JP2009233352A - Ultrasonic imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ultrasonic imaging technique which forms a contrast echo image with high S/N ratio sufficient for confirmed diagnosis based on the contrast echo image by clearly discriminating an echo component generated by being scattered by a microbubble-based contrast agent from a Tissue Harmonic component generated by non-linearly transmitting transmission pulses. <P>SOLUTION: The ultrasonic imaging apparatus transmits/receives ultrasonic pulses to/from a living body to form a contrast image by microbubbles for contrast imaging of inside the living body. When N is set to an integer not lower than 3, under same transmission/reception focus condition, the phase of carrier wave is rotated by 360°/N every time using a transmission wave commonly having envelope signals to transmit/receive N times. By summimg up N time-series reception echo signals (a), (b), and (c) obtained by the transmission/reception at N times to obtain addition signal (d), the contrast image is formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic technique for imaging an inside of a living body by transmitting / receiving ultrasonic waves to / from a living body, and more particularly to an ultrasonic imaging technique for imaging using a microbubble-based contrast agent.

  2. Description of the Related Art An ultrasonic imaging apparatus that transmits and receives pulsed ultrasound to and from a living body and images the inside thereof is widely used for medical diagnosis.

  Among imaging diagnostic modalities, contrast agents have been used for the imaging of blood vessels in the fields of X-rays and MRI. The purpose is to administer a contrast medium in the blood to obtain an image with enhanced contrast in the structure and distribution of the vascular system, and to diagnose diseases reflected in the vascular system such as malignant tumors and infarctions with high accuracy. There is to do.

  On the other hand, contrast agents have not been widely used in ultrasound diagnosis until now, but in recent years, contrast enhancement using a formulation that stabilized microbubbles with micron-order sizes in some way. With the emergence of agents, it has begun to be widely used. This principle is that a microbubble with a diameter of about 1 micron resonates with an ultrasonic wave of several MHz used for ultrasonic diagnosis and vibrates with a large amplitude. As a result, the ultrasonic wave in this frequency range is scattered well, and the contrast is enhanced. It uses the fact that performance occurs.

  The feature of the microbubble ultrasound contrast agent is its strong non-linearity. This is because the microbubble has a property that the volume increase when receiving a negative pressure is much larger than the volume decrease when receiving a positive pressure of the same amplitude. For this reason, the echo signal scattered by the microbubbles contains a lot of second harmonic components having a frequency twice that of the transmission signal. V. L. Newhouse et al. Reported for the first time in 1992 a method for obtaining a blood flow Doppler signal enhanced for soft tissue based on the second harmonic component (see, for example, Non-Patent Document 1).

  Also, PN Burns et al. Have proposed a Pulse Inversion (pulse inversion) method in which transmission / reception is performed twice using a transmission sound pressure pulse waveform in which positive and negative are inverted, and two obtained echo signals are added ( For example, Patent Document 1). By this addition, the fundamental wave component of the echo signal from the soft tissue where the motion can be ignored is canceled because the signal rotated by 180 ° is added, but the second harmonic component is rotated by 360 °. Since things are added, they grow twice as much. Although the required number of transmissions is doubled, the fundamental wave component from the soft tissue can be removed in principle without a band pass filter, so that a second harmonic echo signal with excellent distance resolution can be obtained. In addition, for a scatterer in which changes occurring between two transmissions and receptions such as a microbubble-based contrast agent in the bloodstream cannot be ignored, the fundamental wave echo signal from the scatterer is not completely canceled, This is rather in line with the current purpose of obtaining an echo image in which the contrast medium is emphasized on the soft tissue.

  P. J. Phillips has proposed a method of performing transmission / reception three times by inverting the sign of the transmission sound pressure pulse waveform and simultaneously changing the amplitude (see, for example, Non-Patent Document 2). In this method, the transmission amplitude is modulated to 0.5: -1: 0.5, and echo signals obtained by performing transmission and reception three times are added. That is, while the same pulse waveform is used for the first and third transmissions, the second waveform uses a pulse waveform whose phase is inverted and the amplitude is doubled. The echo signal component from the slow-changing linear scatterer is canceled and the even harmonic component of the echo signal generated by nonlinear scattering or nonlinear propagation is emphasized, as in the normal Pulse Inversion method. In addition to this, all the components of the echo signal generated by nonlinear scattering and nonlinear propagation, including the fundamental wave, are extracted by amplitude modulation, which is equivalent to that of the normal Pulse Inversion method. High sensitivity to echo signals due to nonlinear scattering and nonlinear propagation is expected. This utilizes the fact that the dependence of nonlinear scattering by microbubbles on the incident sound pressure amplitude is much greater than the dependence of nonlinear propagation. This high sensitivity makes it possible to detect the effect of nonlinear scattering even at transmission sound pressures where the effect of nonlinear propagation is relatively small. Therefore, it is easy to distinguish the contrast medium from soft tissue compared to the normal Pulse Inversion method. It is said.

US Pat. No. 6,095,980

1992 IEEE Ultrasonics Symposium Proceedings, pp.1175-1177 2001 IEEE Ultrasonics Symposium Proceedings, pp.1739-1745

  As described above, in the prior art (Non-Patent Document 1), a method of obtaining a blood flow Doppler signal enhanced for soft tissue based on the second harmonic component has been proposed. If only the bandpass filter is used to extract the component from the echo signal, there remains a problem that the pulse of the second harmonic echo signal obtained as the output signal becomes long.

  This is because the amplitude of the fundamental wave component included in the echo signal is at least one digit greater than that of the second harmonic component, so that a filter having a sharp band cutoff characteristic or a narrow band pass characteristic must be used. This problem is particularly serious when the blood flow is displayed in a two-dimensional image because the resolution in the distance direction is deteriorated.

  In the prior art (Patent Document 1), for the purpose of solving this problem, the transmission sound pressure pulse waveform in which the sign is inverted is transmitted and received twice, and the obtained two echo signals are added. Inversion method was proposed.

  The speed of sound in many materials such as living soft tissue is greater under high pressure than under low pressure. Due to this non-linearity, when the ultrasonic pulse propagates through the soft tissue, the high sound pressure part propagates faster than the low part, and as a result, the sound pressure waveform that was originally sinusoidal is propagated. Furthermore, it is known that it suddenly rises and changes to an N-wave shape that falls gently, that is, it has harmonic components such as the second harmonic.

  When this is scattered in the soft tissue, an echo signal having a harmonic component returns from the soft tissue even if there is no microbubble-based contrast agent. The method of forming an echo image based on this harmonic component is called the Tissue Harmonic Imaging method, and it is preferred that the acoustic S / N ratio is higher than the echo image by the fundamental wave component. It came to be able to. However, this means that even if the Pulse Inversion method is used, an echo signal in which a harmonic component generated by scattering by the microbubble contrast agent and a harmonic component generated by propagation of the transmission pulse is mixed is obtained. This means that it is difficult to distinguish the originally intended contrast agent from the soft tissue.

  In general, nonlinear scattering due to a microbubble-based contrast agent tends to be observed even at a low sound pressure as compared with nonlinear propagation in soft tissue. Therefore, it is widely used to suppress the generation of Tissue Harmonic components by the Pulse Inversion method with low transmission sound pressure, and to form echo images mainly by nonlinear components from microbubble contrast agents. Since the amplitude is not sufficient, it is difficult to obtain an echo image with a high S / N ratio that is sufficient to perform a definitive diagnosis expected for contrast diagnosis.

  As a method for solving this problem to some extent, as described above, the prior art (Non-Patent Document 2) proposes a method of performing transmission and reception three times by inverting the sign of the transmission sound pressure pulse waveform and simultaneously changing the amplitude. is doing. However, this method does not remove in principle the Tissue Harmonic echo signal generated by the non-linear propagation of the transmission pulse in the soft tissue.

  In view of such a current situation, the present invention visualizes an echo component generated by being scattered by a microbubble-based contrast agent clearly and distinctly from a Tissue Harmonic component generated by nonlinear propagation of a transmission pulse. It is an object of the present invention to provide an ultrasonic imaging technique that realizes a contrast echo image with a high S / N ratio that is sufficient for performing a definitive diagnosis based on an echo image.

  In order to solve the above-mentioned object, in the present invention, when N is an integer of 3 or more, N transmission / reception waves are performed using transmission pulse waves having different waveforms under the same transmission / reception focus condition, The transmission / reception sensitivity with respect to the component from the fundamental wave of the ultrasonic echo signal from the soft tissue of the living body to the (N-1) th harmonic is suppressed, and the transmission / reception sensitivity with respect to the ultrasonic echo signal from the contrast microbubble is reduced. Configure to get.

  Furthermore, in the present invention, when N is an integer of 3 or more, a transmission pulse wave having a common envelope signal is used under the same transmission / reception focus condition, and the phase of the carrier wave is rotated by 360 ° / N. Thus, the contrast image is formed by performing N times of transmission / reception, adding N time-series reception echo signals obtained by the N times of transmission / reception, and obtaining an addition signal.

  As an example, when N is 3, the envelope signal of the transmission sound pressure pulse waveform is made common, and the phase of the carrier wave is rotated by approximately 120 °, and transmission / reception is performed 3 times. Add two echo signals. By this addition, the fundamental wave component and the second harmonic component of the echo signal scattered by the linear scatterer whose change can be ignored are simultaneously canceled. This is because when the phase of the three echo signals by such a scatterer is focused, the phase of the fundamental component is naturally rotated by about 120 °, and the phase of the second harmonic component is also the fundamental component. This is to rotate approximately 120 ° in the reverse direction.

  On the other hand, the scattered echo signal by the contrast microbubble which is a nonlinear resonator is not canceled. As a result, it is possible to extract a signal derived only from the contrast-enhancing microbubbles from the echo signal without including a signal component derived from nonlinear propagation or the like in the soft tissue.

  This principle is easy to understand when considering the vibration problem of a reciprocating 4-stroke inline engine. When the crankshaft is rotating at a constant angular velocity, the linear velocity at which each piston constituting the reciprocating engine vibrates includes not only a fundamental wave component of this angular velocity but also a harmonic component having a non-negligible amplitude. A four-stroke in-line four-cylinder engine is usually configured such that two sets of two in-phase pistons arranged symmetrically form a crank angle of 180 °. 1A shows the phase relationship of the fundamental wave, and this configuration cancels the fundamental wave component generated by each pair of pistons, while FIG. 1B shows the phase of the second harmonic. The relationship shows that the second harmonic component grows twice, and as a result, vibration having a frequency twice that of the crankshaft rotation speed becomes a problem. In the figure, the solid line indicates the phase of vibration due to the first piston set, and the dotted line indicates the phase of vibration due to the second piston set. The reason why there is a 4-cylinder engine equipped with a balancer that rotates at an angular velocity twice that of the crankshaft is to counteract this vibration.

  On the other hand, a 4-stroke in-line 6-cylinder engine is usually configured such that three sets of two in-phase pistons arranged symmetrically form a crank angle of 120 °. FIG. 2A shows the phase relationship of the fundamental waves. With this configuration, the fundamental wave components generated by each pair of pistons are generated so as to form 120 ° in the crank angle and cancel each other out. (B) of FIG. 2 shows the phase relationship of the second harmonic, and the second harmonic component is also 120 ° × 2 = 240 ° counted from the crank angle as shown in the figure, that is, 120 counted from the reverse side. Since they are generated with a phase of 0 °, they cancel each other. This is why the in-line 6-cylinder engine has less vibration. In the figure, the alternate long and short dash line indicates the phase of vibration caused by the third set of pistons. The configuration of the in-line four-cylinder engine in which the second harmonic vibration is emphasized in principle corresponds to the Pulse Inversion method, and the in-line six-cylinder engine in which not only the fundamental wave but also the second harmonic vibration is canceled in principle. The configuration corresponds to the method of the present invention.

  In general, when N is an integer of 3 or more, the vibration of the in-line 2N cylinder engine is fundamentally canceled, that is, the vibration from the first harmonic to the (N-1) th harmonic is canceled in principle. It is. If this is replaced with the case of ultrasonic imaging of the present invention, the envelope signal of the transmitted sound pressure pulse waveform is made common, and the phase of the carrier wave is rotated by 360 ° / N, and transmission / reception is performed N times. By adding N echo signals, the components from the fundamental wave to the (N-1) th harmonic of the echo signal scattered by the linear scatterer whose change can be ignored for a short time are canceled simultaneously. Become.

  On the other hand, the phase of the echo signal generated by being scattered by the microbubble contrast agent is affected by the envelope amplitude due to its strong non-linear resonance characteristic, and does not have a fixed relationship with the phase of the transmitted signal carrier wave. For this reason, in the case of an echo signal generated by scattering by contrast microbubbles even if three echo signals obtained by performing transmission / reception three times by rotating the phase of the transmission pulse carrier by 120 ° are added. Ingredients that are not counteracted remain. Therefore, since the remaining echo signal component reflects only the presence of the microbubble contrast agent, it is possible to perform ultrasonic imaging in which the contrast agent is clearly distinguished from the soft tissue.

  The features of the ultrasonic imaging method according to the present invention will be described below.

  (1) An ultrasonic imaging method in which ultrasound pulses are transmitted / received to / from a living body into which a contrast microbubble is introduced, and a contrast image inside the living body is formed by the contrast microbubble. When the above integers are used, a step of performing transmission / reception N times using transmission pulse waves having different waveforms under the same transmission / reception focus condition, and N time-series receptions obtained by the N transmission / reception waves By adding echo signals and obtaining an added signal, the transmission and reception sensitivities for components from the fundamental wave to the (N-1) th harmonic of the ultrasonic echo signal from the soft tissue of the living body are suppressed, and the contrast enhancement An ultrasonic imaging method comprising: extracting a signal derived from microbubbles to form the contrast image; and displaying the contrast image.

  (2) In the ultrasonic imaging method according to (1), the amplitude of the sum signal of the N transmission pulse waves is smaller than the individual amplitude of the N transmission pulse waves. Ultrasound imaging method.

  (3) In the ultrasonic imaging method according to the item (1), the N transmission pulse waves have a common envelope signal, and the phase of the carrier wave is different by 360 ° / N. Sound imaging method.

  (4) In the ultrasonic imaging method described in the above item (1), N is 3, the three transmission pulse waves have a common envelope signal, and the phase of the carrier wave is different by approximately 120 °. A characteristic ultrasonic imaging method.

  (5) In the ultrasonic imaging method according to (1), the image of the living body is formed from the amplitude of the sum signal of N time-series received echo signals obtained by the N times of transmission and reception, and the amplitude An ultrasonic imaging method characterized by displaying by luminance display reflecting the above.

  (6) In the ultrasonic imaging method according to (1), the amplitude of the weighted sum signal obtained by combining a plurality of weights of N time-series received echo signals obtained by the N transmission / reception waves An ultrasonic imaging method, wherein an image of a living body is formed and displayed by luminance display reflecting the amplitude.

  (7) The ultrasonic imaging method according to item (6), further including a step of displaying the amplitudes of the weighted addition signals by superimposing them with different display colors.

  (8) In the ultrasonic imaging method according to (6), at least one of the plurality of combinations of weights includes the fundamental wave component of the ultrasonic echo signal from the soft tissue and the even number. It is configured to suppress the transmission / reception sensitivity with respect to the second harmonic component and obtain the transmission / reception sensitivity with respect to the ultrasonic echo signal from the contrast microbubble, and at least one other set includes the soft tissue from the soft tissue. An ultrasonic imaging method characterized by being configured to obtain transmission / reception sensitivity with respect to an ultrasonic echo signal.

  (9) An ultrasonic imaging method for transmitting and receiving ultrasonic pulses to and from a living body into which a contrasting microbubble is introduced to form a contrast image inside the living body by the contrasting microbubble, wherein N is 3 When the above integers are used, a transmission pulse wave having a common envelope signal is used under the same transmission / reception focus conditions, and the phase of the carrier wave is rotated by 360 ° / N, so that N transmissions / receptions are performed. And a step of forming the contrast image by adding N time-series received echo signals obtained by the N times of transmission and reception to obtain an added signal.

  (10) In the ultrasonic imaging method according to the item (9), N is 3, the three transmission pulse waves have a common envelope signal, and the phase of the carrier wave is different by about 120 °. And an ultrasonic imaging method.

  As described above, according to the present invention, from the echo signal, it does not include a signal component derived from non-linear propagation or the like in the soft tissue, and a signal derived only from the contrast microbubbles is extracted. It is possible to provide a diagnostic image having a high S / N ratio that is sufficient for performing a definitive diagnosis based on a contrast echo image. Thus, the medical diagnostic utility of the apparatus embodying the present invention is extremely great, and therefore the significance of the present invention in the industry supporting medical diagnosis is also great.

The figure explaining the principle of Pulse Inversion method. The figure explaining the principle of the 3 pulse method by this invention. The block diagram explaining the structure of the ultrasonic diagnosing device in the Example of this invention. The figure which shows the example of the echo signal by the point reflector in the biological soft tissue with a nonlinear propagation characteristic obtained by this invention. The figure which shows the example of the echo signal by the point reflector in the biological soft tissue with a nonlinear propagation characteristic obtained by Pulse Inversion method. The figure which shows the example of the scattering echo signal by the microbubble for contrast obtained by this invention. The figure which shows the waveform after the band-pass filter of the scattered echo signal by the microbubble for imaging | contrast obtained by this invention. The figure which shows the example of the scattering echo signal by the microbubble for contrast obtained by Pulse Inversion method. The figure which shows the waveform after the band-pass filter of the scattering echo signal by the microbubble for contrast obtained by Pulse Inversion method. The figure which shows the example of the echo signal by the point reflector in the biological soft tissue obtained when the 2nd harmonic is intentionally superimposed on the transmission pulse wave in the present invention. The figure which shows the example of the scattering echo signal by the microbubble for contrast obtained when the 2nd harmonic is intentionally superimposed on the transmission pulse wave in this invention. The figure which shows the waveform after the band-pass filter of the scattering echo signal by the microbubble for imaging | contrast obtained when the 2nd harmonic is intentionally superimposed on a transmission pulse wave in this invention. The figure which shows the example of an adder output signal waveform of the echo signal by the point reflector in a biological soft tissue obtained when there exists an error in the phase of a transmission pulse in this invention. The figure which shows the phase error dependence of the echo signal by the point reflector in a biological soft tissue obtained when there is an error in the phase of a transmission pulse in the present invention, and the output signal amplitude of an adder. The figure which shows an example of the transmission waveform in this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a typical example of a block diagram of an ultrasonic diagnostic apparatus configured to carry out the present invention. Each element constituting the ultrasonic probe 1 is connected to a transmission beam former 3 and a reception beam former 10 via a changeover switch group 2. The transmission beamformer 3 uses the waveform selected and read from the transmission waveform memory 5 by the transmission waveform selection unit 4 according to the control by the transmission / reception sequence control unit 6, and has directivity when transmitted through each element. A signal that is an ultrasonic pulse is generated. This signal is converted into an ultrasonic pulse by each element of the ultrasonic probe 1 and transmitted to the living body. The ultrasonic echo signal reflected or scattered in the living body and returned to the ultrasonic probe 1 is received by each element and converted into an electric signal.

In the receiving beamformer 10, in accordance with control by the transmission / reception sequence control unit 6, a delay time is given to each received signal and added to each other in order to generate reception sensitivity having directivity. The time series signals obtained by the delay addition are once written to one bank in the reception waveform memory 12 selected by the reception memory selection unit 11 according to the control by the transmission / reception sequence control unit 6 and are added to each other. The series signals are read out and then added together by the adder 13. The adder output signal passes through the band-pass filter 14 that removes the noise component, and is then converted into an envelope signal by the envelope signal detector A 16 and input to the scan converter 18.
On the other hand, some of the time-series signals written in the reception waveform memory 12 are read and passed through the band-pass filter 15 that removes noise components without being added to each other, and the envelope signal detector B17. Is converted into an envelope signal and input to the scan converter 18. The scan converter 18 generates and controls signals so that a plurality of input signals are appropriately superimposed and displayed on the display unit 19 in two or three dimensions.

  As shown in FIG. 15, the transmission waveform memory 5 has three ultrasonic pulse waveforms (a), (b), (c )) And a signal to be written to each bank in the reception waveform memory 12 when the transmission waveform selection unit 4 executes a sequence of selecting and transmitting / receiving one of them three times while changing the waveform. Is shown in (a), (b), (c) of FIG. Here, for the sake of simplicity, the received echo signal generated by the transmission ultrasonic pulse propagating through the soft tissue of the living body and reflected by one point reflector is obtained and shown by numerical simulation. The carrier frequency was 2 MHz. (D) in the figure is an output signal obtained when (a), (b), and (c) are input to the adder 13. Since the transmitted ultrasonic pulse propagates nonlinearly in the soft tissue of the living body, (a), (b), and (c) include not only the fundamental wave component but also the second harmonic component, but the adder output result In (d), as predicted from the principle of the present invention, not only the fundamental wave components cancel each other, but also the second harmonic components cancel each other, and the signal amplitude is almost zero.

  For comparison, FIG. 5 shows the results when the Pulse Inversion method is used. In this case, two types of ultrasonic pulse waveforms having a common envelope signal and different in phase of the carrier wave by 180 ° are written in the transmission waveform memory 5, and one of them is selected by the transmission waveform selection unit 4. Send and receive. In the figure, (a) and (b) show signals to be written in each bank in the reception waveform memory 12 when this sequence is executed twice with different waveforms. (C) in the figure is the output signal of the adder 13 obtained at that time, but the fundamental wave components cancel each other, but the second harmonic components are rather emphasized each other. ing. This signal is called the Tissue Harmonic signal, and it has the advantage that a high acoustic S / N ratio can be obtained when rendering soft tissue in a living body, but only the distribution and dynamics of contrast agents are distinguished from the soft tissue. If you want to, it will be the biggest factor that hinders it.

  Next, reception echo signals by contrast microbubbles in the same transmission / reception sequence as in FIGS. 4 and 5 are shown. FIG. 6 and FIG. 8 show, as an example, the results obtained by numerical simulation of received echo signals that are scattered by microbubbles having a radius of 1.5 μm. FIGS. 7 and 9 show the bandpass filter 14 at that time. Input / output signals. Through FIG. 6, FIG. 7, FIG. 8, and FIG. 9, the scale of the vertical axis proportional to the sound pressure is common.

  Describing each correspondence relationship, in the transmission / reception sequence when the present invention is implemented as in the case of FIG. 4, the signals written in the respective banks in the reception waveform memory 12 are (a) and (b) in FIG. 6. (C), and the output signal of the adder 13, that is, the input signal of the band-pass filter 14 obtained at that time is (d) in FIG. 6 and (a) in FIG. (B), (c), (d), (e), and (f) in FIG. 7 respectively represent the passband center frequency as the fundamental frequency (2 MHz), the 1.5-fold harmonic frequency (3 MHz), It is an output signal of the band pass filter 14 when set to the second harmonic frequency (4 MHz), the 2.5 harmonic frequency (5 MHz), and the third harmonic frequency (6 MHz). On the other hand, in the transmission / reception sequence when the Pulse Inversion method is performed as in the case of FIG. 5, the signals written to each bank in the reception waveform memory 12 are (a) and (b) in FIG. The obtained output signal of the adder 13, that is, the input signal of the band pass filter 14, is (c) in FIG. 8 and (a) in FIG. (B), (c), (d), (e), and (f) in FIG. 9 are output signals of the bandpass filter 14 when the passband center frequency is set in the same manner as in FIG. .

  Originally designed to emphasize the second harmonic component in the echo signal, the Pulse Inversion method is used to increase the frequency from the 1.5th harmonic as shown in (c) and (d) of FIG. As a matter of course, a signal derived from microbubbles containing a lot of second harmonic components can be obtained. By the transmission / reception sequence of the present invention devised to cancel out components caused by nonlinear propagation among the second harmonic components in the echo signal, As shown in (d), (e), and (f) in FIG. 7, a signal having a sufficient amplitude derived from microbubbles containing a lot of second to third harmonic components is obtained. , Should be noted. The origin of this unique and useful phenomenon is that the microbubble is a resonator having a large non-linearity, more generally speaking, the delay time has a response characteristic depending on the amplitude. That is, if the delay response time does not depend on the amplitude even if there is nonlinearity between the input and output sound pressures, the second harmonic in the output signal, as shown in (d) of FIG. The ingredient will be countered. On the other hand, a simple linear resonator is out of the question because the second harmonic component itself does not occur.

  In the transmission / reception sequence according to the present invention, a signal having a sufficient amplitude derived from contrast-enhancing microbubbles can be obtained while intentionally superimposing the second harmonic component on the transmission pulse waveform against the background described above. There is also a feature that can be. By intentionally superimposing the second harmonic component on the ultrasonic transmission waveform, the vibration, growth, and collapse of the microbubbles in the living body or in the liquid can be emphasized and vice versa. : IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol.43, no.6, pp.1054-1062). This second harmonic superimposed transmission is also considered useful in the case of ultrasonic imaging using contrast microbubbles.

  FIGS. 10, 11, and 12 show examples of echo signals obtained when the second harmonic component is intentionally superimposed on the transmission pulse waveform. In the transmission waveform memory 5, three ultrasonic pulse waveforms having a common envelope signal and different in phase of the fundamental wave and the second harmonic wave, which are carrier waves, by 120 ° are written. When the sequence of selecting and transmitting / receiving one is executed three times with different waveforms, the signals to be written to each bank in the received waveform memory 12 are obtained in the same manner as in FIG. (A), (b), (c), and the output signal of the adder 13 obtained at that time is shown in (d). Further, the reception echo signal generated by being scattered by the contrast microbubbles is obtained in the same manner as in FIG. 6, and the signals written in the respective banks in the reception waveform memory 12 are shown in FIGS. The output signal of the adder 13, that is, the input signal of the bandpass filter 14 obtained at that time, is shown in (d) in FIG. 11 and (a) in FIG. (B), (c), (d), (e), and (f) in FIG. 12 are output signals of the bandpass filter 14 when the passband center frequency is set in the same manner as in FIG. .

  As apparent from (d) in FIG. 10, even when the second harmonic component is intentionally superimposed on the transmission pulse waveform, the received echo signal that is scattered by the point reflector is input to the adder 13. The second harmonic components of the signals cancel each other out like the second harmonic component generated by nonlinear propagation in the case of FIG. 4, and the adder output signal amplitude is almost zero. On the other hand, the received echo signal generated by being scattered by the contrast microbubbles is not canceled by the addition by the adder 13 and is sufficiently amplified to contain a large amount of the second to third harmonic components as in the case of FIG. The output signal is obtained.

  Further, the error range necessary for obtaining the effect of the present invention was examined for the phase of the transmission pulse wave. As an example, when the phase of the second transmission pulse wave is shifted by 20 °, the output signal of the adder 13, that is, the input signal of the bandpass filter 14, and the passband center frequency are matched with the fundamental wave and the second harmonic. These filter output signals were obtained in the same manner as in FIG. 4 and shown in (b) and (c) of FIG. For comparison, FIG. 5A shows a signal in the case of FIG. 5, that is, when the Pulse Inversion method can be performed without a phase error. (C) in FIG. 13 corresponds to the phase shift of 20 ° of the second transmission pulse wave, and the phase of the third transmission pulse wave is shifted by 10 ° so that the sum signal of the three transmission pulse waves becomes zero. This is a case of adjustment.

When the envelope signal of the transmission pulse wave is written as A (t) as a function of time t, the first, second, and third transmission pulse signals P1 (t) and P2 (t) in the embodiment of the present invention. , P3 (t) is when there is no phase error,
P1 (t) ＝ A (t) sin ωt (1)
P2 (t) = A (t) sin (ωt + 2π / 3) (2)
P3 (t) = A (t) sin (ωt−2π / 3) (3)
Can be written. At this time,
P1 (t) + P2 (t) + P3 (t) = 0 (4)
The relationship is established. When a phase error φ occurs in the second pulse, the second pulse is
P2 (t) = A (t) sin (ωt + 2π / 3 + φ) (5)
Can be written. At this time, the third pulse
P3 (t) = A3 (t) sin (ωt−2π / 3 + φ / 2) (6)
A3 (t) = 2A (t) cos (π / 3 + φ / 2) (7)
(4) can be satisfied regardless of the phase error φ. (C) in FIG. 13 shows the result of such a correction of the third pulse, and the fundamental wave component in the output signal of the adder 13 can be canceled despite the phase error of the second pulse. is made of. In the signal obtained by adding N reception echo signals because (4) is established, and in general, the sum signal of N pulse waveforms used for transmission is substantially zero. The fundamental wave component of is canceled.

  FIG. 14 shows the peak-to-peak value of the output signal amplitude of the adder 13 as a function of the phase error given to the second pulse. The signal amplitude normalized by the value obtained when the Pulse Inversion method can be performed without phase error is corrected when the third pulse is not corrected ((a) in the figure) and when the correction is performed ((b in the figure) )). When the phase error reaches 20 °, even if the third pulse is corrected, the signal amplitude derived from non-linear propagation in the soft tissue and not derived from the contrast microbubbles becomes more than half of the conventional Pulse Inversion method. The effect of the present invention will not be exhibited sufficiently. From this result, it can be said that the phase error of the transmission pulse is desirably about 10 ° or less in order to sufficiently obtain the effects of the present invention.

  As described above, by implementing the present invention, it is possible to extract a signal derived only from contrast-enhanced microbubbles from an echo signal, which does not include a signal component derived from non-linear propagation or the like in soft tissue. it can.

  Such a signal can be obtained as an output signal of the adder 13, and a signal with an improved S / N ratio is obtained as an output signal of the bandpass filter 14, and the envelope signal detector A16 is obtained as the envelope signal. Is output to the scan converter 18 as a signal representing the spatial distribution of contrast microbubbles. On the other hand, an envelope signal is obtained by an envelope signal detector B17 from a signal in which a signal written in one bank in the received waveform memory 12 is passed through a band pass filter 15 and the S / N ratio is improved. A signal representing the position and morphology of the soft tissue is input to the scan converter 18.

  In the scan converter 18, the output signal of the envelope signal detector B17 is used as a background, and the output signal of the envelope signal detector A16 is superimposed and displayed on the display unit 19 with different colors so that it can be easily distinguished from the background. The In this way, the distribution of contrast microbubbles in the body of the patient to be examined can be displayed in an easy-to-understand manner using a two-dimensional or three-dimensional image.

  In the above-described embodiment, the case where a signal written in one bank in the reception waveform memory 12 is used as it is as a signal representing the position and form of the soft tissue has been described. It is possible to use an addition signal obtained by appropriately weighting signals written in the three banks.

  In the series of explanations above, the embodiment using three transmission pulse waves has been described in detail. However, as shown in the principle explanation, three or more integer N transmission pulse waves having a common envelope signal are obtained. The carrier wave phase is rotated by 360 ° / N, N transmissions / receptions are performed, N echo signals obtained are once written in N banks in the reception waveform memory 12, and the read signals are added. The present invention can also be implemented by inputting to the device 13.

  As described above, according to the present invention, from the echo signal, it does not include a signal component derived from non-linear propagation or the like in the soft tissue, and a signal derived only from the contrast microbubbles is extracted. It is possible to provide a diagnostic image having a high S / N ratio that is sufficient for performing a definitive diagnosis based on a contrast echo image. Thus, the medical diagnostic utility of the apparatus embodying the present invention is extremely great, and therefore the significance of the present invention in the industry supporting medical diagnosis is also great.

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic probe, 2 ... Changeover switch group, 3 ... Transmission beam former, 4 ... Transmission waveform selection part, 5 ... Transmission waveform memory, 6 ... Transmission / reception sequence control part, 10 ... Reception beam former, 11 ... Received memory selection unit, 12: Received waveform memory, 13: Adder, 14: Bandpass filter A, 15 ... Bandpass filter B, 16 ... Envelope signal detector A, 17 ... Envelope signal detector B, 18 ... scan converter, 19 ... display.

Claims (19)

An ultrasonic imaging device that performs transmission and reception of ultrasonic pulses on a living body into which a contrast microbubble is introduced, and forms an image inside the living body,
Each of the transmission beamformer for generating a transmission pulse, and receiving the ultrasonic echo signal from the living body, giving each delay time to generate a reception sensitivity with directivity by giving a delay time to each received signal A received beamformer that adds received signals and generates a time-series received echo signal;
An adder for adding the time-series received echo signals;
The transmission beamformer, and a transmission / reception sequence control unit for controlling the reception beamformer,
The transmission / reception sequence control unit includes:
When N is an integer greater than or equal to 3,
Under the same transmission / reception focus condition, N transmission / reception waves are transmitted using the transmission pulse, which is a common envelope signal whose carrier phase is different by 360 / N degrees, to the transmission beamformer and the reception beamformer. Control to let
The addition unit includes a band-pass filter unit that removes a noise component, adds N time-series reception echo signals obtained by the N transmission / reception waves, obtains an addition signal, and among the addition signals, The ultrasonic imaging apparatus, wherein a signal that has passed through the band-pass filter unit outputs the addition signal as a signal representing a spatial distribution of the contrast microbubbles.   2. The ultrasonic imaging apparatus according to claim 1, wherein the addition signal is suppressed in transmission / reception sensitivity with respect to components from a fundamental wave to a harmonic wave of an ultrasonic echo signal from the soft tissue of the living body, and the contrast microbubbles An ultrasonic imaging apparatus characterized in that a transmission / reception sensitivity for an ultrasonic echo signal from is obtained.   2. The ultrasonic imaging apparatus according to claim 1, wherein the component for suppressing the transmission / reception sensitivity is a component from the fundamental wave to the (N-1) th harmonic. 2. The ultrasonic imaging apparatus according to claim 1, wherein an amplitude of a sum signal of the N transmission pulse waves is smaller than an amplitude of each of the N transmission pulse waves.   2. The ultrasonic imaging apparatus according to claim 1, wherein a part of the time-series received echo signal is a signal representing a position and a form of the soft tissue of the living body. 2. The ultrasonic imaging apparatus according to claim 1, wherein N is 3, the three transmission pulse waves have a common envelope signal, and the phases of the carrier waves are different by approximately 120 degrees. Imaging device.   2. The ultrasonic imaging apparatus according to claim 1, wherein the image of the living body is formed from an amplitude of a weighted sum signal obtained by combining a plurality of sets of weights of N time-series received echo signals obtained by the N transmission / reception waves. An ultrasonic imaging apparatus, wherein the display is performed by luminance display reflecting the amplitude.   8. The ultrasonic imaging apparatus according to claim 7, wherein the amplitude of the weighted sum signal is displayed by being superimposed with different display colors.   The ultrasonic imaging apparatus according to claim 7, wherein at least one set of the plurality of sets of weights corresponds to the fundamental wave component and the even-order harmonic component of the ultrasonic echo signal from the soft tissue. The transmission / reception sensitivity is suppressed, and the transmission / reception sensitivity with respect to the ultrasonic echo signal from the contrast-enhancing microbubble is obtained, and at least one other set is configured to respond to the ultrasonic echo signal from the soft tissue. An ultrasonic imaging apparatus configured to obtain transmission / reception sensitivity.   An ultrasound imaging apparatus that transmits and receives ultrasound pulses to and from a living body into which a contrast microbubble is introduced, and forms a contrast image inside the living body by the contrast microbubble, wherein N is an integer of 3 or more , N transmission / reception waves are performed using transmission pulse waves having different waveforms under the same transmission / reception focus condition, and N time-series reception echo signals obtained by the N transmission / reception waves are added. By obtaining the added signal, the transmission / reception sensitivity for the components from the fundamental wave to the (N-1) th harmonic of the ultrasonic echo signal from the soft tissue of the living body is suppressed, and the signal is derived from the contrast microbubbles. An ultrasonic imaging apparatus that extracts an ultrasonic echo signal including the (N-1) th harmonic and forms the contrast image.   An ultrasound imaging apparatus that transmits and receives ultrasound pulses to and from a living body into which a contrast microbubble is introduced, and forms a contrast image inside the living body by the contrast microbubble, wherein N is an integer of 3 or more , Means for performing transmission / reception N times using transmission pulse waves having different waveforms under the same transmission / reception focus condition, and N time-series reception echo signals obtained by the N transmission / reception waves. By adding and obtaining the addition signal, the sensitivity of the transmission / reception with respect to the components from the fundamental wave to the (N-1) th harmonic of the ultrasonic echo signal from the soft tissue of the living body is suppressed, and the contrast microbubble is generated. An ultrasonic imaging apparatus comprising means for extracting an ultrasonic echo signal including the derived (N-1) th order harmonic and forming the contrast image.   The ultrasonic imaging apparatus according to claim 11, wherein the N transmission pulse waves have a common envelope signal, and a phase of a carrier wave is different by 360 ° / N. The ultrasonic imaging apparatus according to claim 11, wherein N is 3, the three transmission pulse waves have a common envelope signal, and the phase of the carrier wave is different by approximately 120 °. Imaging device. An ultrasound imaging apparatus that transmits and receives ultrasound pulses to and from a living body into which a contrast microbubble is introduced, and forms a contrast image inside the living body by the contrast microbubble, wherein N is an integer of 3 or more Then, under the same transmission / reception focus condition, a transmission pulse wave having a common envelope signal is used, and the phase of the carrier wave is rotated by 360 ° / N, N transmissions / receptions are performed, The contrast image is formed from the received echo signal including the (N-1) th harmonic by adding N time-series received echo signals obtained by N transmission / reception waves to obtain an added signal. An ultrasonic imaging apparatus.   15. The ultrasonic imaging apparatus according to claim 14, wherein N is 3, the three transmission pulse waves have a common envelope signal, and the phase of the carrier wave is different by approximately 120 °. Imaging device.   An ultrasound imaging apparatus that transmits and receives ultrasound pulses to and from a living body into which a contrast microbubble is introduced, and forms a contrast image inside the living body by the contrast microbubble, wherein N is an integer of 3 or more Then, under the same transmission / reception focus condition, an ultrasonic wave that transmits and receives N times by using a transmission pulse wave having a common envelope signal and rotating the phase of the carrier wave by 360 ° / N. A probe; an adding means for adding N time-series received waveforms obtained by the N transmission / reception waves; an envelope signal detecting means for detecting an envelope signal from the output of the adding means; and the envelope An echo signal including a (N-1) th harmonic derived from the contrast-enhancing microbubbles, having a scan converter to which an output of the signal detector is input and a display unit for displaying the output of the scan converter; An ultrasonic imaging apparatus and displaying forming said contrast image out.   17. The ultrasonic imaging apparatus according to claim 16, wherein N is 3, the three transmission pulse waves have a common envelope signal, and the phases of the carrier waves are different by approximately 120 degrees. Imaging device.   The ultrasonic imaging apparatus according to any one of claims 10, 11, 14, and 16, wherein a part of the time-series reception echo signal is a signal representing a position and a form of a soft tissue of the living body. A characteristic ultrasonic imaging apparatus.   The ultrasonic imaging apparatus according to any one of claims 1 to 18, wherein the component for suppressing transmission / reception sensitivity is a component from the fundamental wave to the (N-1) th harmonic. Ultrasonic imaging device.

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