JPH021273B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for inspecting objects by ultrasonic echoes, and more particularly to improved ultrasonic echoes for obtaining more useful and quantitative information about the ultrasonic properties of objects to be inspected. This invention relates to a method and device for inspecting objects using echoes.

An overview of the conventional method and apparatus for inspecting objects using ultrasonic echoes is as follows.
In addition, as for the literature related to these conventional techniques, for example, Kanehara Publishing, published in 1972, ME Introduction Mizoza Volume 6
Pages 107 to 138, “Chapter 7 Clinical Applications of Ultrasound,” and Nikkan Kogyo Shimbun, 1978, Ultrasonic Technology Handbook (New Edition), pages 799 to 827, “Chapter 4.1.1.
"Diagnosis using pulses."

When an ultrasonic pulse is emitted from an ultrasonic probe into the inside of an object to be inspected (typically, the frequency is 1 to 30 MHz and the emission time is 1 to several microseconds), the ultrasonic beam with sharp directivity penetrates the inside of the object. It is transmitted almost in a straight line. At this time, if there is a discontinuous surface with acoustic characteristics inside the object, a portion of the ultrasound energy is reflected by the discontinuous surface, and this reflected pulse (echo) reaches the ultrasound probe and is detected and generated. converted into a signal. The time difference t from the emission of the ultrasonic pulse to the detection of the reflected pulse (echo) and the distance x from the ultrasonic probe to the acoustic property discontinuity in the object
and the sound velocity v, there is a relationship as shown in the following equation.

x=v·t/2 The pulses converted into electrical signals by the ultrasonic probe are amplified within the receiver and displayed on a display device such as a cathode ray tube. The following display methods have been put into practical use.

(1) A-mode method: Fix the ultrasonic probe,
Depth (x) is taken on one side of the orthogonal coordinate axes on the display, and echo amplitude is taken on the other side.

(2) M-mode method: The ultrasonic probe is fixed,
Time is plotted on one coordinate axis on the display device, distance in the depth direction is plotted on the other orthogonal coordinate axis, and the amplitude of the echo is displayed by the intensity of brightness.

(3) B-mode method: Move the ultrasonic probe, measure the distance in the depth direction on one side of the orthogonal coordinate axes on the display device, and measure the distance in the axial direction on the other, and adjust the amplitude of the echo by adjusting the intensity of the brightness. (ultrasonic tomography).

By the way, these conventionally used methods provide an accurate indication of the position of the acoustic characteristic discontinuity (if the speed of sound in the object to be inspected is approximately constant); Quantitative evaluation of characteristics using echo intensity is difficult. This means that the inspected object has different ultrasonic properties, for example the proportion of ultrasound energy that is reflected as an echo within tissue, differs not only in the ultrasonic properties at discontinuous surfaces, but also in its geometric shape and size as well as in the use This is due to the fact that it depends on the ultrasonic frequency and that it is difficult to accurately capture the attenuation of the ultrasonic pulse energy between the ultrasonic probe and the discontinuous surface of the ultrasonic characteristic.

The present invention aims to improve the drawbacks of the prior art as described above.

An object of the present invention is to obtain quantitative and more useful information regarding the distribution of ultrasonic characteristics of an object to be inspected by information processing the intensity and distribution of ultrasonic echoes obtained using a plurality of ultrasonic frequencies. is achieved by the method and apparatus described in the claims.

The present invention emits ultrasonic pulses of multiple frequencies into an object to be inspected, receives ultrasonic pulse echoes from an ultrasonic characteristic discontinuous surface within the object, and furthermore, emits ultrasonic pulses of each received frequency. This invention discloses a method for obtaining quantitative information regarding the ultrasonic characteristics of an object to be inspected by appropriately processing the echoes.

Furthermore, the present invention also discloses a suitable apparatus for carrying out the above method.

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

FIG. 1 shows a block diagram of the apparatus according to the present invention, in which an ultrasonic probe 2 is placed on an object 1 to be inspected.
Ultrasonic energy 7 is emitted from the object 1 to be examined, after which echoes from the object 1 to be examined are received by the same probe 2. A transceiver 3 whose operation is switched by a built-in gate circuit is connected to the ultrasonic probe 2. The ultrasonic echo information received by the receiving section of the transceiver 3 is appropriately transmitted to the information processing device 4, and is displayed or recorded by the display and recording device 5 as necessary.

The transceiver 3, information processing device 4, and display and recording device 5 that constitute these block diagrams can all be used by selectively combining well-known devices.

An example of an ultrasonic probe 2 suitable for carrying out the present invention will be disclosed below. However, the details of the acoustic lens and the like are well known and will therefore be omitted.

Referring to FIG. 2, a plurality of ultrasonic transducers 21 mounted on a support body 22 are rotatably disposed in a container 25 filled with an ultrasonic propagation medium 24 as shown by an arrow 23. Each ultrasonic transducer 21 emits and receives ultrasonic waves of a unique frequency f ₁ , f _{2 .} . . f _o . By rotating the support body 22 in the direction of the arrow 23 while operating the ultrasonic transducer 21, ultrasonic beams of each frequency f ₁ , f _{2 .} . . The distribution of echoes can be measured. An electric signal 6 for operating the ultrasonic probe 2 and a received signal ₆ ' are exchanged with the transmitter/receiver 3. The signal 8 in a form suitable for information processing is processed by an information processing device 4 such as a computer, and the processed signal 9 is further led to a display and recording device 5 for measurement, diagnosis, inspection, etc.

In the following embodiments as well, the same configuration is used except for the ultrasonic probe, so a description of that part will be omitted.

The ultrasonic probe 2 shown in FIG. 3 has a plurality of ultrasonic transducers 31 arranged in a straight line and moved in the direction of arrow 33, which is the direction of the arrangement. Thereby, it is possible to measure the echo distribution from the object to be inspected based on the unique frequency of the ultrasonic transducer 31.

The ultrasonic probe 2 in FIG. 4 uses an ultrasonic transducer that can be used in a wide band, such as a polyvinylidene difluoride (PVDF) piezoelectric film, and is capable of emitting and receiving multiple ultrasonic frequencies at a surface 41. . The ultrasonic echo distribution from the object to be inspected can be measured while the probe 2 is fixed or moved.

The ultrasonic probe 2 shown in FIG.
It is possible to receive ultrasonic waves with broadband frequencies. While rotating the probe 2 in the direction of arrow 53, it is possible to emit ultrasonic waves of multiple frequencies or continuous frequency bands and measure the distribution of ultrasonic echoes from the object to be inspected.

The ultrasonic probe 2 shown in FIG. 6 has a plurality of transducer groups 61 with different operating frequencies arranged on a support 62,
This is to move it in the direction of arrow 63. By electronically moving each vibration group 61 while sweeping it in a fan shape or a linear shape, it is possible to measure the distribution of ultrasonic echoes from the object to be inspected.

The ultrasonic probe 2 shown in FIG. 7 uses an ultrasonic transducer such as a PVDF piezoelectric film that can be used in a wide band, and is capable of receiving ultrasonic waves of a wide band and frequency. This probe 2
It is possible to emit ultrasonic waves of multiple frequencies or continuous frequency bands and measure the distribution of ultrasonic echoes from the object to be inspected by moving the probe while electronically sweeping it.

Note that when using the above-mentioned continuous frequencies, frequency analysis is performed using fast Fourier transform (FFT) or the like.

The principle by which quantitative information regarding the ultrasonic characteristics of an object to be inspected can be obtained by information processing the distribution of ultrasonic echo intensities collected by each of the embodiments described above will be disclosed below.

FIG. 8 shows the principle of the ultrasonic echo device. The ultrasonic pulses emitted from the ultrasonic probe 2 are reflected by the acoustic characteristic discontinuous surfaces 111 and 12, respectively, and the respective reflected pulses 15 and 16 are detected by the probe 2. Now, assuming that the time from pulse emission to reception of reflected pulse is t, the distance x from the ultrasonic probe to the acoustic characteristic discontinuous surface is given by the following equation, where v is the speed of sound.

x=vt/2 Here, the intensity of the pulse emitted at frequency f is Io
(f), and when the intensity of the received reflected pulse is I(f, x), the following equation holds approximately.

I(f,x)=I ₀ (f)f ^a(x) g(x)x ^b(x) exp{
−4∫ ^x _p α(f,
)x ^b(x) } ^{−4∫ x} _p α(f, is the target intensity. a
(x) is a(x)=0 on an acoustic property discontinuous surface sufficiently larger than the wavelength, and a(x)=4 on an acoustic property discontinuous surface sufficiently smaller than the wavelength. Therefore, it is considered that a(x) is constant within a certain frequency band, and generally O≦a(x)≦4. In addition, x ^b(x) takes into consideration the effect that the reflected wave intensity at the ultrasound probe position weakens as the reflected waves spread, and b( x) = 0, b on the small acoustic characteristic discontinuity side
(x)=-2. Therefore, in general 0≦b
(x)≦−2. Further, α(f, x) is an ultrasonic attenuation coefficient.

However, in the above discussion, the radiated ultrasound is assumed to be an ideal narrow pencil beam, and the effect of interference between reflected waves from adjacent acoustic discontinuities is ignored.

The principle of obtaining quantitative information about the ultrasonic characteristics of an object to be inspected by processing information from the distribution of echo intensity is
Starting from equation (2). In equation (2), only I(f, x) and Io(f) can be obtained by ultrasonic echo measurement,
{Since I(f, x) is proportional to Io(f), the only information is I(f, x)/Io(f). }The unknown is f ^a(x) ,
Since there are three types, g(x) ^b(x) and α(f, x), it is not possible to obtain any one of these independently by measurement using a single frequency. However, if we measure the echo strength at at least three different frequencies, we can eliminate f ^a(x) , g(x) x ^{b(x) and} α(f,
Quantitative information regarding x) is obtained.

In the following, a case will be considered in which a plurality of different frequencies are used.

Ultrasonic echoes were measured at three different frequencies f ₁ , f ₂ , f ₃ , and the reflected wave intensities I(f ₁ ,
x), I(f ₂ , x) I(f ₃ , x), ln(f ₂ /f ₃ ), ln(
By multiplying and adding f ₃ /f ₁ ) and ln(f ₁ /f ₂ ), the following formula is obtained.

ln(f ₂ / f ₃ ) lnI (f ₁ , x) + ln (f ₃ / f ₁ ) lnI (f ₂ ,
x) + ln (f ₁ / f ₂ ) lnI (f ₃ , x) = ln (f ₂ / f ₃ ) lnIo (f ₁ ) + ln (f ₃ / f ₁ ) lnIo (f ₂
)+ln(f ₁ /f ₂ )lnIo(f ₃ ) −4∫ ^x _p {α(f ₁ , x)ln(f ₂ /f ₃ )+α(f ₂ , x
) ln (f ₃ / f ₁ ) + α (f ₃ , x) ln (f ₁ / f ₂ )} dx……(3
) This equation (3) no longer includes f ^a(x) and g(x) x ^b(x) .

Here, if we calculate the average rate of change in the above equation for the positions x ₁ and x ₂ where echoes are obtained, we get: 1/x ₂ - _{x 1} {ln(f ₂ /f ₃ )lnI(f ₁ , x ₂ )/I ( _f1 ,
x ₁ ) + ln (f ₃ / f ₁ ) lnI (f ₂ , x ₂ ) / I (f ₂ , x ₁ ) + ln
(f ₁ / f ₂ )lnI (f ₃ , x ₂ ) / I (f ₃ , x ₁ )} = −4 / x ₂ −x ₁ [∫ ^x2 _x1 {α (f ₁ , x) ln (f ₂ /f ₃
) + α (f ₂ , x) ln (f ₃ / f ₁ ) + α (f ₃ , x) ln (f ₁ /
f ₂ )}dx〕 ...(4), and the left side is the value obtained by measuring eco,
The right side is a linear expression of the average value of the ultrasonic attenuation coefficient between x ₁ and x ₂ , and is a quantitative value regarding the ultrasonic attenuation coefficient of the object to be inspected. These calculations can be easily performed by a computer or an information processing circuit consisting of a simpler log amplifier, arithmetic circuit, and the like.

In addition, the distribution of echoes from the object to be inspected is measured at two different frequencies f ₁ and f ₂ , and lbI (f ₁ , x) − lnI
When (f ₂ , x) is created, from equation (2), lnI (f ₁ , x) − lnI (f ₂ , x) = lnIo (f ₁ ) − lnIo (
f ₂ ) + a (x) lnf ₁ / f ₂ −4∫ ^x _p α (f ₁ , x) dx……(5)
Here, regarding the positions x ₁ and x ₂ where the echo is obtained,
The following equation is obtained by finding the average rate of change in equation (5).

1/x ₂ −x ₁ {lnI(f ₁ , x ₂ )/I(f ₁ , x ₁ )−lnI(f ₂
, x ₂ )/(f ₂ , x ₁ )} =−4/x ₂ −x ₁ ∫ ^x2 _x1 {α(f ₁ , x)−α(f ₂ , x)
}dx+a( _x2 )-a( _x1 )/ _x2 - _x1ln ( _f1 / _f2 )...(6
) The left side of equation (6) is the value obtained by measuring echoes at different frequencies f ₁ and f ₂ , and the right side is a(x ₂ ) − a(x ₁ )/x ₂ − _{x 1}・ln(f ₁ / f ₂ ), but the difference in the average ultrasonic attenuation coefficient between x ₁ and x ₂ α (f ₁ ,
It is a value proportional to x)-α(f ₂ , x), and quantitative information regarding the ultrasonic characteristics of the object to be inspected can also be obtained by this analysis method.

Note that for a sufficiently large acoustic characteristic discontinuity surface, a(x) = 0, so the error in equation (6) is a(x ₂ ) - a(x ₁ )/x ₂ - _{x 1} ln(f ₁ / f ₂ ) disappears.

By means of the method and apparatus according to the present invention, it is now possible to quantitatively inspect objects using ultrasonic echoes, which were previously observed only qualitatively, and to quantify objects with complex internal configurations. You can obtain specific and useful information.

In the above description, disclosure of well-known parts has been omitted, but the contents can be fully understood by those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a basic block diagram of an apparatus for carrying out the method according to the invention. FIGS. 2 to 7 are explanatory diagrams of various embodiments of the ultrasonic probe used in the apparatus according to the present invention. FIG. 8 is a diagram showing the principle of ultrasonic echo examination. The correspondence of the main reference numbers in the attached figures is as follows. 1: Object to be inspected, 2: Ultrasonic probe, 3: Transmitter/receiver, 4: Information processing device, 5: Recording and display device, 6, 6': Transmission/reception signal, 7: Ultrasonic wave, 15:
Ultrasonic pulse, 16, 17: Ultrasonic echo.

Claims (1)

[Claims] 1. Emitting an ultrasonic pulse having at least three different frequency components toward an object to be inspected, and detecting an echo of the ultrasonic pulse reflected from a discontinuous surface of acoustic characteristics in the object to be inspected. , performs arithmetic processing to eliminate factors other than the ultrasonic attenuation coefficient from the intensity of the reflected echo of each detected frequency, quantitatively determines the ultrasonic characteristics of the object to be inspected, and performs an inspection within this object. Characteristic ultrasonic testing method. 2. An ultrasonic probe that emits ultrasonic pulses of at least three different frequencies toward an object to be inspected simultaneously or with a time lag, and detects ultrasonic echoes reflected within the object; A transmitting/receiving device that transmits pulsed energy to the probe and receives the energy transmitted from the ultrasonic probe, and eliminates factors other than the ultrasonic attenuation coefficient from the intensity of the detected reflected echo of each frequency. an information processing device that performs arithmetic processing to quantitatively determine the ultrasonic characteristics of an object to be inspected; 3. The apparatus according to claim 2, wherein the ultrasonic probe is a plurality of ultrasonic transducers arranged on a rotating support and having transmission and reception characteristics that differ with respect to frequency. 4. The apparatus according to claim 2, wherein the ultrasonic probe is a plurality of ultrasonic transducers arranged on a linearly movable support having different transmission and reception characteristics with respect to frequency. 5. The apparatus according to claim 2, wherein the ultrasound probe is a fixed or movable broadband ultrasound transducer. 6. Claim 2, wherein the ultrasonic probes are a plurality of electronic sweep type ultrasonic probes that have different transmission and reception characteristics with respect to frequency and are arranged on a support that is capable of linear movement. equipment. 7. The apparatus according to claim 2, wherein the ultrasonic probe is an electronic sweep type ultrasonic probe using a broadband ultrasonic transducer.