JPH074370B2 - Method and apparatus for inspecting an object using ultrasound - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a method and apparatus for inspecting an object using ultrasonic waves.

2. Description of the Related Art Conventionally, as a method and apparatus for inspecting an object using an ultrasonic wave, a method based on a so-called linear approximation, which assumes that the amplitude of the ultrasonic wave is infinitely small, has been the mainstream. For example, an ultrasonic diagnostic apparatus using the pulse echo method used in the field of medicine is to inject an ultrasonic wave into the body of a subject, receive the reflected wave, and obtain a spatial distribution of the reflected intensity. But,
There, it is based on the assumption that the fluctuation of the medium itself due to the wave is sufficiently small and that the waveform does not change with the propagation, a so-called linear wave equation. Therefore, according to this pulse-echo method, the obtained information basically relates to the discontinuity of the medium, and although it is possible to visualize the geometrical shape of internal tissues,
No information about the characteristics of the medium can be obtained.

Problems to be Solved by the Invention By the way, among water, which is the main component of biological soft tissues, it is called free water having a random molecular arrangement like ordinary liquid and bound water having a structure like ice. Of water, 2
Contains a variety of water. In the living body, bound water generally has a function of binding to protein molecules that compose tissues and protecting them from stimuli such as pressure and heat, while free water has a function of freely contributing to chemical reactions. Is considered to have. Therefore, the latter is often contained in malignant tumors that are actively growing, and there is a large correlation between the composition ratio of these two types of water and the malignant tumor. This has been clarified by recent research on imaging (MRI) using nuclear magnetic resonance (NMR), and in fact, it can be obtained by utilizing the large difference in spin relaxation time of these two types of water. Diagnosis of malignant tumors is actively made based on the images obtained.

In general, when a wave is applied to a medium, not only linearly propagating in the medium but also the characteristics of the medium are affected, which reversely reflects back to the form of the wave. It is considered that the properties of the medium are reflected in what is seen as a higher-order or non-linear relation between the ultrasonic wave and the medium, and important information about the properties of the medium is included. That is, if such a non-linear relationship can be captured, it can be expected to obtain important information in medical diagnosis such as the composition ratio of the above-mentioned two kinds of water. Nevertheless, in the past, in general, since the effects of such non-linear relations are small and complicated, highly sensitive and sophisticated detection and analysis are required. It can be said that he was trying to ignore it.

On the other hand, taking this non-linear effect into consideration, we have attempted to obtain more important and useful information on the characteristics of biological tissues for medical diagnosis by making more effective and comprehensive use of the information that waves have. Taku Song Sato "Recent few applications of non-linear effects in measurement form using waves" Precision Machinery Vol.49 No.9, 1983, Taku Song Sato, Nobuyuki Ichida "Ultrasonic Nonlinear Parameter Imaging and Its Application "Applied Physics No. 54
Volume No. 10, 1985, JP-A-59-55245, JP-A-59-164
956, JP-A-60-10165, JP-A-60-60837, JP-A-60-119926, JP-A-60-253434, JP-A-59-226841). These are basically to obtain information about the characteristics of the medium by capturing the change in the waveform (nonlinear effect) that the ultrasonic wave undergoes as it propagates through the medium. Among the above-mentioned attempts, there is a reflection type, but even in that case, it is attempted to measure the nonlinear effect received from the emission point to the reflection point during the round trip from the reflection point to the receiving point.

This invention aims to capture the nonlinear effect in the same way as the above-mentioned precedent, but it is not in the direction of capturing the change in the waveform that an ultrasonic wave undergoes while propagating in a medium, but the nonlinearity of scattering itself. It is an object of the present invention to provide a method and an apparatus for inspecting an object by measuring the nonlinearity of the ultrasonic scattering, in order to focus on such properties.

Means for Solving the Problems In the object inspection method of the present invention, an ultrasonic wave is incident on an object, a scattered wave generated inside is received, and the nonlinear dependence of the scattered wave amplitude on the incident wave amplitude is detected. It is characterized by

Further, the object inspection apparatus of the present invention is such that the first wave transmitter for transmitting a probe wave of relatively low sound pressure and high frequency in a burst form and the pump wave of relatively high sound pressure and low frequency are continuously provided. A second transmitter for transmitting a wave, a receiver for receiving a scattered wave of the probe wave, and an envelope of a scattered wave signal obtained from the receiver when the pump wave is turned on and off. And a signal processing device that obtains the amount of change in time, and inspects the object from the degree of variation in the amount of change.

Furthermore, the object inspection device of the present invention has a relatively low sound pressure
A first transmitter for transmitting a high frequency probe wave in a burst form, a second transmitter for continuously transmitting a relatively high sound pressure / low frequency pump wave, and scattering of the probe wave A wave receiver for receiving a wave, a signal processing device for obtaining a change amount of the envelope of a scattered wave signal obtained from the wave receiver when the pump wave is turned on and when the pump wave is turned off, and the change amount And a device for visualizing a distribution regarding non-linearity of scattering in the incident direction of the probe wave displayed with respect to the axis.

It was conventionally thought that the amplitude of scattered waves of action ultrasonic waves is proportional to the amplitude of the incident wave, but it was experimentally found that there is a nonlinear dependence on the amplitude of the incident wave depending on the object (scatterer). I was able to confirm.

As a mechanism for explaining the non-linearity of the scattering, position variation (perturbation) of each scatterer (each minute scatterer inside an object having a fine structure) due to ultrasonic sound pressure is considered.

Therefore, if the non-linear dependence (variation degree) of the scattered wave amplitude on the incident wave amplitude is measured, conversely, information on the difference in the fine structure of the scatterer, that is, the characteristics of the object itself can be obtained.

In addition, it receives the scattered wave when a relatively low sound pressure / high frequency probe wave is transmitted in bursts, and the scattered wave when the high sound pressure / low frequency continuous pump wave is turned on and off. When the change amount of the signal envelope is obtained, this shows the nonlinear dependence of the scattered wave amplitude on the incident wave amplitude.

Furthermore, when the amount of change in the envelope of the scattered wave signal of the probe wave when the pump wave is turned on and off is displayed with respect to the time axis, the distribution regarding the nonlinearity of scattering in the probe wave incident direction is visualized.

Example First, as a first example, a measurement system as shown in FIG. 1 is constructed. Ultrasonic transducer 1 at a distance of 5 cm with respect to the scatterer 11
2 is placed so that the scattered wave scattered in the direction of 45 degrees is received by the broadband hydrophone 13 placed at a position separated by 5 cm. These are placed in the aquarium 18. Scatterer 11
For this, several kinds of sponges and chicken are used, and in the case of sponges, they are soaked in water and deaerated beforehand. The ultrasonic oscillator 12 is driven by an amplifier 15 that amplifies the output of the oscillator 14 that oscillates at a frequency of 500 KHz. The oscillator 14 is controlled by a computer 17 and its amplitude is changed. Thereby, the sound pressure transmitted from the ultrasonic transducer 12 can be changed. The received signal from the hydrophone 13 is input to the computer 17 through the 8-bit digital memory 16 having a dynamic range of 48 dB in this embodiment.

Using this measurement system, a relatively soft scatterer 11, a sponge with a small average scatterer spacing is placed, and a continuous wave with a center frequency of 500 KHz is transmitted from the ultrasonic oscillator 12, and the transmitted sound pressure is 0.015 to 0.3. Change to atm sequentially. The size of this sponge is 3 cm wide and 2 cm thick. The signal received by the hydrophone 13 for each transmitted sound pressure is calculated by the computer 17
The spectrum analysis is performed in order to extract only the fundamental wave component and detect the magnitude of its amplitude. The non-linearity of the electric system such as the oscillator 14 and the amplifier 15 and the non-linear effect due to the propagation of ultrasonic waves in water were corrected by the data measured in advance with the ultrasonic transducer 12 and the hydrophone 13 facing each other. This measurement was carried out a plurality of times by changing the position where the ultrasonic wave hits, and data on the transmitted sound pressure dependence of the fundamental wave component of the scattered wave was obtained as shown in FIGS. 2 (a) to (d). In the figure, the dotted line is a straight line extrapolated based on the data with the minute sound pressure. From this figure, it can be seen that the fundamental wave component of the scattered wave can be regarded as linear with respect to the sound pressure at a small sound pressure, but exhibits a non-linear behavior with respect to the sound pressure at a high sound pressure and deviates from a straight line. Moreover, the deviation from the straight line at the high sound pressure portion is scattered up and down, and is not reproducible even though the scatterer is the same when the position where the ultrasonic wave hits is changed. In addition, the magnitude of the harmonic component measured at the same time is 2
The maximum of the next harmonic is about −40 dB, and the third harmonic is −50 dB or less, which is almost the same value as when the ultrasonic transducer 12 and the hydrophone 13 are opposed to each other at a distance of 10 cm in water. .

From these results, it can be seen that this scattering has one non-linear effect in which the scattered wave amplitude is non-linearly dependent on the transmitted sound pressure in the high sound pressure portion, although the generation of harmonics is hardly accompanied. In addition, even a scatterer that can be regarded as uniform macroscopically does not generally have reproducibility when the position is changed.Therefore, as a characteristic quantity that characterizes this nonlinear effect, a statistical standard such as a standard deviation of variation in a high sound pressure portion is used. You need to choose the amount. In other words, it is possible to identify different types of scatterers by appropriately selecting such characteristic amount.

Therefore, the following parameter Vs is considered as a measure of the degree of non-linearity of scattering for quantitatively measuring and evaluating the non-linearity of scattering. As shown in Fig. 3, the scattered wave amplitude when the scatterer is irradiated with a continuous wave of low sound pressure P1
At As1, the scattered wave amplitude is A when a continuous wave with high sound pressure P2 is applied.
If it is s2, then the deviation from the linear relationship is
As2-As2L. As2L = (P2 / P1) As1. The parameter Vs is defined as Vs = (As2-As2L) / As2L x 100 (%).

This parameter Vs is measured for each scatterer sample. As the scatterer samples, five kinds of samples such as a sponge having a relatively small average scatterer gap, a sponge having a relatively large mean scatterer gap, pork shoulder meat, and chicken were used. P
Vs was measured by selecting 0.075 atm and 0.3 atm as 1 and P2, respectively. The results are shown in FIGS. 4 (a) to 4 (e). From these, it can be seen that the degree of Vs variation depends on the characteristics of each sample.

One possible mechanism for producing such an effect is perturbation of minute positions of the scatterer due to incident sound pressure. By the way, we calculated the change in the scattered wave amplitude after the movement, assuming that a large number of reflection points with minute reflectance of the scatterer were arranged randomly and the reflection points were moved randomly due to external force. The results correspond to the experimental results. It is assumed that the frequency is 500 KHz, the thickness of the scatterer is 2 cm, the reflector is a random scatterer according to Poisson distribution, and the average reflector interval is 0.5 mm. Also, the reflectance of the reflector follows the Rayleigh distribution, and its average reflectance is
It was set to 0.06.

Next, a second embodiment for visualizing the above non-linear effect of scattering will be described. As schematically shown in FIG. 5, the scatterer 21 is irradiated with a probe wave from the ultrasonic oscillator 22 and a pump wave from the ultrasonic oscillator 23, and a reflected wave is received by a wave receiver 24. The pump wave is used to give vibrations to the scatterer 21, low frequency (about 500 KHz), high sound pressure,
It is a continuous ultrasonic wave, and the probe wave is a high-frequency wave (3.5%) for observing the perturbation caused by this pump wave.
~ 5MHz), low sound pressure, burst ultrasonic waves. The ultrasonic transducer 22 is driven by a driving device 25, and this driving device
25 is controlled by a computer 33 to generate burst ultrasonic waves. The ultrasonic transducer 23 is driven by a driving device 26 through a gate 27, and the gate 27 is a computer 33.
The continuous wave from the ultrasonic transducer 23 is turned on or off. The signal from the wave receiver 24 passes through a preamplifier 28 and is a bandpass filter whose center frequency is the probe wave.
29 to the envelope detection circuit 30. The output of the envelope detection circuit 30 is sent to the storage and subtraction circuit 31, and its output is sent to the monitor 32.

In this embodiment, as shown in FIG.
2, 23 and the receiver 24 are separated by 10 cm from the scatterer 21, and 35
They were placed in a water tank 61 at an angle of degrees. When the ultrasonic transducer 22 emits a burst-like probe wave of 10 wavelengths of 5 MHz and 0.06 atm, and the continuous wave pump wave of 500 KHz and 0.3 atm from the ultrasonic transducer 23 is turned on and off. The envelopes Eon and Eoff of the scattered wave received for each of the Here, in order to extract only the frequency component of the probe wave from the received signal, the preamplifier 28
The latter filter 29 attenuates the frequency of 500 KHz by -60 dB with respect to 5 MHz.

Eoff is the envelope of the scattered wave when each minute scatterer inside the scatterer 21 is not perturbed by the strong pump wave, and this is expected from the scattered wave amplitude at the minute sound pressure described above. It corresponds to the scattered wave amplitude As2L at high sound pressure. On the other hand, Eon is the envelope of the scattered wave when it is perturbed by the pump wave, and therefore corresponds to the scattered wave amplitude As2 when the high sound pressure is applied to the scatterer. Therefore, if this difference, that is, the rate of change in pump wave scattered wave amplitude ΔE ΔE = (Eon−Eoff) / Eoff × 100 (%) is obtained, this parameter ΔE is a parameter Vs that represents the nonlinearity of the scattering previously obtained. Similarly, it can be considered to indicate the susceptibility to perturbation by an external force called a pump wave.

The result of using a soft sponge as the scatterer 21 is the 7th.
The results using the hard sponge are shown in FIG. In each of these figures, (a) is Eon, Eoff,
(B) shows ΔE. From FIG. 7, in the case of a relatively soft sponge, the variation of the scattered wave amplitude caused by the pump wave is not uniform, and the value of ΔE is −50% to +150.
You can see that it varies about%. In the case of a relatively hard sponge, it can be seen from FIG. 8 that ΔE varies positively and negatively, but the degree of variation is considerably smaller than that of a soft sponge, about ± 20%. From these results, it can be seen that the two types of sponges differ in the susceptibility of the minute scatterer to perturbation due to the external force of the pump wave, that is, the soft sponge is more susceptible to perturbation. is there.

Then, when two sponges having different characteristics were piled up front and back and the same experiment was performed, the results shown in FIG. 9 were obtained. In this figure, (a) shows Eon and Eoff,
(B) shows ΔE. Here, the soft sponge is located on the side facing the ultrasonic transducers 22, 23 and the wave receiver 24, and the hard sponge is located on the opposite side. As shown in FIG. 9 (b), when the end of the received signal is time 0, about 15 μm at Sakai, −35% to + 50%, the first half of which ΔE is relatively large and ± 20%. It can be seen that it can be divided into the latter half of which the degree of variation is relatively small. Converting the time point of 15 μm, which is the boundary, into a distance, the distance is about 10.5 mm from the front surface of the scatterer. This is in good agreement with the boundary of the two sponges.
Therefore, if ΔE is displayed with respect to the time axis, it is possible to visualize the difference in the characteristic of the susceptibility to perturbation in the depth direction (viewed from the ultrasonic wave incident side).

Figure 10 shows the results of an experiment using chicken breast meat as a scatterer sample. From FIG. 10 (b), it can be seen that the variation degree of ΔE is different from that of the sponge.

In addition, as a more direct expression of the magnitude of the variation of ΔE that is a function of the time T, a certain section (T−
It is also possible to obtain the standard deviation of ΔE in (1 / 2ΔT, T + 1 / 2ΔT) and use this as the characteristic amount for imaging.

Furthermore, the non-linearity of scattering reaches a steady state some time after the pump wave is transmitted, but the time taken until that time depends on the characteristics of each scatterer, and the transient and steady state It is considered that the non-linearity of the scattering in each is also due to the scatterer. Therefore, useful data can be obtained by measurement performed at various points such as a transitional state after the start of pump wave transmission or a steady state.

Although FIG. 5 showing the second embodiment is schematically represented,
The ultrasonic transducer 22 for the probe wave and the wave receiver 24 may be configured by an array transducer of a normal echo scanning device. That is, in this case, the structure is such that an ultrasonic wave transmitter for giving a perturbation is added to the normal echo scanning device. Then, a two-dimensional image can be displayed by scanning the ultrasonic beam in the same manner as a normal echo scanning device.

EFFECTS OF THE INVENTION According to the object inspection method / apparatus of the present invention, it is possible to capture the characteristics of the object itself, which are not detected by ultrasonic waves and which are manifested as non-linearity of scattering, and thus visualization is possible. . Therefore, it is expected to be useful in the diagnosis of cancer, malignant tumor, etc., particularly in the field of medicine.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the first embodiment, and FIGS. 2 (a) to (d).
Fig. 3 is a graph showing the measurement result of the transmitted sound pressure dependence of the fundamental wave component of the scattered wave when a soft sponge is used as the scatterer. Fig. 3 shows the relationship between the transmitted sound pressure and the scattered wave amplitude for explaining the parameter Vs. 4A to 4E are graphs showing the measurement results of variations in Vs values for each sample used as scatterers, FIG. 5 is a schematic diagram of the second embodiment, and FIG. Is a schematic diagram showing the arrangement during the experiment, and FIGS. 7 to 10 are graphs showing the measurement results for each sample. In each of these diagrams, (a) shows envelopes Eon and Eoff, and (b) shows ΔE.
Are shown respectively. 11,21 …… Scatterer, 12,22,23 …… Ultrasonic transducer 13 …… Hydrophone, 14 …… Oscillator 15 …… Amplifier, 16 …… Digital memory 17,33 …… Computer, 18,61… … Water tank 25,26 …… Drive device, 27 …… Gate 28 …… Preamplifier, 29 …… Filter 30 …… Envelope detection circuit 31 …… Memory and subtraction circuit 32 …… Monitor

Claims (4)

[Claims] 1. A method of inspecting an object by injecting an ultrasonic wave into an object, receiving a scattered wave generated inside, and capturing the nonlinear dependence of the amplitude of the scattered wave on the amplitude of the incident wave. 2. The method for inspecting an object according to claim 1, wherein the substance is a scatterer having a fine structure. 3. A first wave transmitter for continuously transmitting a pump wave having a relatively high sound pressure and a low frequency, and a probe wave having a relatively low sound pressure and a high frequency after a lapse of a predetermined time from the start of the wave transmission. Second transmitter for transmitting the pulse wave in the form of a burst, a receiver for receiving the scattered wave of the probe wave, and the pump wave of the envelope of the scattered wave signal obtained from the receiver is turned on. An apparatus for inspecting an object from the degree of variation in the change amount, which has a signal processing device for obtaining the change amount between the time and the off state. 4. A first wave transmitter for continuously transmitting a pump wave having a relatively high sound pressure and a low frequency, and a probe wave having a relatively low sound pressure and a high frequency after a lapse of a predetermined time from the start of the wave transmission. Second transmitter for transmitting the pulse wave in the form of a burst, a receiver for receiving the scattered wave of the probe wave, and the pump wave of the envelope of the scattered wave signal obtained from the receiver is turned on. An object inspection apparatus, comprising: a signal processing apparatus that obtains a change amount between time and off; and a device that displays the change amount with respect to a time axis and visualizes a distribution regarding nonlinearity of scattering in a probe wave incident direction.