JPS60203242A - Reflection type ultrasonic nonlinear reflection coefficient measuring device - 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] [Technical Field of the Invention] The present invention relates to a reflection type nonlinear reflection coefficient measuring device, in which ultrasonic waves irradiated into an ultrasonic medium are affected by nonlinear reflection coefficients within the medium. An ultrasonic application device that measures the nonlinear reflection coefficient within an ultrasonic medium, and further measures its distribution two-dimensionally or three-dimensionally, by utilizing the fact that irradiated ultrasonic waves are reflected depending on the sound pressure. Regarding.

[Prior art to the invention]

The ultrasound diagnostic device 6 using the conventional reflection echo method can extract information related to changes in acoustic impedance within living tissues, that is, the outline of tissues such as the liver, but it is possible to extract information about the nature of the tissue, such as whether the liver is normal or malignant. It was difficult to distinguish whether the liver was affected by a tumor or not. Tissue Characterization is a method that attempts to identify the properties of such tissues.
For example, since the nonlinear parameters of ultrasound vary depending on the nature of the tissue, methods have been devised to measure these nonlinear parameters and identify the nature of the tissue. (Japanese Patent Application No. 58-119100. Patent Application No. 58-119100.
8599) However, among the conventional nonlinear parameter measurement
The transmitting probe and the receiving probe must be placed facing each other with their beam axes aligned, and due to refraction in bones, cavities in body cavities, or tissues that are difficult for ultrasound to pass through, It has the disadvantage of being limited. In addition, a reflection-type device (
Japanese Patent Application No. 5,816,8599) also requires that the ultrasonic burst wave for measurement and the continuous ultrasonic wave for bombing must be arranged orthogonally to each other, and the bombing wave must be a plane wave-like wave that covers the area to be observed. There are many restrictions on the device configuration, such as: As a result, the overall size of the device increases, the number of parts to be observed is limited, and operability is poor.

In addition, although only nonlinear parameters are considered as factors for the sound pressure dependence of the reflection coefficient,

■ Changes in the scattering cross section due to the orientation of minute scattering due to ultrasonic radiation pressure.

■ Changes in the phase of reflected waves from each scattering point due to changes in the ultrasonic medium's fine structure due to ultrasonic radiation pressure.

In order to consider nonlinearity in reflection, it is necessary to consider not only the nonlinear parameters but also the nonlinear reflection coefficient itself.

[Purpose of the invention]

The purpose of the present invention is to irradiate ultrasonic pulses or continuous waves into an ultrasonic medium such as a living tissue, and focus on the nonlinearity of the reflection coefficient itself, which changes depending on the incident sound pressure. An object of the present invention is to provide a reflection type nonlinear reflection coefficient distribution measuring device that can measure the distribution of nonlinear reflection coefficients by measuring a specific frequency component of reflected ultrasonic waves or the time waveform of the frequency component.

The present invention utilizes the fact that an ultrasound medium such as a living tissue has a nonlinear reflection coefficient that changes depending on the sound pressure applied inside the medium, and separates a specific frequency component or its temporal waveform of a reflected echo signal from inside the medium. By measuring
Measure the distribution of the nonlinear reflection coefficient on the axis of the ultrasound beam propagating inside the medium, and repeat this measurement while scanning in one or two dimensions to determine the distribution of the nonlinear reflection coefficient in two or three dimensions. It is designed so that it can be displayed visually.

[Embodiments of the invention]

The reflection coefficient of the reflector at position X within the ultrasound medium (X=0 represents the ultrasound probe surface) is expressed as follows, taking into account its sound pressure dependence.

r(x)=r+(x)+rt(x)P+rs(x)P”
(1) P is the sound pressure applied within the ultrasonic medium,
Regarding the sound pressure P, terms higher than the third power are ignored. Here, the first-order reflection coefficients vi and r+(g) are the reflection coefficients at static pressure, and the second-order reflection coefficients rt(x) and third-order reflection coefficients rfi) are the coefficients of P and P'', respectively. be.

Furthermore, the sound pressure P(x, t) applied at position value x1 at time t.

P (x, t)=f(t-'-) (2) When the sound pressure waveform is expressed as f. However, C is the sound speed at which the ultrasonic wave travels within the medium.

Then, the reflection coefficient rcx*t) at position X9 and time t is.

r (x, t) = rt (X) + rt Cxrf
Ct −j) + rs (yJ(f(t4)H3)
becomes. That is, 1s(x+t
)teeth.

s (x, t) = r (x, t) f (t-, -) =
r*bdf (t4)+rt(x)ge(t-4))”+
r, to)(f(-1 month 3...(4). Considering that the reflected echo returns by going back and forth within the ultrasonic medium, the probe at position IIJ at x = 0 The reflected echo signal from position x that is received at time t is the echo i(x, It can be expressed as a superposition of waves reflected by.

s (t) = / s (x, -B) dx = / (:
rt(x)fc! ;-':) +rt(x)ge(”-:
)]'+rs(x) (”) )”) dx −(
s) becomes C. Here f (i-x) = f (''-x)
Considering the function f2a 2 .

a(t)= /Cr+ (x)? (”--x)7rt
(x) (f('±-X))'2 + rs(x)(f(--x) )") dx=[r+
(x)* f(x)+r*(x)*(P(x))”+
r s (X) * (' (X)) ”) X = -z
−””” (6). However, * indicates the folding and folding operation. The function t indicating the sound pressure waveform applied to the ultrasonic medium is expressed as tp and tll which have different frequency bands as shown in the following equation.
It shall be expressed as the sum of

f = f p + f a (7) Here.

Ifpl>>l? l...Assuming (8), 2
If we approximate s by leaving only the first-order term.

t=fp+fs...(7)? ""t'p+2fp@fm ・・・・・・(9) Ris
:f3p-)3dap'-1......α. Therefore, equation (6) is.

5(t)' (rl d* (dap (X)+ f m
(xi)+rt(yJ*(fp'(x)+2fp(x
)・ri(x))to r3)*Cf P”)+3f
p' (phantom?Hatani))] engineering = 0. ...To obtain the sound pressure waveform 2 expressed by equation 400(7), one probe with two different frequency bands may be used, or different probes with different frequency bands may be used. Children may be lined up and used at the same time.

Here, 01) 7-lies vector f of fp(t) in Eq.
If pC is as shown in Figure 1(a), then (fp
(/11'.

Fourier spectrum G of ($'p(t))'! p (a)
The tGspC waveforms are as shown in Figures 1(b) and (a). However, fP is the center frequency of Gp (c), and at this time, 2
fP and 3fP are respectively GtpCf) and Gs p(a)
is the center frequency of If Gp(f) is a sufficiently narrow band, Gp(f)+Gtp(a), G3 p(f) except for the overlap of the components near fp of Gp(f) and Gs p
) can be separated from other frequency components by Fourier transform of 0 (11).

SO = a + Cf) (GpV) + G island (f)) 10R stupid + (GtP (7') + 2GpV) * Ga (c) 10Rs
(f)-(Gs PCf)+3Gt p(JQ*G
8(7)1. ...[12] However, 8(AGa(1) indicates the Fourier transform of a(t), fa(1). Also, in R order, Rt(A, R5(force is r
+ (Shizuyama σ).

Indicates the 7-Rier transform of 2r-(">.GsV). If the center frequency of GsV is fs, and Gs(f) is a line spectrum or a sufficiently narrow band, Gp (A Gt p(7'), Gm pcf) and GIIV) can be separated. Let the remaining component be S' (c).

S'<f)=2 Rt(A”(G P(f)*
G 14 Cf1)+3Ra(f)・(Gtp(force*G
S))...-03). However, * indicates a convolution operation. Looking at it from a different perspective, equation (13) represents the time signal s
If an appropriate bandpass filter is used for (t), the output a'(t) will be.

s'(t)=(2rt(x)*(fp(x)fa(x)
)+3 rs (x)*(f'p (x) f s (
x))) , = Q4).

Here, Gp (f), Gs (assuming that the frequency spectrum of the force is as shown in Figure 2 (a), from the first term of equation (13), l fP - J knee fm 1. From the second term, l 2f
A frequency component of pffal is generated, as shown in Fig. 2 (axis). However, Gp (7).

The components of G2P (force, GsPv) and Gs(1) are excluded.

However, for example, if there is a relationship f m = 2 Z p, the frequency component of the first term and the frequency component of the second term are both generated by the frequency m and overlap each other, so (1
3) A combination of jp=fm is required in which the frequency component of the first term of the equation and the frequency component of the second term do not overlap.

Here, for example, attention is paid to the frequency component of 12 fp-fal. This component is a component generated as a result of the convolution of GtpCf: and Ga(C) or the product of rtp and fm,
Since Gap(f) and GS(f) or 11p and rs can be measured, the distribution r of the third-order nonlinear reflection coefficient on the ultrasound beam axis can be calculated by deconvolution of the second term of equation 04).
, to) be criticized.

Similarly, if we focus on the 1fp-fal component, from the first term of equation 04), the second-order nonlinear reflection coefficient r! The distribution of (g) can be seen.

For example, if the frequency characteristics of destruction and scattering within an ultrasound medium such as a living body are a problem, for example, the echoes returning from deep within the living body may be amplified by emitting sensitizing tears.
aitlvityTime Control abbreviated as 5T
C) or by applying the inverse characteristics of attenuation and scattering, etc., there is no problem.

By performing this measurement at different locations, a two-dimensional or three-dimensional distribution of nonlinear reflection coefficients can be obtained.

Next, the configuration of the entire device is shown in FIG. 3.

In the figure, 1 is the system controller, which includes a trigger generator 2 and a bandpass filter 9. Control the attenuation/scattering correction section 109 display section 13.

In the figure, 3 and 4 are the transmitter probes 5 and 4. Transmission probe (B) 6
This is an amplifier for driving. The transmitted ultrasonic waves are reflected by the medium 7 and received by the wave receiving probe 8 . The wave transmitting probes 5 and 6 each transmit pulses or continuous waves having a center frequency of fp+f8. The reception probe 8 is assumed to have a sufficiently wide reception band.The 0 reception signal is input to a band pass filter 9, and the system controller 1 controls 6 which band components are allowed to pass. The output is input to the attenuation/scattering correction section 10. The inverse characteristics of the attenuated fist scattering for correction are controlled by the system controller 1.

The signal processing unit 11 performs a deconvolution operation to obtain a nonlinear reflection coefficient. This data is stored in the lffl7 image memory 12 and displayed as an image through the display section 13. [Other Embodiments of the Invention] As another embodiment of the invention, ultrasonic waves having one band are irradiated onto the medium, There is a means of determining the distribution of nonlinear reflection coefficients from the frequency components of echoes that are reflected and returned inside the medium.

That is, in equation (7).

f s = 0, that is, G s = 0
In the case of 5), equations 01) and 02) are.

a(t) = (r+(x)*Pp(x)+r*(x)*
f'p(x) rs(x)* f 5p(yJ)
c t ......-(16) x = T S (Ha = R word power G p (f) + R! (Ha Gtp
f)+R8(haGsp(c...07).If Gp(A, Gtp(A Gsp(a)) can be separated from each other as shown in FIG.

g*(t)=Crt(X)*ftP(7J]ctx=T as(t)=(rs(x)*IPsp(x)) si
-(18)8=2 Or.

Si force = R Baja G weight (C3g(1) = Rs(f)GsI) (can be separated from C. However, Gp(A and Gap(4 components are j
Since they overlap near p, the effective band for G sp V) is only near 3 fp.

Finally, the deconvolution operation of equation (18) or (
From equation 19), the ratio St(c/GipV) of the transmission spectrum Gip(n and reception spectrum Sts) (where 1=2.
3), and from the inverse Fourier transform of this ratio, the sixth-order nonlinear reflection coefficient r, (2)+rJ) is calculated.

Ultrasonic media such as biological tissue greatly attenuates high frequencies, so when the attenuation increases, the high frequency component Glp (c, Gsp
(The force detection sensitivity is limited, but the transmitting probe is 1
It has the advantage of being easy to use.

〔Effect of the invention〕

The nonlinear reflection coefficient, which changes depending on the incident sound pressure of the ultrasonic wave incident on the ultrasonic medium, reflects subtle differences in the physical properties and tissue conditions of biological tissues, etc., and according to the present invention,
Since the distribution of this nonlinear reflection coefficient can be measured, it is possible to discriminate the wire characteristics of biological tissues and the like.

[Brief explanation of the drawing]

Figures 1(a), 1(b), and 1(e) show the sound pressure waveforms tp+c of the ultrasonic medium, respectively k fp, f''p,
f"p (D frequency spectrum GpV) - G*p (Ha*GspV). Figures 2 (a) and (b) show the frequency spectrum of an ultrasound having two different bands and the nonlinear The frequency spectra obtained when a medium with a reflection coefficient is irradiated are shown respectively.
1 is a system controller, 5 and 6 are transmitting probes, 8 is a receiving probe, 9 is a band pass filter, 11 is a signal processing section, and 13 is a display section. )l Cause is $,? i

Claims (1)

[Claims] transmitting an ultrasound pulse or continuous wave with at least one band Ω1 in an ultrasound medium, at least one transmission band Ω, and at least one band Ω other than the transmission band;
, one dual-purpose or separate ultrasonic probe to receive the ultrasonic pulses or (of the continuous wave, the band Ω, and the band ρ of the reflected wave from within the ultrasonic medium) , the frequency component S1(a), S鵞(a) or its time waveform!It(
tl+ at (signal processing circuit that takes t3 and the frequency component S1ω, S*V) or its time waveform s+(t),
1. A reflection type ultrasonic nonlinear reflection coefficient measuring device, comprising a calculation processing circuit that correlates a nonlinear reflection coefficient in the ultrasonic medium with a nonlinear reflection coefficient in the ultrasonic medium.