JPS62207953A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To prevent a reflection by an interface to the body surface of a body to be inspected of an ultrasonic wave radiated from a vibrator, by forming an ultrasonic transmission part which contacts the body to be inspected, by the copolymer resin of a polyamide block and a polyether ester block. CONSTITUTION:A sound absorbing material 2 to which a vibrator 3 consisting of a piezoelectric material such as PZT, etc., is provided in a case 8, and constituted so as to execute an oscillating motion by using a point '0' as a fulcrum in the figure. The rotary motion of a motor 5 fixed to a base 6 is converted by a motion converting mechanism 7, and the sound absorbing material 2, that is, the vibrator 3 is brought to the oscillating motion. The case 8 consists of the lower side case part 8a and the upper side case part 8b, and an ultrasonic transmission part which contacts the body surface of a body to be inspected of the lower side case part 8a is formed by the copolymer resin of the polyamide block and the polyether block. As for the copolymer resin of the polyamide block and the polyether block, both the acoustic impedance and the sound velocity are values being near those of the body surface of the human body, respectively, therefore, there is scarcely the possibility that the performance is deteriorated due to the increase in the thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a probe for an ultrasonic tomography apparatus that has an improved ultrasonic transmitting portion that contacts the body surface of a subject.

[Conventional technology]

FIG. 2 shows a conventional probe of this type, a sector mechanical scanning probe for an ultrasonic tomography apparatus.

In FIG. 2, 1 is a case made of, for example, epoxy resin, and 2 is a sound absorbing material to which a vibrator 3 made of piezoelectric material such as PZT is attached. It is designed to be used as a neck movement. This movement is caused by an electric motor (not shown) installed in the upper case part 1b adjacent to the lower case part 1a of the case 1 filled with oil (not shown), which is an ultrasonic transmission medium. This is achieved by appropriately transmitting the motion to the sound absorbing material 2.

However, in such a probe, the transducer 3 transmits and receives ultrasonic waves using a case 1 made of epoxy resin or the like that has an acoustic impedance different from that of the living body being examined.
(Case 1 is case 1, where the ultrasonic transmission part is made of epoxy resin, etc., which has an acoustic impedance different from that of a living body). Therefore, even if a material whose acoustic impedance is close to that of a living body is used as the transmission medium, Case 1 will not occur. Ultrasonic waves are reflected at the interface with the living body, reducing ultrasound transmittance. Furthermore, if multiple reflections at the interface continue, they will appear superimposed on the tomographic image, causing problems such as deterioration of the image quality.

Therefore, as shown in FIG. 2, a probe was devised in which the part of the case 1 through which the ultrasonic waves are transmitted is formed of a thin vinyl chloride film 4. According to this, the problems of the above-mentioned probe can be solved, but since the vinyl chloride film 4 is flexible, it easily deforms when it comes into contact with a living body. Therefore, when diagnosing by strongly applying the probe to an uneven area such as the vicinity of the ribs, the tip of the probe, that is, the 4 portion of the vinyl chloride film deforms, resulting in the disadvantage of poor operability. The following improvement plan for the probe has also been proposed (Utility Application No. 58-67840).

The proposed improvement will be explained below. In other words, as mentioned above, if a material that forms the ultrasonic transmitting part of the probe that comes into contact with the body surface of the subject is a material that has an acoustic impedance equal to that of the body surface of the living body that is the subject, then one Ultrasonic waves are not reflected at the interface, and image quality degradation due to ultrasonic propagation loss and multiple echoes does not occur. Furthermore, if a material is used that has a thickness and hardness that will not cause deformation even if it is strongly applied to uneven parts such as near the ribs of a living body, operability will not be impaired. Polymethylpentene is a good material for the ultrasound transmitting part that satisfies both of these characteristics. That is, the acoustic impedance of the body surface of a living body, especially the human body, varies from person to person.

Habo 1.55-1.65xlO'kg/rr? Within the range of hm, 1.62 x 10'kg/-(8)
The representative value is 1 (see Proceedings of the 32nd Research Conference of the Japanese Society of Ultrasonics in Medicine, pp. 192-193). It was discovered that the acoustic impedance of polymethylpentene is close to the above representative value, and an example of its characteristics is shown below.
The properties of polymethylpente/MXOO4 manufactured by Mitsui Yuka Co., Ltd. are shown in the table below.

First table density (g/cII) 0.
834 speed of sound (m/flee)
2004 acoustic impedance 7s (kg/1tfl) =
1.67xlO' melting point (tllll')
235-240 thermal deformation degree (c)
85-Bending strength (kg/crA)
250 As can be seen from Table 1, polymethylpentene has the property of not being easily deformed by compression or heat, and also has good chemical resistance and high withstand voltage. It is useful as a member that forms the ultrasonic transmission part of the probe that comes into contact with the body surface of the human body. But the first
As is clear from the table, the sound speed of polymethylpentene is
2004m/set+, which is much larger than that of a living body. Therefore, even if the case 1 of the probe shown in FIG. 2 has a uniform thickness K, a lens effect will occur if a spherical shell shape with a small radius of curvature is used. In particular, in the case of a small probe with a small radius of curvature, the convergence point is different when passing through the center of the case and when passing through the periphery, resulting in a disadvantage that the resolution is reduced.

In this way, even if the acoustic impedance is approximated to that of a living body, if the sound speed is significantly different from that of a living body, it will adversely affect the focusing effect of ultrasound. A tomographic apparatus using a probe using such polymethylpentene has the disadvantage that image quality is degraded.

In order to clarify the above cause, we will examine the influence of the sound velocity on the material of the head case.

Figure 4 shows the lens effect of the head case of the probe. Here, we assumed the following.

Consider ultrasonic waves in terms of geometric optics and ignore interference and diffraction.

Although the O oscillator is made flat, the focusing property is not lost.

0 The head case is a complete spherical shell.

Oscillator radius: r Focal length of the vibrator: f.

Head case radius of curvature: R1 (inner surface), R2 (outer surface)
Distance between transducer and head case: d Speed of sound between probe and head case (inner surface) 201 Speed of sound inside the head case: C2 Speed of sound outside the probe 203 If there is no head case, starting from A The wave travels straight and reaches G. Similarly, a wave starting from any point on the vibrator travels straight and reaches G. If a head case exists, the wave starting from A will reach the inner surface of the head case B.%
It is refracted according to the Sne II law and reaches the outer surface C of the head case. After that, the crossing bends again and reaches D. A wave starting from an arbitrary point on the vibrator is similarly refracted twice and exits to the outside, but the focal lengths do not match, and the head case acts as a lens with aberration.

In ΔA'BP and ΔF'BO in Fig. 4, 几(sinθ
1 +Rr CQSθ1tanψ= r' ・-
・(1) Here r'1=OGtanψ=(f, -d+Rt)tan9'
−(2) tanψ=□
...(3) f.

It is.

From equation (3), sinθ! seek.

The angle of incidence θIl on the inner surface of the head case is given by the following equation.

θ, 1=θ1+ψ...(5
) According to Snell's law, the following relational expression holds true.

... θ... = Nido sin θ... (inner) ・
...(6) When the law of sine is applied to ΔBCO, the following equation holds true.

Therefore, here θyo θ1-/BOC=θI+θ+2-〇, 2...
(9) φth θ, 3-θ ・・
・Set as (10). Also, if H is a point perpendicular to the central axis OG from point C, then CH=R2sinθ−(11
) Therefore, the focal length f is given by the following equation.

f=HD+(OH(Rrd))H=-+Rr2CO3θ+d-R11 tanφ FIG. 5 shows an example of the sound rays indicating the path of the ultrasonic waves emitted from the vibrator using the above analysis method. Here, the head case is assumed to be made of polymethylpentene, and the sound speed is 2000 m/
(8). If the speed of sound in the head case is the same as that in a living body, the sound rays from the vibrator should reach the same point, but as shown in Figure 1, they reach different points depending on the path, resulting in aberrations.

In this way, using polymethylpentene, the curvature is 12.5.
It can be seen that the above-mentioned drawbacks occur in a probe using a spherical helad case with a small R, a thickness of 1.5 fl, and an outer surface of about 14 mm.

[Embodiments of the invention]

Embodiments of the present invention will be described, but prior to the explanation based on the illustrated examples, a description will be given of how the present invention was achieved. In other words, as mentioned above, if a material that is equal to the acoustic impedance of the body surface of the living body is used as the member forming the ultrasonic transmitting part of the probe that comes into contact with the body surface of the subject, the impedance between the body surface and the body surface will be Ultrasonic waves are not reflected at the interface, and image quality degradation due to ultrasonic propagation loss and multiple echoes does not occur. Furthermore, if a material is used that can be sufficiently thick and hard enough to deform even if it is strongly applied to an uneven part such as near the ribs of a living body, operability will not be impaired. Furthermore, if the sound speed is close to that of a living body, no aberration will occur in the focusing of the ultrasound beam on the probe.

As a result of extensive research into the material of the ultrasonic transmitting portion that satisfies the above requirements, the present inventors have found that a copolymer resin of polyamide block and polyether ester block is suitable.

The present inventors have discovered that the acoustic impedance of the above-mentioned copolymer resin approximates the typical value of the acoustic impedance of the surface of the human body, as described above, and that the sound velocity also approximates that of a living body. Table 2 shows the characteristics of Pebax (registered trademark) manufactured by Toshi Co., Ltd. Here Pepatsukuno sample number 63338NO0,5533
8NO0.

m/n in order of 40338NO0, 3533SNOO
It's getting bigger and smaller.

The copolymer resin hapolyamide block of polyamide block and polyether ester block shown here is expressed by the molecular formula of polyether ester block. As n increases, hardness increases, and as inverse Km/n decreases, flexibility increases. It has the property that flexibility can be adjusted over a wide range by changing the m/n ratio. Also m/
The speed of sound could be changed by changing the ratio of n, and it was confirmed that the sound speed approached the speed of sound in a living body. On the other hand, the density is 1.01, which is close to that of a living body, and hardly changes depending on the size of m/n. This means that by using Bebax with an appropriate m/n value, both the speed of sound and the acoustic impedance can be approximated to that of a living body. The inventor took advantage of this and devised the idea of using it in an acoustically transparent window in contact with a living body in a probe.

As can be seen from Table 2, the copolymer resin of polyamide block and polyether block has heat resistance and also has the property of not being deformed by a certain amount of force. Furthermore, since it has properties of chemical resistance and high voltage resistance, it is useful as a member that forms the ultrasound transmitting portion of the probe that comes into contact with the body surface of the subject.

The present invention will be described in detail below with reference to FIG. FIG. 1 is a sectional view showing an example of a probe for an ultrasonic tomography device according to the present invention, in which a mechanical scanning type probe for an ultrasonic tomography device according to the present invention is shown. Similar to FIG. 3, this refers to the sound absorbing material and the vibrator. Reference numeral 5 denotes an electric motor fixed to a table 6, and its rotational motion is converted by a motion conversion mechanism 7 attached to the table 6, causing the sound absorbing material 2, in other words, the vibrator 3, to oscillate around the zero point in the figure as a fulcrum. let

Reference numeral 8 denotes a case that houses each of the above-mentioned members, and includes a lower case part 8a and an upper case part 8b, and a superstructure that contacts at least the body surface of the subject (not shown) in the lower case part 8a. The sound wave transmitting portion 8c is made of a copolymer resin of the above-mentioned polyamide block and polyether block. As described above, the copolymer resin of polyamide blocks and polyether blocks has acoustic impedance and sound velocity close to those of the surface of the human body, so there is little risk of performance deterioration due to increased thickness.

Therefore, it is possible to create a structure that does not easily deform under pressure. Here, of the entire case 8, an ultrasonic transmitting portion 8C is formed of Bebax with an appropriate thickness.

Reference numeral 9 denotes an O-IJ ring made of silicone rubber or the like, which prevents the ultrasonic transmission medium (not shown) filled in the lower case part 8a from leaking to the upper case part 8b and the outside of the case 8. 10 is a cable to the vibrator 3 and the electric motor 5.

〔Effect of the invention〕

The ultrasonic wave transmission and reception operations of the probe of the present invention described above are not particularly different from those of the conventional probe shown in FIGS. 2 and 3.

The probe according to the present invention is characterized in that the ultrasonic transmitting part that comes into contact with the representative of the object to be examined is formed of a copolymer resin of polyamide blocks and polyether ester blocks. Reflection of the transmitted ultrasound waves at the interface with the body surface of the subject can be prevented, and image quality deterioration due to ultrasound propagation loss and multiple echoes will not occur. Furthermore, since the speed of sound is similar to that of a living body, the shape of the case does not cause the sound rays to be refracted, so the ultrasonic beam pattern does not change and the characteristics of the probe do not deteriorate. At the same time, it has some flexibility even when strongly applied to uneven areas such as near the ribs of a living body, so it feels good to the touch and is less likely to deform. Even if there is some change, if the sound speed is the same as that of a living body, the ultrasonic beam shape will hardly change, so the characteristics of the probe will not deteriorate. If the other case parts are made of a hard synthetic resin such as vinyl chloride or polycarbonate, the operability will be improved. In addition, the copolymer resin of polyamide block and polyether ester block has chemical resistance, durability, high withstand voltage, and excellent processability.

Although the above description has been made using a mechanical scanning type ultrasound probe as an example, it goes without saying that the present invention can also be applied to an electronic scanning type ultrasound probe, and the same effects as in the above-mentioned embodiments can be achieved in this case as well. .

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a probe for an ultrasonic tomography apparatus according to the present invention. FIGS. 2 and 3 each show a sectional view of a main part of a conventional probe. FIG. 4 is an explanatory diagram of the lens effect of the Herad case, and FIG. 5 is a diagram illustrating the deterioration of the convergence state by showing sound rays when the head case is TPX. 3... Vibrator, 8... Case, 8a... Polyamide block and polyether ester block copolymer resin Figure 2 Figure 3 Figure z5

Claims (1)

[Claims] 1. A probe for an ultrasonic diagnostic device, characterized in that the ultrasonic transmitting portion that contacts the subject is formed of a copolymer resin of a polyamide block, a polyether ester block, and a polyether ester block.