OPHTHALMIC ULTRASOUND PROCEDURES USING ANNULAR TRANSDUCERS

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention belongs to the field of ophthalmology. More specifically, the invention relates to a method of ophthalmic ultrasound using annular transducers.

[0002] Ophthalmic ultrasound involves acquiring an image of an eye using an ultrasound probe emitting an ultrasound beam. The ultrasound probe is positioned near an eye, typically in contact with the eye, and emits ultrasound waves that propagate into the eye. These ultrasound waves pass through the internal structures of the eye, such as the lens, vitreous body, or retina, and are partly reflected by these structures. The reflected ultrasound waves are captured and recorded by the probe to provide images of the eye. The propagation of ultrasound waves depends not only on their frequency, but also largely on the spatial configuration of the ultrasound probe that emits them.

[0003] Acquiring usable ultrasound images of most of an eye is subject to many constraints with traditional transducers. For example, to examine a complete eye and its orbit with a mechanically oscillating ultrasound probe and obtain the best possible image, it is necessary to emit waves in frequencies ranging from 10 to 25 MHz, in order to reach a depth of more than 45 mm in the eye (between 45 and 60 mm). It is also necessary to vary the emission angle between 45 and 60 °, to focus the transducer at approximately 25 mm (between 18 and 27 mm) just before or on the retina (which constitutes the preferred target), and to ensure an image frequency of at least 8 Hz (between 8 and 16 Hz) to visualize the movements of the vitreous.

[0004] Using a curved single-element transducer with a diameter of 9 mm (maximum diameter to have 50° of travel), one can for example obtain at the natural focal length given by the curvature of the transducer, at an ultrasound frequency of 20 MHz (with a bandwidth of 10 to 30 MHz) a total longitudinal resolution of 75 µm, and a total possible lateral resolution of 200 µm. However, the image quickly becomes blurred with depth since the depth of field at 6 dB is then only 2.5 mm, which means that only a small area around the retina will have an optimum signal-to-noise ratio and resolution.Furthermore, in accordance with Shannon's theorem, it is necessary to sample at least twice the highest frequency of the bandwidth to be processed (30 MHz for a central frequency transducer of 20 MHz), i.e. at 60 MHz and to generate enough lines in order to be at least 2.5 times the total lateral resolution at the focal length, i.e. 360 lines minimum for 50°.

[0005] Concerning the ultrasound emission itself, it is necessary to wait for the end of the echo signal (i.e. the reflected ultrasound) from one ultrasound line to return another, in order to avoid parasitic echoes from one line to the other. We then have an ultrasound line at best every 90 µs for a depth of 60mm, which results in a maximum probe speed of approximately 13hz. However, by accepting certain compromises on the quality of the acquired ultrasound images, it is possible to achieve image frequencies of up to 20 Hz.

[0006] In order to achieve superior resolution and penetration into the eye, it has been proposed to use a ring transducer, i.e. a transducer comprising a plurality of transducer elements organized in concentric rings forming transducer rings. The use of a ring transducer makes it possible to increase the depth of field to have the best possible overall image of the eye regardless of its geometry (small, large, oval, etc.).

[0007] Using the configuration of the single-element transducer example mentioned above (ultrasonic waves at 20 MHz and a diameter of 9 mm), a 6 dB depth of field of 18 mm can be obtained with a transducer with five curved ultrasonic rings, an improvement of approximately a factor of 7. Using a transducer of this type therefore considerably improves the quality of the vitreous and retinal image of the eye. In addition, it also improves the signal-to-noise ratio over the entire depth of field.

[0008] Furthermore, ultrasound waves at higher frequencies ranging from 35 to 50 MHz can be used to increase accuracy when examining the overall anterior pole of an eye. A conventional curved single-element transducer, focused to a depth of about 10 mm, can then examine up to 16 mm deep. The resulting depth of field is then about 1 mm, which is very unsatisfactory. Using a five-ring annular transducer, a depth of field of 8 mm is achieved, which improves the overall image and makes this configuration much simpler to use due to its lower sensitivity to depth adjustment, which must be performed by the operator.

[0009] Using multiple concentric rings, however, requires coordinating the transmission and reception of measurement signals between these rings. Two approaches have been used so far.

[0010] A first approach is similar to the operation of phased array transducers. The transducer rings are emitted with a calculated emission delay between each transducer ring so that the ultrasound waves arrive in phase at a certain depth. The ultrasound lines obtained by receiving the ultrasound echoes by all the transducer rings are then added in real time. This produces a high-quality image around the target depth, and the speed is comparable to that of a single-element transducer.

[0011] For example, patent application US 2005 / 251043 A1 describes a method for exploring and visualizing tissues of human or animal origin, in which: an ultrasonic probe carried by a head controlled by a three-dimensional positioning system, in particular controlled by a computer, is positioned in line with said tissue structure, the probe is controlled so that it generates beams of high-frequency converging ultrasonic waves (of the order of 30 to 50 MHz), these waves being focused at the level of a given zone of tissue structure, according to a penetration distance of between 20 and 30 mm, a scan of the tissue structure is carried out by the positioning system controlled by the computer, while at the same time acquiring, by the computer, the signals reflected by the tissue structure, various signal processing operations are carried out on the data resulting from the scan, to improve the restitution of the information and facilitate interpretation by the practitioner.

[0012] In this patent application US 2005 / 251043 A1, a dynamic focusing probe is used, produced by an electronic or digital control method, consisting of a multi-element probe, with circular symmetry, composed of several concentric annular transducers regularly spaced on a flat or spherically concaved surface. These transducers are independent of each other and are individually controlled on transmission and reception by pulses offset in time. In particular, dynamic focusing is obtained by introducing a phase shift - time delay - on transmission between the different rings. All of the transducer rings transmit with a calculated transmission delay between each transducer ring so that the echographic ultrasonic waves arrive in phase at a certain depth.The ultrasound lines obtained by receiving the ultrasound echoes by all the transducer rings are then added in real time.

[0013] However, when it is desirable to obtain a high-quality overall image of an eye, several depths must be targeted. It is therefore necessary to make several passes by modifying the emission delays affecting each transducer ring to reach different depths. This results in a very long acquisition time since the acquisition frequency is divided by the number of different depths to be analyzed to reconstruct the overall image.

[0014] A second approach is similar to the operation of radars. A single transducer ring is excited and emits ultrasonic waves. However, the signals from all the transducer rings, resulting from the reception by these transducer rings of the reflected ultrasonic waves, are recovered and readjusted (to compensate for the path difference between the transducer rings). In order to obtain the final image, however, it is necessary to use all the transducer rings in transmission, which therefore requires as many transmission-reception iterations as the number of transducer rings. Thus, in an example with five transducer rings, this means carrying out five successive transmissions, with five receptions per transmission, i.e. a total of 25 partial ultrasound lines that must be processed to give an overall ultrasound line. Consequently, this approach requires five times more time than with a single-element transducer.However, speed is important in ophthalmic ultrasound in order to be able to observe the movements of the vitreous body.

[0015] Furthermore, this approach requires significant post-processing due to the many partial ultrasound lines, which implies a significant computation time, which may require management of shifts per slice. In addition, since each emission is only made on one transducer ring, the final result of the signal-to-noise ratio at the focal length is similar to that of a single-element transducer but 6 dB lower than the previous method. Patent application US 2013 / 0093901 A1 uses this approach, and in order to accelerate image acquisition, proposes not to use certain lines, which leads to lower image quality in terms of resolution, sensitivity and penetration. PRESENTATION OF THE INVENTION

[0016] The aim of the invention is to propose an ocular ultrasound method using an ultrasound probe with several transducer rings making it possible to acquire good quality images quickly.

[0017] For this purpose, there is provided an ocular ultrasound method using an ultrasound probe according to claim 1.

[0018] The method is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations: in each cycle, the iterations are performed in the same order; the measurement signal of a transducer ring results from the digitization of the reception signal generated by this transducer ring upon reception by said transducer ring of reflected ultrasonic waves resulting from the emission of ultrasonic waves by a group of transducer rings, a measurement signal being defined as a chronological sequence of discrete points with which corresponding values ​​are associated, and the combination of measurement signals to give an ultrasound line during an iteration consists of adding the values ​​associated with synchronous discrete points of said measurement signals;the combination of measurement signals to give an ultrasound line during an iteration is restricted to a selection of discrete points, said discrete points being selected so as to operate a chronological shift between the measurement signals compensating for the differences in acoustic path resulting from the geometry of the transducer, the synchronism of the discrete points taking into account this shift; discrete points are added to the measurement signal by convolving said measurement signal with a sliding cardinal sine so that a period between the discrete points is less than the inverse of at least ten times the transmission frequency;an ultrasound line is defined as a chronological sequence of discrete points with which corresponding values ​​are associated, and in which the combination of ultrasound lines to give a displayable line consists of adding the values ​​associated with synchronous discrete points of said ultrasound lines; the transducer rings are grouped into k groups of rings each grouping between 2 and n-1 transducer rings, with 1 <k<n; n= 5, la sonde ultrasonore comprenant cinq anneaux transducteurs. ;

[0019] The invention also relates to a computer program product comprising program code instructions recorded on a non-volatile medium usable in a computer for the execution of processing steps of the method according to the invention, when said program is executed on a computer.

[0020] The invention also relates to an ultrasound system comprising an ultrasound probe according to claim 10. PRESENTATION OF THE FIGURES

[0021] The invention will be better understood, thanks to the following description, which relates to embodiments and variants according to the present invention, given as non-limiting examples and explained with reference to the appended schematic drawings, in which: there Figure 1 schematically illustrates the annular configuration of the transducer elements of an ultrasonic probe according to a possible embodiment of the invention, the figures 2 , 3 And 4 schematically illustrate the progress of examples of ultrasound methods according to different embodiments of the invention. DETAILED DESCRIPTION

[0022] In reference to the Figure 1, an ultrasonic probe 1 is used comprising a plurality of transducer elements organized in n concentric rings 2 forming n transducer rings. In the example of the Figure 1, there are five transducer rings, designated respectively from the outside towards the center by 2a, 2b, 2c, 2d and 2e, and consequently n = 5. It is of course understood, however, that n can take other values. However, the number of transducer rings 2 is greater than three (i.e. n>3), and preferably greater than four (i.e. n>4). The transducer elements are for example piezoelectric, configured to emit ultrasound propagating in the eye. These ultrasounds typically have a frequency between 10 and 100 MHz. It should be noted here that the central transducer ring 2e is solid, and therefore constitutes a transducer disc. The central transducer ring 2e could also be hollow, i.e. with an empty center like the other peripheral transducer rings 2a, 2b, 2c and 2d.Since the various transducer rings are concentric, it is necessary for the peripheral transducer rings 2a, 2b, 2c and 2d to be hollow so that they can be nested within each other. There is no such need for the central transducer ring 2e, which can therefore be solid.

[0023] The natural focal length of the ultrasound probe 1 is given by the curvature of the transducer elements or by the addition of a lens opposite its emission face. For ocular examination, this curvature can vary from flat to a radius of curvature of 9 mm, for example. The largest transducer ring 2a has an external diameter of between 3 and 10 mm, for example 9 mm, and has a width of 0.05 mm. The smallest transducer ring 2e has an external diameter of between 0.1 and 0.3 mm, for example 0.2 mm. The transducer rings 2 are separated by a distance of between 0.02 and 0.1 mm, for example 0.05 mm. Preferably, so that the transducer rings have an equivalent power between them, it is possible to seek to have their respective surfaces of similar, and ideally identical, sizes. For this purpose, the width of the transducer rings preferably decreases with their distance from the common center.

[0024] To implement the ophthalmic ultrasound method, the ultrasound probe 1 is positioned relative to an eye, in order to be able to emit and receive ultrasound waves propagating inside this eye. The ultrasound probe 1 can be placed in contact with the eye, that is to say attached to the cornea or the sclera, possibly covered with a gel. It is also possible to provide for the presence of a pocket of liquid such as water between the ultrasound probe 1 and the eye, this pocket typically being formed by a membrane permanently closed on the ultrasound probe 1. The ultrasound probe 1 can also be immersed in a liquid contained in an open cup against the eye, the liquid serving as an intermediate propagation medium between the ultrasound probe 1 and the eye.

[0025] Once positioned, the ultrasonic probe 1 is controlled to transmit and receive ultrasonic waves. Each transducer ring 2 is individually controlled, and in response to an excitation (an electrical voltage signal), a transducer ring 2 transmits ultrasonic waves at a transmission frequency. The transmission frequency is between 10 and 100 MHz. In the following example, a transmission frequency of 20 MHz will be described.

[0026] In the method, the transducer rings 2 are grouped into several groups of rings grouping between 1 and n-1 transducer rings. For example, if n=5, then each group of rings can group one, two, three or four transducer rings 2. The number of groups of rings is k, with 1≤k≤n. Preferably, k is at least equal to two, and preferably 1 <k≤n. De préférence également, 1<k<n. Les anneaux transducteurs sont par conséquent regroupés en plusieurs groupes d'anneaux (k≥2). Ainsi, dans l'exemple de la Figure 2 , n=5 and k=5, in the example of the Figure 3 , n=5 and k=3, in the example of the Figure 4 , n=5 and k=2.

[0027] In order to ensure equivalence between the groups, the different groups of transducer rings preferably have the same number of transducer rings 2. A transducer ring 2 may be part of two groups of rings. However, each group of transducer rings differs from another group of transducer rings by at least one transducer ring 2 different from the transducer rings 2 of said other group of transducer rings. Preferably, each group of transducer rings comprises at least one transducer ring 2 not belonging to any other group of transducer rings.

[0028] For example, in the case of the Figure 3, a first group of transducer rings groups together transducer rings 2a and 2b, a second group of transducer rings groups together transducer rings 2b and 2c, and the third group of transducer rings groups together transducer rings 2d and 2e. It can thus be seen that transducer ring 2b is part of two groups of transducer rings, but also that transducer ring 2a is part of only the first group of rings and no other group of rings, that transducer ring 2c is part of only the third group of rings and no other group of rings, and transducer rings 2c and 2d are part of only the third group and no other group of rings.

[0029] These groupings into different groups result in a common transmission command for the transducer rings 2 of the same group of rings at a transmission time. It is possible to modify the number or the composition of the groups of transducer rings from one implementation of the method to another. It should be noted that it is not necessary to select all the transducer rings 2 of the ultrasonic probe 1 to transmit ultrasound. In certain configurations, transducer rings 2 may not transmit ultrasound and may only be used for reception.

[0030] The method comprises a plurality of cycles. A cycle comprises several iterations of transmitting and receiving ultrasonic waves, each time involving a different group of transducer rings. Each cycle runs through all k groups of transducer rings. During each iteration: a group of transducer rings is excited so that only the transducer rings 2 of said group of transducer rings emit ultrasonic waves at a transmission frequency, while the other transducer rings 2 not forming part of said group of transducer rings do not emit ultrasonic waves at the transmission frequency, and the n measurement signals of all n transducer rings are recovered, each measurement signal resulting from the reception by a transducer ring 2 of reflected ultrasonic waves resulting from the emission of ultrasonic waves by the transducer rings or the group of transducer rings, the n measurement signals are combined to give an ultrasound line.

[0031] Preferably, in each cycle, the iterations are performed in the same order. The iterations of each cycle make it possible to determine and display a displayable line. There are therefore at least as many cycle iterations as there are lines in the displayed image. However, between each cycle, each image or group of images, the emission modalities of the ultrasonic waves can be modified to favor resolution (individual emissions), penetration (emission on grouped rings) or speed (not using all the rings). Knowing that all combinations are possible on each image and possibly on each line in terms of emission, grouping of rings and number of rings used for emission or reception. Emission

[0032] In the example of the Figure 2, each group of transducer rings comprises only one ultrasonic transducer ring 2. The first group of rings consists of ultrasonic transducer ring 2a, the second group of rings consists of ultrasonic transducer ring 2b, the third group of rings consists of ultrasonic transducer ring 2c, the fourth group of rings consists of ultrasonic transducer ring 2d, and the fifth group of rings consists of ultrasonic transducer ring 2e. There are therefore five groups of rings (k=5) for five transducer rings (n=5).

[0033] A first cycle 100 comprises five iterations 101, 102, 103, 104 and 105. In a first iteration 101, only the transducer ring 2a of the first group of rings is excited by an electrical control signal and emits ultrasonic waves. In a second iteration 102, only the transducer ring 2b of the second group of rings is excited by an electrical control signal and emits ultrasonic waves. In a third iteration 103, only the transducer ring 2c of the third group of rings is excited by an electrical control signal and emits ultrasonic waves. In a fourth iteration 104, only the transducer ring 2d of the fourth group of rings is excited by an electrical control signal and emits ultrasonic waves. In a fifth iteration 105, only the transducer ring 2e of the fifth group of rings is excited by an electrical control signal and emits ultrasonic waves.

[0034] Once this first cycle 100 is completed, that is to say when said first cycle 100 has traversed all five groups of transducer rings 101, 102, 103, 104, 105, a second cycle 110 then begins, traversing all five groups of transducer rings during five iterations 111, 112, 113 in the same way as first cycle 100.

[0035] In the example of the Figure 3 , each group of transducer rings consists of two ultrasonic transducer rings. The first group of rings consists of ultrasonic transducer rings 2a and 2b, the second group of rings consists of ultrasonic transducer rings 2b and 2c, the third group of rings consists of ultrasonic transducer rings 2d and 2e. There are therefore three groups of rings (k=3) for five transducer rings (n=5).

[0036] A first cycle 200 comprises three iterations 201, 202, 203. In a first iteration 201, only the transducer rings 2a and 2b of the first group of rings are excited by an electrical control signal and emit ultrasonic waves. In a second iteration 202, only the transducer rings 2b and 2c of the second group of rings are excited by an electrical control signal and emit ultrasonic waves. In a third iteration 203, only the transducer rings 2d and 2e of the third group of rings are excited by an electrical control signal and emit ultrasonic waves. Once this first cycle 200 is completed, that is to say when said first cycle 200 has traversed all three groups of transducer rings, a second cycle 210 then begins, traversing all three groups of transducer rings during three iterations 211, 212, 213 in the same way as the first cycle 200.

[0037] In the example of the Figure 4 , there are two groups of transducer rings, and each group of transducer rings consists of three transducer rings. The first group consists of ultrasonic transducer rings 2a, 2b, and 2c, the second group consists of ultrasonic transducer rings 2c, 2d, and 2e. So there are two groups of rings (k=2) for five transducer rings (n=5).

[0038] A first cycle 300 comprises two iterations 301, 302. In a first iteration 301, only the three transducer rings 2a, 2b, and 2c of the first group of rings are excited by an electrical control signal and emit ultrasonic waves. In a second iteration 302, only the three transducer rings 2c, 2d, and 2e of the second group of rings are excited by an electrical control signal and emit ultrasonic waves. Once this first cycle 300 is completed, that is to say when said first cycle 300 has traveled through all two groups of transducer rings 301, 302, a second cycle 310 then begins, traveling through all two groups of transducer rings during two iterations 311, 312, in the same way as first cycle 300.

[0039] For each iteration, we therefore have an emission of ultrasonic waves, a reception of ultrasonic waves, and the combination of the measurement signals resulting from this reception. Reception

[0040] The emitted ultrasound waves propagate in the eye, pass through the internal structures of the eye, such as the lens, the vitreous body or the retina, and are partly reflected by these structures and returned to the ultrasound probe 1. The reception, by a transducer ring 2, of reflected ultrasound waves generates a measurement signal. All the transducer rings 2 receive these reflected ultrasound waves and generate measurement signals. Thus, in the case where the ultrasound probe comprises five transducer rings 2, five measurement signals are generated and are used.

[0041] More precisely, the reception of ultrasonic waves by a transducer ring 2 causes the appearance of a reception signal, electrical and analog, at the output of said transducer ring 2. This reception signal is then digitized to give a measurement signal. A measurement signal is therefore a digital signal and is defined as a chronological sequence of discrete points to which corresponding values ​​are associated, determined from the reception signal.

[0042] The digitization of the measurement signals can be done at a frequency such that the digitization step is fine enough to then perform an offset compensating for the differences in the path of the ultrasonic waves for the different measurement signals. This digitization frequency should then be at least 10 times the transmission frequency, for example 200 MHz for a transmission frequency of 20 MHz, preferably at least 12 to 15 times the transmission frequency in order to process the entire bandwidth of the signal in reception, which often goes up to 1.5 times the transmission frequency.

[0043] These high digitizing frequencies can lead to complicated digitizers especially for transducers using high frequencies, such as 50 MHz or more. To avoid these problems, alternatively, it is also possible to add discrete points to each measurement signal by convolving said measurement signal with a sliding cardinal sine wave so that a period between the discrete points is less than the inverse of at least ten times the transmission frequency, and preferably less than 12 to 15 times the transmission frequency.

[0044] Once the measurement signals have been obtained either by direct digitization or by adding additional points, a selection of discrete points can be chosen on each measurement signal to restrict the measurement signal to these selected discrete points. The discrete points are selected so as to create a chronological shift between the different measurement signals compensating for the differences in acoustic path resulting from the geometry of the transducer rings 2, the synchronism of the discrete points taking this shift into account.

[0045] Indeed, the ultrasonic waves are emitted and received by different transducer rings 2 arranged at different positions. This results in differences in the acoustic path resulting in time shifts. As an example, Table 1 below shows the absolute delay in nanoseconds affecting the ultrasonic waves during their journey through a focusing point at a depth of 15 mm in the axis of their central point as a function of the transmitting and receiving rings for a transmission frequency of 20 MHz and an ultrasonic probe with a diameter of 9 mm (diameter of the outer transducer ring 2a) naturally focused at 22 mm: Table 1 Ring in reception Ring in emission 2e 2d 2c 2b 2a 2nd ring 25 53 82 112 143 2d ring 53 81 109 140 171 2c ring 82 109 139 169 200 ring 2b 112 140 169 199 230 ring 2a 143 171 200 230 261

[0046] Obviously, the delay is all the greater the further the transducer ring 2 is from their common center, and the outer transducer ring 2a is the most affected. The delay affecting the ultrasonic waves results in time shifts between the measurement signals of the different transducer rings.

[0047] It is this time shift between the measurement signals between the transducer rings 2 which is important in order to be able to exploit the measurement signals coming from different transducer rings 2. Taking the example above again and taking as reference the measurement signal from the central annular transducer 2e for an emission by this central annular transducer 2e, the time shifts affecting the other measurement signals are given by table 2: Table 2 Ring in reception Ring in emission 2e 2d 2c 2b 2a 2nd ring 0 28 57 87 118 2d ring 28 56 84 115 146 2c ring 57 84 114 144 175 ring 2b 87 115 144 174 205 ring 2a 118 146 175 205 236

[0048] This time shift between the measurement signals results, after digitization, in a shift in the number of discrete points. Thus, taking the example above, the point shifts for a digitization with a step of 2 ns are given by table 3: Table 3 Ring in reception Ring in emission 2e 2d 2c 2b 2a 2nd ring 0 14 29 44 59 2d ring 14 28 42 58 73 2c ring 29 42 57 72 88 ring 2b 44 58 72 87 103 ring 2a 59 73 88 103 118

[0049] Therefore, this point shift of the measurement signals must be taken into account to match the information contained therein, which can be done simply by selecting the discrete points of each measurement signal. For example, x t1 is a discrete point of a measurement signal of a first transducer ring 2 corresponding to time t 1 . y t1 is a discrete point of a measurement signal of a second transducer ring 2 corresponding to time t 1 . However, x t1 and y t1 do not report the same ultrasonic waves. Indeed, due to their arrangement on the ultrasonic probe, the sound waves arriving at the second transducer ring 2 have a longer path to travel and arrive with a delay d compared to their arrival at the first transducer ring 2. Therefore, it is the point y t1+d that corresponds to the same ultrasonic waves as the point xt 1 .If the points x t1 , x t2 , x t3 , ... are selected for the first measurement signal, the points y t1+d , x t2+d , x t3+d , ... are selected for the second measurement signal. This allows the time lag between the measurement signals to be taken into account in a simplified manner, without having to implement a time recalibration of the measurement signals. This simplicity allows this taking into account of the time lag to be implemented practically in real time. Combination of measurement signals

[0050] The measurement signals of the different transducer rings are then combined to give an ultrasound line. This ultrasound line is representative of the response of the transducer rings 2 to the emission of ultrasonic waves by the group of transducer rings that emitted them during this iteration. The combination of measurement signals to give an ultrasound line during an iteration consists of adding the values associated with discrete points of said measurement signals, with a shift corresponding to the respective delay affecting each measurement signal.Taking the example above, we add the discrete point x t1 of a measurement signal from a first transducer ring 2 with the discrete point y t1+d of another measurement signal from a second transducer ring 2, the two points being synchronous at time t 1 by means of the delay d affecting the measurement signal from the second transducer ring 2 with respect to the measurement signal from the first transducer ring 2. The ultrasound line can of course undergo various conventional treatments such as filtering, shifting or scaling.

[0051] When there are enough discrete points in each measurement signal, i.e. with a frequency greater than at least 10 times the transmission frequency, we then obtain that the theoretical delay affecting a measurement signal corresponds to a shift in the number of discrete points, as explained above. Since the delays are no longer times, but a shift in the choice of points in the measurement signals, it is possible to combine the measurement signals by adding them practically in real time. The ultrasound line can of course undergo various conventional treatments such as filtering, shifts or scaling. Combination of ultrasound lines

[0052] At each iteration, the above steps are repeated, however modifying the group of transducer rings 2 emitting the ultrasonic waves. An ultrasound line is therefore obtained at each iteration. However, an ultrasound line only represents the response of the transducer rings 2 to the emission of ultrasonic waves by only the transducer rings 2 of the group of ultrasonic rings involved in the iteration.

[0053] It is therefore intended to combine the k ultrasound lines resulting from the k most recent iterations into a displayable line. Ultrasound lines are defined as chronological sequences of discrete points to which corresponding values ​​are associated, and the combination of ultrasound lines to give a displayable line consists of adding the values ​​associated with synchronous discrete points of said ultrasound lines. It should be noted that the combination of these ultrasound lines can be carried out as soon as said ultrasound lines are available. Therefore, the combinations can be carried out in parallel with the continuation of the cycles following the first cycle.

[0054] The k combined ultrasound lines can result from the k iterations of a cycle if it has just ended, or from the last ki iterations of a cycle and the i iterations of the next cycle, with 1 <i<k. Par exemple, en référence à la Figure 2, iterations 101, 102, 103, 104, 105 of the first cycle 100 each give an ultrasound line (k=5). A first combination 106 relates to the ultrasound lines resulting from iterations 101, 102, 103, 104, 105 of the first cycle 100. The second combination 107 relates to the last four ultrasound lines of the first cycle 100, i.e. resulting from iterations 102, 103, 104, 105, and to the first ultrasound line of the second cycle 110, i.e. resulting from iteration 111. The third combination 108 relates to the last three ultrasound lines of the first cycle 100, i.e. resulting from iterations 103, 104, 105, and to the first two ultrasound lines of the second cycle 110, i.e. resulting from iterations 111 and 112. The following combinations take place in a similar manner as follows: following, shifting by one iteration for each new displayable line.

[0055] For example, in reference to the Figure 3, iterations 201, 202, 203 of the first cycle 200 each give an ultrasound line (k=3). A first combination 204 relates to the three ultrasound lines resulting from iterations 201, 202, and 203 of the first cycle 200. The second combination 205 relates to the last two ultrasound lines of the first cycle 200, i.e. resulting from iterations 202 and 203, and to the first ultrasound line of the second cycle 210, i.e. resulting from iteration 211. The third combination 206 relates to the last ultrasound line of the first cycle 200, i.e. resulting from iteration 203, and to the first two ultrasound lines of the second cycle 210, i.e. resulting from iterations 211 and 212. The following combinations proceed in a similar manner and so on, shifting by one iteration for each new displayable line.

[0056] For example, in reference to the Figure 4, iterations 301 and 302 of the first cycle 300 each give an ultrasound line (k=2). A first combination 303 relates to the two ultrasound lines resulting from iterations 301 and 302 of the first cycle 300. The second combination 304 relates to the last ultrasound line of the first cycle 300, i.e. resulting from iteration 302, and to the first ultrasound line of the second cycle 310, i.e. resulting from iteration 311. The third combination 305 relates to the two ultrasound lines resulting from iterations 311 and 312 of the second cycle 310. The following combinations take place in a similar manner and so on, shifting by one iteration for each new displayable line.

[0057] We thus make a sliding combination of the last k ultrasound lines resulting from the k most recent iterations to obtain each of the displayable lines. To display N displayable lines on a screen, we then carry out N+k-1 iterations. For example, to display 400 displayable lines, we carry out 404 iterations if k=5, which represents a negligible additional cost in iterations. To make the digital lines of the signal displayable and thus produce an image, we can of course subject them to various classic treatments such as filtering, rectification, shifting and logarithmic scaling.

[0058] With this approach, it is possible to modify in real time the emission modalities of the ultrasound waves, by modifying the composition of the groups of rings, for example by going from groups of one transducer ring 2 to groups of three transducer rings 2. It is also possible to modify the processing modalities of the measurement signals, by changing the delays affecting them during their combination. Depending on the chosen medical target, it is thus possible to favor the resolution, sensitivity, penetration or speed by using different emission or reception configurations.

[0059] For example, using ring groups consisting of a single transducer ring 2 as in the Figure 1 , we obtain the best compromise between resolution, penetration and sensitivity on the global image of an eye.

[0060] With this approach, the speed is significantly increased compared to the traditional phased array approach, since at each cycle or iteration, the entire inspected depth is examined. There is therefore no longer any need to perform multiple passes over the same location to image at different depths. Compared to the radar-type approach, after the first cycle, one displayable line is obtained per iteration, which allows for much faster operation since the radar-type approach only produces one displayable line per cycle. This results in a speed almost similar to that of a single transducer, which is fundamental in ophthalmology, particularly due to the rapid movements of the eye.

[0061] An automated data processing unit comprising at least one processor and a memory is used for processing the image data, and in particular for combining the measurement signals or lines.

[0062] The invention is not limited to the embodiment described and shown in the attached figures. Modifications remain possible, particularly from the point of view of the composition of the various elements without departing from the scope of protection of the invention.

Claims

1. Ocular echography method using an ultrasound probe (1) comprising a plurality of transducer elements organized in at least n concentric rings forming n transducer rings (2, 2a, 2b, 2c, 2d, 2e), in which the transducer rings are grouped into several ring groups each grouping between 1 and n-1 transducer rings, each ring group differing from another transducer ring group by at least one transducer ring different from the transducer rings of said other transducer ring group, the ring groups being k in number, the method comprising the following steps: a) for each cycle (100, 110, 200, 210, 300, 310) of a plurality of cycles each comprising k transmit-receive iterations (101, 102, 103, 104, 105, 111, 112, 113, 201, 202, 203, 211, 212, 213, 301, 302, 311, 312), each transmit-receive iteration involving a different group of transducer rings, each cycle traversing all k groups of transducer rings, during each transmit-receive iteration of said cycle : - a1) excitation of a group of transducer rings so that the transducer rings of said group of transducer rings emit ultrasonic waves at an emission frequency - a2) recovery of n measurement signals from the n transducer rings, each measurement signal resulting from the reception by a transducer ring of reflected ultrasonic waves resulting from the transmission of ultrasonic waves by said group of transducer rings excited during said transmission-reception iteration ; - a3) combination of the n measurement signals recovered to give an echographic line for said transmit-receive iteration , said echographic line being representative of the response of the n transducer rings to the emission of ultrasonic waves by said group of ultrasonic rings excited during said transmit-receive iteration; b) simultaneously to the continuation of the cycles following the first cycle, combination (106, 107, 108, 204, 205, 206, 303, 304, 305) into a displayable line of k ultrasound lines resulting from the k most recent transmit-receive iterations when said ultrasound lines are available ; c) processing and display of displayable lines.

2. Method according to the preceding claim, in which in each cycle, the transmit-receive iterations are carried out in the same order.

3. Method according to any one of the preceding claims, in which the measurement signal of a transducer ring results from the digitization of the reception signal generated by this transducer ring upon reception by said transducer ring of reflected ultrasonic waves resulting from the emission of ultrasonic waves by a group of transducer rings, a measurement signal being defined as a chronological sequence of discrete points to which corresponding values are associated, and in which the combination of measurement signals to give an echographic line during a transmit-receive iteration consists of summing the values associated with synchronous discrete points of said measurement signals.

4. A method according to the preceding claim, in which the combination of measurement signals to give an echographic line during a transmission-reception iteration is restricted to a selection of discrete points, said discrete points being selected so as to operate a chronological offset between the measurement signals compensating for the differences in acoustic path resulting from the geometry of the transducer, the synchronism of the discrete points taking this offset into account.

5. A method according to one of the two preceding claims, in which discrete points are added to the measurement signal by convolving said measurement signal with a sliding cardinal sine such that a period between the discrete points is less than the inverse of at least ten times the transmission frequency.

6. A method according to one of the preceding claims, in which an echographic line is defined as a chronological sequence of discrete points to which corresponding values are associated, and in which the combination of echographic lines to give a displayable line consists in summing the values associated with synchronous discrete points of said echographic lines.

7. Method according to any of the preceding claims, in which the transducer rings are grouped into k ring groups each comprising between 2 and n-1 transducer rings.

8. Method according to any of the preceding claims, in which n= 5, the ultrasonic probe (1) comprising five transducer rings (2).

9. A computer program product comprising program code instructions stored on a non-volatile medium usable in a computer for executing the processing steps of the method according to any of the preceding claims, when said program is executed on a system according to claim 10.

10. Echography system comprising an ultrasound probe (1) having a plurality of transducer elements organized in at least n concentric rings forming n transducer rings (2, 2a, 2b, 2c, 2d, 2e), a processing unit for said ultrasound probe and a screen, said processing unit being configured to implement the method according to any one of the preceding claims, the transducer rings being grouped into several ring groups each comprising between 1 and n-1 transducer rings, each ring group differing from another transducer ring group by at least one transducer ring different from the transducer rings of said other transducer ring group, the ring groups being k in number, the processing unit being configured to : a) for each cycle of a plurality of cycles, each cycle comprising k transmit-receive iterations, each transmit-receive iteration involving a different group of transducer rings, each cycle traversing all k groups of transducer rings, during each transmit-receive iteration: a1) exciting a group of transducer rings so that the transducer rings of said group of transducer rings emit ultrasonic waves at an emission frequency; a2) recovering n measurement signals from the n transducer rings, each measurement signal resulting from the reception by a transducer ring of reflected ultrasonic waves resulting from the emission of ultrasonic waves by said group of transducer rings excited during said transmit-receive iteration; a3) combining the n measurement signals to give an echographic line, said echographic line being representative of the response of the n transducer rings to the emission of ultrasonic waves by said group of excited ultrasonic rings during said transmit-receive iteration; b) simultaneously to the continuation of the cycles following the first cycle, combining into a displayable line of k echographic lines resulting from the k most recent transmit-receive iterations when said echographic lines are available; c) processing and sending displayable lines to the screen.