JPH04158847A - Ultrasonic diagnosing apparatus - Google Patents

Abstract

PURPOSE:To correct a phase distortion of an ultrasonic pulse based on unevenness of sound velocity in vivo by determining a peak value of an echo signal for each vibrator to correct an arrival time of the echo signal at individual vibrators based on a curve fitting performed over the entire receiving opening. CONSTITUTION:Echo signals received with vibrators comprising a number of vibrators 1a, 1b and 1c are amplified with preamplifier circuits 10a and 10b and then, applied to a receiving delay circuit 11 to be given a desired delay characteristic. The echoes outputted from the receiving delay circuit 11 are inputted into a peak detector 12 to determine a peak position thereof. A least square device 13 performs a curve fitting of the peak position detected at each vibrator over the entire receiving opening and a geometrical delay value with the least error s is determined by computation for the individual vibrators over the entire opening. A correction circuit 14 applies the delay value in the form of the geometrical delay value inverted to the vibrators to correct an average arrival time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Application Field) The present invention relates to an ultrasonic diagnostic apparatus that corrects phase distortion of ultrasonic pulses due to non-uniformity of sound speed within a subject.

(Prior art) In conventional ultrasound diagnostic equipment, a probe with a large number of transducers arranged in an array is used to focus transmitted ultrasound pulses on a certain area within the subject, thereby detecting ultrasound echoes. Based on the signals, ultrasound images are reconstructed and displayed on a display.

Here, there are various tissues in the body, and the sound speed of each of these tissues with respect to ultrasonic waves is not uniform.

For this reason, phase distortion occurs in the ultrasonic pulse due to the non-uniformity of the sound velocity within the body, resulting in a decrease in image quality, and it is therefore necessary to correct this phase distortion.

For this reason, in the past, ultrasonic pulses transmitted from a probe were focused on a certain region within the subject, and echo signals, which were reflected waves from minute scattering objects in the vicinity, were obtained for each transducer within the receiving aperture. A method that calculates a cross-correlation function using signals between at least two transducers of a child group, detects and corrects distortion in the propagation time of an ultrasound pulse caused by non-uniformity of sound speed within the object. is being carried out.

(Problem to be Solved by the Invention) However, in conventional ultrasonic diagnostic equipment, phase distortion is corrected by determining a cross-correlation function, so the hardware configuration becomes large-scale and costs inevitably increase. The problem is that it is not practical.

The present invention has been made in response to the above-mentioned problems.
It is an object of the present invention to provide an ultrasonic diagnostic apparatus that corrects phase distortion using hardware with a simple configuration.

[Configuration of the Invention (Means for Solving the Problems) In order to achieve the above object, the present invention focuses a transmitted ultrasonic pulse on a certain region within a subject and reflects it from a group of minute scatterers in the vicinity. In an ultrasonic diagnostic device that observes incoming ultrasonic echo signals for each transducer within the receiving aperture and corrects them by detecting the arrival time of the ultrasonic echo signal to each transducer, Means for obtaining phase components at each angular frequency by performing orthogonal phase detection on the echo signal received by using a plurality of different angular frequencies within the ultrasonic frequency band as a reference frequency, and determining the arrival time based on the slope of the phase component with respect to the angular frequency. The invention is characterized in that it includes a means for determining.

In another aspect of the present invention, a transmitted ultrasonic pulse is focused on a certain region within the subject, and ultrasonic echo signals reflected from a group of minute scatterers in the vicinity are observed for each transducer within the receiving aperture. , an ultrasonic diagnostic apparatus that corrects this by detecting the arrival time of the ultrasonic echo signal to each transducer,
The present invention is characterized by comprising means for determining the peak position of the echo signal for each transducer, performing curve fitting over the entire receiving aperture, and correcting the arrival time of the echo signal at each transducer based on this curve fitting. It is something.

(Function) According to the configuration of the present invention, the echo signal received by each transducer constituting the probe is subjected to quadrature phase detection using, for example, two different angular frequencies as reference frequencies, and the phase component at each angular frequency is detected. demand. Next, the arrival time is determined based on the slope of the phase component with respect to the angular frequency, and thereby the phase distortion of the ultrasonic pulse due to the non-uniformity of the internal sound velocity is corrected.

According to another configuration of the present invention, the peak value of the echo signal is determined for each transducer constituting the probe, curve fitting is performed over the entire receiving aperture, and based on this curve fitting, the echo signal at each transducer is Correct the arrival time of the signal. As a result, it is possible to correct the phase distortion of the ultrasonic pulse based on the non-uniformity of the sound velocity within the body without complicating the hardware configuration.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the ultrasonic diagnostic apparatus of the present invention, in which 1 is a probe and includes a large number of transducers la, lb,
It is composed of lc,... Hereinafter, only a signal processing system for one vibrator 1 will be described as an example. 2 is a preamplifier that amplifies the echo signal received by the transducer 1; 3 is a mixer 4a, 4b that mixes the received signal with a first reference angular frequency ω1 and a 90° phase shifted signal of this ω1; A quadrature phase detection circuit includes mixers 4c and 4d that mix with a reference angular frequency ω2 and a 90° phase signal of this ω2, and 5 is an LPF (low-pass filter) 5a that passes only the low frequency components of the outputs of the mixers 4a to 4d. L including 5d
PF circuit, 6 is LPF5a.

A first arithmetic circuit 6a and LPFs 5c and 5 that calculate the phase component at the first angular frequency ω1 based on the detection output of 5b.
A calculation circuit including a second calculation circuit 6b that calculates a phase component at a second angular frequency ω2 based on the detection output of d; 7 is a calculation circuit based on the difference between the first calculation circuit 6a and the second calculation circuit 6b; 8 is a difference detection circuit that determines the arrival times, and 8 is a memory that stores these determined arrival times.

Next, the operation of this embodiment will be explained.

The echo signal received by the transducer 1 of the probe 1 passes through a preamplifier 2 and is simultaneously subjected to quadrature phase detection by a quadrature phase detection circuit 3 using two different reference angular frequencies ω1°ω2.

Now, the echo signal received by transducer 1 is expressed by the following formula % formula % (
1)). Here, Ck, (t) is the envelope function, and cos(ω, t+φk(ω1)) is the angular frequency ω1
, and φk(ω1) is a phase term proportional to the arrival time of this signal.

Next, in the quadrature phase detection circuit 3, the echo signal is
C in the mixer 4a using the reference angular frequency ω1 of
By passing the machine number outputs mixed by OS ω1t and sin ω1t by mixer 4b through LPFs 5a and 5b, the following detection output signal r k s
(t), Q k 1(t) is obtained.

I k , (t)=Ck 1(t) cosφk (ω
1) Qkl(t) = −Ck, (t) sinφk (ω
I) Here, Ik, (t) is the in-phase component, Qkl
(t) is the orthogonal component.

Next, the first calculation circuit 6a calculates the phase term φk(ω1) at the angular frequency ω1 by performing calculation processing as shown in the following equation.
seek.

Here, since there is a relationship φk(ω1)=ω1 τk (τ: an amount proportional to the arrival time of the echo signal to the vibrator), based on this, the arrival time τk is determined as shown in the following equation.

ωl Here, if φk (ω1) does not exceed ±π, τk can be calculated correctly, but tan-1= (x) is a periodic function for X, and if 1x1>π, τk cannot be calculated correctly. (this is called folding).

In this embodiment to solve this problem, the processing performed at the first reference angular frequency ω1 is similarly performed at another angular frequency (second reference angular frequency) ω2 within the ultrasonic frequency band used.

That is, the echo signal received by transducer 1 is expressed as Ck 2 (t) cos (ω2t+φk(ω2)) as shown in the following equation.
Assuming that the echo signal is expressed as
cos ω at 2t and sin ω at mixer 4d
Mix each at 2t. Next, each output is passed through LPF5c,
5d, the following detection output signal I
k2 (t).

Obtain Qk2(t).

I k, (t) = Ck2(t) cosφk(ω2)
Q k 2 (t) = Ck2 (t) sinφk
(ω2) Next, the second arithmetic circuit 6b performs arithmetic processing as shown in the following equation to calculate the phase term φk(
Find ω2).

φk(ω2) Here, if an attempt is made to obtain the phase time τk in the same manner as described above using the relationship φk(ω2)=ω2τ, a similar problem of aliasing occurs.

Therefore, the difference between each phase term is determined by the difference circuit 7 using the equations (1) and (2) as shown in the following equation.

Following φk (ω1)-φk (ω2) = (ω1-ω2)τ, the arrival time τk is determined based on this equation as shown in the following equation.

The above signal processing is performed on other transducers in the reception aperture in the same manner as on transducer 1, and the distribution of arrival times on the aperture is determined. Next, the arrival time is corrected using this distribution result, and by focusing the ultrasound pulse on a desired area within the subject and receiving the echo signal, the phase of the ultrasound pulse based on the non-uniformity of the internal sound velocity is determined. Distortion can be corrected.

That is, as shown in FIG. 2, the arrival time τk is determined based on the slope of the phase component for each angular frequency ω1°ω2. Note that ω1. It is assumed that a component included in ω is selected for ω2.

According to this embodiment, the phase distortion of the ultrasonic pulse can be corrected by performing quadrature phase detection using a plurality of different reference frequencies within the ultrasonic frequency band. The purpose can be achieved with a one-ware configuration.

Therefore, increase in cost can be avoided, making it practical.

Furthermore, by using multiple reference frequencies, the problem of aliasing can also be reduced.

Next, other aspects of the present invention will be explained in detail.

First, before explaining the present invention in detail, the premise of the present invention will be explained.

The ultrasonic diagnostic apparatus of the present invention uses the received echo signal of the k-th transducer (channel) and the received echo signal of the +1-th transducer adjacent to it among the large number of transducers constituting the probe. By performing wave detection, the phase difference between signals between adjacent channels is determined. That is, the received RF signal Vk (t
) is expressed as the following formula % formula %). Here, Ck (t) is the envelope function, and cos (ωot+φk) is the angular frequency ω.

, and φ is a phase term proportional to the arrival time of this signal.

Similarly, the received RF signal Vk of the +1st channel
Assume that +1(t) is expressed as in the following equation.

vh+x(t) ”Ck+s (t) CO9((lJ(+1 to l t+φ)) By taking the product of each of these signals Vk(t) and vk, z(t) and removing the 2ω component with a low-pass filter, we get the following The in-phase component Ik(t) is determined as shown in the equation.

cos (one to φ and one to φ++) ・”(3) Similarly, take the product of Vk (t) and a signal obtained by shifting the phase of Vk+I(t) by 90 degrees, and use a lobal filter to obtain 2ω.

By removing the components, the orthogonal component Qk (t) can be found as shown in the following equation.

5in (1 to φ + 1 to φ)...(4) then (3),
Based on equation (4), the arrival time difference Δτk of the signals between the k and +1st two channels is determined as follows.

ω0 Next, as is clear from equations (3) and (4), since the envelopes of these signals are expressed as the product of the envelope functions of the two-channel signals, the time shift of the envelope functions of the two-channel signals is When is large, detection sensitivity is not sufficient and highly accurate phase difference measurement cannot be performed.

FIG. 6 shows reflections from a group of minute scatterers 18 in a subject 17 through a non-uniform medium 16 (a medium in which the sound velocity is different from the area that you want to see as an image, for example, the liver parenchyma) using a probe 1 consisting of an array transducer. This shows the state in which waves (echo signals) are being received.

19 is a transmitted focused beam, 20 is a transmitted wavefront, and 21 is a wavefront after scattering. As shown in FIG. 6, when the thickness of the non-uniform medium 16 is not thin enough compared to the distance between the probe 1 and the micro scatterer group 18 (corresponding to the distance of the transmission focal point F), or when the sound velocity in the medium is If the distribution of the arrival time on the aperture after passing through the inhomogeneous medium 16 (time T1) is significantly different from that of the part you want to see, the distribution (time T1) will be the distribution ( It differs from time T2).

The number indicates the transmission delay time.

This is because the propagation time within the non-uniform medium 16 differs for each vibrator. That is, this is because the proportion of the non-uniform medium in the propagation path from the position of each vibrator to the transmission focal point F differs depending on the vibrator. Figure 6 shows heterogeneous medium 1
6 shows a case where the average speed of sound in the opening is slower than that of the part that is currently desired to be viewed as an image, and the arrival time of the reflected wave is delayed at the end of the opening compared to the part in the middle of the opening. A possible reason for this is that the transmission focal point F of the transmission beam has spread and is no longer a point, and the echo signal returns with a delay for each transducer, making it impossible to detect the phase distortion properly.

The present invention thus provides an ultrasonic diagnostic apparatus that uses quadrature phase detection to avoid the above-mentioned disadvantages when correcting the phase distortion of ultrasonic pulses based on the non-uniformity of the sound velocity in the body. The present invention will now be described in detail with reference to FIG.

1 is a probe (array transducer) consisting of a large number of transducers la, lb, lc, . . . , and the echo signals received by each transducer are sent to a preamplifier circuit 10 (10a).

10b, . . . ) and then added to the reception delay circuit 11 to provide desired delay characteristics. Each echo signal output from the reception delay circuit 11 is input to a peak detector 12 to find its peak position.

13 is for performing curve fitting on the peak position detected for each transducer using a least squares generator over the entire receiving aperture. It can be found by calculation. Reference numeral 14 denotes a correction circuit for correcting the average arrival time by giving each vibrator a delay amount that is an inversion of the geometrical delay amount.

Next, the operation of this embodiment will be explained.

When the transmission focal point F is a point sound source as shown in FIG. After that, by performing desired signal processing, a distribution characteristic of the arrival time on the aperture as shown in FIG. 4(b) can be obtained.

Next, when the echo signal reflected by the minute scatterer 4 is received by each transducer, the preamplifier 10. Reception delay circuit 11
After the peak value of the echo signal applied to the peak detector 12 is determined for each transducer, the least squares unit 13 performs curve fitting over the entire receiving aperture, resulting in the echo signal shown in FIG. 4(C). The average deviation in arrival time is determined as shown. As a result, as shown in FIG. 5, the geometrical delay amount with the smallest error over the entire aperture has been determined. Subsequently, the correction circuit 14 applies a delay amount that is the inversion of the geometric delay amount to each vibrator, thereby correcting the average arrival time.

According to this embodiment, the phase distortion of the ultrasonic pulse can be corrected by using quadrature phase detection, so the purpose can be achieved with a simple hardware configuration and an increase in cost can be avoided. Moreover, according to this embodiment, since the correction is performed by minimizing the temporal deviation of the envelope function between each vibrator, sufficient detection sensitivity can be obtained, and highly accurate phase measurement can be performed.

[Effects of the Invention] As described above, according to each of the present inventions, it is possible to correct the phase distortion of ultrasonic pulses based on the non-uniformity of the sound velocity inside the body with a simple hardware configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the ultrasonic diagnostic apparatus of the present invention, FIG. 2 is a characteristic diagram showing the relationship between angular frequency and phase component, which is the principle of the present invention, and FIG. 3 is a diagram showing another embodiment of the present invention. A block diagram showing an embodiment of the ultrasonic diagnostic apparatus, FIG. 4(a),
(b) and (c) are explanatory diagrams of the operation of this embodiment, FIG. 5 is an explanatory diagram of phase distortion correction in this embodiment, and FIG. 6 is an explanatory diagram of the ultrasonic scanning method. DESCRIPTION OF SYMBOLS 1... Probe, 1k... Vibrator, 3... Quadrature phase detection circuit, 4a to 4d... Mixer, 5... LPF circuit, 6
... Arithmetic circuit, 7... Difference circuit, 12... Peak detector, 13... Least squarer, 14... Correction circuit,
16... Inhomogeneous medium, 18... Minute scatterer group. Agent Patent Attorney Nori Chika / Ken Yudo Konfuji Takeshi Figure 2 I-Hen Ka

Claims (2)

[Claims] (1) The transmitted ultrasonic pulse is focused on a certain region within the subject, and the ultrasonic echo signals reflected from a group of minute scatterers in the vicinity are observed for each transducer within the receiving aperture. In ultrasonic diagnostic equipment that corrects this by detecting the arrival time of ultrasonic echo signals to An ultrasonic diagnostic apparatus comprising means for determining a phase component at each angular frequency by performing quadrature phase detection, and means for determining an arrival time based on the slope of the phase component with respect to the angular frequency. (2) The transmitted ultrasonic pulse is focused on a certain region within the subject, and the ultrasonic echo signals reflected from a group of minute scatterers in the vicinity are observed for each transducer within the receiving aperture. In ultrasonic diagnostic equipment that corrects this by detecting the arrival time of ultrasonic echo signals at An ultrasonic diagnostic apparatus characterized by comprising means for correcting the arrival time of the echo signal at each transducer based on the timing.