WO2014162671A1

WO2014162671A1 - Acousto-optical element and acousto-optical imaging apparatus

Info

Publication number: WO2014162671A1
Application number: PCT/JP2014/001511
Authority: WO
Inventors: 金子　由利子; 卓也岩本; 寒川　潮; 橋本　雅彦
Original assignee: パナソニック株式会社
Priority date: 2013-04-01
Filing date: 2014-03-17
Publication date: 2014-10-09

Abstract

An acousto-optical element disclosed in the present application for detecting, using light, refractive-index variation of a fluid generated by propagation of compressional waves, the acousto-optical element being provided with a support body having an interior space, a fluid (201a) filling the interior space, and a structure body (201b) disposed in the interior space and arranged in contact with the fluid, the structure body (201b) having a plurality of microcavities (201c) divided three-dimensionally, the plurality of microcavities communicating with each other, and the fluid being disposed inside the plurality of microcavities.

Description

Acoustooptic device and acoustooptic imaging apparatus

The present application relates to an acoustooptic device and an acoustooptic imaging device, and more particularly to an acoustooptic imaging device that acquires an ultrasonic echo obtained from a subject as an optical image and an acoustooptic device used therefor.

With the arrival of an aging society and the westernization of food culture, the number of people with cardiovascular diseases such as myocardial infarction and cerebral infarction is expected to increase. In recent years, social demands for the improvement of medical diagnosis technology related to the disease have increased. Under such circumstances, in the medical field of circulatory system, the characteristics as an elastic body of tissues and organs observed through high-speed dynamic behavior of organs are among the diagnostic information useful for grasping the pathology. is there. For example, in the body, by examining the displacement distribution on the heart wall or arterial wall in the frequency region faster than the heartbeat, the characteristics of the affected area as an elastic body can be investigated, and the degree of progression of arteriosclerosis and the size of the affected area can be determined. Efforts to judge are being made.

In such medical diagnosis, an ultrasonic diagnostic apparatus is often used because of the simplicity of the diagnostic method and the low burden on the subject. For example, as disclosed in Patent Document 1, an ultrasonic diagnostic apparatus irradiates an ultrasonic wave from outside the body toward an organ, and uses a scattered ultrasonic wave to generate a two-dimensional or three-dimensional image of the organ or tissue. get. Such an ultrasonic diagnostic apparatus generally performs transmission / reception of ultrasonic waves using a transducer array probe as a piezoelectric element, and uses information on a reflected wave from the living body converted into an electric signal to perform beam forming, etc. The internal structure of the living body is displayed as an image by this signal processing.

Since the information in the body is obtained by scanning an ultrasonic beam under the control of an electronic circuit, it is called an electronic scanning ultrasonic diagnostic apparatus, but a high-speed processing circuit is required to ensure real-time performance.

Japanese Patent No. 58-34580

A non-limiting exemplary acousto-optic imaging device according to the present invention includes an acousto-optic device used in an acousto-optic imaging device capable of widely imaging the inside of a living body without using a signal processing circuit with high calculation processing capability, and An acousto-optic imaging device is provided.

An acoustooptic device according to an aspect of the present invention is an acoustooptic device for detecting a change in the refractive index of a liquid generated by propagation of a dense wave using light, and includes a support having an inner space, A liquid filled in an internal space, and a structure disposed in the internal space and in contact with the liquid, the structure having a plurality of three-dimensionally divided microcavities, The plurality of microcavities communicate with each other, and the liquid is disposed in the plurality of microcavities.

According to the acoustooptic device according to one aspect of the present invention, even if the acoustooptic device is subjected to vibration or temperature change from the outside, the acoustooptic medium is less likely to flow or fluctuate. Therefore, it is possible to realize an acousto-optic imaging device that is less likely to cause image disturbance due to vibration or temperature change.

1 is a schematic diagram illustrating an embodiment of an acousto-optic imaging device of the present invention. It is a schematic diagram which shows embodiment of the acousto-optic device of this invention. It is a schematic diagram which expands and shows the acoustooptic medium of an acoustooptic device. It is a figure which shows the relationship between the frequency | count of substitution to the fluorine-type material in the middle of producing the acousto-optic element of an Example, and a sound speed. It is a figure which shows the transmittance | permeability of the acousto-optic element of an Example. It is a figure which shows the measurement system which evaluates the fluctuation | variation of the diffracted light in the acousto-optic element of an Example and a comparative example. (A) And (b) is a figure which shows the mode of the 1st-order diffracted light in the acousto-optic element of an Example and a comparative example, respectively. It is a figure which shows the result of having evaluated the fluctuation of the light spot of the diffracted light in the acousto-optic element of an Example and a comparative example. It is a figure which shows the conventional acousto-optic imaging device. It is a figure which shows typically the acoustooptic effect by Bragg diffraction.

The inventor of the present application examined a method of acquiring an image in a two-dimensional or three-dimensional manner, instead of obtaining an image by scanning an ultrasonic wave through a tissue inside a subject like a conventional ultrasonic diagnostic apparatus. . As a result, the inventors have conceived that an image of a tissue inside a subject is acquired using an acoustooptic effect that is an interaction between ultrasonic waves and light.

Specifically, as disclosed in Non-Patent Document 1, it has been found that the tissue inside the subject can be imaged by using the Bragg diffraction due to the density produced in the propagation medium by ultrasonic waves. FIG. 8 shows the configuration disclosed in Non-Patent Document 1. As shown in FIG. 8, the monochromatic light beam emitted from the laser light source 1101 is converted into a thick plane wave light beam by the beam expander 1102 and the aperture 1103. The plane wave light flux passes through the acoustic cell 1108 and the cylindrical lenses 1104 (a), 1104 (b), and 1104 (c), and is projected onto the screen 1105. The optical system composed of the cylindrical lenses 1104 (a), 1104 (b), and 1104 (c) has an asymmetric structure in which the convergence state differs between a direction horizontal to the paper surface and a direction perpendicular to the paper surface. For this reason, this optical system has astigmatism.

As indicated by the solid line in FIG. 8, the focal length of the cylindrical lens 1104 (a) is such that the plane wave light beam emitted from the beam expander 1102 is focused at the position of the focal plane 1106 on a plane parallel to the paper surface of FIG. Is set. The light beam that has passed through the focal plane 1106 diverges after passing through the focal plane 1106. The divergent light beam is converged by the cylindrical lens 1104 (b) and refocused on the screen 1105.

On the other hand, in the plane perpendicular to the paper surface of FIG. 8 including the optical axis of the beam expander 1102, the plane wave light beam that has passed through the beam expander 1102 enters the cylindrical lens 1104 (c) as a parallel light beam. Thereafter, the light is focused on the screen 1105 by the condensing action of the cylindrical lens 1104 (c). The positions and lens surfaces of the cylindrical lenses 1104 (a), 1104 (b), and 1104 (c) are enlarged images in the direction parallel to and perpendicular to the paper surface of FIG. 8 of the optical system constituted by these lenses. The ratio (magnification rate = size of the object 1109 to be photographed / size of the image on the screen 1105) is set to be equal.

The object 1109 to be photographed is immersed in an acoustic cell 1108 filled with water 1107. A to-be-photographed object 1109 is irradiated with monochromatic ultrasonic plane waves generated from an ultrasonic transducer 1111 driven by a signal source 1110 via water 1107. At that time, an ultrasonic scattered wave is generated in the object to be imaged 1109, and the scattered wave propagates through a passing region in the water 1107 of monochromatic light from the laser light source 1101. Since the main guided mode of ultrasonic waves propagating in water is a dense wave (longitudinal wave), a sound pressure distribution in water 1107, that is, a refractive index distribution that matches the ultrasonic wave front is generated in water.

Since the ultrasonic scattered wave is monochromatic (= ultrasonic wave having a single frequency), at a certain moment, the refractive index distribution generated in the water 1107 becomes a sinusoidal one-dimensional grating repeated at the ultrasonic wavelength. . Therefore, diffracted light (only the ± first-order diffracted light beam is expressed in the figure) is generated by the one-dimensional grating. The diffracted light appears as a light spot on the screen 1105. The brightness of the light spot is proportional to the amount of change in the refractive index of the one-dimensional grating, that is, the ultrasonic sound pressure.

FIG. 9 schematically shows the acoustooptic effect by Bragg diffraction. In FIG. 9, a point O ₁ is a point sound source (Huigens sound source) and radiates a spherical wave.

The light converges to the point O ₂ with the line segment S ₁ O ₂ and the line segment S ₃ O ₂ in FIG. The density of the acoustic medium caused by ultrasonic, -1-order Bragg diffraction light is generated in a direction that satisfies the Bragg angle theta _B at each point on the arc S ₁ S _3, it converges to a point O _3. From the geometric optical analysis, it is derived that the points O ₁ , O ₂ and O ₃ are located on the same circumference C. The triangle O ₁ O ₂ O ₃ is an isosceles triangle, and the angle O ₂ O ₁ O ₃ is 2θ _B.

In this way, a converging light acts on a diffraction grating formed by an acoustic wave that is a spherical wave, and by utilizing the angular dependence of Bragg diffraction, a spherical light source (arc S ₁ S ₃ ) is virtually generated, At the point O ₃ , the point sound source O ₁ can be generated as an optical image. Further, the ratio of the side O ₁ O ₂ to the side O ₂ O ₃ in the triangle O ₁ O ₂ O ₃ indicates the reduction rate in the image by Bragg diffraction light, and the reduction rate is O ₂ O ₃ / O ₁ O ₂ = λ / Λ. Here, Λ is the wavelength of the sound wave, and λ is the wavelength of the light. These principles are similarly applied to the + 1st order diffraction image, and an optical image of the point sound source O ₁ is generated at the point O ₃ ′ in FIG.

As can be understood from the above description with reference to FIG. 9, image formation based on such a principle is performed by an optical image forming action of a condensing optical system, as in the case of a normal optical camera. In other words, a receiver group required for a conventional electronic scanning ultrasonic diagnostic apparatus, a probe including a large number of ultrasonic transducers with uniform transmission / reception characteristics, and a reception signal group output from the receiver group The tissue in the subject can be imaged without using a high-speed and large-scale arithmetic circuit for performing signal processing such as beam forming for the.

However, Non-Patent Document 1 only discloses the acoustooptic effect by Bragg diffraction, and there is no suggestion how to realize imaging of a tissue in a living body by the acoustooptic effect.

When the inventor of the present application has examined the technology disclosed in Non-Patent Document 1 in detail, according to the configuration disclosed in Non-Patent Document 1, the aqueous medium of the acousto-optic cell flows due to temperature change, external vibration, or the like. It is considered that the image is disturbed.

In the technique of Non-Patent Document 1, the frequency of ultrasonic waves used is as high as 15 MHz or more. This is because the acousto-optic cell is composed of an aqueous medium, and the conditions under which Bragg diffraction occurs are limited by the relationship between the acoustic velocity of water (about 1500 m / s) and the wavelength of ultrasonic waves. . In a living body, absorption attenuation increases substantially in proportion to the frequency. Therefore, it is preferable to use an ultrasonic wave having a frequency of 10 MHz or less in order to image a deep interior of a subject. Therefore, even if the configuration disclosed in Non-Patent Document 1 is used as it is, it is difficult to obtain an image of the tissue in the body of the subject.

The inventor of the present application has studied such a problem in detail and has come up with a novel acoustooptic imaging device and acoustooptic element. An outline of one aspect of the acoustooptic imaging device and acoustooptic element of the present invention is as follows.

The plurality of microcavities may have a size of 1 mm or less.

The structure includes a plurality of unit structures smaller than the wavelength of light for detecting a change in the refractive index of the liquid, and the plurality of unit structures are connected to form the plurality of microcavities. May be.

In the structure, the plurality of unit structures may be connected by partial chemical bonds of molecules, and may form a three-dimensional network structure.

The structure may be transparent to the light.

The structure may be a wet gel having a skeleton formed of siloxane.

The structure may be a silica gel wet gel.

The liquid may contain a fluorine material.

An acoustooptic imaging device according to an aspect of the present invention includes an ultrasonic source that transmits an ultrasonic wave into a subject, and any one of the acoustooptic devices described above, wherein the ultrasonic wave reflected from the subject is reflected by the ultrasonic wave. Acousto-optic elements arranged so that sound waves propagate through the liquid, and convergent light that irradiates the reflected ultrasonic waves propagating through the liquid of the acousto-optic elements in a direction non-parallel to the traveling direction of the reflected ultrasound waves A light source that emits light, an imaging optical system that forms an image of the Bragg diffracted light of the convergent light generated by the acoustooptic device in a plane perpendicular to the propagation direction of the convergent light, and detects the image, And an image receiving unit for converting into a signal.

Hereinafter, embodiments of an acoustooptic imaging device and an acoustooptic device according to the present invention will be described. FIG. 1 is a schematic configuration diagram of an acoustooptic imaging device 100 of the present embodiment.

(Configuration of acousto-optic imaging device 100)
The acoustooptic imaging device 100 includes a light source 1, an acoustooptic element 2, an imaging optical system 3, an image receiving unit 4, and an ultrasonic source 5. As shown in FIG. 1, the propagation direction (optical axis) of the focused light 8 emitted from the light source 1 is the z-axis, and the direction perpendicular to the acoustic aperture 203 that is the surface where the subject 6 and the acoustooptic device 2 are in contact is the y-axis. In the following description, the x-axis is a direction perpendicular to the paper surface, which is a direction perpendicular to the y-axis and the z-axis.

The ultrasonic source 5 is disposed so as to be in contact with the subject 6 at the time of imaging, and transmits the ultrasonic wave 7 to the inside of the subject 6. The ultrasonic wave 7 propagates through the subject 6, and when an object 6a having different acoustic impedance such as an organ or body tissue exists in the subject 6, a reflected ultrasonic wave 7a is generated at the object 6a. The reflected ultrasonic wave 7a is a scattered wave. The acoustooptic device 2 has an acoustic aperture 202 c and is arranged so that the acoustic aperture 203 is in contact with the subject 6. The reflected ultrasonic wave 7a generated in the subject 6 is taken into the acoustooptic device 2 from the acoustic aperture 202c. The acoustooptic device 2 holds an acoustooptic medium 201, and an ultrasonic wave 7 b having information on the subject 6 in intensity and phase distribution propagates through the acoustooptic medium 201, and the refractive index changes due to the density of the acoustooptic medium 201. Produces.

The light source 1 irradiates the focused light 8 toward the acoustooptic device 2. The focused light 8 converges in the y direction in FIG. 1 to have a focal point, and propagates in parallel without converging in the x direction. The propagation direction of the focused light 8 is not parallel to the propagation direction of the ultrasonic wave 7b. The focal point of the focused light 8 is located on the opposite side of the light source 1 with the acousto-optic element 2 interposed therebetween.

In the acoustooptic device 2, the focused light 8 and the ultrasonic wave 7 b having information on the subject 6 in the intensity and phase distribution are in contact with each other to act, as described with reference to FIG. Bragg diffraction occurs due to the change in the refractive index due to the density of the light, and a −1st order diffracted light beam 8a, a 0th order diffracted light beam 8b and a + 1st order diffracted light beam 8c are generated. With the −1st order diffracted light beam 8 a and the + 1st order diffracted light beam 8 c, an image of the subject 6 is formed on the focal plane 9. Here, the focal plane 9 means a plane (xy plane) that passes through the focal point of the focused light 8 and is perpendicular to the propagation direction of the focused light 8.

The image formed on the focal plane 9 is incomplete and forms an image in the direction in which the focused light 8 is focused (y direction), but is not formed in the direction in which the focused light 8 propagates in parallel (x direction). I don't have a statue. The imaging optical system 3 is disposed at a position facing the light source 1 with the acoustooptic element 2 interposed therebetween, and the −1st order diffracted light beam 8a, the 0th order diffracted light beam 8b, and the + 1st order diffracted light beam transmitted through the acoustooptic element 2. 8 c enters the imaging optical system 3. The incomplete image of the subject 6 imaged by the −1st order diffracted light beam 8a and the + 1st order diffracted light beam 8c is also focused in the y direction by the image forming optical system 3, and the y direction and x Projected as a complete image imaged in the direction. The image receiving unit 4 is arranged further downstream of the imaging optical system 3, detects the −1st order diffracted light beam 8a or the + 1st order diffracted light beam 8c formed by the image forming optical system 3, and converts it into an electrical signal. Hereinafter, each component will be described in detail.

(Light source 1)
The light source 1 emits focused light 8 of monochromatic light. As described above, the focal point 9 is focused in the y direction, and the focal point is not propagated in parallel in the x direction. As the light source 1, for example, a gas laser represented by a He—Ne laser, a solid-state laser, a semiconductor laser narrowed by an external resonator, or the like can be used. The light source 1 further includes, for example, a beam expander and a cylindrical lens. The aperture of the light emitted from the laser is widened by the beam expander and focused only in the y direction by the cylindrical lens. The light beam emitted from the light source 1 may be continuous, or may be a pulsed light beam whose emission time can be controlled. By setting the wavelength of the generated focused light 8 to a wavelength band with less propagation loss in the acousto-optic medium 201, a high-luminance image can be obtained.

(Ultrasonic source 5)
The ultrasonic source 5 is disposed in contact with the subject 6 during imaging. The ultrasonic source 5 receives a signal from the ultrasonic signal source 10 and makes a continuous wave or a pulsed ultrasonic wave 7 having a plurality of identical sine waveforms incident on the subject 6. The ultrasonic wave 7 composed of a plurality of waves having the same sine waveform means an ultrasonic wave having a time waveform in which a sine waveform having a constant amplitude and frequency is continuously or continuously for a predetermined time. In addition, the ultrasonic wave 7 irradiates a region to be imaged of the subject 6 with a substantially uniform illuminance. The ultrasonic waves 7 that are incident on the subject 6 by the ultrasonic source 5 may not be plane waves. In the case of using pulsed ultrasonic waves 7, it is preferable that the duration of the time waveform is set to be equal to or greater than the reciprocal (cycle) of the carrier frequency.

The ultrasonic wave 7 is not limited to an acoustic signal having a sine wave as a carrier wave but may be an ultrasonic signal including a repetitive signal having a waveform that is not a sine wave such as a square wave or a sawtooth wave. The adhesion between the ultrasonic source 5 and the subject 6 may be improved by using a matching material such as an ultrasonic gel so that the ultrasonic source 5 can efficiently enter the ultrasonic wave 7 on the subject 6.

(Subject 6)
The subject 6 is made of a material whose ultrasonic wave propagation attenuation is not extremely large. An example of the subject 6 is a living body.

(Ultrasonic 7)
The ultrasonic wave 7 incident on the subject 6 propagates through the subject 6. When an object 6 a having different acoustic characteristics from the substance constituting the subject 6 exists in the subject 6, when the object 6 a is irradiated with the ultrasound 7, the reflected ultrasound 7 a having the same frequency as the ultrasound 7 is generated. Generated. The reflected ultrasonic wave 7a enters the acoustooptic device 2 through the acoustic aperture 202c. The ultrasonic wave 7b incident inside the acoustooptic device 2 has information on the subject 6 in intensity and phase distribution.

(Acousto-optic element 2)
FIG. 1B is a schematic perspective view of the acoustooptic device 2. The acoustooptic device 2 includes a cell 202 as a support and an acoustooptic medium 201 held in the inner space of the cell 202.

The cell 202 has an incident surface 202a on which the focused light 8 is incident, an output surface 202b, and an acoustic aperture 202c. The cell 202 and the acousto-optic medium 201 are made of a material that is transparent to the focused light 8. For example, as the cell 202, a cell such as quartz or glass can be used.

FIG. 2 shows a schematic diagram of the acousto-optic medium 201 held in the cell 202. The acousto-optic medium 201 includes a liquid 201a and a structure 201b in contact with the liquid 201a. As shown in FIG. 2, the structure 201b has a higher rigidity than the liquid 201a and includes a plurality of microcavities 201c that are three-dimensionally partitioned (partitioned). The plurality of microcavities 201c communicate with each other and form a continuous space. That is, the structure 201b is porous.

The liquid 201a is disposed in a space formed by the continuous plurality of microcavities 201c. Since the liquid 201a is arranged in the plurality of minute cavities 201c partitioned, the liquid 201a is less likely to flow or fluctuate even when subjected to vibration or temperature change from the outside of the acoustooptic device 2. For this reason, disturbance of the density of the acoustooptic medium 201 due to the ultrasonic wave 7b propagating through the acoustooptic medium 201 is suppressed, and the occurrence of disturbance in the detected image can be suppressed. Further, since the plurality of minute cavities 201 c communicate with each other, the propagation of the ultrasonic waves 7 b in the acousto-optic medium 201 is not hindered.

The size of the microcavity 201c can be determined according to vibrations and temperature changes that the acoustooptic device 2 receives. For example, when considering a sphere inscribed in each microcavity 201c (a sphere that can be inserted into each microcavity 201c), the diameter of the sphere is about 300 nm or less.

As the structure 201b having such a microcavity 201c, for example, silica wet gel can be used. The silica wet gel is a polymer having a skeleton formed of siloxane, and as shown in FIG. 2, the silica particles 201d are connected to the adjacent silica particles 201d by chemical bonds. Silica particles 201d have a unit structure and form a three-dimensional network structure, thereby forming a plurality of microcavities 201c. In this case, since the silica particles 201d are transparent to light having a wavelength of about 380 nm or more, the light source 1 that emits the focused light 8 having a wavelength of 600 nm or more is preferably used. In order to suppress scattering of the focused light 8 by the silica particles 201d, particularly Mie scattering, the diameter of the silica particles 201d is preferably smaller than the wavelength of the focused light 8, and is preferably 300 nm or less. For example, the diameter of the silica particle 201d is about 20 nm.

As another example of the structure 201b, for example, a porous structure used for a biomaterial such as an artificial bone can be used. Such an artificial bone can be formed, for example, by partially sintering and laminating thin ceramic green sheets of about 1 mm or less with laser light. Also, a resin porous structure may be used. In this case, for example, the resin powder can be formed by a powder sintering additive manufacturing method.

Various liquids such as water can be used for the liquid 201a. When the sound speed of the liquid 201a is small, a high-resolution image can be acquired. For this reason, the liquid 201a preferably contains a fluorine-based material. As described above, the sound speed of water is about 1500 m / sec, but the sound speed of fluorine-based materials is generally smaller than this. For example, the speed of sound of NovecTM 7200 (hydrofluoroether) manufactured by Sumitomo 3M Limited is 630 m / sec, and the speed of sound of fluorine-based liquid materials such as NovecTM 7000, Novec TM 7100, Novec TM 7200, Novec TM 7300, Fluorinert TMFC-72 and FC-3283 is also slow. Material.

The focused light 8 from the light source 1 enters the acoustooptic device 2. The ultrasonic wave 7 b having the information of the subject 6 taken into the acoustooptic device 2 propagates through the acoustooptic medium 201 and comes into contact with the focused light 8. Since the ultrasonic wave 7b propagating through the acoustooptic medium 201 is a dense wave (longitudinal wave), a sound pressure distribution of the acoustooptic medium 201, that is, a refractive index distribution that matches the wavefront of the ultrasonic wave 7b is generated in the medium. . At a certain moment, the refractive index distribution generated in the acousto-optic medium 201 becomes a sinusoidal diffraction grating repeated at the ultrasonic wavelength. Therefore, when the focused light 8 is incident, a diffracted light beam is generated by the diffraction grating. For simplicity, FIG. 1 shows only the −1st order diffracted light beam 8a, the 0th order diffracted light beam 8b, and the + 1st order diffracted light beam 8c. In general, the diffracted light is composed of Bragg diffracted light and Raman-Nath diffracted light. The device according to the invention is applied under conditions where the described Bragg diffracted light becomes the main diffracted light. In this case, the diffracted light generated is only the −1st order diffracted light beam 8a, the 0th order diffracted light beam 8b, and the + 1st order diffracted light beam 8c. The brightness of the diffracted light is proportional to the amount of change in the refractive index of the diffraction grating, that is, the sound pressure of the ultrasonic waves.

Note that the ultrasonic wave 7b continues to propagate after contact with the focused light 8. However, if the ultrasonic wave 7b is reflected at the end of the acoustooptic device 2 and contacts the focused light 8 again, acquisition of an image may be hindered. Therefore, reflection of ultrasonic waves may be prevented by providing the acoustic optical element 2 with the sound wave absorption end 204. In this case, the sound wave absorption end 204 is disposed at a position farther from the acoustic aperture 202 c than the propagation region of the focused light 8 in the acoustooptic device 2.

Note that a matching material such as an ultrasonic gel is provided between the acoustic aperture 203 of the acoustooptic device 2 and the subject 6 so that the reflected ultrasound 7a from the subject 6 is efficiently incident on the acoustooptic device 2. Adhesion may be enhanced by application.

(-1st order diffracted light beam 8a and + 1st order diffracted light beam 8c)
The −1st order diffracted light beam 8a and the + 1st order diffracted light beam 8c generated by the action of the ultrasonic wave 7b having the information of the subject 6 and the focused light 8 in the acousto-optic medium 201 pass through the focal point of the focused light 8 and converge. The focal plane 9, which is a plane perpendicular to the propagation direction of the light 8, is focused in the y direction, and an optical image of the subject 6 is formed on the focal plane 9. However, the optical image of the subject 6 generated at this time is an incomplete optical image that is not formed in the x direction.

(Imaging optical system 3)
The −1st order diffracted light beam 8a, the 0th order diffracted light beam 8b, and the + 1st order diffracted light beam 8c transmitted through the acoustooptic device 2 are incident on the imaging optical system 3. As the −1st order diffracted light beam 8a and the + 1st order diffracted light beam 8c propagate through the imaging optical system 3, an incomplete optical image is focused even in the z direction, and the x and y directions are focused on the imaging surface 91. It is projected as a complete image formed in either direction.

The imaging optical system 3 includes, for example, a cylindrical lens 3a and a cylindrical lens 3b as shown in FIG. The cylindrical lens 3a is arranged so as to have a refractive power in the y direction and no refractive power in the x direction. The cylindrical lens 3b is arranged so as to have a refractive power in the x direction and no refractive power in the y direction.

Similarly, the 0th-order diffracted light beam 8b that has passed through the focal plane 9 is converged in the y direction by the cylindrical lens 3a in the imaging optical system 3, and is focused again on the imaging plane 91. In the x direction, the 0th-order diffracted light beam 8b is incident on the cylindrical lens 3b as a parallel light beam. Then, the third cylindrical lens 3b is focused on the image plane 91 by the light condensing action.

(Image receiving unit 4)
The image receiving unit 4 detects the −1st order diffracted light beam 8 a or the + 1st order diffracted light beam 8 c on the imaging surface 91. As described above, since an image is projected onto the imaging surface 91 as a complete image formed in both the x and y directions, an optical image of the subject 6 is obtained via the ultrasonic wave 7.

The 0th-order diffracted light beam 8b or the other diffracted light beam that does not receive the image may be blocked by the light-shielding unit 15 so that only the −1st-order diffracted light beam 8a or the + 1st-order diffracted light beam 8c is received by the image receiving unit 4.

The image receiving unit 4 is typically a solid-state imaging device such as a CCD or a CMOS, and captures the light intensity distribution of the diffracted image by the −1st order diffracted light beam 8a or the + 1st order diffracted light beam 8c as an optical image to obtain an electric signal. Convert to

As described above, according to the acoustooptic imaging device of the present embodiment, ultrasonic waves are transmitted toward the inside of the subject, and reflected ultrasonic waves obtained from the inside are propagated to the acoustooptic element. By irradiating the reflected ultrasonic wave propagating through the acoustooptic medium of the acoustooptic element with the convergent light, diffracted light mainly due to Bragg diffraction can be obtained. Therefore, an image inside the subject can be optically acquired at high speed without performing complicated ultrasonic signal processing.

In addition, since the sound velocity of the acousto-optic medium is smaller than the sound velocity of the subject, the wavelength of the ultrasonic wave propagating through the acousto-optic medium is shorter than the ultrasonic wave propagating through the subject, thereby transmitting from the ultrasonic transmitter. Therefore, it is possible to reduce the frequency of the ultrasonic wave to be used, and it is possible to use the low-frequency ultrasonic wave that is not easily attenuated inside the subject.

In addition, since the liquid of the acousto-optic medium is disposed in a space formed by a series of partitioned or partitioned microcavities, it receives vibrations from the outside of the acousto-optic element, temperature changes, and the like. However, the liquid is less likely to flow or fluctuate. For this reason, the coarse / fine disturbance of the acoustooptic medium due to the ultrasonic wave propagating through the acoustooptic medium is suppressed, and the occurrence of the disturbance in the detected image can be suppressed. Therefore, according to the acoustooptic device of the present embodiment, the inside of the subject can be imaged with high resolution.

(Example of acoustooptic device)
Hereinafter, the acoustooptic device of this embodiment will be described and the results of the characteristic evaluation will be described.

As the cell 202 of the acoustooptic device 2, a cell produced by bonding five surfaces of synthetic quartz glass (product name: Tempax glass) was used. The cell 202 has a cup shape, and the inner space is filled with the acousto-optic medium 201. Silica wet gel was used for the structure 201b of the acousto-optic medium 201, and NovecTM 7200 manufactured by Sumitomo 3M Limited was used for the liquid.

The silica wet gel was prepared by the following method.
Tetramethoxysilane (hereinafter referred to as TMOS: manufactured by Kanto Chemical Co., Inc.), ethanol (manufactured by Wako Pure Chemical Industries), and aqueous ammonia (0.05 N: manufactured by Wako Pure Chemical Industries, Ltd.) in a weight ratio of 1: 1.62: 0.47 Weighed with.

First, TMOS and ethanol were weighed and mixed, and stirred for about 1 minute. Then, while continuing stirring, ammonia water was added dropwise, and stirring was further performed for about 1 minute. Thus, TMOS was dehydrated and condensed to obtain a sol solution. A sol solution was placed in the cell 202. The cell 202 for preventing the sol solution from drying was placed in an airtight container and allowed to stand for 10 hours or more at a temperature of 40 degrees. During this time, the sol solution gelled, and a structure 201 b made of silica wet gel was synthesized in the cell 202.

Since the completed silica wet gel is in a state of containing ethanol, methanol, aqueous ammonia, etc., these liquids are replaced with Novec ™ 7200. Specifically, a silica wet gel containing these liquids was immersed in Novec ™ 7200. Since NovecTM 7200 has an ether structure, it is soluble in alcohol and the like. For this reason, after the liquid encapsulated in the silica wet gel and the NovecTM 7200 were compatible, the liquid was discarded and again immersed in a new NovecTM 7200. Replacement was performed by repeating this. The liquid encapsulated in the silica wet gel and the NovecTM 7200 were immersed for about one night, and then the liquid was discarded and immersed in the NovecTM 7200 four times to perform the replacement almost completely.

The completion of the replacement was confirmed by measuring the speed of sound of the acousto-optic medium 201. FIG. 3 is a diagram showing that the speed of sound of the acousto-optic medium 201 changes as replacement is performed. The sound speed of ethanol is about 1500 m / s, and the sound speed of NovecTM 7200 is 632 m / s. As shown in FIG. 3, the speed of sound decreases as the number of substitutions increases because the liquid is replaced with NovecTM 7200 from a liquid such as ethanol. In the above-described replacement method, it is difficult to replace 100% with NovecTM 7200, so the sound speed after replacement converged at about 650 m / s. The replacement was completed when the drop in sound speed converged. In the case where it is necessary to proceed with replacement in order to lower the sound speed further, a method of discarding the old immersion liquid while dropping new NovecTM 7200 into the immersion liquid is effective.

Thus, the acoustooptic imaging apparatus 100 including the acoustooptic medium 201 including the structure 201b made of silica wet gel and the liquid 201a made of NovecTM 7200 filled in the microcavity 201c of the structure 201b was completed.

FIG. 4 shows the light transmittance of the acousto-optic imaging device 100. The transmittance was measured using a Hitachi U-4000 spectrophotometer. The measuring device received the transmitted light with an integrating sphere. As a result of the measurement, the transmittance was 70% or more between wavelengths of 360 nm and 1158 nm. This is presumably because the silica particles forming the silica wet gel are sufficiently smaller than the wavelength of light used for the measurement, and NovecTM 7200 has a high transmittance in the above-mentioned wavelength range. The transmittance varies depending on the material used for the acoustooptic medium 201. Since the higher the transmittance, the higher the resolution of the image that can be obtained, the wavelength selection of the light to be used can be performed according to the required resolution.

FIG. 5 schematically shows a measurement system for evaluating the fluctuation of the diffracted light. The acoustooptic device 2 was placed on a SUS case 51 to which a vibrator 50 (manufactured by Fuji Ceramics Co., Ltd., ultrasonic wave (A) 5Z10D-SYX (C-6)) was bonded. In order to smoothly propagate ultrasonic waves, one drop of water was dropped on the case 51, and then the acoustooptic device 2 was arranged. The vibrator 50 was connected to the power source 53 via the function generator 52 and oscillated a 2.6 MHz burst wave. Regarding the electrical characteristics of the vibrator, the voltage was 1 V and the current was 19 mA.

The 2.6 MHz ultrasonic wave oscillated from the vibrator propagates to the acoustooptic device 2. Since the main waveguide mode of the ultrasonic wave propagating to the acoustooptic medium 201 is a sparse / dense wave (longitudinal wave), a refractive index distribution that matches the ultrasonic wavefront is generated in the acoustooptic medium 201. At a certain moment, the refractive index distribution generated in the acousto-optic medium 201 becomes a sinusoidal one-dimensional grating repeated at the ultrasonic wavelength.

When the laser beam 55 (He—Ne laser light source 54: wavelength 632 nm) is transmitted through the acoustooptic medium 201 having a one-dimensional grating, the 0th-order light 56 and the first-order diffracted light 57 appear as light spots. Since the 0th-order light 56 is not an observation target, it was cut with a 0th-order light cut mask and only the 1st-order diffracted light 57 was observed with the CCD 59. The state of the observed spot is shown in FIG. The spot light was traced for 25 seconds to evaluate the fluctuation. The result is shown in FIG.

For comparison, the structure 201b is not arranged in the cell 202, but only the NovecTM 7200 that is the liquid 201a is arranged, and the state of the observed spot is shown in FIG. 6B. Moreover, the evaluation result of fluctuation is shown in FIG.

6A and 6B, it can be seen that the spot of the light spot is smaller in FIG. 6A, and the fluctuation of the diffracted light is suppressed by the structure 201b. Further, as shown in FIG. 7, when the structure 201b is present (example), the fluctuation is suppressed to 1 nm or less, but when there is no structure 201b (comparative example), the fluctuation is 3 nm or more. I understand. From these results, it was found that the structure 201b is effective in suppressing the fluctuation of the acoustooptic medium in the acoustooptic element.

The acoustooptic device and acoustooptic device disclosed in the present application can be used for various ultrasonic diagnoses.

DESCRIPTION OF SYMBOLS 1 Light source 2 Acoustooptic device 3 Coupling lens system 4 Image receiving part 5 Ultrasonic source 6 Subject 7 Ultrasonic wave 8 Focusing light 9

Focal plane

3a, 3b Cylindrical lens 51 Ultrasonic signal source 6a Object 7 Ultrasonic wave 7a Reflected ultrasonic wave 8a -1 Next order diffracted light beam 8b 0th order diffracted light beam 8c + 1st order diffracted light beam 201 Acoustooptic medium 201a Liquid 201b Structure 202 Cell

Claims

An acoustooptic device for detecting, using light, a change in the refractive index of a liquid generated by propagation of dense waves,
A support having an internal space;
A liquid filled in the inner space;
A structure disposed in the inner space and in contact with the liquid;
The structure includes a plurality of three-dimensionally divided microcavities, and the plurality of microcavities communicate with each other.
An acoustooptic device in which the liquid is disposed in the plurality of microcavities.
The acoustooptic device according to claim 1, wherein the plurality of microcavities have a size of 1 mm or less.
The structure includes a plurality of unit structures smaller than the wavelength of light for detecting a change in the refractive index of the liquid, and the plurality of unit structures are connected to form the plurality of microcavities. The acoustooptic device according to claim 2.
The acoustooptic device according to claim 3, wherein in the structure, the plurality of unit structures are connected by partial chemical bonds of molecules to form a three-dimensional network structure.
The acoustooptic device according to claim 3, wherein the structure is transparent to the light.
6. The acoustooptic device according to claim 3, wherein the structure is a wet gel having a skeleton formed of siloxane.
The acoustooptic device according to any one of claims 3 to 5, wherein the structure is a wet silica gel.
The acoustooptic device according to any one of claims 1 to 7, wherein the liquid includes a fluorine-based material.
An ultrasonic source for transmitting ultrasonic waves into the subject;
The acoustooptic device according to any one of claims 1 to 8, wherein the acoustooptic device is arranged such that reflected ultrasound from the ultrasound from the subject propagates through the liquid;
A light source that emits convergent light that irradiates the reflected ultrasonic wave propagating through the liquid of the acousto-optic element in a direction non-parallel to the traveling direction of the reflected ultrasonic wave;
An imaging optical system that forms an image of the Bragg diffracted light of the convergent light generated by the acoustooptic element on a plane perpendicular to the propagation direction of the convergent light;
An acoustooptic imaging device comprising: an image receiving unit that detects the image and converts the image into an electric signal.