JPH03274996A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To obtain a cross sectional picture with excellent resolution without a ghost image by forming the ultrasonic probe in a way that the thickness of the part filled with an ultrasonic wave propagation medium for transmitting an ultrasonic wave is made ununiform so as to suppress the ghost signal. CONSTITUTION:The thickness of an acoustic window 1 in which a lateral ultrasonic wave solely exists in a propagation path and propagates therethrough has a difference t equivalent to a half the wavelength of the lateral ultrasonic wave propagating through the acoustic window 1 with respect to an ultrasonic wave path from the position of the gravity center at a right half of an ultrasonic wave vibrator 5 and with respect to an ultrasonic wave path from the position of the gravity center at a left half of the ultrasonic wave vibrator 5. Thus, generated lateral ultrasonic waves are cancelled together, a ghost signal caused by the lateral ultrasonic wave is suppressed and an excellent picture without a ghost image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used in an ultrasonic diagnostic apparatus, in which at least one ultrasonic transducer is rotated or oscillated as if shaking its head to obtain an ultrasonic tomographic image. Concerning mechanical scanning type ultrasound probes.

BACKGROUND OF THE INVENTION In recent years, with the diversification of medical diagnosis, mechanical scanning type ultrasound probes have come to be used in addition to electronic scanning type ultrasound probes in ultrasound diagnostic apparatuses.

Among these, the mechanical sector scanning probe, which is one of the configurations of the mechanical scanning ultrasonic probe, is described, for example, in "New Ultrasonic Technology" (Nankodo, 1984, p. 68). . Hereinafter, this conventional mechanical sector scanning type ultrasonic probe will be explained with reference to FIG. 3.

In FIG. 3, 51 is an acoustic window, 52 is a support member, and 53
55 is an ultrasonic transducer attached to the support 53; 56 is an acoustic lens provided in front of the ultrasonic transducer 55; 57 is an acoustic lens provided in front of the ultrasonic transducer 55; An acoustic propagation medium enclosed in the acoustic window 51, 58 a lead wire whose one end is connected to the ultrasonic transducer 55, and 59 a lead wire of a cable whose one end is connected to the ultrasound diagnostic apparatus main body (not shown). , 60 are slip rings that electrically connect the lead wires 58 and 59.

61 is a subject (living body), 62 is an ultrasound path from the aperture center 55a of the ultrasound transducer 55, and 63 is the ultrasound transducer 55.
64 is the convergence point of the ultrasonic waves from both end faces 55b and 55c of the opening.

Next, the operation of the above conventional example will be explained. support body 53,
The ultrasonic transducer 55 and the acoustic lens 56 are rotated together at a constant speed by a drive mechanism (not shown). During this time, ultrasonic waves are emitted from the ultrasonic transducer 55 toward the subject 61, and reflected waves generated due to the difference in acoustic impedance within the subject 61 are received by the ultrasonic transducer 55. The received signal is transmitted to the ultrasound diagnostic equipment main body (not shown) through the lead wire 58, slip ring 60, and lead wire 59, and is subjected to appropriate signal processing in the ultrasound diagnostic equipment main body to obtain a sector-shaped ultrasound tomographic image. is displayed on a cathode ray tube (not shown).

Problems to be Solved by the Invention However, in the conventional ultrasonic probe, as is clear from FIG.
The ultrasonic wave path 63 radiated from the acoustic window 5b is incident obliquely with respect to the normal direction of the acoustic window 51. The acoustic propagation medium 57 is a liquid, and only longitudinal ultrasonic waves propagate in the liquid. When longitudinal ultrasonic waves obliquely enter a solid body such as the acoustic window 51, not only longitudinal waves but also transverse waves are generated within the solid body. Since the propagation speed of the transverse wave is slower than that of the longitudinal wave, the acoustic impedance of the transverse wave to the ultrasonic wave is different from the acoustic impedance of the longitudinal wave to the ultrasonic wave. Therefore,
Even if the acoustic impedances of the acoustic propagation medium 57 and the acoustic window 51 are matched for the longitudinal ultrasound, it is not possible to match the acoustic impedance for the transverse ultrasound, so a ghost signal of the shear ultrasound is generated within the acoustic window 51. As a result, as shown in FIG. 4(a), a pulse 66 resulting from the transverse ultrasound generated within the acoustic window 51 is generated after the main ultrasonic pulse 65, and, for example, as shown in FIG. As shown in b), the blood vessel wall image 6 in the sector-shaped ultrasound tomographic image is
There was a problem in that a ghost image 68 of the blood vessel wall image 67 was generated slightly behind the image 7, degrading the image quality. Incidentally, the transverse ultrasonic waves that cause such a ghost image 68 are generated when the ultrasonic waves are obliquely incident on a solid, and are propagated only in the solid, and at the interface of a liquid or a living body, the transverse ultrasonic waves are transmitted again. It is converted into longitudinal ultrasound and propagated.

As a technical means to solve this problem, JP-A-63-22
Although there is a technical means disclosed in Japanese Patent No. 0848, it cannot be said to be sufficient for obtaining good images due to structural limitations.

The present invention solves the above-mentioned conventional problems, and aims to provide an ultrasound probe that can eliminate ghost images caused by transverse ultrasound generated in the acoustic window and obtain tomographic images with good resolution. That is.

Means for Solving the Problems In order to achieve the above object, in the present invention, the ultrasonic wave passing portion of the acoustic window is formed to have a non-uniform thickness.

Further, in the present invention, the ultrasonic wave passing portion of the acoustic window is formed to have an inclination corresponding to a thickness difference corresponding to a 172 wavelength difference of transverse ultrasonic waves generated in the ultrasonic wave passing portion.

Effects The present invention has the following effects due to the above structure. That is, since the ultrasonic wave passing portion of the acoustic window is formed to have a non-uniform thickness, transverse ultrasonic waves generated within the acoustic window are canceled out. In addition, the ultrasonic passing portion of the acoustic window is one of the transverse ultrasonic waves generated in the ultrasonic passing portion.
Since it is formed to have an inclination that corresponds to a difference in thickness corresponding to a difference in wavelength of 72, transverse ultrasonic waves generated within the acoustic window are reliably canceled out.

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

FIG. 1(a) is a schematic front cross-sectional view of an ultrasonic probe according to a first embodiment of the present invention, and FIG. 1(b) is a schematic side cross-sectional view. In FIGS. 1(a) and 1(b), l is an acoustic window. 2 is a support member for the rotating shaft 3; 4 is a support body held by the support member 2 and rotatably supported by the rotating shaft 3 in the direction of arrow A; 5 is an ultrasonic transducer attached to the support body 4; is an acoustic lens provided in front of the ultrasonic transducer 5, 7 is an acoustic propagation medium (ultrasonic propagation medium) sealed in the acoustic window l, and 8 is a lead wire with one end connected to the ultrasonic transducer. , and other terminals are connected to an ultrasonic diagnostic device (not shown) through a slip ring (not shown) to transmit signals. Reference numeral 9 indicates an ultrasonic path from the aperture center 5a of the ultrasonic transducer 5, and 10 indicates both end faces 5b of the aperture of the ultrasonic transducer 5, 5
The ultrasonic path 11 from c passes through the aperture center 5a of the ultrasonic transducer 5' and is perpendicular to the paper surface 18, which is perpendicular to the paper plane and is perpendicular to the rotational axis 3 of the ultrasonic transducer 5, as indicated by the two-dot chain line in the figure. When the ultrasonic transducer 5 is divided into left and right parts, 12 represents the ultrasonic path emitted from the center of gravity of the right half of the ultrasonic transducer 5, and 12 represents the ultrasonic path emitted from the center of gravity of the left half. 13 is a subject (living body).

As can be understood from FIG. 1(b), the acoustic window l has a cylindrical shape with a uniform thickness with respect to the rotation direction A of the ultrasonic transducer 5, and extends in a direction parallel to the zero rotation axis 3. As understood from FIG. 1(a), the distance between the ultrasonic path 11 emitted from the center of gravity of the right half of the ultrasonic transducer 5 and the ultrasonic path 12 emitted from the center of gravity of the left half of the ultrasonic transducer 5 is The ultrasonic wave passing portion of the acoustic window l is formed to have an inclination according to the thickness difference Δt corresponding to the l/2 wavelength difference of the transverse ultrasonic waves generated in the ultrasonic wave passing portion. That is, the shape of the acoustic window 1 is semi-cylindrical, and the thickness changes in the direction of the rotation axis 3.

Next, the operation of the above embodiment will be explained.

The support body 4, the ultrasonic transducer 5 supported by the support body, and the acoustic lens 6 provided on the front surface of the ultrasonic transducer 5 are integrally rotated around the rotating shaft 3 by a drive mechanism (not shown). During this period, the ultrasonic transducer 5 emits ultrasonic waves, and the ultrasonic transducer 5 receives reflected waves from within the subject 12 due to the difference in acoustic impedance. ) and a cable (not shown) to the ultrasound diagnostic equipment main body (not shown), where appropriate signal processing is performed and the sector-shaped ultrasound tomographic image is transmitted to a cathode ray tube (not shown). ) will be displayed. In this case, the ultrasonic waves incident on the acoustic window l are affected by the convergence effect of the acoustic lens 6, the curvature of the supporting body 4 of the acoustic window l in the rotating direction, and the spread of the ultrasonic reception signal. It will exist. When ultrasonic waves are obliquely incident on a solid object such as the acoustic window 1, it is generally known that not only longitudinal ultrasonic waves (transverse ultrasonic waves) are generated at the interface. The propagation speed is slower than that of sound waves, and this is caused by the difference in propagation speed between longitudinal and transverse ultrasonic waves when they propagate from the acoustic window l to the acoustic propagation medium 7 and are converted back to longitudinal ultrasonic waves at the interface. Then, a time-delayed echo is generated at a position corresponding to the thickness of the acoustic window l, which becomes a ghost signal and causes deterioration of the tomographic image.

In this case, in this example, the thickness of the acoustic window l in which only the transverse ultrasonic wave exists and propagates in the propagation path is calculated as shown in Fig. 1 (
As shown in a), a transverse wave propagating within the acoustic window 1 is generated for an ultrasonic path 11 from the center of gravity of the right half of the ultrasonic transducer 5 and an ultrasonic path 12 from the center of gravity of the left half of the ultrasonic transducer 5. Since the thickness difference Δt corresponding to 1/2 of the wavelength of the ultrasonic wave is formed, the generated transverse ultrasonic wave is canceled out, and the ghost signal caused by the transverse ultrasonic wave is suppressed, resulting in a good image without ghost images. is obtained.

FIG. 2(a) is a diagram showing the ultrasonic reception signal received by the right half of the ultrasonic transducer 5, and shows the thickness of the acoustic window l of the passage path of the ultrasonic path 11 from the center of gravity of the right half, and the vertical It is understood that the ghost signal 14 occurs at a position with a time delay corresponding to the difference in propagation speed between the wave ultrasound and the transverse wave ultrasound.

Figure 2(b) shows the ultrasonic path 12 from the left half center of gravity position.
This figure shows how a ghost signal 15 is generated at a position corresponding to the thickness of the acoustic window l of the passage path of the wave and the difference in propagation speed between the longitudinal ultrasonic wave and the transverse ultrasonic wave. The ghost signal 15 in FIG. 2(b) is different from the ghost signal 14 in FIG.
It is shifted by an amount equivalent to two wavelengths. FIG. 2(c) shows the received signal when received by the ultrasonic transducer 5, and the second
This waveform is the sum of the waveforms shown in Figures (a) and 2(b), and ghost signals 14 and 15 are added with a phase difference of 1/2 wavelength and are canceled out, so there is almost no ghost signal. A good ultrasonic reception signal can be obtained.

Further, in the case where the shape of the acoustic window l is spherical as in the second embodiment, by shifting the center of curvature of the outer wall and the center of curvature of the inner wall of the acoustic window l in the direction of the rotation axis, Acoustic window l of the ultrasound path from the center of gravity position of the right half of the transducer 5
Acoustic window 2 of the ultrasonic path from the thickness of the left half center of gravity position
It is possible to provide a difference in thickness corresponding to 1/2 wavelength of the transverse wave, and as in the first embodiment, the ghost signal caused by the transverse ultrasonic wave can be canceled out, and a good ultrasonic reception signal with almost no ghost signal can be obtained. can get.

In the above two embodiments, a mechanical scanning type ultrasonic probe in which the ultrasonic transducer rotates was explained, but a mechanical scanning type in which the ultrasonic transducer repeatedly moves back and forth (oscillates) to swing is explained. The same procedure can be applied to an ultrasonic probe.

Effects of the Invention As is clear from the above embodiments, in the present invention, the ultrasonic wave passing portion of the acoustic window is formed to have a non-uniform thickness, so that transverse ultrasonic waves generated within the acoustic window are canceled out. . Therefore, the ghost signal becomes small and the ghost image becomes difficult to visually recognize. In addition, since the ultrasonic wave passing portion of the acoustic window is formed to have an inclination corresponding to the difference in thickness corresponding to the 1/2 wavelength difference of the transverse ultrasonic wave generated in the ultrasonic wave passing portion, the inside of the acoustic window The transverse ultrasonic waves generated by this system are reliably canceled out. In this way, according to the present invention, a tomographic image with good resolution can be obtained.

[Brief explanation of drawings]

FIG. 1(a) is a partially omitted front sectional view of an ultrasonic probe according to an embodiment of the present invention, and FIG. 1(b) is a partially omitted side sectional view of this ultrasonic probe. Figure 2 (a) is a pulse waveform diagram received by the right half of the ultrasonic transducer, Figure 2 (b) is a pulse waveform diagram received by the left half, and Figure 2 (c) is a diagram of the pulse waveform received by the left half of the ultrasonic transducer.
is a pulse waveform diagram received in front of the aperture of the ultrasonic transducer, Figure 3 is a front sectional view of a conventional ultrasound probe, and Figure 4 (a).
is a pulse waveform diagram received by a conventional ultrasonic probe, and FIG. 4(b) is a tomographic image diagram obtained by the conventional probe. l...acoustic window, 2...support member, 3...rotation shaft,
4... Support body, 5... Ultrasonic transducer, 6... Acoustic lens, 7... Acoustic propagation medium, 8... Lead wire, 9
...Ultrasonic path, lO... Ultrasonic path, 11...
Ultrasonic path, 12... Ultrasonic path, 13... Subject, 14... Ghost signal, 15... Ghost signal,
16...Ghost signal, 17...Ultrasonic echo

Claims (2)

[Claims] (1) An ultrasonic transducer that is placed in an ultrasonic propagation medium and rotates or oscillates, and the ultrasonic propagation medium in which this ultrasonic vibrator is placed is filled, resulting in uneven thickness of the ultrasonic passage area. An ultrasound probe having an acoustic window formed to (2) When the ultrasonic transducer is divided into left and right parts by a plane that passes through the aperture center of the ultrasonic transducer and is perpendicular to the rotation axis or the swing axis of the ultrasonic transducer, the right half of the ultrasonic transducer The ultrasound path of the acoustic window between the ultrasound path radiated from the center of gravity and the ultrasound path radiated from the left half of the center of gravity is 1/2 wavelength of the transverse ultrasound generated in that ultrasound path. The ultrasonic probe according to claim 1, wherein the ultrasonic probe is formed to have an inclination corresponding to the difference in thickness.