JPS6060837A - Reflective type non-linear parameter distribution apparatus of ultrasonic medium - 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 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 (T i
s s u eCharacterization)
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).

However, although there are conventional nonlinear parameter measurement devices of the transmission type, the transmission type requires the transmitting probe and the receiving probe to face each other with their beam axes aligned, and It has the disadvantage that it is affected by sound waves due to gaps in bones, body cavities, and refraction within tissues, which are difficult for sound waves to pass through.

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. The object of the present invention is to provide a nonlinear parameter distribution measuring device for an ultrasonic medium, which is configured and capable of observing the nonlinear effect on the reflection of a measuring burst wave by a pumping wave, and is capable of measuring the nonlinear parameter distribution of each observed part.

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 ultrasound medium is zero is co.

When the density is ρ0, the sound speed C when a sound pressure P is applied from a direction perpendicular to the measurement wave is called a parameter, and in a non-uniform medium, it takes a different value depending on the location. Note that the letter e at the bottom right of the parentheses means equivalent.

i and j are orthogonal directions, and S indicates isentropy.

On the other hand, nonlinear parameters generally used in the field of acoustics are defined as follows.

There is a relationship between 1 and 1, and in liquids and living tissues, the sound pressure C changes by the following.

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 rQ of ultrasonic waves at a discontinuous surface of density and sound velocity of an ultrasonic medium M such as biological soft tissue is given by the following equation.

The density of the tissue and the speed of sound at

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.

However, ωp and △Po are the frequencies of the pump waves, respectively.

It is the sound pressure amplitude. Due to this change in sound pressure, the sound speed in region 1°2 changes, and the nonlinear parameter (B/A
) r and (B/A)2 from equation (5) as follows.

However, Oto and Cx are the sound speeds before the sound pressure changes due to the pump wave.

Here, the sound pressure of the burst wave for measurement was only that of the pump wave.

Therefore, using equations (6) and (8), calculate the reflection coefficient r (△P) when the sound pressure change △P is added. , 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 1 stone, then equation (9) is r (△P)... (10) becomes.

Therefore, if we inject an ultrasonic burst wave A with a frequency ω- 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)j
It is given by ωst. However, if A=Aoe and Ao is the sound pressure amplitude, equation (11) is (B / A) 7 (B / A) 24 ρOC
It becomes O.

In this received signal A', the frequency ωS component is To,
The frequency (ωS+ωp) component will be explained as an example. That is, the spectrum of this reflected signal A' is shown in FIG. 2.

That is, if we take the bandpass filter output near the frequency ωsN for the transfer 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 near the frequency ωS+ωp. If you take it,
A value corresponding to the amount of change in the nonlinear parameter is obtained.

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 apparatus 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 trigger pulses 1 to 1. Burst wave amplifier 3 in response to trigger pulse
A burst wave is output from the transmitting probe 4 and applied to the transmitting 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. No. 11 that has passed through the time gate is passed through a bandpass filter 9 that transmits it at a frequency near ωS or ωS+ωp, and is separated into signals corresponding to changes in tissue reflection coefficients and nonlinear parameters in circuits 10 and 11, 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 under the control of the display side control section 1.3 according to instructions from the system controller. It is scheduled to be displayed on 14.15.

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 delay of the time gate.
Further, scanning in a direction perpendicular to the beam direction is easily possible if the transmitting/receiving probe 4.5 is 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 of the measurement probes, and then moving the entire set of measurement probes two-dimensionally, the intersection point of both beams can be adjusted. 2
It is also possible to scan 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 diagram are
It is similar to the one shown in the figure. 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', and FIG. 3 is a diagram showing the entire configuration of an embodiment of the apparatus. FIG. 4 is a timing chart of signal processing. Further, FIG. 5 is a diagram showing reflection type nonlinear parameter measurement when the ultrasonic continuous wave for bombing is narrowed down. In Figure 3, 4.5 is a probe for transmitting and receiving waves. ] 6 is a pump wave probe, 9 is a pando pass filter, 1
0 is a circuit for calculating a reflection coefficient, and 11 is a circuit for calculating a nonlinear parameter. Figure 1 Hayabusa 2 Figure 't, 4 Figure 5

Claims (1)

[Claims] (a) Sending ultrasonic burst waves for measurement into an ultrasonic medium;
(b) an ultrasonic probe that transmits plane waves of continuous ultrasonic waves for pumping; and (c) ultrasonic waves for measurement. an arrangement in which the burst wave and the pumping ultrasonic continuous wave intersect in the ultrasonic medium; (d) a specific location on the intersecting region where the waves are received by the measurement ultrasonic probe in the arrangement; (b) a signal processing circuit that extracts only a specific frequency component of the reflected ultrasonic burst wave from the intersection area and calculates the amount of change in a nonlinear parameter at a specific location of the intersection area; A reflection type nonlinear parameter distribution measuring device for an ultrasonic medium, comprising means for shifting the specific location and measuring the distribution of the amount of change in the nonlinear parameter.