JP2001212140A - Ultrasonic diagnosing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To draw a clear image by reducing an image quality deterioration at the deep section of a subject. SOLUTION: Ultrasonic wave are transmitted in the same direction by driving an ultrasonic wave transducer 21 which transmits/receives ultrasonic waves by driving pulses of different voltages by a transmitting section 1. Then, the fundamental wave of the reflected signal is received by a fundamental wave- receiving section 3, and at least one of the received signals of the fundamental waves based on the driving pulses of the different voltages is coefficient- multiplied by coefficient circuits 41 and 42. Then, a difference between both signals is obtained by a difference circuit 43. By this constitution, the influence of a side lobe is eliminated, and the image quality at the deep section of the subject is greatly improved, and a clear image can be drawn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus which obtains diagnostic information in a body by using ultrasonic waves radiated from an ultrasonic transducer and reflected wave information obtained when scanning the inside of a subject. The present invention relates to an ultrasonic diagnostic apparatus that realizes a new ultrasonic imaging method using the nonlinear effect of ultrasonic waves.

[0002]

2. Description of the Related Art When an ultrasonic transducer emits an ultrasonic beam into a subject, the ultrasonic beam propagates in a living body, and a boundary of a living tissue such as a blood vessel wall or an organ during propagation, that is, an acoustic impedance. Reflection occurs one after another at the discontinuous surface of the ultrasonic transducer, and returns to the ultrasonic transducer as an echo signal. The amplitude of the echo signal depends on the difference in acoustic impedance at the discontinuous surface. Further, when the ultrasonic beam is reflected on the surface of a moving object such as a blood cell or a heart wall, the echo signal undergoes a frequency shift depending on the velocity component in the beam direction of the moving object due to the Doppler effect. . The ultrasonic diagnostic apparatus is capable of observing a tomographic image, a blood flow velocity, and the like by processing such an echo signal. In general, only the fundamental wave component is used as the echo signal.

In recent years, however, in order to improve the image quality of an ultrasonic image obtained by an ultrasonic diagnostic apparatus, an image is generated by receiving a reflected wave of a harmonic generated during a process in which an ultrasonic beam propagates in a subject. Tissue Harmonic Imaging (hereinafter, referred to as THI) has been developed, and a clear image can be obtained from an ultrasonic transducer particularly at a medium distance of, for example, 2 cm to 10 cm. The reflected wave of this harmonic is generated as a result of the nonlinear phenomenon of the ultrasonic wave, and the effect is larger as the intensity of the ultrasonic wave is stronger. Therefore, a strong ultrasonic wave radiated toward the front and required for image generation, that is, a harmonic having a large nonlinear effect and a strong harmonic is generated in the main lobe in the directivity. On the other hand, when the ultrasonic waves are emitted, side lobes are emitted around the main lobe in another direction. These side lobes are unnecessary ultrasonic waves that cause image artifacts, but the amplitude of the side lobes is 1/10 or less as compared with the main lobe, and the nonlinear effect is very weak. Therefore, harmonics are hardly generated by the side lobe. Therefore, in terms of harmonic components, the side lobe, which is a bad factor for deteriorating the resolution, is extremely small compared to the main lobe required for image generation, which is a major reason that the image quality is improved by THI.

[0004]

However, the ultrasonic wave is attenuated as it propagates through the medium, and as a result, the intensity of the ultrasonic wave becomes weaker toward the deeper part of the subject, and the nonlinear effect is reduced. Further, the higher the frequency is, the more attenuated the ultrasonic wave is. Therefore, the sensitivity of the image generated by using the reflected wave of the higher harmonic wave is inevitably lowered in the deep part, and the image cannot be drawn.
Therefore, the inability to render deep images is the biggest drawback of THI. The present invention has been made in view of such circumstances, and it is an object of the present invention to eliminate the adverse effects of side lobes by utilizing a non-linear phenomenon and obtain a sufficient sensitivity even in a deep part to improve image quality. An object of the present invention is to provide an ultrasonic diagnostic apparatus that realizes an acoustic imaging method.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an ultrasonic transducer for transmitting and receiving an ultrasonic wave, and the ultrasonic transducer is driven by driving pulses of different voltages. A driving pulse generating means for transmitting ultrasonic waves in the same direction, a receiving means for receiving an echo signal received by the ultrasonic transducer, and driving the received signal received by the receiving means to the different voltage. Signal processing means for performing predetermined signal processing between received signals based on pulses to obtain desired information, and display means for displaying an output based on the information obtained by the signal processing means. Things. This allows
By utilizing the non-linear phenomenon, it is possible to draw a clear image in which image quality deterioration due to side lobes in the deep part of the subject is improved.

According to a second aspect of the present invention, there is provided an ultrasonic transducer for transmitting and receiving an ultrasonic wave, and the ultrasonic transducer is driven by a driving pulse of a constant voltage and / or a driving pulse of a different voltage, and Driving pulse generating means for transmitting ultrasonic waves in the direction, receiving means for receiving echo signals received by the ultrasonic transducer, and receiving pulses received by the receiving means, the driving pulse of the constant voltage The received signal based on the received signal is subjected to signal processing to obtain the desired first information, and the received signal based on the driving pulse of the different voltage is subjected to a predetermined signal processing between the two received signals. And a signal processing means for obtaining desired second information, and an output and / or a second signal based on the first information obtained by the signal processing means.
And a display means for displaying an output based on the above information. As a result, it is possible to switch between an image in which the adverse effects of side lobes are eliminated by using a non-linear phenomenon and an image obtained by a conventional method, or to display both images side by side. It can also be used for educational purposes. Also,
According to a third aspect of the present invention, in the ultrasonic diagnostic apparatus according to the second aspect, the received signal received by the receiving unit is temporarily stored for at least one frame, and the information based on the stored received signal is displayed. Means for displaying, and in response to a freeze operation for operating the freeze means, a drive pulse supplied from the drive pulse generation means to the ultrasonic transducer is driven at a different voltage from a drive pulse of a constant voltage. It is characterized by changing to a pulse. As a result, the diagnosis site is searched for in a real-time image with the conventional method,
When a desired diagnostic site is found, the image is switched to an image in which the adverse effects of side lobes are eliminated by using a non-linear phenomenon and the image is frozen, so that a good image can be obtained for the desired diagnostic site.

According to a fourth aspect of the present invention, there is provided an ultrasonic transducer for transmitting and receiving ultrasonic waves, and a drive for transmitting the ultrasonic waves in the same direction by driving the ultrasonic transducer with driving pulses of different voltages. Pulse generating means, fundamental wave receiving means for receiving an echo signal of a fundamental wave component received by the ultrasonic transducer, and receiving a received signal received by the fundamental wave receiving means based on the driving pulses of different voltages. A fundamental signal processing means for performing predetermined signal processing between signals to obtain desired information; and an echo signal of a harmonic component received by the ultrasonic transducer based on a driving pulse from the driving pulse generating means. Receiving means for performing predetermined signal processing on a received signal based on the driving pulses of different voltages received by the harmonic receiving means. A harmonic signal processing means for obtaining information,
Synthesizing means for synthesizing an output based on the information obtained by the harmonic signal processing means and an output based on the information obtained by the fundamental signal processing means, and a display means for displaying the output synthesized by the synthesizing means And characterized in that: As a result, a clear image with little influence of side lobes can be obtained from the shallow part to the deep part of the subject.

[0008] The invention described in claim 5 is the first invention.
5. The ultrasonic diagnostic apparatus according to claim 4, wherein the driving pulses of different voltages supplied from the driving pulse generating means to the ultrasonic transducer include a plurality of low-voltage driving pulses and a single high-voltage driving pulse. And the received signals received by the receiving means or the fundamental wave receiving means are added based on the plurality of low-voltage driving pulses. This allows
Compensation can be performed so that the reception sensitivity of the main lobe does not decrease. The invention described in claim 6 is the first invention.
5. The ultrasonic diagnostic apparatus according to claim 1, wherein the drive pulse of different voltage supplied from the drive pulse generation unit to the ultrasonic transducer is:
The pulse width of the low-voltage drive pulse is longer than the pulse width of the high-voltage drive pulse. As a result, the time required for transmission and reception can be reduced as compared with the case where a plurality of low-voltage drive pulses are used, and an image close to real-time can be observed. According to a seventh aspect of the present invention, in the ultrasonic diagnostic apparatus according to the sixth aspect, the receiving unit or the fundamental wave receiving unit is based on a low-voltage driving pulse having a pulse width longer than the high-voltage driving pulse. The received signal received in the above, based on the driving pulse of the high voltage, is subjected to pulse compression to be substantially equal to the pulse width of the received signal received by the receiving means or the fundamental wave receiving means. is there. As a result, it is possible to observe an image having good real-time properties, and to compensate so that the reception sensitivity of the main lobe does not decrease.

The invention described in claim 8 is the first invention.
In the ultrasonic diagnostic apparatus according to any one of claims 4 to 4, the signal processing unit or the fundamental wave signal processing unit multiplies at least one of the reception signals based on the driving pulses of the different voltages by a predetermined coefficient, It is characterized in that a difference from another received signal is obtained. Thereby, by selecting an appropriate coefficient, when the difference between the two received signals is obtained, the influence of the side lobe can be made close to zero. According to a ninth aspect of the present invention, in the ultrasonic diagnostic apparatus according to the eighth aspect, the coefficient is a voltage of a drive pulse for driving the ultrasonic transducer and / or an ultrasonic wave from the ultrasonic transducer. It is characterized in that it is set according to the distance in the transmission / reception direction. This makes it possible to control the strength and
Coefficients can be set according to how the nonlinear phenomenon occurs. According to a tenth aspect of the present invention, in the ultrasonic diagnostic apparatus according to the eighth aspect, the coefficient is a type of an ultrasonic probe having the ultrasonic transducer and / or an ultrasonic wave transmitted from the ultrasonic probe. It is characterized in that it is set according to the convergence condition of the sound wave. This allows
Coefficients can be set in accordance with how nonlinear phenomena occur due to structural factors of the ultrasonic probe. Claim 11
The ultrasonic diagnostic apparatus according to any one of claims 8 to 10, wherein the coefficient is adjustable with respect to the received signal stored in the freeze means. Is what you do. This allows
Since the coefficient is adjusted for the frozen image, the image quality can be optimized while viewing the image on which the adjustment result is reflected.

According to a twelfth aspect of the present invention, in the ultrasonic diagnostic apparatus according to any one of the first to fourth aspects, the signal processing by the signal processing means or the fundamental wave signal processing means is performed by: The reception is performed by a high-frequency reception signal received by the reception means or the fundamental wave reception means. Thus, signal processing can be performed without losing desired information. Claim 1
According to a third aspect of the present invention, in the ultrasonic diagnostic apparatus according to any one of the first to fourth aspects, the received signal received by the receiving means or the fundamental wave receiving means is temporarily stored for at least one frame. Having freeze means for displaying information based on the received signal stored together with the display means, and performing signal processing on the received signal stored after freezing by the signal processing means or the fundamental signal processing means. It is characterized by the following. This allows
It is possible to obtain a clear image of a frozen desired diagnosis site. Further, the invention according to claim 14 is the invention according to claims 1 to 3 and 5 to 13
5. The ultrasonic diagnostic apparatus according to claim 1, wherein said receiving means receives an echo signal of a fundamental wave component received by said ultrasonic transducer. Thereby, the strongest echo signal can be used.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an ultrasonic diagnostic apparatus according to the present invention will be described below in detail with reference to FIGS. FIG. 1 is a system diagram showing main components of an embodiment of an ultrasonic diagnostic apparatus according to the present invention, and includes a transmitting unit 1, an ultrasonic probe 2, a fundamental wave receiving unit 3, a fundamental wave signal processing unit 4, Harmonic receiver 5, harmonic signal processor 6, detector 7, digital scan converter (Digital Scan C)
onverter: Hereinafter, referred to as DSC. ) Unit 8, control unit 9,
It comprises a display unit 10 and the like. The transmission unit 1 includes a clock circuit 11 and a drive circuit 12. The clock circuit 11 generates a clock pulse for determining the transmission timing of the ultrasonic wave.
A clock pulse is emitted at a rate frequency of z. When the clock pulse from the clock circuit 11 is supplied to the drive circuit 12, the drive circuit 12 generates a trigger pulse having an appropriate delay necessary for determining the directivity of the ultrasonic wave, and synchronizes with the trigger pulse. A high-frequency drive pulse having the center frequency fo is generated and applied to the ultrasonic probe 2.

A number of ultrasonic transducers 21 are arranged at the tip of the ultrasonic probe 2, and drive pulses supplied from the drive circuit 12 are applied to each ultrasonic transducer individually or in units of neighboring groups. Is done. In the conventional ultrasonic diagnostic apparatus, the voltage of the driving pulse is usually from 80 V to 2 for at least one frame.
It is set to a constant value within a range of about 00V. However, according to the present invention, the ultrasonic transducer 21 is driven by driving pulses of different voltages for one frame or one scanning line. That is, when the first clock pulse is sent from the clock circuit 11 to the drive circuit 12, the drive pulse u ₁ having a low voltage of, for example, 50 V is applied from the drive circuit 12 to the ultrasonic transducer 21 of the ultrasonic probe 2. Next, when, for example, 200 μs after the first clock pulse, the second clock pulse is sent from the clock circuit 11 to the drive circuit 12, the drive circuit 12 sends the second ultrasonic pulse to the ultrasonic transducer 2 of the ultrasonic probe 2.
To 1, for example, drive pulses u ₂ of the high voltage of 100V is controlled to be applied. This control is performed by a command from the control unit 9. These low-voltage drive pulses u ₁
And the driving pulse u ₂ of the high voltage, the drive pulses of different voltage, the ultrasonic transducer 21 is alternately driven, the ultrasonic pulses in the same direction F center frequency fo of the object from the ultrasonic probe 2 is fired . The ultrasonic pulse emitted into the subject is reflected by the body tissue, and the reflected wave is received as an echo signal by the same ultrasonic transducer 21 and is converted into a weak electric signal. Then, the fundamental wave component (center frequency fo) of the signal converted into the electric signal is introduced into the fundamental wave receiving unit 3 and becomes a received signal.

The fundamental wave receiving section 3 includes a fundamental wave receiving circuit 3
1, a first memory 32 and a second memory 33 are provided. The signal mainly including the fundamental wave component introduced into the fundamental wave receiving unit 3 is amplified by the fundamental wave receiving circuit 31, and further subjected to the same delay required for determining the reception directivity, for example, as at the time of transmission, thereby receiving the signal. A received signal having directivity is obtained. Then, under the control of the control unit 9, the received signal of the echo based on the ultrasonic pulse emitted from the ultrasonic transducer 21 by the low-voltage driving pulse u ₁ is:
Stored in the first memory 32, similarly, after the first clock pulse, by the driving pulse u ₂ of the high voltage, the received signal of the echo based on the ultrasonic pulse emitted from the ultrasonic transducer 21, the second Is stored in the memory 33. The received signals stored in the first memory 32 and the second memory 33 of the fundamental wave receiving unit 3 are sent to the fundamental wave signal processing unit 4 and subjected to coefficient processing. That is, the received signal stored in the first memory 32 is
For example, the received signal stored in the second memory 33 is multiplied by a factor of b in a second coefficient circuit. The received signals multiplied by the coefficient circuits 41 and 42 are supplied to a difference circuit 43 where the difference is calculated, and the output is detected by a first detection circuit 71 of the detection unit 7 to perform B-mode processing or the like. And the image data is converted to the DSC data.
Is supplied to the synthesizing circuit 81. Note that the second coefficient circuit 4
The coefficient b in 2 is generally a function of the distance from the ultrasonic transducer 21, and is controlled as a function of the arrival time of the reflected wave in the ultrasonic diagnostic apparatus.

[0014] On the other hand, based on said ultrasonic pulses emitted by the drive pulses u ₂ of the drive pulses u ₁ and a high voltage of low voltage, including harmonics components in the reflected wave reflected by the body tissue, the harmonic The components are also received as echo signals by the same ultrasonic transducer 21 and converted into weak electric signals. The signal of the harmonic component (for example, the second harmonic 2fo) converted into the electric signal is introduced into the harmonic receiving unit 5 and amplified to be a harmonic reception signal. The received signal of the harmonic is a low-voltage drive pulse u ₁
Is a different level of the signal based ones and those based on the driving pulse u ₂ high voltage, these processing such is supplied to the harmonic signal processor 6, for example the addition is made. Then, the output of the harmonic signal processing unit 6 is detected by the second detection circuit 72 of the detection unit 7 and subjected to B-mode processing or the like to become image data. This is a THI signal, and this THI signal is also supplied to the synthesizing circuit 81 of the DSC unit 8.
The synthesizing circuit 81 synthesizes a signal mainly including the fundamental wave component input from the first detection circuit 71 and a THI signal mainly including the harmonic component input from the second detection circuit 72, and sends the synthesized signal to the DSC. Supply. That is, since the image data synthesized by the synthesizing circuit 81 is a signal synchronized with the ultrasonic scanning, the DSC 82 synchronizes with the standard television scanning by the DSC 82 so that the image data can be displayed on the display device 10 of the television scanning system. By reading, the scanning method is converted and supplied to the display device 10.

Here, the most common B-mode image (tomographic image)
Image), the low voltage fired in the same direction
Drive pulse u₁And high voltage drive pulse u₂Based on
Signal (received signal) obtained by ultrasonic pulse
Thus, information of one scanning line is obtained, and this is
Written. Then, gradually change the direction of the ultrasonic beam
By doing the same transmission and reception by shifting, about 100
One screen is formed by the scanning lines of
Will be displayed. Note that the combining circuit 81 combines
Of the image data obtained, the first
A signal mainly containing the fundamental wave component input from the detection circuit 71
Provides good image data,
As for the medium distance, it is input from the second detection circuit 72.
Good image data is provided by the THI signal. Yo
Good for short distances (shallow) to long distances (deep)
Good images can be obtained. However, short distances are non-linear
Signal that does not use conventional nonlinear effects
It may be used as it is. Also, a low-voltage drive pulse u₁
Signal obtained based on the ultrasonic pulse fired by the satellite
Since the level of the issue is small, details will be described later, but one run
For example, to obtain the information of the line of sight,
u₂Low-voltage drive pulse u for one ₁5 occurrences
Let That is, the low-voltage drive pulse u₁The voltage of
20V (u₁= 20V), high-voltage drive pulse u₂of
The voltage is, for example, 100 V (u₂= 100V)
Pressure drive pulse u₁5 times ultrasonic transjugation
Drive 21 followed by a high-voltage drive pulse u.
₂Drive the ultrasonic transducer 21 once, and
Fires ultrasonic pulses six times in the direction, shifting the direction
Repeat this.

The first memory 32 adds the received signal mainly composed of the fundamental wave component of the echo signal based on the ultrasonic pulse emitted from the ultrasonic transducer 21 by the low-voltage drive pulse u ₁ . Remember. Similarly, the received signal mainly including the harmonic component is added by the harmonic signal processing circuit 6. Incidentally, the drive pulses u ₁ of the low voltage when fired ultrasonic e.g. 5 times in the same direction, including the drive pulses u ₂ of the high voltage, to make one scan line 6
Since ultrasonic waves are fired twice, it takes six times longer to generate one screen, and the number of frames is reduced. Therefore, usually without the use of drive pulses u ₁ of the low voltage, and visualization of high voltage image by only driving pulses u ₂ of the number of high frame, to figure out the diagnostic site to a desired. This is the same as a conventional ultrasonic diagnostic apparatus using a drive pulse of a constant voltage, and an image with good real-time properties can be obtained. When an image of a desired diagnostic site is captured, image data for one to several frames is temporarily stored using a well-known freeze function provided in a conventional ultrasonic diagnostic apparatus. as to, press the freeze button, in this case, switching operation to fire ultrasonic waves using the drive pulse u ₂ of the drive pulses u ₁ and the high voltage of the low voltage or low voltage of the driving pulse u _The processing of generating an image by emitting ultrasonic waves five times according to ₁ may be performed to obtain a clear image in a deep part.
The data frozen at this time is obtained based on the drive pulses u ₁ and u ₂ of different voltages, and the first memory 32 and the second memory 33 of the fundamental wave receiving unit 3.
First, prepare a memory for freeze. In addition,
In FIG. 1, the first memory 32 and the second memory 33 store the high-frequency output of the fundamental wave receiving circuit 31 before detection, and after being processed by the fundamental wave signal processing unit 4, the first detection circuit 71 It is configured to be detected.

The coefficient b in the second coefficient circuit 42
Is a function of the distance from the ultrasonic transducer 21 and is controlled as a function of the time of arrival of the reflected wave, but the point is that when the difference between the received signals based on the drive pulses of different voltages is taken, This is to make the influence of the side lobe close to zero. Therefore, the coefficient b is determined not only by the distance but also by the driving voltage applied to the ultrasonic transducer 21 and the focusing conditions for focusing the ultrasonic beam emitted from the ultrasonic transducer 21, that is, the ultrasonic frequency, the focal length, and the aperture. It changes. Further, the ultrasonic transducer 2 which is driven simultaneously
The type of the ultrasonic probe 2 depending on the number of 1, the shape of the curve of the surface on which it is arranged, the focal length of the acoustic lens provided on the surface of the ultrasonic transducer 21, and the like;
It changes depending on the subject. Therefore, the coefficient b may be appropriately set in accordance with these factors. In a specific condition, b = 1 may be satisfied, and it is convenient to set an appropriate standard value in advance.

[0018] Then, when to freeze the image, data obtained based on the drive pulses u ₁ of the low voltage is stored in the first memory 32 of the fundamental wave receiving unit 3, the drive pulse u ₂ of high voltage Since the data obtained based on this is stored in the second memory 33, the coefficient value of the second coefficient circuit 42 can be finely adjusted while watching the freeze image displayed on the display device 10. If the coefficient b is adjusted for the frozen image, the image quality can be optimized while reflecting the adjustment result on the image. In this case, an image obtained based on a drive pulse of a constant voltage before and after a freeze and an image obtained based on a drive pulse of a different voltage that is frozen are switched and displayed on the display device 10,
Display both images side by side. In particular, if both images are displayed side by side, it is convenient to use them for comparative evaluation of two images or for educational use. The adjustment of the coefficient and the freeze operation are performed through a CPU provided in the control unit 9. It should be noted that the adjustment of the coefficient b is not necessarily multiplied by b times in the second coefficient circuit 42.
If the received signal stored in the second memory 33 is to be multiplied by 1, the first coefficient circuit 41 multiplies the received signal stored in the first memory 32 by 1 / b.
The coefficient b of the first coefficient circuit 41 may be adjusted.

Next, the reason why a clear image can be obtained by reducing the adverse effect of the side lobe by the ultrasonic diagnostic apparatus configured as described above will be described.
FIG. 2 shows an ultrasonic beam shape used in an experiment for measuring a nonlinear phenomenon of an ultrasonic wave. That is, one side D is 12 mm (D = 12 mm), and the focal point F is 60 mm.
(F = 60 mm), frequency fo is 3.75 MHz (fo =
A pulse generator 26 applies a u-volt pulse voltage u (V) to a rectangular ultrasonic transducer (piezoelectric vibrator) 25 (3.75 MHz) to emit ultrasonic waves into water, and distances X ₁ , X ₂ , X ₃ , the reflected waves from the wire targets T ₁ , T ₂ , T ₃ are received by the receiving circuit 27 and the received voltage v (V) is measured. Here, X ₁ = 20 m
m, X ₂ = 60 mm and X ₃ = 110 mm. In the graph of FIG. 3, the horizontal axis represents applied voltage u (V), and the vertical axis represents received voltage v (V).
The measurement data obtained in this experiment is shown with the positions of the wire targets T ₁ , T ₂ , and T ₃ as parameters. The black circles indicate the wire targets T _{1 at} the position of X ₁ = 20 mm, and the black triangles indicate X ₂ = the wire target _{T 2} is in the 60mm position, black square is by wire target _{T 3} at the position of _X 3 = 110 mm. Each curve is a theoretical curve and is represented by the following equation (1).

[0020]

(Equation 1)

Here, a is a value representing the magnitude of the nonlinear effect. If a = 0, v = ku, and there is no nonlinear effect, and the larger the value of a, the greater the nonlinear effect. Table 1 shows the values of k and a for the distances X ₁ , X ₂ , and X ₃ from the ultrasonic transducer 25.

[0022]

[Table 1]

From such a graph of FIG. 3 and Table 1,
When the distance from the ultrasonic transducer 25 is X ₁ (20
mm), X ₂ (60 mm), and X ₃ (110 mm), the value of a increases as the distance increases, and a non-linear integration effect on the distance can be read. Now, the sound field at a depth of X ₃ = 110 mm from the ultrasonic transducer 25 (that is, directivity)
Consider The directivity function R (θ) of the rectangular vibrator when there is no non-linearity is theoretically obtained and is expressed by equations (2) and (3).

[0024]

(Equation 2)

Here, λ is the wavelength of the ultrasonic wave, and if the sound speed is 1,500 m / s, λ is 0.4 mm. λ = 0.
By substituting 4 mm and D = 12 mm into equation (3) and displaying the directional characteristics in a graph, the result is as shown in FIG. In FIG. 4,
For the sake of simplicity, the vertical axis has R (θ) multiplied by 100, but the height of the first side lobe is about 20% of the main lobe.
It turns out that it is. Next, assuming that the directional characteristic taking into account the nonlinear effect at the applied voltage u (V) is Rn (u),
Equation (4) is obtained.

[0026]

(Equation 3)

As shown in Table 1, the distance 1
The value of a at 10 mm is 0.0249 V ^-1(Below, simply
0.025). And different
Applied voltage u₁And u₂And ultrasonic transducer 25
Are respectively driven to apply an applied voltage u.₁Received signal obtained by
From the applied voltage u₂Multiplied by the coefficient b to the received signal obtained in
The directional characteristic of the difference signal obtained by subtracting the value is ΔR (u₁, U₂)When
If so, this is shown by equation (5).

[0028]

(Equation 4)

Then, the applied voltage u ₁ = 50 (V), u ₂ =
The directional characteristics at 100 (V) are Rn (50),
The directional characteristics ΔR (50, 100) of the difference when Rn (100) and the coefficient b = 8/14 are expressed by Expressions (6) to (8), and these directional characteristics are graphically displayed. Then, the results are as shown in FIGS. 5, 6, and 7, respectively.

[0030]

(Equation 5)

As in a conventional ultrasonic diagnostic apparatus, for example,
When the transducer is driven with a constant applied voltage of 00V and emits ultrasonic waves, as shown in FIG. 5, the amplitude of the main lobe having a large amplitude decreases due to a strong nonlinear effect and the side lobe does not attenuate so much. 1st against robe
The height of the side lobes is as high as 46%, and a fake image due to unnecessary side lobes overlaps with the original image obtained by the main lobe, thereby causing a significant deterioration in image quality. On the other hand, when the vibrator is driven at an applied voltage of 50 V, which is half of 100 V, the nonlinear effect is smaller than that at the time of driving at 100 V, so that the height of the side lobe is reduced to 36% of the main lobe. Further, the coefficient b = from the driving of the vibrator at the applied voltage of 50 V to the driving of the vibrator at the applied voltage of 100 V
When the difference is multiplied by 8/14, the side lobe ratio is greatly improved to 13% as shown in FIG.

However, the amplitude of the main lobe having the difference shown in FIG. 7 is 1/5 of the amplitude of the main lobe in the case of the applied voltage of 100 V shown in FIG. Will be reduced. Therefore, the reflected wave signal low applied voltage u ₁ added together N times, then it is assumed to subtract the high reflected wave signal of the applied voltage u _2. That is, the directional characteristic of the reflected wave signals combined added N times lower applied voltages u ₁ and NRn (u _1), then a high directivity characteristic reflected wave signal and the coefficient b times the applied voltage u ₂ BRN
The directivity characteristic of the difference obtained by subtracting (u ₂ ) is ΔR (N ^* u ₁ ,
u ₂ ), this is represented by equation (9).

[0033]

(Equation 6)

In particular, u ₁ = u ₂ / N, that is, the lower applied voltage is set to 1 / N of the higher voltage, and the reflected signal is N 1
NRn (u ₁ ) = NRn (u ₂ /
N), and the directional characteristic ΔR (N ^* u ₁ ,
u ₂ ) is represented by equation (10).

[0035]

(Equation 7)

FIG. 8 shows that u ₁ = 20 V, u ₂ = 100 V, N
= 5, directional characteristic 5Rn (20), FIG. 9 shows bRn
(U ₂ ) = (8/14) Rn (100) shows the directivity characteristic ΔR (5 ^* 20,100).

Compared with the ratio of the first side lobe to the main lobe shown in FIG. 5 which is 46% and the amplitude of the main lobe is 28.6, the directivity shown in FIG. Is 3.3%, the amplitude of the main lobe is 29.9, the side lobe is greatly reduced to 1/14, and the amplitude of the main lobe is slightly increased. Accordingly, it is found that the fog of the false image due to the side lobe can be reduced to 1/14 while maintaining substantially the same sensitivity, and the image quality is greatly improved. In this case, if transmission and reception are performed five times by low-voltage driving, it takes much time, and there is a problem that observation in real time becomes difficult. To solve this problem, a plurality of low-voltage driving pulses are generated by increasing the pulse width of the low-voltage driving pulse, emitting ultrasonic waves, and subjecting the reflected wave signal to signal processing by pulse compression technology. Is preferably converted into a pulse having a width similar to that obtained by adding the reflected wave signals due to the above and having a high peak value. If the difference between the low-voltage drive reception waveform converted by this pulse compression technology and the high-voltage drive reception waveform is taken, only one low-voltage drive and one high-voltage drive is required, and the number of frames is increased to increase the real-time image. Can be obtained.

The present invention is not limited to the above-described embodiment, but can be implemented in various forms. For example, when the image is frozen, it has been described that the coefficient b can be finely adjusted while viewing the image displayed on the display device 10. However, if the image for a plurality of frames can be frozen, the image can be moved forward by that amount. The coefficient b can also be adjusted for the image that has been frozen, and the best image among the frozen images is selected, and adjustment is performed so that the image has the optimum coefficient, thereby obtaining a better image. it can.
In addition, an image at a short distance or an intermediate distance is mainly obtained by a reception signal based on a driving pulse of a constant voltage or a THI method, and an image at a long distance is mainly obtained by a reception signal based on a driving pulse of a different voltage. Then, by synthesizing them, a clear image with little influence of side lobes can be obtained from the shallow part to the deep part. In this case, the weights may be appropriately changed for the synthesis.

[0039]

As described above in detail, according to the present invention, by utilizing the non-linear phenomenon, the image quality deterioration due to the side lobe in the deep part of the subject is largely improved, and a clear image is drawn. An ultrasonic diagnostic apparatus that enables the above is provided. Further, by synthesizing an image (including THI) acquired by the conventional method and an image acquired by the method of the present invention, a clear image with little influence of side lobes from the shallow part to the deep part of the subject can be obtained. Obtainable.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a beam shape of an ultrasonic wave used in an experiment for measuring a nonlinear phenomenon of the ultrasonic wave.

FIG. 3 is a graph showing measurement data obtained in the experiment of FIG.

FIG. 4 is a directional characteristic diagram for explaining the principle of the present invention, assuming that there is no nonlinearity.

FIG. 5 is a directional characteristic diagram when driven by a high voltage, for explaining the principle of the present invention.

FIG. 6 is a directional characteristic diagram for driving at a low voltage, also shown for explaining the principle of the present invention.

FIG. 7 is a directional pattern showing that side lobes are reduced by performing signal processing in consideration of a nonlinear phenomenon in order to explain the principle of the present invention.

FIG. 8 is a directional characteristic diagram when driven by a low voltage in one embodiment of the present invention.

FIG. 9 is a directional characteristic diagram showing that side lobes are significantly reduced by performing signal processing in consideration of a non-linear phenomenon as one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitting part 2 Ultrasonic probe 3 Fundamental wave receiving part 4 Fundamental wave signal processing part 5 Harmonic receiving part 6 Harmonic signal processing part 7 Detection part 8 DSC part 9 Control part 10 Display

Claims (14)

[Claims] An ultrasonic transducer for transmitting and receiving ultrasonic waves, driving pulse generating means for driving the ultrasonic transducers with driving pulses of different voltages to transmit ultrasonic waves in the same direction, and the ultrasonic transducer Receiving means for receiving the echo signal received by the receiving means, and signal processing for performing predetermined signal processing on the received signal received by the receiving means between the received signals based on the driving pulses of different voltages to obtain desired information And an display unit for displaying an output based on the information obtained by the signal processing unit. 2. An ultrasonic transducer for transmitting and receiving an ultrasonic wave, and a drive for transmitting the ultrasonic wave in the same direction by driving the ultrasonic transducer with a driving pulse of a constant voltage and / or a driving pulse of a different voltage. Pulse generating means, receiving means for receiving an echo signal received by the ultrasonic transducer, and converting the received signal received by the receiving means into a received signal based on the constant voltage drive pulse. To obtain desired first information, and perform predetermined signal processing between the received signals based on the drive pulses of different voltages to obtain desired second information. And output means for displaying an output based on the first information and / or an output based on the second information obtained by the signal processing means. An ultrasonic diagnostic apparatus, comprising: 3. Freezing means for temporarily storing at least one frame of the received signal received by the receiving means and displaying information based on the stored received signal on the display means, and operating the freezing means. The ultrasonic drive according to claim 2, wherein a drive pulse supplied from the drive pulse generating means to the ultrasonic transducer is changed from a drive pulse having a constant voltage to a drive pulse having a different voltage according to a freeze operation. Ultrasound diagnostic device. 4. An ultrasonic transducer for transmitting and receiving ultrasonic waves, driving pulse generating means for driving the ultrasonic transducer with driving pulses of different voltages to transmit ultrasonic waves in the same direction, and the ultrasonic transducer. A fundamental wave receiving means for receiving an echo signal of a fundamental wave component received by the above, and subjecting the received signal received by the fundamental wave receiving means to predetermined signal processing between received signals based on the driving pulses of the different voltages. A fundamental wave signal processing means for obtaining desired information, a harmonic receiving means for receiving an echo signal of a harmonic component received by the ultrasonic transducer based on a driving pulse from the driving pulse generating means, Harmonic signal processing means for performing predetermined signal processing on a received signal based on the driving pulses of different voltages received by the wave receiving means to obtain desired information Combining means for combining an output based on the information obtained by the harmonic signal processing means with an output based on the information obtained by the fundamental signal processing means; and displaying the output combined by the combining means. An ultrasonic diagnostic apparatus comprising: a display unit. 5. The driving pulse of a different voltage supplied from the driving pulse generating means to the ultrasonic transducer comprises a plurality of low-voltage driving pulses and a single high-voltage driving pulse. The ultrasonic diagnostic apparatus according to any one of claims 1 to 4, wherein received signals received by the receiving unit or the fundamental wave receiving unit are added based on the driving pulse. 6. A pulse width of a low-voltage drive pulse among drive pulses of different voltages supplied from said drive pulse generation means to said ultrasonic transducer is longer than a pulse width of a high-voltage drive pulse. The ultrasonic diagnostic apparatus according to any one of claims 1 to 4, wherein 7. A reception signal received by the receiving unit or the fundamental wave receiving unit based on a low-voltage driving pulse having a pulse width longer than the high-voltage driving pulse, the reception signal being received based on the high-voltage driving pulse. 7. The ultrasonic diagnostic apparatus according to claim 6, wherein the pulse compression is performed so that the pulse width of the signal received by the means or the fundamental wave receiving means is substantially equal to the pulse width. 8. The signal processing means or the fundamental wave signal processing means multiplies at least one of the received signals based on the driving pulses of the different voltage by a predetermined coefficient to obtain a difference from another received signal. Claim 1 to Claim 4
The ultrasonic diagnostic apparatus according to any one of the above. 9. The apparatus according to claim 8, wherein the coefficient is set in accordance with a voltage of a driving pulse for driving the ultrasonic transducer and / or a distance in a transmitting and receiving direction of the ultrasonic wave from the ultrasonic transducer. An ultrasonic diagnostic apparatus according to item 1. 10. The apparatus according to claim 8, wherein the coefficient is set according to a type of an ultrasonic probe having the ultrasonic transducer and / or a focusing condition of an ultrasonic wave transmitted from the ultrasonic probe. An ultrasonic diagnostic apparatus as described in the above. 11. The ultrasonic diagnostic apparatus according to claim 8, wherein the coefficient is adjustable with respect to the received signal stored in the freeze unit. 12. The signal processing method according to claim 1, wherein the signal processing by the signal processing means or the fundamental wave signal processing means is performed on a high-frequency reception signal received by the receiving means or the fundamental wave receiving means. The ultrasonic diagnostic apparatus according to any one of claims 4 to 7. 13. Freezing means for temporarily storing at least one frame of a received signal received by said receiving means or fundamental wave receiving means and displaying information based on the stored received signal on said display means, The ultrasonic diagnostic apparatus according to claim 1, wherein the received signal stored after the signal processing is subjected to signal processing by the signal processing unit or the fundamental wave signal processing unit. . 14. The apparatus according to claim 1, wherein said receiving means receives an echo signal of a fundamental wave component received by said ultrasonic transducer. 14. The ultrasonic diagnostic apparatus according to any one of 13.