JPS6243687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic diagnostic apparatus, and particularly to an ultrasonic diagnostic apparatus using an electroacoustic transducer having broadband frequency characteristics.

2. Description of the Related Art Ultrasonic diagnostic apparatuses that perform ultrasonic diagnosis by transmitting ultrasonic pulses into a subject and receiving reflected echoes from a diagnostic site are well known. In this type of ultrasonic diagnostic equipment, the conventional ultrasonic probe that transmits and receives ultrasonic pulses has its transmission frequency set to the resonant frequency of the electroacoustic transducer provided in the probe. Since it is configured to transmit and receive ultrasonic pulses of only one frequency, it has the disadvantage that the diagnostic range is restricted.

For example, in an ultrasonic diagnostic apparatus, the higher the frequency of ultrasonic pulses, the higher the resolution of a displayed image, making it possible to observe minute parts of a subject in detail. However, as the frequency of ultrasound pulses increases, the propagation attenuation of ultrasound waves due to biological tissue increases rapidly, resulting in a problem that sensitivity at long distances decreases. In addition, it has become difficult to display images with good resolution, and it is not necessarily possible to obtain good diagnostic results using only high-frequency ultrasonic pulses, so a probe that can vary the frequency over a wide range has been desired. Furthermore, the propagation attenuation of ultrasound within living tissues differs depending on each tissue, and this also requires changing the frequency of ultrasound pulses for each diagnostic site.

As mentioned above, the transmission frequency of conventional probes is fixed to a single value, so in conventional ultrasound diagnostic equipment, multiple probes with different transmission frequencies are used for each diagnosis site. Alternatively, a method is adopted in which the probe is replaced according to the diagnostic depth. Therefore, conventional devices have disadvantages in that they require complicated probe replacement work, take a long time to diagnose, and significantly impede the advantage of ultrasonic diagnostic devices, which is the ability to observe tomographic images in real time. Ta. In particular, in recent research on tissue characterization, images of the same diagnostic site are displayed at different frequencies, and tissue characteristics are determined from these multiple image changes. It is necessary to obtain an image signal while exchanging the probe, and there is a particular problem that the diagnostic site moves due to movement of the subject, such as the subject's breathing, during the exchange of the probe.
It has been virtually impossible to determine the tissue characteristics of the same diagnostic site with conventional devices.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and its purpose is to improve the ability to utilize ultrasonic pulses with a plurality of transmitting frequencies that vary over a wide range using a single electroacoustic transducer. The purpose of the present invention is to provide an ultrasonic diagnostic device that is

In order to achieve the above object, the present invention provides an electroacoustic transducer that transmits ultrasonic pulses into a subject and receives reflected echoes from the subject, and an electroacoustic transducer that is attached to the wave transmitting/receiving surface of the electroacoustic transducer. Two matching layers whose layer thickness 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 and a plurality of transmitters. a variable frequency ultrasonic probe comprising a number of resonant circuits for supplying ultrasonic pulses at a wave frequency and a selector for selectively connecting the plurality of resonant circuits to an electroacoustic transducer; a transmitter that provides an excitation signal to the frequency ultrasound probe;
The variable frequency ultrasonic probe receives the reflected echoes in synchronization with the switching of the selector, and transmits a high transmission frequency signal at a short distance so that the sensitivity of a low transmission frequency signal increases at a long distance. A receiver that converts the sensitivity characteristics into a brightness modulation signal by switching the sensitivity characteristics using a variable sensitivity control circuit so that the sensitivity of a display device that superimposes and displays images of the above, and a switching circuit that switches and controls a selector of the variable frequency ultrasound probe to variably control the frequency of ultrasound pulses transmitted from the probe. It is characterized by

In the present invention, the switching circuit includes a divided X-axis deflection signal generator, and supplies a divided X-axis deflection signal to the display device in synchronization with frequency switching of the ultrasonic pulse to display a separate image on the display device for each frequency. It is preferable to display.

Further, in the present invention, a variable sensitivity control circuit is connected to the receiver, and the sensitivity characteristics of the receiving system are switched and controlled in synchronization with the switching of the transmission frequency of the ultrasonic pulse,
Preferably, a plurality of display images obtained by changing the transmission frequency are displayed in a superimposed manner on a display.

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

The present invention achieves a response of the electroacoustic transducer by inserting two matching layers 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 the frequency characteristics can be widened, the present invention is characterized by using a probe that can select any transmission frequency within this widened 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 the Journal of the Institute of Electronics and Communication Engineers '73/4 Vol. 56-A No. 4, Nos. 242 to 249.
The page describes it as a piezoelectric transducer with a 1/4 wavelength intermediate medium layer inserted between the piezoelectric transducer and the acoustic field medium. Conventionally, widening the band of such an electroacoustic transducer is simply used to shorten the ultrasonic pulse width, but in the present invention,
This paper focuses on the fact that a variable frequency ultrasonic probe that utilizes this broadband electroacoustic transducer can provide good diagnostic effects.

FIG. 1 shows a preferred embodiment of the variable frequency ultrasonic probe used in the ultrasonic diagnostic apparatus according to the present invention, which transmits ultrasonic pulses into a subject and also transmits ultrasonic pulses reflected from the subject. It includes an electroacoustic transducer element 10 that receives echoes, and two matching layers 12 and 14 attached to the wave transmitting/receiving surface of the electroacoustic transducing element 10. The electroacoustic transducer 10 is made of lead zirconium titanate in the embodiment, and has input terminals 16 and 18.
An excitation signal is supplied from the oscilloscope, and an ultrasonic pulse is transmitted from the wave transmitting/receiving surface through both matching layers 12 and 14 into a subject (not shown) due to the piezoelectric effect. Matching layer 1
2 and 14, each of which has a layer thickness set to approximately 1/4 wavelength of the resonant frequency of the electroacoustic transducer 10, and in the embodiment, the matching layer 12 is made of fused silica,
Furthermore, the matching layer 14 is made of epoxy resin.

Due to the adhesion of the matching layers 12 and 14 described above, the response frequency characteristic of the electroacoustic transducer element 10 becomes broadband, and in FIG. voltage) is taken, the characteristics of the electroacoustic transducer 10 without matching layers 12 and 14 are at 100, and the characteristics when the two matching layers 12 and 14 in this example are pasted are at 200. It is shown. As is clear from Figure 2, the fractional bandwidth for the conventional characteristic 100 is 1/5~
While it is about 1/10, the fractional bandwidth in the example characteristic 200 is expanded to about 1, which shows that the bandwidth has become significantly wider, and at the same time, the sensitivity shown on the vertical axis has increased. It becomes clear that there is. The resonant frequency of the electroacoustic transducer 10 is uniquely determined from its thickness, and as a result, the matching layer 12,
The layer thicknesses of the matching layers 12 and 14 are also set corresponding to the electroacoustic transducer 10. For example, at a resonance frequency of 2 MHz, the layer thicknesses of the matching layers 12 and 14 are set to approximately 0.75 mm.
By setting the width to about 0.33 mm, it is possible to achieve a good wide band.

As is clear from the embodiment shown in FIG.
0 can be effectively damped, and as a result, the Q of the vibration system can be lowered, and the characteristic 200 in FIG. 2 can be further broadened. On the other hand, this has the disadvantage of causing a decrease in transmission and reception sensitivity, and in the embodiment, the acoustic bucking effect of the sound absorbing material 20 is set to a predetermined amount while adjusting the damping of free vibration and the decrease in sensitivity.

As described above, the electroacoustic transducer 10 has a broadband response frequency characteristic due to the matching layers 12 and 14.
A plurality of resonant circuits are connected to the input terminal 1 for switching the transmission frequency of the ultrasonic pulses transmitted from the element 10, and in FIG.
two resonant circuits 22 connected in parallel to 6 and 18;
24, and both resonant circuits 22 and 24 are each formed from a parallel circuit of a resistor and an inductance. Selectors 26 and 28 shown as switches in FIG.
Either one of them is selectively connected to the electroacoustic transducer 10.

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 are two different frequencies, and a desired frequency can be selected by switching the selectors 26 and 28. By setting both of the frequencies within the flat frequency range of the broadband characteristic 200 shown in Figure 2, it is possible to perform wave transmission and reception with uniform sensitivity using ultrasonic pulses of different frequencies. Become.

As described above, according to the probe used in the present invention, it is possible to transmit and receive ultrasonic pulses at arbitrarily selected frequencies within a broadband frequency range, and to It is possible to obtain tomographic images under optimal conditions suitable for depth, etc. with a single probe, and it is possible to continuously send ultrasound pulses of different frequencies into the subject without the need to replace the probe. It becomes possible to observe biological tissue in terms of tissue characteristics by emitting light.

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

FIG. 3 first shows a circuit configuration when two types of images are formed using ultrasonic pulses of different transmission frequencies.

In FIG. 3, a variable frequency ultrasound probe 30
has the configuration shown in FIG. 1, and an ultrasonic pulse that passes through the matching layers 12 and 14 from the electroacoustic transducer element 10 is transmitted into a subject (not shown) by an ultrasonic pulse excitation signal supplied from a transmitter 32. . 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 ultrasound probe 30, a control signal from the synchronous control circuit 38 is supplied to the probe 30 via the switching circuit 40, and a desired transmission frequency is selected. be done.

A preferred embodiment of the switching circuit 40 is shown in FIG.
This trigger signal is applied to a flip-flop 46 to connect the Q output terminal 48 of the flip-flop 46 to the probe 30.
By connecting the output terminal 50 to the first selector 26 and to the second selector 28, both selectors 26 and 28, each consisting of a mechanical switch such as a reed relay or an analog switch using a semiconductor, etc.
Can be selectively controlled on and off. Therefore, according to the ultrasonic diagnostic apparatus shown in FIGS. 3 and 4, the synchronization control circuit 38 controls the probe 3.
The zero transmission frequency is switched and controlled, and in the embodiment, two different ultrasound pulses can be used to transmit two types of ultrasound pulses suitable for diagnostic sites at different depths into the subject.

In the ultrasonic diagnostic apparatus shown in FIGS. 3 and 4, since ultrasonic pulses of different frequencies are transmitted to diagnostic sites at different depths, both ultrasonic pulses are displayed on the display 36. It is necessary to display the obtained tomographic images separately, and for this purpose, the switching circuit 40 in the embodiment is provided with a divided X-axis deflection signal generator to divide the display screen corresponding to both frequencies. A divided X-axis deflection signal is output. That is, the split X-axis deflection signal generator includes an adder 54 to which a normal single-screen Output terminal 56 as X-axis deflection signal
and is supplied to the X-axis deflection input terminal of the display 36.

FIG. 5 shows an example of two tomographic images obtained by using two types of ultrasonic pulses with different frequencies on the display screen of the display 36, and image A is obtained when the transmission frequency of the ultrasonic pulses is low. Although the resolution is slightly inferior, it is possible to obtain clear images up to relatively deep depths. On the other hand, image B is an image obtained by high-frequency ultrasonic pulses, and in the shallow depth region close to the probe 30, it is an image with extremely good resolution, but in the region far from the probe 30, it is an image with extremely good resolution. It is understood that the display is performed with low sensitivity.

FIG. 6 shows a circuit configuration for displaying two types of images obtained using ultrasonic pulses with different transmission frequencies on a single screen in the embodiment. While changing the transmission frequency, the reflected echo signals obtained at each frequency are superimposed and displayed on the same screen of the display 36 as a brightness modulation signal, and the sensitivity characteristics of the ultrasonic diagnostic apparatus are changed in accordance with each frequency, By setting only the sensitivity in the depth region corresponding to the selected transmission frequency to the optimal value and overlapping 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, the receiver 34 is supplied with a control signal from the synchronous control circuit 38 via the variable sensitivity control circuit 58, and the sensitivity characteristics of the receiving system 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 1KHz.
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 change rate of amplification gain switching with respect to time. It becomes possible to eliminate discontinuities at the joints.

As explained above, according to the ultrasonic diagnostic apparatus according to the present invention, it is possible to obtain the optimum ultrasonic frequency according to the diagnostic distance using a single electroacoustic transducer, and the ultrasonic pulse of this optimum frequency can be It is possible to obtain images with good resolution over a wide range from short distances to long distances.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the variable frequency ultrasonic probe used in the present invention, and FIG. 2 is a diagram showing a conventional probe and the variable frequency ultrasonic probe used in the present invention. The response frequency characteristic diagram, Figure 3, shows the characteristics of an ultrasound diagnostic device using a variable frequency ultrasound probe.
A block circuit diagram showing an example of displaying images of types,
Fig. 4 is a block diagram showing 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 example of Fig. 3, and Fig. 6 is a variable frequency ultrasonic probe. 1 is a block diagram showing a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention using 10... Electroacoustic transducer element, 12, 14... Matching layer, 20... Sound absorbing material, 22, 24... Resonance circuit, 26, 28... Selector, 30... Variable frequency ultrasound probe, 32 ...Transmitter, 34...Receiver, 36...Display device, 38...Synchronization control circuit, 4
0...Switching circuit, 44...Trigger signal generator, 5
4... Adder, 58... Variable sensitivity control circuit.

Claims (1)

[Claims] 1 An electroacoustic transducer that transmits ultrasonic pulses into a subject and receives reflected echoes from the subject, and a matching layer that is attached to the wave transmitting/receiving surface of the electroacoustic transducer. Two matching layers whose layer thickness is set to approximately 1/4 wavelength of the resonant frequency of the electroacoustic transducer in order to widen the response frequency characteristic, and to supply ultrasonic pulses of multiple transmission frequencies. a variable frequency ultrasound probe including a plurality of resonant circuits and a selector for selectively connecting the plurality of resonant circuits to an electroacoustic transducer; and an excitation signal to the variable frequency ultrasound probe. A transmitter that supplies a transmitter and a transmitter that receives reflected echoes received by the variable frequency ultrasonic probe in synchronization with the switching of the selector, and transmits signals at a short distance so that the sensitivity of a low transmission frequency signal is high at a long distance. Here we have a receiver that switches and controls the sensitivity characteristics using a variable sensitivity control circuit to increase the sensitivity of high transmission frequency signals and converts them into brightness modulation signals, and a receiver that changes the transmission frequency based on the brightness modulation signal of this receiver. A display device that superimposes and displays a plurality of images obtained by superimposing a plurality of images, and a selector of the variable frequency ultrasonic probe are switched and controlled to variably control the frequency of the ultrasonic pulses transmitted from the probe. An ultrasonic diagnostic device including a switching circuit.