SU1397026A1 - Method and apparatus for determining coefficient of reflection of borders of biological tissue - Google Patents

Description

(21) 4021026 / 28-14

(22) 02/10/86

(46) 05.23.88. Vul. No. 19

(71) All-Union Scientific Research, Design and Technological Institute of High Frequency Currents V.P.Vologdina

(72) L.A. Shifrin, B.E. Mikhalev, K.A. Fedchenkov and A.N. Yablonsky

(53) 615.475 (088.8)

(56) Hevlajs J.F., Tynzer J.K. Ultrasound imaging in medicine. - TIIER, 1979, vol. 67, No. 4, p. 209-234.

US patent number 4414850, CP. G 01 N 29/00, 1980.

(54) METHOD FOR DETERMINING COEFFICIENTS OF REFLECTION OF THE LIMITS OF BIOLOGICAL TISSUE AND DEVICE FOR ITS IMPLEMENTATION (57) - The invention is intended for ultrasonic methods of investigation. The purpose of the invention is to improve the accuracy of determination. The device contains a piezoelectric transducer 1/2, generators

3j4 probing signals, selective filters 5, -6, log-amplifiers -7 8, detectors 9 10, recorder I1, extremum memory circuits, adder, integrator, and anti-logging device. The area under study is exposed to ultrasound using a piezotransducer 1 and generator 3. Ultrasonic signals reflected from the interface are received by the same transducer after amplification and attenuation in the block are displayed by the recorder 11. Additional frequency selection of the echo signals is provided by selective filters 5,6. Logarithmic compression of the amplitude of the echo signals occurs in logarithmic amplifiers 7, 8. The method provides a direct measurement of the reflectivity of the studied tissues without the use of temporal selection of the echo signals and an estimate of the time of their arrival. 2 sec. f-ly, 3 ill.

(L

SAE SO -CH

ABOUT

Yu

about:

Phia.1

The invention relates to ultrasound (US) methods and devices for examining the structure of soft biological tissues.

The purpose of the invention is to improve the accuracy of the determination of the method and increase the speed of the device.

FIG. 1 shows a block diagram of an apparatus for implementing the method; in fig. 2 is a schematic illustration of the operation of a one-dimensional ultrasound location system; in fig. 3 - layered model of the studied medium.

The device contains piezoelectric transducers 1 and 2, generators 3 and 4 zones of dirzpotsih signals and selective filters 5 and 6, operating at the first and second frequencies, respectively, as well as logarithmic amplifiers 7 and 8, detectors 9 and 10, recorder

. (2)

P, circuits 12 and 13 of extremum memorization, adder 14 with a summing input, Based on the above, with a house and two subtractive inputs, the different value of the echo amplitude

Tegrator 15, anti-logging device, can be 25

16, represented as

(3)

The investigated area of the body-a (Fig. 2) consists of alternating layers of tissue with different acoustic nanometers: Z, Z, Z,. The investigated area is irradiated with ultrasound using a piezoelectric transducer 1 and a generator 3; ultrasonic signals reflected from boundaries 18 and 19

. g (-2f with l).

-. I

Similarly, for the second boundary, the ratio

. , (“, / I ,, j) J .. (4) By proposing similar reasoning

section, taken by the same transform for the 1st border of the model (Fig. 3)

After reinforcement and compensation, find

The attenuations in block 17 are displayed by the recorder P.

 ,, l

r.kf n (-2f 0 (, 4 J. (5) Sounding at two Frequencies, each of the layers of the layered model allows one to obtain two relative estimates of the medium (Fig. 3)), which is characterized by a thicker echo intensity signals, the Z1-,. attenuation coefficient, and the interface between adjacent layers, the reflection coefficient k |. It is assumed that the direction of propagation of the ultrasonic wave is perpendicular to the interfaces of the adjacent layers. the boundary is the following chain of events: attenuation in the first layer, ie, from the first boundary, secondary attenuation in the first layer.When a reflected signal is formed from the second boundary, the following phenomena occur: ultrasonic attenuation in the first layer, passing through the 5th edge of the first boundary, and secondary attenuation in the second and first layers.

The ratio of the amplitudes of the received U and the sent U signals at normal -k. P W; exp (-2f, dj, (6)

ri.k. P (, (7) 1

where g-, g - the ratio of the amplitudes of the n and probing signals at frequencies. f / and f, respectively. Prologue the ratio (6) to (7), get

tui

lnr. d, u (f, -f,}.

Substituting (8) into (6), after simple transformations, we obtain

(eight)

The nominal incidence of the ultrasound at the interface between two media can be represented as

d - k-exp (-2f (x) ,, - hi

(one)

where f is the frequency of ultrasound;

X is the distance to the border;

c / is the amplitude coefficient of dying out, dB-cm MHz-;

k is the reflection coefficient associated with the acoustic impedance of the first Z, and the second Z medium by the formula

one ,

The transmission coefficient of a plane wave through the boundary W is related to the reflection coefficient by the formula

. (2)

The outcome of the above, relative (3)

. g (-2f with l).

-. I

Similarly, for the second boundary, the ratio

. , (“, / I ,, j) J .. (4) By proposing similar reasoning

r.kf n (-2f 0 (, 4 J. (5) Sounding at two frequencies) it is possible to obtain two estimates of the relative intensity of the echo signals

r.k. P W; exp (-2f, dj, (6)

r.kf n (-2f 0 (, 4 J. (5) Sounding at two frequencies) it is possible to obtain two estimates of the relative intensity of the echo signals

ri.k. P (, (7) 1

r.kf n (-2f 0 (, 4 J. (5) Sounding at two Frequencies allows one to obtain two estimates of the relative intensity of the echoes

where r-, r is the ratio of the amplitudes of the received and probing signals at frequencies. f / and f, respectively, Prologue the ratio (6) to (7), get

r.kf n (-2f 0 (, 4 J. (5) Sounding at two Frequencies allows one to obtain two estimates of the relative intensity of the echoes

tui

lnr. d, u (f, -f,}.

Substituting (8) into (6), after simple transformations, we obtain

(eight)

) --I .-- Inr,

Inr.From (9), learning (2), it follows that the reflection coefficient of ultrasound from the 1st border can be represented as

f,. fa

i

exp (: s - s- Inr- - - - lnr lirii.- 1 n (l-kj

: i-l (io)

In the amplifier path with a logarithmic amplitude response, signals can be obtained directly.

We illustrate the obtained relation by the following example: the distance to the first boundary () cm and sounding is conducted at two frequencies f, 2 MHz and MHz. The reflection coefficient of the ultrasonic wave from the boundary under consideration is k, 0.05. The average attenuation value of ultrasound in soft tissue is cJ 1 dB MHz cm H Then the attenuation of ultrasound at a low frequency of 20 dB, i.e. echo is attenuated 10 times. Similarly, at high frequency, attenuation is 40 dB or 100 times.

Thus, the relative intensity of the echo signal at a low frequency is equal to 5-10. Corresponding to

, - +

1 at IT T f f {I-2-Ii 1

venno Substituting the obtained values in. (9), we obtain lnk, -2.99 or else, 05. Thus, the proposed method provides a direct measurement of the reflectivity of the studied; tissues without the use of a temporary selection of echo signals and an estimate of the time of their arrival. Correction of the results of deep layers is achieved with

35

PS1-1

.211

P

(eleven)

40

Equation (11) corresponds to the control loop of the adder, integrator, anti-calculator, covered by the feedback circuit, as shown in (Fig. 1). The practical use of the invention by calculating the interactional nature of i that with a large iula (10), namely the denominator

n (i-k,) 4

le p in terms

Lk operation

summation can be replaced by in- example. In the study area by tagging. As a result, the devices simultaneously use transducers 1 and 2 and generators 3 and 4 to emit two packets of 3 oscillations of the first and second frequencies. Acoustic energy, partially reflected from the interfaces of adjacent layers with different impedances, is received by transducers I and 2 in accordance with their resonant frequencies. Additional

55

in 5 FIG. 1) provides an accurate implementation of the proposed method of measurement.

Claims (2)

1. A method for determining the reflection coefficients of biological tissue boundaries by emitting two packets ten The frequency selection of the echo signals is provided by the selective filters 5 and 6. Logarithmic compression of the amplitude of the echo signals occurs in the logarithm 7 and 8. In the detector 9 and 10, the signals are detected. The maxima of the detected signals are in the memory circuits 12 and 13. The adder 14 provides algebraic summation of the amplitudes of logarithmic echo signals with a given weight G f and 2. For automatic f-f 2 T. AND fj. one- J5 who takes the loss of energy into account when passing the boundaries, an integrator 15 is introduced into the device, and the feedback circuit is closed to the subtracting input of the adder 14, 2Q The principle of this circuit automatic control can be explained by the following transformations of expression (9). The logarithm of the product is equal to the sum of the logarithms. 25 factors. In addition, for k 1, the In (l-k) x-k approximation is valid. The magnitude of the reflection coefficient in soft tissues does not exceed 0.1. This allows us to present expression (9) in the following approximate form: fl f T Fri f {I-2-Ii 1 Inr. PS1-1 .211 P (eleven) Equation (11) corresponds to the control loop of the adder, integrator, anti-calculator, covered by the feedback circuit, as shown in (Fig. 1). The practical use of the proposed invention derives from flows from the fact that when large le p in terms Lk operation summation can be replaced by integration. As a result, the device in 5 FIG. 1) provides an accurate implementation of the proposed method of measurement. Invention Formula 1. A method for determining the reflection coefficients of biological tissue boundaries by emitting two packets acoustic signals of different frequencies, reception of echo signals, their frequency selection, logarithmic amplification of signals and detection, which are different in order to increase the accuracy of the determination, measure the maximum values of the detected signals and calculate the reflection coefficient from the biological fabrics according to the formula  exp (f2-fi) (f.r InUu-f lnUb) L. .1 ““ -. ", And --.----- m P (1-kj-) - reflection coefficient from the 1st border of biological tissue; -frequency of two packages. acoustic signals; -maximum values of the detected echo signals, respectively, of the frequencies f and f. trio to determine cats fc.2 This includes two transceiver channels, each of which contains a series-connected generator, a piezo transducer, a selective filter, a logarithmic amplifier, and an amplitude detector, characterized in that, in order to increase speed, with summing and first subtracting inputs of the adder, output which is connected to a series-connected anti-log block and an integrator, the recorder is connected to the integrator input, its output is connected to the second subtractive input adder, the transfer coefficients of the adder for the summing, first and second subtractive inputs, respectively, are equal to the private from dividing the frequency of the second generator by the difference oscillator frequencies, which is a partial dividing of the frequency of the first generator by the difference in the frequencies of the generators and two