EP0069677B1 - Device for ultrasonic echography to scan sectorially - Google Patents

Description

The present invention relates to an ultrasonic pulse ultrasound probe and a device using such a probe and it finds a particularly important application in the medical field.

We already know very many ultrasound ultrasound devices for exploring an organ or internal anatomical structure. Among these devices, many provide focusing at a determined depth, corresponding to an area to be examined, on transmission and / or on reception. This focusing is provided electronically or optically. In the first case, delay lines or phase shift elements are generally used (addition certificate FR-B-2 355 288). One thus arrives, by using only a few elements providing phase shifts or discrete delays, to approach a distribution which would correspond to a rigorous focusing.

Deep exploration of an organ or anatomical structure (ultrasound B) frequently involves scanning. Ultrasound ultrasound devices have already been produced which provide both focusing and linear or sectoral scanning. In the case of medical applications, sector scanning has the great advantage of authorizing the exploration of internal anatomical structures from a very small surface in contact with the skin. It allows in particular to visualize the functioning of the heart muscle using a probe placed so that the ultrasonic beam passes between two successive ribs.

The scanning can be carried out electronically or mechanically. In particular, fully satisfactory devices are known with linear scanning, using a bar comprising a number N of elementary transducers (certificate of addition already mentioned FR-B-2 355 288), the scanning is carried out by moving with each shot the group n of transducers used simultaneously with a distribution of delays or phases ensuring focusing at the required distance. On the other hand, the angular scanning by modification of the phase distribution applied to a group of transducers used for all directions (US Pat. No. 4,070,905) leads to very complicated and high cost electronic technology. As for mechanical sector scanning devices, using a rotary exploration head, they have the disadvantage of being generally much less reliable mechanically than purely electronic devices with fixed exploration head.

In particular, ultrasound devices are known in accordance with the preamble of claim 1 (FR-B-2 355 288, FR-A-2 292 978, FR-A-2 472 753). These devices include a probe having a linear array of transducers and switching means providing focusing and scanning electronically. However, they in no way suggest deviating from the conventional sectoral scanning arrangement, using a probe whose transducers are arranged on a cylindrical surface whose concavity is directed towards the organ to be explored.

This solution has various drawbacks. It leads to a bulky and complex probe and does not lend itself to focusing electronically.

The present invention aims to provide a probe and an ultrasound ultrasound device which respond better than those previously known to the requirements of practice, in particular in that it makes it possible to carry out sectoral scanning in a simple and natural manner, associated with a focusing which can easily be performed at a variable distance, that is to say of the type commonly known as "tracking".

To this end, the invention proposes in particular a probe characterized in that the scanning line is a circular line whose convexity is turned towards said organ or anatomical structure to be explored, that the switching means (34, 35) cause a sectoral scanning around the axis of said circular line which is situated outside said organ or anatomical structure to be explored and in that the delays are provided to ensure focusing along the radius corresponding to the midpoint of the group of n transducers considered, at a distance determined inside the organ or anatomical structure to be explored and outside the circular line.

This is an arrangement which completely opposes that in which the transducers are arranged along a line whose concavity is turned towards the organ to be explored. One would think that, in the latter case, the arrangement of the transducers leads to almost automatic focusing. In fact, there is on the contrary a compulsory divergence, owing to the fact that the ultrasonic beam only penetrates into the organ to be explored beyond its focusing zone, which the very geometry of the probe requires not to do vary (FR-A-2 334117).

The probe and the device defined above have many advantages: they have a great flexibility of operation, since they lend themselves perfectly to dynamic focusing; owing to the fact that the transducers are in the immediate vicinity of the medium to be explored, the density of the lines of exploration will exhibit less variation between surface and deep zones than in the case of flat or concavity probes facing the medium. Focusing by geometric or electronic means remains possible in the direction perpendicular to the plane of the line on which the transducers are distributed. The electronic means of implementation remain very simple, owing to the fact that the angular scanning is carried out automatically according to a sector having for center the axis of distribution of the elementary transducers. The electronics of the device make it possible to work successively with very different probes, in particular as regards the radius of the circle on which the transducers are distributed and the spacing of the transducers.

It may be noted in passing that there are known underwater listening systems comprising hydrophones distributed along a curve, and allowing angular exploration. But this is an extremely different technology from that envisaged here, where the hydrophones are surrounded by the medium to be explored and work under completely different conditions. (DE-A-2 064 588 and FR-A-1 569 897).

It appears in fact that the solution proposed by the invention has hitherto been ruled out by those skilled in the art because, apparently, it goes against the focusing which is sought to ensure good lateral definition. , the distribution along a convex surface tending to supply or collect energy in a beam all the more divergent that the elementary transducers are distributed in a circle of small radius. To arrive at the proposed solution, the inventor had to take the opposite view of such an attitude by extending to such a distribution of elementary transducers the focusing techniques used in particular in the case of flat strips of transducers.

This similarity of focusing techniques means that the same electronics can, at the cost of simple modifications of components or software, be indifferently used with a conventional linear scanning probe or with a sectoral scanning probe of the kind defined above, which constitutes a decisive advantage over conventional devices. Indeed, for an almost unchanged cost, the possibilities of applying a device are practically doubled.

• - des moyens de retard fournissant, sur a voies différentes, à partir d'une même impulsion provenant des moyens d'émission, a impulsions ayant des retards différents,
• - n premiers multiplexeurs permettant chacun de relier temporairement une des a voies à un accès d'entrée-sortie du multiplexeur,
• - et n seconds multiplexeurs dont chacun est interposé entre l'accès d'un premier multiplexeur correspondant et plusieurs des N transducteurs qui sont décalés de n, chaque second multiplexeur permettant de relier un des transducteurs aux premiers multiplexeurs pendant le temps nécessaire à une émission et à la réception correspondante.

The switching means advantageously include:

• - delay means supplying, on a different channels, from the same pulse originating from the transmission means, to pulses having different delays,
• - n first multiplexers each making it possible to temporarily connect one of the a channels to an input-output port of the multiplexer,
• - And n second multiplexers, each of which is interposed between the access of a first corresponding multiplexer and several of the N transducers which are offset by n, each second multiplexer making it possible to connect one of the transducers to the first multiplexers for the time necessary for a transmission and at the corresponding reception.

This arrangement makes it possible to limit the number of first multiplexers to n, whatever the number N of transducers of the probe, which notably reduces the cost and makes it possible to adopt multiplexers having a high number of channels without however resulting in an excessive cost. It is thus easy to adopt a number a of channels and delays at least equal to 16, this number making it possible to fulfill the quality criteria required for medical applications. As for the numbers N and n, they can be 160 and 40 respectively (figures which are rarely exceeded to constitute a lens).

Each of the second multiplexers advantageously comprises a transmission element, ensuring the direct connection between said access and a transducer, and a reception element, ensuring the connection via a preamplifier between the transducer and the access of the first multiplexer and in that said elements are controlled by means synchronized with the transmission means so as to block the transmission element during the reception period and vice versa.

Thanks to this arrangement, different paths are used for transmission and reception, so that the preamplifier can be given a high gain without risking reacting on the transmission. The signals received at low level are thus brought to a sufficient level very early in preamplifiers which can be of quality and very low noise without excessive impact on the cost, since their number is reduced compared to that of the transducers.

Several sets of second multiplexers and of transmission and reception elements adapted to different types of probes can be provided in the device, as well as switching means. The latter allow one or the other of the sets to be implemented depending on the probe used. The switching means can be limited to an address generator causing the implementation of a particular game. The switching means can also be provided to implement at will any one of several storage memories for different delay distributions.

• la figure 1 montre la disposition de principe de n transducteurs élémentaires dans une sonde de mise en oeuvre de l'invention,
• la figure 2 est un diagramme montrant la répartition des retards constants à réaliser sur les transducteurs répartis à intervalles angulaires égaux pour assurer la focalisation à une distance déterminée,
• la figure 3 est une vue en perspective montrant une constitution possible de tête permettant de réaliser une double focalisation avec balayage sectoriel,
• la figure 4 est une vue schématique en coupe de la tête montrant une seconde disposition permettant de réaliser une focalisation dans un plan perpendiculaire au plan de balayage,
• la figure 5 est un schéma de principe d'un circuit permettant de mettre en oeuvre l'invention, en association avec une sonde du genre montré en figure 3.

The invention will be better understood on reading the following description of particular embodiments given by way of nonlimiting examples. The description refers to the accompanying drawings, in which:

• FIG. 1 shows the principle arrangement of n elementary transducers in a probe for implementing the invention,
• FIG. 2 is a diagram showing the distribution of the constant delays to be achieved on the transducers distributed at equal angular intervals to ensure focusing at a determined distance,
• FIG. 3 is a perspective view showing a possible constitution of the head making it possible to achieve double focusing with sector scanning,
• FIG. 4 is a schematic sectional view of the head showing a second arrangement making it possible to achieve focusing in a plane perpendicular to the scanning plane,
• FIG. 5 is a block diagram of a circuit making it possible to implement the invention, in association with a probe of the kind shown in FIG. 3.

As already indicated in the certificate request addition published under FR-B-2 355 288, already mentioned, and patent application n ° FR-A-2492982 to which we can refer, we can focus on transmission or reception at the right of the group of n transducers distributed in a direction x'-x at a distance f _o from a straight line on which the n elementary transducers are distributed, using a distribution of delays between the transducers as a function of the abscissa x to from center 0 of the transducer group.

The invention requires carrying out a similar focusing using a probe of the kind shown in FIG. 1, comprising N elementary transducers 12 ₁ , ..., 12 _; , ..., 12 _N which we assume that n are used for each shot (n being equal to 7 in the illustrated case. The remote focusing f _o of the ultrasonic energy radiated by the transducers distributed over a circle of radius R can be ensured by attacking the n transducers, from a common pulse source, by means of suitable delay members. The delays to be used are substantially the same as those necessary to focus the energy of distributed transducers according to a linear bar at distance F, F being connected R and to f _o by the formula:

In Figure 1, there is shown schematically, downstream of a pulse amplifier 10 constituting the source of energy on transmission, a set of three delay lines 11 ₁ , 11 ₂ and 11 ₃ providing increasing delays and suitable. The excitation pulse is applied directly to the two outermost transducers; via FIG. 11 _i to the two adjunct transducers; via line 11 ₂ to the transducers framing the central transducer; and, via line 11 ₃ , to the central transducer.

The same delay combination allows focusing on reception, after which switching means (not shown) involve a group of n transducers offset from the first group to carry out the scanning.

Once the distance F has been determined, the distribution of the delays to be adopted can be established by applying conventional formulas.

où c est la vitesse des ultrasons dans le milieu de propagation.For example, the delay Δt to be imposed on the excitation of a transducer located at distance x from the center of the group of elementary transducers for focusing at distance F must be, in the Fresnel approximation:

where c is the speed of the ultrasound in the propagation medium.

This variation can be simulated approximately with a small number of delays.

Similarly, it is possible to focus on transmission or reception by assigning to the elementary transducers 12 _; delays staggered according to a law which will approach the theoretical law corresponding to a cylindrical distribution. FIG. 2 shows, in dashed lines, the theoretical distribution of delays which would have to be achieved between the transducers as a function of their distance x from the center of the group for a parabolic law. The solid line curve shows the simulation of the law of variation with sampling at several levels of delay each separated by a constant interval _T. In the embodiment illustrated in FIG. 2, it can be seen that the central transducer and the transducers of order 2, 3 and 4 on each side must receive the signal with maximum delay, the transducers of order 5 and 6 must receive it with a delay decreased by _T , and so on.

Before going on to the description of a particular circuit making it possible to implement the invention, it should be emphasized that the convex arrangement of the elementary transducers shown in FIG. 1 leaves all freedom as regards focusing in a plane perpendicular to the plane of the scanning. In the embodiment of the head shown in FIG. 3, this focusing is ensured at a point N (which may be different from the point M of focusing in the other plane) by giving the generator piezoelectric ceramic 14 common to all transducers a concave shape. In particular, each metallized strip belonging to an elementary transducer can have a circular shape whose radius corresponds to the distance between the ceramic and the point N.

Another solution consists in placing, in front of the elementary transducers, a lens, as illustrated in FIG. 4. In the case, the common ceramic may have the shape of a portion of cylinder. The lens will be convex if the speed of sound in its constituent material (for example hard synthetic elastomer) is lower than the speed of sound in tissue.

We will now describe, with reference to FIG. 5, a circuit making it possible to achieve electronic focusing at a distance F, using a delay stagger to the emission and to the reception of the kind shown in FIG. 2, thus than a sweep. This circuit is designed to be associated with a system of N transducers 12 ₁ , ..., 12 _; , ..., 12 _N , excitable by pulse. On each exploration, it causes the excitation of n transducers 12 _; , with a determined delay distribution: it applies for example the excitation signal with a maximum delay to the order 1, 2, 3 and 4 transducers. It causes a delay of τ on the signal before application to the order transducers 5 and 6, and so on.

The electronics which will now be described make it possible to use a number of transmit and receive multiplexers equal to n, therefore being able to be very much less than the total number N of transducers: it is thus possible, at a given cost, to use multiplexers with higher number of channels, sufficient to have a fine sampling, therefore a high focusing precision, and low side lobes.

The electronics shown in Figure 5 are intended to be associated with a probe comprising N elementary transducers such as 12 each associated with a switching circuit 80.

The electronics comprise a first network of multiplexers 34 in number n equal, not to the total number N of the transducers of the bar, but to the number of n transducers intervening during a shot, that is to say constituting a lens electronic. In practice, we will never exceed n = 40 for a strip of N = 160 elements, i.e. a quarter of the total network. Each of the first multiplexers 34 is used in association with several transducers offset by n. For example, the same multiplexer 34 will be associated with the transducers 12 _; , 12, _{+ n} . 12 _i , ₂₁ , 12, _{+ 3n} in the embodiment envisaged. This first network of multiplexers, which makes it possible to select one of the a delay channels supplied by the transmission means, which include a pilot clock 38, a generator 39 and a register 15, is connected to the corresponding transducers by a second network multiplexers, intended to address the transducers. Each of these second multiplexers comprises a transmission element 81 making it possible to establish a direct connection between the input-output access of the first corresponding multiplexer 34 and the circuit 80 of a transducer. It also includes a reception element 82 allowing the reception signal to pass in the other direction, towards the access of the associated multiplexer 34, through a preamplifier 33. The latter can be particularly neat, given that its cost will have little influence on that of the entire device, since n preamplifiers will suffice for N transducers.

As for the circuits directly associated with the transducers, they can be of simple constitution. They can in particular comprise a single active component on emission, constituted for example by a V MOS transistor which has the advantage of very quickly switching a high power, supplied by a source at voltage -V, under the action of a low intensity control signal from the second multiplexer.

The selection of the channel connected by the first network of multiplexers to the transducers is carried out on the basis of information conveyed by shift registers 35 which, in the case of the use of sixteen channels, may be registers with four times four binary elements. Each of the registers 35 is assigned to a first multiplexer with a = sixteen channels 34; a second register is assigned to each multiplexer, so that all of the switching is performed by a number of elementary circuits 84 (dashed line in Figure 5) equal to n = = 40 only. It should be noted that the transition from a group of n = 40 transducers to the next group is carried out gradually by recirculating the information in the registers 35, as indicated by the multi-channel line 85, and a recirculator 86, constituted by a selector in FIG. 5.

• 1. Configuration de lentille d'émission à nombre pair de transducteurs (40 par exemple).
• 2. Lentille de réception correspondant à la lentille d'émission à 40 transducteurs.
• 3. Configuration de lentille d'émission décalée d'un demi-transducteur par rapport à la précédente, utilisant un nombre impair de transducteurs (par exemple 39).
• 4. Configuration de lentille de réception correspondant à la configuration d'émission à nombre impair de transduteurs.

By providing, for each register, four sets of four binary elements, it is possible to carry out the scanning along a number of transmission and reception lines double the number of transducers, by providing the following four successive configurations:

• 1. Configuration of emission lens with even number of transducers (40 for example).
• 2. Receiving lens corresponding to the transmitting lens with 40 transducers.
• 3. Configuration of emission lens offset by half a transducer with respect to the previous one, using an odd number of transducers (for example 39).
• 4. Reception lens configuration corresponding to the emission configuration with odd number of transducers.

The clock 87 controlling the registers 35 will give a clock tick before each transmission and a stroke after each transmission. An initialization system is provided so that the clock 87 emits a sufficient number of strokes to position the information, taken from a storage means 37, in the first n registers 35. In this particular case, the first shot will be centered on the twentieth transducer of the bar. However, exploration can be started without waiting to have loaded the entire "lens" into the registers.

The second network of multiplexers is associated with a common command generator 88 which, for each shot, issues a common command 89 which unlocks the element 81 for a short period of time tightly framing the group of logic control and transmission signals. element 82 during the additional time. The selection of the transducers supplied by the second network of multiplexers is ensured by information with two binary elements conveyed by shift registers 90 in cascade. This information with two binary elements is produced for each frame by a counter 91 which divides the number of clock strokes by 40. The advance is ensured by a clock (not shown) which provides one stroke for four clock strokes 87 The other elementary electronic circuits, the block diagram of which is shown in FIG. 5, can be relatively conventional and include a delay correction reception circuit 62 (constituted for example by a multiple tap delay line) and a processing circuit. of the signal 25 attacking a display or storage system 57.

We see that the device according to the invention is directly transposable from any existing system with electronic focusing and scanning, at the cost of a simple modification of the law of variation of the delay or of the phase shift; it uses a reduced number of different delays or phase shifts; sector scanning is obtained in a perfectly natural way thanks to the shape of the probe. The difference in density of the scanning lines between the surface zone and the deep zone of the organ to be explored is reduced, because there is no convergence of a beam at the point of entry into the organ. Contrary to what is happening in the disposi With electronic sector scanning using a previously existing flat transducer strip, the acoustic field produced by the device according to the invention does not depend on the angle of observation relative to the median plane. Finally, experience shows that the convex shape of the probe does not constitute a handicap for good contact with the skin.

Claims (6)

1. Ultrasonic echography device for exploring an organ or an internal anatomical structure, comprising a linear array of N identical elementary transducers (12₁, ..., 12_N) distributed at equal intervals along a scanning line, means (37) for storing at least one delay distribution over n successive transducers (n being greater than N) corresponding to focusing at a predetermined distance from the line, switch means (34, 35) enabling one group of n transducers to be tem- porarilly connected to signal transmitting means (15) or receiving means (62) with delays corresponding to said distribution and to shift the group of n transducers for scanning along said line, characterized in that the scanning line is a circular line whose convexity is turned towards said organ or anatomical structure to be explored, in that the switch means (34, 35) cause a sector scan to occur about the axis of said circular line which is located out of said organ or anatomical structure to be explored and in that the delays are proportioned for focusing along that radius which corresponds to the midpoint of the considered group of n transducers, at a predetermined distance within the organ or anatomical structure to be explored and out of the circular line.

2. Echograhpy device according to claim 1, characterized in that the delays are determined by delay lines.

3. Device according to claim 1, characterized in that the delay means (15) consist of elements which make available, on different channels, from a same pulse of the generator (30), pulses which are delayed by r or multiples of _T, and the means for connecting the transducers control amplifiers (13) each associated with a transducer (12i) from the pulse which appears on the appropriate channel, selected by the storing means.

4. Device according to any one of claims 1-3, characterized in that the switch means comprise :

- time delaying means providing, over a different channels, from a same pulse from the transmitting means, a plurality a of pulses having different time delays,

- n first multiplexers each for connecting one of the a channels temporarily to an input-output access of the multiplexer,

- and n second multiplexers each of which is connected between the access of an associated first multiplexer and a plurality of the N transducers which are at intervals of n, each second multiplexer being for connecting one of the transducers to the first multiplexers during the time necessary for transmission and the corresponding reception, each of said second multiplexers comprising a transmission element ensuring direct connection between said access and a transducer, and a receiving element for connection through a pre-amplifier between the transducer and the access of the first multiplexer, and it that said elements are controlled by means synchronized with the transmission means for blocking the transmission element during the time period of reception and conversely.

5. Device according to claim 4, characterized in that it comprises a single set of n first multiplexers and a plurality of sets of second multiplexers, each adapted to a different type of probe, and electronic switching means for operating one or the other of the said sets depending on the probe which is being used.

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