JPS6272332A - Probe for ultrasonic diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is used in an ultrasonic diagnostic device that sends ultrasonic waves into a living body and performs diagnosis using the reflection and absorption characteristics of the ultrasonic waves by body tissues. The present invention relates to an ultrasonic probe, and in particular to an adhesive means for an acoustic lens thereof.

[Technical background of the invention and its problems]

Generally, as shown in Fig. 1, a probe for an ultrasonic diagnostic device includes a piezoelectric vibrator 1 that converts an electric signal (pulse signal) into an ultrasonic wave, and a rear acoustic absorber 2 disposed behind the piezoelectric vibrator 1. , a λ/4 acoustic matching layer 3 for efficiently radiating ultrasonic waves from the piezoelectric vibrator 1 to a living body, and an acoustic lens 4 bonded to the front surface of the matching layer 3 with an adhesive 5. There is. While the acoustic impedance of the piezoelectric vibrator 1 is usually very high at 30 to 40 (X 106 kg/s-m"), the acoustic impedance of a living body is 1.5 to 40.
1.6 (X 10' kg/s - m"), which is quite low. Therefore, in order to achieve acoustic impedance matching between the two, the λ/4 acoustic matching layer 3 has an acoustic impedance of 3. 0-7.0(
Insert a material of about 10'kg/s-m"),
Also, as an acoustic lens, its acoustic impedance is 1
．． Silicone rubber of about 25 to 1.50 (x 10'kg/s-m") is used.

Now, with such a probe, the resolution of the pulse in the time axis direction (distance resolution) of the ultrasonic diagnostic equipment is
In order to improve the acoustic impedance of the probe, as shown in FIG. It is desired that the acoustic impedance smoothly approaches the acoustic impedance of the living body 6, and its pulse response waveform is shown in Figure 3 (a).
It is desirable that the second wave (see Fig. 5, 8) does not occur as shown in Fig. 5, and the frequency response characteristic should not produce ripples (see Fig. 5, 7) as shown in Fig. 3 (b). It is rare.

However, in the conventional probe, the adhesive 5 of the acoustic lens 4 is
The acoustic impedance is 1.0 (X 106kg/
s-m") and the specific gravity is 1.0. The speed of sound is 1000 (m/S
) is used, and its acoustic impedance is low, so the distribution of acoustic impedance in the probe does not become smooth toward the acoustic impedance of the living body, and as shown in Figure 4, the adhesive 5 There was a problem that the position was significantly depressed.

In this way, even if the acoustic impedance of the adhesive 5 is low, there is no problem if the thickness of the adhesive is very thin, 20μ or less, and can be ignored. It is extremely difficult to reduce the thickness of the adhesive to 20μ or less, and it becomes thicker than 20μ, that is, a thickness that cannot be ignored with respect to the wavelength λ of the ultrasonic wave.In that case, the sound waves are reflected, and the adhesive Since the thickness of the probe is not sufficiently thick with respect to the wavelength λ, a frequency characteristic occurs in the reflectance, and a sopple 7 as shown in FIG. 5(b) occurs in the frequency characteristic of the probe. Also, regarding the pulse response waveform,
There is a problem in that a second wave 8 as shown in FIG. 5(a) is generated, which significantly deteriorates the resolution of the pulse in the time direction. That is, for example, if the acoustic impedance of the adhesive is 1.0 (X 10'kg/s-m")
The thickness is 10μ, and the acoustic impedance of vibrator 1 is 35.
(xlO'kg/s - m") and the thickness is λ/2 (
λ is the wavelength), and the acoustic impedance of the first acoustic matching layer is 7.
(XIO6kg/s-m”) thickness is λ/4, acoustic impedance of the second acoustic matching layer is 3 (X 106kg/s
・If the thickness is λ/4 and the acoustic impedance of the acoustic lens is 1.28 (XI O'kg/s-m"), ignore this because the thickness of the adhesive is small. However, in reality, the thickness l of the adhesive exceeds 20μ, so for example ]=40μ (0,
15λ). In this case, the vibrator 1 is
Acoustic impedance Z, looking to the side. is expressed as: Therefore, if the acoustic impedance of the acoustic lens 4 is 24, the reflectance R at the interface 10 between the adhesive 5 and the acoustic lens 4 is Z4 + ZS, which causes a frequency characteristic in the reflectance. Figure 5 (a)
) (b), and the resolution in the pulse time direction deteriorated.

For this reason, in the conventional probe, it is virtually impossible to
) It is difficult to obtain good response characteristics as shown in (b), and it is not possible to improve the resolution of the pulse in the time axis direction, and an improvement measure has been desired.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to match the acoustic impedance of an adhesive to the acoustic impedance of an acoustic lens, and to obtain good pulse response waveforms and frequency response characteristics. The present invention provides a probe for an ultrasonic diagnostic device that can be obtained.

[Summary of the invention]

- The outline of the present invention for achieving the object described in F is as follows. The tentacle is characterized in that the acoustic lens is bonded with a liquid silicone rubber adhesive having approximately the same acoustic impedance as the acoustic lens.

[Embodiments of the invention]

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

In the present invention, the acoustic lens 4 shown in FIG. 1 described above is bonded with a liquid silicone rubber adhesive 5' having approximately the same acoustic impedance as the acoustic lens. In this case, the acoustic lens 4 has an acoustic impedance of 1.25 to 1.50 (X 10'
kg/5-m2), the adhesive 5' is also selected to have approximately the same acoustic impedance. As a result of adhering the acoustic lens 4 in this way,
Good response characteristics as shown in FIGS. 3(a) and 3(b) above were obtained.

This is because by making the acoustic impedance Z4 of the acoustic lens 4 and the acoustic impedance Z of the adhesive very close, the numerator Z a Z s of the 0 formula becomes extremely small, and the 0 formula is transformed into However, in this formula 0 as well, by making the acoustic impedance of the acoustic lens and the acoustic impedance of the adhesive almost equal, the acoustic impedance Z5 of the adhesive and the relationship between the adhesive and the λ/4 acoustic matching layer are Acoustic impedance Z when looking at the vibrator 1 side from the boundary surface 9 of
, are also very close, and “Zq” in the numerator of formula 0
This is because Zs'' has also become extremely small, and the reflectance R at the interface 10 between the adhesive and the acoustic lens has also become extremely small, and the influence of reflection has become so small that it can be ignored.

Next, the acoustic impedance Z of adhesive liquid silicone rubber is the product of its sound velocity ■ and density ρ, that is, Z=v・
However, since the velocity V is almost constant (v=1000 m/s) regardless of the density, the relationship between Z and ρ is as shown in FIG. Therefore, in this example, the density of the adhesive liquid silicone rubber was set to 1.25-1.
50 to obtain the desired acoustic impedance Z. As a means of adjusting the density of the adhesive liquid silicone rubber, we focused on the fact that the density and the amount of silica filler are in a proportional relationship as shown in Figure 7, and adjusted the amount of silica filler. By doing this, an adhesive liquid silicone rubber having a predetermined density is obtained.

Examples of formulations of the adhesive liquid silicone rubber thus obtained are as follows.

Terminal reactive polysiloxane 64.1 parts Silica filler 32.1 parts Crosslinking agent
3.8 parts adhesion improver
Slight hardening agent Slight specific gravity (2
5°C) 1.27 Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and it is understood that modifications can be made as appropriate within the scope of the gist of the present invention. Needless to say. For example, fillers other than silica-based fillers may be used to adjust the density of the adhesive liquid silicone rubber.

〔Effect of the invention〕

As detailed above, according to the present invention, since the acoustic lens is bonded with a liquid silicone rubber adhesive having almost the same acoustic impedance as the acoustic lens, it is possible to obtain good pulse response waveforms and frequency characteristics. This has the effect that the resolution of the pulse in the time axis direction of the ultrasonic diagnostic apparatus can be improved.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the ultrasonic probe, Figures 2 and 4 are diagrams showing the acoustic impedance distribution of the ultrasound probe, respectively, Figures 3 (a), (b) and 5
Figures (a) and (b) are diagrams showing the pulse response waveform and frequency characteristics of the ultrasonic probe, respectively, and Figure 6 is a graph showing the relationship between acoustic impedance and density of liquid silicone rubber.
FIG. 7 is a graph showing the relationship between the density of liquid silicone rubber and the amount of filler. 1... Piezoelectric vibrator, 4... Acoustic lens 5.5'...
·glue. Agent Patent Attorney Ken Nori Chika Sodo Norio Ogo

Claims (3)

[Claims] (1) Equipped with a piezoelectric vibrator that converts electrical signals into ultrasonic waves,
In a probe for an ultrasonic diagnostic device in which an acoustic lens is bonded to the front surface of a λ/4 acoustic matching layer, the acoustic lens is bonded with a liquid silicone rubber adhesive having approximately the same acoustic impedance as the acoustic lens. Characteristic probe for ultrasonic diagnostic equipment. (2) The probe for an ultrasonic diagnostic device according to claim 1, wherein an acoustic lens is bonded with a liquid silicone rubber adhesive having a specific gravity of 1.25 to 1.50. (3) A probe for an ultrasonic diagnostic device according to claim 2, in which an acoustic lens is bonded with a liquid silicone rubber adhesive whose specific gravity is adjusted by adjusting the content of a silica-based filler.