JPH06254100A - Acoustic lens and ultrasonic probe - Google Patents

Abstract

PURPOSE:To provide the acoustic lens which is formed by using a material, such as polymethyl pentene, having an ultrasonic wave propagation speed higher than the propagation rate in a living body, has good contactability with the surface of a living body and can easily be joined to a vibrator and the ultrasonic probe. CONSTITUTION:This acoustic lens 1 having the ultrasonic probe 7 is constituted by forming a lens body 2 of a material having the ultrasonic wave propagation speed higher than the propagation speed in the living body in such a manner that the thickness in the central part is smaller than the thickness in the peripheral part and arranging an acoustic medium 3 in the recessed part of the lens body 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic lens and an ultrasonic probe used in an ultrasonic probe, and more particularly to an acoustic lens and an ultrasonic lens made of a material having an ultrasonic wave propagation velocity higher than that in a living body. Regarding sound wave probes.

[0002]

2. Description of the Related Art An ultrasonic probe provided in an ultrasonic diagnostic imaging apparatus is capable of transmitting and receiving ultrasonic waves with a built-in transducer and imaging the inside of a living body using the received ultrasonic waves. .

Here, the transducer is formed by arranging a plurality of piezoelectric elements called array elements in a predetermined direction, and when transmitting and receiving with these piezoelectric elements, a predetermined time difference is set between the elements. Although the ultrasonic probe can have a desired ultrasonic directivity, an acoustic lens is provided on the piezoelectric element to focus the ultrasonic waves in the direction orthogonal to the array direction (hereinafter referred to as the slice direction). There are many.

The acoustic lens changes the propagation time of the ultrasonic wave according to the difference between the propagation speed of the ultrasonic wave in the lens body and the propagation speed in the living body, and focuses the beam in the slice direction. Must be formed of a material having a propagation velocity different from the ultrasonic propagation velocity in the living body.

On the other hand, the ultrasonic wave generated by the piezoelectric element propagates in the living body through the inside of the acoustic lens and the boundary surface between the acoustic lens and the living body. It is necessary to take care so as not to attenuate as much as possible in the acoustic lens when propagating in the acoustic lens, and to cause as little reflection loss as possible at the interface when the ultrasonic wave passes through the interface.

Conventionally, silicone rubber, polymethylpentene (TPX, Mitsubishi Petrochemical) and the like are known as typical materials that can be used as an acoustic lens.

[0007]

Since the ultrasonic wave propagation velocity of silicone rubber is smaller than the propagation velocity in the living body, the silicone rubber has a peripheral portion thinner than the central portion and is used as an acoustic lens. That is, it may be formed in a convex shape as a whole, and a good acoustic lens can be manufactured in terms of contactability with the surface of the living body.

However, the silicone rubber has a problem that the ultrasonic attenuation factor inside becomes large when it is attempted to improve the matching of the acoustic impedance with the living body, and there is a limit in improving the performance. .

On the other hand, polymethylpentene has an acoustic impedance close to that of living body (acoustic impedance in living body: 1.6 × 10 ⁶ kg / m ² sec, acoustic impedance of polymethylpentene: 1.7 × 10 ⁶ kg / m 2). ² se
c) Furthermore, since the attenuation rate is relatively small at 0.25 dB / MHz · mm, it is a relatively excellent material for the acoustic lens, but the ultrasonic wave propagation velocity is higher than the propagation velocity in the living body. Therefore, in order to use it as an acoustic lens, it is necessary to form the peripheral portion thicker than the central portion, that is, to form a concave shape as a whole.

However, such a shape has a problem that the contact property with the surface of the living body is deteriorated.

If the acoustic lens is formed in a concave shape on the transducer side and the living body contact side is made substantially flat, the problem of contact with the surface of the living body can be avoided. It is necessary to form the transducer in a convex shape corresponding to the concave shape, or to fill the gap formed between the flat transducer and the acoustic lens with an adhesive layer, etc. The production of theducer is complicated and difficult, and the latter causes a new problem of lowering ultrasonic transmission.

The present invention has been made in consideration of the above-mentioned circumstances, and uses a material such as polymethylpentene having an ultrasonic wave propagation speed higher than the propagation speed in the living body and has good contact with the surface of the living body. It is an object of the present invention to provide an acoustic lens and an ultrasonic probe that are easy to bond to a vibrator.

[0013]

In order to achieve the above object, the acoustic lens of the present invention has a structure as described in claim 1.
A material in which the ultrasonic wave propagation velocity is higher than the propagation velocity in the living body, and the lens body is formed so that the thickness of the central portion is thinner than the thickness of the peripheral portion, and the acoustic medium is arranged in the concave portion of the lens body. Is.

Further, the ultrasonic probe of the present invention is defined in claim 2.
As described above, a lens body is formed such that the ultrasonic wave propagation velocity is higher than the propagation velocity in the living body and the thickness of the central portion is thinner than the thickness of the peripheral portion, and the concave portion of the lens body is formed. It is provided with an acoustic lens in which an acoustic medium is arranged.

[0015]

In the acoustic lens of the present invention, since the acoustic medium formed of silicone rubber, water or acoustic jelly is arranged in the concave portion of the lens body, it is bonded to the transducer surface of the ultrasonic probe and brought into contact with the living body surface. In this state, there is no air layer between the lens body and the living body and between the lens body and the vibrator. Therefore, the ultrasonic wave is not attenuated in the air layer when propagating between the transducer and the living body.

In the preferred embodiment of the present invention, since the lens body is made of polymethylpentene, the attenuation of ultrasonic waves in the lens body is reduced, and the ultrasonic transmission at the interface with the living body is improved. .

[0017]

Embodiments of the acoustic lens and ultrasonic probe of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a perspective view showing an acoustic lens 1 included in an ultrasonic probe 7 of this embodiment.

As shown in the figure, the acoustic lens 1 of this embodiment is bonded to the transducer 5 provided with the backing material 4 via the acoustic matching layer 6, and the ultrasonic waves generated by the transducer 5 are It is designed to focus in the lens direction.

The transducer 5 is formed by arranging a plurality of piezoelectric elements called array elements in a predetermined direction (this is called an array direction), and when transmitting and receiving with these piezoelectric elements, a predetermined time difference is generated. By setting the distance between them, the ultrasonic waves can be focused in the array direction.

The acoustic lens 1 is made of a material whose ultrasonic wave propagation velocity is higher than the propagation velocity in the living body, and the lens body 2 is formed so that the thickness of the central portion is thinner than the thickness of the peripheral portion,
The acoustic medium 3 is arranged in the concave portion of the lens body 2. One side of the lens body 2 is substantially flat and the other side is concave, and the flat side is the transducer side.

The lens body 2 is preferably made of polymethylpentene, for example. Polymethylpentene is manufactured and sold by Mitsubishi Petrochemical under the trade name TPX, and as described in the prior art, the acoustic impedance is close to the acoustic impedance of a living body (acoustic impedance in a living body: 1.6 × 10 ⁶ kg / m ² sec, acoustic impedance of polymethylpentene: 1.7 × 10 ⁶ kg / m ² sec), and the attenuation rate is relatively small at 0.25 dB / MHz · mm.

The acoustic medium 3 is preferably made of silicone rubber, for example.

The thickness of the lens body 2 is designed in consideration of the sound velocity of polymethylpentene and silicone rubber.

The acoustic lens 1 of this embodiment is bonded onto the transducer 5 via the acoustic matching layer 6 to form an ultrasonic probe, and in a state where it is brought into contact with the surface of the living body, the lens body 2 and the living body are separated from each other. There is no air layer in between. for that reason,
When propagating between the transducer 5 and the living body, the ultrasonic wave is not attenuated by the influence of the air layer.

Further, the lens body 2 is made of polymethylpentene, and the attenuation of ultrasonic waves in the lens body is extremely small.

As described above, according to the acoustic lens of this embodiment, since the lens body is made of polymethylpentene, the attenuation of ultrasonic waves in the lens body can be greatly reduced as compared with the conventional silicone rubber. it can. In addition, since the acoustic medium made of silicone rubber is placed in the concave portion of the lens body, when contacted with a living body as in the conventional case, an air layer is not present between the living body and contact with the living body. Is greatly improved. Further, since the flat side of the lens body is the transducer side, it is not difficult to manufacture the transducer.

In the above-mentioned embodiment, one side of the lens body is formed to be substantially flat and the other side is concave, and the transducer is bonded to the flat side. However, as shown in FIG. The side may be the biological contact side and the concave side may be the transducer side. In this case, the acoustic medium 3 is arranged between the lens body 2 and the acoustic matching layer 6.

(Second Example) Next, an acoustic lens according to the second example will be described. The parts substantially the same as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 3, the acoustic lens 11 of this embodiment has an acoustic medium 13 enclosed in an enclosure 12 formed of a thin film, and the enclosure 12 is arranged in a concave portion of the lens body 2.

The acoustic medium 13 may be made of a solid material such as silicone rubber, or a fluid such as water or acoustic jelly.

Here, the thin film forming the enclosure 12 is preferably designed in consideration of the matching condition by G. Kossoff et al. That is, when a thin film intervening as the first layer, the acoustic impedance Z ₀ of the thin film, the geometric average of the acoustic impedance Z ₂ of the lens body 2 of the lens body 2 at the side acoustic impedance Z ₁ and the acoustic medium 13 i.e. (Z ₁ · Z
₂ ) ^1/2, and on the living body side, the acoustic impedance Z ₂ of the acoustic medium and the acoustic impedance Z _{3 of the} living body
And the geometric mean value of (Z ₂ · Z ₃ ) ^1/2, and the thickness of the thin film is a quarter of the ultrasonic wavelength λ, that is, λ
It is better to set it to an odd multiple of / 4.

When the enclosure 12 is formed of a thin film of about λ / 4, even if a film having a large attenuation rate is used, the effect on the ultrasonic wave transmission is small, so the material of the enclosure is acoustic impedance. It is possible to select by paying attention only to

In a state where the flat side of the acoustic lens 11 of this embodiment is bonded to the transducer 5 through the acoustic matching layer 6 to form an ultrasonic probe, and the ultrasonic probe is brought into contact with the living body surface,
Similar to the first embodiment, there is no air layer between the living body and the living body.
Also, because the lens body is made of polymethylpentene,
Ultrasonic attenuation in the lens is very small.

Further, the enclosure body in which the acoustic medium is enclosed has its acoustic impedance and thickness set in consideration of the acoustic impedance matching between the lens body and the acoustic medium and the acoustic impedance matching between the living body and the acoustic medium. As a result, the ultrasonic loss when passing through the inclusion body is very small.

As described above, according to the acoustic lens of the present embodiment, in addition to the effect obtained in the first embodiment, the acoustic medium is encapsulated by the encapsulating body formed of a thin film, and the acoustic medium is placed in the concave portion of the lens body. Therefore, by adjusting the thickness of the thin film and the acoustic impedance, it is possible to achieve the matching of the acoustic impedance between the lens body and the acoustic medium and between the acoustic medium and the living body. Therefore, it is possible to enhance the ultrasonic wave permeability at each boundary surface. In addition, since the acoustic medium can be held in the enclosed body, it is possible to employ various fluids having less ultrasonic wave attenuation than the silicone rubber as the acoustic medium.

In the above embodiment, the thin film is provided on both the living body side and the lens body side to form the enclosure, but as a modification, the thin film on the lens body side may be omitted as shown in FIG.

(Third Example) Next, an acoustic lens according to the third example will be described. The parts substantially the same as those in the first or second embodiment are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 5, the acoustic lens 21 of the present embodiment is one in which an enclosure 22 having a cavity inside is made of polymethylpentene and the acoustic medium 13 is enclosed in the cavity. The cavity allows the enclosure 22 to be easily manufactured,
It is preferable to form the acoustic medium into a cylindrical shape in consideration of conditions such as being able to seal the acoustic medium without leaving bubbles.

In the acoustic lens 21, the lens body 23 made of polymethylpentene is formed integrally with the encapsulating body 22 or as a part of the encapsulating body 22 so that the thickness of the central portion is thinner than the thickness of the peripheral portion. I am doing it.

Since the enclosure 22 is made of polymethylpentene, the acoustic impedance is close to the value in the living body and the value of the acoustic medium 13 composed of water or the like, and the matching of the acoustic impedance with the living body or the acoustic medium is taken into consideration. There is little need to do it. Therefore, the thickness t of the enclosure 22 on the living body contact side may be a thickness necessary and sufficient for maintaining a predetermined structural strength in consideration of the pressure applied at the time of contact with the living body surface. However, the thickness t is made substantially uniform.

The enclosure 22 is preferably constructed so that it can be filled with the acoustic medium 13.

FIG. 6 is a sectional view taken along the line AA of FIG. As can be seen in the figure, the enclosure 22 has rubber tubes 25 having a narrow inner diameter near the entrance and exit connected to both ends, so that the acoustic medium 13 is less likely to be washed away from the entrance and exit of the rubber tube 25, It has a structure that can be filled at any time.

In the state where the flat side of the acoustic lens 21 of this embodiment is bonded to the transducer 5 through the acoustic matching layer 6 to form an ultrasonic probe, and the ultrasonic probe is brought into contact with the living body surface,
Similar to the first and second embodiments, no air layer is interposed between the living body and the living body. Further, since the lens body is made of polymethylpentene, the attenuation of ultrasonic waves in the lens body becomes very small.

Further, since the enclosure for enclosing the acoustic medium is made of polymethylpentene whose acoustic impedance is close to the biological value, the loss of ultrasonic waves at the interface between the enclosure and the organism is extremely small.

As described above, according to the acoustic lens of the present embodiment, in addition to the effects obtained in the first and second embodiments, the living body contact side is formed of polymethylpentene, and therefore, the superposition on the living body contact surface is improved. Sound loss can be significantly reduced, and compared to conventional acoustic lenses that use silicone rubber,
It is possible to manufacture an acoustic lens having excellent wear resistance on the living body contact surface.

Further, since the acoustic medium can be filled, the acoustic medium can be replenished at any time so that no bubbles are generated in the enclosure 22 even if the acoustic medium evaporates over time.

Although the lens body is formed on the transducer side in the third embodiment, the lens body may be formed on the living body contact side. Further, the lens body may be formed so that one side is convex and the other side is concave.

FIG. 7 shows an example in which a lens body is formed on the living body contact side. FIGS. 7 (a) and 7 (b) show the lens bodies 31, 32 with the living body contact side being flat, and FIG. (c) and (d)
Shows a lens body 33, 34 having a convex shape on the living body contact side. In FIGS. 7B and 7D, the acoustic medium 13
Are in direct contact with the acoustic matching layer 6.

In the third embodiment, the acoustic impedance of polymethylpentene is close to the values of the living body and the acoustic medium, and it is not necessary to consider the matching of the acoustic impedance with the living body and the acoustic medium. Although it suffices that the contact side has a uniform thickness necessary and sufficient to maintain a predetermined structural strength, since the acoustic impedance values are not completely the same, the contact side contacts the living body as in the second embodiment. The thickness t on the side may be set to an odd multiple of 1/4 of the ultrasonic wavelength.

[0051]

As described above, the acoustic lens of the present invention is made of a material whose ultrasonic wave propagation velocity is higher than that in a living body and whose central portion is thinner than peripheral portions. Since the lens body is formed and the acoustic medium is arranged in the concave portion of the lens body, the lens body using polymethylpentene or the like can be used without lowering the contact property with the living body surface. Therefore, it is possible to significantly improve the ultrasonic attenuation characteristics inside the lens body and the ultrasonic transmission characteristics at the interface with the living body while maintaining the surface contact property to the same level as that of a conventional acoustic lens using silicone rubber. You can

[Brief description of drawings]

FIG. 1 is a perspective view of an acoustic lens of Example 1. FIG.

FIG. 2 is a sectional view according to a modification of the acoustic lens of the first example.

FIG. 3 is a sectional view of an acoustic lens of a second example.

FIG. 4 is a sectional view of an acoustic lens according to a modification of the second embodiment.

FIG. 5 is a perspective view of an acoustic lens of Example 3.

6 is a sectional view taken along the line AA of FIG.

FIG. 7 is a sectional view showing a modification of the acoustic lens of the third example.

[Explanation of symbols]

 1,11,21 Acoustic lens 2,23,31,32,33,34 Lens body 3,13 Acoustic medium 4 Backing layer 5 Transducer 6 Acoustic matching layer 7 Ultrasonic probe 12,22 Inclusion body

Claims (8)

[Claims] 1. A lens body is formed of a material having an ultrasonic wave propagation velocity higher than that in a living body, and a thickness of a central portion thereof is thinner than a thickness of a peripheral portion thereof. An acoustic lens characterized by arranging a medium. 2. A lens body is formed of a material having an ultrasonic wave propagation velocity higher than that in a living body, and a thickness of a central portion is thinner than a thickness of a peripheral portion, and an acoustic wave is formed in a concave portion of the lens body. An ultrasonic probe comprising an acoustic lens in which a medium is arranged. 3. The ultrasonic probe according to claim 2, wherein the lens body is made of polymethylpentene. 4. The ultrasonic probe according to claim 2, wherein the lens body is formed so that one side is substantially flat and the other side is concave. 5. The ultrasonic probe according to claim 2, wherein the lens body is formed so that one side is convex and the other side is concave. 6. The ultrasonic probe according to claim 2, further comprising an enclosure capable of enclosing the acoustic medium. 7. The acoustic impedance of the enclosure is a geometric mean value of the acoustic impedance of the lens body and the acoustic impedance of the acoustic medium on the lens body side, and the acoustic impedance of the acoustic medium and the acoustic sound of the living body on the living body side. In addition to the geometric mean value with impedance,
7. The ultrasonic probe according to claim 6, wherein the thickness of the enclosure is an odd multiple of approximately one quarter of the ultrasonic wavelength. 8. The ultrasonic probe according to claim 6, wherein the enclosure is made of the same material as the lens body, and the lens body is formed integrally with the enclosure or as a part of the enclosure.