JP2006288974A - Ultrasonic diagnostic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ultrasonic diagnostic equipment for generating positional information of a tissue to be an object through the use of continuous wave. <P>SOLUTION: A doppler power detecting part 44 extracts a doppler signal corresponding to the tissue to be an object by each component of a plurality of n-th wave components from a demodulated signal which is converted into a frequency spectrum. Then the power value of each extracted doppler signal is detected. A distance arithmetic part 48 calculates the depth of the tissue to be an object, on the basis of the power of the plurality of detected doppler signals. That is, the distance from a body surface to the tissue to be an object in a viable tissue is calculated. A display processing part 52 forms, for example, doppler waveforms and a graph including information of distance and speed, etc., on the basis of the arithmetic result of the distance and speed of the tissue to be an object so as to make a display part 54 display the formed doppler waveforms and graph, etc. <P>COPYRIGHT: (C)2007,JPO&INPIT

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, Doppler information can be obtained by extracting the information and performing frequency analysis. However, the reflected wave includes information (clutter) from a strong reflector (mainly a stationary body) in the living body. Therefore, it is desired to suppress the clutter as much as possible and extract only Doppler information, but it is difficult to sufficiently remove the clutter particularly in a low-speed observation area.

  Against this background, the inventors of the present application have proposed a technique that can observe Doppler information with high sensitivity while suppressing clutter as much as possible when applying the continuous wave Doppler method (see Non-Patent Document 1).

Masanori Kunida, Masakazu Noda, “Clutter reduction effect by ultrasonic FMCW Doppler measurement system” (The Institute of Electronics, Information and Communication Engineers (basic / boundary) VOL. J87-A No. 10 (October 1, 2004, incorporated association) (Published by IEICE))) JP-A-5-40168

  The technique described in Non-Patent Document 1 transmits an ultrasonic wave to a living body using a modulated transmission signal that is FM-modulated by a modulated wave signal, and demodulates a received signal obtained from the living body using the modulated transmission signal. Thus, a demodulated signal is obtained. Then, by extracting Doppler information from at least one of the fundamental wave component and the harmonic wave component when the modulated wave signal is a fundamental wave from the demodulated signal, it is localized near the DC component in the case of no modulation. This is an epoch-making technique in which the influence of clutter that has been reduced is reduced, and velocity information of the moving body is extracted more appropriately.

  The inventors of the present application have further improved this epoch-making technique and have been researching a method for acquiring position information of a moving body without being limited to speed information of the moving body.

  The present invention has been made in such a background, and an object thereof is to provide an ultrasonic diagnostic apparatus that generates position information of a target tissue using a continuous wave.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes a transmission signal generating unit that generates a modulated transmission signal by performing a modulation process on a carrier wave signal using a modulated wave signal, Transmitting and receiving means for transmitting an ultrasonic wave to a living body by supplying a modulated transmission signal, receiving a reflected wave from the living body and outputting a received signal, and demodulating the received signal using the modulated transmission signal Thus, demodulation means for obtaining a demodulated signal including a plurality of nth-order wave components (n is a natural number of 0 or more) when the modulated wave signal is a fundamental wave, and the demodulated signal from the demodulated signal For each component of the n-th order wave component, Doppler signal extraction means for extracting a Doppler signal corresponding to the target tissue, and position information generation for generating position information of the target tissue based on the intensity of the plurality of extracted Doppler signals Means And wherein the Rukoto. In the above configuration, the modulation wave signal is, for example, a sinusoidal modulation wave signal. However, it is not limited to a sine wave.

  Preferably, the position information generation means calculates the depth of the target tissue as the position information. Preferably, the position information generating means includes a DC component that is a 0th-order wave component and a fundamental wave component that is a first-order wave component among the plurality of nth-order wave components, and a plurality of harmonics in which n is 2 or more. A target tissue Doppler signal extracted from each of the wave components is set as a calculation target, and the depth of the target tissue is calculated based on the power of the plurality of Doppler signals. Desirably, the position information generating means is a target tissue extracted from each of a fundamental wave component that is a first wave component of the plurality of nth wave components and a plurality of harmonic components where n is 2 or more. The depth of the target tissue is calculated based on the power of the plurality of Doppler signals.

  Preferably, the Doppler signal extraction means includes an FFT circuit that converts the demodulated signal into a frequency spectrum, and extracts the Doppler signal using the converted frequency spectrum. Desirably, it has a velocity information generating means for generating velocity information of the target tissue based on the frequency of at least one Doppler signal among the plurality of extracted Doppler signals.

In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention performs a modulation process on a carrier wave signal using a first modulated wave signal having a frequency of f _m1 to obtain a first modulated transmission signal. And transmitting signal generating means for generating a second modulated transmission signal by modulating the carrier wave signal using a second modulated wave signal having a frequency of _fm2 , and the first modulated transmission signal and the second modulated transmission. A transmission / reception means for transmitting an ultrasonic wave to the living body by supplying a signal, receiving a reflected wave from the living body and outputting a reception signal; and demodulating the reception signal using the first modulated transmission signal. Thus, a first demodulated signal including a plurality of nth-order wave components (n is a natural number of 0 or more) when the first modulated wave signal is a fundamental wave is acquired, and the received signal is Demodulate using the second modulated transmission signal, As a result, demodulation means for acquiring a second demodulated signal including a plurality of n'th order wave components (n 'is a natural number of 0 or more) when the second modulated wave signal is a fundamental wave, and the first A Doppler signal corresponding to the target tissue is extracted from the demodulated signal for each component of the plurality of nth-order wave components, and further, each component of the plurality of nth-order wave components is extracted from the second demodulated signal. A Doppler signal extraction means for extracting a Doppler signal corresponding to the target tissue, an index value _km1 obtained based on the strengths of a plurality of Doppler signals extracted from the first demodulated signal, and the second demodulated signal Position information generating means for generating position information of the target tissue based on two index values of the index value _km2 obtained based on the intensities of a plurality of Doppler signals extracted from.

  According to the present invention, position information of a target tissue can be obtained using a continuous wave. For example, the velocity information and the position information of the target tissue can be obtained simultaneously using a continuous wave.

  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. For example, an FM continuous wave (FMCW wave) that has been subjected to FM modulation processing using, for example, a sine wave 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 sine wave 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 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. The 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 reception mixer 30 and only a necessary band after detection is extracted.

As will be described in detail later, the received mixer output signal (demodulated signal), which is the result of the mixing process of the received RF signal and the reference signal executed by each mixer, is supplied from the FM modulated wave oscillator 24. the n order wave component more about the modulation wave frequency f _m of the modulation wave (n is 0 or a natural number) are included. That is, a direct-current component that is the 0th-order wave component, a fundamental wave component that is the first-order wave component, and a plurality of harmonic components in which n is 2 or more are included. That is, a demodulated signal including the plurality of nth-order wave components is output from each of the LPFs 36 and 38.

  FFT circuits (fast Fourier transform circuits) 40 and 42 perform an FFT operation on each demodulated signal (in-phase signal component and quadrature signal component). As a result, the demodulated signal is converted into a frequency spectrum in the FFT circuits 40 and 42. The frequency spectrum output from the FFT circuits 40 and 42 is output as frequency data with a frequency resolution δf depending on circuit setting conditions. The frequency spectrum output from the FFT circuits 40 and 42 will be described in detail later using FIG.

  The Doppler power detection unit 44 extracts a Doppler signal corresponding to the target tissue for each component of the plurality of nth-order wave components from the demodulated signal converted into the frequency spectrum. Then, the power value of each extracted Doppler signal is detected. The distance calculation unit 48 calculates the depth of the target tissue based on the detected powers of the plurality of Doppler signals. That is, the distance from the body surface of the target tissue in the living tissue is calculated. The power detection process by the Doppler power detection unit 44 and the distance calculation by the distance calculation unit 48 will be described in detail later in the explanation of the principle.

  The Doppler frequency detection unit 46 extracts a Doppler signal corresponding to the target tissue for each component of the plurality of nth-order wave components from the demodulated signal converted into the frequency spectrum. Then, the frequency (Doppler shift) of each extracted Doppler signal is detected. The speed calculation unit 50 calculates the speed of the target tissue based on the detected frequency of the Doppler signal.

  Further, the display processing unit 52 forms, for example, a Doppler waveform or a graph including distance and speed information based on the calculation result of the distance or speed of the target tissue, and the formed Doppler waveform or graph is displayed on the display unit 54. To display.

  As described above, in the present embodiment, an ultrasonic wave (FMCW wave) obtained by FM-modulating a continuous wave (CW) with a modulated wave (for example, a sine wave) is transmitted and received, and a plurality of first-order waves related to the modulated wave frequency of the modulated wave are transmitted. A Doppler signal corresponding to the target tissue is extracted from the nth-order wave component, and position information of the target tissue is generated. Then, next, the principle until position information is generated will be described in detail.

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。 FMCW transmission wave subjected to FM modulation by a sine wave of the modulation frequency f _m to the CW of frequency f ₀ can be expressed by 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.

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。 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 .

ここで、数３、数４、数６の算出には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ラム、つまり、図１のＦＦＴ回路４０，４２から出力される周波数スペクトラムを図示すると図２のようになる。 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 reception RF signal, the demodulation system performs multiplication with the reception wave using the FMCW transmission 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 formulas relating to the Bessel function are used for the calculation of Equations 3, 4, and 6.

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.

FIG. 2 shows the frequency spectrum of the output of the receiving mixer expressed by Equation 8, that is, the frequency spectrum output from the FFT circuits 40 and 42 of FIG.

FIG. 2 is a diagram showing the frequency spectrum of the demodulated signal. As shown in Equation 8, the demodulated signal includes a plurality of nth-order wave components (n is a natural number of 0 or more) related to the modulation wave frequency. That is, in FIG. 2, the direct current component that is the zeroth-order wave component, the fundamental wave component that is the first-order wave component (f _m ), and the second harmonic component that is the second-order wave component ( 2f _m ), and the third harmonic component (3f _m ), which is the third-order wave component. Note that there are harmonic components of which n is 4 or more, which is not shown. Each nth-order wave component includes a fixed object echo 60 and a Doppler echo 62.

  The fixed object echo 60 is an echo (clutter echo) from a stationary body, which is a strong reflector in the living body, and becomes a disturbance factor when observing Doppler information. On the other hand, the Doppler echo 62 corresponds to a Doppler signal. That is, when accompanied by a Doppler shift, each of the nth-order wave components of the Doppler signal has a DSB-SC (Double Sideband-Suppressed Carrier) spectrum shape in which the FM modulation frequency is suppressed.

  In the present embodiment, the Doppler echo 62 corresponding to the target tissue is extracted from the frequency spectrum shown in FIG. 2, the distance (depth) of the target tissue is calculated based on the power of the Doppler echo 62, and the frequency (Doppler shift) of the Doppler echo 62 is calculated. The velocity of the target tissue is calculated based on the component. Then, next, the calculation principle of the distance of the target tissue will be described.

また、数８における第ｎ次波成分の電力を次式で表現する。

数９と数１１から次式が導かれる。

そして、数１０、数１１および数１２を用いると次式が導かれる。

数１３は、変数ｋβと復調信号に含まれる複数の第ｎ次波成分の各成分ごとのドプラ信号の電力（Ｐ₀，Ｐ_n）の関係を表している。そして、数１３の右辺は全電力によって規格化されているため左辺の（ｋβ）²は、受信電力に依存しない。そこで、数１３を利用してｋを算出し、これを指標値として次式の関係から距離（深さ）ｄが算出される。

数１３の右辺は、復調信号の周波数スペクトラムから求めることができる。特定のドプラ周波数を持った信号のスペクトラムに着目して数１３の右辺の分母を求める。右辺分母は、複数の第ｎ次波成分の各成分ごとのドプラ信号の電力（Ｐ₀，Ｐ_n）の総和である。つまり、図２において、例えば、固定物エコー６０に隣接しているドプラ信号「１」について、その電力を、直流成分と基本波成分（ｆ_m）と第２高調波成分（２ｆ_m）と第３高調波成分（３ｆ_m）とに亘って全て加算することに相当する。なお、ドプラ信号の電力の総和を厳密に求めるためにはｎが４以上の高調波成分も考慮する必要がある。ただし、高次元の高調波成分が小さい場合などにおいては、有る程度の次数（例えば次数３）までの計算で総和を求めてもよい。なお、数１３の右辺の分子は、ｎが１以上の第ｎ次波成分の各成分ごとのドプラ信号の電力についてｎ²の重みをつけて加算することによって求めることができる。 The first type Bessel function has the following relationship.

Further, the power of the nth-order wave component in Equation 8 is expressed by the following equation.

The following equation is derived from Equations 9 and 11.

Then, using Equation 10, Equation 11, and Equation 12, the following equation is derived.

Equation 13 represents the relationship between the variable kβ and the power (P ₀ , P _n ) of the Doppler signal for each component of the plurality of nth-order wave components included in the demodulated signal. Since the right side of Equation 13 is normalized by the total power, (kβ) ^{2 on the} left side does not depend on the received power. Therefore, k is calculated using Equation 13, and the distance (depth) d is calculated from the relationship of the following equation using this as an index value.

The right side of Equation 13 can be obtained from the frequency spectrum of the demodulated signal. Focusing on the spectrum of a signal having a specific Doppler frequency, the denominator of the right side of Equation 13 is obtained. The right-hand side denominator is the total sum of the Doppler signal powers (P ₀ , P _n ) for each component of the plurality of nth-order wave components. That is, in FIG. 2, for example, the power of the Doppler signal “1” adjacent to the fixed object echo 60 is divided into the direct current component, the fundamental wave component (f _m ), the second harmonic component (2f _m ), and the second power. This corresponds to adding all over the third harmonic component (3f _m ). In addition, in order to obtain | require the sum total of the electric power of a Doppler signal exactly | strictly, it is necessary to consider the harmonic component whose n is 4 or more. However, when the high-dimensional harmonic component is small, the sum may be obtained by calculation up to a certain degree (for example, order 3). Note that the numerator on the right side of Equation 13 can be obtained by adding the weight of n ^{2 to} the power of the Doppler signal for each component of the nth-order wave component where n is 1 or more.

図３は、対象組織の深さｄと指標値ｋとの関係を説明するための図である。図３には、横軸を対象組織の深さｄとした場合における数１４の指標値ｋ、ｋの絶対値、ｋの二乗値がそれぞれ示されている。 Thus, using Equation 13, the absolute value of the index value k is obtained by the calculation of the following equation.

FIG. 3 is a diagram for explaining the relationship between the depth d of the target tissue and the index value k. FIG. 3 shows the index values k, the absolute value of k, and the square value of k when the horizontal axis is the depth d of the target tissue.

As shown in FIG. 3, if the target tissue is a short distance, that is, when d is less than c / 4f _m, is a function of the index value k, the absolute value of k, each of the square value of k increases monotonically Therefore, the depth d is uniquely determined from the index value k in Equation 14.

ｄが０以上でｃ／４ｆ_m以下の場合、図３に示すようにｋは０以上である。ｋが０以上である場合、数１６から次式が導かれる。

つまり、ｄが０以上でｃ／４ｆ_m以下の近距離の場合、距離ｄが次式のようになる。

数１８に示されるように、既知の値である変調周波数ｆ_mおよび変調指数β、復調信号の周波数スペクトラムから求めるドプラ信号の電力（Ｐ₀，Ｐ_n）から、対象組織の深さｄを求めることができる。 Further, the following equation is derived from Equations 14 and 15.

If d is less than c / 4f _m is 0 or more, k as shown in FIG. 3 is 0 or more. When k is 0 or more, the following equation is derived from Equation 16.

That is, when d is less than the near c / 4f _m is 0 or more, the distance d is expressed as follows.

As shown in Equation 18, the modulation frequency f _m and the modulation index is a known value beta, the power of the Doppler signal obtained from the frequency spectrum of the demodulated signal (P _0, P _n), obtaining the depth d of the target tissue be able to.

  The FFT circuits 40 and 42, the Doppler power detection unit 44, and the distance calculation unit 48 of FIG. 1 use the above-described calculation principle. That is, the FFT circuits 40 and 42 perform an FFT operation on each demodulated signal. As a result, the demodulated signal is converted into a frequency spectrum as shown in FIG. The frequency spectrum output from the FFT circuits 40 and 42 is output as frequency data with a frequency resolution δf depending on the setting conditions of the FFT circuits 40 and 42.

And the Doppler electric power detection part 44 extracts the Doppler signal corresponding to an object structure | tissue for every component of several nth order wave component from the frequency spectrum shown in FIG. 2, and detects the electric power _Pn . For example, for the Doppler signal “3” located farthest from the fixed object echo 60 in FIG. 2, the power P ₀ of the Doppler signal “3” in the DC component existing near the origin O and the Doppler in the fundamental wave component (f _m ). power P ₁ of the signal "3", the second harmonic component power P ₂ of the Doppler signal "3" in (2f _m), the third harmonic component (3f _m) power P ₃ of the Doppler signal "3" in the Detect each.

  The Doppler power detection unit 44 extracts a Doppler signal by a bandpass filter. This band pass filter preferably includes a band of the extracted Doppler signal and is set to a band that can efficiently remove noise. Therefore, the band of the band pass filter that extracts the Doppler signal is set to n × δf, for example.

Further, the Doppler power detection unit 44 detects the power of the Doppler signal for each target tissue. That is, in FIG. 2, the power P _n for each n-order wave component is detected for the Doppler signal “3” corresponding to a certain target tissue, and further, for the Doppler signal “1” corresponding to another target tissue having a different speed. detecting the power P _n for each n order wave component, also detects the power P _n for each n order wave component for the Doppler signals corresponding to another target tissue "2".

Then, the distance calculation unit 48 calculates the depth d of the target tissue from Equation 18 based on the power of the Doppler signal detected by the Doppler power detection unit 44. Since the power of the Doppler signal is detected for each target tissue, the distance calculation unit 48 calculates the depth d for each target tissue. That is, when the Doppler signal “1” shown in FIG. 2 corresponds to the Doppler signal of the target tissue 1, the distance calculation unit 48 uses the power P _n for each n-th order wave component related to the Doppler signal “1” according to Equation 18. The depth d of the target tissue 1 is calculated. Further, when the Doppler signal “2” shown in FIG. 2 corresponds to the Doppler signal of the target tissue 2, the depth of the target tissue 2 is calculated from the power P _n for each n-order wave component related to the Doppler signal “2” according to Equation 18. d is calculated. Furthermore, when the Doppler signal “3” shown in FIG. 2 corresponds to the Doppler signal of the target tissue 3, the depth of the target tissue 3 is calculated from the power P _n for each n-order wave component related to the Doppler signal “3” according to Equation 18. d is calculated. Thus, the depth d is calculated for each target tissue.

In the calculation principle described above, the depth d is obtained using the power P ₀ of the Doppler signal in the DC component existing near the origin O. However, in the DC component, leakage from the transmission circuit system or fixed tissue is obtained. Since the reflection (clutter echo) is very strong, the DC component Doppler signal may be buried in those signals. Therefore, a method for calculating the depth d without using a DC component Doppler signal will be described next.

数１９の二つの公式と数１１から次式が導かれる。

数２０の二つの式からαを消去して整理すると次式が導かれる。

数２１の右辺には、直流成分におけるドプラ信号の電力Ｐ₀が含まれていないため、１次以上のｎ次波成分の電力Ｐ_nのみから左辺の（ｋβ）²が求められる。そこで、数２１を利用してｋを算出し、これを指標値として距離（深さ）ｄを算出することにより、直流成分のドプラ信号を利用せずに深さｄを求めることが可能になる。 The first type Bessel function has the following relationship.

From the two formulas in Equation 19 and Equation 11, the following equation is derived.

When α is eliminated from the two equations in Equation 20 and rearranged, the following equation is derived.

Since the right side of Equation 21 does not include the power P ₀ of the Doppler signal in the DC component, (kβ) ^{2 on the} left side is obtained from only the power P _{n of the} first-order or higher-order n-order wave component. Therefore, by calculating k using Equation 21 and calculating distance (depth) d using this as an index value, it is possible to determine the depth d without using a DC component Doppler signal. .

As described above, the distance (depth) d of the target tissue is calculated. In the present embodiment, the speed of the target tissue is also calculated. That is, the Doppler frequency detection unit 46 extracts the Doppler signal corresponding to the target tissue from at least one of the components of the plurality of nth-order wave components from the frequency spectrum shown in FIG. Amount). For example, for the Doppler signal “3” farthest from the fixed object echo 60 in FIG. 2, the frequency of the Doppler signal “3” in the fundamental wave component (f _m ) or the second harmonic component (2f _m ) The frequency of the Doppler signal “3” is detected.

Further, the Doppler frequency detection unit 46 detects the frequency of the Doppler signal for each target tissue. That is, in FIG. 2, for the Doppler signal “3” corresponding to a certain target tissue, for example, the frequency of the Doppler signal “3” in the second harmonic component (2f _m ) is detected, and another target tissue having a different speed is detected. For example, the frequency of the Doppler signal “1” in the second harmonic component (2f _m ) is detected.

  Then, the speed calculation unit 50 calculates the speed for each target tissue based on the frequency (Doppler shift amount) of the Doppler signal detected by the Doppler frequency detection unit 46. For the principle of calculating the speed from the Doppler frequency, a conventionally known method is used. However, in this embodiment, the received signal is demodulated using the modulated transmission signal to obtain a demodulated signal as shown in FIG. 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. Therefore, for example, by using a Doppler signal near at least one of the harmonic components, the influence of the clutter localized in the case of no modulation is reduced, and as a result, the influence of the clutter can be reduced as much as possible. Speed information can be observed with high sensitivity while suppressing.

  As described above, the distance calculation unit 48 calculates the distance (depth) of the target tissue, and the speed calculation unit 50 calculates the speed of the target tissue. The display processing unit 52 forms a display image based on the calculated information and causes the display unit 54 to display the display image. 4 to 6 show examples of display images formed in the display processing unit 52. FIG.

  FIG. 4 is an example in which the speed of the moving tissue at each position in the depth direction is displayed in real time. That is, a graph composed of an axis indicating the velocity of the moving tissue (target tissue), an axis indicating the depth of the moving tissue in the living body, and three axes orthogonal to each other on the time axis is displayed in a perspective view.

In FIG. 4, the change in the graph in the time axis direction shows how the position (depth) and speed of the moving tissue change from time to time as time passes. As time elapses as t ₁ , t ₂ , t ₃ ,..., The display cross section changes toward the front of the figure. Although it is desirable that the velocity of each mobile tissue be on the vertical axis in the figure, the demodulated power from each mobile tissue may be on the vertical axis.

  Further, in the present embodiment, even when mobile tissues having different velocities exist at the same depth, they can be distinguished, so that a cross section of a graph at a certain time may be displayed as a cross section D. In this case, the vertical axis of the cross section D is the speed. In FIG. 4, three types of velocity components are shown as the cross section D. However, in principle, any number of velocity components can be displayed. Further, each speed component may be distinguished by a constant velocity line or a region as shown in FIG. 4 or may be represented by a color such as a color Doppler.

  FIG. 5 is a display example suitable when there are moving tissues of different speeds at the same depth. That is, it is a perspective view of a graph when the power of each velocity component is taken on the vertical axis and the axis indicating the depth of the moving tissue and the axis indicating the velocity are taken in the bottom surface. In the display of FIG. 5, even when there are moving tissues at the same depth and different speeds, mountains are displayed at different positions in the speed axis direction, so it is easy to read the difference in speed. The height of the mountain corresponds to the power of the received signal from each mobile tissue.

  FIG. 6 is a display in which the tomographic image of the target tissue is associated with the speed of each part in the tomographic image. That is, it is a perspective view of a graph in which the tomographic image of the target tissue is associated with the bottom surface and the velocity at each two-dimensional position in the tomographic image is the vertical axis. In the display of FIG. 6, the higher the mountain, the higher the moving speed of the tissue at that position. The power of the tissue at each position in the tomographic image may be the vertical axis. In the display example of FIG. 4, the position of the moving tissue is one-dimensional only in the depth, but in the display example of FIG. In order to give the image of FIG. 6 real-time properties, for example, an ultrasonic beam (sound ray) may be swept about 10 times or more per second and displayed every moment.

In the above embodiment, when the target tissue is a short distance, ie d but is calculated the distance d in the case of the following c / 4f _m is 0 or more, can also expand significantly the depth of the measurable tissue It is. Hereinafter, a second embodiment in which the measurable tissue depth is greatly expanded will be described.

  FIG. 7 shows a second preferred embodiment of the ultrasonic diagnostic apparatus according to the present invention, and FIG. 7 is a block diagram showing the overall configuration thereof. 7, parts having the same configuration and function in the embodiment of FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and description of the parts having the same functions will be simplified as appropriate.

The second embodiment shown in FIG. 7 differs greatly from the embodiment shown in FIG. 1 in that the FM modulated wave oscillator 24 modulates a modulated wave using a sine wave having a modulated wave frequency f _m1 and a modulated wave using a sine wave having a modulated wave frequency f _m2. That is, two types of modulated waves having different frequencies are output. The switching timing of the two types of modulated waves is controlled by the modulated wave control unit 25.

FIG. 8 is a diagram for explaining the switching timing of two types of modulation waves, and shows a modulation wave by a sine wave supplied from the FM modulation wave oscillator 24 to the FM modulator 20. The FM modulation wave oscillator 24 switches and outputs a modulation wave by a sine wave having a modulation wave frequency f _m1 and a modulation wave by a sine wave having a modulation wave frequency f _m2 . The switching timing is controlled by the modulated wave control unit 25.

That is, as shown in FIG. 8, the modulation wave control unit 25 outputs the modulation wave having the modulation wave frequency f _m1 in the time zone t ₁ and outputs the modulation wave having the modulation wave frequency f _m2 in the time zone t _2. Let Then, the time zone t _{1 and} the time zone t ₂ are switched alternately. As a result, the modulation wave supplied from the FM modulation wave oscillator 24 to the FM modulator 20 is alternately switched between the modulation wave having the modulation wave frequency f _{m1 and} the modulation wave having the modulation wave frequency f _m2 as shown in FIG. Is output.

Returning to FIG. 7, the FM modulator 20 generates an FM continuous wave based on the RF wave supplied from the RF wave oscillator 22 and the sine wave modulated from the FM modulated wave oscillator 24. As described with reference to FIG. 8, the modulated wave supplied from the FM modulated wave oscillator 24 to the FM modulator 20 is a modulated wave by a sine wave having a modulated wave frequency f _{m1 and} a sine wave having a modulated wave frequency f _m2. Modulated waves are switched alternately. For this reason, the FM modulator 20 generates an FM continuous wave using the modulation wave having the modulation wave frequency f _m1 in the time zone t ₁ and uses the modulation wave having the modulation wave frequency f _m2 in the time zone t _2. Thus, an FM continuous wave is generated.

  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 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 reference signal supplied to each mixer of the reception mixer 30 is output from the FM modulator 20. This in the second embodiment, when detecting a received signal corresponding to the modulation wave frequency f _m1 is, FM continuous wave corresponding to the modulation wave frequency f _m1 is utilized, whereas, the reception corresponding to the modulation wave frequency f _m2 When detecting a signal, an FM continuous wave corresponding to the modulation wave frequency f _m2 is used.

Therefore, the first demodulated signal corresponding to the modulation wave frequency f _m1 and the modulation wave frequency are obtained as a reception mixer output signal (demodulation signal) as a result of the mixing process of the reception RF signal and the reference signal executed in each mixer. Two kinds of demodulated signals of the second demodulated signal corresponding to f _m2 are obtained alternately. The first demodulated signal includes a plurality of n-th order wave components (n is a natural number of 0 or more) related to the modulated wave frequency f _m1 , and each of the second demodulated signals includes a plurality of modulated wave frequencies f _m2 . The n'th order wave component (n 'is a natural number of 0 or more) is included. Then, the first demodulated signal and the second demodulated signal are alternately supplied to the FFT circuits 40 and 42.

  The FFT circuits 40 and 42 alternately perform FFT operations on the first demodulated signal and the second demodulated signal. As a result, in the FFT circuits 40 and 42, each of the first demodulated signal and the second demodulated signal is converted into a frequency spectrum. The frequency spectrum of each of the first demodulated signal and the second demodulated signal output from the FFT circuits 40 and 42 is the same as the spectrum shape shown in FIG.

  In the second embodiment, the Doppler power detection unit 44 extracts a Doppler signal corresponding to the target tissue for each component of the plurality of nth-order wave components from the first demodulated signal converted into the frequency spectrum. Then, the power value of each extracted Doppler signal is detected. Further, a Doppler signal corresponding to the target tissue is extracted from each of the plurality of n'th order wave components from the second demodulated signal. Then, the power value of each extracted Doppler signal is detected.

Index value calculating section 45, based on the power of a plurality of Doppler signals detected for each of the first demodulated signal and the second demodulated signal, we obtain the two index values of the index value k _m1 and the index value k _{m @ 2.} Furthermore, the distance calculation unit 48 calculates the depth of the target tissue based on the two index values. Therefore, the calculation principle of the distance (depth) of the target tissue in the second embodiment will be described.

なお、数２２において、変調波周波数ｆ_m1に関するドプラ信号の電力Ｐ_nには、その右肩にｍ１の添え字を付しており、一方、変調波周波数ｆ_m2に関するドプラ信号の電力Ｐ_nには、その右肩にｍ２の添え字を付して区別している。 In the second embodiment, in order to greatly extend the depth of the measurable tissue, using two of the modulation wave frequency f _m1, f _{m @ 2,} two index values k _m1 that correspond to each of these, k _{m @ 2} is determined It is done. The index values km ₁ and _{km 2} can be obtained from the following equation for the two modulation wave frequencies f _m1 and f _m2 based on the equation (13).

In _Formula 22, the power P _n of the Doppler signal related to the modulation wave frequency f _m1 is given a subscript m1 on the right shoulder, while the power P _n of the Doppler signal related to the modulation wave frequency f _m2 is added. Is distinguished by attaching an m2 subscript to its right shoulder.

数２３の両式の差をとると次式が導かれる。

そして、数２４の両辺の絶対値をとり整理すると次式のようになる。

ここで、余弦項は次式のように求められる。

ここで、変調波周波数ｆ_m1とｆ_m2の差が小さい場合、数２５の右辺の分母は次式のように整理される。

そして、数２７の関係式を利用して数２５を整理すると次式が導かれる。

図９は、深さｄを変数とした場合の数２８の式を示している。つまり、横軸を対象組織の深さｄとした場合の数２８の式の値が実線で示されている。なお、図９における破線の関数は、変調周波数がｆ_m1の単一変調周波数の場合、つまり、図１の実施形態の場合におけるｋ（数１４）の絶対値を示している。 Further, a relationship of the following equation between the the two modulated wave frequency f _m1, f _{m @ 2} and the index value k _m1, k _{m @ 2.}

Taking the difference between the two equations in Equation 23, the following equation is derived.

Then, the absolute values of both sides of Equation 24 are taken and rearranged as follows.

Here, the cosine term is obtained as follows.

Here, when the difference between the modulation wave frequencies f _m1 and f _m2 is small, the denominator on the right side of Equation 25 is arranged as follows.

Then, the following formula is derived by rearranging the formula 25 using the relational formula of the formula 27.

FIG. 9 shows an expression of Formula 28 when the depth d is a variable. That is, the value of the equation (28) when the horizontal axis is the depth d of the target tissue is indicated by a solid line. The broken line function in FIG. 9 indicates the absolute value of k (Equation 14) when the modulation frequency is a single modulation frequency of f _m1 , that is, in the embodiment of FIG.

図１の実施形態においては、ｄが０以上でｃ／４ｆ_m以下の近距離の場合に有効な深さ測定が可能であった。これを数２９の波長λ₀で表現すると、ｄが０以上でλ₀／４以下となる。 The tissue wavelength λ ₀ of the ultrasonic wave corresponding to the index value k satisfying Expression 14 is given by the following equation.

In the embodiment of Figure 1, d is was possible effective depth measurement if the following short distance c / 4f _m 0 or more. Expressing this wavelength lambda ₀ of the number 29, d is lambda _0/4 or less or equal to 0.

したがって、組織内波長の比較から、図１の実施形態における測定可能距離と、図７の第二実施形態における測定可能距離の比率は次式のようになる。

仮に、第二実施形態におけるｆ_m1，ｆ_m2の差をｆ_m1−ｆ_m2＝１／１０ｆ_mとすると、測定可能距離は次式のように５倍に拡大される。

このように、二つの変調波周波数ｆ_m1，ｆ_m2を利用することにより、測定可能距離を拡大することができる。 On the other hand, the tissue wavelength λ ₁₂ of the ultrasonic wave corresponding to Equation 28 is given by the following equation.

Therefore, from the comparison of the intra-tissue wavelengths, the ratio of the measurable distance in the embodiment of FIG. 1 to the measurable distance in the second embodiment of FIG.

Assuming that the difference between f _m1 and f _m2 in the second embodiment is f _m1 −f _m2 = 1/10 f _m , the measurable distance is expanded five times as shown in the following equation.

Thus, the measurable distance can be expanded by using the two modulation wave frequencies f _m1 and f _m2 .

The Doppler power detection unit 44, the index value calculation unit 45, and the distance calculation unit 48 of FIG. 7 use the calculation principle described above. That is, the Doppler power detection unit 44 extracts the Doppler signal corresponding to the target tissue for each component of the plurality of n-th order wave components from the first demodulated signal converted into the frequency spectrum, and The power value P _n ^m1 is detected. Further, from the second demodulated signal, for each component of the plurality of first n'order wave component, by extracting the Doppler signal corresponding to the target tissue, detecting the power value P _n ^{m @ 2} of the Doppler signal.

Index value calculating section 45 uses the number 22, and calculates an index value k _m1 from the power value P _n ^m1 of a Doppler signal, calculates an index value k _{m @ 2} from the power value P _n ^{m @ 2} of the Doppler signal. Then, the distance calculation unit 48 uses the number 28, and calculates the distance d from the index value k _m1, k _{m @ 2} and a known frequency f _m1, f _m2.

  As described above, also in the second embodiment, the distance (depth) of the target tissue is calculated by the distance calculation unit 48, and the speed of the target tissue is calculated by the speed calculation unit 50 in the same manner as the embodiment of FIG. The The display processing unit 52 forms a display image based on the calculated information and causes the display unit 54 to display the display image. Also in the second embodiment, for example, the display images shown in FIGS. 4 to 6 are formed.

  As described above, according to the embodiment of the present invention (including the second embodiment), the position information (depth) and velocity information of the target tissue can be obtained simultaneously using the continuous wave. An ultrasonic pulse method is well known as a method for acquiring position information of a target tissue.

  In distance / velocity measurement using an ultrasonic pulse, it is necessary to increase the peak power of the ultrasonic pulse in order to improve the SNR. In order to increase the peak power of the ultrasonic pulse, it is necessary to take measures such as a high breakdown voltage of the transmission circuit system and a countermeasure for preventing leakage of the transmission pulse to the reception circuit system. In addition, when the peak power of the ultrasonic pulse is increased, there is a problem that it is necessary to consider the influence of the peak sound pressure on the living body.

  On the other hand, in the present embodiment, since the continuous wave is used, the ultrasonic transmission peak power can be made extremely smaller than that of the pulse method, and as a result, the above-described problem of the pulse method can be solved. . For example, in this embodiment, since a high voltage circuit is not required in the transmission circuit system, the circuit configuration is simplified and the transmission circuit is expected to be downsized. Moreover, it can contribute to the reduction in power of the transmission circuit.

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 demodulated signal. It is a figure for demonstrating the relationship between the depth d of an object structure | tissue, and the index value k. It is the example of a display which displayed the speed | velocity | rate of the moving tissue in each position of a depth direction in real time. This is a suitable display example when there are moving tissues at different speeds at the same depth. It is the example of a display which matched the tomogram of the object tissue, and the speed of each part in a tomogram. It is a block diagram which shows 2nd embodiment of the ultrasonic diagnosing device which concerns on this invention. It is a figure for demonstrating the switching timing of two types of modulation waves. It is a figure which shows several 28 Formula when the depth d is made into a variable.

Explanation of symbols

  20 FM modulator, 22 RF wave oscillator, 24 FM modulated wave oscillator, 40, 42 FFT circuit, 44 Doppler power detector, 46 Doppler frequency detector, 48 distance calculator, 50 speed calculator, 52 display processor.

Claims (7)

Transmission signal generation means for generating a modulated transmission signal by modulating a carrier wave signal using a modulated wave signal;
Transmitting and receiving means 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 reception signal;
The received signal is demodulated using the modulated transmission signal, thereby obtaining a demodulated signal including a plurality of nth-order wave components (n is a natural number of 0 or more) when the modulated wave signal is a fundamental wave. Demodulation means;
Doppler signal extraction means for extracting a Doppler signal corresponding to a target tissue for each component of the plurality of nth-order wave components from the demodulated signal;
Position information generating means for generating position information of the target tissue based on the intensity of the extracted plurality of Doppler signals;
Having
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The position information generating means calculates a depth of a target tissue as the position information;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The position information generation means includes a DC component that is a 0th-order wave component, a fundamental wave component that is a first-order wave component, and a plurality of harmonic components where n is 2 or more among the plurality of n-th order wave components. The Doppler signal of the target tissue extracted from each is a calculation target, and the depth of the target tissue is calculated based on the power of the plurality of Doppler signals.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The positional information generating means is a Doppler signal of a target tissue extracted from each of a fundamental wave component that is a first-order wave component of the plurality of n-th order wave components and a plurality of harmonic components where n is 2 or more. And calculating the depth of the target tissue based on the power of these multiple Doppler signals,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3 or 4,
The Doppler signal extraction means includes an FFT circuit that converts the demodulated signal into a frequency spectrum, and extracts the Doppler signal using the converted frequency spectrum.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 5,
Velocity information generation means for generating velocity information of the target tissue based on the frequency of at least one Doppler signal among the plurality of extracted Doppler signals.
An ultrasonic diagnostic apparatus. A carrier wave signal is modulated using a first modulated wave signal having a frequency f _m1 to generate a first modulated transmission signal, and the carrier wave signal is further modulated using a second modulated wave signal having a frequency f _m2 . Transmission signal generating means for generating a second modulated transmission signal by:
Transmitting and receiving means for transmitting an ultrasonic wave to the living body by supplying the first modulated transmission signal and the second modulated transmission signal, receiving a reflected wave from the living body and outputting a received signal;
The received signal is demodulated using the first modulated transmission signal, thereby including a plurality of nth-order wave components (n is a natural number of 0 or more) when the first modulated wave signal is a fundamental wave. A first demodulated signal is obtained, and the received signal is demodulated using the second modulated transmission signal, whereby a plurality of nth-order wave components in the case where the second modulated wave signal is a fundamental wave Demodulation means for obtaining a second demodulated signal including (n ′ is a natural number of 0 or more);
A Doppler signal corresponding to a target tissue is extracted from the first demodulated signal for each component of the plurality of n-th order wave components, and the plurality of n-th order wave components are further extracted from the second demodulated signal. A Doppler signal extraction means for extracting a Doppler signal corresponding to the target tissue for each of the components,
An index value k _m1 obtained based on the intensities of a plurality of Doppler signals extracted from the first demodulated signal, the index value is determined based on the intensities of a plurality of Doppler signals extracted from the second demodulated signal k _{m @ 2} Position information generating means for generating position information of the target tissue based on the two index values;
Having
An ultrasonic diagnostic apparatus.

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