JPH0321182B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ultrasonic medical diagnostic device that uses, for example, ultrasound to receive reflected signals from inside a human body, displays an image, and performs a medical diagnosis, particularly an internally reflected signal. It concerns the matching of the frequency and the frequency band of the amplifier of the signal.

[Prior Art] Ultrasonic medical diagnostic equipment emits ultrasonic pulses into the human body, receives ultrasound reflection signals from the tissues and tissue boundaries of various internal organs, displays internal tomographic images, and displays internal tomographic images. It performs medical diagnosis regarding the shape and size of organs and the condition of tissues.

Ultrasonic waves are attenuated and scattered in biological tissues within the body. In particular, the attenuation during ultrasound propagation through body tissue depends on its frequency; as the propagation distance increases, the high-frequency components of the ultrasound pulse attenuate significantly, and the center frequency of the received signal shifts to a lower frequency range. As a result, the center frequency of the received signal from deep within the body is shifted to a lower frequency region. On the other hand, since the azimuth and distance resolution of ultrasound medical diagnostic equipment improves as the operating frequency increases, probes with different frequencies are used depending on the diagnosis area, and typically probes with frequencies of 3.5, 5.0, and 7.5 MHz are used. is often used.

FIG. 4 is an example of a block diagram of a conventional ultrasonic medical diagnostic apparatus. 3 is a transmitter equipped with a plurality of transmitting circuits that output transmission pulses whose transmission timings are individually delayed by the transmission delay circuit 2; 4 is a transmitter comprising n vibrations that perform electro-acoustic conversion; 5 is a switch that is individually connected to n transducers and sequentially selects and scans a plurality of adjacent transducers smaller than n at the same time in synchronization with the synchronization signal generating circuit 1; , 6 is a preamplifier that receives internally reflected signals, 10 is a control circuit that outputs a signal corresponding to the passage of time after the ultrasonic pulse is emitted, 12 is an amplifier having a predetermined frequency band that amplifies the received signal, and 13 is a preamplifier that receives an internally reflected signal. 14 is a video amplifier; 16 is a sweep generator; 17 is a display circuit for displaying a tomographic image of a human body in B mode; 18 is a display circuit for individually delaying received signals from a plurality of selected transducers; 19 is a control circuit 10 that adds the signals
This is a bandpass filter whose center frequency and frequency band are controlled by the output.

The conventional electronic scanning ultrasonic medical diagnostic apparatus is configured as described above, and a plurality of adjacent transducers among the n transducers in the probe 4 are simultaneously selected and transmitted by individually delay-controlled transmission pulses. Excited. Ultrasonic pulses emitted into the body are focused to form a focused beam at a predetermined distance.

The received signals from within the body pass through the preamplifier 6, and the delay circuit 18 individually delays a plurality of signals and then adds and synthesizes the signals. Focusing during reception is performed to improve directivity and improve the azimuth resolution of the image. will improve. The internally reflected signal is generated using an amplifier 12 that performs gain control such that the short-range gain is small and the long-range gain is large.
Attenuation due to propagation distance is corrected so that received signal levels from shallow parts of the human body and from deep parts of the human body are equalized. However, in internal ultrasound propagation, the attenuation of an ultrasound pulse is proportional to its frequency, and the frequency distribution of the ultrasound pulse is centered around the fundamental frequency. The frequency shifts to the lower side. For this reason, signal amplification with a good S/N is performed using a bandpass filter 19 whose center frequency is controlled so as to match the deviation of the center frequency described above in the amplification circuit of the received signal. The center frequency of the bandpass filter 19 and its frequency band are periodically controlled by a control circuit 10 that is synchronized with the timing of emission of ultrasonic pulses.

FIG. 5 shows an example of a circuit diagram of a bandpass filter,
In the figure, 23 is a high-pass filter, 24 is a low-pass filter, C ₁ to _{C 7} are capacitors, and Q ₁ to _{Q 6} are FETs. As mentioned above, the band filter 19 is usually
FETQ and capacitor C are connected in multiple stages, and each gate voltage is controlled by control signals 1 and 2 that change periodically from the control circuit 10 output.
The frequency characteristics of the CR filter are controlled by changing the ON resistance.

Typically, ultrasound medical diagnostic equipment uses 3.5, 5.0,
Since various frequencies of 7.5 MHz are used, a plurality of band filters 19 are used to match these frequencies.

[Problems to be solved by the invention] In the conventional ultrasonic medical diagnostic apparatus as described above,
Due to the acoustic properties of living tissues within the body, ultrasound attenuation occurs not only due to propagation distance but also attenuation proportional to the ultrasound frequency.When a high frequency is used to obtain an image with excellent resolution, the attenuation within the body is significant and the received signal from deep within the body is the signal-to-noise ratio of On the other hand, normal ultrasound pulses have broadband characteristics and exhibit a frequency distribution with frequency components on both sides of the fundamental frequency, and in internal ultrasound propagation, reflected signals due to acoustic impedance mismatch in organs etc. The frequency distribution differs from deep within the body, where high-frequency components are significantly attenuated, and the center frequency of the received signal shifts to a lower frequency region. Furthermore, when a high frequency is used, the shift in the center frequency becomes more and more noticeable.

The center frequency of the band filter 19 is matched to the deviation of the fundamental frequency. For example, the band filter 19 is composed of a multi-stage cascade connection of a FETQ and a capacitor C, and further CR is used to obtain a predetermined frequency band and center frequency. Since the type filters are connected in multiple stages, the received signal is significantly attenuated, the signal-to-noise ratio is degraded, and the effective range is limited. Each FETQ
In order to make the ON resistance uniform by gate voltage control, and to obtain the specified characteristics for each stage, FETQ is used.
The gate voltage is adjusted according to the characteristics of the bandpass filter 19, and it takes time to inspect and adjust the bandpass filter 19. Since probes with various fundamental frequencies are used, a plurality of band filters 19 corresponding to these frequencies are required, and the circuit selection section of the filter port becomes complicated. Also,
There is a problem in that the amplifier 12 must have wideband frequency characteristics in order to cope with the frequency shift of the received signal.

This invention was made to solve this problem, and uses an amplifier 12 with narrow band characteristics for the various frequencies of the probe 4 to improve the noise figure and ensure that reflected signals from deep within the body are not sufficiently reflected. An object of the present invention is to obtain an ultrasonic medical diagnostic device that can receive signals with high sensitivity, expand the effective range of medical diagnosis, and obtain clear images with little noise.

[Means for Solving the Problems] The ultrasonic medical diagnostic apparatus according to the present invention includes a control circuit that outputs a signal corresponding to the passage of time after emission of an ultrasonic pulse, and an oscillation frequency that is controlled by the control circuit output. oscillators, a mixer that performs frequency conversion using the received signal and the output of one oscillator selected from the plurality of oscillators, and an amplifier with narrowband characteristics to which the mixer output is input. .

[Operation] In this invention, a plurality of oscillators related to the frequency of the probe are selected, and the oscillator is selected according to the frequency used by the probe, and the received signal and the oscillator output are frequency-converted by a mixer. , the amplifier always has a constant frequency and frequency band regardless of the frequency of the probe. Furthermore, the oscillation frequency is controlled by a control signal synchronized with the timing of ultrasonic pulse emission, and it can be matched with the received signal frequency, which changes depending on the reflection position in the body, so the signal frequency of the mixer output can be adjusted to the reflection position from shallow parts of the body and deep parts of the body. It can always be kept constant regardless. Therefore, the frequency band of the amplifier can be significantly narrowed, the noise characteristics of the amplifier can be improved, and reflected signals from deep parts can be received with high sensitivity.

[Example] An example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.
is exactly the same as the above conventional device. 7 is probe 4
a plurality of oscillators that oscillate frequencies related to the frequency of , 8 a mixer that converts the reflected signal frequency by the oscillation frequency, 9 a filter having constant frequency characteristics that selects a predetermined sideband from the output of the mixer 8; A reactance circuit S-1 whose capacitance value is controlled by the output of the control circuit 10 using, for example, a variable capacitance diode is a switch for selecting the oscillator 7.

In the ultrasonic medical diagnostic apparatus configured as described above, the output of the synchronization signal generation circuit 1 passes through the transmission delay circuit 2 and outputs a plurality of individually delayed pulses from the transmitter 3, which are selected by the switch 5. Each of the transducers in a predetermined probe 4 is excited. The ultrasound pulses emitted into the body are focused at a predetermined location within the body to form a focused beam. The ultrasonic pulse emitted from the probe 4 forms a broadband frequency distribution consisting of various frequency components centered on the fundamental frequency,
During propagation within the body, the ultrasound pulse is attenuated in proportion to its frequency, which is given by α=α ₀ f. Therefore,
Since the attenuation of high frequency components in the frequency distribution of the ultrasonic pulse becomes significant, the center frequency apparently shifts to a lower frequency region. During intracorporeal ultrasound propagation, a reflected signal due to acoustic impedance mismatch of living tissue is received by the transducer in the probe 4 and is applied to the mixer 8 via the preamplifier 6.

Figure 2 shows an example of a reactance circuit. In the figure, D-1 is a variable capacitance diode, R-1 is a bias adjuster, +E is a DC power supply, and the signal level is cycled according to the elapsed time after ultrasonic pulse emission. The output of the control circuit 10 is applied to the reactance circuit so as to match the return time of the reflected signal.

For example, when a variable capacitance diode D-1 is used in the reactance circuit 11, its barrier capacitance changes in proportion to the applied bias voltage, so that the DC voltage of the bias regulator R-1 output and the control circuit 10 output are superimposed. Therefore, the capacitance value of the variable capacitance diode D-1 changes periodically within a predetermined range. When the oscillation frequency of the oscillator 7 is controlled by the output of the reactance circuit 11, a periodically frequency-modulated signal is output, and the frequency change is matched to the deviation of the center frequency due to the propagation distance in the internal body propagation process of the ultrasound pulse. .

The oscillator 7 is composed of a plurality of oscillators 7 corresponding to various frequencies of the probe 4, and a predetermined oscillator 7 is selected by the switch S-1.

In addition, it is also possible to provide a varactor diode in the resonant circuit of the oscillator 7 and adjust the oscillation frequency by changing the voltage applied to the varactor diode.

A mixer 8 converts the frequency of the received signal and the output of the oscillator 7, and a filter 9 selects a sideband wave of a predetermined frequency. Since the oscillation frequency of the oscillator 7 is matched to the frequency deviation due to the reflection position of the reflected signal, the output signal of the mixer 8 always has a constant frequency, and the frequency band of the filter 9 can be narrowed, and a filter with a steep cutoff characteristic is used. can. Therefore, the frequency band of the amplifier 12 to which this signal is input can be made narrow.

Figure 3 shows an example of a human internal ultrasound reception signal,
20-1, 20-2, and 20-3 are reflection positions provided at equal intervals within the body; for example, when ultrasonic pulses are emitted into the body using the 3.5MHz probe 4, The received signal frequency is as follows, and the oscillation frequency of oscillator 7 is, for example, 5.5MHz ~
Set to 4.0MHz. Reflection position Reception frequency Oscillation frequency conversion frequency Body surface 3.5MHz 5.5MHz 2.0MHz 20−1 3.0〃 5.0〃 2.0〃 20−2 2.5〃 4.5〃 2.0〃 20−3 2.0〃 4.0〃 2.0〃 Similarly, for probe 4 Frequency is 5.0MHz and 7.5MHz
For example, the oscillation frequency of oscillator 7 is 7.0 to 4.9M.
Hz and 9.5 to 6.5 MHz, the lower sideband frequencies of the mixer 8 output can be made to match the above frequencies.

Therefore, the oscillator 7 is used for the probe 4 of various frequencies.
is selected and the output of the control circuit 10 synchronized with the synchronization signal generation circuit 1 periodically changes the capacitance value of the reactance circuit 11 to match the oscillation frequency with the deviation of the center frequency of the received signal. The sideband frequency band of the 8 outputs can always be kept at a constant value. Since the frequency band of the amplifier 12 is narrow and constant, it can be used commonly for each frequency.
The signal-to-noise ratio is significantly improved, and even reflected signals from deep within the body can be received with sufficient sensitivity, thereby significantly improving the effective range of medical diagnosis.

Furthermore, with respect to the attenuation of ultrasound pulses due to the propagation distance within the human body, the amplifier 12 with logarithmic characteristics or STC characteristics can perform distance-gain control, thereby reducing the level of reflected signals from areas shallower than the body surface and deep within the body. Corrected to equal level.

Next, the transducers in the probe 4 are sequentially scanned, and similarly, transmission and reception are performed by a plurality of selected transducers. The received signal can be obtained, and an in-body tomographic image can be displayed.

Even with the above configuration, there is no loss in azimuth resolution or distance resolution, and the displayed image has a significantly better signal-to-noise ratio than conventional devices, and the effective range is expanded, so it can be used over the entire effective range for medical diagnosis, with less noise. It can display clear images with high sensitivity, high resolution, and high quality.

The present invention can be applied to various types of electronic scanning diagnostic devices such as linear and sector diagnostic devices.

Furthermore, although the present invention is applicable to probes of various frequencies, it can of course be applied to probes of a single frequency.

[Effects of the Invention] As explained above, the present invention includes a control circuit that synchronizes with the emission of ultrasonic pulses, a plurality of oscillators whose frequency changes in accordance with received signals reflected in the body,
By using a simple structure in which a mixer that performs frequency conversion between the received signal and a selected oscillator is provided, the mixer output signal is kept constant by the received signal and the oscillator output selected from among the oscillators corresponding to probes of various frequencies. Furthermore, the oscillation frequency is controlled so as to synchronize with the timing of ultrasonic pulse emission and match the frequency deviation due to the reflection position of the internally reflected signal, so the frequency band of the sideband wave of the mixer output becomes narrower and can be made equal to the frequency distribution of the ultrasonic pulse.

Therefore, since the frequency band of the amplifier is constant, it can be used commonly for probes of various frequencies, and since the frequency band of the amplifier is narrow, the noise output is reduced, the signal-to-noise ratio is improved, and reflections from deep in the body are reduced. The signal can be similarly improved and contribute to expanding the effective range of medical diagnosis.

Low noise throughout the effective range of medical diagnosis.
High sensitivity, high resolution, and high quality clear images can be displayed. Furthermore, it has the advantage that it can be applied to various types of linear and sector scanning devices.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an example of a reactance circuit, Fig. 3 is an example of an ultrasound reflection signal within a human body, and Fig. 4 is a block diagram of a conventional ultrasonic medical diagnostic device. An example of a diagram, FIG. 5, is an example of a circuit diagram of a bandpass filter. In the figure, 1 is a synchronization signal generation circuit, 2 is a transmission delay circuit, 3 is a transmitter, 4 is a probe, 5 is a switch, 6 is a preamplifier, 7 is an oscillator, 8 is a mixer,
9 is a filter, 10 is a control circuit, 11 is a reactance circuit, 12 is an amplifier, 13 is a detector, 14 is a video amplifier, 16 is a sweep generator, and 17 is a display. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In an ultrasound medical diagnostic device that emits an ultrasound pulse into the inside of a human body and obtains a tomographic image of the inside of the body by receiving a reflected signal due to a mismatch of internal acoustic impedance, A control circuit that outputs a signal corresponding to the passage of time, a plurality of oscillators whose oscillation frequencies are controlled by the output of the control circuit, and a received signal and the output of one of the oscillators selected from the plurality of oscillators. An ultrasonic medical diagnostic apparatus comprising a mixer that performs frequency conversion and an amplifier having a predetermined frequency band into which the output of the mixer is input.