JPH0421493B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reflection type nonlinear parameter distribution measuring device, which transmits an ultrasonic burst wave for measurement and an ultrasonic continuous wave plane wave for pumping so as to intersect within an ultrasonic medium. , the amount of change in the equivalent nonlinear parameter of the intersection area is detected from a specific frequency component of the ultrasonic burst wave reflected from the intersection area, and the distribution of this nonlinear parameter is displayed two-dimensionally or three-dimensionally. Regarding the apparatus for obtaining.

Conventional ultrasonic diagnostic equipment using reflection echo methods can provide information about changes in acoustic impedance within living tissues, in other words the contours of tissues such as the liver, but they cannot provide information on the nature of the tissue, such as whether it is a normal liver or whether it has been invaded by a malignant tumor. It was difficult to distinguish whether the liver had been treated or not. Tissue characteristic discrimination is a method that attempts to identify the properties of such tissues.
For example, since the nonlinear parameters of ultrasound differ depending on the nature of the tissue, a method has been devised to identify the nature of the tissue by measuring these nonlinear parameters (Japanese Patent Application No. 58-39907 issue).

However, conventional nonlinear parameter measurement devices
There is a transmission type, but the transmission type requires a transmitting probe and a receiving probe to face each other with their beam axes aligned. It has the disadvantage of being limited by voids and refraction within the tissue.

An object of the present invention is to use an ultrasonic burst wave for measurement and a continuous ultrasonic wave for pumping, and to make the pumping wave close to a plane wave that covers the area to be observed and intersects the burst wave for measurement. A nonlinear parameter distribution of the ultrasonic medium that can be configured, observe the nonlinear effect on the reflection of the measurement burst wave by the pumping wave, and obtain the distribution of the amount of change in the equivalent nonlinear parameter (B/A) _e of the observed region. To provide measuring equipment.

The present invention utilizes a measuring ultrasonic burst wave and a pumping ultrasonic continuous wave that intersect in an ultrasonic medium, and separates and measures a specific frequency component of the ultrasonic burst wave reflected from the intersecting region. By this, the amount of change in the equivalent nonlinear parameter of the intersection area is detected, and by further moving this intersection area and repeating the measurement, it is possible to display the distribution of the nonlinear parameter two-dimensionally or three-dimensionally. It is something.

The speed of sound when the sound pressure in the ultrasonic medium is zero is C ₀ ,
If the density is ρ ₀ , the sound speed C when a sound pressure P is applied from the direction perpendicular to the measurement wave is C=C ₀ +1/2ρ ₀ C ₀ (B/A) _e P...(1) Here (B/A) _e is defined by the following equation and is called an "equivalent nonlinear parameter" and takes different values depending on the location in a non-uniform medium. Note that the letter e at the bottom right of the katsuko means equivalent.

(B/A) _e = 2ρ ₀ C ₀ (∂Ci/∂Pj) _s ...(2) i and j are orthogonal directions, and S indicates isentropy.

On the other hand, the nonlinear parameter B/A, which is generally used in the field of acoustics, is defined as follows.

B/A=2ρ ₀ C ₀ (∂Ci/∂Ci) _s ...(3) If it is an isotropic body, Poisson's ratio is ν and (B/A) between _e and B/A is (B/ A) _e = (1+2ν-1/1-ν B/A)...(
4) There is a relationship, ν≒0.5 in liquids and biological tissues.
Therefore, it can be regarded as (B/A) _e B/A.

Therefore, due to the sound pressure P of the pumping wave, the sound speed C
will change by △C=1/2ρ ₀ C ₀ (B/A)・P...(5).

Figure 1 shows the principle of measuring nonlinear parameters using the reflection method. Xs and Xp are probes that emit measurement burst waves and pumping continuous waves, respectively;
M indicates an ultrasonic medium. Generally, the reflection coefficient r ₀ of an ultrasound wave at a discontinuous surface of density and sound velocity of an ultrasound medium M such as a biological soft tissue is given by the following equation.

r ₀ = ρ ₁ C ₁ − _{ρ 2} C ₂ / ρ ₁ C ₁ + ρ ₂ C ₂ ...(6) However, ρi and Ci (i=1, 2) are the tissue density and sound speed in region i, respectively. .

Now, suppose that this discontinuous surface is irradiated with a pumping ultrasonic continuous wave (pump wave), and a sound pressure change as shown in the following equation is given inside the tissue.

△P=△P ₀ e ^j 〓 ^pt ……(7) However, ωp and △P ₀ are the frequency of the pump wave, respectively,
It is the sound pressure amplitude. Due to this sound pressure change, area 1,
The sound speed of 2 changes and can be expressed as follows from equation (5) using the nonlinear parameters (B/A) ₁ and (B/A) ₂ in each region.

C ₁ = C ₁₀ + (B/A) ₁ /2ρ ₁ C ₁₀ △P C ₂ = C ₂₀ + (B/A) ₂ /2ρ ₂ C ₂₀ △P ...(8) However, C ₁₀ and C ₂₀ are This is the speed of sound before the sound pressure changes due to pump waves.

Here, the sound pressure of the measurement burst wave is sufficiently small compared to the sound pressure of the pump wave, and the influence of nonlinear parameters brought into the ultrasonic medium is only caused by the pump wave.

Therefore, using equations (6) and (8) to find the reflection coefficient r (△P) when the sound pressure change △P is added, we get r (△P) r ₁₀ + ρ ₁ k ₁ − ρ ₂ k ₂ /ρ ₁ C ₁₀ +ρ ₂ C ₂₀ △
P...(9) becomes. However, k ₁ = (B/A) ₁ /2ρ ₁ C ₁₀ , k ₂ = (B/A) ₂ /2ρ ₂ C ₂₀ , r ₁₀ = ρ ₁ C ₁₀ −ρ ₂ C ₂₀ /
ρ ₁ C ₁₀ +ρ ₂ C ₂₀ and k ₁ , k ₂ <<1.

Furthermore, in biological soft tissue, changes in density and sound speed are small, so if the average density and sound speed inside the tissue are ρ ₀ and ₀ , equation (9) is r(△P) r ₀ + (B/A) ₁ −(B/A) ₂ /4ρ ₀ C ₀ ² △P……(1
0).

Therefore, if we inject an ultrasonic burst wave A with a frequency ωs that continues over a finite time width into the tissue and measure the reflected burst wave from this discontinuous surface, the received signal A' will be A'∝r(△ P)・A ……(11) is given by. However, if A = A ₀ e ^j 〓 ^st and A ₀ is the sound pressure amplitude, then equation (11) becomes A'∝A ₀ {r ₀ e ^j 〓 ^st + (B/A) ₁ − (B/
A) ₂ /4ρ ₀ C ₀ ² △P ₀ e ^j( 〓 ^s+ 〓 ^p)t }...(12).

In this received signal A′, the component of frequency ωs is r ₀ ,
The frequency (ωs+ωp) component is proportional to (B/A) ₁ −(B/A) ₂ /4ρ ₀ C ₀ ² ΔP ₀ .

That is, the spectrum of this reflected signal A' is shown in FIG. 2.

That is, if we take the bandpass filter output around the frequency ωs for the received signal A', we can obtain information that corresponds to the information obtained in the conventional pulse echo method, and we can obtain the bandpass filter output around the frequency ωs + ωp. If we take the value, we can obtain the value corresponding to the amount of change in the nonlinear parameter. When this measurement is performed on one plane, an image corresponding to a conventional B-mode tomographic image and an image corresponding to the distribution of nonlinear parameters are obtained.

Next, the configuration of the entire device is shown in FIG. 3, and the timing chart of signal processing is shown in FIG. 4. The system controller 1 issues a command to the trigger generator 2 to generate a trigger pulse. In response to the trigger pulse, a burst wave is output from the burst wave amplifier 3 and applied to the transmission probe 4. It also causes the delay circuit 6 to specify a delay width and controls the processing of the time gate circuit 7 on the signal received by the receiving probe 5.
This time gate is set so that only the reflected burst wave from the region where the signal wave burst wave intersects with the pump wave passes through. Furthermore, the system controller specifies the intersection area of the pump wave and signal wave and sends a command to the beam controller 8 to move.
The signal that has passed through the time gate is passed through a bandpass filter 9 that transmits the signal at a frequency near ωs or ωs+ωp, and is separated by circuits 10 and 11 into signals corresponding to changes in the tissue reflection coefficient and nonlinear parameters, respectively. After storing this signal in the image memory 12 and further storing signals for one screen, a B-mode image or a nonlinear parameter distribution image is displayed on the displays 14 and 15 under the control of the display control section 13 according to instructions from the system controller. It is now displayed as follows.

Note that 16 is a pump wave probe.

The measurement point can be scanned one-dimensionally along the measurement beam by changing the amount of time gate spread, and scanning in the direction perpendicular to the beam direction can be done using the transmitting/receiving probes 4 and 5. This can easily be achieved by using a linear array type probe or a sector scan type probe. Alternatively, by narrowing down both the measurement beam and the pump wave, fixing the positional relationship between both probes, and then moving the entire pair of probes two-dimensionally, the intersection point of both beams can be adjusted. It is also possible to scan two-dimensionally.

Since the measurement ultrasonic burst wave has a finite duration, the measurement results in a degraded spatial resolution. In order to avoid this, as shown in FIG. 5, a pump wave narrowed as narrow as possible is used, and the burst wave is arranged so as to be orthogonal to the pump wave, so that the crossing area is made small. This improves the deterioration of spatial resolution. However, the symbols in the figure are the same as those in FIG. Of course, narrowing down the pump wave deviates from the assumption that the pump wave is a plane wave, and the sound pressure distribution changes with distance on the pump wave beam axis. Therefore, there is no problem if the sound pressure distribution of the pump wave is measured in advance and the sound pressure of the pump wave is corrected based on the position of the intersection area of the measurement burst wave and the pump wave.

According to the present invention, a distribution image of nonlinear parameters of an ultrasound medium such as a living tissue can be displayed, so that features that cannot be seen in conventional B-mode images can be found.
Furthermore, since it is a reflection type image system, it is easy to handle and can also display conventional B-mode images.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of reflection type nonlinear parameter measurement, Fig. 2 is a diagram showing the spectrum of the received signal A', Fig. 3 is a diagram showing the entire configuration of an embodiment of the device, and Fig. 4 is a diagram showing the signal This is a timing chart of processing. FIG. 5 is a diagram showing reflection type nonlinear parameter measurement when the pumping ultrasonic continuous wave is narrowed down. In FIG. 3, 4 and 5 are transmitting and receiving probes, 16 is a pump wave probe, 9 is a bandpass filter, 10 is a circuit for determining a reflection coefficient, and 11 is a circuit for determining nonlinear parameters.

Claims (1)

[Claims] 1. (a) A dual-purpose or individual ultrasonic probe that transmits and receives ultrasonic burst waves for measurement into an ultrasonic medium; (b) A pumping probe. an ultrasonic probe that transmits a plane wave of a continuous ultrasonic wave; (c) an arrangement in which the measurement ultrasonic burst wave and the pumping ultrasonic continuous wave intersect within the ultrasonic medium; In this arrangement, only a specific frequency component of the reflected ultrasonic burst wave received by the measuring ultrasonic probe from a specific location on the intersection area is extracted, and (e) means for shifting the intersection region or the specific location on the intersection region to obtain a distribution of the variation in the nonlinear parameter; Reflection type nonlinear parameter distribution measuring device for acoustic wave media.