JPWO2010119729A1 - Acoustic lens manufacturing method, ultrasonic probe, and ultrasonic diagnostic apparatus - Google Patents

Abstract

A step of sequentially laminating a material having a propagation speed higher than the propagation speed of the lower ultrasonic wave on each side of the substrate, and a substrate on which the materials are sequentially laminated have a predetermined distance between the first lens surface and the second lens surface. And a step of cutting along a surface orthogonal to the surface on which the materials are laminated so as to have a thickness of 1. The method for manufacturing an acoustic lens, comprising:

Description

  The present invention relates to an acoustic lens manufacturing method, an ultrasonic probe, and an ultrasonic diagnostic apparatus.

  An ultrasonic diagnostic apparatus is a medical imaging device that obtains a tomographic image of soft tissue in a living body in a minimally invasive manner from the body surface by an ultrasonic pulse reflection method. Compared to other medical imaging equipment, this ultrasound diagnostic device has features such as being smaller and cheaper, without exposure to X-rays, etc., being highly safe, and capable of blood flow imaging by applying the Doppler effect. Yes. Therefore, it is widely used in the circulatory system (cardiac coronary artery), digestive system (gastrointestinal), internal medicine system (liver, pancreas, spleen), urology system (kidney, bladder), and obstetrics and gynecology.

  In order to perform transmission and reception of ultrasonic waves with high sensitivity and high resolution, an ultrasonic probe used in such a medical ultrasonic diagnostic apparatus is generally a piezoelectric element made of lead zirconate titanate. used. In this case, as the vibration mode of the transmitting piezoelectric element, a single type probe or an array type probe in which a plurality of probes are two-dimensionally arranged is often used. Since the array type can obtain a fine image, it is widely used as a medical image for a diagnostic examination.

  On the other hand, harmonic imaging diagnosis using harmonic signals is becoming a standard diagnosis method because a clear diagnosis image that cannot be obtained by conventional B-mode diagnosis is obtained.

  Harmonic imaging has many advantages compared to the fundamental wave as follows.

  1. The S / N ratio is good and the contrast resolution is good because the side lobe level is small.

  2. The higher the frequency, the narrower the beam width and the better the lateral resolution.

  3. Multiple reflections do not occur because the sound pressure is small and the fluctuation in sound pressure is small at short distances.

  4). Attenuation beyond the focal point is similar to that of the fundamental wave, and the deep velocity can be increased compared to ultrasonic waves with the harmonic frequency as the fundamental wave.

  Etc.

  As a specific structure of an array-type ultrasonic probe used for harmonic imaging, an array-type transducer that separates the operations during transmission and reception of ultrasonic waves, with the transmission and reception piezoelectric transducers separate. An ultrasound probe has been proposed.

  It is desirable that the receiving piezoelectric vibrator used in such an array type ultrasonic probe can receive a harmonic signal with high sensitivity. However, since the transmission / reception frequency of a piezoelectric element made of lead zirconate titanate or the like depends on the thickness of the piezoelectric element, it is necessary to process the piezoelectric element in a smaller size as the receiving frequency becomes higher, and it is difficult to manufacture. there were.

  In order to solve such a problem, a piezoelectric element for transmission and a sheet-like piezoelectric element for reception having a single layer or laminated structure of sheet-like piezoelectric ceramics are made into a single layer or laminated, and separate transmission and reception piezoelectric elements And a method of obtaining a highly sensitive ultrasonic probe by using a highly sensitive organic piezoelectric element material for reception (see Patent Documents 1, 2, and 3).

  On the other hand, an acoustic lens is conventionally used in an ultrasonic probe to improve resolution by converging an ultrasonic beam. Since the acoustic lens is brought into close contact with the subject (living body), there is a demand for a material that is easily brought into close contact with the subject and has a small attenuation rate at the frequency used for diagnosis.

  Conventionally, silicone rubber has been mainly used as such a material. Silicone rubber has a slower propagation speed of sound waves (hereinafter also referred to as sound velocity) than the subject (living body), so that the central part of the cross-sectional shape is formed in a convex shape, and the ultrasonic wave passes through the thick part at the center. Is made longer than the thin portion to converge the ultrasonic wave.

  However, since silicone rubber has a large ultrasonic wave propagation loss, it is difficult to improve the reception sensitivity of the ultrasonic probe. In particular, since the high-frequency propagation loss is large, it can be said that the material is not suitable for harmonic imaging using harmonic signals.

  On the other hand, for example, polymethylpentene, which is a resin material, is known as a material with low propagation loss. However, since polymethylpentene has a sound speed faster than that of the subject (living body), the central portion of the cross-sectional shape is formed in a concave shape. It is necessary to make the ultrasonic waves converge.

  However, the concave shape has a problem that the contact property with the surface of the subject (living body) is deteriorated.

  For this reason, a method has been disclosed in which a biconvex acoustic region is fixed on a concave acoustic lens using polymethylpentene to improve the contact property with the surface of a subject (living body). (For example, refer to Patent Document 4).

JP 2008-188415 A International Publication No. 2007/145073 Pamphlet International Publication No. 2008/010509 Pamphlet JP-A-6-254100

  However, when a biconvex acoustic region is provided on a concave acoustic lens as disclosed in Patent Document 4, the propagation loss in the acoustic region is added, so that the total propagation loss of the acoustic lens is hardly improved. In particular, when silicone rubber is used as the acoustic region as in Patent Document 4, there is a problem in that reception sensitivity becomes insufficient when high-order harmonics are used due to large ultrasonic wave propagation loss due to silicone rubber. .

  On the other hand, there is a need for an ultrasonic probe provided with acoustic lenses having different focal lengths depending on the region to be measured by the subject. However, since the conventional acoustic lens converges the ultrasonic wave at a predetermined distance by the convex or concave lens surface, it is necessary to accurately form the lens surface of the acoustic lens, and a high-precision mold is necessary. . Therefore, in order to produce an acoustic lens with multiple focal lengths, multiple molds are required, and the mold is modified until an acoustic lens with a predetermined focal length can be produced, which is very burdensome in terms of cost and time. It was.

  The present invention has been made in view of the above problems, and has a method for manufacturing an acoustic lens that has excellent adhesion to a subject and can easily obtain a predetermined focal length, and an ultrasonic probe having the acoustic lens. And an ultrasonic diagnostic apparatus having the ultrasonic probe.

  In order to solve the above problems, the present invention has the following characteristics.

1. In the method of manufacturing an acoustic lens, the ultrasonic wave incident from the first lens surface is emitted from the second lens surface and converged to a predetermined distance.
A process of sequentially laminating materials having a propagation speed faster than the propagation speed of the underlying ultrasonic wave on both sides of the substrate,
Cutting the substrate on which the materials are sequentially laminated along a plane orthogonal to the surface on which the materials are laminated so that a distance between the first lens surface and the second lens surface is a predetermined thickness; ,
A method for producing an acoustic lens, comprising:

2. The material is
2. The method for producing an acoustic lens as described in 1 above, wherein the material is a material in which an additive is added at a rate that provides a predetermined ultrasonic wave propagation speed.

3. The material is
Resin material,
3. The method for producing an acoustic lens as described in 2 above, wherein the layer is formed by applying a resin liquid to which the additive is added in the step of laminating and then curing the resin liquid.

4). In an ultrasonic probe that transmits an ultrasonic wave toward a subject and receives a reflected wave of the ultrasonic wave from the subject,
An acoustic lens manufactured using the method for manufacturing an acoustic lens according to any one of 1 to 3,
An ultrasonic probe that transmits and receives ultrasonic waves, or transmits or receives ultrasonic waves through the acoustic lens.

5. The attenuation characteristic of the acoustic lens is
5. The ultrasonic probe as described in 4 above, wherein the frequency is 5 dB or less at a frequency of 5 MHz.

6). In an ultrasonic diagnostic apparatus that transmits an ultrasonic wave toward a subject and generates an image according to a reflected wave of the ultrasonic wave received from the subject.
An ultrasonic diagnostic apparatus comprising the ultrasonic probe according to 4 or 5 above.

  According to the present invention, the first lens surface and the second lens surface are formed by sequentially laminating a material having a propagation speed higher than the propagation speed of the lower layer ultrasonic wave on both surfaces of the substrate. And the step of cutting along a surface orthogonal to the surface on which the materials are laminated so that the distance between the two and the material becomes a predetermined thickness, and the acoustic lens is manufactured, the cutting surface that becomes the surface in contact with the subject is It is a flat surface, and the focal length can be changed according to the thickness to be cut.

  Therefore, a method for manufacturing an acoustic lens that has excellent adhesion to a subject and can easily obtain a predetermined focal length, an ultrasonic probe having the acoustic lens, and an ultrasonic diagnostic apparatus having the ultrasonic probe Can be provided.

It is a perspective view of the acoustic lens 7 of embodiment. It is explanatory drawing for demonstrating the principle in which the acoustic lens 7 of embodiment converges an ultrasonic wave. It is explanatory drawing explaining an example of the manufacturing method of the acoustic lens 7 which concerns on embodiment. It is sectional drawing which shows the structure of the head part of the ultrasonic probe of embodiment. It is a figure which shows the external appearance structure of the ultrasound diagnosing device in embodiment. It is a block diagram which shows the electrical structure of the ultrasonic diagnosing device in embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiment. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  FIG. 1 is a perspective view of an acoustic lens 7 according to the embodiment. FIG. 2 is an explanatory diagram for explaining the principle by which the acoustic lens 7 of the embodiment converges ultrasonic waves. In the following description, description will be made based on the coordinate axes indicated by X, Y, and Z in the drawing. The X direction is the elevation direction (the dicing direction) of the ultrasonic probe 1 (not shown in FIG. 1) to which the acoustic lens 7 is joined, and the Y direction is the acoustic lens 7 manufacturing process. Is the direction in which the ultrasonic wave is transmitted.

  As shown in FIG. 1, the external appearance of the acoustic lens 7 is a rectangular parallelepiped having a width in the X-axis direction of W, a width in the Z-axis direction of H, and a width in the Y-axis direction of L. Of the two opposing surfaces orthogonal to the Z-axis, the surface in the negative Z-axis direction is a surface (first lens surface) on which ultrasonic waves radiated from a piezoelectric element (not shown) are incident, and is a surface in the positive Z-axis direction. Is a surface (second lens surface) that is brought into close contact with a subject (not shown) and emits ultrasonic waves inside the subject. Both opposing surfaces orthogonal to the Z axis are flat surfaces.

  The acoustic lens 7 includes a central portion 4 and a peripheral portion 8 made of a resin material that has a higher acoustic wave propagation speed (hereinafter also referred to as sound velocity) than the resin material of the central portion 4.

  In the example of FIG. 1, the peripheral portion 8 is composed of 10 layers formed parallel to the two surfaces across the two surfaces facing the X-axis direction of the central portion 4 of the rectangular parallelepiped. That is, the layers 8a, 8b, 8c, 8d, 8e, 8f, 8g, 8h, 8i, and 8j are formed with the width w in the X direction on the left side of the central portion 4, and the layer 8k is formed on the right side of the central portion 4 with respect to the paper surface. , 8l, 8m, 8n, 8o, 8p, 8q, 8r, 8s, and 8t are formed with the same width w. The width of the central part 4 in the X direction is W0, the width of the peripheral part 8 sandwiching the central part 4 is W1, and the widths of the central part 4 and the peripheral part 8 in the Z direction are both H.

  The layers 8a to 8j and the layers 8k to 8t of the peripheral portion 8 are formed of a resin material having a higher sound speed as the layer is farther from the central portion 4.

For example, if the central portion 4 is formed of a resin material sound speed V _1, made of a resin material of higher acoustic velocity Va than the acoustic velocity V ₁ was a peripheral portion 8a and a peripheral portion 8k. The peripheral portion 8b and the peripheral portion 8l are made of a resin material having a sound velocity Vb faster than the sound velocity Va. The peripheral portion 8c and the peripheral portion 8m are made of a resin material having a sound velocity Vc faster than the sound velocity Vb, and the peripheral portion 8d and the peripheral portion 8n are made of a resin material having a sound velocity Vd faster than the sound velocity Vc.

  Similarly, each part of the peripheral part is configured such that the propagation speed of the sound wave increases according to the distance from the central part, and the outermost peripheral part 8j and the peripheral part 8t are the fastest in the acoustic lens 7. It is made of a resin material having a sound velocity Vj.

The principle by which the acoustic lens 7 of the present invention converges ultrasonic waves will be described with reference to FIG. In FIG. 2, for the sake of simplicity, an example in which all the peripheral portions 8 are formed from the same material will be described. The central portion 4 is made of a material having a sound velocity V ₁ , and the peripheral portion 8 is made of a material having a sound velocity V ₂ faster than the sound velocity V ₁ . Further, it is assumed that the surface in the positive direction of the Z-axis of the acoustic lens 7 is in contact with the liquid 50 having the speed of sound V ₀ stored in a container (not shown).

l ₂ indicates a state in which the ultrasonic wave incident from the center of the central portion 4 travels through the central portion 4 and the liquid 50. l ₁ is the ultrasonic wave incident from the center of the left side of the peripheral portion 8, and proceeds the peripheral portion 8 and the liquid 50, shows a state in which converges l ₂ at the position of the focal length f. x is the distance between l ₁ and l ₂ incident on the acoustic lens 7.

Since the sound velocity V _{2 at the} peripheral portion 8 is faster than the sound velocity V ₁ at the central portion 4, the ultrasonic wave incident from the peripheral portion 8 simultaneously enters the liquid 50 earlier than the ultrasonic wave incident from the central portion 4. The wavefront advances concentrically inside.

A time difference t ₁ between the ultrasonic wave incident from the peripheral part 8 and the ultrasonic wave incident from the central part 4 passing through the acoustic lens 7 can be obtained by the following equation (1).

M in FIG. 2 is a distance traveled by the ultrasonic wave incident from the peripheral portion 8 during the time difference t ₁ . When the sound velocity of the liquid 50 is V ₀ , the distance m can be obtained by the following formula (2).

m = V ₀ × t ₁ (2)
The ultrasonic wave incident from the center of the peripheral portion 8 on the left side of the paper travels a distance m and then travels the same distance f as the ultrasonic wave incident from the center of the central portion 4 and converges to the point q. The focal length f can be obtained by the following formula (3) using the Pythagorean theorem.

f = (x ² −m ² ) / 2 m (3)
When the expressions (1) and (2) are substituted into the expression (3), the focal length f can be obtained by the following expression (4).

H is the width (thickness) of the acoustic lens 7 in the Z-axis direction, V ₁ is the sound velocity of the central portion 4, V ₂ is the sound velocity of the peripheral portion 8, and V ₀ is the sound velocity of the liquid 50.

Thus, it is possible to converge the central portion 4 and the ultrasonic l ₁ incident from the ultrasonic l ₂ and the peripheral portion 8 traveling through the central portion 4 by the difference in sound velocity in the peripheral portion 8 to a point.

For example, if V ₀ = 1530 m / sec, V ₁ = 2500 m / sec, H = 2.5 mm, x = 3 mm, and V ₂ = 2771 m / sec, the focal length f = 30 mm. The other values are the same, and changing to H = 5 mm results in a focal length f = 14.9 mm.

  Thus, the focal length f can be easily changed by changing the thickness H of the acoustic lens 7.

As shown in FIG. 1, when the peripheral portion 8 is composed of 10 layers with the central portion 4 in between, the ultrasonic waves traveling inside each layer parallel to the ultrasonic waves traveling inside the central portion 4 are at one point. Set the sound speed of each layer to converge. The speed of sound V ₂ of the resin material forming the peripheral portion 8 that converges at the focal length f can be obtained by the following equation (5).

For example, when the focal length f = 30 mm, V ₀ = 1530 m / sec, V ₁ = 2500 m / sec, H = 2.5 mm, and x = 3 mm, V ₂ = 2771 m / sec.

  Similarly, using the equation (5), the layers 8a, 8b, 8c, 8d, 8e, 8f, 8g, 8h, 8i, 8j and the layers 8k, 8l, 8m, 8n for converging the ultrasonic waves to the same focal length f. , 8o, 8p, 8q, 8r, 8s, and 8t, the sound velocities Va, Vb, Vc, Vd, Ve, Vf, Vg, Vh, Vi, and Vj can be obtained.

  As will be described later, such resin materials having different sound velocities can be obtained by adding an additive to a resin material serving as a base material.

  Next, a method for manufacturing the acoustic lens of the embodiment will be described.

  Drawing 3 is an explanatory view explaining an example of a manufacturing method of an acoustic lens of an embodiment.

<Manufacturing process of resin substrate>
FIG. 3A is an example of a resin substrate that forms the central portion 4. The resin substrate is a rectangular parallelepiped having a width L, a height H1, and a depth M as shown in FIG. The size of the resin substrate is not particularly limited, but as an example, L = 100 mm, M = 150 mm, and H1 = 2 mm.

  Although various resin materials can be used as the material for forming the resin substrate, the attenuation characteristic of ultrasonic waves is preferably a resin material of 2 dB / cm or less at a frequency of 5 MHz. For example, a polymer or copolymer such as methylpentene, styrene, methyl methacrylate, carbonate, propylene can be used.

  The resin substrate in FIG. 3A is produced by casting a resin material into a mold, for example.

<Lamination process>
After applying the resin liquid-1 to which the additive is added at a rate at which a predetermined sound speed faster than that of the central part 4 is obtained on both surfaces of the resin substrate forming the central part 4 so as to obtain a predetermined thickness w, heat curing is performed. I do. Next, after applying the resin liquid-2 to which the additive has been added at a rate at which an even faster predetermined sound speed is obtained to a predetermined thickness w, heat curing is performed. Thus, the application of the resin liquid and the heat curing are sequentially repeated, and the layers that become the layers 8a to 8j and the layers 8k to 8t are formed in the next step as shown in FIG. Note that the number of layers is not limited to the example of FIG. 3B, and may be determined according to the specifications of the acoustic lens 7.

  For example, zinc oxide, aluminum, aluminum oxide, duralumin, titanium, silicon nitride, boron carbide, molybdenum or the like is used as an additive added to the resin material in order to change the sound speed of the resin material of the base material. These additives are preferably added to the resin material of the base material uniformly and used in the form of a powder sufficiently small with respect to the wavelength so as not to cause acoustic mismatch at the base material and additive interface. The diameter is preferably 10 μm or less, more preferably 0.5 μm or less.

The volume ratio P at which the additive is added to the resin material of the base material can be obtained from equation (6), where Vx is the sound speed of the additive, V ₀ is the sound speed of the resin material of the base material, and Vα is the predetermined sound speed.

P = (Vα−V ₁ ) / (Vx−V ₁ ) (6)
For example, when Vx = 6400 m / sec, V ₁ = 2500 m / sec, and Vα = 2277 m / sec, P = 0.0695, and the volume ratio may be 6.95%.

  The mass ratio R is obtained by the equation (7), where the specific gravity ratio C is the specific gravity of the additive and the specific gravity of the base resin material.

R = P × C / ((1-P) + P × C) (7)
For example, when the specific gravity ratio C = 5.41 and P = 0.0695, the mass ratio R is 0.288, and the mass ratio may be 28.8%.

<Cutting and polishing process>
A surface orthogonal to the surface on which the resin materials are stacked so that the distance between the first lens surface and the second lens surface is a predetermined thickness from the state in which the resin materials are sequentially stacked as shown in FIG. 3 (surface in the Y-axis direction in this embodiment), and the cut surface is polished to obtain an acoustic lens 7 as shown in FIG. The acoustic lens 7 in FIG. 3C has the same shape as the acoustic lens 7 described in FIG. 1 and is a view seen from the negative Z-axis direction.

  As a cutting method, a dicing saw, a laser cutter, an ultrasonic cutter, a high-pressure water cutter, or the like can be used.

  As described above, the acoustic lens 7 of the present embodiment has an ultrasonic wave propagation speed while traveling from the first lens surface to the second lens surface according to the position where the ultrasonic waves are incident on the first lens surface. The ultrasonic waves radiated from the second lens surface are converged to a predetermined distance. As a result, even when a resin material having a higher sound speed than the subject is used, the surface in contact with the subject can be formed into a planar shape that can be easily adhered to the subject.

  Since the focal length f can be changed by changing the thickness H of the acoustic lens 7 as described above, if the acoustic lens 7 is cut to a predetermined thickness H in the cutting step, the predetermined focal length can be easily obtained. The acoustic lens 7 of f is obtained.

  In addition, since the acoustic lens 7 of the present embodiment is made of a resin material, the surface in contact with the subject is not easily worn. For this reason, the acoustic lens surface gradually wears off when the jelly-like material applied when using an ultrasonic probe is wiped after use, such as an acoustic lens made of silicone rubber, so that the focus position matches the original design. The problem of disappearing is less likely to occur.

  Furthermore, since the resin material does not easily transmit gas or liquid, the characteristics of the ultrasonic probe are hardly deteriorated due to the disinfection gas or liquid entering from the surface of the acoustic lens 7 on the side in contact with the subject. .

  In addition, since the acoustic lens 7 of the present embodiment can be formed from a resin material with little propagation loss, the acoustic lens 7 with little attenuation can be manufactured. In particular, when a resin material having a frequency of 5 MHz and 2 dB / cm or less is used, an acoustic lens 7 suitable for an array-type ultrasonic probe using a harmonic signal can be produced.

  FIG. 4 is a cross-sectional view illustrating the configuration of the head portion of the ultrasonic probe according to the embodiment.

  In the present embodiment, an example in which the present invention is applied to an array-type ultrasonic probe in which the transmitting piezoelectric element and the receiving piezoelectric element are separated and the operations during transmission and reception of ultrasonic waves are separated will be described. However, the present invention is not particularly limited, and can be applied to a single-type ultrasonic probe that performs transmission / reception with a single piezoelectric element.

  In the following description, description will be made based on the coordinate axes indicated by X, Y, and Z in the drawing. The X direction is the elevation direction (the dicing direction) of the ultrasonic probe 1, and the Z-axis positive direction is the direction in which ultrasonic waves are transmitted. The Z-axis direction is the stacking direction.

  The ultrasonic probe 1 shown in FIG. 4 includes a fourth electrode 15, a transmission element layer 2, a third electrode 14, an intermediate layer 13, a second electrode 10, a reception element layer 3, and a first electrode on a backing material 5. 9, the matching layer 6 and the acoustic lens 7 are laminated in this order.

  Hereinafter, each component will be described in the order of lamination.

(Transmitter element layer)
The transmission element layer 2 is a piezoelectric element made of a piezoelectric material such as lead zirconate titanate, and includes a third electrode 14 and a fourth electrode 15 on both surfaces facing each other in the thickness direction. The thickness of the transmitting element layer 2 is about 320 μm.

  The third electrode 14 and the fourth electrode 15 are connected to a cable 33 (not shown in FIG. 4) by a connector (not shown), and are connected to the transmission circuit 42 via the cable 33. When an electric signal is input to the third electrode 14 and the fourth electrode 15, the piezoelectric element vibrates and transmits ultrasonic waves from the transmitting element layer 2 in the positive Z-axis direction.

  The third electrode 14 and the fourth electrode 15 are formed by vapor deposition or photolithography on both surfaces of the transmission element layer 2 using a metal material such as gold, silver, or aluminum.

(Middle layer)
The intermediate layer 13 absorbs the vibration of the receiving element layer 3 so that the transmitting element layer 2 does not resonate and vibrate when the receiving element layer 3 receives and vibrates the reflected ultrasonic wave reflected by the subject. It is provided for.

  Such an intermediate layer 13 can be formed by molding a resin material. Examples of the resin material used for the intermediate layer 13 include polyvinyl butyral, polyolefin, polyacrylate, polyimide, polyamide, polyester, polysulfone, epoxy, oxetane, and the like.

  The thickness of the intermediate layer 13 is selected depending on the required sensitivity and frequency characteristics, and is about 180 to 190 μm, for example.

  The intermediate layer 13 can be omitted depending on the sensitivity and frequency characteristics to be obtained.

(Receiving element layer)
The receiving element layer 3 is composed of a plurality of piezoelectric elements made of an organic piezoelectric material.

  As the organic piezoelectric material used for the receiving element layer 3, for example, a vinylidene fluoride polymer can be used. Further, for example, a vinylidene fluoride (VDF) copolymer can be used as the organic piezoelectric material. This vinylidene fluoride copolymer is a copolymer (copolymer) of vinylidene fluoride and other monomers. Examples of other monomers include ethylene trifluoride (TrFE) and tetrafluoroethylene (TeFE). Perfluoroalkyl vinyl ether (PFA), perfluoroalkoxyethylene (PAE), perfluorohexaethylene, and the like can be used.

  In general, a piezoelectric element made of a piezoelectric material such as lead zirconate titanate can receive only an ultrasonic wave having a frequency band about twice the frequency of the fundamental wave. For example, ultrasonic waves in a frequency band of about 4 to 5 times the frequency can be received, which is suitable for widening the reception frequency band. Since an ultrasonic signal is received by an organic piezoelectric element having a characteristic capable of receiving such ultrasonic waves over a wide frequency range, the ultrasonic probe 1 and the ultrasonic diagnostic apparatus 100 in the present embodiment are relatively The frequency band can be widened with a simple structure.

  The thickness t of the receiving element layer 3 is appropriately set depending on the frequency of ultrasonic waves to be received, the type of organic piezoelectric material, and the like. When the wavelength of the ultrasonic wave to be received is λ, the receiving efficiency of the receiving element layer 3 is best when the thickness t of the receiving element layer 3 is t = λ / 4.

  Such a receiving element layer 3 is cast from a solution of an organic piezoelectric material to form a film having a predetermined thickness, heated for crystallization, and then molded into a sheet having a predetermined size. Make it.

  A first electrode 9 and a second electrode 10 are formed on both surfaces of the receiving element layer 3 facing each other in the thickness direction (Z-axis direction).

  The first electrode 9 and the second electrode 10 are connected to the receiving circuit 43 via a cable 33 (not shown in FIG. 4).

  When the receiving element layer 3 receives and vibrates the reflected wave of the ultrasonic wave reflected by the subject, an electric signal is generated between the first electrode 9 and the second electrode 10 in the piezoelectric element in accordance with the reflected wave. The electrical signal generated between the first electrode 9 and the second electrode 10 is received by the receiving circuit 43 via the cable 33 and imaged by the image processing unit 44.

(Matching layer)
The matching layer 6 has an acoustic impedance that is intermediate between the acoustic impedances of the human body, which is one of the subjects, and the receiving element layer 3, and matches the acoustic impedance. The matching layer 6 can be formed by molding a resin material, for example.

  The material used for the matching layer 6 is preferably a material having an acoustic impedance of about 1.7 to 1.8 and a sound speed of 1300 m / s to 2200 m / s, which is close to that of the human body. For example, polymethylpentene can be used.

  On the backing material 5, the transmission element layer 2 in which the third electrode 14 and the fourth electrode 15 described so far are formed, the intermediate layer 13, and the reception in which the first electrode 9 and the second electrode 10 are formed. The element layer 3 and the matching layer 6 are laminated in this order by bonding with an adhesive as shown in FIG. After the lamination, dicing is performed from the matching layer 6 in a direction opposite to the ultrasonic radiation direction, and further dicing from the adhesive layer between the backing material 5 and the fourth electrode 15 to a depth of 100 μm in the negative Z-axis direction. After filling the groove formed by dicing with a filler made of silicone resin or the like, the acoustic lens 7 described in FIGS. 1 to 3 is bonded to the uppermost layer.

  The acoustic lens 7 converges the ultrasonic wave transmitted from the transmitting element layer 2 to a predetermined distance.

(Each component and operation of ultrasonic diagnostic equipment and ultrasonic probe)
FIG. 5 is a diagram illustrating an external configuration of the ultrasonic diagnostic apparatus according to the embodiment. FIG. 6 is a block diagram illustrating an electrical configuration of the ultrasonic diagnostic apparatus according to the embodiment.

  The ultrasonic diagnostic apparatus 100 transmits an ultrasonic wave (ultrasonic signal) to a subject such as a living body (not shown), and receives the ultrasonic wave reflected from the received subject (echo, ultrasonic signal). The internal state in the sample is imaged as an ultrasonic image and displayed on the display unit 45.

  The ultrasonic probe 1 transmits an ultrasonic wave (ultrasonic signal) to the subject and receives a reflected wave of the ultrasonic wave reflected by the subject. As shown in FIG. 6, the ultrasonic probe 1 is connected to the ultrasonic diagnostic apparatus main body 31 via a cable 33, and is electrically connected to the transmission circuit 42 and the reception circuit 43.

  The transmission circuit 42 transmits an electrical signal to the ultrasonic probe 1 via the cable 33 according to a command from the control unit 46, and transmits ultrasonic waves from the ultrasonic probe 1 to the subject.

  The receiving circuit 43 receives an electrical signal corresponding to the reflected wave of the ultrasonic wave from the subject via the cable 33 from the ultrasonic probe 1 in accordance with a command from the control unit 46.

  The image processing unit 44 images the internal state in the subject as an ultrasonic image based on the electrical signal received by the receiving circuit 43 according to a command from the control unit 46.

  The display unit 45 is composed of a liquid crystal panel or the like, and displays an ultrasonic image imaged by the image processing unit 44 according to a command from the control unit 46.

  The operation input unit 41 includes a switch, a keyboard, and the like, and is provided for the user to input data such as a command for instructing the start of diagnosis and personal information of the subject.

  The control unit 46 includes a CPU, a memory, and the like, and controls each unit of the ultrasonic diagnostic apparatus 100 according to a programmed procedure based on an input from the operation input unit 41.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to these Examples.

[Example 1 and Example 2]
(Production of acoustic lens)
In Example 1, a rectangular parallelepiped having the same configuration as FIG. 1 and having a width W = 6 mm in the X-axis direction, a width H = 2.5 mm in the Z-axis direction, and a width L = 100 mm in the Y-axis direction, and a focal length f = 30 mm. An acoustic lens was produced according to the procedure described in FIG. Further, the width w of each of the layers 8a to 8j and the layers 8k to 8t was 0.2 mm, and W1 = 2 mm.

  In Example 2, a rectangular parallelepiped having a width W = 6 mm in the X-axis direction, a width H = 5 mm in the Z-axis direction, and a width L = 100 mm in the Y-axis direction having the same configuration as FIG. 1 and a focal length f = 14.9 mm. An acoustic lens was produced by the same procedure. The width w of the layers 8a to 8j and the layers 8k to 8t is the same as that in the first embodiment.

  Hereinafter, it demonstrates in order of a process.

<Manufacturing process of resin substrate>
A copolymer obtained by cross-linking styrene and divinylbenzene at a mass ratio of 95: 5 is cast into a mold as a material, and L = 100 mm, M = 150 mm, and H1 = 2 mm as shown in FIG. A resin substrate for forming the rectangular central portion 4 was produced. Was 2500 m / sec was measured sound velocity _{V 1} of the resin substrate forming the central portion 4.

<Lamination process>
Using Equation 5, the sound velocities V _{a to} V _j required for the layers 8 a to 8 _j and the layers 8 k to 8 t of Example 1 were determined as shown in Table 1.

However, H = 2.5 mm, f = 30 mm, V ₀ = 1530 m / sec, V ₁ = 2500 m / sec, and x is the layers 8 a to 8 j and layers 8 k to 8 t from the center of the central portion 4 in the X-axis direction. The distance in the X-axis direction to each far side was substituted.

  Next, the ratio of adding an additive capable of obtaining the sound speed shown in Table 1 was obtained as shown in Table 2 using Equations (6) and (7).

  In Examples, resin liquids 1 to 10 were prepared by mixing styrene and divinylbenzene with lipophilic zinc oxide nanoparticles as additives and a thermal polymerization initiator at a predetermined mass ratio, and using these resin liquids 1 to 10 Layers 8a to 8j and layers 8k to 8t were formed.

The mass ratio of the additives contained in the resin liquids 1 to 10 is calculated by substituting the sonic velocities V _{a to} V _j obtained in Table 1 into the equation (6), and adding the additive to the base resin material. And converted into a mass ratio by equation (7). However, the specific gravity ratio C = 5.41 between the copolymer of styrene and divinylbenzene and the lipophilic zinc oxide nanoparticles was used.

  Table 2 shows the mass ratios of styrene, divinylbenzene, lipophilic zinc oxide nanoparticles, and thermal polymerization initiator of the resin liquids 1 to 10 thus obtained.

  The lipophilic zinc oxide nanoparticles are VP AdNano Z805 manufactured by Degussa, and the average particle size is 250 nm. As the thermal polymerization initiator, azobisisobutyronitrile was used.

  After the resin liquid-1 was applied to both surfaces of the resin substrate forming the central portion 4 so as to have a thickness w after being heated and cured at room temperature, it was placed in an oven and heated at 120 ° C. for 5 minutes to be cured. Next, after the resin liquid-2 was applied at room temperature so as to have a thickness w after heat-curing, heat-curing was performed under the same conditions. Then, application | coating of a resin liquid and heat-curing were repeated sequentially on the same conditions, and application | coating to resin liquid-10 and heat-curing were performed.

<Cutting and polishing process>
3B, after cutting in the Y-axis direction along a plane orthogonal to the surface where the resin material is stacked every 3 mm in the Z-axis direction from the stacked state, the cut surface is polished and polished. = 2.5 mm, L = 100 mm, W = 6 mm, and the acoustic lens 7 of Example 1 as shown in FIG.

  3B, after cutting in the Y-axis direction along the plane orthogonal to the surface where the resin material is laminated every width 5.5 mm in the Z-axis direction, the cut surface is polished. The acoustic lens 7 of Example 2 as shown in FIG. 3C with H = 5 mm, L = 100 mm, and W = 6 mm was obtained.

  The cutting was performed with a dicing saw.

(Production of ultrasonic probe)
The prototype ultrasonic probe 1 was produced as follows.

  The transmission element layer 2 was made by lapping in a sheet shape having a length of 10 mm in the X direction, a length of 55 mm in the Y direction, and a length (thickness) of 320 μm in the Z direction, using lead zirconate titanate as a material.

  Next, gold was vacuum-deposited on both surfaces of the transmitting element layer 2 to produce a third electrode 14 and a fourth electrode 15 having a thickness of 0.3 μm.

  The intermediate layer 13 was made of polyvinyl butyral as a material, and the length in the X direction was 10 mm, the length in the Y direction was 55 mm, and the length (thickness) in the Z direction was 185 μm.

  The receiving element layer 3 was obtained by heating polyvinylidene fluoride copolymer powder (weight average molecular weight 290,000) having a molar ratio of vinylidene fluoride (hereinafter VDF) and trifluoroethylene (hereinafter 3FE) of 75:25 to 50 ° C. A solution dissolved in a 9: 1 mixed solvent of ethyl methyl ketone (hereinafter MEK) and dimethylformamide (hereinafter DMF) was cast on a glass plate. Thereafter, the solvent was dried at 50 ° C. to obtain a film (organic piezoelectric material) having a thickness of about 140 μm and a melting point of 155 ° C.

  This film was stretched 4 times at room temperature by a uniaxial stretching machine with a load cell capable of measuring the load applied to the chuck. The tension in the direction of the stretching axis at the end of the 4-times stretching was 2.2 N per unit width (mm). The stretching machine was heated while maintaining the stretched length, and heat treatment was performed at 135 ° C. for 1 hour. Then, it cooled to room temperature, controlling the distance between chuck | zippers (relaxation process) so that tension might not become zero. The film thickness of the obtained film after the heat treatment was 40 μm.

  Thereafter, it was formed into a sheet having a length of 55 mm in the Y direction and a length of 10 mm in the X direction. Gold or aluminum is vapor-deposited on both surfaces of the obtained film so that the surface resistance is 20Ω or less, and surface electrodes (first electrode 9 and second electrode 10) with a thickness of 0.3 μm are attached to both surfaces. A sample was obtained.

  Subsequently, the electrode was subjected to a polarization treatment while applying an AC voltage of 0.1 Hz at room temperature. The polarization treatment was performed from a low voltage, and the voltage was gradually applied until the electric field between the electrodes finally reached 100 MV / m. The final polarization amount was obtained from the residual polarization amount when the piezoelectric material was regarded as a capacitor, that is, the film thickness, the electrode area, and the charge accumulation amount with respect to the applied electric field. .

  The matching layer 6 was made of polymethylpentene as a material and had a length of 55 mm in the Y direction, a length of 10 mm in the X direction, and a length (thickness) of 140 μm in the Z direction.

  On the backing material 5, the transmitting element layer 2 in which the third electrode 14 and the fourth electrode 15 are formed, the intermediate layer 13, the receiving element layer 3 in which the first electrode 9 and the second electrode 10 are formed, matching The layers 6 are laminated in the order as shown in FIG. After the lamination, dicing was performed from the matching layer 6 in the negative Z-axis direction, and further from the adhesive layer of the backing material and the fourth electrode to a depth of 100 μm in the negative Z-axis direction.

  Finally, the acoustic lens 7 was bonded to the uppermost layer, and five ultrasonic probes 1 of Examples 1 and 2 were produced.

[Comparative Example 1]
(Production of acoustic lens)
An acoustic lens with a focal length of 30 mm having a convex lens surface having a width W in the X-axis direction of 6 mm, a width in the Y-axis direction of L = 100 mm, and a radius of curvature of 10 mm in the Z-axis direction was produced by molding silicone rubber. The maximum width H in the Z-axis direction is 460 μm.

(Production of ultrasonic probe)
Each layer was laminated in the same procedure as in Example 1. Finally, an acoustic lens made of silicone rubber was adhered to the uppermost layer, and five ultrasonic probes 1 of Comparative Example 1 were produced.

[Evaluation method]
The focal length and attenuation amount of each of the ultrasonic probes of Example 1, Example 2 and Comparative Example 1 were measured, and an average value was obtained. The focal length was measured by the underwater hydrophone method, and the attenuation was measured by the sing-around method.

  Further, the surface of the acoustic lens of Example 1 and Comparative Example 1 was subjected to a friction test 500 times by applying a load of 50 g to a non-woven wiper (BEMCOT M-3II (trade name), manufactured by Asahi Kasei Co., Ltd.), and then again. The focal length was measured.

  [result]

  As shown in Table 3, the focal length of Example 1 before the friction test is 30 mm, and the focal length of Example 2 is 15 mm. By changing the thickness H of the acoustic lens, an acoustic lens having a predetermined focal length can be obtained. I was able to confirm.

  Further, the focal lengths of Example 1 and Comparative Example 1 before the friction test were both 30 mm as shown in Table 4.

  As shown in Table 4, the amount of attenuation was 1.2 dB at a frequency of 5 MHz, 8.3 dB at a frequency of 15 MHz, and Example 2 was 2.4 dB at a frequency of 5 MHz, and 16.6 dB at a frequency of 15 MHz. Since the acoustic lens 7 of Example 1 is H = 2.5 mm, the attenuation characteristic at a frequency of 5 MHz is 4.8 dB / cm. Moreover, since the acoustic lens 7 of Example 2 is H = 5 mm, the attenuation characteristic at a frequency of 5 MHz is 4.8 dB / cm.

  On the other hand, as shown in Table 4, the comparative example 1 has an attenuation of 4.1 dB at a frequency of 5 MHz, 21, 3 dB at a frequency of 15 MHz, about 3 dB at a frequency of 5 MHz, and 13 dB at a frequency of 15 MHz, which is more attenuated than the first example. It has become. Thus, in the present invention, it was confirmed that an acoustic lens with a small propagation loss can be obtained with the same focal length.

  The focal length of Example 1 after the friction test was not changed as shown in Table 4, but the focal length of Comparative Example 1 was changed to 41 mm. From this, it was confirmed that the acoustic lens of the present invention has excellent wear resistance and high durability.

  As described above, according to the present invention, a method for manufacturing an acoustic lens that has excellent adhesion to a subject, little ultrasonic wave propagation loss, and can easily obtain a predetermined focal length, and an ultrasonic wave having the acoustic lens A probe, and an ultrasonic diagnostic apparatus having the ultrasonic probe can be provided.

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Transmitting element 3 Receiving element 4 Center part 5 Backing material 6 Matching layer 7 Acoustic lens 8 Peripheral part 9 1st electrode 10 2nd electrode 13 Intermediate | middle layer 14 3rd electrode 15 4th electrode 20 Substrate material 31 Ultrasound diagnostic apparatus body 33 Cable 41 Operation input unit 42 Transmission circuit 43 Reception circuit 44 Image processing unit 45 Display unit 46 Control unit 50 Liquid 100 Ultrasonic diagnostic device

Claims (6)

In the method of manufacturing an acoustic lens, the ultrasonic wave incident from the first lens surface is emitted from the second lens surface and converged to a predetermined distance.
A process of sequentially laminating materials having a propagation speed faster than the propagation speed of the underlying ultrasonic wave on both sides of the substrate,
Cutting the substrate on which the materials are sequentially laminated along a plane orthogonal to the surface on which the materials are laminated so that a distance between the first lens surface and the second lens surface is a predetermined thickness; ,
A method for producing an acoustic lens, comprising: The material is
2. The method of manufacturing an acoustic lens according to claim 1, wherein the material is a material in which an additive is added at a rate that provides a predetermined ultrasonic wave propagation speed. The material is
Resin material,
The method for producing an acoustic lens according to claim 2, wherein the layer is formed by applying a resin solution to which the additive is added in the step of laminating and then curing the resin solution. In an ultrasonic probe that transmits an ultrasonic wave toward a subject and receives a reflected wave of the ultrasonic wave from the subject,
An acoustic lens produced using the acoustic lens production method according to any one of claims 1 to 3,
An ultrasonic probe that transmits and receives ultrasonic waves, or transmits or receives ultrasonic waves through the acoustic lens. The attenuation characteristic of the acoustic lens is
The ultrasonic probe according to claim 4, wherein the frequency is 5 dB or less at a frequency of 5 MHz. In an ultrasonic diagnostic apparatus that transmits an ultrasonic wave toward a subject and generates an image according to a reflected wave of the ultrasonic wave received from the subject.
An ultrasonic diagnostic apparatus comprising the ultrasonic probe according to claim 4.