JP2606016B2 - Ultrasonic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe used for an ultrasonic diagnostic apparatus.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic probe generally used in an ultrasonic diagnostic apparatus is shown in FIG.
A configuration as shown in FIG.

FIG. 5A is a plan view of a piezoelectric vibrator, and FIG.
(B) is an overall longitudinal sectional view. As shown in FIGS. 5A and 5B, a disc-shaped piezoelectric vibrator 21 is provided on the holding body 20, and a first ultrasonic wave radiating surface of the disc-shaped piezoelectric vibrator 21 is provided on the ultrasonic radiation surface.
And second acoustic matching layers 22 and 23 are sequentially provided, and an acoustic lens 24 is provided on the second acoustic matching layer 23. The acoustic lens 24 is made of a substance having a lower ultrasonic wave propagation speed than the subject M, for example, silicone rubber, and the subject M has a convex surface.

In the above configuration, the surface on the convex side of the acoustic lens 24 is brought into contact with the subject M, and the disc-shaped piezoelectric vibrator 2
1 to apply an electrical signal. Accordingly, the ultrasonic beam radiated from the ultrasonic radiation surface of the disc-shaped piezoelectric vibrator 21 is
The light propagates through the acoustic matching layers 22 and 23 and the acoustic lens 24 and advances into the subject M. The reflected signal from the inside of the subject M follows the path opposite to that described above, is received by the disc-shaped piezoelectric vibrator 21, converted into an electric signal, and sent to an ultrasonic diagnostic apparatus main body (not shown). Image processing is performed, and an ultrasonic diagnostic image is displayed. Then, when the ultrasonic beam is emitted into the subject M as described above, the ultrasonic beam can be focused using the difference in the ultrasonic wave propagation speed between the acoustic lens 24 and the subject M.

[0005]

Generally, the side lobe level is determined by the aperture of the piezoelectric vibrator 21. By controlling the applied voltage or changing the radiation area in the opening of the piezoelectric vibrator 21, the sound pressure is higher at the center and lower at the periphery, so that the side lobe level is reduced. It is well known that can be reduced. However, in the configuration of the related art described above, the acoustic lens 24 is thickest at the center of the opening and becomes thinner toward the peripheral portion. As the sound reaches the periphery, the sound pressure increases and the side lobe level increases. Further, since the propagation attenuation of the ultrasonic wave increases in proportion to the frequency, the gain of the high-frequency component decreases in the frequency band characteristics. For this reason, the ultrasonic diagnostic image is remarkably deteriorated, such as a decrease in resolution or generation of a pseudo echo, which is a factor of causing a misdiagnosis.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, focuses an ultrasonic beam at a predetermined position, suppresses side lobes to a low level, and has a wide frequency band characteristic. Therefore, the resolution can be improved, and the occurrence of a pseudo echo can be prevented, so that a good ultrasonic diagnostic image can be obtained.
It is another object of the present invention to provide an ultrasonic probe capable of improving the contact with the subject without changing the frequency band characteristics.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a disk-shaped piezoelectric vibrator formed in a concave shape in the ultrasonic radiation direction, and an ultrasonic wave generated by the disk-shaped piezoelectric vibrator. An acoustic matching layer provided on the radiation surface, the surface on the piezoelectric vibrator side having a convex shape, and the opposite surface having a planar shape; and an acoustic matching layer provided on the plane side of the acoustic matching layer, opposite to the acoustic matching layer. A first ultrasonic wave propagation material having a concave surface and a predetermined ultrasonic attenuation, and a surface provided on the concave side of the first ultrasonic wave propagation material and facing the first ultrasonic wave propagation material Has a convex shape, and a second ultrasonic wave propagation material whose ultrasonic attenuation is almost zero.

The acoustic matching layer is provided on the piezoelectric vibrator side.
A first acoustic matching layer having a convex surface, and the first acoustic matching layer
A second acoustic matching layer having a plate shape provided between the matching layer and the first ultrasonic wave propagation material. The acoustic impedance Z1 of the _first acoustic matching layer and the acoustic impedance Z1 of the second acoustic matching layer. acoustic impedance Z _2, an intermediate value between the acoustic impedance Z ₀ of the piezoelectric vibrator and the acoustic impedance Z ₃ of the object, set _{Z 0> Z 1> Z 2} > so that the relationship Z ₃ is established Is preferred. Also,
The acoustic impedance of the first ultrasonic wave propagation material and the acoustic impedance of the second ultrasonic wave propagation material are set substantially equal to the acoustic impedance of the subject, and the first ultrasonic wave propagation material is set to a triangular function, a Hanning function, a Hamming Function, Blac
It is preferable to form a concave surface defined by any one of the kman function, Gauss function, and Sine function .

[0009]

Therefore, according to the present invention, an ultrasonic beam can be focused to a predetermined depth by forming a disc-shaped piezoelectric vibrator in a concave shape with a predetermined curvature in the ultrasonic radiation direction, In addition, by reducing the thickness of the first acoustic matching layer from the center to the periphery, acoustic matching can be achieved in a wide frequency range, and the frequency band characteristics can be broadened. Therefore, it is possible to minimize the influence on the image quality due to the reduction of the high frequency component due to the attenuation of the first ultrasonic wave propagation material. Further, since the thickness of the first ultrasonic wave propagation material having a predetermined ultrasonic attenuation is formed so as to increase from the central portion to the peripheral portion, the first ultrasonic wave propagating material extends from the central portion to the peripheral portion. The attenuation due to the propagation material increases, and the sound pressure increases toward the center, and decreases as the area reaches the periphery, thereby lowering the side lobe, which is a cause of deterioration in the resolution of ultrasonic diagnostic images and pseudo echo. Can be suppressed. In addition, since the second ultrasonic wave propagation material whose ultrasonic attenuation is nearly zero is provided between the first ultrasonic wave propagation material and the subject to fill the concave portion of the first ultrasonic wave propagation material, the frequency is reduced. It can be adapted to the subject without changing the band characteristics.

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1A and 1B show an ultrasonic probe according to an embodiment of the present invention. FIG. 1A is a plan view of a piezoelectric vibrator, and FIG. .

As shown in FIGS. 1A and 1B, a disk-shaped piezoelectric vibrator 11 for performing electro-acoustic conversion is provided on a holding body 10.
The piezoelectric vibrator 11 is entirely bent at a predetermined radius of curvature in the ultrasonic wave radiation direction to be formed in a concave shape. The piezoelectric vibrator 1 is placed on the ultrasonic wave emitting surface of the piezoelectric vibrator 11.
A first acoustic matching layer 12 having a convex surface on one side and a planar surface on the opposite side of the subject M is provided, and the ultrasonic wave of the first acoustic matching layer 12 is provided as necessary. A flat second acoustic matching layer 13 is provided on the radiation surface. On the second acoustic matching layer 13, the first ultrasonic wave having a concave shape on the subject M side and the concave side on the subject M side opposite to the second acoustic matching layer 13, and having a predetermined ultrasonic attenuation. A propagation material 14 is provided, and the subject M on the concave side of the first ultrasonic wave propagation material 14 is provided.
On the side, a second ultrasonic wave propagation material 15 having a convex surface on the side of the first ultrasonic wave propagation material 14 and a planar shape on the opposite side is provided, and the ultrasonic attenuation is almost zero.

In the above configuration, the flat surface of the second ultrasonic wave propagation material 15 is brought into contact with the subject M, and an electric signal is applied to the disc-shaped piezoelectric vibrator 11. Accordingly, the ultrasonic beam radiated from the ultrasonic radiation surface of the disc-shaped piezoelectric vibrator 11 is divided into the first and second acoustic matching layers 12 and 13 and the first and second ultrasonic propagation materials 14, 15 and travels into the subject M. The reflected signal from inside the subject M follows the reverse path, is received by the disc-shaped piezoelectric vibrator 11, is converted into an electric signal, and is an ultrasonic diagnostic apparatus main body (not shown).
The image processing is performed here, and an ultrasonic diagnostic image is displayed.

The disc-shaped piezoelectric vibrator 11 includes a one-component piezoelectric ceramic PbTiO ₃ , a two-component piezoelectric ceramic PbZrO ₃ -PbTiO ₃ , and a three-component piezoelectric ceramic Pb (Mg _1/3 Nb). _2/3 ) O ₃ -PbZ
Using rO ₃ —PbTiO ₃ or the like, a concave shape is formed with a predetermined radius of curvature in the ultrasonic radiation direction. The acoustic impedance of these piezoelectric ceramics is approximately 30 to 35 MRay1.
It is. The piezoelectric vibrator 11 can be formed by firing and then polishing the piezoelectric ceramics, or can be formed to have a predetermined curvature during firing. As described above, by forming the piezoelectric ceramic in a concave shape, the ultrasonic beam can be focused at a distance corresponding to the radius of curvature.

The first acoustic matching layer 12 is made of a material obtained by mixing a metal powder such as tungsten with a polymer material such as epoxy resin or vinyl chloride at a predetermined ratio. The piezoelectric vibrator 11 is formed in a convex shape, and the object M on the opposite side is formed in a planar shape. As shown in FIGS. 2A and 2B, the acoustic impedance of the first acoustic matching layer 12 can be changed by a mixing ratio between a polymer material such as epoxy resin and vinyl chloride and metal powder. Therefore, the piezoelectric vibrator 11
The mixing ratio of the metal powder is adjusted so as to have an intermediate value between the acoustic impedance of the second acoustic matching layer 13 and the acoustic impedance of the second acoustic matching layer 13. Further, since this material is fluid, it can be relatively easily formed into various shapes.

The second acoustic matching layer 13 is formed into a flat plate using an epoxy resin. The acoustic impedance of the epoxy resin is about 3 MRayl.

The first and second acoustic matching layers 12
And 13 have a role of efficiently radiating ultrasonic waves to the subject M and efficiently receiving reflected echoes from the subject M.

Generally, the thickness t _n of the acoustic matching layer is λ / 4
It is desirable to set it to. Here, lambda is the wavelength of ultrasonic wave in the acoustic matching layer, the acoustic velocity V _n of the ultrasonic frequency f and the acoustic matching layer, obtained by the equation (1).

[0019]

(Equation 1)

The relationship between the thickness t _n of the acoustic matching layer and the frequency of the ultrasonic wave is represented by (Equation 2), and indicates that the thickness of the acoustic matching layer and the frequency of the ultrasonic wave passing therethrough are related. .

[0021]

(Equation 2)

Therefore, as shown in FIG. 3, the thickness t _n (x) of the first acoustic matching layer 12 having a convex shape on one side and a planar shape on the other side, as shown in FIG. 3)
Is represented by

[0023]

(Equation 3)

Here, R is the radius of curvature, a is the opening diameter of the disc-shaped piezoelectric vibrator 11, t ₀ is the minimum thickness of the first acoustic matching layer 12, and x is the distance from the center line of curvature. As represented by (Equation 3), since the thickness of the first acoustic matching layer 12 changes, the frequency of the ultrasonic wave that passes for each thickness changes, and the ultrasonic probe having a wide frequency band A child can be realized.

As the first ultrasonic wave propagation material 14, a material having an acoustic impedance substantially equal to that of the subject M and having a predetermined ultrasonic attenuation, such as silicone rubber, is used. As the second ultrasonic wave propagation material 15, a material such as butadiene rubber or natural rubber, whose acoustic impedance is almost equal to the subject M and whose ultrasonic attenuation is almost zero, is used. That is, the acoustic impedance of the first and second ultrasonic propagation materials 14 and 15 is made substantially equal to that of the subject M to maintain the acoustic matching condition, and the ultrasonic attenuation of the first acoustic propagation material 14 is utilized.
The weighting of the ultrasonic waves radiated from the ultrasonic probe is performed.

The attenuation coefficient of the first ultrasonic wave propagation material 14 is α
Then, the ultrasonic attenuation A in the first ultrasonic wave propagation material 14 is expressed by the following (Equation 4).

[0027]

(Equation 4)

Here, f is the frequency of the ultrasonic wave, and t is the thickness of the first ultrasonic wave propagation material 14. As is evident from (Equation 4), the attenuation of the ultrasonic wave with respect to the specific frequency is the first.
Is proportional to the thickness of the ultrasonic wave propagation material 14. Therefore, as described above, the surface of the first ultrasonic wave propagation material 14 on the side opposite to the second acoustic matching layer 13 on the subject M side is formed into a concave shape by a predetermined function, thereby reaching the center. According to the following, reduce ultrasonic attenuation, and reach the periphery,
Since the ultrasonic attenuation can be increased, it is possible to suppress the side lobe in the directional characteristics of the ultrasonic waves.

FIG. 4 shows a typical window function, and (Table 1) shows the result of a simulation on the relationship between the window function and the side lobe level.

[0030]

[Table 1]

From the results shown in Table 1, as a window function,
Triangular function or Hanning function or Hamming function or Bl
Using the ackman function, Gauss function, or Sine function,
When the side lobe level of 1 is not weighted at all
Compared to the level (−28.3 dB),
It can be seen that it is significantly lower. Therefore, the first
The thickness of the ultrasonic wave propagation material 14 is determined by the above function.
By forming so as to be one of the functions
Side lobes can be greatly suppressed.

By using a material whose ultrasonic attenuation is close to 0 as the second ultrasonic wave propagation material 15, the weight of the first ultrasonic wave propagation material 14 can be maintained with the subject M without impairing the weighting effect. Contactability can be improved.

[0033]

As described above, according to the present invention,
By forming the disc-shaped piezoelectric vibrator in a concave shape with a predetermined curvature in the ultrasonic radiation direction, the ultrasonic beam can be focused to a predetermined depth, and the thickness of the first acoustic matching layer can be reduced. By reducing the thickness from the center to the periphery, acoustic matching can be achieved in a wide frequency range, and the frequency band characteristics can be broadened. Therefore, the influence on the image quality due to the reduction of the high-frequency component can be minimized.
Further, since the thickness of the first ultrasonic wave propagation material having a predetermined ultrasonic attenuation is formed so as to increase from the central portion to the peripheral portion, the first ultrasonic wave propagating material extends from the central portion to the peripheral portion. The attenuation due to the propagation material increases, and the sound pressure becomes higher toward the center and becomes lower toward the periphery. As a result, it is possible to suppress the side lobe which is a cause of the degradation of the resolution of the ultrasonic diagnostic image and the pseudo echo, to a low level. Therefore, a favorable ultrasonic diagnostic image can be obtained. Also, since the second ultrasonic wave propagation material whose ultrasonic attenuation is almost zero is provided between the first ultrasonic wave propagation material and the subject to fill the concave portion of the first ultrasonic wave propagation material,
Adapt to the subject without changing the frequency band characteristics,
The contact property with the subject can be improved.

Also, by using the first and second acoustic matching layers, the acoustic impedance of both is adjusted to efficiently radiate ultrasonic waves to the subject and efficiently receive reflected echoes from the subject. be able to.

Further, by making the acoustic impedance of the first and second ultrasonic wave propagation materials substantially equal to the acoustic impedance of the object, the reflection of ultrasonic waves at the boundary surface of the object is reduced, and the object is efficiently illuminated. Ultrasonic waves can be emitted inside.

Further, by forming the first ultrasonic wave propagation material into a concave shape defined by a predetermined function, side lobes can be largely suppressed.

[Brief description of the drawings]

FIG. 1A is a plan view showing a piezoelectric vibrator used for an ultrasonic probe according to an embodiment of the present invention. FIG. 1B is a longitudinal sectional view showing the ultrasonic probe.

FIG. 2A is a diagram showing a relationship between a mixing ratio of an epoxy resin and a tungsten powder forming a first acoustic matching layer used in the ultrasonic probe and acoustic impedance; Showing the relationship between the mixing ratio of vinyl chloride and dangsten powder forming the first acoustic matching layer used in the present invention and the acoustic impedance

FIG. 3 is an explanatory diagram for determining a change in thickness of a first acoustic matching layer used in the ultrasonic probe.

FIG. 4 is an explanatory view of a representative window function for forming a first ultrasonic wave propagation material used for the ultrasonic probe.

FIG. 5A is a plan view showing a piezoelectric vibrator used in a conventional ultrasonic probe. FIG. 5B is a longitudinal sectional view showing the ultrasonic probe.

[Explanation of symbols]

 Reference Signs List 10 Holder 11 Disc-shaped piezoelectric vibrator 12 First acoustic matching layer 13 Second acoustic matching layer 14 First ultrasonic wave propagation material 15 Second ultrasonic wave propagation material M Subject

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-42142 (JP, A) JP-A-63-234949 (JP, A) JP-A-2-234749 (JP, A) JP-A-2-42 246957 (JP, A) JP-A-3-151952 (JP, A) JP-A-61-180006 (JP, U) JP-A-58-48213 (JP, U)

Claims (4)

(57) [Claims] 1. A disk-shaped piezoelectric vibrator formed in a concave shape in an ultrasonic radiation direction, and provided on an ultrasonic wave radiation surface of the disk-shaped piezoelectric vibrator, wherein the surface on the piezoelectric vibrator side has a convex shape. And an acoustic matching layer whose opposite surface has a planar shape, and is provided on the planar side of the acoustic matching layer, and the surface opposite to the acoustic matching layer has a concave shape and has a predetermined ultrasonic attenuation. A first ultrasonic wave propagation material, a second ultrasonic wave propagation material provided on a concave side of the first ultrasonic wave propagation material, a surface of the first ultrasonic wave propagation material side having a convex shape, and an ultrasonic attenuation of approximately 0; An ultrasonic probe comprising the ultrasonic wave propagation material. 2. The acoustic matching layer has a convex surface on the side of the piezoelectric vibrator.
A first acoustic matching layer having a shape;
1 consists flat second acoustic matching layer provided between the ultrasonic wave propagation material, the acoustic impedance of the first acoustic matching layer acoustic impedance Z ₁ and the second acoustic matching layer of Z ₂ but an intermediate value between the acoustic impedance Z ₀ of the piezoelectric vibrator and the acoustic impedance Z ₃ of the _{subject, Z 0> Z 1> Z} 2> ultrasound according to claim 1, wherein the relation holds for Z ₃ probe Tentacles. 3. The ultrasonic probe according to claim 1, wherein the acoustic impedance of the first ultrasonic wave propagation material and the acoustic impedance of the second ultrasonic wave propagation material are substantially equal to the acoustic impedance of the subject. 4. The method according to claim 1, wherein the first ultrasonic wave propagation material is a triangular related material.
Number, Hanning function, Hamming function, Blackman function, Gauss
The ultrasonic probe according to claim 1, wherein the probe has a concave shape defined by one of a function and a Sine function .