JP2008173504A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve penetration while maintaining the resolution of an ultrasonic diagnostic apparatus for performing tissue harmonic imaging. <P>SOLUTION: In the ultrasonic diagnostic apparatus, ultrasonic signals including a first waveform and a second waveform are transmitted at two or more times at a time interval in the same direction from a transmission part 3 which transmits the ultrasonic signals to an object through an ultrasonic probe 1, reception signals corresponding to the first waveform and reception signals corresponding to the second waveform, which are received by the ultrasonic probe, are phased and added by a reception part 5, and images are generated on the basis of the phased and added reception signals. In the ultrasonic diagnostic apparatus, the transmission part includes a waveform generation means for generating the waveform which changes so as to increase a frequency, and a time base controller 11 for making the output of the waveform generation means into the first waveform and delaying the output of the waveform generation means timewise and time-inverting it to attain the second waveform. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that images a harmonic signal generated when ultrasonic waves propagate through a subject.

  The ultrasonic diagnostic apparatus transmits an ultrasonic signal into a subject, and obtains information used for diagnosis such as a tomographic image based on a received signal including the echo signal.

In such a technique for displaying a tomographic image, a high-contrast image can be obtained by imaging harmonic components (for example, frequencies 2f ₀ , 3f _0, etc.) with respect to the fundamental wave component (frequency f ₀ ) of the transmission signal. It has been reported. Such an imaging method is called Tissue Harmonic Imaging.

The above-described harmonic components are generated mainly due to nonlinear distortion that occurs when ultrasonic waves propagate through the subject. That is, the ultrasonic wave irradiated into the living body is distorted during tissue propagation due to the non-linear response of the tissue, and the harmonic component increases. As a result, and twice 2f frequency _0, for example, the fundamental wave f ₀ to the echo signal, and may include the components of 3f ₀ triple frequency.

In tissue harmonic imaging, the key is how to extract echoes of strong harmonic components. One example of a conventionally reported tissue harmonic imaging method is called a filter method. This extracts a harmonic component from the received signal, for example 2f ₀ using a bandpass filter of a center frequency for example 2f _0. Another example is called a pulse inversion method. This is because the first and second transmission waveforms whose polarities are reversed with respect to each other are transmitted at time intervals, and the second harmonic component is canceled by phasing and adding the respective echo signals to cancel the fundamental wave component. Is emphasized.

However, since the harmonic component of the ultrasonic signal has a higher frequency than the fundamental component, it is susceptible to attenuation during propagation, and the degree of arrival of the echo signal from the deep part, that is, the penetration is not good. . On the other hand, penetration because less susceptible to attenuation by lowering the center frequency f ₀ of the fundamental wave can be improved, the resolution as is well known is lowered.

  In view of the above-described problems, an object of the present invention is to improve the penetration while maintaining the resolution.

  In order to solve the above-described problems, the present invention is an ultrasonic probe, a transmission unit that transmits an ultrasonic signal to a subject via the ultrasonic probe, and the ultrasonic probe. A receiving unit that processes the received signal, and an image generating unit that generates an image based on the received signal processed by the receiving unit, wherein the transmitting unit receives an ultrasonic signal. The ultrasonic signal transmitted a plurality of times with a time interval in the same direction includes a first waveform and a second waveform, and the receiving unit has the first waveform In the ultrasonic diagnostic apparatus having a function of phasing and adding a corresponding received signal and a received signal corresponding to the second waveform, the transmitting unit has a waveform that changes so that the frequency increases. Waveform generating means for generating the output, the output of the waveform generating means is the first waveform, and the output of the waveform generating means Temporally delayed, and is time-reversed, characterized in that said second waveform.

According to this, the frequency spectrum of the received signal after the phasing addition changes compared to the conventional case where the waveform of the same frequency f ₀ is inverted and transmitted, and the frequency of f ₀ to 2f ₀ is changed. The components in the band can be emphasized. Such a frequency band component has a lower frequency than 2f ₀ , so it is not easily affected by attenuation and has good penetration. Therefore, to extract the frequency component, by generating an image based on this, even without lowering the f _0, i.e. without reducing the resolution, it is possible to improve the penetration of Tissue Harmonic Imaging .

  In particular, the waveform generating means generates a waveform whose frequency increases so that the frequency increases, and this is used as the first waveform as it is, and the output of the waveform generating means or the first waveform is delayed in time and time-reversed. Since two waveforms are generated, the first waveform and the second waveform suitable for improving the penetration in tissue harmonic imaging can be easily generated.

  In this case, the first waveform and the second waveform may transition so that the signal intensity decreases. Thereby, the change of the frequency spectrum of the received signal after phasing addition can be emphasized. Further, the rate of change of the signal intensity of the first waveform and the second waveform can be variably set according to the transmission focus depth. In these cases, since the frequency spectrum of the received signal changes by changing them, the received signal is particularly obtained when obtaining diagnostic information from a deep part (part far from the probe) in the subject. It is better to shift the frequency spectrum to a value that emphasizes penetration. In order to adapt to this, the transmission unit has a function of variably setting the transmission focus depth of the ultrasonic signal, and the rate of change of the frequency of the first waveform and the second waveform depends on the transmission focus depth. It is better to variably set. In addition, the frequency band of the filter for filtering the received signal after the phasing addition can be variably set according to the setting depth of the transmission focus. In other words, the receiving unit can include a filter that extracts a set frequency band of the received signal, and can variably set the frequency band according to the reception timing of the received signal.

  Further, the receiving unit has a function of performing reception focus processing on the received signal and a filter for extracting a set frequency band of the received signal, and the frequency band is set according to the set depth of the received focus. It may be configured to be variably set. According to this, it is possible to adapt to changes in the spectrum of the received signal due to the difference in attenuation due to the difference in the received focus depth, that is, the depth of the region to be diagnosed in the subject, and extract components in a suitable frequency band can do.

  Further, the first waveform and the second waveform may have a line-symmetric shape with respect to an orthogonal line of a time axis.

  Furthermore, the waveform in which the frequency changes may be formed by, for example, connecting one cycle or a plurality of cycles of waveforms having different frequencies. Moreover, it is good also as a structure which connects parts, such as 1/2 cycle, 1/4 cycle, 1/8 cycle, etc. of the waveform from which a frequency differs, Even if it uses a chirp waveform from which a frequency changes continuously. Good.

  According to the present invention, it is possible to improve the penetration while maintaining the resolution.

  Hereinafter, a first embodiment of an ultrasonic diagnostic apparatus to which the present invention is applied will be described. FIG. 1 is a diagram illustrating a configuration of an ultrasonic diagnostic apparatus according to the present embodiment. As shown in FIG. 1, the ultrasonic diagnostic apparatus includes an ultrasonic probe 1, a transmission unit 3 that transmits an ultrasonic signal to a subject (not shown) via the ultrasonic probe 1, an ultrasonic probe, and the like. A receiving unit 5 that receives and processes a received signal including an echo signal from the subject via the touch element 1, and generates and displays a diagnostic image based on the received signal processed by the receiving unit 5. And an image creation / display unit 7. The image creation / display unit 7 includes a video processing unit, a Doppler processing unit, and a scan conversion unit that perform detection, compression, and the like (not shown).

  The wave transmission unit 3 includes an arbitrary waveform generator 9 having a function of generating a transmission signal in which a plurality of waveforms each having a desired amplitude, frequency, and start phase are combined, and a waveform output from the arbitrary waveform generator 9 in time A time axis controller 11 having a function of inverting, and a transmitter 13 having a power amplifier and supplying a drive signal to the ultrasonic probe 1 according to an output signal of the time axis controller 11 are provided. Do it. The time axis controller 11 has a so-called first-in / first-out function and a first-in / last-out function using the output of the arbitrary waveform generator 9 as an input signal, and has a shift register. Yes.

  The reception unit 5 receives a reception signal output from the ultrasonic probe 1 and receives a preamplifier (not shown), a time gain control (TGC) amplifier, and an A / D converter. 15 and a phasing adder 17 for phasing and adding the received signals of the channels corresponding to the respective transducers of the ultrasonic probe 1 output from the receiver 15 and outputting them as RF line signals. A line adder 19 that holds the received signal output from the phase adder 17 first, delays the time, and performs RF addition in consideration of the received signal and phase output later, and a line adder 19 And a band-pass filter 21 having a band-pass digital filter operation function for extracting a specific frequency band from the output signal. A so-called digital beamformer is used as the phasing adder 17 in order to minimize distortion during the addition process. In addition, a system control unit 23 is provided that controls the operation of each element in the above-described transmission unit 3, reception unit 5, and image creation / display unit 7. The ultrasound probe 1 includes a plurality of transducers 25 arranged in a line or a plane so as to face a subject (not shown).

  Next, the operation of the above-described ultrasonic diagnostic apparatus will be described. First, the arbitrary waveform generator 9 generates and outputs a waveform of a transmission signal based on an instruction from the system control unit 23. The output signal waveform of the arbitrary waveform generator 9 is formed by continuing waveforms having different frequencies. This point will be described later in detail. The output signal of the arbitrary generator 9 is input to the time axis controller 11 and is first output as a first waveform without time reversal by the first-in / first-out function. Then, the time axis controller 11 outputs a second waveform that is delayed in time from the first waveform and is time-reversed by the first-in / last-out function. The transmitter 13 performs a known transmission focus process based on these first and second waveforms to generate and output a drive signal for each transducer 25 of the ultrasonic probe 1. The transducers 25 supplied with the drive signal from the transmitter 13 via a transmission / reception wave separation circuit (not shown) each vibrate to generate ultrasonic waves, and in the direction in which the wavefronts of the ultrasonic waves emitted from the respective transducers 25 coincide. A traveling ultrasonic beam is formed in a subject (not shown).

  On the other hand, an ultrasonic signal propagating in the subject as such an ultrasonic beam is reflected at a portion where the acoustic impedance in the subject is different, and this reflected wave returns to the ultrasonic probe 1 as a received signal. Received. The received signal is converted from a sound wave to an electrical signal by the vibrator 25 and input to the receiver 15 through a transmission / reception separating circuit (not shown). In the receiving unit 15, the received signal of each channel corresponding to each transducer 25 is amplified by the preamplifier and the TCG amplifier, A / D converted, and output. The output signal of the receiving unit 15 is input to the phasing adder 17, and a time delay process is performed on the timing difference between the channels of the received signal due to the difference in distance from the reception signal generation site to each transducer 25. Are added after being subjected to a well-known dynamic focus process for performing successive corrections. The processing associated with these receptions is performed for each of the reception signals corresponding to the first waveform and the second waveform described above. The received signal corresponding to the first waveform and the received signal corresponding to the second waveform are such that the line adder 19 temporarily holds the received signal corresponding to the first waveform, and the time delay. Then, it is synthesized by adding to the received signal corresponding to the second waveform, and is output as a synthesized received signal. The band filter 21 extracts a predetermined frequency band component of the combined received signal, and the image creation display unit 7 generates an ultrasound diagnostic image based on the extracted frequency band component signal. indicate. That is, the ultrasonic diagnostic apparatus performs the above operation while scanning the beam direction. In the image creation display unit 7, video processing such as detection and compression, Doppler signal is output to the output of the line adder corresponding to each scanning line. Processing and scan conversion are performed to generate a known B-mode or Doppler mode image. The system control unit 23 controls these series of operations and also generates data of the arbitrary waveform generator 9.

Next, the first waveform, the second waveform, and the frequency spectrum of the transmitted signal and the received signal according to the features of the ultrasonic diagnostic apparatus of the present embodiment will be described. First, in order to make it easy to understand the features of the present embodiment, the simulation results are shown in FIG. 2 for the first waveform, the waveform of the second waveform, and the frequency spectrum of the transmitted signal and received signal in the existing pulse inversion method. ,explain. FIG. 2 (1) is a graph showing the first waveform and the second waveform with time on the horizontal axis and the sound pressure of the transmitted signal on the vertical axis. Here, the first waveform is indicated by a solid line, and the second waveform is indicated by a broken line. As shown in FIG. 2 (1), the first waveform and the second waveform are both subjected to Hanning weights to resemble a waveform in a living body in a series of two sine waves having the same frequency f ₀ (= 2 MHz). Is. And the 1st waveform and the 2nd waveform have the relation which reversed the polarity. That is, the first waveform has a polarity with which the sound pressure falls at the start of the signal, and the second waveform has a polarity with which the sound pressure rises.

FIG. 2 (2) is a graph showing the frequency spectrum of the transmitted signal and the received signal obtained by phasing and adding the received signals corresponding to the first waveform and the second waveform, respectively. In this graph, the horizontal axis represents the specific frequency (f / f ₀ ) with respect to f ₀ = 2.0 MHz, and the vertical axis represents the signal intensity (dB). In FIG. 2 (2), the spectrum of the transmitted signal is indicated by a broken line, and the spectrum of the combined received signal is indicated by a solid line.

As shown in FIG. 2 (2), the spectrum of the transmitted signal has a peak that becomes the first maximum at the frequency f ₀ when the frequency is increased from 0 and the signal intensity is improved. When the frequency is further increased, the signal intensity is reduced. At the frequency 2f ₀ , the signal intensity is reduced to −40 dB or less with respect to the first peak. When the frequency is further improved from the frequency 2f ₀ , the signal intensity starts to improve again, takes a second peak in the vicinity of the frequency 2.3f ₀ , and then decreases again. The signal intensity of the second peak is about −32 dB with respect to the first peak.

On the other hand, the spectrum of the synthesized received signal has a peak signal intensity becomes maximum 0.6F ₀ neighborhood, 2f ₀ neighborhood and 4f ₀ in the vicinity, 1.2f ₀ near a valley signal intensity is minimum And 3.3f near ₀ . The signal intensity of the peaks is maximized is a peak of the 2f ₀ neighborhood, the signal intensity of the peak of 0.6F ₀ neighborhood and 4f ₀ near to this signal strength are both approximately -14 dB. On the other hand, the signal intensity in the valley where the signal intensity is minimum is about −28 dB in the vicinity of 1.2f _{0 and} about −21 dB in the vicinity of 3.3f _{0 with} respect to the signal intensity at the peak of 2f ₀ .

Next, a simulation result is illustrated in FIG. 3 for an example of the waveform of the first waveform and the second waveform in which the frequency shifts in the ultrasonic diagnostic apparatus of the present embodiment, and the frequency spectrum of the transmission signal and the reception signal. To do. FIG. 3A is a graph showing the first waveform and the second waveform with time on the horizontal axis and the sound pressure of the transmitted signal on the vertical axis. Here, the first waveform is indicated by a solid line, and the second waveform is indicated by a broken line. As shown in FIG. 3 (1), the first waveform is configured by continuing the first cycle of the frequency f ₁ (= 1.8 MHz) and the second cycle of the frequency f ₂ (= 2.2 MHz). The polarity is such that the sound pressure falls at the start of the signal. On the other hand, the second waveform, and the first cycle of frequency f _2, is constituted by a continuous and second cycle of frequency f _1, and has a polarity which falls the sound pressure at the signal start. The first waveform and the second waveform are both subjected to the same Hanning weight as the waveform shown in FIG. In other words, the second waveform can be said to be a time reversal of the first waveform.

FIG. 3B is a graph showing the frequency spectrum of the transmitted signal and the received signal obtained by phasing and adding the received signals corresponding to the first waveform and the second waveform, respectively. In this graph, as in FIG. 2 (2), the horizontal axis represents the specific frequency (f / f0) with respect to f ₀ = 2.0 MHz, and the vertical axis represents the signal intensity (dB). In FIG. 3B, the spectrum of the transmitted signal is indicated by a broken line, and the spectrum of the received signal subjected to phasing and addition is indicated by a solid line.

As shown in FIG. 3 (2), the spectrum of the transmitted signal has a peak that is maximized at the frequency f ₀ when the frequency is improved from 0 and the signal intensity is improved. And if the frequency is further improved, the signal strength decreases. In the vicinity of the frequency 2f ₀ , the signal intensity decrease rate decreases, and after the decrease rate becomes substantially zero, the signal intensity decreases again while increasing the decrease rate. Incidentally, the signal intensity in the vicinity of the frequency 2f ₀ is about −23 dB with respect to the peak of the frequency f ₀ .

On the other hand, the spectrum of the phased summed received signal has a peak signal intensity becomes maximum 0.4F ₀ neighborhood, 1.6F ₀ neighborhood and 2.8F ₀ in the vicinity, the signal intensity becomes minimum valley having 0.7F ₀ neighborhood near 2.2f ₀ and near 3.7f _0. The signal intensity of the peaks as the maximum becomes the maximum is a peak of 1.6F ₀ neighborhood, the signal intensity of the peak of 0.4F ₀ and near 2.8F ₀ near to this signal strength about each -12dB And -2 dB. On the other hand, the signal strength at the valley signal intensity becomes minimum is about -14dB in 0.7F ₀ neighborhood, 2.2f ₀ to about near -17 dB, is about -35dB in 3.7F ₀ neighborhood.

As is clear when FIG. 3 (2) is compared with FIG. 2 (2), in the existing pulse inversion method, when the received signals corresponding to the first waveform and the second waveform are synthesized, the vicinity of 2f _{0 is obtained.} It can be seen that, by shifting f ₁ and f ₂ , the signal intensity peak is in the vicinity of 1.6f ₀ , and the frequency spectrum is shifted low.

In the ultrasonic diagnostic apparatus of the present embodiment, the difference Δf (= | f ₁ −f ₂ |) between the frequencies f ₁ and f ₂ is variably set according to the setting depth of the transmission focus. It is characterized by that. Specifically, Δf is variably set so that the frequency spectrum of the signal obtained by synthesizing the reception signals corresponding to the first waveform and the second waveform shifts lower as the transmission focus depth becomes deeper. . At this time, the average frequency of the frequencies f ₁ and f ₂ remains constant at f ₀ . When the transmission focus depth is shallow, Δf is set to 0 and transmission / reception is performed by the existing pulse inversion method. Then, Δf is changed as the transmission focus depth becomes deeper, and transmission is performed so that the peak of the frequency spectrum described above shifts from 2f ₀ to, for example, f ₀ , preferably from 2f ₀ to, for example, 1.5f _0. Generate a signal. For example, in the case of performing well-known transmission multistage focusing in which reception signals of a plurality of ultrasonic beams with different transmission focus depths are connected to complete a reception signal related to one beam line, Δf is varied according to the focus depth. For example, when performing three-stage focusing, Δf of each stage is set so that the peak of the frequency spectrum becomes, for example, 2f ₀ , 1.8f ₀ , 1.6f ₀ when the focus depth is shallow. The setting of Δf according to the transmission focus depth can be performed by simulation or an experiment using an ultrasonic phantom.

  Further, the ultrasonic diagnostic apparatus according to the present embodiment is characterized in that the pass frequency band of the band filter 21 is varied in accordance with the shift of the frequency spectrum described above. Specifically, in order to adapt to the shift of the spectrum of the received signal after phasing addition, the pass frequency band is shifted lower as the transmission focus depth becomes deeper.

Further, the pass frequency band of the band filter 21 can be varied according to the depth of the received focus even when the transmitted signal does not change. That is, FIG. 4 shows a reception spectrum of a received signal from a shallow part of the subject, that is, a part near the ultrasonic probe, and reception from a deep part of the subject, that is, a part far from the ultrasonic probe. It is a schematic diagram which shows the reception spectrum of a signal. In FIG. 4, only 2f ₀ is displayed as the harmonic component for the sake of simplicity. Since the transmitted signal is usually a pulse wave of several cycles, the spectrum has a certain amount of band around f ₀ and 2f ₀ as shown in FIG. As shown in FIG. 4, the spectrum of the received signal from a deep position has a higher harmonic component due to nonlinear distortion when the ultrasonic wave propagates through the living body. When attention is paid, the higher the frequency component, the greater the influence of attenuation during propagation, so the frequency spectrum shifts lower and the center frequency also decreases. Therefore, in order to deal with this, the pass frequency band of the band filter 21 is set so as to shift lower as the focus depth of the reception focus becomes deeper in conjunction with the dynamic focus of the reception focus. Specifically, when a digital FIR filter is used as the band filter 21, the coefficient is preferably variable in conjunction with the received focus depth.

As described above, according to the present embodiment, by phasing and adding the received signals respectively corresponding to the first waveform in which the frequency is increased and the second waveform in which the frequency is decreased, Since the frequency component in f ₀ to 2f ₀ is emphasized, it is less susceptible to attenuation than the existing pulse inversion method that emphasizes 2f ₀ , and the penetration can be improved in a portion with a deep focus depth. Further, since the image is formed with 2f ₀ components in the shallow portion, there is an effect that the resolution can be maintained.

  Also, since the rate of change of the frequency of the first waveform and the second waveform is variably set according to the transmission focus depth, a relatively high frequency component is emphasized at a shallow focus depth to emphasize the contrast. In the deep focus depth, a relatively low frequency component can be emphasized so that penetration is emphasized, and a good image can be generated by adapting to the set depth of transmission focus.

  Furthermore, since the frequency band pass filter operation is performed on the received signal after phasing addition, and this pass frequency band is varied according to the transmission focus depth, the rate of change at which the frequency of the transmitted signal changes It is possible to extract a frequency band that is emphasized according to the above.

  In addition, since this pass frequency band is variably set according to the reception focus depth, the frequency band adapted to the change in the spectrum of the received signal due to the difference in attenuation due to the difference in the propagation distance of the received signal is extracted. can do.

Further, for example, when the penetration is to diagnose relatively shallow portion hardly become a problem, it may be performed extract and image generating high frequency components than 2f _0. For example, looking at FIG. 3 (2), is also seen that there is a peak, for example, it extracts a large peak signal strength of neighboring than this frequency 2f ₀ by the band pass filter to 2.8F ₀ vicinity, Image generation may be performed. According to this, the image contrast at the time of diagnosing a shallow part becomes favorable.

Moreover, when diagnosing such a shallow site | part, you may make it raise the center frequency of a transmission signal. For example, in the example of FIG. 3, the center frequency f ₀ = 2.0 MHz, the first waveform and the second waveform are f ₁ = 1.8 MHz, and f ₂ = 2.2 MHz. _{0 = 2.1MHz, f 1 = 2.0MHz} , may be f 2 = 2.2MHz. According to this, an image with good contrast can be obtained at a relatively shallow depth at which penetration is not a problem.

  In the above-described embodiment, the second waveform is obtained by time-inverting the first waveform by the time axis controller. However, when the arbitrary waveform generator can directly generate the second waveform, the time is An axis controller is not required.

Further, in the above-described embodiment, the first waveform and the second waveform are each formed by continuing two cycles of waveforms, but may be configured by continuing waveforms of three cycles or more. For example, the first waveform is a continuous waveform of f ₁ = 1.8 MHz, f ₂ = 2.0 MHz, and f ₃ = 2.2 MHz, and the second waveform is a time inversion of the first waveform. It may be made. Thus, the first waveform is a continuous one-cycle waveform with center frequencies f1, f2,... Fn,... FN (N ≧ 2), and f1 <f2 <•• <fn <•• <fN. When the second waveform is in a time axis inversion relationship with the first waveform, even if N = 4 or more, the gist of the present invention is not impaired, but when the wave number increases, the difference between the two transmission waves is relatively Since this is mitigated, the present invention is considered to be particularly effective in the range of N <6.

  In the above-described embodiment, the first waveform and the second waveform are each configured by a combination of sine waves having different frequencies for each cycle. For example, the frequencies are changed for every two cycles or more. It may be. Further, for example, the frequency may be finely changed, such as every 1/2 cycle or 1/4 cycle, or a so-called chirp waveform in which the frequency continuously changes may be used.

  Next, a second embodiment of an ultrasonic diagnostic apparatus to which the present invention is applied will be described. Description of the same parts as those in the first embodiment is omitted, and only differences will be described. The ultrasonic diagnostic apparatus of this embodiment is characterized in that the amplitudes of the first waveform and the second waveform both change. That is, the present embodiment is characterized in that the amplitude of the waveform of the first cycle of each of the first waveform and the second waveform is set to be larger than the amplitude of the subsequent waveform.

FIG. 5 shows a simulation result for an example of the waveforms of the first waveform and the second waveform, and the frequency spectrum of the transmitted signal and the received signal in which the frequency and amplitude change in the ultrasonic diagnostic apparatus of the present embodiment. . FIG. 5 (1) is a graph showing the first waveform and the second waveform with time on the horizontal axis and the sound pressure of the transmitted signal on the vertical axis. Here, the first waveform is indicated by a solid line, and the second waveform is indicated by a broken line. As shown in FIG. 5 (1), the first waveform is configured by continuing the first cycle of the frequency f ₁ (= 1.8 MHz) and the second cycle of the frequency f ₂ (= 2.2 MHz). The polarity is such that the sound pressure falls at the start of the signal. On the other hand, the second waveform, and the first cycle of frequency f _2, is constituted by a continuous and second cycle of frequency f _1, and has a polarity which is the sound pressure rises at the signal start. In both the first waveform and the second waveform, the amplitude A2 in the second cycle is set smaller than the amplitude A1 in the first cycle. For example, in the case of FIG. 5A, A2 = 0.9A1 is set. Yes.

FIG. 5B is a graph showing the frequency spectrum of the transmission signal and the reception signal obtained by phasing and adding the reception signals corresponding to the first waveform and the second waveform, respectively. Similar to FIG. 2 (2), the horizontal axis represents the specific frequency (f / f ₀ ) with respect to f ₀ = 2.0 MHz, and the horizontal axis represents the signal intensity (dB). In FIG. 5 (2), the spectrum of the transmitted signal is indicated by a broken line, and the spectrum of the received signal subjected to phasing and addition is indicated by a solid line.

As shown in FIG. 5 (2), the spectrum of the transmitted signal is similar to the transmitted signal spectrum shown in FIG. 3 (2), but the signal intensity near the frequency 2f ₀ is higher than the signal intensity near f _0. About -25dB.

On the other hand, the spectrum of the phased summed received signal has a peak signal intensity becomes maximum 0.4F ₀ neighborhood, 1.6F ₀ neighborhood and 2.8F ₀ in the vicinity, the signal intensity becomes minimum valley having 0.7F ₀ neighborhood near 2.2f ₀ and near 3.8f _0. The signal intensity of the peaks as the maximum becomes the maximum is a peak of 1.6F ₀ neighborhood, the signal intensity of the peak of 0.4F ₀ and near 2.8F ₀ near to this signal strength about each -13dB And about -2 dB. On the other hand, the signal strength at the valley signal intensity is minimum are, 0.7F ₀ about near -17 dB, 2.2f ₀ to about near -10 dB, in 3.8F ₀ neighborhood is equal to or less than -40 dB.

5 (2) and 2 (2) and as is apparent from a comparison of, shifting a frequency f ₁ and f ₂ as in this embodiment, by shifting the amplitude A1 and A2, the signal intensity peaks Is 1.6 f _0, and it can be seen that the frequency spectrum shifts low.

In the ultrasonic diagnostic apparatus of the present embodiment, the difference Δf between the frequencies f ₁ and f ₂ is variably set according to the setting depth of the transmission focus, and the ratio A2 / A1 between the amplitudes A1 and A2 is further set. Variable setting. Specifically, as in the first embodiment, as the transmission focus depth increases, the frequency spectrum of the signal obtained by synthesizing the received signals respectively corresponding to the first waveform and the second waveform shifts lower. Thus, Δf and A2 / A1 are variably set.

  As described above, according to the present embodiment, in addition to the same effects as those of the first embodiment described above, the received signal subjected to phasing addition by shifting the amplitudes of the first waveform and the second waveform together. It is possible to further emphasize the spectral shift of.

Next, a third embodiment of an ultrasonic diagnostic apparatus to which the present invention is applied will be described. The description of the same parts as those of the first embodiment is also omitted, and only the differences are described.
FIG. 6 is a diagram illustrating a configuration of the ultrasonic diagnostic apparatus according to the present embodiment. As shown in FIG. 6, the ultrasonic diagnostic apparatus is not illustrated via an ultrasonic probe or ultrasonic probe 31 having a plurality of ultrasonic transducers or an array of ultrasonic transducers (not shown) and the ultrasonic probe 31. A pulse inversion control unit 33 that controls a transmission signal transmitted to the subject, and a transmission phase phasing circuit 35 that generates a transmission signal in response to an instruction from the pulse inversion control unit 33 and drives the ultrasonic probe 31. And have. The transmission phasing circuit 35 includes a transmission timing generation circuit, a transmission beam former circuit, and a transmission driver (not shown), and supplies a high-pressure transmission signal to the ultrasonic probe 31. At this time, the transmission beam former circuit generates a beam forming signal for forming an ultrasonic beam of a predetermined direction based on the transmission timing signal generated by the transmission timing generation circuit. The beam forming signal is composed of a plurality of drive signals to which time differences corresponding to directions are given.

  In addition, the reception phasing circuit 37 for phasing and adding the received signal received from the subject via the ultrasonic probe over each channel of the plurality of ultrasonic transducers, and the output signal of the reception phasing circuit 37 are variably set. A variable gain circuit 39 that amplifies or reduces in accordance with the gain to be generated, and two beams that temporarily store the output signal of the variable gain circuit 39 and that perform phasing addition with the signal output from the variable gain circuit 39 at time intervals An adder 41 is provided. A variable band filter 43 that performs digital band pass filter operation on the output signal of the two-beam adder 41 is provided. Based on the output signal of the variable band filter 43, detection, logarithmic compression, and enhancement processing are well known. A B-mode processing unit 45 for performing B-mode image processing, a DSC circuit 47, and a monitor 49 for displaying a video signal output from the DSC circuit 47 are provided. A control unit 51 for controlling the variable gain circuit 39 and the variable band filter 43 is provided, and an operation console 53 having input means is connected to the control unit 51. Note that the variable gain circuit 39 uses a known time gain / gain signal based on different gains for a plurality of received signals received at time intervals based on instructions from the pulse inversion control unit 33 and the control unit 51. Has a function to control. Further, the variable band filter 43 has a reception dynamic filter function in which the center frequency and the bandwidth of the pass frequency band are changed according to the reception depth by the time control signal generated by the control unit 51.

Next, the operation of the above-described ultrasonic diagnostic apparatus will be described. In the ultrasonic diagnostic apparatus of the present embodiment, the first waveform and the second waveform are the same as those shown in FIG. 2 (1), that is, two waveforms having the frequency f ₀ are continuously arranged, The same waveform as that of the existing pulse inversion method in which two waveforms have a relationship of time reversal or polarity reversal is used. Then, in the variable gain circuit 39, gains that differ between the received signal corresponding to the first waveform and the received signal corresponding to the second waveform according to the reception timing of the received signal, that is, the depth of the detection region. The time gain control is performed by (amplitude gain), and then the phasing addition is performed in the two-beam adder 41 to form one RF signal.

7 to 9 are graphs showing simulation results of the frequency spectrum of the transmitted signal and the synthesized received signal in the present embodiment, and gains for the received signals corresponding to the first waveform and the second waveform, respectively. Are ratios of 1: 1, 1.2: 0.8, and 1.35: 0.65, respectively. In each figure, as in FIG. 2 (2), the horizontal axis represents the specific frequency (f / f ₀ ) with respect to f ₀ = 2 MHz, and the vertical axis represents the signal intensity (dB). Further, the spectrum of the transmitted signal is indicated by a broken line, and the spectrum of the received signal after phasing addition is indicated by a solid line. Here, needless to say, the spectrum of the transmitted signal is the same as that shown in FIG.

Next, the spectrum of the received signal after phasing addition in each figure will be described. FIG. 7 shows the case where the ratio of gain to the received signal corresponding to the first waveform and the second waveform (hereinafter referred to as “gain ratio”) is 1: 1. As shown in FIG. 7, the spectrum of the received signal has peaks where the signal intensity is maximum in the vicinity of 0.6 f ₀ , 1.9 f ₀ and 3.7 f ₀ . On the other hand, it has a valley signal strength becomes minimal in 1.1f ₀ and near 2.9F ₀ neighborhood. The signal strength is maximized is in the peak of 1.9F ₀ neighborhood, the signal intensity at each peak and valley for the signal strength at this time, about -9dB in 0.6F ₀ near the 1.1f ₀ near about -25dB, 2.9f ₀ to about near -17 dB, it is about -6dB at 3.7F ₀ neighborhood.

FIG. 8 shows the case where the gain ratio is 1.2: 0.8. As shown in FIG. 8, the spectrum of the received signal has peaks at which the signal intensity is maximum in the vicinity of 0.6 f ₀ , 1.9 f ₀ and 3.7 f ₀ . On the other hand, it has a valley signal strength becomes minimal in the vicinity _{f 0} near and 2.9f _0. The signal intensity is maximized at the peak near 1.9f _0. The signal intensity at each peak and valley at this time is about −8 dB in the vicinity of 0.6f _{0 and} about −8 in the vicinity of f _0. It is about −13 dB in the vicinity of 15 dB and 2.9 f _{0 and} about −5 dB in the vicinity of 3.7 f ₀ .

FIG. 9 shows the case where the gain ratio is 1.2: 0.8. As shown in FIG. 9, the spectrum of the received signal has peaks where the signal intensity is maximum in the vicinity of 0.6 f ₀ , 1.9 f ₀ and 3.7 f ₀ . On the other hand, it has a valley signal strength becomes minimal in 0.9F ₀ and near 2.9F ₀ neighborhood. The signal strength is maximized is in the peak of 1.9F ₀ neighborhood, the signal intensity at each peak and valley for the signal strength at this time, about -8dB in 0.6F ₀ near the 0.9F ₀ near about -9dB, 2.9f ₀ to about near -10 dB, it is about -5dB in 3.7F ₀ neighborhood.

As is apparent from a comparison of FIGS. 7 to 9, the spectrum of the received signal phased and added by changing the gain ratio changes. For example, when attention is paid to components in the frequency band from f ₀ to 2f ₀ , FIG. It can be seen that FIG. 9 is more emphasized than FIG. 8 and FIG. For example, paying attention to the signal intensity at 1.5f _0, the signal intensity with respect to the peak of 1.9f ₀ is about −7 dB in FIG. 7, about −5 dB in FIG. 8, and about −3 dB in FIG.

  In the present embodiment, the gain ratio is variably set according to the setting depth of the reception focus. Specifically, the gain ratio is set to increase as the receiving focus depth increases. Such a change in the gain ratio is continuously performed according to the reception timing in conjunction with the well-known reception dynamic focus. That is, time gain control is performed on the received signals corresponding to the first waveform and the second waveform, respectively, with different correlation curves between the reception timing and the gain.

  The variable band filter 43 is configured to variably set the pass frequency band according to the setting depth of the reception focus. Specifically, in a region where the receiving focus depth is shallow, the second harmonic component is allowed to pass in a wide band by setting the pass frequency band wide and setting the center frequency low. Then, as the received focus depth becomes deeper and the fundamental component is emphasized, the pass frequency band of the variable band filter is set narrower, and the center frequency and lower limit frequency are set higher, so that the fundamental component is reduced. We try to reduce it.

As described above, according to the present embodiment, the first waveform and the second waveform have a configuration in which the polarities are inverted from each other, and the received signal corresponding to each of the first waveform and the second waveform has a gain difference. by amplifying or reducing each attached, by changing the frequency spectrum of the received signal after phasing addition, since to no f ₀ can be emphasized component in the frequency band of the 2f _0, without lowering the f ₀ The penetration can be improved without reducing the resolution.

  Since the gain difference and the pass frequency band of the variable band filter are variably set according to the receiving focus depth, the gain difference is reduced or set to 0 at a relatively shallow portion, and the variable band filter By setting a wide pass frequency band, it is possible to emphasize a broadband second-order harmonic component in which the fundamental wave component is canceled. On the other hand, the penetration can be improved by increasing the gain difference, narrowing the pass frequency band, and lowering the center frequency in a relatively deep part.

  In the above-described embodiment, the gain for the received signal corresponding to the first waveform and the gain for the received signal corresponding to the second waveform are both varied, but one is fixed and only the other is varied. It is good also as a structure. For example, the gain corresponding to the first waveform may be fixed to 1 and only the gain corresponding to the second waveform may be varied. For example, the gain ratio may be variably set stepwise such as 1: 1, 1: 0.6, 1: 0.3. Further, in addition to or instead of making the gain for the received signal different, the amplitude at the time of transmission of the first waveform and the second waveform may be made different.

1 is a diagram showing a configuration of a first embodiment of an ultrasonic diagnostic apparatus to which the present invention is applied. It is a graph which shows the simulation result of the transmitted signal waveform by the existing pulse inversion method, and the spectrum of a transmitted signal and a received signal. 3 is a graph showing simulation results of a transmitted signal waveform and a spectrum of a transmitted signal and a received signal in the ultrasonic diagnostic apparatus of FIG. 1. It is a schematic diagram which shows the change of the reception spectrum by the generation depth of a received signal. It is a graph which shows the simulation result of the transmission signal waveform of 2nd Embodiment of the ultrasonic diagnosing device to which this invention is applied, and the spectrum of a transmission signal and a received signal. It is a figure which shows the structure of 3rd Embodiment of the ultrasound diagnosing device to which this invention is applied. It is a graph which shows the simulation result of the spectrum of the transmitted signal of 3rd Embodiment of the ultrasonic diagnosing device to which this invention is applied, and a received signal. It is a graph which shows the simulation result of the spectrum of the transmitted signal of 3rd Embodiment of the ultrasonic diagnosing device to which this invention is applied, and a received signal. It is a graph which shows the simulation result of the spectrum of the transmitted signal of 3rd Embodiment of the ultrasonic diagnosing device to which this invention is applied, and a received signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 3 Transmitter part 5 Receiver part 7 Image preparation display part 9 Arbitrary waveform generator 11 Time axis controller 13 Transmitter 15 Receiver 17 Phased adder 19 Line adder 21 Bandpass filter 23 System Control unit

Claims (10)

  An ultrasonic probe, a wave transmitting unit that transmits an ultrasonic signal to a subject via the ultrasonic probe, and a wave receiving unit that processes a received signal received by the ultrasonic probe; An image generation unit that generates an image based on the reception signal processed by the reception unit, and the transmission unit transmits the ultrasonic signal multiple times at time intervals in the same direction. The ultrasonic signal transmitted a plurality of times includes a first waveform and a second waveform, and the reception unit converts the reception signal corresponding to the first waveform and the second waveform In the ultrasonic diagnostic apparatus having a function of performing phasing addition with a corresponding received signal, the transmission unit includes waveform generation means for generating a waveform whose frequency is increased, and the waveform generation The output of the means is the first waveform, the output of the waveform generating means is delayed in time, and time reversal Ultrasonic diagnostic apparatus was characterized by a second waveform.   The ultrasonic diagnostic apparatus according to claim 1, wherein the transmission unit has a function of variably setting a transmission focus depth of the ultrasonic signal, and a frequency of the first waveform and the second waveform changes. An ultrasonic diagnostic apparatus characterized in that a change rate to be variably set according to the transmission focus depth.   The ultrasonic diagnostic apparatus according to claim 1, wherein the first waveform and the second waveform have a line-symmetric shape with respect to an orthogonal line of a time axis.   2. The ultrasonic diagnostic apparatus according to claim 1, wherein the first waveform and the second waveform further change so that the signal intensity decreases. 3.   5. The ultrasonic diagnostic apparatus according to claim 4, wherein a rate of change in signal intensity of the first waveform and the second waveform is variably set according to the transmission focus depth. Diagnostic device.   The ultrasonic diagnostic apparatus according to claim 1, wherein the reception unit includes a filter that extracts a set frequency band of the reception signal, and variably sets the frequency band according to a reception timing of the reception signal. An ultrasonic diagnostic apparatus.   The ultrasonic diagnostic apparatus according to claim 1, wherein the reception unit includes a filter that extracts a set frequency band of the received signal, and the set frequency band is variably set according to the transmission focus depth. An ultrasonic diagnostic apparatus.   2. The ultrasonic diagnostic apparatus according to claim 1, wherein the first waveform, the second waveform, or both the first waveform and the second waveform increase or decrease in frequency every two cycles or more. Ultrasonic diagnostic equipment.   2. The ultrasonic diagnostic apparatus according to claim 1, wherein the first waveform, the second waveform, or both the first waveform and the second waveform increase and decrease in frequency every less than one cycle. Ultrasonic diagnostic equipment.   The ultrasonic diagnostic apparatus according to claim 1, wherein the first waveform, the second waveform, or both the first waveform and the second waveform continuously increase and decrease in frequency. Ultrasound diagnostic device.

Images