JPH08220124A - Ultrasonic current velocity measuring apparatus - Google Patents

Abstract

PURPOSE: To measure the three-dimensional current velocity distribution of a reflector having different velocity distribution utilizing elements arranged two-dimensionally and continuously. CONSTITUTION: Elements Q are arranged two-dimensionally at intervals Δx and Δy, respectively, in the directions (m) and (n). A part of the element Q is driven through a drive source to transmit repetitive ultrasonic pulse wave to the front of the element, Q. The ultrasonic wave is reflected at point P and a reflection signal is received by elements q (m, n) located at positions (m), (n) in the element Q. The receiving signals are passed through an A/D converter to produce discrete signals which are subjected to differentiation through a filter in order to remove the reflection signal from a stationary object before being subjected to Fourier transform and linear processing. Consequently, the velocity component in the three-dimensional direction of a reflector is determined and thereby the velocity distribution is derived. In other words, among the velocity components of the reflector, the velocity components in the radial direction on a polar coordinates and two perpendicular zenith angle directions (m), (n) in a plane parallel with the element Q are measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a flow velocity measuring device for three-dimensionally measuring the velocity of an object moving in a direction orthogonal to an ultrasonic beam.

[0002]

2. Description of the Related Art Several methods have been proposed as a method for measuring not only the axial direction of an ultrasonic beam, but also the direction component orthogonal to the beam axis of the velocity component of a fluid.

LS Wilson et al. Arrange a series of continuously acquired two-dimensional images along the time axis, and speckle the plane perpendicular to the beam axis and the plane perpendicular to the beam. We have proposed a method to obtain the flow velocity in each direction from the inclination of the projection (Ultrasonic Imaging 15, pp.286-303, 1993, Ultrasonic Imagin
g 15, pp286-303, 1993).

GE Trahey et al. Calculate a correlation coefficient around the target area in continuously acquired images, and determine the moving speed direction of the target and the position from the position where the correlation coefficient is maximum. We are proposing a method for finding size (IEEE Transaction on Biomedical Engineering vol. BME-3
4, No.12, pp.965-967, 1987, IEEE Transactions o
n Biomedical Engineering, vol.BME-34, No.12, pp.96
5-967, 1987).

Bonnefous et al. Calculated the correlation function of the signal in the direction orthogonal to the beam axis,
We have proposed a method for obtaining the velocity component in the direction orthogonal to the beam axis from the time when the maximum value is obtained (Ultrasonics Symposium, pp.795-799, 1988, Ultrasonics
Symposium, pp.795-799, 1988).

Sensors (D. Censor) and others use the fact that the spectrum of the echo signal is a convolution of the function of the aperture diameter and the directivity of the transducer according to the reciprocity theorem, and the beam from the frequency at the end of the envelope of the spectrum of the echo signal is used. We have proposed a method to obtain the velocity component in the direction orthogonal to the axis (IEEE Transaction on Biomedical Engineering, vol.35, No.9, pp740).
~ 751, 1988, IEEE Transactions on Biomedical Engine
ering, vol.35, No.9, pp740-751, 1988).

On the other hand, Katakura et al. Have proposed a method of using elements arranged one-dimensionally to obtain a flow velocity component in the direction orthogonal to the beam from the phase rotation speed of the signals received by those elements (Japanese Patent Application No. Hei 10 (1999) -135242). 1-227360, Japanese Patent Application No. 3-62719, Japanese Patent Application No. 5-82941).

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to measure a three-dimensional blood flow velocity distribution of a reflector having different velocity distributions by utilizing elements arranged two-dimensionally continuously. It is in.

[0009]

According to the present invention, a velocity component in a three-dimensional direction of a reflector is obtained by linearly processing a received signal obtained by a plurality of two-dimensionally arranged elements. It is possible to derive the velocity distribution.

[0010]

It is assumed that the elements Q arranged two-dimensionally as shown in FIG. 1 are used. In the two-dimensionally arrayed elements Q, the intervals between the elements in the m direction and the n direction are Δx and Δy.
A sound wave focused on the point P is transmitted at every time pk from all or a part of the elements Q arranged two-dimensionally. k
Is the transmission number and p is the time interval of transmission. The reflected signal at the point P obtained by this sound wave is at the position (m,
It is received by element q (m, n) in n). When the signal is observed at the time when a certain time S has passed from the transmission, the observation time immediately after the k-th transmission is t = kp + S. Here, the received signal at time t by the k-th transmission is s (k,
m, n).

Since the received signal s (k, m, n) contains not only the signal from the moving reflector but also the reflected signal from the stationary object, it is necessary to remove it. Therefore, the difference s (k, m, n) -s (k + 1, m, n) of the received signals is calculated, and the result sd (m, n, t) is output to remove the signal from the stationary object.

Assuming that the radial velocity of the reflector in the polar coordinates is δ ₀ and the angular velocities in the zenith angle direction of the polar coordinates in the x and y directions are ε ₀ and γ ₀ as shown in FIG. Radius, x-direction and y of the reflector at
The positions rθ, θx, and θy in the zenith angle direction of the polar coordinates in the direction are given by Equations 1, 2 and 3.

[0013]

[Equation 1]

[0014]

[Equation 2]

[0015]

(Equation 3)

At this time, since the wavefront is corrected to be a plane by the delay circuit, if the position of the element q (m, n) is (xm, yn), rxy shown in FIG.
The ultrasonic wave propagation distance r to (m, n) is given by Equation 5, and the element q
The phase rotation amount Ψmn of the signal received by (m, n) is given by the equation 6.

[0017]

[Equation 4]

[0018]

(Equation 5)

[0019]

(Equation 6)

K represents the wave number, and its value is 2πf / c. c is the speed of sound and f is the frequency. Since the constant term of Ψmn can be ignored, it can be removed and set to Eq. Therefore, the received signal sd (m, n, t) is given by Eq.

[0021]

(Equation 7)

[0022]

(Equation 8)

A (m, n) is the aperture diameter function of the transceiver, and a (m, n) is the product of a ₁ (m) and a ₂ (n). Further, b (t) is a weighting function in the measurement time direction.

Then, when sd (m, n, t) is subjected to two-dimensional Fourier transform in the m direction and the n direction, the following equation 9 is obtained.

[0025]

[Equation 9]

Ψxy {} is an operator indicating a two-dimensional Fourier transform in the m direction and the n direction. here,
A (wx, wy) is a two-dimensional Fourier transform of a (m, n) in the m and n directions. Obvious that several 9, R ₂ is the planar ωx = kε ₀ t and plan ωy = kγ ₀ t obtain the maximum value on the straight line intersecting.

Here, if variable conversion is performed using the equations 10 and 11, the equations 12 and 13 are obtained, so that R ₂ can be rewritten as the equation 14.

[0028]

[Equation 10]

[0029]

[Equation 11]

[0030]

(Equation 12)

[0031]

(Equation 13)

[0032]

[Equation 14]

Here, χ and γ are equations 15 and 16
Is.

[0034]

(Equation 15)

[0035]

[Equation 16]

Further, when Fourier transform is performed on R ₂ ′ with respect to t, the following equation 17 is obtained.

[0037]

[Equation 17]

Ft {} is an operator indicating the Fourier transform with respect to t. Therefore, the point where R ₃ gets the maximum value
Since (ξ ₀ , η ₀ , μ ₀ ) satisfies the conditions shown in Formula 18, Formula 19 and Formula 20, the target velocity δ ₀ and the angular velocities ε ₀ and γ ₀ are Formula 21, Formula 22 and Formula 23. Required from.

[0039]

(Equation 18)

[0040]

[Formula 19]

[0041]

(Equation 20)

[0042]

[Equation 21]

[0043]

[Equation 22]

[0044]

(Equation 23)

Beamforming by the parallel beamformer is equivalent to Fourier transform in space. Therefore,
The two-dimensional Fourier transform for the m-direction and the n-direction is shown in FIG.
, The received signal s (k, m, n) is obtained by the plurality of receiving ultrasonic beams sb (k, m, n) shown in FIG. This can be replaced by performing parallel formation of a plurality of reception beams that output simultaneously.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Q is a two-dimensional array of M × N transducer elements, and the spacing between the elements in the two-dimensional array of elements Q in the m and n directions is Δx and Δy. V is driven by a driving source connected to part of the elements V of Q, and a pulsed sound wave is repeatedly transmitted to the front surface of Q with a transmission interval p. The reflected signal at the point P obtained by this sound wave is received by the element q (m, n) at the position (m, n) in Q. When the signal is observed at the time when a certain time S has passed from the transmission, the observation time immediately after the k-th transmission is t = k.
It becomes p + S.

Here, the reflection signal at time t due to the k-th transmission is represented by s (k, m, n) (m = 1, ..., M, n = 1,
, N) is received by Q, and these are discretized by an AD converter to be C (k, m, n). Where t = kT,
T is the sampling interval of the AD converter. Further, in order to remove a reflection signal from a stationary object, a difference processing is performed on a plurality of C (k, m, n) with respect to k by a filter, that is, C (k, m, n) -C (k + 1, m, n). Is obtained, and the output is set as d (k, m, n).
Then, the signal d (k, m, n) is first Fourier-transformed with respect to m by a one-dimensional Fourier transformer,
The output DR ₁ (ωx, n, k) shown in is obtained.

DA1 in the equation 24 is a discrete Fourier transform of the aperture diameter function a ₁ (m) in the m direction as shown in the equation 25.

[0049]

[Equation 24]

[0050]

(Equation 25)

Further, DR ₁ (ωx, n, k) is Fourier transformed with respect to n by a one-dimensional Fourier transformer,
The output DR ₂ (ωx, ωy, k) shown in FIG. DA2 in the equation 26 is the aperture diameter function a ₂ (n) as shown in the equation 27.
Is a discrete Fourier transform in the n direction.

[0052]

(Equation 26)

[0053]

[Equation 27]

If DR ₂ (ωx, ωy, k) is expressed in the Cartesian coordinate space (ωx, ωy, k), its value is the plane ωx.
= Kε ₀ t and the plane ωy = Kγ ₀ t intersect, the maximum value is obtained on the straight line. K indicates the wave number. Since the inclinations of these planes are the equations 10 and 11, the values of the inclinations of the planes are obtained by the least squares method, and the equations 21 and 22 are obtained.
Is calculated and the values of the angular velocities ε ₀ and γ ₀ in the zenith angle direction of the polar coordinates in the x direction and the y direction, that is, the θ direction are obtained.

Further, DR ₂ (ωx, ωy, k) is Fourier-transformed with respect to k by a one-dimensional Fourier transformer, and an output DR ₃ (ξ, η, μ) shown in Expression 28 is obtained. DB in Expression 28 is a discrete Fourier transform in the k direction of the weighting function b (kT) as shown in Expression 29.

[0056]

[Equation 28]

[0057]

[Equation 29]

This final output DR ₃ (ξ, η, μ) is calculated in the Cartesian coordinate space (ξ, η, μ) from the point where the maximum value is obtained, and the value of the velocity δ ₀ in the radial direction is calculated. obtain. Then, the obtained values of δ ₀ , ε ₀ , γ ₀ are displayed on the display as a three-dimensional polar coordinate space, or δ ₀ , ε ₀ , γ
_From the value of ₀ , the velocity components vx, vy, v in the x, y, and z directions in the Cartesian coordinate system are obtained from Equations 30, 31, and 32.
Calculate z and display it on the display as a three-dimensional Cartesian coordinate space.

[0059]

[Equation 30]

[0060]

[Equation 31]

[0061]

[Equation 32]

Since the difference processing for removing the signal from the stationary object may be performed after performing the Fourier transform on m and n, a difference processing filter is provided after the one-dimensional Fourier transformer 2 as shown in FIG. You may connect. Further, since the difference processing may be performed after performing the Fourier transform in the time direction, a difference processing filter may be connected after the one-dimensional Fourier transformer 3 as shown in FIG.

It is known that the Fourier transform related to the space is equivalent to the beam forming by the parallel beam former. Therefore, as shown in FIG. 7, the one-dimensional Fourier transformer 1 and the one-dimensional Fourier transformer 2 that perform Fourier transform on m and n can be replaced with a parallel beam former. That is, as shown in FIG. 2, the one-dimensional Fourier transform in the m-direction and the n-direction is received signal s
(k, m, n) are shown in FIG.
It can be replaced by performing parallel formation of a plurality of reception beams by simultaneously outputting all the reception signals sb (k, m, n) obtained by mn.

As a concrete procedure, a reflection signal s (k, m, n) (m = 1, ..., M, from the reflector to be measured) is used.
(n = 1, ..., N) is received by Q, and a parallel reception beamformer delays each of M × N signals and adds them to receive a reception beam having directivity in a target direction. Signal sb (k, h, l) (h = 1, ..., H, l = 1,
..., L) is made.

As shown in FIG. 3, the plurality of obtained beams have the azimuth difference of the angle ε between the adjacent beams.
Therefore, H × L reception beams sd (k, h, l) within the range of the angle Θ are selected from these reception signals as shown in FIG. Then, this signal is discretized by the AD converter. The output is passed through a difference processing filter, and the output is subjected to Fourier transform with respect to k by the one-dimensional Fourier transformer 3 to obtain the velocity component in the three-dimensional direction.

A two-dimensional display method and a three-dimensional display method can be considered as the display method. For example, as shown in FIG. 8, an arbitrary two-dimensional surface is selected, and the direction of the velocity component parallel to that surface is indicated by an arrow. The size of each velocity component is indicated by the size or thickness of the arrow. Alternatively, as shown in FIG. 9, the direction of the speed component is represented by color, and the size of each speed component is displayed by the shade of color or the level of brightness.

In the three-dimensional display method, the direction of each velocity component is indicated by an arrow as shown in FIG. The size of each velocity component is indicated by the size or thickness of the arrow. Alternatively, as shown in FIG. 11, the direction of the velocity component is represented by color,
The magnitude of each velocity component is displayed by the shade of color or the level of brightness.

[0068]

According to the present invention, the velocities of reflectors having different flow velocities can be measured three-dimensionally.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the operation of the present invention.

FIG. 2 is an explanatory diagram of an operation when a parallel receiving beamformer is used instead of performing Fourier transform in the space of the present invention.

FIG. 3 is an explanatory diagram of an operation when a parallel receiving beamformer is used instead of performing Fourier transform in the space of the present invention.

FIG. 4 is a block diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 6 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 7 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 8 is an explanatory diagram of a display method according to an embodiment of the present invention.

FIG. 9 is an explanatory diagram of a display method according to an embodiment of the present invention.

FIG. 10 is an explanatory diagram of a display method according to an embodiment of the present invention.

FIG. 11 is an explanatory diagram of a display method according to an embodiment of the present invention.

[Explanation of symbols]

Q ... Two-dimensional array element, q (m, n) ... Position in Q (m,
n) elements, P ... Reflector, B ... Parallel beam former, δ ₀ ... Velocity component in radial direction, ε ₀ ... Angular velocity component in zenith angular direction in x direction, γ ₀ ... Angular velocity in zenith angular direction in y direction component.

Claims (7)

[Claims] 1. A two-dimensional array element receives a reflection signal of an ultrasonic wave, obtains a phase rotation speed of each of a plurality of signals, and from these values, a radial direction in polar coordinates of a speed component of a reflector, and the two-dimensional An ultrasonic flow velocity measuring device characterized by measuring velocity components in the zenith angle direction in two directions orthogonal to each other in a plane parallel to the array element. 2. A wave transmitter / receiver having a two-dimensional array, and means for transmitting ultrasonic waves to a measurement object by repeatedly driving a part of elements of the wave transmitter / receiver at a predetermined cycle. A discretizer for discretizing and storing a reflection signal from a measurement target, a means for performing differential processing on signals at a predetermined elapsed time from transmission in each signal, and removing the signal from a stationary object, and those stationary objects A first one-dimensional Fourier transform device for performing a Fourier transform on one of the two-dimensional array directions on the signal after removal of the signal from
A second one-dimensional Fourier transform device that performs a Fourier transform in a direction different from the one direction of the two-dimensional array direction of the received beam, and the sequential output of the first and second Fourier transform devices is repeatedly transmitted. Having a third Fourier transform means for performing a Fourier transform in the time direction, and from the point of obtaining the maximum value in the three-dimensional distribution of the output of the third Fourier transform means, in the radial direction in the polar coordinates of the moving object in the measurement target. An ultrasonic flow velocity measuring device that obtains a velocity component and an angular velocity component in the zenith angle direction in two directions orthogonal to each other in a plane parallel to the two-dimensional array element, and performs three-dimensional display from the obtained velocity component values. 3. The first one-dimensional Fourier transform device and the second one-dimensional Fourier transform device according to claim 1, wherein signals from respective elements of the transceiver are phased to have different directivities. An ultrasonic flow velocity measuring device as a parallel receiving beamformer that outputs received signals by a plurality of receiving beams in parallel two-dimensionally. 4. The means for removing a signal from a stationary object by performing a difference process between signals at a predetermined elapsed time after transmission in each signal according to claim 1 or 2. An ultrasonic flow velocity measuring device placed in the previous stage. 5. The means for removing a signal from a stationary object by performing a difference process between signals at a predetermined elapsed time from transmission in each signal according to claim 1 or 2. An ultrasonic flow velocity measuring device placed in the previous stage. 6. A means for removing a signal from a stationary object by performing a difference process between signals at a predetermined elapsed time from transmission in each signal, in a stage subsequent to the third Fourier transformer. An ultrasonic flow velocity measuring device to be placed. 7. The velocity component in the radial direction in the polar coordinates calculated from the measurement data and the zenith angle direction in two directions orthogonal to each other in a plane parallel to the two-dimensional array element according to claim 1 or 2. An ultrasonic flow velocity measuring device that performs coordinate conversion from the angular velocity components of 3 above, calculates velocity components in 3D directions in Cartesian coordinates, and displays a 3D image from those values.