Patent Description:
The present invention concerns more precisely an ultrasound system comprising:.

It is known to use such ultrasound imaging system to generate an image.

However, such system needs to have a probe with numerous transducers, for example more than <NUM> transducers, and to process a complex beamforming during emitting and/or receiving of ultrasound waves. The beamforming process at least consists of applying an amplification factor and a delay independently to each signal from/to each transducer so as to focalize ultrasound energy to various points inside the medium. Such system therefore comprises as many analog to digital converter (ADC) channels as the number of transducers in the probe. Such system is then complex and expensive.

There is consequently a need for a cheap and easy to use system.

The document <CIT> discloses an ultrasonic apparatus comprising a probe having a plurality of transducers, and transducer-group forming means for forming a group of transducers for each focus point.

The document <CIT> discloses an ultrasonic transducer array comprising transducers in linear phased array formation and electrical interconnections between the transducers to control main lobe.

One object of the present invention is to provide an ultrasound system that is much less expensive than prior art to sense a region of interest inside a medium.

To this end, the ultrasound system further has the following features:.

Thanks to the use of a probe having a Fresnel lens effect for focussing inside the medium and thanks to the processing unit that analyses a plurality of frequencies of received ultrasound waves, the ultrasound system is able to sense a region of interest of the medium. The quality of a produced image might be decreased compared to prior art systems having a huge number of transducers, but the produced quality might be enough for the user. The system is advantageously much simpler and is less expensive than these prior art systems.

In various embodiments of the disclosed ultrasound system, one and/or other of the following features may optionally be incorporated.

According to an aspect, the processing unit controls the probe to emit successively at the plurality of frequencies to move the focal point in the medium, and the processing unit analyses the signals received for each of said frequencies for sensing the medium at said focal points.

According to an aspect, the processing unit controls the probe to emit a ultrasound wave having a broadband characteristic around the nominal frequency, and filters the signals at a plurality of frequencies for sensing the medium at said plurality of focal points.

According to an aspect, the processing unit builds an image of the medium on the bases of a plurality of focal points sensed in the medium.

According to an aspect, the step length is equal to: <MAT> where.

According to an aspect, the focal point difference distance is determined as follow: <MAT> where.

According to an aspect, the p-spaced transducers are connected together with short circuits to add the signals from said p-spaced transducers to form the phased signals.

According to an aspect, the period number is equal to four.

According to an aspect, the probe further comprises a patterned lens layer positioned above the transducers and arranged to be put in contact with the transducers and with the medium.

According to an aspect, the patterned lens layer is a prismatic shape, having a thickness that increases on the side of the transducer that corresponds to the shortest distance to the nominal focal point.

According to an aspect, the probe comprises two portions, a first portion situated on a first side in comparison to a depth direction, said depth direction being perpendicular to the longitudinal direction, and a second portion situated on a second side of said depth direction.

According to an aspect, the first portion and second portion are symmetric relative to the depth direction, the first portion and second portion each have a nominal focal point, and said nominal focal points are identical.

According to an aspect, the processing unit builds a first image with signals from the first portion and a second image with signals from the second portion, said first and second images not overlapping each other, the first image corresponding to a first quadrant in the medium defined in the first side relative to the depth direction, and the second image corresponding to a second quadrant in the medium defined in the second side relative to the depth direction.

According to an aspect, the probe further comprises at least one additional transducer situated between the first and second portions.

According to an aspect, the additional transducer is adapted for generating a vibration propagating inside the medium at a low frequency, said vibration being sensed by the first portion and second portion of the probe, and the processing unit calculates at least one value of elasticity inside the medium on the bases of displacement of said vibration in the medium.

Other features and advantages of the invention will be apparent from the following detailed description of several of its embodiments given by way of non-limiting examples, with references to the accompanying drawings that are provided for illustration purposes. In the drawings:.

<FIG> shows an ultrasound system <NUM> according to the disclosure and adapted for sensing a region of interest ROI inside a medium <NUM>. The ultrasound system may build an image of at least a portion of the region of interest, as it will be explained in the following description.

The medium <NUM> is for instance a living body and in particular human or animal bodies, or it can be any other biological or physic-chemical medium (e.g. in vitro medium). The volume of medium comprises variations in its physical properties. For example, the medium may comprise tissues and blood vessels, each one having various physical properties. For example, the tissue may comprise an area suffering from an illness (e.g. cancerous cells), or any other singular area, having various physical properties in comparison to other area of the medium. Some portions of the medium <NUM> may include some added contrast agent (e.g. micro bubbles) for improving the contrast of physical properties of these portions.

The ultrasound system <NUM> may include:.

More precisely, the processing unit <NUM> can control the probe <NUM> by providing signal(s) to the probe for emitting the emitting ultrasound waves, and by receiving signal(s) from the probe <NUM> corresponding to ultrasound waves arriving on the probe <NUM> from the medium.

The processing unit <NUM> then may sense and/or generate an image of the region of interest ROI inside the medium <NUM> on the bases of said signal(s).

In an embodiment, the processing unit <NUM> may be divided into two devices, an electronic unit 13a for controlling the transducer(s) and converting the signal(s) into data, and a computer 13b for processing the converted data.

The probe <NUM> may be a linear array of transducers. The focussing towards a predetermined position in the medium in front of the probe is performed by phasing the signals. The probe may comprise a number N of transducers 12a, e.g. few tens of transducers (for instance <NUM> to <NUM>) juxtaposed along a longitudinal direction or axis X so as to perform ultrasound focussing into a bi-dimensional (2D) plane. The probe <NUM> can comprise a bi-dimensional array so as to perform ultrasound focussing into a tri-dimensional (3D) volume.

The processing unit <NUM> usually comprise a processor, a memory containing instruction codes for implementing of the method for processing the data, a keyboard and a display for displaying the generated images.

Each transducer 12a emits and/or receives ultrasound waves that can have a broadband characteristic inside a wide frequency bandpass Δf around a predetermined central frequency f.

The ultrasound waves have a central wavelength λ that is equal to λ = c/f where f is the predetermined central frequency, and c is the speed of ultrasound waves inside the medium <NUM>.

The emitted ultrasound waves We, emitted by the probe <NUM>, propagate from the probe, inside the medium <NUM>, in a direction substantially perpendicular to the longitudinal direction X, i.e. in a depth direction Z, and toward the region of interest ROI. Scatters in the medium <NUM> reflect these waves that are returned toward the probe <NUM> as received ultrasound waves Wr.

In the following description of the disclosed embodiments:.

The probe <NUM> according to the disclosure is not an "axisymmetric probe" in the meaning that an axisymmetric probe has an axisymmetric axis and concentric elements organized around said axis, such as a concentric shaped lens or concentric shaped ultrasound transducers. These so called "axisymmetric" probes are usually used to focus high level of energy at an accurate location (one focal point) for medical treatment of this location inside the medium. Some probes of this kind can vary the depth of the focal point by varying the ultrasound frequency. But, these axisymmetric probes are not used in an ultrasound system to produce a two dimensional image of a medium, because of the symmetry of such probe that focusses the ultrasound waves on the axisymmetric axis. This necessitates adding a mechanical displacement device to move the probe itself at least along one or two directions (X, Y). This solution is as a consequence too complex in use.

By "probe", it is understood the active part that emit and/or receive the ultrasound wave. We do not consider the casing that maintains the active part and that is adapted to the hand of user for holding it.

By "linear probe", it is understood a probe that extends in the longitudinal direction X, i.e. having the active part that mainly extends in the longitudinal direction. The aim of such probe is to deliver signal for imaging an ROI of the medium <NUM> according to an X-Z plane. In a transversal direction Y perpendicular to the longitudinal direction X and to the depth direction Z, the probe size is much smaller than in the longitudinal direction X. This probe size can be a small constant, such as a millimeter or few millimeters (eg. Less than <NUM>), or can be dependent on the abscissa in the longitudinal direction X.

Therefore, the probe <NUM> of the current disclosure is not an axisymmetric probe and this probe <NUM> is a linear probe. The probe <NUM> comprises probe sections in a lens layer or in the transducer(s) layer having widths that are not all equal (not regularly spaced), and that increase from a first end to a second end of the probe <NUM>. Thanks to these probe sections, the probe <NUM> is not periodic in the longitudinal direction X. The probe <NUM> is also not symmetric relative to a direction perpendicular to the longitudinal direction X. The features of the probe sections will be more explained in the following disclosed embodiments.

The probe <NUM> then behaves as a Fresnel lens: it is a Fresnel linear device. Such probe <NUM> is then adapted so that the ultrasound system using such probe can provide a two dimensional image (in X-Z plane) of the medium <NUM>.

<FIG> shows a view in the X-Z plane of the probe according to an embodiment of the disclosure. <FIG> shows the probe of <FIG> in a perspective view illustrating that the probe of the current disclosure is not an axisymmetric probe and that this probe is a linear probe aligned in the longitudinal direction X.

In this embodiment, the probe <NUM> comprises:.

The lens layer 12f is in this example a focussing layer secured above the transducer 12a.

The transducer 12a for example transforms mechanical strain in the depth direction Z (said strain corresponding to waves in the medium) into an electric signal S<NUM>, and reciprocally.

The lens layer 12f has a general shape that may be approximatively a curved saw tooth. Then, the lens layer 12f is composed of a plurality of sections F<NUM>, F<NUM>, F<NUM>. Each section is a convex curved shape with:.

On <FIG>, the sections F<NUM>, F<NUM>, F<NUM>. , and Fk of the lens layer 12f correspond to the probe sections having a width that decrease from a first end (left side of probe <NUM> on <FIG>) to a second end (right side of probe <NUM> on <FIG>) of the probe: the widths wL<NUM>, wL<NUM>, wL<NUM>,.

Each first edge E1 of the sections F<NUM>, F<NUM>, F<NUM>. , and Fk emits to and/or receives from the nominal focal point FPn, an ultrasound wave respectively forming a beam B<NUM>, B<NUM>, B<NUM>. , and Bk inside the medium. Each second edge E2 does not substantially contribute to the ultrasound waves, because its surface is not oriented to the nominal focal point FPn.

The surface of the second edge E2 might not be exactly oriented perpendicularly to the direction D for various reasons, such as manufacturing reasons. However, its projected surface in the direction D is much smaller than the projected surface of the first edge E1, for example less than <NUM>% thereof. The second edge does not contribute to the ultrasound waves propagating towards and from the nominal focal point FPn whereas the first edge E1 is the surface that mainly or quasi-totally contribute to the ultrasound waves propagating towards and from the nominal focal point FPn.

The beams B<NUM>, B<NUM>, B<NUM>. , and Bk are inclined relative to the longitudinal direction X and substantially according to the above direction D. The depth direction Z is perpendicular to the longitudinal direction X and it goes through the nominal focal point FPn. A point of origin PO is defined as the intersection of the depth direction Z and the longitudinal direction X. The point of origin PO is then for example distant from a lateral edge of the transducer 12a, in the longitudinal direction X of an offset distance OD. This means that the beams are inclined and that the nominal focal point FPn is not exactly above the probe <NUM>. The transducer 12a is laterally shifted in the longitudinal direction X of said offset distance OD in comparison to the original point OP.

The first edge E1 may be planar or curved, e.g. a convex shape relative to the nominal focal point FPn inside the medium <NUM>.

The second edge E2 is potentially planar, and it is a step in the direction D, i.e. in the direction of the nominal focal point FPn, said step having a step length SL.

The step length SL is approximately equal to a distance so that an ultrasound wave emitted by the transducer in the medium through the lens layer 12f has a phase difference of <NUM>. π between a portion of wave emitted though one section Fk and a portion of wave emitted by a neighbour section Fk+<NUM>, next to said one section Fk, k being an integer as <NUM> <= k <= N, N being the number of sections of the lens layer 12f.

According to a model, the step length SL is for example equal to: <MAT> where.

Thanks to the above geometry of the lens layer 12f, the lens layer 12f behaves as a Fresnel lens that focusses the ultrasound waves towards and from the nominal focal point FPn inside the medium <NUM>.

As illustrated on <FIG>, the probe <NUM> is a linear probe extending along longitudinal direction X, said probe having one transducer 12a and a lens layer 12f having sections F<NUM>, F<NUM>, F<NUM>. , and Fk and forming the probe sections. Such probe <NUM> is not axisymmetric, and is not symmetric. Therefore, contrary to axisymmetric probes, such probe <NUM> is able to focus to various focal points FPj that can be shifted laterally in the longitudinal direction X (direction of such linear probe).

The probe <NUM> has for example a width in the transversal direction Y, a constant width wY, as disclosed on <FIG>. However, in another embodiment, such transversal width wY can vary along the abscissa in the longitudinal direction X. For example, the transversal width can increase from the first end (left side of probe <NUM> on <FIG>) to the second end (right side of probe <NUM> on <FIG>) of the probe <NUM>.

This embodiment may then use a lens layer 12f above a single transducer 12a. The transducer 12a is subjected to all the ultrasound waves arriving from all sections of lens layer 12f, and the transducer 12a combines these ultrasound waves to provide a single electric signal S<NUM> that is transmitted to the processing unit <NUM>.

The processing unit <NUM> is defined as being able to activate the transducer 12a according to various signals for emitting the emitting ultrasound waves. The emitted ultrasound waves may be:.

Then, the processing unit <NUM> analyses signals received from the probe <NUM> at a plurality of frequencies fj around the nominal frequency fn for sensing the medium at a plurality of focal points FPj situated in the medium, j being an index of said specific frequency corresponding to a specific focal point, j being an integer.

Optionally, the processing unit <NUM> generates a plurality of identical emitting sequences of ultrasound waves (e.g. at the same frequency), receives a plurality of signals corresponding to receiving sequences that result from said emitting sequences, and calculate an averaging of said plurality of signals. The processing unit <NUM> then analyses said averaged signal as it is a received signal for sensing the medium This improves the signal to noise ratio.

In a first variant and for the sake of simplicity, the process will be explained in the case of a sinus wave at frequency f.

The processing unit <NUM> is able to change the frequency f of the emitted ultrasound waves to a plurality of frequencies fj. Thanks to this frequency change ( i.e. frequency shift), the inclination of beams is modified, and the focal point is moved inside the medium <NUM> towards other focal points FPj corresponding to said frequencies fj, these other focal points being aligned on a direction of focal points DFP. For the sake of simplicity, the successive other focal points represented on the figures (the locus of the successive other focal points) are aligned according to a straight line, but they may be aligned in some embodiments according to a curved line when frequency is changed. Ideally, the direction (locus) of focal points DFP is substantially parallel to the longitudinal direction X. Alternatively; the direction (locus) of focal points DFP may be inclined relative to the longitudinal direction, depending on geometry of lens layer 12f. For example, when the frequency is increased, the other focal points FPj are moving laterally in the direction DFP, i.e. substantially in a direction parallel to the longitudinal direction X, or according to a curved line predetermined by at least the characteristics of the lens layer 12f. In a similar way, when the frequency is decreased, the other focal points FPj are moving laterally in the direction DFP, on the opposite side of the depth direction Z.

However, the beams associated to the other focal points FPj might not be as well focussed as for the nominal focal point FPn. Moreover, the excitation of transducer(s) is a narrow bandwidth and a quasi-pure frequency. These imperfections and limitations may lead to pixels in the calculated image that are blurrier compared to pixels from a usual ultrasound imaging technique and/or compared to a pixel corresponding to a point in the medium at the nominal focal point FPn.

Then, the processing unit <NUM> analyses the signals received for each one of the plurality of frequencies fj for sensing the medium at corresponding plurality of focal points FPj along said direction (locus) of focal points DFP.

Then, the processing unit <NUM> may also be able to calculate an image of a region of interest inside the medium on the bases of signals received from the probe at the plurality of frequencies fj. The image is for example composed of a grid of pixels in X-Z directions. It is understood that the pixels aligned in the X direction are approximately determined by varying the frequency f and the pixels aligned in the Z direction are approximately determined by the level of signal received for each time of flight (distance to transducer).

By "a grid of pixels", it may be understood a matrix of pixel values (image) that can correspond to a matrix of locations in the medium <NUM>. The matrix of locations can be spatially equally spaced or not. Optionally, the matrix of locations can be associated the matrix of pixel values to define any shape of image (not only a square or a rectangle). Optionally, the location of the pixel can be anywhere inside the medium <NUM>.

In a second variant, the processing unit <NUM> is able to control the probe <NUM> to emit in the medium <NUM> an ultrasound wave having a broadband signal characteristic around the nominal frequency fn.

In that case, the probe <NUM> behaves as if it simultaneously focusses to a plurality of focal points FPj inside the medium corresponding to the bandwidth of said signal.

Then, the processing unit <NUM> filters the received signal from the transducer 12a in response to the emitted broadband signal (corresponding to the emitted wave) so as to sense the medium at said plurality of focal points. Then, the processing unit <NUM> may determine at least an image of the medium on the bases of said plurality of focal points sensed by the system. The filter is advantageously a narrow band filter having a frequency bandwidth adapted to a specific frequency. The system or processing unit may comprise a plurality of filters that simultaneously the received signal so as to simultaneously sense the medium at a plurality of other focal points FPj. The filter(s) are preferably digital filters implemented by software in the processing unit <NUM>.

All variants of the embodiment of <FIG> are using only one signal S<NUM>, the system only needs in this example one analog to digital converter to convert the signal S<NUM> into data. The quantity of the data that must be transferred to the processing unit <NUM> is consequently advantageously very small compared to prior art beamforming systems, and the cost of the system is greatly reduced.

<FIG> shows a view in the X-Z plane of the probe and processing according to another embodiment of the disclosure. <FIG> shows the probe of <FIG> in a perspective view illustrating that the probe of the current disclosure is not an axisymmetric probe and that this probe is a linear probe aligned in the longitudinal direction X.

In this embodiment, the probe <NUM> comprises a plurality of transducer 12a, aligned according to the longitudinal direction X. Each transducer 12a is also referred as Ti, i being an index of the transducer, i being a positive non-null integer, and comprised between <NUM> and N (inclusive). Each transducer Ti receives and/or generates a signal Si, identified by same index i of the corresponding transducer Ti.

The transducers Ti correspond to the probe sections having a width that decrease from a first end (left side of probe <NUM> on <FIG>) to a second end (right side of probe <NUM> on <FIG>) of the probe: i.e. the widths w<NUM>, w<NUM>, w<NUM>,.

The nominal focal point FPn is situated inside the medium <NUM> and in a depth direction Z perpendicular to the longitudinal direction X. The longitudinal direction X and depth direction Z intersects at a point of origin PO. A first transducer T<NUM> situated at a left lateral edge of the probe, is offset from this point of origin PO: They are distant of an offset distance OD. Each transducer Ti emits and/or receives a portion an ultrasound wave, i. e an ultrasound beam Bi directed to the nominal focal point FPn.

The transducers 12a are configured so as any pair of two transducers (Ti, Ti+<NUM>) that are neighbour one to the other have a focal point difference distance Dfpd equal to the wavelength λ divided by a period number p. The focal point difference distance Dfpd is therefore a constant value for the probe <NUM>.

The period number p is an integer greater or equal to two (<NUM>). In the figure, the period number p is equal to four (<NUM>), and the focal point difference distance Dfpd is equal to λ/<NUM>.

The focal point difference distance Dfpd is an absolute value of a difference between a first distance between the nominal focal point FPn and the first transducer Ti of index i belonging to the pair of two transducers (Ti,Ti+<NUM>) (length of first beam Bi) and a second distance between the nominal focal point FPn and the second transducer Ti+<NUM> of index i+<NUM> belonging to the pair of two transducers (Ti, Ti+<NUM>) (length of second beam Bi+<NUM>).

In other words, for each pair of neighbour transducer (Ti, Ti+<NUM>) in the probe <NUM>, the focal point difference distance Dfpd is as follow: <MAT> where.

In the embodiment of <FIG>, a distance to any transducer Ti is for example defined at the geometric center of said transducer, but any other definition can be used; e.g. a distance on the left edge of the transducer, or on the right edge of the transducer, or any other definition.

In this embodiment, as all transducers are aligned according to a longitudinal direction X that is a straight line, and because of the above relations, the transducers 12a are configured with a width wi that changes along said longitudinal direction X: e.g. the second transducer T<NUM> has a width w<NUM> that is shorter than the width w<NUM> of the first transducer T<NUM>, and so on for all of them. The transducer's widths wi are consequently shorter and shorter when going away from the point of origin PO.

Additionally, the beams Bi (line FPn-Ti) from the nominal focal point FPn are more and more inclined when going away from the point of origin PO.

<FIG> is a generalized and enlarged view of two neighbour transducers Ti, Ti+<NUM>. A rectangle triangle (A, B, C) hatched on this <FIG> is defined for each pair of neighbour beams (Bi, Bi+<NUM>). The focus point difference distance Dfpd is represented on this figure, and one can deduce the following relation: <MAT> where.

Then, the wavelength λ corresponds to a full period of ultrasound wave having a phase varying between zero radian to <NUM>. As the focus point difference distance Dfpd is a constant value equal to λ/p, the signals Si, Si+p, Si+2p. respectively from transducers Ti, Ti+p, Ti+2p,. have the same phase, i.e. phase <NUM>, phase (λ/p). π, phase (λ/p). 2p = <NUM>. Therefore, these signals are "in phase" and can be directly added by short circuits from lines at the "in-phase" transducers 12a, as represented in <FIG>. The short circuits 12b are adding the electric charges of the "in phase" transducers 12a (e.g. piezo transducers) and are providing a phase signal Sphm, m being an index of phase signal representing the group of "in-phase" transducers. However, other solutions may be used by a skilled man depending on transducers technology.

In other words, the signals Si from the transducers Ti that are p-spaced one to another are added (e.g. by short circuits) to form a phase signal Sphm. The short circuits of this embodiment are performing a kind of analog addition of the signals from transducers.

In other words, the phased signals Sphm are defined as follow: <MAT> where.

Then, the system comprises N signals Si of transducers (i.e. the number of transducers in the probe). But the system comprises only p phased signals Sphm.

As period number p is an integer that can be relatively small (two or four for instance), the number of phased signals Sphm is relatively small.

This advantageously reduces the number of analog to digital converters needed to convert the phased signals into data in comparison to the number of transducers. This reduces the quantity of said data that must be transferred to the processing unit <NUM>, and as a consequence it reduces the cost of the system.

Thanks to the above features, the probe <NUM> behaves as a Fresnel lens that focusses the ultrasound waves towards and from the nominal focal point FPn inside the medium <NUM>.

As illustrated on <FIG>, the probe <NUM> is a linear probe extending along longitudinal direction X, said probe having a plurality of transducers 12a forming the probe sections. Such probe <NUM> is not axisymmetric, and is not symmetric. Therefore, contrary to axisymmetric probes, such probe <NUM> is able to focus to various focal points FPj that can be shifted laterally in the longitudinal direction X (direction of such linear probe).

The probe <NUM> has for example a constant width in the transversal direction Y, as illustrated on <FIG>. However, in another embodiment, such transversal width wY can vary along the abscissa in the longitudinal direction X. For example, the transversal width can increase from the first end (left side of probe <NUM> on <FIG>) to the second end (right side of probe <NUM> on <FIG>) of the probe <NUM>.

The processing unit <NUM> receives the p phased signals Sphm, and only needs to "rephrase" these signals via a combining process on this reduced number (p) of phased signals so as to form a combined signal S<NUM>* that then allows to sense the medium <NUM>. Then, the processing unit <NUM> may determine values of pixels of an image representing said medium. This combination is for example a beamforming process as it is well known, but based on the p phased signals, and not all the signals Si from the transducers 12a.

Thanks to the above features (the probe <NUM> comprising a plurality of transducers 12a and the addition of the p-spaced signals Si and the combination of phased signals Sphm), the ultrasound system <NUM> behaves as a Fresnel lens that focusses the ultrasound waves towards and from the nominal focal point FPn inside the medium <NUM>.

Then, the processing unit <NUM> is able to implement the first or second variant of the first embodiment, i.e. the processing unit is able to emit a plurality of successive frequencies fj to move the focal point or the processing unit <NUM> is able to emit a wave having a broadband characteristic and to filter the receive signal, as explained in the first embodiment. The focal point is moved successively or virtually simultaneously inside the medium <NUM> towards other focal points FPj corresponding to said frequencies fj. The other focal points are aligned on a direction of focal points DFP (the locus of a plurality of focal points by varying the frequency). The direction of focal points DFP might be substantially parallel to the longitudinal direction X, or inclined relative to the longitudinal direction X, or is a predetermined set of positions relative to the probe <NUM>.

Then, the processing unit <NUM> can calculate an image of a region of interest inside the medium on the bases of the p phased signals Sphm received from the probe at the plurality of frequencies fj. The image is for example composed of a grid of pixels in X-Z directions. It is understood that the abscissa x of a pixel in the longitudinal direction X is determined by varying the frequency f and the ordination z of a pixel in the depth direction Z is determined by the level of a processed signal received for each time of flight (distance to transducer) as it is well known in ultrasound imaging.

In this embodiment, the virtual "Fresnel lens" is digitally recomposed by the configuration of the transducers 12a (their geometry) and the additions of the p-spaced signals from the probe <NUM>. This corresponds to a virtual Fresnel lens that uses discrete (discontinuous) physical elements (transducers) and a specific combination of signals, whereas, in the first embodiment, the simulated Fresnel lens is a continuous physical element (a transducer and a lens layer).

According to another variant of this second embodiment represented on <FIG>, the probe <NUM> further comprises a patterned lens layer 12c positioned above the transducers 12a and in contact with the transducers 12a and in contact with the medium <NUM>. The patterned lens layer 12c is adapted for optimizing the emitted and received ultrasound waves between each transducer Ti and the nominal focal point FPn. This patterned lens layer 12c provides a correction so as the upper surface of each transducer Ti receives an "in-phase" ultrasound wave by correcting time of flight differences between a left end and a right end of each transducer.

To this purpose, the patterned lens layer 12c may have a shape which looks like a saw tooth shape like the lens layer of first embodiment. This shape comprises a plurality of sections, each section facing one transducer Ti in the plurality of transducers.

For example, the patterned lens layer 12c comprises sections 12c<NUM>, 12c<NUM>, 12c<NUM>,. , respectively corresponding to the transducers T<NUM>, T<NUM>, T<NUM>,.

Each section of the patterned lens layer has a thickness that increases on the side of the transducer Ti that corresponds to the shortest distance to the nominal focal point FPn (left end of each transducer in case of the <FIG>).

<FIG> shows a view of the probe and processing according to another embodiment of the disclosure. This figure is a view in XZ plane. But, similarly to the previous embodiments, the probe <NUM> is not an axisymmetric probe and it is a linear probe that extends according to the longitudinal direction X. The probe <NUM> may have a constant width Wy in the transversal direction Y or a width WY in the transversal direction Y depending on the abscissa in the longitudinal direction as already explained.

In this third embodiment, the probe <NUM> comprises at least two portions of probes, a first portion <NUM><NUM> and a second portion <NUM><NUM>.

The first portion <NUM><NUM> is for example situated at a first side in comparison to the depth direction Z (in plane X-Z), i.e. on right side on <FIG>, and the second portion <NUM><NUM> is situated at a second side in comparison to said depth direction Z, said second side being opposite to the first side in comparison to the depth direction Z. In other words, the depth direction Z is located between the first portion <NUM><NUM> and the second portion <NUM><NUM>.

Therefore, the two portions of probe <NUM><NUM>, <NUM><NUM>, are situated on both sides of the depth direction Z, and are each one oriented in the same direction Z, facing the medium <NUM> so as to be able to generate and to receive ultrasound waves from this medium <NUM> (in the upper half plane X-Z on <FIG>).

The fist portion <NUM><NUM> focusses ultrasound waves towards a first nominal focal point FPn1, and the second portion <NUM><NUM> focusses ultrasound waves towards a second nominal focal point FPn2. The two nominal focal points FPn1, FPn2 may be separate one from the other so as to elongate (in the longitudinal direction X) the optimum well focussed area inside the medium <NUM>. Reciprocally, the two nominal focal points FPn1, FPn2 may be the same point (i.e. superposed) so as to improve the accuracy of the image.

The first portion <NUM><NUM> focusses in a first inclined direction (e.g. upper left) whereas the second portion <NUM><NUM> focusses in a second inclined direction (e.g. upper right), the second direction being different to the first direction, and for example opposite relative to the longitudinal direction X.

Then, the first and second portions <NUM><NUM>, <NUM><NUM> of the probe <NUM> may be realized according to the technical features above described in the first embodiment or in the second embodiment, i.e. with a single transducer or a plurality of transducers. The two portions may advantageously be of same type.

The processing unit <NUM> of the third embodiment is then adapted to determine:.

The first image I1 may correspond to an image that is build or calculated for pixels corresponding to focal points located on the first side (right), i.e. in the first quadrant XZ defined in the first side relative to the depth direction. The first quadrant XZ is the quadrant in the XZ plane that extends in the positive longitudinal direction X and in the positive depth direction Z.

The second image I2 may reciprocally correspond an image that is build or calculated for pixels corresponding to focal points located on the second side (left), i.e. in the second quadrant -XZ defined in the second side relative to the depth direction. The second quadrant -XZ is the quadrant in the XZ plane that extends in the negative longitudinal direction X and in the positive depth direction Z.

The processing unit <NUM> then can move the focal point from left to right in the first quadrant XZ of the first portion <NUM><NUM> (i.e. in the positive direction of longitudinal direction X) by increasing the frequency f analysed in the signals from the first portion <NUM><NUM>, and it may move the focal point from right to left in the second quadrant -XZ of the second portion <NUM><NUM> (i.e. in the negative direction of longitudinal direction X) by increasing the frequency analysed in the signals from the second portion <NUM><NUM>. Therefore, the two portions <NUM><NUM>, <NUM><NUM> of probe <NUM> are working symmetrically each one in his plane quadrant for providing signals used to build or calculate pixel in each associated respective quadrant of the plane XZ, i. e, the first or the second quadrant. In this case, the two portions <NUM><NUM>, <NUM><NUM> can be symmetric relative to the depth direction Z, and they provide first image I1 and second image I2 that are scanned symmetrically relative to the depth direction Z if considering increasing frequency for both portions of probe <NUM>.

Then, the processing unit <NUM> determines the pixels of the image representing a region of interest ROI of the medium <NUM> on the bases of the first and the second images I1, I2.

Eventually, the processing unit <NUM> directly determines the pixels of the image representing the region of interest ROI of the medium <NUM> on the bases of the signals and/or phased signals from the first and second portions <NUM><NUM>, <NUM><NUM> of the probe <NUM>, i.e. without calculating intermediate first and second images.

The region of interest of such embodiment having a first and second portion of probe <NUM> may be wider in X direction.

In a variant represented on <FIG>, the system comprises an additional transducer <NUM><NUM>. This additional transducer <NUM><NUM> may be positioned between the first and second portions <NUM><NUM>, <NUM><NUM> of the probe <NUM>. This additional transducer <NUM><NUM> may be adapted so as to focus ultrasound waves on the line of the depth direction Z, between the first and second portions <NUM><NUM>, <NUM><NUM> of the probe.

The additional transducer <NUM><NUM> may be adapted so as to generate an ultrasound wave of a frequency lower than the first and second portions <NUM><NUM>, <NUM><NUM> of the probe <NUM>.

Optionally, the additional transducer <NUM><NUM> is adapted to generate a low frequency vibration inside the medium, whereas the first and second portions <NUM><NUM>, <NUM><NUM> of the probe are adapted to higher frequencies that are used for determining an image or a plurality of time successive images of the same region of interest ROI inside the medium <NUM>.

Then, the first and second portions <NUM>, <NUM> of the probe are used by the processing unit <NUM> so as to sense and/or image the propagation of the vibration inside the medium <NUM>. The time successive images are then combined by the processing unit <NUM> so as to calculate at least one value of elasticity of at least one point inside the medium <NUM>, on the bases displacements of said vibration.

Ideally, the system <NUM> is also able to calculate or determine an image of elasticity of the region of interest ROI in the medium.

Such particular embodiment provides an elasticity imaging device that is particularly of low cost. Such small and economic system is usable in numerous new medical imaging applications.

The above embodiments are provided for illustration purposes only and may be combined in totality or in part, the protection provided by this application being defined by its set of claims.

Thanks to the various technical features of above embodiments, the ultrasound system needs less electronic components than prior art systems. The system is then less costly.

The system <NUM> according to the disclosure also spends less energy in use. It can be easy to carry, and small enough to be a portable system.

Moreover, it is also easier to manufacture. Therefore, the ultrasound system is much less costly.

Claim 1:
An ultrasound system (<NUM>) comprising:
- a probe (<NUM>) adapted for being put into contact with a medium (<NUM>) and comprising at least one transducer (Ti) adapted for emitting and receiving ultrasound waves in said medium, and
- a processing unit (<NUM>) associated to said probe and adapted for processing signals from the probe,
wherein
- the probe (<NUM>) is not axisymmetric but is a linear probe extending according to a longitudinal direction (X),
- the probe (<NUM>) comprises at least one portion comprising along the longitudinal direction (X) a plurality of probe sections having a width that decrease from a first end to a second end of said portion so as to behave as a Fresnel lens in that the probe focusses the ultrasound waves towards and from a focal point (FP) inside the medium, said focal point being different for each frequency of said ultrasound waves, and
- the processing unit (<NUM>) analyses signals received from said probe at a plurality of frequencies (fj) around a nominal frequency (fn) for sensing the medium at a plurality of focal points (FPj) situated in the medium, and
- the processing unit (<NUM>) builds an image of the medium on the bases of a plurality of focal points sensed in the medium, the image being composed of a grid of pixels,
the pixels aligned in the depth direction (Z) perpendicular to the longitudinal direction being determined by the level of the signals received for each time of flight corresponding to a distance between the probe and one of the plurality of focal points (FPj) in the medium, and the ultrasound system being characterized in that
the pixels aligned in the longitudinal direction (X) being determined by the signals at each one of the plurality of frequencies.