JP4688466B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to a transmission / reception technique in a continuous wave (CW) Doppler method.

  In the ultrasonic diagnostic apparatus, in the continuous wave Doppler mode, a transmission wave configured as a sine wave of several MHz is continuously radiated into the living body, and a reflected wave from the living body is continuously received. The reflected wave includes Doppler shift information due to a moving body (for example, blood flow) in the living body. Therefore, a Doppler waveform can be obtained by extracting the information and performing frequency analysis. The reflected wave includes information (clutter) from a strong reflector (mainly a stationary body) in the living body. Although it is desired to suppress the clutter as much as possible and extract only Doppler information, there is a problem that the clutter cannot be sufficiently removed particularly in a low-speed observation area.

JP-A-3-48789

  As described above, when observing Doppler information, clutter is an obstacle, and it is desired to suppress it as much as possible.

  In Patent Document 1, a frequency-modulated sawtooth continuous wave is transmitted into a living body, and a beat signal is generated from a reception signal obtained by receiving a reflected wave and a modulated transmission wave. Has been disclosed. However, the device described in this document does not focus on the harmonic band of the modulated wave.

  An object of the present invention is to enable observation of Doppler information with high sensitivity while suppressing clutter as much as possible when applying the continuous wave Doppler method.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes a transmitter that generates a modulated transmission signal by modulating a carrier wave signal using a modulated wave signal, and the modulated transmission. A transmitter / receiver for transmitting an ultrasonic wave to a living body by supplying a signal, receiving a reflected wave from the living body and outputting a received signal; and demodulating the received signal using the modulated transmission signal; And a demodulating means for obtaining a demodulated signal from the demodulated signal and at least one of a fundamental wave component and an nth (n is a natural number of 2 or more) harmonic component when the modulated wave signal is a fundamental wave. And Doppler information extraction means for extracting Doppler information existing in the vicinity.

  In the above configuration, the modulated transmission signal is generated by modulating the carrier wave signal using the modulated wave signal, and the received signal is demodulated using the modulated transmission signal. For this reason, in the case of an unmodulated carrier signal, an echo (clutter) from a fixed object to be removed that was localized in the vicinity of the frequency of the carrier signal is a fundamental wave component and a harmonic when the modulated wave signal is a fundamental wave. Dispersed into wave components. As a result of the dispersion, the clutter in the vicinity of the fundamental wave component and each harmonic component becomes tens of dB smaller than the clutter in the case of no modulation. In the above configuration, Doppler information in the vicinity of at least one of the fundamental wave component and each harmonic component is extracted, so the influence of clutter localized in the case of no modulation is reduced (not affected at all). Is more desirable). As a result, according to the above configuration, Doppler information can be observed with high sensitivity while suppressing clutter as much as possible.

  Preferably, the demodulation means includes a detection circuit for detecting the received signal using the modulated transmission signal as a reference signal. Note that a quadrature detection circuit that performs quadrature detection processing on the received signal may be used as the detection circuit. Preferably, the Doppler information extraction unit includes a filter unit that extracts a sideband composed of the at least one component and a Doppler signal existing in the vicinity thereof. More preferably, the Doppler information extraction unit includes a Doppler signal extraction unit that extracts the Doppler signal from the sideband. More preferably, the Doppler signal extraction unit includes a detection circuit that detects the sideband wave using at least one of signals obtained by multiplying the frequency of the modulated wave signal by N (N is a natural number) as a reference signal. It is characterized by that.

  Preferably, it includes a delay circuit that performs a delay process on the modulated wave transmission signal applied to the demodulation means. According to this configuration, for example, the ratio of Doppler signal / clutter power can be calculated for each delay time by adjusting the delay time, and the ratio of Doppler power can be adjusted to be as large as possible. Desirably, a delay circuit for delaying the received signal output to the demodulator is included.

  Preferably, it includes a delay circuit that performs a delay process on a reference signal supplied to the Doppler signal extraction unit. Preferably, a delay circuit that performs a delay process on the sideband output to the Doppler signal extraction unit is included.

  Preferably, the Doppler information extraction unit extracts a Doppler signal from each of a plurality of components of a fundamental wave component and an nth (n is a natural number of 2 or more) harmonic component when the modulated wave signal is a fundamental wave. And adding a plurality of extracted Doppler signals. Preferably, the modulated wave signal is a sine wave, a triangular wave, or a sawtooth wave.

To achieve the above object, an ultrasonic diagnostic apparatus which is another preferred embodiment of the present invention, by performing frequency modulation processing by using the modulated wave signal of the frequency f _m of the carrier signal of a frequency f _0, modulation transmission A transmitter that generates a signal, a transmitter / receiver that transmits ultrasonic waves to the living body by supplying the modulated transmission signal, receives a reflected wave from the living body, and outputs a received signal; and On the other hand, a quadrature detection process is performed using the modulated transmission signal as a reference signal, thereby obtaining a demodulated signal, and the fundamental wave component and the nth ( n is a natural number of 2 or more) a bandpass filter for extracting a sideband consisting of at least one of the harmonic components and a Doppler signal present in the vicinity thereof, and a Doppler signal for extracting the Doppler signal from the sideband. It has a plastic signal extraction part and a Doppler information acquisition part which acquires Doppler information about a moving body from the Doppler signal.

Preferably, as the modulation wave signal, a multiplex modulation wave signal obtained by further frequency-modulating the modulation wave signal having the frequency f _{m1 using} the modulation wave signal having the frequency f _m2 is used. By performing frequency modulation in multiple stages, the influence of clutter can be reduced and a Doppler signal can be extracted in a lower speed region.

In order to achieve the above object, an ultrasonic diagnostic apparatus which is another preferred embodiment of the present invention, by performing frequency modulation processing by using the modulated wave signal of the frequency f _m of the carrier signal of a frequency f _0, A transmitter for generating a modulated transmission signal; a transducer for transmitting an ultrasonic wave to a living body by supplying the modulated transmission signal; receiving a reflected wave from the living body; and outputting a received signal; The signal is subjected to quadrature detection processing using the modulated transmission signal as a reference signal, thereby obtaining an in-phase component demodulated signal and a quadrature component demodulated signal, and each of the in-phase component demodulated signal and the quadrature component demodulated signal, A sideband consisting of at least one of a fundamental wave component and an nth (n is a natural number of 2 or more) harmonic component and a Doppler signal present in the vicinity thereof when the modulated wave signal is a fundamental wave. A Doppler signal extraction unit for extracting the Doppler signal from the sideband wave of the in-phase component demodulated signal and the sideband wave of the quadrature component demodulated signal, and the Doppler signal from the Doppler signal. A Doppler information acquisition unit for acquiring, wherein the Doppler signal extraction unit is configured to demodulate the in-phase component using at least one of signals obtained by multiplying the frequency of the modulated wave signal by N times (N is a natural number) as a reference signal. An in-phase component detection circuit for performing quadrature detection processing on the sideband wave extracted from the signal and a quadrature component detection circuit for performing quadrature detection processing on the sideband wave extracted from the quadrature component demodulation signal are included.

  Preferably, the Doppler signal extraction unit applies the Doppler signal in-phase component obtained as the square root of the sum of squares of the two signals output from the in-phase component detection circuit and the two signals output from the quadrature component detection circuit. Two Doppler signal components of the Doppler signal orthogonal component obtained as the square root of the sum of squares are extracted.

  According to the present invention, when applying the continuous wave Doppler method, Doppler information can be observed with high sensitivity while suppressing clutter as much as possible.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof. 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 transmission control unit 14 controls the transmission transducer 10 to perform ultrasonic transmission control. An FM continuous wave (FMCW wave) that has been subjected to FM modulation processing is input to the transmission control unit 14, and a transmission wave corresponding to the FM continuous wave is transmitted from the transmission transducer 10. The FM modulator 20 outputs an FM continuous wave to the transmission control unit 14. The FM modulator 20 generates an FM continuous wave based on the RF wave supplied from the RF wave oscillator 22 and the modulated wave supplied from the FM modulated wave oscillator 24. The waveform of this FM continuous wave will be described in detail later in the explanation of the principle.

  The reception control unit 16 performs reception processing such as amplification processing on the reception signal supplied from the reception transducer 12, forms a reception RF signal, and outputs the reception RF signal to the reception mixer 30. The reception mixer 30 is a circuit that performs quadrature detection on the received RF signal to generate a complex signal, and includes 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 output from the FM modulator 20. That is, the FM continuous wave output from the FM modulator 20 is directly supplied to the mixer 32, while the FM continuous wave is supplied to the mixer 34 via the π / 2 shift circuit 26. The π / 2 shift circuit 26 is a circuit that shifts the phase of the FM continuous wave by π / 2.

As will be described in detail later in the explanation of the principle, the received mixer output signal, which is the result of the mixing process of the received RF signal and the reference signal executed by each mixer, is used to modulate the modulated wave supplied from the FM modulated wave oscillator 24. It contains the fundamental wave component and the harmonic component relating wave frequency f _m. A desired frequency component is extracted from these fundamental wave components and each harmonic component by BPFs (band pass filters) 36 and 38 provided at the subsequent stage of the receiving mixer 30, and the inputs of the two mixers 28 and 29. Become. In the mixers 28 and 29, the fundamental wave component or harmonic component of the modulated wave f _m obtained by multiplying the fundamental wave f _m by N times the N frequency circuit 25 (N is a natural number) is used as a reference signal. The input is quadrature detected and converted to a baseband signal. The two signals converted into the baseband signals are output to the Doppler arithmetic processing unit 40 via the LPFs 37 and 39. As a result, the influence of clutter is reduced in the FM continuous wave (FMCW) of the present embodiment compared to the normal continuous wave CW.

  The Doppler computation processing unit 40 performs Doppler computation based on the signals extracted by the LPFs 37 and 39. That is, the Doppler signal is extracted from the output signals of the LPFs 37 and 39 and, for example, the blood flow velocity is calculated. Of course, it is possible to calculate the speed of a measurement target other than the blood flow. The display processing unit 42 forms, for example, a Doppler waveform based on the speed calculation result, and displays the formed Doppler waveform on the display unit 44.

  As described above, in this embodiment, a Doppler signal generated in the vicinity of a fundamental wave or a harmonic wave of a modulated wave by transmitting and receiving an ultrasonic wave (FMCW wave) obtained by FM-modulating a continuous wave (CW) with a sine wave. By measuring the frequency, the influence of clutter can be reduced. Then, the principle is explained in full detail next.

数１において、Δｆは周波数変動幅の０−Ｐ値（ゼロピーク値）である。また、ドプラシ
フトを伴わない場合のＦＭＣＷ受信波は生体による減衰を無視すると次式で表現できる。

ＦＭＣＷ送信波の周波数スペクトラムは、数１を展開することで得られる。数１に示すＦＭＣＷ送信波は次式のように展開できる。

数３において、J₀（β），J_2n（β），J_2n+1（β）は、第1種ベッセル関数である。各項の振幅は、変調指数βおよびそれに対応するベッセル関数によって決定される。ちなみに、数３に示されるＦＭＣＷ送信波の周波数スペクトルを図示すると図２のようになる。 An FMCW transmission wave obtained by subjecting CW of frequency f ₀ to FM modulation of modulation frequency f _m can be expressed as the following equation.

In Equation 1, Δf is a 0-P value (zero peak value) of the frequency fluctuation range. In addition, the FMCW received wave without Doppler shift can be expressed by the following equation if attenuation by the living body is ignored.

The frequency spectrum of the FMCW transmission wave can be obtained by expanding Equation 1. The FMCW transmission wave shown in Equation 1 can be developed as follows.

In Equation 3, J ₀ (β), J _2n (β), and J _{2n + 1} (β) are Bessel functions of the first kind. The amplitude of each term is determined by the modulation index β and the corresponding Bessel function. Incidentally, the frequency spectrum of the FMCW transmission wave expressed by Equation 3 is illustrated in FIG.

数４に示されるように、受信波の周波数スペクトラムは送信波と同じ周波数成分を持っている。しかし受信波の各周波数成分の振幅は、位相差φ₀とφ_mに応じて変化している。 Further, the frequency spectrum of the received wave v _R (t) without Doppler shift can be obtained by developing Equation 2. The FMCW received wave shown in Equation 2 can be developed as follows.

As shown in Equation 4, the frequency spectrum of the received wave has the same frequency component as the transmitted wave. However, the amplitude of each frequency component of the received wave changes according to the phase differences φ ₀ and φ _m .

なお、数５においてｆ_mに対するドプラシフトは、ｆ₀のシフト分ｆ_dに比較して小さいので無視している。ちなみに、数５に示されるＦＭＣＷ受信波の周波数スペクトルを図示すると図３のようになる。図３において、数５に示されるＦＭＣＷ受信波の周波数スペクトルは破線で示されている。実線で示されるスペクトルはドプラシフトを伴わない場合のＦＭＣＷ受信波の周波数スペクトルを示している。 Furthermore, when accompanied by Doppler shift, v _R (t) in Equation 2 is rewritten as follows.

In Formula 5, the Doppler shift with respect to f _m is neglected because it is smaller than the shift amount f _d of f ₀ . Incidentally, the frequency spectrum of the received FMCW wave shown in Equation 5 is shown in FIG. In FIG. 3, the frequency spectrum of the FMCW received wave shown in Equation 5 is indicated by a broken line. The spectrum indicated by the solid line indicates the frequency spectrum of the FMCW received wave without Doppler shift.

ここで、ベッセル関数に関する次の公式を利用する。

数７の公式を用いると、数６はさらに次式のように計算される。なお、数８では数６における係数１／２を省略する。

数８で表現される受信ミキサ出力の周波数スペクトルを図示すると図４のようになる。図４において線スペクトルで示されるドプラエコー４６がドプラ信号に相当する。つまり、ドプラシフトを伴う場合、受信ミキサ出力の基本波および各高調波成分は、ＦＭ変調周波数が抑圧されたＤＳＢ−ＳＣ（Double Sideband−Suppressed Carrier）のスペクトルの形をしている。つまり、ドプラエコーには、ＦＭ変調周波数（ｆ_m）およびその高調波成分（２ｆ_m，３ｆ_m，・・・）のスペクトラムは存在しない。なお、図４においてＦＭ変調周波数およびその高調波成分に存在する固定物エコー４８のスペクトルについては次のように表現できる。 The reception waveform represented by the above-described formulas 2 and 5 is a signal waveform (received RF signal) received by the ultrasonic transducer. The ultrasonic diagnostic apparatus performs demodulation processing on the received RF signal. When demodulating an FMCW received RF signal, the demodulation system performs multiplication with the received wave using an FMCW wave as a reference signal. The reception mixer output in the demodulation system is calculated by the following equation as a result of multiplying v _T (t) and v _R (t).

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

If the formula of Formula 7 is used, Formula 6 is further calculated as follows: In Equation 8, the coefficient 1/2 in Equation 6 is omitted.

The frequency spectrum of the reception mixer output expressed by Equation 8 is as shown in FIG. A Doppler echo 46 indicated by a line spectrum in FIG. 4 corresponds to a Doppler signal. That is, when Doppler shift is involved, the fundamental wave and each harmonic component of the reception mixer output are in the form of a DSB-SC (Double Sideband-Suppressed Carrier) spectrum in which the FM modulation frequency is suppressed. That is, the spectrum of the FM modulation frequency (f _m ) and its harmonic components (2f _m , 3f _m ,...) Does not exist in the Doppler echo. In FIG. 4, the spectrum of the fixed object echo 48 existing in the FM modulation frequency and its harmonic component can be expressed as follows.

数９に示すように、固定目標からのエコー（クラッタ）は変調周波数ｆ_mの整数倍のところにスペクトラムを生じる。つまり、図４に示した周波数スペクトルにおいて、ＦＭ変調周波数およびその高調波成分に固定物エコー４８のスペクトラムが発生する。 The reception mixer output without Doppler shift can be obtained as follows by setting f _d = 0 for v _D (t) shown in Equation 8. The target in this case is assumed to be a fixed target at the same position as the moving body and having the same reflectance.

As shown in Formula 9, echoes from stationary targets (clutter) produces a spectrum at an integral multiple of the modulation frequency f _m. That is, in the frequency spectrum shown in FIG. 4, the spectrum of the fixed object echo 48 is generated at the FM modulation frequency and its harmonic component.

  The clutter power and the Doppler signal power will be described below using the above principle.

  First, regarding the received RF signal, the clutter power related to normal CW and FMCW is considered. FIG. 5 is a diagram showing the power spectrum of clutter in a normal CW in the received RF signal, and shows each clutter power 50 and its sum 52 according to the in-vivo depth. Since the clutter can be regarded as a collection of echoes from the fixed target, the total power spectrum 52 of the entire clutter has a form obtained by adding the echoes from the fixed target at each depth by the number of fixed targets. Depending on the in-vivo depth of the clutter power, the deeper the clutter power, the smaller the attenuation. The clutter power spectrum is statistically similar to echoes from fixed targets, so the sum of the clutter power spectrum is similar to the clutter from each fixed target.

On the other hand, FIG. 6 is a diagram showing the power spectrum of the clutter in the FMCW in the received RF signal, and shows each clutter power 60 according to the in-vivo depth and its sum 62 for each frequency. The FMCW clutter has the same total power, that is, the sum of the FMCW clutter sum for each frequency over all frequencies, but it is the same as the normal CW. Therefore, it is different from normal CW. That is, in the FMCW, according FM modulation degree is increased, the electric power were concentrated in f ₀ is the fundamental wave of _{f m (f 0 + f m} ) and harmonic _{(f 0 + 2f m, f} 0 + 3f m, f ₀ + 4f _m ,...). Even in FMCW, the clutter power attenuates as the depth increases, but this effect is the same in both normal CW and FMCW.

例えば、ｆ_mの基本波近傍に注目すると、ＦＭＣＷでは、通常のＣＷに比べ、クラッタ電力が７．０ｄＢ低減されている。但し、受信ＲＦ信号は復調処理が実行される前の何らの信号処理も施していない信号である。つまり、受信ＲＦ信号としては、ドプラ情報を必要とする目標からのエコーも、変調度βに応じてクラッタと同様の割合で電力が低減する。ゆえに、受信ＲＦ信号における目標からのエコーのクラッタに対する電力比は、ＦＭＣＷにおいても通常のＣＷと同じである。 In FMCW, (generally, it may be expressed as fundamental and harmonic components of sidebands) voltage of the fundamental wave and the harmonic component of f _m can be represented by a first-order Bessel function. The outline of the first-order Bessel function is shown in FIG. In FIG. 7, the value of β is shown on the horizontal axis, and the value of the Bessel function is shown on the vertical axis. Using this first-order Bessel function curve, that is, J ₀ (β) corresponding to the frequency f ₀ in FMCW, J ₁ (β) corresponding to the fundamental wave of f _m , and J corresponding to the second harmonic. ₂ (β), the value of J ₃ (β) corresponding to the third harmonic is used as the clutter voltage, and the clutter power ratio between normal CW and FMCW is estimated. Assuming that β = 1 as the degree of modulation, the following values are obtained from FIG.

For example, focusing on the fundamental wave near the f _m, the FMCW, compared to conventional CW, clutter power is reduced 7.0 dB. However, the received RF signal is a signal that has not been subjected to any signal processing before the demodulation processing is executed. That is, as the received RF signal, the power of the echo from the target that requires Doppler information is also reduced at the same rate as the clutter according to the modulation degree β. Therefore, the power ratio of the echo from the target to the clutter in the received RF signal is the same as the normal CW in the FMCW.

  Next, the clutter power for normal CW and FMCW is considered for the receiving mixer output. In normal CW, the signal is separated into IQ channels by a receiving mixer and signal processing is performed in the baseband. In this case, since the function of the mixer is a simple frequency shift, the level relationship between the Doppler signal and the clutter in the RF band is maintained as it is in the baseband band. Even when an FMCW wave is transmitted, if a CW signal is used for the reference of the receiving mixer, the level relationship between the Doppler signal and the clutter is maintained as it is in the baseband band. Therefore, the level relationship between the Doppler signal and the clutter is not improved. However, in the FMCW used in the present embodiment, an FMCW wave that is a transmission wave is used as a reference signal (reference) of the reception mixer (reference numeral 30 in FIG. 1). For this reason, the level ratio of the Doppler signal and the clutter can be improved. In this case, the Doppler signal level is affected by a modulation factor β and a parameter k that depends on the distance, as expressed by Equation (8). That is, the echo power increases or decreases depending on the distance. Clutter has the same effect. However, the difference from the case of the Doppler signal is that the clutter is distributed in the depth direction, so that all the distance dependency of the clutter at each location must be considered. This situation is analyzed quantitatively.

ここで、ｄは振動子から目標までの距離である。数１０に示される各パラメータを用いて、J₀（ｋβ）， J₁（ｋβ），J₂（ｋβ），J₃（ｋβ）をｄ＝３０ｃｍまで計算し、横軸を診断の深さ（生体内の深さ）ｄ、縦軸をベッセル関数値としてプロットすると図８のようになる。図８に示される物理的意味は以下のとおりである。 Prior to the analysis, the distance dependency of the Bessel function, which is a coefficient proportional to the amplitude of each component in Equation 8, is obtained. As a representative example, the following conditions are assumed.

Here, d is the distance from the transducer to the target. Using each parameter shown in Equation 10, J ₀ (kβ), J ₁ (kβ), J ₂ (kβ), and J ₃ (kβ) are calculated up to d = 30 cm, and the horizontal axis is the depth of diagnosis ( Plotting the in vivo depth (d) and the vertical axis as a Bessel function value is as shown in FIG. The physical meanings shown in FIG. 8 are as follows.

(1) Since the transmission FMCW wave is used as a reference wave at d = 0, all the harmonic components of the FMCW gather near the direct current (corresponding to f _{0 in the} RF band). In other words, the fundamental wave and the harmonic component of f _m does not appear. (2) as the value of d is gradually increased, Keibeta also increases, fundamental and harmonic components of f _m comes to appear. (3) Therefore, the power of the fundamental and harmonic components of f _m as echo mixer output of the deep is increased. In this example, it increases in the range of 0 to 15 cm, and conversely decreases in the echo at 15 to 30 cm. (4) kβ takes a value between 0 and ± 2 with a period of 30 cm. (5) Therefore, the kβ value of the Bessel function periodically reciprocates between 0 and ± 2. (6) Referring to the graph of FIG. 8, the order of the Bessel function dominant between 0 and 2 is only the 0th order, the 1st order, the 2nd order and the 3rd order. However, this effect tends to increase the dominant order as β increases. (7) Therefore, the harmonic component of the clutter in FMCW is sufficient if the third order is considered when β = 1, but if β is set to a larger value, there is an improvement effect even at the third or higher order.

8 corresponds to how varies with the fundamental wave and the voltage is the depth of the harmonic signal components of f _m in the receiving mixer output of FMCW system. That is, the amplitude of each clutter from the tissue distributed in the living body varies for each fundamental wave and harmonic signal component according to the position. FIG. 9 shows the state again for each frequency component.

  FIG. 9 is a diagram for explaining the depth dependency of the fundamental wave and the harmonic clutter voltage. FIG. 9 shows each clutter power 90 corresponding to the in-vivo depth and the total sum 92 for each frequency. It is shown. FIG. 9 shows the clutter power from each tissue when it is assumed that there is no attenuation in the living body. Since the mixer output is the sum of the clutter from each depth at each frequency, the power spectrum of the sum is different from that in the case of normal CW.

数１１において、０．６に掛けられた２は、生体内での超音波の往復を意味している。 From FIG. 8 and FIG. 9, when β = 1, the frequency band in which the clutter is dominant is DC, the fundamental wave (f _m ), the harmonic band of twice (2f _m ) and three times (3f _m ) thereof. I know that there is. However, the order becomes higher as β increases. FIG. 9 shows that the power of the clutter fluctuates periodically with respect to the apparent depth. These periodic fluctuations correspond to the behavior of the Bessel function shown in FIG. The actual echo is the sum of all echoes in the depth direction. Echoes from each tissue are subject to attenuation in the living body at the same time that they undergo amplitude fluctuations of the fundamental wave and harmonic signal components according to their positions. The attenuation characteristic in the living body shown in FIG. 9 expresses the attenuation characteristic in the living body qualitatively. The attenuation characteristic in the living body is given by the following equation when the depth of the tissue is d (cm).

In Equation 11, 2 multiplied by 0.6 means the reciprocation of the ultrasonic wave in the living body.

なお、表２では、各成分の相対電圧積分値をそれぞれ求め、相対電圧の合計が“１”となるように規格化した。 In FIG. 9, the attenuation characteristic of Formula 11 is also expressed. The attenuation characteristic (Attenuation) in FIG. 9 is obtained by plotting the calculation result when f ₀ = 3 MHz in Equation 11. The sum of clutter may be obtained by obtaining the attenuation characteristics and the components in the depth direction for each frequency component for each depth in FIG. That is, the actual mixer output is proportional to the value (voltage) obtained by multiplying the Bessel function value at each depth by the attenuation amount in FIG. In order to calculate the clutter power, all echoes from the depth direction may be added for each frequency. That is, the clutter power can be obtained by obtaining the area of the curve obtained by multiplying each Bessel function and the attenuation curve. However, it is assumed that fixed targets having the same reflection coefficient are uniformly distributed in the tissue. Table 2 shows the power results thus calculated.

In Table 2, the relative voltage integral value of each component was obtained and normalized so that the sum of the relative voltages was “1”.

表３では、いずれの方式でも、送信ＣＷ電力が一定であれば、クラッタ電力の総和は不変であるということを前提としている。この表のなかで、相対電力とは、通常のＣＷクラッタ電力の総和を０ｄＢとした場合の相対値である。例えば、ＦＭＣＷのｆ_o 成分が−１．９ｄＢということは、受信ＲＦ信号で、無変調の場合にくらべ、ＦＭ変調により、ｆ_o の成分の電力が１．９ｄＢだけ高調波に移動し、その分だけｆ_o の電力が減少しているということを意味している。 Here, the results shown in Table 1 for the received RF signal and Table 2 for the received mixer output are summarized in Table 3.

In Table 3, it is assumed that the sum of the clutter power remains unchanged if the transmission CW power is constant in any method. In this table, the relative power is a relative value when the sum of normal CW clutter power is 0 dB. For example, if the F _o component of FMCW is −1.9 dB, the power of the component of f _o is shifted to a harmonic by 1.9 dB by FM modulation compared to the case of no reception modulation in the received RF signal. This means that the power of f _o is reduced by the amount.

Table 3 shows the following. (1) There is no great difference in power between the component of f _o or the DC component, whether it is a received RF signal or a received mixer output. This is because the clutter DC component generated by multiplying the received RF signal by the reference signal having almost no time difference is dominant in the receiving mixer output. The clutter power from the deep part appears to increase the modulation degree, and the contribution of the DC component is not only reduced, but also the attenuation is large, so that the power is very small compared to the DC component. (2) clutter f _m fundamental component of the receiving mixer output is compared with the normal CW, 25.7DB (about 1/370) low. This is because the receiving mixer output by multiplying the reference signal, because the fundamental wave component and harmonic components of f _m is extremely suppressed. This suppression effect is more effective as the clutter is closer to the body surface. As the depth increases, this suppression effect decreases. That is, because of the time difference between the reference signal and the clutter, the fundamental wave component and harmonic components of f _m increases. However, the clutter from these deep regions is almost negligible because the attenuation term of Formula 11 becomes dominant. (3) Since the clutter components of the fundamental wave component and harmonic of f _m is tens dB compared to the clutter components of f _o is suppressed, by extracting the Doppler signal of the fundamental wave component or harmonic vicinity of f _m In this case, the clutter can be removed very easily.

深さによるｋβの影響は、図８における１５ｃｍでのＪ₁（ｋβ）の値として、０．５８と求めることができる。０．５８の意味は、ＦＭＣＷ方式において、受信ミキサのレファレンスとして送信ＦＭＣＷ波を用いると、通常のＣＷにくらべ、往復で信号が０．５８（電力比で、０．３４倍、−４．７ｄＢ）となるということである。信号レベルとして、第2高調波２ｆ_mの近傍のドプラ信号抽出を行う場合は、図８における１５ｃｍでのＪ₂（ｋβ）の値として、０．３７（電力比で、０．１３７倍、−８．６ｄＢ）を得ることができる。 Next, consider the Doppler signals for normal CW and FMCW for the receiving mixer output. As an example, an echo from a depth of 15 cm is assumed as the signal level. With respect to the normal CW clutter, as a signal level, it is assumed Doppler signal extracted in the vicinity of the fundamental wave f _m. According to Equation 8, the fundamental wave signal is expressed by the following equation.

The influence of kβ due to the depth can be obtained as 0.58 as the value of J ₁ (kβ) at 15 cm in FIG. The meaning of 0.58 means that when a transmission FMCW wave is used as a reference of the reception mixer in the FMCW system, the signal is 0.58 (round and round by power ratio, 0.34 times, -4.7 dB) compared to normal CW. ). As a signal level, when performing Doppler signal extraction in the vicinity of the second harmonic 2f _m is the value of J ₂ (kβ) at 15cm in FIG 8, 0.37 (power ratio, 0.137 times, - 8.6 dB) can be obtained.

表４において、相対電圧は図８における１５ｃｍでの各ベッセル関数の値であり、相対電圧の２乗として相対電力が示されている。 On the other hand, a Doppler signal in a normal CW has no distance dependency associated with FM modulation like FMCW. Therefore, assuming that attenuation by the living body is common, the FMCW Doppler signal is 4.7 dB lower for the fundamental wave and 8.6 dB lower for the second harmonic wave than the normal CW. The results are summarized together with the Doppler signal power in the vicinity of the direct current and the third harmonic 3f _m is as in Table 4.

In Table 4, the relative voltage is the value of each Bessel function at 15 cm in FIG. 8, and the relative power is shown as the square of the relative voltage.

表５では、通常のＣＷドプラ信号電力のクラッタ電力に対する比をαｄＢとした。また、クラッタは生体内のすべてのエコーからの総電力和、ドプラ信号は深さ１５ｃｍにおける移動目標からの信号を想定した。さらに、表５に示されるドプラ信号電力とクラッタ電力との電力比関係を図１０に示す。図１０は、通常のＣＷとＦＭＣＷのそれぞれについて、横軸を周波数、縦軸を電力値としてドプラ信号電力１００とクラッタ電力１０２のそれぞれの波形が示されている。 Table 5 shows a further summary of Table 2 showing the result of the clutter power of the reception mixer output and Table 4 showing the result of the Doppler signal power of the reception mixer output.

In Table 5, the ratio of normal CW Doppler signal power to clutter power is α dB. The clutter was assumed to be the sum of the total power from all echoes in the living body, and the Doppler signal was assumed to be a signal from a moving target at a depth of 15 cm. Furthermore, the power ratio relationship between the Doppler signal power and the clutter power shown in Table 5 is shown in FIG. FIG. 10 shows the respective waveforms of the Doppler signal power 100 and the clutter power 102 for normal CW and FMCW, with the horizontal axis representing the frequency and the vertical axis representing the power value.

  From Table 5 and FIG. 10, it can be seen that the FMCW can suppress the clutter as follows when the depth is 15 cm and β = 1 as compared with the normal CW. (1) When extracting the Doppler near the fundamental wave: 21.0 dB (about 1/126), (2) When extracting the Doppler near the second harmonic: 30.8 dB (about 1/1200), (3 ) When extracting Doppler in the vicinity of the third harmonic: 45.6 dB (about 1/36000). As described above, by using the FMCW wave, that is, by the ultrasonic diagnostic apparatus shown in FIG. 1, the influence of clutter can be reduced as compared with normal CW.

  FIG. 11 shows an ultrasonic diagnostic apparatus in which the influence of clutter is further reduced by improving the ultrasonic diagnostic apparatus shown in FIG. The difference from FIG. 1 is that in the ultrasound diagnostic apparatus shown in FIG. 11, the variable delay circuit 110 adjusts the delay time of the transmission FMCW modulated wave used as the reference wave to optimize the Doppler signal power / clutter power. Is to do.

  Depending on the depth in the living body, the relationship between the relative magnitudes of the accumulated clutter power and Doppler signal power at the output of the receiving mixer differs. Table 5 shows the results of calculation assuming that the depth in the living body is 15 cm, but the ratio of Doppler signal to clutter power varies depending on the depth. Since the diagnostic depth is determined according to the position of the target, it cannot be easily changed. However, by adjusting the reference wave supplied to the receiving mixer by providing a delay time, it becomes possible to change the position of the target, that is, the diagnostic depth in a pseudo manner. Therefore, in the ultrasonic diagnostic apparatus shown in FIG. 11, the variable delay circuit 110 is provided in the preceding stage of the reception mixer so that the delay time of the reference wave can be adjusted. As a result, it is possible to adjust the delay time, calculate the ratio of Doppler signal power / clutter power for each delay time, and adjust the Doppler signal power ratio to be as large as possible. On the other hand, by changing the modulation frequency and the amplitude of the modulation wave (by changing β), it is possible to improve the relative ratio of the accumulated clutter power and the Doppler signal power at the output of the receiving mixer according to the depth in the living body.

  The delay time may be adjusted with respect to the reception RF signal supplied to the reception mixer 30. That is, by providing a variable delay circuit in the subsequent stage of the reception control unit 16 and adjusting the delay time of the reception RF signal supplied to the reception mixer 30, the same effect as the delay time adjustment of the reference wave can be obtained. .

  FIG. 12 shows an ultrasonic diagnostic apparatus in which the ultrasonic diagnostic apparatus shown in FIG. 11 is further improved. The difference from FIG. 11 is that the variable delay circuit 112 is provided in the subsequent stage of the N-times circuit 25 in the ultrasonic diagnostic apparatus shown in FIG.

したがって、ミキサ２８の参照信号としては、ｃｏｓ（２πｆ_mｔ＋φ_m／２）を用いるのがＳＮＲ（信号対ノイズ比）の良い乗算結果となる。このため、可変遅延回路１１２は、Ｎ倍回路２５から出力される参照信号の位相を調整してミキサ２８にｃｏｓ（２πｆ_mｔ＋φ_m／２）の参照信号を供給する。この結果、ＳＮＲの良い乗算結果を得ることができる。 The mixer 28 and 29, the fundamental wave f _m as N times (N is a natural number) the reference signal fundamental wave component or a harmonic component of the modulation wave f _m obtained by N times circuit 25, is output from the BPF36,38 Each signal is orthogonally detected and converted to a baseband signal. The receiving mixer output signal output from the receiving mixer 30 includes a fundamental wave component and the harmonic component about the modulation wave frequency f _m of the modulation wave supplied from the FM modulation wave oscillator 24. An example of the reception mixer output signal is expressed by the mathematical formula 8 described above. The BPFs 36 and 38 extract a desired frequency component from the fundamental wave component and the harmonic components related to f _m shown in Equation 8 and output them to the two mixers 28 and 29. For example, the BPF 36, when the fundamental wave component relating f _m as shown in Equation 8 is extracted, the signal supplied from the BPF 36 to the mixer 28 is expressed by the following equation.

Therefore, using cos (2πf _m t + φ _m / 2) as a reference signal for the mixer 28 is a multiplication result with a good SNR (signal to noise ratio). Therefore, the variable delay circuit 112 adjusts the phase of the reference signal output from the N-times circuit 25 and supplies the reference signal of cos (2πf _m t + φ _m / 2) to the mixer 28. As a result, a multiplication result having a good SNR can be obtained.

  The delay time may be adjusted for the outputs of the BPFs 36 and 38. In other words, by providing a variable delay circuit in the subsequent stage of each of the BPFs 36 and 38 and adjusting the delay time of the signals supplied to the mixers 28 and 29, the same effect as that of adjusting the delay time of the reference signal can be obtained. Can do.

  Here, the adjustment of the delay time when detecting the Doppler signal will be considered.

The baseband signal demodulated to the low frequency band by the receiving mixer 30 (hereinafter referred to as “first mixer” as necessary) in FIG. 12 is mixed with the mixers 28 and 29 (hereinafter referred to as “second mixer” as necessary). Is converted into a Doppler signal in the vicinity of DC. As shown in FIG. 13, in the FMCW, the Doppler signal (Doppler echo 46) at the first mixer output is a solid object echo of the FM modulation frequency (f _m ) and its harmonic components (2f _m , 3f _m ,...). Since it appears in the form of DSB-SC (Double Sideband-Suppressed Carrier) in the vicinity of (clutter signal) 48, a demodulation process corresponding to AM synchronous detection is required to convert this signal to a band near DC. Become.

For example, to extract Doppler signals have emerged as a side band harmonic component 2f _m is the first mixer output to synchronous detection by the second reference wave frequency 2f _m in the second mixer. In FIG. 12, this process can be realized by setting the order N of the N multiplication circuit 25 to 2. Since the BPFs 36 and 38 subsequent to the first mixer function as a low-pass filter, the synchronous detection process for the Doppler signal in which the second harmonic component is selected can be expressed as follows.

また、周波数２ｆ_mの第２参照波を次式のように表現する。

数１４および数１５から、第１ミキサ後段のＢＰＦ３６により第２高調波成分を選択したドプラ信号に対する同期検波過程は、次式によって表現される。

数１６は、第２ミキサ出力をＬＰＦ３７によりドプラ周波数帯域以上の高域成分を除去した結果に相当する。 First, the first mixer output (in this case, the output of the I-channel mixer 32 is assumed) can be expressed by the above equation (8). When the second harmonic component is selected by the BPF 36, the following signal is extracted.

Also, to represent the second reference wave frequency 2f _m as follows.

From the equations 14 and 15, the synchronous detection process for the Doppler signal for which the second harmonic component is selected by the BPF 36 subsequent to the first mixer is expressed by the following equation.

Equation 16 corresponds to the result of removing the high-frequency component higher than the Doppler frequency band from the second mixer output by the LPF 37.

According to Equation 16, the amplitude of the Doppler signal v _D2 (t) depends on J ₂ (kβ), φ _m and φ _r . J ₂ (kβ) and φ _m are determined by the depth of the target, φ _r is a parameter set in the signal processing system (for example, variable delay circuit 112 in FIG. 12), and v _D2 (t) is φ _r It changes periodically.

FIG. 14 shows the result of measuring the power of the second mixer output v _D2 (t) when the depth of the Doppler target is fixed and the phase φ _r of the second reference wave v _r2 (t) is changed.

In FIG. 14, (a) is the fundamental wave (FM modulation frequency f _m ) component, (b) is the second harmonic component, and (c) is the measurement result regarding the third harmonic component, and the horizontal axis represents the delay time. (Phase φ _r ) is represented, and the vertical axis represents the second mixer output power. In FIG. 14, the white circle is the I-channel second mixer output measurement value, the black circle is the Q-channel second mixer output measurement value, the dotted line is the extrapolation curve of the I-channel measurement value, and the two-dot chain line is the Q-channel measurement value. Extrapolated curves and solid lines show calculated values.

From Figure 14, the Doppler signal it can be seen that changes periodically in accordance with the change of the phase phi _r. Further, considering Equation 16, it can be understood that the Doppler signal periodically changes even if the depth of the target is changed with the phase φ _r fixed. The phenomenon that the Doppler signal periodically changes depending on the depth of the target is that if the expression is changed, the reception sensitivity of the Doppler signal varies depending on the depth of the target, and this is applied to an ultrasonic diagnostic apparatus. Measures against fluctuations in reception sensitivity (depth dependence of Doppler signals) are desired.

  FIG. 15 shows an ultrasonic diagnostic apparatus in which the ultrasonic diagnostic apparatus shown in FIG. 12 is improved to avoid the depth dependence of the Doppler signal. The ultrasonic diagnostic apparatus shown in FIG. 15 is different from FIG. 12 in that the output of the BPF 36 is subjected to detection processing by the quadrature detection method, and further, the output of the BPF 38 is subjected to detection processing by the quadrature detection method. is there. Hereinafter, the ultrasonic diagnostic apparatus of FIG. 15 will be described with a focus on differences from FIG.

In FIG. 15, the BPFs 36 and 38 extract a desired frequency component from the fundamental wave component and each harmonic component related to f _m shown in Equation 8. That is, a sideband consisting of at least one of the fundamental wave component and the nth (n is a natural number of 2 or more) harmonic component and a Doppler signal existing in the vicinity thereof is extracted.

  The signal (sideband signal) output from the BPF 36 is subjected to synchronous detection and quadrature detection by the two mixers 150 and 152 and the two low-pass filters (LPF) 160 and 162, and further output from the BPF 38. The signal (sideband signal) is subjected to synchronous detection and quadrature detection by two mixers 154 and 156 and two low-pass filters (LPF) 164 and 166.

Mixer 150, 154 are, is N times the fundamental wave f _m N times circuit 25 (N is a natural number) and the reference signal fundamental wave component or a harmonic component of the modulation wave f _m obtained by. On the other hand, the mixers 152 and 156 use the signal supplied via the π / 2 shift circuit 180 after the fundamental wave f _m is multiplied N times (N is a natural number) by the N multiplication circuit 25 as a reference signal. The π / 2 shift circuit 180 is a circuit that shifts the phase of the input signal by π / 2.

  With this configuration, detection processing by the quadrature detection method is executed on the output of the BPF 36, and detection processing by the quadrature detection method is executed on the output of the BPF 38. Note that the detection processing using the mixers 150, 152, 154, and 156 and the detection processing using the mixers 32 and 34 are detection by digital processing (for example, including sampling processing) in addition to detection processing by an analog circuit. Processing is also acceptable.

Then, the square sum square root calculation unit 170 calculates the square sum square, that is, (I ² + Q ² ) ^1/2 from the output (I component) of the LPF 160 and the output (Q component) of the LPF 162. Similarly, the square sum square root calculation unit 172 calculates the square sum square root from the output (I component) of the LPF 164 and the output (Q component) of the LPF 166.

  The calculation result in the square sum square root calculation unit 170 is output as a Doppler signal in-phase component, and the calculation result in the square sum square root calculation unit 172 is output as a Doppler signal orthogonal component. The Doppler calculation processing unit 40 performs Doppler calculation based on the Doppler signal in-phase component and the Doppler signal quadrature component.

  As described above, the ultrasonic diagnostic apparatus shown in FIG. 15 avoids the depth dependence of the Doppler signal by performing the detection processing by the orthogonal detection method on each of the output of the BPF 36 and the output of the BPF 38. The principle is as follows.

その結果、ＬＰＦ１６０の出力は次のように表現される。

First, assuming that the second harmonic component is selected by the BPF 36, the signal of Expression 14 is extracted. Then, the reference signal of the mixer 150 is expressed as in Expression 17.

As a result, the output of the LPF 160 is expressed as follows.

その結果、ＬＰＦ１６２の出力は次のように表現される。

Further, the reference signal of the mixer 152 is expressed as in Expression 19.

As a result, the output of the LPF 162 is expressed as follows.

数２１におけるｖ_D3I（ｔ）には、数１６のｖ_D2（ｔ）に含まれていたφ_mおよびφ_rが存在しない。したがって、ｖ_D3I（ｔ）には、深さ依存性が存在しないことになる。 Further, in the square sum square root calculation unit 170, the square root of the square sum of the two signals obtained by Expression 18 and Expression 20 is calculated as follows.

In v _D3I (t) in _Equation 21, φ _m and φ _r included in v _D2 (t) in _Equation 16 do not exist. Therefore, there is no depth dependence in v _D3I (t).

数２２におけるｖ_D3Q（ｔ）にもφ_mおよびφ_rが含まれず、したがって、深さ依存性が存在しないことになる。 The output of the square sum square root calculation unit 172 is also calculated by the same calculation process as the output of the square sum square root calculation unit 170 as follows.

V _D3Q (t) in _Equation 22 also does not include φ _m and φ _r , and therefore there is no depth dependency.

  Equations (21) and (22) are quadrature detection outputs of the Doppler signal, and based on these outputs, the Doppler computation processing unit 40 computes the velocity component of the target and the like by conventional signal processing conventionally known.

  As described above, the depth dependence of the Doppler signal can be avoided by the ultrasonic diagnostic apparatus of FIG. That is, regardless of the depth of the Doppler target, the Doppler signal can be extracted as a signal that does not depend on the depth, and in the subsequent processing, as in normal Doppler signal processing, an image is obtained by FFT and a display system. Can observe.

  FIG. 16 shows an ultrasonic diagnostic apparatus in which the ultrasonic diagnostic apparatus shown in FIG. 11 is further improved. In the ultrasonic diagnostic apparatus shown in FIG. 16, three circuits of a 1 × circuit 25a, a 2 × circuit 25b, and a 3 × circuit 25c are provided instead of the N × circuit 25 of FIG. Corresponding to each, the subsequent stage of the receiving mixer 30 is separated into three systems.

BPF36a, 38a, respectively, to extract the fundamental component about the modulation wave frequency f _m from the output signal of the receiving mixer 30, and outputs the mixers 28a, to 29a. Mixers 28a, 29a, respectively, as a reference signal to the fundamental wave component of the modulated wave f _m obtained from 1-fold circuit 25a, BPF36a, by detecting a signal outputted from 38a into a baseband signal. Further, BPF36b, 38b, respectively, to extract the second harmonic component about the modulation wave frequency f _m from the output signal of the receiving mixer 30, and outputs the mixer 28b, the 29b. Mixers 28b, 29 b, respectively, as a reference signal to the second harmonic component of the modulation wave f _m derived from doubled circuits 25b, BPF36b, by detecting a signal output from 38b converts the baseband signal. Furthermore, BPF36c, 38c, respectively, to extract the third-order harmonic component about the modulation wave frequency f _m from the output signal of the reception mixer 30, the mixer 28c, and outputs it to 29c. Mixer 28c, 29c, respectively, as a reference signal to the third harmonic component of the modulation wave f _m obtained from 3-fold circuit 25c, BPF36c, converted into a baseband signal by detecting the signal output from 38c.

  The signals output from the mixers 28a, 28b, and 28c are added in the adder 120 and output to the Doppler arithmetic processing unit 40, and the signals output from the mixers 29a, 29b, and 29c are added to the adder 122. Is added to and output to the Doppler computation processing unit 40. Adders 120 and 122 perform addition processing by weighting the signals output from the mixers.

Thus, the ultrasonic diagnostic apparatus illustrated in FIG. 16, extracts the fundamental wave, Doppler information by adding treated twice the harmonic and 3-fold, respectively extracted signal from harmonic (Doppler signal) of the modulation wave frequency f _m To do. Therefore, as in the ultrasonic diagnostic apparatus shown in FIG. 11, to improve the SNR as compared with the case of using the Doppler signal corresponding to one of the fundamental wave component and harmonic components of the modulated wave f _m it can.

  If necessary, a circuit for adjusting the phase and voltage is added to the subsequent stage of each of the 1 × circuit 25a, 2 × circuit 25b, and 3 × circuit 25c in FIG. 16 to add 1 × circuit 25a, 2 × circuit 25b. The phase and voltage may be adjusted for the reference signal output from each of the triple circuit 25c. The phase and voltage of the reference signal can be adjusted so that optimum detection (for example, detection with good SNR) is performed.

  Further, in addition to the 1 × circuit 25a, the 2 × circuit 25b, and the 3 × circuit 25c, a higher order reference signal such as a 4 × circuit or a 5 × circuit may be used. Further, when a higher-order reference signal is used, the subsequent stage of the reception mixer 30 is also expanded to four systems or five systems in accordance with each dimension of the reference signal.

  FIG. 17 shows an ultrasonic diagnostic apparatus in which the ultrasonic diagnostic apparatus shown in FIG. 1 is simplified. In the ultrasonic diagnostic apparatus shown in FIG. 17, one mixer 33 is provided in place of the mixers 32 and 34 in FIG. 1, and one mixer 27 is provided in place of the mixers 28 and 29. That is, the quadrature detection performed in the mixers 32 and 34 and the mixers 28 and 29 in the ultrasonic diagnostic apparatus of FIG. 1 is simplified to simple detection in FIG. With the simplification of the simple detection, the π / 2 shift circuit 26, the BPF 38, and the LPF 39 that are required in FIG. 1 are omitted in FIG.

  In the ultrasonic diagnostic apparatus shown in FIG. 17, information relating to the direction of blood flow is lost because simple detection is performed instead of quadrature detection, but blood flow velocity measurement is approximately the same as in quadrature detection. Is possible. In addition, the configuration of the apparatus can be simplified as compared with the ultrasonic diagnostic apparatus of FIG. In FIG. 17, a wall motion filter (WMF) 130 is provided after the LPF 37, and clutter is removed in the WMF 130.

As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above is only a mere illustration in all the points, and does not limit the scope of the present invention. For example, an example of the FM-modulated by a sine wave of a frequency f _m in the above embodiment, by forming the FMCW transmission wave subjected to FM modulation by the modulation wave of further frequency f _m2 to the modulation wave frequency f _m1 Also good. By performing FM modulation in multiple stages, the influence of clutter can be reduced and a Doppler signal can be extracted in a lower speed region.

Also, although an example of the FM-modulated by a sine wave of a frequency f _m in the above embodiment, instead of the sine wave may be utilized triangular wave 140 of the period f _m shown in FIG. 18 for example. Of course, a sawtooth wave may be used as the triangular wave.

1 is a block diagram showing an overall configuration of an ultrasonic diagnostic apparatus according to the present invention. It is a figure which shows the frequency spectrum of a FMCW transmission wave. It is a figure which shows the frequency spectrum of a FMCW received wave. It is a figure which shows the frequency spectrum of a receiving mixer output. It is a figure which shows the power spectrum of the clutter in normal CW in a received RF signal. It is a figure which shows the power spectrum of the clutter in FMCW in a received RF signal. It is a figure which shows a primary Bessel function. It is the figure which plotted the horizontal axis as the depth of diagnosis and the vertical axis as the Bessel function value. It is a figure for demonstrating the depth dependence of a fundamental wave and a harmonic clutter voltage. It is a figure for demonstrating the power ratio relationship of Doppler signal electric power and clutter electric power. It is a figure which shows the whole structure of another ultrasonic diagnostic apparatus which concerns on this invention. It is a figure which shows the whole structure of another ultrasonic diagnostic apparatus which concerns on this invention. It is a figure for demonstrating the Doppler signal in a 1st mixer output. It is a figure for demonstrating the reference wave delay time dependence of 2nd mixer output electric power. It is a figure for demonstrating the ultrasonic diagnosing device which avoided the depth dependence of the Doppler signal. It is a figure which shows the whole structure of another ultrasonic diagnostic apparatus which concerns on this invention. It is a figure which shows the whole structure of another ultrasonic diagnostic apparatus which concerns on this invention. It is a figure for demonstrating a triangular wave.

Explanation of symbols

  20 FM modulator, 22 RF wave oscillator, 24 FM modulated wave oscillator, 26 π / 2 shift circuit, 30 receiving mixer, 40 Doppler arithmetic processing unit.

Claims (17)

A modulation unit that modulates a carrier wave signal using a modulated wave signal, thereby generating a continuous wave modulated transmission signal whose frequency is periodically changed ; and
A transmitter / receiver for transmitting an ultrasonic wave to a living body by supplying the modulated transmission signal, receiving an ultrasonic wave from the living body and outputting a reception signal;
Demodulating means for demodulating the received signal using the modulated transmission signal, thereby obtaining a demodulated signal;
Doppler information existing in the vicinity of at least one of the fundamental wave component and the n-th (n is a natural number of 2 or more) harmonic component when the modulated wave signal is a fundamental wave is extracted from the demodulated signal. Doppler information extraction means;
An ultrasonic diagnostic apparatus comprising: The ultrasonic diagnostic apparatus according to claim 1,
The demodulating means includes a detection circuit that detects the received signal using the modulated transmission signal as a reference signal.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The demodulating means includes a quadrature detection circuit that performs quadrature detection processing on the received signal using the modulated transmission signal as a reference signal.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The Doppler information extraction unit includes a filter unit that extracts a sideband composed of the at least one component and a Doppler signal existing in the vicinity thereof.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 4,
The Doppler information extraction unit includes a Doppler signal extraction unit that extracts the Doppler signal from the sideband.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 5,
The Doppler signal extraction unit includes a detection circuit that detects the sideband using at least one of signals obtained by multiplying the frequency of the modulated wave signal by N (N is a natural number) as a reference signal.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
Including a delay circuit that performs a delay process on a reference signal to be supplied to the demodulation means
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
A delay circuit that performs a delay process on the received signal output to the demodulating means;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 6,
A delay circuit that performs a delay process on a reference signal to be provided to the Doppler signal extraction unit;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 6,
Including a delay circuit that performs a delay process on the sideband output to the Doppler signal extraction unit,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The Doppler information extraction unit extracts and extracts a Doppler signal from each of a plurality of components of a fundamental wave component and an nth (n is a natural number of 2 or more) harmonic component when the modulated wave signal is a fundamental wave. Add multiple Doppler signals
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 11,
The modulated wave signal is a sine wave;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 11,
The modulated wave signal is a triangular wave or a sawtooth wave,
An ultrasonic diagnostic apparatus. By frequency modulation processing by using the modulated wave signal of the frequency f _m of the carrier signal of a frequency f _0, and a transmission unit for generating a modulated transmission signal,
A transmitter / receiver for transmitting ultrasonic waves to a living body by supplying the modulated transmission signal, receiving a reflected wave from the living body and outputting a reception signal;
A detection circuit that performs quadrature detection processing on the received signal using the modulated transmission signal as a reference signal, thereby obtaining a demodulated signal, and
From the demodulated signal, from at least one of the fundamental wave component and the n-th (n is a natural number of 2 or more) harmonic component when the modulated wave signal is a fundamental wave, and a Doppler signal present in the vicinity thereof A bandpass filter for extracting sidebands consisting of:
A Doppler signal extraction unit for extracting the Doppler signal from the sideband;
A Doppler information acquisition unit that acquires Doppler information about the moving body from the Doppler signal;
An ultrasonic diagnostic apparatus comprising: The ultrasonic diagnostic apparatus according to claim 14,
As the modulation wave signal, a multiplex modulation wave signal obtained by further frequency-modulating the modulation wave signal of frequency f _{m1 using} the modulation wave signal of frequency f _m2 is used.
An ultrasonic diagnostic apparatus. By frequency modulation processing by using the modulated wave signal of the frequency f _m of the carrier signal of a frequency f _0, and a transmission unit for generating a modulated transmission signal,
A transmitter / receiver for transmitting ultrasonic waves to a living body by supplying the modulated transmission signal, receiving a reflected wave from the living body and outputting a reception signal;
A detection circuit that performs quadrature detection processing on the received signal using the modulated transmission signal as a reference signal, thereby obtaining an in-phase component demodulated signal and a quadrature component demodulated signal;
From each of the in-phase component demodulated signal and the quadrature component demodulated signal, at least one of a fundamental wave component and an nth (n is a natural number of 2 or more) harmonic component when the modulated wave signal is a fundamental wave; A bandpass filter that extracts sidebands composed of Doppler signals present in the vicinity thereof;
A Doppler signal extraction unit that extracts the Doppler signal from the sideband wave of the in-phase component demodulated signal and the sideband wave of the quadrature component demodulated signal;
A Doppler information acquisition unit that acquires Doppler information about the moving body from the Doppler signal;
Have
The Doppler signal extraction unit performs quadrature detection processing on the sideband extracted from the in-phase component demodulated signal, using at least one of the signals obtained by multiplying the frequency of the modulated wave signal by N (N is a natural number) as a reference signal. Including an in-phase component detection circuit and a quadrature component detection circuit for performing quadrature detection processing on the sideband wave extracted from the quadrature component demodulated signal,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 16, wherein
The Doppler signal extraction unit obtains the Doppler signal in-phase component obtained as the square root of the sum of squares of the two signals output from the in-phase component detection circuit, and the square sum of the two signals output from the quadrature component detection circuit. Extract the two Doppler signal components of the Doppler signal orthogonal component obtained as the square root,
An ultrasonic diagnostic apparatus.

Images