Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52046—Techniques for image enhancement involving transmitter or receiver
  • G01S7/52049—Techniques for image enhancement involving transmitter or receiver using correction of medium-induced phase aberration
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/18—Methods or devices for transmitting, conducting or directing sound
  • G10K11/26—Sound-focusing or directing, e.g. scanning
  • G10K11/34—Sound-focusing or directing, e.g. scanning using electrical steering of transducer arrays, e.g. beam steering
  • G10K11/341—Circuits therefor
  • G10K11/346—Circuits therefor using phase variation
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2200/00—Details of methods or devices for transmitting, conducting or directing sound in general
  • G10K2200/10—Beamforming, e.g. time reversal, phase conjugation or similar

Definitions

• Therapy device for the destruction of a target by acoustic signals comprising a time reversal
• the invention essentially relates to a therapy device for the destruction of a target by acoustic signals comprising a time reversal.
• acoustic must be taken in a general sense, without limitation to the audible frequencies.
• the therapy device of the invention makes it possible to identify and destroy targets present on or in the tissues of living beings, in particular mammals, preferably an animal or a human being, these targets having an acoustic independence different from that from the surrounding environment.
• the invention is applicable in therapy:
• the movements may be due, for example, to the patient's breathing. They may also be due to operator movements in the case of a hand-held device.
• the new signals reflected by said medium are memorized and the time reversal operation is repeated.
• a small number of iterations suffices to show only the signals reflected by the most important reflector in the medium or by the most reflecting point of an extended reflecting target, in the form of a set of signals having a maximum pronounced on each of the reception channels each corresponding to one of the transducers of the network.
• the time distribution of the signal maxima is stored for later use.
• the timing of the signals is determined by intercorrelation between pairs of signals. The latter solution however requires heavy calculations. Either solution does not directly give a directly interpretable indication of the location of the target or targets present in the environment.
• the present invention aims in particular to provide a device for detecting, monitoring and insonifying, that is to say, concentrating acoustic energy, of a target as defined above, responding better than those previously known to the requirements of practice, this device being in particular particularly suitable for carrying out therapy for the destruction of said target.
• the invention aims in particular, although not exclusively, to solve various problems related to the technique of time reversal as defined above.
• this time reversal had only been envisaged to cause an autofocusing which results in an optimal focusing of a transmission in the presence of a target.
• the method was intended to create maximum sound pressure at the location of the target.
• it remains necessary or at least desirable to locate the target in space, once the presence of a target has been recognized.
• it is often desirable to characterize the previously detected target by forming an ultrasound-like image before destroying it as part of said therapy. This makes autofocusing necessary at reception.
• the method defined above if it gives favorable results, has in return a limitation when one wishes to increase the number of iterations: the echographic signals become longer and longer as the we repeat the time reversal sequences, this which results in a loss of axial resolution detrimental in some cases to the quality of the images.
• the invention starts from the observation that in the presence of a reflecting target, in the zone selected by choice of a time window, an odd number of time reversals gives rise, on each channel, to an echographic signal of symmetrical shape, having a maximum corresponding best to the location of the wavefront due to the reflection on the target, or in other words to the surface of this acoustic wavefront.
• the invention applies this new principle to therapy, in particular in the context of a therapy device, but also in the context of a method of therapeutic treatment which immediately appears to those skilled in the art from of the description of the therapy device as well as of the method described.
• the invention provides a therapy device for the destruction of a target present on or in the tissues of living beings in particular mammals, preferably an animal or a human being, such as stones. in the tissues, in particular the kidney, the gall bladder, the bladder or the urethra, or a tumor comprising means of detection and destruction comprising:
• the locating means further comprise: - means for determining the maxima of the signals received after an odd number of iterations.
• the therapy device comprises writing means and reading means of the aforementioned storage means and connected to calculation means.
• the therapy device is characterized in that it comprises means for calculating the position of the target from the time delays of the aforementioned maxima.
• the therapy device is characterized in that it comprises calculation means for selecting a time window of duration T containing the part of the echo signal corresponding to the target, collected by the transducers of the matrix, the aforementioned storage means only storing the signals contained in said time window.
• the therapy device according to the invention is characterized in that the abovementioned calculation means look for the spherical wavefront representing at best the delays of the maxima of the signals received.
• the therapy device is characterized in that the abovementioned calculation means determine the center of the sphere thus obtained and considers that this center represents the position of the target.
• the therapy device is characterized in that it comprises amplifying means producing a very strong amplification of the signal applied to each transducer, for the treatment of the aforementioned target.
• the aforementioned amplifying means are coupled to delay application means corresponding to the focusing of the signals at the center of the aforementioned sphere for the processing of the target.
• the therapy device is characterized in that it comprises means for summing the signals reflected in the aforementioned time window.
• the means of emission / reception / reversal, memorization and calculations make it possible to create delays of the signals emitted such that the matrix of the transducers emits a succession of offset wave fronts, focusing near the target and are capable of move the focus point by correcting the delay values.
• the aforementioned circuit and the aforementioned calculation means offset the received signals according to a determined delay value and a summation of these signals received over the entire matrix of the transducer.
• digital reception memories are assigned to each channel, that is to say to each transducer used at reception, and the instants of arrival of the signal maxima on each transducer are determined by scanning the contents of the successive addresses of the memories assigned to the samples.
• the time delay law can be used to re-emit a new illumination wavefront by emitting signals of the same shape on all channels and of very short duration, at a time defined for each transducer by the complement of the law of distribution of the maxima, the first maxima corresponding to the signals which will be emitted last.
• the invention makes it possible in particular, once a target has been located, to synthesize an intense ultrasonic beam converging towards the most reflecting point of the target or towards an area to be treated situated around this point, which can be materialized by an echogenic marker, by example by scanning as described in the prior document of the applicant FR-A-2 686499, which is incorporated here in its entirety by reference, in particular in the case where it is sought to destroy this target or to treat the surrounding area, which is the case in therapy.
• the temporal delay law obtained can also be used to sum all the reception signals after having readjusted them by application of the delay law, over the entire duration of the temporal window. It is thus possible to synthesize the optimal wave surface, then subsequently perform a focusing in transmission and / or in reception.
• the determination of the relative position of the maxima and the readjustment of the signals in transmission and / or in reception should in general be carried out only if one has firstly noted the presence of an edge wave from a target in the window where the measurement, then the time reversal.
• the time reversal window is chosen to correspond to the interesting parts of the medium to be explored.
• the window can be known a priori, which is for example often the case in therapy where a target has been previously identified by ultrasound or X-ray. It can also be determined by roughly evaluating the flight time corresponding to the selected target . The location and width of the time window are chosen so that the signals due to reflection or diffraction on this target are certainly included in the window. One can also, as for example in the search for defects in a material of great thickness, divide the depth of exploration in several windows and check after several iterations of time reversal, if there are significant echoes within the window.
• the target does not stay only a few moments at the place where it was located by ultrasound or X-ray. It is then possible to locate the target when it is in this position, then to vary the time reversal window according to the movements of the target, for example so that the target is always substantially in the center of the window.
• the preliminary location for example by ultrasound or X-rays, makes it possible to know approximately the time of flight from the initial position of the target.
• the tracking cycle by time reversal then makes it possible to know the exact flight time corresponding to the position of the target.
• One can then for the following time reversal cycle choose windows whose location and width are a function of the flight times measured during the previous cycles.
• the window is dynamically adapted according to the movements of the target.
• Yet another procedure is to compare the signals received in the window for two successive iterations. This last procedure is particularly interesting in the case where the presence of defects is sought within a diffusing medium formed of small heterogeneities distributed in a dense and random manner.
• the signals picked up by the network transducers come from a reflecting target, their spatial structures will remain practically unchanged from one shot to the next. If on the contrary the signals collected during two successive shots are not correlated, it is because they come from diffusers which are too nested in the medium to be able to be separated by the time reversal operation.
• a measurement of the correlation or the degree of resemblance between the echo signals coming from two successive iterations can be obtained by summing the intercorrelation coefficients of two consecutive shots, for each of the transducers.
• T is the width of the time window.
• the correlation coefficient is equal to the maximum value of c ( ⁇ ). When this maximum is close to 1, we can deduce that the window contains a reflective target. When it is below a determined threshold, selected according to the experimental conditions and for example equal to 0.5, it can be deduced therefrom that the medium observed is diffusing and does not contain a predominant target.
• the time windows (which may be the same or different during successive shots) will be chosen so as to eliminate the echoes on the interface proper, as well as on a possible rear interface.
• the above operations can be considered as looking for the presence of a possible target. It remains to locate or locate the target, and destroy it.
• an ultrasound method providing an image of the area surrounding the target which generates the identified wavefront, by determining the relative time positions of the maxima of the wave front.
• the sum of the reception signals is then summed, readjusted by application of the time delays.
• Another approach is to perform a sectoral exploration around the first line of the image.
• the delay law previously modified is modified by summing it with another delay law corresponding to a deflection of the ultrasonic beam by a small angle ⁇ , according to the so-called phase grating technique.
• the new law of delay in emission and reception one then obtains, by again summing the received signals, an echographic image focused in a direction making an angle ⁇ compared to the axis of the target.
• delay laws corresponding to different angulations an image is obtained by sequential scanning.
• the lateral focusing is then better than that resulting from the emission of a simple wave surface, but in return the axial resolution is reduced.
• This variant is particularly useful when it is necessary to refocus through highly inhomogeneous media, because it improves lateral refocusing. It results from the fact that the optimal focusing at a point is obtained by re-emitting a "wave volume" rather than a wave surface. For the same reason, it can be advantageous to improve the focusing in reception, especially in the case of an inhomogeneous medium, by making the product of convolution of the echographic signals and temporal retounes of the emission signals.
• the problem is further simplified in the particular case of a practically homogeneous medium, since the wave front coming from a point can then be assimilated to a spherical surface.
• This case is, for example, that of medical lithotripsy performed at low frequency, generally with ultrasound at around 500 KHz.
• We can then assimilate the distribution law of the maxima to that of the sphere which best corresponds to it, according to a predetermined criterion, such as that of the least squares of the deviations.
• An evaluation of the validity of the approximation can be made by determining the variance of the deviations. If it is low enough, we can correct the experimental errors.
• a therapy generator can be equipped for the destruction of an aforementioned target, for example stones or a tumor, of only a few transducers whose exclusive role is to detect, monitor and locate the stones or tumor by time reversal.
• the focal point of the therapy generator is directed by conventional methods, such as mechanical for example, towards the target or the surrounding area.
• the aforementioned matrix of transducers is arranged to constitute a therapy generator focusing the acoustic waves at a focal point intended to be placed in coincidence with the target or the surrounding area of the target.
• FIGS 1, 2 and 3 are block diagrams showing three successive phases including timing diagrams showing the appearance of the electrical signals respectively: applied to at least one transducer (Figure 1) during first shot; obtained from the first shot ( Figure 2); and applied to the transducers ( Figure 3) after a time reversal;
• - Figure 3A shows a mode of synthesis of spherical wavefront
• - Figure 4 is a block diagram of a measurement channel associated with a particular transducer in a device according to a particular embodiment of the invention
• FIG. 5 shows a possible matrix arrangement of the transducers in a therapy device for implementing the invention
• FIG. 6 is a timing diagram showing the echo signals provided by thirty two of the transducers constituting a network according to the diagram of Figure 5, at the first reflection on a single extended target (gallstones for example) located in the environment studied , in response to the sending of a pulse by the central transducer;
• FIG. 7 is a timing diagram showing the signals received by the same thirty two transducers among those having the matrix arrangement of Figure 5, after the first time reversal;
• FIGS. 11 and 12 show the pressure field measured in the plane containing three targets and obtained by transmitting the time feedback of the signals of FIGS. 8 and 10, respectively after a first reversal and after five reversals and, in the latter case, with activation of the transducers according to a "spherical" law, in the case of a device whose transducers are distributed within the network of FIG. 5;
• - Figure 13 shows a distribution in time of the maxima of the various channels of Figure 10, in the case of the same medium as that which gave rise to the signals of Figures 8 to 10;
• - Figure 14 shows the distribution in time of the signals sent to reconstruct a spherical wave surface which best approximates the distribution of Figure 13;
• Figures 15 and 16 show the variation over time t of the inconsistent sum ( Figure 15) and the coherent sum (Figure 16) of the signals received on the different channels in the case of echo signals from a medium solid having two clear interfaces and a defect localized in volume, at the stage of the return of an emission at the level of FIG. 3;
• FIG. 17 shows a summation mode, after convolution product of the signals received after a time reversal transmission by the returned transmission signals.
• the invention is capable of being implemented using a device of the type described in document EP-A-O 383 650, already mentioned. Consequently, this device will only be briefly described here. As shown in Figures 1 to 3, the implementation of the method according to the invention is intended to cause the gradual formation of a sound pressure field converging towards the main target 10 placed in a medium 18. This method will thus be put implemented with the therapy device.
• a step (a) the zone in which the target 10 to be located is located is illuminated with the aid of a wide unfocused beam (FIG. 1).
• These transducers will often be distributed in a two-dimensional matrix, although the transducers are shown in a single line.
• the matrix can be flat or concave. It can be rectangular network.
• the transducers can also be distributed according to concentric circles, as indicated in FIG. 5, or even according to a incomplete distribution of space.
• the matrix transducers for the first illumination.
• the central transducer is excited, during the first illumination, by a circuit 14. On thus obtains an unfocused beam illuminating the target 10, located in a medium 18.
• Circuit 14 can be a short pulse generator driving one or more transducers.
• a step (b) the echo signal received by the transducers of the matrix 12 is captured and the shape and the relative position in time t of the signals are memorized, using a circuit 16 (figure 2).
• These first echo signals have for example the form shown in FIG. 2 since the electrical excitation signal of step (a) is a short pulse.
• the examination, for example on an oscilloscope or a television monitor, of the signals received makes it possible to select a time window of duration T containing almost all of the energy reflected and collected by the transducers of the matrix 12. These are only the signals contained in this time window which will be memorized in the circuit 16.
• the signals collected during the time window T are returned for a first time and re-emitted (FIG. 3) with an amplification gain which can be the same for all the transducers. It is set automatically to meet a condition: none of the channels must be saturated on reception, inside the time reversal window.
• the wavefront thus formed is automatically symmetrized and the echo received in return by the transducers of the matrix 12 will appear, at the output of each of these transducers, in the form of a signal symmetrical with respect to a maximum central value.
• the line or the simple geometric surface 40 (such as a sphere) closest to the wave front 42 defined as the surface passing through the maxima of the different signals.
• the advantage of making an approximation of the wavefront in the form of a surface or a simple geometric curve is that it makes it possible to easily determine the center or focus of the surface and know exactly the position of the most reflective area of the target.
• the final operation consisting of a destruction operation, can be carried out at a very strong amplification of the signal applied to each transducer and readjustment of each of the signals by application of a delay corresponding to the focusing at the center of the surface 40.
• the probability that the center of the sphere corresponds to the location of an area of the calculation to be destroyed must be close to 100%.
• a verification will generally be carried out: it consists in determining the variance of the differences between the surface 40 and the locations of the maxima. The surface 40 is then discarded as a representation of the wavefront when the variance exceeds a predetermined value. Thanks to the analysis of the signals collected during the last iteration carried out, it is also possible to detect any transducer elements whose amplitude of the signals collected are very low, a sign that they did not participate in the reversal process. .
• reception can also be focused by shifting all the reception signals, according to the law of returned transmission delays and summation on all channels.
• Figure 9 or 10 which allows a representation in ultrasound mode B or C from the delays of Figure 14 which is a mode A.
• the size of the part can be evaluated from the distance d beyond which the maximum amplitude is less than a threshold s.
• the search for the geometic surface 40 which can be represented by a polynomial equation, best corresponding to the wavefront 42 can be carried out by a conventional method of polynomial approximation and in general the least squares method will be used.
• each measuring channel 20 associated with a transducer of order ia the constitution shown in FIG. 4.
• the channel 20 includes a sampler 22 which provides analog samples of the signal received by the transducer i, at the frequency of a clock 24, during the time windows T fixed by the timer 26.
• the samples digitized by a converter 28 are stored in a memory 30 organized in a waiting stack or LIFO.
• the timer 26 is programmed so as to cause the emission of the wavefront returned after a determined period after the end of the echo.
• the channel 20 comprises a digital / analog converter 32 followed by an amplifier 34.
• the channel 20 shown comprises an amplifier 38 followed by an attenuator 40 of which the attenuation coefficient is modified as a function of time, by a programmer 42 which contains the inverse function of the negative exponential dd-sorption in the medium.
• the device also includes calculation means 36 for accessing the memory 30 in read and write mode, making it possible to determine, for each stored signal, the temporal location of the maximum, containing a program for determining the area having the best possible match with the temporal distribution of the maxima obtained by reading the memories 30 and possibly making it possible to modify, in each memory 30, the value and the temporal position of the samples so as to make the last shot correspond exactly to the geometric approximation made of the front of wave.
• the electronics of the device can have other constitutions than that shown in FIG. 4. In particular, it is possible to use an arrangement of the kind described in patent application FR-91.13629 where each channel successively comprises a logarithmic amplifier with control gain, an analog-to-digital converter that samples the signal and quantifies each sample.
• the digitized signal can be communicated to a video bus allowing viewing. It is also applied to a storage and depth compensation system having a random access memory and an adder-subtractor making it possible to add a memorized digital ramp to the signal.
• the channel will be completed by a sign detector placed at the input of the logarithmic amplifier.
• the part of the device devoted to re-transmission comprises an exponentiation circuit (random access memory for example).
• the digital signals obtained have no sign due to the logarithmic conversion. A sign is assigned to them, for example by adding a sign bit.
• the memory is read in time reversal.
• the polarized digital samples read from memory are put into analog form by a digital-analog converter, and applied to a linear amplifier driving the transducer from which the signal comes.
• the transducers can be distributed according to matrices of very diverse natures.
• FIG. 5 shows, by way of example, a matrix with 121 transducers, numbered from 0 to 120, defining an appropriate acoustic surface according to an advantageous embodiment of a therapy device according to the invention.
• Figures 6 and 7 show the signals which appear in a device implementing the method according to the invention, with a matrix of 121 transducers, in the case of a medium such as tissues containing a single highly reflective target, such as 'a stone or tumor.
• FIG. 6 shows the variation over time of the echo signals supplied by the thirty two transducers (the transducer 1 being the farthest from the axis) in response to illumination by the central transducer only, that is to say say the signals obtained during step (b) defined above. It can be seen that the signals are very asymmetrical and do not allow precise localization of the maximum of the wavefront.
• step (c) the echo signals received after the first time reversal (step (c)), illustrated in FIG. 7, clearly show on the one hand symmetrization, on the other hand the presence of a net maximum, already allowing a good approximation.
• the concentration of the beam on the target still continues during the possible subsequent iterations, the echo signal being symmetrical at each odd iteration.
• the maxima are aligned along an oblique line.
• FIG. 8 and 9 are similar to Figures 6 and 7, but correspond to the case of three targets distributed in the medium; FIG. 10 is obtained after five time reversals.
• Figures 11 and 12 show, on the ordinate, the sound pressure measured in the target plane.
• the targets had the same distribution as in Figures 8, 9 and 10 and were three in number.
• Figure 11 shows the distribution of sound pressure obtained after the first time reversal: the presence of three maxima corresponding to the three targets already appears clearly. This location disappears at the end of the second time reversal.
• Figures 13 and 14 show, by way of example, the results obtained with a network of 121 transducers and an observed medium identical to that which gives rise to the signals of Figures 8 to 10.
• the search for maxima from the signals of the Figure 10 for example by determining the addresses of the samples of maximum value, gives the distribution shown in Figure 13 where we note the presence of outliers, such as those surrounded by a circle in phantom.
• outliers such as those surrounded by a circle in phantom.
• the wavefront represented by samples in Figure 13 allows the target coordinates to be calculated.
• the time window it is possible to search for the time window to be used by performing, over the entire duration of the signals received, the sum of the envelopes of the signals received on each channel, that is to say a sum inconsistent, to verify that the resulting signal has a local maximum in the selected window.
• FIG. 15 shows the shape of the variation of the sum S of the signals received on the different channels, after a reversal, in the case of a network and of a medium studied constituted by a solid block having a defect localized in volume . It is also possible to carry out the coherent sum of the signals, that is to say a sum after time registration and in this case, we arrive at a distribution of the kind shown in FIG. 16 which highlights the presence of the targets even better. Finally, when optimal focusing when receiving signals from an inhomogeneous medium is necessary, the simple time shift of the ultrasound signals can be replaced by a convolution operation between the ultrasound signals 44 and the signals 46 constituting the time signals returned. of emission (figure 17). The convolution products, obtained in individual convolvers 48, are added in a s ⁇ mmateur 50. We will then generally use digital systems and we can adapt the time window ⁇ T used for each channel so that it is optimal.
• the invention also covers all the means constituting technical equivalents of the means described as well as their various combinations.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Computer Networks & Wireless Communication (AREA)
• Multimedia (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
• Ultra Sonic Daignosis Equipment (AREA)
• Surgical Instruments (AREA)
• Transducers For Ultrasonic Waves (AREA)

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• 1992
  • 1992-10-02 FR FR9211659A patent/FR2696573B1/fr not_active Expired - Fee Related
• 1993
  • 1993-09-24 US US08/125,855 patent/US5428999A/en not_active Expired - Lifetime
  • 1993-09-29 IL IL10715993A patent/IL107159A/en not_active IP Right Cessation
  • 1993-09-30 WO PCT/FR1993/000956 patent/WO1994008253A1/fr not_active Application Discontinuation
  • 1993-09-30 EP EP93921972A patent/EP0615625A1/de not_active Withdrawn
  • 1993-09-30 JP JP24536393A patent/JP3623246B2/ja not_active Expired - Lifetime
  • 1993-10-01 DE DE69325868T patent/DE69325868T2/de not_active Expired - Lifetime
  • 1993-10-01 CA CA002107525A patent/CA2107525C/en not_active Expired - Lifetime
  • 1993-10-01 EP EP93402409A patent/EP0591061B1/de not_active Expired - Lifetime
  • 1993-10-01 ES ES93402409T patent/ES2137238T3/es not_active Expired - Lifetime

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