JPH05212032A - Ultrasonic doppler diagnostic system - Google Patents

Abstract

PURPOSE:To prevent the folding phenomena while keeping the constant speed measurement accuracy by properly selecting multiple speed calculation systems. CONSTITUTION:A first speed calculator 30 calculates the speed of the reflector of in vivo movement and the distribution value of the speed by means of the self correlation of a complex signal. A second speed calculator 32 obtains the self correlation signal by means of the self correlation of the complex signal and calculates the speed of the motion reflector based on the conjugate product or the complex product of the self correlation signal. A discrimination device 34 controls a switching device 38 and selects the output of the second speed calculator when the speed of the motion reflector is beyond the prescribed range and the distributed value of the speed is within the prescribed range. Otherwise, the output of the first speed calculator is selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an ultrasonic Doppler diagnostic apparatus for measuring the speed of a moving reflector in a living body such as blood flow and the dispersion value of the speed and displaying the image.

[0002]

2. Description of the Related Art An ultrasonic wave is transmitted into a living body, a reflected wave that has undergone a Doppler shift by an in-vivo motion reflector such as a bloodstream is received, and Doppler information included in a received signal obtained by this There is known an ultrasonic Doppler diagnostic apparatus that analyzes the velocity and the like of the motion reflector to display an image.

As a conventional basic device, Japanese Patent Publication No.
-44494 discloses a pulse Doppler type ultrasonic Doppler diagnostic apparatus. According to such an apparatus, the velocity distribution of a motion reflector on an ultrasonic beam can be obtained substantially in real time. Thus, the blood flow velocity distribution and the like can be two-dimensionally displayed in real time so as to be superimposed on the B-mode tomographic image.

In this conventional apparatus, the received signal is first mixed with a predetermined reference signal and converted into a complex signal. Then, the velocity of the motion reflector and the motion direction of the motion reflector are obtained from the declination of the vector (the signal of the real part and the signal of the imaginary part) obtained by the autocorrelation of the complex signal. In addition,
An ultrasonic Doppler diagnostic apparatus for obtaining the dispersion value of the velocity from the declination as well as the velocity of the motion reflector has been put into practical use (see, for example, Japanese Patent Publication No. 2-16139).

However, in the ultrasonic Doppler diagnostic apparatus described in Japanese Patent Publication No. 62-44494, when measuring blood flow at a relatively high speed, a so-called turn-back phenomenon occurs, and the effective speed of the apparatus is measured. There is a problem that the actual accurate value cannot be obtained for the speed exceeding the range. Here, the effective speed measurement range will be described.

Generally, in the case of discriminating only the absolute value of velocity, f _dmax = f between the maximum measurable Doppler frequency f _dmax and the ultrasonic pulse transmission repetition frequency f _r.
There is a relation of _r , and on the other hand, when discriminating not only the absolute value of the velocity but also its positive / negative, there is a relation of f _dmax = f _r / 2.
Therefore, in a device that also determines whether the velocity is positive or negative, the maximum Doppler frequency f _dmax is f _dmax = f ₀ · k · V _max = f _r / 2 (1) where f _{0 is the} emitted ultrasonic wave. Frequency, k: Constant V _max : Maximum speed, so the maximum measurable speed V _max is V _max = _fr / (2f ₀ · k) (2). This V _max is the upper limit of the effective speed measurement range described above, and there is a limit to the expansion of V _max in the above device in view of the required diagnostic depth and resolution.

Therefore, an ultrasonic Doppler diagnostic apparatus in which the speed measurement range is expanded by the two-cycle method is disclosed in Japanese Patent Publication No. 3-23050.
It has been proposed in the publication. In this device, ultrasonic waves of a constant frequency are alternately transmitted in the same direction with two pulse repetition periods, and the received signal obtained by this is first mixed with a predetermined reference signal to obtain a complex signal. And the autocorrelation signal is obtained by the autocorrelation of the complex signal. Then, from the result of the conjugate product or complex product of the autocorrelation signal obtained by the previous transmission and the autocorrelation signal obtained by the subsequent transmission, the velocity of the in-vivo motion reflector is calculated by the above-described declination. Is required. Therefore, according to the improved conventional ultrasonic Doppler diagnostic apparatus, for example, a high-speed blood flow in the heart can be measured without causing a folding back phenomenon in the enlarged fixed range.

In addition to the above, as a method for expanding the velocity measurement range, a two-frequency method (see, for example, "High-speed blood flow measurement by two-frequency method" in May 1990, Proceedings of the Japanese Society of Ultrasonic Medicine), pseudo-2 Frequency method (for example, Japanese Patent Laid-Open No. 63-
179275), AM modulation method (see, for example, Japanese Patent Application Laid-Open No. 2-147914), 2 reference frequency method (see, for example, Japanese Patent Application Laid-Open No. 1-190340), and cross-correlation method (Japanese Society of Ultrasonics Medicine lecture) Proceedings p363-p36
4 May 1989, “Velocity measurement by time-domain echo cross-correlation method”) and the like are proposed.

[0009]

However, when an ultrasonic Doppler diagnostic apparatus having an expanded velocity measurement range as described above is used to measure a blood flow at a relatively low speed, a measurement error is generally large. Therefore, there is a problem that accurate speed measurement cannot be performed. For example, the above Japanese Patent Publication No. 3-23
As a result, the device described in the '050 publication obtains the velocity of the moving reflector from the autocorrelation calculation of the autocorrelation. If the argument of each autocorrelation is small, the difference in the argument causes the S / N ratio to deteriorate, resulting in an increase in measurement error. Also, when the velocity dispersion value is large, the error tends to increase as in the above case.

Therefore, when measuring the velocity of a slow-moving reflector, the above-mentioned Japanese Patent Publication No. 62-62 is used rather than using the ultrasonic Doppler diagnostic device whose velocity measuring range is expanded as described above.
In some cases, the device described in Japanese Patent No. 44494 can perform more accurate measurement. The same may be said when the velocity dispersion value is large.

However, in such a device, as described above, the velocity of the high-speed motion reflector cannot be measured, so that
There has been a demand for a device that meets two contradictory requirements. The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to apply a speed measurement method in which a speed measurement range is expanded to a high-speed motion reflector, and to a low-speed motion reflector. Another object of the present invention is to provide an ultrasonic Doppler diagnostic apparatus capable of applying a speed measurement method capable of maintaining accuracy and an appropriate speed measurement method according to the speed of a motion reflector.

Another object of the present invention is to provide an ultrasonic Doppler diagnostic apparatus capable of selecting an appropriate speed measuring method in consideration of the dispersion value of the speed in addition to the speed of the motion reflector.

[0013]

To achieve the above object, the present invention transmits an ultrasonic pulse into a living body and receives a reflected wave that has undergone Doppler shift by a motion reflector in the living body. An ultrasonic Doppler diagnostic apparatus that analyzes the velocity of the motion reflector from the received signal obtained by mixing reference signals having mutually different 90-degree phases with the received signal and converting the received signal into a complex signal. A complex signal converter that
A calculator for calculating the velocity of the motion reflector by the autocorrelation of the complex signal, wherein the effective velocity measurement range is first.
A first velocity calculator that is a velocity measurement range, and a calculator that calculates an autocorrelation signal by autocorrelation of the complex signal and further calculates the velocity of the motion reflector from the conjugate product or complex product of the autocorrelation signal. A second speed calculator having a second speed measurement range expanded from the first speed measurement range, and a speed signal from the first speed calculator,
The second velocity calculator is selected when the velocity of the motion reflector is outside the first velocity measurement range, and the first velocity is selected when the velocity of the motion reflector is within the first velocity measurement range. And a selection circuit for selecting an arithmetic unit.

In the ultrasonic Doppler diagnostic apparatus of the present invention, a velocity dispersion calculator for calculating a dispersion value of the velocity of the motion reflector from the autocorrelation of the complex signal is provided.
The selection circuit selects the second speed calculator only when the speed of the motion reflector is outside the first speed measurement range and the dispersion value of the speed is within a predetermined range, and in other cases. It is characterized in that the first speed calculator is selected.

[0015]

According to the above construction, the speed calculator can be selected according to the speed of the motion reflector by the selection circuit.
For high-speed motion reflectors that are difficult to measure with a speed calculator,
By selecting the second speed calculator, it is possible to display the speed without the aliasing phenomenon. On the other hand, for slow motion reflectors,
From the second speed calculator that tends to increase the error,
By switching the selection to the speed calculator, accurate speed measurement can be secured. Here, as the second speed calculator, for example, a speed calculator based on the two-period method, the two-frequency method, or the like is used.

Further, by providing the speed dispersion calculator and considering the dispersion value of the speed in the selection circuit, when it is expected that the dispersion value of the speed becomes large and the speed measurement error by the second speed calculator becomes large. Can preferentially select the first speed calculation circuit to ensure effective speed measurement.

Therefore, according to the present invention, it is possible to realize an ultrasonic Doppler diagnostic apparatus according to the motion state of the motion reflector while maintaining a constant speed measurement accuracy.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

(A) Description of Overall Configuration FIG. 1 shows the overall configuration of an ultrasonic Doppler diagnostic apparatus according to the present invention. In FIG. 1, a timing signal generator 10 gives a transmission repetition signal 100 that determines a transmission repetition frequency to a transceiver 11, and the transceiver 11 generates a transmission drive signal in accordance with the signal and sends it to an ultrasonic probe 12. Supply. Thereby, as will be described later, an ultrasonic transducer (not shown) provided in the ultrasonic probe 12 radiates an ultrasonic pulse of a predetermined frequency into the living body at a predetermined transmission repetition period. ..

The reflected wave that has undergone the Doppler shift by the motion reflector such as the blood flow in the living body is received by the ultrasonic transducer of the ultrasonic probe 12, and the received signal is phase-combined by the transceiver 11. After performing high frequency amplification, etc., the complex signal converter 1
4 and the detector 16.

The detector 16 detects the received signal in order to obtain a B-mode tomographic image of the living body, and the detected black and white tomographic image signal is a digital scan converter (hereinafter referred to as DSC).
It is output to 18).

The complex signal converter 14 is for converting a received signal into a complex signal, and includes two mixers 20a, 20b and two low-pass filters 22a, 22b provided in parallel with each other. It is configured. Here, the reference signals 102a and 102b whose phases are different from each other by 90 degrees are supplied from the timing signal generator 10 to the mixers 20a and 20b.
Are supplied separately. These reference signals 1
02 has a frequency that is an integral multiple of the transmission repetition frequency.

Therefore, the received signal is first transmitted to the mixer 20a,
At 20b, mixed detection with the reference signals 102a and 102b is performed,
As a result, a signal having frequency components of the sum and difference of both signals appears at the outputs of the mixers 20a and 20b. Then, the signal having the sum frequency component is supplied to the low-pass filter 22.
a and 22b, and only the signal having the difference frequency component is output. With the above operation, the received signal is the real part signal x ₁ corresponding to the real part
And the imaginary part signal y ₁ corresponding to the imaginary part is converted into a complex signal Z ₁ .

By the way, in addition to the Doppler information of the motion reflector such as the blood flow to be measured, the received signal is relatively strong from the slow-moving part or the stationary part such as the heart wall which is not originally the object to be measured. And contains unnecessary Doppler information. Therefore, in order to accurately measure the velocity of the motion reflector to be measured, it is necessary to eliminate the unnecessary Doppler information.

Therefore, in this embodiment, a complex delay line canceller 24 is provided. The complex delay line canceller 24 includes two A / D converters 26a and 26b, two adders 28a and 28b, and two delay lines 30a, which are provided in parallel.
30b and. Here, the delay lines 30a and 30b delay the reception signal by the transmission repetition period (T).

Therefore, the complex signal Z ₁ from the complex signal converter 14 is first converted into a digital signal by the A / D converters 26a and 26b, and is added to the complex signal of which the phase has been inverted one cycle before. It will be. As a result, the signal at the present time of the stationary part or the slow-moving part does not change much from the signal of the previous cycle, so they cancel each other, and as a result, the motion reflection with a certain speed that fluctuates during one cycle. Only the body signal component remains, and the complex delay line canceller 24 outputs the complex signal Z ₃ from which unnecessary Doppler information is removed.

The received signal processing up to this point is shown below by mathematical expressions.

The reference signal 102a has a frequency f ₀ that is an integral multiple of the transmission repetition frequency f _r , and if its amplitude is 1, it is expressed by the following third equation. sin (2πf ₀ t) (3) Similarly to the above, the reference signal 102b is represented by the following fourth equation. cos (2πf ₀ t) (4) On the other hand, the received signal from the ultrasonic probe 12 is represented by the following fifth equation with the Doppler shift frequency being f _d . sin (2πf ₀ t + 2πf _d t) (5) Since the received signal is a pulse wave, sin {2π (f ₀ ± nfr _r ) t + 2πf _d (1 ± nfr _r / f ₀ ) t is generally used. } (6) (where n is 0, 1, 2, ...
, Which is an integer), but in the following description, for simplification of description, the received signal represented by the above-mentioned fifth equation when n = 0 will be described.

In the mixer 20a, the product of the received signal and one of the reference signals 102a is obtained, so that the following equation, which is twice the product of the third and fifth equations, is obtained. cos (2πf _d t) -cos (4πf ₀ t + 2πf _d t) (7) Then, this signal is 2f ₀ + f in the low-pass filter 22a.
The frequency component of _d is removed, and the output signal becomes cos (2πf _d t) (8). On the other hand, similarly to the above, the output signal that has passed through the mixer 20b and the low-pass filter 22b becomes sin (2πf _d t) (9). Therefore, if the above equation 8 is the real part and the above equation 9 is the imaginary part, the complex signal Z ₁ output from the complex signal converter 14 is Z ₁ = cos (2πf _d t) + i · sin (2πf It can be expressed as _d t) (10).

The complex delay line canceller 24 adds the complex signal Z _{1 to} the phase-inverted signal of the signal Z ₂ delayed by one period T. Here, the signal Z ₂ is expressed as Z ₂ = cos {2πf _d (t−T)} + i · sin {2πf _d (t−T)} (11), and the output Z _{3 of the} adder 28 Is Z ₃ = Z ₁ -Z ₂ = -2sin {2πf _d (T / 2)} · sin {2πf _d (t−T / 2)} + i · 2sin (2πf _d (T / 2)} · cos { 2πf _d (t−T / 2)} (12), and if this twelfth equation is expressed as Z ₃ = x ₃ + i · y ₃ (13), then x ₃ and y ₃ are _{x 3 = -2sin {2πf d (} t-T / 2)} · sin {2πf d (t-T / 2)} ··· (14) y 3 = 2sin (2πf d (T / 2)} · cos {2πf _d (t−T / 2)} (15)

Next, the complex delay line canceller 24
The following configuration will be described.

The complex signal Z ₃ output from the complex delay line canceller 24 is branched into two parts and sent to the first speed calculator 30 and the second speed calculator 32.

The first velocity calculator 30 calculates the velocity V ₁ of the in-vivo motion reflector by the autocorrelation of the complex signal Z ₃ , and in this embodiment also calculates the velocity variance value σ ^2. is doing. Here, in the first speed calculator 30, the speed measurement range in which the folding phenomenon does not occur is defined as the first speed measurement range.

On the other hand, the second velocity calculator 32 obtains an autocorrelation signal by the autocorrelation of the complex signal, and further calculates the velocity V _{2 of the} moving reflector from the conjugate product or complex product of the autocorrelation signal.
And has a second speed measurement range that is expanded (the expansion ratio is α) from the first speed measurement range.

Therefore, even if the velocity of the motion reflector exceeds the first velocity measurement range and the loopback phenomenon occurs at the output of the first velocity calculator 30, the second velocity calculation is performed up to the second velocity measurement range. The velocity of the motion reflector can be obtained by the device 32 without causing the folding back phenomenon. In addition, regarding the first speed calculator 30 and the second speed calculator 32,
It will be described in detail later.

The variance value signal σ ² output from the first speed calculator 30 and the speed signal V ₂ output from the second speed calculator 32 are output to the determination circuit 34. On the other hand, the first
The variance value signal σ ² output from the velocity calculator 30 is output to the DSC 18 for image display of the variance value, and the other velocity signal V ₁ is multiplied by 1 / α by the coefficient multiplier 36, The signal V ₁ ′ is output to the switch 38.

In this embodiment, the determiner 34 determines that V ₂ is valid when the velocity of the motion reflector exceeds the first velocity measurement range and the velocity dispersion value is within the predetermined range. , Otherwise, V ₁ is determined to be valid. Then, the determination result is given to the switch 38 as a switching control signal, and either V ₁ or V ₂ multiplied by 1 / α is selected as appropriate. The specific configuration of the determiner 34 will be described later.

The velocity signal selected by the switch 38 is output to the DSC 18 as image data together with the variance value signal σ ² and the B-mode tomographic image signal from the detector 16. Then, the image data output from the DSC 18 is sent to the CRT 40, and the CRT 40 displays a color image. In this image display, in the present embodiment, the velocity and the dispersion value of the blood flow and the like are two-dimensionally displayed by being superposed on the black-and-white B-mode tomographic image, and the velocity and the dispersion value of the blood flow are identified by color.

(B) Description of First Speed Calculator FIG. 2 shows the configuration of the first speed calculator 30.
Of these, the configuration indicated by 300 in the figure is basically the same as the autocorrelator shown in Japanese Patent Publication No. 62-44494.

The complex signal Z ₃ (specifically, the real part signal x ₃ and the imaginary part signal y ₃ ) output from the complex delay line canceller 24 is first delayed by the delay lines 42a and 42a.
At b, it is delayed by one cycle (T) of the transmission repetition frequency, and a complex signal Z ₄ is generated. This complex signal Z ₄ is
It is expressed by the following equation. _{Z 4 = x 4 + i ·} y 4 ··· (16) _{However, x 4 = -2sin {2πf d} (T / 2)} · sin {2πf d (t-3T / 2)} ··· (17) y ₄ = 2sin {2πf _d (T / 2)} · cos {2πf _d (t-3T / 2)} (18) Then, the signal Z having a complex conjugate relationship with this complex signal Z _4
4 ^* = a x ₄ -i · y _4, the the complex signal Z _3, by the finding that as the conjugate product following autocorrelation is calculated. ^{_{Z 3 · Z 4 * = (}} x 3 + i · y 3) (x 4 -i · y 4) = x 3 · x 4 + y 3 · y 4 + i (x 4 · y 3 -x 3 · y 4) · .. (19) Multipliers 44a and 44 are used to perform the operation of the nineteenth expression.
b, 44c, 44d are provided, and further adders 46a,
46b is provided.

If the output of the adder 46a is R, the 14th
From the equation, the fifteenth equation, the seventeenth equation, and the eighteenth equation, R = x ₃ · x ₄ + y ₃ · y ₄ = ₄ sin ² {2πf _d (T / 2)} · cos (2πf _d T) ( 20), and if the output of the adder 46b is I, then I = x ₄ · x ₃ −x ₃ · y ₄ = ₄ sin ² {2πf _d (T / 2)} · sin (2πf _d T) ························································································· (() ((1 (2) (2))) (2)

In order to remove the noise component contained in the output S, an averaging circuit composed of 48 and 49 is provided.

Here, 48a and 48b add a plurality of times, and the added values are divided by the number of additions by dividers 49a and 49b to average them.

From the above calculation formula, the velocity of the motion reflector is calculated by calculating the deviation angle θ between the real part R and the imaginary part I of the complex signal S.
Calculated from The deviation angle θ is obtained as θ = tan ⁻¹ (I / R) = 2πf _d T (23), and from this, the Doppler shift frequency f _d is f _d = θ / (2πT) ... (24) is obtained from the deflection angle θ. Since the velocity of the motion reflector is proportional to the Doppler shift frequency f _d , its f
Calculated from _d . At this time, I and R take positive or negative values, and the motion direction of the motion reflector is obtained from the sign of the argument θ. Further, since θ can be actually measured within the range of ± π, the first speed measurement range in which the folding phenomenon does not occur is defined in that range.

It is the declination calculator 45 that calculates the velocity of the moving reflector from this complex signal S, and the complex signal S
The variance calculator 47 calculates the velocity variance value σ ² from the above. Regarding this distributed computing unit 47,
No. 16139.

(C) Description of the First Embodiment of the Second Speed Calculator When the first speed calculator 30 is used to measure the speed of the high-speed motion reflector, the above-mentioned folding phenomenon occurs,
Originally, it is not possible to calculate the speed. Therefore, a second speed calculator 32 is provided which has a speed measurement range expanded from the first speed measurement range and which is an improvement of the first speed calculator 30. If the second speed calculator 32 measures the speed of the low-speed motion reflector, or if the dispersion value of the speed is large, the measurement error increases as described above. The existence of the arithmetic unit 30 is significant. That is, the present invention, according to the measurement target,
The outputs of these two speed calculators are switched to make the most of their advantages.

FIG. 3 shows the configuration (32-1) of the first embodiment of the second speed calculator. In addition, this configuration is
Basically, it is the same as the speed measurement calculator based on the two-period method described in JP-B-3-23050.

By the way, FIG. 4A shows a waveform of a general ultrasonic wave transmitted to the inside of a living body. T in (A) is a transmission repetition period, and ultrasonic waves of a constant frequency are transmitted in a pulsed manner at a period T.

Next, (B) shows the waveform of ultrasonic waves when the second speed calculator 32-1 of the first embodiment is applied. That is, ultrasonic waves are transmitted from the ultrasonic probe 12 in a periodic pattern in which the periods T ₁ and T ₂ are alternately combined. The frequency of ultrasonic waves is constant.

In FIG. 3, the configuration indicated by 302 in the figure is basically the same configuration as the configuration 300 for obtaining the autocorrelation shown in FIG. 2, and the same reference numerals are given and the description thereof is omitted. However, the delay lines 42a, 42 in FIG.
In 2b, in order to realize the two-cycle method, the delay amounts of the reception signals relating to the transmission repetition periods T ₁ and T ₂ are alternately switched to T ₁ or T ₂ . Also,
The delay line delay amount in the averaging circuits 48a and 48b is T ₁ + T ₂ .

Here, assuming that the absolute value of the autocorrelation value calculated in the configuration 302 is | S |, the autocorrelation signals R and I are R = | S | cos θ (25) I = | It is represented by S | sin θ (26).

Of the two transmission repetition periods,
If the autocorrelation signals R and I obtained by the previous transmission are used as the first autocorrelation signal and the autocorrelation signal obtained by the subsequent transmission is used as the second autocorrelation signal, in the present embodiment, Of the autocorrelation signals, R is delayed by T ₁ or T ₂ at the delay line 50a, and I is delayed line 5
It is delayed by T ₁ or T ₂ at 0b. On the other hand, R and I of the second autocorrelation signal are input to the next multiplier without any delay.

In FIG. 3, in the present embodiment, four multipliers 52a, 52b, 52c, 52d and two adders 54a, 54b are used to generate the first autocorrelation signal and the second autocorrelation signal.
The conjugate product with the autocorrelation signal is calculated. Here, the conjugate product refers to the product of either one of the first autocorrelation signal and the second autocorrelation signal and the other conjugate complex number.
Therefore, the multiplier group 52 executes the following calculation. _{(R 1 + i · I 1} ) (R 2 + i · I 2) = R 1 R 2 + I 1 I 2 + i (I 1 R 2 -R 1 I 2) = x 7 + i · y 7 ··· (27) Here, R ₁ and I ₁ are the real and imaginary parts of the first autocorrelation signal, and R ₂ and I ₂ are the real and imaginary parts of the second autocorrelation signal. Be done. R ₁ = | S | cos θ ₁ (28a) I ₁ = | S | sin θ ₁ (28b) θ ₁ = 2πf _d T ₁ R ₂ = | S | cos θ ₂ (29a) I _{2 = | S | sinθ 2 ··} (29b) θ 2 = 2πf d T 2 Thus, substituting this 28 formula and 29 formula to the 27 _{equation, x 7 = R 1 R 2} + I 1 I 2 = | S | ² (cos θ ₁ cos θ ₂ + sin θ ₁ sin θ ₂ ) ... (30) y ₇ = I ₁ R ₂ −R ₁ I ₂ = | S | ² (sin θ ₁ cos θ ₂ −cos θ ₁ sin θ ₂ ) ... (31) x ₇ , which is the result of the conjugate product obtained as described above,
y ₇ is sent to the declination calculator 56. In addition, the reversing device 58
Is for returning the sign of y ₇ which is alternately inverted for each transmission.

Then, the argument calculator 56 performs the following calculation. θ ₁ −θ ₂ = tan ⁻¹ (x ₇ / y ₇ ) = 2πf _d (T ₁ −T ₂ ) = 2πf _d ΔT (32) Therefore, f _d is ΔT (T ₁ −T ₂ ). And Δθ (= θ ₁ −
θ ₂ ) and the velocity V ₂ of the motion reflector can be obtained from f _d . Here, as is clear from Expression 32, as a result, the same Doppler information as that of transmitting the ultrasonic wave with the transmission repetition period of ΔT is obtained. That is, the effective speed measurement range can be expanded without changing the maximum measurement depth.

Although the conjugate product of the first autocorrelation signal and the second autocorrelation signal is calculated in this embodiment, a complex product may be calculated.

(D) Description of Second Embodiment of Second Speed Calculator In addition to the two-cycle method described above, for example, the following two-frequency method can be applied to expand the speed measurement range. ..

FIG. 5 shows a second embodiment 3 of the second speed calculator.
The overall configuration of 2-1 is shown. In the second embodiment, as shown in FIG. 4C, ultrasonic waves of two different frequencies f _c1 and f _c2 are alternately transmitted at a constant transmission repetition period T. The frequencies of the reference signals 102a and 102b supplied to the complex signal converter 14 shown in FIG. 1 are alternately switched to f _c1 or f _c2 according to the frequency of the transmitted ultrasonic waves. In this embodiment, the ultrasonic waves of f _{c1 and} the ultrasonic waves of f _c2 are alternately transmitted, but they may be alternately transmitted a plurality of times or other transmission patterns.

The configuration 306 in FIG. 5 is basically the same as the configuration 302 shown in FIG. 3, and the configuration 308 in FIG. 5 is basically the same as the configuration 304 shown in FIG. Are denoted by the same reference numerals, and description thereof will be omitted. However, the delay lines 42a and 42b in the second embodiment perform a delay of twice the transmission repetition period T. Further, the delay lines included in the averaging circuits 48a and 48b are also delayed by 2T as described above.

When the operation of the second embodiment is applied to the calculations from the above 16th equation to the 31st equation, if the Doppler frequency for f _c1 is f _d1 and the Doppler frequency for f _c2 is f _d2 , then Similar to the equation 32, θ ₁ −θ ₂ = 2π (2f _d1 −2f _d2 ) T = 2π · 2 · Δf _d · T (33), and the velocity of the motion reflector can be easily _calculated. Desired. Note that in Formula 33, the fact that f _d1 and f _d2 are doubled is because the delay lines 42a and 42 shown in FIG.
This is because the delay amount of 2T is set in b.

In the second embodiment as well, the complex product may be calculated as in the first embodiment.

(E) Description of Judgment Device FIG. 6 shows a specific configuration of the judgment device 34. As described above, the determiner 34 selects one of the outputs of the first speed calculator and the second speed calculator according to the speed of the motion reflector and the dispersion value of the speed. Is more appropriate.

In FIG. 6, the speed signal V ₂ output from the second speed calculator 32 is input to the absolute value calculator 60 including a ROM or the like, and the absolute value of the speed is obtained. Then, the absolute value signal from the absolute value calculator 60 is supplied to the comparator 6
2 and is compared with a predetermined speed comparison signal V _th . Here, the speed comparison signal V _th indicates one upper limit of the first speed measurement range. Then, when the absolute value of the velocity is between 0 and _Vth , "1" is output from the comparator 62, and when it is outside 0 to _Vth ,
"0" is output.

On the other hand, the variance value signal σ ² output from the first speed calculator 30 is input to the comparator 66 and compared with a predetermined variance comparison signal σ ² _th . As described above, in the second speed calculator 32, the measurement error tends to increase when the dispersion value of the speed becomes higher than a certain value. Therefore, the comparator 66 determines whether or not the actual variance value is within the range that the second speed calculator 32 can allow. That is, the variance comparison signal σ ² _th indicates the upper limit of the allowable variance value range.

Then, the comparator 66 outputs the variance value signal σ
^2, when there between 0～Shiguma ² _th outputs "0", if in addition 0～Shiguma ² _th outputs "1".

The output signals of the comparators 62 and 66 are
It is input to the OR circuit 64, and the OR of both signals is taken. Therefore, when the velocity of the motion reflector is outside the first velocity measurement range and the velocity dispersion value is within the above-mentioned predetermined range, "0" is output from the OR circuit, and in other cases, , "1" is output.

The output signal from the OR circuit is sent to the switch 38 shown in FIG. 1 as a switching control signal. When the output signal is "0", the speed output signal of the second speed calculator 32 is output. V ₂ is selected, and in the case of “1”, the speed output signal V ₁ of the first speed calculator 30 passing through the coefficient multiplier 36 is selected. As a result, the folding phenomenon can be avoided as much as possible while maintaining a constant speed measurement accuracy.

In this embodiment, the dispersion value of the speed is taken into consideration, but when giving priority to the prevention of the aliasing phenomenon, only the speed may be used as the judgment parameter. Further, the variance value of the velocity may be obtained by the second velocity calculator and supplied to the determiner 34.

(F) Description of Velocity Display Although various display systems can be applied to the velocity display of the motion reflector, FIG. 7 shows a display example of the apparatus of this embodiment. In FIG. 7, (A) shows the first speed measurement range and the expanded second speed measurement range. Also,
(B) shows the relationship between the speed of the motion reflector and its display color. Here, for example, the upper limit of the first speed measurement range is ± 50 cm / s, and the upper limit of the second speed measurement range is ± 150 cm / s.

As shown in (B), in the first speed measurement range, the speed in the direction is displayed in red light and dark as in the conventional art, and the speed in the negative direction is displayed in light and dark blue. Then, the velocity exceeding the first velocity measurement range in the positive direction is indicated by the color change from red to light pink, while the velocity exceeding the negative direction is indicated by the color change from blue to light purple. Note that FIG. 8 shows the brightness values R, G, and B when the above speed display is actually formed on the display device 40 in association with the speed.

According to the speed display of this embodiment, whether the first speed calculator 30 or the second speed calculator 30 is applied to the display image can be judged by the display color. As described above, according to the ultrasonic Doppler diagnostic apparatus of the present embodiment, it is possible to realize an appropriate speed calculation according to the speed of the motion reflector and the dispersion value of the speed. As the second speed calculator, various speed calculations described in the conventional example can be applied in addition to the above-described embodiment, and the first speed calculator and the second speed calculator share an overlapping component. It is also suitable to simplify the configuration.

[0071]

As described above, according to the present invention,
The second speed calculator can be applied to the high-speed motion reflector to avoid the aliasing phenomenon, and for the low-speed motion reflector in which the measurement error increases in the second speed calculator,
The measurement can be performed by applying the first speed calculator. Therefore, according to the present invention, the advantages of both of the two speed calculators can be effectively utilized.

Further, by taking into consideration the velocity dispersion value as well as the velocity dispersion of the motion reflector as a selection criterion for the computing unit,
A more appropriate choice can be made.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an ultrasonic Doppler diagnostic apparatus according to the present invention.

FIG. 2 is a block diagram showing a configuration of a first speed calculator.

FIG. 3 is a block diagram showing a configuration of a first embodiment of a second speed calculator.

FIG. 4 is an explanatory diagram showing a concept of a cycle of ultrasonic waves to be transmitted.

FIG. 5 is a block diagram showing a configuration of a second embodiment of the second speed calculator.

FIG. 6 is a block diagram showing a configuration of a determiner.

FIG. 7 is an explanatory diagram showing a relationship between a speed measurement range and display colors.

FIG. 8 is an explanatory diagram showing luminance values R, G, B in speed display.

[Explanation of symbols]

 11 Transmitter / receiver 14 Complex signal converter 24 Complex delay line canceller 30 First speed calculator 32 Second speed calculator 34 Judgment device 38 Switching device

Claims (4)

[Claims] 1. An ultrasonic pulse is transmitted into a living body, and a velocity of the moving reflector is measured from a received signal obtained by receiving a reflected wave that has undergone Doppler shift by the moving reflector in the living body. In the ultrasonic Doppler diagnostic apparatus, a reference signal having a phase difference of 90 degrees from each other is mixed into the reception signal separately, and a complex signal converter for converting the reception signal into a complex signal, and the motion by the autocorrelation of the complex signal. A calculator for calculating the speed of the reflector, where the effective speed measurement range is the first
A first speed calculator that is a speed measurement range, and an autocorrelation signal is obtained by autocorrelation of the complex signal,
And a second speed calculator having a second speed measurement range expanded from the first speed measurement range, the calculator calculating the speed of the motion reflector from the conjugate product or complex product of the autocorrelation signals. Receiving a velocity signal from the first velocity calculator, selecting the second velocity calculator when the velocity of the motion reflector is out of the first velocity measurement range, and determining the velocity of the motion reflector. An ultrasonic Doppler diagnostic apparatus comprising: a selection circuit that selects the first speed calculator when the speed is within the first speed measurement range. 2. The ultrasonic Doppler diagnostic apparatus according to claim 1, further comprising: a velocity dispersion calculator that calculates a dispersion value of the velocity of the motion reflector from the autocorrelation of the complex signal, wherein the selection circuit includes: The second speed calculator is selected only when the speed of the motion reflector is out of the first speed measurement range and the dispersion value of the speed is within a predetermined range, and in other cases, the first speed calculator is selected. An ultrasonic Doppler diagnostic apparatus, characterized in that 3. The ultrasonic Doppler diagnostic apparatus according to claim 1, wherein ultrasonic waves of a constant frequency are transmitted in a periodic pattern in which two different pulse repetition periods are combined in the same direction. The velocity calculator calculates the velocity of the moving reflector from the conjugate product or complex product of the autocorrelation signal of the earlier transmission and the autocorrelation signal of the later transmission of the two different pulse repetition periods. A characteristic ultrasonic Doppler diagnostic device. 4. The ultrasonic Doppler diagnostic apparatus according to claim 1, wherein ultrasonic waves having two different frequencies are transmitted in a predetermined order in the same direction in the same direction, and the second velocity The calculator calculates the velocity of the moving reflector from a conjugate product or a complex product of an autocorrelation signal generated by transmitting ultrasonic waves of one frequency and an autocorrelation signal generated by transmitting ultrasonic waves of the other frequency. A characteristic ultrasonic Doppler diagnostic device.