JPH0460651B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an ultrasound imaging device that transmits and receives ultrasound waves by interposing water as an acoustic medium between an ultrasound transducer and a subject. [Technical background of the invention] In ultrasonic diagnostic equipment, an ultrasonic transducer converts an electrical signal into an ultrasonic wave and emits the ultrasonic wave into a living body, and also emits the ultrasonic wave reflected from within the living body. Convert it back into an electrical signal,
Information is obtained from within the body. Among such transducers, transducers for mammary gland diagnosis and the like, as shown in the conceptual diagram in Figure 1, place the transducer 1 in a water tank and point it toward the subject 2 also in the tank. While emitting ultrasonic waves 3, the transducer is moved in a direction 4 perpendicular to the emitting direction 3 to transmit and receive the ultrasonic waves. The water temperature is usually 20 to 40℃, especially in order not to cause discomfort to the subject and to perform measurements under constant conditions.
The temperature is set at a constant temperature around 38℃. [Problems with the background technology] In the case of such ultrasonic examination in the aquarium, the aquarium 5
If it is large enough, there is no problem, but if it is not, not only the reflected sound waves from the subject but also the reflected sound waves from the inner wall of the water tank are generated, which causes noise. Furthermore, when performing an examination using ultrasonic waves, there is a limit to the size of the water tank that can be used, and since there is reflection from the walls, the above-mentioned noise problem is especially serious. For this reason, a sound absorbing material is attached to the inner wall of the aquarium to prevent scattered sound waves from being scattered by the inner wall of the aquarium. However, as shown in the partially enlarged view near the inner wall of the water tank in the conventional commercially available acoustic absorbing material,
Although the absorption attenuation rate of the sound wave 9 transmitted through the acoustic absorbing material 8 through the boundary surface 7 of the acoustic absorbing material is certainly large,
The problem that the sound waves 10 directly reflecting into the water from the interface 7 are very large and generates noise has not been solved. Incidentally, reflected waves 9' on the inner wall surface 7' of the water tank (boundary surface between the acoustic absorbing material and the inner wall of the water tank) also pose a problem, but since they pass through the layer of the acoustic absorbing material 8 again, they are attenuated and become smaller. Compared to this, the influence of the reflected sound waves 10 from the above-mentioned -acoustic absorbing material interface 7 is a particularly serious problem, and countermeasures against this problem are a problem when using this type of transducer. [Object of the Invention] The present invention has been made in view of the above circumstances, and suppresses the generation of reflected sound waves at the interface between water and acoustic absorbing material, removes noise caused by scattered sound waves, and improves the image quality of ultrasound images. It is an object of the present invention to provide an ultrasonic imaging device that can be improved. [Summary of the Invention] The outline of the present invention for achieving the above object is to provide an ultrasonic imaging device that transmits and receives ultrasonic waves to and from a subject by placing an ultrasonic transducer in a water tank. It is characterized in that an acoustic absorbing material containing 53 to 65% by weight of silica of ~20 μm in silicone rubber is attached to the inner wall surface of the water tank. [Embodiment of the Invention] Hereinafter, details of the present invention will be explained based on an embodiment of a mammary gland diagnostic apparatus. Fig. 3 is a sectional view of a water tank in which an ultrasonic transducer is placed, Fig. 4 is a schematic perspective view showing the scanning mechanism of the ultrasonic transducer, and Fig. 5 is a block diagram of the ultrasonic diagnostic device. FIG. 6 is a sectional view showing the wall surface of the water tank. In FIG. 3, a water tank 11 contains water as an acoustic medium. A water pipe 12 is connected to the lower end of the water tank 11 so that water can be supplied by the action of a pump 13. In addition, a window 11 is provided at the top of this water tank 11.
A is formed in the window 11a, and a coupler film 14 made of silicone rubber or the like that comes into contact with the subject is placed in the window 11a. And the pump 13
The amount of water supplied through the water pipe 12 is adjusted to such an extent that the coupler membrane 14 swells outward. In addition, the water temperature in this water tank 11 is
A predetermined water temperature, for example, in the case of human body diagnosis, is adjusted to approximately 38° C., which is approximately the same temperature as body temperature, by a water temperature adjusting device (not shown). An ultrasonic transducer 15 is disposed at a lower portion of the water tank 11 facing the coupler membrane 14 and is supported by a guide portion 16 and movable in the direction A in the figure.
The ultrasonic transducer 15 transmits and receives ultrasonic waves to and from the subject via water as an acoustic medium and the coupler membrane 14. As shown in FIG. 4, the ultrasonic transducer 15 is inserted into and supported by two guide rails 17, 17 attached to the guide portion 16, and is driven by a drive device (not shown). 17. Note that 18 is a signal lead line of the ultrasonic transducer 15. Including this ultrasonic transducer 15, an ultrasonic diagnostic apparatus is constructed from each component shown in FIG. That is, a transmitting circuit 21 and a receiving circuit 23 drive the ultrasonic transducer 15 and transmit received signals, and a transmitting control circuit 20 and a receiving control circuit 22 control the setting of delay time during transmission and reception. , addition processing for the received signal,
Signal processing circuit 2 that performs log conversion, filter processing, etc.
4, a memory circuit 25 that A/D converts and stores this signal, an image display system 26 that D/A converts the signal read out from the memory circuit 25, processes it into a video signal, and displays it, and a memory circuit. The arithmetic circuit 27 performs arithmetic processing such as C-mode conversion and aperture synthesis on the signals read out from the aperture 25 for display. Next, the sound absorbing material 30 attached to the inner wall surface of the water tank 11 will be explained. Sound absorbing material 30
is attached to the entire inner wall surface of the water tank 11, as shown in FIG. This acoustic absorbing material 30 has a difference in acoustic impedance between water, which is an acoustic medium, and the acoustic absorbing material within ±0.03×10 ⁶ [Kg/m ² ·s], that is, the acoustic impedance of the acoustic absorbing material changes depending on the operating temperature.
At 20℃ 1.45 to 1.51×10 ⁶ [Kg/m ²・s] or
A filler-containing silicone rubber having a density of 1.49 to 1.55×10 ⁶ [Kg/m ² ·s] at 40° C. is used. especially,
When diagnosing the human body, the diagnostic temperature is 35℃~40℃
Acoustic impedance Z = 1.50 to 1.55× ¹⁰⁶ in the range of
It is preferable to apply an acoustic absorbing material 30 of about [Kg/m ² ·s]. Such silicone rubber is made of polydiorganosiloxane, in which most or all of the organic groups are methyl groups, as a base polymer, mixed with an inorganic filler, and cured (vulcanized) using an appropriate method to form a rubber-like material. Forms an elastic body. In other words, millable silicone rubber is made by combining polydiorganosiloxane, which has a small amount of vinyl groups bonded to silicon atoms and residual methyl groups and has an average degree of polymerization of over 1000, by the action of organic peroxides or together with polyorganohydrodiene siloxane. Cures by reaction in the presence of a platinum-based catalyst. In addition, liquid silicone rubber is made of polydiorganosiloxane with a reactive group at the end of the molecule and an average degree of polymerization of 100 to 1000.
It cures at room temperature or by heating in the presence of a crosslinking agent and a catalyst, and is broadly classified into addition type and condensation type depending on the curing mechanism. In the present invention, any of these silicone rubber types can be used. By the way, the acoustic impedance Zw of water is 20~
The acoustic impedance of general polymeric materials decreases as the temperature increases, while the acoustic impedance of general polymeric materials increases as the temperature increases, reaching 1.48 to 1.52×10 ⁶ [Kg/m ² ·s] at 40°C. Therefore, acoustic impedance is adjusted by filling silicone rubber with a silica-based filler. Examples of this silica-based filler include silica such as fumed silica, precipitated silica, crushed quartz, and fused silica, as well as diatomaceous earth and calcium carbonate. Finely powdered silica is preferable in order to provide stable properties in water, and among these, finely powdered silica with an average particle size of 0.5 to 20 μm is suitable in order to obtain the filling amount necessary to obtain the desired acoustic impedance. There is. If the particle size is smaller than this, it will not be possible to incorporate the amount necessary to obtain the desired acoustic impedance, and if the particle size is larger than this, the surface of the rubber will become rough, and sufficient mechanical strength will not be obtained. I can't. Examples of such fine powder silica include crushed quartz and fused silica. The appropriate amount of finely powdered silica to be blended into the silicone rubber is 53 to 65% by weight in the silicone rubber, which is calculated from the respective specific gravity of polydimethylsiloxane and finely powdered silica having the above particle size. Approximately 30-42% by volume. The above-mentioned base polymer and filler are kneaded together with processing aids and other additives as necessary, and then mixed with a crosslinking agent, a crosslinking agent, etc. depending on the curing mechanism.
A rubber-like elastic body can be obtained by adding a catalyst and the like, thoroughly mixing the mixture, forming it into a sheet, and heating it at room temperature to a necessary temperature. During the mixing, either the crosslinking agent or the catalyst may be added during the first stage of kneading. The sheet may be directly molded and vulcanized to desired dimensions as described above, or may be cut to desired dimensions after vulcanization, and the silicone rubber thus obtained may be used as the acoustic absorbing material 3
It is attached to the inner wall of the water tank 11 as a. As an example of attaching this acoustic absorbing material 30 to the inner wall of the aquarium 11,
As shown in FIG. 6, a plurality of concave notches 11b may be provided on the inner wall surface of the water tank 11, and the sound absorbing material 30 may be provided with protrusions 30a that tightly fit into the notches 11b. It should be noted that what is indicated by 31 in the figure is the boundary surface between the inner wall surface and the acoustic absorbing material 30. The operation of the device configured as above will be explained. A subject such as a mammary gland is placed in close contact with the coupler membrane 14, and the ultrasonic transducer is driven to transmit and receive ultrasonic waves to and from the subject, while the ultrasonic transducer 15 scans in the horizontal direction. Collect ultrasound image information.
At this time, since the ultrasonic waves emitted from the ultrasonic transducer spread, they reach not only the subject but also the water tank 11 and are reflected. here,
There are two types of ultrasonic waves that reach the water tank 11 and are reflected. One of them is the reflected wave 32 that is reflected on the surface of the acoustic absorber 30 shown in FIG. The reflected wave 33 is transmitted through the boundary surface 30 and reflected at the boundary surface 31. Regarding the reflected wave 33,
Since the sound travels back and forth through the acoustic absorbing material 30, very little of it is reflected back into the water. Here, when the sound pressure reflectance R on the surface of the acoustic absorbing material 30, the acoustic impedance of the acoustic absorbing material 30 is Z, and the acoustic impedance of water is Zw, it is expressed as R=20log|Z-Zw/Z+Zw|. For example, the acoustic impedance of water at a water temperature of 38°C is Zw=1.50×10 ⁶ [Kg/m ²・s]
Then, R=-40dB. Therefore, the reflected waves 32 are also small, and the noise entering the ultrasonic transducer is also extremely reduced. On the other hand, if the absorption attenuation rate of the acoustic absorbing material 30 is 1.0 dB/mm/MHz, the thickness of the acoustic absorbing material 30 is 5 mm, and the ultrasonic frequency is 5.0 MHz, the The rate at which a sound wave is attenuated is T=-
It becomes 50dB. Therefore, the reflected wave 33 also becomes smaller. In this way, by setting the absorption attenuation rate to about 1.0 dB/mm/MHz, there is an effect that the thickness of the acoustic absorbing material for obtaining a predetermined attenuation rate can be kept to about several mm. Furthermore, considering the diffusion effect of ultrasonic waves, the reflected waves 32 and 3 are received by the ultrasonic transducer 15 as noise.
3 is extremely small and has almost no effect on the image. An example of such an acoustic absorbing material 30 will be described. In the following description, all parts represent parts by weight. The magnitude of the reflected wave is expressed in decibels compared to a metal plate, which is a perfect reflector. As an example, two rolls of 130 parts of crushed quartz with an average particle size of 3 μm are added to 100 parts of polydiorganosiloxane with an average degree of polymerization of 5500, in which 0.1 mol% of the organic groups bonded to silicon atoms are vinyl groups and the remainder are methyl groups. A base compound was obtained by thoroughly kneading the mixture. Take 100 parts of this base compound, 2,5-dimethyl-2,
Add 0.3 parts of 5-di-t-butylperoxyhexane, knead further, and put into a mold with a depth of 10 mm.
A vulcanized silicone rubber sheet was obtained by press molding at 170°C for 30 minutes and further heating at 200°C for 4 hours. The amount of filler in this silicone rubber is determined by the specific gravity ratio.
The specific gravity at 62% and 38°C was 1.60 [g/cm ³ ]. When we measured the acoustic impedance of this silicone rubber at 38℃, it was 1.51×10 ⁶ [Kg/m ²
s]. This silicone rubber was attached to the inner wall of the water tank 11 to form the acoustic absorbing material 30. This water tank was filled with water, an ultrasonic transducer was placed in it, the temperature was set to 38℃, ultrasonic waves with a frequency of 5MHz were generated, and the magnitude of the reflected waves was measured.
It was -50dB. Next, the relationship between the acoustic impedance of the acoustic absorbing material 30 and the water temperature used in the water tank 11 will be explained with reference to FIG. 7. In FIG. 7, the horizontal axis represents the temperature t, the vertical axis represents the acoustic impedance Z, and the acoustic impedances Z ₁ , Z ₂ , Z ₃ of the acoustic absorbing material 30 are plotted using the acoustic impedance Zw of water and the filling rate of the filler as parameters. This is what is shown. Acoustic impedance of water Zw
increases with temperature. On the other hand, the acoustic impedance of the acoustic absorbing material 30 decreases as the temperature rises, but the acoustic impedance increases as the filling rate of the filler increases. In FIG. 7, the filling rate of the filler in the acoustic absorbing material corresponding to illustration _Z1 is the lowest, and the filling rate of the filler in the acoustic absorbing material corresponding to illustration _Z3 is the highest. Therefore, when diagnosing the water temperature in the water tank 11 at different set temperatures such as t ₁ , t ₂ , t ₃ , each water temperature t ₁ , t ₂ , t ₃
The acoustic absorbing material may be created by changing the filling rate so that it has an acoustic impedance that is closest to the acoustic impedance Zw of water at the time. here,
An example of varying the amount of silica filler is shown below. Silicone rubber sheets A to E were obtained in the same manner as in the previous example except that crushed quartz having an average particle size of 2 μm was used as the silica-based filler, and the blending amount was varied as shown in the table below. However, A and E
This is a comparative example sample. For these samples, 25
The density, acoustic impedance, and magnitude of reflected waves at 35°C, 35°C, and 40°C were measured.
Regarding Samples C and D, the above characteristics were further measured at 38°C. These results are shown in the table. As is clear from the table, sample B was at 25℃ and sample C was
At 35°C and 38°C, D is suitable for use as an antireflective agent at 35-40°C.

【table】

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to suppress the generation of reflected sound waves at the interface between water and acoustic absorbing material, remove noise caused by scattered sound waves, and improve the quality of ultrasound images. A sonic imaging device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the scan of a breast diagnostic probe, Fig. 2 is a cross-sectional view of the inner wall of the aquarium on which acoustic absorbing material is pasted, and Fig. 3 shows an embodiment of the present invention, in which ultrasonic waves are 4 is a schematic perspective view showing the traveling mechanism of the ultrasonic transducer, FIG. 5 is a block diagram of the ultrasonic diagnostic device, and FIG. 6 is a wall of the water tank. The cross-sectional view and FIG. 7 are temperature characteristic diagrams of the acoustic impedance of the acoustic absorbing material and water with the filling rate of the filler as a parameter. 11...Water tank, 15...Ultrasonic transducer, 30...Sound absorbing material.

Claims (1)

[Claims] 1. In an ultrasonic imaging device in which an ultrasonic transducer is disposed in a water tank to transmit and receive ultrasonic waves to and from a subject, silica with an average particle size of 0.5 to 20 μm is contained in silicone rubber containing 53 to 65 μm of silica. An ultrasonic imaging device characterized in that an acoustic absorbing material filled with a weight percent is attached to the inner wall surface of the water tank. 2 The acoustic absorbing material has an acoustic impedance of 1.45 to 1.55×10 ⁶ at a temperature between 20°C and 40°C.
The ultrasonic imaging device according to claim 1, characterized in that it is made of filler-containing silicone rubber of [Kg/m ² ·s]. 3. The acoustic absorbing material has a absorption attenuation rate of ultrasonic waves.
Claim 1 which is about 1.0dB/mm/MHz
The ultrasound imaging device according to item 1 or 2.