of oscillator 1, i.e. point P1
The output signal in is as shown in FIG. 3(A),
Only the RF multiplied signal of frequency f exists. After that, R.F.
When the signal passes through the amplifier 4 and is amplified, harmonic components are generated. At this time, since the RF amplifier 4 uses a push-pull type, due to its characteristics, odd-numbered harmonic components are large and even-numbered harmonic components are small. Therefore,
The output of the RF amplifier 4, that is, the output signal at point P2 becomes as shown in FIG. 3(B), and the third harmonic component 3f becomes large.

As described above, since the LPF 5 is set to have an attenuation pole at the third harmonic 3f, it is possible to remove harmonic components centered on the third harmonic. Therefore, L.P.
The output of F5, that is, the output signal at point P3 is shown in Figure 2 (C
), and R contains almost no harmonic components.
F times signal can be obtained.

In this way, in this embodiment, a push-pull type is used as the RF amplifier 4, and the LPF 5 having an attenuation pole at the third harmonic 3f is used to remove the harmonic component. It is possible to obtain an RF multiplied signal with reduced components and less harmonic distortion. In addition, the LPF 5, which has an attenuation pole at the third harmonic 3f, can be configured with a simple circuit, making it possible to save space and cost.
Adjustment operations are also simplified.

[Effect of the invention] As explained above, in the present invention, the push-pull type R
The F amplifier amplifies the RF signal, and a low pass filter (LPF) having an attenuation pole at the third harmonic removes the harmonic component. Therefore, it is possible to reduce harmonic components and obtain an RF pulse signal with less high frequency distortion. Further, the low-pass filter can be configured with a simple circuit, and the adjustment operation can be simplified.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an embodiment of the present invention, Figure 2 is an LP
FIG. 3 is a diagram showing the output signals at each point p, . . . p2°P3, and FIG. 4 is a diagram showing a conventional example. 1... Oscillator 4... RF amplifier 5...
・Low pass filter (LPF) Figure 1

Claims (1)

[Claims] Amplifying the RF signal output from the oscillator with an RF amplifier,
In an RF pulse oscillation device that supplies harmonic components to an RF coil after removing harmonic components with a low-pass filter, the RF amplifier is of a push-pull type, and the low-pass filter removes third-order harmonic components generated from the RF amplifier. An RF pulse oscillation device characterized by having an attenuation pole at a frequency corresponding to a wave.