Abstract:
A system for positioning with respect to a patient&#39;s body an observation and/or intervention device comprising at least a mechanical part and a system for actuating the mechanical part, the actuation system comprising a piston capable of sliding a rod and connected to means for supplying a fluid under pressure; a drive element connected to the mechanical part and comprising dissymmetrical teeth; and a bearing element assembled on the rod and capable, on displacement of the rod along a determined direction, of cooperating with a tooth of the drive element to displace the drive element by a determined distance and/or angle, the bearing element, on displacement of the rod along the direction opposite to the determined direction, exerting a substantially zero force on the drive element to avoid displacing the drive element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a system for positioning on a patient an observation and/or intervention device, for example, an observation and/or intervention device having a portion penetrating into the patient&#39;s body. It for example applies to medical analysis devices, such as needles, and it will be more specifically described in the case of the use of a hollow needle in a biopsy.  
         [0003]     2. Discussion of the Related Art  
         [0004]     In such a type of operation, a hollow needle formed of a thin tube is inserted, for example, in the patient&#39;s abdomen, thorax, or back through a small incision performed at the patient&#39;s level. The operation is generally carried out with the assistance of images obtained by a medical imaging method, for example, a scanner imaging or magnetic resonance imaging (MRI) method, to help the radiologist visualize the patient&#39;s interior.  
         [0005]     The puncture operation then generally comprises the alternation of image acquisition phases and of phases where the actual puncture is performed. The obtained images are cross-section views enabling the radiologist to determine whether the needle orientation is or not correct, and, possibly, to correct this orientation. Such a transcription of the needle position in the three-dimensional space from the position of the needle on two-dimensional images is difficult and requires much experience from the radiologist for the intervention to be accurately performed.  
         [0006]     Further, if the used imaging system is a scanner and if the radiologist must remain in the room where the patient is, for example, to maintain the needle during the image acquisition, he is then submitted to the radiations emanating from the imaging system, which may be dangerous, given the number of interventions performed by the radiologist along the year.  
         [0007]     Further, when the used imaging system is an MRI system, it is necessary to use a so-called “open” MRI system, comprising a tunnel which is not completely closed to enable access to the patient. Such systems provide images having a lesser quality than that obtained with so-called “closed” MRI systems.  
         [0008]     To overcome the previously-described disadvantages, robotic systems have thus been developed to handle the needle instead of the radiologist.  
         [0009]     As an example, French application 02/05848 filed by PRAXIM Company describes a system for positioning on a patient an observation and/or intervention device taking up a small volume. The displacement and the orientation of the positioning system are then generally performed based on the analysis of the images obtained by the used imaging system. The positioning system is displaced and oriented via electric actuators. The electric actuators may be arranged at the positioning system level and then directly drive mechanical parts of the positioning system, possibly by gear reduction and transmission systems. The electric actuators may be arranged at a distance from the positioning system, each electric actuator then driving a cable connected to a mechanical part of the positioning system.  
         [0010]     A disadvantage of such a positioning system is that it is generally difficult to make it compatible with the sterility constraints specific to a medical operation. Indeed, it is then necessary to provide a method for sterilizing the positioning system, but also electric actuators and/or cables connecting the electric actuators to the positioning system, which may turn out to be difficult and/or expensive.  
         [0011]     Another disadvantage is that electric actuators, or the cables connecting the electric actuators to the positioning system, in addition to leaving marks on an image obtained by currently-used medical imaging methods, may deform the rest of the image, which may hinder the analysis thereof.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention aims at obtaining a system for positioning on a patient an observation and/or intervention device and which is actuated via actuators that may easily be made compatible with the sterility constraints specific to a medical operation.  
         [0013]     According to another object, the present invention provides a positioning system actuated by actuators that may, if necessary, be formed of materials leaving little or no marks on images obtained by medical imaging methods of scanner or MRI type or at least, if they leave marks on such images, that do not deform the rest of the images.  
         [0014]     To achieve these objects, the present invention provides a system for positioning with respect to a patient&#39;s body an observation and/or intervention device comprising at least a mechanical part and a system for actuating the mechanical part. The actuation system comprises a piston capable of sliding a rod and connected to means for supplying a fluid under pressure; a drive element connected to the mechanical part and comprising dissymmetrical teeth; and a bearing element assembled on the rod and capable, on displacement of the rod along a determined direction, of cooperating with a tooth of the drive element to displace the drive element by a determined distance and/or angle, the bearing element, on displacement of the rod along the direction opposite to the determined direction, exerting a substantially zero force on the drive element to avoid displacing the drive element.  
         [0015]     According to an object of the present invention, the drive element is a ratchet wheel.  
         [0016]     According to an object of the present invention, the fluid is air.  
         [0017]     According to an object of the present invention, the actuation system is totally formed of materials leaving no marks on an image obtained by a scanner imaging or magnetic resonance imaging system or leaving marks on said image without deforming the rest of said image.  
         [0018]     According to an object of the present invention, the positioning system comprises a drive system comprising a shaft and first and second actuation systems, the first actuation system being capable of rotating the shaft along a determined rotation direction and the second actuation system being capable of rotating the shaft along the direction opposite to the determined rotation direction.  
         [0019]     According to an object of the present invention, the positioning system comprises a base to which said device is connected according to a number of degrees of liberty; flexible connection means, each of which is arranged between the base and a frame solid with the patient&#39;s support or the patient himself; and drive means for modifying the length/tension of the connection means.  
         [0020]     According to an object of the present invention, the positioning system comprises a base laid on the patient&#39;s body; means for supporting the device, formed of at least a first portion movably assembled on the base according to a connection with one degree of liberty, and of a second portion movably assembled on the first portion according to a connection with one degree of liberty and connected to the device; and a first system for driving the first portion with respect to the base, and a second system for driving the second portion with respect to the first portion.  
         [0021]     According to an object of the present invention, the first portion is a mobile ring comprising a toothed wheel having an axis substantially perpendicular to the patient&#39;s body, the first drive system comprising an endless screw fixedly attached to the shaft and capable of cooperating with the toothed wheel to rotate the toothed wheel around its axis.  
         [0022]     According to an object of the present invention, the second portion is pivotally assembled on the mobile ring along an axis substantially tangent to the patient&#39;s body, a toothed wheel sector being attached to the mobile ring, the second portion comprising an endless screw cooperating with the toothed wheel sector, the shaft of the second drive system rotating the endless screw.  
         [0023]     According to an object of the present invention, the means for supporting the device comprise a third portion slidably assembled on the second portion and connected to the device, the system comprising a third system for driving the third portion with respect to the second portion.  
         [0024]     The foregoing objects, features, and advantages of the present invention, as well as others, will be discussed in detail in the following non-limiting description of a specific example of embodiment in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a simplified top view of an example of the forming of a positioning system according to the present invention;  
         [0026]      FIG. 2  is a perspective view of a portion of the positioning system of  FIG. 1 ;  
         [0027]      FIG. 3  is a simplified view illustrating the operation of an actuator of the positioning system according to the present invention;  
         [0028]      FIG. 4  is a cut-away view of a portion of  FIG. 1 ; and  
         [0029]      FIG. 5  is a cut-away view of a portion of  FIG. 1 .  
     
    
     DETAILED DESCRIPTION  
       [0030]     For clarity, same elements have been designated with same reference numerals in the different drawings.  
         [0031]      FIGS. 1 and 2  show an example of the forming of positioning system  10  according to the present invention. Positioning system  10  comprises a frame  12 , formed of two lateral members  13 ,  14 , an upper member  15 , and a lower member  16 . Positioning system  10  is intended, for example, to be placed at the level of the abdomen, the thorax, or the back of a patient who is, for example, lying on an operating table. Lateral walls  13 ,  14  of frame  12  are then attached to the operating table, upper and lower walls  15 ,  16  overstriding the patient&#39;s abdomen, thorax, or back.  
         [0032]     Two drive systems  18  are attached on each lateral members  13 ,  14 . The drive systems are attached, for example, substantially symmetrically with respect to the center of frame  12 . Each drive system  18  is capable of exerting a stronger or lighter traction on a flexible strip  20  having an end connected to a loop  22 . The four loops  22  are pivotally assembled at the four ends of a substantially rectangular base  24  and laid on the patient&#39;s abdomen, thorax, or back. The control of drive systems  18  enables exerting different tractions on flexible strips  20 , causing the displacement of base  24  on the patient&#39;s abdomen, thorax, or back.  
         [0033]     Base  24  supports a mobile ring  26  of axis Δ substantially perpendicular to the plane tangent to the abdomen, to the thorax, or to the back at the level where the incision must be performed. Mobile ring  26  is rotatably assembled around axis Δ on base  24  via a bearing, not shown.  
         [0034]     A stirrup  28  is pivotally assembled on mobile ring  26  along an axis Γ substantially perpendicular to axis Δ, and substantially comprised in the plane tangent to the abdomen, to the thorax, or to the back at the incision level. A head  30  is slidably assembled on stirrup  28 . Head  30  comprises pliers  31  intended to receive an observation and/or intervention device (not shown), for example, a puncture needle penetrating into the patient through a small incision. Head  30  may be displaced with respect to stirrup  28  to be brought closer or moved away from the patient. A drive system  32  is attached to base  24  and enables driving mobile ring  26  around axis Δ with respect to base  24 . A drive system  34  is attached to stirrup  28  and enables pivoting stirrup  28  with respect to mobile ring  26  around axis Γ. A drive system  36  is attached to stirrup  28  and enables causing the displacement of head  30  with respect to stirrup  28  to bring it closer or move it away from the patient. Positioning system  10  may comprise a drive system, not shown, capable of actuating pliers  31  or head  30 . All drive systems  18 ,  32 ,  34 , and  36  according to the present invention have a similar structure.  
         [0035]      FIG. 3  illustrates the operating principle of an actuation system  45  which forms the base element of each drive system  18 ,  32 ,  34 , and  36  of the positioning system according to the present invention.  
         [0036]     Actuation system  45  comprises an output shaft  50  on which is assembled a ratchet wheel  51 . Ratchet wheel  51  comprises dissymmetrical teeth  52 , each comprising a first face  53 A and a second face  53 B. First face  53 A is comprised within a plane containing the axis of wheel  51  and second face  53 B is comprised within a plane inclined with respect to the plane of the corresponding first face  53 A. The rotating of ratchet wheel  51  is performed by rod  54  of a piston  55 . Rod  54  supports at one end a bearing element  56  assembled on the end of rod  54  around an axis parallel to the axis of shaft  50 , to be able to pivot with respect to rod  54  from an idle position in the rotation direction indicated by arrow  57 . From the idle position shown in  FIG. 3 , bearing element  56  cannot pivot with respect to rod  54  in the rotation direction opposite to arrow  57 . Bearing element  56  comprises a bearing surface  58  capable of cooperating with first face  53 A and second face  53 B of dissymmetrical teeth  52  of ratchet wheel  51  on displacement of rod  54 . Piston  55  is capable of sliding rod  54  in the direction indicated by arrow  60  or in the opposite direction. Advantageously, piston  55  is a dual-effect air piston comprising an enclosure  64  in which a wall  66  tightly separating enclosure  64  in two chambers  68 ,  70  can slide. Each chamber  68 ,  70  may be supplied with air under pressure, for example, compressed air under three bars, through openings  72 ,  74  connected to feed pipes  76 ,  78 . Stops  79  are provided in each chamber  68 ,  70  to limit the travel of wall  66  and thus the travel of rod  54 .  
         [0037]     The operating principle of actuation system  45  is the following. Ratchet wheel  51  is in an idle position such that first face  53 A of a tooth  52  is substantially parallel to bearing surface  58 . When rod  54  displaces along the direction indicated by arrow  60 , which means that air under pressure is sent into chamber  68 , bearing surface  58  of bearing element  56  bears against first face  53 A of a tooth  52  of wheel  51 . Since bearing element  56  then cannot pivot with respect to rod  54 , it exerts a thrust on tooth  52 , which causes the rotating of wheel  51  in the rotation direction indicated by arrow  80  while head  58  cooperates with tooth  52 . At one time, the progress of rod  54  and the rotating of wheel  51  are such that bearing element  56  is no longer in contact with tooth  52 , immobilizing wheel  51 . Wheel  51  has then generally moved by a determined angle which corresponds to the angle between two planes containing two first faces  53 A of two adjacent teeth  52  of wheel  51 .  
         [0038]     When rod  54  is placed along the direction opposite to arrow  60 , which means that air under pressure is sent into chamber  70 , bearing element  56  comes into contact with another tooth of wheel  51  that then takes up the initial place where the tooth with which bearing element  56  has come into contact in the previous motion of rod  54  used to be. Bearing element  56  then pivots with respect to rod  54 . No action is thus applied by bearing element  56  on ratchet wheel  51 . Ratchet wheel  51  is then not rotated in a back motion of rod  54 .  
         [0039]      FIG. 4  shows a cut-away view of drive system  32 . Drive system  32  comprises two actuation systems  45  such as previously described, and which have the same output shaft  50 . The actuation systems are arranged at the level of each end of shaft  50 . An endless screw  81  is assembled to move along with shaft  50 . Actuation systems  45  are arranged so that the driving of a ratchet wheel of one of the actuation systems causes the rotating of shaft  50  in a rotation direction and the driving of the ratchet wheel of the other actuation system causes the rotating of shaft  50  in the opposite rotation direction. Mobile ring  26  comprises a toothed wheel  82  which permanently meshes with endless screw  81 . A rotation of endless screw  81  then rotates toothed wheel  82  around axis Δ. A reciprocal motion of the piston  55  of an actuation system  45  causing the rotation of the associated ratchet wheel  51  by a determined angle, this results in a rotation by an also determined angle of toothed wheel  82 . The rotation of toothed wheel  82 , and thus of mobile ring  26 , with respect to base  24  can thus be controlled by the control of the two actuation systems  45  of drive system  32 .  
         [0040]      FIG. 5  shows a cut-away view of drive system  18 . Drive system  18  comprises two actuation systems  45 , such as previously described, and which have the same output shaft  50 . The actuation systems are arranged at the level of a same end of shaft  50 . An endless screw  90  is assembled to move along with shaft  50 . Actuation systems  45  are arranged so that the driving of a ratchet wheel  51  of one of the actuation systems causes the rotating of shaft  50  in a rotation direction and the driving of ratchet wheel  51  of the other actuation system causes the rotation of wheel  50  in the opposite rotation direction. Endless screw  90  cooperates with a toothed wheel  92  coaxially assembled with a pulley  94  on which flexible strip  20  is wound. A reciprocal motion of a piston  55  of an actuation system  45  causing the rotation of an associated ratchet wheel  51  by a determined angle, this results in a displacement of a determined length of flexible strip  20  (which depends on the strip length wound around pulley  94 ). The rotation of toothed wheel  82 , and thus the traction of flexible strip  20  can thus be controlled by the control of the two actuation systems  45  of drive system  18 .  
         [0041]     Drive systems  34 ,  36  have a structure similar to that of drive system  18 . As appears in further detail in FIGS.  1  and  2 , positioning system  10  comprises a toothed wheel sector  96  attached to mobile ring  26 . An endless screw  98  is rotatably assembled on stirrup  28  while being maintained fixed in translation along its axis with respect to stirrup  28 . Endless screw  98  cooperates with toothed wheel sector  96  and is rotated by a transmission gear wheel  100 , itself driven by the common output shaft  50  of actuation systems  45  of drive system  34 .  
         [0042]     Similarly, the displacement of head  30  with respect to stirrup  28  may be obtained by an endless screw (not shown) driven by the common output shaft of actuation systems  45  of drive system  36  and which cooperates with a finger provided at the level of head  30 .  
         [0043]     The feed pipes of the pistons of the actuation systems of drive systems  18 ,  32 ,  34 , and  36  are connected to a control package containing valves controlled by means of a computer.  
         [0044]     The displacement motion of head  30  with respect to stirrup  28  may be performed in two steps. A fast displacement of head  30  may be obtained by means of an air piston, not shown, having its rod directly driving head  30 . This especially enables piercing the skin or capsules of certain organs. A slow displacement of head  30  with respect to stirrup  28  can then be obtained by drive system  36 .  
         [0045]     According to a variation of the present invention, the pistons associated with the ratchet wheels may be hydraulic pistons.  
         [0046]     The present invention enables forming all the components of the previously-described drive systems in materials “compatible” with scanner imaging or MRI methods. These are materials, such as for example plastic materials, which leave no or little marks on images obtained by such imaging methods, or materials, such as for example, titanium, carbon fibers, ceramics, etc., which, although they can leave marks on the obtained images, do not modify the rest of the images. Further, in the case where the fluid used by the pistons of the actuation systems is air, the presence of marks on images obtained by scanner or MRI is further reduced.  
         [0047]     Further, since the previously-described drive systems may be formed of materials from among plastic matters, titanium, ceramics, carbon fibers, etc., the replacing or the sterilization thereof may easily be provided on each operation to fulfill the sterilization constraints imposed by the envisaged operation. Further, in the case where the fluid used by the pistons of the actuation systems is air, infection risks are limited in case of a leakage at the piston level.  
         [0048]     Of course, the present invention is likely to have various alterations and modifications which will readily occur to those skilled in the art. In particular, in the previously-described example of embodiment, the different motions of the robot are obtained in each case by the driving of a shaft by means of a ratchet wheel, itself actuated by a mobile piston. A rectilinear bar comprising dissymmetrical teeth similar to the teeth of a ratchet wheel may as a variation be provided. The bar displacement would then be performed similarly to what has been previously described via a piston rod. Further, in the previously-described example of embodiment, the pistons are of dual-effect type. Single-acting pistons may of course be provided, the return motion of the piston rod being then obtained by a pull-back system, for example, a spring. Moreover, the flexible strips connected to the base may be replaced with cables or threads.  
         [0049]     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.