JP2714042B2 - Pulse Doppler measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting the speed of an object using ultrasonic waves, and more particularly to an apparatus for measuring a blood flow in a living body in real time.

[Conventional technology]

Various devices are known for determining the flow velocity of an object by the Doppler effect of a sound wave. In particular, the pulse-Doppler method (eg, The Acoustical Society of Japan, Vol. 29, No. 6, (1973) 35
In devices using p.1 to 352), ultrasonic pulses (Pu
It is known that the measurement site can be specified by repeatedly transmitting the lsed Continuos Wave and applying a time gate corresponding to the distance to the measurement site to the received signal.

[Problems to be solved by the invention]

Assuming that the transmission interval of the ultrasonic pulse is T (sec), the range of the Doppler frequency that can be measured by the conventional pulse Doppler measurement method is ± 1 / 2T (Hz). For example, when T = 250 μsec, it is ± 2 kHz. Doppler frequencies beyond this range, for example 2.5 kHz, are erroneously measured in the prior art as -1.5 kHz. Considering the direction of the blood flow, if the direction of the blood flow with a positive Doppler frequency is called the forward direction, and the direction of the blood flow with a negative Doppler frequency is called the reverse direction, if the direction of the blood flow in the forward direction is large, The blood flow in the opposite direction will be displayed.

It is an object of the present invention to eliminate erroneous measurement of blood flow direction by correcting Doppler frequency measured by a conventional method.

[Means for solving the problem]

The transmission interval of the ultrasonic pulse is usually constant at T (sec). Following these transmit, perform the transmitting of little long T + T _S from T. Reflecting object is Doppler frequency ω _d (rad / sec)
During the transmission interval T, the phase angle is ω _d T
And at the transmission interval T + T _S , the phase angle is ω
there is a change of _d (T + T _S). Thus, the change in phase angle between T and T + T _S is ω _d T _S. The measurement limit in the conventional method is But with the new method, the new measurement limits And the conventional limit is extended to T / T _S times. (A method which exceeds this conventional limit has already been disclosed as a prior application in Japanese Patent Laid-Open No. 62-16 / 1987.
9073). Therefore, if an index indicating how many times the limit has been increased is η (η: real number), η can be expressed by the following equation.

If the output of the phase comparator (phase vector) and V _n, the complex of the transmitting interval T, the phase difference vector conjugate vector V * _n-1 of the vector V _n-1 before V _n and a time instant It is obtained by performing multiplication. Expressed the phase difference vector Y _n Y _n is given by the following equation.

_{Y = V n V * n-} 1 ... (4) adding the phase difference vectors Y _n for noise suppression.

For the equally-spaced transmission T, the phase difference is determined using equation (5). That is, Therefore, the Doppler frequency is obtained by the following equation.

On the other hand, if the phase difference between vectors Y 'obtained by adding about transmitting interval T + T _S Next, complex multiplication of Y's conjugate vector Y * and Y is performed to obtain a vector of the phase difference between Y and Y '. Assuming that the vector of the phase difference is Z, Z is given by the following equation.

Therefore, at this time, the Doppler frequency is given by the following equation.

ArgY according to the conventional method expressed by equation (7)
Compared to, the argument argZ in equation (10) is In a relationship. By rewriting equation (11), argY = η · argZ (12)

Therefore, from equation (7) Get the relationship.

If argY in equation (7) exceeds the range of ± π, an error will occur. Therefore, argY is corrected according to the value of η · argZ as follows. (When | ω _d T | <5π) ω _d T = argY−4π for −5π ≦ η · argZ <−3π = argY−2π for-3π ≦ η · argZ <−π = argY for−π ≦ η · argZ ≦ π = argY + 2π forπ <η · argZ ≦ 3π = argY + 4π for3π <η · argZ ≦ 5π (14) Generally, ω _d T = argY + k · 2πfor (2k−1) π ≦ η · argZ <(2k −1) π, k = −1,2,... = ArgYfor−π ≦ η · argZ ≦ π = argY + k · 2πfor (2k−1) π <η · argZ ≦ (2k−1) π, k = −1, 2,... (15) [Action] Accordingly, even if the angle argY obtained by the conventional method exceeds the limit, it is possible to correct the correction of argY by using η · argZ to determine the range of π. If this is done, aliasing can be prevented and correct measurement of the drup frequency is possible.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, a portion 16 is called a correction value detection circuit which is a main circuit newly added to the conventional pulse Doppler device.

In FIG. 1, in the conventional pulse Doppler device, a transmitting circuit 12 and a receiving circuit 13 are connected to the ultrasonic transducer 1. At a predetermined frequency ω ₀ from the transmitting circuit 12,
A pulsed sound wave having a center frequency component of ω ₀ is transmitted to a reflecting object 2 which is provided with a short pulsed transmission signal and a transmission interval T or T + T _S repeating ultrasonic transducer 1. . The reflected wave from the reflecting object 2 is detected by the ultrasonic transducer 1. The detected reception signal is input to the phase comparator 3 via the reception amplifier 13.
FIG. 2 shows the configuration of the phase comparator 3. Two mixers 31,3
2 the represented reference wave at α = Acosω ₀ t, respectively and the reception signal, α '= Asinω ₀ t mixes the reception signal and expressed reference wave. The output of each mixer is reduced filter 3.
Output via 3,34. That is, the outputs V _R and V _I are 9
0 ° is a low-frequency component of two mixed waves of the reference waves α and α ′ having different phases and the received signal.

FIG. 3 shows operation waveforms of the above-described portions of the present embodiment. The transmission by the transmission circuit 12 is performed at the timing shown in FIG. 3B. The distance in the first transmission pulse interval from a ₁ to a second transmission pulse a ₂ is T, a ₂ from the third transmission pulse a ₃ T, to the eighth transmission pulse a ₈ subsequent , And the transmission interval of each pulse is T. But from a ₈ ninth transmission pulse a ₉ is the interval T + T _S, the interval T + T _S from a ₉ to transmission pulse a ₁₀ in FIG. 10, each pulse until subsequent seventeenth transmission pulse a ₁₇ transmit interval is T + T _S. Equally spaced T transmissions are performed eight times,
Next, transmission at equal intervals of T + T _S is performed eight times. Here, T, T + T _S , and T _S are all integral multiples of the period 2π / ω ₀ of the transmission pulse and the reference wave. FIG. 3A shows a transmission waveform in the conventional pulsed Doppler method, all of which are at equal intervals T for comparison.

In this embodiment, the received signals of reflected sound waves obtained by performing the transmission shown in FIG. 3B are as shown by C ₁ , C ₂ , C ₃ ... In FIG. 3C. Are the transmission pulses a ₁ , a ₂ , a ₃ …
.. Has a delay of the round-trip time τ ₀ of the sound wave between the transducer 1 and the reflecting object 2. This received signal
c _1, c _2, and the c ₃ ...... and two reference waves shown in FIG. 3 D are each mixed with a phase comparator, it is compared in phase. c
_n (n = 1, 2, 3,...) are output by V _Rn , V _In
When represented by (n = 1, 2, 3,...), V _Rn and V _In can be expressed by the following equations.

_{V Rn = A n cosθ n V} In = A n sinθ n ... (16) For simplicity, will be referred to collectively At the the _{V n = V Rn + jV In} = A n exp (jθ n) ... (17) .

Considering V _Rn and V _In as a real part and an imaginary part, respectively, the phase angle θ _n of the vector V _n becomes a constant value θ ₀ as shown in FIG. 3E if the reflecting object is immobile. Show.

On the other hand, the reflector 2 is When in motion Doppler angular frequency omega _d composed speed, only the reference signal α, α 'ω _d becomes angle per unit time relative to the phase angle Fig. 3 D of the received signal rotates Then it can be approximated. Therefore, since the phase angle θ _n of the vector V _n rotates at the angular frequency ω _d , the phase difference φ _B between V _n and V _n−1 for the transmission interval T is φ _B = ω _d T. (18) Similarly, for the transmission interval T + T _S , the phase difference φ _C between V _n and V _n−1 becomes φ _C = ω _d (T + T _S ) (19). In the conventional method, the phase angle φ _B is detected, that is, ω
The first is to find _d T and calculate the Doppler angular frequency from this.
This is the Doppler angular frequency detection circuit 17 in the figure. Before describing the Doppler shift detection circuit 17, an MTI filter and a correction value detection method will be briefly described. The MTI filter is used in the human body to separate the movement of a blood vessel wall such as a blood vessel wall or the heart from the blood flow and detect a Doppler signal from the blood flow. However, the MTI filter is an abbreviation of the fixed object removing filter. The operation of the MTI filter will be described with reference to FIG. In FIG. 4, the output signal of the v ₁ ′, v ₂ ′... V ₁₄ ′ phase comparator 3 is converted into time-series data (Doppler signal series) using an A / D converter 4. In FIG. 1, if the output of the MTI filter 5-2 is denoted by v _1n (n = 1, 2,...) (With respect to the transmission interval T), V _1n = v _{n + q} + b ₁ v _n (20) Can be represented by For the transmission interval T + T _S, if the output of the MTI filter 5-2 is v _2n (m = 1, 2,...), Then v _2m = v _{m + p} ′ + b′v _m (21) Can be expressed. Where p = η _q and b ₁ , b ₁ ′ are filter coefficients. Next, the output of the MTI filter 5-2 is input to the autocorrelator 6-2. In the autocorrelator 6-2, the vector
For v _1n , a vector Y _1n indicating a phase difference from the vector v ₁ , _n−1 delayed by one time by the delay unit 11-2 is detected. Y _1n
It expressed the v _{1, n-1} of the complex conjugate v _{1, n-1} * with _{Y 1n = v 1n · v 1} , n-1 * ... (22). Since the vector Y _1n fluctuates due to the influence of noise, the detection of the vector Y _1n is repeated for the repeatedly reflected signal, and Y _1n is added by the vector adder 10-2. When a plurality of times (e.g. 4 times) result of addition and Y ₁ However, the symbol "~" represents an average value. Figure 4 is the same for the Doppler signal v ₈ '~v _14', MTI filter 5
2 is input to the autocorrelator 6-2. For the autocorrelator 6-2 vector v _2n, detecting a vector Y _2n indicating a phase difference between one clock delayed vector v _{2, n-1.} Y _2n is Y _{2, n-1} of the complex conjugate v _{2, n-1} * with _{Y 2n = v 4n · v 2} , n-1 * by expressed. Since the vector Y _2n varies due to the influence of noise, detection of the vector Y _2n is repeated for the reflected signal which can be repeated in the same manner, and Y _2n is added by the vector adder 10-2. When a plurality (e.g., four times) the result of addition to Y ₂ However, the symbol "~" represents an average value.

Where the phase difference , That is, ω _d T _S. For this purpose, Y ₁ and Y ₂ are detected by a phase difference detector (autocorrelator) 6-3.
(A vector of the phase difference difference) Z indicating the phase difference of The configuration of the phase difference detector 6-3 is the same as that of the phase difference detector 6-2, and the vector Z of the phase assist difference can be expressed by the following equation.

Next, by inputting Z to the angle detector 8-2, Get an angle. Angle detector 8-2 , And T _S is a smaller value than T.
Between T and T _S is the relationship T = ηT _S ((3) type). A circuit for multiplying the the control device 14 eta and angle Q _A.
That is, the correction value ηQ _A = η · argZ (28) is obtained as the output of the correction value detection circuit 16.

For the Doppler signals v ₁ ′ to v ₁₄ ′, a conventional Doppler frequency detection calculation is performed as shown in the upper part of FIG. In both the transmission interval and T + T _S ,
After input to the next MTI filter 5-1, a correlation operation is performed. In the embodiment shown in FIG. 1, the Doppler detection circuit 17 and the correction value detection circuit 16 are processed in parallel.

If the output of the third-order MTI filter 5-1 is v _3n (n = 1, 2,...) (With respect to the transmission interval T), v _3n = v _{n + 3} ′ + K ₁ v _{n + 2} ′ + K ₂ v _{n + 1} ′ + K ₃ v _n ′ (29) For the transmission interval T + T _S, if the output of the MTI filter 5-1 is v _4m (m = 1,2,...), V _4m = v ′ _{m + 3 + 7} + K′v ′ _{m + 2 +7 + K 2 'v m +} 1 + 7 + K 3'
v ′ _{m + 7} (30) It can be similarly expressed (FIG. 5). Filter coefficients K ₁ , K ₂ , K ₃ ,
By changing K ₁ ′, K ₂ ′, and K ₃ ′, the filter characteristics of v _3n and v _4m can be approximated. The configuration of the correlator 6-1 is the same as that of 6-2. Vector v
Vector delayed by one time by delay unit 11-1 for _3n
The phase difference vector Y _3n with v ₃ , _n−1 is detected. Y _3n is v ₃ , _n-1
By using the complex conjugate v ₃ , _n-1 * of Y _3n = v _3n · v ₃ , _n−1 (31) Y _3n is obtained as the output of the autocorrelator 6-1. Y _3n from can vary due to the influence of noise, the repeated obtaining reflected signal, repeating the detection of the Y _3n, Y _3n
Are added by the vector adder 10-1. Multiple times (for example, 4
When times) result of addition and Y ₃ Can be represented by Y ₃ is the output of the vector adder 10-1.
By inputting Y ₃ to the angle detector 8-1, Get an angle. The angle detector 8-1 is Is a circuit for calculating. If Q _B is divided by the transmission interval T, And the frequency variation due to the Doppler effect Is obtained, and the speed of the reflector is known.

Similarly, for the transmission interval T + T _S , the phase vector v
_4n , a vector delayed by one time by the delay unit 11-1
The phase difference vector Y _4n with v ₄ , _n−1 is detected. Y _4n is v ₄ , _n-1
By using the complex conjugate vector v ₄ , _n-1 * of the above, Y _4n = v _4n · v ₄ , _n-1 *... (35) Y _4n is obtained as the output of the autocorrelator 6-1. Y _4n from can vary due to the influence of noise, the repeated obtaining reflected signal, repeating the detection of the Y _4n, Y _4n
Are added by the vector adder 10-1. Multiple times (for example, 4
When times) result of addition to Y ₄ Can be represented by Y ₄ is the output of the vector adder 10-1.
By inputting Y ₄ to the angle detector 8-1, Get an angle. The angle detector 8-1 is Is a circuit for calculating. If Q _C is divided by the transmission interval T + T _S And the frequency variation due to the Doppler effect Is obtained, and the speed of the reflector is known. However, there is a restriction on the range of the Doppler frequency to be obtained. The limit is as follows from the equation (34) for the transmission interval T: And for the transmission interval T + T _S from equation (36) It is. Doppler frequencies beyond this range are measured in the wrong direction and magnitude (due to aliasing). Therefore,
It is necessary to correct the Doppler frequency exceeding this range.
The correction value is obtained by the correction value detection circuit 16 described above.

In the correction circuit, the correction angle θα is set to the first value according to the value of the output (correction value) η · argZ of 16 under the command of the control device 14.
It is calculated as shown in the table. Table 1 shows that η is 4, that is, T / T _S =
4 is shown. In Table 1,
Y _B represents a Y _3, Y _4. At this time, if the corrected angles are respectively Q _T and Q _{T + TS} Becomes In the correction circuit 9-1, the transmission interval T, T + T _S
T , Q _{T + TS} divided, Is output. Next, in the averaging circuit 10-3, Averaging Is output. argY ₃ and argY ₄ are angles obtained by conventional Doppler operation detection, obtained with normal accuracy, and SN
There is no deterioration. When the correction is not required, θα is always set to zero according to an instruction on the operation panel via the control device 14. In this case, the present apparatus displays the result according to the conventional method. The control device 14 can easily display the result of the conventional method and the result of the new method in parallel on the display.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

(1) If the Doppler frequency of the reflecting object is within the range of the conventional measurement limit, the conventional measurement can be performed.

(2) If the Doppler frequency of the reflecting object is out of the range of the conventional measurement limit, correct display of the blood flow direction and error can be performed with the same SN as that of the conventional one by correctly correcting the blood flow direction and velocity.

(3) If the conventional mode is used by switching the mode, the apparatus can be used as the conventional apparatus, and if the mode is switched to the new mode, the corrected blood flow is displayed. Therefore, the difference between the results in the conventional mode and the new mode can be easily compared.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of a phase comparator in the above embodiment, and FIG. 3 is a time chart showing the operation of the above embodiment. FIG. 4 is a diagram showing the flow of signal processing in the above embodiment, and FIG. 5 is a tertiary MTI filter. 5-1, 5-2: MTI filter, 6-1, 6-2, 6-3: correlator (phase difference detector), 16: correction value detection circuit, 17:
Doppler angular frequency detection circuit, 14 ... Control device.

Continuation of the front page (56) References JP-A-62-204733 (JP, A) JP-A-62-204734 (JP, A) JP-A-60-139238 (JP, A)

Claims (2)

(57) [Claims] 1. A first time interval T in a first time interval
In the second time interval, the second time interval (T + T _S )
A transmitter / receiver that transmits a plurality of ultrasonic pulses to an inspection target and obtains, as a reception signal, a reflected wave from the inspection target due to the plurality of ultrasonic pulses, and two transmission / reception units having 90 ° phases different from each other. Mixing a reference wave and the reception signal generated by the transmission at the first time interval to mix a first complex signal, and mixing the two reference waves and the reception signal generated by the transmission at the second time interval; And a first comparator of a first average phase difference vector, which is an average of a first phase difference vector representing a phase difference between successive first complex signals. An angle detecting means for obtaining a second angle of the second average phase difference vector, which is an average of a second phase difference vector representing an angle and a phase difference of the continuous second complex signal; A first position representing a phase difference of the first complex signal; The difference between the first average phase difference vector, which is the average of the difference vectors, and the second average phase difference vector, which is the average of the second phase difference vectors representing the phase difference between the successive second complex signals, Vector declination,
Means for calculating the product of (T / T _S ), a first fixed object filter arranged between the phase comparator and the argument detecting means, and means for calculating the product of the phase comparator and And a second fixed object filter arranged between the
A pulse Doppler measuring apparatus comprising: means for correcting the first argument and the second argument, wherein the argument detecting means and the means for calculating the product operate in parallel. 2. The pulse Doppler measuring apparatus according to claim 1, wherein T, (T + T _S ) is an integral multiple of a period of the transmitted ultrasonic pulse.