Abstract:
The present disclosure relates to a device for positioning and/or orienting, in the body of a patient, a surgical tool carried by a tool-holder, including a platform capable of being placed on the body of the patient, an orientable carrier, at least one part of which is rigidly connected to the tool-holder, means for guiding the orientable carrier rotationally relative to the platform in two directions of a plane parallel to the platform, at least 2 pneumatic actuators which engage with the orientable carrier such that a variation in pressure of at least one of the pneumatic actuators causes the orientable carrier to rotate in the first direction and/or the second direction, in which the pneumatic actuators are volumes that can deform in a predetermined direction as a function of the internal pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Phase entry of International Application No. PCT/EP2009/059767, filed on Jul. 28, 2009, which claims priority to French Application Serial No. 0855189, filed on Jul. 29, 2008, both of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a device for positioning a surgical tool in the body of a patient. 
       BACKGROUND OF THE INVENTION 
       [0003]    Scientific interest for the development of automated medical aid systems has considerably increased since the 1990s. Several medical fields have seen the arrival of generic or dedicated systems like in the cases of the Da Vinci™ robot used in laparoscopy but also of systems for tele-operation or for a cardiac application. The advantages of minimally invasive surgery have contributed to the development of particular sensors and actuators. A panorama of the development of medical robots is provided in the article “Medical Robotics in Computer-Integrated Surgery” of Taylor et al, IEEE Transactions on Robotics and Automation, Vol. 19, No. 5, October 2003, where a significant number of robots for different medical specialties is considered. 
         [0004]    Generally, tool holder sub-systems (endoscope, laparoscope or needle) have a maximum of 4 degrees of freedom allowing the orientation of the tool, its insertion and its axial rotation. The orientation of the tools outside the body of the patient as well as their insertion are accomplished with actuators. Several kinds of actuators have been considered for robotic systems such as electric motors, ultrasonic motors, piezo-electric motors, harmonic and planetary hydraulic/pneumatic motors or the artificial muscles of McKibben. Artificial muscles use compressed air as a power source and are used in antagonism; therefore their compression rate is low and they bear metal portions which are not desirable in the gantry of tomography or magnetic resonance apparatuses. 
         [0005]    In minimally invasive surgery or in puncture procedures, the surgical tools are sometimes orientated or moved manually or with electric actuators which generally are incompatible with the environments of tomography and/or of magnetic resonance, or with other slow actuators. Several automated systems are incompatible with the mentioned environments since they have been built with metal, paramagnetic or diamagnetic materials. These drawbacks are related to mechanical design and to how the systems are actuated. 
         [0006]    A lightweight pneumatic robot and compatible with tomography and magnetic resonance environments is presented in the article of E. Taillant et al., “CT and MR Compatible Light Puncture Robot: Architectural Design and First Experiments”, Proceedings of Medical Image Computing and Computer Assisted Intervention (MICCAI), Lecture Notes in Computer Science, Springer Verlag, Vol. 3216, pp. 145-152, 2004. This system is adapted to thorax and abdomen puncture under a scanner or magnetic resonance while being interdependent on the body of the patient. With this robot, it is possible to orient the needle holder by means of two rotations: a first rotation of the base of the robot relatively to a platform firmly attached to the body of a patient, of 360° around an axis perpendicular to the body of a patient, and a second rotation of the needle holder, relatively to the base, in a limited angular range. 
         [0007]    This orientation device consists of conventional pneumatic actuators, i.e. each comprising a piston sliding in a cylinder fed with compressed air on either side of the piston. Each piston cooperates with a toothed wheel, itself connected to a worm screw, thereby forming a pneumatic step motor. Because of its design, this device therefore only allows positioning of the tool according to a plurality of discrete positions. 
         [0008]    This orientation device is also relatively slow, with a frequency of the order of 3 Hz. Moreover, a slipping and adherence (so-called “stick-slip”) phenomenon of the piston in the chamber was observed when the piston is motionless, leading to a sudden movement upon its setting into motion and to generation of a delay in the response of the actuator. Finally, another drawback of this robot is its non-compliant nature: because of the rigidity of the drive chain, this robot is not able to absorb large forces so that the latter are capable of injuring the patient when the tool is inside his/her body. 
         [0009]    One of the objects of the invention is therefore to design a system allowing fast orientation or displacement of a tool holder (endoscope holder, needle holder or trocar), having a minimum size. This system should also allow continuous variation of the positions of the tool holder. Another object of the invention is that such a system may be compatible with tomography and magnetic resonance environments. Another object of the invention is to provide a lightweight system, guaranteeing the safety of the patient in the case of generation of forces capable of injuring him/her. 
       SUMMARY 
       [0010]    According to the invention, a device is proposed for positioning or/and orientation in the body of a patient, comprising:
       a platform capable of being placed on the body of the patient,   an orientable support, at least one portion of which is rigidly bound to the tool holder,   means for guiding in rotation the orientable support relatively to the platform in two directions of a plane parallel to the platform,   at least two pneumatic actuators cooperating with said orientable support so that a change in pressure of at least one of the pneumatic actuators generates a rotation of the orientable support in the first direction and/or the second direction,
 
wherein said pneumatic actuators are deformable volumes in a direction determined according to the internal pressure, each having a face firmly attached to the platform or guiding means and a face firmly attached to the orientable support, so that a change in the internal pressure causes displacement of the face firmly attached to the orientable support.
       
 
         [0015]    According to a first embodiment of the invention, the pneumatic actuators are four in number, the orientable support comprises two pairs of plates, both plates of each pair being parallel to each other and orthogonal to the plates of the other pair, and the pneumatic actuators are laid out as antagonistic pairs so that the internal pressure of an actuator firmly attached to a plate of the orientable support varies in the direction opposite to the internal pressure of the actuator firmly attached to the plate opposite said plate. More advantageously, the guiding means comprise two semi-circular guides positioned longitudinally in the first direction and a second pair of plates in the orientable support has means for sliding along said guides. Said semicircular guides are further mobile in rotation around the first direction and firmly attached to the second pair of plates of the orientable support. 
         [0016]    According to a second embodiment of the invention, the pneumatic actuators are three in number and the orientable support is a prism with a triangular base, so that each of the actuators is firmly attached to one of the three side faces of the orientable support. Moreover, the tool holder advantageously comprises means for guiding the tool in translation, in a direction parallel to the axis of the tool holder, said means for guiding the tool cooperating with deformable pneumatic actuators in a determined direction depending on the internal pressure, so that a change in pressure of at least one of said pneumatic actuators causes translation of the tool. 
         [0017]    If the translation axis of the tool coincides with the axis of the tool holder, said pneumatic actuators are preferably toroidal cylinders, so that the tool slides inside the toruses. If the translation axis of the tool is distinct from the axis of the tool holder, said pneumatic actuators are cylinders. 
         [0018]    The device further comprises means for connecting the platform to the arm of a surgical aid robot; said means comprise at least one passive rotoid joint. More advantageously, the platform, the orientable support, the pneumatic actuators and the means for guiding in rotation the orientable support are in non-metal and non-magnetic materials, so that said device is capable of being used in tomography and/or magnetic resonance. 
         [0019]    According to another aspect, the invention relates to a tool holder adapted so as to be used in the device which has just been described. Said tool holder comprises means for driving the tool into translation along an axis, a piston rigidly bound to the tool, slidably mobile in a casing along a longitudinal direction parallel to said axis. Said means advantageously comprise two pneumatic actuators located in the casing on either side of the piston, deformable in a direction determined according to the internal pressure, and cooperating with the piston so that a change in pressure in at least one of the actuators generates sliding of the piston along said direction. 
         [0020]    In a particular embodiment of the tool holder, in which the translation axis of the tool and the sliding direction of the piston coincide, the pneumatic actuators are toroidal cylinders, the inner diameter of which is greater than the diameter of the tool. According to an alternative, the translation axis of the tool and the sliding direction of the piston are distinct and the casing has a longitudinal slot for sliding a member connecting the piston and the tool. 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0021]    Other features and advantages of the invention will become apparent from the detailed description which follows, with reference to the appended drawings wherein: 
           [0022]      FIG. 1  is an exploded view of a first embodiment of the device according to the invention; 
           [0023]      FIG. 2  illustrates a method for attaching an actuator onto the platform; 
           [0024]      FIG. 3  illustrates two possible orientations of the platform depending on the breathing of the patient; 
           [0025]      FIG. 4  illustrates the orientable support for the tool holder; 
           [0026]      FIG. 5  shows the angular movements which the tool holder may adopt; 
           [0027]      FIG. 6  illustrates the extreme positions which the tool holder may reach according to one of the degrees of freedom; 
           [0028]      FIG. 7  illustrates the displacement according to a first degree of freedom of the tool holder under the effect of the antagonistic work of both actuators; 
           [0029]      FIG. 8  illustrates the displacement according to a second degree of freedom of the tool holder resulting from the antagonistic work of two other actuators; 
           [0030]      FIG. 9  illustrates a first embodiment of the tool holder; 
           [0031]      FIG. 10  illustrates a second embodiment of the tool holder; 
           [0032]      FIG. 11  illustrates an alternative embodiment of the device according to the invention; 
           [0033]      FIG. 12  shows the forces applied to the orientable support in the device of  FIG. 11 ; and 
           [0034]      FIG. 13  illustrates in a more detailed way the construction of the design of the device of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    By tool in this text is meant any device which may be used during a surgical operation: it may thereby be a surgical instrument (such as a needle for example) or else a medical imaging system, such as an endoscope or a laparoscope. By tool holder in this text is meant a device bearing the surgical instrument which will be inserted into the body of a patient. Depending on the instrument used, the tool holder may thereby be described as a needle holder, endoscope holder or further a trocar. 
         [0036]    During a surgical operation on a patient, such as a puncture or a laparoscopy, a tool (such as a needle  10  or an endoscope for example) borne by a tool holder  8  as illustrated in  FIG. 1  has to be oriented and displaced. The device according to the invention allows the surgeon to orient by means of two rotations, the tool holder  8  along the axes a 1  and a 2  and to translate the tool along the axis a 3 . The orientation of the tool holder  8  is controlled via the orientation of the orientable support  9 , to which the tool holder  8  is rigidly bound. The tool holder  8  is bound to the orientable support  9  by conventional mechanical means such as screws or clip-fastening means (i.e. by mechanical pressure). 
         [0037]    The overview  FIG. 1  and the detailed  FIGS. 4 ,  5 ,  7 , and  8  illustrate a preferred but non-limiting embodiment of the invention. According to this preferred embodiment, the device comprises a circular platform  1  comprising four hollow spaces  2  in order to reduce the weight of the system, two hollow spaces  3  for receiving the two rectangular platforms  6  and a circular cavity  4  for defining the working area i.e. the area for introducing the tool into the body of the patient. The platform  1  typically has a diameter of 10 cm. 
         [0038]    It is laid on the body of the patient, so that the circular cavity  4  is substantially centered on the area for introducing the tool. In the case of a puncture, the point  17  represents the point of insertion of the needle  10 , invariant under the aforementioned rotations. The platform  1  is substantially planar, and the axes a 1  and a 2  along which the tool holder  8  is orientable are located in a plane parallel to the plane of the platform. The platform  1  may be held by an external mechanical arm (not shown), either rigid or not, of a surgical aid robot, which may be suitably adapted to the contemplated medical applications. The link between the platform and this arm will be described below. 
         [0039]    The device moreover comprises two platforms  6  connected through two semicircular guides  7  allowing the angular displacement of the tool holder  8  to be guided by rotation around the axis a 2  by means of the orientable support  9 . As this will be seen in the description of  FIG. 8 , the assembly formed by the platform  6  and the semi-circular guides is not rigidly bound to the platform  1  but is rotationally mobile around the axis a 1  by means of smooth bolts. 
         [0040]    The orientation movements of the tool holder  8  are ensured by pneumatic actuators  11  and  12  which are deformable volumes in a preferential direction depending on the internal pressure. By this is meant that this is the casing defining said volume which deforms, unlike a standard pneumatic actuator in which the cylindrical casing is rigid and the shape of which does not vary. Moreover, the movement produced by a standard pneumatic actuator is always linear while the one produced by pneumatic actuators with a deformable volume follows a preferential direction defined by the shape of the actuator. 
         [0041]    The casing of the actuators is for example made in flexible plastic. Here, the actuators appear as portions of toruses, the neutral fiber of which follows approximately a semi-circle. The actuators are capable of elongating or retracting along the neutral fiber. 
         [0042]    Two actuators  11  (only one of which is illustrated in  FIG. 1 ) are assembled on the two rectangular platforms  6  by means of the surfaces  13  and on the orientable support  9  by means of the surfaces  14 . A change in pressure of one of the actuators  11  therefore allows the orientable support  9  to be tilted in a plane containing the axis a 1 . Also, two actuators  12  (only one is illustrated in  FIG. 1 ) are assembled on the two rectangular areas  5  of the platform  1  by means of the surfaces  15  and on the orientable support  9  by means of the surfaces  16 , thereby allowing the orientable support  9  to be tilted along a plane containing the axis a 2 . 
         [0043]    With reference to  FIG. 2 , the assembling of each actuator may be carried out by means of plastic screws accommodated in orifices  15   b  allowing tabs  15   a  located on the outside of the actuator  12  to be secured in the extension of the surface  15 , or else by a mechanical clip-fastening means. Each of the actuators is connected to a compressed air circuit (not shown) provided with means for controlling the pressure in each of them. The handling of the pressures in the different actuators depending on the desired orientation of the tool holder is ensured by an electronic interface (not shown). 
         [0044]    Each pair of actuators of the same type work antagonistically, i.e. when the compressed air pressure increases in one of the actuators, that of its antagonist actuator decreases and vice versa. This allows the movements of the orientable support  9  to be balanced. However, it is understood that a single actuator  11  and a single actuator  12  would be sufficient for tilting the orientable support  9 . It is therefore understood that these novel actuators give the possibility, unlike conventional pneumatic actuators of the piston-cylinder type, of avoiding the “stick slip” phenomenon, thereby guaranteeing smooth operation of the system. 
         [0045]    The two holes  18  shown in the platform  1  of  FIG. 1  are used for introducing two cylinders or fingers d associated with two passive rotoid joints r 1  and r 2  allowing free movement of the system for example produced by the breathing of the patient as illustrated in  FIG. 3 . Both fingers d are connected to an automated arm allowing translation of the robot in three-dimensional space. Indeed, the device is interdependent on the body of the patient and changes the orientation of the platform  1  depending on the natural movements of the patient. 
         [0046]      FIG. 3  illustrates two instants when the orientation of the platform  1  has to move freely and naturally, in apnea and during inspiration.  FIG. 4  illustrates in more detail the orientable support  9  which comprises two plates  19  which are used for receiving both contact surfaces  14  of both actuators  11 . These plates  19  are rigidly bound to two followers  20  bearing spherical balls in order to reduce the friction between the followers  20  and the internal surfaces of the guides  7 . 
         [0047]    Both plates  22  are used for receiving both contact surfaces  16  of two actuators  12  and are rigidly bound to the external surfaces of the semi-circular guides  7 . The plates  22  are centered relatively to the guide  7 , i.e. they are symmetrical with respect to a plane perpendicular to the plane of the platform and comprising the axis a 2 . It will be noted that as the plates  19  and  22  are not rigidly bound, the tool holder  8  is only rigidly bound to one or two of the plates  19 , but not to the plates  22 . 
         [0048]    The orientation of the tool holder  8  is defined by two angular movements in two perpendicular planes π 1  and π 2 , as illustrated in  FIG. 5 . The plane π 1  is the plane perpendicular to the plane of the platform and comprising the axis a 1 ; the plane π 2  is the plane perpendicular to the plane of the platform comprising the axis a 2 . The axis a 3  shown in  FIG. 5  is the initial position (perpendicular to the platform) from which the tool holder  8  has to be oriented. 
         [0049]    The two angular movements are therefore respectively associated with the angles φ and θ measured from the axis a 3  shown in  FIG. 5 . From its initial position φ=0 and θ=0, the tool holder  8  may, via the antagonistic actuators, attain for each of the degrees of freedom φ or θ, a maximum position φ max  or θ max  and a minimum position φ min  or θ min , as this is illustrated in  FIG. 6  for the angle φ and for one of the actuators  11  with the contact surfaces  13  and  14 . 
         [0050]      FIG. 7  illustrates the movement produced on the tool holder by the antagonistic work of both actuators  11  drawn in dotted lines. In the case shown, the compressed air pressure P 1  of the left actuator is less than the pressure P 2  of the right actuator. This pressure difference allows the followers  20  to move on the guide  7 , thereby changing the angular position of the tool holder. 
         [0051]    The generated angle φ is therefore measured between the axis a 3  associated with the initial position and the axis a 4  associated with the final position of the tool holder. This angular movement is defined by a rotation R 1  carried out with respect to the axis a 2  of  FIG. 7 . 
         [0052]    It is possible to observe in this figure that the imaginary circumference with radius  21  is used for designing the guide  7  and that the axis a 2  is lower than the plane of the rectangular platforms  6 . Indeed, the circumference arc defining the guide  7  is designed and placed in such a way that the point  17  for inserting the needle  10  is on the lower plane of the platform  1  coinciding with the skin of the patient. The same principle of actuation is used for producing the rotation by an angle θ of the tool holder, by the antagonistic work of both actuators  12  drawn in dotted lines in  FIG. 8 . 
         [0053]    When the pressures P 3  and P 4  are equal, the position of the tool holder is the one shown in  FIG. 8  by solid lines. If P 4  increases by the same value by which P 3  decreases, the tool holder moves by an angle θ and reaches its final position drawn in dotted lines in this figure. The tool holder turns with respect to the axis a 1  defining a rotation R 2 . 
         [0054]    The rigid assembly of both rectangular platforms  6  and of both circular guides  7  rotate with the tool holder by means of two plates  22  receiving both contact surfaces  16  of the actuators  12  and by means of two smooth bolts  23  ensuring their assembling with the platform  1 . The generated angle θ is measured between the axis a 3  associated with the initial position and the axis a 4  associated with the final position of the tool holder. Because of its design, the device allows the angular position of the tool holder to be varied continuously, with great rapidity, so that the response of the system does not have practically any delay. More advantageously, the design of the tool holder is based on the same principle as the one of the positioning device, i.e. pneumatic actuation by deformable volumes in a direction determined according to their internal pressure. 
         [0055]    The tool holder then appears as a casing, for example a cylindrical casing, inside which is laid out a piston rigidly bound to the tool and surrounded by two deformable pneumatic actuators, so that a change in pressure of at least one of the actuators causes sliding of the piston in the casing. Depending on the needs, the translation axis of the tool may coincide with that of the sliding of the piston, or else be distinct from the latter. 
         [0056]      FIG. 9  illustrates one of the possible designs of the tool holder  8 . This tool holder contains the surgical tool such as needle  10  or an endoscope as well as the members guaranteeing the translation T 1  of the surgical tool, following the direction ζ along the axis a 4 . 
         [0057]    Inside the cylindrical casing  24  two deformable actuators  25  and  26  are found, made in flexible plastic and working antagonistically. These actuators are toroidal cylinders allowing the passage of the tool placed on the piston  27  being used as an interface between both actuators. If the tool is a needle, its upper portion  28  may be connected to another device for example a catheter. 
         [0058]    The pressure difference between the values of P 5  and P 6  will cause displacement of the piston  27  and therefore of the surgical tool. The travel of the tool is in this case defined by the length of the actuators. 
         [0059]    A second possible design of the tool holder  8  is shown in  FIG. 10  where the axis of the tool does not coincide with that of the tool holder but where both of these axes are parallel. In this case, the actuators  25  and  26  are simple cylinders working with the same principle as in the previous case. 
         [0060]    The piston and the casing bear circular guides  29   a  and  29   b  with diameters generally different being used for maintaining parallelism between the axis of the tool and that of the tool holder. The guide  29   a  rigidly assembled to the piston  27  and to the tool  10  may move translationally inside the slot  30  made in the casing  24 . The travel of the tool is in this case defined by the length of the slot  30 . The guide  29   b  is fixed relatively to the tool holder and guides the displacement of the tool. 
         [0061]    It is obvious that the tool holder which has just been described is fully a subject matter of the present invention. More advantageously, the whole of the components of the device (notably the platform, the orientable support, the actuators, the tool holder) may be in non-metal and non-magnetic, for example plastic, materials. Thus, the device is compatible with magnetic resonance and tomography environments. 
         [0062]    Moreover, the thereby formed device has a particularly reduced size, since it is comprised in a tube with a side of about 10 cm, which simplifies its installation in the operating environment. It also has the advantage of being very lightweight. Thus, the mass of the prototype developed by the inventors is less than 1 kilogram. 
         [0063]    Finally, the natural compliance of the device promotes the safety of the patient during the generation of forces capable of injuring the patient. Indeed, if the surgical tool is a needle, the deformable pneumatic actuators have sufficient flexibility for allowing the needle, when it is inside the body of the patient, to move following the movements of breathing and of the organs, which allows the risk of injuries to be reduced. On the other hand, if the system was not compliant (this would be the case with a system holding the needle rigidly, such as pneumatic actuators of the piston-cylinder type of the prior art), the movements due to breathing and to the organs would be able to cause injuries by scratching or perforating the organs. Thus, for a compliant system, when there exists a significant force acting on the system, the latter reacts following the direction of the force and does not oppose this force. 
         [0064]    Different configurations for the actuation with pneumatic chambers may be contemplated; in particular, concerning the geometry of the pneumatic actuators and their arrangement.  FIG. 11  thereby illustrates an alternative embodiment of the invention comprising a triangular arrangement of the actuators  11 A,  11 B and  11 C with which, depending on the three pressure values PT 1 , PT 2 , and PT 3 , a final position of the tool holder  8  may be obtained, associated with a combination of the values of the angles φ and θ. In this device with three actuators, the latter are placed at 120° from each other. 
         [0065]    The tool holder therefore receives, through the action of three pressures on three contact surfaces, three forces (F 1 , F 2  and F 3 ) acting towards the axis of the tool holder, as illustrated in  FIG. 12 . When these forces have the same value (i.e. the resulting force is 0), the axis of the tool holder is vertical. A rotoid joint placed in proximity to the point for inserting the tool allows the tool holder to be oriented following the direction of the resulting force. 
         [0066]    The principle of operation remains similar to the case of four actuators where contact plates are used for ensuring power transmission by means of the pneumatic pressures in each actuator. The tool holder  8  is then a sort of mast rigidly bound to an orientable support appearing as a triangular prismatic structure  31  in order to receive three contact surfaces, one for each of the three actuators. 
         [0067]    In  FIG. 13 , the actuator  11 A may thus be observed in contact with the triangular prism  31  on the one hand and with one of the three plates  32  resting on the platform  33  similar to the platform  1  of  FIG. 1 , on the other hand. The tool holder remains in contact with the spherical surface  34  (which forms a large rotoid joint) by means of three telescopic mechanical members  37  which bend or extend depending on the combinations of the pressures in the three pneumatic chambers. These telescopic members  37  are attached to the tool holder  8  and to the platform  35  through passive rotoid joints  36 . The platforms  33  and  35  are bound by three rigid members shown in the same figure. On the edge of the platform  33 , the two holes used for receiving the fingers d shown in  FIG. 3  may also be observed. 
         [0068]    Finally, it is obvious that the examples which have just been given are only particular illustrations, by no means limiting as to the fields of application of the invention.