JPH04269949A - High limit speed pulse doppler measuring apparatus - Google Patents

Abstract

PURPOSE:To maintain an S/N ratio at almost the same value as in the past along with a decrease in erroneous measurement in the direction of blood stream by expanding a limit of a maximum Doppler frequency, measurable without uncertainty, more than several times than that in the past. CONSTITUTION:An average phase difference DELTAthetaG and a phase difference DELTADELTAthetaof the difference are determined from a transmission frequency f0 and a larger transmission frequency f0<1>. Among the results, the phase difference DELTADELTAtheta of the difference is large in error at a low S/N ratio. But, as a rough phase difference is determined, the phase difference DELTADELTAtheta of the difference will not exceed + or -pieven when the phase difference exceeds + or -pi between the respective transmission frequencies and a reception frequency. Thus, +2pi is added to the average phase difference DELTAthetaG using the value to correct the aliasing of the phase difference DELTAthetaG. Moreover, a correction error preventing processing is performed to correct a wrong direction of speed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a device for detecting the velocity of an object using ultrasonic waves, and in particular to a high-limit-velocity pulsed Doppler measurement device that can expand the measurable depth range and measure the blood flow velocity in a living body in real time. It is related to.

0002

2. Description of the Related Art Conventionally, the movement and position of a subject have been detected by injecting ultrasonic waves into a human body and measuring the reflected waves or transmitted waves. In other words, when an ultrasonic wave is emitted, the reflected wave returns to the emission point with a delay equal to the time it takes to travel back and forth from the emission point to the reflector. By displaying the intensity along the vertical axis, a tomographic image of the straight-line tissue structure of the subject, that is, the organ, can be obtained. In addition, in the ultrasonic Doppler apparatus, the movement of the irradiated object can be measured by irradiating the moving object with ultrasonic waves and measuring the difference in frequency between the irradiated wave and the reflected wave (difference due to the Doppler effect). Note that when selectively obtaining information only at a specific depth position, the modulated Doppler method may be used. Various devices are known as devices that detect the speed of an object using the Doppler effect of ultrasonic waves. In particular, in an apparatus using the pulsed Doppler method using phase difference detection, by measuring the phase difference of the received signal at each transmission pulse interval, it is possible to measure the velocity of each part at the entire measurement depth in real time.

FIG. 7 is a block diagram of a conventional ultrasonic velocity calculation circuit. In FIG. 7, 1a to 1d are blood particles, 2 is a transducer, 3 is an ultrasonic wave transmitting circuit, 4 is an ultrasonic wave receiving circuit, 5 is a phase comparison circuit, and 66 is a moving object detection filter (MTI filter). , 77 is a phase difference (velocity) calculation circuit that detects the phase difference Δθ from the phase. transducer
The sensor 2 transmits ultrasound pulses toward blood flow (for example, blood flow in the heart) in response to transmission pulses sent from the ultrasound transmission circuit 3 at a predetermined pulse repetition rate. . Further, the transducer 2 is configured to detect particles 1a to 1d in the liquid.
receives the echo waves reflected by the
The signal is sent to the ultrasonic receiving circuit 4. Let the velocity of blood flow be v(
(constant speed), and the repetition period of wave transmission is T, the distances between the approaching blood particles 1a→1b and the far away blood particles 1c→1d are both vT. Here, the period T of the transmission pulse
The relationship between and the required observation depth L is 2L/c=T based on the round-trip propagation time of the ultrasonic wave. Here, c is the ultrasonic velocity in the living body (approximately 1500 m/sec). Reflection signal from blood flow and reference signals α, α for the n-th transmitted wave
A phase comparator 5 performs a phase comparison with 1. What is a reference signal?
This is a clock signal that is the basis of the transmitted signal, and has a phase difference of 90° from the reflected signal. Letting the phase comparison outputs be V0 and V1, respectively, they are expressed by the following equations. V0=Acosθ V1=Asinθ When these are collectively expressed as a vector, they are expressed by the following equation. V=V0+jV1=Aexp(jθ)...
(1) The MTI filter 6 is used to detect the blood flow signal in the blood vessel wall signal from the complex phase signal V. Regarding the speed detection of the pulsed Doppler method shown in FIG. 7, for example, see ``Proceedings of the European Congress on Ultrasonics in Medicine'' (Brandestini M.:
Application of the pha
se detection principle i
na transcutaneous vel
ocity profilemeter, Proc.
of theSecondEuropean
Congress on Ultrasonic
s in Medicine) 1975. pp.
144.

0004

In the conventional pulsed Doppler method, if the repetition period of the transmitted pulse is T, then the maximum measurable Doppler deviation frequency F is 1/2T. On the other hand, if the ultrasonic propagation speed (sound speed m/sec) is c, the maximum measurable depth D is T/2. Therefore, since the product of F and D is c/4 (constant), there is a limit to the measurable speed or measurable depth. Beyond that limit, the measured value becomes uncertain. As described above, the problem with conventional methods is that there is a limit to the speed that can be measured, and at higher speeds, aliasing occurs, for example, the direction of blood flow is reversed, and even though blood flow is far away, , I misjudged the direction as if it was coming towards me. Now, if the transmission interval of ultrasound pulses is T (μsec), the range of Doppler frequencies that can be measured with conventional pulsed Doppler measurement equipment is ±1/2T (Hz), so for example, T = 250
When it is μsec, it is ±2KHz. If this range is exceeded, for example at a Doppler frequency of 2.5 KHz,
Conventional equipment incorrectly measures -1.5KHz. That is, a positive speed (displayed in red in CFM) is erroneously measured as a negative speed (displayed in blue). When considering the direction of blood flow, the direction of blood flow with positive Doppler frequency is the forward direction,
When we refer to the opposite direction of blood flow at negative Doppler frequency,
High velocity blood flow in the forward direction will be displayed as blood flow in the reverse direction, which is a very serious error.

[0005] For example, US Pat.
In specification No. 80837 (inventor Namekawa), f1 and a higher frequency f2 are used as the transmission frequency, and f2
This problem is attempted to be solved by obtaining the differential phase difference ΔΔθ from the phase difference Δθ1 of f1 and the phase difference Δθ of f1. However, there is a lack of correlators, and the project is incomplete. Furthermore, Japanese Patent Application Laid-Open No. 2-147914 (inventor,
In the Rayner-Fehr system, the frequency spectrum of the periodic transmit pulse sequence generated by the transmitter is in separate adjacent frequency bands. Since the two frequency bands are close to each other, they have substantially the same amount of attenuation as they pass through the circuit. If f1 is the center frequency of one frequency band, f2 is the center frequency of another frequency band, f0 is the frequency that defines the boundary between frequency bands, and the separation between frequencies f1 and f2 is defined as the frequency interval Δf, then f2- f0=
f0−f1=Δf/2. The two transmitted pulses are then transmitted successively such that the signal has a location at its center where a phase reversal occurs. This improves the sensitivity of the device and improves the signal to noise. However, even with this method, there are still problems with the SN, and there is also large variation in the measurement frequency, so there are points that need to be improved.

The purpose of the present invention is to solve these conventional problems, expand the maximum measurable Doppler frequency to several times the conventional limit, and achieve high-speed blood flow without reducing the SN and keeping the measurement depth deep. An object of the present invention is to provide a high critical speed pulsed Doppler measuring device that can accurately measure flow.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the high-limit-velocity pulsed Doppler measuring device of the present invention repeatedly applies first and second pulses of different frequencies to an object multiple times at a predetermined period. A wave transmitting/receiving means for transmitting waves toward the target object and detecting reflected waves from the object, a phase comparison means for detecting the phase of the reflected waves, and filtering for removing fixed object signals from the phase signals sequentially obtained from the phase comparison means. means and
A first phase difference for determining a phase difference vector Y corresponding to the frequency of the first transmitted pulse and a phase difference vector Y' corresponding to the frequency of the second transmitted pulse among the output phase signals of the filtering means. a vector detection means, a means for adding and averaging each of the phase difference vectors output from the first phase difference vector detection means to obtain average phase difference vectors Z, Z', and adding the average phase difference vectors Z, Z'; means for obtaining a sum phase difference vector Z0; a means for obtaining an average phase difference ΔθG from the sum phase difference vector Z0; and a second position for obtaining a phase difference vector U from the average phase difference vectors Z and Z'. A phase difference vector detection means, a means for obtaining a phase difference difference ΔΔθ from a phase difference difference vector U, and an erroneous average phase difference Δ according to the index E0 as an index E0 based on the phase difference difference ΔΔθ.
The present invention is characterized by having means for correcting θG by adding +n·2π and means for correcting a correction error caused by the correction means.

[0008]

[Operation] In the present invention, (a) As shown in FIG. 2(a), ω0, ω0'
The signals of two frequencies are transmitted at a constant period, and the phase difference between the received signal and the transmitted signal is defined as a phase difference Δθ0 and a phase difference Δθ0′. As shown in FIG. 2(b), the phase difference Δθ
When 0 and Δθ01 each exceed ±π, the direction of blood flow is reversed and an aliasing phenomenon occurs. Therefore, by taking the difference ΔΔθ between these phase differences, each phase difference Δθ0, Δ
Even when θ0' exceeds ±π, the phase difference ΔΔθ has a small value and takes a value within ±π, so that no aliasing phenomenon occurs. Thereby, the measurement range can be expanded several times compared to the conventional method (for example, 5.5 times). (b) However, if the phase difference ΔΔθ of the difference is taken and displayed directly, there is a problem that the SN is poor. Using the phase difference ΔθG, this value is taken as the output of the angle detector. For this purpose, by taking into account the value of the differential phase difference ΔΔθ, n·2π is added to the average phase difference ΔθG and displayed. Thereby, measurement can be performed with almost the same SN as in the conventional method. Furthermore, in this embodiment, color Doppler display is used, and the + side, that is, the direction of approaching blood flow, is displayed in red, and the - side, that is, the direction of blood flow that is moving away, is displayed in blue.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operating principle and embodiments of the present invention will be explained in detail below with reference to the drawings. First, the operating principle of the present invention will be explained in detail. First, a method of correcting the phase difference Δθ using the phase difference ΔΔθ will be described. Now, it is assumed that the ultrasonic pulses are transmitted repeatedly at equal intervals T. For example, when the transmission frequency is f0 and a higher frequency f0', the phase difference Δθ obtained corresponding to the transmission frequency f0' is
0' and the phase difference Δθ0 obtained corresponding to the transmission frequency of f0, the average phase difference Δθ and the phase difference ΔΔθ between them can be obtained. Therefore, the phase difference Δθ0 is calculated from the phase difference vector Z0 with respect to f0 of the transmission frequency.
Also, from the phase difference vector Z0' with respect to f0', the phase difference Δ
θ0' are obtained respectively. These phase difference vectors Z0
, Z0', the Doppler velocity v obtained from the sum vector is ±
The limit is reached at πc/{(ω01+ω0)T}, and aliasing occurs at a speed higher than that. Here, ω0
, ω0′ are the angular frequencies of the two transmitted waves, respectively. At this time, the phase difference Δθ obtained from the sum vector is the average phase difference Δθ. On the other hand, the complex conjugate product Z0・Conj of the phase difference vector Z0 and the conjugate Conjg0[Z0'] of Z0'
The phase difference difference ΔΔθ obtained from the vector of g0 [Z0′] (phase difference difference vector) has a large error when the S/N is low, but approximately the value of the phase difference can be obtained. Therefore, using this approximate value of the phase difference ΔΔθ as an index,
Aerising of the phase difference Δθ, which is the vector sum of the phase difference Δθ0 and the phase difference Δθ0′, is corrected. In other words, when the index E0, which is obtained by multiplying the phase difference ΔΔθ by (ω0'+ω0)/2(ω0'-ω0), indicates +π to +3π, the average without aerising can be calculated by adding +2π to the average phase difference Δθ. A phase difference Δθ is obtained. However, in that case,
As the SN decreases, a correction error occurs near the boundary of ±(2n-1)π (where n is an integer) (for example, +π). Therefore, an error-proofing algorithm is required. Therefore, the phase difference ΔΔθ and (ω0′+ω0)/2(ω0
Even if the index E0 multiplied by '-ω0) shows +π to +3π, when the average phase difference Δθ does not exceed +π and is around +π, the correction is made by subtracting -2π from the corrected average phase difference Δθ. An error-free average phase difference Δθ is obtained. This makes it possible to correct the wrong direction of velocity. In other words, high-speed blood flow in the reverse direction exceeding -π (blood flow away from the probe) and high-speed blood flow in the forward direction exceeding +π (blood flow away from the probe).
The blood flow toward the probe can be measured without error. The measurement limit speed v according to the present invention is ±πc/2
Since it is (ω0'-ω0)T, it is (ω0'+ω0)/2(ω0'-ω0) times the limit speed according to the conventional method. For example, when ω2=3.6 MHz and ω1=3 MHz, the measurement range increases from ±π to ±5.5π, and the measurable frequency without velocity uncertainty becomes 5.5 times as large. Furthermore, since no processing other than subtractable calculation is performed for correction,
The same level of SN as before can be achieved.

An embodiment and its operation will be explained in detail with reference to the drawings. 1A and 1B are block configuration diagrams of a pulsed Doppler measurement device showing one embodiment of the present invention, FIG. 2 is an explanatory diagram of the principle of the pulsed Doppler measurement method of the present invention, and FIG. 8 is a diagram for comparison with this. FIG. 2 is a diagram illustrating the principle of a conventional pulsed Doppler measurement method. As mentioned above, the relationship between the period T of the transmitted pulse and the required observation depth L is determined from the round-trip propagation time of the ultrasonic wave, as follows:
2L/c=T holds true. Here, c is the ultrasonic velocity in the living body (approximately 1500 m/sec). A phase comparator performs a phase comparison between the reflected signal from the blood flow for the n-th transmitted wave and the reference signals α and α'. Letting the phase comparison outputs be V0 and V1, respectively, they are expressed by the following equations. V0=Acosθ V1=Asinθ When these are collectively expressed as a vector, they are expressed by the following equation. V=V0+jV1=Aexp(jθ)...
(1) An MTI filter is used to detect the blood flow signal in the blood vessel wall signal from the complex phase signal V. Since the reflector moves by a distance vT within time T, there is a difference between the phases of the reflected signals at adjacent times as shown in (a) Trans. As shown in waveform, a phase difference Δθ occurs. Here, a pulse with a large amplitude is a transmitted wave transmitted every period T, and a pulse with a small amplitude is a reflected signal. Δθ=2kvT=(2v/c)ω0T=ω5T...
・・・・・・・・・(2) Here, ω5=(2v/c)
ω0, which is usually called the Doppler frequency (rad/s). Further, k is the wave number (2π/λ). This phase difference Δθ is obtained as follows. First, the phase difference vector Yn is expressed by the following formula, so Yn=Vn+1・Conjg0[Vn]...
(3) From the phase angle of this phase difference vector Yn, the argument Yn is obtained by the following equation. Arg. [Yn]=Arctan(YIn/YRn
)=Δθ (4) Here, YRn is the real part of Yn, and YIn is the imaginary part of Yn. The phase difference Δθ is determined from this, and the velocity of blood flow is determined. Note that Conjg0[Vn] is a complex conjugate,
Arg. [ ] represents the declination angle. Lo in FIG. 8(b)
As shown in w speed, the phase difference Δθ is correctly measured when the blood flow is at a normal speed. However, Fig. 8(c)
As shown in High speed, this phase difference Δ
If θ exceeds ±π, the leading and slowing phases will be reversed, resulting in incorrect blood flow direction. This limit is when Δθ=±π and is in the following range. ｜Δθ｜≦π・・・｜ω5T｜≦π ・・・｜(2v/c)ω0T｜＜=π・・・・・・・・・
・・・・・・・・・(5) Here, in the above formula (5), ω0
By selecting a small value, it is also possible to expand the measurement region of ω5. That is, the measurement depth L (=cT/c
) is the measurable depth (depth that can be measured without uncertainty), and measurement of cardiac blood flow requires a distance of approximately L = 15 cm, so there is a limit to reducing the transmission interval T. (T=about 250 μm).

The apparatus block of the present invention will be explained with reference to FIGS. 1A and 1B, and the operating principle of the present invention, that is, the method of expanding the normal limit by more than five times, will be explained with reference to FIG. Figure 2(a)
Trans. As shown in waveform, in the present invention, two types of transmission frequencies f0 (=ω0/2π), f0
'(=ω0'/2π) at equal intervals T. Figure 1A
, B, transducer 1, wave transmitter 3, wave receiver 4, phase comparators 5, 6, A/D converters 7, 8, MTI filters 9, 10, delay circuits 11, 12, autocorrelation Vessel 13
, 14, and the correlator 15 have the same circuit configuration as the conventional circuit. The newly provided circuit in the pulsed Doppler measurement device of the present invention is
These are ATAN memories 17 and 18, a phase difference correction circuit 19, a phase difference correction error corrector 20, a divider 21, and a complex adder 16. The ATAN memory 17 is a memory for converting a phase difference vector into a phase difference, the ATAN memory 18 is a memory for converting a difference phase difference vector into a difference phase difference, and the corrector 19 and the corrector 20 are These are a circuit that corrects the average phase difference ΔθG using the differential phase difference ΔΔθ, and a circuit that corrects the correction error. As shown in Figures 1A and B, the outputs of the measuring device are A2, A3, A
Take out the three types of output displays in step 4. A4 is the display output of the average phase difference ΔθG, which is the average of the phase differences between two types of transmitted pulses and received pulses, and A3 is the display output of the difference phase difference ΔΔθ
The average phase difference Corr. is corrected by adding ±nπ to the average phase difference ΔθG. It is the display output of [ΔθG], and A
2 is the velocity of blood flow v=c/(ω0′+ω0)・(Corr
．． This is the display output of [ΔθG]/T). As shown in FIGS. 1A and 1B, the wave transmitting unit 3 repeatedly transmits ultrasonic pulses of different frequencies ω01 and ω0 toward the blood flow 2 at a transmission interval T. In the phase comparator 5, a reference signal α=Acosω0 consisting of a reflected signal from the blood flow and a reference frequency of frequency ω0 is generated.
A phase comparison is made with t, α'=A sin ω0't. However, it is assumed that ω0′>ω0. Further, in the phase comparator 6, a reference signal β consisting of the reflected signal and a reference frequency of frequency ω0'
A phase comparison is made with =Acosω0't and β1=Asinω0't. The phase difference Δθ in this case has the following value with respect to the transmission frequency f0. Δθ=2kvT=(2v/c)ω0T=ω5T
(6) Here, k=2π/λ1. λ1 is the wavelength of the signal of frequency f0. Also,
For the transmission frequency f0', a slightly larger phase difference Δθ'
becomes. Δθ′=2k′vT=(2v/c)ω0′T=ω5
'T...(7) Here, ω5'=(2v/
c) ω0′ and k′=2π/λ2. In addition, λ
2 is the wavelength of the signal of frequency f0'. If the average phase difference between the phase difference Δθ' and the phase difference Δθ is the phase difference ΔθG, then
It becomes as shown in Low Speed in FIG. 2(b). ΔθG=(Δθ′+Δθ)/2 ・・・・・・
・・・・・・・・・ (8-1) = (k
′+k)vT・・・・・・・・・・・・・・・・・・
(8-2) =2π(1/λ2+1/λ
1) vT・・・・・・・・・(8-3)
=2π(f0+f0′)vT・・・・・・・・・
・・・・・・・・・(8-4) ={2(ω
01+ω0)/c}vT・・・・・・・・・・・・ (
8-5) The MTI filters 9 and 10 in FIGS. 1A and 1B perform high-pass filtering on the phase signals output from the phase comparators 5 and 6, and remove low frequency components due to movement of the blood vessel wall. In this case, the phase difference vectors Yn, Yn' corresponding to the respective transmission frequencies are calculated using a complex correlator (autocorrelator).
13 and 14 in sequence. Yn=Bexp(jΔθ) ・・・・・・・・・
・・・・・・・・・(9-1) Yn′=B′exp(
jΔθ) ・・・・・・・・・・・・・・・(9-2
) Since the phase angles of these vectors Yn and Yn' vary due to the influence of noise, they are determined by averaging the phase difference vectors Yn and Yn' sequentially obtained by a complex correlator (not shown). That is, ZK=ΣYn=Aexp(jΔθ)...
...... (10-1) ZK'=ΣYn'=
A′exp(jΔθ′)・・・・・・・・・(10−
2) are sequentially taken out as the output of the complex adder 16. In this way, a phase difference vector ZK regarding the phase difference Δθ of f0 and a phase difference vector ZK' regarding the phase difference Δθ' of f0' can be obtained for the two types of transmitted waves. The Doppler frequency obtained from these phase differences is ±
Aliasing occurs at 1/2T. From the viewpoint of SN, in order not to reduce the frame rate, the number of additions within a packet is halved, resulting in a reduction of 3 dB compared to the conventional method. Therefore, the average phase difference ΔθG of the phase differences Δθ0 and Δθ0′ is used. Therefore, the previous formula (10-1) (10
−2), the following equation is derived. Z=ZK+ZK1=Bexp(jΔθG)...
・・・・・・・・・(11) Furthermore, ZK=Aexp(j
Δθ), ZK'=A'exp(jΔθ').

FIG. 3 is an explanatory diagram of the phase difference vector in the present invention. FIG. 3(a) shows the phase difference vector of ZK', and FIG. 3(b) shows the phase difference vector of ZK. By adding and combining these phase difference vectors ZK and ZK', a combined vector Z as shown in FIG. 3(c) is obtained. Therefore, the average phase difference ΔθG is expressed by the following equation. ΔθG=Arctan(IZ/RZ)...
・・・・・・・・・(12-1) =(k
′+k)vT・・・・・・・・・・・・・・・・・・
(12-2) = {(ω0'+ω0)/c}
vT ・・・・・・・・・・・・(12-3)
=ω7'T ・・・・・・・・・・・・
(12-4) Note that RZ is the real part of Z, and IZ is the imaginary part of Z. The value of the above equation (12-4) is obtained as the output of the ATAN memory 17 in FIGS. 1A and 1B. The adder circuit 16 remains the same as before, and the SN of the phase difference ΔθG increases by 3 dB and remains the same as before. Further, the speed measurement limit is when the phase difference ΔθG=±π, that is, as shown in the following equation. ｜ΔθG｜≦π ｜ω7′T｜≦π ｜{(ω0′+ω0)/c}vT｜≦π ・・・
・・・・・・・・・(13-1) |v|≦c/(ω0
'+ω0)・(π/T) ・・・・・・・・・(13
-2) Therefore, in the measurement of high-speed blood flow, if this phase difference ΔθG exceeds the phase of ±π, an aerising phenomenon occurs and the direction is not accurate. Therefore, as described above, it is necessary to correct the average phase difference ΔθG using the differential phase difference ΔΔθ. On the other hand, by using the high critical speed method, Lo
As shown in w Speed, the phase difference difference ΔΔθ (=
Δθ′−Δθ) is expressed by a complex conjugate product. U=ZK′・Conjg[ZK] =AK′AKexp{j(Δθ′−Δθ)}
=AK′AKexp{j(ΔΔθ)} =
AK'AKexp{j2(k'-k)vT}...
...(14-1) =AK'AKexp{j(
2(ω0′-ω0)/c)vT}...(14-2) In this way, the phase difference ΔΔθ of the difference is converted into the output of the complex correlator 15 shown in FIG. 1 by the complex conjugate product. Obtained as a vector of differences. Therefore, the phase difference ΔΔθ can be obtained as the output of the ATAN memory (angle detection bag) 18. ΔΔθ=Arctan (IU/RU)...
・・・・・・・・・・・・(15-1) =
2(k'-k)vT = (2(ω0'-
ω0)/c)vT = ω7Conjg[
ZK〕T・・・・・・・・・・・・・・・(15-2)
Note that RU is the real part of U, and IU is the imaginary part of U. When the phase difference ΔΔθ is low in SN, the error and variation are large, but approximately the value of the phase difference can be obtained. Note that at this time, the speed measurement limit occurs when ΔΔθ=±π. That is, the limit formula is as follows. |ΔΔθ|≦π |ω7Conjg[ZK]T|≦π |{2(ω
0'-ω0)/c}vT|≦π ・・・・・・・・・
・(16-1) |v|≦{c/2(ω0′-ω0)
}・(π/T) ・・・・・・(16-2) Previous formula (1
By comparing 3-2) and the above formula (16-2),
The measurement limit of the present invention is the conventional {(ω0'+ω0)/2(ω
0'-ω0)} times.

FIGS. 4A, 4B and 5 are explanatory diagrams showing the algorithm of the phase difference correction method of the present invention, respectively. Using the phase difference ΔΔθ of the difference in the previous equation (15-1) as an index,
The average phase difference Δ is the vector sum of the phase differences Δθ and Δθ1
A method for correcting aliasing of θG will be explained with reference to FIGS. 4A and 4B. The following equation is used as the correction algorithm. Corr. [ΔθG]=ΔθG+n・2π (where n is an integer)...(17-1) The conditions at that time are (
2n-1)π<E0≦(2n+1)π Here, E0
=ΔΔθ((ω0′+ω0)/2(ω0′−ω0))・
...(17-2) Also, Corr. [ΔθG] represents the corrected average phase difference ΔθG. In this method, if the index of the above equation (17-2) is correctly determined with a range resolution of 2π, the average phase difference ΔθG can be corrected correctly. FIG. 4A is a diagram showing the value of the differential phase difference ΔΔθ, and FIG. 4B is a diagram showing the value of the average phase difference ΔθG,
The respective vertical axes are +2π, +4π, +6π, −2π, −
4π and -6π are common scales in (a) and (b). In FIG. 4B, the solid line represents ΔθT, the dashed line represents Δθ'T, and the dotted line represents ΔθGT. For example, as shown in FIG. 4B, in equation (17-1), n=1 is the phase difference Δ
This means that θG corrects one degree of aerising in the negative direction. That is, +2π operation is performed on the actual broken line. Further, n=-2 means that the phase difference ΔθG correctly corrects 2 degrees of aliasing in the positive direction. That is, -4π operation is performed on the actual broken line. Furthermore, when n=0, the phase difference ΔθG is within the conventional measurement range, so the phase difference ΔθG
There is no need for correction. FIG. 5 shows countermeasures against correction errors. If E0 is π<E0≦π+δ' and the phase difference ΔθG is ΔθG>π-γ', the corrected phase difference Corr. [ΔθG] is Corr. [ΔθG]-2π
is corrected. In this way, in FIG. 5, three values of the phase difference ΔθG (phase close to +π, phase near −π, −
By correcting the phase (all phases close to π are shown by white circles), the phase is increased by +2π (the phase close to +3π, the phase near +π, and the phase close to +π are all shown by black circles). Furthermore, the phase difference Corr. indicated by the first black circle. [ΔθG]
jumps to around +3π due to a correction error, which means that it has been corrected (white circle) as described above.

FIG. 6 is a flowchart of the operations of the phase difference corrector and correction error corrector in FIG. 1 for detailed explanation. The phase difference corrector 19 performs correction processing using an algorithm shown at 22 in FIG. 6, and the correction error corrector 20 performs error correction processing using an algorithm shown at 23 in FIG. In step 22, the previous formula (16-1)
The correction value of the second term of the difference phase difference ΔΔθ and (ω0′+ω
0)/2(ω0'-ω0) (step 22-1), and the average phase difference ΔθG, which is the output of the ATAN memory (angle detector) 17, and the correction value (n
・2π) is added (step 22-2). However, when the SN is low, for example, when the phase difference is near +π, the index E0 erroneously indicates a value exceeding +π even though the true value does not exceed +π due to noise. Therefore, the correction algorithms (17-1, 17-2) incorrectly set n=1 when n=0, and correct the average phase difference ΔθG to the incorrect ΔθG+2π. This is a serious problem. Conversely, if you mistakenly specify a value that does not exceed +π even though the true value exceeds +π,
In the correction algorithm (17-1), n=0 instead of n=1, and the average phase difference ΔθG is corrected to the error ΔθG. In other words, the aliasing that should be corrected remains as it is, which is a serious problem in this case as well. Phase difference correction error corrector 20 of the present invention
solves this problem by correcting the phase difference error. That is, as shown in algorithm 23 of FIG.
(16-2) The phase difference ΔΔθ and (ω0′+ω0)
The index E0 multiplied by /2(ω0'-ω0) is +π~+3
When indicating π (step 23-1), the phase difference ΔθG is +
By adding 2π (step 23-2), the phase difference Corr. [ΔθG] should be obtained. However, in that case, depending on the decrease in SN, it is necessary to move around the ±(2n+1)π boundary (n is an integer), for example +
A correction error occurs in this case. Even if the index E0 indicates +π to +3π, if the phase difference ΔθG does not exceed +π and is around +π, -2π is subtracted from the corrected phase difference ΔθG (step 23-4), so that there is no correction error. Phase difference Corr. [ΔθG] is obtained (18-1,
18-2). That is, the error correction algorithm of the following equation (18) operates on the corrected phase difference ΔθG using the index E0. (b) Corr. [ΔθG]=Corr. [ΔθG]+
2π ・・・・・・(18-1) The condition at this time is (2n+1)π−δ′<E0≦(
2n+1)π Δ
θG<-π+γ' ・・・・・・・・・・・・(18-
2) Here, E0=ΔΔθ{(ω0′+ω0)/2
(ω0′−ω0)} 0<γ′≦
0.5π, 0<δ'≦π (b) Corr. [Δ
θG]=Corr. [ΔθG]-2π ・・・・・・
(18-3) The condition at this time is (2n+1)π<E
0≦(2n+1)π+δ′
ΔθG>π−γ′ Here, E0=ΔΔθ
{(ω0′+ω0)/2(ω0′−ω0)}
0<γ'≦0.5π, 0<δ'≦
πHere, for example, γ′=0.5π, δ′=0.95
This is effective when π is low SN (approximately 15 dB) or less.

The divider 21 in FIG. 1 calculates the corrected average phase difference Corr. This is a divider for finding the Doppler angular frequency from [ΔθG]. Therefore, the Doppler angular frequency ω5' is
It is determined by the divider 21 using the following equation. ω5′=Corr. [ΔθG]/T...
・・・・・・・・・・・・(19) Here, ω5′
= {(ω0′+ω0)/c}v Therefore, the above formula (19
) is obtained from the output terminal A2 of the divider 21 in FIG. In this case, the blood flow velocity is expressed by the following equation. v=c/(ω0'+ω0)・(Corr. [ΔθG
]/T) (20) Doppler angular frequency ω5 or velocity v is output to the output terminal A2 according to the division values T and c/T (ω01+ω0). Note that the terminal A3 has an average phase difference Corr. [ΔθG
], but terminal A4 also has an average phase difference ΔθG before correction.
is output. In this way, in the case of fast blood flow as shown in FIG. 2(c), the blood flow velocity can be measured correctly without erroneous direction even when +π is exceeded.

[0016] In this way, by using two different transmission frequencies, for example f0 and f0', it is possible to prevent high-speed blood flow that would otherwise be difficult to distinguish due to the aliasing phenomenon and result in erroneous measurements. On the other hand, according to the present invention, the speed can be measured in an accurate direction and can be measured using the same SN as the conventional method. Here, the measurable Doppler angular frequency ω5
The range of ' is as follows. |ΔθG|≦π{(ω0′+ω0)/2(ω0′−
ω0)} |ω51|≦(π/T) {(ω0′+ω0
)/2(ω0'-ω0)}...(21) As is clear from the above equation (21), the limit in the conventional method is π/T as mentioned above, whereas the limit in the present invention Then, the maximum Doppler frequency that can be measured without uncertainty is (π/T) {(ω
0'+ω0)/2(ω0'-ω0)}. Therefore,
Compared to the conventional method, the limit is (ω0'+ω0)/2(ω0
'-ω0) times. For example, ω0
=3 MHz, ω0'=3.6 MHz, the measurement range changes from ±π/T to ±5.5π/T, which can be expanded by 5.5 times. Here, since the wave transmission period T is the same as the conventional one, it is possible to accurately measure high-speed blood flow while keeping the measurement depth deep. In addition, in the present invention, since ordinary complex correlation processing is used, the obtained Doppler frequency is calculated using CFM (Colorflow Mapping).
) is the center of gravity frequency used in That is, since a method is used to correct the phase difference measured using the normal method, the same SN as before can be maintained. In addition, in the embodiment shown in FIG. 2(a), one frequency ω0 is transmitted multiple times with a period T, and then another frequency ω0' is transmitted multiple times with a period T, but other implementations As an example, two transmission frequencies ω0
The present invention is also applicable to the case where waves ω0′ and ω0′ are transmitted alternately at a constant period T. Furthermore, in the embodiment of FIG. 1, it is also possible to use a two-axis arithmetic unit that detects a phase difference vector by adding the sine and cosine components of the phase θ, respectively, instead of the autocorrelator. Further, the present invention can also be applied to a Doppler measuring device that has been proposed in the past, for example, described in Japanese Patent Application Laid-Open No. 2-147914. Although ultrasonic waves have been described in the embodiments, the present invention is also applicable to general waves such as light, electromagnetic waves, and lasers.

[0017]

[Effects of the Invention] As explained above, according to the present invention,
(b) The limit of the maximum measurable Doppler frequency can be expanded by more than five times compared to conventional methods without uncertainty, and (b) Since no processing other than addition and subtraction is performed for correction, the signal-to-noise ratio is Almost the same as before. Furthermore, (c) since the wave transmission period T is the same as the conventional one, high-speed blood flow can be accurately measured while keeping the measurement depth deep. Furthermore, (d) since the correlation method is used, it is extremely effective for reducing the gain at the zero point of the filter.

[0018]

[Brief explanation of the drawing]

FIG. 1A is a part of an overall block diagram of a pulsed Doppler measurement device showing an embodiment of the present invention.

FIG. 1B is another part of an overall block diagram of a pulsed Doppler measuring device showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the operating principle of the present invention.

FIG. 3 is an explanatory diagram of a phase difference vector obtained by adding and combining vectors ZK and ZK' in the present invention.

FIG. 4A is a part of a conceptual diagram of a phase difference correction algorithm of the present invention.

FIG. 4B is another part of a conceptual diagram of the phase difference correction algorithm of the present invention.

FIG. 5 is an explanatory diagram of a phase difference correction method in FIG. 4;

FIG. 6 is an operation flowchart of a phase difference corrector and a phase difference correction error corrector in the present invention.

FIG. 7 is a conceptual diagram of a conventional pulsed Doppler measurement device.

FIG. 8 is a diagram showing the operating principle of a conventional pulsed Doppler measurement method.

[Explanation of symbols]

1 Transducer 2 Blood flow 3 Wave transmitter 4 Wave receiver 5, 6 Phase comparator 7, 8 A/D converter 9, 10 MTI filter 11, 12 Delay circuit 13, 14 Autocorrelator 15 Correlator 16 Addition circuit 17 ATAN memory (for phase difference ΔθG) 18 A
TAN memory (for phase difference ΔΔθ) 19 Phase difference corrector 20 Correction error corrector 21 Divider

Claims (2)

[Claims] 1. Wave transmitting/receiving means for repeatedly transmitting first and second pulses having different frequencies toward a target object multiple times in series at a predetermined period, and detecting reflected waves from the target object. , a phase comparison means for detecting the phase of the reflected wave, a filtering means for removing a fixed object signal from the phase signals sequentially obtained from the phase comparison means, and an output phase signal of the filtering means. A first phase difference vector Y corresponding to the frequency of the first transmitted pulse and a phase difference vector Y' corresponding to the frequency of the second transmitted pulse are determined.
means for calculating the average phase difference vectors Z, Z' by respectively adding and averaging the phase difference vectors output from the first phase difference vector detecting means; ′ to obtain a sum phase difference vector Z0; means to obtain an average phase difference ΔθG from the sum phase difference vector Z0; second phase difference vector detection means for obtaining a vector U; means for obtaining a phase difference difference ΔΔθ from the phase difference difference vector U; A high-limit speed pulse Doppler measurement device comprising: means for correcting the phase difference ΔθG by adding +n·2π; and means for correcting a correction error caused by the correction means. 2. Transmitting means for periodically and continuously generating pulses of at least two frequency spectra in a predetermined pulse repetition period; an ultrasonic transducer for receiving two groups of corresponding reflected waves; and a receiving means connected to the ultrasonic transducer for separately processing the two groups of reflected waves to generate Doppler information. , and evaluation processing means connected to the receiving means and evaluating the reflected waves to determine the moving speed of the object, the phase difference vector Y corresponding to each of the two groups,
a first phase difference detection means for calculating Y'; a means for calculating average phase difference vectors Z and Z' by averaging each of the phase difference vectors obtained by the first phase difference detection means;
means for adding the average phase difference vectors Z and Z' to obtain a summed phase difference vector Z0;
a second phase difference detection means for obtaining a phase difference vector U from the average phase difference vectors Z and Z'; means for obtaining the difference ΔΔθ of the phase difference, and the difference ΔΔθ of the phase difference.
is used as an index, and the incorrect phase difference ΔθG is calculated as Δθ according to the index.
A high-limit-velocity pulse Doppler measuring device comprising means for correcting G+n·2π and means for correcting correction errors that may occur due to the correction means.