GB2223641A - Method for determining the position of moving boundaries between biological tissues and a device for carrying same into effect - Google Patents

Description

2223641 I- - -I- TaTHOD FOR DETERMINING TIE POSITION OF MOVING BOUNDARIES

BETWEEN BIOLOGICAL TISSUES AND A DEVICE FOR CARRYING SALTE INTO EFFECT The invention relates generally to measuring instru- -hods for deter5 ments and, more specifically, it concerns met mining the position of moving, boundaries between biological tissues and devices for carrying said methods into effect.

The inventi= can find application in medicine and in some other branches of engineering, wherein there is neces- sary to determine the moving boundaries between the media conducting electromagnetic radiation, e.g., for determining the liquid level or height in closed reservoirs or tanks.

-e present state of the art Llhod for Known in th is a me' determining disorders of contractility of the right. cardiac ventricle by electrokynographic examination, for which purpose the boundary between different biological tissues is to be determined. For such an examination, the patient has to assume a definite position and is subjected to X-raying, -ricle are visualized whereupon the motions of the right vent on the screen of the X-ray unit, a photocell is placed on the screen which converts the motion of the right ventricle silhouette as viewed on the screen into electric current oscillations which are then written down on a recorder. However, in some instances the method fails to provide an eleetrokymogram of the right cardiac ventricle nor is it capable of identifying with an adequate accuracy the distur-bances of contractility of the right ventricle ryocardium.

C) The method cannot be applied on a wide scale since it involves a certain X-ray radiation dose of the patient in question. Besides, for carrying out an electrokymographic examination the patient should assume the standing posture and hold breathing, which rules out of the patientst contingent to be examined such patients as suffering from myocardial infarction in an acute period, patients in grave state, tients. The examination involves a children and pregant pat special room provided with X-ray screens, and sophisticated equipment.

It is echocardiography that proves to be most inforz-a- -,1ve among noninvasive introscopic examination techniques applicable to biologIcal tissues.

However, the heart and especially its right ventricle are covered by the sternum and ribs which are impervious to ultrasonic waves. That is why the necessity to place an ultrasonic sensor only in the intercostal, supraand substernal spaces makes it less possible to set said sensor in an optimum, position. Inadequate width of the intercostal spaces and impossibility of optimum positioning of such a sensor affect- adversely the examinatlion, render the provis- ion of adequate information on myocardial contractility less probable, especially of the right cardiac ventricle, and place limitation upon the contingent of patients to be examined.

Known in the art is also utilization of ultra-high and super-high frequency electromagnetic radiation, since the radiation of the above frequency bands is but slightly reflected from the sternum and ribs as compared with ultrasonic waves, as well as low absorption of the radio-frequency 1 waves by said tissues contribute to their application for noninvasive introscopic examination of the heart and other moving (pulsating) organs of the thoracic cavity.

When a probe shaped as a flat spiral coil which is a part of an LC, oscillatory circuit, is placed on or positioned above the human body, any motion of tissues situated in the effective area of said probe, or any change in the blood content of said tissues causes changes in absorption of the energy of electromagnetic field emitted by the coil.

Increased energy absorDkllion results in a reduction of the natural frequency of oscillations generated by said LC-circuit. Then frequency changes are converted into a vol,age irrpressed upon a recording device. The thus -rec,..)rde d si.--nal represents largely the motion of the tissues in the zone of "coverage" irirediately below the probe.

Moltion of the tissues exposed to the effect of an electrom,gnetic field, changes its capacity and, hence, the field oscillation fre-quency. Then the frequency changes are converted into a voltage proportional to the motion of the tissues involved.

The methods discussed above provide the recording of only the resultant vector of motion of the various cardiac structures, which is difficult to interpret, while the motion (pulsation) of some separate cardiac structures is impossible to be recorded, which impedes widespread practical implementation of the method under consideration.

Thus, the ability of bones to reflect ultrasonic waves hampers examination of cardiac structures, especially the - ventricle, due to impossibility of placing an ultraso- right cl C i nic sensor in the optimum position. On the other hand, the bones impede but lightly the propagation of super-high frequency electromagnetic waves, though the heretoforeknown methods for their application have not found practical use due to impossibility to examine separately the contractility of the various cardiac structures and of major vessels, in particular, the right ventricle.

One prior-art ultrasonic echoencephalngraph is known 'Llo comprise a probe to emit ultrasonic waves to the biological tissues under study, and a probe to receive the return sig- nal reflected from the biological tissues, a probing pulse shaper having a blocking oscillator, a sweep unit and a prob- ing pulse oscillator. The ulae shaper is connected to p ultrasonic wave emitting probe, while the return signal re- ceiving probe is connected to the input of the return signal metering unit which comprises a video-amplifier and is connected to the pulse recording unit provided with a cathode-ray tube.

The sync-pulse generator operates in a free-run-niniz mode to produce the sweep unit trigger pulses, negative pulses for shaping the markers in the metering unit, and trigger pulses for the probing pulse generator. The ultrasonic wave emitting probe is driven by electric pulses produced by the probing pulse generator, When. the probe is set on the object under study through an intermediate contact layer so as to provide transmission of ultrasonic wave energy thereinto, ultrasonic waves while passing through the tissues, are partly reflected at the boundaries between the structures having different density, e.g., fat-to- muscle, muscle-to-bone, and partly penetrate through said structures. In the location mode of operation return (reflected) pulses are employed as useful information, said return pulses propagating along the same path in the opposite direction and are picked up by the same probe within an interval between two emissions, that is, the probe corbines the functions of a transmitting and receiving device.

The return pulses picked up by the probe are delivered to the receiver, amplified in the video-amplifier and applied to the cathode-ray tube of the pulse recording unit, where they are represented as vertical pulses Then a saw-tooth voltage is shaped in the sweep unit in response to the pulses of the sync-pulse generator, said vol- -uage providing the sweeping of the echo signals reflected from the boundaries between the biological tissues, on the cathode-ray tube screen in the recording unit.

To determine the location depth of the reflecting structure or the size of the object under study one should measure the distance to a respective pulse on the echogram, 4'he measurement being carried out with the aid of a time marker Produced by the metering unit.

-ion to provide a method It is an object of the invent and a device for determining the position of moving bounda- ries between biological tissues which would make it possible to study deeply seated moving structures of biological tissues.

It is another object of the invention to provide a possibility of separately recording the motion of the structu- res of cardiac ventricles and atria, the aorta, pulmonary artery and other major vessels.

It is one more object of the invention to provide a posdial contractility dis- sibility of early diagnosis of myocar" orders, including those of the right cardiac ventricle.

The objects of the invention are accomplished due to the fact &that in a method for determining the position off moving boundaries between biological tissues, consisting in that the biological tissuesunder study are irradiated with an electromagnetic flux to obtain a return signal reflected from the moving boundary between the biological tissues, according to the invention, the electromagnetic flux is applied in the form of radio-fre-quency pulses having a central spectrum frequency in the range of 0.5 to 10 GHz, and a spa- tial position of the moving boundary between the biological tissues is determined against a phase shift of the reflected impulse signal with respect to the irradiating signal applied.

It is expedient that the impulse signal reflected from the moving boundary be measured and analyzed by strobing so as to isolate separate measurement phases of said signal which correspond to different moving boundaries between the biological tissues situated at different depths.

The electromagnetic flux applied can be polarized and so directed that the direction of polarization should coincide with orientation of the biological tissues under study.

It is desirable that the electromagnetic flux applied have a power under 10YW/cm 2 a 1.1i The aforegoing and other objects of the invention are accomplished due to the fact that a device for determining the position of moving boundaries between biological tissues, according to the invention, comprises a probing pulse shaper, a probe for applying the emitted pulse to the biological tissues, which is in fact a transmitting antenna connected to the output of the probing pulse shaper, a probe for picking C., up a return pulse reflected from the biological tissues under -u study, which is in fact a receiving antenna, a ret rn pulse -he receiving anten10 metering unit to whose input is connected ".

na and which comprises a stroboscopic converter, a pulse be'he return pulse metering unit, ing shaped at the output of t which corresponds to the position of the biological tissues under study, and a recording unit to record a pulse co. -res- ponding to the position of the biological tissues under study, which is connected to the output of the return pulse metering unit.

It is expedien-It-, that the return pulse metering unit co-rprise- seriesconnected a circuit for eliminating the effect of a return pulse reflected from stationary biological tissues and/or structures and a circuit for reducing the effect of return pulse oscillations having a respiration rate, -roboscoboth circuits being connected to the output of the st pie converter, as well as a signal differentiating circuit connected to the output of the stroboscopic converter and aimed at isolating the characteristic points in the return pulse which define the phases of motion of the biological tissues under study.

It is also favourable that the transmitting antenna and the receiving antenna comprise each a plate made of a current-conducting material and having recesses shaped as tivo equilateral triangles having, a common vertex, while the ad5 jacent sides of the triangles define an angle smaller than 90 degrees therebetween.

The transmitting and receiving antennas can be made ph.,,.rsically integral on the same plate, and the adjacent equilateral triangles of one of the antennas are facing with their free vertices oppositely to the free vertices of the equilateral triangles of the other antenna.

Further objects and advantages of the present invention will hereinafter become evident from a consideration of some specific exemplary embodiments thereof with reference to the accompanying draiv.ngs, wherein:

C> tation of Fig. 1 a, b, c shows a diagrammatic represent motion performed by the anterior wall of the left cardiac ventricle when the heart is isolated from the human bodv and is activated by an extracorporeal circulation apparatus; Pig. 2 a, b, c,, d, c, fl g, h,, i shows diagrams per taining to the left cardiac ventricle; Fig. 3 a, b. cy d. e. f. g, hq i_. shows diagrams per taining to the right cardiac ventricle; Fig. 4 presents a structural diagram of a device, ac- cording to the invention; Fig. 5 illustrates the device of Fig. 4 featuring an alternative embodiment of the metering unit, according to the invention; he mr-.ter- Fig. 6 shows the device of Fig. 4, wherein t ing unit incorporates a differentiating circuit, according to the invention; Fig. 7 presents the device of Fig. 4 featuring another alternative embodiment of the metering unit, according to the invention; Fig. 8 illustrates a structural diagram of the strobo'he invention; scopic converter, according to 1.

Fig. 9 depicts a structural diagram of the probing pulse shaper. according to the invention; Fig. 10 is a view of a transmitting antenna and a re- ceiving antenna, according to the invention; and the return Fig. 11 is an elementary electric diagram of pulse metering unit. according to the invention.

C> The present method for determining the position c' nov- L L ing boundaries between biological tissues is applicable for finding out the mutual arrangement of diverse moving biological structures at various time instants, e.g., for examination of donor's organs used for transplantation purposes.

The method of the invention is carried into effect as follows. A donor's organ, e,g., the heart intended for transplantation is placed in a liquid medium and the cardiac chambeisare made to perform their natural motions with the aid of conventionally known extracorporeal circulation equipment.

Then the donor's heart is irradiated with an electro- magnetic flux which is applied in the form of separate radio-frequency signals hereinafter referred to as pulees and having a central spectrum frequency within a range of 0.5 to 10 GHz, The central spectrum frequency above 10 GHz results in much increased loss of energy in biological tissues and complicates technical implementation of a device for carrying the method into effect, whereas said frequency belnw 0.5 GHz ' due to affects adversely the depth resolution of the metho" a greater probing wavelength, as well as measurement accuracy.

An optimum range of the central spectrum Jrequency lies within 1 and 8 G1111Z proceeding from contradictory requirements of absorption and resolution.

A return pulse results from the effect nf said electromagnetic flux on the heart, which is picked up and carries information on mutual arrangement of the various stationary and moving structures of the cardiac tissues, as well as on their presence and location, such as epicardial surface ol. the anterior ventricular and atrial walls, and the posterior wall of the sarhe cardiac structures.

Fig. 1 a, b, c. depicts a return pulse reflected from the cardial surface of the left ventricle showing the conse- cutive measurement phases.

Proceeding in the same way one can perform contractility study of the right ventricle myocardium and that of the right atrium with a high degree of intelligence Y;.t,.ich exceeds the examination accuracy attainable by some other non- invasive methods, including echocardiography (Fig. P a, b), since the aforesaid cardiac portions are examined under adverse conditions (i.e., radiation is directed at an angle) which affect the examination accuracy.

As a result of exposure to said electromagnetic flux of a human's heart, a return signal sets in carrying information on mutual position of the various moving and stationary tissue structures, as well as on their presence and location in the area of the probe "coverage", viz., the epicardial surface of the anterior ventricular and atrial walls and the posterior wall of the same cardiac structure, major vessels, the ribs, adipose tissue and other tissues structures.

Fig, 2 a, b., c- presents diagrams pertaining to the left cardiac ventricle taken at a speed of about 5 mm/s using the method of the invention. Pig. 2 -d. e. f. g, h$ i shows diagrams taken at a speed of about 50 mm/s and corresponding to certain preselected portions of the return pulse in the diagram of Fig. 2a. Accordingly, t.here are presented an electrocardiogram (Fig. 2f), a phonocardiogran (Fig. 2g), C) C> ' a carotid sphygmogram (Fig. 2h), and a diagram of the thoracic cage respiratory movements (Fig. 21), all taken by con.ho" ventional met Is.

Proceeding from the dip-grams presented in Fig. 2 a, b, d, e. there is carried out a phase analysis of the left ventricle contractions, the diastole inclusive, while their comparison with the known diagrams confirms correctness of the proposed method. Besides. the method of the invention is advantageous in being not an Indirect method as all the methods listed above but is instrumental in a direct study of biological tissues, cardiac tissues inclusive.

It is evident from the abovesaid diagrams that each of the contraction phases of the left ventricle corresponds stably to a specific portion on the diagram of a return 191-, 1 ll, pulse, as well as to an additional information, i.e., early phases of the diastole. These return pulse diagrams are taken under free respiration conditions which also adds to their intelligence and to the accuracy of analysis of a functional state of the left ventricle myo-cardium.

Fig. 3 a, b,, c, d, e, f, g, h, i indicates siT-nj-1a.dip-grams of contractility of the right ventricle ryncardiom, of which diagrams those taken according to the proposed method (Fig. 3 a, b, d, c) feature higher intelligence and ac- JO curacy which exceeds the examination accuracy attainable by other conventional methods. echocardiography Inclusive. Examination of the right atrium can be performed in a similar way. Such examinations are more accurate compared to the conventional methods, since the abovesaid car"iac structures are situated behind the sternum. which is iwiervini.,s to, eg., ultrasound waves. Fig. 3 a, bs c represents diagrams of a return pulse reflected from the right ventricle, and Fig. 3.fy gy hIp i. shows an electrocardiogram, phonocardiogram, jugular phlebogram, and a diagram of the thoracic cage res- piratory movements, respectively.

The method under consideration is also highly noise-im-he adopted irradiation technique.

mune due to t When carrying the method into effect a certain measurement phase of a return pulse is to be selected and there are taken down oscillations of a preselected portion of the return pulse, which result from mobility of the boundary between the biological tissues under study.

The measurement phase is to be selected in that pe%rtion of a return pulse, wherein there occurs the maximum ampli- I 1 1,1,' tude at the point of extrema of the return pulse envelope (Fig. 2a, 3a). For studying different depths of location o.."' moving boundaries between biological tissues use is made of consecutive signal phases having maximum oscillation ampli 5 tudes.

Thie thus-obtained diagrams of return pulses (Figs la, b; 2a, b) can be measured and analyzed most efficiently by meanns of strobing (see diagram of Figs 2c, 3c), for which purpose a measurement phase, i.e., the point strobing is selected on an appropriate diagram portion (which is marked out with vertical lines in Figs 1, 2, 3) with simultaneously changing the sweeping range, if necessary. Then the measurement phase is taken down and changes in its position are isolated against maximum pulse values in said phase of change of the whole return pulse with time. Then these changes are recorded as a curve represented in Figs 2d, e; 3d, e.

The strobing phase (i.e., measurement phase) is selected depending on the position of the biological tissue being studied in a structure as for depth, that is, at a depth where maximum pulsations (oscillations) of the return pulse amplitude are observed. For the myocardium it is, for instance, a first portion where maximum return pulse pulsations are observed, which corresponds to the epicardial surface of the atrial or ventricular anterior wallg or that of vessels, a next portion exhibiting maximum oscillations of the return pulse corresponds to the inner surface of the anterior wall of said structures, said surface being situated_behind the epicardial surface and somewhat deeper, and so on.

I_j -14-.

The diajrams obtained as a result of strobinG (after pulse fsedin- as per Figs 2c, 15c) and ShDYM in Fi s 2d, e;..;5d e have a cyclic pattern representinG carGiae eDntrac- t ' oscillatinj, r-Dtion, the r-,-.uual Uions, z.axim--- and minima D-L U a.r.ranGer-ent of which is different for the atria, ventricles and central vessels and corresponds tuD tube Generall,, adopted conception of the kind of DscillatiDns of the epiCaZd-alL SU-- face D', the aforesaid cardiac structures. TInius, the -!b.--ve dis;rams cD7_=1j Y.Ith the 1.0 and can be P-.,-,-lyzed b,. any here'Ur,'Li).re "znDwn method.

lt beCDr-es ve------ i'Dr tIhe present LA U U U utilize the D.E an electro--- -nettic ra d ia t i o n t D p Z -,, C; xize, vihereb., such a ra%,3ia-,jiDn can be orieritued so the CirectiDr. Df& t.Dlarizatirr, be as close as possil,-',t; ej.- pectued orientuatior. of the s-uruet,.=e under study. it::rDve-= to be especiaally efficient v;hen s"udyir,,F; Dblong szrucv=e-c:, ki e.c,.5 bubDSe P2ranged Square to each other, such as t,e pu_=D_ nary vein and the pulmonary Ertery, or the aorta cnd the superior vena cava.

L, The device for determining the position D1 =-Dving boandaries between biological tissues Comprises a probing pulse shaper 1 (Fig 4), said probing pulse being emitted in the.LD.rin of an electromagnetic flux and applied by means of a probe for transmitting the pulse emitted, said probe being in fact a transmitting antenna 2. The pulse thus emitted is reflected fror, the biological tissues irradiated by said pulse, and the resulting return pulse is pieked up by a re- probe v.-bich is in -Ipsct a receiving an.;,jenm- The device comprises also a return pulse metering unit 4 to one of whose inputsis connected the receiving antenna 3 and to the other input, the output of the pulse shaper 1, while a pulse is shaped at the output of the unit 4, corresponding to the position of the biological tissues under study. Connected to the output of the unit 4 is a recording unit 5 to - ion of record a pulse corresponding to the posit L' the biological tissues involved, said recording unit being built around of, e.g., an oscilloscope.

C3 According to the invention, the unit 4 incorporates a stroboscopic converter 6.

In addition, the unit 4 comprises a circuit 7 (Fir,. 5) -urn pulse reflected fror.

for eliminating the effect of a ret stationary biological tissues and/or structures, said cir- cuit 7 being connected to the output of the stroboscopic converter 6, and a circuit 8 for reducing the effect of a return pulse oscillations having a respiration rate, said circuit 8 being connected in series with the circuit 7.

Connected to the output of the stroboscopic converter 6 (Fig. 6) is also a signal differentiating circuit 9 adapted for isolating the characteristic points in a return pulse, which define the phases of motion of the biological tissues under study.

To attain higher measurement accuracy and extend operating capabilities of the device the unit 4 comprises a mains interference eliminating circuit 10 (Fig. 7) which is connected to the output of the stroboscopic converter 6, and an inverter 11 whose input is connected to the output of the circuit 10 while its output is connected to the respective C' X-inputs of the circuits 7 and 9.

Fig. 8 presents a block diagram of an embodiment of the stroboscopic converter 6 which comprises a sweep unit 12 connected to the output of the pulse shaper 1, a discriminator 13 of instantaneous values of the pulse being measured, whose inputs are connected to the outputs of the receiving antenna 3 and of the sweep unit 12, respectively, whilt-' il-S output is in fact the output of the stroboscopic converter 6 (Fig. 4). Connected to the other input of the sweep unit 12 (Fig. 8) is a sweep control unit.

The sweep control unit 1A comprises series-connected a multivibrator 15, a counter 16 and a digital - ILI o-analogue converter 17, all of these being connected, via a selector switch 18, to the input of an operational amplifier 19, while connected to the other input of the amplifier 10 is a threshold signal setting element made as a potentiometer.

The output of the amplifier 19 is connected to the input of a sweeping range selector 21 of the sweep unit 12, while the output of the selector 21 is connected to one of inputs of a gate pulse shift circuit 22, while connected to the other input of the circuit 22 is an inverter 23 connected to the output of the pulse shaper 1 (Fig. 4). The output of the circuit 22 (Fig. 8) is connected to the input of a monostable multivibrator 24 to which are series-connected an amplifier 25 and a voltage follower 26 whose output is at the same time the output of the sweep unit 12.

The measured pulse instantaneous value discriminator 13 comprises a strobing difference shaper 27 whose output is connected to one of the inputs of a comparator circuit 28, while connected to the other input thereof is a self-compensation circuit 29, and the output of the circuit 28 is connected to the input of a pulse shaper 30. The discriminator 13 comprises also a direct-current generator 31 and an impulse current gene-ator2,the outputs of both generators being connecta tDthe inputs of an integrator 33. The input of the generator 32 is connected to output of the pulse shaper -egrator 33 is connected to the in- 30, the output of the in'. put of a voltage follower 34 whose output is cnnnected to the inputs of the self-compensation circuit 29, while an nutput 36 of a voltage follower 35 is in fact the output of the discriminator 13 and, hence, of the entire strnbnscoDic con- verter 6 (Fig. 4).

The pulse shaper 1 (Fig. 4) comprises series-connected a clock pulse generator 37 (Fig. 9) and a delay unit 38. The output of the generator 37 is connected to the input of the unit 4 (Fig. 4) and the output of the delay unit 38 (Pig. 9) is connected to the transmitting antenna 2 (Fig. 4).

Fig. 10 illustrates the transmitting antenna 2 and the receiving antenna 3, each of said antennas comprising a plate made of a current -conducting material. In the hereindisclosed embodiment the antennas 2 and 3 are integrated on the same plate 39 which has recesses shaped as two equilateral triangles 40, 41 of the transmitting antenna 2 and simi- lar equilateral triangles 42, 43 of the receiving antenna 3.

The triangles 40, 41 and 42, 43 have a common vertex 44, 45, respectively, for each pair of the trianRles, while adjacent sides 46, 47 and 48, 49 of said triangles define an angle smaller than 90 degrees therebetween. If the angle r 1 confined between the adjacent sides of the triangles is greater than 90 degrees this will result in badly increased interference with the useful signal which will distort a return pulse. Free vertices 50, 51 of the triangles 40, 41 of one antenna (i.e., 2) are facing oppositely to free vertices 52, 53 of the triangles 42, 43 of the antenna (i.e., 3).

The common vertices 44, 45 of the triangles are isolated from each other by a portion of the plate 39. Cables 54 and 55 of the respective antennas 2 and 3 are connected to the plate 39, i.e., to its portion isolating the antennas 2 and 3 from each other and to its portions at the vertices 44, 45 of the triangles 40, 41, 42, 43, respectively. Fig. 11 represents an elementary electric diagram of one of the embodiments of the unit 4. The circuit 10 is built around an operational amplifier 56 and comprises resistors 57, 58, 59, 60, 61 and capacitors 62, 63, 64. The inverter 11 comprises an operational amplifier 65 with resistors 66 and 67. The differentiating circuit 9 comprises an operational amplifier 68 with capacitors 20 69, 70 and resistors 71, 72, while the circuits 7 and 8 (Fig. 5) are in fact a filter built around an operational amplifier 73(Fig. 12), resistors 74, 75, 76 and capacitors 77, 78,70-,,aD.A selector switch 81 is out in between the inverter 11 and the circuits 9, 7 and 8. 25 The device for determining the position of moving boundaries between biological tissues operates as follows. The probing pulse shaper 1 generates square clock pulses which are applied to the stroboscopic converter 6, wherein probing pulses are formed from said square pulses 1 1 in the form of voltage differences, which are then applied to the transmitting antenna 2. The transmitting antenna 2 and the receiving antenna 3, both of the wide-band mar-netic dipole type, are located close to each other and directed towards the object being studied. The antennas are placed on the patient's body (on the skin surface) just above the moving boundary between biological tissues that is to be studied, and are oriented about a central axis so that. a direction AB of polarization (Fig.10) should be as close as possible to the expected orientation of the organ under study. Part of the radiation emitted as radio-frequency pulses by the transmitting antenna 2 is picked up immediately by the receiving antenna 3 as a spurious signal, while another part of the emitted radiation is reflected from the bounda- ries between the stationary and moving tissues and is also applied to the receiving antenna 3 as a useful signal. The picked up signal is supplied from the receiving antenna 3 to the stroboscopic converter 6 of the return pulse metering unit 4. Next the measured return pulse is impressed on the Y input of an oscilloscope (omitted in the Drawing) in the pulse recording unit 5, wherefrom it is delivered for further processing to the input of the mains interference eliminating circuit 10 which is in fact a rejection filter. Further on the return pulse is fed via the inverter 11 to the input of the circuit 7 for eliminating the effect of a pulse reflected from stationary biological tissues and to the input of the signal differentiating unit 9. From the output of the circuit 7 the return pulse is supplied to the input of the circuit 8 for reducing the effect of a return pulse os- 1 \_ 1 cillations having a respiration rate. The functions of the both circuits 7 and 8 are performed by a high-frequency filter having a cutoff frequency of 0.7 GHz. When leaving the output of the circuit 8 the return pulse appears as pulsa- -ween the biological tions of the studied moving boundary bet tissues, such as the anterior wall of the right cardiac ventricle, whereupon the return pulse is impressed on the input of a single -coordinate recorder in the pulse recording unit 5, whereas a differentiated signal from the output of the circuit 9 is applied to the other input of the recording unit 5.

The multivibrator 15 of the sweep control unit 14 produces square pulses 'which are applied to the binary counter 16, whereupon the digit -toanalogue converter 17 connected to the outputs of the counter 16, shapes a voltage level corresponding to the binary code supplied. The thus-shaped saw-tooth voltage which is dependent on the position of the selector switch 18, or a certain direct- voltage level set by the potentiometer 20, is impressed on the noninverting input of the amplifier 19.

Then the signal in the form of a saw-tooth or direct voltage is delivered from the output of the amplifier 19 to the X input of the oscilloscope (omitted in the Drawing) in the pulse recording unit 5 and to the range selector 21 in the sweep unit 12. Clock pulses sent from the output of the probing pulse shaper 1 are applied, via the inverter 23, to the gate pulse shift circuit 22, said gate pulses be ing produced by the monostable mu'livibrator 24 The amount of shift of the gate pulses with respect to the clock j 0. - - %1-) pulses depends on the value Of control voltage at the output of the selector 21 and can be either constant or variable according to the saw- tooth pattern. The gate pulses are intensified by the amplifier 25 and are applied, via the voltage follower 26, to the strobing difference shaper 27 in the measured pulse instantaneous value discriminator 13.

At the instant when the strobing voltage difference is delivered from the shaper 27 the comparator circuit 28 compares the sum of an instantaneous value of the input pulse from the receiving antenna 3 and the voltage of a feedback pulse having the value of a certain threshold and sent by the self-compensation circuit 29. When the sum of the instantaneous value exceeds the threshold value a pulse appears at the output of the circuit 28, otherwise no pulse is pre- sent. A pulse shaped in the shaper 30 is delivered to the impulse current generator 32. The thus-shaped current pulses charge the integrator 33 which is discharged into the direct-current generator 31. The voltage of the integrator 33 is supplied, via the voltage follower 34, to the input of the self-compensation circuit 29 and further on the comparator circuit 28 a feedback voltage which automatically monitors an instantaneous value of the input signal. A pulse appearing at the output of the voltage follower 35 is in fact the output pulse for the stroboscopic converter 6; it is then applied to the Y input of the oscilloscope (omitted in the Drawing) in the recording unit 5 and is sent for further processing to the inputs of the circuits 7, 9 or 10.

Application of the present method makes it possible to obtain the following advantages. The method is capable of 1 1 -22separately recording Motions of the epicardial surface of the cardiac struct=es, including the right ventricle end the right atrium. Studies DI the various portions of the seme return pulse makes it possible to CX8Mine deep CC2dieC S tr uc t ur c S 3 as well as to diagnose early disorders of the right ventricular mvocardium contractility.

The here in-considered met-od and device for deterMininj the position of movinj boundaries be'ui,.,een biDID-."iCal tissues feature the follozing -; n me. - advantajes over the knD Ii tbDdSy e.,C,. y those ultrasonic radiation.

1 Ebe proposed radiation is not reflected from Osseous uLssL,e r.hicb makes it possible 5D study the moving bDUndexies betweer, the bioloGical tissues situated behind the bones, since the latter (e.g., the steraum and ribs) ir-pede but a litutle the of an elect-D::ia.-ne'uic rad-La'uicn.

L:olecular dielectric permittivity of tissues ranSes within _S and 50l while the density oil soft tissues is variable within but a few percent. Such a broad rance of varia- cj t bive of a Uion c;ll dielectric permittivity is ink,:iica-U b e 'u,-; to attain better tissue identification whern p-Dbin t with an electrDMa7,netic radiation as compared with UltreSD- U nic one.

Polarization of the electromagnetic radiation makes it posible to isolate a return pulse reflected from oriented biological structures (such as the pulmonarj., artery, PUIrID- nary veins, and others).

Realization of the proposed method does not involve application of an intermediate layer (e.g.$ of water, liiuid petrolatum, and others) to patient's skin for better con- tact with the probe. Examination can be performed even through patient's underwear which saves time. The method makes it possible to carry out differentiation of a curve representing a change in the distance from antennas to mov- ing boundary between biological tissues, which, in turn, enables one to isolate the instants when the motion speed of the moving boundary varies, which instants are characteristic from viewpoint of diagnosis. Besides, there are isolated the points representing the phases of cardiac con10 tractions, the early diastole inclusive.

1

Claims (11)

WHAT WE CLAIM IS:

1. A method for determining the position of moving C) boundaries between biological tissues, consisting in that the biological tissues are irradiated with an electromagne- tic flux in the form of radio-frequency pulses having a central spectrum frequency within 0.5 to 10 GHz, an impulse signal reflected from the moving boundary between the biological tissues is obtained, and a spatial position of the moving boundary between the biolnzical tissues is de.'1- Iermined against a phase shift of the return impulse signal with respect to the irradiating impulse signal applied.

2. A method as claimed in Claim 1, consisting in that the i=.pulse signal reflected from the moving boundary is analyzed by strobing to isolate separate portions of the signal, each of which corresponds to the boundary between the biological tissues situated at different depths.

3. A method as claimed in Claim 1 or 2, consisting in that the electromagnetic flux is polarized and is so directed that the direction of polarization corresponds to orien- -',ation of the biological tissue under study.

4. A method as claimed in any one of Claims 1 to 3, consisting in that the electromagnetic flux applied has a power under 10jMW cm 2.

5. A device for determining the position of moving boundaries between biological tissues, comprising a probing pulse shaper, a probe to apply the emitted pulse to the biological tissues, which is in fact a transmitting antenr connected to the output of the probing pulse shaper, a probe to pick up the pulse reflected from the biological tissues, which is in fact a receiving antenna, a return pulse metering unit to whose input the receiving antenna is connected, which metering unit comprises a stroboscopic converter, a pulse being shaped at the output of the metering unit, corresponding to the position of the biological tissues under study, and a unit for recording a pulse that corresponds to the position of the boundaries between the biological tissues, connected to the output of the return pulse metering unit.

6. A device as claimed in Claim 5, wherein the return pulse metering unit comprises series-connected a circuit for eliminating the effect of a pulse reflected frnm the stationary biological tissues and/or structures, and a circuit CD for reducing the effect of a return pulse oscillations ha%ring a respiration rate, both circuits being connected to the output of the stroboscopic converter.

7. A device as claimed in Claim 5 or 6, wherein the return pulse metering unit incorporates a signal differentiat- ing circuit connected to the output of the stroboscopic converter and aimed at isolating the characteristic points in -ine the phases of motion of the the return pulse which deL biological tissues under study.

8. A device as claimed in any one of Claims 5 to 7, wherein the transmitting and receiving antennas each comprise a plate made of a current-conducting material and having recesses shaped as two equilateral triangles having a common vertex and whose adjacent sides define an angle smaller than 90 degrees.

C

9. A device as claimed in Claim 8, wherein the transmitting and receiving antennas are made physically integral on the same plate, and the adjacent equilateral triangles of the one antenna are so arranged that their free vertices are opposite to the free vertices of the equilateral triangles of the other antenna.

10. A method for determining the position of moving nveen biological tissues substanti ally as des- boundaries bet cribed hereinbefore with reference to, and as illustrated 13 in the accompanying Drawings 1 to 4.

11. A device for determining the position of moving boundaries between biological tissues substantially as described hereinbefore with reference to, and as illustrated in the accompanying Drawings 5 to 11.

Published 1990 atThe Patent Office, State House, 66 71 High Holborn. LondonWCJR4TP.Purther copies maybe obtainedfrom The Patent Office Sales Branch. St Mary Cray. Orpington. Kent BR5 3PD. Printed by Multiplex techniques ltd, St Mary Cray. Kent. Con 1 877