JPH0779973A - Method for transmission of ultrasonic waves by dispersion and compression and apparatus for transmission of ultrasonic waves by dispersion and compression - Google Patents

Abstract

PURPOSE:To set better time side lobe by using FM chirp signal. CONSTITUTION:In an apparatus for transmission of ultrasonic waves by dispersion and compression, a measure for creation of wave sending signals 11 which creates double apodization chirp signal charged with apodization of Gaussian distribution against the chirp signal charged with cosine square wave form, as wave sending signal, a measure for sending and receiving waves 21 which irradiates wave sending signals as ultrasonic waves at the target and receives reflected waves and generates them as receiving signals, and cross correlation between the signal wave form of signals received and the signal wave form of signals sent are required as correlated relationship. By this, the apparatus is an apparatus for transmission of ultrasonic waves by dispersion and compression which is also equipped by a means for process of signals received 33 which obtains generation of compression and demodulation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic dispersion compression transmission / reception method and an ultrasonic dispersion compression transmission / reception apparatus, and more particularly to an ultrasonic dispersion compression transmission / reception method and an ultrasonic dispersion compression transmission / reception apparatus using an FM chirp signal. .

[0002]

2. Description of the Related Art A medical ultrasonic device is a kind of extremely short-range sonar, and has a large acoustic property of lossy dispersiveness of a target (observation target: in this case, the abdominal cavity of a subject) and diagnostic According to the demand for the spatial resolution of the image system according to the demand,
The specific bandwidth of an acoustic signal system is very large (that is, the impulse response is very important), and the demand for the dynamic range of the system is always the limit value.

The characteristic of the target as an echo source of the soft tissue of the living body is that the point source is an echo source such as clutter on the contrary to the point target, and is based on speckle property, and an exceptionally hard echo is a special case such as bone. Except for

Rather, it is possible to identify a portion having slightly different properties in the area of speckle echo such as sand sprinkling of parenchymal tissue, whether the contents of the liquid-filled luminal organ are really transparent, or something. It is a very important issue whether there is a foreign object that emits an echo. Therefore, I hate all ghosts and spurious responses. In other words, the essential condition is that it is essentially high-fidelity and clean.

The demand for such an observation system or a signal system is
It can be said that it is similar to the situation in an audio system and a synthetic aperture radar for resource exploration, but there are also major differences. That is, real-time and safety are required. The real-time property means that an immediate observation of a moving body, that is, an observation without delay of a moving organ (including Doppler shift observation) is required. In addition, securing safety for living tissues is an essentially important issue for medical instruments.

In other words, in order to improve the search capability of the device while ensuring both safety and transmission power, a time-bandwidth product is used instead of a pulse-echo system with a single pulse having a large amplitude or a CW system with a single frequency. Distributed compression transmission / reception using a spread spectrum method in which (TB product) is much larger than 1 is effective.

[0007]

An FM chirp signal is a decentralized signal that can be adopted in the echo search of a medical ultrasonic apparatus in view of the above circumstances. Even if the sharpness and shape of the main lobe depend on the circumstances, it is generally at least necessary that the time side lobe of the transmitted signal in its own system principle is approximately -60 dB or less. . This originates from the level distribution of the echo source in the living tissue, and is the distribution range itself.

When a complementary sequence such as a Golay code is used as a phase-modulated code signal in a time division manner, the time side lobes are completely erased by linearly combining the results after reception correlation processing of each code. , It gives almost ideal results for stationary targets. However, this method is inherently vulnerable to targets with Doppler shift, and there are restrictions on the applicable situations.

[0009] Further, there is a system that exhibits complementarity only with respect to a certain specific value of the shift number of the bin, but the system is not a synchronous system, and the echo sources are distributed everywhere and the speckle property is strong. Therefore, any undesired response other than the main lobe literally becomes a ghost source.

FIG. 7 is a waveform diagram showing an example of a waveform of a linear FM chirp signal without apodization having a total length of about 50 wavelengths, and FIG. 8 is obtained by cross-correlation between the reception result of the waveform of FIG. 7 and the original waveform. It is a characteristic view which shows the result. In these figures, the horizontal axis represents the sample number and the vertical axis represents the signal level [dB]. The same applies to the following waveform diagrams and characteristic diagrams.

As can be seen from FIGS. 7 and 8, the side lobe of the cross-correlation by the chirp signal without apodization stays at about -30 dB at most. Therefore, the medical ultrasonic device cannot be used practically.

FIG. 9 is a waveform diagram showing a waveform of an apodization chirp signal with cosine square modification, and FIG. 10 is a characteristic diagram showing a result obtained by cross-correlation between the reception result of the waveform of FIG. 9 and the original waveform. . By using the cosine square modified apodization chirp signal as described above, the side lobe becomes about −60 dB.

However, the propagation non-linearity or frequency dependent attenuation inherent to the medium, the distortion of the electronic circuit of the system, the A / D
There are many other factors that worsen the time side lobes, such as the coarseness of the quantization of the transform. For this reason, assuming that the side lobes that are very close to the required specification of -60 dB can be suppressed in the signal design for transmission and reception, there is no resource that can be allocated to the deterioration due to these other factors, and the overall system is practical. Above requirements cannot be met. That is, it is strongly desired that the time side lobes are all minimal.

The present invention has been made in view of the above points, and an object thereof is to realize an ultrasonic dispersion compression transmission / reception method and an ultrasonic dispersion compression transmission / reception apparatus having a good time side lobe by using an FM chirp signal. is there.

[0015]

[Means for Solving the Problems] The above-mentioned problem is to generate a double apodization chirp signal in which apodization of Gaussian distribution is applied to a chirp signal in which apodization of cosine square waveform is applied as a transmission signal, Irradiating the target as an ultrasonic wave, receiving the reflected wave of the target and outputting it as a reception signal, and obtaining the compression demodulation output by obtaining the cross-correlation between the received signal waveform and the signal waveform of the transmitted signal as the correlation result. And an ultrasonic dispersion compression transmission / reception method.

Further, in the ultrasonic dispersion compression transmitting / receiving apparatus, a transmission signal generating means for generating as a transmission signal a double apodization chirp signal in which a Gaussian distribution apodization is applied to a chirp signal in which a cosine square waveform apodization is applied. And a wave transmission / reception means for irradiating a target with a transmission signal as an ultrasonic wave and receiving a reflected wave and outputting it as a reception signal, and a cross-correlation between a signal waveform of the reception signal and a signal waveform of the transmission signal as a correlation result. This is solved by an ultrasonic dispersion compression transmission / reception device, characterized in that it comprises a received signal processing means for obtaining a compressed demodulation output by obtaining.

[0017]

In this ultrasonic dispersion compression transmission / reception method and ultrasonic dispersion compression transmission / reception device, a double apodization chirp signal in which a Gaussian distribution apodization is applied to a chirp signal in which a cosine square waveform apodization is applied is transmitted and received. By obtaining the compression demodulation output by obtaining the cross-correlation between the signal waveform of the received signal and the signal waveform of the transmitted signal as the correlation result, it is possible to perform ultrasonic dispersion compression transmission / reception with good time side lobes using the chirp signal. Will be realized.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an ultrasonic dispersion compression transmission / reception apparatus for realizing an embodiment of the present invention, focusing on the part that performs distributed compression transmission / reception. FIG. 2 is a configuration diagram showing a main part of the ultrasonic dispersion compression transmitting / receiving apparatus shown in FIG.

First, distributed compression transmission / reception using a chirp signal will be described with reference to FIGS. The code generation unit 11 receives a command from a control unit (not shown) or the like and generates a predetermined code. In this embodiment, the upper and lower frequency ratio is 2: 1.
A linear chirp signal having a cosine squared amplitude modification with a total length of about 50 wavelengths is generated, and a code of the signal to which apodization of Gaussian distribution is applied is generated. As the apodization of this Gaussian distribution, a Gaussian distribution according to the square of the distance from the center can be used.

The transmitted signal thus generated is converted from a digital signal to an analog signal by the D / A converter 12, amplified by the amplifier 13, and then transmitted / received by the transmitter / receiver 2.
The signal is transmitted from 1 to the subject.

Then, the transmitter / receiver 2 receives the reflected wave from the subject.
The signal is received by 1, amplified by the amplifier 31, and converted into a digital signal by the A / D converter 32. Then, the reception signal processing unit 3
In 3, cross-correlation processing is performed between the transmitted signal and the received signal, and respective correlation results are obtained. Display is performed on a display device (not shown) with reference to the correlation result thus obtained.

The cross-correlation processing will be described in more detail. The reception waveform digitally converted by the A / D converter 32 is temporarily stored in the reception waveform temporary storage unit 33a and supplied to one input of the correlator 33c. In addition, the code for generating the waveform is notified from the code generating unit 11 to the sample waveform generating unit 33b, and a sample waveform (double apodization chirp signal in this embodiment) having the same waveform as the transmitted signal is generated. It Then, this sample waveform is supplied to the other input of the correlator 33c. In the correlator 33c,
Cross-correlation processing is performed between the received waveform and the sample waveform.
Further, integration processing is performed in the integrator 33d. As described above, the cross-correlation processing (dechirp processing) is performed on the double apodization chirp signal, and the obtained correlation result is stored in the display temporary storage unit 33e.

As a result of the above configuration, according to the result obtained by the inventor of the present application conducting an experiment, the result of the characteristic as shown in FIG. 4 is obtained by using the double apodization chirp signal shown in FIG. I was able to get it. The signals in FIG. 3 are used as an example, and in this example, when a part of the source program written in FORTRAN is used as a signal generation expression, i is set to 1 to 1024 as shown in the following expression. It is defined. sin (i / 3.0 + i * i / 3600.0) * (0.5 + 0.5 * cos ((i-512) * 1.22718
5E-02 * 0.5)) * exp (-((abs (i-512) /320.0) ** 2) In the results shown in Fig. 4 obtained using the above signals, the time side lobe is − It has cleared 120 dB.

FIG. 5 is a waveform diagram showing a signal waveform when a slightly steep bimodal bandpass characteristic is imposed only on the reception signal side. Further, FIG. 6 is a characteristic diagram showing characteristics obtained by cross-correlation using the reception waveform of FIG. In this case, the pedestal level did not increase, but it was observed that the skirt of the main lobe was widening.

In the above embodiment, the medical ultrasonic device has been described as an example, but in addition to this, the invention is applied to a device such as a radar for observing rainfall on a satellite, which does not like the influence of the time side lobe. It is also possible.

[0026]

As described in detail above, a double apodization chirp signal in which a Gaussian distribution apodization is applied to a chirp signal in which a cosine square waveform apodization is applied is transmitted and received. By obtaining the compression demodulation output by obtaining the cross-correlation with the signal waveform of the transmission signal as the correlation result, ultrasonic dispersion compression transmission / reception with good time side lobe is realized using the chirp signal. Therefore,
An ultrasonic dispersion compression transmission / reception method and an ultrasonic dispersion compression transmission / reception apparatus with good time side lobes can be realized using FM chirp signals.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a configuration related to transmission / reception of an ultrasonic dispersion compression transmission / reception device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a main part relating to received signal processing of the ultrasonic dispersion compression transmission / reception device of one embodiment of the present invention.

FIG. 3 is a waveform diagram showing a signal waveform by distributed compression transmission / reception according to an embodiment of the present invention.

FIG. 4 is a characteristic diagram showing characteristics due to cross-correlation by distributed compression transmission / reception according to an embodiment of the present invention.

FIG. 5 is a waveform diagram showing an example of a waveform by distributed compression transmission / reception according to an embodiment of the present invention.

FIG. 6 is a characteristic diagram showing an example of characteristics due to cross-correlation by distributed compression transmission / reception according to an embodiment of the present invention.

FIG. 7 is a waveform diagram showing a waveform of a transmission / reception signal of conventional distributed compression transmission / reception.

FIG. 8 is a characteristic diagram showing characteristics of processing results of conventional distributed compression transmission / reception.

FIG. 9 is a waveform diagram showing a waveform of a transmission / reception signal of conventional distributed compression transmission / reception.

FIG. 10 is a characteristic diagram showing characteristics of processing results of conventional distributed compression transmission / reception.

[Explanation of symbols]

 11 Code Generator 12 D / A Converter 13 Amplifier 21 Transducer 31 Amplifier 32 A / D Converter 33 Received Signal Processor

Claims (2)

[Claims] 1. A double apodization chirp signal obtained by applying a Gaussian distribution apodization to a chirp signal subjected to apodization of a cosine square waveform is generated as a transmission signal, and the transmission signal is irradiated to a target as ultrasonic waves, An ultrasonic dispersion characterized in that a compressed demodulated output is obtained by receiving the reflected wave of the target and outputting it as a received signal, and obtaining the cross-correlation between the received signal waveform and the signal waveform of the transmitted signal as the correlation result. Compressed transmission / reception method. 2. An ultrasonic dispersion compression transmitting / receiving apparatus, wherein a transmission signal generating means generates a double apodization chirp signal in which apodization of Gaussian distribution is applied to a chirp signal in which apodization of cosine square waveform is applied, as a transmission signal. (11), a wave transmitting / receiving means (21) for irradiating a target with a transmission signal as an ultrasonic wave, receiving a reflected wave of the target and outputting as a reception signal, a signal waveform of the reception signal and a signal of the transmission signal An ultrasonic dispersion compression transmitting / receiving apparatus, comprising: a reception signal processing means (33) for obtaining a compression demodulation output by obtaining a cross correlation with a waveform as a correlation result.