JPH04198789A - Pulse compressor for ultrasonic diagnosis - Google Patents

Abstract

PURPOSE:To improve resolution and sensitivity by providing a Fourier transformation section Fourier-transforming the correlation-calculated signal and a reverse Fourier transformation section reverse Fourier-transforming the signal converted into the square root by a spectrum processing section. CONSTITUTION:Reflection layer distribution ¦R(wx)¦e<-jtheta(wx)> is once Fourier- transformed by a Fourier transformation section 28, then the square root is obtained by a spectrum processing section 29 via numerical calculation. The square root of the spectrum power is obtained, and the phase is processed to a half. The processed data become ¦R(wz) ¦e<-jtheta>R<(wx)> ¦H(w,x)¦, and the wave- form information arranged with the pulse wave having the frequency component ¦H(wx)¦ according to the reflection layer distribution is obtained. It is transformed into the wave-form data on the surface by a reverse Fourier trans formation section 31. Good pulse compression can be performed, and resolution and sensitivity can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pulse compression device for ultrasound diagnosis, and particularly to a pulse compression device for ultrasound diagnosis that uses ultrasound to diagnose the characteristics of a living body or other subject. It is related to.

[Conventional technology] Conventionally, an ultrasonic transducer is placed at the tip of an endoscope, and this ultrasonic transducer generates ultrasonic pulses, and the echoes reflected from the diagnostic part inside the body are captured as received waves. , and various ultrasonic diagnostic apparatuses that obtain tomographic images of the inside of the body by scanning these have been developed.

Such diagnostic equipment usually uses pulse waves, so when diagnosing a subject such as a living body, in order to make the diagnostic distance as long as possible and the distance resolution as good as possible, the transmitted pulse Increasing the amplitude of the signal and widening the band of the resonator were essential conditions. These conditions are extremely difficult to satisfy at present due to issues such as safety to the living body, circuits for implementation, and manufacturing limitations of the vibrator.

Therefore, inventions have been made that attempt to dramatically improve diagnostic distance and resolution by applying a method called pulse compression (frequency synthesis), which is practically used in radars and the like, to ultrasonic diagnostic equipment. That is, as shown in FIG. 2, linear FM modulation (chirp) is applied to the ultrasonic transmission wave and the wave is transmitted.

By applying a matched filter to the received wave during reception, it is possible to compress the received signal as shown in FIG. The matched filter is optimized by dynamically varying the filter characteristics so that the compressed waveform of the received wave is good. Therefore, a correlation calculation means using a circuit system is implemented so that a filter function prepared in advance can be selected at any time.

[Problems to be Solved by the Invention] Incidentally, ultrasonic waves are attenuated greatly in the living body, and depending on the depth at which the reflected echo returns, the frequency components of the reflected echo signal, that is, the received wave, will vary. , as shown in FIG.

In other words, the high frequency band is attenuated, and only low frequency components can be obtained as received waves in deep places.

In addition, phase distortion occurs in the transducer when electroacoustic conversion is performed or when ultrasound propagates in the living body.
The signal waveform given to the transducer during transmission differs from the frequency spectrum during reception depending on the depth.

Furthermore, regarding the basic principle that a transmitted wave for pulse compression, in the conventional example described above, an FM modulated wave (hereinafter referred to as a chirb wave) is propagated in the living body, and reflected echoes from the distributed reflective layer are obtained as a received wave. It can be thought of as follows. The transmitted wave is f(t) as a function of time t, the received wave is g(t), and the distribution of the reflective layer in the living body is defined as ``(X)'' as a function of depth X.The transmitted wave is distributed in the living body. The isolated reflected waves at each reflective layer are delayed by a time corresponding to the interval between the reflective layers, and become the received wave in a superimposed form.Also, as mentioned above, the depth of the reflective layer When a transmitted wave travels back and forth between the reflective layer and the vibrator, it is affected by attenuation and phase distortion.

If this effect is viewed broadly as a type of filter function that depends on frequency, it can be considered that the transmitted wave is subjected to a filter function that differs depending on the depth.

When expressing the received wave using these functions, g(t) = f
``h(t-x,x)r(x)dx-(1)where h(t,x) indicates an isolated received wave returned from depth X when transmitting wave f(t) is transmitted.

it is conceivable that. Equation (1) above is an isolated waveform in which the transmitted wave f (t) is subjected to attenuation and phase distortion that are also a function of depth X at any depth is superimposed according to X. Therefore, for ease of explanation,
Focusing on the reflected wave from only an arbitrary depth X and looking at it on the Fourier plane, Flh (t,
−jθu(1/′”) −(2) Here, F represents the Fourier transform at t, and θB represents the phase of each frequency component on the Fourier plane.

When performing pulse compression, a correlation calculation is performed on the reference wave rer(t) and the received wave g (t), so a correlation calculation is also performed on the isolated received wave h (t, x). That will happen. That is, F (h (t, x)★rer(t))−1it(
v, x) 1e-jθ++ (' °x) -1Re
r(v) 1 e JθR(v)−IH(v,x)
l 1Rer(v) 1e-j(0H("x)-θR(
v)1...(3) Here, ★ indicates a correlation operation, and Ref (w) is Ref
(w) shows the complex conjugate.

In order to obtain a pulse compression wave, in equation (3), the amplitude component l11(v,x) l 1Ref(v) l
must be determined so that it becomes the power spectrum of the desired compressed waveform, for example, the power spectrum of a Gaussian waveform or a raised cosine waveform. Moreover, the phase term (θ□
(w,x)-θll (w)l must be zero.

However, it can be seen that both the amplitude term and the phase term in the above equation (3) depend on the depth X. This means that not only the optimal reference wave must be dynamically changed depending on the depth, but also the attenuation and phase distortion must be known. Since it is very difficult to know the depth of the living body to be diagnosed, it is difficult to perform optimal pulse compression from shallow to deep areas.

When using a fixed reference wave, for example, as shown in FIGS. 2 and 3, when attempting to phase match the Chirb wave by autocorrelation calculation, F + f (t) according to the above equation (3). ★f(t)] -P(v)e'θ"", F(v)ejθF(V)-I
F(W)+2 . . . (4), it is impossible to obtain a good compressed waveform as shown in FIG. 3.

This invention was made in view of the above-mentioned points, and it is possible to perform good pulse compression in the entire range from shallow to deep diagnostic depth without preparing an optimal reference wave. An object of the present invention is to provide a pulse compression device for ultrasound diagnosis with improved resolution and sensitivity.

[Means for Solving the Problems] In other words, this invention has the advantage that the frequency components of each
means for generating a chirb waveform to be transmitted to an ultrasonic transducer with a phase difference of degrees; and means for receiving and accumulating two echo signals having the phase difference obtained from the ultrasonic transducer; , a correlation unit that performs a correlation calculation on the two accumulated echo signals, a Fourier transform unit that performs a Fourier transform on the signal subjected to the correlation calculation by the correlation unit, and a spectral signal that has been Fourier transformed in the Fourier transform unit. The present invention is characterized by comprising a spectrum processing section that squares the signal, and an inverse Fourier transform section that performs inverse Fourier transform on the signal squared by the spectrum processing section.

[Function] In the ultrasonic diagnostic pulse compression device of the present invention, first and second pulses having a phase difference of 180 degrees with respect to an ultrasonic transducer are used.
Chilb wave signals are generated by the harmonic wave generating means, and these are alternately switched so that the reflected echo of the same diagnostic site is received twice. Then, in the buffer memory, the first and second
The first and second received signals due to the chirb wave signal of
The D-converted signal is once stored, and the stored first and second received signals are subjected to a correlation calculation by a correlation means. The signal after this correlation calculation is subjected to Fourier transform in a Fourier transform means, and then the square root of the waveform power is taken in a spectrum processing section as a complex Fourier signal, and then inverse Fourier transform is performed in an inverse Fourier transform section. As a result, an ultrasonic tomographic signal as a -scanning line is obtained.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of a pulse compression device for ultrasound diagnosis according to the present invention.

In the figure, a control signal 12 from a control section 11 is shown.
At a predetermined timing, the first and second chirb wave generators (chirb wave generator 1, chirb wave generator 2) 13
The signals generated in and 14 are alternately selected by the transmission wave selection section 15 and sent to the ultrasonic transducer I7 via the transmission amplifier 16. The ultrasonic reflected wave oscillated from this ultrasonic transducer 17 and reflected from the reflective layer in the living body is converted again into an electric signal by the ultrasonic transducer 17, and is sent to the receiving amplifier 1B and a low-pass filter (LPF) as a received signal.
) Sample hold (S/H) and A/D via 19
It is sent to the converter 20. This S/H and A/D converter 2
0 is controlled by a control signal 2I from the control unit 11, and the A/D converted received signal data is stored in the first buffer memory (buffer memory 1) 22 if it is based on the first chirb wave. The one caused by the chirp wave No. 2 is stored in the second buffer memory (buffer memory 2) 23,
Each is selected according to the control signal 24 of the control unit 11 and stored at a predetermined timing.

The received data once stored in the first and second buffer memories 22 and 23 is sent to the correlation unit 26 as appropriate by a control signal 25 from the control unit 11. Further, in accordance with the control signal 27 from the control section 22, the output from the correlation section 26 is sent to the Fourier transform section 28 and transformed, and then the square root is taken at the spectrum processing section 29. The output of the spectrum processing section 29 is subjected to inverse Fourier transform in an inverse Fourier transform section 31 according to a control signal 30 from the control section 11 and then sent to an observation device 32 .

Next, the operation of this embodiment will be explained.

In response to a control signal I2 from the control unit 11, the first and second chirve wave generation units 13 and 14 generate a first chirve wave signal and a second chirve wave signal at predetermined timing. These first and second chirb wave signals have exactly the same amplitude, frequency band, and duration, but their phases are 180 degrees different from each other.

These first and second chirb wave signals are alternately selected by the transmission wave selection section 15 and transmitted by the transmission amplifier 16.
is sent to the ultrasonic transducer 17 via. That is, one of the scanning lines in which a first chirb wave signal and a second chirb wave signal are each transmitted once at a predetermined interval for the same voltage in the living body to form an ultrasound diagnostic image. A scan line will be obtained by subsequent processing.

In this way, the ultrasonic reflected waves oscillated from the ultrasonic transducer 17 and reflected from the reflective layer in the living body are transmitted to the ultrasonic transducer 17.
The signal is again converted into an electrical signal and sent as a reception signal to a sample hold (S/H) and A/D conversion unit 20 via a reception amplifier 1g and a low pass filter (LPF) 19. The execution timing of the sample hold and A/D conversion of this S/H and A/D conversion section 20 is determined by the control section 1.
It is controlled by a control signal 21 from 1. Then, the A/D-converted received signal data is stored in the first buffer memory 22 according to the control signal 24 of the control unit 11, and the data based on the first chirb wave is stored in the first buffer memory 22.
The second chirb wave is caused by the second buffer memory 2.
3 and stored at a predetermined timing. The received data once stored in the first and second buffer memories 22 and 23 is sent to the correlation unit 2B as appropriate by the control signal 25 from the control unit 11, and is sent to the correlation unit 2B in the first and second buffer memories 22 and 23. A correlation calculation is performed between the received data of the chirb wave and the received data of the second chirb wave.

This can be explained as follows in relation to the formula for explaining the principle described above. In the above equation (3), if the received wave from the depth X due to the first chirb wave is h (t, t) l-H(v, x) -18(v, x) lejθH(WoX) ,,
<c,> is considered.

Performing the correlation operation of these two signals means that in the Fourier plane, P(h(t,x)*ref(Moon−IH(v,x)
2-(6), the term representing the distribution of the reflective layer including biological attenuation and phase distortion at an arbitrary depth This means that a pulse wave having the same frequency distribution is applied.

After all, from the above equation (1), after the correlation between the first and second received waves, PIg+(t)*g2(t)1 −jθR(VX) −IR(wx) Ie ・IR(W) Ie
-joR(vx)・IH(w,x)12-IR(vx
) l 2e-j2θR(” ・III(w,x)12
...(7). Reflective layer distribution I R (w x ) l e-j
o''x) C. After the above processing, the signal is squared as shown in equation (7), so after being once Fourier transformed by the Fourier transform section 28, the square root is taken by the spectrum processing section 29 by numerical calculation. Here, the power of the spectrum is raised to the 1/2 power, and its phase is halved.

The data after such processing is I R(w, ) le-joR(vx) I H(
w, x) l, and the pulse wave with the frequency component IH(w, x) l (this changes depending on the depth Motsu.

Therefore, the inverse Fourier transform section 31 converts this into actual waveform data. As a result, an ultrasonic reflection image signal as if obtained by a pulse waveform having a band component that changes depending on the depth inside the living body is obtained. However, since this signal is obtained by phase matching the Chirb wave, the amplitude of its peak value can be obtained large.

The signal thus subjected to inverse Fourier transform by the inverse Fourier transform section is sent to observation device 32 and can be observed as a diagnostic image.

In this way, the phase of the received wave transmitted by the Chilb wave is matched while maintaining a band that changes depending on the depth of the living body, so the reflected echo is shaped by a pulse with a band that varies depending on the depth. can be obtained.

Therefore, deterioration of the pulse compression waveform due to correlation with a reference wave that cannot be matched with the received wave can be removed, and it becomes possible to obtain a good compression waveform.

[Effects of the Invention] As described above, according to the present invention, it is possible to perform good pulse compression in the entire range from the shallow diagnosis depth to the deep diagnosis depth without preparing an optimal reference wave, and its resolution can be improved. It is also possible to provide a pulse compression device for ultrasonic diagnosis with improved sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the ultrasonic diagnostic pulse compression device of the present invention, and FIGS. 2 and 3 explain conventional pulse compression technology. Figure 3 shows an example of applying linear FM modulation to the transmitted wave.
The figure shows an example in which a received wave is applied with a matched filter to compress the signal, and FIG. 4 is a characteristic diagram showing the sensitivity characteristics of a conventional echo spectrum with respect to the depth of the living body. DESCRIPTION OF SYMBOLS 11... Control part, 13... First chirve wave generation part (chirve wave generation part 1), 14... Second chirve wave generation part (chirve wave generation part 2), 15... Transmission Wave selection unit, 16... Transmission amplifier, II... Ultrasonic transducer,
18...Reception amplifier, 19...Low pass filter (
LPF), 20... Sample hold (S/H) and A/D conversion section, 22... First buffer memory (buffer memory 1), 23... Second buffer memory (buffer memory 2) , 26... Correlation unit, 28... Fourier transform unit, 29... Spectrum processing unit, 31...
- Inverse Fourier transform unit, 32... observation device. Applicant's representative Patent attorney Atsushi Tsuboi Figure 2 Figure 3

Claims (1)

[Claims] Means for generating a chirp waveform to be transmitted to an ultrasonic transducer with a phase difference of 180 degrees in frequency components; a means for receiving and accumulating two echo signals having the same function, a correlating means for performing a correlation operation on the two accumulated echo signals, a Fourier transform section for Fourier transforming the signal subjected to the correlation operation by the correlation means; It is characterized by comprising a spectrum processing section that performs an inverse Fourier transform on the spectrum signal that has been Fourier transformed in the Fourier transform section, and an inverse Fourier transform section that performs an inverse Fourier transform on the signal that has been raised to the 1/2 power in the spectrum processing section. A pulse compression device for ultrasound diagnosis.