JPH0431263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic Doppler diagnostic apparatus, and particularly to a receiving circuit for receiving reflected echo signals from a subject.

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

A schematic configuration of a conventional diagnostic device is shown in FIG. 3. A probe 10 is supplied with an ultrasonic transmission signal from a transmitter 12, and the probe 10 emits ultrasonic waves into the subject. be done. Then, the echo signal reflected from the subject is converted into an electrical signal by the probe 10 and supplied to the receiver 14, and after a predetermined amplification, the received signal is input to the demodulator 16.

This demodulator 16 converts the echo signal into, for example, a complex signal in order to detect the amount of Doppler frequency deviation of the echo signal, and for this purpose, the demodulator 16 includes a frequency mixer. Then, this frequency mixer multiplies the echo signal by a reference wave signal having the same frequency as the transmission signal. That is,
The reference wave signals are signals having the same frequency and a phase difference of 90 degrees, and these signals are multiplied by the echo signal in the respective demodulators 16a and 16b, thereby converting the echo signal into a complex signal. (The combined output of the two demodulators 16 becomes a complex signal).

Also, the output signal of this demodulator 16 is passed through the filter 1
After the extra signals are removed in step 8, the frequency analyzer 2
0, and this frequency analysis unit 20 calculates the amount of Doppler frequency deviation (based on the Doppler effect).
calculations are performed. This frequency deviation amount corresponds to the speed of the moving part within the subject, and the state of the moving part is displayed as an image on the display unit 22 from the deviation signal.

[Problems to be Solved by the Invention] However, since the frequency mixer provided in the demodulator 16 normally calculates the product between input signals using the nonlinear characteristics of the elements, it is not always possible to perform ideal multiplication. No effect can be obtained, and intermodulation signals other than the originally required Doppler frequency components, such as second-order distortion signals and third-order distortion signals, will also appear at the same time. Therefore, it was not possible to obtain a highly accurate Doppler signal for obtaining a Doppler shift frequency.

It has also been proposed to perform analog-to-digital (A/D) conversion of the echo signal itself at high speed and process the multiplication digitally in order to achieve ideal multiplication, but the circuit in this case would be complicated. There are also problems with the high speed of the A/D converter.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an ultrasonic Doppler diagnostic device that can easily and accurately extract Doppler signals using a simplified circuit. There is a particular thing.

[Means for Solving the Problems] In order to achieve the above object, the present invention emits an ultrasonic pulse into a subject, receives a reflected echo signal from within the subject, and demodulates the received signal. In ultrasonic Doppler diagnostic equipment that measures and displays the state of moving parts within a subject by demodulating it in a circuit,
The demodulation circuit includes a sample trigger generator that outputs two sample trigger signals having phases different by 90 degrees from each other and each having a period equal to or an integral multiple of the transmission frequency of the ultrasonic pulse as a reference wave signal. , two sample circuits each receiving the sample trigger signal, sampling the received signal at the cycle of the sample trigger signal, and A/D converting the sample circuit.

[Operation] According to the above configuration, the echo signal that has undergone Doppler frequency shift is demodulated by the sampling circuit, but the discretized signal of this sampling circuit is the period of the reference wave signal or an integer of this period. It consists of twice the period. Since the frequency of this discretized signal (1/1 of the period) is the same as the carrier frequency of the ultrasonic wave, if the echo signal is not subjected to Doppler frequency shift, the signal obtained from the discretized signal will have frequency components. However, if the signal is subjected to Doppler frequency shift, the signal obtained as a discretized signal becomes a signal with frequency components.

Therefore, the Doppler frequency shift can be detected from the sample circuit output signal.

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

FIG. 1 shows the circuit configuration of an ultrasonic Doppler diagnostic device. A transmitter 12 is connected to a probe 10 that comes into contact with a subject, and a crystal oscillator 24 is connected to this transmitter 12. A wave generator 26 and a gate generator 28 are connected. The highly stable oscillation signal output from the crystal oscillator 24 is transmitted to the reference wave generator 2.
The reference wave generator 26 outputs the reference wave generator 26 through a gate generator 28 and outputs it as a transmission signal. The transmitter 12 drives the transducer within the probe 10 using a built-in drive circuit, thereby making it possible to transmit pulsed ultrasonic waves into the subject.

On the other hand, the reflected echoes reflected from the moving parts within the subject are converted into electrical signals by the probe 10 and then supplied to the receiver 14, where they are amplified in a predetermined manner. The output of the receiver 14 is then supplied to a bandpass filter 15 to remove signal components in unnecessary bands, and then the output of the bandpass filter 15 is used for demodulation for Doppler signal extraction.

A characteristic feature of the present invention is that the echo signal is demodulated by a sample circuit, and in the embodiment, the sample circuit includes two samplers 30a and 30b for converting into a complex signal and a sample trigger. A generator 32 is provided. This sampler 30 digitizes and takes in the output of the bandpass filter 15, and the timing of this digitization is formed by a sample trigger generator 32. In this case, the period of discretization is equal to the period of the reference wave or a period that is an integral multiple of the period (in terms of frequency, it is an integral multiple of the period)
), and at the same time each sampler 30a, 30b
The phase of the discretized signal is shifted by π/2. By providing this π/2 phase difference, the echo signal can be converted into a complex signal for obtaining Doppler frequency deviation.
A sin trigger signal is supplied to the sampler 30b, and a cos trigger signal is supplied to the sampler 30b.

In this embodiment, the sampler 30 is A/
A D converter is used, and this A/D converter has the advantage of being able to simultaneously perform signal discretization and analog-to-digital conversion. The sampler 30 is provided with high-pass filters 34a and 34b for removing unnecessary signal components from the output, and the frequency analyzer 20 and the display section 22 are connected to the high-pass filter 34.

Further, a sample-and-hold circuit may be used as the sampler 30. In the case of a sample-and-hold circuit, the discretized signal is passed through two types of filters, a high-pass filter (HPF) and a low-pass filter (LPE), to eliminate unnecessary signals. After the signal is removed, it is converted into an analog-to-digital signal and supplied to the frequency analysis section 20.

Furthermore, when detecting speed with an ultrasonic diagnostic device, there are two cases: continuous waves and pulsed waves. When using pulsed ultrasonic waves, the transmitter 12 and the sample trigger generator 32 are used. A sample circuit can be easily constructed by simply multiplying the gate by .

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

When, for example, pulsed ultrasound is emitted from the probe 10 into the subject under transmission control of the transmitter 12, echo signals subjected to the Doppler effect are reflected from the moving parts of the subject and returned to the probe 10. It's coming. Then, the echo signal becomes a received signal amplified by a predetermined amplification factor in the receiver 14, and unnecessary signals are removed from this received signal in the band pass filter 15.

The output of the bandpass filter 15 is then used for signal demodulation to extract the Doppler frequency shift. First, the principle of Doppler signal detection by discretizing the sampler 30 will be explained.

When the reflected echo signal is f(t), it can be expressed by the following equation.

f(t)=cos( _ω0 + _ωd )t...(1) Here, _ω0 is the transmission wave frequency (also the reference frequency), _ωd is the Doppler shift frequency, and the signal amplitude is simplified. and set it to 1.

Consider the case where this echo signal is discretized at the reference wave frequency, and if the discretized signal sequence is Xk and the discretization period is T (T = 2π/ω ₀ ), then Xk = f (kT) = cos (ω ₀ +ω _d ) kT = cos {2πk + (ω _d / ω ₀ ) 2πk} = cos2πk cos (ω _d / ω ₀ ) 2πk − sin2πksin (ω _d / ω ₀ ) 2πk, where cos2πk〓1, sin2π If 0, then Xk=cos(ω ₀ /ω _d )2πk = cosω _d kT ……(2) is derived.

The above equation (2) is equivalent to the Doppler signal having an angular frequency ω _d that is discretized with a period T. This holds true even if the discretization period T is an integer multiple.

To explain the above discretization using the waveform diagram in Figure 2,
As shown in Figure a, if the reference wave signal for demodulation is 100 in the diagram, then the discretized signal is, for example, arranged at the same time in the order of 0 → 1 → 0 → -1 → 0 → 1 →... on the time axis. Let it be a signal that appears at intervals.

Then, as shown in Figure b, if the received signal is a signal 200 that has not undergone Doppler shift, the signal obtained by the discretized signal becomes a direct current (DC) signal indicated by 201, and the Doppler frequency is not detected. However, as shown in Figure c,
In the case of the signal 300 receiving the Doppler frequency (signal in which the moving part moves away), the signal obtained by the discretized signal becomes the signal shown by 301, and as shown in the figure, the signal obtained with the frequency shift is the signal 300. Become.

Since the output of the sampler 30 obtained in this way does not use a conventional mixer or multiplier,
No distortion signal is generated by the mixer, and the circuit is also simplified. Furthermore, as mentioned above,
By using the sampler 30 as an A/D converter,
Demodulation and digital conversion can be performed simultaneously, resulting in an efficient circuit configuration.

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.If the velocity is determined by the monument frequency analysis section 20, the motion The speed of each section can be displayed on the display section 32.

The output of the frequency analysis unit 20 is a signal containing only speed information, but the display in this case is not limited to the M mode display but can also be a B mode display. In this case, the signal obtained from the receiving transducer 10b The echo signal is processed separately to obtain a tomographic image inside the subject.
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 sampler circuit that discretizes the echo signal with the period of the reference wave signal or an integer multiple thereof is provided as a demodulator. Doppler signals can be extracted, accurate velocity can be detected with a simple circuit configuration, and the state of movement can be displayed as an image.

Also, if the sampler circuit is implemented with an A/D converter,
Demodulation and digital-to-analog conversion can be performed simultaneously, making it possible to provide an extremely efficient device.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration of the ultrasonic Doppler diagnostic device according to the present invention, Fig. 2 is a waveform diagram explaining signal processing of the sampler, and Fig. 3 shows the circuit configuration of the conventional ultrasonic Doppler diagnostic device. FIG. DESCRIPTION OF SYMBOLS 10... Probe, 12... Transmitter, 14... Receiver, 20... Frequency analyzer, 30... Sampler, 32... Sample trigger generator, 34... Filter.

Claims (1)

[Claims] 1. Emitting ultrasonic pulses into the subject, receiving reflected echo signals from the subject, and demodulating the received signals in a demodulation circuit, thereby controlling the moving parts within the subject. In an ultrasound Doppler diagnostic device that measures and displays a state, the demodulation circuit generates two sample trigger signals whose phases are 90 degrees different from each other and whose periods are the same as the transmission frequency of the ultrasound pulse or an integral multiple thereof. a sample trigger generator that outputs the sample trigger signal as a reference wave signal; and two sample circuits that each receive the sample trigger signal, sample the received signal at the period of the sample trigger signal, and A/D convert it. An ultrasonic Doppler diagnostic device featuring: