JPH0147182B2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Technical Field of the Invention The present invention relates to an ultrasonic diagnostic processing method, in particular, in which the sound velocity of a measurement wave is modulated in a manner corresponding to a nonlinear constant of a medium under sound pressure in the presence of a pumping wave. When performing diagnosis using this, the frequency of the pumping wave is swept to obtain the measurement wave phase deviation amount for each frequency, and the phase deviation amount is Fourier-transformed to detect the above-mentioned The present invention relates to an ultrasonic diagnostic processing method that measures the spatial distribution of nonlinear constants on a measurement wave scanning line.

(B) Background and problems of the technology Computer tomography technology using X-rays has been known for a long time, and as the concept is shown in Figure 1, this technology transmits and receives X-rays to, for example, a living body 1. X-rays are irradiated by the X-ray transceivers 2A and 2B, and the reception result by the receiver 2B is regarded as the cumulative result of the influence of the tissue on the illustrated line 2C. By changing the irradiation position on the living body 1 and solving n-dimensional simultaneous equations, the mode of each mesh 3 on the living body 1 is determined. However, in diagnosis using ultrasound, the transmission of ultrasound is hindered by, for example, the presence of gas in the living body or the presence of bones in the living body. For this,
It is difficult to adopt a method of determining the mode of ultrasonic transmission from all directions to the living body 1 and solving simultaneous equations.

For this purpose, as shown in FIG. 2, ultrasonic waves are applied to the living body 1 by ultrasonic transceivers 4A and 4B, and each position 5 on the scanning line 4C through which the ultrasonic waves can propagate is applied.
-1, 5-2, ... directly from the reception result by receiver 4B (not in the form of solving simultaneous equations)
It is desirable that the

On the other hand, it has been conventionally known that a high frequency sound wave that intersects with a low frequency sound wave field undergoes frequency modulation. It is believed that such interaction of sound waves is caused by nonlinearity within the medium. This means that the sound speed C in the ultrasonic medium is C=C ₀ +1/2ρ ₀ C ₀ (B/A) ΔP+... -(1) (where ΔP: sound pressure C ₀ :When ΔP=0 Sound velocity ρ ₀ :density when ΔP=0 B/A: nonlinear parameter) This can also be expressed as changing depending on the presence of sound pressure ΔP. Note that when the ultrasound medium is biological tissue, the above B/
A is considered useful for distinguishing between healthy and diseased tissue.

Although the value of B/A mentioned above can be either positive or negative, the following explanation will be continued assuming that B/A>0.

If B/A>0, it means that the speed of sound increases in places where the sound pressure is high, and as shown in Figure 3A, when the sound pressure ΔP creates a sine wave of the frequency and the sound wave travels. , the whole moves at a speed of C ₀ , but it moves faster in the high-pressure area and slower in the low-pressure area, deforming as shown in Figures B and C.
Under the condition shown in Figure 3C, a shock wave is generated in which the pressure changes discontinuously, and the ultrasonic energy is converted into other types of energy, and the pressure distribution does not change any further and progresses rapidly. It undergoes attenuation, the pressure decreases, and it disappears.

In this way, by performing frequency analysis of the received ultrasound, it is possible to measure the nonlinear parameter B/A. In this case, the energy of the second harmonic component is particularly large, and the second harmonic component is quantitatively measured. However, (i) as mentioned above, the second harmonic component is a function of not only the sound pressure ΔP but also the passing distance, and the form of this function is not linear; It is very difficult to obtain the above B/A from the second harmonic component and has a large error.

(ii) Also, the higher the frequency, the more likely harmonics are generated and the higher the sensitivity can be obtained. However, on the other hand, it is known that in living tissue, the pressure attenuation during penetration is exponentially attenuated with distance, and the attenuation coefficient is proportional to frequency. This makes it difficult to measure using high frequencies.

(iii) Furthermore, if the sound pressure attenuates exponentially depending on the distance as described above, as can be seen from equation (1) above, the analysis of the above B/A becomes complicated,
In most cases, it is difficult to calculate B/A.

(iv) On the other hand, needless to say, sufficient sensitivity cannot be obtained if a low frequency signal whose attenuation of sound pressure due to distance is virtually negligible is used.

(v) In addition, in the case of a method that measures the second harmonic component of the propagated ultrasonic wave, the effect on the propagation path is received as an accumulated effect, so the spatial distribution on the propagation path can be measured. I can't ask for it.

For the reasons mentioned above, it is not practical to apply an ultrasonic wave of a predetermined frequency and frequency-analyze the sound pressure waveform when it propagates in a medium such as a living body. To solve this problem, a relatively low-frequency pumping wave is supplied to create a sound pressure field, and a relatively high-frequency measurement wave is applied across the field, so that the measurement wave undergoes frequency modulation. A method is being considered to examine the manner in which it is received. That is, a method is being considered in which the sound pressure ΔP in equation (1) is given by a pumping wave and the state in which the measurement wave is subjected to frequency modulation is investigated. However, in this method, for the same reason as the above-mentioned item (v), that is, since the effect is received as a result of accumulation, only the average value of B/A can be detected. In other words, it was not possible to detect each B/A at each position 5-1, 5-2, . . . on the propagation path shown in FIG.

(C) Object and structure of the invention The present invention aims to solve the above-mentioned points, and while adopting the method using the pumping wave described above, the nonlinear parameter B/
The purpose is to be able to determine A. Therefore, the ultrasonic diagnostic processing method of the present invention measures the spatial distribution in the ultrasonic medium of a nonlinear physical constant or its related quantity with respect to ultrasonic sound pressure. A relatively low-frequency pumping wave is supplied to the medium to generate pressure within the medium, and a relatively high-frequency measurement wave is applied to the medium in a direction crossing the traveling direction of the pumping wave. and means for changing the frequency of the pumping wave, the reception phase of the measurement wave in the absence of the pumping wave and the reception phase of the measurement wave in the presence of the pumping wave. The amount of phase deviation is determined for each frequency of the pumping wave, and the amount of phase deviation is the measured wave of the pumping wave when the distribution of the nonlinear constant or its related quantity is inversely Fourier transformed into the spatial frequency domain. By assuming that the effective wavelength on the scanning line is a spatial frequency component and Fourier transforming the phase shift amount, the nonlinear constant or its related quantity on the measurement wave scanning line in the medium can be calculated. The feature is that it measures the distribution. This will be explained below with reference to the drawings.

Note that in the present invention, the form for determining the frequency function F(w) of the time function f(A) is called Fourier transform,
The form of determining the frequency function F(w) or time function f(t) is called inverse Fourier transform.

(D) Embodiments of the Invention FIG. 4 is an explanatory diagram for explaining the principle of the present invention, FIG. 5 shows the configuration of an embodiment of the invention, and FIG. 6 shows another embodiment of the invention.

In FIG. 4, symbols 1, 4A, 4B, and 4C correspond to those in FIG. 2, 6 is a pumping wave generator that generates continuous plane waves, 7-1, 7-2,
. . . represents the maximum sound pressure point of each generated continuous plane wave.

The whole shown is immersed in water, for example, and a pumping wave generator 6 generates a relatively low frequency signal ( _p =
Ultrasonic waves (0.2, 0.4, 0.8, 1.6MHz, etc.) are generated as pumping waves. On the other hand, the ultrasonic transmitter 4
Ultrasonic waves of relatively high frequency ( _n = 3.5 MHz, etc.) are continuously generated from A (for example, a concave transducer) as measurement waves. The measurement wave is then received by the receiver 4B.

If the traveling directions of the pumping wave and the measuring wave intersect at an angle θ, then the scanning line (propagation path)
The measurement wave that was above the indicated maximum sound pressure point a on 4C traveled by λ _p in the Z-axis direction shown while the pumping wave traveled by one wavelength λ _p (that is, after λ _p /C ₀ time elapsed). At point _a1 , the pressure of the pumping wave at that time is such that the phase is advanced by δ = 2π/λ _p (λ _p /cosθ−λ _p )cosθ = 2π (1−cosθ) − (2). There is. Therefore,
The measurement wave traveling on the scanning line 4C has an apparent angular velocity ω _e (or frequency e or wavelength λe), The frequency is modulated by the pumping wave.

That is, the speed of the measurement wave is influenced by the pressure _Δp of the pumping wave and the own pressure Δpm from the time it leaves the transmitter 4A until it is received by the receiver 4B, and the measurement wave is integrated over the entire path. In other words, the phase is shifted by Δφ shown in the following equation from the phase when no pumping wave is present.

That is, Δφ changes from "the phase φΔp when the measurement wave propagates the distance L when the pressure Δp _p exists" to "the phase φ ₀ when the measurement wave propagates the distance L when the pressure Δp _p is zero" Δφ=−2πC ₀ /λm [∫ ^L ₀ dz/C ₀ +ΔC−∫ ^L ₀ dz/C ₀ ] ≒2πC ₀ /λm∫ ^L ₀ ΔC/C ₀ ² dz=2π/ λm∫ΔC(dz/C
₀ ). Strictly speaking, when integrating, we are not integrating from 0 to L, but from 4A to 4B as shown in Figure 4, so becomes. Here, ΔC is given by ΔC≒1/2ρ ₀ C ₀ [B/A]ΔP(z), and the position where the measurement wave is superimposed on the pump wave changes with the frequency fe as shown in equation (3). do. Therefore, the sound pressure ΔP changes with distance as follows. That is, (However, || is the peak sound pressure of the pump wave.) Therefore, by substituting ΔC into the formula for Δφ, By substituting ΔP(z) into the equation for Δφ, equation (4) can be obtained. That is, It will be given by Note that ΔC shown in Figure (4) indicates the sum of the second term and subsequent terms on the right-hand side of equation (1), and can be approximately considered to be the second term on the right-hand side of equation (1) itself. It is. Also, ρ ₀ C ₀ is the position (y,
z), but it can be approximated to be approximately uniform in living organisms, and furthermore, if the pressure _Δp of the pumping wave is sufficiently larger than the pressure Δpm of the measurement wave, |Δp _p |≫|Δpm| It is assumed. Although the pressure |Δp _p | of the pumping wave is precisely a function of the position (y, z) due to attenuation, it can be considered that the frequency f _p of the pumping wave is relatively low and approximately constant.

Here, the form of equation (4) above is It can be seen that it has the following form.

This is the formula when the function f(t) is Fourier transformed and its inverse Fourier transform F(ω)=∫f(t)e ^-j 〓 ^t・dt f(t)=1/2π∫F( The form corresponds to the latter Fourier inverse transform of the relationship ω)e ^+j 〓 ^t・dω, that is, Δφ becomes f(t), (B/
A) (y, z) respectively correspond to F (ω), and the function F (ω) corresponding to the above (B/A) (y, z)
can be obtained by Fourier transforming the function f(t) as F(ω)=∫f(t)e ^-j 〓 ^t dt, so the nonlinear parameter (B/A) on medium 1 is can be determined as a function of position by sweeping the frequency of the pumping wave, determining the amount for each frequency, and performing Fourier transformation on the phase shift amount Δφ given by the above equation (4).

In other words, when the distribution of nonlinear parameters on the scanning line 4C in the medium 1 is inversely Fourier transformed into the spatial frequency domain, the spatial frequency component whose wavelength is the apparent wavelength of the pumping wave seen on the scanning line 4C is The distribution of the nonlinear parameters can be extracted by performing Fourier transformation assuming that the amount of phase shift is Δφ.

By doing this, it is possible to obtain the spatial distribution of the nonlinear parameter B/A on the z-axis when the pressure of the pumping wave |Δp _p | is substantially constant regardless of the position (y, z). It becomes possible. That is, the nonlinear parameter B/A at each point 5-1, 5-2, . . . shown in FIG. 2 can be determined. However, if the frequency f _p of the pumping wave becomes high and the attenuation of the pressure of the pumping wave cannot be ignored, in equation (4), (B/A)・|Δp _p | is expressed as a function of the position (y, z). , the same Fourier transform as above is performed to obtain the spatial distribution of the values (B/A)·|Δp _p |.

In calculating the above nonlinear parameter B/A, it is assumed that |Δp _p | is approximately constant on the z-axis when the angle θ = 90°, even if the pressure at the pumping frequency causes attenuation. It has the advantage of being relatively easy to do. In addition, in this case, if a liquid with an attenuation constant close to the average attenuation constant of a living body and a propagation velocity close to that of a living body is used instead of the water that immerses the entire system, the above pressure |Δp _p | It can be substantially constant on the z-axis.

FIG. 5 shows the configuration of an embodiment of the present invention.
Symbols 1, 4A, 4B, 4C, and 6 in the figure correspond to those in Figure 4, and 8 is a liquid tank in which the system containing medium 1 is immersed, and the inner wall is covered with a non-reflective sound-absorbing material. , 9 is a measurement system, 10 is a pumping wave drive system, 1
1 is a measurement wave drive circuit, which is a clock control system 18.
For example, a 3.5MHz sine wave is generated in synchronization with the pumping wave oscillator 21 under the control of the transmitter 4A.
12 is a variable phase shift circuit that adjusts the phase so that the indicated output R takes the maximum value and the indicated output I becomes zero when no pumping wave output is present; 13, 14 are respectively multiplier quadrature detectors, 15 is an approximately 90° phase shifter, 16, 17
18 is a clock controller that performs clock and time control of the entire system, and 19 is a computer that calculates the above-mentioned phase shift amount Δφ based on the above outputs R and I. ²⁰ represents the output result.

Further, 21 is a pumping wave original frequency f generator, and 22 is an amplifier, which is a pumping wave generator 6.
It represents what drives the. The generator 21 generates a sine wave signal of f=1.6 MHz, for example, and synchronizes with the clock of the clock controller 18 in response to an instruction from the computer 19.
Frequency signals (pumping waves) of f/2, f/4, . . . are generated.

In the case shown, as explained with reference to FIG.
Measured values are applied to the medium 1 under pumping wave conditions and received at the receiver 4B. The illustrated outputs R and I correspond to the real component and the imaginary component in the received wave, and the computer 19 outputs the
The phase shift amount Δφ〓 _e corresponding to Equation (4) can be obtained according to Equation (6). Then, the computer 19 performs Fourier transform on the deviation amount Δφ based on these results, thereby making it possible to obtain the distribution of the nonlinear parameter B/A on the desired scanning line 4C.

That is, equation (4) is, as mentioned above, From equation (3), 1/λe=f _p (1-cos θ)/C ₀ . Therefore Also, if we set t=1−cosθ/C ₀・z, Δφ(ω _p , y)=K∫[B/A](y, t)e ^j 〓 ^pt dt−
(8) becomes. Note that Δφ(y) in equation (7) is the frequency f _p
Since it is also a function of Δφ in equation (8),
It is expressed as (ω _p , y).

Generally, as mentioned above, the formula obtained by Fourier transform of the function f(t) is F(ω)=∫f(t)e ^-j 〓 ^t dt−(9), and the formula obtained by inverse Fourier transform of equation (9) is f(t)=1/2π∫F(ω)e ^j 〓 ^t・dω −(10).

From this, in equation (8), if we consider [B/A] _(y , _t) → F (ω) t → ω dt → dω Δφ (ω _p , y) → f (t), then the (8th ) formula corresponds to formula (10), and as a formula corresponding to formula (9), [B/A] _(y , _t) = K′∫Δφ(ω _p , y) e ^-j 〓 ^pt dω _p
−(11) is derived from equation (8).

Equation (11) corresponds to obtaining the nonlinear parameter distribution [B/A] _(y , _t) by performing Fourier transformation with the phase shift amount Δφ (ω _p , y). That is, the computer 19 measures the phase shift Δφ (ω _p , y) by changing the pump wave frequency f _p [=ω _p /2π], and calculates the parameter distribution according to equation (11). obtain.

FIG. 6 shows another embodiment of the present invention, in which a two-dimensional and/or three-dimensional distribution of the nonlinear parameter B/A on the medium 1 is obtained. Codes 1, 4A, 4B, 4 in the diagram
C, 6, 8, 9, and 10 correspond to FIG. Further, 22 is a transmitter/receiver mounting member that can move the transmitter/receiver together in a predetermined positional relationship, 23 is a motor that drives the transmitter/receiver mounting member, and 24 is a scan control system. 25 is an image memory which indicates the position of the scanning line by ultrasonic waves, and 25 is an image memory which stores the distribution result of the nonlinear parameter B/A for each scanning line position obtained from the measurement system and displays the result of the distribution of the nonlinear parameter B/A for each scanning line position. 26 represents a display device.

(E) Effects of the Invention As explained above, according to the present invention, the phase shift amount Δφ obtained in the form as shown in equation (4) is obtained by sweeping the frequency of the pumping wave, and is calculated by Fourier transform processing. Therefore, the spatial distribution of the nonlinear parameter B/A or its related quantity can be extracted.

[Brief explanation of drawings]

Figures 1 to 3 are explanatory diagrams for explaining the prerequisite problems of the present invention, Figure 4 is an explanatory diagram for explaining the principle of the present invention, Figure 5 is an embodiment of the configuration of the present invention, and Figure 6 is an illustration of the present invention. Another embodiment of the invention will be shown. In the figure, 1 is an ultrasonic medium (or living body), 4A is a measurement wave transmitter, 4B is a measurement wave receiver, 4C is a scanning line (or propagation path), 6 is a pumping wave generator, 8 is a liquid tank, 9 is the measurement system, 10 is the pumping wave drive system, 2
4 represents a scan control system, and 26 represents a display device.

Claims (1)

[Scope of Claims] 1. An ultrasonic device that applies ultrasonic sound pressure to an ultrasonic medium and measures the spatial distribution in the ultrasonic medium of a nonlinear constant of a physical constant or its related quantity with respect to the ultrasonic sound pressure. In the sonic diagnostic processing method,
A relatively low-frequency pumping wave is supplied to the medium to generate pressure within the medium, and a relatively high-frequency measurement wave is applied to the medium in a direction crossing the traveling direction of the pumping wave. and means for changing the frequency of the pumping wave, the receiving phase of the measuring wave when the pumping wave is not present and the receiving phase of the measuring wave when the pumping wave is present. The amount of phase deviation between the pumping wave and By treating the above phase shift as a spatial frequency component whose wavelength is the effective wavelength on the measurement wave scanning line, the nonlinear constant or its relation on the measurement wave scanning line in the medium can be determined. An ultrasonic diagnostic processing method characterized by measuring the distribution of quantity. 2. The device is configured such that the scanning line position of the measurement wave can be changed, and measures the two-dimensional and/or three-dimensional spatial distribution of the nonlinear constant or its related quantity within the ultrasonic medium. An ultrasonic diagnostic processing method according to claim 1.