JPS599859B2 - variable frequency ultrasound transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable frequency ultrasonic probe, and particularly to a variable frequency ultrasonic probe using an electroacoustic transducer having broadband 5-frequency characteristics.

There are 10 well-known ultrasonic probes that perform ultrasonic flaw detection or ultrasonic diagnosis by transmitting ultrasonic pulses into a sound field medium and receiving reflected echoes from the sound field medium. A metal weld, a subject to be diagnosed, etc. are known as the medium. The conventional ultrasonic probe has a configuration 15 whose transmission frequency is set to the resonant frequency of the electroacoustic transducer provided in the probe, and which transmits and receives ultrasonic pulses of a single frequency. The drawback was that the range of use of the tentacles was restricted. For example, in an ultrasonic diagnostic device that uses ultrasonic pulses to display a tomographic image of a subject on a cathode ray tube or the like, the higher the frequency of the ultrasonic pulses, the higher the resolution of the displayed image 20, which improves the resolution of minute parts of the subject. It becomes possible to conduct detailed observations.

However, as the frequency of the ultrasonic pulse increases, the propagation attenuation of the ultrasonic wave due to biological tissues increases rapidly, resulting in a problem that the sensitivity at long distances decreases.
It becomes difficult to display images of objects with a large depth range uniformly and with good resolution, and it is not always possible to obtain good diagnostic results with high-frequency ultrasonic pulses alone, and the frequency can be varied over a wide range. A probe was desired.
Furthermore, the propagation attenuation of 30 ultrasonic waves within a living tissue differs depending on each tissue, and this also requires changing the frequency of the ultrasonic pulse for each diagnostic site. As mentioned above, the transmission frequency of conventional probes is fixed to a single value, so in conventional ultrasonic 35 diagnostic equipment, multiple probes with different transmission frequencies are used for each diagnosis. A method is adopted in which the device is replaced according to the location or diagnostic depth.

However, conventional devices require complicated probe replacement work and take a long time to diagnose, which significantly impedes the advantage of ultrasound diagnostic devices, which is the ability to observe tomographic images in real time. There was a drawback.

Especially in recent years, tissue characteristics
In research such as rizatiOn), images of the same diagnostic site are displayed at different frequencies, and tissue characteristics are determined from these multiple image changes, and image signals are obtained while exchanging multiple probes. However, there are problems such as the diagnosis site moving due to the movement of the subject during probe exchange, such as the subject's breathing. It was impossible to judge. The present invention has been made in view of the above-mentioned conventional problems,
The purpose is to provide an improved variable frequency probe that can obtain ultrasonic pulses with widely varying transmit frequencies using a single probe.

In order to achieve the above object, the present invention includes an electroacoustic transducer that transmits ultrasonic pulses into a sound field medium and receives reflected echoes from the sound field medium, and an electroacoustic transducer that is attached to the wave transmitting/receiving surface of the electroacoustic transducer. A matching layer deposited on the electroacoustic transducer, the layer thickness of which is set to approximately 1/4 wavelength of the resonant frequency of the electroacoustic transducer in order to widen the response frequency characteristics of the electroacoustic transducer; It is characterized by including a plurality of resonant circuits for switching the transmission frequency of the ultrasonic pulses transmitted from the conversion element, and a selector for selectively connecting the plurality of resonant circuits to the electroacoustic conversion element. do.

Preferred embodiments of the present invention will be described below with reference to the drawings.

The present invention improves the response frequency characteristics of the electroacoustic transducer by inserting a matching layer having a layer thickness of approximately 1/4 wavelength of the resonant frequency of the electroacoustic transducer between the electroacoustic transducer and the sound field medium. Focusing on the fact that it can be made into a wide band, the present invention is characterized by forming a probe that can select any transmission frequency within this wide band frequency range.

The principle of widening the response frequency characteristic of such an electroacoustic transducer element has been analyzed by the present inventors, for example, in pages 242 to 249 of Journal of the Society of Electronics and Communication Engineers 73/4V01.56-Afu 4. It is described as a piezoelectric transducer in which a 1/4 wavelength intermediate medium layer is inserted between the piezoelectric transducer and the acoustic field medium.

Conventionally, widening the band of such an electroacoustic transducer is used simply to shorten the ultrasonic pulse width, but in the present invention, this broadband electroacoustic transducer is used to perform variable frequency ultrasonic detection. The focus was on the fact that tentacles can be obtained. FIG. 1 shows a preferred embodiment of the variable frequency ultrasonic probe according to the present invention, which transmits ultrasonic pulses into a sound field medium such as a subject and emits reflected echoes from the sound field medium. The electroacoustic transducer 10 includes an electroacoustic transducer 10 that receives waves, and two matching layers 12 and 14 attached to the wave transmitting and receiving surfaces of the electroacoustic transducer 10.

In the embodiment, the electroacoustic transducer element 10 is made of lead zirconium titanate, and excitation signals are supplied from input terminals 16 and 18, and ultrasonic pulses pass through both matching layers 12 and 14 from the transmitting and receiving wave surface due to the piezoelectric effect, as shown in the figure. The waves are transmitted into a sound field medium such as an object that does not The matching layers 12 and 14 each have a layer thickness that is approximately 1/4 of the resonant frequency of the electroacoustic transducer 10.
In one embodiment, matching layer 12 is comprised of fused silica and matching layer 14 is formed from epoxy resin. By pasting the matching layers 12 and 14 described above, the electroacoustic transducer 10 has a wide response frequency characteristic,
In FIG. 2, the transmitting and receiving overall response characteristics (receiving voltage/transmitting voltage) are plotted on the vertical axis with respect to the frequency f on the horizontal axis, and the matching layer 12,
The characteristics of the electroacoustic transducer 10 without 14 are shown at 100, and the characteristics when the two matching layers 12 and 14 of this example are attached are shown at 200.

As is clear from FIG. 2, while the fractional bandwidth in the conventional characteristic 100 is about 1/5 to 1/10, the fractional bandwidth in the example characteristic 200 is expanded to about 1, and the bandwidth is significantly increased. It is understood that the range is getting wider, and at the same time it becomes clear that the sensitivity shown on the vertical axis is increasing. The resonant frequency of the electroacoustic transducer 10 is uniquely determined from its thickness, and as a result, the layer thicknesses of the matching layers 12 and 14 are also set corresponding to the electroacoustic transducer 10, for example, 2MH
At the resonant frequency of z, by setting the layer thickness of each of the matching layers 12 and 14 to about 0.3751110.3311, it is possible to achieve a good wide band. As is clear from the embodiment shown in FIG. 1, a sound absorbing material 20 having an acoustic backing effect is provided on the back surface of the electroacoustic transducer 10, and effectively damps the continuation of mechanical free vibration of the electroacoustic transducer 10. As a result, the Q of the vibration system can be lowered, and the characteristic 200 in FIG. In the embodiment, the acoustic backing effect of the sound absorbing material 20 is set to a predetermined amount while adjusting the damping of free vibration and the reduction in sensitivity. As described above, a plurality of resonant circuits for switching the transmission frequency of ultrasonic pulses transmitted from the element 10 are connected to the electroacoustic transducer element 10 whose response frequency characteristics have been made broadband by the matching layers 12 and 14. In FIG. 1, the resonant circuit consists of two resonant circuits 22 and 24 connected in parallel to input terminals 16 and 18, and both resonant circuits 22 and 24 are each formed from a parallel circuit of a resistor and an inductance. There is.

Selectors 26 and 28 shown as switches in FIG. Connected. In the present invention, by selectively connecting the resonant circuits 22 and 24 to the electroacoustic transducer 10, the frequencies of the ultrasonic pulses transmitted from the electroacoustic transducer 10 become two different frequencies, and the selector 26 , 28, a desired frequency can be selected. By setting both of the frequencies within the flat frequency range of the broadband characteristic 200 shown in FIG. 2, it is possible to perform transmission and reception operations with uniform sensitivity using ultrasonic pulses of different frequencies. Become. As described above, according to the present invention, it is possible to transmit and receive ultrasonic pulses of arbitrarily selected frequencies within a wideband frequency range,
It is possible to obtain tomographic images under the optimal conditions suitable for the diagnostic site or diagnostic depth of the subject using a single probe, and it is possible to obtain continuous tomographic images at different frequencies without the need to replace the probe. By emitting ultrasonic pulses into the subject, it becomes possible to observe biological tissue in terms of tissue characteristics.

In the embodiment, two resonant circuits are used, but any number of circuits can be set, and it is also possible to use a variable frequency resonant circuit that continuously changes the resonant frequency. The selector is not only a simple switch, but also a selector that electronically selects the resonance characteristic.

Further, in the embodiment, only a configuration using a single electroacoustic transducer element is shown, but in the present invention, each element of an array type probe in which a plurality of electroacoustic transducer elements are arranged in a plane. It is also possible to obtain a variable frequency ultrasonic probe by connecting a plurality of resonant circuits and a selector that selectively connects the plurality of resonant circuits to the electroacoustic transducer.

FIG. 3 shows a preferred first embodiment of an ultrasonic diagnostic apparatus using a variable frequency ultrasonic probe according to the present invention.

In FIG. 3, a variable frequency ultrasonic probe 30 has the configuration shown in FIG.
, 14 are transmitted into the subject.

The reflected echo reflected from the subject is received by the probe 30, received and detected by the receiver 34, and the reflected echo signal is supplied as a luminance modulation signal to a display 36 such as a cathode ray tube. A control signal is supplied from a synchronization control circuit 38 to the transmitter 32, receiver 34, and display 36 described above, and transmission/reception control and sweep control of the display 36 are performed.
In order to selectively switch and control the transmission frequency of the variable frequency ultrasonic probe 30, a signal from the synchronous control circuit 38 is supplied to the probe 30 via the switching circuit 40, and the desired transmission frequency is set. is selected. A preferred embodiment of the switching circuit 40 is shown in FIG. 4, in which the control signal of the synchronous trigger circuit 38 is supplied from an input terminal 42 to a trigger signal generator 44, which trigger signal is applied to a flip-flop 46, By connecting the Q output terminal 48 of 46 to the first selector 26 and the Q output terminal 50 to the second selector 28, a double selector consisting of a reed relay or the like or an analog switch using a semiconductor, etc. 26 and 28 can be selectively turned on and off.

Therefore, according to the ultrasonic diagnostic apparatus shown in FIGS. 3 and 4, the transmission frequency of the probe 30 is switched and controlled by the synchronous control circuit 38, and in the embodiment, two different transmission Depending on the frequency, it is possible to transmit two types of ultrasound pulses suitable for diagnosis sites at different depths in the subject. In the first embodiment of the ultrasonic diagnostic apparatus shown in FIGS. 3 and 4, since ultrasonic pulses of different frequencies are transmitted to diagnostic sites at different depths, the display 3
6, it is necessary to display the tomographic images obtained from both ultrasonic pulses separately, and for this purpose, the switching circuit 40 in the embodiment has a dividing X-axis for dividing the display screen corresponding to both frequencies. A deflection signal is output.

That is, a normal single-screen X-axis deflection signal is supplied to a terminal 52, and this deflection signal is added to the Q output of the flip-flop 46 in an adder 54, and output from the output terminal 56 to the display 36 as a divided X-axis deflection signal. Supplied to the X-axis deflection input terminal. FIG.
An example of two tomographic images is shown, and image A is a case where the transmission frequency of the ultrasonic pulse is low, and although the resolution is slightly inferior, it is possible to obtain a clear image to a relatively deep depth.

On the other hand, image B is an image obtained by high-frequency ultrasonic pulses, and is an image with extremely good resolution in a shallow depth region close to the probe 30, but in a region far from the probe 30. It is understood that the display is performed with low sensitivity. In the first embodiment of the ultrasonic diagnostic apparatus, the fifth
As is clear from the figure, since a separate image is displayed for each ultrasonic pulse having a different frequency, it is possible to uniformly control the sensitivity of the diagnostic apparatus itself. FIG. 6 shows a second embodiment of an ultrasonic diagnostic apparatus using a variable frequency ultrasonic probe 30 according to the present invention, and the same members as those in the embodiment of FIG. 3 are given the same symbols. The explanation will be omitted. The second embodiment is characterized in that a single image is displayed on the display screen of the display 36, and for this purpose, while changing the transmission frequency of the ultrasonic pulse, the reflected echoes obtained at each frequency are The signals are superimposed and displayed on the same screen of the display 36 as brightness modulation signals, and the sensitivity characteristics of the ultrasonic diagnostic device are changed corresponding to each frequency, so that only the sensitivity in the depth region corresponding to the selected transmission frequency is displayed. By setting the value to an optimal value and superimposing the images multiple times, it is possible to obtain images with good resolution over a wide range from short distances to long distances.

In FIG. 6, a variable sensitivity control circuit 58 is connected to the receiver 34.
A signal from the synchronous control circuit 38 is supplied through the synchronous control circuit 38, and the sensitivity characteristics are switched and controlled in synchronization with the switching of the transmission frequency.

That is, when using high-frequency ultrasonic pulses, the amplification gain of the receiver 34 is lowered for long-distance reflected echoes, and as a result, an image in which only short-distance reflected echoes are emphasized is supplied to the display 36. In addition, when using a low-frequency ultrasonic pulse, the variable sensitivity control circuit lowers the amplification gain for the short-distance reflected echoes so that only the long-distance reflected echoes are emphasized and supplied to the display 36. Select the sensitivity characteristics of By selecting such sensitivity characteristics, it is possible to obtain images of good quality over the entire depth range, making it possible to obtain accurate diagnostic information. Normally, the repetition frequency of the trigger signal of the trigger signal generator 44 is 1Vk,
Therefore, flickering does not occur in the image on the display 36 due to frequency switching, and sensitivity characteristics can be selected by appropriately setting the rate of change with respect to time when switching the amplification gain. It becomes possible to eliminate discontinuities in the connecting portions. As explained above, according to the variable frequency ultrasonic probe according to the present invention, it is possible to transmit and receive ultrasonic pulses of multiple frequencies using a single probe.

Therefore, detailed image information can be obtained in real time with a marked reduction in diagnostic time, and images at different frequencies can be obtained from the same diagnostic site. Furthermore, it becomes possible to observe the characteristics of living tissue from the reflected echo intensity due to the difference in frequency, and it becomes possible to use it in a wide range of ultrasonic diagnostic devices. The probe according to the present invention can be applied not only to ultrasound diagnostic equipment but also to a wide range of other equipment that utilizes ultrasound.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the variable frequency ultrasonic probe according to the present invention, and FIG. 2 shows the response frequencies of a conventional probe and the variable frequency ultrasonic probe according to the present invention. Characteristic diagram,
FIG. 3 is a block circuit diagram showing a preferred first embodiment of an ultrasound diagnostic apparatus using a variable frequency ultrasound probe according to the present invention, and FIG. 4 is a preferred embodiment of the switching circuit in FIG. 3. FIG. 5 is an explanatory diagram showing an example of a display image in the first embodiment of the ultrasonic diagnostic apparatus, and FIG. 6 is an ultrasonic diagnostic apparatus using the variable frequency ultrasonic probe according to the present invention. FIG. 3 is a block diagram showing a second preferred embodiment of the invention. 10... Electroacoustic conversion element, 12, 14...
... Matching layer, 20 ... Sound absorbing material, 22, 24.
... Resonance circuit, 26, 28 ... Selection circuit, sonic probe. 30...Variable frequency exceeds

Claims (1)

[Claims] 1. An electroacoustic transducer that transmits ultrasonic pulses into a sound field medium and receives reflected echoes from the sound field medium;
This is a matching layer attached to the wave transmitting/receiving surface of the electroacoustic exchange element, and in order to widen the response frequency characteristics of the electroacoustic transducer, the layer thickness is approximately 1 of the resonant frequency of the electroacoustic transducer.
/4 wavelength, a plurality of resonant circuits for switching the transmission frequency of the ultrasonic pulses transmitted from the electroacoustic transducer, and an electroacoustic transducer that selectively switches between the plurality of resonant circuits. a selector connected to the variable frequency ultrasound transducer; 2. In the probe according to claim 1, the matching layer is composed of a plurality of stacked matching layers, and the thickness of each matching layer is set to approximately 1/4 wavelength of the resonant frequency of the electroacoustic transducer. A variable frequency ultrasonic probe characterized by: 3. A variable frequency ultrasonic probe according to claim 1 or 2, characterized in that a sound absorbing material is provided on the back surface of the electroacoustic transducer.