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JP2011193895

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DESCRIPTION JP2011193895
An acoustic lens with low attenuation of ultrasonic waves, a method of manufacturing the
acoustic lens, an ultrasonic probe having the acoustic lens, and an ultrasonic diagnostic
apparatus having the ultrasonic probe are provided. Do. The speed of propagation of the sound
wave of the additive is different from that of the base material, and the volume ratio of the
additive in the base material makes the ultrasonic wave incident on the incident surface of the
ultrasonic wave so that the ultrasonic wave converges to a predetermined distance. An acoustic
lens characterized by being continuously changed according to the position of a sound wave.
[Selected figure] Figure 1
Acoustic lens, ultrasonic probe, ultrasonic diagnostic device, and method of manufacturing
acoustic lens
[0001]
The present invention relates to an acoustic lens, an ultrasound probe, an ultrasound diagnostic
apparatus, and a method of manufacturing an acoustic lens.
[0002]
An ultrasonic diagnostic apparatus is a medical imaging apparatus that obtains a tomogram of
soft tissue in a living body from the body surface in a minimally invasive manner by an ultrasonic
pulse reflection method.
03-05-2019
1
Compared with other medical imaging devices, this ultrasound diagnostic device has features
such as small size, low cost, high safety with no exposure to X-rays, and the ability to perform
blood flow imaging by applying the Doppler effect. There is. Therefore, it is widely used in the
circulatory system (coronary of the heart), digestive system (gastrointestinal), internal medicine
(liver, pancreas, spleen), urology (kidney, bladder), and obstetrics and gynecology.
[0003]
An ultrasonic probe used for such a medical ultrasonic diagnostic apparatus generally uses a
piezoelectric element made of lead zirconate titanate to transmit and receive ultrasonic waves
with high sensitivity and high resolution. used.
[0004]
In addition, an acoustic lens is used for an ultrasound probe in order to focus a beam of
ultrasound to improve resolution.
Since the acoustic lens is in close contact with the subject (living body), it is easy to cause the
subject to be in close contact with the subject, and a material having a small attenuation factor at
the frequency used for diagnosis is required.
[0005]
Conventionally, silicone rubber is mainly used as such a material. Since silicone rubber has a
slower propagation velocity of sound waves (hereinafter also referred to as sound velocity) than
a subject (living body), the central portion of the cross-sectional shape is formed in a convex
shape, and the time for ultrasonic waves to pass through the thick central portion Was made
longer than the thinner part to focus the ultrasound.
[0006]
By the way, harmonic imaging diagnosis using a harmonic signal is becoming a standard
diagnostic method since a clear diagnostic image which can not be obtained by the conventional
B-mode diagnosis can be obtained.
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2
[0007]
In order to obtain an ultrasonic signal sufficient for performing harmonic imaging, it is important
to design how to efficiently receive harmonics that are higher in frequency and easier to
attenuate than the fundamental wave.
[0008]
However, since silicone rubber has a large propagation loss of ultrasonic waves, it is difficult to
improve the receiving sensitivity of the ultrasonic probe.
In particular, since the high frequency propagation loss is large, it can be said that the material is
unsuitable for harmonic imaging using harmonic signals.
[0009]
On the other hand, polymethylpentene which is a resin material, for example, is known as a
material having a small propagation loss, but polymethylpentene has a higher speed of sound
than a subject (living body), so the center of the cross-sectional shape is formed concave. It is
necessary to make the ultrasound converge.
[0010]
However, in the concave shape, the contact with the surface of the subject (living body) is poor,
and a clear image can not be obtained.
[0011]
Therefore, the flat side of the concave acoustic lens using polymethylpentene is the biological
contact side, the concave side is the piezoelectric element side, and the concave portion is filled
with the acoustic medium made of silicone rubber so that the air layer is not interposed.
Japanese Patent Application Laid-Open Publication No. 2000-147118 discloses a method of
[0012]
Moreover, in the conventional ultrasonic probe, although the matching layer which laminated |
stacked the layer from which an acoustic impedance differs between the piezoelectric element
and the acoustic lens is provided, since an acoustic impedance differs greatly in the boundary of
each layer of a matching layer, Since the reflection of ultrasonic waves is generated and
03-05-2019
3
attenuated, it causes the reduction of the transmission / reception sensitivity of ultrasonic waves.
[0013]
Therefore, an additive is added so that the content ratio changes as it is separated from the
piezoelectric element, and a layer in which the acoustic impedance between the piezoelectric
element and the acoustic lens is gradually changed is stacked to improve the transmission /
reception sensitivity of ultrasonic waves. An ultrasonic probe provided with an acoustic matching
lens is proposed (for example, see Patent Document 2).
[0014]
However, in order to increase the number of layers constituting the acoustic matching layer and
to improve the transmission / reception sensitivity of ultrasonic waves, there are the following
problems, and conventionally, the limit is two or three.
[0015]
For example, since it is necessary to make the thickness of each layer as thin as possible in order
to suppress the propagation loss of ultrasonic waves in the acoustic matching layer, the process
of laminating a large number of thin films takes time and there is a problem of poor yield.
Moreover, since an adhesive is used when bonding each layer together, there is a problem that
reflection of an ultrasonic wave arises also in a layer.
[0016]
As a method of solving such a problem of multiple reflections, it is known to use an acoustic
medium in which the acoustic impedance is continuously changed by mixing tungsten powder
into a resin material and naturally curing the tungsten powder while settling. (See, for example,
Patent Document 3).
[0017]
JP-A-6-254100 JP-A-2006-263385 JP-A-54-21082
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4
[0018]
However, as disclosed in Patent Document 1, when the acoustic medium is provided to fill the
concave portion of the acoustic lens, the acoustic impedance is largely different at the boundary
between the acoustic lens and the acoustic medium, so that the reflection of the ultrasonic wave
occurs. , There is a problem that the transmission and reception sensitivity of ultrasonic waves is
lowered.
[0019]
On the other hand, in the acoustic matching lens disclosed in Patent Document 2, a convex
curved surface is provided on one of three matching layers in which an additive is added to
silicone rubber to converge ultrasonic waves, but the number of matching layers is small.
Therefore, the difference in acoustic impedance at the interface is large, and the reflection of
ultrasonic waves can not be sufficiently suppressed.
[0020]
Further, in the patent documents 1 and 2, since silicone rubber is used, there is a problem that
the propagation loss of ultrasonic waves due to the silicone rubber is large and the reception
sensitivity becomes insufficient when using higher harmonics.
[0021]
Although it is conceivable to use the acoustic matching layer disclosed in Patent Document 3 as
the acoustic medium of the acoustic lens of Patent Document 1, it is possible to reduce the
difference in acoustic impedance at the boundary between the acoustic lens and the acoustic
medium, The presence of the bonding surface also causes the reflection of ultrasonic waves at
the interface.
Also, the manufacturing process is complicated to join two different parts.
[0022]
The matching layer of the acoustic matching lens disclosed in Patent Document 2 uses silicone
rubber and has different characteristics such as acoustic impedance and propagation velocity of
sound waves, so the acoustic matching disclosed in Patent Document 3 as it is Layers can not be
replaced.
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[0023]
The present invention has been made in view of the above problems, and is an acoustic lens with
less attenuation of ultrasonic waves, a method of manufacturing the acoustic lens, an ultrasonic
probe having the acoustic lens, and the super An object of the present invention is to provide an
ultrasonic diagnostic apparatus having an acoustic wave probe.
[0024]
In order to solve the above-mentioned subject, the present invention has the following features.
[0025]
1.
An acoustic lens formed by curing a dispersion liquid in which a liquid base material and an
additive having different propagation speeds of sound waves are added to a liquid base material,
wherein the volume ratio of the additive in the base material is an ultrasonic wave. An acoustic
lens characterized by being continuously changed in accordance with the position of the
ultrasonic wave incident on the surface on which the ultrasonic wave is incident, so as to
converge at a predetermined distance.
[0026]
2.
The acoustic impedance of the additive is different from that of the base material, and the volume
ratio of the additive in the base material is continuously changed according to the distance from
the surface on which the ultrasonic wave is incident. The acoustic lens as described in 1 above.
[0027]
3.
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6
An acoustic lens formed by curing a dispersion liquid in which a liquid base material and an
additive having different propagation speeds of sound waves are added to a liquid base material,
wherein the volume ratio of the additive in the base material is an ultrasonic wave. An acoustic
lens characterized by being continuously changed in accordance with the position of an incident
plane of ultrasonic waves so as to converge on a predetermined distance.
[0028]
4.
In the ultrasonic probe for performing at least one of transmission of ultrasonic waves toward a
subject and reception of reflected waves of ultrasonic waves from the subject, the acoustic lens
according to any one of 1 to 3 above An ultrasound probe comprising: transmitting and receiving
ultrasound waves via the acoustic lens; and transmitting or receiving ultrasound waves.
[0029]
5.
An ultrasonic diagnostic apparatus for transmitting an ultrasonic wave toward a subject and
generating an image in accordance with a reflected wave of the ultrasonic wave received from
the subject, comprising: the ultrasonic probe according to the above 4; The ultrasound diagnostic
device that features.
[0030]
6.
A manufacturing method of an acoustic lens formed using a dispersion liquid in which a liquid
base material and an additive having different propagation speeds of sound waves are added to a
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liquid base material, which is a dispersion liquid in which the additive is dispersed in the liquid
base material. And a settling step of settling the additive for a predetermined time, and a curing
step of curing the dispersion while settling the additive after the predetermined time, and After
performing the sedimentation step and the curing step while rotating the mold in which the
dispersion is injected so that the liquid surface of the injected dispersion becomes concave by
centrifugal force, the portion cured in a concave shape is A manufacturing method of an acoustic
lens characterized by performing a process processed into a plane.
[0031]
7.
A manufacturing method of an acoustic lens formed by using a dispersion liquid in which a liquid
base material and an additive having different propagation speeds of sound waves are added to a
liquid base material, which is a dispersion liquid in which the additive is dispersed in the liquid
base material. Injecting step into the mold, settling step for settling the additive for a
predetermined time, curing step for curing the dispersion while settling the additive after the
predetermined time, and the curing step generated in the curing step A method of manufacturing
an acoustic lens, comprising: a bonding step of bonding two compositions with the surfaces of
the respective compositions having the slower sound propagation speeds facing each other.
[0032]
The acoustic lens of the present invention is formed by curing a dispersion obtained by adding
an additive having different propagation speeds of the base material and the sound wave to a
liquid base material, and the volume ratio of the additive in the base material is ultrasonic wave.
In order to converge to a predetermined distance, it is in a state of being continuously changed
according to the position of the ultrasonic wave incident on the surface on which the ultrasonic
wave is incident.
[0033]
In this case, since no interface is provided inside the acoustic lens, reflection of ultrasonic waves
by the interface does not occur.
[0034]
Therefore, an acoustic lens with low attenuation of ultrasonic waves, a method of manufacturing
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the acoustic lens, an ultrasonic probe having the acoustic lens, and an ultrasonic diagnostic
apparatus having the ultrasonic probe are provided. be able to.
[0035]
FIG. 7 is a cross-sectional view for explaining a manufacturing process of the acoustic lens 8
according to the first embodiment.
It is a perspective view explaining the composition 72 comprised with the type | mold 70. FIG.
FIG. 7 is a process diagram illustrating a manufacturing process of the acoustic lens 8;
It is a graph which shows the volume ratio of the zinc oxide which occupies to the medium in the
depth to the depth direction (Z-axis direction) of acoustic lens 8 as an example.
It is a graph which shows an example of the relationship between the volume ratio of zinc oxide,
and an acoustic impedance.
It is a graph which shows an example of the relationship between the volume ratio of zinc oxide,
and the propagation velocity (sound speed) of a sound wave.
It is a graph which shows the change with respect to the depth direction of the acoustic
impedance of the acoustic lens 8 as an example.
It is a graph which shows the change with respect to the depth direction of the acoustic velocity
of the acoustic lens 8 as an example.
It is a graph which shows an example of a volume ratio of zinc oxide to a medium in the depth to
a depth direction (Z-axis direction) from each position on upper surface 75 of acoustic lens 8 of a
1st embodiment as an example. .
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It is an explanatory view explaining a manufacturing process of acoustic lens 7 of a 2nd
embodiment. It is process drawing explaining the manufacturing process of acoustic lens 7 of a
2nd embodiment. It is a graph which shows as an example the relationship between the distance
of the X-axis direction from the center X0 of width W3 of acoustic lens 7 of a 2nd embodiment,
and the sound speed of the medium in the distance. It is a sectional view showing an example of
composition of ultrasonic probe 1 in an embodiment. It is a figure showing the appearance
composition of the ultrasonic diagnostic equipment in an embodiment. It is a block diagram
which shows the electric constitution of the ultrasound diagnosing device in embodiment. It is a
graph which compares the frequency characteristic of transmission / reception sensitivity of the
piezoelectric element which laminated the acoustic matching layer.
[0036]
Hereinafter, one embodiment according to the present invention will be described based on the
drawings, but 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, and abbreviate | omits the description.
[0037]
The following 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 direction in which dicing is
performed) of the ultrasonic probe 1 (not shown in FIG. 1) for joining the acoustic lens 8, and the
Y direction is the longitudinal direction of the acoustic lens 8, Z axis positive. The direction is the
direction in which the ultrasound is transmitted.
[0038]
Next, the manufacturing process of the acoustic lens 8 of the first embodiment will be described.
[0039]
FIG. 1 is a cross-sectional view for explaining the manufacturing process of the acoustic lens 8
according to the first embodiment, FIG. 2 is a perspective view for explaining the composition 72
composed of the mold 70, and FIG. It is process drawing explaining a process.
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10
[0040]
In the acoustic lens 8 according to the first embodiment, in order to cause the ultrasonic waves
to converge at a predetermined distance, the volume ratio of the additive according to the
position in the X axis direction of the incident ultrasonic waves and the distance in the Z axis
direction from the incident surface. Is continuously changing.
[0041]
Arrow X3 in FIG. 1 indicates an ultrasonic wave incident from the lower surface 76 and traveling
at the center of the width of the acoustic lens 8 in the X-axis direction, and arrow X5 indicates
the periphery of the width of the acoustic lens 8 in the X-axis direction. The arrow X4 indicates
an ultrasonic wave traveling near the middle of the arrows X5 and X3.
[0042]
The example which produces the acoustic lens 8 of 1st Embodiment of rectangular
parallelepiped shape is demonstrated along the flowchart of FIG.
[0043]
S1: Dispersion Liquid Production Step Various resin materials can be used as the base material of
the dispersion liquid, but a resin material that can be cured in a short time, for example, a
photocurable resin material that can be cured in a short time by irradiating light preferable.
[0044]
Further, a resin material having an ultrasonic wave attenuation characteristic of 2 dB / cm or less
at a frequency of 5 MHz is preferable.
For example, polymers or copolymers of acrylate, methyl pentene, styrene, methyl methacrylate,
carbonate, propylene and the like can be used.
[0045]
As additives to be added to the base material, zinc oxide, aluminum, aluminum oxide, duralumin,
03-05-2019
11
titanium, silicon nitride, boron carbide, molybdenum and the like can be used.
These are preferably dispersed in the matrix uniformly and added, and are preferably used in the
form of a powder sufficiently small with respect to the wavelength so that no acoustic mismatch
occurs at the interface between the matrix and the additive, and the particle size is 10 μm or
less More preferably, it is 0.5 μm or less.
[0046]
In the present embodiment, an example will be described in which a dispersion is prepared in
which zinc oxide is uniformly dispersed as an additive, using the ultraviolet-curable photocurable
resin material of Table 1 as a base material.
[0047]
[0048]
The photocurable resin A in Table 1 is a mixture of isocyanuric acid EO modified di- and
triacrylates (ALONIX M-313; manufactured by Toagosei Co., Ltd.), and the photocurable resin B is
ditrimethylolpropane tetraacrylate (ALONIX M-408; Manufactured by Toagosei Co., Ltd.).
[0049]
The additive is lipophilic zinc oxide nanoparticles (VP AdNano Z805 manufactured by Degussa)
having an average particle diameter of 250 nm.
The photopolymerization initiator is bis (2,4,6-trimethyl benzoyl) -phenyl phosphine oxide
(photopolymerization initiator IRGRACURE 819; manufactured by BASF AG).
[0050]
For example, the photocurable resins A and B are used as a base material at a ratio shown in
Table 1, and the photopolymerization initiator and the zinc oxide of the additive are stirred and
uniformly dispersed to produce a dispersion.
03-05-2019
12
[0051]
S2: Injection Step FIG. 1 (a) is a cross-sectional view of a mold 70 into which the dispersion liquid
71 is injected.
As shown in FIG. 1A, the dispersion 71 in which the additive is uniformly dispersed in the base
material is poured into a mold 70 having a rectangular recess.
In the present embodiment, the shape of the recess is such that the width W3 = 10 (mm), the
height H3 = 4 (mm), and the length L1 = 70 (mm).
[0052]
S10: Sedimentation Step FIG. 1 (b) and FIG. 2 (a) are a sectional view and a perspective view of a
mold 70 into which the dispersion liquid 71 attached inside the centrifugal separator 80 is
injected.
In the sedimentation step of the first embodiment, the mold 70 into which the dispersion liquid
71 is injected is attached to the inside of the centrifugal separator 80 as shown in FIG. 1 (b), and
additives are rotated while rotating in the arrow direction with O as the rotation center. To settle
for a predetermined time.
Then, the liquid surface of the dispersion 71 injected into the mold 70 becomes concave due to
centrifugal force as shown in FIG. 1 (b).
The additives are also distributed concavely by the centrifugal force, and more additive is
collected at the periphery than at the center of the mold 70.
[0053]
S11: Curing Step While rotating the mold 70 into which the dispersion liquid 71 has been
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injected, ultraviolet rays are irradiated from the upper surface of the dispersion liquid 71 for a
predetermined time to cure.
Thereafter, the mold 70 is removed from the centrifuge 80, and heated to be further cured to
obtain a composition 72 as shown in FIG. 2 (b).
[0054]
S13: Cutting Process As shown in FIG. 1 (c), the concave portion of the composition 72 is cut by a
dotted line indicated by C, and processed into a rectangular solid of height H4 as shown in FIG. 1
(d). Get eight.
[0055]
In the acoustic lens 8 obtained by such a simple process, since the additive is hardened while
settling in the direction of the lower surface 76, depending on the depth from the upper surface
81 in the direction of the lower surface 76, The volume fraction of the additive contained in the
medium is increasing.
[0056]
The graph of FIG. 4 is a graph showing an example of the volume ratio of zinc oxide in the
medium at the depth with respect to the depth direction (Z-axis direction) of the acoustic lens 8.
The horizontal axis in FIG. 4 is the depth (mm) from the upper surface 81 of the acoustic lens 8
at the position of arrow X3, and the vertical axis is the volume percentage (volume%) of zinc
oxide in the medium at that depth .
[0057]
In the example of FIG. 4, on the upper surface 81, the volume ratio of zinc oxide is 0 (volume%),
and for a medium with a depth of 1.2 (mm), the volume ratio is 9.8 (volume%), corresponding to
a depth of 2 mm On the lower surface 76, the volume ratio is 65 (volume%), and the volume ratio
of zinc oxide increases continuously according to the depth.
[0058]
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14
The volume ratio of zinc oxide can be determined by surface elemental analysis.
The volume ratio of zinc oxide at the position in the depth direction (Z-axis direction) can be
determined by cutting the surface from the upper surface 81 to a predetermined depth and
performing surface elemental analysis.
[0059]
Next, an example of characteristics of a sample cured with the photocurable resins A and B in
Table 1 being uniformly dispersed by changing the volume ratio of zinc oxide to a base material
will be described using FIGS. 5 and 6. .
FIG. 5 is a graph showing an example of the relationship between the volume fraction of zinc
oxide and the acoustic impedance.
FIG. 6 is a graph showing the relationship between the volume fraction of zinc oxide and the
propagation velocity of sound waves (hereinafter also referred to as the speed of sound).
[0060]
As shown in FIG. 5, in the volume ratio 0 (volume%) of zinc oxide, in the acoustic impedance 3
(Pa · s · m <−1>), in the volume ratio 70 (volume%), the acoustic impedance 23 (Pa · s) M <-1>).
Further, as shown in FIG. 6, at a volume ratio of zinc oxide of 0 (volume%), the velocity of sound
is 2700 (m / s), and at a volume ratio of 70 (volume%), the velocity of sound is 5200 (m / s). The
acoustic impedance and the speed of sound increase as the volume fraction of the volume
increases.
[0061]
From the volume ratio of zinc oxide of the acoustic lens 8 at the depth from the upper surface
shown in FIG. 4 and the characteristics shown in FIGS. 5 and 6, changes in the velocity of sound
and the acoustic impedance in the depth direction are determined.
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[0062]
FIG. 7 is a graph showing an example of the change in acoustic impedance of the acoustic lens 8
in the depth direction, and FIG. 8 is a graph showing the change of the speed of sound of the
acoustic lens 8 in the depth direction.
The horizontal axis in FIGS. 7 and 8 is the depth (mm) from the upper surface 81 of the acoustic
lens 8, and the vertical axis in FIG. 7 is the acoustic impedance (Pa · s · m <−1>), The vertical axis
is the velocity of sound (m / s).
[0063]
As shown in FIG. 7, on the upper surface 81, the acoustic impedance 23 (Pa · s · m <−1)
corresponds to the acoustic impedance 3 (Pa · s · m <−1>) and the depth 2 mm. And the acoustic
impedance increases continuously according to the depth.
[0064]
Further, as shown in FIG. 7, the sound velocity is 2200 (m / s) on the upper surface 81, and the
sound velocity 5200 (m / s) on the lower surface 76 corresponding to a depth of 2 mm. The
speed of sound is increasing.
[0065]
The acoustic impedance of the piezoelectric element is generally about 24 to 36 Pa · s · m <-1>. If
the acoustic impedance of the lower surface 76 to be joined to the piezoelectric element is a
value close to that of this example, it occurs at the joining surface Reflection of ultrasonic waves
can be suppressed.
[0066]
The acoustic impedance of the human body which is the subject is about 1.8 Pa · s · m <-1>, and
the acoustic lens in contact with the subject also has an acoustic impedance close to this value.
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Therefore, if the acoustic impedance of the upper surface 81 to be joined to the acoustic lens is
set to a value close to that of the acoustic lens as in this example, it is possible to suppress the
reflection of the ultrasonic waves generated at the junction as well.
[0067]
In the present embodiment, there is no interface between the lower surface 76 and the upper
surface 81, and the acoustic impedance changes continuously according to the depth (distance).
It does not happen.
Therefore, the acoustic lens 8 of the present embodiment has less attenuation of ultrasonic
waves.
Such an acoustic lens 8 can be manufactured by simple equipment and simple processes.
[0068]
FIG. 9 shows zinc oxide occupying the medium at the depth in the depth direction (Z-axis
direction) from each position on the upper surface 75 of the acoustic lens 8 of the first
embodiment thus manufactured. It is a graph which shows the volume ratio of as an example.
The horizontal axis in FIG. 9 is the depth (mm) from the upper surface 75 of the acoustic lens 8,
and the vertical axis is the volume percentage (volume%) of zinc oxide in the medium at that
depth. Further, X3, X4, and X5 in FIG. 9 correspond to X3, X4, and X5 indicated by arrows in
FIG. 1 (d). That is, the volume ratio of zinc oxide which changes according to the distance in the
depth direction (the negative direction of the Z-axis) from the upper surface 75 of the position in
the X-axis direction indicated by X3, X4, and X5 is shown.
[0069]
At any position of the center X3 in the X-axis direction of the acoustic lens 8, the peripheral
portion X5, and the middle portion X4 of X3 and X5, the volume ratio of zinc oxide is 0 (volume
%), The volume ratio is 65 (volume%) on the lower surface 76 corresponding to the depth 2
(mm), and the volume ratio of zinc oxide increases continuously according to the depth from the
upper surface 75 There is.
03-05-2019
17
[0070]
On the other hand, since an increase in the volume ratio starts from the depth close to the upper
surface 75 in the order of X5, X4, and X3, the oxidation in the peripheral portion X5 occupies
between the upper surface 75 and the lower surface 76 of the acoustic lens 8 on average. There
is a large volume proportion of zinc.
For example, while the volume ratio of the medium having a depth of 1.2 (mm) is 9.8 (volume%)
in the central area X3, the volume ratio is 61.4 (volume%) in the peripheral area X5.
[0071]
As described in FIG. 6, the sound velocity also increases as the volume fraction of zinc oxide
increases. Therefore, the ultrasonic waves traveling in the Z-axis direction from the peripheral
portion as indicated by X5 have a high percentage of passing through the region having a higher
sound velocity than central portion X3, and the time taken to pass between upper surface 75 and
lower surface 76 It becomes short.
[0072]
As described above, the ultrasonic wave indicated by X5 traveling in the peripheral part is an
ultrasonic wave indicated by X3 simultaneously incident on the lower surface 76 because the
distance traveling along the region higher in sound velocity than the ultrasonic wave indicated by
X3 advancing in the center is long. The upper surface 75 is reached earlier than before.
[0073]
As for the acoustic impedance, as described in FIG. 5, as the volume fraction of zinc oxide
increases, the acoustic impedance also increases.
From the volume ratio of zinc oxide, the acoustic impedance of the acoustic lens 8 is the acoustic
impedance 3 (Pa · s · m <-1>) on the upper surface 75 and the acoustic impedance 23 (Pa · s · m <
-1>), and the acoustic impedance increases continuously according to the depth.
03-05-2019
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[0074]
As described above, the acoustic impedance of the piezoelectric element is generally about 24 to
36 Pa · s · m <-1>, and the acoustic impedance of the lower surface 76 joined to the piezoelectric
element has a value close to that as in this example. Then, the reflection of the ultrasonic wave
generated at the bonding surface can be suppressed.
[0075]
The acoustic impedance of the human body which is the subject is about 1.8 Pa · s · m <−1>, and
the acoustic impedance of the upper surface 75 is a value close to this value.
[0076]
In the following description, the upper surface 75 is in contact with the subject.
[0077]
The ultrasonic wave traveling in the peripheral portion indicated by X5 is incident on the subject
earlier than the ultrasonic wave traveling in the center indicated by X3, and therefore travels a
distance that is greater by the time difference, It converges with the ultrasonic wave shown by S1
which travels on the central part.
Further, X4 is incident on the object between X3 and X5, and converges with the ultrasonic wave
indicated by X3 traveling in the central portion at a distance f.
[0078]
The focal length of the acoustic lens 8 thus changes according to the relationship between the
position at which the ultrasonic wave is incident on the lower surface 76 and the time it travels
from the lower surface 76 to the upper surface 75, which varies with the volume fraction of the
additive.
[0079]
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In the present embodiment, since there is no interface between the lower surface 76 and the
upper surface 75, and the acoustic impedance changes continuously according to the depth
(distance), reflection of ultrasonic waves occurs inside the acoustic lens 8. Absent.
In addition, the acoustic lens 8 can converge the ultrasonic wave at a predetermined distance.
[0080]
Furthermore, since the surface in contact with the subject is flat, the contact with the surface of
the subject is good and the subject and the acoustic lens 8 can be easily brought into close
contact with each other.
[0081]
As described above, the acoustic lens 8 of the present embodiment has less attenuation of
ultrasonic waves, and the acoustic lens 8 of the present embodiment is manufactured by a simple
installation and a simple process by the method of manufacturing the acoustic lens 8 of the
present embodiment. Can.
[0082]
Next, the manufacturing process of the acoustic lens 7 of the second embodiment will be
described.
[0083]
FIG. 10 is an explanatory view for explaining a manufacturing process of the acoustic lens 7 of
the second embodiment, and FIG. 11 is a process diagram for explaining a manufacturing process
of the acoustic lens 7.
[0084]
Similarly to the acoustic lens 8 of the first embodiment, the acoustic lens 7 of the second
embodiment has an additive according to the position of the incident ultrasonic wave in the Xaxis direction in order to converge the ultrasonic wave to a predetermined distance. The volume
fraction is configured to change continuously.
[0085]
The example which produces the acoustic lens 7 of 2nd Embodiment of rectangular
03-05-2019
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parallelepiped shape along the flowchart of FIG. 11 is demonstrated.
[0086]
S1: Dispersion Liquid Production Step Since the same dispersion liquid as the dispersion liquid
described in the first embodiment can be used, the same dispersion liquid production step can be
used.
[0087]
In this embodiment, as in the first embodiment, an example will be described in which zinc oxide
is stirred as an additive and uniformly dispersed in the base materials of the photocurable resins
A and B at the ratio shown in Table 1 .
[0088]
S2: Injecting Step As the mold for injecting the dispersion liquid 71, the mold 70 shown in FIG.
1A and FIG. 2A can be used as in the first embodiment.
As shown in FIGS. 1 (a) and 2 (a), a dispersion 71 in which additives are uniformly dispersed in a
base material is poured into a mold 70 having a rectangular recess.
In the present embodiment, the shape of the recess is such that the width W2 = 10 (mm), the
height H2 = 4 (mm), and the length L2 = 70 (mm).
[0089]
S3: Sedimentation Step After pouring the dispersion 71 into the mold 70, it is left for a
predetermined time to precipitate the additive.
[0090]
S4: Curing Step The top surface of the dispersion liquid 71 is cured by irradiation with ultraviolet
light for a predetermined time.
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Thereafter, it is heated to be further cured and removed from the mold 70 to obtain a
composition 72.
In this step, as shown in FIG. 10A, two compositions 72a and 72b used in the bonding step of the
next step are produced.
[0091]
Since the compositions 72a and 72b are hardened while the additive settles in the direction of
the lower surface 76a and 82b, depending on the depth from the upper surface 81a and 81b to
the lower surface 76a and 82b, the base material The volume fraction of additives in the
[0092]
S5: Bonding Step The two compositions 72a and 72b generated in the curing step of S4 are
arranged such that the upper surface 81a and the upper surface 81b with low density of the
additives of the respective compositions 72a and 72b face each other as shown in FIG. Join as
shown in (b).
[0093]
S6: Cutting and Polishing Step The compositions 72a and 72b joined as shown in FIG. 10 (b) are
cut in a plane perpendicular to the joint surface as shown by dotted lines, and the cut surface is
polished to obtain the surface shown in FIG. Thus, the acoustic lens 7 is obtained by processing
into a rectangular shape having a thickness d.
[0094]
FIG. 13 is a graph showing an example of the relationship between the distance in the X-axis
direction from the center X0 of the width W3 of the acoustic lens 7 of the second embodiment
manufactured in this manner and the speed of sound of the medium at that distance. .
[0095]
The acoustic lens 7 is manufactured by facing the upper surfaces 81a and 81b having a low
volume ratio of the additive to the base material facing each other and joining them, so the center
X0 of the width W3 which is the position of the joining surface is the most additive volume The
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22
proportion is lower, and the volume proportion of the additive is higher as it goes away from X0
in the X-axis direction.
In the Z-axis direction, the volume fraction of the additive contained in the medium is constant.
[0096]
As described in FIGS. 5 and 6, as the volume fraction of zinc oxide increases, the velocity of
sound and the acoustic impedance increase.
Therefore, the sound velocity and the acoustic impedance increase as the distance from X0 in the
X-axis direction increases, and is constant in the Z-axis direction.
[0097]
The horizontal axis in FIG. 12 is the distance (mm) in the X-axis direction from the center X0, and
the vertical axis is the sound velocity (m / s) of the medium at that distance.
[0098]
As shown in FIG. 12, when the distance in the X-axis direction from the center X0 increases, the
speed of sound increases, so a position away from the center X0 in the Z-axis direction from
ultrasonic waves traveling from the center X0 to the Z-axis direction A traveling ultrasonic wave
has a shorter time to pass between the first lens surface 84 and the second lens surface 85.
[0099]
As described above, since the ultrasonic wave incident from X1 travels in a region where the
sound velocity is higher than the ultrasonic wave incident from the center X0, it simultaneously
reaches the second lens surface 85 earlier than the ultrasonic wave incident from the center X0.
[0100]
The ultrasound incident from X1 travels in the medium in contact with the second lens surface
85 faster than the ultrasound incident from the center X0, and converges with the ultrasound
incident from the center X0 at a predetermined distance.
03-05-2019
23
[0101]
Since the convergence distance of the ultrasonic waves changes depending on the time difference
of the ultrasonic waves passing between the first lens surface 84 and the second lens surface 85,
the acoustic lens 7 of this embodiment is cut in the cutting step of S6. The focal length can be
changed by changing the thickness d.
[0102]
In the present embodiment, since there is no interface between the first lens surface 84 and the
second lens surface 85 and the acoustic impedance in the direction in which the ultrasonic wave
travels is constant, the reflection of the ultrasonic wave occurs inside the acoustic lens 7. Absent.
[0103]
Therefore, the acoustic lens 7 of the present embodiment has less attenuation of ultrasonic
waves.
In addition, by using the method of manufacturing an acoustic lens according to the present
embodiment, an acoustic lens with an arbitrary focal length with less attenuation of ultrasonic
waves can be manufactured with a simple installation and a simple process.
[0104]
Furthermore, since the surface in contact with the subject is flat, the contact with the surface of
the subject is good and the subject and the acoustic lens 8 can be easily brought into close
contact with each other.
[0105]
FIG. 13 is a cross-sectional view showing the configuration of the head portion of an ultrasonic
probe using the acoustic lens 8 or the acoustic lens 7.
[0106]
In the present embodiment, an example in which the present invention is applied to a single type
ultrasonic probe that performs transmission and reception with a single piezoelectric element
will be described, but the present invention is not particularly limited and a transmission
03-05-2019
24
piezoelectric element and a reception piezoelectric element Can also be applied to an array-type
ultrasound probe in which the operations at the time of transmission and reception of ultrasound
are separated.
[0107]
The following 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 of the ultrasound probe 1 (the direction in which dicing
is performed), and the Z-axis positive direction is the direction in which ultrasound is transmitted.
The Z-axis direction is the stacking direction.
[0108]
The ultrasound probe 1 shown in FIG. 13 is laminated on the backing material 5 in the order of
the first electrode 15, the transmission / reception element layer 2, the second electrode 14, the
acoustic lens 8, or the acoustic lens 7.
[0109]
Hereafter, each component is demonstrated in order of lamination | stacking.
[0110]
(Transmission / reception element layer) The transmission / reception element layer 2 is a
piezoelectric element made of a piezoelectric material such as lead zirconate titanate, and
includes the second electrode 14 and the first electrode 15 on both sides facing each other in the
thickness direction.
The thickness of the transmission / reception element layer 2 is about 320 μm.
03-05-2019
25
[0111]
The second electrode 14 and the first electrode 15 are connected to a cable 33 (not shown) in
FIG. 13 by a connector (not shown), and connected to the transmission circuit 42 via the cable
33.
When an electric signal is input to the second electrode 14 and the first electrode 15, the
piezoelectric element vibrates, and ultrasonic waves are transmitted from the transmitting /
receiving element layer 2 in the positive Z-axis direction.
[0112]
The second electrode 14 and the first electrode 15 are formed on both surfaces of the
transmission / reception element layer 2 using a metal material such as gold, silver, or aluminum
by using a vapor deposition method or a photolithography method.
[0113]
The second electrode 14 and the first electrode 15 are also connected to the receiving circuit 43
via a cable 33 (not shown) in FIG.
[0114]
When the transmitting / receiving element layer 2 receives and vibrates the reflected wave of the
ultrasonic wave reflected by the object, an electrical signal is generated between the second
electrode 14 and the first electrode 15 according to the reflected wave.
An electrical signal generated between the second electrode 14 and the first electrode 15 is
received by the receiving circuit 43 via the cable 33 and is imaged by the image processing unit
44.
[0115]
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26
The transmitting / receiving element layer 2 in which the second electrode 14 and the first
electrode 15 are formed on the backing material 5, the acoustic lens 8 or the acoustic lens 7 are
sequentially adhered by an adhesive and laminated as shown in FIG.
In addition, an intermediate layer having an intermediate acoustic impedance may be provided
between the transmission / reception element layer 2 and the acoustic lens 8 or the acoustic lens
7 as necessary.
[0116]
After lamination, dicing is performed from the transmission / reception element layer 2 in the
direction opposite to the ultrasonic radiation direction, and dicing is further performed from the
adhesive layer of the backing material 5 and the first electrode 15 to a depth of 100 μm in the
negative Z-axis direction.
A groove made of dicing is filled with a filler made of silicone resin or the like, and then an
acoustic lens 7 or an acoustic lens 8 is adhered to the uppermost layer.
[0117]
(Each Configuration and Operation of Ultrasonic Diagnostic Apparatus and Ultrasonic Probe) FIG.
14 is a view showing an appearance configuration of the ultrasonic diagnostic apparatus in the
embodiment.
FIG. 15 is a block diagram showing an electrical configuration of the ultrasonic diagnostic
apparatus in the embodiment.
[0118]
The ultrasonic diagnostic apparatus 100 transmits an ultrasonic wave (ultrasound signal) to a
subject such as a biological body (not shown), and the ultrasonic wave reflected by 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.
03-05-2019
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[0119]
The ultrasound probe 1 transmits ultrasound (ultrasound signal) to a subject, and receives a
reflected wave of ultrasound reflected by the subject.
As shown in FIG. 15, the ultrasound probe 1 is connected to the ultrasound diagnostic apparatus
main body 31 via the cable 33, and is electrically connected to the transmission circuit 42 and
the reception circuit 43.
[0120]
The transmission circuit 42 transmits an electrical signal to the ultrasound probe 1 via the cable
33 according to a command from the control unit 46, and causes the ultrasound probe 1 to
transmit ultrasound to the subject.
[0121]
The receiving circuit 43 receives an electric signal corresponding to the reflected wave of the
ultrasonic wave from the inside of the subject from the ultrasonic probe 1 through the cable 33
according to the command of the control unit 46.
[0122]
The image processing unit 44 images the internal state inside the subject as an ultrasound image
based on the electrical signal received by the receiving circuit 43 according to an instruction
from the control unit 46.
[0123]
The display unit 45 includes a liquid crystal panel or the like, and displays an ultrasonic image
imaged by the image processing unit 44 according to an instruction from the control unit 46.
[0124]
The operation input unit 41 includes a switch, a keyboard, and the like, and is provided to input
data such as a command that the user instructs to start diagnosis and personal information of the
subject.
03-05-2019
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[0125]
The control unit 46 includes a CPU, a memory, and the like, and controls the respective units of
the ultrasonic diagnostic apparatus 100 according to a procedure programmed based on the
input of the operation input unit 41.
[0126]
Hereinafter, the present invention will be described by way of examples, but the present
invention is not limited to these examples.
[0127]
Example 1 (Production of Acoustic Lens 8) In Example 1, the width W3 = 10 mm in the X-axis
direction, the height H4 = 2 mm in the Z-axis direction, and the length in the Y-axis direction of
the same configuration as FIG. A rectangular parallelepiped acoustic lens 8 having a length L1 of
70 mm was produced by the procedure described in FIG.
[0128]
S1: Dispersion Liquid Production Step In this example, a dispersion liquid composed of the
materials in Table 1 was used.
[0129]
The photocurable resins A and B were used as base materials, photopolymerization initiators, and
lipophilic zinc oxide nanoparticles as additives were stirred at a ratio shown in Table 1 and
dispersed uniformly.
[0130]
The photocurable resin A is an isocyanuric acid EO modified di- and triacrylate mixture (Alonix
M-313; manufactured by Toagosei Co., Ltd.), and the photocurable resin B is
ditrimethylolpropane tetraacrylate (Allonix M-408; Toho synthesized stock Company company)
was used.
[0131]
The average particle size of the lipophilic zinc oxide nanoparticles (VP AdNano Z805
03-05-2019
29
manufactured by Degussa) is 250 nm.
Further, as a photopolymerization initiator, bis (2,4,6-trimethyl benzoyl) -phenyl phosphine oxide
(photopolymerization initiator IRGRACURE 819; manufactured by BASF) was used.
[0132]
S2: Infusion Step As shown in FIG. 1A, the dispersion liquid 71 in which the additive is uniformly
dispersed in the base material was poured into a mold 70 having a rectangular recess.
In the present embodiment, the shape of the recess is such that the width W3 = 10 (mm), the
height H3 = 4 (mm), and the length L1 = 70 (mm).
[0133]
S10: Sedimentation Step As shown in FIG. 1 (b), the mold 70 in which the dispersion 71 was
injected was installed inside the centrifugal separator 80 with a rotation radius M = 30 mm, and
was rotated for 5 minutes.
[0134]
S11: Curing Step While rotating the mold 70 into which the dispersion liquid 71 is injected, the
upper surface of the dispersion liquid 71 is irradiated with ultraviolet light for 2 minutes to be
cured.
Thereafter, the mold 70 was removed from the centrifugal separator 80, heated at 180 ° C. for
10 minutes to be further cured, and removed from the mold 70 to obtain a composition 72.
[0135]
S13: Cutting step As shown in FIG. 1 (c), the concave portion of the composition 72 is cut by a
dotted line indicated by C, and processed into a rectangular parallelepiped shape of height H4 =
2 mm as shown in FIG. 1 (d) An acoustic lens 8 was obtained.
03-05-2019
30
[0136]
The acoustic lens 8 of Example 1 was laminated on a piezoelectric element having the same
specifications as the piezoelectric element used in Example 1.
[0137]
Comparative Example Comparative Example 1 For comparison, the same piezoelectric element as
the piezoelectric element used in Example 1 was used alone.
[0138]
(Comparative Example 2) S1 described in FIG. 11: Dispersion liquid production step and S2:
Injection step After injection into the mold 70, the additive is uniformly dispersed in the
dispersion liquid 71, and ultraviolet light is irradiated for 2 minutes in a state where the additive
is uniformly dispersed. It was allowed to cure.
Thereafter, S4: A curing step is performed to prepare a composition A having a width W1 = 10
mm, a height H1 = 1 mm in the Z-axis direction, and a length L1 = 70 mm in the Y-axis direction.
[0139]
Also, after injecting a base material to which 74% by mass of the photocurable resin A, 25% by
mass of the photocurable resin B, and 1% by mass of the thermal polymerization initiator as in
Example 1 were added to the mold 70, ultraviolet rays were applied. Irradiated for 2 minutes to
cure.
Then, it is further cured by heating at 180 ° C. for 10 minutes, and it is removed from the mold
70 and does not contain an additive having a width W1 = 10 mm, a height H1 = 1 mm in the Z
axis direction, and a length L1 = 70 mm in the Y axis direction. Composition B was made.
[0140]
03-05-2019
31
The composition A and the composition B were stacked and bonded in the Z-axis direction, and
an acoustic matching layer having the same shape as that of Example 1 was produced.
Next, the surface on the acoustic matching layer composition A side of Comparative Example 2
was bonded and laminated to the same piezoelectric element as the piezoelectric element used in
Example 1.
[0141]
The center frequency of the piezoelectric element used in the experiment is 4 MHz, and the
acoustic impedance is 36 (Pa · s · m <−1>).
[0142]
[Evaluation Method] The acoustic lens 8 of Example 1 produced in this manner and the acoustic
matching layer of Comparative Example 2 are respectively laminated on the piezoelectric
element, and transmission and reception are performed from the piezoelectric element to the
planar metal plate in water, Frequency characteristics were measured.
The focal length was measured using the underwater hydrophone method.
[0143]
[Results] As shown in FIG. 16, the transmission and reception sensitivity at 4 MHz of Example 1
is about 7 dB higher than that in the case where the acoustic matching layer of Comparative
Example 1 is not provided, and the transmission and reception sensitivity of Comparative
Example 1 in the measured 0 to 12 MHz range. Exceeds.
[0144]
On the other hand, the transmission and reception sensitivity at 4 MHz of Comparative Example
2 is equivalent to that of Example 1, but the transmission and reception sensitivity is reduced at
6 MHz or more, and is lower than Comparative Example 1 at around 8 MHz.
[0145]
This is because the acoustic matching layer of Comparative Example 2 has the same acoustic
03-05-2019
32
impedance on both sides as in Example 1, but is composed of two layers, so reflection of
ultrasonic waves occurs and is attenuated at the interface, and the transmission and reception
sensitivity is It is considered to have fallen.
[0146]
In addition, it has been confirmed that an acoustic focus can be obtained at a position of 60 mm
from the acoustic lens 8.
[0147]
Example 2 (Production of Acoustic Lens 8) In Example 2, the width W3 = 8 mm in the X-axis
direction, the height d = 3 mm in the Z-axis direction, and the length in the Y-axis direction of the
same configuration as FIG. A rectangular acoustic lens 7 having a length L1 = 70 mm, and a
rectangular acoustic lens 7 having W3 = 8 mm, d = 2 mm, and L1 = 70 mm were manufactured
in the procedure described with reference to FIG.
[0148]
S1: Dispersion Liquid Production Step The same dispersion liquid as in Example 1 was used.
[0149]
S2: Infusion Step As shown in FIG. 1A, the dispersion liquid 71 in which the additive is uniformly
dispersed in the base material was poured into a mold 70 having a rectangular recess.
In the present embodiment, a mold 70 having a shape of width W2 = 10 (mm), height H2 = 4
(mm) and length L1 = 70 (mm) is used.
[0150]
S3: Sedimentation Step After pouring the dispersion 71 into the mold 70, it is left for 5 minutes
to precipitate the additive.
[0151]
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33
S4: Curing Step The top surface of the dispersion liquid 71 is cured by irradiation with ultraviolet
light for 2 minutes.
Thereafter, the composition was further cured by heating at 180 ° C. for 10 minutes, and
removed from the mold 70 to obtain two compositions 72a and 72b.
[0152]
S5: Bonding step The two compositions 72a and 72b generated in the curing step of S4 are each
provided with the upper surface 81a of the slower one of the respective compositions 72a and
72b (the one in which the volume fraction of the additive is lower) and the upper surface. The
surfaces 81b were adhered to each other as shown in FIG. 11 (b).
[0153]
S6: Cutting and Polishing Step The compositions 72a and 72b joined as shown in FIG. 11B are
cut and the cut surfaces are polished to produce an acoustic lens 7 of thickness d = 3 mm and an
acoustic lens 7 of thickness d = 2 mm. did.
[0154]
Next, the acoustic lenses 7 having different thicknesses prepared in Example 2 were laminated
on piezoelectric elements having the same specifications as the piezoelectric elements used in
Example 1, respectively.
[0155]
[Evaluation Method] In the same manner as in Example 1, the focal length was measured using
an underwater hydrophone method.
[0156]
[Results] It was confirmed that an acoustic lens 7 with a thickness d of 3 mm can obtain an
acoustic focus at a position of 30 mm, and an acoustic lens 7 with a thickness d of 2 mm can
obtain an acoustic focus at a position of 42 mm.
[0157]
As described above, according to the present invention, an acoustic lens with less attenuation of
ultrasonic waves, a method of manufacturing the acoustic lens, an ultrasonic probe having the
03-05-2019
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acoustic lens, and the ultrasonic probe It is possible to provide an ultrasonic diagnostic apparatus
having the
[0158]
Reference Signs List 1 ultrasound probe 2 transmitting / receiving element 5 backing material 7
acoustic lens 8 acoustic matching layer 9 acoustic matching layer 14 second electrode 15 first
electrode 31 ultrasonic diagnostic apparatus main body 33 cable 41 operation input unit 42
transmission circuit 43 reception circuit 44 Image processing unit 45 Display unit 46 Control
unit 71 Dispersion liquid 72 Composition 75 Upper surface 76 Lower surface 80 Centrifuge 81
Upper surface 84 First lens surface 85 Second lens surface 100 Ultrasonic diagnostic device
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