JPH03114451A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To minimize the effect due to the multiple reflection of an ultrasonic echo by calculating the phases of a signal at a plurality of positions from the content of a memory means and shifting the signal so that the phase difference of an echo signal approaches zero and performing operational processing due to averaging or the like. CONSTITUTION:The ultrasonic signal transmitted into an examinee 40 from a transmitting part 25 through an ultrasonic vibrator 41 is reflected by the reflecting body 42 in the examinee 40 to be again received by the vibrator 41. The echo signal thereof is sent to a receiving part 32. At each time when the echo signal is outputted, the moving quantity of the vibrator 41 moved by a vibrator moving part 22 is measured by a moving quantity measuring part 23 and the data thereof is stored in a moving quantity data memory 24. The echo signal inputted to the receiving part 32 is converted to a digital signal by an A/D converter to be successively stored in an echo data memory 33. In a multiple reflection reducing part 34, an echo signal reduced in a multiple reflection signal component is outputted to a detection part 35 from the data stored in both memories using a multiple reflection reducing processing method to be detected and subjected to D/A conversion to be displayed on a display part 47 as a visible image.

Description

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

[Prior Art] As is well known, an ultrasound diagnostic device is a device that transmits ultrasound waves into a subject from an ultrasound probe, receives echoes from an internal reflector, and displays a tomographic image. . Ideally, it is required that a tomographic image corresponding only to the internal tissue of the subject be displayed. However, in reality, due to the difference in acoustic impedance between the ultrasound probe and the surface of the subject, ultrasound echoes are reflected at the boundary between the two, and some of the echoes that entered the ultrasound probe enter the subject again. . Therefore, multiple reflections of multiple orders occur between the surface of the object and the reflector inside the object. Therefore, ghosts due to multiple reflections may appear in the image displayed on the display of the device.

Since ghosts caused by multiple reflections have a negative effect on diagnosis, 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
There are methods described in No. 1 and Japanese Unexamined Patent Publication No. 117150/1983. In these methods, when an echo signal without multiple reflections, that is, a single signal component, is received at a sand diameter of t of the transmitted wave, 2t, 3
Assuming that multiple reflected signal components are received at the sand diameter, t, taking into account attenuation parameters, pseudo signals are generated at 2L, 3L,... sand diameter, respectively, and subtracted from the multiple reflected signal. , thereby eliminating multiple reflected signal components.

[Problems to be Solved by the Invention] However, in the conventional method, a pseudo multiple reflection signal is generated from a single reflection signal which is an echo signal. Therefore, for example, if noise is input to the t sand diameter of the transmitted wave, 2t, 3
Even though similar noise does not exist in the echo signal after L, . . . seconds, an old multiple reflection signal component containing noise is generated. Therefore, if there are multiple reflected signal components,
We perform subtraction with this, but it is not possible to reduce this.
The signal transmitted from the probe is reflected by the reflector and returns to the probe, but due to the inclination of the reflector, the center of the reflected wave is shifted by a distance d from the position from which the signal was transmitted. At this position, a portion of the signal is reflected again at the probe surface and enters the subject. If the signal is reflected back to the probe, the receiving position will be further shifted by a distance approximately equal to 3d. Furthermore, multiple reflections occur once again, and when the signal is received by the probe, the position is shifted by a distance approximately equal to 5d from the position where the first multiple reflections were received. Therefore, multiple reflected signals may or may not be received by the probe depending on the delicate positional relationship between the reflector and the probe. Therefore, whether it is a single reflection signal or a multiple reflection signal! 1=t (If it is not sufficient to identify whether the signal is G or not, not only the multiple reflection signal component cannot be reduced, but also the single reflection signal component will be removed.

An object of the present invention is to solve these problems and provide an ultrasonic diagnostic apparatus in which the influence of multiple reflections of ultrasonic echoes is minimized.

[Means for Solving the Problems] According to the present invention, the multiple reflection signal component is determined from the difference between the displacement amount of the single reflection signal component and the displacement amount of the multiple reflection signal component obtained by moving the probe in the ultrasound transmission direction. Reflected signal components are effectively reduced.

According to the present invention, an ultrasonic wave having an ultrasonic diagnostic means transmits an ultrasonic wave from an ultrasonic transducer into a subject, receives an echo reflected from the subject, and outputs a signal represented by the echo. The diagnostic device includes a moving means for moving the ultrasound transducer between at least a first and a second position in the ultrasound transmission direction, and a movement amount measuring means for measuring the amount of movement of the ultrasound transducer by the moving means. , a first storage means for storing the amount of movement, and a first storage means for storing the amount of movement, and a first
and second storage means for storing the signal at at least one of the second positions, and the phase of the signal at the first and second positions is determined based on the amount of movement based on the stored contents of the first and second storage means. The ultrasonic diagnostic means outputs the processed signal.

According to the present invention, the ultrasonic diagnostic apparatus also includes an ultrasonic propagation means interposed between the surface of the subject and the surface of the ultrasonic transducer, and the ultrasonic propagation means moves the ultrasonic transducer. may directly include a medium that has little influence on the measurement of the reflector distribution within the object.

According to the present invention, in the ultrasonic diagnostic apparatus, the calculation means performs calculation to shift the signal at the second position relative to the signal at the first position in accordance with the amount of movement.

According to the present invention, the shift further comprises: ? ! The phase difference between several echo signals is substantially eliminated.

[Function] According to the present invention, the transducer is moved in the wave transmission direction by the transducer moving means, echo signals and multiple reflection signals are received at a plurality of positions, and these are stored in the second storage means. The movement 14 measured by the movement amount measuring means is stored in the first recording/hearing means. The calculation means calculates the phase of the signal at a plurality of positions from the contents of the storage means, shifts the signal so that the phase difference of the echo signal approaches zero, and performs calculation processing such as averaging. This reduces multiple reflected signal components in which one phase difference is not zero. Thereafter, the echo signal is displayed on one display as a visible image showing the tomographic image of the subject. The signal to be processed may be a signal after detection or a signal before detection 6 [Example] Hereinafter, an example of the ultrasonic diagnostic apparatus according to the present invention will be described in detail with reference to the drawings. explain.

The outline of the method of the present invention is as follows. That is, the ultrasonic transducer array is moved to a plurality of positions in the wave transmission direction, and the amount of movement to the moved position, the echo signal, and its multiple reflection signal are stored in a memory. The phase of the signal train at the moved position is determined from the amount of movement, and the signal train is shifted so that each echo signal has the same phase, thereby reducing multiple reflected signal components.

FIG. 1 shows a basic configuration diagram of an embodiment of an ultrasonic diagnostic apparatus, and FIG. 4 shows its waveform diagram. The ultrasonic diagnostic apparatus l shown in FIG. The ultrasonic transducer 41 is an electro-acoustic transducer that transmits ultrasonic waves to the subject 40 and receives echoes from a reflector inside the subject 40. The ultrasonic transducer 41 is supported by a support body 46 on a moving device 44, which is a device that moves the ultrasonic transducer 41 by a small distance in the wave transmission direction. Vibrator 4
1 is connected to a movement measuring device 45, which is connected to the vibrator 4.
This device measures the displacement position δ of the distance between 1 and a reflector 42 in a subject 40. Note that in this example, the subject 40
The speed of sound inside is constant and its value is C. Although the sound speed within the ultrasonic propagation material 43 is not necessarily uniform in reality, it is assumed here to be the sound speed C for simplicity.

FIG. 4(^) shows a received waveform when the vibrator 41 transmits an ultrasonic wave at a sound speed of C to the reflector 42 at a distance.

An echo signal without the influence of multiple reflections, that is, a half-reflection component 51, is received at time A of time interval 2L/c, and is received at the second and third times at time B and C of time interval 2L/c, respectively. Certain multiple reflected signal components 52 and 53 appear. In this example, it is assumed that the received waves after the fourth time were attenuated and could not be measured.

FIG. 4 (81 shows the waveform when the distance 1iIIL is moved by a minute amount δ. Time interval 2 (L + δl/c)
There are echo signals 54 and multiple reflection signal components 55 and 56 at 3, E, and F. From the point of waveform fBl, E, F
are delayed by 2δ/C14δ/C16δ/C, respectively, compared to the corresponding points A, B, and C of the same +Al.6 Figure 4 (C1 shows the waveform obtained by shifting the waveform fBl by the time 2δ/C. (Comparing Al and TCI, echo signals A and Do are in the same phase, multiplexed signal component E° lags B by time 2δ/C, and F゛ lags C by time 4δ/C. .

Specifically, in the apparatus according to the embodiment shown in FIG. By shifting to the position, the waveform manipulation described above is performed. As a result, the echo signal A in the initial state and the echo signal D after movement are at the same position, and the other component B
, C and E゛, Fo are out of position. Therefore, component A
, B, C and Do, E゛, Fo, the fourth
As shown in Figure (D), the amplitude of the echo signal component remains unchanged, and the amplitude of the multiple reflection signal component is attenuated to an extent close to 1/2.

The above is an example in which the vibrator 41 is moved once and two sets of waveform sequences are synthesized in order to simplify the process. However, it is also possible to move multiple times, for example twice, to obtain three sets of waveforms, shift each echo signal to the same position, and average the three sets of waveforms.In this way, the amplitude of the echo signal are the same, and the amplitude of the multiple reflection signal component approaches l/3.

When the number of echo signals to be processed is n, the amplitude of the multiple reflection signal component approaches l/n because the transmitted signal is a pulse wave, and the pulse wave of the multiple reflection signal component of the shifted echo signal is , are separated from each other. However, even if the pulse waves of the multiple reflection signal components are not separated, the tendency for the multiple reflection signal components to become smaller by performing the above-described processing remains the same.

In the above explanation, waveform manipulation was performed on the detected echo signal. However, waveform manipulation may be performed on the echo signal before detection, that is, at the RF stage. For example, instead of simply averaging the single reflection signal components after shifting them to the same position, deriving an equation from a model and solving that equation can reduce the multiple reflection signal components with even greater precision. It is possible to do so.

Next, an example of multiple reflection signal processing when the transducer 41 is moved once is shown.For simplicity, the signal transmitted from the transducer 41 is a continuous sine wave, and the ultrasonic wave inside the object 40 is attenuated. is so small that it can be ignored. Further, it is assumed that only the first multiple reflection signal is measured.

First, assuming that the vibrator is at the reference position and the echo signal at that time is C3 (tl), then Co (Ll ・A
s1n ((11t+θ, l+Bs1n ((IJ can be expressed as 10b1...+11.(1)
In the formula, A is the amplitude of the single reflection signal component, B is the amplitude of the multiple reflection signal component, C1 and θゎ are the phase differences in the initial state of the single reflection signal component and the multiple reflection signal component, respectively, and ω is the angular velocity, It is determined by the frequency of the transmitted ultrasonic wave, and is the same for both single reflection and multiple reflection signal components.

Next, when the vibrator 41 moves by a distance δ, the received echo signal is shifted by -4πδ,/λ and then c
, (tl).

1, + (tl = Asin (ωt + θ,) + Bs1
n(ca+ (t÷2δ+/c)÷θl, 1...12
).

Similarly, when the vibrator 41 moves by a distance δ2, the received echo signal shifted by -4πδ2/ is C2(tl, then C2(tl = Asin 1(11t÷θ,)÷Bs
1n(ω (t ÷2δ 2/c) 10 I, 1.
,,(:11.

(21 (Decompose the second term of equation 31 using the addition theorem.

a = Asin(ωt+01) β: Bs1n(ωt+θIl) γ=Bcos(ωL÷θIl) And then.

Co (t)・α-striped β ,,,
(11'C+(t)・a+βcos(2(A)δ1/c
)÷ ysini 2(Llδ+/c) , , -
(2) C2(tl □ a÷βcos(2(41δ2/
c) + γ5in (2ωδg/cl, -(3)'
In the equation (11' + 2) ' (3) ', the unknown is a
, β, and γ, one formula il+ ' +21 '
(If 31' is a three-dimensional simultaneous equation, and α is calculated, 5inl 2ω1δ, -δ-)/c) +5in(2ωδa/cl -5in (2ωδ1/c
),,+41. Since a is a single reflection signal component, an echo signal without multiple reflection signal components can be obtained by calculating equation (4).

In the above description, the transmitted signal was assumed to be a continuous sine wave for the sake of simplicity; however, a normal ultrasonic diagnostic apparatus generally uses a short pulse wave in the form of a burst of liquid droplet. However, the amounts of movement δ1 and δ2 of the transducer 41 need only be less than the ultrasonic wavelength λ inside the subject, and burst waves of the size of liquid droplets can also be considered part of continuous waves when viewed microscopically. The process holds true approximately.

In the above embodiment, no limit was placed on the detection of the amounts of movement δ6 and δ2 of the vibrator 41, but by setting the amount of movement of the vibrator to λ/4.

Signal processing can be simplified. This process corresponds to the process of shifting the waveform fil with respect to the waveform (A) in FIG. 4 to reduce multiple reflection signals.

If the phase difference 2ωδ+/c in equation (2) is θ, then ω; 21C/E, θ, = 4πδ1/E. From δ,・E/4, θ1=π
becomes.

Therefore, the formula 2 is C+ fL) = Asin (ω is 10,) ÷ Bs1n (
ωt+π + θl, 1 ,, (51(1
Find the sum of equation 1 and equation (5).

Cofj)+C+lj)・As1nl ωt+θ,
)÷Bs1n(ω t+θ I,)+As1n lω is 10 θml”Bs1n(ωtax+θb)=2Asin
((IJ t+θa) ,,,(61,
Multiple reflection components are removed.

FIG. 5 shows the waveform of equation (6). Note that in the figure, the echo signal is not displayed as a continuous wave but as a pulse wave of the length of the liquid droplet. In FIG. 5, a waveform 92 is expressed by the formula C6 (tl, and waveforms 90a and 91a are an echo signal component and a first multiple reflection signal component, respectively.A solid line 95 of a waveform 93 indicates that the transducer 41 is The broken line 96 shows the echo signal obtained by shifting it by -26+/c, i.e., the formula % waveform 94 is C3(tl +C+ +1, and the single reflection component is waveform 90c. It can be seen that the multiple reflection components are reduced as shown in waveform 91c.

In the above embodiment, the amount of movement of the vibrator 41 is /4
Echo signals were captured at a certain position.

However, the present invention is not limited to this, and the amount of movement of the vibrator 41 is O1λ/2.
A plurality of n echo signals of n, 2λ/2n, 3e/2n, (n-11e/2n) are taken in, and each is adjusted to 0 so that the single reflection component of the echo signal is in the same phase.
By performing addition after shifting twice, multiple reflection components can be further reduced.

The sum total of n types of echo signals in which single reflection components have the same phase can be expressed as in equation (7).

(Note that n≧2) = nA sin (ωt + 01) + BΣ5in (ωt + θb
+ ix/n1=nA sin ((IJ is 10,) I BΣ1 sin (ωt+θl1) cost ix
/nl+ cos(ωt÷θblsin(ix/nu
= 口Asi口(ω L+θ ,) + 5in(ω t+θ h)Σcos(ix/n)
+ Bcos (ω to 10.) Σ5ini ix
/n) Here, Σ5inix=sinifn+llx/21sin(n
x/2)/5inlx/2)Σ”, cosix=co
sf(n+llx/2) sinfnx/21/5inf
x/2), Σ-5in(im/nl=Σ5inf ix/n, 1=
sin(in+Il π/2nlsin(i/2)/
5in(π/2n) =0 , , , f8
1Σcost iπ/n)=Σcos(ix/n1=
cos ((n+0 π/2tGsin(π/2)/5
inl π/2n) =0 , , ,
(91+71 (8) (5=nA sin lωt+θ from formula 91,)
, 11) In this way, when the echo signals are continuous waves with the same amplitude, it is possible to remove multiple reflection components.

Note that in this case, n is a natural number of 2 or more, and the case of n·2 corresponds to the above-mentioned equation (6).

FIG. 2 shows an example of the configuration of a movement measuring device 45 for measuring the movement amount of the ultrasonic transducer 41 in the ultrasonic diagnostic apparatus l shown in FIG. The transducer 61 for position measurement, which is a child and is placed in a container 48 filled with an ultrasonic propagation substance 43 together with the transducer 61 for position measurement, transmits ultrasonic pulses to the transducer 60 by driving the transmission circuit 62. It sends waves to the wall, receives the echo reflected by the wall, and outputs an echo signal. The echo signal is amplified by the receiving circuit 63 and sent to the movement amount determining circuit 64.

Circuits 62 to 64 and memory circuit 65 operate in synchronization with a synchronization signal from synchronization circuit 60. The movement amount determining circuit 64 is set with a threshold value including the magnitude of the transmitted signal, the attenuation rate of the ultrasonic propagation material 43, etc. The circuit 64 compares the data of the transfer signal with the threshold value, Calculate the time when the value of increases. The circuit 64, which calculates the amount of movement of the ultrasonic transducer 60 by dividing this time by the speed of sound, determines the amount of movement each time the transducer 41 is moved, and stores the data in the memory 65.
to be memorized.

Next, the block diagram of FIG. 3 shows a specific example of the configuration of an ultrasonic diagnostic apparatus l incorporating the above-mentioned multiple reflection signal component reduction processing method.
The transducer is placed inside the body and placed on the subject 40, and its position is moved minutely by the transducer moving unit 22. Movement amount measuring section 23
measures the amount of movement.

This is stored in the movement amount data memory 24. The ultrasonic propagation material 43 is configured so that the movement of the transducer 41 can directly minimize the influence on the measurement of the reflector distribution inside the object 40 and allow the movement amount measuring section 23 to accurately measure the amount of movement. It is the medium of The transmitter 25 is a vibrator 41
is driven to transmit ultrasonic waves to the subject 40. Receiving section 3
2 amplifies the echo signal and stores the echo data in the echo data memory 33. The multiple reflection reduction unit 34 performs the aforementioned multiple reflection signal component reduction processing on the echo data in the memory 33, and the detection unit 35 detects the processed echo signal and displays a tomographic image of the subject 40 represented by the detected signal. 40. The synchronization control unit 31 performs control to synchronize these series of processes.

The ultrasonic signal transmitted from the transmitter 25 into the subject 40 via the ultrasonic transducer 41 is reflected by the internal reflector 42 (FIG. 1).
The wave is reflected by the oscillator 41 and received again by the vibrator 41. The echo signal is sent to the receiving section 32. Every time this echo signal is output, the movement amount measuring section 23 measures the amount of movement of the transducer 41 by the transducer moving section 22, and stores the data in the movement amount data memory 24. The echo signal input to the receiving section 32 is A/D converted and sequentially stored in the echo data memory 33. Here, the storage order of the memories 33 and 24 is matched by the synchronization control section 31.

From the data stored in both memories, the multiple reflection reduction unit 3
In step 4, an echo signal in which multiple reflection signal components have been reduced is output to the detection unit 35 using the multiple reflection reduction processing method described above from the plurality of echo signal data and data on the amount of transducer movement corresponding thereto. Here, the echo signal is detected and D/
A conversion is performed and the image is displayed on the display 40 as a visible image.

The present invention not only reduces the multiple reflected signal components described above, but also widens the directivity (side lobe) of the vibrator 41.
It is also effective in reducing virtual image components. If the directivity due to side lobes of the transducer 41 is spread, unless the waveform manipulation according to the present invention is performed, the transducer 4 of the subject 40 will
Echo signals from reflectors other than those directly below the transducer 41 will also be received, and an image will be formed using the received signals as those directly below the transducer 41.However, by moving the transducer 41, it is possible to reduce the virtual image component. can.

In FIG. 6, a reflector 88 is located on the central axis Y of the directivity (main lobe) of the ultrasonic transducer 41, and the reflector 88 is located at an angle θ from the Y axis.
, if there is another reflector 81 at a distance, an echo signal 83 (FIG. 7) due to a side lobe is received from this, and a virtual image 82 is generated by this at a distance from the vibrator 41 on the Y axis.

At a position 84 where the vibrator 41 is moved by a distance δ in the Y-axis direction from this state, an echo signal 8 due to the side lobe
6 (FIG. 7), a virtual image 82 appears on the Y axis. Comparing the two echo signals 83 and 86, the deviation of the echo of the reflector 88 is 2δ/C with respect to the amount of transducer movement, but the deviation of the virtual images 82 and 85 due to the side rope is 26 s.
/c, which is different from the amount of shift of the reflector 88 on the Y-axis.

Here, δ,=Jt2÷2Lδcosθ÷δ2−L.

When the waveforms 83 and 86 are shifted so that the phase difference between the single reflection signal components becomes 0, and the aforementioned multiple reflection reduction processing is performed, an echo signal like the waveform 87 shown in FIG. 7 is obtained. That is, the amplitude of the echo caused by the side lobe is smaller than that of the echo caused by the main rope, and it can be confirmed that the virtual image component is reduced.

As described above, the present invention is effective in reducing not only multiple reflection signal components but also other virtual image components.

[Effect of the Invention 1] As described in detail above, the ultrasound diagnostic apparatus according to the present invention moves the ultrasound transducer that transmits and receives ultrasound signals within the subject in the wave transmission direction, and calculates the By shifting multiple echo signals so that the phase difference of their single reflection signal components becomes O, and performing calculations between the shifted multiple echo signals, the virtual image components of the tomographic image due to multiple reflections and side lobes can be removed. can be effectively reduced.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention, FIG. 2 is a circuit diagram of a movement measuring device in the embodiment shown in FIG. 1, and FIG. FIG. 4 is a functional block diagram showing a more detailed configuration example of the ultrasound diagnostic device. FIG. 4 is a waveform diagram of multiple reflection signal processing when the transducer is moved once in the device shown in FIG. FIG. 3 is a diagram showing an example of a waveform expressed by an arithmetic expression for wave signal processing. FIG. 6 is an explanatory diagram when the multiple reflection signal processing of the present invention is used to reduce virtual images due to side lobes, and FIG. 7 is a waveform diagram showing signal waveforms in the example shown in FIG. 6. 10゜Main opening, C'' explanation, ultrasonic diagnostic equipment transducer moving part movement measuring part, movement data memory transmitting part synchronization control part, receiving part echo data memory multiple reflection reduction part, detection part object, ultrasonic Sound wave transducer, ultrasonic propagation material, moving device movement measurement device display section

Claims (1)

[Claims] 1. Ultrasonic diagnostic means that transmits ultrasonic waves from an ultrasonic transducer into a subject, receives echoes reflected from the subject, and outputs signals represented by the echoes. An ultrasonic diagnostic apparatus comprising: a moving means for moving the ultrasonic transducer between at least first and second positions in the ultrasound transmission direction; a movement amount measuring means for measuring the movement amount of the child; a first storage means for storing the movement amount; and a signal at at least one of the first and second positions obtained by the ultrasonic diagnostic means. a second storage means for storing, and a phase of the signal at the first and second positions is determined from the amount of movement from the stored contents of the first and second storage means, and thereby multiple reflection signals included in the signal are determined. an arithmetic unit that performs arithmetic processing to reduce the ultrasonic diagnostic apparatus, wherein the ultrasonic diagnostic unit outputs the arithmetic-processed signal. 2. The apparatus according to claim 1, wherein the apparatus includes an ultrasonic propagation means interposed between the surface of the subject and the surface of the ultrasonic transducer, and the ultrasonic propagation means An ultrasonic diagnostic apparatus characterized in that the movement of an ultrasonic transducer directly involves a medium that has little influence on the measurement of reflector distribution within the subject. 3. In the device according to claim 1, the calculation means:
An ultrasonic diagnostic apparatus characterized in that an operation is performed to shift a signal at a second position with respect to a signal at the first position in accordance with the amount of movement. 4. The ultrasonic diagnostic apparatus according to claim 3, wherein the shift substantially eliminates a phase difference between the plurality of echo signals.