Method and device for line-column addressing ultrasound imaging

Abstract

Method and Device for Row-Column Addressed Ultrasound Imaging. This description concerns a method for acquiring an image of a body using an array of ultrasonic transducers connected in rows and columns. The method comprises: - making N successive shots (TX) of the same ultrasonic wave in the direction of the body, where N is an integer greater than or equal to 2; - after each shot, implementing a reception phase (RX) of a returning ultrasonic wave reflected by the body, in which, during each reception phase (RX), a variable electrical quantity representative of the received wave is read on each row electrode (Ri) of the device, and in which, between any two reception phases among the N reception phases (RX), the sign of the individual contribution (eij) of at least one elementary ultrasonic transducer of the array is changed. Figure for the abstract: Fig. 7

Description

Title of the invention: Method and device for line-column addressing ultrasound imaging Technical field

[0001] The present description relates to the field of ultrasound imaging, and more particularly relates to a device comprising a matrix of ultrasonic transducers with row-column addressing, and a method for acquiring an image of a body by means of such a device. Prior art

[0002] An ultrasound imaging device conventionally comprises a plurality of ultrasound transducers, and an electronic control circuit connected to the transducers. In operation, all of the transducers are arranged facing a body of which an image is to be acquired. The electronic control circuit is configured to apply electrical excitation signals to the transducers, so as to cause the emission of ultrasound waves by the transducers, in the direction of the body or object to be analyzed. The ultrasound waves emitted by the transducers are reflected by the body to be analyzed (by its internal and / or superficial structure), then return to the transducers which convert them again into electrical signals. These electrical response signals are read by the electronic control circuit, and can be stored and analyzed to deduce information about the body studied.

[0003] The ultrasonic transducers can be arranged in a bar in the case of a two-dimensional image acquisition device, or in a matrix in the case of a three-dimensional image acquisition device. In the case of a two-dimensional image acquisition device, the acquired image is representative of a section of the body studied in a plane defined by the alignment axis of the transducers of the bar on the one hand, and by the emission direction of the transducers on the other hand. In the case of a three-dimensional image acquisition device, the acquired image is representative of a volume defined by the two alignment directions of the transducers of the matrix and by the emission direction of the transducers.

[0004] Among the three-dimensional image acquisition devices, a distinction can be made between so-called fully populated devices, in which each transducer of the matrix is ​​individually addressable, and so-called row-column addressing or RCA devices, in which the transducers of the matrix are addressable by row and by column.

[0005] Fully populated devices offer greater flexibility in shaping the ultrasonic beams for transmission and reception. The matrix control electronics are, however, complex, with the number of transmission / reception channels required being M*N in the case of a matrix of M rows by N columns. In addition, the signal-to-noise ratio is generally relatively low since each transducer has a small surface area for exposure to ultrasonic waves.

[0006] RCA type devices use different ultrasonic beam shaping algorithms. The beam shaping possibilities can be reduced compared to fully populated devices. However, the matrix control electronics are considerably simplified, the number of required transmit / receive channels being reduced to M+N in the case of a matrix of M rows by N columns. In addition, the signal-to-noise ratio is improved due to the interconnection of the transducers in rows or columns during the transmission and reception phases.

[0007] We are particularly interested here in devices and methods for acquiring three-dimensional images with row-column addressing (RCA).

[0008] It would be desirable to improve at least in part certain aspects of the devices and methods for acquiring three-dimensional ultrasound images with row-column addressing. Summary of the invention

[0009] For this, one embodiment provides a method for acquiring an image of a body by means of a matrix ultrasound imaging device with row-column addressing, the device comprising a matrix of elementary ultrasound transducers connected in rows and columns by row electrodes and column electrodes respectively, the method comprising: - carry out N successive shots of the same ultrasonic wave towards said body, where N is an integer greater than or equal to 2; and - after each shot, implement a reception phase, by means of said device, of a return ultrasonic wave, reflected by said body, in which, during each of the reception phases, a variable electrical quantity representative of the received background is read on each line electrode of the device, and in which, between any two reception phases among the N reception phases, the sign of the individual contribution of at least one elementary ultrasonic transducer of the matrix is ​​modified.

[0010] According to one embodiment, during each of the N reception phases, each column electrode of the matrix is ​​maintained at a DC bias voltage, and, between any two reception phases among the N reception phases, the sign of the DC bias voltage applied to at least one of the column electrodes of the device is modified.

[0011] According to one embodiment, the signs of the bias voltages applied respectively to the column electrodes of the device during the N reception phases are coded by the vectors of an orthogonal matrix, for example a Hadamard matrix.

[0012] According to one embodiment, the N successive shots are carried out by means of said row-column addressing matrix ultrasound imaging device, and, during each of the N shots, each column electrode of the matrix is ​​maintained at a DC bias voltage, and an AC excitation voltage superimposed on the DC bias voltage is applied to said column electrode, and, during each shot, the signs of the DC bias voltages respectively applied to the column electrodes of the matrix are the same as the signs of the DC bias voltages respectively applied to the column electrodes during the subsequent reception phase.

[0013] According to one embodiment, between any two reception phases among the N reception phases, the electrical connection of at least one elementary transducer between the row and column electrodes is reversed by means of a system of switches, so as to modify the sign of the individual contribution of said at least one elementary ultrasonic transducer of the matrix.

[0014] According to one embodiment, the ultrasonic transducers are CMUT or PMUT transducers.

[0015] According to one embodiment, the matrix comprises N rows and N columns of elementary ultrasonic transducers.

[0016] According to one embodiment, the method comprises a step of calculating, by means of an electronic processing device, by linear combinations of the variable electrical quantities read on the line electrodes of the device during the N reception phases, an individual contribution of each of the elementary transducers of the matrix.

[0017] According to one embodiment, the variable electrical quantity read on each row electrode of the device is a voltage.

[0018] Another embodiment provides a row-column addressing matrix ultrasound imaging device, the device comprising a matrix of elementary ultrasound transducers connected in rows and columns by row electrodes and column electrodes respectively, and a control circuit configured to implement a method as defined above.

[0019] According to one embodiment, the ultrasonic transducers are CMUT or PMUT transducers. Brief description of the drawings

[0020] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0021] [Fig.l] is a top view schematically and partially illustrating an example of a row-column addressing matrix ultrasound imaging device;

[0022] [Fig.2] comprises a sectional view along a plane AA of [Fig.l], and a sectional view along a plane BB of [Fig.l], illustrating in more detail an exemplary embodiment of the device of [Fig.l];

[0023] [Fig.3] is an equivalent electrical diagram of a 2x2 row-column addressing matrix ultrasound imaging device operating in reception mode;

[0024] [Fig.4] is an equivalent electrical diagram of a matrix ultrasound imaging device with row-column addressing of dimensions NxN operating in reception;

[0025] [Fig.5] schematically illustrates, in the form of diagrams, the behavior of an example of an ultrasonic transducer in emission;

[0026] [Fig.6] schematically illustrates, in the form of diagrams, the behavior of an example of an ultrasonic transducer in reception;

[0027] [Fig.7] schematically illustrates a TX transmission step and an RX reception step of an embodiment of a method for acquiring an image of a body by means of a matrix ultrasound imaging device with row-column addressing of dimensions NxN;

[0028] [Fig.8] schematically illustrates steps of a method for acquiring an image of a body by means of a 2x2 row-column addressing matrix ultrasound imaging device; and

[0029] [Fig.9] schematically illustrates steps of a method for acquiring an image of a body using a 4x4 row-column addressing matrix ultrasound imaging device. Description of the embodiments

[0030] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0031] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the various applications that the imaging devices and methods described may have have not been detailed, the embodiments described being compatible with the usual applications of ultrasound imaging solutions. In particular, the properties (frequencies, shapes, amplitudes, etc.) of the electrical excitation signals applied to the ultrasound transducers have not been detailed, the embodiments described being compatible with the excitation signals usually used in ultrasound imaging systems, which can be chosen according to the application considered and in particular the nature of the body to be analyzed and the type of information that one seeks to acquire. Similarly, the various processing operations applied to the electrical signals provided by the ultrasound transducers to extract useful information on the body to be analyzed have not been detailed, the embodiments described being compatible with the processing operations usually implemented in ultrasound imaging systems.In addition, the control circuits of the ultrasonic transducers of the described imaging devices have not been detailed, the embodiments being compatible with all or most of the known circuits for controlling ultrasonic transducers of row-column addressed matrix ultrasonic imaging devices, or the realization of these circuits being within the scope of the person skilled in the art upon reading the present description. In addition, the realization of the ultrasonic transducers of the described imaging devices has not been detailed, the described embodiments being compatible with all or most of the known structures of ultrasonic transducers.

[0032] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0033] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0034] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0035] [Fig. 1] is a top view schematically and partially illustrating an example of a row-column addressing matrix ultrasound imaging device 100.

[0036] [Fig.2] comprises two sectional views (A) and (B) of the device 100 of [Fig.l] according to planes AA and BB of [Fig.l] respectively.

[0037] The device 100 comprises a plurality of ultrasonic transducers 101 arranged in a matrix according to M rows R; and N columns Q, with M and N integers greater than or equal to to 2, i integer ranging from 1 to M, and j integer ranging from 1 to N.

[0038] In [Fig.l], four rows Rb R2, R3, R4 and four columns Cb C2, C3, C4 have been shown. In practice, the numbers M of rows and N of columns of the device 100 can of course be different from 4.

[0039] Each transducer 101 of the device 100 comprises a lower electrode E1 and an upper electrode E2 (Figures 2A and 2B). When an appropriate excitation voltage is applied between its electrodes E1 and E2, the transducer emits an ultrasonic acoustic wave. When the transducer receives an ultrasonic acoustic wave in a certain frequency range, it provides between its electrodes E1 and E2 a voltage representative of the received background.

[0040] In this example, the transducers 101 are capacitive membrane transducers, also called CMUT transducers (from the English "Capacitive Micro-machined Ultrasonic Transducer").

[0041] In each column Q of the transducer matrix, the transducers 101 of the column have their respective lower electrodes El connected to each other. The lower electrodes El of transducers 101 of separate columns are not, however, connected to each other. In addition, in each row R; of the transducer matrix, the transducers 101 of the row have their respective upper electrodes E2 connected to each other. The upper electrodes E2 of transducers 101 of separate rows are, however, not connected to each other.

[0042] In each column Q of the device 100, the lower electrodes El of the transducers 101 of the column form a continuous conductive or semiconductive strip 103, extending over substantially the entire length of the column. As a variant, each strip 103 of electrodes El comprises a vertical stack of a semiconductive strip and a conductive strip each extending over substantially the entire length of the column. In addition, in each row R; of the device 100, the upper electrodes E2 of the transducers 101 of the row form a continuous conductive or semiconductive strip 105, extending over substantially the entire length of the row. As a variant, each strip 105 of electrodes E2 comprises a vertical stack of a semiconductive strip and a conductive strip each extending over substantially the entire length of the row.For the sake of simplification, only the lower 103 and upper 105 electrode strips are shown in [Fig.l].

[0043] In the example shown, the strips 103 forming the column electrodes are made of a doped semiconductor material, for example doped silicon. In addition, in this example, the strips 105 forming the row electrodes are made of metal. For example, in top view, the lower strips 103 are parallel to each other, and the upper strips 105 are parallel to each other and perpendicular to the strips 103.

[0044] In the example of [Fig.l], the device 100 comprises a support substrate 110, for example made of a semiconductor material, for example silicon. The matrix of ultrasonic transducers 101 is arranged on the upper face of the substrate 110. More particularly, in this example, a dielectric layer 112, for example a layer of silicon oxide, forms an interface between the substrate 110 and the matrix of ultrasonic transducers 101. The dielectric layer 112 extends for example continuously over the entire upper surface of the support substrate 110. By way of example, the layer 112 is in contact, by its lower face, with the upper face of the substrate 110, over substantially the entire upper surface of the substrate 110.

[0045] The lower electrode strips 103 are arranged on the upper face of the dielectric layer 112, for example in contact with the upper face of the dielectric layer 112. The strips 103 may be separated laterally from each other by dielectric strips 121, for example made of silicon oxide, extending parallel to the strips 103 and having a thickness substantially identical to that of the strips 103.

[0046] Each transducer 101 comprises a cavity 125 formed in a rigid support layer 127, and a flexible membrane 123 suspended above the cavity 125. The layer 127 is for example a layer of silicon oxide. The layer 127 is arranged on the upper surface, for example substantially flat, of the assembly formed by the alternating strips 103 and 121. In each transducer 101, the cavity 125 is located opposite the lower electrode E1 of the transducer.

[0047] In the example shown, each transducer 101 comprises a single cavity 125 opposite its lower electrode EL. As a variant, in each transducer 101, the cavity 125 can be divided into a plurality of elementary cavities, for example arranged, in top view, in a matrix according to rows and columns, separated laterally from each other by side walls formed by portions of the layer 127.

[0048] In the example shown, at the bottom of each cavity 125, a dielectric layer 129, for example made of silicon oxide, coats the lower electrode E1 of the transducer, so as to prevent any electrical contact between the flexible membrane 123 and the lower electrode E1 of the transducer. As a variant, to ensure this electrical insulation function, a dielectric layer (not shown) can coat the lower face of the membrane 123. In this case, the layer 129 can be omitted.

[0049] In each transducer 101, the flexible membrane 123, covering the cavity 125 of the transducer, is for example made of a doped or undoped semiconductor material, for example silicon.

[0050] In each transducer 101, the upper electrode E2 of the transducer is arranged on and in contact with the upper face of the flexible membrane 123 of the transducer, directly above the cavity 125 and the lower electrode E1 of the transducer. Alternatively, in the case of a semiconductor membrane, the upper electrode E2 of each transducer 101 may be formed by the membrane itself, in which case the layer 105 may be omitted.

[0051] By way of example, in each line R; of the device 100, the flexible membranes 123 of the transducers 101 of the line form a continuous membrane strip extending over substantially the entire length of the line, separated laterally from the membrane strips of the neighboring lines by a dielectric region. In each line R;, the membrane strip 123 of the line coincides, for example, in top view, with the upper electrode strip 105 of the line.

[0052] For each line R; of the transducer matrix 101, the device 100 may comprise a transmission circuit, a reception circuit, and a controllable switch for, in a first configuration, connecting the electrodes E2 of the transducers of the line to an output terminal of the transmission circuit of the line, and, in a second configuration, connecting the electrodes E2 of the transducers of the line to an input terminal of the reception circuit of the line.

[0053] In addition, for each column Cj of the transducer matrix 101, the device 100 may comprise a transmission circuit, a reception circuit, and a controllable switch for, in a first configuration, connecting the electrodes El of the transducers of the column to an output terminal of the transmission circuit of the column, and, in a second configuration, connecting the electrodes El of the transducers of the column to an input terminal of the reception circuit of the column.

[0054] For the sake of simplification, the transmission and reception circuits and the switches of the device 100 have not been shown in the figures. In addition, the embodiment of these elements has not been detailed, the embodiments described being compatible with the usual embodiments of transmission / reception circuits of matrix ultrasound imaging devices with row-column addressing. By way of non-limiting example, the transmission / reception circuits may be identical or similar to those described in French patent application No. 19 / 06515 filed by the applicant on June 18, 2019.

[0055] The acquisition of an ultrasound image of a body by means of a row-column addressing matrix ultrasound imaging device, for example of the type described in relation to Figures 1 and 2, may comprise a phase of transmitting an ultrasound wave, followed by a phase of receiving a return ultrasound wave, reflected by the body.

[0056] For example, during the transmission phase, the row electrodes of the transducer matrix (corresponding to electrodes 105 in the example of Figures 1 and 2) are maintained at a fixed reference potential, for example ground, and a potential of continuous bias Vbias is applied to each of the column electrodes of the matrix (corresponding to the electrodes 103 in the example of figures 1 and 2). An alternating excitation voltage Vexc is further applied to each of the column electrodes of the matrix. Thus, each transducer 101 of the matrix sees, between its electrodes E1 and E2, the alternating excitation voltage Vexc superimposed on a continuous bias voltage Vbias. This causes a vibration of the transducer membrane, leading to the emission of an ultrasonic acoustic wave.

[0057] During the reception phase, the column electrodes can be maintained at the DC bias potential Vbias. An AC voltage superimposed on the DC bias voltage Vbias then appears between the electrodes E1 and E2 of each transducer 101 under the effect of the return acoustic background. The AC voltages produced individually by the elementary transducers of the matrix, also called individual contributions of the elementary transducers, combine on the row and column electrodes of the matrix and resulting voltages can be read on said row and column electrodes.

[0058] An object of an embodiment is to provide a method for acquiring an ultrasound image by means of a matrix ultrasound imaging device with row-column addressing, making it possible to trace the individual contributions of the elementary transducers of the matrix, so as to benefit from both the advantages of fully populated devices in terms of imaging resolution, and of row-column addressing devices in terms of electronic complexity.

[0059] [Fig.3] is an equivalent electrical diagram of a matrix ultrasound imaging device with row-column addressing of 2 rows and 2 columns, during a reception phase of an ultrasonic wave.

[0060] Each elementary transducer can be modeled by a voltage generator ey in series with an impedance Zth between a row electrode R; (corresponding to an electrode 105 in the implementation example of FIGS. 1 and 2) and a column electrode Q (corresponding to an electrode 103 in the implementation example of FIGS. 1 and 2). Each voltage value ey is representative of the vibration of the elementary transducer of coordinates i,j in the matrix under the effect of the received ultrasonic background, and corresponds to the individual contribution of the elementary transducer to the voltages measured on the row and / or column electrodes of the device. In addition, for each row of the matrix, a load impedance ZR between the row electrode R; and the ground, and, for each column of the matrix, a load impedance Zc between the column electrode Q and the ground.The impedances Z* of the different elementary transducers of the matrix are for example all identical or substantially identical. The load impedances ZR connected to the different line electrodes R; of the matrix are for example all . identical or substantially identical. The load impedances Zc connected to the different column electrodes Cj of the matrix are for example all identical or substantially identical. Here we denote by VRi the alternating voltage appearing on the line R; during a reception phase of an ultrasonic wave, and by VCj the alternating voltage appearing on the column Q during a reception phase of an ultrasonic wave.

[0061] By applying the principle of superposition, we can write the following system of equations: [Math.l] IV RI + a\2R\^e\2 + a2ïR\*e2ï + a22R\^e22 VR2 ~ a\ ÏR2*e\ 1 + al2R2*e 12 + ^21^2^21 + ^22^2^22 VC1 = ÛHCÎ + «12C1 *^12 + a2lCl ^21 + a22Cl ^22 VC2 “ û i lC2*el I + a12C2 *^12 + a2lC2 ^21 + a22C2 ^e22 where each coefficient aijRk is representative of the weight of the contribution of the generator ey to the voltage VRk of the line Rk, with k being an integer from 1 to N, and where each coefficient aijCk is representative of the weight of the contribution of the generator ey to the voltage VCk of the column Ck.

[0062] [Fig.4] is an equivalent electrical diagram of a row-column addressing matrix ultrasound imaging device of N rows and N columns. The equivalent electrical diagram of [Fig.4] is similar to that of [Fig.2]. For the sake of simplification, the load impedances ZR connected on the rows and the load impedances Zc connected on the columns have not been shown in [Fig.4].

[0063] Using the previous notations, the aforementioned system of equations [Math 1] can be rewritten in matrix form as follows: [A]*[e]=[V]

[0064] With: [Math.2] 1 1 1 al 1 RI aî2Rl H\ N - 1)R1 aNNRl ' aiiR2 aI2R2 aN(N- 1)R2 aNNR2 A — aHRN a12RN aN(N - 1)RN aNNRN ai ICI a12Cl i N 1)CI aNNCl aHC(N-1) ai2C(Nl) » )Ci\ I) aNNC(N-1) । i ( aliCN a12CN aN(N - 1)CN aNNCN (

[0065] And:

[0066] [Math.3]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] The 2N*(N*N) coefficients of the matrix [A] can be determined beforehand during a characterization or simulation phase of the device, and stored in a memory of an electronic processing device. The 2N vector voltages [V] can be read on the row and column electrodes of the matrix. We thus obtain a system with 2N equations and N*N unknowns (the N*N voltage values ​​ey). As it stands, this system cannot be solved, the number of independent equations being less than the number of unknowns. According to one aspect of an embodiment, it is provided, as will be explained in more detail below, to increase the number of discriminating equations of the system, by carrying out several successive firings of the same ultrasonic wave (i.e. a beam with the same characteristics) in the direction of the body to be analyzed, and by modifying each time, during the return wave reception phase, the sign of at least one generator ey. According to a preferred embodiment, provision is made, at each shot, to modify the sign of the bias voltage applied to at least one of the column electrodes of the matrix during the return reception phase, so as to invert the sign of all the generators ey of said at least one column. This takes advantage of the symmetrical voltage behavior of the CMUT transducers, which will be recalled below in relation to Figures 5 and 6. More generally, the preferred embodiment detailed below applies to any type of transducer exhibiting symmetrical behavior, in particular in reception, for example PMUT transducers (from the English "Piezoelectric Micromachined Ultrasonic Transducers"). By symmetrical reception behavior, we mean here that the sign of the alternating voltage produced by the transducer during a reception phase of an ultrasonic wave is reversed when the sign of the direct polarization voltage applied to the transducer during this same reception phase is reversed.

[0073] [Fig.5] schematically illustrates the behavior of an example of a CMUT transducer in transmission.

[0074] [Fig.5] includes a diagram (a) representing an example of a voltage VcMUT that can be applied between the electrodes of the transducer during an emission phase. In this example, the voltage VcMUT is a positive voltage corresponding to the superposition (or sum) of a positive DC bias voltage Vbias, and an AC excitation voltage Vexc. In this example, the AC excitation voltage is a square wave voltage successively comprising a high state, a low state, a high state, and a low state.

[0075] The application of the voltage VcMut across the transducer terminals leads to a vibratory displacement of the transducer membrane along a z axis orthogonal to the membrane, illustrated by a diagram (b) in [Fig.5]. In this diagram, position 0 corresponds to the mechanical equilibrium position of the membrane, in the absence of any electrical polarization.

[0076] This vibratory displacement of the membrane leads to the emission of an acoustic wave illustrated by a diagram (c) in [Fig.5].

[0077] [Fig.5] further comprises a diagram (a1) representing another example of a voltage VcMUT that can be applied between the electrodes of the transducer during an emission phase. In this example, the voltage VcMUT is a negative voltage corresponding to the opposite of the voltage VcMUT of the diagram (a). Thus, in this example, the voltage VcMUT corresponds to the superposition of a negative DC bias voltage V bias, and an AC excitation voltage Vexc. The DC bias voltage Vbias of the diagram (a1) corresponds to the opposite of the DC bias voltage Vbias of the diagram (a), and the AC excitation voltage Vexc of the diagram (a1) corresponds to the opposite of the AC excitation voltage Vexc of the diagram (a). Thus, in this example, the AC excitation voltage is a square wave voltage successively comprising a low state, a high state, a low state, and a high state.

[0078] As illustrated in [Fig.5], the application of the voltage VcMUT of diagram (a1) to the terminals of the transducer leads to a vibratory displacement identical to that obtained with the application of the voltage VcMut of diagram (a), and, consequently, to the emission of an acoustic wave identical to that obtained with the application of the voltage VcMut of diagram (a). Thus, the inversion of the sign of the voltage applied to the transducer does not modify the behavior of the transducer in emission.

[0079] [Fig.6] schematically illustrates the behavior of an example of a CMUT transducer in reception.

[0080] [Fig.6] includes a diagram (a) representing an example of an acoustic wave received by the CMUT transducer.

[0081] [Fig.6] further comprises a diagram (b) illustrating the vibrational displacement of the transducer membrane under the effect of the received acoustic background, when the transducer is polarized at a direct voltage Vbias. It will be noted that this displacement is independent of the sign, positive or negative, of the voltage Vbias.

[0082] [Fig.6] further comprises a diagram (c) representing the voltage VcMUT at the terminals of the transducers during a reception phase. In this example, the DC bias voltage Vbias applied to the terminals of the transducer is a positive voltage. The voltage VcMUT is then a positive voltage corresponding to the superposition or sum of the voltage Vbias, and an AC voltage Vrec generated under the effect of the vibration of the membrane.

[0083] [Fig.6] further illustrates a diagram (c1) representing the voltage VcMut at the terminals of the transducers during a reception phase. In this example, the DC bias voltage Vbias applied to the terminals of the transducer is a negative voltage. More particularly, in this example, the DC bias voltage Vbias applied to the terminals of the transducer is the opposite of that applied in the example of diagram (c). The voltage VcMut is then a negative voltage corresponding to the superposition of the voltage Vbias, and of an AC voltage Vrec generated under the effect of the vibration of the membrane. As illustrated in [Fig.6], the voltage Vrec of diagram (c1) is the opposite of the voltage Vrec of diagram (c). Thus, the inversion of the sign of the DC bias voltage Vbias in reception leads to an inversion of the sign of the AC voltage Vrec generated at the terminals of the transducer under the effect of a received acoustic wave.

[0084] By taking up the previous notations and considering an elementary transducer of a matrix ultrasound imaging device with row-column addressing, the alternating voltage Vrec appearing at the terminals of the transducer under the effect of a received acoustic wave corresponds to the contribution ey of the transducer to the voltage signals read on the row electrodes R; or column electrode Q of the device.

[0085] Thus, by inverting the DC bias voltage Vbias of a receiving column, the sign of the contributions ey of the transducers of the column is inverted. This makes it possible, as will be described in more detail below, to obtain additional discriminant equations making it possible to go back to the individual contributions of the elementary transducers of the matrix.

[0086] It will be noted that to the extent that the response of the transducers remains linear, the same weighting coefficient can be applied to the continuous polarization voltages. Vbias and / or on the alternating excitation voltages Vexc, this coefficient being able to be modified between two successive shots or between two successive reception phases of the process. A rectification can be applied during the reconstruction of the individual contributions of the transducers to take this weighting into account.

[0087] [Fig.7] schematically illustrates a TX transmission step and a RX reception of a method for acquiring an image of a body using a matrix ultrasound imaging device with row-column addressing of dimensions NxN.

[0088] In this example, during the TX transmission phase, a DC bias voltage Vb;as and an AC excitation voltage Vexc are applied to the odd-rank Q column electrodes, and an opposite DC bias voltage -Vbias and an opposite AC excitation voltage -Vexc are applied to the even-rank Cj column electrodes. In [Fig.7], each elementary transducer is represented by an impedance Z* during the TX transmission phase. During the RX reception phase, the DC bias voltages VbiaS and -VbiaS applied respectively to the odd-rank Q column electrodes and to the even-rank Q column electrodes remain unchanged.

[0089] As explained above in relation to [Fig.5], the inversion of the sign of the voltages Vbias and Vexc on the columns of even rank has no impact on the acoustic background emitted by the transducers of the column. In other words, the emitted ultrasonic background is the same as if the signs of the voltages Vb;as and Vexc were the same on all the columns.

[0090] In reception, the inversion of the sign of the DC polarization voltage in the even-rank columns leads, on the other hand, to inverting the signs of the contributions ey of the elementary transducers of said columns, as explained above in relation to [Fig.6].

[0091] By carrying out several successive shots of the same ultrasonic wave, by modifying each time the sign of the polarization voltages applied to certain columns in the reception phase, and by carrying out linear combinations of the voltages measured on the line electrodes R;, it is possible to go back to the individual contributions ey of each of the elementary transducers of the matrix.

[0092] [Fig.8] schematically illustrates an example of an embodiment of a method of acquiring an image of a body using a 2x2 row-column addressing matrix ultrasound imaging device.

[0093] The method of [Fig.8] comprises two successive shots of the same ultrasonic wave towards the body to be analyzed.

[0094] More particularly, the method comprises a first step of transmitting TX1 an ultrasonic wave (first shot), followed by a first step of receiving RX1 a

[0095]

[0096]

[0097]

[0098]

[0099] return wave reflected by the body to be analyzed, followed by a second step of emission TX2 of an ultrasonic wave (second shot) identical to that emitted in step TX1, followed by a second step of reception RX2 of a return wave reflected by the body to be analyzed. During the emission step TX1, the column electrodes Ci and C2 are polarized at the same direct voltage Vbias, and receive the same alternating excitation voltage Vexc superimposed on the voltage Vbias. During the reception phase RX1, the column electrodes Ci and C2 remain polarized at the voltage Vbias, and alternating voltages y^ and y^ are read respectively on the row electrodes Ri and R2. The following system of equations can then be written: [Math.5] VÆ1 = “HJ?! ^11 + «12Æ! 12 + Û21 RI '^21 + fl22Àl *e22 . V R2 = al lR2^e\ 1 + ^12^2^12 + ^21^2^21 + a22R2*e22 During the emission step TX2, the column electrodes Ci and C2 are polarized res respectively to the Vbias voltage and to the -Vbias voltage, and receive respectively the alternating excitation voltage Vexc and the opposite alternating excitation voltage -Vexc- During the RX2 reception phase, the column electrodes Ci and C2 remain po larized respectively to the voltage Vbias and to the voltage -Vbias, and voltages al ternatives v2 VR1 and v2 VR2 are read respectively on the line electrodes Ri and R2.

[0100] The following system of equations can then be written: [Math.6] = ^11^1^11 ' ^12^1^12 + ^2] -^22^1^^22 . Vr2 = ^11^2^11 ' a 12 R2^e\2 + a2\R2 @2\ ~ a22R2*e22

[0101] By summing the two systems of equations [Math 5] and [Math 6] above, we obtain a system with two equations and two unknowns which can be rewritten in matrix form as follows: [A]*[e]=[V], with: [Math.7] [a] = a HRi 1 J LallR2 a21Rl ' a21R2.

[0102] And :

[0103] [Math. 8] r re,. LJ e2i. And :

[0104] Since the matrix A is invertible, the system can be solved, which makes it possible to determine the respective contributions en and e2i of the elementary transducers of rank i=l and of rank i=2 of the column of rank j=l.

[0105] Similarly, by subtracting the two systems of equations [Math 5] and [Math 6] above, we obtain a system with two equations and two unknowns which can be rewritten in matrix form as follows: [A]*[e]=[V], with: [Math. 10] a12RI .a12R2 a22Rl a22R2

[0106] And : [Math. 11] laughed LJ e22.

[0107] And : [Math. 12]

[0108] Here again, the matrix A being invertible, the system can be solved, which makes it possible to determine the respective contributions e^ and e22 of the elementary transducers of rank i=1 and of rank i=2 of the column of rank j=2.

[0109] Thus, by means of two shots of the same ultrasonic wave, by inverting the sign of the polarization voltage Vbias of one of the columns between the two corresponding reception phases, and by carrying out linear combinations of the alternating voltages measured in reception on the electrodes, it is possible to go back to the individual contributions ey of each of the four elementary transducers of the matrix.

[0110] It will be noted that as explained above in relation to [Fig. 5], the inversion of the sign of the bias voltages Vbias and excitation Vexc during the emission phase has no effect on the emitted ultrasonic background. Thus, it could be planned to carry out the two shots with the same bias and excitation voltages, and modify the sign of the bias voltage of one of the columns only during the reception phase RX2. In practice, however, it may prove difficult to reverse the sign of the bias voltage of a column between the emission phase and the reception phase of the same ultrasonic wave. The sign of the polarization voltage of the column electrode C2 will therefore preferably be modified from the emission phase TX2.

[0111] This mode of operation can be generalized regardless of the number N of rows and columns of the matrix.

[0112] For a matrix of dimensions NxN, it will be necessary to carry out at least N successive shots TX1,... TXN, each time modifying the sign of the polarization voltage applied to at least one of the column electrodes of the matrix during the respective subsequent reception phase RX1,... RXN.

[0113] Preferably, the signs of the bias voltages applied respectively to the N column electrodes Ci,... CN during the N reception phases RX1,... RXN are coded by the vectors of an orthogonal matrix, for example a Hadamard matrix. By using N linear combinations of the voltage measurements carried out on the row electrodes R; of the matrix, we obtain N subsystems of matrix equations of type [A]*[e]=[V] with, for each subsystem, an invertible matrix A of dimensions N*N. We can thus go back to the individual contributions ey of the N*N elementary transducers of the device.

[0114] [Fig.9] schematically illustrates, as an illustrative example, a mode of implementation implementation of a method for acquiring an image of a body using a 4x4 row-column addressing matrix ultrasound imaging device. The person skilled in the art will be able to adapt the method described regardless of the number N of rows and columns of the device.

[0115] [Fig.9] more particularly represents the signs of the polarization voltages ap applied to the Q column electrodes of the matrix during the four successive reception phases RX1, RX2, RX3 and RX4 of the process. In this figure, a + sign is shown at the head of the column when the bias voltage applied to the column is equal to Vbias, and a - sign at the head of the column when the bias voltage applied to the column is equal to -Vbias.

[0116] During the reception phase RX1 following the first shot, the column electrodes Ci, C2, C3 and C4 are all positively polarized (++++). During the reception phase RX2 following the second shot, the column electrodes Cb C2, C3 and C4 are respectively positively, negatively, positively and negatively polarized (-1—F-). During the reception phase RX3 following the third shot, the column electrodes Cb C2, C3 and C4 are respectively positively, positively, negatively and negatively polarized (-H—). During the reception phase RX4 following the fourth shot, the column electrodes Ci, C2, C3 and C4 are respectively positively, negatively, negatively and positively polarized (-1—t).

[0117] For each of the reception phases RX1, RX2, RX3 and RX4, a system of equations of the same type as the systems [Math 5] and [Math 6] described above can be written, with, each time, N equations per system and N*N ayRi*ey terms per equation.

[0118] Hereinafter, T1, T2, T3 and T4 denote the N=4 corresponding systems of equations.

[0119] By carrying out N=4 linear combinations of the systems T1, T2, T3 and T4, we obtain N=4 subsystems of matrix equations of type [A]*[e]=[V] with, for each subsystem, an invertible matrix A of dimensions N*N=16. This makes it possible to go back to the individual contributions ey of the N*N=16 elementary transducers of the device.

[0120] The N linear combinations of the systems T1, T2, T3 and T4 are for example coded by the same vectors as those used to code the signs of the polarization voltages applied to the columns of the matrix during N reception phases RXi.

[0121] By performing the summation T1+T2+T3+T4, we obtain a first subsystem of type [A]*[e]=[V]

[0122] With: [Math. 16] allRl a21Rl a31Rl a41Rl ' al!R2 a21R2 a31R2 a41R2 aliR3 a21R3 a31R3 a4!R3 . allR4 a21R4 a31R4 a41R4.

[0123] And: [Math. 17] [Math. 18] Vr1 + ^Rl + ^Rl + 4 1 1 4 vk + V*4 + V^4 + ^4 4 4

[0125] Since the matrix A is invertible, the system can be solved, which makes it possible to de terminate the respective contributions in elementary transducers of the column of rank j=l.

[0126] By carrying out the summation T1-T2+T3-T4 we can, in a similar way, determine the respective contributions ei2 of the elementary transducers of the column of rank j=2.

[0127] By carrying out the summation T1+T2-T3-T4 we can, in a similar way, determine the respective contributions ei3 of the elementary transducers of the column of rank j=3.

[0128] By carrying out the summation T1-T2-T3+T4 we can, in a similar way, determine the respective contributions ei4 of the elementary transducers of the column of rank j=4.

[0129] Thus, by carrying out N*N linear combinations of the N*N voltages measured on the N line electrodes R; at the end of the N shots of the device respectively, and by multiplying the resulting vector of dimensions N*N by a matrix of N*(N*N) coefficients a^R, predetermined, we directly obtain the respective contributions ey of the N*N elementary transducers of the device.

[0130] An advantage of the proposed acquisition method is that it allows to benefit from both the advantages of fully populated devices in terms of imaging resolution, and of row-column addressing devices in terms of electronic complexity.

[0131] Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will occur to those skilled in the art. In particular, the described embodiments are not limited to the particular example embodiment of the matrix of elementary transducers described in relation to Figures 1 and 2.

[0132] Furthermore, although, in the examples described above, the DC bias voltages Vbias and -Vbias applied to the different column electrodes Cj of the device are all of the same amplitude in absolute value, the embodiments described are not limited to this particular case. As a variant, the amplitude levels of the DC bias voltages applied to the different column electrodes Q, in transmission and / or in reception, can be differentiated. Similarly, the AC excitation voltages Vexc applied to the column electrodes Q in transmission can be differentiated by column.

[0133] Furthermore, the embodiments described are not limited to the examples detailed above in which the inversion of the sign of the contribution ey of the elementary transducers of a column is obtained by inverting the sign of the continuous bias voltage Vbias applied to this column. More generally, any other means making it possible to invert the sign of the contribution ey of one or more elementary transducers between two successive shots of the same ultrasonic wave can be provided. By way of example, each elementary transducer of position (i,j) in the matrix is ​​associated with a system of switches, for example electromechanical switches canics, allowing to reverse the direction of connection of the transducer electrodes between the row electrodes R; and column electrodes Q of the matrix. In other words, in a first configuration of the switch system, the transducer has a first electrode connected to the electrode R; and a second electrode connected to the electrode C j, and, in a second configuration of the switch system, the transducer has its first electrode connected to the electrode Q and its second electrode connected to the electrode R;. Thus, by changing, between two successive shots of the same ultrasonic wave, the configuration of the switch system associated with an elementary transducer of position (i,j), the sign of the contribution ey of this transducer is reversed. This makes it possible to increase the number of discriminant equations of the system and thus to go back to the individual contributions ey of all the elementary transducers of the matrix.In this embodiment, the switch systems associated with the individual transducers can be controlled individually, transducer by transducer, or simultaneously by column. It will be noted that this embodiment is compatible with any type of ultrasonic transducers, including transducers not exhibiting voltage symmetrical behavior. In particular, this embodiment is not limited to CMUT and PMUT transducers.

[0134] Furthermore, although examples of implementation based on voltage measurements on the electrodes of the device have been described above, the described embodiments are not limited to this particular case. As a variant, the described embodiments can be adapted to trace the individual contributions of the elementary transducers from measurements of another variable electrical quantity, for example a current, charges or an impedance, on the electrodes of the device.

[0135] Furthermore, although the above detailed examples of the proposed acquisition method have been given for square transducer matrices of N lines by N columns, the described embodiments are not limited to this particular case. On reading the present description, the person skilled in the art will know how to adapt the proposed method to matrix devices of M lines by N columns, with M different from N.

[0136] Furthermore, in the embodiments described above, at each ultrasonic waveform shot, the waveform is generated by the same matrix device as that used for receiving the return waveform. The embodiments described are not, however, limited to this particular case. As a variant, the transducer matrix is ​​used solely as a receiving device, to receive the ultrasonic waveform returned by the body to be analyzed, and a separate transmitting device (not detailed) is used to transmit the ultrasonic waveform towards the body to be analyzed. The transmitting device and the receiving device are then synchronized to implement the N alternating TX transmission phases and the N alternating RX reception phases.

[0137] Furthermore, the practical implementation of the described embodiments and variants is within the reach of the person skilled in the art from the functional indications given above. In particular, the production of the electronic circuits for controlling the transmitter and receiver devices to implement the proposed method has not been detailed, the production of these circuits being within the reach of the person skilled in the art upon reading this description. In addition, the production of the electronic processing devices making it possible to trace the individual contributions of the elementary transducers from the quantities measured on the electrodes of the device has not been detailed, the production of such devices being within the reach of the person skilled in the art from the teachings of this description.

[0138] Furthermore, it will be noted that in the examples described above, the row and column names are arbitrary and can of course be reversed.

Claims

Claims

1. Method for acquiring an image of a body by means of a row-column addressing matrix ultrasound imaging device (100), the device (100) comprising a matrix of elementary ultrasound transducers (101) connected in rows and columns by row electrodes (R;) and column electrodes (Cj) respectively, the method comprising: - carrying out N successive shots (TX1, ...TXN) of the same ultrasound wave in the direction of said body, where N is an integer greater than or equal to 2; - after each shot, implementing a reception phase (RX1, ...RXN), by means of said device, of a return ultrasonic wave, reflected by said body, in which, during each of the reception phases (RX1, ...RXN), a variable electrical quantity representative of the received background is read on each line electrode (R;) of the device, and in which, between any two reception phases among the N reception phases (RX1, ...RXN), the sign of the individual contribution (ey) of at least one elementary ultrasonic transducer (101) of the matrix is ​​modified, the method further comprising a step of calculating, by means of an electronic processing device, by linear combinations of the variable electrical quantities (VRi) read on the line electrodes (R;) of the device during the N reception phases (RX1, ...RXN), an individual contribution (ey) of each of the elementary transducers (101) of the matrix.

2. Method according to claim 1, in which, during each of the N reception phases (RX1, ...RXN), each column electrode (Cj) of the matrix is ​​maintained at a DC bias voltage (Vbias, -V bias)i and in which, between any two reception phases among the N reception phases (RX1, ...RXN), the sign of the DC bias voltage (Vbias, -Vbias) applied to at least one of the column electrodes (Cj) of the device is modified.

3. Method according to claim 2, in which the signs of the bias voltages (Vbias, -Vbias) applied respectively to the column electrodes (Cj) of the device during the N reception phases (RX1, ...RXN) are coded by the vectors of an orthogonal matrix, for example a Hadamard matrix.

4. A method according to claim 2 or 3, wherein the N successive shots (TX1,... TXN) are performed by means of said row-column addressing matrix ultrasound imaging device (100), and wherein, during each of the N shots (TX1,... TXN), each column electrode (Q) of the matrix is ​​maintained at a DC bias voltage (Vbias, -Vbias), and an AC excitation voltage (Vexc) superimposed on the DC bias voltage is applied to said column electrode (Cj), and wherein, during each shot, the signs of the DC bias voltages respectively applied to the column electrodes (Cj) of the matrix are the same as the signs of the DC bias voltages respectively applied to the column electrodes (Cj) during the subsequent reception phase.

5. Method according to claim 1, in which, between any two reception phases among the N reception phases (RX1, ...RXN), the electrical connection of at least one elementary transducer (101) between the row (R;) and column (Cj) electrodes is reversed by means of a system of switches, so as to modify the sign of the individual contribution (ey) of said at least one elementary ultrasonic transducer (101) of the matrix.

6. A method according to any one of claims 1 to 5, wherein the ultrasonic transducers (101) are CMUT or PMUT transducers.

7. Method according to any one of claims 1 or 6, wherein said matrix comprises N rows and N columns of elementary ultrasonic transducers (101).

8. Method according to any one of claims 1 to 7, in which the variable electrical quantity (VRi) read on each row electrode (R;) of the device is a voltage.

9. A row-column addressing matrix ultrasound imaging device (100), the device (100) comprising a matrix of elementary ultrasound transducers (101) connected in rows and columns by row electrodes (R;) and column electrodes (Q), respectively, and a control circuit configured to implement a method according to any one of claims 1 to 8.

10. Device according to claim 9, wherein the ultrasonic transducers (101) are CMUT or PMUT transducers.

Images