Method and apparatus for ultrasonic imaging using row-column addressing

Description

[0001] The present application is based on, and claims priority from, French patent application FR2106871 filed on June 25, 2021 and entitled “Method and device for ultrasonic imaging with row-column addressing”. Technical field

[0002] 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

[0003] An ultrasound imaging device typically comprises a plurality of ultrasound transducers and an electronic control circuit connected to the transducers. In operation, all of the transducers are positioned 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 transducers to emit ultrasound waves toward 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 surface structure), then return to the transducers, which convert them back 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 being studied.

[0004] 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.

[0005] Among the three-dimensional image acquisition devices, we can distinguish between so-called fully populated devices, in which each transducer in the matrix is ​​individually addressable, and so-called row-column addressing or RCA devices, in which the transducers in the matrix are addressable by row and by column.

[0006] Fully populated devices offer greater flexibility in shaping the transmit and receive ultrasonic beams. However, the array control electronics are complex, with the required number of transmit / receive channels being M*N in the case of an M-row by N-column array. In addition, the signal-to-noise ratio is generally relatively low since each transducer has a small surface area exposed to the ultrasonic waves.

[0007] RCA-type devices use different ultrasonic beam shaping algorithms. The beam shaping capabilities may be reduced compared to fully populated devices. However, the matrix control electronics are considerably simplified, with the required number of transmit / receive channels being reduced to M+N in the case of an M-row by N-column matrix. In addition, the signal-to-noise ratio is improved due to the interconnection of the transducers in a row or column during the transmit and receive phases.

[0008] We are particularly interested here in devices and methods for acquiring three-dimensional images with row-column addressing (RCA).

[0009] It would be desirable to improve at least some aspects of the devices and methods for acquiring three-dimensional row-column addressed ultrasound images. The article by C. Ceroici et al. entitled "Fast Orthogonal Row-Column Electronic Scanning With Top-Orthogonal-to-Bottom Electrode Arrays" (IEEE Transactions On Ultrasonics Ferroelectrics and Frequency Control, vol. 64 no. 6, June 1, 2017, pages 1009-1014, XP011650924), the article by C. Ceroici et al. entitled "Fast Orthogonal Row-Column Electronic Scanning With Top-Orthogonal-to-Bottom Electrode Arrays" (IEEE Transactions On Ultrasonics Ferroelectrics and Frequency Control, vol. 66 no. 6, June 1, 2019, pages 1093-1101, XP011728147), and document US2019 / 235077 describe example methods and devices for ultrasound imaging. Summary of the invention

[0010] The invention is defined by appended claim 1. One embodiment provides a method for acquiring an image of a body by means of 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, the method comprising: carrying 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, implementing 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 wave is read on each row 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] According to one embodiment, the ultrasonic transducers are CMUT or PMUT transducers.

[0016] According to one embodiment, the matrix comprises N rows and N columns of elementary ultrasonic transducers.

[0017] According to the invention, 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.

[0018] According to one embodiment, the variable electrical quantity read on each row electrode of the device is a voltage.

[0019] 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.

[0020] According to one embodiment, the ultrasonic transducers are CMUT or PMUT transducers. Brief description of the drawings

[0021] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which: there Figure 1 is a top view schematically and partially illustrating an example of a row-column addressing matrix ultrasound imaging device; Figure 2 includes a sectional view along a plane AA of the Figure 1 , and a sectional view along a plane BB of the Figure 1 , illustrating in more detail an example of the implementation of the device of the Figure 1 ; there Figure 3 is an equivalent electrical diagram of a 2x2 row-column addressing matrix ultrasound imaging device operating in reception mode; Figure 4is an equivalent electrical diagram of a matrix ultrasound imaging device with row-column addressing of dimensions NxN operating in reception; the Figure 5 schematically illustrates, in the form of diagrams, the behavior of an example of an ultrasonic transducer in emission; Figure 6 schematically illustrates, in the form of diagrams, the behavior of an example of an ultrasonic transducer in reception; Figure 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; figure 8 schematically illustrates steps of a method for acquiring an image of a body using a 2x2 row-column addressing matrix ultrasound imaging device; and figure 9schematically 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

[0022] 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.

[0023] For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed. In particular, the various applications that the imaging devices and methods described may have 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 ultrasonic transducers to extract useful information about 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 for the ultrasonic transducers of the imaging devices described have not been detailed, the embodiments being compatible with all or most of the known control circuits for ultrasonic transducers of row-column addressing matrix ultrasound imaging devices, or the production of these circuits being within the scope of the person skilled in the art upon reading the present description.Furthermore, the construction of the ultrasonic transducers of the described imaging devices has not been detailed, the described embodiments being compatible with all or most known ultrasonic transducer structures.

[0024] Unless otherwise specified, when two elements are connected together, this means directly connected without intermediate elements other than conductors, and when two elements are connected (in English "coupled") together, this means that these two elements can be connected or be connected by means of one or more other elements.

[0025] 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.

[0026] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0027] There Figure 1 is a top view schematically and partially illustrating an example of a row-column addressing matrix ultrasound imaging device 100.

[0028] There Figure 2 comprises two sectional views (A) and (B) of the device 100 of the Figure 1 according to plans AA and BB of the Figure 1 .

[0029] The device 100 comprises a plurality of ultrasonic transducers 101 arranged in a matrix according to M rows R i and N columns C j , with M and N integers greater than or equal to 2, i integer ranging from 1 to M, and j integer ranging from 1 to N.

[0030] On the Figure 1 , four rows R 1 , R 2 , R 3 , R 4 and four columns C 1 , C 2 , C 3 , C 4 have been represented. In practice, the numbers M of rows and N of columns of the device 100 can of course be different from 4.

[0031] 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 a voltage representative of the received wave between its electrodes E1 and E2.

[0032] In this example, the transducers 101 are capacitive membrane transducers, also called CMUT transducers (from the English "Capacitive Micromachined Ultrasonic Transducer" - micro-machined capacitive ultrasonic transducer).

[0033] In each column C j of the transducer matrix, the transducers 101 of the column have their respective lower electrodes E1 connected to each other. The lower electrodes E1 of transducers 101 of separate columns are not connected to each other. In addition, in each row R i 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 not connected to each other.

[0034] In each column C j of the device 100, the lower electrodes E1 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 E1 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 i 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 the . Figure 1 .

[0035] 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.

[0036] In the example of the Figure 1, 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.

[0037] 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.

[0038] 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.

[0039] In the example shown, each transducer 101 comprises a single cavity 125 opposite its lower electrode E1. 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] For example, in each line R i 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 i , the membrane strip 123 of the line coincides, for example, in top view, with the upper electrode strip 105 of the line.

[0044] For each line R i 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.

[0045] In addition, for each column C j 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 E1 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 E1 of the transducers of the column to an input terminal of the reception circuit of the column.

[0046] 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.

[0047] Acquiring an ultrasound image of a body by means of a row-column addressed matrix ultrasound imaging device, for example of the type described in connection with Figures 1 and 2 , may include a phase of transmitting an ultrasonic wave, followed by a phase of receiving a returning ultrasonic wave, reflected by the body.

[0048] 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 continuous bias potential V bias is applied to each of the column electrodes of the matrix (corresponding to electrodes 103 in the example of Figures 1 and 2 ). An alternating excitation voltage V exc 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 V exc superimposed on a direct bias voltage V bias . This causes a vibration of the transducer membrane, leading to the emission of an ultrasonic acoustic wave.

[0049] During the reception phase, the column electrodes can be maintained at the DC bias potential V bias . An AC voltage superimposed on the DC bias voltage V bias then appears between the electrodes E1 and E2 of each transducer 101 under the effect of the return acoustic wave. 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.

[0050] An object of an embodiment is to provide a method for acquiring an ultrasound image using a row-column addressing matrix ultrasound imaging device, 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.

[0051] There Figure 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.

[0052] Each elementary transducer can be modeled by a voltage generator e ij in series with an impedance Z th between a line electrode R i (corresponding to an electrode 105 in the implementation example of the Figures 1 and 2) and a column electrode C j (corresponding to an electrode 103 in the implementation example of the Figures 1 and 2). Each voltage value e ij is representative of the vibration of the elementary transducer of coordinates i,j in the matrix under the effect of the received ultrasonic wave, 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 i and ground has been represented, and, for each column of the matrix, a load impedance Z c between the column electrode C j and ground. The impedances Z th of the different elementary transducers of the matrix are, for example, all identical or substantially identical. The load impedances ZR connected to the different row electrodes R i of the matrix are, for example, all identical or substantially identical.The load impedances Z c connected to the different column electrodes C j of the matrix are for example all identical or substantially identical. Here we denote by V Ri the alternating voltage appearing on the line R i during a reception phase of an ultrasonic wave, and by V cj the alternating voltage appearing on the column C j during a reception phase of an ultrasonic wave.

[0053] By applying the principle of superposition, we can write the following system of equations: V R 1 = a 11 R 1 ∗ e 11 + a 12 R 1 ∗ e 12 + a 21 R 1 ∗ e 21 + a 22 R 1 ∗ e 22 V R 2 = a 11 R 2 ∗ e 11 + a 12 R 2 ∗ e 12 + a 21 R 2 ∗ e 21 + a 22 R 2 ∗ e 22 V C 1 = a 11 C 1 ∗ e 11 + a 12 C 1 ∗ e 12 + a 21 C 1 ∗ e 21 + a 22 C 1 ∗ e 22 V C 2 = a 11 C 2 ∗ e 11 + a 12 C 2 ∗ e 12 + a 21 C 2 ∗ e 21 + a 22 C 2 ∗ e 22 where each coefficient a ijRk is representative of the weight of the contribution of the generator e ij to the voltage V Rk of the row R k , with k being an integer from 1 to N, and where each coefficient a ijck is representative of the weight of the contribution of the generator e ij to the voltage V ck of the column C k .

[0054] There Figure 4is an equivalent electrical diagram of a line-column addressing matrix ultrasound imaging device of N lines and N columns. The equivalent electrical diagram of the Figure 4 is similar to that of the Figure 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 on the Figure 4 .

[0055] Using the previous notations, the aforementioned system of equations [Math 1] can be rewritten in matrix form as follows: [A]*[e]=[V] With : A = a 11 R 1 a 12 R 1 ⋯ a N N − 1 R 1 a NNR 1 a 11 R 2 a 12 R 2 ⋯ a N N − 1 R 2 a NNR 2 … ⋯ ⋯ ⋯ ⋯ a 11 RN a 12 RN ⋯ a N N − 1 RN a NNRN a 11 C 1 a 12 C 1 ⋯ a N N − 1 C 1 a NNC 1 ⋯ ⋯ ⋯ ⋯ ⋯ a 11 C N − 1 a 12 C N − 1 ⋯ a N N − 1 C N − 1 a NNC N − 1 a 11 CN a 12 CN ⋯ a N N − 1 CN a NNCN And : e = e 11 e 12 ⋮ e NN − 1 e NN And : V = V R 1 ⋮ V RN V C 1 ⋮ V CN

[0056] 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*(N*N) coefficients of the matrix [A] are for example non-zero and non-unitary (in absolute value).

[0057] The 2N vector voltages [V] can be read on the row and column electrodes of the matrix.

[0058] We thus obtain a system with 2N equations and N*N unknowns (the N*N voltage values ​​e ij ).

[0059] As it stands, this system cannot be solved, the number of independent equations being less than the number of unknowns.

[0060] According to one aspect of an embodiment, it is provided, as will be explained in more detail below, to increase the number of discriminant 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 reception phase of the return wave, the sign of at least one generator e ij .

[0061] According to a preferred embodiment, provision is made, at each shot, to modify the sign of the polarization voltage applied to at least one of the column electrodes of the matrix during the reception phase of the return wave, so as to invert the sign of all the generators e ij 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 the figures 5 And 6. More generally, the preferred embodiment detailed below applies to any type of transducer exhibiting symmetrical behavior, particularly in reception, for example PMUT transducers (from the English "Piezoelectric Micromachined Ultrasonic Transducers"). By symmetrical behavior in reception, it is meant here that the sign of the alternating voltage produced by the transducer during a reception phase of an ultrasonic wave reverses when the sign of the direct bias voltage applied to the transducer during this same reception phase is reversed.

[0062] There Figure 5 schematically illustrates the behavior of an example of a CMUT transducer in transmission.

[0063] There Figure 5includes a diagram (a) representing an example of a voltage V cMUT that can be applied between the electrodes of the transducer during an emission phase. In this example, the voltage V cMUT is a positive voltage corresponding to the superposition (or sum) of a direct bias voltage V bias positive, and an alternating excitation voltage V exc . In this example, the alternating excitation voltage is a square wave voltage successively comprising a high state, a low state, a high state, and a low state.

[0064] The application of the voltage V cMUT across the transducer terminals leads to a vibrational displacement of the transducer membrane along a z axis orthogonal to the membrane, illustrated by a diagram (b) on the Figure 5 . In this diagram, position 0 corresponds to the mechanical equilibrium position of the membrane, in the absence of any electrical polarization.

[0065] This vibratory displacement of the membrane leads to the emission of an acoustic wave illustrated by a diagram (c) on the Figure 5 .

[0066] There Figure 5further comprises a diagram (a') representing another example of a voltage V cMUT that can be applied between the electrodes of the transducer during an emission phase. In this example, the voltage V cMUT is a negative voltage corresponding to the opposite of the voltage V cMUT of the diagram (a). Thus, in this example, the voltage V cMUT corresponds to the superposition of a negative DC bias voltage V bias, and an AC excitation voltage V exc . The DC bias voltage V bias of the diagram (a') corresponds to the opposite of the DC bias voltage V bias of the diagram (a), and the AC excitation voltage V exc of the diagram (a') corresponds to the opposite of the AC excitation voltage V exc 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.

[0067] As illustrated by the Figure 5 , the application of the voltage V cMUT of diagram (a') to the terminals of the transducer leads to a vibratory displacement identical to that obtained with the application of the voltage V cMUT of diagram (a), and, consequently to the emission of an acoustic wave identical to that obtained with the application of the voltage V cMUT 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.

[0068] There Figure 6 schematically illustrates the behavior of an example of a CMUT transducer in reception.

[0069] There Figure 6 includes a diagram (a) representing an example of an acoustic wave received by the CMUT transducer.

[0070] There Figure 6further comprises a diagram (b) illustrating the vibrational displacement of the transducer membrane under the effect of the received acoustic wave, when the transducer is polarized at a direct voltage V bias . It will be noted that this displacement is independent of the sign, positive or negative, of the voltage V bias .

[0071] There Figure 6 further comprises a diagram (c) representing the voltage V cMUT at the terminals of the transducer during a reception phase. In this example, the DC bias voltage V bias applied to the terminals of the transducer is a positive voltage. The voltage V cMUT is then a positive voltage corresponding to the superposition or sum of the voltage V bias , and an alternating voltage V rec generated under the effect of the vibration of the membrane.

[0072] There Figure 6further illustrates a diagram (c') representing the voltage V cMUT at the terminals of the transducer during a reception phase. In this example, the DC bias voltage V bias applied to the terminals of the transducer is a negative voltage. More particularly, in this example, the DC bias voltage V bias applied to the terminals of the transducer is the opposite of that applied in the example of diagram (c). The voltage V cMUT is then a negative voltage corresponding to the superposition of the voltage V bias , and an alternating voltage V rec generated under the effect of the vibration of the membrane. As illustrated in Figure 6 , the voltage V rec of the diagram (c') is the opposite of the voltage V rec of the diagram (c). Thus, the inversion of the sign of the continuous polarization voltage V bias in reception leads to an inversion of the sign of the alternating voltage V rec generated at the terminals of the transducer under the effect of a received acoustic wave.

[0073] By taking up the previous notations and considering an elementary transducer of a matrix ultrasound imaging device with row-column addressing, the alternating voltage V rec appearing at the terminals of the transducer under the effect of a received acoustic wave corresponds to the contribution e ij of the transducer to the voltage signals read on the row electrodes R i or column electrodes C j of the device.

[0074] Thus, by inverting the DC bias voltage V bias of a receiving column, the sign of the contributions e ij of the column's transducers is inverted. This allows, as will be described in more detail below, to obtain additional discriminant equations allowing us to go back to the individual contributions of the elementary transducers of the matrix.

[0075] It should be noted that since the response of the transducers remains linear, the same weighting coefficient can be applied to the continuous bias voltages V bias and / or to the alternating excitation voltages V exc , 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.

[0076] There Figure 7 schematically illustrates a TX transmission step and an RX reception step 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.

[0077] In this example, during the TX transmission phase, a DC bias voltage V bias and an AC excitation voltage V exc are applied to the column electrodes C j of odd rank, and an opposite DC bias voltage -V bias and an opposite AC excitation voltage -V exc are applied to the column electrodes C j of even rank. On the Figure 7 , each elementary transducer is represented by an impedance Z th during the TX transmission phase. During the RX reception phase, the continuous bias voltages V bias and -V bias applied respectively to the odd-rank column electrodes C j and to the even-rank column electrodes C j remain unchanged.

[0078] As explained above in relation to the Figure 5, the inversion of the sign of the voltages V bias and V exc on the even-ranked columns has no impact on the acoustic wave emitted by the transducers of the column. In other words, the emitted ultrasonic wave is the same as if the signs of the voltages V bias and V exc were the same on all the columns.

[0079] 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 e ij of the elementary transducers of said columns, as explained above in relation to the Figure 6 .

[0080] 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 i , it is possible to go back to the individual contributions e ij of each of the elementary transducers of the matrix.

[0081] There figure 8 schematically illustrates an example of an embodiment of a method for acquiring an image of a body using a 2x2 row-column addressing matrix ultrasound imaging device.

[0082] The process of the figure 8 includes two successive shots of the same ultrasonic wave towards the body to be analyzed.

[0083] More particularly, the method comprises a first step TX1 of emitting an ultrasonic wave (first shot), followed by a first step RX1 of receiving a return wave reflected by the body to be analyzed, followed by a second step TX2 of emitting an ultrasonic wave (second shot) identical to that emitted in step TX1, followed by a second step RX2 of receiving a return wave reflected by the body to be analyzed.

[0084] During the emission step TX1, the column electrodes C 1 and C 2 are polarized at the same direct voltage V bias , and receive the same alternating excitation voltage V exc superimposed on the voltage V bias .

[0085] During the RX1 reception phase, the column electrodes C 1 and C 2 remain polarized at the voltage V bias , and alternating voltages V R 1 1 And V R 2 1 are read respectively on the row electrodes R 1 and R 2 .

[0086] The following system of equations can then be written: V R 1 1 = a 11 R 1 ∗ e 11 + a 12 R 1 ∗ e 12 + a 21 R 1 ∗ e 21 + a 22 R 1 ∗ e 22 V R 2 1 = a 11 R 2 ∗ e 11 + a 12 R 2 ∗ e 12 + a 21 R 2 ∗ e 21 + a 22 R 2 ∗ e 22

[0087] In the transmission step TX2, the column electrodes C 1 and C 2 are biased respectively at the voltage V bias and at the voltage -V bias , and receive respectively the alternating excitation voltage V exc and the opposite alternating excitation voltage -V exc .

[0088] During the RX2 reception phase, the column electrodes C 1 and C 2 remain polarized respectively at the voltage V bias and at the voltage -V bias , and alternating voltages V R 1 2 And V R 2 2 are read respectively on the row electrodes R 1 and R 2 .

[0089] The following system of equations can then be written: V R 1 2 = a 11 R 1 ∗ e 11 − a 12 R 1 ∗ e 12 + a 21 R 1 ∗ e 21 − a 22 R 1 ∗ e 22 V R 2 2 = a 11 R 2 ∗ e 11 − a 12 R 2 ∗ e 12 + a 21 R 2 ∗ e 21 − a 22 R 2 ∗ e 22

[0090] 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: A = a 11 R 1 a 21 R 1 a 11 R 2 a 21 R 2 And : e = e 11 e 21 And : V = V R 1 1 + V R 1 2 2 V R 2 1 + V R 2 2 2

[0091] Since the matrix A is invertible, the system can be solved, which makes it possible to determine the respective contributions e 11 and e 21 of the elementary transducers of rank i=1 and i=2 of the column of rank j=1.

[0092] Similarly, subtracting the two systems of equations [Math 5] and [Math 6] above, we obtain a system with two equations and two unknowns that can be rewritten in matrix form as follows: [A]*[e]=[V], with: A = a 12 R 1 a 22 R 1 a 12 R 2 a 22 R 2 And : e = e 12 e 22 And : V = V R 1 1 − V R 1 2 2 V R 2 1 − V R 2 2 2

[0093] Here again, the matrix A being invertible, the system can be solved, which makes it possible to determine the respective contributions e 12 and e 22 of the elementary transducers of rank i=1 and of rank i=2 of the column of rank j=2.

[0094] Thus, by means of two shots of the same ultrasonic wave, by reversing the sign of the polarization voltage V bias of one of the columns between the two corresponding reception phases, and by making linear combinations of the alternating voltages measured in reception on the electrodes, we can go back to the individual contributions e ij of each of the four elementary transducers of the matrix.

[0095] It will be noted that as has been explained above in relation to the Figure 5, the inversion of the sign of the bias voltages V bias and excitation V exc during the emission phase has no effect on the emitted ultrasonic wave. Thus, one could plan 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 can be 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. It is therefore preferable to modify the sign of the bias voltage of the column electrode C 2 from the emission phase TX2.

[0096] This mode of operation can be generalized regardless of the number N of rows and columns of the matrix.

[0097] 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.

[0098] Preferably, the signs of the polarization voltages applied respectively to the N column electrodes C 1 , ... 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 i 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 e ij of the N*N elementary transducers of the device.

[0099] There figure 9 schematically illustrates, by way of illustrative example, a mode of implementation of a method for acquiring an image of a body by means of a matrix ultrasound imaging device with row-column addressing of dimensions 4x4. 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.

[0100] There figure 9 represents more particularly the signs of the bias voltages applied to the column electrodes C j 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 V bias , and a - sign at the head of the column when the bias voltage applied to the column is equal to -V bias .

[0101] In the reception phase RX1 following the first shot, the column electrodes C 1 , C 2 , C 3 and C 4 are all positively polarized (++++). In the reception phase RX2 following the second shot, the column electrodes C 1 , C 2 , C 3 and C 4 are respectively positively, negatively, positively and negatively polarized (+-+-). In the reception phase RX3 following the third shot, the column electrodes C 1 , C 2 , C 3 and C 4 are respectively positively, positively, negatively and negatively polarized (++--). In the reception phase RX4 following the fourth shot, the column electrodes C 1 , C 2 , C 3 and C 4 are respectively positively, negatively, negatively and positively polarized (+--+).

[0102] 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 terms a ijRi *e ij per equation.

[0103] Hereinafter, we designate T1, T2, T3 and T4 the N=4 corresponding systems of equations.

[0104] 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 e ij of the N*N=16 elementary transducers of the device.

[0105] 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.

[0106] By performing the summation T1+T2+T3+T4, we obtain a first subsystem of type [A]*[e]=[V] With: A = a 11 R 1 a 21 R 1 a 31 R 1 a 41 R 1 a 11 R 2 a 21 R 2 a 31 R 2 a 41 R 2 a 11 R 3 a 21 R 3 a 31 R 3 a 41 R 3 a 11 R 4 a 21 R 4 a 31 R 4 a 41 R 4 And : e = e 11 e 21 e 31 e 41 And : V = V R 1 1 + V R 1 2 + V R 1 3 + V R 1 4 4 V R 2 1 + V R 2 2 + V R 2 3 + V R 2 4 4 V R 3 1 + V R 3 2 + V R 3 3 + V R 3 4 4 V R 4 1 + V R 4 2 + V R 4 3 + V R 4 4 4

[0107] Since the matrix A is invertible, the system can be solved, which makes it possible to determine the respective contributions e i1 of the elementary transducers of the column of rank j=1.

[0108] By carrying out the summation T1-T2+T3-T4 we can, in a similar way, determine the respective contributions e i2 of the elementary transducers of the column of rank j=2.

[0109] By performing the summation T1+T2-T3-T4 we can, in a similar way, determine the respective contributions e i3 of the elementary transducers of the column of rank j=3.

[0110] By carrying out the summation T1-T2-T3+T4 we can, in a similar way, determine the respective contributions e i4 of the elementary transducers of the column of rank j=4.

[0111] Thus, by carrying out N*N linear combinations of the N*N voltages measured on the N line electrodes R i 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) predetermined coefficients a ij R i, we directly obtain the respective contributions e ij of the N*N elementary transducers of the device.

[0112] An advantage of the proposed acquisition method is that it allows to benefit from the advantages of both fully populated devices in terms of imaging resolution, and row-column addressing devices in terms of electronic complexity.

[0113] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations 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 connection with the Figures 1 and 2 .

[0114] Furthermore, although, in the examples described above, the DC bias voltages V bias and -V bias applied to the different column electrodes C j 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 C j , in transmission and / or in reception, can be differentiated. Similarly, the AC excitation voltages V exc applied to the column electrodes C j in transmission can be differentiated by column.

[0115] Furthermore, the embodiments described are not limited to the examples detailed above in which the inversion of the sign of the contribution e ij of the elementary transducers of a column is obtained by inverting the sign of the DC bias voltage V bias applied to this column. More generally, any other means making it possible to invert the sign of the contribution e ij 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, making it possible to invert the direction of connection of the electrodes of the transducer between the row electrodes R i and column electrodes C j 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 i 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 C j and its second electrode connected to the electrode R i . 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 e ij 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 e ij 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.

[0116] Furthermore, although implementation examples based on voltage measurements on the electrodes of the device have been described above, the described embodiments are not limited to this particular case. Alternatively, the described embodiments may 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.

[0117] 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. Upon reading this 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.

[0118] Furthermore, in the embodiments described above, at each firing of the ultrasonic wave, the wave is generated by the same matrix device as that used for receiving the return wave. The embodiments described are however not limited to this particular case. As a variant, the transducer matrix is ​​used only as a receiving device, to receive the ultrasonic wave returned by the body to be analyzed, and a separate transmitting device (not detailed) is used to transmit the ultrasonic wave 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.

[0119] Furthermore, the practical implementation of the embodiments and variants described 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.

[0120] Furthermore, it should be noted that in the examples described above, the row and column names are arbitrary and can of course be reversed.

Claims

1. A method of acquiring an image of a body by means of a row-column addressed matrix ultrasonic imaging device (100), the device (100) comprising an array of elementary ultrasonic transducers (101) connected in rows and columns by respectively row electrodes (Ri) and column electrodes (Cj), the method comprising: - performing N successive shots (TX1, ...TXN) of the same ultrasonic wave towards 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 wave is read at each row electrode (Ri) of the device, and in which, between any two of the N reception phases (RX1, ...RXN), the sign of the individual contribution (eij) of at least one elementary ultrasonic transducer (101) of the array is modified, the method further comprising a step of calculating, by means of an electronic processing device, by linear combinations of the electrical variable quantities (VRi) read on the row electrodes (Ri) of the device during the N reception phases (RX1, ...RXN), of an individual contribution (eij) of each of the elementary transducers (101) of the array.

2. The method of claim 1, wherein the calculation of the individual contributions (eij) of the elementary transducers (101) of the array comprises a multiplication of the electrical variable quantities (VRi) read on the row electrodes (Ri) of the device during the N reception phases (RX1, ...RXN) by coefficients of a matrix [A], previously determined during a characterization or simulation phase and stored in a memory of the electronic processing device.

3. The method of claim 1 or 2, wherein, during each of the N receiving phases (RX1, ...RXN), each column electrode (Cj) of the array is maintained at a DC bias voltage (Vbias, - Vbias), and wherein, between any two of the N receiving phases (RX1, ...RXN), the sign of the DC bias voltage (Vbias, - Vbias) applied to at least one of the device's column electrodes (Cj ) is changed.

4. The method of claim 3, wherein the signs of the polarization 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.

5. The method of claim 3 or 4, wherein the N successive shots (TX1, ... TXN) are performed by means of said row-column-addressed matrix ultrasonic imaging device (100), and wherein, during each of the N shots (TX1, ... TXN), each column electrode (Cj) of the array is held 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 applied respectively to the column electrodes (Cj) of the array are the same as the signs of the DC bias voltages applied respectively to the column electrodes (Cj) in the subsequent receiving phase.

6. The method of claim 1, wherein, between any two of the N receiving phases (RX1, ...RXN), the electrical connection of at least one elementary transducer (101) between the row (Ri) and column (Cj) electrodes is reversed by means of a system of switches, so as to modify the sign of the individual contribution (eij) of said at least one elementary ultrasonic transducer (101) of the array.

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

8. The method of any one of claims 1 to 7, wherein said array comprises N rows and N columns of elementary ultrasonic transducers (101).

9. The method of any one of claims 1 to 8, wherein the electrical variable quantity (VRi) read on each row electrode (Ri) of the device is a voltage value.

10. A row-column addressed matrix ultrasonic imaging device (100), the device (100) comprising a array of elementary ultrasonic transducers (101) connected in rows and columns by respective row electrodes (Ri) and column electrodes (Cj), and a control circuit configured to implement a method according to any one of claims 1 to 9.

11. The device of claim 10, wherein the ultrasonic transducers (101) are CMUT or PMUT transducers.