EP0098202A1 - Ultrasonic probe and acoustic imaging system using this probe - Google Patents

Abstract

Ultrasound probe fitted with an incremental encoder. According to the invention, the movable assembly (14) of the probe comprises at least one angular tracking track (19) on which pulses representative of the angular position of the probe are recorded and fixed reading means (20) are arranged. next to this track. Application to ultrasound.

Description

The invention relates to an ultrasonic probe, sector scanning, designed to emit bursts of ultrasound in different directions and receive corresponding echoes; it relates more particularly to means for angular location of the mobile assembly of the probe. The invention also relates to an improved ultrasound installation, equipped with such a probe.

A conventional ultrasound probe comprises a mobile assembly mounted in rotation on an axis, in a box and capable of radiating an ultrasonic beam towards the outside of the box and receiving the corresponding echoes so as to carry out the complete exploration of a given sector , in order to reconstruct an image. Thus, for each transmission-reception sequence made for a given angular position of the moving assembly, there corresponds a "line" of the image reconstructed subsequently. The mobile assembly can be constituted by the piezoelectric transducer itself or by a mirror reflecting the ultrasonic beam emitted by a fixed transducer. Sector scanning can be obtained by oscillating the moving element around its axis; it is also possible to obtain an equivalent result thanks to a cylindrical mobile assembly provided with several transducers and driven in rotation at constant speed.

One of the problems posed by these types of probes (mainly the oscillating probe) is the precise tracking of the angular position of the moving equipment at all times, with a view to always triggering the emission salvos or "shots" at the same angular positions. The precision of the respective positions of the different shots necessary for the reconstruction of an image indeed constitutes an important characteristic for the quality of the image. Good accuracy makes it possible to correctly locate the different lines in relation to each other in the image and also to stabilize the positions of lines from one image to another. We tried to solve this problem by linearizing as much as possible the oscillating movement of the moving assembly by means of a servo chain looped on the drive motor thereof. Another way of proceeding consists simply in carrying out an angular location of the moving assembly and in triggering the "shots" from signals representative of this location. In both cases, the devices which have been associated with the motor (precision potentiometers, for example) either to generate the error signal of the servo-control or to concretize the angular location, are bulky and subject to drift over time . The sheer size of such a device necessitates having it at a certain distance from the moving assembly. The coupling is therefore necessarily carried out by a mechanical return system. Whatever the quality of execution of this system, the clearances can never be completely eliminated and play a particularly critical role in the oscillating moving equipment probes, since they are called upon each reversal of the direction of movement. This is one of the main causes of wear and deregulation of this type of probe.

Furthermore, the accuracy of all these tracking devices providing a so-called "analog" signal is intrinsically limited so that the use of incremental encoders providing information usable by digital processing systems, appears more and more desirable. The invention provides a solution to all the problems set out above by proposing the adaptation of an incremental encoder to a mechanical sector scanning probe.

More specifically, the invention therefore relates to an ultrasound probe comprising a rotating moving element, in particular an oscillating rotary element, generating a sectoral scanning of an ultrasonic probe, characterized in that said moving element carries at least one angular tracking track on which information is written, this tracking track describing a certain route determined by the movement of said mobile assembly and in that means for reading said information are arranged opposite a point of said path.

The tracking track defined above can be magnetic in nature (a simple magnetic tape on which a succession of pulses carrying out an incremental magnetic code has been recorded) or else optical in nature (materialized by a succession of small reflective zones separated by absorbent areas). Of course, in the first case, the aforementioned reading means will consist of a magnetic head while in the second case these reading means may be embodied by an arrangement of optical fibers connected to an opto-electric converter. Whatever the embodiment adopted, it is easily understood that the means described constitute an incremental angular encoder which is extremely faithful and precise, capable of delivering trains of electric pulses (after shaping and amplification) directly representative of the movement of the moving equipment, each pulse representing a predetermined elementary angle of rotation. No drift in time of this type of incremental coding is to be feared because the track - of angular location is integral with the moving assembly.

Pulse trains can be operated in different ways.

Firstly, it is clear that the pulses can be used to directly trigger the "shots" of ultrasound and control the addressing means of a refresh memory responsible for storing the information resulting from the processing of the echoes received after each shot.

In this spirit, the invention therefore also relates to an ultrasound installation associated with a probe according to the above definition and comprising a generator of excitation signals supplying an ultrasound transducer of said probe, characterized in that said generator comprises synchronization means, one input of which is connected to the aforementioned means for reading the information written on said angular tracking track.

It should be noted that the "shots" thus synchronized by the pulses coming from the aforementioned reading means, can be carried out without inconvenience in the outward and return movement of the moving equipment while the analog servo systems previously used most often only allowed one useful scan per cycle due to technological difficulties in obtaining a perfectly symmetrical movement. One of the advantages of the invention is therefore to allow a significant increase in the frame rate.

The pulses from the incremental encoder associated with the probe can also be used to control means for controlling the speed of the drive motor of the moving assembly. This eliminates brutal accelerations which could prevent receiving certain echoes and therefore disturb the reconstruction of the image.

Finally, these pulses can also be used to control means for controlling the position of the drive motor of the moving assembly. In certain examinations, in particular cardiac examinations, it is indeed desirable to immobilize the mobile assembly of the probe according to a chosen firing position (corresponding to a line of the image) so as to visualize the movements of the organ examined according to this direction.

A position control, controlled by the incremental encoder associated with the moving element itself considerably improves the precision and the stability of the orientation of the moving element in such a type of examination.

• - la figure 1 est une vue en perspective, avec arrachement d'un premier mode de réalisation d'une sonde à ultrasons selon l'invention ;
• - la figure 2 est une vue en perspective avec arrachement d'un second mode de réalisation d'une sonde à ultrasons selon l'invention ;
• - la figure 3 illustre la forme des signaux électriques dérivés du codeur incrémental equipant une sonde à ultrasons selon l'invention, par exemple celle de la figure 2 ; et
• - la figure 4 est un schéma-bloc simplifié d'une installation d'échographie conçue pour être équipee d'une sonde selon l'invention.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, given with reference to the appended drawings in which:

• - Figure 1 is a perspective view, broken away of a first embodiment of an ultrasonic probe according to the invention;
• - Figure 2 is a perspective view with cutaway of a second embodiment of an ultrasonic probe according to the invention;
• - Figure 3 illustrates the shape of the electrical signals derived from the incremental encoder equipping an ultrasonic probe according to the invention, for example that of Figure 2; and
• - Figure 4 is a simplified block diagram of an ultrasound installation designed to be equipped with a probe according to the invention.

The probe illustrated in FIG. 1 comprises a box 11 provided with an opening 12 closed by a flexible wall 13, acoustically transparent opposite which a mobile assembly 14 is mounted oscillating around an axis 15. The oscillating mobile assembly 14 comprises a piezoelectric crystal 16 disposed in front of the opening 12 and extended towards the rear of the case by a block of composite material 17. Conventionally, this block can for example be made of synthetic resin loaded with a heavy material such as tungsten to absorb the rear wave or, on the contrary, light material to reflect it towards window 12 in phase with the front wave. According to the invention, this block 17 conforms as a half-cylinder admitting the axis 15 as an axis of symmetry and the portion of cylindrical lateral surface 18 parallel to this axis carries an angular tracking track 19 on which information is written. This tracking track therefore describes a certain path following an arc of a circle determined by the movement of the moving assembly 14. Means 20 for reading said information are arranged opposite a point on this path. In the example of FIG. 1, the track 19 has been materialized on a section of magnetic tape 19a. A train of pulses of rigorously constant frequency has been recorded on this section of magnetic tape. Each pulse is therefore representative of a predetermined angle of rotation of the moving element. Of course, the reading means 20 are here constituted by a simple magnetic head, the air gap of which is disposed opposite the track 19. As will be seen below with reference to FIG. 2, it may be advantageous to include several tracks such as 19 on the surface of the magnetic strip section 19a. In this case, the magnetic head 20 comprises as many gaps as there are pre-recorded tracks and as many coils. Conventionally, the crew mobile 14 is driven by means of a motor (not shown) by means of any suitable movement transformation mechanism. This motor 21 is however shown diagrammatically in FIG. 4.

In the second embodiment of the probe, shown in FIG. 2, the similar structural elements bear the same numerical references and will not be described again. This probe differs from the previous one by the fact that the optical encoder associated with it is optical rather than magnetic. The lateral surface 18 of the block 17 carries at least one and preferably two angular tracking tracks 29, 30. Each track is materialized by a plurality of reflecting zones 39 regularly spaced apart and separated by absorbing zones and the reading means comprise an arrangement of optical fibers 32, 33, 34 and an opto-electric converter 36. In the example shown, the fibers are associated in pairs and the two fibers of a pair have their ends arranged side by side opposite a track of marking, the opto-electric converter being coupled to the other ends of said fibers. In each pair of fibers, one (32a, 33a, 34a) is associated with a light source (located inside the converter 36) while the other (32b, 33b, 34b) is permanently coupled to a optical signal input from the converter. The latter comprises three identical sections 132, 133, 134 respectively processing the optical signals produced by the pairs of fibers, 32, 33 and 34 and each comprising respectively an electrical signal output SI, S2 and S3. The optical fibers 32a and 32b have their ends arranged opposite the track 29 while the fibers 33a and 33b have their ends arranged opposite the track 30. The fibers 34a and 34b have their ends arranged opposite an additional track 31 which has only one reflecting zone, for example at one end of the cylindrical surface 18. The role of this additional track is to generate a cycle start signal appearing periodically at the output 53 of the opto-electric converter. At each half period of oscillating movement of the moving part, two trains of electrical pulses appear respectively at outputs SI and S2. The reflective zones of tracks 29 and 30 are phase shifted by 90 ° so that this phase shift is found between the trains of electrical pulses available simultaneously at outputs SI and S2, as shown in FIG. 3. The outputs SI and S2 are connected to the two inputs of a gate of the exclusive OR type 38 so that the signal available at the output S of this gate has a double frequency (see FIG. 3).

There are two advantages to using 90 ° phase shifted signals on two parallel tracks read at the same time. We divide the pitch of the angular coding by two as clearly shown in Figure 3 and we are also able to know at any time the direction of the oscillating movement of the moving element 14 as a function of the sign of the phase shift between the signals available at the outputs SI and S2.

Of course, this multitrack arrangement is perfectly transposable to the embodiment of FIG. 1.

FIG. 4 represents an ultrasound installation associated with a probe in accordance with FIG. 1 or 2. This installation conventionally comprises a transceiver unit 40 comprising an excitation signal generator 41 and a reception circuit 42 coupled (link 43) to the transducer 16. The circuit 42 receives and processes the echo signals perceived by the probe after each shot and develops digital information which is sent to a refresh memory 43, by means of addressing 44. The refresh memory 43 is re-read at the rate of a clock H to reconstruct an image on the screen of a cathode-ray tube 45.

According to another aspect of the invention, the excitation signal generator 41 includes synchronization means, an input 46 of which receives the signals produced by the reading means of the incremental encoder of the probe. More precisely, the input 46 is connected to the output S of the exclusive OR gate 38. Likewise, the addressing means 44 also include a control input 47 S connected to the output of the gate 38. In addition, as mentioned above, the installation _of ultrasound is supplemented by speed control means V of the motor 21 which are also controlled by the signal available at the output S of door 38. Finally, according to another advantageous possibility offered by the invention, it is possible to substitute position control means P for speed control means (switch 48) in order to stop the oscillating movement of the probe in a given angular position, the position control means P being themselves controlled by the signals available at the output S of the gate 38.

In normal operation, the transceiver unit 40, the addressing means 44 and the speed-controlled motor 21 are therefore controlled by the pulse trains which appear at the output S of the gate 38 and all the information digital memories will be representative of the echoes received at angular positions, very precise and invariable, of the moving equipment 14. On the other hand, when the position control means are put into service via the switch 48, the counting the pulses delivered to the output S will make it possible to bring the mobile assembly 14 to a chosen angular position and to maintain it there. In this mode of operation, we will no longer be able to visualize the image of the region examined but the evolution of the echoes following a very precise direction of fire.

Of course, the invention is not limited to the probe and to the ultrasound installation which have just been described. in particular, with regard to the probe, it is quite clear that the means forming the incremental encoder can easily be adapted to a wheel probe carrying several piezoelectric transducers at its periphery. The angular tracking track (s) could in this case be easily arranged on a part of the lateral surface of the wheel carrying the transducers; the electrical signals produced from this incremental encoder would then be used in particular for triggering ultrasound shots and for regulation of the wheel rotation speed. Other modifications can be made, for example, in the embodiment of FIG. 2 where a pair of optical fibers has been shown associated with each angular tracking track. We could perfectly consider using only one optical fiber per track operated alternately in transmission and reception. This means that the invention covers all the technical equivalents of the means involved if these are used in the context of claims that follow.

Claims (11)

1. Ultrasound probe comprising a rotating moving element (14), in particular an oscillating rotary element, generating a sectoral scanning of an ultrasonic wave, characterized in that said moving element carries at least one angular tracking track (19, 29 , 30) on which information is written, this tracking track describing a certain path determined by the movement of said moving assembly and in that means for reading (20, 32, 33) of said information are arranged opposite a point of said path. 2. Probe according to claim 1, characterized in that said movable assembly (14) comprises a portion of cylindrical lateral surface (18) parallel to its axis of rotation (15) and carrying said angular tracking track. 3. Probe according to claim 1 or 2 characterized in that said angular tracking track (19) is a magnetic track and that said reading means (20) are essentially constituted by a magnetic head. 4. Probe according to claim 1 or 2, characterized in that said angular tracking track (29, 30) comprises a plurality of reflecting zones (39) regularly spaced apart and separated by absorbing zones and in that the reading means comprise at least one optical fiber (32, 33) one end of which is placed opposite said path and an opto-electric converter (36) coupled to the other end of said optical fiber. 5. A probe according to claim 4, characterized by two parallel optical fibers (32a - 32b, 33a - 33b) each having one end disposed opposite said angular tracking track, in that one is permanently associated with a source luminous and in that the other is permanently coupled to an optical signal input of said opto-electric converter (36). 6. Probe according to one of the preceding claims, characterized in that it comprises two parallel angular tracking tracks (29, 30), associated with respective reading means (32, 33) and in that each track carries a recorded periodic signal, these two signals being 90 ° out of phase. 7. A probe according to claim 6 characterized in that it comprises a third angular tracking track (31) and corresponding reading means (34), said tracking track carrying a single recorded pulse. 8. Ultrasound installation associated with a probe according to one of the preceding claims and comprising an excitation signal generator (41) supplying an ultrasound transducer (16) of said probe, characterized in that said generator comprises synchronization means, one input (46) of which is connected to the aforementioned means for reading information written on said angular tracking track. 9. Ultrasound installation according to claim 8, comprising a memory (43) arranged to store the signals representative of the echoes received by said transducer, characterized in that addressing means (44) of said memory are connected to said means of read and piloted by them. 10. Ultrasound installation according to one of claims 8 or 9, characterized in that it comprises speed control means (V) of a drive motor (21) of said movable assembly and that these means servo are connected to said reading means to be controlled by them. 11. Ultrasound installation according to one of claims 8 to 10, characterized in that it comprises position control means (P) of a drive motor (21) of said movable assembly and that these means servo _sont connected to said reading means for receiving corresponding signals, which are used to determine a given angular position of said moving element.

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