Abstract:
The inventive probe comprises a tubular body ( 1, 2 ) that accommodates a transducer ( 11 ), which emits a focused incident ultrasonic wave toward structures to be examined and which receives the ultrasonic waves reflected by these structures. This transducer ( 11 ) is coupled to actuating means ( 4 ), comprises a piezoelectric assembly ( 15 ) capable of focusing the emitted beams and, adjacent to this assembly, comprises a spherical layer ( 20 ) made of a material that ensures a good transmission of the ultrasonic waves.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an echographic probe with sector scanning using a transducer capable of coming into contact with the structure to be examined. 
     It is notably but not exclusively applied to echography of eye structures. 
     2. Description of the Prior Art 
     Generally, it is known that in opthalmology, 2-D echography at 10 MHz is used in current practice for exploring the anatomy and pathologies of eye structures and more particularly that of the posterior pole (retina, optical nerve, vitreous). 
     The technique of the probes uses sector scanning, with which probes may be obtained of small sizes, comparatively to bar probes. 
     In order to perform this type of scan, echographic probes are used, including an open tubular casing in its front portion and the inner volume of which is divided into two compartments by a sealed partition, i.e.:
         a rear compartment which extends on the side of the bottom of the casing: this compartment comprises motorization and power supply circuits for the control and processing parts of the apparatus,   a front compartment adjacent to the aperture of the casing, which contains a mobile transducer as well as all or part of its actuation mechanism.       

     The aperture of the front compartment is usually closed by a flexible or hard sealed membrane, in order to obtain a sealed interior space containing a coupling liquid which should have high transmissibility for ultrasonic waves. 
     This membrane which is intended to come into contact with the eye of the patient, should be made in a biocompatible material which does not damp high frequency ultrasound. It confines the coupling liquid while allowing the eye to be protected from any accidental contact with mechanical parts, i.e., notably the transducer and/or its actuation mechanism. Now, these are results which are difficult to obtain, which explains the invention&#39;s advantage of reducing these problems to the making of the transducer itself, i.e., at the source of ultrasound, so as to be able to act more easily on the global features of the transducer. 
     Echographic apparatuses of this type nevertheless prove to have a certain number of drawbacks. Indeed: 
     Before reaching the eye, the ultrasonic wave focused by the concave curvature of the piezoelectric element of the transducer, has to pass through several layers of material having different properties and this, with different propagation velocities, the path of these waves inside these layers varying according to the (variable) position of the transducer. 
     This causes variations in the focal length of the transducer and inaccuracies in the obtained echographic image. 
     Moreover, it is seen that in the case of a high frequency transducer (from 15 MHz), liquids and membranes become increasingly absorptive. Consequently, the frequencies which effectively penetrate the tissues are much less than the frequencies emitted by the transducer. 
     Thus, as an example, for a transducer emitting with a frequency of 20 MHz, the transmitted central frequency will be 18 MHz with a loss of 10 dB. 
     Within the scope of open probes, all these drawbacks are suppressed since the coupling medium consists in a water bath which has good acoustic properties. However, the transducer performs its motion at a very small distance from the structure to be examined and even if it has a circular shape, its edges are aggressive and accordingly, it is not possible to suppress any risk of trauma by accidental contact of the transducer with the eye (scratching of the cornea by the circular edge of the transducer). 
     OBJECT OF THE INVENTION 
     Accordingly, more particularly, the object of the invention is to suppress these drawbacks. 
     SUMMARY OF THE INVENTION 
     For this purpose it proposes an echographic probe with sector scanning comprising a tubular body at least partially housed in its front end, a transducer designed so as to emit an incident ultrasonic wave focused in the direction of the structures to be examined and to receive ultrasonic waves generated by these structures under the effect of this incident wave, this transducer being associated with actuation means so as to be able to perform displacements, at least partially in rotation in order to obtain a sector scan of the structures to be examined. 
     According to the invention, the transducer comprises a piezoelectric assembly having a power of focusing emitted beams while having at its end, an axisymmetric surface, the generatrix of which has a curved shape and the director axis of which corresponds to the axis of rotation of the transducer, this surface being intended to come into contact with the structure to be examined. This curved shape may be circular in order to obtain a toric shape or a spherical shape. 
     By means of these arrangements, the presence of any aggressive edge in the transducer portion which may come into contact with the eye is suppressed. The first problem of the open probes is thereby solved, as the transducer will no longer be a member capable of damaging the eye and this, even in the case of a wrong move by the clinician. On the other hand, the material used is such that it withstands all decontamination protocols with soakings. 
     With the direct transducer/tissue-to-be-examined contact, the aforementioned inaccuracies may be avoided. Only the application of a gel on the tissues is required for providing good transmission of ultrasound. 
     The frequencies which effectively penetrate into the tissues are actually those emitted by the transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be described hereafter, as non-limiting examples, with reference to the appended drawings wherein: 
         FIG. 1  is an axial section of a probe with a spherical transducer; 
         FIG. 2  is a 90° axial section of the section illustrated in  FIG. 1 ; 
         FIG. 3  is a sectional view with a reduced scale of a probe of the type shown in  FIGS. 1 and 2  applied on the eye of a patient; 
         FIG. 4  is a schematic illustration of an alternative embodiment of the probe according to the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the example illustrated in  FIGS. 1 and 2 , the probe has a double-walled tubular body, partly illustrated, including an outer wall  1 , for example in stainless steel, and an inner wall  2 , for example in plastic. 
     The inner wall  2  delimits two successive compartments, i.e.:
         a rear compartment  3 , in which is housed a coaxial gear motor  4 , the central shaft  5  of which drives into rotation a driving rotating plate  6  bearing a permanent magnet  7 , and   a front compartment  8 , open at its end opposite to the posterior compartment  3 .       

     The separation between both compartments  3 ,  8 , is provided by a spherical partition  9 , obtained by molding or machining with the inner wall  2  and the concavity of which is directed towards the front compartment  8 . This spherical partition  9  is found in the extension of an inner flange  10  forming a throat between both chambers  3 ,  8 . 
     The permanent magnet  7  housed in a cavity of the rotating plate  6  has a cylindrical and frustro-conical shape obliquely centered relatively to the drive axis  5  of the motor  4  and the large base of which extends tangentially to the spherical partition  9 . 
     Inside the front chamber  8 , a spherical transducer  11  is rotatably mounted, including a main supporting part  12  with a substantially cylindrical shape and a staged bore, rotatably mounted on the inner wall  2  by means of two coaxial pins  13 ,  14 , centered perpendicularly to the main axis of the part  12 . In this example, both pins  13 ,  14  are borne by bearings mounted in coaxial cylindrical housings provided in the inner wall  2 . 
     This main supporting part  12  comprises on one side at a predetermined distance from the axis of both pins  13 ,  14 , a bore discontinuity delimiting a cavity open outwards in which a piezoelectric assembly  15  is positioned, having a outward focusing power and its outer shape  20  of which is spherical. 
     On the side of the axis of the pins, opposite to the element  15 , the main supporting part forms a shell which delimits a cavity into which a drive permanent magnet  17  is engaged, having a spherical surface centered perpendicularly to the axis of the pins  13 ,  14 , thereby fitting to the shape of the spherical partition  9 . 
     On the lateral sides of the main supporting part  12 , which extend parallel to the axis of the pins  13 ,  14 , two respective side magnets  18 ,  19  are attached ( FIG. 2 ), intended for cooperating with a Hall effect detector in order to determine the angular position of the transducer  11 . These side magnets  18 ,  19  have an outer spherical shape concentric with the transducer  11 . 
     According to the invention, the front part of the transducer  11  (located on the side of the piezoelectric element, relatively to the axis of the pins) is coated with a molded material layer  20  with high transmissibility for ultrasonic waves emitted by the piezoelectric assembly  15 . 
     In this example, this layer  20 , which has a spherical outer surface coaxial with the transducer  11 , stops at a height of about 5° relatively to the equatorial plane of the transducer  11 . This layer  20  coats the transducer sufficiently so as to provide contact with the structures to be explored during the whole rotation. 
     The seal between the outer  7  and inner  2  walls in the vicinity of the orifice, is for example provided by a elastomeric gasket  22  with a cylindrical shape including a radial flange  23  directed towards the inside, which will cover the end of the inner wall  2  in order to rest with its inner edge on the spherical surface of the layer  20 . 
     With this gasket  22 , it is therefore possible to avoid introduction of liquid or solid material inside the front chamber  8  of the probe  11 . 
     By means of the arrangements described earlier, by supplying electrical energy to the motor  4 , the rotary plate  6  and therefore the magnet is caused to rotate, the magnet performing a circular trajectory around the longitudinal axis of the probe in the immediate vicinity of the spherical partition  9 . 
     Under the effect of the rotating magnetic field generated by the magnet  7 , the permanent magnet  17  is subject to an attractive/repulsive force which causes an alternating rotary movement of the spherical transducer  11  around the axis of the pins  13 ,  14 . The transducer  11  performs a sector scan, the angular position of which is detected by means of the action of the side magnets  18 ,  19  on the Hall effect detector. 
     The front part of the spherical transducer  11 , which emerges from the flange  23  of the elastomeric gasket  22 , may be directly put into contact with the eye, as indicated in  FIG. 3 . Only a slight gel layer may be applied on the eye to provide good transmission of ultrasound and to improve the sliding between the eye and the spherical transducer. 
     Of course, the invention is not limited to the embodiment described earlier. 
     Thus, for example, the probe  25  ( FIG. 4 ) may comprise a spherical transducer  26  rotatably mounted around an axis parallel to the longitudinal axis of the body of the probe  25 . 
     In this case, the piezoelectric element  27  may be centered perpendicularly to the axis of rotation of the transducer  26  as illustrated in  FIG. 4 . 
     In this case, the piezoelectric assembly  27  is coated in a spherical part  28  in a material providing proper transmission of ultrasonic waves. 
     Driving the assembly  27  into rotation is here provided by means of a motor  31  coaxial with the probe and the output shaft thereof connected to the transducer by means of a transmission component  32 , provides the mechanical attachment of the spherical part  28 . 
     The electrical connection of the active component is achieved by the screw connector  35  of the SMC or equivalent type, accessible through the recessed portions of the transmission element  32 . A permanent magnet  29  facing a Hall effect sensor  30  integral with the casing of the probe  25 , enables the position information to be sent back to the card  33  controlling the motor for an alternating reciprocal movement. 
     Taking into account the fact that the angular sector scanned by the transducer  27  is centered perpendicularly to the axis of the probe  25 , the front end of the body of the probe  25  ends on one side as a slightly curved bevel so as to delimit an oblique aperture and to expose the useful area of the transducer  27  which should be applied to the eye. The advantage of this solution consists in that during echography, vision of the eye of the patient by the operator is only very partially hidden by the probe  25  (only by its front end). The hand which holds the probe  25  will be outside the field of vision, which was not the case in the example described earlier. 
     Moreover, the movements of the transducer are not limited to simple alternating rotational movements. Indeed, these movements may be of the arc-shaped type. In this case, the transducer may be mounted on an actuated device for example of the type of the one which is described in Patent Application No. 02 05780 as of May 7, 2002, on behalf of the applicant. 
     In this case, the spherical shape of a transducer provides considerable limitation of the risk of any accident.