JPS6036038A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus, and particularly to an ultrasonic diagnostic apparatus that displays tomographic images.

BACKGROUND TECHNOLOGY Ultrasonic diagnostic equipment usually employs the pulse echo method1, and this type of ultrasound diagnostic equipment includes a probe that transmits and receives an ultrasonic pulse beam into the subject. A tomographic image is displayed based on the echo signal. In other words, in the pulse-echo method, an ultrasonic pulse beam is emitted from a probe into the subject, the reflected waves from various depths are detected, and the intensity is displayed on a CRT as a function of depth. Since reflection of ultrasonic waves occurs at parts of the subject where acoustic impedance changes, the pulse echo method allows for image display of interfaces between organs and the like within the subject. Therefore, according to the pulse echo method, morphological information of the subject can be obtained, but there is a problem in that it is difficult to qualitatively diagnose the living tissue.

Therefore, research is being conducted to measure all the attenuation coefficients of living tissues and use this for qualitative diagnosis of living tissues.
Tomography) has been proposed. The principle of ultrasonic CT is to transmit ultrasonic waves into the subject from many different directions, perform reconstruction calculations based on the intensity of these transmitted ultrasonic waves, and calculate the attenuation coefficient of the living tissue. . However, since this ultrasound CT-C uses the principle of detecting transmitted waves of ultrasound, if there are substances in the subject that are difficult for ultrasound to pass through, such as bone or air, However, there was a drawback that the attenuation coefficient of living tissue could not be measured.

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 diagnostic apparatus that can easily measure the attenuation coefficient of a subject from reflected echo signals.

Structure of the Invention In order to achieve the above object, the present invention provides an ultrasonic diagnostic apparatus that transmits and receives an ultrasonic pulse beam to and from a subject and displays a tomographic image based on reflected echo signals from the subject.
A bandpass filter and a detection circuit extract a specific frequency component from a reflected echo signal, a logarithmic converter performs full logarithmic conversion of the signal from the bandpass filter and detection circuit, and a logarithmic converter converts the signal from the logarithmic converter and this signal into a predetermined signal. a subtraction circuit that calculates the total difference between the delayed signal and the delayed signal delayed by a time interval;
The present invention is characterized in that the attenuation effect of the ultrasonic wave for the specific frequency component is measured.

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

The principle of the present invention will be briefly explained. The attenuation coefficient α of ultrasonic waves is a function of the frequency r, and is expressed as α(f).

Among the reflected echo signals from the object, those reflected from the part far from the probe have a longer propagation path within the object, so they are much larger than the echo signals from near the probe. Attenuation of sound waves increases. Also, the attenuation coefficient is a function of frequency, so not only does the intensity of the ultrasound wave decrease;
The spectrum of the reflected echo signal will also change. The present invention takes advantage of this property, focuses on a specific frequency in the spectrum, and measures the attenuation coefficient for the specific frequency based on the change.

FIG. 1 shows a block circuit according to the principles of the invention.

The probe 10 is excited by an oscillator 12 to emit an ultrasonic pulse beam to a subject (not shown), and a reflected echo from the subject is received by the probe 10 . Probe 1
0 is connected to a bandpass filter 14, which allows a specific frequency component to be extracted from the reflected echo signal. Here, reflected ego =
The signal is measured as a function of time t, and considering that in the frequency band of ultrasound used in ultrasound diagnostic equipment, the speed of sound is constant regardless of frequency, 11, this speed of sound 1c
Expressed as , the position X where the reflected echo occurs and the time t when the probe detects the reflected echo have the following relationship.

x=Ct/2 (1) Therefore, in the following explanation, the position X within the subject and the time t may be treated equally.

It is assumed that the impulse response $b(t) of the bandpass filter 14 is given by the following equation.

h (t) = a (t) (2πf, t) ==
= j2) In equation (2), fl is bandpass filter 1
4, and a (t) l means the envelope of the impulse response. Then, the bandpass filter 14 is a causal system, ・(t)−〇(t〈0). (,〉,.)°゛′°゛(3).

If the reflected echo signal to be input to the bandpass filter 140 is represented by p (t), then this bandpass filter 14
The output signal b(t) can be expressed as follows using equation (2).

Here, the result of tooling transformation of p(τ) t) e becomes as follows.

Therefore, using equation (5), equation (4) is transformed as follows.

b (t) = A (r+, t) low (2πf, j+ξ
DI, t)1 ... (6) Here, ξ(r+, t,)
is the phase term. The meaning of this equation (6) is as follows. Zunaji, the envelope A(f, t) of the output signal of the bandpass filter 14 is the function p(τ)Xa(−τ
) is the absolute value at the frequency "1" of the Fourier spectrum. t-τ) to give the absolute value of the component of frequency f included in the extracted signal.

Next, we will explain how the attenuation coefficient α([) is related to A(f,,t), that is, the output signal of the detection circuit 16.
The means for requesting the damping coefficient α(f) from fl, t) will be explained.

As mentioned above, since the attenuation coefficient α(f) is a function of the frequency f, the waveform of the reflected echo signal depends on the depth of the reflector. Then, the reflection coefficient at position X in the subject is 1 kr.
(x), the reflected echo signal PX(τ) reflected from this position X is as follows.

Here, 5(f) is the Fourier transform of the ultrasonic pulse waveform incident on the subject. Using this equation (7), the reflected echo signal P(τ) from the subject is expressed as f! ,Z
).

Next, consider the signal obtained by multiplying the window function a( by the equation -τHr-+81.

FIG. 2 shows various waveforms based on the principle of the present invention. In FIG. 2, the horizontal axis indicates the time τ (or position As described above, the position X has the relationship expressed by equation (1).

Figure 2 (in aJ, reflection coefficient r(x) inside the subject)
is shown, and the reflection coefficient fir(x) is shown as an impulse train because it exists only at interfaces where acoustic impedance changes within the subject. Further, in FIG. 2 (bl), the reflected echo signal P(τ) expressed by equation (8) is shown, and in FIG. 2 (tc), k', the pass filter 1
The envelope curve (t-τ) of the impulse response of 4 is shown, and in FIG. 2(d), the above tbl and td)
In other words, the signal obtained by multiplying the reflected echo signal P(τ) by the window function a(−τ) is shown.

As is clear from Figure 2, if the bandpass filter 4 is selected so that the window function a(t-τ) is close to a rectangle,
l) (τ)・a(−τ) means that the position X is calm <
It can be approximated as a reflection 2 echo from a reflector in the range of X<Ct. That is, Ct. When this equation (9) is Fourier transformed with respect to τ, 1, S L r) e-affl tC-2"y"e is obtained.

Then, the output signal of the detection circuit 16 is f
It is the absolute value of the value when = f. Therefore, it is expressed as ...(l]J.

A logarithmic amplifier 18 is connected to the detection circuit 16.
The output signal from the detection circuit 16 is logarithmically converted by the logarithmic amplifier 18 . Therefore, vs. 13! The output signal 4(r,,t) of the amplifier 18 is obtained by logarithmically transforming the above equation (1η), and is expressed as %(fI,t)-ln A(f,,t)-An l s
(r,)l−α(f,)tCtenε(to,t,fI)
It can be expressed as +・+ aa. However, in equation (b), the logarithm of the integral term in equation 01) is expressed as ε(tO+t,
r, ).

Next, in order to obtain the difference between the output signal from the logarithmic amplifier 18 and a signal obtained by delaying this output signal by a delay time d, a delay circuit 20 and a subtraction circuit 2275 are provided.
Output G of this subtraction circuit 22. (I,,t) is Go(f
I, t)-8z(r++t-d)-Ag([+,t)-
α(f,)-d, C-ε(to, LJ+ > tenε(t
o, t-d, f, )...OJ. According to this equation 04, 5(f
l) Output signal G from the Seiji circuit 22, which can be completely erased. (fI, t) is the damping coefficient α at frequency f1
(fl) is multiplied by the delay time d of the delay circuit 20 and the speed of sound C, and this is added as an error term (-ε(to, t, L)+ε(
to, td mountain)) is added.

Therefore, this error term (-ε(to, t, fI)+ε(t
o, td mountain)) We will focus on the integral term of the t1υ equation. The reflection coefficient r (x ten rainbows) in the integral term should be viewed as a probability reflection. That is, the reflection coefficient r inside the object
Since (x) varies due to respiratory movement of the living body, movement due to pulse membranes, movement due to blood flow, etc., it cannot be considered to wait for a definite value. Therefore, if the systematic properties of the subject can be considered uniform within the range indicated by the delay time d, then f
Considering f, ε(to, the mountain) and ε(tti+ ”
−+ fl) have the same expected value μ. Therefore, the error term (-ε(to, t, fI)+6(to, t-
d, fl)), we get E(-ε(tO+t+
”+)+ε(to,t-d,fl))”Ef-ε(t
o t f, l+E(ε(tot-d fI)1=-μ
10 μ = O. That is, the error term (-ε(to, t, r+)+
ε(jo.

The average value of t-d, f, )) is 0.

Therefore, in the above equation 04, if we take the expected values of both sides,
That is, when the average value of the output signal from the subtraction circuit 1i22 is subtracted, the error term (-ε(t, , tJ,)+ε(to.

``Since Lf+)l approaches 0, it is difficult to understand why α(fl)・d−C is so large.

Therefore, an averaging circuit is provided in order to average all the output signals from the subtraction circuit 22 and obtain the average value of the output signal GO (fI, t). 26 and a delay circuit 28.

Note that the delay time of the delay circuit 28 is set equal to the return frequency of the oscillator 120, and changing the entire weight determined by the reducer 26 corresponds to changing the average number of times.

The output signal G from the subtraction circuit 22 is obtained as described above.

The average value of (f, , t) is determined, and the delay time d
Since the sound velocity and sound velocity V are known, the attenuation coefficient α(fl) can be calculated based on the above formula 03, and by correcting this appropriately, the attenuation coefficient α(fl) at the frequency f1 of the subject is applied to the display wave ft30. fl) will be displayed.

In the above explanation, the attenuation coefficient α(fl
) is constant within the subject, but as can be easily understood from the above explanation, the attenuation coefficient α(f) does not need to be uniform throughout the subject, and the delay of the delay circuit 20 It is sufficient if it can be approximated that the attenuation coefficient α(f) is constant within the range of time d.

As described above, according to the principle of the present invention, the attenuation coefficient g-1 of the object can be easily measured based on the reflected echo signal, and thereby the attenuation coefficient for a specific frequency within the object can be measured in an image. can be displayed.

Referring next to FIG. 3, an embodiment of the present invention is shown. A block circuit of an ultrasonic diagnostic apparatus is shown, and in the block circuit of FIG. can be followed.

In the block circuit shown in FIG.
-2, logarithmic amplifier 18-1.18-2, delay circuit 20-
1.20-2, subtraction circuit 22-1.22-2, addition Jf
Circuit 24-1.24-2, Growth 626-1, 26-2,
And the delay circuit 28-1.28-2 has a specific frequency gauze f,
, f2 are provided with two systems, A1, respectively, and this allows the specific frequency r, , r2 of the two Germans to be connected to
It becomes possible to measure 51 damping coefficients α(fl) and α(f2).

In general, in living tissue, the attenuation coefficient α([)
is proportional to the frequency, and the proportionality constant of the attenuation coefficient to this frequency edge is an important parameter for tissue diagnosis. Therefore, if this constant of proportionality is β, the constant of proportionality β is β-(α(fI)-α(f2)l/(fl-f2)
...9, and the proportionality constant β is the frequency f, , f
2 and damping coefficients α(fl) and α(f2).

Therefore, according to the block circuit of FIG. 3, the reduction factor α(
fl), α(f2), ratio 1+1] constant β and a normal pulse echo image can be displayed. See, below, Figure 3 for details of the block circuit.

In FIG. 3, the transmission signal from the oscillating j finger 12 is co-supplied to the probe 1o via the drive circuit 32.
0 is transmitted to the ultrasonic pulse beam gold wave specimen 34, and the reflected echo from the specimen 34 is received by the probe 10 and converted into an electrical signal. After the signal is reflected by the high-frequency amplifier 36, the detection circuit 38, and the video transmitter 4o, it is sent to the display device (via the multiplexer 42). The display device t130 displays a normal B mode or IV mode tomographic image.

A scanning suppression circuit 44 is provided to mechanically or drowsily scan the ultrasonic pulse beam emitted from the probe 10, and a sweep circuit 44 is provided to perform sweep control of the display device 30. 46 is provided, and the sweep circuit 46 supplies a sweep l trigger signal 104 to the display device 30 based on the scan position signal 100 from the scan control fi111 circuit 44 and the same J41j signal 1[12 from the oscillator 12. Further, the synchronizing signal 102 from the oscillator 12 is used not only as a synchronizing signal for the sweep circuit 46 but also as a synchronizing signal for each part of the device.

The first embodiment is characterized by measuring the attenuation coefficients α(fI) and α(f2) with respect to the frequencies f, , f2, and for this purpose, the reflection from the probe 10 -
After being subjected to a predetermined amplification effect by the high-frequency amplifier 48, the L-co signals are supplied to band-pass filters 14-1, 14-2 having center frequencies f, , f2 that are h different from each other. Then, by the same action as the block circuit in FIG. 1 described above, the subtractor Oα(r,
> , α(f2) is determined.

Note that the amplitude of the reflected echo signal decreases over time due to growth within the subject 34. Therefore, in order to prevent the amplitude of the input signal to the band-pass filter 14-1, 14-2 from fluctuating greatly, the gain of the high-frequency amplifier 48 must increase with time. A signal generator 50 is provided, with which the high frequency amplifier 48 can be controlled.

Further, a subtraction circuit 52-1 is provided between the logarithmic amplifier 18-1 and the subtraction circuit 22-1, and similarly, a subtraction circuit 52-1 is provided between the logarithmic amplifier 18-2 and the arithmetic circuit 22-2. Reduction time 1
A column 52-2 is provided, the subtraction circuit 52-1.52-2
J:9, the variation in the gain of the high frequency amplifier 48 can be corrected. That is, logarithmic amplifier 1.8-1°18-
The logarithm of the gain of the high-frequency amplifier 48 is added to the output signal from the signal generator 50, and the output signal from the signal generator 50 is logarithmically converted by the V amplifier 54. 52
By subtracting by -1.52-2, the high frequency amplifier 4
It becomes possible to completely correct the variation in gain of 8.

Further, the delay time of the delay circuits 28-1 and 28-2 is set equal to the repetition period of the oscillator 12.

Then, the output signals from the adder circuits 24-1 and 24-2 are amplified or attenuated by the amplifiers 56-1 and 56-2, respectively, and then from the amplifier 56-1. The attenuation coefficient signal 106-1 from the amplifier 56-2 indicates the attenuation coefficient α([1), and similarly, the attenuation coefficient signal 106-1 from the amplifier 56-2
2 indicates the number of attenuated threads α(f2). The attenuation coefficient signals 106-i, 106-2 are sent to the multiplexer 4
The attenuation coefficients α(r+) and α(f2) are supplied to the display device 30 via the display device 30 through the display device 30.

Also, the attenuation coefficient signal 106-1. H]6-2 is supplied to the system subtraction circuit 58, and is connected to the system subtraction path 58 and the system subtraction circuit 58. I get criticized. That is, α(r+)−α(f2) is determined by the system subtraction circuit 58, and the first gain of the amplifier 60 is 17(r,−r,).
Therefore, it is possible to calculate the proportionality constant β based on the above equation (14). Then, the signal of the proportionality constant β determined by the system subtraction circuit 58 and the amplifier 60 is supplied to the display device 30 via the multiplexer 42.
1. The proportionality constant β is displayed by the display device 30.

In the embodiment, since the multiplexer il 2 is connected upstream of the display device 30, the multiplexer 42 allows the attenuation coefficient α(fI) for the frequency [,
The attenuation coefficient α (f2) for the frequency f2, the ratio 1 Tali constant β, and the normal B-mode or M-mode tomographic image of one or more tusks are selected as appropriate and displayed simultaneously on a display device. 30 can be displayed.

As described above, according to the embodiment, two types of frequencies fx
bchif, , f2ViC sentence "suru damping 1 thread count 1fl)
.

Therefore, it becomes possible to display the attenuation coefficient distribution and the distribution of the slope of the attenuation coefficient with respect to frequency, and it becomes possible to provide all the information effective for diagnosis of the lesion.

In the above embodiment, two systems of blocks for measuring the attenuation coefficient are provided, and two frequencies df are provided.

Although we have measured the damping coefficients α(r+) and α(f2) for f2, it is also possible to set up three or more blocks to measure the damping coefficients and measure the damping coefficients for three or more frequencies. .

As described in detail, according to the present invention, the attenuation coefficient of a subject can be easily measured from a reflected echo signal. Therefore, the attenuation coefficient of the subject can be measured and this can be effectively used for qualitative diagnosis of living tissue.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram according to the principle of the present invention, FIG. 2 is a waveform diagram according to the principle of the present invention, and FIG. 3 is a block circuit diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. Bandpass filter 16...detection circuit 18...logarithmic amplifier 20...delay circuit 22...subtraction circuit 24...addition circuit 26...attenuator 28...delay circuit 34...subject 58...・System subtraction circuit. Applicant: Aloka Co., Ltd.

Claims (1)

[Scope of Claims] (1) In an ultrasonic diagnostic apparatus that transmits and receives an ultrasonic pulse beam to a subject and displays a tomographic image based on a reflected echo signal from the subject, a specific frequency component is detected from the reflected echo signal. A band-pass filter and a detection circuit for extracting, a logarithmic converter for logarithmically converting the signals from the band-pass filter and the detection circuit, and a signal from the logarithmic converter and a delayed signal obtained by delaying this signal by a predetermined time interval. an ultrasonic diagnostic device M, comprising: a subtraction circuit that calculates the difference between the two; (2. In the apparatus according to claim (1), an averaging circuit for averaging all the signals from the subtraction circuit is provided, and the averaging circuit reduces adverse fluctuations in the reflection coefficient within the subject. (3) In the device according to claim (1) or (2), the bandpass filter and the detection circuit, the V converter, and the subtraction circuit include a plurality of specific A multiple copying system is provided for each frequency component, and a system subtraction circuit that calculates the difference in signals from each system is provided.Each system measures the attenuation coefficient for multiple specific frequency components, and the system subtraction circuit calculates the attenuation coefficient for the frequency component. An ultrasonic diagnostic device characterized by measuring a proportionality constant of a coefficient.