JPS63315037A - Ultrasonic continuous wave doppler diagnostic apparatus - Google Patents

Abstract

PURPOSE:To perform good signal processing within the dynamic range of a circuit for demodulation and to accurately analyze Doppler deflection frequency by an apparatus utilizing an ultrasonic continuous wave, by providing a band removing filter having a sharp blocking characteristic to the pre-stage of an amplifying part and removing the low frequency region of an echo signal before signal processing. CONSTITUTION:Two demodulation parts are provided to an amplifying part 24. Orthogonal signals different by 90 deg. in a phase are supplied to the demodulation parts 26a, 26b and a sin signal is inputted to the demodulation part 26a and a cos signal is inputted to the demodulation part 26b. Filter parts 28a, 28b each removing the unnecessary band of each signal are provided to the demodulation parts 26a, 26b and a frequency analyzing part 30 for analyzing Doppler deflection frequency is provided to the filter parts 28a, 28b and a display part 32 is connected to said analyzing circuit 30. Doppler deflection frequency is the speed component corresponding to the speed of a motion body and the magnitude of the speed can be calculated from the magnitude of said Doppler deflection frequency. This speed signal is inputted to the display part 32 to be displayed thereon as a pixel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic continuous wave Doppler diagnostic apparatus that continuously emits ultrasonic waves to a subject, and particularly to a receiving circuit for a reflected echo signal from the subject.

[Prior Art] Ultrasonic Doppler diagnostic equipment that measures and displays the velocity of a moving object such as a high-speed blood flow inside a living subject is well known, and can be used to determine the direction of the moving object and the state of motion such as vortices. is being displayed as an image.

The pulse method in which ultrasonic waves are emitted into the subject at a constant repetition rate is often used for the ultrasound used in such devices. In recent years, continuous Doppler method using continuous waves, which theoretically does not cause aliasing, has been attracting attention because of the problem that there is a limit to the speed at which aliasing can occur.

[Problems to be solved by the invention] In this continuous Doppler method, a temporally continuous ultrasound beam is continuously emitted into the subject, so all information on the ultrasound beam axis in the subject is received at the same time. Ru. That is,
Weak signals affected by the Doppler effect (Doppler shift) and high-level signals that are not affected by the Doppler shift, for example, in the case of the heart, signals that are stationary or slowly moving (clutter signals)
There will be a mixture of

This mixed signal has a strong clutter signal superimposed with a weak blood flow signal and is distributed over a wide band of 80 dB or more. Therefore, in the receiving system that demodulates the echo signal, the signal level exceeds the dynamic range of the circuit,
There have been problems with the generation of harmonics and lack of sensitivity.

Furthermore, conventional methods have been used to remove extraneous signals such as clutter signals after demodulating the echo signal, but this alone was not sufficient to faithfully extract Doppler shift signals. .

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems.
The purpose is to provide an ultrasonic continuous wave Doppler diagnostic device that can obtain highly sensitive signals by preventing the generation of harmonics caused by the dynamic range of the circuit.

c. Means for Solving Problems] In order to achieve the above object, the present invention continuously radiates an ultrasound beam into a subject and receives and processes reflected echo signals from within the subject. In an ultrasonic continuous wave Doppler diagnostic device that measures and displays the state of moving parts within a subject, a band-removal filter with a steep cutoff characteristic is provided in front of an amplifier section that amplifies the echo signal before demodulating the signal. It is characterized by removing carrier signals that have not undergone Doppler shift.

[Operation] According to the above configuration, the reflected echo of continuous ultrasound waves from within the subject is supplied from the receiving transducer to the receiving system, but this echo signal is A removal filter removes frequency components in a predetermined band. This band-removal filter has a steep cutoff characteristic, and when the ultrasonic carrier frequency is used as a reference, the low frequency region portion of the received signal is removed.

Therefore, the received signal is only a signal from the moving part, and the Doppler shift can be detected satisfactorily within the dynamic range of the circuit.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows the circuit configuration of an ultrasonic continuous wave Doppler diagnostic device, in which a probe 1o is brought into contact with a subject 12, and a continuous wave Sound waves are emitted. For this ultrasonic emission, a highly stable crystal oscillator 14, a carrier wave generating section 16, and a transmitting section 18 are connected to the transmitting vibrator 10a.
The output is sent to a carrier wave generating section 16, where an orthogonal signal having a desired frequency, for example, a frequency of 2 to 3 MIIz is formed.

Then, one of these orthogonal signals, in the embodiment, C
The OS signal is sent to the transmitting section 18, and the transmitting transducer 10a is driven by this signal to radiate continuous wave ultrasound to the subject 12.

On the other hand, an echo signal reflected from within the subject 12 is converted into an electrical signal by the receiving transducer 10b, and is conventionally supplied to the amplifying section 24 via the impedance converter 20.

A characteristic feature of the present invention is that clutter components of the received signal are removed in accordance with the dynamic range of the receiving circuit, and a band-removal filter 22 is inserted before the amplifying section 24. Therefore, the impedance converter 20 matches the filter characteristic impedance of the band-removal filter 22.

Further, the band-removal filter 22 is made of a crystal filter in this embodiment, and is a narrow-band filter having a steep cut-off characteristic as shown in FIG. That is, the band rejection filter 22 has a cutoff frequency of 100 to 2001 MHz above and below the ultrasonic frequency of 2 to 3 MHz.
1z, and both are in the range of 200 to 40011z, thereby blocking low frequency signal components of 100 to 200 fiz. This low frequency signal component is a carrier component that has not undergone Doppler shift, that is, a signal that includes a strong clutter signal.

Therefore, by passing through the band rejection filter 22,
The clutter signal is removed and a low level signal is obtained.

The amplification unit 24 also includes two demodulation units 2 which are orthogonal detection units.
6a and 26b are provided, and the demodulator 26 is supplied with orthogonal signals having a phase difference of 90 degrees.
A sine signal is input to the demodulator 26b, and a COS signal is input to the demodulator 26b. The demodulation sections 26a and 26b are provided with filter sections 28a and 28b for removing unnecessary bands of the signal, and the filter section 28 is provided with a frequency analysis section 30 that analyzes the Doppler shift frequency, and then a display section 32
is connected.

The embodiment has the above configuration, and its operation will be explained below.

First, the continuous wave ultrasound according to the present invention is transmitted by the transmitting transducer 10a.
is radiated into the subject 12 from
0 to the band-rejection filter 22. 100 to 2 as shown in FIG.
The low frequency signal component of 00 Hz is removed, resulting in a low level signal from which the clutter signal has been removed.

In this way, the filter output from which the low wave number signal has been removed is amplified by a predetermined amplification factor in the amplifier section 24, and then
The signal is supplied to the demodulator 2δ. The filter output in this case is
Since the signal level is not as high as in the conventional case, the amplification section 24
This also means that signal processing can be performed in good condition with the dynamic range of the demodulator 26.

In the demodulation section 26, the output signal of the amplification section 24 holding the Doppler shift information and the carrier frequency signal are mixed, thereby extracting the Doppler shift frequency signal. and,
After unnecessary noise signals are removed by the filter section 28, the Doppler shift frequency is determined by the frequency analysis section 30.

This Doppler shift frequency is a velocity component corresponding to the velocity of the moving body, and the magnitude of the velocity can be determined from the magnitude of this Doppler shift frequency. This speed signal is displayed on the display section 3.
2 and the image is displayed.

In this case, the output of the frequency analysis unit 3o is a signal containing only speed information, so the display is M mode display, but B mode display is also possible. In this case, the receiving transducer 1
The echo signal obtained from 0b is separately processed to obtain a tomographic image inside the subject, and the velocity information is superimposed on this tomographic image and displayed on the display unit 32.

[Effects of the Invention] As explained above, according to the present invention, a band-rejection filter with a steep cutoff characteristic is provided before the amplification section, and the low frequency region of the echo signal is removed before signal processing. Therefore, good signal processing can be performed within the dynamic range of conventional demodulation circuits, and accurate Doppler shift frequency analysis can be performed using a device that uses ultrasonic continuous waves.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an ultrasonic continuous wave Doppler diagnostic apparatus according to the present invention, and FIG. 2 is an explanatory diagram showing filter characteristics of a band-rejection filter. 10a... Transmitting transducer 10b... Receiving transducer 18... Transmitting section 22... Band rejection filter 24... Amplifying section 26... Demodulating section

Claims (2)

[Claims] (1) By continuously emitting an ultrasound beam into the subject and receiving and processing the reflected echo signals from within the subject,
In continuous-wave ultrasound Doppler diagnostic equipment that measures and displays the state of moving parts within a subject, a band-rejection filter with a steep cutoff characteristic is installed in front of the amplifier section that amplifies the echo signal before demodulating it. An ultrasonic continuous wave Doppler diagnostic device characterized in that a carrier wave signal that is not subjected to deviation is removed. (2) An ultrasonic continuous wave Doppler diagnostic apparatus according to claim (1), characterized in that a crystal filter is used as the band elimination filter.