DEVICE AND METHOD FOR CONTINUOUS EMISSION AND RECEPTION ULTRASOUND IMAGING

Abstract

The invention relates to an ultrasound imaging device and its associated method, comprising: - at least one transmitting element configured to emit a continuous excitation signal (Sem) into a medium, the excitation signal being encoded to form a succession of N ultrasonic waves, each 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 emission of the excitation signal emitted by said transmitting element, the echo signal being generated by the excitation of the medium by the excitation signal; and - filtering means configured to determine, by decoding each of the signatures, the contribution of each wave to the echo signal, so as to generate an image. Figure for the abstract: Fig. 1

Description

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

[0001] The invention relates to an ultrasound imaging device and method, combining two ultrasonic transducers allowing respectively to simultaneously and continuously transmit and receive an acoustic signal and to record the echoes generated by the medium. State of the art

[0002] Ultrasound is an imaging technique that uses sound waves to visualize a medium such as soft tissues like tendons, muscles, joints, blood vessels, and internal organs. Unlike computed tomography (CT) scanners, which use X-rays, and magnetic resonance imaging (MRI) scanners, which use radio waves, ultrasound scanners use sound waves to create images.

[0003] One of the main components of an ultrasound scanner is the probe, which is called a "transducer". It generally produces a short signal (called a pulse) of ultrasound waves that travels at a known speed of approximately 1540 m / s. The tissues and structures that this wave encounters absorb, reflect, 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 the screen in shades of grey. Blood and other fluids are represented in black, while soft tissue / bone interfaces are revealed in white.

[0006] High-frequency transducers make it possible to produce very detailed and well-resolved images of surface elements, whereas low-frequency transducers are better suited to produce 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 emission mode, each first sending an ultrasonic wave pulse and then in reception mode to receive the echoes of each pulse, the whole of the echoes being processed to reconstruct the image of the observed medium.

[0008] In order to improve the quality of the image, 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 related 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 penetration power.

[0010] That is why 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 to the patient.

[0012] Increasing the transmitted energy can also be achieved by lengthening the pulse duration, which inevitably leads to the appearance of so-called blind spots corresponding to the closest depths in contact with the probe, and reduces the resolution. Indeed, current ultrasound techniques 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 round-trip 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 simultaneously and continuously an acoustic signal.

[0015] This allows for the transmission of more energy without loss of resolution and decouples 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 is coded to form a succession of N ultrasonic waves, which may or may not overlap, and each with its own respective signature,

[0018] - at least one receiving element, distinct from said emitting element, and configured to receive 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 signatures, 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 their possible combinations, the different optional features 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 allowing to overcome the heating phenomena of at least one emitting element and at least one receiving element, due to the continuous emission and reception of ultrasonic waves, the ultrasonic imaging device includes means for cooling at least one emitting element and 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 to form a succession of N ultrasonic waves, overlapping or not, and each endowed with a respective signature,

[0025] - 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.

[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 on the order of 1.5 times the maximum values ​​allowed for diagnostic applications, for its use in a therapeutic method.

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

[0029] - a step of emitting, by at least one emitting element, a continuous signal excitation, the excitation signal being coded to form a succession of N ultrasonic waves, overlapping or not, each with its own respective signature,

[0030] - a simultaneous reception step, by at least one receiving element, distinct from said emitting 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, incorporating, according to all their possible combinations, the different optional features set out below.

[0033] According to a preferred aspect allowing 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 for rapid encoding and decoding of waves, the ultrasonic waves are non-concordant with each other.

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

[0036] According to yet another preferred aspect allowing access to a high-speed imaging process, the refresh rate of the signal(s) is greater than the round-trip time 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 proceed simultaneously to the emission stage,

[0039] - a second plurality of receiving elements, distinct from said emitting elements, and forming a second transducer, which proceed to the reception stage. List of figures

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

[0041] [Fig.1] Fig.1 is a schematic view of a continuous emission and reception ultrasound imaging device according to an 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 an acceleration and then a deceleration.

[0045] [Fig. 5] Figure 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 in a rapid sinusoidal motion and with 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 fast sinusoidal motion and a high amplitude. Description of a method of implementation

[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 emitting element, and configured to to receive 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 signatures, the contribution of each wave in the echo signal, these filtering methods ultimately generating an image.

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

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

[0053] The effect is reciprocal, that is to say that if a potential variation (therefore an electric charge variation) is applied via electrodes to two opposite faces of such a crystal, its thickness will vary in one direction or the other (increase or decrease) according to the polarity of the applied potential.

[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 (on 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 acoustic pressure experienced by the The piezoelectric crystal is transformed into an alternating variation of electrical potential, which can then be measured and recorded at the electrodes. This is called ultrasonic echo recording.

[0056] Other technologies besides piezoelectricity can be used, such as those using cMUT-type transducers. Micro-machined capacitive transducers (cMUTs) are capable of converting mechanical energy, supplied by ultrasonic waves, into electrical energy suitable for powering very low-power electronic devices.

[0057] There are different ways of visualizing 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-motion which is used in the results in Figures 2 to 6) allows the movement of the organs to be tracked by adding a temporal 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 that the ultrasonic firing line crosses on the screen.

[0061] The electronic structure for processing echoes, then visualizing and finally recording images can be summarized using the steps 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 and then demodulated before being definitively amplified.

[0063] Rectification aims to retain only a positive signal, while amplitude demodulation allows only the signal envelope to be retained. The main function of the amplification stage is to amplify the signals without distorting them, with the particular aim of compensating for the attenuation effects of ultrasound in 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 a grey scale.

[0066] However, for better visualization of the interesting echoes, that is to say originating from the deep organs that one wishes to observe, it is necessary to "compress" the grey scale more or less to offer the widest range of levels for these echoes.

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

[0068] The factors that 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 cutting 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 related to the equipment used.

[0071] a) Spatial resolution: lateral and axial; it is related to the ultrasound frequency, the pulse duration, and the focusing (fixed mechanical or electronic), as we saw previously. However, the density of the ultrasonic beam lines (parallel or diverging, depending on the type of scanning mechanical or electronic linear probe) must also be taken into account. The number of beam lines is related to the frame 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 discussed above. Therefore, the grayscale can and should be adapted according to clinical requirements.

[0073] c) Dynamic resolution is the ability to follow moving organs; it depends of course on the frame rate.

[0074] d) Noise, which consists of signals that do not contain any information useful to the image and that degrade its quality. Part of the noise is a function of the ultrasound scanner's electronic circuits, while another part depends on the diffusion phenomena described previously. Overall, all the noise can be considered random and can be reduced by averaging the images.

[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), and factors related to the operator (too rapid movement of the probe, for example).

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

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

[0078] In its basic version using a transmitting element and a receiving element, and 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, forming a first transducer, each configured to emit a continuous excitation signal into a medium, with a second plurality of receiving elements, forming a second transducer. The receiving elements are, of course, distinct from the emitting elements and are configured to each receive an echo signal simultaneously with the emission of all 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] Regarding the process, it comprises at a minimum:

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

[0083] - a simultaneous reception step R, by at least one distinct receiving element 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

[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 emitting elements, and forming a second transducer Trprocent to the reception stage (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 the receiver to compress the pulse, in order to increase the resolution along the ultrasonic axis of the measurement as well as the signal-to-noise ratio.

[0090] Waves exhibit 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 indeed contain a temporally variable and identifiable acoustic signature in order to be able to be found in the received echo signal.

[0092] Waves can be coded according to a pseudo-random coding such as Golay or Gold type codes 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 within 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 perform the decoding using appropriate filtering or another suitable technique. The length of the desired acoustic signature and the refresh rate or overlap between the desired signatures are the two adjustable parameters that allow setting the temporal resolution and refresh rate of the signals.

[0096] The filtering step (F) preferably implements a mismatched filter, allowing the received echoes to be decoded with respect to a portion of the transmitted signal. The latter is identified in an optimized manner, according to a given criterion, within the echoes to reconstruct an image, subsequently relying on the transit times. The objective is to obtain the best noise reduction relative to white noise in the least-squares sense. Thus, if the reference signal for the convolution is not exactly a replica, the filter can be said to be mismatched.

[0097] The "mismatched" filter, denoted q, used is based on minimizing the ISLR (integrated SideLobe Ratio) criterion on the emitted signal, denoted s: S — [51, ^2, , 5w] r

[0098] The output signal of the filter y is introduced: y — A æ (s) q

[0099] Where: Â'columns

[0100] is the matrix concatenating all the portions of the signal s for all the delays. The optimization problem solved to obtain this filter for a given emitted signal is: min q y H Fy = min q ||F l / 2 y^ = min q HFy)| 2 st s w q = s H 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 ultrasound waves are mismatched with each other in that they each exhibit strong autocorrelation and very weak intercorrelations. This makes it possible to obtain a spreading function of the imaging system that is as similar as possible to a Dirac delta function. Mismatched filtering at the receiver also helps to improve the actual correlation properties.

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

[0104] This is shown in Figures 2 to 6, in which a better spatiotemporal resolution can be observed with the ultrasound scanner according to the invention versus a conventional pulsed ultrasound scanner, whether for a static medium or dynamic, including for a medium 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 higher than at least 1.5 times 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 probed medium 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 bandwidth of the excitation signal.

[0109] Ultrasound can indeed be used to treat certain inflammatory conditions. The vibrations generated by ultrasound increase local blood circulation and help to flush out inflammatory fluid. This ultrasound facilitates the entry of nutrients and the removal of waste products from injured tissues.

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

[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 The temperature of the absorbing medium increases. This temperature rise is due to the viscosity of the medium, which generates frictional forces at the molecular level. These forces are dissipative, and the energy consumed is converted into heat. Generally, the temperature rise increases steadily until it reaches a plateau, indicating thermal equilibrium corresponding to the dissipation of heat in the intracellular and extracellular environments. For the ultrasound intensities used in echography, this corresponds to a temperature increase of 1° to 2°C if the examination duration is estimated at 10 minutes, which is negligible. The most important parameters involved in this process are: the acoustic intensity, the focus, the tissue characteristics (viscosity, specific heat), and the duration of the examination.

[0113] 2) Cavitation, whereby, under certain conditions, the ultrasonic beam can Cavitation develops cavities or bubbles in the medium through which it passes. For this to occur, gas or vapor molecules must be present in the medium. Cavitation is a complex phenomenon that includes both the formation and implosion of cavities.

[0114] Two cases are distinguished:

[0115] (i) Stable cavitation: cavities form under the effect of acoustic pressure in The general oscillatory pattern is relatively weak, and microflows are observed at the periphery of the cavities. In the 1 to 4 MHz range, this effect can occur beyond the threshold of 1 W / cm².

[0116] (ii) Transient or implosive cavitation: This is a more violent effect that only occurs at 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) the direct effects that can produce the rupture of macromolecules up to the DNA breakage and the acceleration of chemical reactions, similar to an enzyme, have also been observed in vitro. Changes in electrical charges on the surface of cells subjected to ultrasonic fields have also been observed.

[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 flow jet mapping, potentially compression wave velocity mapping, etc.).

[0119] The temporal accumulation of 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 basis for image creation.

[0121] The inventiveness lies in the fact of continuous transmission. The entire paradigm of ultrasound since its invention has been based on the implementation of short transmissions guaranteeing good temporal resolution and reception with the same transducer.

[0122] Transmitting long codes leads to a blind area on the image (impossibility of transmitting and receiving at the same time) and continuous transmission makes it impossible without a coding-decoding phase to have the depth information of the received echoes.

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

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

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

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

[0127] - to visualize and understand structures moving too fast for the 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 Therefore, the sensitivity of the imaging system to image where it is not currently possible because the attenuation is too strong.

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

[0131] From a medical perspective, 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 cell imaging, that is, the dynamic observation of cells and their movements. This technology could also enable the bioprinting of three-dimensional organs, that is, 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 seabed exploration, facilitating detailed mapping of underwater structures.

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

[0135] Te transmitter transducer

[0136] Tr transducer receiver

[0137] Sem Continuous emission signal

[0138] Echo Signal

[0139] Sk coded emitted wave

Claims

Demands

1. An ultrasound imaging device comprising: - at least one emitting element configured to emit a continuous excitation signal (Sem) into a medium, the excitation signal being coded to form a succession of N overlapping ultrasonic waves, each having a respective signature (Sk), k=[1, 2, 3,............., N], - at least one receiving element, distinct from said emitting element, and configured to receive an echo signal (Secho) simultaneously with the emission of the excitation signal emitted by said emitting element, the echo signal being generated by the excitation of the medium by the excitation signal, 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. Ultrasonic imaging device according to claim 1 or 2, characterized in that it comprises means for cooling at least one emitting element and 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 having 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. 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 on the order of 1.5 times the maximum values ​​allowed for diagnostic applications, for its use in a therapeutic method.

7. A method for imaging a medium by ultrasound comprising: - an emission step (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 overlapping ultrasonic waves, each having a respective signature (Sk), k=[1, 2, 3,............., N], - a simultaneous reception step (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) to determine by decoding each of the signatures, the contribution of each wave in the echo signal, to generate an image.

8. A method for imaging a medium by ultrasound according to claim 7, wherein the ultrasonic waves are non-concordant with each other, in that each exhibits a strong autocorrelation and very weak intercorrelations with each other.

9. Method for imaging a medium by ultrasound according to any one of claims 7 or 8 wherein the N signatures are spatiotemporal signatures, i.e. a function of the amplitude, frequency and / or phase of the ultrasonic waves of the excitation signal.

10. A method for imaging a medium by ultrasound according to any one of claims 7 to 9 wherein the refresh rate of the signal enabling the generation of an image is greater than that based on the round-trip time of the ultrasonic waves.

11. A method for imaging a medium by ultrasound according to any one of claims 7 to 10 wherein the filtering step (F) implements a so-called "mismatched" filter.

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

Images