JP2006149596A - Ultrasonic doppler rheometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic doppler rheometer of a high S/N and a high frame rate. <P>SOLUTION: The ultrasonic doppler rheometer comprises a clutter component estimation part 10 for estimating the amplitude and speed of clutter components and a clutter component removal part 11 for removing the clutter components from echo signals on the basis of clutter information estimated by obtaining the speed of the clutter components from the phase angle of a correlation vector obtained by the correlation computing processing of the plurality of echo signals by the clutter component estimation means. After removing the clutter components, they are inputted to a wall filter 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic Doppler blood flow meter that measures the blood flow in the body and displays an image using the ultrasonic Doppler phenomenon in the medical field.

  There is known an ultrasonic Doppler blood flow meter (color flow device) that uses ultrasonic Doppler phenomenon to display the blood flow distribution in the living body corresponding to color and superimposed on a black and white two-dimensional tomographic image. Yes. The configuration of a conventional ultrasonic Doppler blood flow meter is shown in FIG.

  The transmission unit 91 irradiates an ultrasonic pulse via the probe 92. The echo of the irradiated ultrasonic pulse is converted into an electrical signal by the probe 92 and input to the receiving unit 93. The receiving unit 93 amplifies a weak signal and converts it from an analog signal to a digital signal by an A / D converter (not shown). Thereafter, it is input to the phase detector 94 and becomes an echo signal converted to baseband. The echo signal converted into the baseband is input to the wall filter 95. The wall filter 95 is generally constituted by a several-order FIR type filter or IIR type filter, and functions to remove a signal from unnecessary body tissue, which is a low-frequency signal component usually called a clutter.

FIG. 10 shows an essential part of an example of a wall filter constituted by a secondary IIR filter. The wall filter 95 configured as described above can flexibly change the cutoff characteristic by changing the feedback coefficients K1 and K2. The echo signal from which clutter has been removed by the wall filter 95 has its blood flow velocity calculated by the velocity calculator 96 and is input to a digital scan converter (hereinafter referred to as DSC) 98 together with the B-mode signal from the envelope detector 97. . In the DSC 98, the B-mode signal and the blood flow signal are mixed, and a two-dimensional blood flow image is displayed on the monitor 99 (for example, Non-Patent Document 1).
Seo and Iinuma, “Principles and Apparatus of Color Doppler Tomography” Journal of the Japanese Society of ME BME, Vol. 1, no. 4, 1987 (P22-27)

  However, in the conventional ultrasonic Doppler blood flow meter, it is desirable that the wall filter has a steep characteristic in order to obtain more accurate blood flow information. However, on the other hand, a large transient response occurs, and accurate blood flow information cannot be obtained by data including such a transient response.

  In addition, in order to accurately calculate the blood flow velocity, a lot of data must be discarded in order to eliminate the influence of the transient response, which reduces the number of data points sent to the velocity calculator and the average number of times. The signal / noise ratio is reduced.

  Furthermore, in order to increase the number of data samples to supplement the discard data, the number of repeated transmission / reception of sound waves in the same direction is increased, and there is a problem that the frame rate is lowered.

  The present invention has been made to solve the conventional problems, and provides an ultrasonic Doppler blood flow meter capable of removing clutter signal components from echo signals without using a steep wall filter. For the purpose.

  An ultrasonic Doppler blood flow meter according to the present invention includes a clutter component estimating means for estimating the amplitude and velocity of a clutter component from a plurality of echo signals for a plurality of ultrasonic pulses transmitted into a test organism, and the clutter component estimating means. Is provided with a clutter component removal means for removing the clutter component from the echo signal based on the amplitude and velocity information of the clutter component estimated by. With this configuration, it is possible to remove sufficient clutter components without using a steep wall filter, and it is possible to improve the signal / noise ratio and the frame rate.

  Further, in the ultrasonic Doppler blood flow meter of the present invention, the clutter component estimation means obtains the velocity of the clutter component from the phase angle of the correlation vector obtained by the correlation calculation processing of the plurality of echo signals, and the plurality of echo signals The amplitude of the clutter component is obtained from the average value of the amplitudes. With this configuration, the velocity component and amplitude component of the clutter can be obtained with relatively simple hardware.

  Furthermore, in the ultrasonic Doppler blood flow meter of the present invention, the clutter component removing means calculates each clutter signal for each echo signal from the estimated clutter velocity and clutter amplitude, and subtracts each clutter signal from each echo signal. It has a configuration. With this configuration, the clutter component can be removed by calculating and subtracting the clutter signal for each echo.

  The present invention provides a clutter component estimating means for estimating the amplitude and speed of a clutter component, and a clutter component removing means for removing a clutter component from the echo signal based on the amplitude and speed information of the clutter component estimated by the clutter component estimating means. Providing an ultrasonic Doppler blood flow meter that has the effect of removing a sufficient clutter component without using a steep wall filter, improving the signal / noise ratio, and improving the frame rate. Is something that can be done.

  Hereinafter, an ultrasonic Doppler blood flow meter according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows an ultrasonic Doppler blood flow meter according to the first embodiment of the present invention.

In FIG.
Since the configuration and operation of the transmitter 1, probe 2, receiver 3, phase detector 4, velocity calculator 6, envelope detector 7, DSC 8, and monitor 9 are the same as those in the background art described above, the description thereof will be given. Omitted.

  A feature of the present invention resides in that a clutter component estimation unit 10 and a clutter component removal unit 11 are provided before the wall filter 5. FIG. 2 shows a detailed block diagram of the clutter component estimation unit 10 and the clutter component removal unit 11 in the first embodiment of the present invention.

The clutter component estimation unit 10
A phase angle estimator 12 that receives a baseband echo signal from the phase detector 4 and estimates a phase angle of a clutter signal included in each sample data;
An amplitude estimation unit 13 that receives the baseband echo signal from the phase detection unit 4 and estimates the amplitude of the clutter signal included in each sample data;
The clutter signal calculation unit 14 calculates a clutter signal from the phase angle from the phase angle estimation unit 12 and the amplitude from the amplitude estimation unit 13.

  The clutter component removal unit 11 temporarily stores the baseband echo signal from the phase detection unit 4, and a subtractor that calculates the difference between the echo signal output from the memory 15 and the clutter signal from the clutter component estimation unit 10. 16 is composed.

  The operations of the clutter component estimation unit 10 and the clutter component removal unit 11 configured as described above will be described using mathematical expressions.

  Hereinafter, the baseband signal from the phase detection unit 4 is treated as a complex number having the in-phase component as a real part and the quadrature component as an imaginary part. The baseband echo signal (E (t)) from the phase detector 4 is expressed by (Equation 1) as a combination of the clutter signal component (C (t)) and the blood flow signal component (B (t)). .

  The clutter signal component (C (t)) is expressed by (Equation 2) where the amplitude is ac (t) and the phase angle is θc (t).

  If the clutter component does not move, ac (t) is a constant, θc (t) is also a constant, and C (t) is a direct current component.

  In general, however, the clutter signal varies with time due to the movement of the living tissue due to the respiratory motion or heartbeat motion of the test subject. However, since the period of movement of living tissue is 1 to several seconds, the sampling period of a series of echo signals is very short, at most several milliseconds, so during the sampling period of a series of echoes, The amplitude (ac (t)) and the phase angle (θc (t)) can be approximated by a relatively low-order polynomial with respect to time.

  In the following, a case where approximation is performed using a linear expression will be described.

  The amplitude (ac (t)) of the clutter and the phase angle θc (t) are expressed by a linear expression at time t as follows (Equations 3 to 4).

  When the signal amplitudes of the clutter signal component (C (t)) and the blood flow signal component (B (t)) in (Equation 1) are compared, the clutter signal component (C ( The amplitude of t)) is a very large amplitude of several tens to several hundred times the blood flow signal component (B (t)). Therefore, the phase angle and amplitude of the echo signal (E (t)) can be regarded as substantially equal to the phase angle and amplitude of the clutter signal component (C (t)). That is, in estimating g and h in (Equation 3) and m and n in (Equation 4), the echo signal (E (t)) can be regarded as a clutter signal component (C (t)).

First, the phase angle estimation unit 12 calculates m and n in (Equation 4). The sampling times of the N echo signals are T1, T2,.
age,
Sampling time at regular intervals. Also, the actual echo signal sample data
E1, E2, ... EN
And In order to obtain the phase difference n of each sample, the correlation calculation used in the blood flow information calculation unit 6 is used (Expression 5) and (Expression 6).

  If the sampling times are not equal, it can be calculated by averaging the phase differences between the samples as follows instead of (Equation 6) (Equation 7).

Also, from the echoes E1 and EN at the first and last time of a series of samples (Equation 8)
It is also possible to obtain it in a simplified manner. In this case, there is an advantage that fewer calculation resources are required to calculate n.

  From m and n obtained as described above, the output of the phase angle estimation unit 12 for the echo signal at time (Tk) is calculated by (Equation 9).

First, the amplitude estimation unit 13 calculates g and h in (Equation 3). The method is as follows: times T1, T2,.
(Ac (t)) is obtained by the method of least squares so that the absolute value | E1 |, | E2 |,... | EN | of the sample data E1, E2,. 10-11).

  As for the amplitude, in T1, T2,... TN during a series of sample periods, the amplitude can be regarded as a constant in many cases (Equation 12 to 13). It is possible to reduce 13 computing resources.

  Based on g and h obtained as described above, the output of the amplitude estimation unit 13 for the echo signal at time (Tk) is calculated by (Equation 14).

  The clutter signal calculation unit 14 calculates the clutter signal (C (Tk)) from the output (θc (Tk)) of the phase angle estimation unit 12 and the output (ac (Tk)) of the amplitude estimation unit 13 using the equation (15). According to the output.

  The memory 15 in the clutter component removal unit 11 serves to supply the echo signal (Ek) to the subtracter 16 in accordance with the timing of the clutter signal (C (Tk)) output from the clutter component estimation unit 10. This is a storage unit for delay.

  The subtracter 16 subtracts the clutter signal (C (Tk)) estimated by the clutter component estimation unit 10 from the echo signal (Ek) (from (Expression 1) to B (t) = E (t). -C (t)), only the blood flow signal component in the echo signal (Ek) is supplied to the wall filter 5 in the subsequent stage.

  Since the signal input to the wall filter 5 is a signal including only a blood flow signal component, sufficient performance can be obtained even with a high-pass filter having a gentle characteristic as compared with the conventional wall filter. For example, (Expression 16)

Even if such a primary filter is used for the wall filter 5, blood flow velocity calculation in the blood flow information calculation unit 6 can be performed with sufficient accuracy.

  The signal of each part at the time of giving the simulation signal as an input about the above process is shown in figure.

FIG. 3 is a plot of a complex signal simulating an output signal from the phase detector 4 as a locus on a two-dimensional plane.
Clutter component amplitude: 100, velocity 0.05, blood flow component including fluctuation of amplitude of about 1% amplitude: 1, velocity 0.5
It is a simulation signal when assuming that. The blood flow velocity is normalized with the Nyquist velocity as 1.

  FIG. 4 shows an output signal from the clutter component removal unit 11. Compared with the signal of FIG. 3, the locus of the signal is a locus that rotates closer to the origin.

  FIG. 5 is an output from the wall filter 5. Compared to FIG. 4, the signal trajectory approaches the origin and is a rotational trajectory centered on the origin, the clutter component is sufficiently removed, and the blood flow velocity is about 0.5 in the velocity calculator 6. Therefore, the blood flow component rotates by about 90 ° and can be calculated as described above.

  On the other hand, FIG. 6 shows an output when the signal of FIG. 3 is directly input to the wall filter 5 in the conventional configuration. In this signal, the clutter component is not sufficiently removed, and it is impossible for the velocity calculation unit 6 to accurately estimate the blood flow velocity.

  According to the ultrasonic Doppler blood flow meter of the first embodiment of the present invention, the clutter component estimation unit 10 and the clutter component removal unit 11 are provided in the previous stage of the wall filter 5 to increase the clutter component. The removed echo signal can be input to the wall filter 5, and only blood flow information can be sufficiently extracted even when the wall filter 5 having a gentle characteristic is used. As a result, the number of data discards due to the transient response of the wall filter 5 can be greatly reduced, and the signal / noise ratio and the frame rate can be improved.

(Embodiment 2)
Next, FIG. 7 shows a detailed block diagram of the clutter component estimation unit 10 and the clutter component removal unit 11 in the ultrasonic Doppler blood flow meter according to the second embodiment of the present invention.

The clutter component estimation unit 10
A phase angle estimator 12 that receives a baseband echo signal from the phase detector 4 and estimates a phase angle of a clutter signal included in each sample data;
The clutter signal calculation unit 17 calculates a clutter signal from the phase angle from the phase angle estimation unit 12.

  The clutter component removal unit 11 temporarily stores a baseband echo signal from the phase detection unit 4, and a divider 18 that divides the echo signal output from the memory 15 and the clutter signal from the clutter component estimation unit 10. Consists of

  Operations of the clutter component estimation unit 10 and the clutter component removal unit 11 according to the second embodiment of the present invention configured as described above will be described using mathematical expressions.

  The phase angle estimation unit 12 first calculates m and n in (Equation 4) and estimates the phase angle for the echo signal at time (Tk), as in the operation in the first embodiment of the present invention. The output (θc (Tk)) of the unit 12 is calculated according to (Equation 9).

  The clutter signal calculation unit 17 outputs a clutter signal (C (Tk)) from the output (θc (Tk)) of the phase angle estimation unit 12 according to the following equation.

  This is a unit vector having the same phase angle as the clutter signal.

  Similar to the operation in the first embodiment of the present invention, the memory 15 in the clutter component removal unit 11 echoes in accordance with the timing of the clutter signal (C (Tk)) output from the clutter component estimation unit 10. This is a data delay storage unit that functions to supply the signal (Ek) to the divider 18.

  The divider 18 divides the echo signal (Ek) by the clutter signal (C (Tk)) estimated by the clutter component estimation unit 10. As a result, the output signal E (Tk) from the divider 18 becomes (Equation 18).

  The first term on the right side of (Equation 18) means that the output signal (E (Tk)) from the divider 18 contains only the fluctuation component of the clutter amplitude. Since the fluctuation component is very small and its frequency is very low, sufficient performance can be obtained even with a high-pass filter having a gentle characteristic as compared with the conventional wall filter.

  Further, the second term on the right side of (Equation 18) means that the phase term added by the movement of the clutter is removed from the blood flow component, and the blood vessel itself is moved by the movement of the clutter. This means that the velocity component of the blood flow can be canceled out and the relative velocity in the living body can be calculated.

  The divider 18 divides a complex number, and an actual calculation is performed by using the conjugate complex number of the clutter signal (C (Tk)) from the clutter component estimation unit 10 and the echo signal (Ek) from the memory 15. This can be implemented by multiplying by.

  According to the ultrasonic Doppler blood flow meter of the second embodiment of the present invention, the clutter signal calculation unit 17 that calculates the clutter signal from the phase angle from the phase angle estimation unit 12, the echo signal, and the clutter signal By providing a divider 18 that divides the clutter signal from the calculation unit 17, an echo signal from which clutter components are largely removed can be input to the wall filter 5, and the wall filter 5 having a gentle characteristic is used. It is possible to extract only blood flow information sufficiently, and at the same time, it can cancel the blood flow velocity component due to the movement of the blood vessel itself and calculate the relative blood flow velocity in vivo. It becomes.

(Embodiment 3)
Next, FIG. 8 shows a detailed block diagram of the clutter component estimation unit 10 and the clutter component removal unit 11 in the ultrasonic Doppler blood flow meter according to the third embodiment of the present invention.

The clutter component estimation unit 10
A phase angle estimator 12 that receives a baseband echo signal from the phase detector 4 and estimates a phase angle of a clutter signal included in each sample data;
An amplitude estimation unit 13 that receives the baseband echo signal from the phase detection unit 4 and estimates the amplitude of the clutter signal included in each sample data;
The clutter signal calculation unit 17 calculates a clutter signal from the phase angle from the phase angle estimation unit 12.

  The clutter component removal unit 11 temporarily stores a baseband echo signal from the phase detection unit 4, and a divider 18 that divides the echo signal output from the memory 15 and the clutter signal from the clutter component estimation unit 10. And a subtracter 19 that subtracts the signal from the amplitude estimation unit 13 from the output signal of the divider 18.

  The operations of the clutter component estimation unit 10 and the clutter component removal unit 11 configured as described above according to the third embodiment of the present invention will be described using mathematical expressions.

  In the phase angle estimator 12, as in the operations in the first and second embodiments of the present invention, first, m and n in (Equation 4) are calculated, and the phase with respect to the echo signal at time (Tk) is calculated. The output (θc (Tk)) of the angle estimation unit 12 is calculated according to (Equation 9).

  The clutter signal calculation unit 17 outputs a clutter signal (C (Tk)) from the output (θc (Tk)) of the phase angle estimation unit 12 according to the following equation (Equation 19).

  This is a unit vector having the same phase angle as the clutter signal.

  Similar to the operation in the first embodiment of the present invention, the amplitude estimation unit 13 first calculates g and h in (Equation 3), and then calculates the amplitude estimation unit 13 for the echo signal at time (Tk). (Ac (Tk)) is calculated according to (Equation 14).

  The memory 15 in the clutter component removal unit 11 matches the timing of the clutter signal (C (Tk)) output from the clutter component estimation unit 10 as in the operations in the first and second embodiments of the present invention. And a data delay storage unit that serves to supply an echo signal (Ek) to the divider 18. The divider 18 divides the echo signal (Ek) by the clutter signal (C (Tk)) estimated by the clutter component estimation unit 10 in the same manner as in the operation of the second embodiment of the present invention. (E (Tk)) represented by (Equation 18) is output.

  The subtracter 19 subtracts the output (ac (Tk)) of the amplitude estimation unit 13 from the output (E (Tk)) of the divider 18. As a result, the output signal (E (Tk)) of the subtractor 19 becomes (Equation 20).

  From (Equation 19), the output signal (E (Tk)) of the subtracter 19 does not include the clutter signal component, and the movement of the clutter cancels out the velocity component of the blood flow due to the movement of the blood vessel itself. It means that blood flow component is included.

  According to the ultrasonic Doppler blood flow meter of the third embodiment of the present invention, the clutter component is provided by providing the subtracter 19 that subtracts the signal from the amplitude estimation unit 13 from the output signal of the divider 18. It is possible to input an echo signal from which almost all of the blood flow has been removed to the wall filter 5 and sufficiently extract only blood flow information even if the wall filter 5 having a gentler characteristic than that of the second embodiment of the present invention is used. At the same time, the blood velocity component due to the movement of the blood vessel itself can be canceled out, and the relative blood flow velocity in the living body can be calculated.

  In the above description, it has been described that separate hardware is used as a means for processing a signal. However, even if a high-speed microprocessor is used, the same processing can be performed.

  Although the correlation calculation processing has been described in the first to third embodiments, the speed of the clutter component can be obtained using Fourier transform.

As described above, the ultrasonic Doppler blood flow meter according to the present invention is
By providing a clutter component estimating means for estimating the amplitude and speed of the clutter component, and a clutter component removing means for removing the clutter component from the echo signal based on the amplitude and speed information of the clutter component estimated by the clutter component estimating means. It is possible to remove a sufficient clutter component without using a steep wall filter, and to improve the signal / noise ratio and frame rate. In the medical field, it measures blood flow in the body. It is useful as an ultrasonic Doppler blood flow meter for displaying images.

Block diagram of the ultrasonic Doppler blood flow meter in the first embodiment of the present invention The block diagram explaining the detailed structure of the clutter component estimation means and the clutter component removal means in the 1st Embodiment of this invention The figure explaining the echo signal output from the phase detection part in the 1st Embodiment of this invention The figure explaining the echo signal output from the clutter component removal part in the 1st Embodiment of this invention The figure explaining the echo signal output from the wall filter in the 1st Embodiment of this invention The figure explaining the echo signal output from the wall filter in the conventional ultrasonic Doppler blood flow meter using the low-order wall filter The block diagram explaining the detailed structure of the clutter component estimation means and the clutter component removal means in the ultrasonic Doppler blood flow meter in the 2nd Embodiment of this invention The block diagram explaining the detailed structure of the clutter component estimation means and the clutter component removal means in the ultrasonic Doppler blood flow meter in the 3rd Embodiment of this invention Block diagram of a conventional ultrasonic Doppler blood flow meter Block diagram of wall filter used in conventional ultrasonic Doppler blood flow meter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,91 Transmitter 2,92 Probe 3,93 Receiver 4,94 Phase detector 5,95 Wall filter 6,96 Blood flow information calculation unit 7,97 Envelope detector 8,98 Digital scan converter 9,99 Monitor DESCRIPTION OF SYMBOLS 10 Clutter component estimation part 11 Clutter component removal part 12 Phase angle estimation part 13 Amplitude estimation part 14 Clutter signal calculation part 15 Memory 16 Subtractor 17 Clutter signal calculation part 18 in 2nd and 3rd embodiment of this invention 18 Divider 19 in the second and third embodiments 19 Subtractor in the third embodiment of the present invention

Claims (7)

Based on the clutter component estimation means for estimating at least the clutter component speed from a plurality of echo signals for the plurality of ultrasonic pulses transmitted into the test organism, and the speed information of the clutter component estimated by the clutter component estimation means An ultrasonic Doppler blood flow meter comprising clutter component removal means for removing a clutter component from an echo signal. The clutter component estimation means estimates the amplitude and speed of the clutter component, and the clutter component removal means removes the clutter component from the echo signal based on the amplitude and speed information of the clutter component from the clutter component estimation means. Item 2. The ultrasonic Doppler blood flow meter according to Item 1. 2. The ultrasonic Doppler blood flow meter according to claim 1, wherein the clutter component estimating means obtains the velocity of the clutter component from the phase angle of the correlation vector obtained by correlation calculation processing of the plurality of echo signals. The clutter component estimation means obtains the speed of the clutter component from the phase angle of the correlation vector obtained by the correlation calculation processing of the plurality of echo signals, and obtains the amplitude of the clutter component from the average value of the amplitudes of the plurality of echo signals. The ultrasonic Doppler blood flow meter according to claim 2. 5. The clutter component estimation means calculates each clutter signal for each echo signal from the estimated clutter speed and clutter amplitude, and the clutter component removal means subtracts each clutter signal from each echo signal. The ultrasonic Doppler blood flow meter according to any one of the above. The clutter component estimating means calculates the phase angle of each clutter signal with respect to each echo signal from the estimated clutter speed, and the clutter component removing means divides each echo signal by each clutter signal. The ultrasonic Doppler blood flow meter according to any one of the above. The clutter component estimation means calculates the phase angle and amplitude of each clutter signal for each echo signal from the estimated clutter speed and clutter amplitude, and the clutter component removal means divides each echo signal by the phase angle of each clutter signal. The ultrasonic Doppler blood flow meter according to any one of claims 2 to 4, wherein the amplitude of each clutter signal is subtracted.

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