JPH05285132A - Ultrasonic transmitter/receiver - Google Patents

Abstract

PURPOSE:To decrease a difference of azimuth resolution caused by a radiation angle, and to obtain a satisfactory picture quality thereby by providing additionally a means for changing an aperture, in the ultrasonic transmitter/receiver in which the direction for transmitting or receiving an ultrasonic wave is varied by a signal frequency. CONSTITUTION:The ultrasonic transmitter/receiver uses a vibrator array 1 inverted and polarized alternately, and changes the direction for transmitting or receiving an ultrasonic wave by a signal frequency. That is, in the ultrasonic transmitter/receiver in which the direction for transmitting or receiving an ultrasonic wave is varied by a signal frequency, the azimuth resolution is improved by changing its aperture, and a satisfactory ultrasonic beam is obtained. For instance, a hot electrode is divided, and the vibrator array 1 is driven. In a word, an aperture D of the vibrator array 1 is divided into plural apertures D1 to D3, and the array is driven by plural hot electrodes 2a to 2c. Subsequently, the ultrasonic beam in the direction theta1 by a driving frequency f1, and the ultrasonic beam in the direction theta2 by a driving frequency f2 are driven by the hot electrode 2a, and each hot electrode 2a to 2c, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave transmitter / receiver, and more particularly to an ultrasonic wave transmitter / receiver for electrically sector-scanning an ultrasonic beam with a small number of signal lines.

[0002]

2. Description of the Related Art An ultrasonic wave transmitter in which the directions of transmission and reception of ultrasonic waves change depending on the signal frequency is described in "High Speed 2" published in the Proceedings of the Japan Society of Ultrasonics in Medicine (November 1974).
3D imager ". The operating principle of such an ultrasonic wave transmitter / receiver will be described with reference to FIG.
As shown in FIG. 2, the ultrasonic wave transmitter / receiver includes an oscillator array 1 that is inverted polarized (directions of polarization are alternately indicated by arrows having different directions), and ground electrodes 3 provided on both surfaces thereof.
And hot electrode 2. When a burst wave (1/2 wave of the number of elements, 2 waves because there are 4 elements in this example) is applied between the electrodes, a different direction θ (θ is the emission or incident surface of ultrasonic waves, that is, vibration) depending on the signal frequency. The ultrasonic beam can be emitted and made incident at an angle formed by the normal direction of the child array surface and the emission or incident direction of the ultrasonic wave. The arc line shown in FIG. 2 indicates the wavefront, and the phase differs by 180 degrees between the solid line and the broken line. Since the phases of adjacent wavefronts at the same time are reversed, they are canceled in the normal direction, and the incident radiation of the ultrasonic beam is two directions symmetrical to the normal direction of the emission surface of the ultrasonic wave (shown in FIG. 2). The direction of the solid line and the dotted line). This incident radiation angle θ
Is given by the equation 1 as the oscillator pitch d, the driving frequency f, and its wavelength λ. θ = sin ⁻¹ (λ / (2d)) (1) Further, the far distance sound field directivity characteristic R (θ) at this time is given by the following equation 2. R (θ) = sin (0.5n (φ−γ)) / sin (0.5 (φ−γ)) φ = π, γ = 2πdsin (θ) / λ (2) Utilizing these relationships The ultrasonic beam is scanned, and the ultrasonic beam can be sector-scanned by frequency sweeping with one signal line. Regarding variable aperture scanning, Japanese Patent Publication No. 54-18932 describes controlling the ultrasonic beam width by selecting a transducer.

[0003]

In the above-mentioned prior art, the directivity of the ultrasonic beam changes depending on the signal frequency, and the so-called azimuth resolution is low when the ultrasonic beam and the emitting angle θ are large due to the high frequency signal with a small emitting angle θ. There was a problem that the frequency signals were different. An object of the present invention is to reduce the difference in lateral resolution due to the radiation angle θ. Another object is to reduce the difference in azimuth resolution also in the direction (short axis direction) orthogonal to the scanning surface of the ultrasonic beam. Furthermore, it aims at improving range resolution.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to have means for changing the diameter of an ultrasonic wave transceiver in which the direction of transmitting or receiving an ultrasonic beam changes depending on the signal frequency, and the ultrasonic wave transceiver. This can be achieved by changing the aperture depending on the signal frequency or the radiation direction of.
Further, it is achieved by two-dimensionally changing the means for changing the diameter on the ultrasonic wave emitting surface of the ultrasonic wave transmitter / receiver. Another object is achieved by changing the wave number of a signal that drives the ultrasonic transducer according to the aperture.

[0005]

In general, the zero point of the beam due to the diffraction of the rectangular oscillator having the diameter d is given by the equation 3.

R (θ) = sin (z) / z (3) z = (πd / λ) sin (θ) The inverted polarization array shown in FIG. 2 is obliquely arranged, and a beam of 60 ° is swept from θ = 30 °. Then, dc for 30 degrees
The substantial aperture of the ultrasonic beam can be approximated as os (30 °). As is clear from Equation 3, the angle of the zero point changes by changing the aperture d. That is, the azimuth resolution can be controlled. The same applies to the direction orthogonal to the scanning direction of the ultrasonic beam, that is, the short axis direction. A good ultrasonic beam can be obtained in the depth direction by transmitting and receiving multiple times in the same direction and changing the aperture. Also, by changing the aperture depending on the sweep angle, a good ultrasonic beam can be obtained, and the difference in lateral resolution due to the sweep angle can be reduced. In addition, since an ultrasonic beam can be basically formed with a burst wave having a half of the number of elements forming the aperture, when the aperture is changed, it is driven with a burst wave having a half of the number of elements included in the aperture. Therefore, the distance resolution can be improved. In other words, if the total aperture is composed of 20 elements, it is possible to form an ultrasonic beam by driving with 10 waves, but if the variable aperture is reduced to 10 elements, it becomes 5
An ultrasonic beam can be formed by the driving wave number of the wave. Therefore, since the range resolution is almost inversely proportional to the wavelength and the wave number, the range resolution can be improved.

[0007]

Embodiments of the present invention will be described below with reference to FIGS. 1 and 4 to 6. By using the transducer array 1 in which the ultrasonic transducers are alternately inverted and polarized, it is possible to change the direction in which ultrasonic waves are transmitted or received depending on the signal frequency. A method for obtaining a good ultrasonic beam by changing the aperture and improving the azimuth resolution in an ultrasonic transducer in which the direction of transmitting or receiving ultrasonic waves changes depending on the signal frequency will be described. FIG. 1 shows a first embodiment in which a hot electrode is divided and a vibrator array 1 is driven. In FIG. 1, the diameter D of the vibrator array 1 is divided into a diameter D ₁ , a diameter D ₂ and a diameter D ₃ and driven by the hot electrodes 2a, 2b and 2c (the ground electrode is not shown). Drive diameter D ₁ is hot electrode 2
It is possible to change the aperture by a and perform variable aperture scanning. The ultrasonic beam in the direction θ _{1 at} the driving frequency f ₁ is driven by the hot electrode 2a, and the ultrasonic beam in the direction θ _{2 at} the driving frequency f _{2 is} driven by the hot electrodes 2a, 2b, 2c. In FIG. 1, the ultrasonic wave transmitter / receiver 1 is held in a tilted state, and an ultrasonic beam in the direction θ ₁ at the driving frequency f _{1 and} an ultrasonic beam pattern in the direction θ _{2 at} the driving frequency f ₂ are shown for comparison. . In specific real diameter of the ultrasonic beam approximation, direction theta ₁ at _{d 1 = D 1 · cos (} θ 1), the in direction _{θ 2 d 2 = D · cos} (θ 2).

On the other hand, the diameter D of the ultrasonic transmitter / receiver 1
FIG. 3 shows an ultrasonic beam pattern according to a conventional driving method in which the laser beam is driven by the hot electrode 2d without dividing (the ground electrode is not shown). In Figure 3, but to drive the respective ultrasound beams in a direction theta ₂ by way theta ₁ and the driving frequency f ₂ by same driving frequency f ₁ and FIG. 1, substantially the diameter of the ultrasonic beam is an approximation, the direction theta _{In 1} d ₁ = D · cos
(Θ ₁ ) and in the direction θ ₂ , d ₂ = D · cos (θ ₂ ).
In the conventional driving method of FIG. 3, there is a large difference in the effective aperture between the directions θ ₁ and θ ₂ and a large difference in the lateral resolution. In FIGS. 1, 2, 3, and 6, arrows indicate the wavefront propagation directions,
In FIGS. 1 and 3, the ultrasonic beam in the direction θ ₂ is indicated by a thick line. The diffraction effect appears from the far sound field, and the distance is represented by Equation 4. ^{x = D 2 / λ (4} ) D: diameter, lambda: wavelength, x: as shown in distance Figure 1 near field, as well a substantially diameter d ₂ direction theta _2, the direction theta ₁ By changing the substantial aperture by the hot electrode 2a, it is possible to eliminate the difference in the actual aperture of the ultrasonic beam between the direction θ ₁ and the direction θ ₂ . As a result,
There is almost no difference in azimuth resolution between the directions θ ₁ and θ ₂ . Of course, the influence of frequency occurs in the region where the diffraction angle is large. Also, by using an acoustic lens or by making the shape of the ultrasonic transmitter / receiver itself curved, it is possible to improve the azimuth resolution in the same manner even when the ultrasonic beam is converged. However, in this case, it is necessary to consider the influence of spherical aberration.

A method of changing the wave number of a signal for driving an ultrasonic wave transmitter / receiver according to the aperture to improve the distance resolution and a method of scanning a variable aperture also in the direction (short axis direction) orthogonal to the scanning plane of the ultrasonic beam are described. To do. FIG. 4 shows the configuration of the ultrasonic transducer of the second embodiment capable of variable aperture scanning including the short axis direction (upper and lower arrows indicate polarization directions).
In the present embodiment, the means for changing the diameter changes the diameter two-dimensionally on the ultrasonic wave emitting surface of the ultrasonic transducer. A rectangular hot electrode 2e is provided in the center of the surface facing the ground electrode 3, a hot electrode 2f electrically insulated and isolated is provided around this, and a hot electrode 2e electrically insulated and isolated around the hot electrode 2f is provided. An electrode 2g is provided. In this example, a desired number of electrically isolated hot electrodes are concentrically arranged. FIG. 4 shows an example of three divisions.
A non-conduction process is performed between the hot electrodes. For example, each hot electrode is separated by providing a gap between the hot electrodes or providing an insulator. Of course, the oscillator array 1 itself may be provided with grooves or separated. In this way, the direction orthogonal to the scanning plane of the ultrasonic beam (short axis direction)
Also, the variable caliber becomes possible.

FIG. 5 shows an example of an ultrasonic beam according to the second embodiment of the present invention. FIG. 5 is an ultrasonic beam of multi-stage transmission / reception in the same direction when the portion of the ultrasonic transmission / reception device divided by the hot electrodes 2e and 2f in the second embodiment shown in FIG. The shape is shown. A small-aperture drive by the hot electrode 2e transmits and receives a short distance, and a large-aperture drive by the hot electrodes 2e and 2f performs a long-distance transmission and reception, and a good ultrasonic beam can be obtained over the entire depth. Further, in the conventional method shown in FIG. 2, the distance resolution is poor because driving is performed with a wave that is half the number of elements forming the aperture. Therefore, in addition to the variable aperture scanning, depending on the number of elements forming the aperture, as shown in FIG. 4, for example, when the number of elements is 4, the hot electrode 2e is 2 waves and when the number of elements is 8, the hot electrode 2e is 4 waves. And 2f, 12 elements produce 6 waves with hot electrodes 2e, 2f and 2g.
Thus, each can be driven to improve the distance resolution. FIG. 6 shows a third embodiment of another variable aperture scanning (upper and lower arrows indicate polarization directions). The hot electrode of the array transducer 1 including 8 elements is, for example, a wave transmitter / receiver divided into 2i and 2h. Since there are 8 elements, a driving wave number of 4 waves is required, but both large and small diameters are driven by 2 waves. When the aperture is small, switch off. Therefore, a signal is applied only to the hot electrode 2h, and signals are transmitted and received with a diameter of 4 elements. When the diameter is large, the switch is closed and the hot electrodes 2h and 2i are operated. At this time, since the delay time τ is inserted in the hot electrode 2h, when the two waves are radiated from the hot electrode 2h, the two waves radiated from the hot electrode 2i end, and the two ends from the beginning. Up to 4 waves. Therefore, although the aperture is 8 elements of large aperture, it can be driven by 2 waves of 4 elements of small aperture. As a result, while having the azimuth resolution for large aperture and the distance resolution for small aperture. Can be realized. The reception of waves can be realized by providing similar delay control means.

As described above, the aperture is changed in accordance with the frequency for driving the ultrasonic wave transmitter / receiver or the direction of emission of the ultrasonic wave and the ultrasonic wave is transmitted or received a plurality of times to electrically scan the ultrasonic beam with a small number of signal lines. The ultrasonic beam can be improved and good image quality can be obtained. The configuration for improving the ultrasonic beam of the ultrasonic transducer has been described above, but it is possible to incorporate the ultrasonic transducer into a catheter, combine it with laser treatment, apply it to a catheter for balloon pumping, etc. .. Further, a blood pressure measuring piezoelectric vibrator, a blood flow velocity measuring piezoelectric vibrator, and the like may be combined with the catheter. Further, although the ultrasonic transducer having an evenly-spaced transducer array has been described, it is also applicable to an ultrasonic transducer having an array of transducers with irregular intervals such as M series and Barker series. is there. Further, the electrodes may be arranged with the same polarization direction and different electrode pitches and electrode widths. Further, the signal processing method can be changed to another method capable of time compression such as a correlation method. Further, it is naturally possible to apply to two-dimensional, three-dimensional or Doppler measurement. Furthermore, it is possible to use all of them together with the known technology regarding a normal inverted polarization array sound source such as curved surface array and addition of acoustic lens.

[0012]

As described above, according to the present invention, it is possible to improve the ultrasonic beam of the ultrasonic transducer which can electrically scan the ultrasonic beam with a small number of signal lines and obtain a tomographic image. Image quality can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an ultrasonic transducer according to a first embodiment in which a hot electrode is divided and driven according to the present invention.

FIG. 2 is a view for explaining the principle of driving a polarized array of transducers that are alternately inverted by frequency sweeping.

FIG. 3 is a diagram showing an ultrasonic beam pattern according to a conventional driving method.

FIG. 4 is a perspective view showing the configuration of an ultrasonic wave transmitter / receiver according to a second embodiment of the present invention, which is capable of scanning a variable aperture including the direction of the short axis.

FIG. 5 is a perspective view showing an example of an ultrasonic beam according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing a third embodiment of another variable aperture scanning according to the present invention.

[Explanation of symbols]

1 ... Array transducer, 2, 2a, 2b, 2c, 2d, 2e,
2f, 2g, 2h, 2i ... Hot electrode, 3 ... Ground electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Narendra Sangbi 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (7)

[Claims] 1. An ultrasonic wave transmitter / receiver having means for changing a diameter of an ultrasonic wave transmitter / receiver in which a direction of transmitting or receiving an ultrasonic wave changes depending on a signal frequency. 2. The ultrasonic transducer according to claim 1, wherein the means for changing the diameter can be changed two-dimensionally on a radiation surface of the ultrasonic transducer. 3. The ultrasonic wave transmitter / receiver according to claim 1, wherein the wave number of the drive signal of the ultrasonic wave transmitter / receiver is changed depending on the diameter. 4. The ultrasonic transducer according to any one of claims 1 to 3, wherein the diameter is changed according to the driving frequency of the ultrasonic transducer or the radiation direction of the ultrasonic waves. 5. The ultrasonic wave transmitter / receiver according to claim 1, wherein the ultrasonic wave is transmitted or received a plurality of times by changing the aperture in the drive frequency or the ultrasonic wave emission direction. The ultrasonic transmitter / receiver described. 6. The ultrasonic transducer according to claim 1, wherein the ultrasonic transducer comprises an array of transducers that are alternately inverted and polarized. 7. A catheter incorporating the ultrasonic transducer according to any one of claims 1 to 7, which has a visual field in the advancing direction of the catheter.