JP2801450B2 - Ultrasonic tissue displacement measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical ultrasonic apparatus and, more particularly, to an ultrasonic tissue displacement measuring apparatus for measuring minute displacement and displacement speed of tissue in a living body by ultrasonic waves.

[0002]

2. Description of the Related Art In recent years, ultrasonic diagnostic apparatuses have been used in various medical fields. According to this ultrasonic diagnostic apparatus,
It can display a tomographic image of a living body and a blood flow velocity distribution by an ultrasonic Doppler method, but in particular, recently, uses an ultrasonic pulse Doppler method to measure a minute displacement of an internal tissue of a living body that is smaller than an ultrasonic wavelength. Research and research on its clinical application are becoming active.

According to the measurement of the minute displacement, there is a possibility that information useful for identifying a site such as myocardial infarction or arteriosclerosis or diagnosing a benign or malignant tumor in the liver may be provided.
For example, when microscopic observation of an in-vivo organ such as the liver is performed, the tissue in contact with the blood vessel is minutely displaced by the pulsation of the artery in the organ, and the displacement is transmitted to the surrounding tissue. Here, when the normal tissue and the abnormal tissue are compared, the way of transmitting the above-mentioned displacement may be different due to a difference in the tissue composition.
Therefore, there is a possibility of diagnosing, for example, a malignant tumor by observing the tissue displacement, and the diagnosis based on the tissue displacement has recently attracted attention.

As an apparatus for measuring such tissue displacement, an ultrasonic diagnostic apparatus capable of measuring tissue displacement has been proposed. This device is based on the principle of the ultrasonic Doppler diagnostic method, and calculates the displacement of the tissue on the ultrasonic beam based on the phase difference between the transmitted ultrasonic wave and the received ultrasonic wave. is there. Therefore, according to this principle, micron-order tissue displacement can be measured with a resolution shorter than the wavelength of the ultrasonic wave.

Here, the principle of measuring the minute displacement of the tissue in a living body using the ultrasonic pulse Doppler method will be described using a calculation formula.

An ultrasonic reception signal S ₁ (t) reflected from a scatterer in a living body is expressed by the following equation (1). Here, A ₁ (t) indicates the amplitude, Φ ₁ (t) indicates the phase, and ω ₀ indicates the angular frequency of the transmission signal.

[0007] orthogonal _{S 1 (t) = A 1} (t) exp _{[-j (ω 0 t + Φ 1} (t)) ] ... (1) the reference signal of the received signal S ₁ (t) is the angular frequency ω _r Assuming that the detected signal is f ₁ (t), this is given by the following equation (2).

[0008] _{f 1 (t) = S 1} (t) exp (jω r t) = A 1 (t) exp _{[-j ((ω 0 -ω r)} t + Φ 1 (t)) ] ... (2) = I ₁ (t) + jQ ₁ (t) The argument of the quadrature detection signal f ₁ (t) is given by the following equation (3).

Θ ₁ (t) = arg (f ₁ (t)) (3) = atan (Q ₁ (t) / I ₁ (t)) The received signal when the entire scattering medium is displaced by δx is represented by S _Two
Assuming (t), this is expressed by the following equation (4).

S ₂ (t) = S ₁ (t−δt) = A ₁ (t−δt) exp [−j (ω ₀ · (t−δt) + Φ ₁ (t−δt))] (4) Here, δt is a propagation time difference (moving time) when the scattering medium is displaced by δx, and is represented by the following equation (5).
Here, c is the speed of sound.

[0011] δt = 2 · δx / c ... (5) to a quadrature detection signal with the reference signal of the received signal S ₂ (t) the angular frequency omega _r and f ₂ (t), which follows (6 ) Expression.

[0012] _{f 2 (t) = S 2} (t) exp (jω r t) = A 1 (t-δt) exp _{[-j ((ω 0 -ω r)} (t-δt) + Φ 1 (t- .DELTA.t))] _{exp (jω r δt) = f} 1 (t-δt) argument of _{exp (jω r δt) ... (} 6) the orthogonal detection signals f ₂ (t) is given by the following equation (7) Can be

[0013] _{θ 2 (t) = θ 1} (t-δt) + ω r δt ... (7) Therefore, the phase difference δθ _c of both before and after displacement, the following (8)
Given by the formula.

Δθ _c = θ ₂ (t) −θ ₁ (t) (8) Accordingly, the displacement δx _c due to the movement is given by the following equation (9).

Δx _c = (c / 2ω _r ) δθ _c (9) Here, the phase difference δθ _c is, for example, the Japanese Patent Publication No. 62-4449.
It is determined by an autocorrelation method or the like used in a normal color Doppler apparatus as disclosed in Japanese Patent Application Laid-Open No. 4 (1999) -1994. Therefore, the displacement δx _c can be easily obtained from the equation (9).

[0016]

In the conventional ultrasonic tissue displacement measuring apparatus, since the angular frequency ω ₀ of the transmission signal shown in the above equation (1) is fixed, the following problem arises. Was. Hereinafter, the conventional problems will be described with reference to FIG.

FIG. 3A shows the depth of the tissue in the living body (horizontal axis).
FIG. 3 shows the distribution of the amplitude (vertical axis) of the received signal with respect to FIG.
(B) shows the distribution of the tissue displacement (vertical axis) with respect to the depth (horizontal axis) of the tissue in the living body. As shown in FIG. 7A, in the reflected wave signal from the living body, for example, due to interference or the like, there are minimum points A, B, and the like having amplitudes equal to or less than a certain threshold value E _th above the noise level. is there. In such a case, if the amount of tissue displacement is directly obtained from the amplitude of the received signal, the displacements at these points will not show correct values as shown in FIG. That is, in the conventional ultrasonic tissue displacement measuring apparatus, if the amplitude of the reflected wave signal (hereinafter, simply referred to as echo amplitude) is too small, the error of the displacement measurement increases, and an accurate value cannot be obtained. was there.

Therefore, there is a problem that the above problem must be solved. The present invention has been made in order to solve such a problem, and an object of the present invention is to provide an ultrasonic tissue displacement measuring device capable of accurately measuring a small displacement over the entire diagnostic distance of a tissue in a living body.

[0019]

An ultrasonic tissue displacement measuring apparatus according to the first aspect of the present invention transmits an ultrasonic pulse into a living body at a constant repetition period and receives a reflected wave from the living body tissue. In a medical ultrasonic apparatus that measures minute displacement in a living tissue based on a phase change of an ultrasonic wave, (i) a quadrature detection unit that performs mixed detection of a received signal from a living tissue and a predetermined reference signal, (ii) amplitude calculating means for calculating the amplitude of the received signal based on the output of the quadrature detecting means, (iii) comparing means for comparing the amplitude calculated by the amplitude calculating means with a predetermined threshold, (iv) As a result of the comparison by the comparing means, when the amplitude calculated by the amplitude calculating means is equal to or less than the threshold value, there is provided a transmission frequency varying means for transmitting the ultrasonic pulse by shifting the transmission frequency by a small amount. is there.

According to a second aspect of the present invention, there is provided an ultrasonic tissue displacement measuring apparatus which transmits an ultrasonic pulse into a living body at a constant repetition cycle, receives a reflected wave from a tissue in the living body, and receives the ultrasonic wave. In a medical ultrasonic apparatus that measures a minute displacement in a living tissue based on a phase change, (i) a quadrature detection unit that performs mixed detection of a reception signal from the living tissue and a predetermined reference signal, and (i)
(i) amplitude calculating means for calculating the amplitude of the received signal based on the output of the quadrature detecting means, (iii) comparing means for comparing the amplitude calculated by the amplitude calculating means with a predetermined threshold, (i)
v) reference frequency varying means for shifting the frequency of the reference signal input to the quadrature detection means by a small amount when the amplitude calculated by the amplitude calculation means is less than or equal to the threshold value as a result of the comparison by the comparison means. Things.

[0021]

In the ultrasonic tissue displacement measuring apparatus according to the present invention, when the reflected echo amplitude is equal to or smaller than a predetermined threshold, the transmission frequency is shifted by a small amount, or the frequency of the reference signal input to the quadrature detector is shifted by a small amount. As a result, the minimum position of the amplitude is shifted.

[0022]

The present invention will be described in detail with reference to the following examples. Here, the description will be made assuming that the component in the direction along the ultrasonic beam among the minute displacements of the tissue in the living body is measured,
Of course, it is easy to apply the embodiment described below to an apparatus for measuring tissue displacement two-dimensionally.

FIG. 1 shows an ultrasonic tissue displacement measuring apparatus according to an embodiment of the present invention, which measures a minute displacement of a tissue in a living body by applying an ultrasonic Doppler method. This apparatus is provided with a timing signal generator 11, which outputs a predetermined timing signal 13 to a scanning controller 12, and outputs signals 90 to each other to a quadrature detector 25 described later.
° Reference signals 15 and 16 having different phases are output.

The scanning controller 12 outputs a control signal 17 relating to the scanning of the ultrasonic beam to the transceiver 18 based on the timing signal 13. The transceiver 18 receives the control signal 1
According to 7, an ultrasonic pulse 20 is generated at a predetermined transmission repetition cycle and supplied to the probe 19.

An ultrasonic transducer (not shown) is provided in the probe 19, and ultrasonic waves are radiated into the living body 22 from the transducer excited by the ultrasonic pulse 20. The reflected wave from inside the living body 22 is received by the ultrasonic transducer of the probe 19, and the received signal is transmitted to the transceiver 18.
After processing such as phase synthesis is performed by the amplifier 24,
And to the quadrature detector 25.

Received signal 2 amplified by amplifier 24
Reference numeral 6 denotes a digital scan converter (hereinafter, referred to as DS) for performing B-mode tomographic image formation after being detected by a detector 27 and converted into a digital signal by an A / D converter 28.
C) 31 and temporarily stored here.

On the other hand, the quadrature detector 25 performs mixed detection of the received signal 33 and the above-mentioned reference signals 15 and 16, and outputs complex signals I and Q. These complex signals I and Q are each branched into two and input to an autocorrelator 34 and an amplitude calculator 35.

The autocorrelator 34 calculates the conjugate complex product of the real part signal I and the imaginary part signal Q, which are complex signals, to obtain the autocorrelation. Autocorrelation result is output to the displacement calculation unit 36, wherein the computation of the displacement .delta.x _c in vivo tissue is performed. The above-described received signal processing until the tissue displacement δx _c is obtained is realized by the above-described equations (1) to (9). As described above, for example, Japanese Patent Publication No. Sho 62-444
No. 94 is an application of the autocorrelation method.

The amplitude calculator 35 is provided with the quadrature detector 25.
Based on the complex signals I and Q output from, an echo amplitude A of the tissue is calculated by the following equation (10) and output to the amplitude comparator 37.

A = (I ² + Q ² ) ^1/2 (10) The amplitude comparator 37 compares the value of the input amplitude A with a preset threshold E _th, and sets the amplitude A to the threshold E _th When it becomes smaller, a switching signal 39 is output to the switching controller 38 and the timing signal generator 11. Thus, the switching controller 38 controls the transceiver 18 to increase or decrease the transmission frequency by δf at the timing of the next transmission cycle. As a result, the resulting echo amplitude A still if the threshold E _th is smaller than the increase or decrease again by δf the transmission frequency at the timing of the next transmission cycle. The above processing is performed until the echo amplitude A becomes larger than the threshold value _Eth . The shift amount δf per transmission frequency is, for example, 100
It is conceivable to swing up to about 500 kHz up and down by about kHz.

The displacement signal δx _c output from the displacement calculator 36 is temporarily stored in the memory 41 and then read out, sent to the above-described DSC 31 and temporarily stored therein.

As described above, the DSC 31 stores the tomographic image data of the biological section and the tissue displacement data corresponding to the biological section. And these data are DS
After being read from C31 and converted into an analog signal by the D / A converter 42, it is sent to the display 43. As a result, the display 43 displays a tomographic image of the biological section and a tissue displacement corresponding to the biological section.

By switching the transmission frequency, a minimum point of the echo may be newly generated and the error of the displacement measurement may be increased. As a countermeasure, for example, the memory 41 may be a line memory, and the threshold may be equal to or larger than the threshold _Eth. Only the displacement obtained from the echo of the target may be displayed. Thereby, low-precision data can be truncated and only high-precision data can be displayed, and errors in tissue displacement measurement can be reduced.

FIGS. 2A and 2B show the amplitude and displacement after removing the drop in echo amplitude by switching the transmission frequency in this manner. As shown in this figure, the drop of the echo amplitude as shown in the conventional example (FIG. 3) is removed, and the minute displacement of the living tissue is displayed accurately over the entire diagnostic distance. In this embodiment, the method of switching the transmission frequency has been described. However, a similar effect can be obtained by slightly shifting the frequency of the reference signals 15 and 16. However, there is a restriction that the frequency in this case is an integral multiple of the transmission pulse repetition frequency.

In the present embodiment, only the amplitude (echo) and displacement of the tissue are displayed. In addition, a wall filter for canceling the motion of the heart wall is added, and the blood flow velocity is displayed. You may make it combine with the color Doppler apparatus which displays a distribution. In this case,
The two-dimensional distribution of the three information of tissue echo, displacement, and blood flow velocity can be displayed simultaneously, and more information useful for clinical diagnosis can be provided.

[0036]

As described above, according to the present invention,
When the reflected echo amplitude is equal to or less than a predetermined threshold, the transmission frequency or the reference signal frequency is changed by a small amount to shift the minimum position of the amplitude, so that errors in displacement measurement can be reduced, and accuracy can be reduced over the entire diagnostic distance. There is an effect that minute displacement can be measured well.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an ultrasonic tissue displacement measuring device according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a measurement result of a reflected echo amplitude and a biological tissue displacement obtained by the ultrasonic tissue displacement measuring device.

FIG. 3 is an explanatory diagram showing an example of a measurement result of a reflected echo amplitude and a biological tissue displacement obtained by a conventional ultrasonic tissue displacement measuring device.

[Explanation of symbols]

 15, 16 Reference signal 18 Transceiver 19 Probe 20 Ultrasonic pulse 22 Living body 25 Quadrature detector 34 Autocorrelator 36 Displacement calculator 37 Amplitude comparator 38 Switching controller

Claims (2)

(57) [Claims] 1. A medical device for transmitting an ultrasonic pulse into a living body at a constant repetition period, receiving a reflected wave from a living body tissue, and measuring a minute displacement in the living tissue based on a phase change of the ultrasonic wave. In the ultrasonic apparatus, quadrature detection means for mixing and detecting a reception signal from a tissue in a living body and a predetermined reference signal; amplitude calculation means for calculating an amplitude of the reception signal based on an output of the quadrature detection means; Comparing means for comparing the amplitude calculated by the calculating means with a predetermined threshold value; and, as a result of the comparison by the comparing means, when the amplitude calculated by the amplitude calculating means is equal to or smaller than the threshold value, An ultrasonic tissue displacement measuring device, comprising: a transmission frequency variable unit that transmits a transmission by shifting the transmission frequency by a small amount. 2. A medical device for transmitting an ultrasonic pulse into a living body at a constant repetition period, receiving a reflected wave from a living body tissue, and measuring a minute displacement in the living body tissue based on a phase change of the ultrasonic wave. In the ultrasonic apparatus, quadrature detection means for mixing and detecting a reception signal from a tissue in a living body and a predetermined reference signal; amplitude calculation means for calculating an amplitude of the reception signal based on an output of the quadrature detection means; A comparing means for comparing the amplitude calculated by the calculating means with a predetermined threshold; and, as a result of the comparison by the comparing means, when the amplitude calculated by the amplitude calculating means is equal to or less than the threshold, the quadrature detecting means An ultrasonic tissue displacement measuring device, comprising: a reference frequency varying means for shifting a frequency of an input reference signal by a small amount.