FR2480955A1 - METHOD AND DEVICE FOR ULTRASONIC ECHOGRAPHY - Google Patents

Abstract

AN ULTRASOUND ECHOGRAPHY DEVICE INCLUDES IN PARTICULAR A NETWORK OF TRANSDUCERS 10 WHICH RECEIVE THE ULTRASONIC ENERGY EMITTED BY AN EMISSION TRANSDUCER 12 AND REFLECTED IN THE OBJECT EXAMINED; A MEMORY 24 IN WHICH THE SIGNALS WHICH RESULT FROM THE ECHOES ARE WRITTEN IN THE SEQUENTIAL ORDER OF THEIR OCCURRENCE AND ARE READ IN REVERSE ORDER, A NETWORK OF TRANSDUCERS 27 WHICH ARE EXCITED BY THE OUTPUT SIGNALS OF THE MEMORY AND ARE COUPLED TO A MEDIUM OF RECONSTRUCTION 30; AND ACOUSTO-OPTICAL CONVERSION MEANS 32 WHICH PRESENT ON A DISPLAY DEVICE 36 AN OPTICAL IMAGE CORRESPONDING TO ACOUSTIC REFLECTION SURFACES IN THE OBJECT EXAMINED.

Description

"Ultrasound ultrasound method and device"

  The invention relates generally to a device

  positive ultrasound echog4aphy giving a presentation in real time. The invention relates more particularly to a real-time ultrasound ultrasound device in

  which we build a visual image from an ima-

  acoustic age formed in a reconstruction environment, in

  using acousto-optical techniques.

  Very specifically, the invention relates to an ultrasound ultrasound device which comprises a first network of transducer elements designed so

  à Being coupled to an object to be examined. Under the effect of energy

  ultrasonic sound which is emitted in the object, the network re-

  receives ultrasonic echo signals representative of acoustically reflective surfaces inside the object. The received echo signals are

  converted by network reception elements in

  electrical signals which are processed by an

  time version and are then used to excite a second network of transducer elements coupled to a reconstruction medium. The ultrasonic signals which are emitted by the second network under the effect of the electrical signals subjected to time inversion produce in the reconstruction medium an reconstructed acoustic image of the reflecting surfaces, to the point of

  acoustic view of the object. We get a visual image-

  the acoustic image reconstructed using mo-

  acousto-optic yen, like a Schlieren device.

  As will be described later, it is pos-

  likely to obtain isochronous images, i.e.

  images in which the complete acoustic image appears

  appears simultaneously in the reconstruction environment,

  the latter being excited by a light source

  pulsing, to obtain a visual image-

  the acoustic field, or to obtain aniso-

  chrones, in which case the image is formed at different pro-

  foundry in the reconstruction medium, as a function of time, and the reconstruction medium is explored by a light source to obtain a visual image

acoustic chnp.

  The configuration of the invention, with mo-

  minor difictions, is useful for obtaining ima-

  gespe pulse echo as by Doppler effect. In or-

  You can display a presentation in M mode, simul-

  image in real time. The scanning line of the M mode presentation can be obtained from the reception network and the transmission pulses which are used to obtain the image in real time, using conventional phase network techniques, to form a beam. receiving ultrasound in the direction chosen for M-mode imaging

  The high exploration frame rate that

  fre the device of the invention makes it possible to remove

  practically the granularity configurations. The con-

  granularity figurations in training devices

  image information are described in detail in the article

  titled "Acoustic Speckle: Theory ans Experimental Analysis" by John G. Abbott and F.L. Thurstone, Ultrasonic Imaging, vol. 1, no. October 4, 1979, pages 303-324, Academic

Press, New York and London.

  In the prior art, and in particular in US Pat. No. 4,174,634, a lens and a mirror are used.

  acoustics to create an acoustic image in a mid

  place of reconstruction. By using a training system

  Ination of acousto-optic inage, we converge into a re-

  visual presentation the acoustic image present in the environment of this reconstruction. The configuration of art

  has several disadvantages and, in part

  particular, the image size is reduced but the

  solution is limited by the wavelength of the frequency

  quence ult'asonore of origin which is emitted and received. The length of the path in water has the effect of reducing both image resolution and sensitivity, because the dispersion of the acoustic energy is

  proportional to the square of path length.

  In addition to the aforementioned patent, the related documents

  in the prior art include US Pat. No. 4,0G,627, se-

  which ultrasonic signals are emitted in half

  reconstruction site comprising a cistalline material.

  In US Patent 4,157,665, signals received $ nt processed by a system which includes a high frequency oscillator, so as to produce a frequency signal of

  beat which has the effect of converting a different beam

  gent in a beam which converges to form an image Oc da.su a reconstruction medium,

  In none of the configurations of the prior art

  reu.r mentioned above, we do find an inversion

  of electrical signals produced by echoes.

  In the invention, the electrical signals produced by the echoes, which result from echoes in the exanated object, are processed and recorded sequentially within one

  r: 3reire associated with each transducer element of the

  receiving bucket. The signals are read from the memory.

  re according to an order corresponding to a time inversion,

  that is, the last signal recorded sequentially-

  The first signal read is also in memory. The if-

  general readings are further processed and finally applied to transducer elements

  partners in the reconstruction network. The network of re-

  à5 construction, in acoustic coupling with a medium of

  reconstruction, emits signals in the middle of

  acoustic sound under the effect of electrical signals

  caused by echoes and subject to time inversion.

  Depending on the reconstruction environment,) n uses the

  techniques of Schlieren, Bragg, interferometry or.

  other acousto-optical conversion techniques to build the visual image. Optical imaging techniques are well known and are described, for example, in the book Biomedical Ultrason: cs by PeN. To

  Wells, 1977, Academic Press, pages 98 to 1 # 6, in the ar-

  "A New Ultrasonic Focusing System f4r Materials Inspection" by P.D. Hanstead, J. Phys. D- Apple Physo, vol 7, 1974, pages 226 to 241 and in the GoBo bzevet

i 364 254.

  The configuration of the invention makes it possible to read

  data stored in memory at jrp rate

  less than that to which the data has / written in the memory. Similarly, it can be seen that the data can be read at the same rate or at a faster rate.

slow than the writing rate.

  A modified version of the configuration of

  the invention makes it possible to obtain Doppler images. An au-

  be modified version allows to obtain images in

their.

  A main object of the invention is to realize

  be a real-time ultrasound ultrasound system

  including a time reversal memory.

  Another important object of the invention is to provide a time ultrasound ultrasound device.

  real which reduces the granularity configurations.

  Another object of the invention is to reduce the time necessary to acquire a data frame. We

  can use many ways the increase re-

  resulting from the information bandwidth, such as to increase the time resolution, to

  reduce parasites from granularity, and / or to -

  get DorSpler images in real time.

  Another important object of the invention is to provide a time ultrasound ultrasound device

  real including a network of reconstruction transducers

  tion and a reconstruction environment, in which data

  born corresponding to electrical signals produced by

  echoes are read from a memory in a corresponding order

  laying down to an inversion in time and with a cadence equal, superior or inferior to the cadence at which

  the data has been written to memory.

  The invention also aims to achieve

  a real-time ultrasound ultrasound system

  taking a memory from which electrical signals produced by echoes are read in an order corresponding to an inversion in time, and with a cadence necessary to form an isochronous image

in a reconstruction environment.

  The invention will be better understood on reading

  the description which follows of embodiments, gives

  born without limitation. The rest of the description is

  refers to the accompanying drawings in which: Figure 1 is an electrical block diagram of a preferred embodiment of the invention;

  Figure 2 is a block diagram of a part

  tie of the configuration of Figure 1; Figure 3 is a diagram of another part of the configuration of Figure 1; Figure 4 is an electrical block diagram of another embodiment of the invention; Figure 5 is a diagram of part of the embodiment of Figure 1; and

  FIG. 6 is a diagram showing a modification

  cation of a part of the embodiments shown

in Figures 1 and 4.

  We will now refer to the drawings on the-

  which Figure 1 shows an electrical block diagram

  stick of a preferred embodiment of the invention, intended for pulse ultrasound. A network 1

  electroacoustic receiver elements 10 is in

  acoustic range with an object to be examined. Element 12,

  At the same time, the network is a transmission element or an element.

  transmission / reception ment. Although in the figure the

  ment 12 is placed in the middle position in the network, this eminent can be placed at one end

  either side of the network, anywhere

  termrdiary, or even remote from the network 1. The transmitting element 12 is preferably placed at a position

  in which the emitted ultrasonic energy is not blocked -

  qu4e by a non-emitting element. For example, if lob-

  jet to be examined is a human heart, the & emenllt 12 would be placed in a clear position in relation to a rib or

  to a costal cartilage. In one embodiment,

  the network 1 comprises 32 to 100 elements 10.

  A clock 14 applies trigger pulses

  at a pulse generator 18, at Lue frequency which

  depends on the speed of sound in the object and the depth

  maximum value to be examined in the object. The repetition frequency of the trigger pulses is typically in the range from Hz to 2 kHz, and in the case of a cardiologic examination

  for an adult or abdominal ultrasound, the frequency

  preferred frequency is about 1 kHz. The image generator

  impulses 18 in turn applies pulses of excitation

  emitting element 12. The emitting element 12 con-

  the excitation pulses from the genera

  pulse generator 18 in energy emission pulses

  which are sent cyclically in the object to be examined

  ner, usually so as to illuminate a complete plan

  of the object to be examined. Meeting a discontinuity

  acoustic tee or border in the object (again

  called reflector or diffuser), a party of the energy

  gie of the ultrasonic emission pulse is retrodif-

  rocket to receiving elements 10 in the form

  echo signals. The receiving elements 10 conver-

  weave the echo signals received into electrical signals

produced by echoes.

  The electrical signals produced by the echoes are applied to a respective amplifier among high frequency amplifiers 20 associated with each of the

  network receiving elements 10.

  A first gain compensation circuit as a function of time, 22, applies to each high frequency amplifier 20 a compensation signal intended for

  adjust the amplifier 20 in such a way that

  mgme level echo signals from se reflectors

  found at different depths in the object exa-

  mined have the same amplitude at the output of the amplifia-

  high frequency generator 20. The structure of the

  gain compensation as a function of time is well con-

  naked. The output signal of each amplifier 20 is applied, as a function of time, to. unlenmoire 24, and

  each output signal is written simultaneously in the same

  moire 24, depending on the tempse According to memory 24 par-

  particular that is used; an analog converter -

  digital and / or a driver amplifier may be in-

  tercalé in the circuit between the amplifier 20 and the

moire 24.

  Although memory 24 is represented on

  i0 the drawings in the form of a discrete memory associated

  ciee each element 1 0, a real structure usually includes a memory of which separate parts are

  associated with each item. to record and read if-

  simultaneously data associated with each element res-

reception network.

  When the signals from each element

  network reception 10 are stored in the

  moire 24, as a function of time, the data is read from the memory in an order corresponding to an inversion

  in time, and in parallel for each element 10.

  Thus, the last signal written in memory 24 asso-

  ciée to each element 10 is the first signal read, and so on. Signal data is written to

  memory 24 for the time necessary for a Si-

  general echo reflected by a reflector located at the maximum depth in the object examined reaches the reception elements 10 and is written in the memory 24 & The reading speed can be 8tre higher less than or equal to the writing speed La speed

  reading is set as described below

  after, depending on the reconstruction environment and according

  that the image to be created is an isochronous or anisochro-

born.

  Data from the strongest echoes

  ches from the receiving network are received, processed and

  stored first in memory. The pro data

  coming from discontinuities which are at the point furthest from the object to be examined are received, processed and recorded in the Côn ernier memory. To reconstruct the image in the reconstruction environment 30, the fronts

  waveform and images from the most distant points

  problems with the network must be issued first in the reconstruction environment. This principle appears most clearly in the case of an isochronous imaging configuration. To obtain an isochronous image, the last data recorded in the memory 24 must be the first data read and transmitted in the reconstruction medium. This temp inversion principle is

  of great importance in the invention, as we ex-

will detail below

  In the case of the formation of an animated image

  sochronous, the principle of time inversion is also

  important because a diffuser (or reflector) differs

  fuses the ultrasonic energy in all directions

  cidente. Fractions of the scattered energy arrive at different times at different elements of the network

  because of the different lengths of dhe-

  min between the diffuser and the respective elements of the

  bucket 10. By applying to the elements of the network of rec-

  truction 26 of the data signals inverted in time,

  re-emitted signals will follow in the reconstruction environment

  30 paths converging at pre-

  feeling in relation to the reconstruction network 26 the same

  relate to me that the locations of the diffusers compared

  port to the reception network 10o It is the desire to meet

  truire the diffusers in the reconstruction medium 30 which requires the use of the inversion principle of

time.

  The inverted output signal in the% nips of the

  memory 24 is applied to the elements 27 of the network of

  construction 26 by means of attack circuits

  as respective 28. The elements 27 emit acoustic energy signals in a reconstruction medium 30 under the effect of the inverse time signals applied to them. A second time-dependent gain compensation circuit, 58, applies

  compensation to driver amplifier circuits 28 res-

  pective, to compensate for the inverted output signals over time in order to take account of the energy dispersion which manifests in the reconstruction medium 30, so that equivalent level reflectors located at different distances in the reconstruction medium 30

  are represented by equivalent pressure amplitudes

  Depending on the particular memory that is used, a digital-analog converter can be inserted in the circuit between the memory 24 and the driver amplifier 28o Acousto-optical conversion means are associated with the reconstruction medium 30 to form an optical image configurations of acoustic energy emitted in the medium 30 by the elements of the network 26e If the reconstruction medium is an optically transparent medium, such as for example water or a

  gas in a tank, we can use a Schlieren system.

  If the reconstruction medium is an optically medium

  opaque, like a solid consisting of a piezoelectric crystal

  rod or a crystalline metal, we can use a Sokolov tube, a Bragg refraction device, or a

  interferometer. Converting an energy configuration

  acoustic sound in an optical image is well known and is described in the patents as well as in the aforementioned Biomedical Ultrasonics book.

  In the case where the reconstructed image is iso-

  chrone, which requires a single pulse of light, -0 coming for example from a pulse laser or a flash lamp in a Schlieren system to form the image, as in the case where the image is anisochronous and where the midpoint of reconstruction is scanned by a light source, the acousto-optical conversion means are synchronized with the triggering pulse by means of a delayed clock signal coming from a

  delay 34. The optical image provided by the communication means

  acousto-optical version 32 is applied to a device 1 0

  display 36. The display device 36 can present

  ter a video image by means of a vidicon tube or a

  screen, to allow direct observation of the pro-

  coming from the acousto-optical conversion means 32.

  The reconstruction medium 30 can be a solid, a liquid or a gas. A gas, like air, offers the advantage that the size of the image and of the acousto-optic means can be reduced by factor

  of three, compared to water, but it presents the in-

  corresponding convenience consisting in that the reconstruction network 26 must be made with dimensions

  much lower than those of the reception network 11.

  After having generally described a preferred embodiment, we will now consider FIG. 2 which represents a detailed block diagram of a

  channel of the previous configuration. Note that each

  that element 10 of network 1 has an associated channel.

  The received echo signals are converted by a respective receiving element 10 of the network into electrical signals produced by the echoes which are applied to

  a preamplifier 40. The output signal of the preamplifier

  ficitor 40 is applied to an amplifier 44 which amplifies

  relies on the output signal from the preamplifier 40 and which

  on distance compensation to take into account

  the attenuation of the echo signal as a function of the depth

  this compensation is effected by means of a time-dependent gain compensation signal which comes from the time-dependent gain compensation circuit 22. The output signal of the amplifier 44

  is applied to a driver circuit 46.

  Because in the embodiment of the

  figure 2 memory 24 is a memory device vi-

* ve with selective access, an analog converter - nu-

  meric 48 is connected-in the circuit between the circuit

  bake 46 and memory 24. Note that for other memory devices, such as analog devices, for example a charge coupled device, the analog-to-digital converter 48 is useless.

  The 48 ap analog to digital converter

  sequentially plots digital data in memory 24

  that correspond to the echo signals received by the

  respective 10. The duration during which the signals are received, processed and recorded in memory 24 is determined as a function of the maximum examination depth desired in the object examined. Note that the process

  recording takes place simultaneously for each element

ment 10 of the receiving network.

  In addition to the function of applying trigger pulses to the pulse generator 18 and synchronization pulses to the delay circuit

  34, to synchronize the acousto-conversion means

  optics 32, the clock 14 applies a pulse to a

  delay circuit 50. The delay circuit 50 is adjusted so that a reversible counter 52

  starts counting at a predetermined time after ltap-

  application of a trigger pulse to the transmission element 12. The reversible counter 52 acts as an address sequencer for the random access memory

selective 24.

  The counting rate by the reversing counter

  sible is determined by the connection of the clock 51

  or from the clock 53 to the reversible counter 52, by the

  term of a switching element 55. The counting direction, the counting rate and the operation of the random access random access memory in data write mode or in data read mode are all

  determined by a control unit 54.

  The clock 51 supplies pulses at a high frequency which is typically a frequency in the range between 10 MHz and 100 MI4z. When the reversible counter 52 counts in a

  first sense, the digital output data from the con-

  analog - digital pitchers are saved in a

  the random access memory / selective access 24 at an address position

  which is determined by the account which is presented at the output of the counter 52. After all the data have been recorded in the memory 24, a signal coming from the control unit 54 connects the clock 53 to the counter 52,

  which causes the reading of the data in the memory vi-

  ve with selective access 24 and counts the reversing counter

sible 52 in the opposite direction.

  In the preferred embodiment, the fre-

  quence of the clock 53 (reading rate) is adjusted so that the data are read from the memory 24 and the acoustic energy is emitted by the associated element 27

  in the middle of reconstruction-30 at an appro- priate rate

  required to form an isochronous image. Settling

  the frequency of the clock 53 on any other value

  causes an anisochronous image to form in the mid

reconstruction site 30.

  To properly set the cadence of

  reading, we will first assume that the speed

  reconstruction middle tick is the same as that

  of the object to be examined. In this case, the cadence of lec-

  ture will be equal to twice the writing rate. In

  considering figure 5, the time required to receive

  see an echo from a point in the object being examined and

  to reconstruct this same point in the middle of recons-

  truction is expressed as follows: T -2 dx / Vo + X / Vr ^ R + dX / Vr R

  In this expression, T is the time necessary for

  record data from maximum depth

  le to be examined, dX is the distance between the center of the

  bucket 1 and point X in the object, as well as the distance

  between the center of the network 26 and point X in the middle

  place of reconstruction; Vo is the acoustic speed in the object examined; Vr is the acoustic speed in

  the reconstruction environment; and R is the cadence of lec-

  ture. On the other hand, the time necessary to reconstruct a point Y in the reconstruction medium 30 is: T - 2y / Vo + dy / vr R by designating by dy the distance between the center of the network

  1 and point Y in the object to be examined, as well as the

  tance between the center of the network 26 and the point Y in the reconstruction medium. This analysis is simplified insofar as we consider only a transmission / reception element and a reconstruction element, and insofar as the points

  X and Y are located along the common axis which is recognized

  trout. We can show that we get similar results

  areas with off-axis points and multiple element networks. We present the simplified analysis for the purpose

  describe the general principle involved.

  The time intervals T - 2dx / Vo and RT - 2dy / V are the time intervals necessary R to read in the memory 2 'the data recorded for the respective points X and Y. The quotients dX / Vr and d / Vr are the time intervals required for training

  points X and Y in the reconstruction medium.

  To obtain an isochronous image in the middle

  reconstruction site 30, all points must be formed at the same time. We must therefore have the following relation for an isochronous image: T - 2dx / VO T - 2d / Vo R + Il / r = R y / Vr We will initially assume that the acoustic speed in

  the object (Vo) and the acoustic velocity of the medium of re-

  construction (Vr) are equal, that is, we have Vo = Vr, and we will also assume that the dimensions of the object examined and those of the reconstruction medium are equal. Under these conditions, solving the above equation for any point3X and Y shows that R must be equal to two. Consequently, the rate at which the data is read from the memory 24 and 14 applied to a reconstruction medium 30 having the same

  acoustic speed and the same dimensions as the object examined

  mined is equal to twice the writing rate.

  With regard to the reconstruction of the points placed off axis, we see that the length of the starting path

  of the central emission element 12, going up to the reflective

  and returning to the receiving element, differs from the length of the path in the reconstruction medium between the element of the reconstruction network and the reflector from which the image is formed. We will assume that the acoustic speed and that of the reconstruction medium are practically equal and that the data subjected to time inversion

  are read at twice the rate of writing.

  Under these conditions, by mutually separating the juxtaposed elements 27 of the reconstruction network from a distance

  equal to half the distance between the jux- elements

  tapped 10 of the receiving network, the distortion due to the different lengths of the acoustic paths in the

  respective backgrounds can be reduced in the far field-

  tain, that is to say for points located far from the network

  reconstruction 26. In the near field, that is

  say for points closer to the network of recon-

  truction 26, there is a distortion. This distortion re-

  sults from the desire to obtain isochronous images. We can

  vary the empirical spread slightly

  between the juxtaposed elements, from the gap

  half, in order to reach a compromise between

  distortion of the image in near field and in far field-

damn.

  In the case where the object and the medium of re-

  construction have the acoustic speed rhyme, and in the-

  which the reading rate is taken equal to the rate

  writing, the reconstructed image does not have the

  near field torsion mentioned. The resolution

  near field improvement has training as a counterpart

  of an anisochromatic image instead of an isochronous image.

  ! 5 In the case of isochronous images as anisochronous images, one can use a reconstruction medium having an acoustic speed different from that of the object examined, to change the size of lti. reconstructed image If the reading speed is constant and if all the di-

  reconstruction network menses feels changed proportionally

  tional to the wavelength of the ultrasound in the reconstruction medium, the ratio between the size of Ilimage in the reconstruction medium and the size in 3 V object examined will be equal to the ratio fVoo _ shown in Figure 2, we see that the data read in the random access memory 42

  are applied to a digital coin converter - analogi-

  that 56 (if a random access memory is used for the memory device; however, the digital to analog controller is useless if a di: positive memory analog is used as a memory device

  charge coupled memory) The second com-

  thought of gain as a function of time, 58, co-orders the

  gain of the driver amplifier circuit 28 to compensate

  ser the output signal from the digital converter ana-

  logic 56 in order to take into account the dispersion of the disadvantage-

  in the reconstruction environment 30 con-ne described above

above.

  Although the above description relates to

  a memory device of the random access memory type s-

  can also be used with a

  load range which sequentially records values

  their analogs and provides analog output signals in an order corresponding to a time inversion. So the last recorded signal is the first

  signal presented as output Random access memory

  tif may be replaced by means of registration

  magnetic or acousto-optical means9 such as li-

  acoustic delay genes and a reading device with

  laser. The necessary modifications to the mode of realization

  tion of Figure 1 to use a memory device

  re equivalent to $ 7, such as deleting lin-

  1 6, troduction -les dompes au, novrni D'ôu] siLial d rlor lodge when using an analogical menoLire device.,

  will clearly appear in the art Vhommai.

  Acou1sto-optiqu coiversion- ntOus images-

  Reconstructed ticks can be done by any known process, Danas a preferred mode of realization dan.-ls

  which the reading rate is set t Ir-

  sea an isochronous image, as described above, the mo-

  yen dle acousto-optic conversion 32 consist of

  preferably by a laser Sehlieren device working-

  coming in impulses. A Schlieren laser device

  with scanning can be used for anisoclastic images

  nes. Of course, you can also use liffrac-

  Bragg tion, interferometry or polarization filters

  cross station, depending on the reconstruction medium.

  Each of these techniques is known, as follows for example from the aforementioned patents, from the book Biomedical úLtrasonics

  or from the Jlanstead article mentioned above.

  Figure 3 shows a method of using a Schlieren device to perform the conversion.

  acousto-optics. A laser or a light source

  tapping cn pulses, 62, produces a pulse of lu-

  miere which crosses mie converging lens 66, and is

  then directed towards a divergent lens 68 and a mid

  concave roir 70. The parallel beam of light piove-

  from the mirror 70 passes through the reconstruction medium. 30

  in a direction which is generally perpendicular to

  area to the direction of acoustic energy 6 put in

the middle 30 by the network 26.

  - After going through the reconstruction environment-

  tion optically transparent 30, the light beam is reflected by another concave mirror 72 and brought to a

home in a plan 74.

  The lens which is diffracted / the coirig-rapa-

  acoustic conditions formed in the reconstruction environment

  tion 30 travels different distances we cross: sant the rest of the system, that is to say an element of ecultation in the plane 74 and a lens 76, to reach a

  vidicon 78. The output signal from vidicon 78 is applied

  than the display 36. The diffracted light and the non-diffracted light interfere with each other to produce an image of the acoustic configuration in the plane 75. It is possible to modify the image by placing

  various filters in the Fourier 74 plan.

  Although the lenses are represented as simple single elements, all or part

  of them can be in practice multi-lens

  elements, to contribute to the precision with which the light rays are directed and focused to form

it final image.

  We can reduce the physical size of the con-

  figuration of Schlieren using mirrors to

fold the light path.

  Of course, if the reconstruction environment

  is optically opaque, we can use other tech-

  acousto-optic cojnversion niqus, as it was

indicated previously.

  The configuration of Figure 3 is before-

  when using a working laser

  coming in impulses. More precisely when isochronous images are formed in the reconstruction medium, the instant of appearance of the light pulse is synchronized by means of the delay circuit 30, so

  to produce a pulse of light which illuminates the mid

  place 30 at the time when the acoustic image is formed.

  According to a variant, if we create images

  anisochrones, we first form the images with lvex-

  middle hopper 30 which is furthest from the re-

  bucket 26, then at locations closer to the

  bucket 26. Known scanning means, such as those

  described in the aforementioned US Pat. No. 4,174,634, can be used to scan the medium with the laser,

  in synchronism with the formation of the image. The ba-

  layage is usually done in the form of cer-

  keys with radii that decrease as the scanning of the reconstruction medium approaches 1 8

  elements 27. The light beam is controlled in a

  optical, electrical or mechanical lesson, in order to scan the

  reconstruction environment in synchronism with the location-

  ment to which the image is formed in the middle of recon-

  truction (see the aforementioned US Pat. No. 4,174,634). According to yet another variant, due to the large quantity of images formed per second (equal to the

  repetition rate of the trigger pulses

  coming from the clock 14) it is possible to make

  that each laser pulse illuminates parts or sections

  selected teurs of the reconstruction environment, instead of illuminating the entire reconstruction environment with

a single laser pulse.

  As is the case with a laser operating in pulses, it is possible to scan the middle of

  reconstruction by narrow sectors, instead of the ba-

layer by lines.

  According to another variant, the ultrasonic signal

  our emitted can come from several transmitting or transmitting / receiving elements placed in different locations,

  either along the network or at a distance from it.

  The purpose of using several sources of transmission signal is to modify the configuration of granularity from one frame to another in the visual image. Because

  that the frame rate is high, the eye does the

  ne of a large number of frames for each image perceived.

  As a result, the changing granularity configuration

  is canceled out by the average effect while the confi-

  fixed guration which results from the reflectors located in

the object is reinforced.

  The use of ultrasonic signals pro-

  from multiple sources does not affect processing

  electrical signals produced by echoes, in particular

  particular with regard to the time inversion of

recorded data.

  We can minimize the granular configuration

  larity by changing the position of the transmitting element for successive pulses, or by changing the

  frequency of pulses emitted. It is easier to change

  manage the frequency that the change in the position of the emitting element is in fact unchangemnelt of the origin of reconstruction, which causes a change in the configuration of laser scanning (aniso-

  chrone) or a switch to other elements of the re-network

mission (isoclhrone image).

  Those skilled in the art will appreciate that the trans-

  ductors 10 can be made up of emissive elements

  sion / reception instead of: Stre constituted by elements functioning only on reception and by a single element dem'1i3s.onio It is also possible to cause the transmission elements in the manner of a phase network

  to change the focal area and / or directivity of the lens

  ultrasonic seal emitted It is also possible to emit

  to be a beam of exploration to examine the

  whole age or examine a narrower section than one

  can be moved or scanned to deexa-

  undermining the entire image plane with several exploration pulses The reception network 10 can consist of a single linear network, of several network segments or of a two-dimensional network0 In addition, the reception network can comprise several rows of 'elements

  to facilitate dynamic focusing in the direction

  tion perpendicular to the scanning plane.

  Figure 4 shows a modified version of the

  embodiment of FIG. 1, useful for measurements

  Doppler type sures. Ultrasonic energy is emitted

  in the object to be examined via a trans-

  emission conductor 80 which is distant from the elements of the reception network 10O A transmitter 82 operating in continuous waves excites 1 transducer element 80 so

  to emit ultrasonic signals into the object to be examined

  nore narrow band, in continuous waves o According to a

  variant, narrow band excitation can be obtained

  naked by impulses of long duration, instead of if-

  gnauc on CW. The echo signals received by the elements 10 are converted into electrical signals

  produced by the echoes and they are applied to amplifiers

  high frequency crackers 20. The gain of an amplifier

  is adjusted by means of a compensation signal

  tion from a gain compensation circuit in

  function of time, 22, to make sure that if-

  signals from reflectors of the same value located at

  different depths in the object have the same magnitude

  plitude at the output of the amplifier 20. The output signals of the amplifiers 20 are applied to associated crevice filters 84. The crevice filter 84 separates the Doppler frequency offset signals from the electrical signals produced by the echoes and subjected

  compensation for gain as a function of time. The if-

  general filtered present at the output of the crevice filter 84 is recorded in the memory 24 and it is retransmitted by the reconstruction network 26 in the same way as the pulse echo signals described above. The reconstruction medium only forms the image of the Doppler signal, instead of forming that of the signals

  pulse echo. The modified embodiment fone-

  Furthermore, it operates practically in the manner described above. An important difference from the pulse echo technique is that the

  emission transducer 80 emits ultrasonic energy

  nore narrow band in CW in the object

  which is being reviewed. Because we use ultra-

  stored in CW, memory 24 can be programmed to start recording at any time and continue recording for an interval of time necessary for signals from the maximum depth to be received, processed and saved. Once the data recording is completed, the recorded data is read in the sequence corresponding to the inversion of

* time, as described above.

  In a variant of the configuration described, it is possible to write data for a period of time

  much shorter than the frequency period cen-

  1lutrason, and read the data repeatedly

  titive, with time inversion, until the wave fronts have propagated to the maximum depth of the reconstruction medium.

  In a modified version of the embodiment

  tion of Figure 4, we compute the Fourier transform

  data signals, for example by means of a device

  sitive performing the fast Fourier transformation, and it is saved in memory. The recording of the

  Fourier transform reduces the volume of data to

  register and delete the crevice filters 84, if you

  neglects the spectral components close to the frequency

  central frequency of the emitted ultrasound After having recorded

  recorded the Fourier transform data without the data relating to the spectra close to the frequency

  central, we easily synthesize the corresponding signals

  responding to the time reversal, from the data

recorded spectral data.

  It is well known that when using Doppler techniques, it is essential to align the emission and reception transducers so that the length of the path associated with a movable reflector

  presents notable variations under the effect of the

  reflector. To achieve the highest sensitivity for echo signals from circulating blood cells, regardless of the direction of circulation, it is advantageous to use multiple emission transducers placed at a distance from the

  reception network. The different emission transducers

  can be excited sequentially or simultaneously

  nement. If the transducers are placed correctly, in a known manner, a velocity vector from any direction produces a large Doppler shift

  and easily detestable in the electrical signal pro-

smelled by echoes.

  In the pulse echo configuration as in the Doppler configuration, the reception network can have any shape, straight or curved. The

  reconstruction network must have a form linked to it

  the receiving network so that the re-emitted wave fronts reconstruct the configuration of diffusers. It is even possible, as shown in Figure 6, to do

  so that the shape of the receiving network is regulated

  ble to conform to the outline of the object which is exa-

  mine. In FIG. 6, the reception network comprises, for example, two rectilinear segments lt and 1 "joined by a hinge 80. Similarly, the reconstruction network comprises two rectilinear segments 26 'and 26" joined by a hinge 82. We can use

  electrical means intended to maintain the same rela-

  spatial tion between network segments, such as a

  servomechanism comprising an angle sensor 86 which

  applies a feedback signal representative of the angle between the segments to a servo amplifier 90

  1t and 1 "mains. The output signal from the amplifier

  servo tor 90 is applied to a servo motor 88 to adjust the angle between the segments 26 'and 26 "which are coupled to the servo motor 88. The segments are coupled to the servo mechanism so that the angles A are identical in the receiving network and in the reconstruction network. In the embodiment considered, if we assume that the reconstruction medium

  consists of a tank filled with water, the network of

  construction is placed in the tank full of water.

  When reconstructing an image in the mid-

  reconstruction place 30 it occurs some

  distortion. The ultrasonic emission pulse is emitted.

  itself, for example, by the transmission element 12 which is

  placed in the middle position in network 1. The distance

  what the ultrasonic pulse travels from the element

  ment 12 to a reflector and then reflector

  up to an element 10 of the receiving network, is

  different from the distance the signal is traveling

  trout from an element of the reconstruction network 26

  up to the reflector whose image is formed in the middle

  place of reconstruction 30. This distortion is more

  apparent in the near field. In the far field, the diff-

  the length of the paths becomes negligible. To try to compensate for this difference in

  path length, it is possible to give the elements

  27 of. reconstruction network a profile such that they emit elliptical wave fronts instead of fronts

  spherical wave. The focal points of the ellip- wave fronts

  ticks intended to simulate the length of the path from the center

  from the network to the reflector and then to a receiving element are the position of the element

  reception and the center of the reconstruction medium.

  This results in better near-field resolution.

  In the far field, ellipses degenerate into circles

  and do not bring a significant improvement in the reso-

image playback.

  According to another modification of the configuration

  tion, the transmitting transducer located at a distance can be oriented so that the emitted plane wave propagates

  in a direction perpendicular to the image plane.

  This modification allows the sound field to light up

  at the same instant the whole plane of the image. Lehom-

  Those skilled in the art will note that under these conditions, the fact of retransmitting with time inversion the data of electrical signals produced by the echoes, in a reconstruction medium having the same acoustic speed as the object examined, gives isochronous images without use an increased rate of data reading o In this case, the reconstruction network must have the

  same dimensions as the reception network.

  It is also possible to provide a pre-

  color feeling, especially when using

  Doppler techniques to represent the circulation

  blood lation. Among simple techniques for

  create a presentation in color, we can cite the

  reading of a colored structure covering an image

  black and white echo, or the use of three

  emission pulse frequencies, applying the ima-

  ges from a first frequency to a barrel of a color video receiver, the images corresponding to a second frequency to another barrel of the receiver and the images corresponding to a third frequency at

  third barrel of the receiver. A review can be found

  carved out of a process for obtaining such a presentation

  tion in color in US Patent 3,156,110.

  We have just described and represented a mo-

  preferred embodiment of a pulse ultrasound device using a reversal memory of

  time and a Doppler ultrasound device used

  having a time inversion memory, as well as

  various variants and modifications of these devices,

  but it is evident that many other modifications

  cations can be added to the devices and methods described and shown, without going outside the scope

of the invention.

Claims (7)

  1. Ultrasound ultrasound system, characterized   in that it comprises: transducer means (12) which   designed to be coupled to an object to be examined, to emit ultrasonic energy into the object; a network of reception transducers (1) which comprises several juxtaposed reception elements (10) placed so as to receive echo signals which appear when   ultrasonic energy meets acoustic reflectors   located in the object, and converting these echo signals into electrical signals produced by the echoes; a   memory (24) connected to the network of transducers of   ception (1) so as to record sequentially, while   function of time, data linked to electrical signals   that produced by the echoes that are associated with each   receiving element (10), and providing this data to-   recorded in an order corresponding to a time inversion with respect to the sequential recording, a reconstruction medium (30) which conducts the ultrasonic energy signals and in which a   acoustic image; a network of recon transducers   truction (26) which comprises several juxtaposed emission elements (27) which are connected to the memory (24) and are coupled to the reconstruction medium (30) so that these emission elements emit in the reconstruction medium (30 ) signals of ultrasonic energy under the effect of the signals subjected to a time inversion which are supplied, in order to form a reconstructed image of the acoustic reflectors; means of conversion   acousto-optics (32) which are coupled to the re-   construction in order to convert the acoustic image recons-   trout in an optical image; control means (54) which are connected to the memory (24) so as to control the rate of data recording and the rate of   read data in the order corresponding to an in-   time version; and display means (36) which are connected to the acousto-optical conversion means in order to to represent the optical image.   2. Ultrasound ultrasound system according to the res   dication 1, characterized in that the transducer means   tors (12) emit ultrasonic energy into the object by emitting ultrasonic emission pulses into the object.   3. Ultrasound ultrasound system according to the res   dication 1, characterized in that the transducer means   torers (12) emit ultrasonic energy into the ob-   jet by emitting an ultrasonic signal in continuous waves into the object, and crevice filtering means   (84) are connected to the network of receiver transducers   tion (10) so as to receive the electrical signals   produced by the echoes, to form an output signal re-   presentation of the Doppler frequency shift of the electrical signals produced by the echoes, and to apply this   memory output signal (24).   4. Ultrasound ultrasound system according to the res   dication 1, characterized in that the transducer means   teurs (12) emit ultrasonic energy into the object by emitting into the object an ultrasonic signal in the form of a narrow band pulse, of long duration,   and crevice filtering means (84) are connected   tees to the receiving transducer network (10) in order to receive the electrical signals produced by the echoes, to form an output signal representative of the Doppler frequency shift of the electrical signals produced by the echoes, and to apply this output signal to the memory (24).   5. Method for obtaining an optical image in   an ultrasound ultrasound system, c a r a c t e r i-   s in that: ultrasonic energy is emitted into an object to be examined; receiving echo signals which occur when ultrasonic energy encounters an acoustic reflector in the object, and converting these echo signals into electrical signals produced by the echoes; we record data related to signals   electrics produced by the echoes, in sequential order   tiel in which these signals are received - we read the data -   data recorded in an order corresponding to an in-   time version; under the effect of the data read and   set to time inversion, energy signals are emitted   ultrasound in a reconstruction medium, to form a reconstructed acoustic image of the reflector   acoustic 5 and we convert this acoustic image built into an optical image.   6th Method for obtaining an optical image according to claim 5, characterized in that one emits   ultrasonic energy in the form of pulse   if we. 7. Method for obtaining an optical image according to claim 5, characterized in that it emits   ultrasonic energy in the form of ultrasonic signals our on-air waves.   8. Method for obtaining an optical image according to claim 5, characterized in that it emits   ultrasonic energy in the form of ultrasonic signals   ours consist of narrow band pulses and long term.   9. Method for obtaining an optical image   according to any one of claims 7 or 8, charac-   terified in that a signal representative of the Dopplet frequency offset of the electrical signals is produced   produced by the echoes that are recorded in the gold-   dre sequential in which they are received.