JP2017042189A - Ultrasonic probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic probe capable of improving detection performance (S/N) of an ultrasonic wave from a subject.SOLUTION: In order to reduce multiple reflection of an ultrasonic wave generated between a subject and a part of a housing where a sensor is not installed, an ultrasonic probe 180 includes a plurality of ultrasonic sensors 200, and a housing which has a concave part recessed toward a subject 120 to be arranged at a measurement position when measurement is performed, and supports the plurality of ultrasonic sensors. The ultrasonic sensors are arranged so that the sensor surfaces are directed toward a subject side. The housing includes an ultrasonic reflection control layer on the subject side surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic probe used as an ultrasonic transducer (transducer) and an apparatus using the same.

  Conventionally, micromechanical members manufactured by micromachining technology can be processed on the micrometer order, and various micro functional elements are realized using these. Capacitance type electromechanical transducers such as cMUT (Capacitive Micromachined Ultrasonic Transducer) using such a technique have been studied as an alternative to piezoelectric elements. According to such a capacitive electromechanical transducer, an acoustic wave such as an ultrasonic wave or a photoacoustic wave (which may be represented by an ultrasonic wave in this specification) is transmitted and received using the vibration of the vibrating membrane. In particular, excellent broadband characteristics can be easily obtained in a liquid.

  The photoacoustic diagnostic apparatus irradiates a subject with light, receives a photoacoustic signal from the subject with a sensor such as a piezoelectric element or a capacitive transducer, and based on the received signal, a photoacoustic image of the subject Is a device used for diagnosis. Receives photoacoustic waves (typically ultrasonic waves) generated in the subject by irradiating the subject with pulsed light from the light source and absorbing the energy of the pulsed light that propagates and diffuses in the subject, and receives the received signal Research on imaging a subject based on the above is being actively promoted in the medical field.

  Patent Document 1 proposes a photoacoustic diagnostic apparatus that receives an acoustic wave using piezoelectric elements discretely arranged on a hemispherical surface to form a photoacoustic image. An example is disclosed in which piezoelectric elements are spirally arranged on a hemisphere and the hemisphere itself is scanned.

US Patent Publication No. 2013/0217995

  When using the photoacoustic diagnostic apparatus as described above, if the ultrasonic wave, which is a photoacoustic wave generated from the subject, is reflected by a portion where the sensor is not disposed, the reflected ultrasonic wave reaches the subject and the subject There is a possibility of distorting ultrasonic waves generated from the specimen. Further, since the light is reflected again by the subject and returned to the sensor, it becomes noise when a desired ultrasonic wave is detected. Further, not only the photoacoustic diagnostic apparatus but also a transmission / reception probe that transmits ultrasonic waves from a sensor to a subject and receives ultrasonic waves reflected by the subject is pointed out. In other words, multiple ultrasonic reflections occur between the subject and the portion where the sensor is not arranged, which may reduce the detection performance of the desired ultrasonic waves. In particular, when the sensors are sparsely arranged, that is, sparsely arranged, the number of areas where the sensors are not arranged increases, and thus the detection performance may be significantly degraded due to multiple reflections of ultrasonic waves. In addition, as the distance between the subject and the sensor becomes shorter, it becomes difficult to separate desired ultrasonic waves from ultrasonic waves due to multiple reflection, and the detection performance is likely to deteriorate significantly.

  In view of the above problems, an ultrasonic probe of the present invention has a plurality of ultrasonic sensors and a concave portion that is concave toward a subject to be placed at a measurement position at the time of measurement, and the plurality of ultrasonic sensors And a housing that supports. The ultrasonic sensor is arranged so that the sensor surface faces the subject side, and the casing has an ultrasonic reflection control layer on the subject side surface.

  In the present invention, the detection performance (S / N) of the ultrasonic wave from the subject is improved by reducing the multiple reflection of the ultrasonic wave generated between the subject and the part of the casing where the sensor is not arranged. Things will be possible.

The block diagram of an example of the photoacoustic diagnostic apparatus of this invention. The perspective view of an example of the ultrasonic probe used for the photoacoustic diagnostic apparatus of this invention. FIG. 3 is an enlarged view of a part of the ultrasound probe on the subject side. The outside enlarged view of an example of an ultrasonic probe. FIG. 4 is a cross-sectional view taken along line AB in FIG. 3. The subject side enlarged view of an example of the ultrasonic probe before sensor arrangement | positioning. The perspective view which shows the CD cross section of FIG. The figure which shows an example (Example 1) of the ultrasonic sensor of this invention. FIG. 9 is an XZ axis slice diagram of FIG. 8 (a diagram obtained by slicing along a plane including the X axis and the Z axis). The figure which shows an example of the receiving surface of the sensor of FIG. EF sectional drawing of FIG. Sectional drawing which shows an example of the manufacturing method of an electrostatic capacitance type electromechanical transducer. Sectional drawing similar to FIG. 3 of the ultrasonic probe of Example 2. FIG. Sectional drawing similar to FIG. 3 of the ultrasonic probe of Example 3. FIG.

  In the following embodiments and examples, the ultrasonic sensor is arranged so that the sensor surface faces the subject side, and the housing that supports the plurality of ultrasonic sensors should be arranged at the measurement position at the time of measurement. A concave portion that is concave toward the subject is provided, and an ultrasonic reflection control layer is provided on the subject-side surface. The ultrasonic reflection control layer has a function of controlling the amount of reflected waves including absorption, scattering, interference, and the like. The concave portion of the casing is typically substantially spherical, but for example, the casing may be formed in a polyhedral structure, and the concave portion of the housing may be formed by connecting planes. .

  Hereinafter, embodiments of the present invention will be described. Although the photoacoustic diagnostic apparatus is described in the present embodiment, an ultrasonic diagnostic apparatus that does not include a light source may be used, and the present invention is not limited to the present embodiment.

<System configuration>
A configuration example of an ultrasonic probe or a photoacoustic diagnostic apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of this embodiment. The photoacoustic diagnostic apparatus according to the present embodiment includes an attachment unit 100, a shape holding unit 110 that holds a subject 120, an acoustic matching material 130, an optical system 140, a light source 150, a processing unit 160, an image display unit 170, and an ultrasonic probe. 180 included. The measurement is performed by inserting the breast of the subject 120 into the shape holding unit 110. The pulsed light generated from the light source 150 is guided in the direction of the shape holding unit 110 from the vicinity of the vertex of the ultrasonic probe 180 via the optical system 140 that forms a part of the light irradiation unit for irradiating the subject with light. The subject 120 is irradiated. When a part of the energy of the light propagating through the subject is absorbed by a light absorber such as blood, an acoustic wave is generated due to thermal expansion of the light absorber of the subject 120. The acoustic wave generated in the subject 120 propagates in all directions, propagates through the acoustic matching material 130, is received by each of the ultrasonic sensors 200 disposed in the ultrasonic probe 180, and is analyzed by the processing unit 160. . The analysis result is output to the image display unit 170 as an image representing the characteristic information of the subject 120.

<Light source 150>
The light source 150 is a device that generates pulsed light. The light source is preferably a laser light source, but a light emitting diode, flash lamp, or the like can also be used. Irradiation timing, waveform, intensity, and the like are controlled by a light source control unit (not shown). In order to effectively generate the photoacoustic wave, it is necessary to irradiate light in a sufficiently short time according to the thermal characteristics of the subject 120. When the subject 120 is a living body, the pulse width of the pulsed light generated from the light source is preferably about 10 to 50 nanoseconds. Further, the wavelength of the pulsed light is desirably a wavelength at which the light propagates to the inside of the subject. Specifically, it is desirable that the thickness be about 600 nm or more and 1200 nm or less. The light in this region can reach relatively deep in the living body, and information on the deep portion can be obtained. Furthermore, it is desirable that the wavelength of the pulsed light has a high absorption coefficient with respect to the observation target.

<Optical system 140>
The optical system 140 is means for guiding the pulsed light generated by the light source 150 to the subject 120. Specifically, the optical member is composed of an optical fiber, a lens, a mirror, a diffusion plate, or the like so as to obtain a desired beam shape and light intensity distribution. In addition, when guiding light, the shape and the light density may be changed so as to obtain a desired light distribution using these optical devices. The optical apparatus is not limited to those listed here, and any optical apparatus may be used as long as it satisfies such functions.

<Shape holding part 110>
The shape holding unit 110 is a member for keeping the shape of the subject 120 constant. The shape holding part 110 is attached to the attachment part 100. When irradiating the subject 120 with light through the shape holding unit 110, the shape holding unit 110 is preferably transparent to the irradiation light. For example, as a material of the shape holding member 110, polymethylpentene, polyethylene terephthalate, or the like can be used. Further, when the subject 120 is a breast, the shape holding unit 110 is preferably a shape obtained by cutting a sphere in a certain cross section in order to keep the shape constant while reducing deformation of the breast shape. Note that the shape of the shape holding unit 110 can be appropriately designed according to the volume of the subject 120 and the desired shape after holding. It is preferable that the shape holding unit 110 is configured to fit the outer shape of the subject 120 and the shape of the subject 120 is substantially the same as the shape of the shape holding unit 110. The photoacoustic diagnostic apparatus may perform measurement without using the shape holding unit 110.

<Subject 120>
The subject 120 is a measurement target. Specific examples include a living body such as a breast, and a phantom that simulates the acoustic characteristics and optical characteristics of a living body when adjusting the apparatus.

<Acoustic matching material 130>
The acoustic matching material 130 fills the space between the subject 120 and the ultrasonic probe 180 and acoustically couples the subject 120 and the ultrasonic probe 180. In the present embodiment, the acoustic matching material 130 can be disposed between the ultrasonic probe 180 and the shape holding unit 110. An acoustic matching material 130 is also disposed between the shape holding unit 110 and the subject 120. An acoustic matching material 130 made of a different material may be disposed between the ultrasonic probe 180 and the shape holding unit 110 and between the shape holding unit 110 and the subject 120.

  In addition, it is preferable that the acoustic matching material 130 is a material in which a photoacoustic wave is hard to attenuate inside. The acoustic matching material 130 is preferably a material that transmits the pulsed light generated by the light source 150. The acoustic matching material 130 is preferably a liquid. Specifically, water, castor oil, gel, or the like can be used as the acoustic matching material 130.

<Ultrasonic probe 180>
The ultrasonic probe 180 is a means for converting an acoustic wave generated inside the subject 120 into an analog electric signal. The ultrasonic probe 180 has a concave portion that is concave toward the subject placed at the measurement position. In this embodiment, the ultrasonic probe 180 has a hemispherical bowl shape. The radius of the concave portion on the subject side is, for example, several mm to several tens of cm, and may be changed according to the size of the subject. The difference between the thickness of the concave portion, that is, the radius of the surface of the concave portion on the subject side (inner surface) and the radius of the concave portion on the non-subject side (outer surface) is several mm to several centimeters. What is necessary is just to change according to the magnitude | size of the whole apparatus.

  A plurality of ultrasonic sensors 200 are arranged on the ultrasonic probe 180. The ultrasonic sensor 200 only needs to be capable of receiving at least ultrasonic waves. It may be capable of both reception and transmission. For example, a piezoelectric ceramic material typified by PZT (lead zirconate titanate) or a polymer piezoelectric film material typified by PVDF (polyvinylidene fluoride) can be used. Further, an element other than the piezoelectric element may be used. For example, a capacitive element such as cMUT, an acoustic wave receiving element using a Fabry-Perot interferometer, or the like can be used. It is preferable that a seal member is provided between the ultrasonic sensor 200 and a later-described casing 184 to prevent an acoustic matching material from entering between the ultrasonic sensor 200 and the casing 184 described later.

  The configuration of the ultrasonic probe 180 will be described with reference to FIGS. FIG. 2 is a diagram of an example of the ultrasonic probe of the photoacoustic diagnostic apparatus of the present embodiment, and FIG. 3 is an enlarged view of the inner surface of a portion 183 surrounded by a broken line in FIG. 4 is an enlarged view of the outer surface showing the back surface of FIG. 3, and FIG. 6 is an enlarged view of a portion 183 surrounded by a broken line in FIG. 2 before the ultrasonic sensor 200 is arranged.

  The ultrasonic sensor 200 is arranged so that the ultrasonic reception surface (sensor surface) faces the subject 120 side. The acoustic wave probe 180 is composed of an inner side 182 and an outer side 181, and the ultrasonic sensor 200 on the outer side 181 is connected to the processing unit 160 through a wiring 202 such as a conducting wire or a cable. The light reflection control layer 220 and the ultrasonic reflection control layer 230 are disposed on the inner side 182 of the casing 184 where the ultrasonic sensor 200 is not disposed. A light reflection layer 201 is disposed on the ultrasonic wave receiving surface of the ultrasonic sensor 200. The material of the housing 184 of the ultrasonic probe 180 may be any material that can be formed by processing into a concave shape such as a hemispherical shape, such as metal, ceramic, or resin.

  The light reflection control layer 220 only needs to be able to control light reflection, and may be a light reflection layer. The light reflecting layer has a function of reflecting light having a wavelength emitted from the light source 150 used for generating a photoacoustic wave by irradiating the subject 120 with pulsed light from the light source 150. The light reflection layer may be a film having a high reflectance with respect to the wavelength of the light source 150. As the film having a high reflectance, Al, Au, a dielectric multilayer film, or the like is used. The reflectance of the light reflection layer is preferably 80% or more, and more preferably 90% or more in the light used. The light reflecting layer preferably has a function of transmitting acoustic waves generated from the subject 120. In general, since the acoustic impedance of the acoustic matching material is 1 MRayls to 5 MRayls, the acoustic impedance of the light reflecting layer is preferably 1 MRayls or more and 5 MRayls or less. By making the acoustic impedance close to that of the acoustic matching material, it is possible to reduce the reflection of ultrasonic waves at the interface. Further, it is preferable that the thickness is sufficiently thin with respect to the frequency (wavelength) of the photoacoustic wave. By having the light reflection layer, the photoacoustic wave signal from the housing 184 that is generated when the housing 184 is irradiated with pulsed light due to scattering of the pulsed light generated from the light source 150 or reflection at the shape holding unit 110. Generation can be reduced.

  The ultrasonic reflection control layer 230 may control the reflection of ultrasonic waves, and preferably includes an ultrasonic absorption layer, an ultrasonic scattering layer, or both layers. A configuration including an ultrasonic interference layer that suppresses the return of ultrasonic waves by using ultrasonic interference may be used. The ultrasonic reflection control layer only needs to be configured to prevent multiple reflection in which ultrasonic waves are reflected back to the subject when the ultrasonic waves reflected or generated from the subject reach the case 184. . The ultrasonic absorption layer has a function of absorbing photoacoustic waves generated by irradiating the subject 120 with pulsed light from the light source 150. Any layer having a high absorption rate for the photoacoustic wave may be used. As the ultrasonic absorption layer, commercially available Atec Flex-F28 and AptFlex-F36 manufactured by ESTEC can be used. Ultrasonic absorption based on solvent containing fine particles such as cross-linked butyl rubber, glass epoxy, silicone gel, silicone rubber, urethane rubber, tungsten, alumina, copper or its compound, platinum, iron or its compound, ferrite powder, etc. A layer can be made. As for the ultrasonic scattering layer, ultrasonic waves can be scattered by roughing the surface of the housing 184 on the inner side 182 of the hemispherical ultrasonic probe 180 into a conical projection shape such as a cone. Multiple reflections can be reduced by scattering. Further, by providing an ultrasonic absorption layer on the housing 184 having a roughened surface, ultrasonic waves that could not be absorbed by the ultrasonic absorption layer were scattered by the ultrasonic scattering layer, and the scattered ultrasonic waves were converted into ultrasonic waves. It can also be absorbed by the absorbent layer. By having both the ultrasonic absorption layer and the ultrasonic scattering layer, the thickness of the ultrasonic reflection control layer can be reduced. Further, the ultrasonic absorption layer may be formed into a two-layer structure and roughened inside the ultrasonic absorption layer. By roughening the inside of the ultrasonic absorption layer, it is possible to absorb ultrasonic waves and absorb scattered ultrasonic waves inside the ultrasonic absorption layer. The ultrasonic interference layer has a layer structure in which the layer thickness is appropriately set so that the phase difference of reflected ultrasonic waves from each interface in consideration of the refractive index of the material is approximately an odd multiple of π / 2 (half wavelength). Can be realized. The acoustic impedance of the ultrasonic absorption layer is generally 1 MRayls to 5 MRayls since the acoustic impedance of the acoustic matching material is generally 1 MRayls to 5 MRayls. By making the acoustic impedance close to that of the acoustic matching material, it is possible to reduce the reflection of ultrasonic waves at the interface.

  By including the ultrasonic reflection control layer 230, it is possible to reduce the multiple reflection inside the ultrasonic probe 180 of the photoacoustic wave generated from the subject 120 by the pulsed light from the light source 150. The light reflection control layer 220 is preferably provided on the inner surface 182 of the ultrasonic probe 180, and the ultrasonic reflection control layer 230 is preferably provided between the light reflection control layer 220 and the housing 184. When the light reflection control layer 220 is a light reflection layer, the case 184 reflects the pulsed light when the case 184 is irradiated with pulsed light due to scattering of the pulse light from the light source 150 or reflection at the shape holding unit 110. The generation of a photoacoustic wave signal from can be reduced. The photoacoustic wave generated from the subject 120 is absorbed by the ultrasonic absorption layer when it passes through the light reflection layer and reaches the ultrasonic reflection control layer 230, and multiple reflection of the photoacoustic wave inside the ultrasonic probe 180 is performed. Can be reduced.

  When the distance between the ultrasonic probe 180 and the subject 120 is large, there is a time difference from the first photoacoustic wave signal generated from the subject 120 even if multiple reflections of the photoacoustic wave occur. These signals detected by the sonic sensor 200 can be separated. However, as the distance between the ultrasound probe 180 and the subject 120 approaches, it becomes difficult to separate the target signal from the signal due to the multiple reflection or the like, and the detection performance decreases. For this reason, it is preferable to reduce the multiple reflection of photoacoustic waves by using the ultrasonic reflection control layer 230 as an ultrasonic absorption layer.

  It is preferable to provide a light reflection layer 201 on the ultrasonic receiving surface of the ultrasonic sensor 200 that detects the photoacoustic wave generated from the subject 120. When pulsed light is incident on the ultrasonic sensor 200 due to scattering of pulsed light from the light source 150 or reflection from the shape holding unit 110, a photoacoustic wave is generated from the ultrasonic sensor 200. Thereby, the photoacoustic wave generated from the subject 120 is distorted, and the detection performance is lowered. By providing the light reflection layer 201 on the ultrasonic wave receiving surface of the ultrasonic sensor 200, generation of photoacoustic waves from the ultrasonic sensor 200 can be reduced.

  In the state before the ultrasonic sensor 200 is arranged, the ultrasonic probe 180 has a cavity 185 at a portion where the ultrasonic sensor 200 is arranged as shown in FIGS. 6 and 7. As shown in FIG. 7, the ultrasonic probe 180 in a state before the ultrasonic sensor 200 is arranged has a light reflection control layer 220 and an ultrasonic reflection control layer 230 on the housing 184. The ultrasonic probe 180 can be manufactured by inserting and fixing the ultrasonic sensor 200 in the cavity 185. The size of the ultrasonic probe 180 may be set to a desired size according to the characteristics of the subject 120. The number of ultrasonic sensors 200 to be arranged may be provided at a desired location according to the characteristics of the subject 120 and the size of the ultrasonic probe 180. In FIG. 5, the sensor 200 is inserted into the cavity 185 from the outer side 181 of the ultrasonic probe 180, and the insertion direction is positioned by the protrusion of the ultrasonic sensor 200. The ultrasonic sensor 200 may be fixed to the casing 184 with an adhesive or the like, or the contact surface of the casing 184 and the ultrasonic sensor 200 may be sealed through a resin or rubber O-ring, It may be fixed by screwing. Further, the ultrasonic sensor 200 may be inserted and fixed from the inner side 182 or may be fixed by positioning with a jig or the like without providing a positioning projection on the ultrasonic sensor 200.

<Processing unit 160>
Returning to FIG. 1, the processing unit 160 and the image display unit 170 will be described. The photoacoustic wave is detected by the ultrasonic sensor 200 disposed on the ultrasonic probe 180. The photoacoustic wave generated from the subject is detected in the direction of approximately 360 degrees × 180 degrees. For image reconstruction, for example, back-projection in the time domain or Fourier domain, which is usually used in tomography technology, is used. In order to acquire a high-resolution three-dimensional image, the Fourier domain method is often used, but is not limited thereto. Here, the intensity of the photoacoustic wave emitted from the site of the subject 120 is calculated by the processing unit 160. In order to speed up the image forming process, the processing unit 160 calculates a value determined by the position of the ultrasonic sensor 200, the position of the part of the subject 120, and the reception time as a function of the radius of the sphere of the ultrasonic probe 180. The coefficient is stored in the memory. Image data is formed by multiplying the reception signal of each ultrasonic sensor 200 by the coefficient and accumulating the multiplication results for each part. Thus, by calculating the image data on the spherical surface and performing image processing on this image data by the Fourier domain method, a high-resolution three-dimensional image of the subject can be displayed on the image display unit 170.

Hereinafter, the present invention will be described in detail with reference to more specific examples.
Example 1
A specific example of the ultrasonic probe or the photoacoustic diagnostic apparatus described in the above embodiment will be described. A near-infrared nanopulse laser is used as the light source. Here, a titanium sapphire laser is used, and an Nd: YAG laser is used as an excitation source. Irradiates a wavelength of around 800 nm to generate a photoacoustic wave signal. A breast phantom is used as the subject 120. The shape holding unit 110 uses a polymethylpentene film. The acoustic matching material 130 fills water between the shape holding unit 110 and the ultrasonic probe 180. The ultrasonic probes 180 are arranged so that the radius of the inner side 182 of the hemispherical surface is about 120 mm and the ultrasonic receiving surface of the ultrasonic sensor 200 faces the inner side of the hemispherical surface. The ultrasonic sensor 200 is a capacitive electromechanical transducer, and the outer diameter of the tip of the ultrasonic sensor 200 is 10 mm. The light reflection control layer 220 of the ultrasonic probe is a light reflection layer, and the ultrasonic reflection control layer 230 is an ultrasonic absorption layer. The housing 184 of the ultrasonic probe 180 is aluminum.

  A capacitive electromechanical transducer (ultrasonic sensor) will be described with reference to FIGS. 8 is an example of an ultrasonic sensor, and FIG. 9 is an XZ axis slice diagram of FIG. The ultrasonic sensor includes a light reflection layer 201, a main body 204, and a wiring 202, and has a protrusion on a part of the main body 204. In the main body 204, a capacitive electromechanical transducer (transducer) 205, a first flexible wiring 207, a second flexible wiring 209, and a reception preamplifier 210 are arranged. As described above, the ultrasonic sensor 200 includes the conversion element 205 that performs at least one of conversion of an acoustic wave into a reception signal and conversion of a transmission signal into an acoustic wave on the sensor surface.

  The capacitance type electromechanical transducer is described with reference to FIGS. 10 and 11. FIG. 10 is an enlarged schematic diagram of the receiving surface side of the ultrasonic sensor. FIG. 11 is a cross-sectional view taken along line EF in FIG. The transducer 205 includes a silicon substrate 1, a first insulating film 2, a first electrode 3, a second insulating film 4 on the electrode 3, and a third insulating film 6 formed with a gap (cavity) 5 therebetween. A vibration film 9 including a second electrode 7 on the insulating film 6 and a fourth insulating film 8 on the electrode 7 is provided. On the vibration film 9, a support member 11 on which a light reflection layer 12 is formed is bonded via an adhesive 10 to form a protective layer 201. A plurality of cells 203 constituted by these constitute a capacitive electromechanical transducer 205. In FIG. 10, one electrostatic capacity type electromechanical transducer 205 is composed of 36 cells, but there may be one or many cells. Further, the cell arrangement may be lattice, staggered or honeycomb, and the shape of the cell is not limited to a circle but may be a rectangle, a square or a polygon. Further, the shape of the capacitive electromechanical transducer 205, which is an aggregate of cells, is not limited. The first electrode 3 is connected to the first flexible wiring 207 by the first electrode pad 206 and is connected to the circuit board 212 inside the main body 204, and is drawn to the outside by the wiring 202. The second electrode 7 is connected to the second flexible wiring 209 by the second electrode pad 208 and is connected to the reception preamplifier 210 on the circuit board 212 through the inside of the main body 204. In FIG. 10, the first electrode 3 and the second electrode 7 are drawn out from the receiving surface side by the flexible wiring, but a through hole is provided in the silicon substrate 1 and the electrode is formed directly on the back side of the silicon substrate 1. You may connect with a circuit board.

  A protective layer 201 including a light reflecting layer is formed on the surface of the capacitive electromechanical transducer 205. The light reflection layer is for reducing photoacoustic waves generated by scattering of pulsed light from the light source 150 and irradiation of reflected light from the shape holding unit 110 to the electromechanical conversion device. The light reflecting layer 12 is a vapor deposition film of Au, and a PET film having a thickness of 12 μm is used as the support member 11 for vapor deposition of Au. The adhesive layer 10 is made of a protective layer 201 using a silicon-based adhesive. The types and thicknesses of the light reflection layer 12, the support member 11, and the adhesive layer 10 are not limited to these.

  The ultrasonic sensor can apply a bias voltage to the first electrode 3 by voltage application means. When a bias voltage is applied to the first electrode 3, a potential difference is generated between the first electrode 3 and the second electrode 7. Due to this potential difference, the vibrating membrane 9 is displaced until the restoring force of the vibrating membrane and the electrostatic attractive force are balanced. When the ultrasonic wave reaches the vibration film 9 in this state, the vibration film 9 vibrates, so that the capacitance between the first electrode 3 and the second electrode 7 changes, and a current flows to the second electrode 7. Flows. This current can be taken out as an ultrasonic electric signal. At the time of reception, a bias voltage is applied from the bias voltage control unit in accordance with a reception bias voltage instructed from a system control unit (not shown). A reception signal obtained by receiving the photoacoustic wave generated from the subject by the ultrasonic sensor is amplified by the reception preamplifier 210 and sent to the processing unit 160.

  An example of a method for manufacturing a capacitive electromechanical transducer will be described with reference to FIG. As shown in FIG. 12A, the first insulating film 2 is formed on the substrate 1. The substrate 1 is a silicon substrate, and the first insulating film 2 is for forming insulation with the first electrode 3. Next, the first electrode 3 is formed. The first electrode 3 is preferably a conductive material having a small surface roughness, such as titanium, tungsten, or aluminum. When the surface roughness of the first electrode 3 is large, the distance between the first electrode and the second electrode varies between the elements due to the surface roughness. Therefore, a conductive material having a small surface roughness is desirable. Next, the second insulating film 4 is formed. The second insulating film 4 is also preferably made of an insulating material having a small surface roughness. This is because the first electrode and the second electrode when a voltage is applied between the first electrode and the second electrode. It is formed in order to prevent electrical short circuit or dielectric breakdown between them. Further, it is formed to prevent the first electrode 3 from being etched when the sacrificial layer is removed in the subsequent process of this process. The second insulating film 4 is, for example, a silicon nitride film or a silicon oxide film.

  Next, as shown in FIG. 12B, a sacrificial layer 55 is formed. The sacrificial layer 55 becomes the void 5 later. The sacrificial layer 55 is preferably made of a material having a small surface roughness. When the surface roughness of the sacrificial layer is large, the distance between the first electrode and the second electrode varies between elements due to the surface roughness. Therefore, a sacrificial layer having a small surface roughness is desirable. In addition, in order to shorten the etching time for etching to remove the sacrificial layer, a material having a high etching rate is desirable. Examples of the sacrificial layer material include amorphous silicon, polyimide, chromium, and the like. Since the chromium etching solution hardly etches the silicon nitride film or the silicon oxide film, it is desirable when the insulating film and the vibration film are a silicon nitride film or a silicon oxide film.

  Next, as shown in FIG. 12C, a third insulating film 6 is formed. The third insulating film 6 desirably has a low tensile stress. For example, a tensile stress of 500 MPa or less is preferable. The silicon nitride film can be stress-controlled and can have a low tensile stress of 500 MPa or less. When the vibration film has a compressive stress, the vibration film causes sticking or buckling and is greatly deformed. On the other hand, in the case of a large tensile stress, the third insulating film 6 may be destroyed. Therefore, it is desirable that the third insulating film 6 has a low tensile stress. For example, it is a silicon nitride film capable of controlling the stress and having a low tensile stress. Next, the second electrode 7 is formed. The second electrode 7 is preferably made of a material having a small residual stress, and examples thereof include aluminum, metals such as aluminum / silicon alloys and titanium, but are not limited thereto.

Next, as shown in FIG. 12D, an etching hole 56 is formed in the third insulating film 6. The etching hole 56 is a hole for introducing an etching solution or an etching gas in order to etch and remove the sacrificial layer 55. Thereafter, the sacrificial layer 55 is removed to form the gap 5. The sacrificial layer removal method is preferably wet etching, dry etching, or the like. When chromium is used as the sacrificial layer material, wet etching is preferable.
Next, as shown in FIG. 12E, a fourth insulating film 8 is formed to seal the etching hole 56. A vibration film 9 is formed by the third insulating film 6, the second electrode 7, and the fourth insulating film 8. As the sealing material, the same material as that of the third insulating film 6 is preferable because of high adhesion. When the third insulating film 6 is silicon nitride, the fourth insulating film 8 is also preferably silicon nitride.

  In FIG. 11 and FIG. 12, a configuration in which the second electrode 7 is sandwiched between the third insulating film 6 and the fourth insulating film 8 is shown as an example. However, after the third insulating film 6 is formed, an etching hole 56 is formed and sacrificial layer etching is performed. Then, after the fourth insulating film 8 is formed, the second electrode can be provided. However, if the second electrode 7 is exposed on the outermost surface, there is a high possibility that the element will be short-circuited by a foreign substance or the like. Therefore, the second electrode 7 is preferably provided between the insulating films. In this embodiment, dicing is performed to the size of the conversion element 205 to form an ultrasonic sensor. Through the above steps, a capacitance type electromechanical transducer as shown in FIGS. 10 and 11 can be manufactured.

  Such a capacitive electromechanical transducer is fixed to the support member 211 shown in FIG. 9 using a resin adhesive such as epoxy, and the first flexible wiring 207 is connected to the first electrode 206. The second flexible wiring 209 is connected to the electrode 208. The flexible wiring is connected to the wiring board 212 on which the reception amplifier 210 is arranged. A product in which the capacitive electromechanical transducer 205, the flexible wiring, and the wiring board 212 are integrated is stored in the main body 204. The main body 204 can be made of resin or the like. After being stored in the main body 204, the main body 204 is sealed with an adhesive so that an acoustic matching material or the like does not flow into the main body 204. A protective layer 201 having the light reflecting layer 12 is formed on the surface of the conversion element 205 stored in the main body 204. The light reflecting layer 12 is made of Au. As the support member 11, a PET film having a thickness of 12 μm is used. First, Au is vapor-deposited on the support member 11, and the support member 11 on which Au is vapor-deposited is adhered to the surface of the capacitive electromechanical transducer 205 using a silicon-based adhesive. By cutting the excess support member 11 after bonding, the protective layer 201 of the capacitive electromechanical transducer 205 can be produced. The ultrasonic sensor 200 as shown in FIGS. 8 and 9 can be manufactured through the above steps. Here, the first electrode pad 206 is connected to a power source for applying a bias voltage through the wiring 202, and the second electrode pad 208 is connected to the reception amplifier 210 through the flexible wiring 209, To the processing unit 160.

  Next, the housing 184 is manufactured. Aluminum is used as the housing material, and the housing is cut so that the inner radius of the hemisphere is 120 mm and the wall thickness is 20 mm. Next, an ultrasonic absorption layer is produced as the ultrasonic reflection control layer 230 inside the housing 184. The ultrasonic absorption layer can be produced by applying AptFlex-F36 sold by EASTEC Co. to the inside of the casing 184 and curing it. A coating thickness of 10 mm is preferable because a 2 MHz ultrasonic wave can be attenuated by about 45 dB. The acoustic impedance of the ultrasonic absorption layer is about 1.4 MRayls, and when the acoustic matching material 130 is water, the difference in acoustic impedance with this is preferably 10% or less. Further, by applying a mixture of urethane rubber and tungsten fine particles of about 10 wt% to the inside of the housing 184 and curing it, 1 MHz ultrasonic waves can be attenuated by about 50 dB. The acoustic impedance at this time is about 1.8 MRayls, and when the acoustic matching material 130 is water, the difference in acoustic impedance is preferably 20% or less.

  Next, a light reflection layer is produced on the ultrasonic absorption layer as a light reflection control layer. A light reflection layer is produced by plating Au on the ultrasonic absorption layer to a thickness of 100 nm. This light reflecting layer is preferable because it can reflect light by 90% or more. Further, since the thickness of the light reflecting layer is as thin as 100 nm, the reflection of the ultrasonic wave generated by the difference between the acoustic impedance of the acoustic matching material 130 and the acoustic impedance of the light reflecting layer hardly occurs. Therefore, it is preferable that the propagated ultrasonic wave can be propagated to the ultrasonic absorption layer with almost no reflection.

  Next, a cavity 185 is provided in the housing 184 in order to arrange the ultrasonic sensor. Since the outer diameter of the ultrasonic sensor is 10 mm, cavities having an inner diameter of 182 to 11 mm are formed at 250 locations and the distance between the cavities is 21.2 mm. On the outer side 181 of the cavity 185, a 13.5 mm hole obtained by adding 0.5 mm to the outer diameter of the fitting cap 13 mm is provided at the same position as the cavity 185 in order to fit the fitting cap 186 later. The portion is threaded to form a fitting receiving portion 187. At the bottom of the inner side 182 of the hemispherical casing 184, a cavity for the optical system is provided in order to install the optical system 140 later (see FIG. 1).

  Next, the ultrasonic sensor is disposed in the housing 184. Adhesive is applied to the outer peripheral portion of the outer side of the ultrasonic sensor, and the ultrasonic sensor is inserted from the outside of the housing 184. Thereafter, the ultrasonic sensor 200 is fixed to the housing 184 by fitting the fitting cap 186 into the fitting receiving portion 187. At that time, the adhesive applied to the outer peripheral portion escapes and hardens in the gap (1 mm) between the outer peripheral portion (10 mm) and the cavity (11 mm) and the gap (0.5 mm) between the fitting receiving portion and the fitting cap. In this way, the ultrasonic probe 180 can be manufactured.

  Next, as shown in FIG. 1, the wiring 202 of the ultrasonic sensor 200 fixed to the housing 184 is connected to the processing unit 160, and the sapphire 140 is installed in the cavity for the optical system to transmit the pulsed light. The light source 150 is installed outside the ultrasonic probe 180. The light source is composed of an optical component such as a lens and a diffusion plate in addition to the laser, and the pulsed light from the light source has a distribution such that the entire breast 120 is irradiated with light. The pulsed light is irradiated with a pulse width of several nanoseconds or less. As a result, the entire breast is photoexcited to generate a photoacoustic wave, and the photoacoustic wave can be received by the ultrasonic sensor 200 disposed in the ultrasonic probe, so that image information of the entire breast can be acquired. .

  The reception signal obtained from each ultrasonic sensor 200 arranged on the ultrasonic probe 180 is sent to the processing unit 160. The time-series received signal is converted into a digital signal and stored. Spatial two-dimensional and three-dimensional object information is generated based on the stored received signal. The image reconstruction algorithm uses back projection in the time domain or the Fourier domain. Further, regarding the influence on the photoacoustic wave from the shape holding unit 110 and the acoustic matching material 130, the information is acquired in advance and stored in the memory, and the information is stored when the information from the subject 120 is acquired. Information can be read and its influence can be eliminated.

  In this way, subject information can be acquired by performing processing based on the image reconstruction algorithm on the received photoacoustic wave signal. The object information obtained in this step is obtained by receiving and processing an acoustic wave generated from the object in a direction of approximately 360 degrees × 180 degrees, so that the resolution and quantitativeness of the object information (for example, blood vessels) Characteristics of being able to quantify the running and oxygen saturation of the vehicle.

  When the photoacoustic wave generated from the subject is incident on a part other than the ultrasonic sensor, the ultrasonic probe 180 of the present embodiment can transmit the light reflection control layer and absorb it by the ultrasonic reflection control layer. . The ultrasonic reflectance of the light reflection control layer with respect to 2 MHz ultrasonic waves is almost 0%, and the ultrasonic attenuation rate of the ultrasonic reflection control layer is 45 dB. % Or more can be attenuated. Thereby, 99% or more of the multiple reflection in the ultrasonic probe of the ultrasonic wave incident on the part other than the ultrasonic sensor which has occurred conventionally can be reduced, and the S / N of the subject information can be increased. .

  In this example, the multiple reflection of 2 MHz ultrasonic waves was reduced, but a light reflection control layer and an ultrasonic reflection control layer necessary for reducing ultrasonic waves of a desired frequency may be provided as appropriate. It is not limited to the examples. Further, in this embodiment, the light reflection control layer is provided, but a configuration including only the ultrasonic reflection control layer may be used. In the case of an ultrasonic diagnostic apparatus that does not include a light source, it is not necessary to provide a light reflection control layer.

(Example 2)
In Example 2, a case where the light reflection control layer 220 is a light reflection layer and an ultrasonic scattering layer is used as the ultrasonic reflection control layer 230 will be described. Other configurations are the same as those of the first embodiment. 13 is a cross-sectional view similar to the cross-sectional view taken along the line AB of FIG. 3 of the ultrasonic probe of the second embodiment. In FIG. 13, the casing 184 on the ultrasonic receiving surface side is roughened. By roughing the surface, ultrasonic waves can be scattered on the roughened surface. A light reflecting layer is provided thereon, and for this, Au of 100 nm is used as in the first embodiment.

  The formation of the ultrasonic scattering layer inside the housing 184 will be described. The housing 184 is provided with unevenness as shown in FIG. The size of the unevenness may be adjusted to the frequency of the ultrasonic wave to be scattered, and is preferably about the same as the wavelength of the ultrasonic wave. For example, the wavelength of the ultrasonic wave of 2 MHz is about 750 μm because the speed of sound in water as an acoustic matching material is 1500 m / s. The surface of the housing 184 is roughened with the shape of the concavity and convexity being a cone-shaped protrusion, the interval between the crests of the concavity and convexity and the depth of the concavity and convexity being 750 μm. As a rough surface processing method, mold processing, wet etching, dry etching, or the like can be applied.

  Next, a light reflection layer is formed as a light reflection control layer on the surface of the housing 184 that has been roughened. A light reflecting layer is prepared by plating Au on the ultrasonic scattering layer to a thickness of 100 nm. This light reflecting layer is preferable because it can reflect light by 90% or more. In addition, since the thickness of the light reflection layer is as thin as 100 nm, the reflection of ultrasonic waves caused by the difference between the acoustic impedance of the acoustic matching material 130 and the acoustic impedance of the light reflection layer hardly occurs. Furthermore, since the attenuation is small, it is preferable that the transmitted ultrasonic waves can be propagated to the roughened surface layer with little reflection and attenuation. The photoacoustic diagnostic apparatus is manufactured through the same process as that of the first embodiment based on the casing 184 thus manufactured.

  When the photoacoustic wave generated from the subject is incident on a part other than the ultrasonic sensor, the ultrasonic probe 180 of the present embodiment reflects the pulsed light by the light reflection control layer 220 and transmits the light reflection control layer. The photoacoustic wave can be scattered by the ultrasonic reflection control layer 230. The light reflection control layer transmits almost 100% of a 2 MHz photoacoustic wave. The ultrasonic waves that reach the ultrasonic reflection control layer are scattered in all directions. As a result, the generation of photoacoustic waves due to pulsed light incident on portions other than the ultrasonic sensor 200 that has conventionally occurred can be reduced, and multiple reflections of ultrasonic waves in the ultrasonic probe can be reduced. The S / N of the subject information can be increased.

  In this example, an ultrasonic scattering layer subjected to roughening was used as the ultrasonic reflection control layer. However, an ultrasonic absorption layer is arranged between the ultrasonic scattering layer and the light reflection control layer. Also good. By providing an ultrasonic absorption layer on the housing 184 that has been roughened, ultrasonic waves that could not be absorbed by the ultrasonic absorption layer were scattered by the ultrasonic scattering layer, and the scattered ultrasonic waves were scattered by the ultrasonic absorption layer. Can be absorbed. In this embodiment, the light reflection control layer is provided. However, the light reflection control layer is not provided, and only the ultrasonic scattering layer may be provided. In the case of an ultrasonic diagnostic apparatus, it is not necessary to provide a light reflection control layer.

  In this embodiment, the multiple reflection of 2 MHz ultrasonic waves is reduced. However, according to circumstances, a light reflection control layer and an ultrasonic reflection control layer necessary for reducing ultrasonic waves of a desired frequency can be appropriately provided. The embodiment is not limited to this embodiment.

(Example 3)
In Example 3, the light reflection control layer 220 is a light reflection layer, the ultrasonic reflection control layer 230 is an ultrasonic absorption layer, and the inside of the ultrasonic absorption layer is subjected to a rough surface treatment. Absorbs and scatters sound waves. Other configurations are the same as those of the first embodiment. 14 is a cross-sectional view similar to the cross-sectional view taken along the line AB of FIG. In FIG. 14, ultrasonic waves can be absorbed by roughing the inside of the ultrasonic absorption layer, and ultrasonic waves can be scattered and further absorbed by the roughened surface. A light reflecting layer 220 is provided thereon, and 100 nm of Au is used as in the first embodiment.

  In the rough surface processing inside the ultrasonic absorption layer, the first ultrasonic absorption layer is formed on the inner surface of the housing 184 as in the first embodiment. After that, similar to the method of roughening the casing in Example 2, the first ultrasonic absorbing layer may be roughened by molding, wet etching, dry etching, or the like. An ultrasonic absorption layer as shown in FIG. 14 can be provided by forming a second ultrasonic absorption layer thereon by the same method as in the first embodiment. On top of that, the light reflection control layer 220 is formed by the same method as in the first embodiment, and the photoacoustic diagnostic apparatus can be manufactured through the same steps as in the first embodiment.

  The ultrasonic probe 180 of the present embodiment transmits the light reflection control layer 220 and absorbs it by the ultrasonic reflection control layer 230 when the photoacoustic wave generated from the subject is incident on a portion other than the ultrasonic sensor. Can do. The ultrasonic reflectance of the 2 MHz ultrasonic light reflection control layer 220 is approximately 0%, and the ultrasonic attenuation rate of the ultrasonic reflection control layer 230 is 45 dB. 99% or more of sound waves can be attenuated.

  Thereby, 99% or more of the multiple reflection in the ultrasonic probe of the ultrasonic wave incident on the part other than the ultrasonic sensor which has occurred conventionally can be reduced, and the S / N of the subject information can be increased. . In this embodiment, the multiple reflection of 2 MHz ultrasonic waves was reduced, but a light reflection control layer and an ultrasonic reflection control layer necessary for reducing ultrasonic waves of a desired frequency may be provided as appropriate. There is no limitation to the embodiment. Further, although the light reflection control layer is provided in this embodiment, a configuration including only the ultrasonic reflection control layer may be used. In the case of an ultrasonic diagnostic apparatus, it is not necessary to provide a light reflection control layer.

  The present invention can be applied to an optical imaging apparatus that obtains in-vivo information, a conventional ultrasonic diagnostic apparatus, and the like. That is, it is possible to realize an object information acquisition apparatus that receives acoustic waves from an object and acquires information about the object using the ultrasonic probe of the present invention. As an example of the information acquisition apparatus, an ultrasonic wave that includes an ultrasonic probe that transmits an acoustic wave to a subject and detects an ultrasonic wave reflected from the subject, and a signal processing unit that converts the detected signal into image information. There is a diagnostic device. A light source for irradiating the subject with light; an ultrasonic probe for detecting an acoustic wave from the subject excited by the light irradiation; and a signal processing unit for converting the detected signal into image information. There is an ultrasound diagnostic device. The signal processing unit forms a subject image by processing the signal. Furthermore, the present invention can be applied not only to a capacitive electromechanical transducer, but also to a conventional piezoelectric ultrasonic probe. Furthermore, it can be applied to other uses such as an ultrasonic flaw detector.

  120 object, 180 ultrasonic probe, 184 housing, 200 ultrasonic sensor, 230 ultrasonic reflection control layer

Claims (15)

An ultrasonic probe comprising: a plurality of ultrasonic sensors; and a housing that has a concave portion that is concave toward a subject to be placed at a measurement position during measurement and that supports the plurality of ultrasonic sensors. There,
The ultrasonic probe, wherein the ultrasonic sensor is arranged so that a sensor surface faces the subject side, and the casing has an ultrasonic reflection control layer on the subject side surface.   The ultrasonic probe according to claim 1, wherein the concave portion of the housing has a substantially spherical shape.   The ultrasonic probe according to claim 1, wherein the ultrasonic reflection control layer includes at least one of an ultrasonic absorption layer, an ultrasonic scattering layer, and an ultrasonic interference layer.   The ultrasonic probe according to claim 3, wherein an acoustic impedance of the ultrasonic absorption layer is 1 MRayls or more and 5 MRayls or less.   The ultrasonic probe according to claim 1, wherein a light reflection control layer is formed on the subject side of the ultrasonic reflection control layer.   6. The ultrasonic probe according to claim 5, wherein an acoustic impedance of the light reflection control layer is 1 MRayls or more and 5 MRayls or less.   The ultrasonic probe according to any one of claims 1 to 6, wherein a light reflection layer is formed on a sensor surface of the ultrasonic sensor.   The ultrasonic probe according to any one of claims 1 to 7, wherein a seal member that prevents an acoustic matching material from entering between the ultrasonic sensor and the housing is provided.   9. The ultrasonic sensor according to claim 1, wherein the ultrasonic sensor includes a conversion element that performs at least one of conversion of an acoustic wave into a reception signal and conversion of a transmission signal into an acoustic wave on the sensor surface. The ultrasonic probe according to claim 1.   The ultrasonic probe according to claim 9, wherein the conversion element is a capacitive electromechanical conversion element.   The ultrasonic probe according to claim 1, wherein the ultrasonic sensor is fitted into a hollow portion of the casing.   The ultrasonic probe according to any one of claims 1 to 11, wherein a light irradiation unit for irradiating the subject with light is attached to the housing.   An object information acquiring apparatus that receives information about an object by receiving an acoustic wave from the object using the ultrasonic probe according to any one of claims 1 to 12. An ultrasonic diagnostic apparatus comprising: an ultrasonic probe for transmitting an acoustic wave to a subject and detecting an acoustic wave reflected from the subject; and a signal processing unit for converting the detected signal into image information,
The ultrasonic probe according to any one of claims 1 to 12, wherein an object image is detected by processing the signal detected by the ultrasonic probe and the converted signal by the signal processing unit. An ultrasonic diagnostic apparatus characterized by comprising. Ultrasound including a light source for irradiating light on a subject, an ultrasonic probe for detecting an acoustic wave from the subject excited by light irradiation, and a signal processing unit for converting the detected signal into image information A diagnostic device,
The ultrasonic probe according to any one of claims 1 to 12, wherein a photoacoustic wave generated by irradiating a subject with light from the light source is detected by the ultrasonic probe. A photoacoustic diagnostic apparatus characterized in that a subject image is formed by processing the converted signal in the signal processing unit.

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