JPS633614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic diagnostic apparatus used to emit ultrasonic pulses into a living body, receive and display reflected waves or transmitted waves thereof, and diagnose conditions inside the living body.

In order to improve diagnostic accuracy in ultrasonic diagnostic equipment, it is necessary to increase resolution. For this reason, attempts have been made to increase the ultrasonic carrier frequency and narrow the ultrasonic pulse width. However, the higher the ultrasound carrier frequency is, the more rapidly the attenuation of the ultrasound pulse in the living body increases. Therefore, in order to obtain a reflected wave with a sufficient SN ratio, the transmitted wave power must be increased.
However, there are currently no high-frequency, high-output transducers available, and even if such a transducer were available, the peak value of the ultrasonic pulse would be high because the output is increased with narrow pulses. This may result in adverse effects on living organisms. In other words, from the point of view of safety for living organisms, it is desirable to keep the average ultrasonic power to about 10 mV/cm ² or less and to keep the peak value as small as possible. From this point of view, conventionally 2.5~
A frequency of around 5MHz was used, and resolution was limited at this frequency.

An object of the present invention is to provide an ultrasonic diagnostic apparatus that can obtain high resolution without using a large peak power even though it uses a high carrier frequency.

According to the present invention, the frequency modulation means sequentially changes the carrier wave of the ultrasonic signal pulse from a low frequency to a high frequency during its pulse width, and emits an ultrasonic pulse whose carrier frequency changes in this way during the pulse. . The received reflected wave is supplied to a delay means whose delay time is longer as the frequency decreases in accordance with the change in the carrier wave frequency, and a compressed pulse is obtained from the output of the delay means and this is displayed on a display. do. By doing this, the pulse width of the transmitted pulse can be made relatively large, the peak value can be made small, and the carrier frequency can be made relatively high, and an output with a narrow pulse width can be obtained from the delay means, allowing high-resolution display. becomes.

Next, an embodiment of the ultrasonic diagnostic apparatus according to the present invention will be described with reference to the drawings. The output of the ultrasonic carrier signal generator 12 is pulse-modulated by the pulse from the pulse generator 11 in the modulation circuit 13, and this modulated output is applied to the ultrasonic transducer 14, which generates ultrasonic pulses. is emitted into a living body (not shown). The reflected wave of the ultrasound pulse from inside the living body is received by the ultrasound transducer 14, and the received signal is amplified by the amplifier 15 and displayed on the display 16.
supplied to For example, a cathode ray tube display is used as the display 16, and horizontal scanning is performed at the repetition period in synchronization with the transmitted pulse, and vertical deflection is performed using the received signal, or the emission point of the ultrasonic pulse is moved. At the same time, the bright spot is intensity-modulated on one scanning line according to the intensity of the received signal, and the scanning line is displayed by sequentially moving in synchronization with the movement of the radiating point.

In this invention, the carrier frequency of the transmitted ultrasonic pulse is gradually changed from lower to higher within its pulse width. For example, pulse generator 1
driving the sawtooth wave generator 17 with a pulse of 1;
A voltage signal whose voltage changes linearly in a fixed direction from the leading edge of the pulse is obtained. Further, a carrier wave signal generator 12 whose frequency is changed by voltage is used, and this carrier wave signal generator 12 is controlled by the output of a sawtooth wave generator 17 to change the frequency of the generated carrier wave signal. As such a variable frequency carrier wave signal generator, a so-called voltage controlled oscillator can be used. For example, a barrier capacitance of a hyperstep junction diode is used as a frequency determining capacitor of an LC oscillator, and a sawtooth wave generator 17 is connected to the diode. can be applied such that the frequency of the generated carrier signal varies with time. In this case, the frequency changes gradually from low to high.

In order to change the carrier frequency in this way, it is preferable that the ultrasonic transducer 14 has high sensitivity and a wide band. In conventional ultrasonic diagnostic equipment, the carrier wave frequency is fixed, so ultrasonic transducers generally use Q to increase conversion efficiency.
Narrowband devices with high efficiencies were used. However, in the diagnostic device of the present invention, an ultrasonic transducer using a PZT transducer with a wide band is used, for example.

Furthermore, in the present invention, the reflected wave received by the transducer 14 is supplied to a delay means 18. The delay means 18 has a delay characteristic in which the lower the frequency in the change band of the ultrasonic carrier frequency, the longer the delay time is. This delay characteristic is preferably such that the low frequency component at the leading edge of the received signal pulse and the high frequency component at the trailing edge coincide at the output side of the delay means 18. Such a delay means can be constructed using, for example, a dispersive filter of an all-pass band network.

In the ultrasonic diagnostic apparatus with this configuration, even if an ultrasonic pulse with a relatively small pulse amplitude and a wide pulse width is transmitted, the reflected wave will be reflected at the output side of the delay means 18 due to its delay characteristics. Detected as narrow. In other words, if the width of the ultrasonic pulse is Tμs and the variation width of the carrier wave frequency during the pulse width is △fMHz, the width of the output pulse of the delay means 18 is approximately 1/△f (μs), and the amplitude is multiplied by √△. . Therefore, resolution is not reduced. On the other hand, if the ultrasonic pulse width is the same as the conventional one, the resolution can be increased, and the peak value of the ultrasonic pulse can be made lower than the conventional one, so there is no risk of adverse effects on the living body. For example, T=20μs, △f=
In the case of 2MHz, T=50μs, and Δf=8MHz, the output pulses of the delay means 18 are 0.5μs and 0.13μs, respectively.

According to experiments, the pulse width T of the ultrasonic pulse is 3 μs.
△f is set to 1.9MHz with a center frequency of 11MHz, and the second
Using an ultrasonic transducer having the frequency characteristics shown in the figure, and using the delay means 18 having the characteristics shown in FIG. 3, it was possible to obtain a compressed pulse of approximately 0.6 μs in the output of the delay means 18. Note that the resolution of current ultrasound diagnostic equipment is approximately 2 mm, so in order to further increase the resolution by 10 times, that is, approximately 0.2 mm, the frequency change width △f must be 3.5 MHz when the center frequency is 11 MHz.
A certain degree is fine. Therefore, it is sufficient to change the frequency by about 0.32 in the fractional band.

As described above, according to the ultrasonic diagnostic apparatus of the present invention, when the ultrasonic pulse width is the same as that of the conventional one, the resolution can be increased compared to the conventional one, and the peak value of the transmitted pulse can be made smaller. I can,
Therefore, it becomes possible to further increase the carrier wave frequency, and it becomes possible to further improve resolution, and there is no risk of adverse effects on living organisms. Note that in the above, the carrier frequency was changed from a low frequency to a high frequency, but it may also be changed from a high frequency to a low frequency, and in that case, the delay means on the receiving side increases the delay time as the frequency increases. do. Further, the present invention can be applied to a diagnostic device that receives not only reflected ultrasound waves but also transmitted waves.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an ultrasound diagnostic apparatus according to the present invention, FIG. 2 is a diagram showing an example of the frequency characteristics of the ultrasound transducer 14, and FIG. 3 is a diagram showing an example of the characteristics of the delay means 18. It is a diagram. 11: Pulse generator, 12: Ultrasonic carrier signal generator, 13: Modulator, 14: Ultrasonic transducer, 1
6: Display device, 17: Sawtooth wave generator, 18: Delay means.

Claims (1)

[Claims] 1 Give an ultrasonic signal pulse to an ultrasonic transducer to emit the ultrasonic pulse to a living body, receive the reflected wave or transmitted wave by the ultrasonic transducer, and supply the received signal to a display device. In the ultrasonic diagnostic apparatus, the frequency modulation means sequentially changes the carrier frequency of the ultrasonic signal pulse applied to the ultrasonic transducer in one direction during the pulse width of the ultrasonic signal pulse. and the received signal is supplied, and in the frequency change band of the carrier wave, the carrier frequency closer to the leading edge of the pulse of the ultrasonic signal pulse has a delay frequency characteristic where the delay time is longer, and the output is narrower than the pulse width, An ultrasonic diagnostic apparatus characterized by comprising: delay means for obtaining a pulse having a larger peak value than the input and for supplying the output pulse to the display device.