JPH0431264B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an ultrasonic Doppler diagnostic device, which uses ultrasonic waves capable of detecting or measuring the velocity of moving reflectors such as blood flow within the heart or blood vessels. Related to improvements in Doppler diagnostic equipment.

[Prior Art] A motion reflector within a subject, for example, an organ such as the heart,
The ultrasonic pulsed Doppler method has been put to practical use in order to measure the blood flow and body fluid flow in the circulatory system and blood vessels, or the velocity of movement reflectors such as myocardium. The motion velocity of the motion reflector can be electrically detected based on the Doppler frequency shift. In other words, ultrasonic pulses are emitted at a constant repetition frequency, the reflected waves from a moving reflector are received, and the distance to the reflector is measured by comparing the transmission time and reception time. The velocity of the reflector can be measured by calculating the deviation.

In this case, the repetition frequency for emitting ultrasonic pulse waves is generally selected depending on the distance to the motion reflector. However, when measuring a long-distance object, if a higher frequency is selected compared to the repetition frequency determined according to the distance to the reflector, as is well known, reflected echoes may occur at a distance closer than the actual distance. appears, making it difficult to judge distance.

In addition, a phenomenon similar to the above occurs when measuring the velocity of a moving reflector, and if a repetition frequency that is lower than the Doppler frequency due to the velocity of the reflector is selected, it appears as a low frequency due to the folding phenomenon.
It becomes difficult to determine the speed.

In order to measure both distance and velocity without causing aliasing, the maximum Doppler frequency f _d
and repetition frequency f _r , in the case of a device that can determine not only the absolute value of velocity but also its sign, f _d
= f _r /2, and it is widely known that in the case of a device that detects and measures only the absolute value of velocity, it is necessary to satisfy the relationship f _d = f _r .

Here, in a device that can determine whether the velocity is positive or negative, f _d = f ₀ · k · V = f _r /2 However, f ₀ : Emitted ultrasonic frequency, f _r : Repetition frequency, f _d : Maximum Doppler frequency, k: constant, V: maximum speed. Therefore, the maximum measurable speed V is V=f _r /(2f ₀ · k).

[Problems to be solved by the invention] First problem However, the above-mentioned maximum measurable speed V
As can be understood from the equation, if we try to increase the repetition frequency f _r in order to increase the maximum velocity V, the maximum distance of the reflector that can be measured without causing aliasing becomes smaller, so it is difficult to move at high speeds. When measuring reflectors that move, there is a drawback that velocity cannot be measured over long distances.

In addition, if we try to select a low ultrasonic frequency to emit, it is not only difficult to form a transmitted wave with a narrow pulse width, but also a sharp radiation beam cannot be formed, resulting in a decrease in distance resolution and azimuth resolution. There was a problem that the distance to the reflector, which is far away and moving at high speed, and the speed of the reflector could not be determined at the same time.

Second problem In addition, as a Doppler device that accurately measures the motion velocity of a motion reflector in real time, the present applicant has developed a velocity calculation device using an autocorrelation method, published in Japanese Patent Laid-Open No.
188433 has already been filed.

According to this device, the Doppler received signal obtained from within the subject is converted into a complex signal, the conjugate product and complex product of the complex signal are determined by the autocorrelation method, and the Doppler frequency shift is calculated from this autocorrelation value. are doing. The Doppler frequency shift obtained in this way corresponds to the velocity of the motion reflector, and the accurate velocity can be determined from this frequency shift amount.

However, in such a device, there is a problem in that the velocity obtained with a single beam is only the radial velocity moving in the direction of the ultrasonic beam, and the direction of velocity cannot be accurately displayed.

For this reason, in the past, complex ultrasound beams were emitted from different positions a certain distance apart to the same position within the subject, and the multiple velocity signals obtained were synthesized to determine the motion reflector including the direction of motion. I'm looking for speed.

However, this method not only complicates the device, but also has the disadvantage that it cannot be applied to areas where the insertion position and angle of the ultrasound beam are limited, such as the heart. It was hot.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to eliminate the aliasing phenomenon, to satisfactorily measure the speed of a reflector moving at a high speed at a long distance, and at the same time. An object of the present invention is to provide an ultrasonic Doppler diagnostic device that can accurately determine velocity with a simple device without emitting ultrasonic beams from different positions.

[Means for Solving the Problems] In order to achieve the above object, the present invention emits an ultrasonic pulse wave with a constant repetition frequency into the subject, compares the transmitted signal and the received signal, and calculates the motion reflection. Ultrasonic Doppler diagnostic equipment that detects the distance to the body and the speed of motion reflectors generates multiple ultrasound pulse waves with different frequencies in the same direction in a time-division manner at intervals that are an integral multiple of the repetition period. A transmitting/receiving means for transmitting and receiving time-division ultrasonic pulse waves to and from the subject while changing the direction in order, and first and second received signals having minute radiation angle differences obtained from the transmitting/receiving means at respective desired frequencies. Converting the received signal to find the first and second radial velocities,
The present invention is characterized by comprising a velocity component calculation means for comparing the first and second radial velocities and calculating a tangential velocity in the tangential direction of the sector scanning arc.

That is, the present invention is characterized in that orthogonal components, that is, radial velocity (ultrasonic pulse wave radiation axis direction) and tangential velocity are determined in order to calculate vector velocity, and the velocity of the orthogonal component in this case is determined with high accuracy. In order to accurately determine the velocity of this orthogonal component, the transmitting and receiving means time-divisionally transmits and receives ultrasonic pulse waves with different frequencies, and the velocity component calculating means converts the frequency of the received Doppler signal to a desired frequency. A first comparator is provided for.

In addition, in order to obtain the orthogonal component of the vector velocity, the transmitting/receiving means transmits the first and second components having a small angular difference.
The first and second radial velocities are calculated from the first and second received signals in the velocity component calculation means, and the tangential velocity is calculated from the first and second radial velocities. A second comparator is provided.

[Operation] According to the above configuration, first, the transmitting/receiving means emits a plurality of ultrasonic pulse waves having different frequencies in a time-division manner, and simultaneously receives reflected waves from the driving reflector within the subject. Then, in the velocity component calculation unit, the first radial velocity in an arbitrary direction is immediately determined and stored in the delay device, and the first radial velocity in the receiving direction having a slight deflection angle difference from the receiving direction of the first radial velocity is calculated. When the second radial speed is output, the tangential speed is determined by comparing the second radial speed with the first radial speed. This tangential velocity indicates the velocity change in the tangential direction of the sector scanning arc at the same distance within the subject, and from this tangential velocity and radial velocity, the vector velocity, that is, the absolute value of the velocity and the vector angle can be determined. .

This vector angle indicates the direction of motion of the motion reflector, and the vector velocity including the direction of motion can be found for all of the velocity distribution within the same ultrasound beam and for all of the ultrasound transmission/reception area. The velocity distribution of the motion reflector can be displayed as an image based on the precise direction of motion.

In addition, in the velocity component calculator, the velocity component obtained by time-divisionally emitting multiple ultrasonic pulse waves with different frequencies is subjected to frequency conversion processing in a comparator, and the frequency is actually different from the repetition period of the ultrasonic pulse waves. A velocity component equivalent to that obtained when radiating an ultrasonic pulse wave is obtained, and thereby a highly accurate velocity can be determined.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an overall diagram of an embodiment of the ultrasonic Doppler diagnostic apparatus according to the present invention, a complex signal converter is shown in FIG. 2, a complex autocorrelator is shown in FIG. 3, and a first comparator is shown in FIG. The circuit configurations of the second comparator and the second comparator are shown in FIG. 9 and FIG. 10, respectively. Transmission/reception processing, velocity component calculation processing, and velocity vector calculation processing will be explained below in this order.

Transmission/Reception Processing In FIG. 1, the output of a crystal oscillator 10 that generates a stable high-frequency signal is supplied to a frequency division synchronization circuit 12, and various output signals of desired frequencies are obtained by this frequency division synchronization circuit 12. These output signals include transmission repetition frequency signals 101 and 102 for ultrasonic pulse beam transmission, a complex reference signal 103 for outputting a complex reference signal 105 for complex conversion, and
104 and various signals such as a clock signal for synchronizing each part of the device. In the present invention, the frequencies of the complex reference signals 103 and 104 are the same as the frequencies of the transmission repetition frequency signals 101 and 102.

The first characteristic of the present invention is that a plurality of ultrasonic pulse waves with different frequencies are emitted in the same direction in a time-division manner, and the transmitting/receiving means repeats the ultrasonic pulse waves of a plurality of frequencies with an integral number of repetition periods. It is generated in time division at twice the time. Therefore, the frequency division synchronization circuit 12 outputs pulse signals 101 and 102 having two types of burst frequencies with different repetition periods T. The burst transmission frequency signals are two signals with frequencies f ₁ (for example, 2.5 MHz) and f ₂ (for example, 3 MHz). In addition, multiple reference signals 103, 10
4 is a continuous wave with frequencies f ₁ and f ₂ .

Switchers 14 and 16 are provided to switch these signals when transmitting and receiving ultrasonic pulse waves, and this switching is performed in synchronization with an integral multiple of the repetition period.

The output of this switch 14 is supplied to the probe 22 via a drive circuit 18 and a transmission/reception switching circuit 20.
By exciting the probe 22, an ultrasonic pulse beam is emitted into the subject 23.

The reflected echo from the subject 23 includes not only reflected waves from tissues but also weak signals representing the state of movement from blood, etc., and this reflected echo is converted into an electrical signal by the probe 22. After the signal is converted and sent from the transmission/reception switching circuit 20 to the high frequency amplifier 26 where a desired amplification effect is performed, one of the outputs is supplied to the display section as a normal B mode display signal or M mode display signal.

The output signal for normal B mode display or M mode display is sent to the detector 28 and amplifier 30.
The reflected echoes are supplied to the CRT display section 32 via the CRT display section 32, thereby displaying an image by modulating the brightness of the CRT display section 32 according to the intensity of the reflected echo.

The ultrasonic pulse beam of the probe 22 is scanned by mechanical or electrical angle deflection, and the object 23 is periodically scanned with the ultrasonic pulse beam, or the object 23 is scanned at a desired deflection angle. A scan controller 24 is provided for stopping, and a sweep synchronization signal is output from a sweep synchronization circuit 34 based on the scan position signal of the scan controller 24.
Sweep control of the CRT display section 32 is performed.

On the other hand, the other output of the high frequency amplifier 26 is subjected to velocity calculation processing, and in the embodiment, it is converted into a complex signal and subjected to autocorrelation calculation.

That is, first, the Doppler reception signal obtained from the high frequency amplifier 26 is supplied to the complex signal converter 40 shown in detail in FIG.
0 is a pair of mixers 41a and 41 including a phase detector.
b, and in each mixer 41, the Doppler received signal is mixed with the complex reference signal 105, respectively. In this case, the complex reference signal 105 becomes two signals having a complex relationship with a phase difference of 90 degrees from each other by the 90 degree phase shifter 42, and each signal is input to the mixer 4 separately.
1a and 41b. Therefore, each mixer 4
In step 1, the received signal is converted into a complex signal, which is done by performing mixed detection on the received signal and the complex reference signal to output a signal with a frequency of the sum and difference of both frequencies. The low-pass filter 43a, 4
3b and extracts only the difference frequency component.

In the mixed detection function of the mixer 41, the complex reference signal 105 is a continuous wave with a single frequency;
Since the received signal, which is the other input signal, is a pulse wave containing Doppler information, a large number of spectral components appear in the output of the low-pass filter 43.

This complex transformation will be explained below using arithmetic expressions.

The frequency f ₁ (2.5M
A received burst pulse signal 101 of Hz) is generated at a repetition frequency f _r (4kHz) and a frequency f ₂ (3MHz).
The transmission/reception burst pulse signal 102 has a repetition frequency
Occurs at f _r (4kHz).

Then, the pulse signal is periodically switched by the switch 14, and the switching period is selected to be an integral multiple of the repetition period T, for example, six times.

Further, a continuous wave with a frequency f ₁ is generated in the signal 103 and a continuous wave with a frequency f ₂ is generated in the signal 104, and these are supplied to the complex signal converter 40 as a complex reference signal 105 by the switch 16.

In this case, if the amplitude of the signal is 1 and the spectrum fundamental wave of the received signal is expressed as shown in the following equation.

cos2π(f ₁ +kf ₁ V)t...(1) cos2π(f ₂ +kf ₂ V)t...(2) Here, k is the proportionality constant, V is the velocity, and kf ₁ V
kf ₂ V indicates the change in frequency due to the Doppler effect.

Both signals shown in equations (1) and (2) above have a repetition period T
This is a time-division signal that appears alternately. Further, the complex reference signal supplied to the mixer 41a has an amplitude of 1
, cos2πf ₁ t and cos2πf ₂ t (3), then the complex reference signals supplied to the mixer 41b are sin2πf ₁ t and sin2πf ₂ t (4).

If the above equation (3) is the real part of a complex number and equation (4) is its imaginary part, then both equations together become a complex signal, so
The outputs of the mixers 41a and 41b are signals having a complex relationship with each other. Therefore, at the output of the mixer 41a, two signals proportional to the product of equations (1) and (2) and (3) are generated, and these signals are expressed by the following equations.

cos2πf ₁ kVt+cos2π(2f ₁ +f ₁ kV)t...(5) cos2πf ₂ kVt+cos2π(2f ₂ +f ₂ kV)t...(6) The signal expressed by equations (5) and (6) above is every 6 cycles. However, since the signals 2f ₁ and 2f ₂ are blocked by the low-pass filter 43a that blocks high frequencies (for example, 1 MHz or higher), cos2πf ₁ kVt...(7 )cos2πf ₂ kVt...(8) Both signals are time-divided and appear as a force 106 of the low-pass filter 43a.

Similarly, two signals proportional to the product of equations (1) and (2) and (4) are generated at the output of the mixer 41b, and the output 107 of the low-pass filter 43b is sin2πf ₁ kVt... …(9) sin2πf ₂ kVt …This is the time-divided version of both signals shown in (10). The outputs of the low-pass filters 43a and 43b appearing at the same time form a complex signal.

Therefore, the above-mentioned equations (7) and (9), as well as equations (8) and (10) can be collectively expressed as complex signals Z ₁₁ and Z ₁₂ as shown in the following equations.

Z ₁₁ = x ₁₁ + iy ₁₁ Z ₁₂ = x ₁₂ + iy ₁₂ ... (11) Here, i is a complex symbol, x ₁₁ , y ₁₁ and x ₁₂ ,
y ₁₂ is expressed by the following formula.

x ₁₁ = cos2πf ₁ kVt y ₁₁ = sin2πf ₁ kVt x ₁₂ = cos2πf ₂ kVt y ₁₂ = sin2πf ₂ kVt ... (12) The complex signals Z ₁₁ and Z ₁₂ in equation (11) above are time-divisionally converted into complex signals. is obtained as the output of the device 40.

Complex signals Z ₁₁ , Z ₁₂ obtained as above
is an analog signal, but in order to improve calculation accuracy, it is supplied to A/D converters 35a and 35b and converted into a digital signal.

The complex signal obtained in this way is subjected to velocity component calculation.

Velocity Component Calculation Process In the embodiment, a complex autocorrelation method is used as a velocity calculation means, and this will be explained based on the complex autocorrelator 60 shown in FIG.

First, the output signal 108 (1
09), when the time-division complex signals Z ₁₁ and Z ₁₂ are collectively expressed as a complex signal Z ₁ , the complex signal Z ₁ is expressed by the following equation.

Z ₁ = x ₁ + iy ₁ This complex signal Z ₁ is connected to the delay lines 61a, 61
The output signal Z ₂ is obtained by being delayed by one period by b. This output Z ₂ is expressed by the following formula.

_Z2 = _x2 + _iy2x2 =cos2πfkV(t-T)...(13) _y2 =sin2πfkV(t-T)...(14) Here _, f represents _f1 or _f2 .

The conjugate signal of the signal Z ₂ is Z ₂ ^* =x ₂ −iy ₂ , and the autocorrelation is calculated by finding the conjugate product of Z ₁ and Z ₂ ^* using the following equation.

Z ₁ Z ₂ ^* = (x ₁ + iy ₁ ) (x ₂ − iy ₂ ) = x ₁ x ₂ + y
₁ y ₂ +i (x ₂ y ₁ −x ₂ y ₁ )...(15) In order to obtain this correlation, the complex autocorrelator 60 has two delay lines 61a, 61b,
four multipliers 62a, 62b, 63a, 63b,
Addition and subtraction units 64a and 64b are provided to perform the correlation calculation.

If the output of the adder/subtractor 64a is R, then from each of the relational expressions (13), (14), and (15), the following can be obtained: R=x ₁ x ₂ + y ₁ y ₂ = cos2πfkVT (16), Also, if the output of the adder/subtractor 64b is I, then I=x ₂ y ₁ −x ₁ y ₂ =sin2πfkVT (17) is obtained similarly, and the autocorrelation signal by combining the outputs of both adders/subtracters 64 is as follows. As shown in Eq.

S=R+iI...(18) Since this output S includes signal fluctuation components and noise components generated from the equipment, the average circuit installed in the next stage removes these noise components. This average is expressed as =+i.

This averaging circuit includes adders 65a and 65b, delay lines 66a and 66b, and a weighting circuit 67.
a and 67b, the output delayed by one cycle by the delay line 66 is added to the input signal at the current time by the adder 65, and the operation of supplying this output to the delay line 66 is repeated, and this addition is completed. If, for example, is constructed from a digital circuit, the average value can be obtained by outputting the upper bits of the summation output. However, if this operation is simply repeated, the output value will gradually increase as the number of adder circuits increases, and will eventually reach saturation. Therefore, in the embodiment, a weighting circuit 67 is provided to attenuate the output and add it to the input. In other words, if the attenuation amount is α, a signal 10 cycles earlier than the current time signal will be attenuated by α ¹⁰ and added to the current time signal, so the influence on the output will be small and the low-pass filter or It becomes possible to perform the same averaging function as a moving average circuit. Furthermore, by changing the weighting amount of the weighting circuit 67, it is possible to change the degree of averaging.

In this way, the autocorrelation of the complex signal is calculated, and in the present invention, this is performed for each ultrasonic pulse wave emitted in a time-division manner _.
If an ultrasonic pulse wave of f ₂ is emitted every 6 times and the averaging circuit is cleared every 6 times, the complex autocorrelator 60 will output the averaged self for each received signal of each frequency. We can obtain the correlation signal, which is the average value of the autocorrelation signal for frequency f ₁
If the average value in the case of S _1a and f ₂ is S _2a , then the following equation is obtained.

S _1a = _1a + i _1aHere , _1a = |R ₁ |cos2πf ₁ kVt _1a = |R ₁ |sin2πf ₁ kVt ...(19) S _2a = _2a +i _2aHere , _2a = |R ₂ |cos2πf ₂ kVt _2a = |R ₂ |sin2πf ₂ kVt...(20) As described above, in this embodiment, an autocorrelation signal is obtained by finding the conjugate product of complex signals, and the speed is calculated from this autocorrelation signal. In the present invention, the tangential velocity is determined by comparing signals in two directions separated by a minute angle, and Fig. 4 shows how to determine the tangential velocity in B-mote scanning. .

As shown in Fig. 4, an arbitrary direction O→a and a small deflection angle Δφ apart from this O→a direction O→b
Consider the case of transmitting and receiving ultrasonic pulse waves in the following directions.

Therefore, in the present invention, the reflected echo from the O→a direction becomes the first received signal consisting of a pulse train, and the O
→The pulse train of the reflected echo from direction b becomes the second received signal.

If the angle formed by the flow velocity v in a certain direction and the ultrasonic beam is φ, then the radial velocity Vr in the beam direction can be expressed as Vr=vcosφ, so
When K is a proportionality constant, the real part and imaginary part of the above equations (19) and (20) can be expressed by the following equations.

_1a = |R ₁ |cos(Kf ₁ cosφ) _1a = |R ₁ |sin(Kf ₁ cosφ) ……(21) _2a = |R ₂ |cos(Kf ₂ cosφ) _2a = |R ₂ |sin(Kf ₂ cosφ) ...(22) In addition, Fig. 5 shows the reception status of the received signal and the time _relationship of its processing. This is followed by six pulses of frequency f ₂ for a period of 6T, resulting in a total of 12T of time-division radiation. After that, a pulse of frequency f ₁ is applied for a time of 6T in the a direction and the b direction of the small angle Δφ, and then for another 6T.
emits a pulse of frequency f ₂ for a time of .

Here, to briefly explain the process of finding the velocity component based on FIG. ₅ , as shown in _FIG . , the argument angle θ of the autofunction signal S is determined as shown in FIG. Then, the deflection angle in Figure B is delayed by 6T to become the signal in Figure C, or delayed by 12T to become the signal in Figure E.

Next, as shown in Figure D, the radial velocity V _ra is calculated by calculating from Figure C to Figure B, for example θ _1a - θ _2a . On the other hand, as shown in Figure F, Figure B - Figure E,
For example, by calculating θ _1b −θ _1a , the tangential velocity V _t1 is determined. Then, as shown in Figure G, the signal in Figure F is
Delayed by 6T, V _t1 +V _t2 is calculated and the tangential velocity V _tp is obtained as shown in Figure H. This V _tp
is not necessarily required, but is optional.

As described above, an autocorrelation signal every 6T shown in FIG.

S _1b = _1b + i1b where, _1b = |R ₁ | cos {Kf ₁ cos (φ
−Δφ)} _1b = |R ₁ |sin{Kf ₁ cos(φ−Δ
φ)}...(23) S _2b = _2b + i _2b where, _2b = |R ₂ | cos {Kf ₂ cos(φ
−Δφ)} _{Responsibility2b} =｜R ₂ ｜sin｜Kf ₂ cos
(φ−Δφ)} ...(24) Thus obtained, the radial velocity and tangential velocity are determined by the comparator.

First Example of Comparator FIG. 6 shows a comparator consisting of the simplest circuit, and is used in place of the first comparator and second comparator of FIG. 1, which will be described later.

That is, as the first comparator, the argument calculator 1
71, a delay memory 172, a subtracter 173, and a switch 174 are provided, and a delay memory 182, a subtracter 183, and a delay addition circuit 89 are provided as a second comparator.
It is controlled by a memory controller 36 shown in the figure.
Further, the delay addition path 89 is connected to the delay line 1
85, an adder 186, and a switch 184. Then, the argument calculator 171 calculates the argument θ of the autocorrelation signal S from the following equation.

θ=tan ^-1 (/) ...(25) Therefore, from the above equation, the argument angle θ _1a ′θ _2a ′θ _1b ′θ _2b corresponding to each autocorrelation signal can be found, and it becomes as follows. .

θ _1a = Kf ₁ cosφ θ _2a = Kf ₂ cosφ θ _1b = Kf ₁ cos (φ − Δφ) θ _2b = Kf ₁ cos (φ − Δφ) ... (26) This argument θ _1a ′θ _2a ′θ _1b 'θ _2b is obtained every 6T, as shown in FIG. remember exactly. The read signal of this delay memory 172 is
It is designed to be delayed by a period of 6T, and as shown in Fig. 5C.
As shown in , the declination signal is output with a time delay of 6T.

A subtracter 173 is provided to compare received signals of the same frequency, and θ _1a and θ _2a and θ _1b and θ _2b are input to this subtracter 173. Therefore, the velocity component output from the subtractor 173 is a radial velocity, and if the velocity component in the a direction is V _ra and the velocity component in the b direction is V _rb , then V _ra = θ _1a − θ _2a = k(f ₁ −f ₂ ) cosφ ... (27) V _rb = θ _1b −θ _2b = k (f ₁ − f ₂ ) cos (φ − Δφ)
...The signal shown in (28) is output.

In addition, as shown in FIG. 5D, V _ra and V _rb
Since an unnecessary signal X is generated between the two, the output of this signal is prohibited by the switch 174.

The radial speed V _r obtained in this way is
As is clear from the above equation, this is a Doppler signal obtained when transmitting a frequency of _f1 - _f2 . Therefore, in the example, since f ₁ = 3 MHz and f ₂ = 2.5 MHz, the difference between them is equal to the output obtained by transmitting an ultrasonic pulse wave with a frequency of 500 kHz, and the output is equal to the output obtained by transmitting an ultrasonic pulse wave with a frequency of 500 kHz. Measurements can be made six times faster than when pulse waves are transmitted.

In addition, according to this, the frequency of the Doppler signal can be converted without significantly changing the ultrasound frequency or repetition frequency, so by appropriately selecting frequencies f ₁ and f ₂ according to the speed of detection or measurement, It is possible to measure speed with high precision in accordance with the target area.

On the other hand, the memory of the delay memory 182 is read out with a delay of 12T from its input, and is supplied to the subtracter 183. Therefore, this subtracter 183 calculates the difference between the signals shown in B and E in FIG. 5, and outputs a velocity component, that is, a tangential velocity, shown in the following equation.

V _t1 = θ _1b −θ _1a = Kf ₁ {cos (φ−Δφ)−cosφ} = Kf ₁ {cosφcosΔφ+sinφsinΔφ−cosφ} Here, since Δφ is a small angle (for example, 1.5°), cosΔφ1, sinΔφΔφ For example, the above equation is: V _t1 Kf ₁ Δφsinφ (29) Then, the velocity component signal V _t2 that appears after the next 6T
Similarly, V _t2 Kf ₂ Δφsinφ ...(30) becomes.

The velocity component V _t1 expressed by these equations (29) and (30),
V _t2 can be selected by a switch 184 that operates every 6T.

Also, the delay line 185 receives the input signal.
Output the signal delayed for a period of 6T to the adder 186,
This adder 186 adds the output of the adder/subtracter 183 and the output of the delay line 185 to obtain the sum of the signals F and G in FIG.
Outputs the velocity component V _tp shown in .

This tangential speed V _tp is V _tp = V _t1 + V _t2 = K (f ₁ + f ₂ ) Δφ sinφ (31), which is the speed obtained when transmitting the frequency of (f ₁ + f ₂ ) Δφ. This results in a tangential velocity component, which allows the signal to be extracted in a good manner as described below.

Velocity vector calculation processing Velocity components V _t1 , V _t2 obtained as above
is supplied to the vector velocity calculator 90.

FIG. 7 shows the internal circuit of the vector velocity calculator 90, which is composed of a multiplier 91, an absolute value calculator 92, an angle calculator 93, and a subtracter 94.

That is, the tangential velocity V _t inputted from the comparator of FIG. 6 is multiplied by a constant Ko in a multiplier 91, and its magnitude is corrected.

When V _tp is input as this tangential velocity,
The output of the multiplier 91 is V _tp =Ko(f ₁ +f ₂ )Δφsinφ (32). For example, when φ=45°, the constant Ko is determined so that V _t =V _r holds true.

That is, from the above equations (27) and (32), Ko (f ₁ + f ₂ ) = f ₁ - f ₂ ... (33), and therefore the tangential velocity V _t is V _t = K (f ₁ + f ₂ ) sinφ...(34) This V _t becomes the true tangential velocity with respect to the radial velocity V _r , but when Δφ is not scanned at a constant angle, the above Ko must be determined while correcting so that the above equation (32) always holds true. is also possible.

Then, the absolute value calculator 92 calculates the absolute value of the vector velocity using the following equation.

|V|=√ _t ² + _r ² (35) Further, the angle calculator 93 calculates the vector angle using the following equation.

φ=tan ^-1 (V _t /V _r )...(36) The vector velocity can be found using these two equations, but the absolute value |V| is the true velocity of the motion reflector in the O→a direction. Also, the vector angle represents the direction of movement, and accurate information on the movement situation can be obtained from this vector velocity.

In this case, it is practical to correct the angle φ to an angle with respect to the reference line.
As shown in the figure, the scan angle is converted into a vector angle γ with respect to the center line OP, and the scan angle β is subtracted from the φ using a subtractor 94, and the vector angle γ is calculated using the following formula. There is.

γ=φ−β (37) This scanning angle β is determined by the scanning address data supplied from the scanning control section 24. If this address data is read and calculated, the vector angle will be converted to a vector angle with the center line as a reference.
Further, this reference can also be taken as the scanning start line OQ.

In this way, the minute deflection angle Δφ is changed to 2Δφ,
3Δφ, .

The output of this vector velocity calculator 90 is D/A
After being converted into an analog signal by the converter 37
The vector velocity supplied to the CRT display 32 and represented by |V|, γ is written to the DSC in the display and displayed on the CRT. In this case, it is possible to superimpose the vector velocity of the motion reflector on the tomographic image and display it in color.

As explained above, the present invention is based on the radial speed
Since V _r operates at a frequency that is the difference between f ₁ − f ₂ , it is possible to measure speeds up to high speeds without aliasing, and the tangential speed V _t is f ₁ + f ₂ (or f ₁ , f ₂ ). However, since Δφ is minute, measurement can be performed without any aliasing phenomenon.

Moreover, in this case, there is an advantage that a decrease in detection sensitivity due to Δφ can be prevented. That is, since the above-mentioned equation (33) holds true, Ko may be a small value, and therefore the detection sensitivity becomes high.

Furthermore, as the tangential velocity V _t , K(f ₁ −f ₂ )Δφsinφ can be detected instead of the above equation (31), but in this method, since (f ₁ −f ₂ )Δφ is small,
The influence of the noise component becomes large, and even if the constant Ko is increased and multiplied later, the signal-to-noise ratio remains unchanged, making detection difficult.

Therefore, in the example, (f ₁ +f ₂ )Δφ or f ₁ Δφ,
It is detected by f ₂ Δφ, and according to this,
For example, (f ₁ + f ₂ )/(f ₁ − f ₂ ) = (3MHz + 2.5M
Hz)/(3MHz-2.5MHz) = 11 (times), allowing detection with a good signal-to-noise ratio.

In this way, the present invention can measure the absolute flow velocity of a motion reflector without an aliasing phenomenon, thereby making it possible to accurately display an image of a flow such as blood flow.

Complex day-rate canceller When measuring the velocity of a motion reflector such as blood flow in a blood vessel of a subject, the intensity of the reflected signal from a stationary part such as the blood vessel wall or heart or a slow-moving part is greater than the strength of the blood flow signal. are strong, and when these signals are mixed in, it becomes difficult to accurately measure the speed of a reflective object such as blood flow that moves at high speed. In order to eliminate strong reflected signals from stationary parts or low-speed moving parts within the subject and accurately measure the velocity signals of only the moving reflectors, a complex delay canceller is installed at the position surrounded by the dotted line in Figure 1. can be inserted.

That is, in the embodiment, a complex delay canceller 50 shown in FIG. 8 is provided, thereby making it possible to significantly improve the quality of the image signal.

This complex delay canceller 50 has delay lines 52a and 52b having a delay time that corresponds to one cycle T of a repetitive signal. It can be formed from a memory or a shift register consisting of identical storage elements. Difference calculators 54a and 54b are connected to these delay lines 52, respectively. The difference between one cycle of the signal is calculated by sequentially comparing the depth. Therefore, the difference output of the difference calculator 54 is close to zero because there is no change in the reflected signal from the stationary or low-velocity living tissue and the signal at the current time and the signal one cycle ago, or the change is small. On the other hand, a differential output of a blood flow signal having a high velocity, for example, is detected as a large value, and thereby reflection signals from living tissues, that is, clutter can be suppressed.

Second Example of Comparator Next, a second example of the comparator will be explained based on FIGS. 9 and 10.

According to this, it is possible to calculate the velocity component more accurately, and as shown in FIG. 1, the first comparator 70 (FIG. 9) and the second
A comparator 80 (FIG. 10) is provided, and these first and second comparators 70 and 80 are constructed from a conjugate product calculator similar to the complex autocorrelator 60 described above.

That is, the first comparator 70 has two delay lines 71a and 71b and four multipliers 72a and 72.
2b, 73a, 73b, adder/subtractor 74a, 74
b, and an argument calculator 75,
The delay lines 71a and 71b are configured similarly to the delay memory 172 in FIG. 6 (first example of the comparator), and the input signal is output after being delayed by a time of 6T. Then, as in the case of the autocorrelator 60, the conjugate product of the input and output of the delay line 71 is calculated by multipliers 72 and 73.

The input in this case is expressed as a complex signal Z ₇ in the following equation.

Z ₇ =+i=｜R｜cosθ _2a +i｜R｜
sinθ _2a This θ _2a is the deviation angle in the case of the ultrasonic pulse wave of frequency f ₂ shown in FIG. 5B, and the output of the delay line 71 is as shown in FIG. 5C. This is the signal of the declination angle θ _1a 6T hours before the declination angle θ _2a . If this is Z ₈ , then Z ₈ = |R | cos θ _1a + i | R | sin θ _1a , and in the first comparator 70, the complex signal Z ₇ and
A conjugate product with Z ₈ is calculated, and adder/subtractor 74a, 74
The output Z ₉ of b is given by the following equation.

Z ₉ = Z ₈ Z ₇ ^* = |R | ² (cosθ _1a +isinθ _1a )・(cosθ _2a isinθ _2
a = |R | ² {cosθ _1a・cosθ _2a + sinθ _1a・sinθ _2a +i(sinθ _1a・cosθ _2a −cosθ _1a・sinθ _2a )} = |R| ² {cos(θ _1a −θ _2a ) + sin(θ _1a −θ _2a } Therefore, the argument calculator 75 calculates the radial velocity in the a direction using the following equation.

V _ra = tan ^-1 {｜R｜ ² sin(θ _1a −θ _2a )/｜
R| ² cos(θ _1a −θ _2a )}=θ _1a −θ2a In addition, the radial velocity component V _rb in the b direction is calculated in the same manner [FIG. 5D]. And the velocity component
The unnecessary signal X existing between V _ra and V _rb is removed by the switch 76 as in the case of FIG.

Next, a second comparator 80 shown in FIG.
is composed of two delay lines 81a, 81b, four multipliers 82a, 82b, 83a, 83b, adders/subtractors 84a, 84b, and a declination calculator 85.
has a delay time of 12T and calculates the conjugate product of the signals shown as B and E in FIG. Therefore, from the argument calculation unit 85, the tangential velocity V _t1 =θ _1b −θ _1a , V _t2 =
θ _2b −θ _2a is output, and this output becomes a signal similar to the output of adder 183 in FIG.

Further, the output of the argument calculation unit is supplied to a delay addition circuit 89 composed of a delay line 185, an adder 186, and a switch 184, thereby outputting a tangential velocity V _tp 'V _t1 .

Here, the delay lines 71, 81, 185 can be constructed more economically by using delay memories that store signals for one cycle and read out at integral multiples of cycles.

Such ultrasonic Doppler equipment can be used in M mode, B mode for two-dimensional step scanning,
Alternatively, it can be applied to a moving target detection device (MTI), etc., and can be displayed superimposed on a tomographic image inside a subject.

According to the embodiment, the CRT display 32 selectively or simultaneously receives both the normal image signal from the amplifier 30 and the vector velocity signal from the D/A converter 37 using a switch (not shown). Any arbitrary image or a superimposed display of both images can be displayed.

[Effects of the Invention] As explained above, according to the present invention, a plurality of ultrasonic pulse waves having different frequencies are emitted in a time-division manner, and the radial velocity is determined from two received signals having a minute deflection angle difference. Since the velocity components orthogonal to the tangential velocity and the tangential velocity are obtained, a Doppler shift signal can be obtained to obtain the accurate velocity obtained when an ultrasonic pulse wave of a desired frequency is radiated. It is possible to accurately measure the distance to a high-velocity moving reflector and the speed of the reflector.

At the same time, it is possible to obtain tangential velocity, which could not be obtained conventionally, and vector velocity can be determined based on this tangential velocity and radial velocity, and ultrasonic beams are emitted from different positions a certain distance apart. The velocity of the motion reflector, which represents the exact direction of motion, can be easily obtained without having to do so.

As a result, in addition to the tomographic image information displayed by conventional ultrasound diagnostic equipment, accurate blood flow velocity and blood flow velocity distribution can be displayed simultaneously, making it possible to provide an extremely large amount of diagnostic information in practical use. It becomes possible to obtain an ultrasonic diagnostic device.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the ultrasonic Doppler diagnostic apparatus according to the present invention, FIG. 2 is a block diagram showing the circuit configuration of a complex signal converter, and FIG. 3 is a circuit diagram showing the circuit configuration of a complex autocorrelator. Block diagram shown, No. 4
FIG. 5 is an explanatory diagram showing the relationship between tangential velocity, radial velocity, and vector velocity, FIG. 7 is a block diagram showing the first example of a comparator with a simple circuit configuration for speed component calculation, FIG. 7 is a block diagram showing the circuit configuration of a vector speed calculator, and FIG. 8 is a complex delay canceller. Figure 9 is a block diagram showing the circuit configuration of the
FIG. 10 is a block diagram showing a second example of the circuit configuration of the second comparator used for tangential velocity calculation. 10... Crystal oscillator, 12... Frequency division synchronous circuit,
14, 16...Switcher, 24...Scanning controller, 2
6...High frequency amplifier, 32...CRT display, 3
6...Memory controller, 40...Complex signal converter,
50... Complex delay canceller, 60... Complex autocorrelator, 61a, 61b... Delay line, 62a, 62b, 63a, 63b... Multiplier, 64a, 64b... Adder/subtractor, 70... Th. 1
comparator, 80...second comparator, 89...delay addition circuit, 90...vector velocity calculator, 171
... Argument calculator, 172, 182 ... Delay memory, 173, 183 ... Subtractor, 101, 103
... _f1 frequency signal, 102,104... _f2 frequency signal.

Claims (1)

[Claims] 1. Ultrasonic waves that emit ultrasonic pulse waves with a constant repetition frequency into a subject and compare transmitted and received signals to detect the distance to a moving reflector and the speed of the moving reflector. In Doppler diagnostic equipment, multiple ultrasound pulse waves with different frequencies are generated in the same direction in a time-division manner at intervals of an integral multiple of the repetition period, and these time-division ultrasound pulse waves are sequentially directed to the subject. a transmitting/receiving means for transmitting and receiving the received Doppler signal of the time-divided ultrasonic pulse wave and converting it into a complex signal by mixed detection with a complex reference signal; and velocity component calculation means for calculating a radial velocity component and a tangential velocity component from a second complex signal, the velocity component calculation means comprising: a complex self-correlation calculation means for calculating an autocorrelation of each complex signal based on the complex signal. a correlator; a declination calculator that calculates the declination of the autocorrelation; a first delay device that delays the declination by a delay time between ultrasonic pulse waves of different frequencies transmitted and received in the same direction; A first step of calculating a difference between the output declination of the declination calculator and the output of the first delay device to obtain a radial velocity component from the declination difference obtained from received signals of different frequencies in the same direction. a subtracter; a second delay device that delays the declination by a delay time between ultrasonic pulse waves of the same frequency in different directions with a small angular difference between adjacent ones; an output declination of the declination calculator; a second subtracter that calculates a difference between the output of the second delay device and the tangential velocity component from the argument difference obtained from the received signals in different directions of the ultrasonic pulse waves having the same frequency; An ultrasound Doppler diagnostic device comprising: 2. In the device according to claim 1, the first
and the second subtractor calculates a conjugate product of complex outputs of complex autocorrelation. 3. An ultrasonic Doppler diagnostic apparatus according to claim 1, further comprising a vector velocity calculator that calculates a vector velocity from a radial velocity component and a tangential velocity component. 4. The device according to claim 3, wherein the vector velocity calculator calculates the absolute value of the vector velocity from the square root of the sum of the square of the radial velocity component and the square of the tangential velocity component. Ultrasonic Doppler diagnostic equipment. 5. The ultrasonic Doppler diagnostic apparatus according to claim 3, wherein the vector velocity calculator calculates the vector angle by calculating the arctangent of the ratio of the radial velocity component and the tangential velocity component. 6. The ultrasonic Doppler diagnostic apparatus according to claim 5, wherein the vector angle is corrected by a scanning angle and calculated as an angle with respect to a reference direction of sector scanning.