JPH0324861B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an ultrasonic Doppler diagnostic device, in particular, detects movement reflectors such as blood flow inside a living body to measure blood flow velocity, blood flow volume, etc. The present invention relates to an improved ultrasonic Doppler diagnostic device for displaying an image of the velocity status of a vehicle.

[Prior art] Pulse waves are emitted at a constant repetition frequency, reflected waves from a reflector within the object are received, and shifts in the reception frequency of these received signals are detected to detect and display the velocity of the reflector. Pulsed Doppler equipment is widely used.

In such a device, generally under a constant transmission repetition frequency (reciprocal of the repetition period), the velocity of the moving reflector that can be unambiguously detected has an upper limit based on the sampling theorem, as is well known.

In other words, when ultrasonic waves are emitted at a repetition frequency lower than the Doppler frequency due to the speed of the reflector, that is, at a long period, a so-called folding phenomenon occurs.
The Doppler frequency is folded back to the lower frequency side, making it difficult to determine the speed.

For example, as shown in FIG. 5, the Doppler signal 100 from low velocity blood flow has a detectable ±V _nax
Doppler signal from within range but high velocity blood flow 2
00 wraps past the upper limit of +V _nax and -
It will appear as a signal 201 above V _nax . Therefore, it becomes difficult to detect high-velocity blood flow exceeding a certain velocity, and the detection speed is limited by the transmission repetition frequency.

In a system for determining the direction of velocity, the relationship between the maximum Doppler frequency fd _nax that can be detected without causing this aliasing phenomenon and the repetition frequency fr is expressed by the following equation.

fd _nax = 1/2fr (1) Moreover, the maximum detectable speed V _nax is expressed by the following formula.

V _nax = 1/4 cos θ·f _r /f ₀ (2) where f ₀ is the center frequency of the radiated ultrasound, and θ is the angle between the blood flow and the ultrasound beam.

[Problems to be Solved by the Invention] Therefore, as can be understood from equation (2) above, in order to increase the maximum detection speed, it is necessary to increase the transmission repetition frequency fr or lower the transmission center frequency f0. There is.

However, the transmission repetition frequency fr is selected according to the diagnostic distance, and if this frequency is increased, it will become difficult to actually detect reflected echoes from a long distance due to the relationship with the sampling period.
Diagnostic distance becomes shorter. On the other hand, the center frequency of transmission f ₀
If the value is lowered, it is not only difficult to form a transmission wave with a narrow pulse width, but also a sharp radiation beam cannot be formed, resulting in deterioration of distance resolution and azimuth resolution. As described above, the conventional Doppler diagnostic apparatus using the pulsed Doppler method has a problem in that it is not possible to simultaneously determine the position and velocity of high-speed blood flow deep within a living body.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to accurately detect and display a wide range of velocities of motion reflectors, especially high velocities deep in the body, by eliminating the folding phenomenon. An object of the present invention is to provide an improved ultrasonic Doppler diagnostic device.

[Means for Solving the Problems] In order to achieve the above object, the present invention emits an ultrasonic pulse wave into a subject, receives a reflected wave from a motion reflector, and calculates the received Doppler signal. In an ultrasonic Doppler diagnostic device that displays the velocity status of a moving part by detecting a Doppler shift frequency, a transmitting circuit that alternately outputs pulse waves with two different transmission repetition periods multiple times in the same scanning direction; , a conversion means for converting two signals with a repetition period obtained alternately from within the subject into complex signals, and a delay circuit for delaying each of the two complex signals obtained by the conversion means for a predetermined time, a first complex multiplier that calculates the conjugate product of complex signals of the same repetition frequency with a predetermined time difference between the delayed complex signal from the delay circuit and the complex signal that has not passed through the delay circuit; This first
A delay circuit that delays two complex signals obtained from received waves of the same repetition period of the complex multiplier by a predetermined time, respectively, a delayed complex signal from this delay circuit, and a complex signal that has not passed through this delay circuit. Among the outputs having a predetermined time difference, the second complex multiplier calculates a conjugate product or a complex product of two complex signals having a predetermined delay time difference and having different repetition periods. .

[Operation] According to the above configuration, two ultrasonic pulse waves with different transmission repetition periods are transmitted inside the subject, and Doppler signals with two types of cycles are alternately transmitted from within the subject. You will get it. Then, the received Doppler signal is converted by a period conversion circuit into a desired repetition period, for example, a repetition period of about one-tenth.

Therefore, according to this method, a Doppler signal can be obtained when a pulse wave with a substantially short repetition period, that is, a high transmission repetition frequency, is transmitted and received inside the subject, and this Doppler signal can be used to detect the presence deep within the subject. It becomes possible to detect and display the high speed of the motion reflector well.

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

FIG. 1 shows a basic circuit block of an ultrasonic Doppler diagnostic apparatus according to the present invention.

The output of the oscillator 10, which generates a stable high-frequency signal, is supplied to a frequency division synchronization circuit 12, and the frequency division synchronization circuit 12 generates various signals for controlling the device of the present invention. These output signals include a transmission repetition signal for ultrasonic pulse transmission, a complex reference signal for complex conversion, a sweep synchronization signal for display on a CRT (cathode ray tube), etc., and the complex reference signal 102 shown in the figure. 104 have a frequency that is an integral multiple of the transmission repetition frequency, and have a phase difference of 90 degrees from each other.

The characteristic feature of the present invention is that two ultrasound waves with different transmission repetition periods are alternately emitted, and the two Doppler signals obtained thereby are converted into a Doppler signal with a desired repetition period, Two pulse waves with different repetition periods are generated by a transmitting circuit. This transmitting circuit includes the above-mentioned oscillator 10,
It is composed of a frequency division synchronization circuit 12, a signal switch 14 that switches and outputs two pulse waves with different repetition periods, a drive circuit 16, and a transmission/reception switching circuit 18.

The frequency division synchronization circuit 12 outputs two transmission repetition signals 106 (period T ₁ ) and 108 (period T ₂ ), and these signals are sequentially switched by the signal switch 14 and alternately supplied to the drive circuit 16. be done. In this case, in the embodiment, one pulse wave is alternately switched, but two or three pulse waves may be consecutively and alternately supplied in the same scanning direction. The output of the drive circuit 16 is then supplied to the probe 20 via the transmission/reception switching circuit 18, and the ultrasonic pulse beam formed by the probe 20 is radiated into the subject 22.

This reflected signal from the object 22 is transmitted to the probe 20.
is converted into an electrical signal by the transmission/reception switching circuit 18
The signal is then sent to the high frequency amplifier 24 and amplified to a desired level. One output of the high frequency amplifier 24 is supplied to a display 30 via a wave detector 26 and a video signal amplifier 28, and this display 30 is controlled by a scanning signal from a scan controller 34 supplied via a sweep circuit 32. A B-mode or M-mode image is displayed using a brightness-modulated signal.

Then, the other output 1 of the high frequency amplifier 24
14 is a mixed detector 36, 38 and a low-pass filter 4
0,42 to a complex signal conversion unit consisting of
A decomposition of the velocity information is performed.

First, complex transformation will be explained using the following arithmetic expression.

There are many Doppler spectra in a pulse wave received signal, but to simplify the explanation, the amplitude will be assumed to be 1 and the following equation will be used to focus on the Doppler shift spectrum of the center frequency.

e(t)=cos(2πf ₀ t+2πf _d t) (3) Here, f ₀ is the center frequency of transmission, and f _d is the Doppler shift frequency.

The mixed detectors 36 and 38 take the product of the complex reference signals (frequency f ₀ ) 102 and 104 and the received signal 114, and the low-pass filters 40 and 42 remove the sum frequency component and obtain the difference frequency component. Make sure that you only get the following. As a result, two low-pass filters 40,
The output of 42 is as shown in the following equation.

I(t)[cos(2πf ₀ t+2πf _d t)×2cos(2πf
₀ t)] _LP = cos2πf _d t...(4) Q(t) [cos(2πf ₀ t+2πf _d t)×−2sin(2
πf ₀ t)] _LP = sin2πf _d t...(5) When I(t) is the real part and Q(t) is the imaginary part, the Doppler signal Z ₁ (t) is a complex signal expressed by the following equation. Become.

Z ₁ (t) = I (t) + jQ (t) = cos (2πf _d t)
+jsin(2πf _d t)=e ^j2 〓 ^fdt ...(6) And the fixed object (living tissue) inside the subject 22
The outputs 120, 120,
122 is supplied to clutter removal filters 44 and 46, and then converted by a period conversion circuit 48 into Doppler signals having substantially different repetition periods.

FIG. 2 shows an internal circuit of the period conversion circuit 48, which includes delay circuits 54 and 56 that delay the complex signal by a predetermined delay time, and two delay circuits 54 and 56 with the same repetition period having a predetermined delay time difference. A first complex multiplier 5 that calculates the conjugate product of complex signals
8, delay circuits 60 and 62 that delay the output of the first complex multiplier 58 for a predetermined time, and complex signals of two different repetition periods having a predetermined delay time difference among the outputs of the first complex multiplier 58. and a second complex multiplier 64 that calculates a conjugate product or a complex product.

The real part I(t) and the imaginary part Q(t) of the complex signal input to the period conversion circuit 48 are transferred to a delay circuit 54,
56, the time T (in the embodiment, the transmission period T1+
T2) after which the first complex multiplier 58
is supplied to At this time, the other input of the first complex multiplier 58 is connected to the clutter removal filters 44 and 46.
The real part I(t) and the imaginary part Q of the complex signal directly from
A signal (t) is supplied, and the complex conjugate product of the same period signals is calculated here.

That is, the clutter removal filters 44, 4
6 outputs as Z ₁ (t), Z ₁ (t) = e ^j2 〓 ^fdt ...(7), and on the other hand, the outputs of the delay circuits 54 and 56 are expressed as Z ₂ (t).
Then, Z ₂ (t)=Z ₁ (t-T)=e ^j2 〓 ^fdt(tT) ...(8). Therefore, the complex conjugate product of equations (7) and (8) above can be expressed as Z ₃
Then, it becomes as follows.

Z ₃ (t)=Z ₂ ^* (t)・Z ₁ (t)e ^-j2 〓 ^fdt(t
-T)・e ^j2 〓 ^fdt =e ^j2 〓 ^fdT ...(9) Then, the Doppler complex signal converted to a predetermined repetition period based on the output of the first complex multiplier 58 is sent to the second complex multiplier 64. required.

That is, if the complex conjugate products obtained from the pulse trains of repetition periods T ₁ and T ₂ among the outputs of the first complex multiplier 58 are Z ₃₁ (t) and Z ₃₂ (t), respectively,
From the above equation (9), two Doppler signals expressed by the following equations are obtained.

Z ₃₁ (t)=e ^j2 〓 ^fdTl ……(10) Z ₃₂ (t)=e ^j2 〓 ^fdT2 ……(11) These complex conjugate products Z ₃₁ (t) and Z ₃₂ (t) have different repetition periods. This is a complex signal, and in order to multiply the two, the complex signal output earlier is delayed by delay time _T1 in delay circuits 60 and 62. Therefore, complex signals with different repetition periods are simultaneously supplied to the second complex multiplier 64, and the complex conjugate product of both signals can be calculated here.

That is, the complex conjugate product S of different periodic signals from the two Doppler signals expressed by equations (10) and (11) above is
is calculated using the following formula.

S=Z ₃₁ ^*・Z ₃₂ = e ^-2j 〓 ^fdTl −e ^j2 〓 ^fdT2 = e ^j
2 〓 ^fd(T1-T2) =R+jI...(12) The complex conjugate product S obtained by this second complex multiplier 64 removes random fluctuation components of the signal and noise components generated from the device. average circuit 66
is supplied to The output of this averaging circuit 66 is expressed by the following equation.

= + j = e ^j2 〓 ^fd (T2 - T1) ... (13) The speed of the thus averaged output is calculated by the speed calculation circuit 52, which is determined by the argument angle φ of the output of the averaging circuit 50. The deviation frequency of the Doppler signal is determined. This deviation angle φ and deviation frequency
fd can be expressed by the following formula.

φ=tan ^-1 (/)=2π(T ₂ −T ₁ ) ……(14) =φ/(2π(T ₂ −T ₁ )) ……(15) Therefore, it can be understood from the above equation (15) To be,
The final deviation frequency is determined by the transmission repetition period
T ₂ −T ₁ (repetition frequency is 1/(T ₂ −T ₁ )), which is the same as the Doppler shift frequency obtained when a pulse wave is radiated.

This is ( _{T 2 −}
This means that the maximum speed that can be _detected has been expanded by a factor of _{T 1 /} (T ₂ −T ₁ ).

For example, when T ₂ =1.1T ₁ , the maximum detectable speed is 10 times higher than when the repetition period T ₁ is constant. In this case, it is possible to detect 10 times faster with a cycle change of about 10%, and by appropriately selecting different repetition cycles T ₁ and T ₂ , the detectable diagnostic distance can be maintained without changing, and the aliasing phenomenon can be reduced. High-velocity blood can be detected well without causing any problems.

FIG. 3 shows a time chart of the operation of the apparatus of the present invention explained using the above calculation formula, and the operation of the ultrasonic Doppler diagnostic apparatus will be briefly explained below.

In the figure, pulse waves with different transmission periods T ₁ and T ₂ are alternately output from the frequency division synchronization circuit 12,
Ultrasonic waves with a repetition period of T ₁ and T ₂ are transmitted into the subject's body 22 multiple times. _{Then , as shown} in _{FIG .} The above-mentioned signal Z ₁ (t) is obtained.

And as shown in figure d, periods T ₁ and T ₂
C ₁₁ , which is the complex signal Z 3 (t) described above, is delayed by a delay time T, which is the sum of C ₃ (t), and the complex conjugate product with the next received Doppler signal is taken in the first complex multiplier 58. _C21 to _C1o and _C2o are obtained.

The output of this first complex multiplier 58 is delayed by a delay time T ₁ , as shown in figure f, which is then applied to the output of the first complex multiplier 58 and the second complex multiplier. A complex conjugate product S is taken in a device 64. From this complex conjugate product S, the outputs of the averaging circuit 66 and speed calculating circuit 68 as shown in Figures h and i are obtained.

As a result, the Doppler shift frequency signal output from the velocity calculation circuit 68 has a signal waveform 302 shown in FIG. 4a.

That is, the output of the second complex multiplier 64 has a period
The Doppler signal has a repetition period of the difference obtained by subtracting the period T ₁ from T ₂ , and in terms of the output signal waveform of the velocity calculation circuit 68, the signal obtained from the Doppler signal with the repetition period T ₂ is a waveform 300. Further, the signal obtained from the Doppler signal with a repetition period T ₁ becomes a waveform 301, and these waveforms exceed the maximum Doppler frequency V _nax , but the signal waveform 302 of the Doppler shift frequency due to the repetition period of the difference is at the maximum Doppler frequency. within the range and becomes detectable. Therefore,
This means that the speed of the high-speed movement reflector deep within the body of the subject can be detected and displayed well.

Next, a case where the second complex multiplier 64 calculates a complex product of complex signals will be described.

In the present invention, by calculating the conjugate product of the complex signals in the second complex multiplier 64, it is possible to detect a high velocity well deep inside the subject, that is, at a long distance. By doing so, it is possible to accurately determine the speed over a short distance.

In this case, the output of the second complex multiplier 64 is expressed by the following equation.

S＝Z ₃₁・Z ₃₂ ＝e ^j2 〓 ^fdTl・e ^j2 〓 ^fdT2 ＝e ^j2
〓 ^fd(T1+T2) =R+jI...(16) Therefore, similarly to the above equation (15), the Doppler shift frequency is as shown in the following equation.

=φ(2π(T ₁ +T ₂ )) ... (17) As understood from the above equation (17), the complex product obtained by the second complex multiplier 64 has a transmission repetition period of T ₁ +T ₂ ( The repetition frequency is 1/(T ₁ + T ₂ )),
This is the same Doppler shift frequency obtained when a pulse wave is emitted.

Therefore, compared to the conventional Doppler shift frequency obtained by ultrasound with a constant repetition period T ₁ , it is expanded by a factor of (T ₁ + T ₂ )/T ₁ , and the maximum detectable velocity is T ₁ / This means that it has been compressed by (T ₁ + T ₂ ) times.

That is, as shown in FIG. 4b, the signal waveform 400 of the Doppler shift frequency obtained with ultrasound with a repetition period T ₁ and the signal waveform 401 obtained with ultrasound with a repetition period T ₂ are as shown in the figure. In contrast, the signal number waveform 402 obtained by ultrasonic waves with a repetition period of T ₁ +T ₂ has a large amplitude, so it is difficult to detect distance and low velocity blood flow in a short distance. Speed can be determined with high accuracy.

As described above, according to the present invention, the transmission repetition period can be substantially converted to T ₂ −T ₁ or T ₁ +T ₂ without significantly changing the transmission repetition period, and the repetition period of the difference can be converted to According to the Doppler signal, it is possible to detect and display high-velocity moving reflectors in the deep part of the subject, and according to the Doppler signal with the repetition period of the sum, it is possible to detect and display low-velocity moving reflectors in shallow parts. It becomes possible to detect and display speed with high accuracy.

Further, according to the present invention, by appropriately changing the two different transmission repetition periods T ₁ and T ₂ , it is possible to perform highly accurate speed detection corresponding to the target region.

[Effects of the Invention] As explained above, according to the present invention, two pulsed ultrasound waves having different transmission repetition periods are alternately emitted multiple times, and the received signal obtained from the motion reflector is emitted. Since it is converted into a Doppler signal that is the difference or sum of transmission repetition periods, it is possible to eliminate the aliasing phenomenon and accurately detect and display the velocity of motion reflectors such as blood flow. It becomes possible to display images well.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a preferred embodiment of the ultrasonic Doppler diagnostic device according to the present invention, Fig. 2 is a block diagram showing the configuration of a period conversion circuit, and Fig. 3 is a time chart showing the operation of the embodiment device. 4 is a signal waveform diagram showing the Doppler shift frequency obtained with the apparatus of the embodiment, and FIG. 5 is a signal waveform diagram showing the Doppler shift frequency obtained with the conventional apparatus. 10... Oscillator, 12... Frequency division synchronous circuit, 14
... Signal switcher, 48 ... Period conversion circuit, 54,
56, 60, 62...delay circuit, 58...first complex multiplier, 64...second complex multiplier.

Claims (1)

[Claims] 1. Emit ultrasonic pulse waves into the subject, receive reflected waves from a moving reflector, and detect the Doppler shift frequency of this received Doppler signal to determine the velocity status of the moving part. The ultrasonic Doppler diagnostic device that displays the data includes a transmission circuit that alternately outputs pulse waves with two different transmission repetition periods multiple times in the same scanning direction, and a transmission circuit that alternately outputs pulse waves with two different transmission repetition periods in the same scanning direction. A conversion means for converting each signal into a complex signal, a delay circuit for delaying each of the two complex signals obtained by the conversion means for a predetermined time, a delayed complex signal from the delay circuit, and the delay circuit. A first complex multiplier that calculates the conjugate product of complex signals of the same repetition frequency with a predetermined time difference among the complex signals that have not undergone A delay circuit that delays each of the obtained two complex signals by a predetermined time, and a predetermined one of the outputs having a predetermined time difference between the delayed complex signal from the delay circuit and the complex signal that has not passed through the delay circuit. An ultrasonic Doppler diagnostic apparatus comprising: a second complex multiplier that calculates a conjugate product or a complex product of two complex signals of different repetition periods having a delay time difference of .