JPH0440020B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a mechanical scan ultrasound probe, and more specifically, to a mechanical scan ultrasound probe that scans an ultrasound beam inside a subject at a scanning angle larger than the swing angle of an ultrasound transducer. This invention relates to a mechanical scan ultrasonic probe that can perform

[Technical background of the invention and its problems]

In an ultrasound diagnostic apparatus, the resolution in a direction perpendicular to the propagation direction of ultrasound waves is determined by the beam diameter of the ultrasound waves. Generally, in order to improve this resolution, an ultrasonic diagnostic apparatus employs a method of converging an ultrasonic beam at a predetermined focal point to reduce the beam diameter. The beam diameter of the ultrasonic wave at the focal point is determined by the vibration surface aperture of the ultrasonic transducer and the ultrasonic frequency. The larger the vibrating surface aperture and the higher the ultrasonic frequency, the smaller the ultrasonic beam diameter becomes, and therefore the resolution improves.

The structure of the head of a conventional mechanical scan ultrasound probe is shown in FIG.

As shown in FIG. 1, the head of the mechanical scan ultrasound probe is housed in a housing 4 that encloses a liquid 3 as an acoustic coupling material and has a subject contacting surface (acoustic window) 5 with a width L. A support 9 having an ultrasonic transducer surface having a diameter D and swinging at a fulcrum 2
The ultrasonic transducer 1 is provided with an ultrasonic transducer 1 which is held at a position and capable of scanning an ultrasonic beam within a scanning angle range of 2θ.

In the mechanical scan ultrasonic probe having the above configuration, in order to improve the resolution, the aperture D of the ultrasonic transducer surface must be increased as described above.

However, when the aperture D is increased, the width L of the acoustic window 5 must be increased in order not to hinder the propagation of the ultrasound beam 11 to the subject 6 at the maximum scanning angle. In this case, by enlarging the acoustic window 5, the head of the mechanical scan ultrasonic probe itself becomes large and heavy, making it difficult to operate the probe with one hand. In addition, if the acoustic window 5 is large, the area within the body that the ultrasound beam scans becomes wider, and as a result, the ultrasound beam is blocked by bones, gas in the gastrointestinal tract, etc., so the area that can be manipulated by ultrasound becomes wider. You will be restricted.

[Purpose of the invention]

This invention was made in view of the above circumstances, and provides a mechanical scan ultrasonic probe that is compact in overall shape and lightweight, yet can widen the ultrasonic scanning angle and maintain high resolution. The purpose is to provide the following.

[Summary of the invention]

The outline of this invention for achieving the above object is as follows:
A casing having an acoustic window on a subject contacting surface and having a liquid as an acoustic medium sealed therein; and an ultrasonic transducer housed in the casing so as to be swingable at a predetermined swing angle. In the mechanical scan ultrasonic probe that is capable of scanning in a fan shape with an ultrasonic beam, the liquid sealed in the housing is a liquid that transmits ultrasonic waves at a sound speed lower than the sound speed in a living body. It is characterized by enabling ultrasonic beam scanning at a scanning angle larger than the swing angle.

[Embodiments of the invention]

First, the principle of this invention will be explained.

This invention utilizes the principle that sound waves undergo a refraction effect at the boundary between two types of media (acoustic media) having different sound velocities.

As shown in Figure 2, the sound speeds are V ₁ and V _{2 ,} respectively.
When _{two types of} media _, where When propagating through a medium, the following first equation holds true according to Snell's law.

sinθ ₂ /sinθ ₁ =V ₂ /V ₁ ...(1) Therefore, if V ₁ <V ₂ , then θ ₁ <θ ₂ ,
A large angle of refraction can be obtained with a small angle of incidence. For example, V ₁ = 1000m/s, V ₂ = 1500m/s
s, θ ₂ =48.6° for θ ₁ =30°.

Next, an embodiment of the present invention utilizing the above principle will be described with reference to the drawings.

As shown in FIG. 3, the mechanical scan ultrasonic probe, which is an embodiment of the present invention, has a head encased in a liquid 12 that propagates sound waves at a sound speed of 80% or less of the sound speed in a living body. l acoustic window 1
3, an ultrasonic transducer 17 is provided in a casing 14 having an ultrasonic transducer surface having a diameter D and is held by a support 16 that swings at a fulcrum 15 within a range of swing angle 2θ ₁ . be done.

The liquid 12 has a sound velocity in a living body of, for example, 1500 m/s.
For example, when a sound wave propagates at a sound speed of 1000 m/s, which is about 67%, as shown in Figure 4,
When obtaining an ultrasound beam scanning angle of 90° (±45°) in a living body (medium), the scanning angle 2θ ₁ of the ultrasound transducer can be set to 2 x 28° = 56° using the first equation above. . On the other hand, if the sound velocity in the liquid 3, which is the acoustic coupling material, is 1500 m/s as in the past, as shown in Figure 4,
In order to obtain a scanning angle of 90° (±45°), the swing angle 2θ of the ultrasonic transducer 17 must be 90°. Therefore, if the liquid 12 is one that propagates sound waves at a sound speed of 80% or less of the sound speed inside the living body, it is possible to scan the beam within the living body at a wide scanning angle even if the swing angle of the ultrasonic transducer is small. can do. Note that at the boundary between the liquid 12 and the living body,
Reflection of ultrasonic waves also occurs, and it is preferable to keep this reflection of ultrasonic waves as small as possible. Therefore, sound waves propagate at a speed of sound that is less than 80% of the sound speed within a living body, and the acoustic impedance is equal to that of the living body (approximately 1.5×10 ⁵ Kg/m ²・s).
It is preferable to use a liquid 12 that approximates the above, and examples of such liquid 12 include carbon tetrachloride, chloroform, and the like.

As described above, by reducing the scanning angle of the ultrasonic transducer 17, the width l of the acoustic window 13 can be made much smaller than the conventional width L, and the mechanical scan ultrasonic probe can be downsized. can do. Furthermore, it is possible to scan the beam at the same in-vivo scanning angle as with the ultrasound transducer (aperture D) in a conventional mechanical scan ultrasound probe, and to maintain almost the same resolution. can.

How small the width l of the acoustic window 13 can be depends on the aperture D of the ultrasonic transducer 17 and the distance from the center of oscillation of the transducer surface. In Figure 4, when the aperture D of the ultrasonic transducer 17 is approximately 20 mm and the distance from the center of rotation of the transducer surface (fulcrum 15) is 7 mm, the width of the acoustic window 13 to obtain a scanning angle of 90° in the living body. l
(2l ₂ ) is approximately 35 mm, and the width L (2l ₁ ) of the conventional acoustic window 5 is approximately 54 mm (in this case as well, the sound speed in the medium is 1000 m/s, and the sound speed in the medium is 1500 m/s). /s).
In addition, in FIG. 4, when the diameter of the ultrasonic transducer 17 is 25 mm and the distance of the transducer surface from the fulcrum 15 is 10 mm, the ultrasonic transducer 17 to obtain a scanning angle of 90° in the living body is The swing angle is 25.4°×2=50.8°, and the width l (2l ₂ ) of the acoustic window 13 is approximately 45 mm.

Although one embodiment of the present invention has been described in detail above, it goes without saying that the present invention can be modified and implemented as appropriate within the scope of the gist of the invention.

The mechanical scan ultrasonic probe according to the present invention may be one that swings the ultrasonic transducer at a predetermined swing angle. For example, as shown in FIG. The ultrasonic transducer 17 may be oscillated so that the center of rotation of the transducer 17 is located at the center 19 of the acoustic window 13.

Further, the shape of the acoustic window 13 is not limited to a planar shape, but may be spherical or cylindrical.

〔Effect of the invention〕

According to this invention, in order to improve resolution, even if the diameter of the ultrasonic transducer is as large as that of conventional devices, the ultrasonic transducer is sealed with a liquid that propagates sound waves at a speed of sound that is less than 80% of the sound speed in a living body. By utilizing the refraction effect of sound waves between two different types of media, it is possible to scan the beam within a living body at a wide scanning angle even though the swing angle of the ultrasound transducer is small. can. Therefore, it is possible to construct a compact and lightweight mechanical scan ultrasonic probe with a small acoustic window, improve its operability, and maintain resolution at approximately the same level as conventional devices. . Also,
Since the acoustic window is made small, it is possible to prevent the range that can be diagnosed with the ultrasound beam from being limited.

[Brief explanation of drawings]

Figure 1 is a partially cutaway sectional view showing a conventional device;
The figure is an explanatory diagram showing the refraction of sound waves between two types of media, FIG. 3 is a partially cutaway sectional view showing one embodiment of the present invention, and FIG. 4 is a diagram showing the difference between the above embodiment and a conventional device. and FIG. 5 are partially cutaway sectional views showing another embodiment of the present invention. 12...liquid, 14...casing, 17...ultrasonic transducer.

Claims (1)

[Claims] 1. A casing having an acoustic window on the subject contacting surface and having a predetermined size, and a casing that is swingably housed within the casing at a predetermined swing angle allowed by the size of the casing. an ultrasonic transducer, and a liquid sealed in the housing that transmits ultrasonic waves at a sound velocity lower than that in a living body, and the liquid transmits ultrasonic waves at a scanning angle larger than a swing angle of the ultrasonic transducer. A mechanical scan ultrasonic probe characterized by being capable of beam scanning.