JP4232134B2 - Ultrasound contrast drawing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasound contrast drawing apparatus that draws information necessary for diagnosis such as blood flow distribution information using an ultrasound contrast agent, and more particularly to a technique that enables a contrast agent distribution to be drawn as a clear image.
[0002]
[Prior art]
As a method for measuring blood flow distribution information in a living tissue, an ultrasonic contrast drawing method and apparatus using an ultrasonic contrast agent have been studied. For example, the document “Ultrasound in Medicine & Biology, Vol. 26, No. 6, p.965, 2000,” Ultrasound Contrast Imaging: Current and New Potential Methods: Peter JA Frinking et al. . ""It is described in.
[0003]
An ultrasound contrast agent is generally formed by mixing a large number of bubbles in a medium such as physiological saline. The bubble is, for example, an inert gas (C ₃ F ₈ , C ₄ F ₁₀ Etc.) is covered with a protein membrane or a lipid membrane. The particle size distribution of the bubbles is, for example, a Gaussian normal distribution, and the average particle size is several μm. However, it is known that 0.5 μm or less aggregate each other and become a substantially large particle size, resulting in a distorted normal distribution.
[0004]
Such a contrast agent is generally injected into a living body from a vein. When an ultrasound beam is irradiated onto a contrast medium injected into a living body, when the sound pressure is low, bubbles are deformed, and acoustic information associated with the deformation is mixed with the reflected signal and emitted as an ultrasonic response signal. . When the sound pressure is high, the bubbles are destroyed and strong acoustic information is emitted. That is, the ultrasonic contrast agent exhibits a non-linear response to the irradiation of ultrasonic waves, and has a fundamental frequency f. ₀ When the ultrasonic wave is irradiated, the fundamental frequency component f is included in the response signal ₀ In addition to the signal corresponding to 2nd harmonic component 2f ₀ The signal is said to be included.
[0005]
Therefore, conventionally, the center frequency is 2f. ₀ Using a relatively narrow bandpass filter ₀ The presence of a contrast agent is detected by extracting. That is, 2f ₀ 2f corresponds to the presence or absence of contrast agent, 2f ₀ Since this corresponds to the spatial density distribution of the contrast medium, it is possible to draw which part of the tissue the contrast medium flows into.
[0006]
By the way, in the drawing method using a contrast agent, it is divided roughly into an early stage and a late stage according to the time phase after the contrast agent is injected into the vein. The initial phase is a time phase in which an ultrasound contrast agent injected from a vein flows into a tissue such as a liver to be diagnosed by blood circulation. Further, the latter phase is a time phase in which the ultrasound contrast agent flowing or distributed in the tissue is sufficiently flowed out of the tissue by blood circulation after 3 to 8 minutes after the contrast agent is injected from the vein. In the initial time phase, in general, an ultrasonic sound pressure (for example, MI: mechanical index = 0.2) that does not destroy the contrast agent but generates sufficient harmonics is used. In the late time phase, most of the contrast agent flows out of the tissue, but some is trapped in the tissue. The presence or absence of this trap is considered to be different between the diseased part and the healthy part of the tissue. In this late time phase, when an ultrasonic wave with a high sound pressure (for example, MI = about 0.8 or more) that destroys the contrast agent is irradiated, strong reflection occurs when the contrast agent is destroyed. Produces a signal. Therefore, by detecting this, a region where the contrast agent is trapped, that is, a diseased part, and a region where it is not trapped, that is, a healthy part can be distinguished, which can contribute to diagnosis.
[0007]
On the other hand, U.S. Pat. No. 5,632,277 and U.S. Pat. No. 5,706,819 have been proposed as methods for extracting harmonics using the nonlinearity of the frequency of the contrast agent response signal without using a band pass filter. According to these, after the ultrasonic pulse based on the first ultrasonic signal is irradiated into the living body and the response signal is received, the second is obtained by inverting the polarity of the first ultrasonic signal at a short time interval. An ultrasonic pulse based on the ultrasonic signal is irradiated and a response signal is received. Then, by adding these received signals, etc., the component corresponding to the fundamental frequency component in the response signal is removed, and the harmonic component is extracted or emphasized, thereby detecting the contrast agent with high accuracy. is there.
[0008]
Japanese Patent Laid-Open No. 2000-300554 discloses a period t in which the first ultrasonic signal has a positive signal level. ₁ And a period t during which the signal level is a negative constant value. ₂ Have a waveform that continues in this order, and it has been proposed that the first ultrasonic signal be a second ultrasonic signal having a waveform that is inverted with respect to the time axis. According to this, the symmetry of the ultrasonic pulse based on the first and second ultrasonic signals can be increased, and the signal of the fundamental wave component (linearity component) can be reduced.
[0009]
[Problems to be solved by the invention]
Any of the conventional techniques described above is effective for extracting or enhancing harmonic components caused by a contrast agent. However, no consideration is given to the case where the harmonic component contained in the tissue response signal is so large that it cannot be ignored compared to the harmonic component contained in the contrast agent response signal. For this reason, harmonic components included in the contrast agent response signal may not be extracted at a high rate.
[0010]
That is, the non-linear phenomenon that is the key to conventional contrast medium detection also occurs when ultrasonic waves propagate through the tissue in addition to the contrast medium. In this case, the fundamental frequency frequency f of the irradiated ultrasonic wave ₀ 2f harmonic component 2f ₀ Was found to occur. In particular, the harmonic component 2f included in the tissue response signal ₀ The signal increases in intensity as the depth increases. Therefore, the harmonic component 2f included in the response signal of the contrast agent ₀ As compared with the above signal, the contrast medium detection accuracy decreases when the signal level is equal to or larger than the above signal. For example, when detecting a contrast medium in a blood vessel buried in a tissue, such as a blood flow in the liver, 2f from both the contrast medium and the tissue. ₀ Therefore, the presence of the contrast agent may be detected erroneously.
[0011]
Therefore, an object of the present invention is to discriminate and extract a harmonic component included in a response signal of a biological tissue and a harmonic component included in a response signal of a contrast agent.
[0012]
[Means for Solving the Problems]
First, the solution principle of the present invention will be described with reference to FIG. FIG. 2 is a result of a detailed examination of the nonlinear response between the contrast agent and the tissue with respect to the ultrasound irradiation, and schematically shows the spectrum of the response signal when the contrast agent distributed in the tissue is irradiated with the ultrasound. In the figure, the horizontal axis indicates the frequency, and the vertical axis indicates the signal intensity of each component. FIG. 6A shows a response signal from a relatively shallow part close to the probe, and FIG. 4B shows a response signal from a relatively deep part far from the probe. As can be seen from these drawings, the response signal 1 of the contrast medium has a fundamental frequency f in both the shallow part and the deep part. ₀ In addition to the fundamental wave component corresponding to, harmonic components over a wide frequency band are included. On the other hand, the tissue response signal 2 has a fundamental frequency f. ₀ Fundamental wave component 2a and double harmonic 2f ₀ And appearing separately from the higher harmonic component 2b. In the case of the shallow part, the harmonic component 2b is not so strong, but becomes very strong in the deep part and becomes stronger than the signal intensity of the response signal 1 of the contrast agent. As described above, this is because the harmonic component 2b included in the tissue response signal is generated by a nonlinear effect when the ultrasonic wave propagates in the tissue, and therefore propagates as it becomes deeper away from the probe. This is because the length increases. Therefore, as in the prior art, the harmonics 2f are uniform. ₀ Even if an attempt is made to enhance the response signal of the contrast agent by extracting the component of the contrast medium, the harmonic component 2f of the tissue is removed except for a shallow region. ₀ Is emphasized, so that the sharpness of the contrast image cannot be improved.
[0013]
Here, items derived from the consideration of FIG. 2 will be organized.
(1) The frequency component (nonlinear response) of the response signal of the contrast agent is 2f ₀ It is not localized in and is distributed over a wide band. This tendency becomes more prominent as the frequency spectrum of the ultrasonic signal to be transmitted is wider.
(2) The response signal of the contrast agent strongly depends on the diameter of the contrast agent, and is remarkably emphasized at the free resonance frequency fR of the contrast agent. As described above, since the contrast agent has a particle size distribution, harmonics appear in a wide frequency band.
(3) The fundamental wave component of the contrast agent response signal is as strong as the fundamental wave component of the tissue response signal.
(4) The harmonics of the tissue response signal are relatively 2f regardless of the strength of the ultrasonic sound pressure. ₀ Localized in the vicinity.
(5) The harmonic of the response signal of the tissue is significantly weaker than the harmonic component of the contrast agent in the case of a relatively low ultrasonic sound pressure and in a shallow region.
[0014]
In view of the above considerations (1) to (5), the present invention solves the above problems by means of a solution having the following characteristics.
(First feature)
The receiving unit is provided with a filter for extracting a specific frequency component from the response signal, and the passband width of this filter is set to the average frequency of the ultrasonic signal transmitted to the ultrasonic probe. ₀ 0.8f ₀ To 2.5f ₀ It is characterized by being set within the range. That is, in view of the fact that the contrast agent response signal is distributed over a wide frequency band and the signal intensity is high over a wide frequency band, ₀ Wide frequency band not limited to 0.8-2.5f ₀ Is extracted with a band pass filter. Thereby, the response signal of the contrast agent can be relatively emphasized as compared with the response signal of the tissue. In particular, in the case of a relatively weak sound pressure (initial time phase), the harmonic component 2f of the tissue ₀ Is effective because it can be ignored.
[0015]
By the way, in the case of high sound pressure (late time phase), the harmonic component 2f of the tissue ₀ May not be ignored. In this case, the bandwidth of the band pass filter is 0.8 to 1.8 f. ₀ The harmonic component 2f of the tissue ₀ Is preferably removed. In other words, the harmonic component 2f that was exclusively emphasized in the prior art. ₀ There is another feature of the present invention in removing or attenuating. In this case, 2f ₀ 0.8 to 1.8f with attenuation of harmonic components related to the contrast agent distributed in the vicinity ₀ Since the response signal of the contrast agent distributed in the wide frequency band in the vicinity is extracted, the above attenuation is more than compensated.
[0016]
In addition, the harmonic component 2f of the tissue at a shallow depth region and a deep depth region. ₀ The strength of will change. Therefore, the time position of the response signal corresponding to the depth part of the ultrasonic beam is determined, and the harmonic component 2f is obtained for the response signal having a depth deeper than the set depth. ₀ It is desirable to switch the passband width of the filter in real time so as to attenuate the noise. Note that the harmonic component 2f ₀ As a filter that attenuates the center frequency, in addition to a band pass filter, the center frequency is 2f. ₀ Can be used. Furthermore, f ₀ The fundamental wave component of the tissue response signal existing in the vicinity includes a component associated with breathing and pulsation of the human body, and may be an artifact in the contrast agent image. In this case, the passband width of the filter is slightly narrowed to 1.2 to 1.8 f. ₀ It is preferable to set.
[0017]
In this way, the tissue harmonic 2f ₀ And harmonics contained in the response signal of the contrast agent can be discriminated. Then, by detecting and drawing the contrast medium based on the harmonic of the response signal of the contrast medium extracted by discrimination, the SN ratio of the contrast image can be improved as compared with the conventional technique.
(Second feature)
As described above, the first feature of the present invention is that the passband width of the filter of the receiving unit is widened in order to emphasize and extract the response signal component of the contrast agent. In order to further promote the effect of the first feature, it is preferable that the frequency of the ultrasonic wave applied to the contrast agent is widened. That is, it is desirable that the transmission unit is configured to transmit an ultrasonic signal having a plurality of frequency components to the ultrasonic probe. That is, since the contrast agent has a distributed free resonance frequency corresponding to the particle size distribution, more contrast agents respond by distributing the frequency spectrum of the irradiated ultrasound over a wide band, and the contrast agent The response signal itself is enhanced. As a result, the tissue response signal is f ₀ And 2f ₀ In contrast, since the response signal of the contrast agent appears at a strong level over a wider frequency band, it becomes easier to distinguish the harmonics of the tissue from the harmonics of the contrast agent.
(Third feature)
The first and second features described above are for the case where contrast drawing is performed based on a response signal received by one irradiation of an ultrasonic beam. However, the first and second features of the present invention are not limited to the one-irradiation contrast-enhanced drawing of the ultrasonic beam, but the so-called two-irradiation-type (or multiple-irradiation-type) contrast drawing method described below. It can also be applied to. In particular, the multiple-irradiation method is effective when drawing is performed by detecting in real time the disappearance due to the movement or destruction of the contrast agent. That is, when detecting the movement or disappearance of the contrast agent, two images before and after the movement or before and after the disappearance are required. However, when the contrast medium is drawn by the one-time irradiation method, the time interval between the two images is limited to one frame time interval (10 to 20 milliseconds). Therefore, when detecting a site where the blood flow velocity is high or a contrast medium rupture, a multiple irradiation method is preferable. In the multiple irradiation method, an ultrasonic beam is irradiated twice or more in the same direction at an extremely short time interval, and the response signal corresponding to each irradiation is compared, and the contrast agent is placed on the ultrasonic beam within a predetermined time interval. It can be detected by comparing the response signals whether the contrast medium has moved or the contrast medium has been destroyed and disappeared.
[0018]
Specifically, the ultrasonic wave transmission unit has a function of transmitting an ultrasonic beam a plurality of times (M, where M ≧ 2 is a natural number) at intervals in the same direction, and each of the ultrasonic signals has a frequency. It is assumed that the amplitude of the first waveform is larger than the amplitude of the continuing waveform group, and the signals at each time are set asymmetric with respect to polarity inversion and time axis inversion and the waveform is transmitted. . In accordance with this, the receiving unit attenuates the response signal of the biological tissue by adding or subtracting the response signal subjected to the phasing process and the function of phasing the response signal of a plurality of (M) ultrasonic signals. It is characterized by having a function to perform. In this case, the average frequency f of each of the first waveform and the second waveform ₀ Are most preferably equal.
[0019]
According to this, since the frequency band of the ultrasonic wave irradiated into the living body is widened compared with the conventional two-time irradiation method, the harmonic component included in the response signal of the contrast agent can be strengthened over a wide frequency band. . At the same time, the frequency spectrum of the response signal of the contrast agent is also shifted in frequency and added or subtracted to obtain 1.2f. ₀ To 1.8f ₀ It will be widely distributed in nearby bands. As a result, the harmonic component contained in the response signal of the living tissue can be discriminated from the harmonic component contained in the response signal of the contrast agent. Then, by detecting and drawing the contrast agent by the harmonic of the response signal of the contrast agent thus discriminated, the SN ratio of the contrast image can be improved as compared with the conventional case.
[0020]
For example, the frequency spectrum of the response signal of the contrast agent obtained by addition or subtraction processing is 1.2f ₀ To 1.8f ₀ Emphasized in nearby bands, 2f ₀ Rather it is attenuated in the vicinity. Therefore, by receiving and processing the response signal over a wide frequency band, the response signal SN ratio of the contrast agent can be increased, and the response signal of the contrast agent can be selectively drawn.
[0021]
In particular, each of the above-mentioned waveforms consists of N waveforms having frequencies f1, f2,..., Fn,..., FN (where N ≧ 2 is a natural number), and the average frequency of f1 to fN is represented by f. ₀ When the frequency distribution width Δf of f1 to fN is 0.0f ₀ To 0.4f ₀ It is preferable to set within the range. According to this, the response signal component of the contrast agent can be further enhanced. Further, there is no particular limitation on the frequency distribution width Δf, but preferably 0.1 f. ₀ To 0.4f ₀ And 0.2f ₀ To 0.3f ₀ If it is within the range, it is practical from the viewpoint of circuit configuration. Further, the frequency distribution width Δf of f1 to fN is set to 0.0 f for a predetermined time after injection of the contrast agent, for example, 2 minutes. ₀ And after 2 minutes, 0.0f ₀ To 0.4f ₀ It may be variably set within the range.
[0022]
Note that a unit waveform forming the first waveform or the second waveform can use a half cycle of a sine wave, one cycle or more. Conversely, it is possible to use a chirp waveform in which the frequency is made finer, such as ¼ cycle and 、 cycle, and the frequency continuously increases and decreases. In the case of a chirp waveform, the start phase of the first irradiation waveform is actually different, but a chirp waveform whose amplitude gradually decreases from the start waveform toward the subsequent waveform, that is, an amplitude-enhanced chirp waveform is suitable for the present invention. It is. According to this, the difference in the frequency spectrum of the contrast medium between the two irradiations can be further enhanced by increasing the first amplitude.
[0023]
Further, the first waveform and the second waveform are set by a code f (A, θ) that defines the frequency f, the amplitude A, and the start phase θ, and the first waveform is f1 (A1, θ1) <f2 (A2, θ2) <... <fn (An, θn) <... <fN (AN, θN), N waveforms are continuous, the amplitude is A1 = A2 =... = An =... = AN, and the phase is .theta.1 = .theta.2. = ... = θn = ... = θN = 0 ° (or 180 °). On the other hand, the second waveform is f1 ′ (A1 ′, θ1 ′)> f2 ′ (A2 ′, θ2 ′)>...> Fn ′ (An ′, θn ′)>...> FN ′ (AN ′, θN ′). N waveforms are continuously arranged, the amplitude is A1 ′ = A2 ′ =... = An ′ =... = AN ′, and the phase is θ1 ′ = θ2 ′ =. Or 180 °). That is, the first waveform and the second waveform may have the frequency sequence increase / decrease relationship reversed, the start phase may be the same, and the amplitude may be the same or different. In this case, the response signal subjected to phasing is subtracted to attenuate the response signal of the living tissue. When the phases are different, the response signal subjected to phasing is added to attenuate the response signal of the living tissue.
[0024]
In addition, when the start phase of the first waveform is 180 °, it starts from the falling (negative polarity side), so that the waveform continues from the low frequency f1 <fN, and conversely, the start phase of the second waveform is set to 0. When it is set to °, since it starts from the rising edge (positive polarity side), it is characterized in that the waveform is continuous from the high frequency fN ′> f1 ′. That is, when the ultrasonic wave is irradiated with the falling waveform, the bubbles of the contrast medium start to deform from the expansion, so that the frequency distribution of the response signal has an average frequency f ₀ It shifts to a lower frequency side. On the other hand, when the ultrasonic wave is irradiated with the rising waveform, the contrast medium starts to be deformed from the contraction, so that the frequency distribution of the response signal has an average frequency f. ₀ It shifts to a higher frequency side. Therefore, by setting in this way, the frequency distribution of the response signal of the contrast agent can be further expanded, and the response signal component of the contrast agent can be further enhanced.
[0025]
Also in the third feature, it is desirable to variably set the passband width of the filter in accordance with the first feature. Moreover, it is preferable to variably set according to the depth of the response signal or the ultrasonic sound pressure to be irradiated. For example, the band pass width of the filter can be widened at a shallow part or an initial time phase, and the filter band pass width can be narrowed at a deep part or a late time phase.
(Fourth feature)
In the third feature, the response signal of the contrast agent is emphasized by gradually increasing or decreasing the plurality of frequencies f1, f2,..., FN forming the first waveform and the second waveform, respectively. . In contrast, the fourth feature further enhances the response signal of the contrast agent by making the amplitude A of at least the first half wave of the first waveform and the second waveform larger than the amplitude of the subsequent waveform. There is.
[0026]
The present inventors have found this characteristic through simulation and experiment, and the physical background is not necessarily clear, but it is easy to explain if the contrast agent is considered as a kind of resonator. That is, among the sound pressure waveforms irradiated to the contrast agent, the frequency, phase, and amplitude of the start waveform are considered to determine the start response of the contrast agent, but once the shape of the response is determined by the start waveform The behavior tends to follow the response defined by the initial response even if the frequency, phase, and amplitude of the subsequent waveform change. A system that has just started to resonate at a certain frequency is usually difficult to respond to an input that deviates from the resonance frequency, but in the case of contrast agents, this tendency is remarkable due to its nonlinearity. it can. The fourth feature of the present invention is that this initial waveform dependence of the contrast agent response, in other words, the initial transient response dependence, is used to make the amplitude A of the first half wave of the starting waveform greater than the amplitude of the subsequent waveform. By doing so, the contribution of the frequency component of the starting waveform is further emphasized.
[0027]
Thereby, the harmonic component contained in the response signal of a contrast agent can be emphasized rather than the harmonic component contained in the response signal of a biological tissue, and can be generated over a wide frequency band. That is, since the amplitude of the irradiation start waveform is increased, it is possible to further increase the response signal due to the contrast agent generated by the deformation accompanying the expansion and contraction of the contrast agent.
[0028]
As a result, since the signal component of the contrast agent is emphasized at a high rate, it can be extracted by being distinguished from the harmonics of the tissue, and drawing based on this can improve the SN ratio of the contrast image compared to the conventional case. be able to.
[0029]
Specifically, the first waveform and the second waveform are set by a code f (A, θ) that defines the frequency f, the amplitude A, and the start phase θ, and the first waveform is f1 (A1, θ1) < f2 (A2, θ2) <... <fn (An, θn) <... <N waveforms of fN (AN, θN) are continued, and the amplitude is set to A1>A2>...>An>...> AN. θ1 = θ2 = ... = θn = ... = θN = 180 °, and the second waveform is expressed as f1 ′ (A1 ′, θ1 ′)> f2 ′ (A2 ′, θ2 ′)>...> fn ′ (An ′ , Θn ′)>...> FN ′ (AN ′, θN ′), N waveforms are continued, the amplitude is A1 ′> A2 ′>...> An ′>...> AN ′, and the phase is θ1 ′ = θ2. '= ... = θn' = ... = θN '= 0 ° can be set.
[0030]
In the above description, the waveform of the ultrasonic signal supplied to the ultrasonic probe has been described. However, the present invention also holds true for the waveform of the ultrasonic sound pressure applied to the contrast agent itself. In other words, if the frequency response characteristics of recent ultrasonic probes have a relative bandwidth of 60% or more with respect to the center frequency, it is confirmed that the theory of the waveform of the ultrasonic signal is directly applied to the theory of the acoustic waveform. Yes.
[0031]
Embodiment
Hereinafter, the present invention will be described based on embodiments shown in the drawings. In addition, this invention is not limited by embodiment shown below.
(First embodiment)
FIG. 1 shows an overall configuration diagram of an ultrasonic contrast drawing apparatus according to an embodiment to which the present invention is applied. This embodiment is suitable for implementing the third and fourth features of the present invention. That is, an image in which an ultrasonic signal is transmitted twice in the same direction of the ultrasonic beam with a time interval and the response signal of the contrast agent is emphasized based on the response signals of the first and second ultrasonic signals. Is going to get.
[0032]
As shown in FIG. 1, the ultrasound contrast imaging apparatus 100 includes a probe 10, a wave transmission unit 20, a wave reception unit 30, an image creation display unit 40, and a system control unit 50. The wave transmission unit 20 includes an arbitrary waveform generator 21 and a wave transmitter 23. The wave receiving unit 30 includes a wave receiver 31, a phasing adder 32, a line adder 33, and a band selection filter 34.
[0033]
The arbitrary waveform generator 21 of the wave transmission unit 20 includes the first waveform 61, 71, 81 and the second waveform 62, 72, 82 shown in FIGS. 3 (A), 4 (A), and 5 (A). It is configured to generate a sound wave signal. The output of the arbitrary waveform generator 21 is supplied to the broadband ultrasonic probe 10 via the transmitter 23. A power amplifier having a necessary number of channels corresponding to the array-type ultrasonic probe 10 is provided in parallel at the output unit of the transmitter 23. In this way, the average frequency f from the ultrasonic probe 10 is as follows. ₀ Is irradiated to the living tissue. The response signal from the contrast agent distributed in the living tissue and the response signal from the living tissue are received by the ultrasonic probe 10 as a mixed signal.
[0034]
The response signal received by the ultrasonic probe 10 is input to the receiver 31. The receiver 31 includes a preamplifier having the required number of channels, a TGC amplifier, an A / D converter, and the like. The input response signal is amplified and then converted into a digital signal and output to the phasing adder 32. To do. The phasing adder 32 adjusts and adds phases of response signals from a plurality of transducers related to one ultrasonic beam. A specific example of the phasing adder 32 is preferably a so-called digital beamformer in order to minimize the occurrence of distortion during the addition process. The reason is that an unnecessary harmonic 2f is generated by the phasing addition process. ₀ This is because no component is generated.
[0035]
The response signal subjected to the phasing addition by the phasing adder 32 is obtained by adding or subtracting two response signals corresponding to the two-time irradiation in the line adder 33 based on a command from the system control unit 50. Output to. The bandwidth of the band pass filter 34 can be variably adjusted as will be described later. The band-pass width is adjusted by forming the band-pass filter 34 with a digital filter known as a digital FIR filter, and each coefficient sequence of the digital FIR filter by the system control unit 50 according to the depth or the ultrasonic sound pressure. This can be realized by varying the value. As the digital filter, a third-order Chebyshoff type filter is particularly suitable. The response signal having the frequency component selected and extracted by the band pass filter 34 is sent to the image creation / display unit 40 as a signal caused by the contrast agent in common or in parallel with processing other than the contrast agent mode. The image creation display unit 40 performs processing including image processing such as normal detection and compression, Doppler processing such as color flow, or scan conversion processing.
[0036]
The above processing operations are performed while scanning the direction of the ultrasonic beam as many times as necessary to cover a desired cross section or region of the living tissue. And by the process of the image preparation display part 40, it displays on a display part as image information, such as a brightness | luminance as distribution of a contrast agent and a magnitude | size. The system control unit 50 controls the series of operations described above.
[0037]
The characteristic operation of the embodiment of FIG. 1 configured as described above will be described next. In contrast agent mode imaging performed by injecting contrast agent, for example, a B-mode tomographic image is captured and displayed on a display monitor, and the contrast mode image obtained by imaging in contrast agent mode is converted into a normal B-mode image. Usually, the images are displayed in an overlapping manner.
[0038]
A normal B-mode image is captured from the arbitrary waveform generator 21 based on a control command from the system control unit 50. ₀ This is performed by generating an ultrasonic signal having a single frequency and performing transmission focus processing in the transmitter 23, amplifying and supplying the ultrasonic signal to the ultrasonic probe 10, and irradiating the living body with the ultrasonic beam. The response signal from the living body is amplified by the receiver 31 and converted into a digital signal, and then the phase of the response signal from the same part received by the plurality of transducers is matched in the phasing adder 32. A response signal of a specific frequency component is selected and extracted from the response signal for each ultrasonic beam subjected to phasing and addition by the band pass filter 34. In the case of normal B-mode image capturing, the bandwidth of the bandpass filter 34 is the fundamental frequency f. ₀ Is adjusted to a band having a center frequency. The image creation / display unit 40 detects the output of the bandpass filter 34, performs image processing such as compression or scan conversion processing, and creates a two-dimensional image (B-mode image) of the living tissue to display the display (display). To draw.
[0039]
Next, imaging and drawing of a contrast agent mode image according to the features of the present invention will be described. The basic procedure and operation for capturing and drawing a contrast agent mode image are the same as those for normal B-mode image capturing.
(When realizing the third feature)
The arbitrary waveform generator 21 is configured to generate an ultrasonic signal having a first waveform 61 or a second waveform 62 as shown in FIG. As will be described later, the first waveform 61 and the second waveform 62 can be coded by frequency, starting phase, and amplitude, and the coded one-cycle waveform is continuously generated as an arbitrary waveform. Can do.
[0040]
The arbitrary waveform generator 21 generates two ultrasonic signals having the first waveform 61 of FIG. 3A with a time interval in the same ultrasonic beam direction under the control of the system control unit 50. The generated first ultrasonic signal is input to the ultrasonic probe 10 via the transmitter 23. On the other hand, the generated second ultrasonic signal is input to the ultrasonic probe 10 through the transmitter 23 as the second waveform 62 of FIG. When the arbitrary waveform generator 21 has a function of generating both the first waveform 61 and the second waveform 62, the data selector selects both waveforms.
[0041]
When the ultrasonic signals of the first waveform 61 and the second waveform 62 are irradiated on the living body, two response signals for the signals are input to the receiver 31. These two response signals are response signals for ultrasonic beams in the same direction, and are input with a time lag. In the receiver 31 and the phasing adder 32, these two response signals are separately amplified, A / D converted, and phasing addition processing is performed, and a line adder / subtracter is provided as a response signal (RF line signal) having phase information. To 33. The line adder / subtracter 33 adds the two response signals to the RF in consideration of the phase, and obtains one response signal (RF line signal) to be displayed.
[0042]
In this way, in the response signal obtained by adding / subtracting the response signal of the two ultrasonic irradiations, the same component (linear component) included in the two response signals is attenuated, and the harmonics of the contrast agent and tissue Non-linear components such as components are input to the band pass filter 34. The passband filter 34 has the same configuration as that described in the embodiment of FIG. 1, and the passband width according to the depth of the response signal component and the time phase of the contrast agent based on a command from the system control unit 50. The response signal relating to the desired contrast agent is enhanced.
[0043]
The system control unit 50 controls a series of operations related to the arbitrary waveform generator 21, the receiver 31, the phasing adder 32, the line adder / subtractor 33, and the band pass filter 34. For example, the first waveform 61 and the second waveform 62 of the ultrasonic wave are issued to the arbitrary waveform generator 21 according to a predetermined code.
[0044]
Here, a simulation result will be described that the contrast mode response signal can be effectively enhanced by performing contrast mode imaging using the first waveform 61 and the second waveform 62 shown in FIG. 3B, when the ultrasonic signal having the first waveform 61 in FIG. 3A is irradiated for the first time and the ultrasonic signal having the second waveform 62 in FIG. 2 shows an example frequency spectrum obtained by simulating a signal output from a signal. The horizontal axis of FIG. ₀ The vertical axis represents the normalized signal intensity. In FIG. 5B, the line 63 is the frequency spectrum of the transmitted ultrasonic wave, and the line 64 is the frequency spectrum of the response signal output from the line adder / subtractor 33.
[0045]
In this simulation, the first waveform 61 of the first transmission has a frequency of f1 (= 1.8 MHz) in the first one cycle, and a frequency of f2 (= 2.2 MHz) in the next one cycle. f ₀ Was set to 2 MHz. The second waveform 62 of the second transmission has a frequency of f2 (= 2.2 MHz) in the first cycle, a frequency of f1 (= 1.8 MHz) in the next cycle, and an average frequency f. ₀ Was set to 2 MHz. That is, the first waveform 61 and the second waveform 62 indicate that the code “frequency f (amplitude A, phase θ)” of the first waveform 61 of the first transmission is 1.8 MHz (1.0, 180 °), 2.2 MHz (1.0, 180 °). The codes of the second waveform 62 of the second transmission are 2.2 MHz (1.0, 0 °) and 1.8 MHz (1.0, 0 °). The frequency change width is 0.4 MHz, and the amplitude change width is 0.0. Each waveform is resembling a waveform in a living body by applying a Hanning weight in the time axis direction. The simulation is a differential equation that governs the change in the diameter of a known contrast agent, and finds the change in the contrast agent diameter when a sound pressure waveform of MI = 0.7 is added to a contrast agent having a diameter of 2 microns. The radiation wave when the diameter change is regarded as a secondary sound source is observed at an observation point far from the contrast agent.
[0046]
Here, the characteristics of the frequency spectrum of the response signal obtained by the present embodiment shown in FIG. 3B will be described in comparison with the frequency spectrum of the double irradiation method according to the prior art. FIG. 6A shows a conventional ultrasonic transmission waveform, and FIG. 6B shows a frequency spectrum of the transmission signal and the response signal. Their vertical and horizontal axes are the same as in FIG. In FIG. 6A, a first waveform 91 indicates a first transmission waveform, and a second waveform 92 indicates a second transmission waveform. These frequencies are all fundamental frequencies f ₀ = 2MHz is set. In FIG. 6B, line 93 is the frequency spectrum of the transmission ultrasonic wave, and line 94 is the frequency spectrum of the response signal output from the line adder / subtractor 33.
[0047]
When the line 64 in FIG. 3B is compared with the line 94 in FIG. ₀ The nearby response signal component is greatly attenuated and 2f ₀ The harmonic components of nearby tissues are emphasized. This is suitable for so-called tissue harmonic imaging (called Tissue Harmonic Imaging). ₀ ~ 2f ₀ In contrast, the response signal component of the contrast agent that is widely distributed is attenuated. In particular, the fundamental wave component f of the contrast agent response signal ₀ Is significantly attenuated. Therefore, in the case of the conventional two-time irradiation method shown in FIG. 6, it is not possible to satisfy the objective of distinguishing and highlighting the response signal of the contrast agent from the harmonic of the tissue. This is because if the polarity or time axis of the ultrasonic signal waveform of the two-time transmission according to the prior art is simply reversed, 2f ₀ In addition to emphasizing together the harmonic components of the tissue response signal localized nearby, the fundamental component f of the contrast agent response signal distributed over a wide range ₀ This is because it is significantly attenuated.
[0048]
In this regard, according to FIG. 3B according to the present invention, the discrimination ratio between the contrast agent response signal and the harmonic of the tissue response signal is 1.2 f on the spectrum. ₀ To 1.8f ₀ Since it is the area ratio (energy ratio) of the nearby band, it is approximately 10 dB to 20 dB.
[0049]
Therefore, the signal obtained by the line addition / subtraction 32 is 0.8 f when drawing a shallow part. ₀ To 2.5f ₀ Since the response signal of the contrast agent spread over a wide band in the vicinity is included, the pass band width of the band pass filter 34 is 0.8 f. ₀ To 2.5f ₀ And is drawn as it is as an effect signal of the contrast medium. The same applies to normal contrast medium drawing in which the ultrasonic sound pressure is MI = 0.2 to 0.7. On the other hand, when the ultrasonic sound pressure is high MI value (eg, 1.3), 0.8f ₀ To 1.8f ₀ To. 2f ₀ May be replaced with a band elimination filter having a center frequency. 2f for drawing deep parts ₀ In order to attenuate nearby tissue harmonics and to reduce artifacts of the fundamental tissue due to body movements, the bandwidth is reduced to 1.2f. ₀ To 1.8f ₀ Change to
[0050]
Although not shown, even if the frequencies f1 and f2 of the first waveform 61 and the second waveform 62 in FIG. 3A are interchanged, that is, the frequency f1 of the first code and the frequency f2 of the second code. Even if the relationship is f1> f2, the same effect can be obtained.
[0051]
As described above, in the first embodiment, each waveform of one cycle constituting the ultrasonic transmission waveform is coded by the frequency f, the amplitude A, and the start phase θ, and these waveforms are made continuous. In particular, as in the waveform shown in FIG. 3A, the frequency of the ultrasonic transmission signal irradiated twice is emphasized by making the first cycle 61 and the second waveform 62 have different frequencies in the first cycle. It is characterized by. Then, when the transmission signal with the frequency emphasized in this way is transmitted twice and the response signal is added, the spectrum of the contrast agent response signal is 2f. ₀ A low frequency shift of the frequency spectrum occurs from a distribution in which a strong signal appears in a band centered at (FIG. 6B) to a distribution in which a strong signal appears in a band from 1.2f0 to 1.8 (FIG. 3B). It has been found.
[0052]
The reason why the spectrum of the response signal shifts at a low frequency cannot be clearly understood because the contrast agent has a nonlinear response. However, it can be considered as follows. First, the first waveform 61 starts from the fall (negative polarity side) because the start phase is 180 °. Conversely, the second waveform 62 starts from the rising edge (positive polarity side) because the start phase is 0 °. Here, when the irradiation of the ultrasonic wave is started with the falling waveform, the bubbles of the contrast medium start from the expansion, and therefore the frequency distribution of the response signal has an average frequency f. ₀ It can be considered that the frequency shifts to a lower frequency side. On the other hand, when the irradiation is started with the rising waveform, the bubbles of the contrast medium start from contraction, so that the frequency distribution of the response signal has an average frequency f ₀ It can be considered that the frequency shifts to a higher frequency side. Accordingly, it is considered that the nonlinear response of the contrast agent changes depending on the relationship between the start phase and the frequency of the first waveform 61 and the second waveform 62, and the frequency spectrum of the response signal varies. In other words, by making the frequency of the start waveform different from the frequency of other waveforms that follow, the frequency spectrum of the contrast agent response signal obtained by the two irradiations is not the same, and the frequency distribution of the response signal of the contrast agent is It can be further expanded to emphasize the response signal component of the contrast agent.
[0053]
In the above embodiment, the case of irradiating ultrasonic waves twice with a time interval has been described, but the present invention can also be applied to the case of irradiating three times or more. That is, the arbitrary waveform generator 21 has a function of generating at least one cycle of an ultrasonic signal of a sine wave shape at a time interval in the same direction of the ultrasonic beam (M, where M ≧ 2 is a natural number) times. Shall. The generated ultrasonic signals are two types of ultrasonic signals of a first waveform and a second waveform that are symmetrical with respect to the phase axis or polarity. The first waveform and the second waveform have a plurality of frequency components formed by consecutive N waveforms having frequencies f1, f2,..., Fn,..., FN (where N ≧ 2 is a natural number). And Then, the ultrasonic signals of the first waveform and the second waveform are alternately switched every transmission and transmitted. In this case, the average frequency f1 to fN of the first waveform and the second waveform f ₀ Are most preferably equal. The frequency distribution width Δf of f1 to fN is 0.0f. ₀ To 0.4f ₀ Set within the range. However, preferably 0.1f ₀ To 0.4f ₀ And 0.2f ₀ To 0.3f ₀ It is practical from the viewpoint of circuit configuration to be in the range.
[0054]
Note that a unit waveform forming the first waveform or the second waveform can use a half cycle of a sine wave, one cycle or more. Conversely, it is possible to use a chirp waveform in which the frequency is made finer, such as ¼ cycle and 、 cycle, and the frequency continuously increases and decreases. In the case of a chirp waveform, the start phase of the first irradiation waveform is actually different, but a chirp waveform whose amplitude gradually decreases from the start waveform toward the subsequent waveform, that is, an amplitude-enhanced chirp waveform is suitable for the present invention. It is. According to this, the difference in the frequency spectrum of the contrast medium between the two irradiations can be further enhanced by increasing the first amplitude.
[0055]
Further, the first waveform and the second waveform are set by a code f (A, θ) that defines the frequency f, the amplitude A, and the start phase θ, and the first waveform is f1 (A1, θ1) <f2 (A2, θ2) <... <fn (An, θn) <... <fN (AN, θN), and N waveforms are continuous, the amplitude is A1 = A2 =... = An =... = AN, and the phase is .theta.1 = .theta.2. = ... = θn = ... = θN = 180 °. On the other hand, the second waveform is f1 ′ (A1 ′, θ1 ′)> f2 ′ (A2 ′, θ2 ′)>...> Fn ′ (An ′, θn ′)>...> FN ′ (AN ′, θN ′) N waveforms are continuous, the amplitude is A1 '= A2' = ... = An '= ... = AN', and the phase is θ1 '= θ2' = ... = θn '= ... = θN' = 0 ° Set. That is, the first waveform and the second waveform may have the frequency sequence increase / decrease relationship reversed, the start phase may have a 180 ° difference, and the amplitude may be the same or different. In this case, the response signal subjected to the phasing process is added to attenuate the response signal of the living tissue. The start phase may be the same. In this case, the response signal subjected to the phasing process is subtracted to attenuate the response signal of the living tissue.
[0056]
Further, the frequency distribution widths Δf and Δf ′ of f1 to fN and f1 ′ to fN ′ are set to 0.0 f according to the depth of the ultrasonic irradiation focus, respectively. ₀ To 0.4f ₀ It is preferable to variably set within the range. Alternatively, the frequency distribution widths Δf and Δf ′ of f1 to fN and f1 ′ to fN ′ are set to 0.0 f for 2 minutes after the injection of the contrast agent. ₀ And after 2 minutes, 0.0f ₀ To 0.4f ₀ Can be variably set within the range.
[0057]
For example, when N = 3, f1 = 1.8 MHz, f2 = 2 MHz, and f3 = 2.2 MHz. Further, even if N = 4 or more, the gist of the present invention is not impaired. However, as the wave number increases, the difference between the waves is relatively reduced, and it has been confirmed that a wave number of about N <6 is effective. In addition, in the case of M ≧ 3, the addition / subtraction processing extracts the response signal component of the contrast agent, for example, by adding the odd response signals and adding or subtracting the even response signals according to the signal polarity. To do.
(When realizing the fourth feature)
Here, another embodiment according to an ultrasonic contrast rendering apparatus that realizes the fourth feature of the present invention will be described. This embodiment can be realized by using the ultrasonic contrast drawing apparatus shown in FIG. The third feature is that the function of the arbitrary waveform generator 21 is different. That is, the arbitrary waveform generator 21 generates the first waveform 71 and the second waveform 72 shown in FIG. 4 (A), or the first waveform 81 and the second waveform 82 shown in FIG. 5 (A). Is different. Others are the same as those of the ultrasonic contrast drawing apparatus shown in FIG. 1, and therefore, different features will be mainly described.
[0058]
4A and 5A are different from FIG. 3A in that the amplitude of the waveform of the first cycle of the first waveform and the second waveform is set larger than the amplitude of the subsequent waveform. There is in being. 4B and 5B show the same simulation results as in FIG. 3B, lines 73 and 83 are the frequency spectrum of the irradiated ultrasound, and lines 74 and 84 are response signals that have undergone addition / subtraction processing. This is the frequency spectrum.
[0059]
The code f (A, θ) of the first waveform 71 in FIG. 4A is 1.7 MHz (1.1, 180 °) and 2.3 MHz (0.8, 180 °) in this order, and the code f (A) of the second waveform 72 , Θ) are 2.3 MHz (1.1, 0 °) and 1.7 MHz (0.8, 0 °) in this order. That is, the frequency change width Δf is 0.6 MHz with respect to 0.4 MHz in FIG. 3, and the amplitude change width ΔA is 0.3 with respect to 0.0 in FIG.
[0060]
According to the ultrasonic waveform of FIG. 4A, the reception spectrum of the contrast agent response signal obtained by adding the response signals corresponding to two ultrasonic transmissions is clear from FIG. And the fundamental wave f ₀ Shift to the side. Harmonic component 2f of tissue ₀ Although the attenuation is slightly inferior, the distribution of the response signal obtained by addition is 1.2f. ₀ To 1.8f ₀ By detecting the response signal of the contrast medium that is shifted and distributed to the contrast medium, it is possible to emphasize the contrast medium and attenuate tissue harmonics. Therefore, the harmonics of the tissue can be attenuated exclusively in the region where the movement due to the respiration and pulsation of the tissue is not remarkable, and the discrimination ratio between the response signal of the contrast agent and the harmonics of the tissue can be further improved.
[0061]
The code f (A, θ) of the first waveform 81 in FIG. 5A is 1.8 MHz (1.0, 180 °) and 2.2 MHz (0.9, 180 °) in this order, and the code f (A) of the second waveform 82 , Θ) are 2.2 MHz (1.0, 0 °) and 1.8 MHz (0.9, 0 °) in this order, and their average frequency is 2 MHz in any case. That is, the frequency change width Δf is the same as 0.4 MHz in FIG. 3, and the amplitude change width ΔA is set to 0.1 with respect to 0.0 in FIG.
[0062]
According to this, as compared with FIG. ₀ Therefore, the discrimination ratio between the response signal of the contrast agent and the harmonics of the tissue can be further improved. In the case of three irradiations, the amplitude change of each waveform may be A1 = 1.1, A2 = 1.0, and A3 = 0.9.
[0063]
Thus, by adopting the waveforms shown in FIGS. 4 (A) and 5 (A), that is, the ultrasonic wave of the ultrasonic waveform emphasizing the frequency and amplitude of the first one-cycle waveform is irradiated twice. By adding the response signals, the spectrum of the contrast agent response signal is 2f. ₀ From the stress, 1.2f ₀ To 1.8f ₀ This causes a low frequency shift of the frequency spectrum to the stress of the band. As described above, the reason why this frequency transition occurs is that the non-linear response of the contrast agent differs depending on the relationship between the polarity of the waveform of the start of ultrasonic irradiation and the frequency, and therefore the frequency spectrum transitions. In addition, it is considered that the difference in the non-linear response of the contrast agent is emphasized by increasing the amplitude of the starting waveform. In other words, by making the frequency of the starting waveform different from the frequency of other sequential waveforms, the frequency spectrum of the contrast agent obtained by two transmissions is not the same, and the amplitude of the starting waveform is different from the other By making it larger than the sequential waveform sequence, it is possible to further emphasize the difference in spectrum.
[0064]
As described above, in the conventional technique, even if the same waveform shown in FIG. ₀ The ingredients can be emphasized. However, as shown in FIGS. 3 (A), 4 (A), and 5 (A) of the present invention, the frequency is different for each cycle. In particular, by changing the frequency of the first cycle of the transmission waveform, 1.2f ₀ To 1.8f ₀ The signal of ₀ Ingredients can be attenuated. In particular, if the amplitude of the first cycle of the transmission waveform is increased compared to the second and subsequent cycles, the frequency component of the first cycle can be emphasized. As a result, the spectrum after addition processing is 2f. ₀ Since it can be shifted from the center to the low frequency region, the harmonics of the tissue can be easily distinguished. In addition, the frequency transition of the response signal to the low frequency region can be controlled by changing the frequency of the first cycle of the transmission waveform and the degree of amplitude enhancement.
(When implementing the first and second features)
When the first feature of the present invention is realized using the embodiment of FIG. 1, a single fundamental frequency f is generated from the arbitrary waveform generator 21 as in the case of imaging of a tissue. ₀ Is generated, and an ultrasonic beam is scanned and irradiated on a desired part of the living body. Similarly to the case of tissue imaging, the response signal from the living body is amplified and phased by the receiver 31 and the phasing adder 32 as in the case of tissue imaging. In this case, the line adder 33 in FIG. 1 is not necessary. That is, the band pass filter 34 that extracts the contrast agent-derived response signal included in the response signal subjected to the phasing process is a characteristic element. That is, as described with reference to FIG. 2, the response signal 1 caused by the contrast agent has a higher signal strength and exists over a wide frequency band than the fundamental wave component 2a and the harmonic component 2b of the tissue response signal. . The band pass width of the band pass filter 34 is widened to emphasize the contrast agent response signal relative to the tissue response signal. In particular, the bandwidth of the band pass filter 34 is preferably variably adjusted as in the following (A), (B), and (C).
(A) 0.8f in the case of a shallow part depending on the depth of contrast medium distribution ₀ To 2.5f ₀ If it is deep, adjust to 0.8f ₀ To 1.8f ₀ And preferably 1.2f ₀ To 1.8f ₀ (Or 1.1f ₀ To 1.8f ₀ ).
(B) In the initial phase after contrast agent injection, the amplitude of the ultrasonic signal to be transmitted is set to the initial low sound pressure (MI = about 0.4 to 0.7). And in the case of a shallow part, it is 0.8f like (1). ₀ To 2.5f ₀ Adjust to.
(C) In the later time phase after contrast medium injection, the bandwidth of the bandpass filter 34 is 0.8 f in conjunction with the later high sound pressure (MI = about 1.0 to 1.3) in accordance with the amplitude of the transmitted ultrasonic signal. ₀ To 1.8f ₀ And preferably 1.2f ₀ To 1.8f ₀ (Or 1.1f ₀ To 1.8f ₀ ).
[0065]
That is, in the case of a relatively weak sound pressure or in the initial time phase, the harmonic component 2f of the tissue ₀ Can be ignored. Therefore, wide frequency band 0.8 ~ 2.5f ₀ The response signal of the contrast agent can be relatively emphasized relative to the response signal of the tissue. When the depth is deep, the high-frequency component 2f of the tissue ₀ Is stronger, 0.8-2.5f ₀ The response signal of the contrast agent can be emphasized as compared with the conventional technique. On the other hand, when the sound pressure is high as in the later phase, the harmonic component 2f of the tissue ₀ Can not be ignored, so the bandwidth is 0.8-1.8f ₀ The harmonic component 2f of the tissue ₀ Is removed or attenuated. In this case, 2f ₀ It is accompanied by attenuation of harmonic components related to the contrast agent distributed in the vicinity. However, since the response signal of the contrast agent distributed over a wide frequency band is extracted, there is a sufficient compensation for attenuation. F ₀ When the fundamental wave component of the response signal of the tissue existing in the vicinity includes a component accompanying breathing or pulsation of the human body and an artifact occurs in the contrast agent image, the passband width of the filter is slightly narrowed to 1.2 to 1.8 f. ₀ (Or 1.1f ₀ To 1.8f ₀ ) Is preferable.
[0066]
The switching of the bandwidth is controlled by the system control unit 50 based on the set transmission focus or reception focus. For example, since the depth of the response signal corresponds to the time axis, the system control unit 50 sets the bandwidth to 0.8 f when the time position of the response signal input to the band pass filter 34 is shallower than the set depth. ₀ To 2.5f ₀ The deep range is 1.2f ₀ To 1.8f ₀ Switch to real time.
[0067]
By adjusting the bandwidth of the passband filter 34 in this way, the harmonics 2f of the tissue ₀ And harmonics contained in the response signal of the contrast agent can be discriminated. Then, by detecting and drawing the contrast medium based on the harmonic of the response signal of the contrast medium extracted by discrimination, the SN ratio of the contrast image can be improved as compared with the conventional technique. Note that the harmonic component 2f ₀ In addition to the band pass filter 34, the center frequency is 2f. ₀ Can be used.
(When realizing the second feature)
In order to further enhance the effect of enhancing and extracting the response signal component of the contrast agent by expanding the pass band width of the bandpass filter 34 described above, as shown in the second feature, the contrast agent is irradiated. It is desirable to make the frequency of the ultrasonic wave wide. That is, the ultrasonic signal generated by the arbitrary waveform generator 21 has a plurality of frequencies and has an average frequency f, for example, as a waveform 61 shown in FIG. ₀ Thus, a signal having a wide range of frequency components is obtained. In FIG. 3A, a waveform 61 has a frequency f. ₁ , F ₂ Of the sine wave of one cycle and the frequency f ₁ , F ₂ The average frequency is f ₀ It is. In the illustrated example, f ₁ <F ₂ Is set to The average frequency f ₀ Selects a frequency suitable for the tissue and device. As is well known, a known Hanning weight is applied in the time axis direction to resemble the waveform in the living body. By irradiating the living body with such ultrasonic signals having a plurality of frequencies, the response signal of the contrast agent becomes stronger over a wide frequency spectrum. That is, since the contrast agent has a distributed free resonance frequency corresponding to the particle size distribution, more contrast agents respond by distributing the frequency spectrum of the irradiated ultrasound over a wide band, and the contrast agent This is because the response signal itself is enhanced. The tissue response signal is f ₀ And 2f ₀ There is no change to things centered around. However, since the contrast agent response signal appears at a strong level over a wider frequency band, it becomes easier to discriminate between the harmonics of the tissue and the harmonics of the contrast agent.
[0068]
Where frequency f ₁ , F ₂ Absolute value of difference | f ₁ -F ₂ |, That is, the distribution width Δf of the component frequency is 0.0 f. ₀ ~ 0.4f ₀ Select within the range. Preferably 0.1f ₀ ~ 0.4f ₀ Better, more preferably 0.2f ₀ ~ 0.3f ₀ Is good. The arbitrary waveform generator 21 has two frequencies f described above. ₁ , F ₂ As described later, a waveform having N (≧ 2) frequencies can be applied.
[0069]
【The invention's effect】
As described above, according to the present invention, the harmonic component included in the response signal of the contrast agent can be extracted as a relatively strong signal by distinguishing it from the harmonic component included in the response signal of the biological tissue. The sharpness of the agent drawing can be improved.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an ultrasonic contrast drawing apparatus according to a first embodiment of the present invention.
FIG. 2 is a graph for explaining the principle that a contrast agent response signal of the present invention can be extracted at a high rate.
FIG. 3 is a graph showing an example of a two-irradiation transmission waveform related to frequency enhancement according to an embodiment of the present invention, and a simulation result of a frequency spectrum of a transmission signal and an obtained response signal according to the transmission waveform.
FIG. 4 is a graph showing an example of a transmission waveform of twice irradiation according to frequency and amplitude enhancement according to an embodiment of the present invention, and a simulation result of a frequency spectrum of a transmission signal and an obtained response signal according to the transmission waveform.
FIG. 5 is a graph showing another example of a two-irradiation transmission waveform related to frequency and amplitude emphasis according to an embodiment of the present invention, and a simulation result of a frequency spectrum of a transmission signal and an obtained response signal according to the transmission waveform. is there.
FIG. 6 is a graph showing a simulation result of a transmission waveform of a two-time irradiation according to the prior art and a frequency spectrum of a transmission signal and the response signal obtained by the transmission waveform for comparison.
[Explanation of symbols]
10 Ultrasonic probe
20 Transmitter
21 Arbitrary waveform generator
23 Transmitter
30 Receiver
31 Receiver
32 Phased adder
33 line adder
34 Band pass filter
40 Image creation display
50 System controller
61, 71, 81 First waveform
62, 72, 82 Second waveform
63, 73, 83 Transmission signal spectrum
64, 74, 84 Response signal spectrum

Claims (8)

An ultrasonic probe that transmits and receives ultrasonic waves to and from a living body, a transmitter that transmits ultrasonic signals to the ultrasonic probe, and an ultrasonic response signal received by the ultrasonic probe. A receiving unit for processing, and a drawing unit for creating a tomographic image of the living body based on the response signal processed by the receiving unit;
The transmitting unit has a function of transmitting an ultrasonic beam a plurality of times (M, where M ≧ 2 is a natural number) times at a time interval in the same direction, and each time an ultrasonic signal is obtained by continuation of waveforms having different frequencies. At least the amplitude of the leading waveform is larger than the amplitude of the continuing waveform group, and the signals of each time are set asymmetric with respect to polarity inversion and time axis inversion,
The receiving unit attenuates the response signal of the living tissue by performing a phasing process on the response signal of the plurality of (M) times of ultrasonic signals and adding or subtracting the phasing process response signal. An ultrasonic contrast drawing apparatus having a function. 2. The ultrasonic contrast-enhanced drawing apparatus according to claim 1, wherein the waveforms having different frequencies are alternately inverted in polarity and are cycle waveforms having the same frequency. An ultrasonic probe that transmits and receives ultrasonic waves to and from a living body, a transmitter that transmits ultrasonic signals to the ultrasonic probe, and an ultrasonic response signal received by the ultrasonic probe. A receiving unit for processing, and a drawing unit for creating a tomographic image of the living body based on the response signal processed by the receiving unit;
The transmitting unit has a function of transmitting an ultrasonic beam a plurality of times (M, a natural number of M ≧ 2) at time intervals in the same direction, and the frequency of each ultrasonic signal is f1, f2,. fn, ..., fN (where natural number N ≧ 2) is the average signal of a frequency _{f 0} are N comprising a by continuous waveform, the frequency distribution width Δf of the f1 to fN are 0.0f ₀ to 0.4F ₀ And at least the amplitude of the first waveform is larger than the amplitude of the continuing waveform group, and each time signal is set asymmetric with respect to polarity inversion and time axis inversion,
The receiving unit attenuates the response signal of the living tissue by performing a phasing process on the response signal of the plurality of (M) times of ultrasonic signals and adding or subtracting the phasing process response signal. An ultrasonic contrast drawing apparatus having a function. Each waveform is set by a code f (A, θ) that defines a frequency f, an amplitude A, and a starting phase θ,
f1 (A1, θ1) <f2 (A2, θ2) <... <fn (An, θn) <... <fN (AN, θN), and the amplitude is A1>A2>.An>...> AN, the first waveform is set to a phase of θ1 = θ2 = ... = θn = ... = θN = 180 °,
f1 ′ (A1 ′, θ1 ′)> f2 ′ (A2 ′, θ2 ′)>...> fn ′ (An ′, θn ′)>...> fN ′ (AN ′, θN ′) The second waveform is set with an amplitude of A1 '>A2'>...> An '>...>AN' and a phase of θ1 '= θ2' = ... = θn '= ... = θN' = 0 °. The ultrasound contrast imaging apparatus according to claim 2, wherein: The receiving unit includes a filter that extracts a specific frequency component from the response signal in which the response signal of the living tissue is attenuated, and a pass bandwidth of the filter is 0.8 f with respect to the average frequency f _{0. 0} to ultrasound contrast drawing apparatus according to any one of claims 1 to 4, characterized by being set to 1.8F _0. The reception unit includes a filter that extracts a specific frequency component from the response signal in which the response signal of the living tissue is attenuated, and a pass bandwidth of the filter is 1.2 f with respect to the average frequency f _{0. 0} to ultrasound contrast drawing apparatus according to any one of claims 1 to 4, characterized by being set to 1.8F _0. The receiving unit includes a filter that extracts a specific frequency component from the response signal in which the response signal of the living tissue is attenuated, and a pass bandwidth of the filter is 0.8 f with respect to the average frequency f _0. 5. The ultrasonic contrast-enhanced drawing apparatus according to claim 1, wherein the ultrasonic contrast-drawing apparatus is variably set in a range of _{0 to} 1.8 f ₀ according to the depth of the response signal. An ultrasonic probe that transmits and receives ultrasonic waves to and from a living body, a transmitter that transmits ultrasonic signals to the ultrasonic probe, and an ultrasonic response signal received by the ultrasonic probe. A receiving unit for processing, and a drawing unit for creating a tomographic image of the living body based on the response signal processed by the receiving unit;
The transmitting unit has a function of transmitting an ultrasonic beam a plurality of times (M, where M ≧ 2 is a natural number) times in the same direction at time intervals, and each time an ultrasonic signal has a different frequency component. And at least the amplitude of the first half-wave is greater than the amplitude of the half-wave group that continues to it, and the half-wave group is set asymmetric with respect to the phase axis or polarity,
The receiving unit attenuates the response signal of the living tissue by performing a phasing process on the response signal of the plurality of (M) times of ultrasonic signals and adding or subtracting the phasing process response signal. An ultrasonic contrast drawing apparatus having a function.

Images