Abstract:
The invention relates to an interventional device ( 10 ) including a plurality of signal assemblies, a method of assembling such interventional device ( 10 ), an assembling system for such interventional device ( 10 ) and a corresponding software product. In order to provide a number of signal assemblies including, for example, ultrasound transducers ( 40 ) in an interventional device ( 10 ) with a reduced risk of thrombi formation or similar complications a desired flush and smooth surface of a casing ( 15 ) of the interventional device ( 10 ) is achieved if the signal assemblies are inserted in such a manner that they are urged into their respective positions from inside the casing ( 15 ) after such insertion.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an interventional device including a plurality of signal assemblies, a method of assembling such interventional device, an assembling system for such interventional device and a corresponding software product. 
       BACKGROUND OF THE INVENTION 
       [0002]    An example for the use of an interventional device is cardiac ablation which is a procedure for curing cardiac arrhythmia. Preferably, the process of the cardiac ablation is monitored in situ. An ablation catheter with multiple ultrasound transducers in its tip enables the physician in the electro-physiology lab to assess in real time certain relevant parameters of the heart wall from the inside. 
         [0003]    An example of an ultrasound transducer system for cardiac ablation monitoring in discussed in WO 2012/066430 A1. 
         [0004]    However, unless a casing transparent to the monitored signal (e.g. ultrasound) is employed, i.e. if there are openings in the casing of the interventional device through which signals are emitted or received, complications during the treatment procedure may be caused by discontinuities in the surface of the interventional device. 
         [0005]    In particular, if there is a mechanical discontinuity on the ablation catheter tip, there is a potential of thrombi formation, which can cause thromboembolic events with severe consequences (e.g. a stroke). 
         [0006]    Openings which are provided in the case for irrigation purposes, for example, usually do not pose such threat as there is a (continuous) flow of saline irrigation fluid during the procedure. In contrast, in the case of an opening of the casing which might even include a distinct step between a surface of the transducer arrangement and the outer surface of the casing, such step is a potential site for thrombi formation due to the lack of a forced flow in such regions during treatment procedure. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide an interventional device with a reduced risk of thrombi formation or similar complications, together with a method of assembling such interventional device, an assembling system for such interventional device and a corresponding software product. 
         [0008]    In a first aspect of the present invention an interventional device is presented, comprising a casing with a side wall having a plurality of openings extending in a directions oblique to a longitudinal axis of the casing, and a plurality of signal assemblies, each including a sensor and/or an emitter, each signal assembly being aligned with a respective opening of the casing for receiving and/or emitting signals through the opening, wherein each signal assembly of the plurality of signal assemblies extends from the inside of the casing into the respective opening such that an outer surface of the signal assembly and an outer surface of the casing are flush at an edge of the opening and the outer surface of the signal assembly and the outer surface of the casing form a smooth outer surface of the interventional device, wherein the signal assemblies are fixed in the respective openings from inside the casing by a fixing element. 
         [0009]    In a further aspect of the present invention a method of assembling an interventional device is presented, comprising the steps of providing a casing with a side wall having a plurality of openings extending in a directions oblique to a longitudinal axis of the casing, inserting a plurality of signal assemblies into the casing, each signal assembly including a sensor for receiving and/or an emitter for emitting signals through an opening of the casing, and aligning each signal assembly of the plurality of signal assemblies with a respective opening of the casing, and urging the signal assemblies into the respective openings such that outer surfaces of the signal assemblies and an outer surface of the casing are flush at edges of the openings and the outer surfaces of the signal assemblies and the outer surface of the casing form a smooth outer surface of the interventional device, wherein the urging is provided by inserting a fixing element into the casing, the inserted fixing element fixing the signal assemblies in the respective openings from inside the casing. 
         [0010]    In yet a further aspect of the present invention assembling system for an interventional device is presented, comprising a holder for a casing with a side wall having a plurality of openings extending in directions oblique to a longitudinal axis of the casing, a first inserter for a plurality of signal assemblies, each signal assembly including a sensor for receiving and/or an emitter for emitting signals through respective opening of the casing, and a second inserter for a fixing element, the fixing element being provided for fixing the signal assemblies in the casing, wherein the second inserter is arranged for urging the signal assemblies of the plurality of signal assemblies, each signal assembly being aligned with the respective opening of the casing, into the respective openings such that outer surfaces of the signal assemblies and an outer surface of the casing are flush at edges of the openings and the outer surfaces of the signal assemblies and the outer surface of the casing form a smooth outer surface of the interventional device, the urging being provided by inserting the fixing element into the casing. 
         [0011]    It was realized by the inventors that—in order to provide a number of signal assemblies like ultrasound transducers in an interventional device with a reduced risk of thrombi formation or similar complications—it would be necessary to provide the signal assemblies such that the outer surfaces of the signal assemblies and the outer surface of the casing are flush at edges of the openings and the outer surfaces of the signal assemblies and the outer surface of the casing form a smooth outer surface of the interventional device. In order to have such flush and smooth surfaces, however, it is necessary to at least partially place portions of the signal assemblies such that the outer surface of the casing is smoothly extended into the area of the openings. Even though with a rigid casing the insertion of a rigid structure of such signal assemblies is not possible, the flush and smooth surface may be achieved if the signal assemblies are inserted in such a manner that they are urged into their respective positions from inside the casing after such insertion. 
         [0012]    It is to be noted that the term “smooth” does not exclude the case a portion of a signal assembly projects beyond the general surface of the casing or is recessed from such general surface of the casing but it is be understood as an indication that the surface is multiple times differentiable (i.e. not necessarily continuously differentiable). 
         [0013]    However, in view of a danger of tissue ruptures or current concentrations at protruding or recessing portions (possibly causing, for example, blood to be coagulated in the pool created by the mechanical discontinuity), generally an overall even and flat surface of the interventional device is preferred. 
         [0014]    The definition that an opening extends in a direction oblique to the longitudinal axis of the casing means that a boring (i.e. the inner side walls of the opening) provides for a surface which is not parallel to the longitudinal axis. Accordingly, is a signal assembly in inserted into the opening such that an side surface of the signal assembly abuts the inner side walls of the openings, the direction of such insertion (and that of a force employed therefore) is inclined in relation to the longitudinal axis of the casing. In other words, an opening extending in an oblique direction in relation to the longitudinal axis would result from drilling through the wall of the casing with a drill which axis is not parallel to the longitudinal axis of the casing. 
         [0015]    The oblique direction also includes the case that the direction is perpendicular to the longitudinal axis. 
         [0016]    In a preferred embodiment, the signal assemblies are positively locked, respectively, between the casing and the fixing element and/or to the fixing element. 
         [0017]    By virtue of a positive locking the signal assemblies are mechanically locked inside the casing, wherein therefore the fixing does not depend on a fixing like gluing (which is not excluded from being additionally provided) which might deteriorate under operation conditions. The positive lock of a signal assembly may be achieved by locking the signal assembly between the casing and the fixing element and/or by locking the signal assembly to or into the fixing element. It is to be noted that the locking may also be an indirect one, as for example, there might be a lining between the casing and the signal assembly. A locking of the signal assembly to or into the fixing element may be provided, for example, by a protrusion of the fixing element engaging into an undercut of the fixing element. 
         [0018]    If the signal assemblies (and correspondingly other elements inside the casing) are locked inside the casing mechanically and not only by adhesive bonding or the like, a concern of losing parts due to failure of such bonding in view of stress caused by differential expanding/shrinking of materials in the context of thermal aspects (e.g. RF ablation) is addressed. 
         [0019]    In a preferred embodiment, the interventional device further comprises one or more conduits defined by the casing, at least respective two of the signal assemblies and the fixing element. 
         [0020]    By urging the signal assemblies into the respective openings of the casing, there might be provided an empty space between the signal assemblies, which is further enclosed by the inner wall surface of the casing and an outer surface of the fixing element. Such space then extends along a longitudinal axis of the interventional device forming a conduit between the casing, adjacent signal assemblies and the fixing element. 
         [0021]    By means of an appropriate internal structure inside the interventional device two or more of such conduits may be brought into fluid connection, wherein then a fluid may flow into the interventional device in one conduit and flow out of the interventional device through another conduit. 
         [0022]    In a modification of the above preferred embodiment of the interventional device, the casing further includes one or more through-holes in fluid connection to the one or more conduits. 
         [0023]    If there is a fluid connection of a conduit as discussed above the outside (at the front end) of the interventional device, fluid may be delivered and/or removed through said through-holes. Thus, irrigation fluid (typically including saline) may be supplied to the tip or another portion of the interventional device; while alternatively or additionally body fluids (e.g. blood) may be sampled from the areas surrounding the interventional device. 
         [0024]    In addition and/or alternative to a through-hole other means for exchange or transfer of fluids and/or components of fluids may be used, e.g. a semi-permeable membrane. 
         [0025]    Alternatively or additionally to the above provision of conduits due to the positioning of the signal assemblies, the signal assemblies as such and/or the fixing element (as well as the casing as such) may include conduits formed therein, which might be used in a corresponding manner. 
         [0026]    In a preferred embodiment of the interventional device, a signal assembly includes a signal interface at least partially covering the sensor and/or emitter such that the outer surface of the signal assembly is at least partially a surface of the signal interface. 
         [0027]    Depending on the circumstances of the signal emission or reception it might be advantageous to provide an interface between the sensor/emitter and the surrounding area to be monitored or to be provided with a signal. 
         [0028]    In consideration of the reverberation caused by the excitation pulse of an ultrasound transducer, for example, it is preferable that the transducer is placed at a distance from the surface to be imaged (e.g. in case of imaging thin tissue of 0.5 to 2-4 mm). 
         [0029]    If a transducer is excited, an echo resulting from tissue close by is very difficult if not impossible to detect as such echo arrives back at the transducer prior to a sufficient fading of the reverberations of the transducer caused by the excitation itself. 
         [0030]    If however, there is provided a signal interface the ultrasound path to the region of the tissue at interest may be long enough for the reverberations to fade sufficiently. 
         [0031]    Furthermore, if the interventional device has a curved circumference (e.g. is round in cross-section), for the outer surface of the casing and the outer surfaces of the signal assemblies being flush and forming a smooth outer surface of the interventional device, the outer surface of a signal assembly would typically also have to be curved. In most situations, it is easier and more cost effective to provide a signal interface having such curved outer surface on a conventionally flat signal emitter or receiver (sensor) than to provide a signal emitter or a sensor having such curved surface itself. 
         [0032]    In a preferred embodiment of the interventional device, at least a part of said outer surface of a signal assembly is a surface of the sensor and/or emitter of the signal assembly. 
         [0033]    Under circumstances differing from those discussed with respect to the previous embodiment, there might also be advantages involved with providing a surface of the sensor and/or emitter directly at the outer surface of the interventional device. If, for example, a sensor is provided for picking up electric or thermal signals, the present embodiment allows this without or at least with a reduced influence of additional material otherwise covering the sensor surface. A further case in which the sensor/emitter surface might coincide with the outer surface of the interventional device is one of optical fibers embedded in mechanical retention pieces, for which the end surfaces of the fiber are flush with the outer surface of the casing. 
         [0034]    In a preferred embodiment of the interventional device, a signal assembly includes an adaptor provided between the sensor and/or emitter of the signal assembly and the fixing element. 
         [0035]    It is preferable to provide a defined surface of the sensor assembly by providing an adaptor arranged between the sensor/emitter of the signal assembly and the fixing element in an assembled state of the interventional device. Similar to the above, most commercially available signal emitter or sensors (signal receiver) have a basically flat surface. In order to, for example, avoid the need for checking a particular orientation of the parts to be assembled, it is preferable to provide a configuration indifferent to the orientation: If the fixing element has a circular circumference in cross-section along the longitudinal axis of the interventional device and the adaptor comprises a corresponding concave shape, the fixing element may be inserted in any rotational state. Nevertheless, orientation indifference with a reduced degree is achievable by providing symmetry of rotation (e.g. a rectangular cross-section for indifference against a rotation by 180°, a triangular cross section for 120°, a square cross-section for 90°, etc.). 
         [0036]    If, nevertheless, a particular orientation or rotational state of the fixing element in relation to the casing and/or the sensor assemblies is desirable, this might be achieved by providing, for example, one or more matching pairs of recess/protrusion for the related parts. 
         [0037]    The signal assemblies, according to a further embodiment modifying the above, may be provided as having an integral element forming both, a signal interface and an adaptor, into which the sensor and/or emitter is included or inserted. In such case, the sensor interface and the adaptor might be of the same material (e.g. formed by injection molding). Nevertheless, suitable productions techniques (e.g. 2K-extrusion) may also allow for the use of different materials. 
         [0038]    In a preferred embodiment of the interventional device, the casing further includes a front wall having a front opening, wherein the interventional device further includes a further signal assembly including an emitter for emitting and/or a sensor for receiving signals through the front opening, the further signal assembly extending from the inside of the casing into the front opening such that an outer surface of the further signal assembly and an outer surface of the front casing are flush at an edge of the front opening and the outer surface of the further signal assembly and the outer surface of the casing form a smooth outer surface of the interventional device. 
         [0039]    In addition to obliquely directed signal assemblies (including a radial orientation), the interventional device may also have one or more sensors and/or emitters arranged such that the respective signal assembly may be inserted into the corresponding (front) opening of the casing in a direction along the longitudinal axis of the interventional device. 
         [0040]    It is to be noted that this arrangement also applies to a case in which a signal assembly is directed in an oblique direction with respect to the longitudinal axis of the interventional device if the corresponding opening is provided that the signal assembly may be inserted therein just or basically by movement along the longitudinal axis of the casing, i.e. if the boring of the opening provides for a surface parallel to the longitudinal axis. 
         [0041]    The casing, the fixing element and/or the portion of the signal assembly preferably allow for an efficient cooling of the sensors/signal emitters, which is advantageous in particular in case of a continuous operation or in case of other reasons for production of heat, especially in the context of (cardiac or other) ablation. 
         [0042]    Aside from such considerations, however, the choices for the materials of the parts involved in the interventional device according to the present invention are generally only limited by their respective purposes and the constraints given for their operation. Generally, metallic material, ceramics, plastics and combinations thereof are suitable materials. 
         [0043]    In a preferred embodiment of the method of assembling, the fixing element is provided with a chamfer on its distal end and/or is tapering at its distal end, wherein the signal assemblies are guided by the chamfer and/or tapering to an outer surface of the fixing element upon inserting the fixing element. 
         [0044]    A fixing element provided with a chamfered or tapered front end allows for an easy insertion, in particular as there is a self-centering effect involved. 
         [0045]    In a preferred embodiment of the method of assembling, the inserting of the fixing element includes a turning of the fixing element inside the casing. 
         [0046]    In addition to the above or alternatively the fixing element may include protrusions or projections which urge the signal assemblies (which might be provided with corresponding elements) into the openings upon turning or rotating the fixing element (either in its completely inserted position or at an earlier stage of the insertion). 
         [0047]    In a preferred embodiment of the method of assembling, the inserting of the fixing element includes a deforming of the fixing element inside the casing. 
         [0048]    If, for example, the fixing element is loaded with a pressure along the longitudinal axis of the casing/interventional device (i.e. along the direction of insertion) and the fixing element reacts to such pressure by deformation, the deforming of the fixing element may be used for urging the signal assemblies into their respective openings. 
         [0049]    In a modification of the above preferred embodiment of the method of assembling, the fixing element is inserted in compacted form and the deforming of the fixing element includes an expansion. 
         [0050]    Prior to inserting into the case, the fixing element and the signal assemblies may be provided together, wherein a radially acting pressure is applied such that the fixing element (basically surrounded by the signal assemblies) is compacted. The pressure/compaction is maintained and the fixing element is inserted into the casing together with the signal assemblies and the fixing element is allowed to relax (i.e. to expand) inside the case, thus urging the signal assemblies into their designated positions. Alternatively, the signal assemblies may be provided inside the casing already, wherein the compacted fixing element is inserted (e.g. kept compacted by means of a shell), followed by an expansion (e.g. due to removal of the shell) inside the casing. 
         [0051]    In a preferred embodiment of the method of assembling, at least one of the signal assemblies is inserted into the casing such that a deformable surface of said signal assembly is aligned with the respective opening of the casing, wherein the inserting of the fixing element causes, upon urging said signal assembly, a deforming of the deformable surface. 
         [0052]    In case of a substantially rigid (surface of the) signal assembly, the signal assembly includes a protrusion or swell which, in the assembled state, extends into the respective opening. If the (surface of the) signal assembly is deformable (e.g. elastic or otherwise compressible), however, the signal assembly in its undeformed state may have no such protrusion or swell or a smaller one in comparison to the above case, wherein the extending of the signal assembly into the respective opening (i.e. the flush outer surface of the interventional device) is provided by inserting the fixing element, which deforms (e.g. compresses) the signal assembly, Accordingly, a substantially or at least mostly undeformed portion of the signal assembly extends into the opening and a deformed portion of the signal assembly abut (directly or indirectly) the inner surface of the casing and is compressed between the casing and the fixing element. 
         [0053]    In a further aspect of the present invention a software product for assembling an interventional device is presented, the software product comprising program code means for causing the assembling system according to the present invention to carry out the steps of the method according to the present invention when the software product is run on the assembling system. 
         [0054]    It shall be understood that the interventional device of claim  1 , the method of assembling an interventional device of claim  9 , the assembling system of claim  14 , and the software product of claim  15  have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims. 
         [0055]    It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or above embodiments with the respective independent claim. 
         [0056]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0057]    In the following drawings: 
           [0058]      FIG. 1  shows an ablation catheter tip with integrated sensors, 
           [0059]      FIG. 2   a  and  2   b  show different views of an ablation catheter tip in accordance with an embodiment of the invention, 
           [0060]      FIG. 3   a  to  3   e  show elements of an ablation catheter tip in accordance with the embodiment of  FIG. 2   a  and  2   b,    
           [0061]      FIG. 4   a  to  4   k  illustrate an assembling of the ablation catheter tip using the elements shown in  FIG. 3   a  to  3   e,    
           [0062]      FIG. 5   a  to  5   c  show sectional views of an ablation catheter tip in accordance with another embodiment of the invention, 
           [0063]      FIG. 6  shows an assembling system for an interventional device in accordance with a further embodiment of the invention, and 
           [0064]      FIG. 7  shows a flow diagram illustrating a method of assembling an interventional device in accordance with yet a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0065]      FIG. 1  shows an ablation catheter tip  1 , which includes one front transducer  3  and three further transducers  3  directed side wise, which are provided inside a casing  4  of the ablation catheter tip. The casing  4  comprises openings  2 , through which the transducers  2  transmit and receive ultrasound signals. The transducers  3  do not extend into the openings  2  and accordingly the surface of the ablation catheter tip  1  includes recesses and the position of the openings  2 . 
         [0066]      FIG. 2   a  shows a first view of an ablation catheter tip as an example of an interventional device in accordance with an embodiment of the invention. The ablation catheter tip  10  includes a casing  15  having plural openings  20  and several through-holes  25 .  FIG. 2   b  shows another view of the ablation catheter tip  10  of  FIG. 2   a,  where the casing  15  is shown as being transparent for illustrative reasons. Inside the casing  15 , signal interfaces  30  of the signal assemblies of the ablation catheter tip can is shown together with wiring  35  of the signal assemblies. The signal interfaces  30  extend into the openings  20  of the casing  15  such that the outer surfaces of the signal interfaces  30  are flush with the outer surface of the casing  15  and the combined surface of the casing  15  and the signal interfaces  30  is smooth. 
         [0067]      FIG. 3   a  shows transducers  40  of an ablation catheter tip in accordance with the embodiment of  FIG. 2   a  and  FIG. 2   b  in unassembled state together with their respective wiring  35 . 
         [0068]      FIG. 3   b  shows adaptors  45  of an ablation catheter tip in accordance with the embodiment of  FIG. 2   a  and  FIG. 2   b.  The adaptors  45  each comprise a seat  46  provided to receive the transducers  40 . Further, the adaptors each include an inner seat surface  47 , which in assembled state will be in contact with the fixing element (see  FIG. 3   d ). The adaptors further have outer seat surfaces  48  which will be in contact, in assembled state, with an inner surface of the casing  15  (see  FIG. 3   e ). Further, the adaptors  45  are provided with contact surfaces  49 , which are in abutment with corresponding contact surfaces  49  of adjacent adaptors in a state of the assembling prior to the insertion of the signal assembly into the casing (see  FIG. 4   g ). 
         [0069]      FIG. 3   c  shows a signal interface  30  of an ablation catheter tip in accordance with the embodiment of  FIG. 2   a  and  2   b.  The signal interface  30  includes projections for radial interfaces  31  and a projection for an axial interface  32 , wherein these projections, in assembled state, extend into the openings of the casing in order to achieve a flush outer surface. 
         [0070]      FIG. 3   d  shows a fixing element  50  of an ablation catheter tip in accordance with the embodiment of  FIG. 2   a  and  2   b.  The fixing element  50  is provided as a hollow tube having a nozzle  51  therein, through which the wiring  35  of the front transducer is provided. The front portion of the fixing element  50  is provided with a chamfer  52  for easing the insertion of the fixing element between the adaptors  45  upon inserting the fixing element  50  into the casing  15 . 
         [0071]      FIG. 3   e  shows a casing  15  of an ablation catheter tip in accordance with the embodiment of  FIG. 2   a  and  FIG. 2   b.    
         [0072]    The casing  15  is provided with an opening  20  at the front end openings  20  at the side wall of the casing  15 . Further, the casing  15  is provided with through-holes  25  provided in an area between the front opening  20  and the side wall openings  20 . 
         [0073]      FIG. 4   a  illustrates a first step of an assembling of the ablation catheter tip using the elements shown in  FIG. 3   a  and  3   b.  The transducers  40  intended for the side openings of the casing are provided with their respective adaptors  45 . For the front transducer there is no adaptor provided.  FIG. 4   b  illustrates a further step of the assembling of the ablation catheter tip using the elements shown in  FIG. 4   a  and  FIG. 3   c.  The signal interface  30  is provided on the transducers  40  shown in  FIG. 4   a  combined with their respective adaptors  45 . 
         [0074]      FIG. 4   c  shows a different view of the assembling state illustrated in  FIG. 4   b.    
         [0075]      FIG. 4   b  and  FIG. 4   c  show a sub-assembly  55  including the plurality of signal assemblies including the transducers  40 , their adaptors  45  and the signal interfaces  30 . 
         [0076]    It is to be noted that the order of assembly indicated in  FIG. 4   a  to  4   c  may also be changed depending on the circumstances, e.g. it is also possible to attach the transducers  40  first to the signal interface  30  (or vice versa) and to add thereafter the adaptors  40  to complete the sub-assembly  55 . It is further possible to provide a mixture of these approaches, e.g. to attach some of the adaptors  40  to the transducers (or vice versa), followed by attaching (some of) the signal interfaces  30 , followed by attaching further adaptors  40 , etc. 
         [0077]    The signal interfaces do not necessarily have to be connected to each other, even though such connections by runners or the like provides an advantage in basically fixing the spatial relation between the transducers (signal emitters/sensors) (while maintaining a possibility of flexing the runners), facilitating any easy handling of the sub-assembly  55 . 
         [0078]    In this embodiment, the radial transducers  40  are glued to the adaptors  45  (using an epoxy resin adhesive like Araldite™and also to the signal interface  30  (made of polyether block amide, PEBAX). If, as in this case, the material of the signal interface is transparent, UV curing may be used for binding the pieces together. 
         [0079]      FIG. 4   d  shows a further step of the assembling of the ablation catheter tip using the elements shown in  FIGS. 4   b,    4   c  and  4   e.  The sub-assembly  55  shown in  FIG. 4   b  and  FIG. 4   c  is folded such that the adaptors  45  of the transducers provided for the side openings of the casing are almost in abutment with the wiring of the front transducer  40 , wherein the total cross section of the sub-assembly  55  is narrow enough to be inserted into the casing  15 . 
         [0080]      FIGS. 4   e  and  4   f  illustrate a further state of the assembling of the ablation catheter tip resulting from a partial insertion of the sub-assembly shown in  FIG. 4   d  into the casing  15 . As it can been seen in  FIG. 4   e,  the contact surfaces  49  of the adaptors  45  are in contact with each other such that the total cross-section of the sub-assembly  45  is small enough to fit into the casing  15 . 
         [0081]      FIG. 4   g  shows a cross-sectional view of the stat shown in  FIG. 4   e  and  FIG. 4   f.  The adaptors  45 , the contact surfaces  49  of which are in contact with each other are arranged around the wiring  35  of the front transducer (not shown), while the transducers  40  are provided in the adaptors. The transducers  40  are covered, respectively, by the signal interfaces  31  which are to be provided eventually into the openings of the casing  15 . Between the wiring  35  and the inner surface  47  of the adaptors  45  there is space for an initial insertion of the fixing element. 
         [0082]      FIG. 4   h  shows a further state in the assembling of the ablation catheter tip following the state shown in  FIGS. 4   e  to  4   g.  The transducers  40  inside the signal assemblies including the signal interface  30  and the adaptors  45  are basically provided in alignment with the openings of the casing  15 . The front transducer  40  with the respective axial interface  32  is aligned with an opening on the front of the casing, while the other transducers  40  are provided with the radial interfaces  31  (only one shown) at the openings in the side wall of the casing  15 . Along the wiring  35  of the front transducer  40 , the fixing element  50  is provided and inserted between the adaptors  45 , urging the adaptors  45  outwards and therefore urging the radial interfaces  31  into the openings of the casing  15 . 
         [0083]      FIG. 4   i  shows a further step in the assembling of the ablation catheter tip following the state of  FIG. 4   h.  Following the state of the assembling as illustrated in  FIG. 4   h,  in  FIG. 4   i  the fixing element  50  is completely inserted between the adaptors  45  and is now further in abutment with the front transducer  40 , also fixing the front transducer  40  in position, with the axial interface  32  being fixed in the front opening  20  of the casing  15 . 
         [0084]    The outer surfaces of the radial interfaces  31  and the axial interface  32  are flush with the outer surface of the casing  15  (and the edges of the openings), wherein furthermore the combination of the surfaces of the interfaces  31 ,  32  and the casing  15  is smooth. 
         [0085]      FIG. 4   j  and  FIG. 4   k  show two cross sectional views of the state illustrated in  FIG. 4   i  of the assembled ablation catheter tip. As indicated above, the outer surfaces of the radial interfaces  31  are flush with the outer surface of the casing  15 . The adaptors  45  are urged outwards and separated from each other by the fixing element  50 , such that the contact surfaces  49  of the adaptors  45  are separated from each other. Thus, by the inner surface of the casing  15 , the contact surfaces  49  of the adaptors  45  and the outer surface of the fixing element  50 , conduits  60  are formed, which are in fluid connection with the through-holes  25  of the casing  15 . 
         [0086]      FIG. 5   a  to  FIG. 5   c  show sectional views of an ablation catheter tip  11  in accordance with another embodiment of the invention. The ablation catheter tip  11  as another example of an interventional device according to the present invention differs from the ablation catheter tip  10  discussed above in that the separately provided signal interface  30  and the adaptors  45  are replaced by an integral combination  65 , providing the functionality of the interface  30  and the adaptors  45 . The combination  65  is provided with the transducers  40  in corresponding manner and also the other steps of the assembling discussed above are provided in a corresponding manner. 
         [0087]    As it can be seen in particular in  FIGS. 4   i,    4   j,    4   k,    5   a,    5   b  and  5   c,  as well as  FIG. 2   b,  the signal assemblies which here include the signal interfaces  30 , the transducers  40  and the adaptors  45  or the combinations  65  and the transducers  40 , respectively, are locked in place between the casing  15  and the fixing element  50  such there is no danger of a portion of these elements “falling” out of the interventional device  10  during operation thereof. 
         [0088]      FIG. 6  shows an assembling system  70  for an interventional device in accordance with a further embodiment of the invention. The assembling system  70  includes a holder  75 , a first inserter  80  and a second inserter  85 . The holder  75  is provided for holding a casing  15 , wherein the first inserter is provided for the sub-assembly  55  (see above) with the second inserter  85  being provided for the fixing element  50  (see above). Once the sub-assembly  55  is inserted by the first inserter  80  in the casing  15  hold by the holder  75 , the second inserter  85  urges the fixing element into the casing, thereby urging the signal assemblies of the sub-assembly  55  into the respective openings of the casing  15  such that the outer surfaces of the signal assemblies and an outer surface of the casing are flush and edges of the opening and the outer surfaces of the signal assemblies and the outer surface of the casing form a smooth outer surface of the interventional device. 
         [0089]      FIG. 7  shows a flow diagram illustrating a method of assembling an interventional device in accordance with yet a further embodiment of the invention. 
         [0090]    The method of assembling  100  includes the steps of providing a casing (step  105 ), inserting a plurality of signal assemblies into the casing (step  110 ) and urging the signal assemblies into respective openings (step  115 ). The casing is provided with a side wall having a plurality of openings extending in a direction oblique of openings extending in a direction oblique to a longitudinal axis of the casing (see  FIG. 3   e ). Upon inserting (step  110 ) the plurality of signal assemblies into the casing, each signal assembly is aligned with one of the openings of the casing, wherein each signal assembly includes a sensor for receiving and/or an emitter for emitting signals through said opening. The urging (step  115 ) is provided by inserting a fixing element into the casing, such that the inserted fixing element fixes the signal assemblies and the respective openings from inside the casing (see  FIGS. 4   h,    4   i  and  5   a ). 
         [0091]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
         [0092]    Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 
         [0093]    Even though the fixing element is illustrated herein as being one piece or integral, the present invention allows also for the fixing element comprising sub-elements, which might, for example, also interact with each other or with the other portions of the interventional device before, upon and/or after inserting the fixing element. 
         [0094]    The shape of the openings is illustrated as being basically circular in the illustrated embodiments, while also other shapes are possible. The openings are further illustrated as corresponding to a boring (i.e. having basically constant cross-sections from the inside the casing to the outside of the casings). Nevertheless, the present invention is not limited to such form and the opening may, for example, also be (partially) tapering and/or may include a chamfer on the inside of the casing. 
         [0095]    Additional sensors such as one or more thermocouples, optical fibers, etc. can be easily integrated in the interventional device making use of the space provided with the assembling technique when elements are locked into position (the fixing element may be hollow, there is available space between the sensor assemblies, etc.). 
         [0096]    The above illustrative embodiments focus on the case of an ablation catheter tip, whereas the invention is limited neither to this particular field nor to the example of a catheter as an interventional device. An interventional needle or other interventional catheters, for example, may also be provided according to the present invention. 
         [0097]    The number of signal assemblies is four in the illustrated embodiments (one front signal assembly and three signal assemblies directed outwards), while the present invention is not limited to such number and to such directions. Each individual senor may represent an array of sensors. 
         [0098]    The present invention is not limited to ultrasound transducers as examples of the signal assemblies as also other sensors and emitters are possible and combinable (e.g. measuring an electric or magnetic signal, a temperature, a pH-value, etc.) 
         [0099]    In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. 
         [0100]    A single processor, device or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
         [0101]    Operations like the control of steps for the assembling system can be implemented as program code means of a computer program and/or as dedicated hardware. 
         [0102]    A computer program or software product may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. 
         [0103]    Any reference signs in the claims should not be construed as limiting the scope.