JPH03114452A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To reduce the artifact component of a tomographic image by vibrating an ultrasonic vibrator transmitting and receiving an ultrasonic signal with respect to the interior of an examinee in a transmitting direction and removing a multiple reflection signal component from a plurality of echo signals. CONSTITUTION:An ultrasonic vibrator 600 transmits an ultrasonic wave into an examinee 601 and receives the reflected echo to convert the same to an electric signal. A vibrator moving apparatus 603 mechanically moves the vibra tor 600 forwardly or rearwardly in the transmitting direction and a transmitting circuit 604 drives the vibrator 600 to transmit an ultrasonic wave and a receiv ing circuit 605 amplifies the echo signal received by the vibrator 600 to output the same. A multiple reflection reducing circuit 608 reads a digital signal from a memory 607 and executes multiple reflection removing algorithm to remove the multiple reflection signal component of the echo signal and outputs the echo signal reduced in the multiple reflection component. A D/A converter circuit 609 converts the output of the circuit 608 to an analogue signal to output the same to a display part 610. For example, the display part 610 is an image display apparatus such as a CRT and the tomographic image of the examinee 601 minimized in a multiple reflection component is displayed.

Description

[Detailed description of the invention] [Industrial application field 1 The present invention relates to an ultrasonic diagnostic apparatus.

[Prior Art] An ultrasonic diagnostic apparatus is an apparatus that transmits ultrasonic waves into a subject from an ultrasonic probe, receives echoes from one reflector, and displays a tomographic image represented by the echoes. If the echo is reflected once inside the subject and received by the probe, the tomographic image will be displayed as a clear image without ghosts. Such an echo signal will be referred to as a single reflection signal.

However, in actual operation of the device, echoes are reflected at the boundary between the probe and the surface of the object due to the difference in acoustic impedance between the probe and the surface of the object, and a portion of the ultrasound signal that should be received by the probe is lost. It may enter the subject again. For this reason, multiple reflections occur between the surface of the object and the reflector inside the object, and multiple ghosts may appear on the image displayed on the display of the device while fishing on a boat. Such signals that are reflected multiple times between the probe and the reflector and received by the probe, that is, images containing multiple reflection signals, have a negative impact on diagnosis, and it is desirable to remove the multiple reflection signal components. .

Japanese Patent Application Laid-Open No. 56-14315 as a method for removing multiple reflected signals
1 and JP-A-60-117150. In these methods, when a single signal component is received by the t sand diameter of the transmitted wave,
Assuming that multiple reflected signal components will be received after 2t, 3t,... seconds, taking into account attenuation parameters, etc.
The multiple reflected signal components are removed by shifting the single signal components to 2t, 3t, . . . , sand diameters and attenuating them from the echo signal.

[Problem to be solved by the invention 1 However, JP-A-56-143151 and JP-A-60
- In the method of removing multiple reflections in November 50, when noise is input to the t sand diameter of the transmitted wave, even though similar noise does not exist in the echo signals of the sand diameters of 2t, 3t,... , there is a risk that subtraction will be performed assuming that there are multiple reflected signal components. Also, if the reflector is diagonal to the probe, the signal sent from the probe will be reflected by the reflector and returned to the probe, but because the reflector is diagonal, the center of the reflected wave will be It comes to a position shifted by a distance d from the waved position. At that position, a portion of the signal is reflected again at the probe surface and enters the subject.

When the signal that has entered the subject is reflected and returns to the probe, the position where the signal is received will be further shifted by a distance approximately equal to 3d. When another multiple reflection occurs and the signal is received by the probe, the position will be shifted by a distance equal to approximately 5d from the position where the first multiple reflection was received. Therefore, the multiple reflection The signal may or may not be received by the probe depending on the delicate positional relationship between the reflector and the probe. Therefore, when processing an echo signal, it may be difficult to recognize whether it is a single reflection signal or a multiple reflection signal. In this case, not only the multiple reflection signal component cannot be reduced, but also the single reflection signal component is removed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic diagnostic apparatus that solves the above problems and effectively reduces multiple reflected signal components.

[Means for Solving the Problems] In the ultrasonic diagnostic apparatus according to the present invention, the probe is moved in the ultrasound transmission direction, and the difference between the amount of displacement of one reflected signal component and the amount of displacement of multiple reflected signal components is determined. 6. Effectively reducing multiple reflected signal components According to the present invention, an ultrasound transducer transmits an ultrasound wave into the subject, and the ultrasound transducer receives the reflected echo and generates an echo. An ultrasound diagnostic apparatus that forms a tomographic image represented by a signal includes a moving means for moving an ultrasound transducer in a wave transmission direction, a storage means for storing an echo signal, and at least A control means for causing an ultrasonic transducer to receive a plurality of echo signals at two positions and storing the plurality of echo signals in a storage means, and a multiple reflection signal for removing a multiple reflection signal component from the plurality of echo signals. the multiple reflected signal reducing means relatively shifting the plurality of echo signals;
echo signal difference means for calculating the difference between the two; pseudo multiple reflection signal generation means for generating a pseudo multiple reflection signal component based on the difference information between the echo signals by the signal difference means; and a plurality of echo signals and pseudo multiple reflection signal components. pseudo-single-reflection signal generating means for obtaining a pseudo-single-reflection signal component by taking a difference between the pseudo-single-reflection signal component and the pseudo-single-reflection signal component, and obtaining a half-reflection signal that satisfies predetermined conditions from the plurality of pseudo-single-reflection components; and single reflection signal determining means.

According to the present invention, in an ultrasonic diagnostic apparatus, an ultrasonic propagating body is interposed between the surface of a subject and the surface of an ultrasonic transducer, and the ultrasonic propagating body is directly affected by the movement of the ultrasonic transducer. Contains materials that have little effect on the measurement of reflector distribution within the subject.

According to the present invention, in the ultrasonic diagnostic apparatus, the multiple reflection signal reduction means outputs an echo signal when a semi-reflection signal satisfying a predetermined condition cannot be determined.

According to the present invention, in the ultrasonic diagnostic apparatus, the pseudo multiple reflection signal determining means assumes that the difference signals from the echo signal differentiating means have equal waveforms overlapping with a phase difference corresponding to the shift amount. A pseudo multiple reflection signal component is extracted by performing frequency conversion, removing the phase difference, and performing inverse frequency conversion.

According to the present invention, furthermore, in the ultrasonic diagnostic apparatus, the pseudo single reflection signal generating means calculates the difference between the plurality of echo signals and the signal from the pseudo multiple reflection signal generating means, taking into consideration the amount of shift. , generates a plurality of pseudo single reflection signal components.

According to the present invention, in the ultrasonic diagnostic apparatus, the single reflection signal determining means calculates a correlation between the plurality of pseudo single reflection signals obtained by the pseudo single reflection signal generating means, and the correlation exhibits a peak. Let the pseudo-single reflection signal at the time be a half-reflection signal.

[Function 1] The ultrasonic diagnostic apparatus according to the present invention receives a plurality of echo signals while moving the transducer forward or backward in the wave transmission direction by the transducer moving means, and stores the data of the echo signals in the storage means. Remember.

Among multiple echo signals recorded/recorded in the storage means.

The two echo signals are sent to multiple reflection removal means, where the relative phase difference between the two echo signals is gradually shifted to obtain a pseudo single reflection signal component. When a peak of the correlation between the two semi-reflection components appears, the pseudo single reflection signal there is determined to be the true half-reflection signal.

Furthermore, if the correlation peak does not appear, the echo signal itself is treated as a semi-reflection signal. This method allows multiple reflection signals to be removed from echo signals.

[Example] Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

Echo signals received by ultrasound diagnostic equipment generally include semi-reflection signals and multiple reflection signals.A "semi-reflection signal" is a signal transmitted from an ultrasound transducer that is reflected by a reflector within the subject. The echo signal is reflected and received by the ultrasonic transducer,
Additionally, a "multiple reflection signal" is a signal transmitted from an ultrasound transducer that is received by the ultrasound transducer after being reflected multiple times between the reflector inside the subject and the surface of the transducer. It is defined as an echo signal. Desirably, this multiple reflection signal is essentially completely eliminated. Conventionally, it has been almost impossible to distinguish between a single reflection signal and a multiple reflection signal among echo signals and to remove only the multiple reflection signal.

The present invention reduces multiple reflected signal components by moving the ultrasonic transducer in the wave transmission direction, but there is no need to know the amount of movement. In other words, for both the single reflection signal and the multiple reflection signal, the shift amount is frequency converted, the pseudo multiple reflection signal is removed, this is inversely frequency converted to obtain the correlation value, and the peak of the correlation value is detected. This determines the shift amount of the echo signal and reduces multiple reflected signal components.

The principle of the method for reducing multiple reflected signal components of the present invention will be explained with reference to FIG. For simplicity, the transmitting and receiving signals of the ultrasound probe are sinusoidal pulse waves of l wavelength, and reflection occurs only between the point reflector and the vibrator inside the object, which complicates the system such as attenuation and scattering. Assume that the parameters can be ignored. In addition, both single reflection and multiple reflection signals are assumed to be time-invariant signals.
It is assumed that the time until each delivery changes depending on the minute displacement of the probe, and each signal distribution remains unchanged.

The received signal at the initial position of the probe, that is, the echo signal, is the reflected signal s, where t is the elapsed time from the time of transmission.
(t) and the multiple reflection signal va (tl) (1)
The formula %formula %(1) is obtained, and its waveform 100 is shown in the figure. The echo signal when the probe is moved forward or backward by a displacement amount δ in the direction of the reflector is expressed by equation (2), %, and the waveform 102 is shown in the same figure. T is the time conversion coefficient of δ. It is.

The signal obtained by giving a phase difference τδ in the positive direction on the time axis to E, (tl is the waveform 104 in the same figure, that is, Eb(t-t
d), the sine pulse wave 106 on the left side is a single reflection signal component, and the sine pulse wave 108 on the right side is a multiple reflection signal component. Further, d is a variable, and in this case, it can take any value.

Now, when d=δ, E, (t) and Eh(t-td
). In this case, the single reflection signal components of the two echo signals have the same phase, and the multiple reflection signals differ in phase by td. If E, (t) - Eh (t - d) is calculated here, the single reflection signal component is canceled out, and a signal is obtained in which multiple reflection signal components whose phases differ by td are superimposed.

That is, E - (t) E bit-z d) = s It)
10m (t) -s (t) -ta lt+ td
)= ta (t) −va (t+τd)
-(31) Here, the Fourier transform FT of equation (3) becomes as shown in equation (4).

FT (E, (t) - E, (t - te d) = FT (n + (tl - n + (t÷τd)) = FT
(Fog(tl)-FT(■(t+τd11=Mlul-M
lu) exp(i2x u td) = (1-expl
i2z ur, d) ) Mtu)
+++ (4, where FT indicates Fourier transform. Also, FT (Il(t) l ; M (u
l, and i indicates an imaginary number.

Here, E , , E , , d are known, so (4
) can be modified to obtain M(ul).

By performing inverse Fourier transform TFI on M(u) obtained by equation (5), the multiple reflection signal component m (t) can be obtained.

ta (tl = FT (M (ul l
= (6) However, IFT indicates inverse Fourier transform. In this way, a pseudo multiple reflection signal component is obtained on the assumption that d=δ.

here.

ε,' it) = E, (t)-m(tl :s
It) = (7)Eb' (t)
= E bit) −m (t+zτd)= s (
tl r dl = 18), for both E, '(t), and tb' (tl, the pseudo multiple reflection signal component is eliminated from the original echo signal, and the echo of only the pseudo half-reflection signal component is signal, and its phase difference is τd.In other words, if Eゎ°(tl is shifted to the left by τd and the correlation is taken with E,'(t), it should be I.However, the correlation D (d) shall be defined by equation (9).

However, in equation (9), for D (d) to be 1, there must be the premise that d=δ. Further, δ is an unknown value, and d cannot be uniquely determined. but,
When d is near δ, the absolute value of d−δ is small, so D (di
tends to approach l.

Therefore, while changing the value of d little by little, calculate D(di) and calculate s ft when the peak closest to l is detected.
) becomes the true semi-reflection signal component.

By performing a series of calculations as described above, it is possible to obtain an echo signal from which multiple reflection signal components are removed from the two echo signals.

In addition, if no clear peak is detected, it means that there is no multiple reflection signal component in the received echo signal, or the signal is extremely weak. In such cases, the echo signal is considered to be a semi-reflection signal component. Display the echo signal directly.

Next, an embodiment will be described in which one or more systems for removing multiple reflected signal components are incorporated into an ultrasonic diagnostic apparatus.

FIG. 1 shows a block diagram of an ultrasonic diagnostic apparatus incorporating a multiple reflection signal component removal system. In the same figure, the ultrasonic diagnostic apparatus of this embodiment has an ultrasonic transducer 600, transmits ultrasonic waves from the ultrasonic transducer 600 into a subject 601, and generates an echo based on the reflected echo signal. This is a device that displays a tomographic image represented by a waveform on a display unit 610. This has an ultrasonic transducer 600, and the ultrasonic transducer 600 comes into contact with a subject 601 via an ultrasonic propagating substance 602. This ultrasonic propagation material 602 includes a material in which the movement of the ultrasonic transducer 600 has little direct effect on the measurement of the reflector distribution within the subject 601. The ultrasound transducer 600 is an electrical/acoustic transducer that transmits ultrasound waves into the subject 601, receives echoes reflected from the ultrasound waves, and converts them into electrical signals.

The transducer moving device 603 is a device that mechanically moves the transducer 600 forward or backward in the wave transmission direction. The transmitting circuit 604 drives the vibrator 600 to transmit ultrasonic waves. The receiving circuit 605 amplifies and outputs the echo signal received by the vibrator 600. The synchronization circuit 611 is the transmission circuit 6
04 transmission, receiving circuit 605 echo reception, mobile device 6
This is a circuit that synchronizes the movement operations of 03. A/D
The conversion circuit 606 converts the echo signal output from the reception circuit 605 into a digital signal and stores it in the memory 607.

The multiple reflection reduction circuit 608 is a circuit that reads a digital signal from the memory 607, executes a multiple reflection removal algorithm to be described later to remove the multiple reflection signal component, and outputs the result. The D/A conversion circuit 607 converts this output into an analog signal and outputs it to the display section 610. The display section 610 is an image display device such as a CRT, and a Subject 601
tomographic images are displayed.

A configuration example of the multiple reflection reduction circuit 608 is shown in FIG.
The echo data is read out, the multiple reflection removal algorithm described above is executed, and then other processing routines in the program memory 607 are performed, such as signal processing such as absolute value conversion by detection, logarithmic conversion, and data compression, to obtain the results. image data is written into the image memory 702. Data in image memory 702 is sent to D/A conversion circuit 609 via data bus 704.

A dual-board T-RAM is advantageously used as the image memory, and one of the display sections 61 is
For example, the contents of the image memory 702 are read out at the scanning timing of the CRT. As a result, a tomographic image from which multiple reflection components have been removed is displayed. The above series of operations is executed at high speed, and the display unit 610 displays the fault 19 in real time.FIGS. 3A to 3C show the flow of the multiple reflection removal process described above. First, the echo signals (E'a(t), Ewa(t)) received by the ultrasound probe 600 are stored in the memory 6.
07. The processor 700 stores the two echo signals (E, (t), Eb(lull) in the memory 60
Read from 7 +5011 and set d to the minimum value of δ that can be expected (initial setting value) (502) Next, compare d with the maximum value of δ that can be expected (maximum setting value) 503), d is less than the maximum setting value,
Shift Ebftl by d and get f504), E,
Calculate ftl +505+.

Then, E, ft) is subjected to Fourier transform (5061. The converted value is divided by l - expfi 2 x t d)507), and the result is inverse Fourier transformed to calculate the pseudo multiple reflection signal component mft) +5081°E
, (jl, Eb(The pseudo multi-reflection signal component s ftl is obtained by subtracting m ftl from El (509), and E
, (t,), E, (calculate the correlation D[dl of the single reflection signal components obtained from each of jl (510). Then, store D fdl and 5ft) and +5111. Increase the value of d (5121, return to process 503. If d exceeds the maximum setting value, detect a peak close to 1 in D (d) written = R until now +5131. A peak is detected. Then, s ft) at that time is E, (tl, Ewa f
tl as a true single reflection signal (5141 If no peak is detected, it is assumed that there is no multiple reflection signal component in the input echo signal, and the echo signal is output as it is as a single reflection signal (5151, a series of Terminates the process.

The algorithm for removing multiple reflections is not limited to the one described above. Instead of setting the initial setting value of d to the maximum value of δ and taking the correlation value while gradually decreasing d, or detecting the peak of D (d), simply find the minimum value and combine that value with the threshold. Even if d is calculated by comparing the magnitude of , almost the same result can be obtained.

In addition, in the above explanation, only the multiple reflection signal component is calculated by shifting the single reflection signal components so that they are in the same phase, taking the difference, and performing Fourier transform, division, and inverse Fourier transform on that signal. Taking into account the phase difference, E, (
tl, E b (Two single reflection signal components were calculated by subtracting from tl. However, even if the method of calculating the single reflection signal component and the multiple reflection signal component is reversed, D ( The distribution of dl is obtained.

In other words, first shift the multiple reflection signal components so that they are in the same phase, take the difference, calculate only the single reflection signal component by Fourier transform, division, and inverse Fourier transform of that signal, and then convert the signal to the phase difference. Taking into account E, ftl,
By subtracting the two multiple reflection signal components from Eb(tl and taking the correlation, D
The distribution shown in (d) is obtained.

In the present invention, the multiple reflection signal component is removed by detecting the peak of the correlation between two pseudo multiple reflection signals. However, if there are no multiple reflection signal components, or if the signal is extremely weak, the correlation peak will not be detected, so the configuration is such that the echo signal is displayed as is. This feature is less susceptible to noise etc. than the prior art such as JP-A No. 56-143151, and improves the reliability of the device. The invention vibrates an ultrasound transducer that transmits and receives ultrasound signals within a subject in an ultrasound diagnostic device in the transmission direction, removes multiple reflection signal components from multiple echo signals, and eliminates artifact components in tomographic images. It has the effect of reducing Unlike the conventional method, which generates a pseudo multiple reflection signal from a single reflection signal, the multiple reflection signal component is removed only when the multiple reflection signal component exists in the echo signal, which improves the reliability of the device. is extremely high.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing one embodiment of an ultrasonic diagnostic apparatus according to the present invention; FIG. 2 is a functional block diagram showing an example of the configuration of a multiple reflection reduction circuit of the apparatus shown in FIG. 1; FIG. 3A; Figures 3B and 3C are flow diagrams showing an example of the multiple reflection elimination algorithm; Figure 4 shows the waveform of the echo signal at the initial position of the probe, the waveform of the echo signal at the moved position, and the waveform obtained by shifting the waveform. FIG. Description of main part 1 600, , , Ultrasonic transducer-602, , Ultrasonic propagation material 603, , Transducer moving device 604, , Transmitting circuit 605, , Receiving circuit 606, , A /D conversion circuit 608, , multiple reflection reduction circuit 609, , /A conversion circuit 610, , display section 611, , same amount circuit

Claims (1)

[Claims] 1. Ultrasonic waves that transmit ultrasonic waves into a subject from an ultrasonic transducer and receive reflected echoes with the ultrasonic transducer to form a tomographic image represented by the echo signals. The diagnostic apparatus includes: a moving means for moving the ultrasonic transducer in a wave transmission direction; a storage means for storing echo signals; control means for causing the ultrasonic transducer to receive a plurality of echo signals at different positions and storing the plurality of echo signals in the storage means; and multiple reflection for removing multiple reflection signal components from the plurality of echo signals. and a signal reduction means, the multiple reflected signal reduction means comprising: echo signal difference means for relatively shifting the plurality of echo signals and taking a difference between the two; and difference information between the echo signals by the signal difference means. a pseudo multiple reflection signal generating means for generating a pseudo multiple reflection signal component based on the above; An ultrasonic diagnostic apparatus comprising: pseudo single reflection signal generating means for obtaining a reflected signal component; and single reflection signal determining means for obtaining a single reflection signal satisfying a predetermined condition from the plurality of pseudo single reflection components. 2. In the apparatus according to claim 1, an ultrasonic propagation body is interposed between the surface of the subject and the surface of the ultrasonic transducer, and the ultrasonic propagation body is configured to move the ultrasonic transducer. An ultrasonic diagnostic apparatus characterized in that the material includes a material that has little influence on the measurement of the reflector distribution within the subject. 3. The ultrasonic diagnostic apparatus according to claim 1, wherein the multiple reflection signal reducing means outputs the echo signal when a single reflection signal satisfying the predetermined condition cannot be determined. . 4. In the apparatus according to claim 1, the pseudo multiple reflection signal determining means determines the difference signal from the echo signal differentiating means by assuming that equal waveforms overlap with a phase difference corresponding to the shift amount. An ultrasonic diagnostic apparatus characterized in that a pseudo multiple reflection signal component is extracted by performing frequency conversion, removing a phase difference, and inverse frequency conversion. 5. In the apparatus according to claim 1, the pseudo single reflection signal generating means calculates the difference between the plurality of echo signals and the signal from the pseudo multiple reflection signal generating means, taking into account the shift amount. An ultrasonic diagnostic apparatus characterized by generating a plurality of pseudo single reflection signal components. 6. In the apparatus according to claim 1, the single reflection signal determining means calculates a correlation between the plurality of pseudo single reflection signals obtained by the pseudo single reflection signal generating means, and the correlation reaches a peak. An ultrasonic diagnostic device characterized in that a pseudo single reflection signal at a time is a single reflection signal.