JP2002143160A - Ultrasonic diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve precision for detecting the speed of an ultrasonic wave reflection body inside a living body concerning an ultrasonic diagnostic device provided with a function for obtaining blood stream information in the living body by the use of an ultrasonic Doppler method and adopting it as diagnostic information. SOLUTION: The device is provided with a calculating means for previously calculating an offset amount to be added to the actual part of a complex autocorrelation value due to a noise component and a storage means for holding the offset amount obtained by the calculating means. A velocity detecting circuit detects the velocity of the ultrasonic reflection body inside the living body based on the declination of the complex autocorrelation value after correction by which the offset amount stored in the storage means is corrected from the actual part of the complex autocorrelation value which is obtained by a complex autocorrelation circuit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus having a function of obtaining blood flow information in a subject by an ultrasonic Doppler method and using the information as diagnostic information.

[0002]

2. Description of the Related Art Recently, a blood flow velocity distribution in a living body is measured by using the ultrasonic Doppler method, and the blood flow velocity distribution is displayed in color on a monochrome tomographic image obtained by a pulse reflection method. Such an ultrasonic diagnostic apparatus is known. The measurement principle of this blood flow velocity distribution is based on the Doppler effect, which radiates an ultrasonic beam into a living body with a pulse at a fixed cycle by a vibrator array, receives reflected waves from a reflector inside the living body, and is included in the received signal. The movement speed of the reflector is measured by detecting the frequency change component, the position is obtained from the time until the reflected wave returns, and this is displayed in color as two-dimensional blood flow information in real time. .

FIG. 1 is a configuration diagram of a conventional ultrasonic diagnostic apparatus.

The ultrasonic diagnostic apparatus 100 shown in FIG. 1 is provided with a probe 1, and a vibrator such as a piezoelectric ceramic is arranged at the tip of the probe 1. The transmission circuit 2 and the reception circuit 4 are connected to the probe 1. The pulse generator 3 generates a timing signal S11 (rate pulse) for giving a transmission repetition cycle (for example, 4 KHz) and supplies it to the transmission circuit 2. The transmission circuit 2 includes, for example, a 64 channel pulse driver and a delay circuit. The pulse driver generates a drive pulse having a period equal to the transmission frequency (for example, 2.5 MHz) at the timing of the rate pulse, and applies the drive pulse to the transducer of the probe 1. The delay circuit gives a predetermined delay to the pulse generation timing for each channel in order to converge the ultrasonic beam and give directivity. As a result, the ultrasonic beam is pulsed in a direction corresponding to the directivity. Thus, at the rate pulse period,
Toward the inside of a living body (not shown), transmission and reception in the same direction (for example, the direction a in FIG. 1) are performed, for example, six times,
Further, one scan for obtaining a tomographic image is performed, and one cycle (line cycle) is completed by a total of seven scans.
While switching the scanning direction between c and d, the same processing is performed on, for example, 64 scanning lines, and scanning for one frame is completed.

On the other hand, the echo reflected from the discontinuous surface of the acoustic impedance in the living body is transmitted via the probe 1 to the receiving circuit 4.
Is received for each channel. The receiving circuit 4 includes a preamplifier, a delay circuit, and an adding circuit. The received signal is amplified by a preamplifier, given a predetermined delay for each channel by a delay circuit, and added by an adder circuit. Thus, an echo from a direction corresponding to the directivity is received.

[0006] The received signal output from the receiving circuit 4 is input to a mixer circuit 5. The mixer circuit 5 performs quadrature detection by mixing a pair of reference signals generated by an oscillator (not shown) having the same period as the transmission frequency and having a phase difference of 90 ° with the received signal, thereby performing Doppler signal detection. The in-phase signal S12a and the quadrature signal S12b are output. The two low-pass filters 6a and 6b are respectively
The harmonic components of the in-phase signal S12a and the quadrature signal S12b of the Doppler signal resulting from the mixing are removed.

The output signals of the low-pass filters 6a and 6b are sampled by the A / D converters 7a and 7b at a constant sampling period in the depth direction, for example, at 256 points, and are converted into digital values. Is done. MTI
The filters 8a and 8b remove low-frequency components due to wall motion of the organs contained in the Doppler signal and extract only blood flow components, and are composed of, for example, a primary echo canceller shown in FIG.

The autocorrelation circuit 9 includes an MTI filter 8a,
8b, the autocorrelation circuit 9 receives
Complex autocorrelation (R (1)) where the in-phase signal of the Doppler signal obtained at intervals of the repetition period is the real part and the quadrature signal is the imaginary part
Is calculated for data of six repetition periods. Assuming that the output signals of the MTI filters 8a and 8b at a specific depth are x (k) and y (k), this calculation is represented by Expressions (1a) and (1b) for each real part and imaginary part.

[0009]

(Equation 1)

[0010]

(Equation 2)

The calculation result is sequentially extracted for each depth in synchronization with the timing of the fifth rate pulse of each scanning line for each real part and imaginary part.

The speed detection circuit 10 receives an autocorrelation value (R (1)) obtained as a result of the operation of the autocorrelation circuit 9, and receives its argument (arctan （Im [R (1)] / Re [R].
(1)]｝) is calculated. This declination value gives an amount proportional to the Doppler shift frequency. This declination value is sent to the image processing circuit 12 as average speed data.

On the other hand, the output signal of the receiving circuit 4 is also sent to the tomographic image processing section 11. After detecting the envelope of the received signal, the tomographic image processing unit 11 performs A / D conversion and outputs it as monochrome luminance data.

The image processing circuit 12 applies a predetermined color scheme to the sequentially input average speed data based on the direction and the absolute value thereof, and two-dimensionally combines the monochrome speed data of the tomographic image with the scanning direction and the depth. And store it as image data in an image memory (not shown). Further, the image data is read from the image memory at a predetermined cycle, and a diagnostic image in which a monochrome image representing a tomographic image and a color image representing a blood flow are combined is displayed on the TV monitor 13.

[0015]

As described above, the conventional apparatus calculates the autocorrelation of the Doppler signal in order to detect the average speed of the reflector. However, the received signal always contains a certain amount of noise, which may affect the calculation result. If the white noises are uncorrelated with each other, they are averaged and canceled in the Σ calculation of the autocorrelation calculation. However, the presence of the aforementioned MTI filter causes the white noise to have a correlation between the sample values, thereby biasing the calculated value.

That is, the MTI filter is a first-order echo canceller as shown in FIG. 7 and i (k), q (k)
Is the sample value sequence of the in-phase component and the quadrature component of the Doppler signal at the input of the MTI filter, respectively, n
₁ (k), white noise mixed with n ₂ (k), x
If (k) and y (k) are the outputs of the respective filters, x (k) = {i (k) + n ₁ (k)} − {i (k−1) + n ₁ (k−1)} ( 3a) y (k) = {q (k) + n ₂ (k)} − {q (k−1) + n ₂ (k−1)} (3b) The first in the real part of the autocorrelation of equation (1a) Σ ｛x of item
(K) · x (k−1)} is {x (k) · x (k−1)) = {[[((i (k) + n ₁ (k)) − (i (k−1) + n _{1 (k-1))]} ] · [(i (k-1) + n 1 (k-1)) - (i (k-2) + n 1 (k-2))]] here, sigma [i (K−j) · n ₁ (k−j)] ≒ 0 and Σ [n ₁ (k) · n ₁ (k−j)] ≒ 0, so that Σ ｛x (k) · x (k− 1) ≒ Σ [i (k) · i (k−1) − (i (k−1)) ² −i (k) · i (k−1) + i (k−1) · i (k− 2) − (n ₁ (k−1)) ² ] (4a) Similarly, {y (k) · y (k−1)} of the second item in the real part of the autocorrelation of equation (1a) is {Y (k) .y (k-1)} {[q (k) .q (k-1)-(q (k-1)) ^2- q (k) .q (k-1) + q (K-1) · q (k-2)- _{n 2 (k-1))} 2] (4b) , and the formula (4a), the last term of (4b), represents the noise component _{- (n 1 (k-1} )) 2, - (n 2 (k -1)) Item ² appears. That is, the real part is sum-Σ ｛(n ₁ (k−
1)) ² + (n ₂ (k-1)) ² }.

On the other hand, with respect to the imaginary part of the autocorrelation given by the equation (1b), x (k-1) .y (k) and x (k)
The noise terms appearing in y (k-1) are not a problem because they cancel each other out.

As noise sources, there are acoustic noise input to the probe, electric noise generated by the amplifier, and the like, all of which have whiteness. By the way, since an ultrasonic wave is attenuated in a living body, the intensity of the reflected echo becomes smaller as it goes deeper. Therefore, in the conventional apparatus, TGC (Time Gain Co) is used.
A technique referred to as “ntrol” is used. This is to amplify a deeper one of the detected reflected echoes with a larger amplification factor. Therefore, in general, the noise level becomes higher as the depth increases.

As described above, in the conventional apparatus, since the real part of the autocorrelation value is biased by the noise, not only does the accuracy of speed detection deteriorate, but also in some cases, the sign of the real part is inverted, thereby causing The direction of the flow may be reversed, which has reduced the diagnostic ability.

The present invention has been made in view of the above circumstances, and has as its object to provide an ultrasonic diagnostic apparatus in which the accuracy of speed detection of an ultrasonic reflector in a subject is improved.

[0021]

An ultrasonic diagnostic apparatus according to the present invention that achieves the above object transmits an ultrasonic pulse into a subject and receives reflected ultrasonic waves that have returned after being reflected within the subject. Is repeated a plurality of times, after quadrature detection of the signal obtained during this repetition and further removal of clutter components, the complex autocorrelator converts the in-phase signal and the quadrature signal obtained by quadrature detection to the real part and A complex autocorrelation value as an imaginary part is obtained, and the speed detector detects the speed of the ultrasound reflector in the subject based on the argument of the complex autocorrelation value. Calculating means for calculating in advance the offset amount to be added to the real part of the complex autocorrelation value, and storage means for holding the offset amount obtained by the calculating means. phase The velocity of the ultrasonic reflector in the subject based on the corrected angle of the complex autocorrelation value obtained by correcting the offset amount stored in the storage means from the real part of the complex autocorrelation value obtained by the detector Is detected.

Here, in the ultrasonic diagnostic apparatus of the present invention, the calculating means recalculates the offset amount each time at least one of the at least one element that changes the offset amount is changed. It is preferable to update the offset amount held in the storage means.

The offset amount to be added to the real part of the autocorrelation value due to noise is stored in advance in the above-mentioned storage means, and is read out and subtracted at the time of calculating the argument, so that its influence is canceled. In addition, whenever at least one element that changes the offset amount such as a gain change is changed, the offset amount is automatically recalculated and the data in the storage unit is updated. Correction is always performed with an accurate offset amount.

[0024]

Embodiments of the present invention will be described below.

FIG. 2 is a configuration diagram of an embodiment of the ultrasonic diagnostic apparatus of the present invention. The same components as those of the conventional ultrasonic diagnostic apparatus shown in FIG. 1 are denoted by the same reference numerals as those of FIG.

The ultrasonic diagnostic apparatus according to the present embodiment has two operation states, namely, an operation state (diagnosis mode) for measuring an offset amount due to noise of an autocorrelation value, in addition to an operation state (measurement mode) for performing normal measurement. Take.

First, the normal measurement mode will be described.

The ultrasonic diagnostic apparatus 200 shown in FIG. 2 is provided with a probe 1, and a transducer such as a piezoelectric ceramic is arranged at the tip of the probe 1. The transmission circuit 2 and the reception circuit 4 are connected to the probe 1. The pulse generator 3 generates a timing signal S11 (rate pulse) for giving a transmission repetition cycle (for example, 4 KHz) and supplies it to the transmission circuit 2. The transmission circuit 2 includes, for example, a 64 channel pulse driver and a delay circuit. The pulse driver generates a drive pulse having a period equal to the transmission frequency (for example, 2.5 MHz) at the timing of the rate pulse, and applies the drive pulse to the transducer of the probe 1. The delay circuit gives a predetermined delay to the pulse generation timing for each channel in order to converge the ultrasonic beam and give directivity. As a result, the ultrasonic beam is pulsed in a direction corresponding to the directivity. As described above, transmission and reception in the same direction (for example, the direction a in FIG. 2) are repeatedly performed, for example, six times toward the inside of the living body (not shown) at the rate pulse cycle, and once for obtaining a tomographic image. , And one cycle (line cycle) is completed by a total of seven scans, and b, c, d
While switching the scanning direction, the same processing is performed on, for example, 64 scanning lines, and scanning for one frame is completed.

On the other hand, the echo reflected on the discontinuous surface of the acoustic impedance in the living body is transmitted via the probe 1 to the receiving circuit 4.
Is received for each channel. The receiving circuit 4 includes a preamplifier, a delay circuit, and an adding circuit. The received signal is amplified by a preamplifier, given a predetermined delay for each channel by a delay circuit, and added by an adder circuit. Thus, an echo from a direction corresponding to the directivity is received.

The received signal output from the receiving circuit 4 is input to the mixer circuit 5. The mixer circuit 5 performs quadrature detection by mixing a pair of reference signals generated by a transmitter (not shown) having the same period as the transmission frequency and having a phase difference of 90 ° with the received signal, thereby performing Doppler signal detection. The in-phase signal S12a and the quadrature signal S12b are output.
The two low-pass filters 6a and 6b respectively remove harmonic components of the in-phase signal S12a and the quadrature signal 12b of the Doppler signal resulting from the mixing.

The output signals of the low-pass filters 6a and 6b are sampled by the A / D converters 7a and 7b at a constant sampling period in the depth direction, for example, at 256 points, and converted into digital values. Is done. MTI
The filters 8a and 8b remove low-frequency components due to wall motion of the organs contained in the Doppler signal and extract only blood flow components, and are composed of, for example, a primary echo canceller shown in FIG.

Although the normal measurement mode has been described halfway, the operation of the diagnostic mode for measuring the offset amount is as follows.

FIG. 6 is a timing chart in the diagnosis mode.

In the diagnostic mode, the transmission of the ultrasonic pulse is 64
Stops for one line cycle. This is realized by setting the voltage applied to the pulse driver (not shown) of the transmission circuit 2 to zero. Therefore, no voltage pulse is applied to the probe 1 and no ultrasonic beam is emitted. Therefore, there is no reflected wave, and the amplitude of the signal component of the output of the receiving circuit 4 becomes zero. Therefore, sampling data of only the noise signal is input to the MTI filters 8a and 8b. The autocorrelator 9 calculates the autocorrelation of the noise signal separated by one repetition period for data having six repetition periods.

For a point at a certain depth, the MTI filter 8
The noise signals input to a and 8b are respectively n
Assuming that ₁ (k) and n ₂ (k), k = 1, 2,..., 5, the output value S15a of the real part of the autocorrelation is given by the following equation (4a).
In equation (4b), i (k) = i (k-1) = i (k
-2) = q (k) = q (k-1) = q (k-2) = 0,

[0036]

(Equation 3)

Is as follows. This is input to the correction circuit 14.

FIG. 3 is a block diagram of the correction circuit 14, and FIG.
FIG. 5 is a diagram showing a memory map of a correction data memory forming the correction circuit of FIG. 3, FIG. 5 is a diagram showing a memory map of a correction data memory forming the correction circuit, and FIG. 6 is a timing chart in the diagnosis mode. .

In FIG. 3, a correction control circuit 30 is a circuit for controlling each part of the correction circuit. A system clock S21 serving as a reference clock for circuit operation is supplied from a timing generation circuit (not shown), and a mode selection signal S22 is supplied from a system controller (not shown). Is entered from The mode selection signal S22 is a signal for determining the measurement mode and the diagnosis mode. In the diagnosis mode, the mode selection signal S22 is set to the LOW level for 64 line cycles.

At the timing of the sixth rate pulse in each line cycle including the falling of the mode selection signal S22,

[0041]

(Equation 4)

The autocorrelation values of the corresponding noise signal to (the offset amount e _n) is outputted from the autocorrelator 9, which is input to the sequential correction circuit 14 for each depth in synchronism with the system clock S21. The accumulator 32 accumulates the offset amount, which is input at intervals of the line period, 64 times for each depth. Then, the final accumulated value is sequentially output at the timing of the fifth rate pulse in the 64th line cycle. Shift circuit 34 is the average offset amount by the cumulative value 6 bit right shift (1/64 _{fold) <e n> (n =} 0,1, ..., 255) to output a.
The correction data memory 31 is for storing an average offset amount for each depth, and writing and reading are controlled by the memory control circuit 35. Memory control circuit 35
Is the average offset amount for each depth from the shift circuit <
e _n > is input and stored in the correction data memory 31 in the order of addresses as shown in FIG. The calculation process of the offset amount is completed by the procedure described above. After that, the mode selection signal S22 is set from the LOW level to the HIGH level, the diagnostic mode is changed to the normal measurement mode, and the transmission of the ultrasonic pulse is restarted.

Here, referring again to the timing chart in the measurement mode shown in FIG. 6, the description will return to the measurement mode, which is the operation state for performing the normal measurement in the present embodiment. As described above, in the measurement mode, normal transmission of ultrasonic waves is performed, and signals received and detected include noise in addition to Doppler signals. MTI filters 8a, 8
The sample value series of the Doppler signal input to b is i (k) and q (k) (k = 1, 2,... Nc), and the noise signal added thereto is n ₁ (k),
When n ₂ (k) is set, the output signals x (k) and y (k) of the MTI filters 8a and 8b are expressed by Expressions (3a) and (3b), respectively. The autocorrelator 9 calculates the autocorrelation of the complex signal at intervals of one repetition period for data having six repetition periods. That is,

[0044]

(Equation 5)

By the operation, the real part becomes

[0046]

(Equation 6)

The imaginary part is obtained by the following operation. Here, the real part of the autocorrelation value depends on the noise component as described above.

[0048]

(Equation 7)

The following offset amount is added.

The real part of the autocorrelator 9 autocorrelation values including the offset amount _{(X n + e n; n} = 0,1, ... 25
5) is output at the timing of the fifth rate pulse in the line cycle, and is input to the correction circuit 14 at each depth in synchronization with the system clock S21. Wherein X _n and e _n is the offset amount of the signal component, and the noise component in the autocorrelation value

[0051]

(Equation 8)

Is shown.

The real part S 15 a of the autocorrelation value input to the correction circuit 14 is applied to one input of a subtractor 36. Furthermore the memory control circuit 35 at the timing of each round of rate pulse read from the correction average offset amount stored in the data memory 31 <e _n> address 0 in synchronism with the system clock, other one of the subtractor 36 so Feed to the input. The real part X _{n of the} autocorrelation value input from the autocorrelator 9 at the timing of the sixth rate pulse
+ From e _n, the correction average offset amount read from the data memory 31 <e _n> is subtracted for each depth by the subtractor 36, the corrected real part of the autocorrelation _{X n + e n - <e} n
> Are sequentially output for each depth.

The speed detection circuit 10 receives the real part S16 of the corrected autocorrelation value (R (1)) from the correction circuit 14 and the imaginary part S15b of the autocorrelation value from the autocorrelator 9 and inputs its argument (arctan). Calculate {Im [R (1)] / [R (1)]}, the declination value gives an amount proportional to the Doppler shift frequency, and the declination value is used as the average speed data in the image processing device 12. Sent to

On the other hand, the output signal of the receiving circuit 4 is sent to the tomographic image processing section 11. After detecting the envelope of the received signal, the tomographic image processing unit 11 performs A / D conversion and outputs it as monochrome luminance data.

The image processing device 12 applies a predetermined color scheme to the sequentially input average speed data based on the direction and the absolute value thereof, and, together with the monochrome luminance data of the tomographic image, performs two-dimensional processing in accordance with the scanning direction and depth. And store it in an image memory (not shown) as image data.
Further, the image data is read from the image memory at a fixed cycle, and a diagnostic image in which a monochrome image representing a tomographic image and a color image representing a blood flow are combined is displayed on the TV monitor 13.

The diagnostic mode is first executed in the initial setting process when the apparatus is started. After the initial setting is completed, the measurement mode is set to perform normal measurement. If a specific setting that changes the noise level or its distribution, such as the analog gain or TGC setting, is changed in the measurement mode, the measurement mode is automatically set. Then, the mode is shifted to the diagnosis mode, and the calculation of the offset amount is executed again. Therefore, a system controller (not shown) constantly monitors the operation panel to monitor whether or not there is a change in the specific setting.

In the present embodiment, the case of using a first-order echo canceller as the MTI filter has been described. However, the present invention can be similarly applied to a case where a higher-order filter is used.

[0059]

According to the present invention, the offset amount of the autocorrelation value conventionally caused by the noise included in the received signal can be greatly reduced. As a result, the accuracy of measuring the average speed is improved, and the S / N of the image is improved, so that a higher-quality diagnostic image can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional ultrasonic diagnostic apparatus.

FIG. 2 is a configuration diagram of an embodiment of an ultrasonic diagnostic apparatus of the present invention.

FIG. 3 is a configuration diagram of a correction circuit.

FIG. 4 is a diagram showing a memory map of a correction data memory constituting the correction circuit of FIG. 3;

FIG. 5 is a diagram showing a memory map of a correction data memory constituting the correction circuit.

FIG. 6 is a timing chart in a diagnosis mode.

FIG. 7 is a circuit block diagram of a first-order echo canceller used as an MTI filter.

[Explanation of symbols]

 Reference Signs List 1 probe 2 transmission circuit 3 pulse generator 4 reception circuit 5 mixer circuit 6a, 6b low-pass filter 7a, 7b converter 8a, 8b MTI filter 9 autocorrelation circuit 10 speed detection circuit 11 tomographic image processing unit 12 image processing circuit 13 TV monitor 30 correction control circuit 31 correction data memory 32 cumulative adder 34 shift circuit 35 memory control circuit 36 subtracter 200 ultrasonic diagnostic apparatus

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4C301 DD04 EE11 JB17 JB29 5J083 AA02 AB17 AC18 AD08 AE08 BA01 BD06 BE09 BE53 BE57 CB14 CC02 DA01 DC07

Claims (2)

[Claims] 1. A method for transmitting an ultrasonic pulse into an object and receiving reflected ultrasonic waves reflected back from the object is repeated a plurality of times, and a signal obtained during the repetition is orthogonalized. After detecting and further removing clutter components, by a complex autocorrelator, the in-phase signal and the quadrature signal obtained by the quadrature detection are obtained as complex real and imaginary complex autocorrelation values, respectively, by a speed detector. In an ultrasonic diagnostic apparatus for detecting a velocity of an ultrasonic reflector in the subject based on an argument of the complex autocorrelation value, an offset added to a real part of the complex autocorrelation value due to a noise component Calculating means for calculating the amount in advance;
Storage means for holding the offset amount obtained by the calculation means, wherein the speed detector is stored in the storage means from a real part of the complex autocorrelation value obtained by the complex autocorrelator. An ultrasonic diagnostic apparatus for detecting the velocity of the ultrasonic reflector in the subject based on the corrected argument of the complex autocorrelation value obtained by correcting the offset amount. 2. The calculation means recalculates the offset amount each time at least one element that changes the offset amount is changed, and calculates the offset amount held in the storage means. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is updated.