JP2012095896A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately extract required Doppler information concerning technique for extracting the Doppler information from a target position by using a continuous wave.SOLUTION: The frequency spectrum SP of a demodulation signal is divided into multiple frequency bands for each modulation frequency f. Then, peaks P0, P1, P2, ..., where the power of the spectrum becomes the maximum are specified in the bands for each block, and from among the multiple peaks concerning the multiple blocks. the peak P1 with the maximum power is set to be the maximum spectrum. Besides, the power of the peak P0 being next to the maximum spectrum is set as a threshold. A signal component being the power exceeding the threshold is extracted as a Doppler signal from the frequency spectrum SP of the demodulation signal.

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 inventors of the present application have further researched on this groundbreaking technology improvement. In particular, research has been conducted focusing on techniques for extracting in-vivo information such as Doppler information from target positions using continuous waves.

  The present invention has been made in such a background, and an object of the present invention is to appropriately extract necessary Doppler information in a technique for extracting Doppler information from a target position using a continuous wave. is there.

  An ultrasonic diagnostic apparatus suitable for the above object includes a transmission signal processing unit that outputs a continuous wave transmission signal whose frequency is periodically changed according to a modulation frequency, and an ultrasonic transmission wave corresponding to the transmission signal. Using a reference signal in which the correlation between the transmitting / receiving unit that transmits a wave to a living body and receives a reception wave accompanying the transmission wave from the living body to obtain a reception signal and the target position in the living body is adjusted , By performing a demodulation process on the received signal, a received signal processing unit that obtains a demodulated signal corresponding to the target position, and a maximum spectrum that maximizes the signal strength from the frequency spectrum of the demodulated signal, And a Doppler information extraction unit that extracts a signal component including the maximum spectrum from the demodulated signal as a Doppler signal.

  In a preferred embodiment, the Doppler information extraction unit divides the frequency spectrum of the demodulated signal into a plurality of frequency bands for each modulation frequency, specifies a peak spectrum that maximizes the signal strength for each frequency band, Among the plurality of peak spectra corresponding to the frequency band, the maximum spectrum is the one having the maximum intensity.

  In a desirable specific example, the Doppler information extraction unit sets a threshold relating to the strength of the signal based on the frequency spectrum of the demodulated signal, and extracts a signal component having an intensity exceeding the threshold from the demodulated signal as the Doppler signal. It is characterized by that.

  In a preferred embodiment, the Doppler information extraction unit is characterized in that the threshold value is the intensity of a peak spectrum next to the maximum spectrum among a plurality of peak spectra corresponding to a plurality of frequency bands.

  In a preferred embodiment, the Doppler information extraction unit uses the intensity of a spectrum separated from the maximum spectrum by the modulation frequency as the threshold value.

  In a preferred embodiment, the ultrasonic diagnostic apparatus further includes a display unit that displays a Doppler waveform obtained by performing visual identification processing on the extracted Doppler signal.

  According to the present invention, it is possible to appropriately extract required Doppler information in a technique for extracting Doppler 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 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 which shows the extraction process of the Doppler signal with a comparatively narrow spectrum. It is a figure which shows the extraction process of the Doppler signal with a comparatively wide spectrum.

  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 FM modulator 20 outputs an FM continuous wave to the transmission beam former 14. The FM modulator 20 generates an FM continuous wave by performing frequency modulation on the RF wave (carrier wave signal) supplied from the RF wave oscillator 22 using the modulation signal supplied from the modulation wave generating unit 24. To do. 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 FM modulator 20. That is, the FM continuous wave output from the FM modulator 20 is subjected to delay processing in the delay circuit 25, and the FM continuous wave subjected to delay processing is directly supplied to the mixer 32, while the FM continuous wave subjected to delay processing is supplied to the mixer 34. A 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.

  The FFT processing unit (fast Fourier transform processing unit) 42 performs an FFT operation on each demodulated signal (in-phase signal component and quadrature signal component). As a result, the FFT processing unit 42 converts the demodulated signal into a frequency spectrum. The frequency spectrum output from the FFT processing unit 42 is output as frequency spectrum data having a frequency resolution δf depending on circuit setting conditions and the like.

  The Doppler information extraction unit 44 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 extraction unit 44 selectively extracts a Doppler signal from the target position. For example, the Doppler information extraction unit 44 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 46 displays the waveform of the Doppler signal formed in the Doppler information extraction unit 44. Each unit in the ultrasonic diagnostic apparatus shown in FIG. 1 is controlled by the system control unit 50. That is, the system control unit 50 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. Therefore, the principle of selectively extracting Doppler information from the target position will be described in detail. 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 the following expression, 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 index (modulation depth) It is.

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. In the following equation, the Doppler shift with respect to f _m is neglected because it is smaller than the shift amount f _d of f ₀ .

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, the FM continuous wave output from the FM modulator 20 is used as a reference signal, delayed in the delay circuit 25, and the FM continuous wave subjected to delay processing is directly input to the mixer 32. The FM continuous wave subjected to delay processing is supplied to the mixer 34 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 as follows.

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, using the formula of Formula 5 regarding the Bessel function, Formula 4 is further calculated as Formula 6.

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 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 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.

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 a Bessel function, only the value of the 0th-order Bessel function is 1 and the values of the other Bessel functions are 0 due to the nature of the first-order Bessel function. When the result shown in Equation 10 is applied to Equation 8 and Equation 9, Equation 11 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 received waveform of Equation 2 described above is a waveform of a received signal from a certain depth. On the other hand, the reception signal actually obtained by the receiving vibrator 12 using the FMCW transmission wave is a reception signal obtained by combining signals from a plurality of depths. In the reception mixer 30, a process corresponding to multiplication of a reception signal obtained by combining signals from a plurality of depths and a reference signal is executed.

J ₀ (kβ) that dominates the amplitude of the Doppler signal corresponding to the DC signal component appearing in Equation 8 or the like is 1 which is the maximum value when kβ is 0, due to the nature of the first-order Bessel function. When the value deviates from 0, it rapidly decreases. Therefore, when φ _mr is adjusted in the delay circuit 25 so as to coincide with φ _{m of the} received signal obtained from the target position, J ₀ (kβ) at the target position becomes 1, which is the maximum value, and J ₀ (J ₀ ( kβ) is an extremely small value. Therefore, the Doppler signal (DC signal component) at the target position can be selectively extracted by adjusting φ _mr in the delay circuit 25 and matching it with φ _{m of the} received signal obtained from the target position.

  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 50 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, a required Doppler signal is extracted from a demodulated signal including an unwanted wave component accompanying the influence of frequency modulation. Therefore, unnecessary wave components accompanying frequency modulation and required Doppler signal extraction 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. In the ultrasonic diagnostic apparatus of FIG. 1, FM continuous waves are used, and the frequency (instantaneous frequency) of the FM continuous waves periodically changes as shown in Equation 1. 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. 2 is a diagram for explaining the influence of the periodicity of the FM continuous wave on the Doppler frequency. FIG. 2 shows an FM continuous wave 70 not affected by the Doppler shift and an FM continuous wave 72 affected by the Doppler shift. 2 is the time axis, and the vertical axis in FIG. 2 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. Become.

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 equation (13) as a speed 2v in a reciprocating manner. Furthermore, when the Doppler frequency change expressed by Equation 13 is converted into an instantaneous phase, Equation 14 is obtained.

The instantaneous phase expressed by Equation 14 is the Doppler shift caused by the modulated wave expressed by the second term in addition to the Doppler shift caused by the carrier wave f ₀ expressed by the first term with respect to the instantaneous phase of the received wave from the moving body. 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 Expression 16, the output of the reception mixer 30 (for example, the output of the LPF 36) can be expressed as Expression 17. Further, when the calculation is further advanced with respect to the result of Expression 17, Expression 18 is obtained.

The number 18 formula, the Doppler signal, which means that equal to the frequency-modulated signal by the newly defined modulation β'(see number 17 formula) modulation frequency f _m.

  FIG. 3 is a diagram for explaining a Doppler signal affected by frequency modulation. FIG. 3 shows a frequency spectrum of the Doppler signal corresponding to Equation 18. In FIG. 3, the horizontal axis represents frequency and the vertical axis represents power.

Figure 3 and as shown in Equation 18 Equation, 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. 4 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. 4 shows time-varying waveforms for the direct current 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. 4 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. That is, the primary component (−1st order component), the secondary component, the tertiary component,..., Which are aliasing components, are used as unnecessary wave components, and are required from the demodulated signals including these unnecessary wave components. Doppler signal is extracted.

<About required Doppler signal extraction>
FIG. 5 is a diagram illustrating extraction processing of a Doppler signal having a relatively narrow spectrum. The waveform shown in FIG. 5 is the frequency spectrum of the demodulated signal obtained by the FFT processing unit 42, and is the frequency spectrum when the spectrum of the Doppler signal (band of the Doppler signal) is relatively narrow.

  The Doppler information extraction unit 44 specifies the maximum spectrum that maximizes the signal strength (for example, power and amplitude) from the frequency spectrum of the demodulated signal, and the signal component including the maximum spectrum from the demodulated signal is the Doppler signal. Extract as For example, in the example of FIG. 5, P0 having the maximum spectrum power is set as the maximum spectrum from the frequency spectrum, and a signal component including this P0 is extracted as a Doppler signal.

In the extraction of the Doppler signal, the Doppler information extraction unit 44 divides into a plurality of frequency bands (blocks) the frequency spectrum of the demodulated signal for each modulation frequency f _m. For example, along the frequency axis in FIG. 5 (horizontal axis), 0 block 0 of ≦ f _{<f m,} the first block of _{f m} ≦ _f <2f _m, second block of 2f _m ≦ f <3f _m・ It is divided like

Then, the Doppler information extraction unit 44 specifies a peak having the maximum spectrum power in each band for each block, and sets a maximum spectrum as a maximum spectrum among a plurality of peaks related to a plurality of blocks. For example, in the example of FIG. 5, the peak P0 is identified in the 0th block of 0 ≦ f _{<f m,} a peak P1 is identified in the first block of _{f m ≦ f <2f m,} -f m ≦ f A peak P1 'is specified in the <0'th 1' block, and the peak P0 having the maximum power among these peaks is set as the maximum spectrum.

  Further, the Doppler information extraction unit 44 sets the intensity of the second largest peak after the maximum spectrum among the plurality of peaks as a threshold for extracting the Doppler signal. For example, in the example of FIG. 5, the power value of the next largest peak P1 or peak P1 ′ after the peak P0 is set as the threshold value.

  In this way, the Doppler information extraction unit 44 extracts a signal component having an intensity exceeding the threshold from the frequency spectrum of the demodulated signal as a Doppler signal. For example, in the example of FIG. 5, a spectrum portion whose power is greater than or equal to the threshold corresponding to the peak P1 or peak P1 ′ is extracted as a Doppler signal.

  FIG. 6 is a diagram illustrating extraction processing of a Doppler signal having a relatively wide spectrum. The waveform shown in FIG. 6 is the frequency spectrum of the demodulated signal obtained in the FFT processing unit 42, and is the frequency spectrum when the spectrum of the Doppler signal (band of the Doppler signal) is relatively wide.

  As shown in FIG. 6, when the spectrum of the Doppler signal is relatively wide, a required Doppler signal, that is, a zero-order component signal and a signal such as a primary component that is an unnecessary wave component overlap. The frequency spectrum SP of the demodulated signal has a waveform indicated by a solid line. Even in this case, the Doppler signal is extracted by the processing described with reference to FIG.

  In other words, the Doppler information extraction unit 44 specifies the maximum spectrum that maximizes the signal strength (for example, power and amplitude) from the waveform of the frequency spectrum SP indicated by the solid line in FIG. Is extracted as a Doppler signal. For example, in the example of FIG. 6, P1 in which the power of the spectrum is maximum is set as the maximum spectrum from the frequency spectrum, and a signal component including this P1 is extracted as a Doppler signal.

In the extraction of the Doppler signal, the Doppler information extraction unit 44 divides into a plurality of frequency bands (blocks) the frequency spectrum of the demodulated signal for each modulation frequency f _m. Then, the Doppler information extraction unit 44 specifies a peak having the maximum spectrum power in each band for each block, and sets a maximum spectrum as a maximum spectrum among a plurality of peaks related to a plurality of blocks. For example, in the example of FIG. 6, the peak P0 is identified in the 0th block of 0 ≦ f _{<f m,} a peak P1 is identified in the first block of _{f m ≦ f <2f m,} 2f m ≦ f < identified peak P2 in the second block of 3f _m, power from these peaks peak P1 is the largest is the maximum spectrum.

  Further, the Doppler information extraction unit 44 sets the intensity of the second largest peak after the maximum spectrum among the plurality of peaks as a threshold for extracting the Doppler signal. For example, in the example of FIG. 6, the power value of the peak P0 that is the second largest after the peak P1 is set as the threshold value.

  In this way, the Doppler information extraction unit 44 extracts a signal component having an intensity exceeding the threshold from the frequency spectrum of the demodulated signal as a Doppler signal. For example, in the example of FIG. 6, a spectrum portion whose power is greater than or equal to the threshold value of the peak P0 is extracted as a Doppler signal.

Incidentally, the Doppler information extraction unit 44, the intensity of the spectrum separated by the modulation frequency f _m from the maximum spectrum may be a threshold. For example, peak P1 shown in FIG. 6, the spectrum of power at frequencies spaced apart by -f _m or + f _m along the frequency axis direction may be a threshold. In addition, based on the measurement results already obtained, a power difference between the maximum spectrum and the unwanted wave component may be set in advance, and the power that is reduced by the power difference from the power of the maximum spectrum may be used as a threshold value. .

  When the Doppler signal is extracted, the Doppler information extraction unit 44 forms a display waveform showing the time change of the frequency spectrum shown in FIG. 5 or FIG. 6, for example. That is, a display waveform similar to the time change waveform shown in FIG. 4 is formed.

  However, for example, in the example shown in FIG. 5 or FIG. 6, if the power difference between the Doppler signal and the unnecessary wave component is small, the required Doppler signal (DC component) and the unnecessary wave are included in the time-varying waveform shown in FIG. There may be a case where it is not easy to distinguish components (−1st order component, 1st order component, 2nd order component). Also, for example, as in the example shown in FIG. 6, even when the spectrum of the Doppler signal is relatively wide, it may not be easy to distinguish between the required Doppler signal and the unnecessary wave component.

  Therefore, the Doppler information extraction unit 44 performs visual identification processing such as coloring processing on the Doppler signal extracted by the processing described with reference to FIG. 5 or FIG. A display waveform similar to the change waveform is formed. Thereby, for example, in the time-varying waveform shown in FIG. 4, only the required Doppler signal (DC component) is colored, so that the required Doppler signal can be easily discriminated visually. . Note that visual identification processing may be performed only on the portion of the maximum spectrum described with reference to FIG. 5 or FIG. Further, instead of the coloring process or together with the coloring process, a visual identification process based on a difference in luminance, line type, or the like may be performed. Furthermore, only the required Doppler signal may be displayed in the time-varying waveform shown in FIG.

  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.

  20 FM modulator, 22 RF wave oscillator, 24 modulated wave generator, 25 delay circuit, 30 reception mixer, 42 FFT processor, 44 Doppler information extractor.

Claims (6)

A transmission signal processing unit that outputs a continuous wave transmission signal whose frequency is periodically changed according to the modulation frequency;
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 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;
A Doppler information extraction unit that identifies a maximum spectrum in which the signal intensity is maximum from the frequency spectrum of the demodulated signal, and extracts a signal component including the maximum spectrum from the demodulated signal as a Doppler signal;
Having
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The Doppler information extraction unit divides the frequency spectrum of the demodulated signal into a plurality of frequency bands for each modulation frequency, identifies the peak spectrum where the signal intensity is maximum for each frequency band, and supports a plurality of frequency bands Among the plurality of peak spectra, the one having the maximum intensity is the maximum spectrum.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The Doppler information extraction unit sets a threshold relating to the intensity of the signal based on the frequency spectrum of the demodulated signal, and extracts a signal component having an intensity exceeding the threshold from the demodulated signal as the Doppler signal.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
The Doppler information extraction unit uses, as the threshold value, the intensity of a peak spectrum next to the maximum spectrum among a plurality of peak spectra corresponding to a plurality of frequency bands.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
The Doppler information extraction unit uses the intensity of the spectrum separated from the maximum spectrum by the modulation frequency as the threshold.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5,
A display unit for displaying a Doppler waveform obtained by performing visual identification processing on the extracted Doppler signal;
An ultrasonic diagnostic apparatus.

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