JPH04340463A - Reflection type ultrasonic image apparatus - Google Patents

Abstract

PURPOSE:To obtain the image of the part near to the surface of an object to be inspected without superposing the contrast of the surface of the uneven shape of the object to be inspected. CONSTITUTION:Ultrasonic waves are allowed to be incident to the measuring point P of an object 6 to be inspected from an ultrasonic transmitter-receiver 8 and the reflected waves to the incident waves are received by a phase conjugate mirror 18. The phase conjugate mirror 18 allows the phase conjugate waves to the received reflected waves to be incident to the measuring point P of the object 6 to be inspected. At this time, the strain of the wave front of the reflected waves caused by the surface uneven shape of the object 6 to be inspected is set off by the time reversal properties of the phase conjugate waves. The reflected waves from the measuring point P to the phase conjugate waves arm received by the transmitter-receiver 8 and converted to the electric signal corresponding to the intensity thereof. This electric signal output is different according to the acoustic impedance of the measuring point P. Therefore, by scanning the measuring point P by an XY scanner 20 and plotting the reflected wave output at each scanning point on a display 16, the image of the part near to the surface of the object 6 to be inspected is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type ultrasonic imaging device that forms an image of the surface or near surface of a subject using reflected ultrasound waves from the subject.

0002

2. Description of the Related Art Ultrasonic microscopes and ultrasonic flaw detectors are known as devices for observing the subsurface of an optically opaque object using ultrasonic waves. In these methods, high-frequency ultrasound in the MHZ to GHZ band is focused on a subject, and reflected waves or transmitted waves from the subject are received.

[0003] By displaying changes in the intensity or phase of the received waves while scanning the convergence position of the ultrasound along the surface of the object, an image below the surface of the object can be obtained.

[0004] Transmission type ultrasound imaging devices using phase conjugate waves are also known. In this device, an ultrasonic transducer and a phase conjugate mirror that generates a phase conjugate wave are placed opposite to each other with the subject in between. Since the phase conjugate wave has the ability to compensate for wavefront distortion, this device can obtain images of the subsurface of the subject without being affected by the unevenness of the subject's surface.

[0005]

[Problems to be Solved by the Invention] Ultrasonic microscopes and ultrasonic flaw detection devices have a problem in that internal images and surface images overlap. That is, when observing a subject with an uneven surface, the refraction angle of the ultrasonic wave on the subject's surface varies depending on the irradiation position, which changes the wavefront shape of the reflected wave. The effect becomes a surface image, which is superimposed on the internal image to be observed.

[0006] Therefore, in an image of a subject having an uneven surface, it is difficult to determine whether the contrast is due to the internal state of the subject or to the unevenness of the surface. Furthermore, more detailed information inside the subject,
For example, it is much more difficult to determine whether a defect in a material is a void or rust.

Although the above-mentioned difficulties can be solved by a transmission-type ultrasound imaging device using phase conjugate waves, in order to form an image using ultrasound transmitted through the object, it is made of a solid material with high acoustic impedance. It cannot be applied to a subject or a relatively thick subject.

The present invention has been made in view of the above problems, and its purpose is to obtain an image below the surface of a subject without being affected by the unevenness of the surface of the subject, and to reduce the acoustic impedance. It is an object of the present invention to provide a reflection type ultrasound imaging device that can be applied to tall or relatively thick objects.

[0009]

Means for Solving the Problems In order to achieve the above object, a reflection type ultrasound imaging apparatus according to claim 1 of the present invention comprises:
A transmitting means that forms an image corresponding to the acoustic impedance distribution on the surface or near the surface of the subject based on the reflected ultrasound waves from the subject, and transmits the ultrasonic waves to a measurement point on the subject. and a phase conjugate wave generating means for receiving the reflected ultrasound from the measurement point and generating a phase conjugate wave of the reflected ultrasound, and receiving a reflected wave of the phase conjugate wave from the measurement point; a wave receiving means for outputting an electrical signal corresponding to the intensity of the reflected wave; a scanning means for two-dimensionally scanning the measurement point along the surface of the object; The present invention is characterized by comprising an image display means for displaying an image according to the acoustic impedance distribution under the surface or near surface of the subject based on the reflected wave output of the wave receiving means.

The reflection type ultrasound imaging apparatus according to claim 2 of the present invention also provides an image corresponding to the surface shape of the object and an image corresponding to the surface or near surface of the object based on the reflected ultrasound from the object. It selectively forms an image corresponding to the acoustic impedance of a phase conjugate wave generating means for generating a phase conjugate wave of the reflected ultrasound; a first reflected wave at the measurement point of the phase conjugate wave from the phase conjugate wave generating means; and a first reflected wave of the incident ultrasound from the wave transmitting means. a wave receiving means for receiving either of the second reflected waves at the measurement point and outputting an electrical signal corresponding to the intensity of these reflected waves, and a reflected wave received by the wave receiving means, a tilting means for integrally tilting the wave transmitting means and the wave receiving means with respect to the surface of the object so as to selectively switch between the first reflected wave and the second reflected wave; and the measuring point. Acoustic impedance distribution on the surface or near surface of the object based on the output of the wave receiving means at each measurement point scanned by the scanning means and the acoustic impedance distribution at each measurement point scanned by the scanning means. and an image display means for displaying an image corresponding to the surface shape of the subject and an image corresponding to the surface shape of the subject.

[0011]

[Operation] According to the above structure, the wave transmitting means, the wave receiving means, and the phase conjugate wave generating means are arranged in a reflective type. In the reflection type ultrasound imaging apparatus according to the first aspect of the present invention, the ultrasound waves transmitted from the wave transmitting means are reflected by the subject and received by the phase conjugate wave generating means. The phase conjugate wave generating means transmits a phase conjugate wave to the received reflected wave to the subject, and the reflected wave from the subject is received by the wave receiving means. That is, the ultrasonic wave follows a path (hereinafter referred to as a first path) from the wave transmitting means to the subject to the phase conjugate wave generating means to the subject to the wave receiving means.

[0012] Here, the path of the reflected wave from the object to the phase conjugate wave transmitting means in the first path is the outward path, and the path of the phase conjugate wave from the phase conjugate wave transmitting means to the object is the return path. Consider the transmission and reception of ultrasound between the conjugate wave transmitting means and the subject.

In this case, the phase conjugate wave on the return path is
It has time reversal properties for waves on the outward path. Therefore, even if the reflected wave undergoes some kind of wavefront distortion on the path from the phase conjugate wave transmitting means to the phase conjugate wave generating means, the wavefront distortion will affect the path of the phase conjugate wave from the phase conjugate wave transmitting means to the wave receiving means. will be canceled out.

Therefore, the reflected wave (
The wavefront of the reflected wave of the phase conjugate wave is always the same regardless of the shape of the object. Therefore, the influence of unevenness on the surface of the subject does not appear on the image. However, the intensity of the reflected wave varies depending on the acoustic impedance at the measurement point on the subject. Therefore, by scanning the incident position of the ultrasonic wave on the object two-dimensionally along the object's surface, the image contrast that shows the acoustic impedance distribution on the surface or near the surface of the object can be adjusted according to the intensity of the reflected waves. generated.

Further, according to the reflection type ultrasound imaging apparatus according to claim 2, by tilting the wave transmitting means and the wave receiving means integrally with respect to the surface of the subject, the waves are received by the wave receiving means. The reflected wave is selectively switched to a reflected wave of the phase conjugate wave and a direct reflected wave from the subject that has not passed through the phase conjugate wave generating means. Of these, the path of the ultrasound in the former case is the same as the first path. On the other hand, in the latter case, the ultrasonic waves transmitted from the wave transmitting means are reflected by the subject and received by the wave receiving means. That is, the ultrasound waves follow a path (hereinafter referred to as a second path) from the wave transmitting means to the subject to the wave receiving means.

When the first path is selected as the ultrasound path, an image similar to that of the reflection type ultrasound imaging device according to the first aspect is formed.

Further, when the second path is selected, the reflected wave received by the wave receiving means is affected by the unevenness of the surface of the subject. That is, since the reflected wave output of the wave receiving means includes information about the unevenness of the surface of the subject, an image of the surface shape of the subject can be formed based on this reflected wave output.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings.

In the reflection type ultrasound imaging apparatus shown in FIG. 1, a water tank 2 contains water 4 as an ultrasound propagation medium, and a subject 6 is immersed in the water.

An ultrasonic transducer (wave transmitting means, wave receiving means) 8 placed above the subject 6 includes a piezoelectric transducer 8a and an acoustic lens 8b made of, for example, sapphire glass.
is pasted on the lower end surface of the acoustic lens 8b,
A concave surface 8c is formed. In such an ultrasonic transducer 8, when the concave surface 8c is immersed in water 4, the center of curvature of the concave surface 8c is in a predetermined direction with respect to the normal direction of the surface of the subject 6 at the measurement point P. They are arranged to form an acute angle.

Further, a circulator 10 is connected to the piezoelectric transducer 8a of the ultrasonic transducer 8 for separating an input signal and an output signal of the transducer 8a. A high frequency oscillator 12 is connected to the input signal side of the circulator 10, which oscillates high frequency voltage pulses for causing the piezoelectric transducer 8a to generate ultrasonic waves. Furthermore, a known signal processing circuit 14 for forming an image from the output signal of the piezoelectric transducer 8a and a display 16 for displaying the image are connected in this order to the output signal side of the circulator 10. These signal processing circuit 14 and display 16 constitute image display means in the present invention.

A phase conjugate mirror (phase conjugate wave generating means) 18 is arranged above the object 6 to receive the reflected wave reflected from the object 6 at the measurement point P through the water 4. . The phase conjugate mirror 18 transmits an ultrasonic wave that is phase conjugate to the received reflected wave through the water 4 to the measurement point P.

[0023] The subject 6 is an XY scanner (scanning means)
Holding arm 22 that can be driven in two-dimensional XY directions by 20
is maintained. This holding arm 22 allows the object 6 to be
By moving in the X and Y directions, the ultrasonic measurement point P on the surface of the subject 6 is scanned along the surface of the subject 6.

[0024] The high frequency oscillator 12 and the signal processing circuit 14
and the XY scanner 20 are controlled by a controller 24.

Next, the operation of the reflection type ultrasound imaging apparatus as described above will be explained.

A high frequency voltage pulse generated by the high frequency oscillator 12 according to a command from the controller 24 is applied to the piezoelectric transducer 8a of the ultrasonic transducer 8 via the circulator 10. This allows the piezoelectric transducer 8
Ultrasonic waves are emitted from a into the acoustic lens 8b. This ultrasonic wave is made into a convergent wave by the lens action of the concave surface 8c, is obliquely incident on the measurement point P on the surface of the subject 6 through the water 4, and is converged at the measurement point P.

With respect to this incident wave, the reflected wave reflected at the measurement point P has its wavefront distorted by the unevenness of the surface of the subject 6. This reflected wave with a distorted wavefront is received by the phase conjugate mirror 18. The phase conjugate mirror 18 generates a phase conjugate wave for the received reflected wave and transmits it to the subject 6 . This phase conjugate wave follows a path opposite to that of the reflected wave and re-enters the measurement point P of the subject 6.

Here, the phase conjugate wave is a wave obtained by replacing the function representing the spatial portion of the reflected wave received by the phase conjugate mirror 18 with its complex conjugate function. In other words, the reflected wave is

0029
]

[Math 1]

If it is expressed as, the phase conjugate wave for this is:

[0031]

[Math 2]

It is expressed as follows. Here, due to the mathematical properties of complex conjugate functions, the right side of equation (2) above is

[0033]

[Math 3]

It is expressed as follows. The right side of this equation (3) is the above (
1) Since it is a time reversal of equation, the phase conjugate wave is as follows with respect to the reflected wave:

[0035]

[Math 4]

It is expressed as follows. Therefore, the phase conjugate wave behaves as a time-reversed wave of the reflected wave. Therefore, distortion of the wavefront of the reflected wave is canceled out by the phase conjugate wave. That is, even if the ultrasonic waves undergo some kind of wavefront distortion on the path from the ultrasonic transducer 8 to the phase conjugate mirror 18, it is because the phase conjugate waves are on the path from the phase conjugate mirror 18 to the ultrasonic transducer 8. canceled out. In this case, due to the time-reversal property of the phase conjugate wave described above, the wavefront of the reflected wave received by the concave surface 8c is always the same regardless of the unevenness of the surface of the subject 6. Therefore, the influence of the unevenness of the subject 6 does not appear in the images described below.

The reflected wave of this phase conjugate wave from the measurement point P of the subject 6 is received by the concave surface 8c of the ultrasonic transducer 8.

The received reflected wave is converted into an electric signal as a reflected wave output by the piezoelectric transducer 8a,
Output.

The controller 24 also gives a drive command to the XY scanner 20 to drive the subject 6 in the XY directions via the holding arm 22. Thereby, the measurement point P is scanned along the surface of the subject 6.

For each scanning point, by transmitting and receiving ultrasonic waves along the path from the ultrasonic transducer 8 to the object 6 to the phase conjugate mirror 18 to the object 6 to the ultrasonic transducer 8, The reflected wave output of each scanning point is obtained. The intensity of this reflected wave output varies depending on the acoustic impedance of the subject 6 at the measurement point P.

These reflected wave outputs are given to the signal processing circuit 14 via the circulator 10. Signal processing circuit 1
4 plots the reflected wave output corresponding to the coordinate position on the screen of the display 16 according to the XY coordinates of the measurement point P given from the XY scanner 20 via the controller 24. As a result, an image below the surface of the subject 6 is formed. At this time, image contrast is generated due to the above-mentioned difference in acoustic impedance.

FIGS. 2(A) to 2(C) show examples of test objects 6 having the same convex portion (bulge shape) 6a on the surface and differing only in the internal state below the near surface. FIG. 2(A) shows a case where the internal state is homogeneous, FIG. 2(B) shows a case where a void G exists under the surface, and FIG. 2(C) shows a case where rust R has occurred under the surface. These subjects6 with conventional ultrasound imaging equipment
When observed, it was difficult to distinguish the differences in the internal states shown in FIGS. 2(A) to 2(C) from the images because the convex portions 6a on the surface added strong contrast to the images. However, according to the ultrasound imaging apparatus of the present invention, the contrast caused by the convex portions 6a on the surface disappears, and differences in acoustic impedance due to differences in the internal state of the subject 6 are accurately imaged. That is, in the case of FIG. 2(A), no contrast is added to the image, and in the cases of FIG. 2(B) and FIG. 2(C), due to the difference in contrast between the void G and the rust R, the void G is rusted. It has stronger contrast than R. Therefore, the three internal states shown in FIGS. 2(A) to 2(C) can be distinguished by the images on the display 16. Note that the ultrasonic imaging apparatus of the present invention is effective not only for examining the internal state under the near surface of the subject 6 but also for differences in acoustic impedance on the surface of the subject 6. For example, as shown in FIG. 3, the specimen 6 has convex portions 6a and concave portions 6b on its surface, and the surface itself has different compositions distributed in two dimensions due to grain boundaries, stress, effects of heat treatment, etc. (The difference in composition is indicated by different hatching in the diagram). When imaging the object 6 as shown in FIG. 3 using a conventional apparatus, it is necessary to polish the surface of the object 6 flat in order to remove the influence of the convex portions 6a and recesses 6b. However, according to the device of the present invention,
Since it is not affected by the uneven shape of the surface of the subject 6, the composition distribution on the surface of the subject 6 can be imaged based on the difference in acoustic impedance without polishing the surface.

[0043] Furthermore, as shown in FIGS. 4 and 5, the ultrasonic imaging apparatus of the present invention has an added function of forming not only an image of the near surface of the subject 6 but also an image of the surface of the subject 6. can be done. 4 and 5, the ultrasonic transducer 8 is tiltably supported by an angle adjustment device (tilting means) 26 for adjusting the angle with respect to the surface of the subject 6. The configuration except for this angle adjustment device 26 is the same as that in FIG. 1. By tilting the ultrasonic transducer 8 by the angle adjustment device 26, the reflected wave of the incident wave from the ultrasonic transducer 8 to the subject 6 is received by the phase conjugate mirror 18 as in FIG. Alternatively, it is possible to selectively receive the waves directly by the ultrasonic transducer 8 without passing through the phase conjugate mirror 18.

As shown in FIG. 4, it is assumed that the center of curvature of the concave surface 8c of the ultrasonic transducer 8 is aligned with the normal direction of the surface of the subject 6. When the incident wave from the wave receiver 8 is focused on the surface of the subject 6 or its vicinity in this state, the reflected wave is received by the wave receiver 8 and converted into a reflected wave output. Since this reflected wave output is affected by the unevenness of the surface of the object 6, by performing the same scan as in Fig. 1, an image that sensitively corresponds to the unevenness of the surface of the object 6 can be obtained. It can be formed on the display 16.

Next, as shown in FIG.
It is assumed that the receiver 8 is tilted by the angle adjustment device 26 while maintaining the state of , so that the reflected wave is received by the phase conjugate mirror 18 . In this case, as in the explanation with reference to FIGS. 1 to 3, an image formed by the difference in acoustic impedance on the surface or near the surface is obtained, regardless of the uneven shape of the surface of the subject 6.

By comparing the images obtained in each of the states shown in FIGS. 4 and 5, it is possible to obtain the correspondence between the surface shape of the subject 6 and the acoustic impedance distribution.

[0047]

[Effects of the Invention] As explained above, according to the reflection type ultrasound imaging device of the present invention, even if there are irregularities on the surface of the subject, the acoustic impedance distribution can be handled without being affected by the shape of the irregularities. images of the surface or near-subsurface of a subject can be formed. Furthermore, since a reflection type arrangement is adopted and differences in reflected wave intensity due to acoustic impedance are detected, it can be applied to subjects with high acoustic impedance or relatively thick subjects.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram schematically showing a reflection type ultrasound imaging device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a cross section of a test object with the same surface shape but different internal states, including (A), (B), and (C), where (A) has a convex portion on the surface. , (B) is a cross-sectional view showing a test object with a homogeneous interior, (B) is a cross-sectional view showing a test object with a space inside, and (C) is a cross-sectional view showing a test object with rust inside.

FIG. 3 is a cross-sectional view showing a specimen having an uneven surface and a plurality of different compositions distributed along the surface.

FIG. 4 is a configuration diagram schematically showing a reflection type ultrasound imaging device according to a second embodiment of the present invention, in which an ultrasound transducer transmits and receives ultrasound through a path that does not pass through a phase conjugate mirror. FIG.

FIG. 5 is a configuration diagram schematically showing a reflection type ultrasound imaging device according to a second embodiment of the present invention, showing a state in which an ultrasound transducer transmits and receives ultrasound through a path passing through a phase conjugate mirror. FIG.

[Explanation of symbols]

6... Subject, 8... Ultrasonic transducer (wave transmitting means, wave receiving means), 14... Signal processing circuit (image display means), 16... Display (image display means), 18... Phase conjugate mirror (phase conjugate wave generating means), 20...XY scanner (scanning means),
26... Angle adjustment device (tilting means).

Claims (2)

[Claims] [Claim 1] Based on reflected ultrasound waves from a subject,
The device forms an image corresponding to the acoustic impedance distribution on the surface or near the surface of the object, and includes a transmitting means for sending ultrasonic waves to a measurement point on the object, and a transmission means for transmitting the reflected ultrasonic waves from the measurement point. a phase conjugate wave generating means that receives a wave and generates a phase conjugate wave of the reflected ultrasonic wave; and an electrical signal that receives a wave reflected from the measurement point of the phase conjugate wave and corresponds to the intensity of the reflected wave. a wave receiving means for outputting a signal; a scanning means for two-dimensionally scanning the measurement point along the surface of the subject; 1. A reflection-type ultrasound imaging device comprising: an image display means for displaying an image according to an acoustic impedance distribution under the surface or near surface of a subject. [Claim 2] Based on reflected ultrasound waves from the subject,
It selectively forms an image corresponding to the surface shape of the object and an image corresponding to the acoustic impedance at or near the surface of the object. a wave means, a phase conjugate wave generation means for receiving the reflected ultrasound from the measurement point and generating a phase conjugate wave of the reflected ultrasound, and the measurement point of the phase conjugate wave from the phase conjugate wave generation means. a first reflected wave at the measuring point of the incident ultrasonic wave from the wave transmitting means, and outputs an electrical signal corresponding to the intensity of the reflected waves. a wave means, and the wave sending unit to the surface of the object such that the reflected wave received by the wave receiving unit is selectively switched to either the first reflected wave or the second reflected wave. a tilting means for integrally tilting the means and the wave receiving means; a scanning means for two-dimensionally scanning the measurement point along the surface of the object; and the wave reception means at each measurement point scanned by the scanning means. an image display means for displaying an image according to the acoustic impedance distribution on the surface or near the surface of the object and an image according to the surface shape of the object based on the output of the reflection apparatus. type ultrasound imaging device.