JPS59209335A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic diagnostic apparatus that separates a pulse echo signal from a living body into a specular component representing the outline of a tissue and a random component effective for extracting characteristic parameters inside the tissue. O relates to an apparatus that can simultaneously display shape information and quantitative information based on characteristic parameters in an ultrasound tomogram. Conventional tissue quantification using ultrasound is based on the spectral frequency of the echo signal (random) component in a weakly heterogeneous medium. This can be done based on dependence, or by measuring the frequency distribution of the amplitude or time interval of this signal. However, if a large reflected echo signal (specular) component due to the discontinuity of the Mi band is superimposed on this signal, an error will occur in the above quantification.

Furthermore, in conventional B-mode images, specular components and random components are not separated and are displayed side by side, so there is a drawback that tissue boundaries cannot be clearly defined.

An object of the present invention is to separate and process a pal-echo signal from a living body into a specular component representing the annular elevation of the tissue and a random component effective for extracting characteristic parameters inside the tissue. It is an object of the present invention to provide a device capable of simultaneously displaying quantitative information based on quantitative information and characteristic parameters as an image.

The present invention enables easier separation of specular components and random components by (1) providing a separation circuit; and (2) using a pulse echo signal from a living body as a separation circuit in combination with not only a linear filter but also a nonlinear filter. This makes it possible to simultaneously display quantitative information such as the shape 8 of the biological tissue.

A separation circuit consisting of a filter detects large echo signals (specular) returned by distinct tissue discontinuities within the body.
Eiy, S(t) and a weak echo signal (random) component R(t) returning from the fine weak heterogeneous structure of the tissue. Extract characteristic parameters using linear filters and nonlinear filters. This repetition is performed two-dimensionally, and the tissue outline and characteristic parameters are displayed simultaneously as images.

FIG. 2 shows a block diagram of the m-minute circuit shown in FIG.

This is an example in which individual filters are combined using a limited deconvolution filter and a convolution filter as an axial filter, and a non-relaxed matched filter as a nonlinear filter. The echo signal X(1) is represented by a dish of specular component s(t) and random component R(t), i.e. x(t)=S(t)+R(t)
(1)-:3-, where 5(t) is ideally determined by the electrical characteristics, with impulse response h(t) of the resonator, delay time τ1, and amplitude fLl as parameters, 5(t)=Σath (t-4t)=[Σalδ(
is expressed as −τI) (*) h (t) (2). However, ■ indicates convolution, and δ(1) indicates a delta function. Conventionally, specular component S (t
), for example, the impulse response ψ(1
) and x (t), and assumed that a specular reflector exists at a position that shows a large peak value. For example, it is better to use a nonlinear matched filter whose output is the reciprocal of the error power between the reference function and the input function (when a match is achieved, the error becomes almost zero, giving a very large output, If there is even a slight deviation from the matching point, the error will increase and the output will become smaller), resulting in a very sharp peak in the output, improving position accuracy. However, when using a nonlinear filter, the principle of superposition of linear systems does not apply, and if two or more specular reflected waves that overlap, even partially, are input, it may not be possible to separate them well. , problems such as a significant drop in the output of the filter for each specular reflected wave occur. Therefore, as shown in claim 1, the received signal x (t) is first deconvolved (linear filter operation) using the impulse response of the vibrator to shorten the pulse duration of x (t). The nonlinear filtering described above may be performed after minimizing the deviation between the specular reflected waves as much as possible.

An example of a procedure for estimating al and τ1 in equation (2) will be shown below.

(1) In consideration of the band limit of the vibrator, the estimated value g (t) of the impulse response is obtained using limited inverse convolution assuming that the noise variance is known.

(11) A signal obtained by discarding the low-level waveform of this g (t) signal is passed through a nonlinear matched filter as shown below to obtain the sign 5srnra+)c'τtG of al.

For the non-1ν type renal filter described here, calculate the delta function when the band is limited according to the band of the oscillator.
Two delta functions δ+(1) and δ−(
t) The following is used as the K reference signal.

Calculate the impulse response g (t) which is the output of the deconvolution filter with the lower level truncated, and the reciprocal numbers N'' and N- of the next two error powers within an appropriate interval Δ.

N(τ+) −I, l kg(t) −δ−(−τt)
l”dt (4) Here, k is a normalization constant that equalizes the impulse response g (t) and the maximum amplitude of the delta function within the interval Δ. Since τi is not shifted within the interval, N+ (τ
+) and N (τ1), when the correlation between the impulse response and the delta function is strong, one of them gives a sharp peak. A threshold value is detected, and the peak position at this time is τl. However, the symbol “Δ” indicates the estimated value
- The sign of 8gn (IILI) increases depending on whether it is plus or minus, depending on which one gives the peak.

θ10 Convolution composite value ip (t-9t) I Qt l sgn(Qt)l
. Adaptively find la+18 so that the square of the error between h(1) and the input signal x (t) is minimized. This operation is performed within a certain gated time width.

(ψ The composite value by al that minimizes the square of the error gives the specular component itself (t), and the error M x (t)
−△ S (t) is the rerandom component R(t) from equation (1), R(t) = x(t) −5(t)
(5) becomes.

Figure 3 shows the echo obtained for an acrylic plate with a thickness of 3 mm.
An example of the filter output of No. 1B is shown. The vibrator used has a center frequency M 2.25 M)[z.

Figure (4) shows the original waveform reflected from the front and back surfaces of the acrylic plate. 0(B) shows the output (impulse response of the acrylic plate) after the original waveform is deconvoluted and passed through a filter. (C) is the result of passing this impulse response further through a nonlinear matched filter.

7- Two sharp peaks corresponding to the front and back surfaces of the acrylic plate are obtained.

FIG. 4 shows the processing results of echo signals for chicken meat. Similarly, a vibrator with a center frequency of 2.25 MHz was used◇(
5) shows the fall type 003) its impulse response (output of the deconvolution filter), and (C) shows the delta function when the band is limited according to the band of the resonator used, and this is the reference signal of the nonlinear matched filter. 0 used as
(2) is the output result of the nonlinear matched filter. ■)■
represent the finally separated specular component and random component, respectively.

In Figure 1, the specular component is used to clearly show the contour of the tissue, but when determining the specular component, the impulse response from the tissue or the output of the nonlinear matched filter is used, so this output is When applied to ring S display using this method, it is possible to image with higher distance resolution than envelope detection.

According to the present invention, a pulse echo signal from a living body can be separated into a specular component representing the contour of the tissue and a random component effective for tissue characterization such as extraction of characteristic parameters of a part of the inside of the tissue. 0 that enables simultaneous image display of shape information in an image and quantitative information based on feature parameters.

[Brief explanation of drawings]

FIG. 1 shows the entire configuration of the device. FIG. 2 is a block diagram of the signal separation system. FIG. 3 shows an example of a filter output of an echo signal obtained for an acrylic plate. FIG. 4 shows a processing result of an echo signal for chicken meat.

Claims (1)

[Claims] 1) Ultrasonic pulses are transmitted to a living body, and the ultrasound echo signals received from the living body are divided into large echo signal (specular) components that return from distinct tissue discontinuities within the living body, and It has a circuit that separates a weak echo signal (random) component returned from a minute weak heterogeneity structure and a weak echo signal (random) component returned from the structure, and a circuit that extracts and displays tissue characteristic parameters using the specular component and/or the random component. 2) The ultrasonic diagnostic apparatus according to claim 1, wherein the circuit for separating the specular component and the random component is a combination of a linear filter and a nonlinear filter. 3) The ultrasonic tomographic image according to claim 2, wherein the nonlinear filter is a nonlinear matched filter, and its output is the reciprocal of the error power in the matching section. 4) The ultrasonic diagnostic apparatus according to any one of claims 1 to 3, wherein the display circuit includes a circuit for two-dimensionally displaying a tissue contour based on the specular component.