JPS6031738A - 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 Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus, and particularly to an ultrasonic diagnostic apparatus capable of displaying an ultrasonic diagnostic image with a high 111 resolution.

BACKGROUND ART In recent years, devices have become well known that transmit and receive ultrasonic waves to and from a subject and display the echo signals obtained from this and the resulting image on a CRT screen. Since various internal information can be obtained, it is widely used for various diagnostic purposes.

FIG. 1 shows the basic structure of such an ultrasonic diagnostic device, and this device transmits an ultrasonic pulse 5(t) from a transducer 1o to a subject 12. ing. The ultrasonic pulse 5(t) transmitted in this way is transmitted to the subject 12.
It propagates inside, is reflected one after another at each boundary surface a, b, c, d, e, etc. with different acoustic impedance inside the object 12, and returns to the vibrator 10 as an echo signal e([). come.

Therefore, by detecting this echo signal e(t), performing predetermined image processing on it, and displaying it on a CRT, it is possible to display the acoustic characteristic distribution inside the subject as an image, and the The presence or absence of an abnormality existing inside the subject 12 and its location can be known from the image pattern.

The higher the distance resolution of the image, the more reliable it is to judge the presence or absence of such an abnormality, and for this reason, we have been developing and putting into practical use each insertion U to increase the distance resolution of the obtained image. is being carried out.

As one such device, for example, after performing a predetermined detection to remove the carrier frequency from the echo signal e(t) received by the transducer 10, the echo signal is subjected to predetermined differential processing. There are known methods for increasing the distance resolution of signals.

However, the ultrasonic pulse 5(t) transmitted from the transducer 10 generally exhibits a predetermined impulse response waveform of the transducer, as shown in FIG. Such an ultrasonic pulse sB)
The disadvantage is that the distance resolution is determined by the waveform of the ultrasonic pulse S(t). Therefore, in such a conventional ultrasonic diagnostic apparatus, the ultrasonic pulse S(
The echo signals from two reflectors that are close to each other within the pulse width of [) are observed to be completely unified. It was not possible to obtain sufficient distance resolution, and effective countermeasures were sought.

For this reason, in conventional ultrasonic diagnostic apparatuses, when a high resolution diagnostic image is required, a high frequency transducer with a short wavelength is used as the transducer 10.

By doing this, the pulse width of the ultrasonic pulse sB ) transmitted from the vibrator 10 becomes shorter, so that
The distance resolution of the obtained echo signal e([) is relatively improved, making it possible to obtain a high-resolution diagnostic image.

However, in general, high-frequency ultrasound waves have a higher attenuation rate than low-frequency ultrasound waves inside a living body, so when such high-frequency ultrasound pulses are used, it is not possible to obtain sufficient skin sensitivity deep inside the body. The obtained echo signal e(t)
There was a problem in that the signal-to-noise ratio was lowered and the 1!7i layer image of the deep part of the living body could not be blued.

Purpose of the Invention The present invention has been made in view of such conventional problems, and its purpose is to provide an ultrasonic diagnostic Igi device that can obtain an ultrasonic diagnostic device with excellent distance resolution and signal-to-noise ratio. There is a particular thing.

Structure of the Invention In order to achieve the above-mentioned object, the apparatus of the present invention is an ultrasonic diagnostic apparatus that transmits and receives ultrasonic waves toward a subject and displays a diagnostic image of the subject based on the obtained echo signals. A delay circuit that performs delay processing and outputs the delayed signals as a plurality of delayed signals delayed at fixed time intervals, and a weighting circuit that performs predetermined weighting processing on each delayed signal are circuits 117 and 11m,
The apparatus is characterized in that it includes an echo signal deconvolution circuit including an adder that adds and outputs the eliminated delayed signals, and obtains an image signal with high distance resolution from the echo signals.

Example Next, preferred embodiments of the present invention will be described based on the drawings.

1. In FIG. 1, an ultrasonic pulse S(t) is transmitted from the transducer 10 to the subject 12. Here, r(t) is the reflection series tj on each boundary surface a, 'b, c, d, e; Ultrasonic pulse 5 (t) within
Assuming that does not change, the echo signal e([) obtained from the subject 12 is the reflection series r(t
') and the ultrasonic pulse S([).

e(t)=Nt)*S(1)-(1) where 4; represents a convolution.

When the equation (1) is Fourier transformed and each corresponding function is expressed in capital letters, the equation (1) becomes the following equation F (f )=
R(f)S(f) (2) Therefore, the reflection M sequence R<f) can be determined as follows.

RCf>-E(f') (3) S (f) Such a method is generally called deconvolution.

The feature of the present invention is that this J:Una deconvolution method is applied to an ultrasonic diagnostic device, and by inverse Fourier transforming R(f), which is 1q according to the above equation (3), It is possible to obtain a reflection sequence r([) of the subject 12 with respect to the transmitted wave of the sound wave pulse 5(t). Therefore, if r(t) obtained in this way is used as an image signal to display a diagnostic image of the subject, the ultrasound pulse S(
It is possible to obtain diagnostic images with excellent distance resolution without being limited by the pulse width of [).

Further, according to the present invention, a high-frequency ultrasonic pulse s(t
), it is possible to obtain a diagnostic image with a high distance resolution, so it is possible to obtain a diagnostic image with a high SN ratio and a high distance resolution even from the deep part of the subject where the influence of ultrasound attenuation is large.

Here, in the actual device, the ultrasonic pulse 5(t)
and the echo signal e(t > is affected by noise1).

In order to remove the influence of such noise, a window function W(f) is used to extract R(r) in a predetermined band from R([) in equation (3), and R(l is Preferably, it is based on the formula.

Therefore, by determining S(') in advance by actual measurement and determining the window function W(f) in consideration of noise, the test object 12 is determined based on the obtained echo signal E(f).
The reflection series R(f) can be determined. Then, by inverse Fourier transforming R < f ) obtained in this way, it is possible to obtain a desired reflection sequence r(t), and it becomes possible to obtain a good diagnostic image with high distance resolution and S/N ratio. .

Experimental data Next, the principle of the present invention described above is
Experimental data confirmed using a concave vibrator 10 with a diameter of 20 mm will be explained.

FIG. 2 shows the ultrasonic pulse s(t) transmitted from the transducer 10, and in the embodiment, this s
(t), the transducer 10 is placed in water, and an ultrasonic wave is transmitted toward a flat perfect reflector placed at its focal point (13 cm from the transducer), and the echo obtained from the perfect reflector is is limped at a period of 20 ns.

FIG. 3 is a frequency spectrum of S([) obtained by Fourier transforming the ultrasonic pulse sB ) shown in FIG. 2.

FIG. 4 shows a subject 1 at the focus of the vibrator 10 underwater.
2, an acrylic plate with a thickness of ICl 1l is placed, and the echo No. 18 e obtained from the front and rear surfaces of the object 12 when an ultrasonic pulse s (, t) is transmitted from the transducer 10 to the object 12. ([).

FIG. 5 shows a frequency spectrum of E<r) obtained by Fourier transforming the echo signal eB) shown in FIG.

S ('') and E in Figures 3 and 5 obtained in this way
Considering the noise level of (f), 5(f) and E([
) to determine the window function W(f) without extracting the signal in a predetermined band.

Figure 6 shows that using such a window function W(f'),
It is a frequency spectrum of cW<f)/S'(f).

Therefore, E (f ) shown in Figure M5 and W (
By multiplying f)/5(f), the above (4th
), R(f) can be set as shown in the formula.

Figure 7 shows the frequency spectrum of R(1>) determined in this way, and Figure 8 shows the reflection obtained by inverse Fourier transforming R(f) shown in Figure 7. Series r(t
)It is shown.

This J: reflection sequence r(t), as shown in FIG. 8, has a small pulse width, and the reflection echo e('t') shown in FIG. It shows.

Therefore, C1, which is not shown in FIG. 3, is determined in advance by determining the window function W(fl) that takes S(, f) and noise into account, and then processes the echo signal E(l by Deni-1 convolution based on equation (4) above. R
<t>, and further performs an inverse Fourier transform on this R(f), it is possible to obtain the foul sequence r(t) of the object 12 with a higher resolution than the echo signal e,(t). Become.

Specific Embodiment FIG. 9 shows a preferred embodiment of the ultrasonic diagnostic device 11i of the present invention.

The device of the embodiment has a switch 16 including a focus circuit that performs focusing adjustment of the transducer 10 and a switching circuit that performs electronic switching scanning of the transducer 10, and transmits ultrasonic pulses from the oscillator circuit 18 to the scan sensor 16. When a trigger pulse that determines the repetition period is input, the scanner 16 controls the excitation of the transducer 10 at intervals of the input of the trigger pulse, and transmits an ultrasonic pulse e(t) to the subject 12. .

The ultrasonic pulse e(,t) transmitted in this way is
While propagating inside the subject 12, the light is reflected one after another at each interface having a different acoustic impedance.

Then, the reflected echo e(t) is received by the vibrator 10, where it is converted into an electric signal, and further transmitted through a focus circuit installed in the spacer 16, which is a characteristic component of the present invention. The signal is input to a deconvolution circuit 20.

In the apparatus of the present invention, the deconvolution circuit 20 includes a logic M circuit for delay processing an echo signal and outputting it as a plurality of delayed signals delayed at regular intervals, and a logic M circuit for delay processing the echo signal and outputting it as a plurality of delayed signals delayed at regular intervals, and a deconvolution circuit 20 for applying a predetermined weight to each delayed signal. The attached circuit includes a weighting circuit for processing and an adder for adding the weighted delayed signals, and these circuits are used to deconvolve the input echo signal e(t). The signal r(t) obtained thereby is output to the amplifier 22.

The signal r(t) thus input to the amplifier 22 is amplified with a predetermined amplification factor and then input to the memory 26 via the detection circuit 24. The convolution circuit 20 can be roughly classified into two types: non-recursive type and recursive type.

A preferred embodiment of this deconvolution circuit 20 will be described below.

10 shows a non-recursive deconvolution circuit 20.
A preferred embodiment is shown in which the circuit of the embodiment inputs the echo signal eB) outputted from the scanner 16 as it is to the delay circuit 30, and performs non-recursive deconvolution processing on the echo signal eB). ing.

Here, the delay circuit 30 performs predetermined delay processing on the input echo signal e([), and performs predetermined delay processing on the input echo signal e([).
A plurality of delayed signals e(-τ), e(t-, zτ)... e(t-n
τ) to the weighting circuit 32.

The market fζ1-digit circuit 32 generates a plurality of weights corresponding to each delayed signal based on a signal from a control circuit (not shown).
1, a2...an, a weight f] generator 34,
These weightings are performed by a plurality of multipliers 36-1, 36-2, . . . that multiply the signal and each delayed signal output from the delay circuit 30.
36-n, and a predetermined weight (=I) is applied to the delayed signal outputted from the delay circuit 30.

In this way, the weighting is carried out by the weight output from the circuit 32, and each delayed signal is added in the adder 38 and sent to the amplifier 22 as a deconvolved image signal @r(t). direction is output.

Therefore, the signal r(t) output from the adder 38 is expressed by the following equation.

Here, when both sides of the above equation (5) are Fourier transformed, and when this equation (6) is compared with the above equation (4), the following relationship is obtained, and this equation (7) is expressed as W(f)/
ai can be determined by subjecting S (f ) to 1'' inverse Fourier transform.

Therefore, by setting W(r)/S<f) and performing inverse Fourier transform on this, the a required for deconvolution is
i can be predetermined, and by outputting the weighted ai obtained in this way from the weighting unit 34, the signal r(t> of the equation (5) output from the adder 38 becomes an echo It is also possible to use the deconvolution process of @e(t).

Therefore, according to the device of this embodiment, the weighted t-shaped device 3
By determining the weights al, a2, a3, ... output from 4 by inverse Fourier transform of W(r)/S'(f), the input echo signal e(t) is automatically calculated. Image signal r(
t), and a diagnostic image with excellent distance resolution and signal-to-noise ratio can be displayed on the CRT'28.

Deconvolution Circuit 2 FIG. 11 shows a preferred embodiment of a recursive deconvolution circuit.

The circuit of the embodiment uses the echo signal e output from the scanner 16.
Subtractor 40 that subtracts the output signal of adder 38 from (t)
The signal "(t) output from the subtracter 40 is input to the delay circuit 30, and recursive deconvolution processing is performed on the echo signal e(t).

Here, the delay circuit 30 outputs a manually inputted signal r([
) is subjected to predetermined delay processing, and multiple delayed signals r(−τ) and r(t −
2τ〉... "(to transform into -nτ).

Each delayed signal outputted in this manner is subjected to a predetermined weighting process by the weight 4=J circuit 32, and each weighted delayed signal is outputted from the adder 38 as an addition signal expressed by the following equation. . Therefore, the output of the subtracter 40 that subtracts the output of this adder 38 from the echo signal e(t) @
r(t) is expressed by the following equation, and when both sides of equation (9) are Fourier transformed, the following equation is obtained.

When formula (10) obtained in this way is rearranged with respect to R([), its value becomes the following formula. Here, when comparing formula (11) with formula (4), it is found that both The relationship expressed by the following equation holds between the equations.

Therefore, in the deconvolution circuit of this embodiment, S(1>/W(r) is determined in advance, and based on that value, equation (12) is inversely Fourier transformed to determine ai. By outputting the collected ai as a weighted signal from the weight numbering unit 34, the echo signal e(t) is automatically deconvoluted and a high resolution signal @r(t) is output to the subtracter. 40 to the amplifier 22, and the CRT 28
It becomes possible to display a diagnostic image with excellent distance resolution and signal-to-noise ratio.

Note that the ultrasonic pulse s(t
) changes its waveform during propagation within the subject 12 due to predetermined attenuation and focusing of the sound wave of the vibrator. Therefore, in an apparatus such as the apparatus of this embodiment, in which a focus circuit is provided in the scanner 16 to perform dynamic focusing of the ultrasonic pulse 5(t), the weight angle is adjusted according to the focal length of the ultrasonic pulse. It is necessary to perform deconvolution processing with .

For this reason, each weighting device 34 shown in FIGS. 10 and 11 switches the values of the weighting constants a1, a2, . . . in conjunction with the dynamic focus of the ultrasonic pulse 5(t). , and weighting that matches the focal length of the ultrasonic pulse S([) is formed to enable processing.

Therefore, in the apparatus of this embodiment, it is possible to perform optimal deconvolution processing on each echo signal obtained from the shallow part to the deep part within the subject 12, and as a result, the CRT
It becomes possible to display a diagnostic image with excellent resolution and a good signal-to-noise ratio on the screen 28.

Furthermore, in order to obtain high-resolution diagnostic images, the device of the present invention does not need to use high-frequency ultrasonic pulses unlike conventional devices. A diagnostic image of the deep part of the subject 12 can be displayed as an image with excellent signal-to-noise ratio and resolution using the ultrasonic pulses.

1 ri 1 ■ 1114 As explained above, according to the device of the present invention, the echo signal obtained by transmitting and receiving the ultrasonic beam is deconvoluted! l! By doing so, it is possible to obtain good diagnostic images with high distance resolution.

Furthermore, according to the apparatus of the present invention, it is possible to obtain diagnostic images with high distance resolution without using high-frequency ultrasound pulses with large attenuation. It also becomes possible to obtain diagnostic images with excellent distance resolution.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the transmission and reception of ultrasonic pulses, Figs. 2 to 8 are explanatory diagrams of waveforms of experimental data obtained by transmission and reception of ultrasonic waves, and Fig. 9 is an explanatory diagram of the ultrasonic diagnostic apparatus of the present invention. Block Diagram Showing Preferred Embodiment FIGS. 10 and 11 are block diagrams of a first embodiment and a second embodiment of a deconvolution circuit, which is the main part of the present invention. 12... Subject 20... Deconvolution circuit 32...
Weighting circuit 34 ... Weighting device 36 ... Multiplier 38 ... Adder. Applicant Aloka Co., Ltd.

Claims (1)

[Scope of Claims] (1) In an ultrasound diagnostic device that transmits and receives ultrasound waves to and from a subject and displays a diagnostic image of the subject based on the obtained echo signals, the echo signals are delayed and delayed for a certain period of time. a delay circuit that outputs a plurality of delayed signals that are delayed at intervals; a weighting circuit that performs a predetermined weighting process on each delayed signal; and an adder that outputs each of the weighted delayed signals; What is claimed is: 1. An ultrasonic diagnostic device comprising: an echo signal deconvolution circuit including an echo signal deconvolution circuit, and obtaining an image signal with high distance resolution from the echo signal. (2. In the apparatus according to claim (1), the deconvolution circuit inputs the echo signal directly to the delay circuit and performs non-recursive deconvolution processing on the echo signal. Apparatus. (3) In the apparatus according to claim (1), the deconvolution circuit includes a subtracter that subtracts the output of the decorator from the echo signal, and the echo signal output from the subtracter 7)) An ultrasonic diagnostic apparatus characterized by inputting the signal into a delay circuit and performing recursive deconvolution processing on each signal. (4) In the apparatus according to any one of claims (1) to 3), the weighting is performed by the circuit I, and the switching control of the weighting process is performed in conjunction with the dynamic focus of the ultrasound. An ultrasonic diagnostic device characterized by: