JPH11235341A - Ultrasonograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonograph capable of reducing the effect on image quality of significant deflection of the received signals of some of vibrators in a bore due to refraction or multiple reflections, etc. SOLUTION: Excitation signals of plural vibrators aligned and received signals obtained when the vibrators receive ultrasonic waves reflected from a subject are individually given delay times to impart the directivity of transmission and reception to the ultrasonic waves and to scan the inside of the subject using the ultrasonic waves given directivity, thus obtaining an ultrasonogram. In that case, a received signal evaluating part 21 evaluating the deflection of the received signal for each vibrator and an aperture control part 23 controlling at least either the strength of the excitation signal or the amplification factor of the received signal according to the result of evaluation are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave that imparts transmission and reception directivity to an ultrasonic wave by delay control, and scans the inside of a subject with the ultrasonic wave having the directivity to obtain an ultrasonic image. It relates to a diagnostic device.

[0002]

2. Description of the Related Art There are various medical applications of ultrasonic waves, and the mainstream is an ultrasonic diagnostic apparatus for obtaining a tomographic image of a soft tissue of a living body using an ultrasonic pulse reflection method. This ultrasonic diagnostic apparatus displays a tomographic image of a tissue by a non-invasive examination method, and includes an X-ray diagnostic apparatus, an X-ray CT apparatus, and an MR apparatus.
Compared to other diagnostic devices such as I and nuclear medicine diagnostic devices,
It has unique features such as real-time display, small and inexpensive device, high safety without exposure to X-rays, and blood flow imaging by ultrasonic Doppler method.

[0003] Therefore, it is widely used in the heart, abdomen, mammary gland, urology, obstetrics and gynecology, and the like. In particular, with the simple operation of simply assigning the ultrasound probe from the body surface, the state of the heart beat and the movement of the fetus can be obtained in real time display,
In addition, the safety is high, so that the inspection can be repeated, and the inspection while moving to the bedside can be easily performed.

As is well known, a plurality of transducers are arranged one-dimensionally or two-dimensionally on an ultrasonic probe as shown in FIG. 17, and the ultrasonic transducers are directed toward a living body from these plural transducers. The delay time is individually set to the excitation signal for transmitting the ultrasonic wave and the reception signal obtained by these transducers receiving the ultrasonic reflected wave from the living body according to the geometric position information of each transducer. Given (so-called delay control), a focal point is formed in transmitted ultrasonic waves and received signals from each transducer. Hereinafter, the operation of delaying the excitation at the time of transmission and the operation of phasing addition at the time of reception are referred to as transmission beam formation and reception beam formation, respectively.

In some cases, the transmission beam formation and the reception beam formation are performed not by using all the transducers but by selectively using the transducers. In this case, the transmission / reception aperture ((the transducer used for transmission / reception) is used. Number) × transducer pitch) and the distribution of gains to be assigned to each transducer in the aperture, based on the position of the object to be imaged, the maximum number of driving elements of the device, the frequency band of the ultrasonic wave used, etc. Is set in advance to a value that the user considers optimal.

For example, as shown in FIG. 18, when the aperture is increased, the beam at the focal point becomes narrower, and an image with high resolution can be obtained. The beam spreads out, resulting in poor resolution. Based on such a beam forming principle, beam forming conditions for transmission and reception are determined in advance, and the apparatus operates under these conditions to obtain an image.

[0007] Such operating conditions for beam forming determined in advance are determined on the assumption that acoustic characteristics in a living body are uniform. However, the acoustic characteristics of the medium in the living body are not uniform, and due to the non-uniformity, in an actual living body, the beam shape deteriorates from the beam shape expected from the operating conditions of beam forming. is expected. As a phenomenon supporting this point, it is pointed out that the image quality of the ultrasonic image is good or bad depending on the subject.

[0008] The cause of the dependence of the image quality is the remarkable non-uniformity of the sound speed between the transducers. By paying attention to this cause, the actual reception timing of the received signal is measured, and the transmission and reception are thereby performed. Has been proposed for correcting the delay time of the data.

However, if the degree of non-uniformity of the sound velocity becomes strong, not only the propagation time of the ultrasonic wave to each transducer varies, but also the refraction at the boundary of the acoustic impedance appears strongly as shown in FIG. It is also conceivable that the waveform of the received signal is greatly distorted due to the influence of the refraction, thereby deteriorating the beam obtained by the phasing addition.

In addition to the non-uniformity of sound speed, FIG.
As shown in the figure, when the probe is placed on the chest wall assuming a heart examination, multiple reflections occur between the probe and the ribs due to the presence of ribs whose acoustic impedance is significantly different from the surrounding soft tissue, Similarly, it is conceivable that the waveform of the received signal is greatly distorted.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is not to compensate for the remarkable variation in the sound speed of the former, but to remarkably cause the reception signals of some of the transducers within the aperture to be remarkable due to refraction or multiple reflection as in the latter. An object of the present invention is to provide an ultrasonic diagnostic apparatus that can reduce the influence on image quality when distortion occurs.

[0012]

According to the present invention, an excitation signal of each of a plurality of transducers arranged and a reception signal obtained by the transducers receiving an ultrasonic wave reflected from a subject are separately provided. In the ultrasonic diagnostic apparatus for giving the transmission and reception directivity to the ultrasound by giving a delay time to the ultrasound and scanning the inside of the subject with the ultrasound having the directivity to obtain an ultrasound image, the reception signal And a means for controlling at least one of the intensity of the excitation signal and the amplification factor of the received signal in accordance with the evaluation result.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An ultrasonic diagnostic apparatus according to the present invention will be described below with reference to the drawings. The present invention evaluates the degree of distortion of a received signal due to refraction or multiple reflection, for each transducer based on the received signal before phasing addition, and when it is evaluated that the distortion is relatively large with respect to a certain transducer, The gain of the received signal received by the vibrator (hereinafter, referred to as “reception gain”) is made lower than the received signal obtained by another vibrator having relatively small distortion, or the excitation of the vibrator is performed. Signal strength (hereinafter “excitation strength”
This is intended to reduce the adverse effect that a received signal with large distortion degrades image quality by suppressing the degree of distortion to be lower than other vibrators having a relatively small degree of distortion.

That is, when the waveform distortion is large due to refraction, multiple reflection, etc., the received signal is regarded as unfavorable for the reception beam formation, and the reception amplification factor is set lower than the other reception amplification factors. The control is performed so that the signal distortion is not adversely affected on the image quality. Of course, by setting the reception amplification factor to substantially zero and excluding the received signal from the phasing addition, the adverse effect of the received signal can be completely eliminated.

Further, the fact that the received signal is not preferable for phasing addition (receiving beam formation) means that the ultrasonic wave transmitted from the vibrator is also not preferable for transmission beam formation, and the excitation of the vibrator is not excited. Decrease strength. Of course, by setting the excitation intensity of the vibrator to zero and excluding the vibrator from transmission beam formation, the adverse effect of distortion in the vibrator can also be completely eliminated.

On the other hand, however, making the reception amplification factor completely zero or the excitation intensity completely zero results in a decrease in aperture, and a sudden change in control may give an unnatural feeling to an image. Considering that there is
It is not always good. Therefore, it is possible to completely reduce the reception amplification factor of the vibrator where the distortion of the reception signal becomes large,
It can be said that it is preferable not to completely reduce the excitation intensity to zero, but to reduce the reception amplification factor and the excitation intensity to some extent.

In order to evaluate the degree of distortion of the received signal waveform due to refraction, multiple reflection, etc., that is, to evaluate whether the received signal is preferable for beam forming, the inventor uses the following two evaluation methods. is suggesting. (1) Similarity of received signal waveform between transducers (2) Power of received signal Hereinafter, the purpose of each evaluation will be described and an actual evaluation method will be described. (1) Similarity of Received Signal Waveform FIG. 1 shows the angle dependence of the receive beam directivity when the receive beam is deflected little by little with respect to a point sound source fixed on the aperture center line. The vertical axis in FIG. 1B represents the intensity of the phasing addition signal, for example, the amplitude. The thin line in FIG. 1B is an ideal characteristic in the case of a uniform medium. When a medium such as a rib having extremely different acoustic characteristics exists in the propagation medium, the thin line is drawn as a thick line. It is expected that the directivity will be disturbed. In the figure, point A coincides with the point sound source and the focal point of reception, the directivity is maximum, and point B is a place where it is desired to reduce the gain in directivity. The detailed process will be qualitatively described with reference to FIGS.

FIG. 2 is based on the assumption that a uniform medium is propagated by ultrasonic waves. The received signals obtained by the transducers within the aperture have basically the same waveform, and are time-dependent according to the propagation time. The relationship is that the position on the axis is slightly different. By the reception delay control for convergence, the signals are controlled so that the positions on the time axis are the same, that is, the phases are aligned and added.
This operation is an operation called so-called phasing addition.

In this case, since all the signals have the same phase (for example, the positive vertices are at the same position on the time axis of the signal), the signals are emphasized by the addition, and a large gain is obtained at the point A. Is obtained. On the other hand, at point B, the delay operation of reception is performed so as to converge on point B, so that the signals from the point sound sources do not match in phase and work so as to cancel each other out, so that the gain is low. Become.

As described above, the places where the phases of the received signals from the respective transducers within the aperture are aligned are emphasized, and the gain is reduced as the elements whose phases cancel each other out become strong in other places. Thus, a directivity pattern as shown in FIG.

In FIG. 3, the waveform of the received signal obtained by the vibrator near this one end is compared with the waveform of the received signal of the other vibrator mainly due to the multiple reflection mainly due to the influence of the rib existing near one end of the aperture. It shows that it has been extremely distorted. In such a case, even if focusing is performed at point A, the received signal of one vibrator is distorted and the waveform is different from the received signal of the other vibrator. The emphasis is not always on each other, and the gain is reduced. On the other hand, in the case of focusing on the point B, conversely, due to the difference in the waveform, the phase cannot be canceled well,
The gain is apparently large.

Loss of similarity in the waveforms impairs sharp beam formation, as well as inadequate delay times due to variations in propagation times. The gist of the present invention is to remove the distorted received signal from the phasing addition for beam forming, or to reduce the reception amplification factor and participate in the phasing addition to reduce the adverse effect on the image quality. We are trying to reduce it.

In general, when evaluating the similarity between signals, the peak value (maximum value) of the correlation function ρ _xy (Z) is used. However, hereinafter, the peak value of the correlation function is simply referred to as “correlation coefficient”. The definition formula of the correlation function is described below.

[0024]

(Equation 1)

Referring to FIG. 4, what this similarity means will be described. When the similarity of the waveforms of the two received signals is high, the position of the peak of the correlation function indicates the time lag between the two waveforms, and the peak value reflects the similarity between the two waveforms. That is, when a correlation function is derived between completely the same waveforms, the peak value is “1.0” indicating the maximum similarity even if the phases do not match. On the other hand, when the similarity of the waveforms is low, the peak value is low.

Using such a meaningful peak value, that is, a correlation coefficient, whether or not it is preferable for beam formation is to be evaluated for each transducer. The question is whether a correlation coefficient is to be obtained between a pair of transducers having an appropriate positional relationship. In this regard, it must first be specified that the similarity of the two received signals obtained within the aperture decreases as the distance between the transducers from which they are obtained is increased.
Basically, the similarity of the received signals of the two transducers decreases as the distance between the two transducers increases (the correlation coefficient decreases), and moreover, the degree to which the transmission beam Thickness has the property that the decrease proceeds rapidly. When the signals are separated to some extent, the received signals become completely uncorrelated (the correlation coefficient approaches zero).

FIG. 5 shows the position distribution of the correlation coefficient obtained by plotting the correlation coefficient obtained between the central oscillator within the aperture and each of the other oscillators at the position of the other oscillator. Is conceptually shown. For example, the correlation coefficient obtained between the center oscillator (A) and the oscillator (B) is plotted at the position of the oscillator (B). It can be seen from FIG. 5 that the correlation coefficient is very strongly dependent on the distance from the central oscillator. From this, it can be seen that it is not preferable to obtain a correlation coefficient between a received signal of a vibrator at the center of the aperture and a received signal of another vibrator, for example.

Further, even when the correlation coefficient is obtained between transducers that are too close together, for example, between adjacent transducers, most of the phases are obtained except when the waveform change due to the in-vivo structure occurs extremely abruptly. It is also expected that the relationship number will be close to "1.0" and the effects of refraction and multiple reflections cannot be captured.

In consideration of this point, it is preferable to select the interval between the oscillators so that the correlation coefficient is appropriately dispersed from the theoretical correlation coefficient pattern expected from the transmission conditions, the depth of the observation point, and the like. . As for how many intervals are appropriate,
Probably empirical accumulation will be required and will vary from subject to subject, and thus cannot be limited to specific values here. Of course, the optimum oscillator interval may be determined empirically irrespective of the theoretical value of the correlation coefficient, but the theoretical interval can be theoretically determined by using the theoretical value.

The correlation coefficient between the received signals is determined at the transducer interval determined empirically or theoretically as described above, and the value of the correlation coefficient is applied to the center position of both transducers. By repeating this operation while shifting the pair of transducers one by one, it is possible to obtain a position distribution on the aperture of the correlation coefficient as shown in an example in FIG. Of course, at the end of the aperture, a predetermined interval between the transducers cannot be secured, so that a special operation such as reducing the interval between the transducers as needed is required.

Various methods are conceivable as to how to control the reception amplification factor and the excitation intensity at the time of transmission by using the distribution of the correlation coefficient thus obtained. As one method, as shown in FIG. 6, a threshold value is determined based on a theoretical value derived assuming the above-described uniform medium, and a receiver having a correlation coefficient equal to or less than the threshold value has a reception amplification factor. Or the excitation intensity may be made substantially zero, or may be continuously changed according to the value of the correlation coefficient.

(2) Intensity or Power of Received Signal As described above, the method considering the similarity of the received signals has been described. The method using the correlation coefficient requires a large amount of calculation. In consideration of this point, as a method of reducing the amount of calculation, simplifying the operation, and maintaining a certain effect, the intensity (amplitude) and power (square of the amplitude of the received signal are integrated over time,
A method based on the value standardized in unit time) is also conceivable. Here, the description will be made as power.

FIG. 7 assumes a situation in which the heart is examined transthoracically. As shown in FIGS. 7A and 7B, the right end of the aperture (region B in the drawing) has a lung underneath, and the received signal of the transducer located in the region B is a beam due to the influence. Distorted to an undesirable degree for formation. It is considered that this inappropriateness can be reached by the method using the correlation coefficient. However, assuming that the power of the received signal is also reduced due to the scattering by the lungs, by distributing the received signal and power of each transducer on the diameter axis, a distribution similar to that in FIG. 6 can be obtained. After obtaining such a position distribution of power, as in the case of using the correlation coefficient, a target whose power is equal to or less than a threshold determined based on a theoretical value derived assuming a uniform medium is targeted. The reception amplification factor and the excitation intensity are made substantially zero, or are continuously changed according to the value of the correlation coefficient.

By the way, it is easy to think that the adverse effect on the image quality is small because the power of the received signal is small, but the dynamic range of the ultrasonic image is quite wide, 40-80 dB, and the power is small, so The adverse effects are not always small.

As described above, a common problem in handling the similarity and power of received signals is that if these values are obtained by using all of the received signals, the correlation coefficient is excessively reduced, Further, since the power becomes excessively high, these values do not disperse satisfactorily, and there is a problem that an appropriate evaluation cannot be performed. Therefore, it is necessary to obtain a correlation coefficient and power using a part of the received signal.

FIG. 8A shows an ultrasonic image of the heart. However, basically, no signal can be obtained from the inside of the heart, and the reception of a depth corresponding to the inside of the heart is performed. When the evaluation is performed using a part of the signal, the similarity of the electrical noise is evaluated, and the correlation coefficient naturally decreases. In this case, most of the vibrators are lower than the threshold value shown in FIG. 6, which may lead to a situation where scanning is impossible.

In order to avoid such a situation, it is necessary to set a part of the received signal used for the evaluation in an appropriate area constituted by the reflection from the organ in the living body. FIG.
Describes how to do this.

First, a signal after phasing and addition is used for selecting an appropriate area. It is considered to be better to use the signal of one frame before, considering the flow of signal processing from the actual device configuration. FIG. 8B shows a signal waveform after phasing addition corresponding to the scanning line indicated by the thick line in the image of FIG. The amplitude of the phasing addition signal is first extracted by detection (envelope detection), and smoothing is performed in the time direction in order to eliminate the influence of fine speckle fluctuation. The envelope after smoothing is shown by a thin line in FIG.

In order to correct the depth dependence of attenuation in a living body, an amount corresponding to an average biological attenuation is made to act on this envelope as an amplification amount (attenuation correction). The envelope after the attenuation correction is shown by a thick line in FIG.

With respect to this envelope, a plurality of regions exceeding a certain threshold are selected as candidates, and a region closest to a preset reference depth is selected from the candidates. That is, the correlation coefficient and the power are obtained by using the portion corresponding to the selected area in the received signal from each transducer.

The evaluation and the control of the aperture need not be performed using only one signal as described above. Similarly, evaluation is performed on a plurality of regions, and based on the results,
Transmission and reception may be controlled.

Such a principle will be better understood from the description of the following embodiment. (First Embodiment) FIG. 9 shows a configuration of an ultrasonic diagnostic apparatus according to a first embodiment. The ultrasonic probe 1 is provided with a plurality of transducers at its distal end in order to mediate between a side that handles electric signals and a subject side that applies amplitude modulation or frequency modulation to ultrasonic waves to give internal information. They are arranged. The form of the probe 1 may be any of a sector correspondence, a linear correspondence, a convex correspondence, and the like. Here, the sector will be described as an example.

A transmission drive unit 3 and a reception amplifier 6 are selectively connected to the probe 1 by a transmission / reception switch 2 at the time of transmission and at the time of reception. The transmission driver 3 is generally composed of a clock circuit, a rate pulse generator, a transmission delay circuit, and a pulser. The clock oscillated from the clock circuit is frequency-divided, and a rate pulse is generated by the rate pulse generator to determine the transmission rate of ultrasonic waves (the number of transmissions per second). The rate pulse is distributed to, for example, 100 channels and sent to a transmission delay circuit, where a delay time necessary for determining the directivity of the ultrasonic wave is individually given and supplied to the pulser. The pulser is a so-called power amplifier, which amplifies a rate pulse and applies it to each transducer of the probe 1.

The delay time given to the rate pulse of each channel by the transmission delay circuit is changed little by little when the ultrasonic pulse is transmitted once or a predetermined number of times. Thereby, the direction of the transmission beam moves little by little. Such delay control is performed by the transmission delay control unit 4.

The amplification rate of the rate pulse in the pulser is arbitrarily controlled by the transmission aperture control unit 5 for each channel. The transmission aperture control unit 5 makes the amplification rate of the rate pulse corresponding to some of the vibrators on the end side in the vibrator row extremely small so that substantially no ultrasonic wave is emitted from the vibrator. By doing so, the aperture can be arbitrarily changed. In the present embodiment, the control of the excitation intensity according to the correlation coefficient and the power as described above is performed by using the aperture control.

The transducer of the probe 1 is excited by the excitation signal, and generates an ultrasonic wave. The ultrasonic wave propagates in the living body, and is reflected one after another at a discontinuous surface of acoustic impedance in the middle of the ultrasonic wave. Since this reflection intensity mainly depends on the difference in acoustic impedance, it can be said that this movement is close to amplitude modulation. Ultrasound waves are also reflected on the heart wall and blood cells, and the reflections on these moving bodies include movement of frequency modulation due to the Doppler effect.

Such a reflected wave returns to the probe 1 and vibrates each vibrator. As a result, a weak reception signal is generated from each of the vibrators. After these received signals are individually amplified by the receiving amplifier 6, they are sent to the phasing addition processing section 8 and the adaptive aperture control section 20 via the analog-to-digital converter (A / D) 7.

The amplification factor of the received signal in the receiving amplifier 6 is
It is arbitrarily controlled by the reception aperture control unit 9 for each channel. The reception aperture control unit 9 can change the aperture arbitrarily by extremely reducing the amplification factor of the reception signals from some of the transducers on the end side in the transducer row. This aperture control is mainly used for a so-called dynamic aperture that dynamically changes the aperture according to the reflection depth, and a weighting process for lowering the side lobe level of the beam, that is, a so-called apotization process. In the present embodiment, the aperture control is performed in accordance with the correlation coefficient and the power as described above using the aperture control.

The phasing addition processing section 8 is generally composed of a reception delay circuit and an adder. The amplified reception signal is sent to a reception delay circuit, where a delay time necessary for determining the reception directivity of the ultrasonic wave is individually given, and added by an adder. The delay time given to each reception signal by the reception delay circuit is changed little by little in synchronization with the transmission delay control. As a result, the direction of the reception beam moves little by little according to the transmission beam, and sector scanning is realized. Such delay control is performed by the transmission delay control unit 4. The received signal given the delay time is added by an adder.

The phasing addition signal is supplied to the B mode processing unit 1
1 and a processing unit 12 for color flow mapping (CFM) and a processing unit 13 for spectrum Doppler as well as a new adaptive aperture control unit 20. B-mode processing unit 1
1 generally comprises a detection circuit and a logarithmic amplifier. First, the detection circuit detects the envelope of the phasing addition signal,
Then, logarithmic amplification is performed by a logarithmic amplifier.

The color flow mapping processing unit 12
It generally includes a mixer, a low-pass filter, an MTI filter, an autocorrelator, and a calculation unit. The mixer and the low-pass filter constitute a quadrature phase detection circuit. The reference signal having the same center frequency as the transmission frequency and the reference signal shifted by 90 ° from the reference signal are individually multiplied with the phasing addition signal, and the multiplication is performed. By removing the high frequency component from each of the obtained signals, the shift frequency component is extracted and output as a Doppler signal. The Doppler signal includes a high-frequency component that is mainly frequency-modulated by reflection from a fast moving body such as blood cells, and a low-frequency component that is mainly frequency-modulated by reflection from a slow moving body such as a heart wall. And are included.

The MTI filter functions as a high-pass filter, passes only high-frequency components (blood flow components) which are mainly frequency-modulated by reflection from a fast moving body such as blood cells, and mainly passes through a slow moving body such as a heart wall. The low-frequency component (clutter component) that has been frequency-modulated by the reflection at is removed. And
The Doppler signal containing only the blood flow component is frequency-analyzed by an autocorrelator to determine a shift frequency due to blood cells. Based on the shift frequency, the calculation unit calculates the blood flow velocity (average velocity), its variance, and the power mainly reflecting the blood flow (square of the Doppler signal amplitude).

The spectrum Doppler processing section 13 generally comprises a mixer, a low-pass filter, a sample-and-hold circuit, a band-pass filter, and a frequency analyzer.
As in the case of the color flow mapping processing unit 12,
The shift frequency component is extracted from the phasing addition signal by the mixer and the low-pass filter, and a part corresponding to the depth of the designated sample volume is cut out from the Doppler signal,
Only a high-frequency component (blood flow component) is extracted from this part of the signal by a bandpass filter, and the Doppler signal that has been converted to only the blood flow component is subjected to frequency analysis by fast Fourier transform (FFT) to determine the shift frequency due to blood cells. Ask.

The output signals from the processing units 11, 12, and 13 are appropriately combined into one screen by the display system 14, and T
The images are rearranged into the V-scan system, supplied to the monitor 15, and displayed as a tomographic tissue image (density image), a blood flow image (color image), and a blood flow M-mode image.

The adaptive aperture control section 20 controls the transmission aperture control section 5 and the reception aperture control section 9 to adjust the excitation intensity and the reception amplification factor for the vibrator which is undesirably affected by the tissue in the living body. It is provided to control and reduce the adverse effect on the image quality due to the distortion, and includes an evaluation area selection unit 21, a reception signal evaluation unit 22, and an aperture control unit 23.

The basic operation will be briefly described. First, the evaluation area selection unit 21 uses the phasing addition signal to select an optimum area for obtaining a correlation coefficient between received signals. Information on the selected optimum area is temporarily stored in a memory and used for evaluating a received signal of the next frame. Then, the received signal evaluation unit 22 calculates the correlation coefficient between the transducers using the received signal of the current frame as described above, and controls the excitation intensity and the reception amplification factor in the aperture control unit 23 according to the calculation result. .

FIG. 10 shows the detailed configuration of the evaluation area selection unit 22. For simplicity, the operation limited to one frame will be described, but the same operation is repeated in each frame. The phasing addition signal is supplied to the detector 2 at any time in each scanning line.
11, and the amplitude component of the phasing addition signal is extracted. The amplitude signal is subjected to smoothing processing in the time direction (depth direction) by the low-pass filter 212, and fine fluctuations are leveled out evenly. Further, the signal is amplified by the amplifier 213 in order to correct the average in-vivo attenuation. However, the amplification amount for correcting the in-vivo attenuation is changed according to the value of the so-called STC, which is an amplification factor control for each depth, which is performed by an operator to adjust the brightness of the B-mode image. The dependency may be corrected.

The threshold value determination section 214 compares the amplitude signal whose attenuation has been corrected with a preset threshold value, and determines a plurality of areas in the amplitude signal exceeding the threshold value in a portion for obtaining a correlation coefficient. Extract as candidates. The area determination unit 215 selects an area closest to the area to be evaluated (reference depth) from the plurality of extracted areas. The area storage unit 216 stores the information on the selected area for every scanning line included in the frame, and supplies this information to the received signal evaluation unit 22 in the next frame. Of course, if the received signals of the transducers before the phasing addition are stored for at least one scanning line, the area is determined by the evaluation area selection unit after the normal phasing addition processing, and the received signal is stored. After the evaluation of (1), the aperture control for the same scanning line can be performed again to perform the phasing addition processing for the display image.

FIG. 11 shows a detailed configuration of the received signal evaluation unit 22 and the aperture control unit 23. Buffer memory 221
Are prepared for the number of transducers driven to form one scanning line (one ultrasonic beam), and two memory elements each having a capacity for storing a reception signal from the corresponding transducer are provided. By switching these in a toggle manner, the signal writing from the oscillator and the correlation operation unit 222 are performed.
And the reading for supplying the received signal of the immediately preceding scanning line to the scanning line. This correlation operation unit 22
Similarly to the buffer memory 221, the number 2 is prepared for the number of transducers driven to form one scanning line (one ultrasonic beam), and a correlation coefficient can be obtained for each transducer. It has become.

A received signal of a certain transducer is directly supplied from the buffer memory 221 to the correlation calculating section 222, and a received signal of another transducer is supplied via the switch 223. By switching the switch 223, the interval between the transducers to be subjected to the correlation coefficient calculation can be arbitrarily changed. In FIG. 11, the interval is written in a configuration that can be selected from 0 to 3.

The correlation coefficient calculating section 222 also has a function of controlling the reading of the buffer memory 221. According to the area selected by the evaluation area selecting section 21, a signal portion used for the correlation coefficient calculation is cut out from the received signal. Calculate the correlation coefficient. The obtained correlation coefficients are sent to the aperture control unit 23.

In the aperture control unit 23, first, the parallel-serial conversion unit 231 serially converts the correlation coefficient values output in parallel from the correlation coefficient calculation unit 222, which is usually 100 or more. After that, the stabilization processing unit 232 stabilizes the correlation coefficient value, for example, (1) averages over several surrounding points, and (2) performs median filter processing using several surrounding points. This is shown in FIG. In the drawing, the position distribution of the correlation coefficient value before the stabilization processing is represented by a thin line. It can be seen that the fluctuation of the correlation coefficient value strongly appears due to the statistical fluctuation and noise of the received signal. In this state, even if the oscillator has a small distortion, the correlation coefficient is less than or equal to the threshold value, and the excitation intensity and the reception amplification factor of the oscillator are lowered, or the oscillator having a large distortion is not preferable. Even so, there is a possibility that the correlation coefficient exceeds the threshold value and the excitation intensity or the reception amplification factor of the vibrator is maintained at the reference value without lowering, so that good control cannot be performed. On the other hand, in order to stabilize the correlation coefficient, a low-pass filter process such as averaging using several surrounding points or a median filter process is performed to obtain a coefficient distribution as shown by a thick line. And good diameter control becomes possible.

Using the stabilized correlation coefficient position distribution,
The aperture control for transmission and reception is performed by the aperture corrector for transmission 233A and the aperture corrector for reception 233B, respectively. The aperture control is performed by, for example, a relationship between a predetermined correlation coefficient as shown in FIG. 13 and a correction coefficient for a reference value of the excitation intensity or the reception amplification factor. , B.

The horizontal axis may be a correlation coefficient value, or may be normalized by dividing a measured value by a theoretical value obtained based on transmission conditions, the interval between transducers used for the correlation coefficient calculation, and the like. In the latter case, it is expected that there is no need to change the contents of the table due to transmission conditions and the like, and control can be performed more easily. The vertical axis is a coefficient indicating how much correction is to be performed on the originally set reception amplification factor and transmission excitation signal strength. For example, for a transducer whose coefficient is determined to be 0.5, the gain of the received signal is halved.
In the figure, the thin line sets the coefficient to 0 or 1.0. In other words, ON /
The control for performing the OFF operation is shown, and the thick line indicates the case where the correlation coefficient is continuously evaluated.

The aperture control information thus obtained is
At any time, the data may be sent directly to the transmission aperture control unit 5 and the reception aperture control unit 9 shown in FIG. 9 or the aperture correction data for one frame is temporarily stored in the memories 234A and 234B as shown in FIG. After storing, it may be transferred at the beginning of the next frame. In any case, the actual aperture is controlled in the next frame after the evaluation of the received signal.

As described above, according to the present embodiment, the degree of distortion due to refraction or multiple reflection is evaluated based on the correlation coefficient between received signals, and when the correlation coefficient is lower than the threshold value according to the obtained correlation coefficient. When the excitation intensity or the reception amplification factor is lower than the reference value and the correlation coefficient is higher than the threshold value, at least one of the excitation intensity and the reception amplification ratio is controlled so that the excitation intensity or the reception amplification ratio is maintained at the reference value. As a result, it is possible to reduce the adverse effect of the distortion on the image quality.

In this embodiment, the degree of distortion is evaluated by the correlation coefficient. However, the evaluation may be performed based on the power of the received signal as described above. In the following embodiment,
The degree of distortion is evaluated based on the power of the received signal.

(Second Embodiment) In the second embodiment, the power of the received signal is obtained instead of the correlation coefficient in the evaluation of the distortion of the received signal. Received signal evaluation section 22 having different form and configuration
Only the aperture control unit 23 will be described, and description of the same components as those in the first embodiment will be omitted.

FIG. 14 shows the received signal evaluation unit 2 of this embodiment.
2 shows the configuration of the aperture control unit 23 in detail. The signal power calculator 222 calculates the power of the portion of the received signal in the evaluation area by the following equation.

[0070]

(Equation 2)

The power value is stored in the aperture controller 23 in the same manner as in the first embodiment.
After being serially rearranged at 31, the stabilization processing unit 23
2 and smoothed there. The power value is also sent to the average calculation unit 235, where the average value of the power is obtained. The aperture control is determined by the transmission aperture 233A and the reception aperture corrector 233B based on the two pieces of information of the power value and the average value of these transducers. First, the power of each transducer is normalized by the average value and the directivity parameter according to the following equation, and then a correction coefficient is determined for each transducer according to the relationship shown in FIG.

Power of each vibrator / (average value of power × directivity parameter of each vibrator) To use the average value of power, it is necessary to use the signal strength from a target area as a factor for normalization. The reason why the directivity of each transducer is used is to correct that the power of the received signal is affected by the directivity of the transducer alone depending on the positional relationship between the transducer and the focal point.

In this embodiment, the power of the signal is used, but similar information such as the signal amplitude may be used. Other operations are basically the same as those of the first embodiment. According to the second embodiment, similarly to the first embodiment, the degree of distortion is evaluated in accordance with the power of the received signal of each transducer, and for those having strong distortion, the excitation intensity and the reception amplification factor are reduced. In addition, it is possible to reduce the adverse effect of the distortion on the image quality. In addition, the processing amount for this is significantly smaller than that in the first embodiment for obtaining the correlation coefficient.

The first and second embodiments are not limited to the case where the transducers are arranged one-dimensionally on the probe as shown in FIG. it can. However, the above two embodiments do not describe a control method peculiar to a two-dimensional array, and this will be described in detail in the following third and fourth embodiments.

(Third Embodiment) In the third embodiment,
This relates to a case where control for a two-dimensional array is performed using a correlation coefficient. The difference between the one-dimensional array and the two-dimensional array is that in the two-dimensional array, various methods of grouping the evaluation of the received signal can be considered. Please refer to FIG. 17 again. In the one-dimensional array, the transducers are arranged in one row only in the direction of the X-axis in the figure, and in that direction,
It suffices to evaluate the distortion by the correlation coefficient for each transducer. However, in a two-dimensional array, the X-axis, Y-axis, and
It is also possible to evaluate the vibrator obliquely. Here, in the case of a correlation coefficient, the direction in which evaluation is performed means the direction in which transducer pairs are used for calculating the correlation coefficient.

There are several methods for two-dimensional evaluation. An example is given below. (Method 1) Two-dimensional evaluation is not performed, and it is considered that only one-dimensional arrays are arranged on the Y-axis, and the aperture control uses the result of each one-dimensional array as it is.

(Method 2) Evaluation is performed as a one-dimensional array in the X-axis direction and the Y-axis direction, and the average value of the evaluation results is used. Or, if you want to focus on either result,
The weighted average may be calculated by the following equation.

Α · ρ _x + (1−α) · ρ _y α: Weighting coefficient ρ _x : Correlation coefficient in the x direction with respect to the vibrator ρ _y : Correlation coefficient in the y direction with respect to the vibrator (fourth embodiment Mode) When the amplitude or power of the received signal is used as the evaluation parameter, the evaluation can be performed more easily. The calculation of the average value shown in FIG. 14 may be performed two-dimensionally and the result may be used and controlled in the same manner as in the second embodiment.

(Fifth Embodiment) The gist of the present invention is preferable when the waveform is distorted due to refraction, multiple reflection, etc., and an image cannot be sufficiently solved even after the above-described correction of the variation in the propagation time. The goal is to reduce or eliminate the effects of no oscillator from beamforming. That is, if the effect of the vibrator having a large waveform distortion can be reduced or eliminated according to the present invention, it is expected that a larger improvement effect can be obtained by correcting the variation of the propagation time with respect to the remaining vibrators. You. Conventional techniques can be used for the method of correcting the propagation variation. Of course, other methods may be used.

FIG. 16 shows the configuration of an ultrasonic diagnostic apparatus according to the fifth embodiment. The information of the adaptive aperture control unit 20 is
The information of the adaptive delay control unit 30 for correcting variations in the propagation time at the same time as being transmitted to the aperture control units 5 and 9 for transmission and reception is transmitted to the transmission and reception delay control units, and using the information in the living body, Optimal aperture control and delay control are performed.

It is needless to say that the present invention is not limited to the embodiments described above, but can be implemented in various modifications.

[0082]

According to the present invention, a good ultrasonic beam can be obtained even when the waveform of a received signal is distorted due to refraction or multiple reflection and the image quality is degraded.
A good image can always be provided regardless of the constitution of the subject.

[Brief description of the drawings]

FIG. 1 is a diagram showing the angle dependence of reception directivity in sector scanning.

FIG. 2 is a diagram illustrating a series of phasing addition processing and the principle by which reception directivity is obtained by the processing;

FIG. 3 is a diagram showing a distortion of a received signal waveform caused by a rib and an influence of the distortion on a phasing addition process.

FIG. 4 is a diagram showing a relationship between similarity of two received signal waveforms and a correlation function.

FIG. 5 is a diagram showing the position dependence of a correlation coefficient obtained between a central oscillator within an aperture and another oscillator.

FIG. 6 is a diagram showing a position distribution on a caliber of a correlation coefficient obtained between two transducers spaced at appropriate intervals.

FIG. 7 is an explanatory diagram relating to the effect of the lung on the received signal waveform.

FIG. 8 is an explanatory diagram regarding optimization of a depth region used for distortion evaluation.

FIG. 9 is a block diagram showing a configuration of the ultrasonic diagnostic apparatus according to the first embodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration of an evaluation area selection unit in FIG. 9;

FIG. 11 is a block diagram showing a configuration of a reception signal evaluation unit and a diameter control unit in FIG. 9;

12 is a comparison diagram of the position distribution of the correlation coefficient subjected to the stabilization processing by the stabilization processing unit of FIG. 11 and the position distribution of the correlation coefficient before the stabilization processing.

13 is a diagram showing excitation intensity and reception amplification factor correction coefficients assigned to correlation coefficients in the transmission aperture correction unit and the reception aperture correction unit of FIG. 11;

FIG. 14 is a block diagram showing a configuration of a reception signal evaluation unit and a diameter control unit of the ultrasonic diagnostic apparatus according to the second embodiment of the present invention.

FIG. 15 is a diagram illustrating excitation intensity and reception amplification factor correction coefficients assigned to correlation coefficients in the transmission aperture correction unit and the reception aperture correction unit of FIG. 14;

FIG. 16 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to a fifth embodiment.

FIG. 17 is a diagram showing a general transducer array of an ultrasonic probe.

FIG. 18 is a diagram showing the relationship between the size of a transmission / reception aperture and the beam thickness.

FIG. 19 is a diagram showing the effect of refraction on a received signal.

FIG. 20 is a diagram showing the effect of multiple reflection on a received signal.

[Description of Signs] 1 ... Ultrasonic probe, 2 ... Transmission / reception switch, 3 ... Transmission drive unit, 4 ... Transmission delay control unit, 5 ... Transmission aperture control unit, 6 ... Reception amplifier, 7 ... Analog digital Converter, 8: phasing addition processing section, 9: reception aperture control section, 10: reception delay control section, 11: B mode processing section, 12: color flow mapping processing section, 13: spectrum Doppler processing section, 14 ... display system, 15 monitor, 20 adaptive aperture control section, 21 evaluation area selection section, 22 received signal evaluation section, 23 aperture control section, 211 detection section, 212 low-pass filter, 213 amplifier, 214 .. Threshold determination unit, 215 area determination unit, 216 area recording unit, 221 buffer memory, 222 correlation coefficient operation unit, 223 selection switch, 231 parallel serial Conversion unit, 232 ... stabilization processing unit, 233A ... transmission aperture control unit, 233B ... reception aperture control unit.

Claims (14)

[Claims] 1. An excitation signal of each of a plurality of arranged transducers and a transmission signal obtained by receiving an ultrasonic wave reflected from an object by each of the transducers by individually giving a delay time to the signals. In an ultrasonic diagnostic apparatus that obtains an ultrasonic image by scanning the inside of a subject with an ultrasonic wave having this directivity, the distortion of the received signal is evaluated for each transducer. And a means for controlling at least one of the intensity of the excitation signal and the amplification factor of the received signal in accordance with the evaluation result. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein said evaluation means evaluates said distortion based on a similarity of a received signal between transducers. 3. The ultrasonic diagnostic apparatus according to claim 2, wherein said similarity is obtained according to a correlation coefficient of a received signal between transducers. 4. The apparatus according to claim 3, wherein the relationship between the oscillators for obtaining the correlation coefficient is determined based on a theoretical value of the correlation coefficient obtained assuming a uniform medium. Ultrasound diagnostic device. 5. The super-correlation apparatus according to claim 3, wherein the correlation coefficient is obtained between a transducer having a relationship other than the relationship between the central transducer in the bore and another transducer and an adjacent relationship. Ultrasound diagnostic device. 6. The apparatus according to claim 3, wherein at least one of the intensity of the excitation signal and the amplification factor of the reception signal is controlled based on a theoretical value of a correlation coefficient obtained assuming a uniform medium. An ultrasonic diagnostic apparatus as described in the above. 7. When the correlation coefficient is equal to or less than a predetermined value, at least one of an intensity of the excitation signal of the vibrator and an amplification factor of the reception signal is reduced according to the correlation coefficient. The ultrasonic diagnostic apparatus according to claim 3, wherein 8. When the correlation coefficient is equal to or less than a predetermined value, at least one of an intensity of the excitation signal of the vibrator and an amplification factor of the reception signal is made substantially zero. 4. The ultrasonic diagnostic apparatus according to 3. 9. The ultrasonic diagnostic apparatus according to claim 1, wherein said evaluating means evaluates said distortion based on at least one of the intensity and power of a received signal of each transducer. 10. The method according to claim 1, wherein the distortion is evaluated based on a result of comparing at least one of the intensity and the power of the received signal of each of the transducers with an average value of all transducers within the aperture. Item 10. An ultrasonic diagnostic apparatus according to item 9. 11. When at least one of the intensity and power of the received signal is equal to or less than a predetermined value, at least one of the intensity of the excitation signal of the vibrator and the amplification factor of the received signal is determined by the intensity of the received signal. The ultrasonic diagnostic apparatus according to claim 9, wherein the power is decreased according to at least one of the values of power and power. 12. When at least one of the intensity and power of the received signal is equal to or less than a predetermined value, at least one of the intensity of the excitation signal of the vibrator and the amplification factor of the received signal is made substantially zero. The ultrasonic diagnostic apparatus according to claim 9, wherein: 13. From a received signal of each of the vibrators,
The apparatus according to claim 1, further comprising: means for estimating a variation in propagation time of the ultrasonic wave, and means for correcting at least one of a delay time given to the excitation signal and a delay time given to the received signal based on the estimation result. 2. The ultrasonic diagnostic apparatus according to claim 1. 14. The evaluation means evaluates the distortion based on a part of a received signal, and evaluates the part in an area closest to a reference depth in a plurality of areas where the amplitude of the received signal exceeds a predetermined value. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein: