JP2011036506A - Ultrasonograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an unnecessary wave component in a technique for extracting data in vivo from a target position using continuous waves. <P>SOLUTION: A first FM modulator 21 is constituted so as to subject a feed wave signal to the modulation processing of frequency on the basis of a modulation signal to form the transmission signal of the continuous wave and a receiving mixer 30 uses a reference signal adjusted in the correlation with the target position in a living body to apply demodulation processing to a receiving signal to thereby obtain the demodulation signal corresponding to the target position. In this transmission and reception processing, a second FM modulator 22 subjects the feed wave signal to the modulation processing of frequency on the basis of the modulation signal in the same way as the first FM modulator 21 to form the reference signal. The intensity of the modulation in the modulation processing of frequency of the reference signal is adjusted to reduce the unnecessary wave component contained in the demodulation signal corresponding to the target position. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus using a continuous wave.

  A continuous wave Doppler is known as a technique using a continuous wave of an ultrasonic diagnostic apparatus. In continuous wave Doppler, for example, a transmission wave that is a sine wave of several MHz is continuously emitted into the living body, and a reflected wave from the living body is continuously received. The reflected wave includes Doppler shift information by a moving body (for example, blood flow) in the living body. Therefore, by extracting the Doppler shift information and performing frequency analysis, a Doppler waveform reflecting the velocity information of the moving body can be formed.

  Continuous wave Doppler using a continuous wave is generally superior in speed measurement at a higher speed than pulse Doppler using a pulse wave. Under such circumstances, the applicant of the present application has conducted research on continuous wave Doppler. As one of the results, Patent Document 1 proposes a technique related to continuous wave Doppler (FMCW Doppler) subjected to frequency modulation processing.

  On the other hand, with continuous wave Doppler, position measurement is difficult due to the use of continuous waves. For example, a conventional general continuous wave Doppler device (a device that does not use FMCW Doppler) cannot perform position measurement. On the other hand, the applicant of the present application proposes a very innovative technique in Patent Document 2 that can selectively extract Doppler information from a desired position in a living tissue by FMCW Doppler.

JP 2005-253949 A JP 2008-289851 A

  The technology of FMCW Doppler described in Patent Literature 1 and Patent Literature 2 is an epoch-making technology with the possibility of ultrasonic diagnosis that has never existed before. The inventor of the present application has further studied further about this revolutionary technology improvement. In particular, research has been conducted focusing on techniques for extracting in vivo information from target positions using continuous waves.

  The present invention has been made in such a background, and an object thereof is to reduce unnecessary wave components in a technique for extracting in vivo information from a target position using a continuous wave.

  An ultrasonic diagnostic apparatus suitable for the above object includes a transmission signal output unit that outputs a continuous wave transmission signal obtained by modulating a carrier wave signal, and an ultrasonic transmission wave corresponding to the transmission signal to a living body. A transmission / reception unit that obtains a reception signal by receiving a reception wave accompanying the transmission wave from a living body, a reference signal output unit that outputs a reference signal obtained by modulating the carrier wave signal, A received signal processing unit that obtains a demodulated signal corresponding to the target position by performing a demodulation process on the received signal using a reference signal whose correlation with the target position in the body is adjusted, and the target An in-vivo information extracting unit that extracts in-vivo information from the demodulated signal corresponding to the position, and adjusting the intensity of the modulation in the modulation processing to obtain the reference signal, thereby corresponding to the target position To reduce unwanted wave component contained in the tone signal, characterized in that.

  Preferably, the intensity of the modulation is adjusted by increasing or decreasing the degree of modulation in the modulation processing for obtaining the reference signal.

  Preferably, the modulation degree of the reference signal is adjusted according to the speed of the moving object at the target position.

  Preferably, the modulation degree of the reference signal is set to a modulation degree corresponding to the speed of the moving object at the target position, so that the DC component, the fundamental component of the modulation frequency, and the harmonics included in the demodulated signal corresponding to the target position. Of the wave components, the fundamental wave component and the harmonic component, which are the unnecessary wave components, are reduced.

  As a preferred specific example, the transmission signal output unit outputs a continuous wave transmission signal obtained by frequency-modulating a carrier signal, and the reference signal output unit is obtained by frequency-modulating the carrier signal. The reference signal to be output is output.

  As a preferred specific example, the transmission signal output unit forms a continuous wave transmission signal by frequency-modulating a carrier signal with a modulation factor β using a modulation signal, and the reference signal output unit outputs the modulation signal. And the reference signal is formed by frequency-modulating the carrier signal with a modulation degree (β + Δβ).

  Preferably, the modulation degree (β + Δβ) of the reference signal is adjusted so that Δβ = 2vβ / c (c is an ultrasonic wave propagation velocity) according to the velocity v of the moving object at the target position. And

  According to the present invention, it is possible to reduce unnecessary wave components in a technique for extracting in-vivo information from a target position using a continuous wave.

1 is a diagram illustrating an overall configuration of an ultrasonic diagnostic apparatus that is preferable in the practice of the present invention. It is a figure for demonstrating the transmission wave and reception wave which were frequency-modulated. It is a figure which shows a mode that k (beta) changes in the shape of a sine wave depending on the depth d. It is a figure explaining the influence which the periodicity of FM continuous wave has on the Doppler frequency. It is a figure for demonstrating the Doppler signal influenced by the frequency modulation. It is a figure which shows the time change waveform of the Doppler signal influenced by the frequency modulation. It is a figure for demonstrating reduction of the unnecessary wave component by adjustment of a modulation degree. It is a figure which shows the removal of the unnecessary wave component of the Doppler signal containing a some frequency component.

  FIG. 1 is a diagram showing an overall configuration of an ultrasonic diagnostic apparatus suitable for implementing the present invention. The transmitting vibrator 10 continuously transmits a transmission wave into the living body, and the receiving vibrator 12 continuously receives a reflected wave from the living body. In this way, transmission and reception are performed by different vibrators, and transmission / reception is performed by a so-called continuous wave Doppler method. The transmitting transducer 10 includes a plurality of vibration elements, and the plurality of vibration elements are controlled to form an ultrasonic transmission beam. The receiving vibrator 12 also includes a plurality of vibration elements, and signals obtained by the plurality of vibration elements are processed to form a reception beam.

  The transmission beamformer (transmission BF) 14 outputs transmission signals to a plurality of vibration elements included in the transmission transducer 10. For example, an FM continuous wave (FMCW wave) that has been subjected to FM modulation processing using a sine wave is input to the transmission beam former 14. The transmission beamformer 14 applies a delay process corresponding to each vibration element to the FM continuous wave to form a transmission signal corresponding to each vibration element. Note that power amplification processing may be performed on the transmission signal corresponding to each vibration element formed in the transmission beam former 14 as necessary. Thus, a transmission beam by FM continuous waves is formed.

  The first FM modulator 21 outputs an FM continuous wave to the transmission beam former 14. The first FM modulator 21 performs frequency modulation on the RF wave (carrier wave signal) supplied from the RF wave oscillator 23 using the modulation signal supplied from the modulation wave generator 24, thereby generating an FM continuous wave. appear. The waveform of the FM continuous wave will be described in detail later.

  The reception beam former (reception BF) 16 forms a reception beam by phasing and adding a plurality of reception signals obtained from a plurality of vibration elements included in the reception transducer 12. That is, the reception beamformer 16 performs a delay process corresponding to the vibration signal obtained from each vibration element and adds a plurality of reception signals obtained from the plurality of vibration elements. Form a beam. Note that a plurality of received signals may be supplied to the reception beam former 16 after processing such as low noise amplification is performed on the received signals obtained from the respective vibration elements. In this way, a reception RF signal along the reception beam is obtained.

  The reception mixer 30 is a circuit that performs quadrature detection on the received RF signal to generate a complex baseband signal, and is composed of two mixers 32 and 34. Each mixer is a circuit that mixes the received RF signal with a predetermined reference signal. The reference signal supplied to each mixer of the reception mixer 30 is generated based on the FM continuous wave output from the second FM modulator 22.

  Similar to the first FM modulator 21, the second FM modulator 22 uses the modulation signal supplied from the modulation wave generator 24 to frequency modulate the RF wave (carrier signal) supplied from the RF wave oscillator 23. To generate an FM continuous wave as a reference signal. By adjusting the intensity of the modulation in the frequency modulation process, unnecessary wave components included in the demodulated signal corresponding to the target position are reduced. The unnecessary wave component included in the demodulated signal and the reduction of the unnecessary wave component will be described in detail later.

  The FM continuous wave (reference signal) output from the second FM modulator 22 is delayed in the delay circuit 25, and the FM continuous wave subjected to delay processing is directly supplied to the mixer 32, while the mixer 34 is subjected to delay processing. The FM continuous wave is supplied via the π / 2 shift circuit 26.

  The π / 2 shift circuit 26 is a circuit that shifts the phase of the delayed FM continuous wave by π / 2. As a result, an in-phase signal component (I signal component) is output from one of the two mixers 32 and 34, and a quadrature signal component (Q signal component) is output from the other. Note that high-frequency components of the in-phase signal component and the quadrature signal component are cut by LPFs (low-pass filters) 36 and 38 provided at the subsequent stage of the receiving mixer 30, and a demodulated signal of only a necessary band after detection is obtained. Extracted. Demodulated signals output from the LPFs 36 and 38 are output to the FFT processing unit 50.

  The FFT processing unit (fast Fourier transform processing unit) 50 performs an FFT operation on each demodulated signal (in-phase signal component and quadrature signal component). As a result, the demodulated signal is converted into a frequency spectrum in the FFT processing unit 50. The frequency spectrum output from the FFT processing unit 50 is output as frequency spectrum data having a frequency resolution δf depending on circuit setting conditions and the like.

  The Doppler information analysis unit 52 extracts a Doppler signal from the demodulated signal converted into a frequency spectrum. As will be described in detail later, in the ultrasonic diagnostic apparatus of FIG. 1, a target position is set by delay processing in the delay circuit 25, and a Doppler information analysis unit 52 selectively extracts a Doppler signal from the target position. For example, the Doppler information analysis unit 52 forms a display waveform of a Doppler signal that changes with time. In addition, Doppler signals are extracted for each depth (each position) in the living body, and for example, the velocity of the tissue in the living body is calculated for each depth on the ultrasonic beam (sound ray) and output in real time. May be. Alternatively, the velocity of each position of the in-vivo tissue may be calculated two-dimensionally or three-dimensionally by scanning an ultrasonic beam.

  The display unit 54 displays the waveform of the Doppler signal formed in the Doppler information analysis unit 52. Each unit in the ultrasonic diagnostic apparatus shown in FIG. 1 is controlled by the system control unit 60. That is, the system control unit 60 performs transmission control, reception control, display control, and the like.

  As outlined above, in the ultrasonic diagnostic apparatus of FIG. 1, a reception signal is obtained by transmitting and receiving an ultrasonic wave (FMCW wave) obtained by FM-modulating a continuous wave (CW) with a modulated wave. Doppler information is selectively extracted. Further, the intensity of modulation in the frequency modulation processing related to the reference signal is adjusted, and unnecessary wave components included in the demodulated signal are reduced. Therefore, the position selectivity from which Doppler information from the target position is selectively extracted and the reduction of unnecessary wave components will be described in detail below. In addition, about the part (structure) shown in FIG. 1, the code | symbol of FIG. 1 is utilized also in the following description.

<About position selectivity>
RF wave of a frequency _{f 0} with respect to (a carrier wave), FMCW transmission wave subjected to FM modulation by a sine wave of a frequency _{f m} can be expressed by the following equation.

In equation (1), Delta] f is 0-P value of the frequency fluctuation range is (zero peak value maximum frequency shift), is the ratio of the maximum frequency deviation Delta] f and the modulation frequency f _m beta is FM modulation factor (modulation index ).

  In addition, the FMCW received wave with Doppler shift can be expressed by the following equation, where α is a round-trip attenuation in the living body.

Incidentally, the Doppler shift with respect to f _m in equation (2) is ignored so small compared to the shift amount f _d of f _0.

  FIG. 2 is a diagram for explaining a transmission wave and a reception wave subjected to frequency modulation processing. FIG. 2A shows the waveform of the FMCW transmission wave (transmission signal) (see Equation 1), where the horizontal axis is the time axis and the vertical axis is the amplitude. FIG. 2B shows the instantaneous frequency change for each of the FMCW transmission wave (transmission signal) and the FMCW reception wave (reception signal). In FIG. 2B, the horizontal axis is the time axis, and the vertical axis is the frequency (instantaneous frequency). Note that the time axes of FIG. 2A and FIG. 2B are aligned with each other.

As shown in FIG. 2 (b), the transmission signal (broken line) has a continuous wave of varying frequency at a period T _{m =} 1 / f _m. Further, the received signal (solid line) is delayed by φ _m in phase angle from the transmitted signal. In FIG. 2B, the received signal attenuation and Doppler shift shown in Equation 2 are omitted.

The received waveform represented by the equation 2 is a signal waveform (received RF signal) received via the ultrasonic transducer. In the FMCW Doppler, in the demodulation process for the received RF signal, the received wave is multiplied with the FMCW transmission wave as a reference signal. As described with reference to FIG. 1, after the FM continuous wave formed by the same processing as the FM continuous wave output from the first FM modulator 21 is output from the second FM modulator 22, the delay is performed in the delay circuit 25. As a reference signal, the mixer 32 is directly supplied with the delayed FM continuous wave, while the mixer 34 is supplied with the delayed FM continuous wave via the π / 2 shift circuit 26. . Therefore, the reference signal v _rI (t) supplied to the mixer 32 and the reference signal v _rQ (t) supplied to the mixer 34 can be expressed by the following equations.

In Equation 3, φ _mr represents the phase of the reference signal that can be arbitrarily set by the delay processing in the delay circuit 25, and φ _0r represents the phase change of the carrier wave determined in accordance with the phase of the arbitrarily set reference signal Indicates the amount.

In the receiving mixer 30, quadrature detection is performed as demodulation processing. That is, the mixer 32 executes a process corresponding to the multiplication of the received RF signal v _R (t) and the reference signal v _rI (t), and the mixer 34 receives the received RF signal v _R (t) and the reference signal v. A process corresponding to the multiplication of _rQ (t) is executed.

The multiplication v _DI (t) of the reception RF signal v _R (t) and the reference signal v _rI (t) in the mixer 32 is expressed by the following equation. Note that the component of the frequency 2f ₀ is deleted during the calculation of the following equation. This is removed by the LPF 36.

  Here, the following formula for the Bessel function is used.

  Using the formula of Formula 5, Formula 4 is further calculated as the following formula.

On the other hand, the multiplication v _DQ (t) of the reception RF signal v _R (t) and the reference signal v _rQ (t) in the mixer 34 is expressed as follows. Note that the component of the frequency 2f ₀ is deleted during the calculation of the following equation. This is removed by the LPF 38.

Here, a complex baseband signal is defined based on v _DI (t) in Expression 6 and v _DQ (t) in Expression 7. _{First, v} DI (t) and _v DC contained in the DQ (t) (DC) component, the even-order harmonics of the modulation frequency _{f m} expressed by the following equation.

_{Then, v} DI (t) and _v DQ (t) in the included components of the modulation frequency _{f m,} expressed by the following equation odd harmonics component of the modulation frequency _{f m.}

More of the equation (8) and equation (9), in the baseband signal after the quadrature detection, Doppler signal containing Doppler shift f _d is composed of a DC component as the modulation frequency f _m and harmonic components of the modulation frequency f _m It can be seen that it appears as a double sideband wave for each of the components. In communications engineering, this type of signal format is called Double-Sideband Suppressed-Carrier (DSB-SC).

Here, consider the case where the phases of the received signal and the reference signal are aligned with each other, that is, the case where φ _mr is adjusted by delay processing in the delay circuit 25 so as to coincide with φ _m (φ _mr = φ _m ). When φ _mr and φ _m are matched, k in Equation 4 is 0. When this result is applied to the Bessel function of Equation 5, only the value of the 0th-order Bessel function is 1 and the values of the other Bessel functions are 0, as shown in the following equation.

  When the result shown in Equation 10 is applied to Equation 8 and Equation 9, the following equation is obtained.

Equation 11 shows that if the phase φ _mr of the reference wave (reference signal) is set to the phase difference φ _m between transmission and reception, only the Doppler signal corresponding to the DC component (DC signal component) can be extracted by compression conversion. Yes. The value and the polarity of the resulting complex Doppler frequency f _d represents the speed and the polarity of the fluid, such as blood flow. It can also be seen that the amplitude of the Doppler signal does not depend on the phase of the carrier wave and the reference wave.

This fact can also be interpreted as follows. The delay circuit 25 in FIG. 1 serves to set the phase φ _mr of the modulated wave in the reference wave (reference signal) to the phase difference φ _m of the modulated wave between transmission and reception. However, the delay circuit 25 changes not only the phase of the modulated wave but also the phase of the carrier wave. This value is _φ0r . Since the phase of the carrier wave changes according to the phase φ _mr of the modulated wave in the reference wave, it cannot be set to a specific value corresponding to the phase difference of the modulated wave between transmission and reception. However, as shown in Equation 11, φ _0r does not affect the amplitude, frequency, and polarity of the Doppler signal as long as quadrature detection is performed, regardless of the value, as in φ _0. .

  Therefore, for example, only the modulation signal (modulation wave) is delayed by a delay amount corresponding to the depth of the target position to form a delay modulation signal, and the carrier signal is modulated using the delay modulation signal. A signal may be formed and demodulated using the reference signal and a reference signal shifted in phase by π / 2.

In the ultrasonic diagnostic apparatus of FIG. 1, as described below, Doppler information at a specific position can be obtained with a relatively good SNR similar to that of CW Doppler, similarly to PW Doppler (pulse Doppler). In Equation 6 to Equation 9, kβ that is a factor of J ₀ (kβ) that controls the amplitude of the Doppler signal will be considered. From the definition of k in Equation 4, kβ can be expressed as follows.

  Equation 12 means that kβ changes in a sine wave shape depending on the depth d.

FIG. 3 is a diagram illustrating a state in which kβ changes in a sine wave shape depending on the depth d. Due to the nature of the first-order Bessel function, when kβ is 0, J ₀ (kβ) becomes the maximum value. In the waveform of kβ indicated by a solid line in FIG. 3, there are three depths where the depth d from the body surface is 0 in the positive range. This means that the amplitude of the Doppler signal obtained from these three depths is maximized.

From Equation 12, etc., if the phase φ _m of the received signal from the target depth matches the phase φ _{mr of the} reference wave, kβ can be set to 0, and at a depth at which kβ becomes 0, J ₀ (kβ) is maximized and the amplitude of the Doppler signal is maximized. That is, in the delay circuit 25, the phase φ _m of the received signal from the target depth is matched with the phase φ _{mr of the} reference wave so that the amplitude of the Doppler signal from the target depth is maximized. Thus, the Doppler signal can be selectively extracted.

  As described above, the target position from which the Doppler signal is selectively extracted is determined based on the delay processing in the delay circuit 25. The system control unit 60 in FIG. 1 controls the delay time in the delay circuit 25 according to the depth of the target position.

  Further, in the ultrasonic diagnostic apparatus of FIG. 1, the unnecessary wave component of the Doppler signal due to the influence of frequency modulation is reduced, and the required Doppler signal is extracted. Therefore, the unnecessary wave component accompanying frequency modulation and the reduction of the unnecessary wave component will be described in detail below. In addition, about the part (structure) shown in FIG. 1, the code | symbol of FIG. 1 is utilized also in the following description.

<Unwanted wave components accompanying frequency modulation>
In the basic principle of the Doppler method, the Doppler frequency (Doppler shift frequency) relating to the moving body (for example, blood flow) is proportional to the frequency of the ultrasonic wave used for measurement and the speed of the moving body. The ultrasonic diagnostic apparatus in FIG. 1 uses an FM continuous wave, and the frequency (instantaneous frequency) of the FM continuous wave changes periodically as described in FIG. Therefore, even when the speed of the moving body is constant, if the Doppler frequency of the moving body is measured using the FM continuous wave, the Doppler frequency periodically varies with the periodicity of the FM continuous wave.

  FIG. 4 is a diagram for explaining the influence of the periodicity of the FM continuous wave on the Doppler frequency. FIG. 4 shows an FM continuous wave 70 not affected by the Doppler shift and an FM continuous wave 72 affected by the Doppler shift. 4 is the time axis, and the vertical axis of FIG. 4 shows the instantaneous frequencies of the FM continuous waves 70 and 72.

The instantaneous transmission frequency of the ultrasonic transmission signal in the ultrasonic diagnostic apparatus of FIG. 1 periodically changes into a sine wave like an FM continuous wave 70. Therefore, even when the speed of the moving body is constant, the Doppler shift periodically changes, and as a result, a waveform like the FM continuous wave 72 is obtained. That is, at a time when the instantaneous frequency of the FM continuous wave 70 is low (small), the Doppler frequency f _dL is relatively small, and at a time when the instantaneous frequency of the FM continuous wave 70 is high (large), a relatively large Doppler frequency f _{dH is obtained.} It becomes.

As described above, the Doppler frequency fluctuation obtained by using the FM continuous wave 70 is periodic corresponding to the periodicity of the FM continuous wave 70. In particular, when the speed of the moving body is high, the difference between the Doppler frequency f _dL and the Doppler frequency f _dH also increases, and the periodicity of the Doppler frequency becomes relatively significant. On the other hand, when the speed of the moving body is low, the difference between the Doppler frequency f _dL and the Doppler frequency f _dH becomes small, and the periodicity of the Doppler frequency becomes relatively inconspicuous.

Ultrasonic transmission signal in the ultrasonic diagnostic apparatus of Figure 1, RF wave of a frequency f ₀ with respect to (a carrier wave), a FMCW transmission wave subjected to FM modulation by a sine wave of a frequency f _m, the signal is above It is as the number 1 formula. The instantaneous angular frequency of the transmission signal (FMCW transmission wave) is expressed as follows by differentiating the phase term of Equation 1 with respect to time.

  Here, the Doppler shift is defined as the amount of change in the instantaneous frequency by the ratio of the sound speed (ultrasonic speed) c and the speed v of the moving object. In this case, the change in Doppler frequency with respect to the relative speed v is expressed by the following equation as a speed 2v in a reciprocating manner.

  When the Doppler frequency change expressed by Equation 14 is converted into an instantaneous phase, the following equation is obtained.

In addition to the Doppler shift by the carrier wave f ₀ expressed by the first term, the Doppler shift by the modulated wave expressed by the second term is applied to the instantaneous phase expressed by the equation (15). It means to be added. The third term is an integration constant, which means the phase of the Doppler frequency. In general, velocity information such as blood flow does not require phase information of Doppler frequency. Further, since it is a phase component that does not change with time, it is considered that it does not have a physically significant meaning in speed measurement.

  Since the received wave arrives later than the transmitted wave by the transmission / reception time difference (round-trip propagation time to the target position) τ, the received wave is expressed as follows in consideration of the transmission / reception time difference τ.

  In the reception mixer 30, processing corresponding to multiplication of the reference wave (reference signal) having substantially the same waveform as the transmission wave by the reception wave (the following equation) is executed.

When the frequency component of 2f ₀ is removed by the low-pass filter from Equation 17, the output of the reception mixer 30 (for example, the output of the LPF 36) can be expressed as the following equation.

  When the calculation is further advanced with respect to the result of Expression 18, the following expression is obtained.

The Formula 19, the Doppler signal, which means that equal to the frequency-modulated signal by the newly defined modulation β'(see number 18 formula) modulation frequency f _m.

  FIG. 5 is a diagram for explaining the Doppler signal affected by the frequency modulation. FIG. 5 shows the frequency spectrum of the Doppler signal corresponding to Equation (19). In FIG. 5, the horizontal axis represents frequency and the vertical axis represents power.

Figure 5 and as shown in Formula 19, the Doppler signal affected by the modulation signal, in addition to the modulation frequency f _m direct current component J ₀ is a zero-order component of _(.beta. '), 1-order component J ₁ (Β ′), secondary components J ₂ (β ′), tertiary components J ₃ (β ′),... Are included. Note that the DC component is emerging from the frequency 0 to a position spaced Doppler frequency f _d, 1-order component is emerging from the frequency f _m to a position spaced Doppler frequency f _d, 2-order component from the frequency 2f _m appearing in a position spaced apart by the Doppler frequency f _d.

FIG. 6 is a diagram showing a time-varying waveform of a Doppler signal affected by frequency modulation, and shows a time-varying frequency spectrum of FIG. That is, FIG. 6 shows a time-varying waveform for each of the DC component, the primary component (−1st-order component), and the secondary component of the Doppler signal. When the speed of such blood flow to be measured with the lapse of time shown in the horizontal axis changes, so does the Doppler frequency f _d in accordance with a change in velocity. Therefore, the waveform of each component shown in FIG. 6 changes in the frequency direction shown on the vertical axis as time passes on the horizontal axis.

  In the ultrasonic diagnostic apparatus of FIG. 1, a DC component that is a zero-order component is extracted as a required Doppler signal. Therefore, these unnecessary wave components are reduced by using the primary component, the secondary component, the tertiary component,.

<About reduction of unnecessary wave components>
As shown in Equation 19, since the Doppler signal is a signal frequency-modulated by the modulation factor β ′ changed from the modulation factor β, the primary component, the secondary component, the tertiary component,.・ Appears. In view of this, a method of reducing, preferably completely removing, the primary component, the secondary component, the tertiary component, and the like, which are unnecessary wave components, by shifting the modulation factor related to the reference signal in advance by the change in the modulation factor between transmission and reception. It was investigated.

  First, a reference signal obtained by changing the modulation degree of an FM continuous wave as a transmission wave by Δβ is represented by the following equation. A reference signal of the following formula is formed in the second FM modulator 22.

  The received signal that has undergone Doppler shift is expressed by Equation 16. The output of the multiplication result in the reception mixer 30 is calculated by the following equation as a result of multiplying the reference signal and the reception signal.

When the frequency component of 2f ₀ is removed by the low-pass filter from Equation 21, the output of the reception mixer 30 (for example, the output of the LPF 36) can be expressed as the following equation.

Number 22 Expression of results, by the modulation signals of each frequency omega _m, shows a signal frequency-modulated by the modulation degree (β'-Δβ). Δβ in Equation 22 is a change in the degree of modulation related to the reference signal (see Equation 20). By adjusting this Δβ as the following equation, the term of frequency modulation in the result of equation 22 can be made zero.

  Then, by adjusting Δβ as shown in Expression 23, a Doppler signal represented by the following expression of a baseband (demodulated signal) that is not frequency-modulated can be obtained.

  In this way, by adjusting Δβ included in the modulation degree (β + Δβ) in the second FM modulator 22, unnecessary waves such as a primary component, a secondary component, and a tertiary component included in the Doppler signal of the demodulated signal are obtained. The components can be reduced, preferably completely removed.

  FIG. 7 is a diagram for explaining the reduction of unnecessary wave components by adjusting the modulation degree. FIG. 7A shows temporal changes in the instantaneous frequency (each frequency) related to the transmission signal 82, the received signal 84 that has undergone Doppler shift, and the reference signal 90 whose modulation degree is adjusted, with the horizontal axis as the time axis.

As described with reference to FIG. 4, at the time when the instantaneous frequency of the FM continuous wave 70 is low (small), the Doppler frequency f _dL becomes relatively small, and at the time when the instantaneous frequency of the FM continuous wave 70 is high (large). Becomes a relatively large Doppler frequency f _dH .

Also in FIG. 7, the Doppler shift of the reception signal 84 becomes relatively small at a time when the instantaneous frequency of the transmission signal 82 is low (small), and at the time when the instantaneous frequency of the transmission signal 82 is high (large), Doppler shift becomes relatively large. For example, the maximum value of the instantaneous frequency related to the transmission signal 82 is (ω ₀ + Δω), and the maximum value of the reception signal 84 corresponding to this value is (ω ₀ + Δω) + (ω _d + Δω _d ). On the other hand, the minimum value of the instantaneous frequency related to the transmission signal 82 is (ω ₀ −Δω), and the minimum value of the reception signal 84 corresponding to this value is (ω ₀ −Δω) + (ω _d −Δω _d ). Δω _d is a Doppler shift component associated with Δω, and is defined as the following equation.

Therefore, the modulation degree is changed as shown in Equation 20, and the reference signal 90 shown in FIG. 7 is formed. For example, when the Doppler shift is positive, the modulation degree of the reference signal 90 is slightly increased as compared with the transmission signal 82. As a result, the maximum value of the instantaneous frequency related to the reference signal 90 increases from the transmission signal 82 by Δω _d , and the minimum value of the instantaneous frequency related to the reference signal 90 decreases from the transmission signal 82 by Δω _d .

  7B shows the time difference between the transmission signal 82 and the reception signal 84 (broken line) and the difference signal between the reference signal 90 and the reception signal 84 (dashed line) on the same time axis as FIG. 7A. It shows a change. From FIG. 7B, it can be seen that the Doppler frequency is constant regardless of the time of the difference signal from the received signal 84, that is, the demodulated signal obtained by multiplication, by the reference signal 90 with the modulation degree adjusted.

  In this way, by adjusting the modulation degree of the reference signal, if the Doppler signal is distributed in a narrow frequency band expressed by a line spectrum, the primary component and the secondary component that are unnecessary wave components are used. , Tertiary components and the like can be almost removed. However, for example, the Doppler frequency obtained from blood flow or the like is generally composed of a plurality of frequencies. In this case, in order to completely remove unnecessary wave components, a reference signal corresponding to each of a plurality of frequency components may be prepared, and the modulation degree may be adjusted according to each frequency component. However, there may be cases where it is difficult to remove the principle completely due to restrictions on the circuit scale. Therefore, an example of realistic removal of unnecessary wave components will be described.

  FIG. 8 is a diagram illustrating removal of unnecessary wave components from a Doppler signal including a plurality of frequency components. Similar to FIG. 6, FIG. 8 shows time-varying waveforms for each of the DC component, primary component (−1st-order component), and secondary component of the Doppler signal.

In Figure 8, among the plurality of frequency components shown on the vertical axis, to adjust the modulation index according to the frequency components corresponding to the Doppler shift v _d. This frequency component is, for example, the component having the largest power among the plurality of frequency components. For example, an image corresponding to FIG. 8 is displayed on the display unit 54 (FIG. 1), and the user specifies the frequency component with the highest power from the image whose luminance is adjusted according to the power level. Further, the user adjusts the degree of modulation using an operation device such as a knob so that the unwanted wave component is as small as possible. Thereby, compared with FIG. 6, as shown in FIG. 8, the primary component (-1st order component) and secondary component which are unnecessary wave components can be reduced.

Further, based on the Doppler shift v _d specified by the user, the ultrasonic diagnostic apparatus of FIG. 1 uses the equation (23) from the velocity v corresponding to the Doppler shift v _d to obtain Δβ = 2vβ / c (c is the ultrasonic wave). The modulation degree (β + Δβ) of the reference signal may be adjusted so as to be (propagation speed).

  The preferred embodiments of the present invention have been described above, but the above-described preferred embodiments of the present invention are merely examples in all respects, and do not limit the scope of the present invention. The present invention includes various modifications without departing from the essence thereof.

  21 first FM modulator, 22 second FM modulator, 23 RF wave oscillator, 24 modulation wave generator, 25 delay circuit, 30 reception mixer, 50 FFT processor, 52 Doppler information analyzer.

Claims (7)

A transmission signal output unit that outputs a continuous wave transmission signal obtained by modulating the carrier wave signal;
A transmission / reception unit for obtaining a reception signal by transmitting an ultrasonic transmission wave corresponding to the transmission signal to a living body and receiving a reception wave associated with the transmission wave from the living body;
A reference signal output unit that outputs a reference signal obtained by modulating the carrier wave signal;
A received signal processing unit that obtains a demodulated signal corresponding to the target position by performing a demodulation process on the received signal using a reference signal whose correlation with the target position in the living body is adjusted;
An in-vivo information extraction unit for extracting in-vivo information from the demodulated signal corresponding to the target position;
Have
By adjusting the intensity of modulation in the modulation process for obtaining the reference signal, the unnecessary wave component included in the demodulated signal corresponding to the target position is reduced.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
Adjusting the intensity of the modulation by increasing or decreasing the degree of modulation in the modulation process for obtaining the reference signal;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
Adjusting the modulation degree of the reference signal according to the speed of the moving object at the target position;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
By setting the modulation degree of the reference signal to a modulation degree corresponding to the speed of the moving object at the target position, the DC component, the fundamental component of the modulation frequency, and the harmonic component included in the demodulated signal corresponding to the target position Among them, the fundamental wave component and the harmonic component which are the unnecessary wave components are reduced.
An ultrasonic diagnostic apparatus. In the ultrasonic diagnostic apparatus according to any one of claims 1 to 4,
The transmission signal output unit outputs a continuous wave transmission signal obtained by subjecting a carrier wave signal to frequency modulation processing,
The reference signal output unit outputs a reference signal obtained by frequency-modulating the carrier signal.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 5,
The transmission signal output unit forms a continuous wave transmission signal by frequency-modulating the carrier signal with a modulation factor β using the modulation signal,
The reference signal output unit forms a reference signal by frequency-modulating the carrier signal with a modulation degree (β + Δβ) using the modulation signal.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 6,
The modulation degree (β + Δβ) of the reference signal is adjusted so that Δβ = 2vβ / c (c is the ultrasonic wave propagation velocity) according to the velocity v of the moving body at the target position.
An ultrasonic diagnostic apparatus.

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