METHOD AND SYSTEM FOR PROCESSING A SET OF SIGNALS RECEIVED BY A TRANSDUCER ELEMENT

Abstract

The invention relates to a method for processing a set of signals of a transducer device comprising a respective set of transducer elements, the method comprising the following steps: a processing step in which the received set of signals is processed to a plurality of synthetic waves, and an output step in which the plurality of synthetic waves is outputted through a plurality of channels.

Claims

1. A method for processing a received set of signals of a transducer device comprising a respective set of transducer elements, the method comprising: processing the received set of signals to a plurality of synthetic waves; and outputting the plurality of synthetic waves through a plurality of channels.

2. The method according to claim 1, wherein at least one of: a number of the plurality of channels is less than a number of transducer elements of the set of transducer elements; the number of channels corresponds to a number of the plurality of synthetic waves; and a data rate of the plurality of synthetic waves is reduced compared to a data rate of the received set of signals when digitalized.

3. The method according to claim 1, wherein the plurality of synthetic waves is at least one of re-combinable and compoundable to approximate a backscattered wave represented by the received set of signals.

4. The method according to claim 1, wherein at least one of: the plurality of synthetic waves is at least one of: a plurality of diverging waves, a plurality of plane waves, and a plurality of waves of different phases, and the received set of signals is a set of backscattered signals.

5. The method according to claim 1, further comprising, before processing the received set of signals: transmitting at least one pulse into a medium, and receiving a set of echo signals from the medium by the set of transducer elements, the set of echo signals being the received set of signals.

6. The method according to claim 1, wherein at least one of: the received set of signals is a set of ultrasound signals; the transducer device is an ultrasound transducer device; and the transducer device is a matrix array transducer device.

7. The method according to claim 1, wherein processing the received set of signals comprises beamforming the received set of signals to obtain the plurality of synthetic waves.

8. The method according to claim 1, further comprising, after outputting the plurality of synthetic waves: forming an echographic image based on the plurality of outputted synthetic waves.

9. The method according to claim 8, wherein forming the echographic image comprises at least one of: processing a focused beamforming based on the plurality of outputted synthetic waves; and forming the echographic image as a function of a geometry of the synthetic waves.

10. The method according to claim 1, wherein the plurality of channels comprise at least one of physical channels and multiplexed channels.

11. A computer program comprising computer-readable instructions which when executed by a data processing unit cause the data processing unit to carry out the method according to claim 1.

12. A system for processing a set of signals received by a transducer device comprising a respective set of transducer elements, the system comprising a pre-processing unit configured to: process the received set of signals to a plurality of synthetic waves; and output the plurality of synthetic waves through a plurality of channels.

13. The system according to claim 12, wherein at least one of: the pre-processing unit is configured to output the plurality of synthetic waves via the plurality of channels to an external processing system configured to form an echographic image based on the plurality of outputted synthetic waves; and the pre-processing unit is one of separate and remote from a main processing unit.

14. The system according to claim 12, further comprising a probe which comprises the pre-processing unit and the transducer device.

15. The system according to claim 14, wherein the probe is configured to output the plurality of synthetic waves to an external processing system via a cable or a wireless communication interface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] FIG. 1 shows an exemplary embodiment of the method according to embodiments of the present disclosure;

[0068] FIG. 2 schematically shows an exemplary transducer elements array and an incoming plane wave according to embodiments of the present disclosure;

[0069] FIG. 3a schematically shows a spherical wave which is backscattered from a single target reflector in the medium;

[0070] FIG. 3b schematically shows the principle of using synthetic plane waves for approximating a backscattered wave according to embodiments of the present disclosure;

[0071] FIG. 4a schematically shows a conventional RF data matrix of backscattered signals of a single target reflector;

[0072] FIG. 4b schematically shows a plane waves RF data matrix according to embodiments of the present disclosure;

[0073] FIG. 5a schematically shows an exemplary reception scheme of a conventional image formation process using signals received by a transducer element array;

[0074] FIG. 5b schematically shows an exemplary reception scheme of an image formation process according to embodiments of the present disclosure, and

[0075] FIG. 6 shows an exemplary embodiment of a system according to embodiments of the present disclosure, in particular of an ultrasound platform according to embodiments of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

[0076] Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Moreover, the features explained in context of a specific embodiment, for example that one of FIG. 1, also apply to any one of the other embodiments, when appropriate, unless differently described.

[0077] FIG. 1 shows an exemplary embodiment of the method according to embodiments of the present disclosure. The method may be carried out by means of a system 1, more in particular by an ultrasound platform 20. Examples are described in context of FIGS. 2 and 5.

[0078] The method may be an ultrasound method carried out by an ultrasound system. Possible ultrasound methods comprise B-mode imaging, shear wave elastography imaging (such as ShearWave® mode developed by the applicant, ultrafast™ Doppler imaging or angio mode named under Angio P.L.U.S™ ultrasound imaging or any other ultrasound imaging mode. However, the method according to the present disclosure may also be applied to other technical fields than ultrasound examination. In particular, any technical field is possible which use a plurality of transducer elements to acquire data/signals of an examined medium or environment and/or which may optionally use a beamforming technique based on the collected data/signals. Examples comprise methods using a radar system, sonar system, seismology system, wireless communications system, radio astronomy system, acoustics system, Non Destructive Testing (NDT) system and biomedicine system. The principle of acquiring data by a plurality of transducer elements, what would conventionally lead to a corresponding number of channels, is always similar. Accordingly, the method according to the present disclosure may in each of these cases achieve the same positive technical effects as described above, for example of a data reduction. However, for mere illustration purposes of the present disclosure, in the following it is referred to the example of an ultrasound method.

[0079] Steps A1 to A4 may be carried out by the system 1 according to the present disclosure, more for example by an ultrasound probe 1. The system is desirably a hand-held system. For example, the system may comprise a transducer elements 6 which may carry out steps A1 and A2 and a pre-processing unit 11 which may carry out steps A3 and A4. The output of the system 1 may be transmitted via an interface 10 to a central or main or external processing system 4.

[0080] Step B1 may be carried out by a central (or main or external) processing system 4. Step C1 may be carried out by a display or screen 4a associated with the processing system 4. However, step B1 may also be carried out by the system 1. For example, the image data generated in B1 may then be transmitted from the system 1 to a display 4a (for example wirelessly). It is also possible that the system 1 comprises a display and carries out all steps A1 to C1.

[0081] Steps A1 to C1 may be carried out successively, i.e. one after another. However, steps A1 and A2 may be carried out several times before step A3 is carried out based on the collected echo signals of the several steps A2. For example, reception step A2 may be carried out several times (for example 512 times) for each transmission step A1. Moreover, the system 1 may first collet the data of these several steps A2 before outputting them together, and/or the system 4 may also buffer these outputs before steps B1 and B3 are carried out. In addition, the method of FIG. 1 may be carried out repeatedly.

[0082] The method may comprise the following steps:

[0083] In an optional step A1 at least one pulse is transmitted into a medium. For example, the transmission step may comprise insonification of the medium with a cylindrical wave that focuses on a given point and/or plane waves of different angles. More in particular, in the transmission step a plurality of ultrasonic waves may be transmitted into an imaged region.

[0084] In an optional step A2 a set of echo signals is received from the medium by the set of transducer elements, the set of echo signals being the set of received signals. In the reception step the backscattered echoes of the insonification of step A1 may be used. More in particular, in the reception step a set of raw data may be acquired by a set of transducer elements in response to each ultrasonic wave. The received set of signals may be a set of ultrasound signals.

[0085] In a step A3 the received set of signals is processed to a plurality of synthetic waves. For example, the processing step may comprise a (pre-) beamforming step in which the received set of signals is beamformed to obtain the plurality of synthetic waves. an exemplary embodiment is described below in context of FIG. 2. The pre-beamforming step may be performed prior to analogic to digital conversion, i.e. using an analogic processor, or it may be performed after analogic to digital conversion, thus using a digital processor.

[0086] In a step A4 the plurality of synthetic waves is outputted through a plurality of channels, for example via the interface 10 to an external system 4.

[0087] In an optional step B1 an echographic image is formed based on the plurality of outputted synthetic waves. This image formation step may comprise a focused beamforming process based on the plurality of outputted synthetic waves. The beamforming process may take into account the geometry of the synthetic waves, for example the angles of synthetic plane waves.

[0088] In an optional step C1 the formed image is displayed on an electronic display or a screen.

[0089] FIG. 2 schematically shows an exemplary transducer elements array and a plane wave according to embodiments of the present disclosure.

[0090] The transducer elements 6 may be arranged in the form of a transducer element array along an x-axis with transducer elements X.sub.0 to X.sub.N−1. The received signals τ(x.sub.0-N−1, θ) representing ultrasound waves are collected and processed together by the pre-processing unit 11 to obtain a plurality of synthetic plane waves with different phases or angles θ.

[0091] Generally, the expression of a plane wave in a specific plane may have the form: s(x, z, t, θ), where x is the coordinate along which the transducer elements are arranges, z is the coordinate representing the depth direction of the medium, and t is the time. A plane wave may be determined by:

s(x,z,t,θ)=Ae.sup.i(ωt−kxsinθ−kzcosθ)   (1)

taking into account:

[00001]$\begin{array}{cc}\omega =2\pi f,k=\frac{2\pi }{\lambda },\lambda =\frac{c}{f}& \left(2,3,4\right)\end{array}$

where A is a predefined amplitude which may be set as a function of the power of the received ultrasound signals, c is the wave speed and f is the central wave frequency.

[0092] The synthetic plane waves processed and output by the system 1 may have the form: p(t, θ). The processing (i.e. calculation steps) are explained in the following with reference to a Fourier transform.

[0093] Generally, a Fourier transform can be described by:

[00002]$\begin{array}{cc}s\left(t,x,z\right)\stackrel{\mathrm{FT}}{.Math.}S\left(f_t,f_x,f_z\right)& \left(3\right)\end{array}$$\begin{array}{cc}S\left(f_t,f_x,f_z\right)=\stackrel{+\infty }{\underset{-\infty }{\int \int \int }}s\left(t,x,z\right)e^{-2i\pi \left(f_{t}t+f_{x}x+f_{z}z\right)}\mathrm{dtdxdz}& \left(4\right)\end{array}$$\begin{array}{cc}s\left(t,x,z\right)=\stackrel{+\infty }{\underset{-\infty }{\int \int \int }}S\left(f_t,f_x,f_z\right)e^{2i\pi \left(f_{t}t+f_{x}x+f_{z}z\right)}{\mathrm{df}}_t{\mathrm{df}}_x{\mathrm{df}}_z& \left(5\right)\end{array}$

[0094] The Fourier transform can be seen as an expansion of a function s(t,x,z) into a linear combination of elementary functions of the form e.sup.2iπ(f.sup.t.sup.t+f.sup.x.sup.x+f.sup.z.sup.z),

[0095] Now, with reference to the present disclosure, in particular with reference to the synthetic waves to be processed by the method according to the present disclosure, e.sup.2iπ(f.sup.t.sup.t+f.sup.x.sup.x+f.sup.z.sup.z) can be considered as a plane wave with temporal frequency f.sub.t and angle θ:

[00003]$\begin{array}{cc}\theta =a\tan \left(\frac{f_x}{f_z}\right)& \left(6\right)\end{array}$

[0096] Accordingly, the Fourier transform can be seen as an expansion of a function s(t,x,z) into a linear combination of plane waves.

[0097] Taking discrete version of eq. (5) yields to:

[00004]$\begin{array}{cc}s\left(n_t,n_x,n_z\right)={.Math.}_{m_t=0}^{M_t-1}{.Math.}_{m_x=0}^{M_x-1}{.Math.}_{m_z=0}^{M_z-1}S\left(m_t,m_x,m_z\right)e^{2i\pi \left(\frac{m_t{n}_t}{M_t}+\frac{m_x{n}_x}{M_x}+\frac{m_z{n}_z}{M_z}\right)}& \left(7\right)\end{array}$

with the following approximation:

[00005]$\begin{array}{cc}s\left(n_t,n_x,n_z\right)\cong {.Math.}_{m_t=0}^{M_t-1}{.Math.}_{m_x=0}^P{.Math.}_{m_z=0}^{Q}S\left(m_t,m_x,m_z\right)e^{2i\pi \left(\frac{m_t{n}_t}{M_t}+\frac{m_x{n}_x}{M_x}+\frac{m_z{n}_z}{M_z}\right)}& \left(8\right)\end{array}$

with P<M.sub.x, Q<M.sub.z, where P*Q is the number of used synthetic waves, and t is a discretized time value, x is a discretized x-axis value, and z is a discretized z-axis value, Mt is the number of samples (in the example of FIG. 4b M.sub.t is 512), and M.sub.x, M.sub.z are predefined selectable values.

[0098] Consequently, as far as the Fourier transform of a wave (function of time and space) exists, it can be expanded (or approximated) into (by) plane waves series. The error depends on P and Q with respect to the frequencies content of the wave.

[0099] FIG. 3a schematically shows a spherical wave which is backscattered from a single target reflector in the medium (indicated by a cross). Correspondingly, in a conventional method a dynamic receive focusing may be performed to obtain an ultrasound image. However, in the present disclosure another technique is illustrated as shown for example in FIG. 3b.

[0100] FIG. 3b schematically shows the principle of using synthetic plane waves for approximating a backscattered wave according to embodiments of the present disclosure. As shown, the plane waves having different angles can approximate the backscattered spherical (and diverging) wave of FIG. 3a and hence the conventional dynamic receive focusing. The synthetic plane waves may be obtained in a pre-beamforming step in the system 1 before being outputted to an external system 4. The plane waves may then be beamformed, for example in the system 4, to obtain a dynamic receive focusing.

[0101] For example, around 40 plane waves allow to obtain an equivalent final image (in view of image resolution and/or quality) as focused that would conventionally requires around 120 acquisition channels provided by a respective number of transducer elements (for example 128 transducer elements or more). Hence, the proposed method can overcome the framerate lowering caused by propagation time between the system 1 (being for example a probe 1) and the external system 4. This allows hence a decrease of the amount of RF data to be transferred from the system 1 to system 4 by a factor >3. The method further allows an optimised trade-off between image quality and framerate. Moreover, the method works both on conventional imaging system (focused transmit) and synthetic aperture-based systems, for example B mode, color Doppler, shear wave elastography, ultrafast Doppler or Angio Plus.

[0102] The theory of wave expansion described above can be easily extended to 3 dimensions for matrix array transducer elements. In that case, the factor of data size reduction is elevated to the square (factor 3 becomes 9).

[0103] FIG. 4a schematically shows a conventional RF data matrix of backscattered signals of a single target reflector with a transducer index on its horizontal (here “x-”) axis and time (in μs) on its vertical axis. In the shown example, a transducer elements with 256 transducer elements is used and 512 samples are collected. Consequently, 256 elements×512 samples=131072 samples are collected per acoustic firing. Said raw RF data would conventionally be outputted by a conventional probe and be transmitted to an external system. Assuming 128 acoustic firings per image, 2 bytes per acquired data sample, and an 80 Hz imaging frame rate, the correspondingly required data bandwidth would hence be more than 5 GB/s.

[0104] FIG. 4b schematically shows a plane waves RF data matrix according to embodiments of the present disclosure indicating a RX plane wave angle (°) (i.e. phase) on its horizontal axis and time (in μs) on its vertical axis. The synthetic plane waves may be obtained based on a respective transformation of the original RF data collected by the transducer (for example as shown in FIG. 4a). The slightly bent shape of the exemplary RF data matrix shown in FIG. 4b may be due to time delays caused by the angles of the synthetic plane waves. Such angle dependent propagation delays may be compensated in an image formation process according to embodiments of the present disclosure, as described in the following in context of FIG. 5b.

[0105] In the shown example, 60 plane waves are used and 512 samples are collected. Consequently, 60 plane waves×512 samples=30720 samples are collected per acoustic firing. Said raw RF date would conventionally be outputted by a conventional probe and be transmitted to an external system. The correspondingly required data bandwidth would hence be more less than a fourth compared to the conventional example of FIG. 4a.

[0106] FIG. 5a schematically shows an exemplary reception scheme of a conventional image formation process using signals received by a transducer element array. FIG. 5b schematically shows an exemplary reception scheme of an image formation process according to embodiments of the present disclosure. In both FIGS. 5a and 5b the transducer elements 6 may be arranged in the form of a transducer element array along an x-axis (i.e. the horizontal axis in FIGS. 5a and 5b). For example, the transducer element array may correspond to that one described in context of FIG. 2. The width of a single transducer element may be L. The distance between two adjacent transducer elements may be d.sub.x.

[0107] The z-axis in FIGS. 5a and 5b (i.e. the vertical axis) may represent a principal scanning direction of the transducer element array and/or a direction into the interior of a scanned medium. In particular, FIGS. 5a and 5b may show exemplary reception schemes of a wave backscattered from a point P(x,z) using for example transducer element 61 (and/or any other transducer element). Said point may be at the position x=−D.sub.3, z=D.sub.1.

[0108] In the method according to the present disclosure the signals received by the transducer elements may be collected and processed together to obtain a plurality of synthetic plane waves with different angles or angles. In the exemplary reception scheme of FIG. 5b one exemplary synthetic plane wave with an angle θ is shown.

[0109] An echographic image may be formed based on the plurality of synthetic plane waves. This image formation process (or step) may comprise a focused beamforming process based on the plurality of synthetic waves. The image formation process may take into account the geometry of the synthetic waves, in particular the angles of the synthetic plane waves. Accordingly, the reception delay D.sub.2/c of a conventional reception scheme (as shown in FIG. 5a) may be replaced by D′.sub.2/c (as shown in FIG. 5b), c being the speed of the wave in the medium. The propagation delay D.sub.1/c may remain unchanged, i.e. the same in the reception schemes of FIGS. 5a and 5b. It is noted that in FIGS. 5a and 5b the distances D.sub.2/D′.sub.2 are only schematically shown, in order to reflect the influence of angle θ of the exemplary synthetic plane wave in FIG. 5b.

[0110] Therefore, in an image formation process the propagation delay may be compensated as a function of the geometry of the synthetic waves, in particular the angles of the synthetic plane waves. As a consequence, the image quality of a formed image is advantageously not deteriorated by the respective propagation delays.

[0111] FIG. 6 shows an exemplary embodiment of a system according to embodiments of the present disclosure, in particular of an ultrasound platform according to embodiments of the present disclosure. The platform 20 may comprise the system 1 according to the present disclosure. The system and/or the platform may be configured to carry out the method according to the present disclosure.

[0112] The platform 20 shown in FIG. 6 may be configured to provide ultrasound images of a viscoelastic medium 2. In response to compressional ultrasound waves the medium 2 scatters. The medium may be for example a human or animal body, for example a part of the body of a patient (breast, liver, abdomen, . . . ), in the case of medical applications. This system 1 is also configured to monitor the propagation of elastic shear waves to provide images of the elasticity of the medium 2.

[0113] The images of the medium are produced, for example, by means of a processing system 4 (comprising at least an input interface 4b such as a keyboard or the like, and an output interface 4a such as a screen or the like) or any other electronic central unit, which causes compressional ultrasonic waves to be sent into the medium 2 from its outer surface 3. Said waves interact with scattering particles 5 contained in the medium 2, which particles are reflective for the compressional ultrasonic waves. The particles 5 can be constituted by any heterogeneity of the medium 2, and in particular, when it comes to a medical application, by collagen particles present in human tissues (these particles form on the ultrasound images points known as “speckle”).

[0114] In order to observe the medium 2 and to generate images of the medium, a system in the form of an ultrasound probe 1 may be used, placed against the outer surface 3 of the observed medium 2. This probe, in particular its transducer elements 6, sends, along a Z axis, compressional ultrasonic wave pulses of the type commonly used in echography, at a frequency of, for example, between 0.5 and 100 MHz and preferably between 0.5 and 15 MHz, for example of the order of 4 MHz.

[0115] The transducer elements 6 may consist of an array of n ultrasonic transducer elements T1, T2, . . . , Ti, . . . , Tn, n being an integer greater than or at least equal to one (1).

[0116] This transducer elements 6 may be, for example, in the form of a linear array which can comprise, for example, n=128 or 256 transducer elements aligned along an X axis perpendicular to the Z axis. The transducer elements in question may also be a two-dimensional array (planar or not) of transducer elements.

[0117] The transducer elements T1, T2, . . . Tn may be controlled independently of each other by the pre-processing unit 11 and/or the processing system 4. The the pre-processing unit 11 and/or the processing system 4 may comprise at least one central processing unit (CPU) and/or at least one graphic processing unit (GPU).

[0118] The transducer elements T1-Tn may thus selectively emit: [0119] either a “plane” compressional ultrasonic wave (i.e. in this case a wave whose wavefront is rectilinear in the X, Z plane) or any other type of unfocused wave illuminating the entire field of observation in the medium 2, for example a wave generated by having the various transducer elements T1-Tn emit random acoustic signals, [0120] or a compressional ultrasound wave focused on one or more points of the medium 2.

[0121] Optionally a synthetic imaging technique may be applied that uses several unfocused compressional waves, for example plane waves of different angles. Respective echo waves of these plane waves may be combined to obtain in an image of the medium with improved quality.

[0122] The system 1 may in particular be in the form of an ultrasound probe which comprises a transducer elements 6 and a pre-processing unit 11. The transducer elements 6 may collect a set of signals and transmit it to the pre-processing unit 11 The pre-processing unit processes the set of signals to a plurality of synthetic waves. The plurality of synthetic waves is outputted by the system, more in particular by the pre-processing unit 11, via a transmission interface 10 (for example a cable or a wireless communication interface) to the processing system 4.

[0123] The interface 11 may comprise a multi-channel link (for example physical channels or and/or logical multiplexed channels). The number of channels desirably corresponds to the number of synthetic waves. Due to the data reduction according to the present disclosure, the required data bandwidth of the interface may be for example less than 1 GB/s.

[0124] The pre-processing unit may comprise one or several sub-units (not shown in FIG. 6), for example at least one of: a transmit-receive switch connected to the transducer elements, a signal conditioning unit, connected to the transmit-receive switch, a RX (i.e. receive) flat processing unit connected to the signal conditioning unit. The RX (i.e. receive) flat processing unit may be configured to process and/or transform the set of signals to a plurality of synthetic waves, as for example described above. The flat processing unit may for example be configured to carry out a beamforming step in which the received set of signals is beamformed to obtain the plurality of synthetic waves. The flat processing unit may hence for example be a receive plane waves (RX flat) beamformer.

[0125] Accordingly, a receive plane waves (RX flat) beamformer may be inserted in the conventional architecture of an ultrasound probe/system in between the signal conditioning unit and the bus or interface that connects the probe/system 1 and the processing system 4. Then the receive focused beamformer may be adapted to incoming plane waves to ensure dynamic receive focusing. It has been shown that for example 40 plane waves approximate a diverging or focusing wave. Conventional architectures propose up to for example 256 receive channels corresponding to 256 transducer elements. Using the proposed architecture results in a for example 40 channels (one per synthetic wave) transmission link to connect the system (i.e. the probe) to the processing system 4, that can be a factor 6 in terms of reduction of data to be transferred for the same acquisition. Accordingly, this technique can be used to decrease the capacity of the transmission link 10 or to increase the framerate at a constant channel capacity.

[0126] Throughout the description, including the claims, the term “comprising a” should be understood as being synonymous with “comprising at least one” unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms “substantially” and/or “approximately” and/or “generally” should be understood to mean falling within such accepted tolerances.

[0127] Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.

[0128] It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.

[0129] A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.