CONTINUOUS TRANSMISSION AND RECEPTION ULTRASOUND IMAGING DEVICE AND METHOD

Abstract

The invention relates to an ultrasound imaging device, as well as to its associated method, comprising:- at least one transmitting element configured to transmit a continuous excitation signal (Sem) into a medium, the excitation signal being coded so as to form a succession of N ultrasonic waves each provided with a respective signature (Sk), k=[1, 2, 3, …………. , N],- at least one receiving element, distinct from said transmitting element, and configured to receive an echo signal (Secho) simultaneously with the transmission of the excitation signal transmitted by said transmitting element, the echo signal being generated by the excitation signal of the medium, and- filtering means configured to determine by decoding each of the signatures, the contribution of each wave in the echo signal, so as to generate an image. Figure for the abstract: Fig. 1

Description

Title of the invention: DEVICE AND METHOD FOR ULTRASOUND IMAGING WITH CONTINUOUS EMISSION AND RECEPTION

[0001] The invention relates to a device and a method for ultrasound imaging, combining two ultrasonic transducers allowing respectively the simultaneous and continuous transmission and reception of an acoustic signal and the recording of the echoes generated by the medium. State of the art

[0002] Ultrasound is an imaging technique that uses ultrasound to visualize an environment such as soft tissues like tendons, muscles, joints, blood vessels, and internal organs. Unlike CT scanners, which use X-rays, and MRI machines, which use radio waves, ultrasound scanners use ultrasound waves to create images.

[0003] One of the main components of an ultrasound scanner is the probe, called a "transducer." It generally produces a short signal (called a pulse or pulse in English) of ultrasonic wave that travels at a supposedly known speed of the order of 1540 m / s. The tissues and structures that this wave encounters absorb it, reflect it or refract it.

[0004] When Fonde returns to the transducer, the latter converts the pressure field at its interface into electrical signals. The signals are then processed and shaped to reconstruct an image of the medium during acquisition.

[0005] Soft tissues and organs appear on screen in grayscale. Blood and other fluids are shown in black, while soft tissue / bone interfaces are shown in white.

[0006] High frequency transducers are capable of producing very detailed and well-resolved images of surface features, while low frequency transducers are better suited to producing an image of deeper parts but in less detail and with lower resolution.

[0007] Generally, ultrasound scanners use a single transducer grouping together a set of piezoelectric or other elements, which operate alternately in transmission mode, each first sending an ultrasonic wave pulse and then in reception mode to receive the echoes of each pulse, all of the echoes being processed to reconstruct the image of the observed medium.

[0008] In order to improve image quality, it is necessary to optimize the resolution, the resolution being defined as the smallest distance separable by an instrument, as well as the contrast of the image.

[0009] When ultrasound is used, the intrinsic resolution, which is directly linked to the wavelength itself, is better for high frequencies, but there is then a greater attenuation of the ultrasound in the medium which results in a lower penetrating power.

[0010] Therefore, it is necessary to transmit more energy.

[0011] The increase in transmitted energy can be achieved by increasing the amplitude of the emitted waves, which is not without risk for the patient.

[0012] Increasing the transmitted energy can also be done by lengthening the duration of the pulses, which inevitably leads to the appearance of so-called blind zones corresponding to the closest depths in contact with the probe, and reduces the resolution. Indeed, currently ultrasound methods do not consider the possibility of simultaneously emitting and receiving ultrasonic waves.

[0013] Furthermore, improving image quality and obtaining three-dimensional (3D) images requires reducing echo acquisition times, which is not compatible with the transmission and reception operation of current transducers which, with this operation, induce an incompressible outward and return propagation time.

[0014] In order to overcome all or part of these drawbacks, the invention proposes to combine two ultrasonic transducers allowing respectively to transmit and receive an acoustic signal simultaneously and continuously.

[0015] This makes it possible to transmit more energy without losing resolution and to decouple the acquisition time from the round trip time of the ultrasonic wave. Description of the invention

[0016] Therefore, the invention proposes an ultrasound imaging device comprising

[0017] - at least one emitting element configured to emit a continuous excitation signal in a medium, the excitation signal being coded so as to form a succession of N ultrasonic waves, which may or may not overlap, and each having a respective signature,

[0018] - at least one receiving element, distinct from said transmitting element, and configured to receiving an echo signal simultaneously with the emission of the excitation signal by said emitting element, the echo signal being generated by the excitation of the medium by the excitation signal, and

[0019] - filtering means configured to determine by decoding each of the si gnatures, the contribution of each wave in the echo signal, to generate an image.

[0020] Various embodiments of the invention are provided, incorporating according to all of their possible combinations of the various optional characteristics set out below.

[0021] In order to ensure good separability, in terms of image resolution, of spatially close elements in the medium as well as sufficient image contrast, decoding by filtering of the "mismatched" type is preferred.

[0022] According to another preferred aspect making it possible to overcome the heating phenomena of the at least one emitting element and the at least one receiving element, due to the continuous emission and reception of the ultrasonic waves, the ultrasound imaging device comprises means for cooling the at least one emitting element and the at least one receiving element.

[0023] According to yet another preferred aspect allowing access to two-dimensional (2D) or three-dimensional (3D) imaging, the device comprises:

[0024] - a first plurality of emitting elements configured to each emit a excitation signal in a medium, each excitation signal being coded so as to form a succession of N ultrasonic waves, overlapping or not, and each having a respective signature,

[0025] - a second plurality of receiving elements, distinct from said transmitting elements, each configured to receive an echo signal simultaneously with the emission of the excitation signal emitted by the associated emitting element, each echo signal being generated by the excitation of the medium by said associated excitation signal.

[0026] According to a certain application aspect of the invention, the device is configured so that the N ultrasonic waves admit frequencies between 1.5 and 50 MHz, for its use in a medical diagnostic method.

[0027] According to another application aspect of the invention, the device is configured so that the N ultrasonic waves admit thermal and / or mechanical indices at least of the order of 1.5 times the maximum values ​​admitted for diagnostic applications, for its use in a therapeutic method.

[0028] The invention also relates to a method for imaging a medium using ultrasound comprising:

[0029] - a step of transmitting, by at least one transmitting element, a continuous signal excitation, the excitation signal being coded so as to form a succession of N ultrasonic waves, overlapping or not, and each having a respective signature,

[0030] - a step of simultaneous reception, by at least one receiving element, distinct from said transmitting element of an echo signal, the echo signal being generated by the excitation of the medium by the excitation signal, and

[0031] - a filtering step to determine by decoding each of the signatures, the contribution of each wave in the echo signal, to generate an image.

[0032] Various embodiments of the invention are provided, integrating according to all of their possible combinations the different optional characteristics set out below.

[0033] According to a preferred aspect making it possible to limit the noise of estimation of the medium in the echo signal, the filtering step (F) implements a filter of the “mismatched” type.

[0034] According to another preferred aspect allowing rapid coding and decoding of the waves, the ultrasonic waves are non-concordant with each other.

[0035] According to yet another preferred aspect, the N signatures are spatio-temporal signatures.

[0036] According to yet another preferred aspect allowing access to a high-speed imaging method, the refresh rate of the signal(s) is greater than the round-trip duration of the ultrasonic waves.

[0037] According to yet another preferred aspect allowing access to two-dimensional (2D) or three-dimensional (3D) imaging, the method implements:

[0038] - a first plurality of emitting elements forming a first transducer, which simultaneously carry out the emission step,

[0039] - a second plurality of receiving elements, distinct from said transmitting elements, and forming a second transducer, which carry out the receiving step. List of figures

[0040] Other features and advantages of the invention will emerge from the detailed description of a non-limiting embodiment, and from the appended drawings in which:

[0041] [Fig.l] [Fig.l] is a schematic view of a continuous emission and reception ultrasound imaging device according to one embodiment of the invention.

[0042] [Fig.2] [Fig.2] is a comparison between the image (in this case a line) obtained by means of continuous excitation versus the image obtained by means of excitation by a pulse of two diffusing elements, one being fixed, the other in motion.

[0043] [Fig.3] [Fig.3] is a comparison between the image (in this case a line) obtained by means of continuous excitation versus the image obtained by means of excitation by a pulse of a diffusing element moving at constant speed.

[0044] [Fig.4] [Fig.4] is a comparison between the image (in this case a line) obtained by means of continuous excitation versus the image obtained by means of excitation by a pulse of a diffusing element moving with acceleration then deceleration.

[0045] [Fig.5] [Fig.5] is a comparison between the image (in this case a line) obtained by means of continuous excitation versus the image obtained by means of excitation by a pulse of a diffusing element moving according to a rapid sinusoidal movement and an average amplitude.

[0046] [Fig.6] [Fig.6] is a comparison between the image (in this case a line) obtained by means of continuous excitation versus the image obtained by means of excitation by a pulse of a diffusing element moving in a very rapid sinusoidal movement and a high amplitude. Description of an embodiment

[0047] According to the principle of the invention and as shown in [Fig. 1], the ultrasound imaging device comprises:

[0048] - at least one emitting element configured to emit a continuous excitation signal Sem in a medium, the excitation signal being coded so as to form a succession of N ultrasonic waves, which may or may not overlap, each with a respective signature Sk, k=[l, 2, 3, .... , N],

[0049] - at least one receiving element, distinct from said transmitting element, and configured to receiving an echo signal SechO simultaneously with the emission of the excitation signal by said emitting element, the echo signal being generated by the excitation of the medium by the excitation signal, as well as:

[0050] - filtering means configured to determine by decoding each of the si signatures, the contribution of each wave in the echo signal, these means of filtering ultimately generating an image.

[0051] The at least one emitting element as well as the at least one receiving element are elements capable of transforming electrical energy into ultrasonic energy and vice versa. The mechanism of operation of these elements can be based on the physical effect called piezoelectricity.

[0052] Certain crystals called piezoelectric, such as quartz or tourmaline, naturally develop electrical charges on their faces when they are subjected to a variation in mechanical pressure.

[0053] The effect is reciprocal, that is to say that if we apply, by means of electrodes, a variation of potential (therefore of electric charges) on two opposite faces of such a crystal, its thickness will vary in one direction or the other (increase or decrease) depending on the polarity of the potential applied.

[0054] In turn this variation in thickness will act on the medium like the vibration of a piston. The vibration frequency of the crystal is controlled by the frequency of the alternating variation of the applied potential difference.

[0055] If this frequency is high (of the order of MHz), then an ultrasonic wave is produced. Conversely, when the ultrasonic wave reflected by the medium is received by the receiving element, the variation in the acoustic pressure experienced by the piezoelectric crystal is transformed into an alternating variation in electrical potential which can then be measured and recorded at the electrodes. This is what is called recording the ultrasonic echo.

[0056] Technologies other than piezoelectricity can be used, such as those using cMUT type transducers. Micromachined capacitive transducers (cMUT) are capable of converting mechanical energy, provided by ultrasonic waves, into electrical energy capable of powering very low-consumption electronic devices.

[0057] There are different ways of viewing the ultrasound image.

[0058] The representation of the images can be the result of an amplitude modulation of the echoes (one-dimensional ultrasound or A mode), or the result of a modulation of the intensity (or brightness) of the ultrasound spot (B mode or two-dimensional image).

[0059] The TM mode (time movement which is used in the results in figures 2 to 6) makes it possible to follow the movement of the organs by adding a time scan to the one-dimensional B mode (a single line of fire).

[0060] We therefore see the movement of the more or less intense spots (representing the echoes) of the mobile organic tissue structures crossed by the ultrasonic firing line scrolling across the screen.

[0061] The electronic structure for processing the echoes, then visualizing and finally recording the images can be summarized using the stages of acquisition, signal processing and visualization.

[0062] The probe delivers an alternating signal pulse when it records an ultrasonic echo. This signal, after pre-amplification, is first rectified then demodulated before being definitively amplified.

[0063] The purpose of rectification is to retain only a positive signal, amplitude demodulation allows only the envelope of the signal to be retained. The main function of the amplification stage is to amplify the signals without distorting them with the particularity of seeking to compensate for the attenuation effects of ultrasound in the tissues.

[0064] The gain G of an amplifier is defined as the ratio of the input voltage to the output voltage.

[0065] The range of amplitudes of the received echoes is converted into gray scale.

[0066] However, for better visualization of the interesting echoes, i.e. coming from the deep organs that we wish to observe, it is advisable to "compress" the gray scale more or less to offer the widest range of levels for these echoes.

[0067] An analog / digital converter has the function of transforming an analog signal (i.e. a continuous variation in voltage generated by the echo) into a series of discrete digital values ​​which can then be subject to mathematical processing capable of modifying these values ​​according to requirements (amplification, non-linear filtering, etc.).

[0068] The factors which are likely to affect the quality of the ultrasound image are therefore essential.

[0069] The so-called subjective factors are related to the correct interpretation of the section plane, the recognition of normal and abnormal structures, the recognition of induced movements (due to breathing, coughing, postural changes, etc.) and natural movements (cardiac, peristaltic, fetal movements, etc.), the discrimination of artifacts.

[0070] The so-called objective factors are linked to the equipment used.

[0071] a) spatial resolution: lateral and axial; it is linked to the frequency of the ultrasound, the duration of the pulses and the focusing (fixed mechanical or electronic) as we have seen previously. But it is also necessary to take into account the density of the ultrasonic firing lines (parallel or divergent depending on the type of mechanical scanning probe or electronic linear). The number of firing lines is linked to the image rate (number of images per second). The higher the number of lines, the better the lateral resolution.

[0072] b) the quality of the contrast or contrast resolution depends on the dynamic compression that we discussed above. Thus the gray scale can and must be adapted according to clinical requirements.

[0073] c) dynamic resolution is the ability to track moving organs, it obviously depends on the image rate.

[0074] d) noise which corresponds to signals which do not contain any information useful to the image and which will degrade the quality of the latter. Part of the noise is a function of the electronic circuits of the ultrasound scanner itself, another part depends on the diffusion phenomena seen previously. Overall, all of the noise can be considered random here and can be reduced by an image averaging operation.

[0075] e) artifacts correspond to images that are artificial and not representative of an anatomical structure. There are three main causes of artifacts: physical causes (multiple reflections for example), factors related to the instrumentation (poor gain compensation for example), factors related to the operator (moving the probe too quickly for example).

[0076] Advantageously, the ultrasound imaging device comprises means for cooling the at least one emitting element and the at least one receiving element. These cooling means comprise, for example, a cooling loop in which a refrigerant circulates.

[0077] This loop makes it possible to limit the heating of the transmitting and receiving elements which are continuously solicited by the excitation signals.

[0078] In its basic version using a transmitter element and a receiver element, and such as shown in Figures 2 to 6, the device reconstructs only one line of the image.

[0079] For the purpose of performing two-dimensional (2D) or three-dimensional (3D) imaging, it is advantageous to combine a first plurality of emitting elements, then forming a first transducer, each configured to emit a continuous excitation signal into a medium, with a second plurality of receiving elements, then forming a second transducer. The receiving elements are of course distinct from said emitting elements, and are configured to each receive an echo signal simultaneously with the emission of the set of excitation signals by the first plurality of emitting elements.

[0080] The first and second transducers can be combined in a housing commonly called a “probe”.

[0081] Now concerning the process, it comprises at least:

[0082] - a step of transmitting E, by at least one transmitting element, a continuous signal excitation signal Sem, the excitation signal being coded so as to form a succession of N ultrasonic waves each with a respective signature Sk, k=[l, 2, 3, .............,N],

[0083] - a step of simultaneous reception R, by at least one distinct receiving element said emitting element, an echo signal Secho, said excitation signal, the echo signal being generated by the excitation of the medium by the excitation signal, and

[0084] - a filtering step F to determine by decoding each of the signatures, the contribution of each wave in the echo signal, to generate an image.

[0085] The method can be implemented to obtain a two-dimensional (2D) or three-dimensional (3D) image with the following steps:

[0086] - a first plurality of emitting elements forming a transducer Te proceed simultaneously with the emission step E.

[0087] - a second plurality of receiving elements, distinct from said transmitting elements, and forming a second transducer Tr proceed to the receiving step (R).

[0088] The excitation signal Sem of each emitting element is continuous and is modulated according to a succession of N ultrasonic waves which may or may not overlap depending on the length of the codes used.

[0089] The emitted signal is subjected to modulation allowing pulse compression upon reception, in order to increase the resolution along the ultrasonic axis of the measurement as well as the signal-to-noise ratio.

[0090] The waves have a spatiotemporal coding, that is to say a signature which is a function of their amplitude, their frequency and / or their phase.

[0091] The transmitted signal must in fact contain a temporally variable and identifiable acoustic signature in order to be able to be found in the reception echo signal.

[0092] The waves can be coded according to a pseudo-random coding such as codes of the Golay or Gold type for example.

[0093] The coding preferentially uses code division multiplexing (CDM) which is a multiplexing technique that uses spread spectrum communication. In spread spectrum communications, a narrowband signal is spread over a wider frequency band or over several channels by division. It does not restrict the digital signals or frequencies in the bandwidth.

[0094] In order to recover the signal from the medium, as if it came from the interaction of a short pulse with the medium, a decoding operation is necessary.

[0095] It is recommended to carry out decoding using suitable filtering or another technique. The length of the acoustic signature being sought and the refresh rate or overlap between the signatures being sought are the two adjustable parameters which make it possible to set the temporal resolution and the refresh rate of the signals.

[0096] The filtering step (F) preferentially implements a filter of the “mismatched” type, making it possible to decode the echoes received with respect to a portion of the transmitted signal. The latter is identified in an optimized manner, with respect to a given criterion, in the echoes to reconstruct an image by subsequently relying on the travel times. The objective is to obtain the best noise gain compared to white noise in the least squares sense. Thus, if the reference signal for the convolution is not exactly a replica, it can be said that the filter is “mismatched”.

[0097] The “mismatched” filter, noted q, used is based on the minimization of the ISLR criterion (integrated SideLobe Ratio) on the emitted signal noted s: T S = [>S'i, SA, . . . , S .y]

[0098] We introduce the output signal of the filter y: y = A (s) q

[0099] Where: ^colutnns

[0100] is the matrix concatenating all portions of the signal s for all delays. The optimization problem solved to obtain this filter for a given transmission signal is: min q y^Fy = min q ||F s / 3 y||^ = min q |[FyJj| st = s ;z s.

[0101] The solution is obtained using Lagrange multipliers. The results show that the filter performs well with respect to ISLR in high noise environments.

[0102] Preferably, the ultrasonic waves are mutually mismatched in the sense that they each have a strong autocorrelation and very weak intercorrelations between them. This makes it possible to obtain a spreading function of the imaging system as similar as possible to a function of the Dirac distribution type. The "mismatched" filtering at reception also contributes to improving the real correlation properties.

[0103] With the device and method according to the invention, a refresh rate is obtained at least 10 times higher than conventional approaches requiring waiting for the round-trip propagation time of the acoustic Fonde, since it becomes possible to reconstruct the signal in a quasi-continuous manner. A transition from 20 kHz to 200 kHz is, for example, entirely accessible.

[0104] This is what is shown in Figures 2 to 6, in which we can observe a better spatiotemporal resolution with the ultrasound scanner according to the invention versus a conventional pulse ultrasound scanner, whether for a static medium or dynamic, including for an environment moving at high speeds or over a very short distance.

[0105] In the case where the imaging device is used for medical diagnostic purposes, i.e. as a medical ultrasound scanner, the emitted signal is coded according to N ultrasonic waves which admit frequencies between 1.5 and 50 MHz.

[0106] In the case where the imaging device is used for therapeutic purposes, i.e. as a medical ultrasound scanner, the N ultrasonic waves admit thermal and / or mechanical indices at least of the order of 1.5 times higher than the maximum values ​​allowed for diagnostic applications.

[0107] The thermal index (TI) is defined as the acoustic output power of the transducer divided by the estimated power required to increase the temperature of the medium being probed by 1°C.

[0108] The mechanical index (MI) is defined as being equal to the maximum rarefaction pressure divided by the square root of the center frequency of the excitation signal bandwidth.

[0109] Ultrasound can indeed be used to treat certain inflammatory conditions. The vibrations generated by ultrasound increase blood circulation locally and help flush out inflammatory fluid. These ultrasounds facilitate the entry of nutrients and the elimination of waste from injured tissues.

[0110] The complete mechanisms of the biological effects of ultrasound absorption by human or animal tissues are beginning to be understood.

[0111] Ultrasound absorbed by tissues can give rise to three main effects:

[0112] 1) thermal effects in which the absorption of ultrasound produces an elevation temperature of the absorbent medium. This increase in temperature is due to the viscosity of the medium which is the origin of friction forces at the molecular level. These forces are dissipative and the energy consumed degrades into heat. In general, the temperature rise increases steadily until a plateau which reflects a thermal equilibrium corresponding to the dissipation of heat in the intra and extra cellular environments. For the ultrasound intensities used in echography this corresponds to an increase of 1° to 2° C if the duration of the examination is estimated at 10 minutes, which is completely negligible. The most important parameters involved in this process are the following: acoustic intensity, focusing, tissue characteristics (viscosity, specific heat), duration of the examination.

[0113] 2) Cavitation according to which, under certain conditions, the ultrasonic beam can develop cavities or bubbles in the medium being crossed. For this to happen, gas or vapor molecules must be present in the medium. Cavitation is a complex phenomenon that includes the formation of cavities but also their implosion.

[0114] We distinguish two cases:

[0115] (i) stable cavitation: the cavities are formed under the effect of acoustic pressure in generally oscillatory but of relatively low intensity, and microflows are observed at the periphery of the cavities. In the range of 1 to 4 MHz this effect can occur beyond the threshold of 1 W / cm2.

[0116] (ii) transient or implosive cavitation: this is a more violent effect which only exists for high intensities (well beyond the values ​​used in diagnostic ultrasound). The implosion of gas cavities under the action of the ultrasound field can have secondary effects such as shock waves leading to the degradation of certain macromolecules, significant temperature increases, modifications of existing chemical reactions or the initiation of new reactions (analogous to ionizing radiation) or even sonoluminescence (light emission).

[0117] 3) direct effects which can produce the breaking of macromolecules up to the DNA breakage, and the acceleration of chemical reactions as an enzyme would do. Changes in electrical charges on the surface of cells subjected to ultrasonic fields have also been observed in vitro.

[0118] In summary, the device and method according to the invention can be used in any context in which the imaging rate is a limiting factor (high-rate 3D US imaging, aortic jet flow mapping, potentially compression wave velocity mapping, etc.).

[0119] The temporal accumulation of the collected signal also allows an increase in sensitivity and makes it possible to image in anatomical areas which are not currently within the scope of ultrasound (behind the bone such as the brain, or even in the lung).

[0120] This type of sequence can also be used to perform ultrasound therapy and imaging simultaneously, with the therapy signal serving as the medium for creating the image.

[0121] The inventiveness lies in the fact of transmitting continuously. The whole paradigm of ultrasound since its invention lies in the implementation of short transmissions guaranteeing good temporal resolution and reception with the same transducer.

[0122] Transmitting long codes leads to a blind zone on the image (impossibility of transmitting and receiving at the same time) and transmitting continuously without a coding-decoding phase prohibits having the depth information of the echoes received.

[0123] This approach based on two separate transducers with continuous transmission and reception is a departure from the approach of ultrasounds using pulsed signals, which use the same transducer for transmission and reception.

[0124] Thus the method and the device according to the invention allow:

[0125] - to obtain a considerable gain in terms of refresh rate,

[0126] - to access faster ultrasound imaging rates that make possible thus ultra-fast 3D imaging,

[0127] - to visualize and grasp structures in motion that are too fast for them current systems,

[0128] - to visualize and understand very short physical phenomena,

[0129] - to transmit more signal and thus increase the signal to noise ratio and so the sensitivity of the imaging system to image where it is not currently possible because the attenuation is too strong.

[0130] In addition, the ultrasound imaging device and method according to the present invention offer diverse application potential, both in the medical field and in other sectors.

[0131] On the medical level, this technology could improve the quality of images subsequently used for diagnostic purposes.

[0132] In the field of biology and biomedical research, this technology could enable real-time cellular imaging, i.e., allow the dynamic observation of cells and their movements. This technology could also enable the bioprinting of organs in three dimensions, i.e., real-time monitoring of the bioprinting process for optimal precision.

[0133] However, the applications are not limited to medicine. In the underwater field, for example, the device could be used for exploring the seabed, facilitating detailed mapping of underwater structures.

[0134] Finally, in terms of non-destructive testing, the invention could be used in industry to inspect the quality of certain materials without altering their integrity. Nomenclature

[0135] The transmitter transducer

[0136] Tr transducer receiver

[0137] Sem Continuous transmission signal

[0138] Echo Signal Echo

[0139] Sk coded emitted wave

Claims

Claims

1. An ultrasound imaging device comprising: - at least one transmitting element configured to transmit a continuous excitation signal (Sem) into a medium, the excitation signal being coded so as to form a succession of N ultrasonic waves each having a respective signature (Sk), k=[l, 2, 3,............., N], - at least one receiving element, distinct from said transmitting element, and configured to receive an echo signal (Secho) simultaneously with the transmission of the excitation signal transmitted by said transmitting element, the echo signal being generated by the excitation signal of the medium, and - filtering means configured to determine by decoding each of the signatures, the contribution of each wave in the echo signal, so as to generate an image.

2. Ultrasound imaging device according to the preceding claim, characterized in that the filtering means are configured to implement a so-called “mismatched” filter.

3. An ultrasound imaging device according to claim 1 or 2, characterized in that it comprises means for cooling the at least one emitting element and the at least one receiving element.

4. An ultrasound imaging device according to any one of the preceding claims, characterized in that it comprises: - a first plurality of emitting elements each configured to emit a continuous excitation signal into a medium, each excitation signal being coded so as to form a succession of ultrasonic waves each provided with a respective signature, - a second plurality of receiving elements, distinct from said emitting elements, each configured to receive an echo signal simultaneously with the emission of the excitation signal emitted by the associated emitting element, each echo signal being generated by the excitation of the medium by said associated excitation signal.

5. An ultrasound imaging device according to any one of the preceding claims, characterized in that the device is configured so that the N ultrasonic waves admit frequencies between 1.5 and 50 MHz, for its use in a medical diagnostic method.

6. Ultrasound imaging device according to any one of the preceding claims, characterized in that the device is configured so that the N ultrasonic waves admit thermal and / or mechanical indices at least of the order of 1.5 times the maximum values ​​admitted for diagnostic applications, for its use in a therapeutic method.

7. Method for imaging a medium by ultrasound comprising: - a step of emission (E), by at least one emitting element, of a continuous excitation signal (Sem), the excitation signal being coded so as to form a succession of N ultrasonic waves each provided with a respective signature (Sk), k=[l, 2, 3,............., N], - a step of simultaneous reception (R), by at least one receiving element, distinct from said emitting element, of an echo signal (SechO) of said excitation signal, the echo signal being generated by the excitation of the medium by the excitation signal, and - a filtering step (F) for determining by decoding each of the signatures, the contribution of each wave in the echo signal, to generate an image.

8. A method of imaging a medium using ultrasound according to claim 7, wherein the ultrasonic waves are mutually non-concordant.

9. Method for imaging a medium by ultrasound according to any one of claims 7 or 8 in which the N signatures are spatiotemporal signatures.

10. A method of imaging a medium using ultrasound according to any one of claims 7 to 9 wherein the refresh rate of the signal is greater than the round trip duration of the ultrasonic waves.

11. Method for imaging a medium by ultrasound according to any one of claims 7 to 10 in which the filtering step (F) implements a so-called “mismatched” filter.

12. Method for imaging a medium by ultrasound according to any one of claims 7 to 11 in which: - a first plurality of emitting elements forming a first transducer (Te) carry out the emission step (E), - a second plurality of receiving elements, distinct from said emitting elements, and forming a second transducer (Tr) carry out, simultaneously with the emission step (E), the reception step (R).

Images