JPS60166859A - Ultrasonic image pick-up apparatus - Google Patents

Abstract

PURPOSE:To impart a good reflected signal even to a specimen inferior to a reflective characteristic and to easily discriminate the reflected sonic wave from the interface of water and a lens, and that from the specimen, by providing an acoustical reflective mirror to the lower part of the specimen. CONSTITUTION:An RF electric signal is applied to the lens 120 provided to a piezoelectric thin film 110 to generate focusing ultrasonic beam 170. A specimen system, wherein an organism specimen 140 is held between two extremely thin Mylar films 130, 150, is placed to the focal region of beam. In this invention, a concaved reflective mirror 160 arranged so as to be positioned at the common focus with the lens 120 is provided and the specimen system surrounded by a medium 180. When this constitution is used and ultrasonic beam generated in the lens 120 transmits the specimen 140, it is reflected by a reflective mirror 160 and again transmits the specimen 140 to be condensed by the lens 120. Because the reflected ultrasonic wave obtained by this constitution transmits the specimen 140 two times, the transmission information of the specimen 140 is reflected in the similar way as conventional constitution.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an imaging device using high-frequency ultrasonic energy;
Regarding the sonic microscope.

[Backbone of invention]

Mechanical scanning ultrasonic microscopy is performed using ultrahigh-frequency sound waves with a sound frequency of I GHz, which corresponds to a sound wave depth of about 1 micron meter underwater.
Microscope (hereinafter abbreviated as SAM) has been proposed.

12+1 1. As shown in the IEI diagram, a 20'-year-old cylindrical crystal such as sapphire is optically polished on one end surface and has a flat surface and a concave hemispherical hole in the other end surface.

RF is transmitted from the signal source 10 to the piezoelectric thin film 15 created on the flat plate surface.
[Apply a low signal to emit a plane wave RF sound wave within the crystal 20.] This plane sound wave is focused at a predetermined focal point F by a positive focusing lens that utilizes the difference in sound speed between the two regions at the interface 25 between the crystal 20 and *Ik 30 (usually water) formed in the concave hole. As is well known, when the ratio of the focal length of the lens to the aperture diameter, that is, the P number representing the brightness of the lens, is sufficiently small, an extremely narrow ultrasonic beam can be created with this configuration.

This focused sound wave is reflected by the sample placed near the focus,
Since it is subject to disturbances in terms of scattering and transmission attenuation, by detecting such disturbed sound wave energy with the above lens system or another similar lens system, the elastic properties of the microscopic region of the sample can be reflected ( Therefore, while the sample is mechanically scanned in two dimensions, this electric signal is displayed in brightness on the CRT in synchronization with the mechanical scanning.
As a result, a sound wave microscopic image can be obtained.

The configuration of a SAM that detects such disturbance energy is shown in Figure 2 (a) and Figure 2 (bl). 2(b) shows another probe system 50 which is the same as the probe system 40. A transmission type configuration is shown in which the two are placed facing each other at a confocal position and the sound waves transmitted through the sample 60 are detected.

The reflective type is used to observe devices such as ICs and LSIs, and thick metal samples, while the transmission type is used for thin samples and especially biological samples. Because it is very similar to acoustic impedance, it is difficult to obtain a sufficient reflected ultrasound signal, so images are taken exclusively in a transmission configuration.

[Object of the Invention] One object of the present invention is to provide a configuration that provides a good reflection signal even to a sample that does not exhibit good reflection characteristics, such as a biological sample.

Another object of the present invention is to provide a structure that allows easy discrimination between the sound waves reflected from the interface between water and the lens and the sound waves reflected from the sample.

[Summary of the invention]

When detecting reflected ultrasonic waves, only the reflected ultrasonic waves from a sample are detected by temporally discriminating transmitted pulses and received echo pulses using a so-called pulse echo method.

FIG. 3 shows an example of the waveform of the receiver in the video domain when an RF pulse electric signal with a certain repetition period t8 is applied. Waveform A shows the applied RF pulse itself, a reflected echo from the interface with the waveform Bat lens surface water, and waveform C shows a reflected echo from the sample.

In order to obtain a high quality image, it is necessary to distinguish and detect only this waveform C independently from the waveform H. Waveform B and waveform C
The time interval t8 between the distance between the lens and the sample (which is approximately equal to the focal length of the lens) 2 and the sound velocity of water vw
Since t is given by 2Z/VW, it can be seen that as 2 becomes smaller, the above-mentioned time discrimination task becomes rapidly difficult.

In fact, in ultrasonic microscopes, sound waves are attenuated severely in water, the medium that fills the gap between the lens and the sample, and when trying to increase the resolution by increasing the frequency, the distance between the lens and water must be reduced to avoid this attenuation. Because it needs to be extremely short (for example, 1G)
40 μm at Hz), this particular condition is an obstacle to improving resolution. Therefore, in the present invention, it is an object of the present invention to easily distinguish the reflected signal from the sample from the reflected signal from the interface between the lens and water in terms of time.

C1 The present invention has been made in view of the above-mentioned two objects, and attempts to solve the above-mentioned problems by providing a reflection mirror on the back side of the sample at a certain distance with a one-reflection type configuration. Hereinafter, the present invention will be explained in detail using FIGS. 4 and 5.

[Embodiment of the Invention] In Fig. 94, a lens 120 provided with a piezoelectric thin film 110 is shown.
An air signal is applied to the RF' to generate a focused ultrasound beam 170. A sample system in which a biological sample 140 is sandwiched between two extremely thin sheets of Mylar 8!41130°150 (for example, 1 μm thick) is placed in the focal region of the beam. In the present invention, a concave reflecting mirror 160 is arranged to be confocal with the lens 120.
is provided, and the sample system is surrounded by a medium (eg, water) 180.

When such a configuration is used, the ultrasonic beam generated by the lens 120 passes through the sample 140, is reflected by the reflection ψ160, passes through the sample 140 again, and returns to the lens 120.
The sound is collected by As is clear from the propagation situation of the ultrasound beam, the reflected ultrasound obtained with this configuration is
Since the light passes through the sample 140 twice, the transmitted information of the sample 140 is reflected as in the conventional configuration. That is, according to this configuration, a transmitted image can be obtained despite the reflective configuration. As mentioned above, with the conventional reflection method that detects direct reflected ultrasound from the sample surface t1, only extremely weak reflected ultrasound can be detected because the acoustic impedance of water stone biological samples is extremely low. Therefore, this configuration has the advantage that a sufficiently auspicious transmitted signal can be used.

=1g Figure 5 shows a received waveform when a reflected ultrasound is detected by the pulse echo method using this configuration. Waveform A shows the applied RF signal i, the signal itself, and waveform 1 shows the reflected echo from the interface between the lens 120 and the medium 180. Waveform C shows the surface t1 of the sample 140.
Waveform C' is a waveform of a reflected sound wave generated for the first time by this configuration. Waveform B and waveform C
The time interval between them is t using the above symbols, and that between waveform B and waveform C' is clearly 2t.

In this way, the reflected echo C' with this configuration appears 2t apart from the lens echo B, so it can be easily distinguished from the Lelans echo B in time. It is possible to resolve situations that overlap with B. As explained above, according to the present invention, even for samples that do not exhibit good reflection characteristics, such as @1ζ biological samples, it is possible to give a rare reflection signal, and a signal that is equivalent in terms of transmission configuration. No, $2 plus 1 lens
Only the echoes that reflect the elastic properties of the sample can be selectively detected by time discrimination without being affected by the echoes reflected from the interface between the sample 20 and the medium 180.

FIG. 6 is a diagram in which this configuration is replaced with an equivalent transmission system by utilizing the reflecting mirror property of the concave reflecting mirror 160. The area above the mirror surface is the same as in FIG. 4, and the area below the mirror surface is in a mirror image relationship with respect to this surface. Concave reflector 160, 16
0a can be regarded as a lens imaging system that converts a point object 145 on the focal plane F of the lens 120 into an image 145b as shown in this figure. If the point object 145 is deviated by ΔX from the axis, the image 145b will also be deviated by ΔX in the opposite direction as shown in the figure, but the object 1 that is transmitted by this image (sound pressure distribution)
Since 45a is shifted in the same direction as 145, the object 145a is 2Δ from the center of the main beam of image 145b.
It means that there is an X difference.

Therefore, it can be seen that the imaging system below the mirror surface is equivalent to the conventional transmission imaging system with doubled frequency.

From the above discussion, we will examine the nature of the resolution of the imaging device with this configuration. Assuming that the transmitting characteristics of the lens system 120 are P(rl) and the receiving characteristics of the concave reflecting mirror 160 are P2(rl (here, r is the abscissa taken on the sample surface), the second (al( b1
In the conventional configuration shown in the figure, both transmitting and receiving comprehensive directional characteristics P, (r
) is given by P, (rl=P: (r) (2). On the other hand, in this configuration, based on the above discussion, the transmitting and receiving comprehensive directivity characteristic P, (r) is given by:

P, (r) = P: (r) - P2 (zr) (3), and only the term P, (2r) improves the directivity compared to the conventional method, and also has the effect of providing a higher resolution image. It means that you have it. In fact, the lens 12 is used as the concave reflector 160.
Let's examine this situation using the same thing as 0. 7, where the F number of the lens 120 is F and λ is the sound wave length;
Equation (21(3) can be written as % expression % ) (5). Here, Jl() is a Bessel function of the first kind. Fig. 7 A, M, Conventional method p, Cr1s when F=0.63 P, (r) with this configuration
This is a comparison of the resolution. In the figure, the vertical axis represents the transmitting/receiving directivity characteristics P, (r), P, (r) on a linear scale, and the horizontal axis represents the horizontal coordinate in wavelength units. As described above, according to this configuration, the resolution defined by the half-width is approximately 1
It can be seen that the area where unnecessary side lobes occur is halved, greatly contributing to the improvement of image quality with high resolution and high gradation.

The shape of the concave reflection @160 used in the present invention does not need to have the same focal length or F number as the lens 120. Of course, the same effect as the present invention can be obtained even if a system having other focusing means such as a cylindrical lens or a cylindrical reflecting mirror is used.

Further, the material constituting such a reflecting mirror may be a crystal such as quartz glass or sapphire, which has been conventionally used as a lens material, or a metal having a sufficiently large acoustic impedance compared to water.

f4i may be a thin film of metal or the like lined with air, or a multilayer structure material using a so-called L/4 wavelength matching plate.

〔Effect of the invention〕

As described above, according to the present invention, first, it is possible to obtain an image equivalent to the transmission image obtained with the transmission configuration with the reflection configuration as it is, and second, it is possible to obtain an image equivalent to the transmission image obtained with the transmission configuration, and secondly, it is possible to avoid C interference when detecting the above-mentioned signal. The time discrimination between the lens surface reflection signal and the above signal becomes easy and the third
It was possible to produce a remarkable effect in that the resolution of the imaging system was twice as high as that of the conventional configuration, and the contribution to the industry of ultrasonic microscopes, ultrasonic spectroscopy, etc. was extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of the main parts of a conventional ultrasonic imaging device, FIGS. 4 is a diagram showing the configuration of an embodiment of the present invention. FIG. 5 is a diagram showing the received waveform. FIG.
FIG. 7, which shows the configuration of another embodiment of the present invention, is a characteristic curve diagram showing resolution. Fig. 1 Fig. 2ρ Fig. 2 (a) Fig. 2 (4!) Fig. 3 He/★-beat 7 Fig. 4 Fig. 5 Fig. IL8 Low t Fig. 6 t/ρ

Claims (1)

[Claims] An imaging device that obtains an ultrasonic image of the sample using sound waves transmitted from the sample using a sonic probe system that generates and detects focused ultrasonic waves, characterized in that an acoustic reflecting mirror is provided below the sample. Ultrasonic imaging device 0