JPS60116341A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an ultrasonic signal processing device, which transmits an excitation signal to an ultrasonic transducer that transmits ultrasonic waves to a living body, and also converts ultrasonic echo signals into signals. The present invention relates to an ultrasonic diagnostic apparatus that processes and obtains an ultrasonic image signal.

[Technical background of the invention and its problems]

It is well known that when ultrasonic waves propagate within a living body, attenuation occurs depending on the frequency of the ultrasonic waves, and the amount of attenuation is greater as the frequency increases.

Generally, in ultrasonic diagnostic equipment, the frequency bandwidth is 1~
Although a pulse wave of about 10 MHz is used, the spectrum of the ultrasonic echo signal is greatly attenuated depending on the propagation distance of the ultrasonic wave due to the above-mentioned in-vivo attenuation.

This situation will be explained based on FIG. 1(a).

In the figure, the horizontal axis shows the frequency 1. The vertical axis represents the power spectrum of the ultrasonic wave, and shows the state of change in the center frequency of the ultrasonic echo signal.

As is clear from the figure, as the depth to the living body increases, that is, as the propagation distance increases, the power spectra of the ultrasound echo signals A, B, and C decrease, and the center frequency fO+foj+f02 moves to a lower frequency range. .

On the other hand, the resolution of the ultrasound diagnostic apparatus in the ultrasound transmission direction (hereinafter referred to as "W distance resolution") is better as the frequency band of the ultrasound signal is wider.

Therefore, in order to achieve high distance resolution, the passing frequency physical properties of the electrical circuit system after the ultrasonic echo is received by the ultrasonic transducer must include the frequency components of the ultrasonic echo signal. That's it.

Therefore, if an electrical circuit system with sufficiently wide passing frequency discrimination is used for ultrasonic echo signals, high distance resolution can be achieved for near-distance reflectors, but for long-distance reflectors. , since the ultrasonic echo signal has attenuated cylindrical frequency components, it is not possible to expect similar distance resolution, and conversely, due to high frequency noise components, only images with degraded S/N ratio can be viewed. was there.

To solve this problem, in order to obtain images with high distance resolution at short distances and a slightly low S/N ratio at long distances, we use high frequency broadband for short distances and relatively low frequency narrow bands for long distances. A first stage filter having band-pass properties is used in electrical circuit threads.

Then, the ultrasonic echo signal that has passed through the first stage filter is amplified and tr! After the A wave is generated, the carrier wave component is removed by a low-pass filter to obtain a video signal.

In this case, the frequency of the carrier wave component will decrease as the center frequency of the ultrasound echo signal decreases due to the above-mentioned in-vivo attenuation, but since the cut-off frequency of the low-pass filter in conventional devices is constant, This causes problems such as:

In other words, as shown in Figure 2, the @ output from the S-wave device is
The spectrum of the wave output A+ r B1+C+ becomes narrower as the depth increases, whereas if the cut-off frequency property of the low-pass filter is set to the broken line (+) in the same figure, the cut-off frequency f
In the region above 3, the high frequency component of the ultrasonic echo signal Al+B+ from a short distance is suppressed, and the distance resolution is degraded.

On the other hand, the cut-off frequency physical properties of the low-pass filter are expressed by the broken line (I
I), and when the cutoff frequency is set to f1, the noise component of the ultrasonic echo signal C1 from a long distance cannot be removed, or even the removal of the carrier wave is insufficient.

This situation will be explained more specifically.

As shown in Fig. 3(a), when an ultrasonic echo signal E from a short distance and an ultrasonic echo signal E from a long distance are obtained, the video signal that is the output of the low-pass filter has a cutoff frequency f3. In this case, the solid line DI in Fig. 3(b).

As shown by El, the temporally expanded distance resolution with respect to the ultrasonic echo signal E is degraded, and in the case of the cutoff frequency f1, the broken line D2. As shown by E2, ripples remain.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and
By changing the frequency cut-off characteristics of the low-pass filter after the P-wave generator according to the propagation time of the ultrasound, we can produce ultrasonic waves with high resolution and a good S/N ratio, taking into account the attenuation of ultrasound in the body. The purpose of the present invention is to provide an ultrasonic diagnostic apparatus that can provide ultrasound images.

[Overview of the invention]

To achieve the above object, the transplantation machine of the present invention includes a group of ultrasonic transducers that transmit and receive ultrasonic waves to and from a living body to obtain ultrasonic echo signals, a detector that detects the ultrasonic echo signals, and a detection output. In an ultrasonic diagnostic apparatus having a low-pass filter that outputs a video signal by applying a filter to the ultrasonic wave, a control means for transmitting an average transmission time signal of ultrasonic waves transmitted from a group of ultrasonic transducers is provided. The symptoms of wheezing are changes in cut-off frequency physical properties over time.

[Embodiments of the invention]

Examples of the present invention will be specifically described below.

FIG. 4 is a block diagram showing an embodiment of the present invention. a pulser group 2 that sends an excitation signal to the ultrasonic transducer group 1, a preamplifier group 3 that amplifies the ultrasonic echo signal output as an electrical signal from the ultrasonic transducer group 1, and a predetermined delay time given to each output signal of the preamplifier group 3. an adder 5 that adds the outputs of the delay circuit group 4, an echo filter 6 that filters the output signal of the adder 5, and a detector 7 that detects the output signal of the echo filter 6; It has a low-pass filter 8 that applies a low-pass filter to the detected output, and a control means 9 that controls the pulsar group 2, delay circuit group 4, and echo filter 6.

The control means 9 is configured to send an average transmission time signal of the ultrasonic waves transmitted from the ultrasonic transducer group 1 to the echo filter 6.

The echo filter 6 that receives this average transmission time signal is configured so that its passage characteristics change over time as shown in FIG. 1(b).

That is, for an ultrasonic echo signal with a small delay from the ultrasonic transmission time (short propagation time), the passage characteristic A2'f, which is high frequency, wide band, and has a center frequency of f4, has a delay. For large ultrasonic echo signals, pass characteristic C2 with a low frequency, narrow band, and center frequency of f6 is adopted, and for ultrasonic echo signals between the two, pass characteristic B2 with center frequency of f5 is adopted. It has become. It is assumed that the center frequency f5 coincides with the center frequency f shown in FIG. 1(a).

Also, the cutoff frequency of the low-pass filter 8 is the echo filter 6
is installed at 1/2 of the bandwidth of the echo filter 6.
0 passing characteristic A2. B2. The trap is designed to change over time in response to C2.

The output signal of the low-pass filter 8 is sent to an image display means (not shown) as a video signal.

Next, the operation of the device having the above configuration will be explained.

The control means 9 sends a transmission time signal to the pulsar group 2 so that the ultrasonic waves emitted from each lifter of the ultrasonic transducer group 1 are focused on a fixed point.

The pulser group 2, which has received the transmission time signal, sends excitation pulses to the corresponding transducers, and as a result, the ultrasonic transducer group 1 is excited and emits ultrasonic waves into the living body.

This ultrasonic wave is reflected in the living body and becomes an ultrasonic echo and is received by the ultrasonic transducer group 1, but at this time, it is attenuated in the living body depending on the propagation distance in the living body and the frequency of the ultrasound. .

The ultrasonic echo is converted into an ultrasonic echo signal, which is a spot signal, by the ultrasonic transducer group 1, amplified by the preamplifier group 3, and then focused by the delay circuit group 4 during reception. Adder 5 is given a delay of time
is input.

The delay time of the delay circuit group 4 is set by a control signal from the control means 9.

The ultrasonic echo signal output from the adder 5 is input to an echo filter 6 and filtered. At this time, the passband characteristic of the echo filter 6 obtained from the control means 9 is the A 2 r B 2 +
C2 changes over time as described above.

Therefore, an ultrasonic echo signal from a short distance passes through the echo filter 6 almost unchanged, and an ultrasonic echo signal from a long distance has its noise component removed and is converted into an e-wave by the M-wave unit 7, respectively.

The output signal of the detector 7 includes a carrier wave component and a low frequency component modulated by the reflecting object. This output signal is further filtered by a low pass filter 8.

Since the cutoff frequency of the low-pass filter 8 for the short distance signal corresponds to a leap in the bandwidth of the pass characteristic A2, that is, its center frequency f4, the high frequency component of the short distance signal is not suppressed.

- Since the cutoff frequency for the long-distance signal is equivalent to 1/2 of the bandwidth of the pass characteristic C2, that is, its center frequency 16, the carrier wave component and noise component contained in the long-distance signal are removed. Only low-pass components corresponding to ultrasonic echoes will pass through the low-pass filter 8.

The output signal of the low-pass filter 8 is sent as a video signal to an image display means, and an ultrasonic image having high distance resolution and a good S/N ratio can be obtained on the TV screen.

It goes without saying that the present invention is not limited to the embodiments described above, and that various modifications can be made within the scope of the invention.

〔Effect of the invention〕

According to the present invention described in detail above, the detected output of the ultrasonic echo signal is passed through a low-pass filter whose cut-off frequency changes in accordance with the average transmission time signal from the control means, and is output as a video signal. Because it is a high-resolution S/N that corresponds to in-vivo attenuation and does not include carrier wave components.
It is possible to provide an ultrasonic diagnostic apparatus that can obtain ultrasonic images with good ratios.

[Brief explanation of drawings]

FIG. 1(a) is a graph showing changes in ultrasonic echo signals due to propagation distance, FIG. 1(b) is a graph showing frequency passing characteristics of the filter used in the embodiment of the present invention, and FIG. A graph showing the low-band spectrum of the detection output of the ultrasound echo signal in the diagnostic device. Figure 3 (a) is the spectrum of the detection output of the ultrasound echo signal, and Figure 3 (b) is the low-band spectrum of the detection output of the ultrasound echo signal with different cutoff frequencies. FIG. 4 is a block diagram showing the circuit configuration of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Ultrasonic transducer group, 7... Detector, 8... Low pass filter, 9... Control means.

Claims (1)

[Claims] A group of ultrasonic transducers that send and receive ultrasonic waves to and from a living body to obtain ultrasonic echo signals, a detector that detects the ultrasonic echo signals, and a low-pass filter that filters the detected output and outputs a video signal. In the ultrasonic diagnostic apparatus having the above, the cut-off frequency characteristic of the low-pass filter is changed over time by a control means that transmits an average transmission time signal of the ultrasonic waves transmitted from the ultrasonic transducer group. Ultrasound diagnostic equipment for distinguishing symptoms.