Abstract:
A system for performing a medical intervention in a subject&#39;s body includes a medical device ( 10 ) having several segments ( 12, 15 ) to be navigated through the body lumens; an external magnet; and a control unit connected with the magnet. The magnet generates control signals for the external magnet to generate a magnetic field (B) having a direction ( 40 ) to orient a magnetically responsive element ( 25 ) in the distal end portion ( 20 ) of the medical device ( 10 ), especially to cause the distal end portion ( 20 ) of the medical device ( 10 ) to bend in a given direction ( 30 ) for improving navigation. The control unit is configured to limit the generation of control signals for the external magnet that the direction ( 40 ) of the magnetic field (B) is limited within a field limiting frame ( 60 ) around the longitudinal axis ( 30 ) of the distal end portion ( 20 ) of the medical device ( 10 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The instant application claims the priority date of Feb. 6, 2015, the filing date of European patent application EP 15 154 187.7. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a system for performing a medical intervention in a subject&#39;s body, or in other words a system for interventional navigation with a medical device, wherein the medical device comprises several segments to be navigated through the body lumens or cavities, an external magnet and a control unit connected with the external magnet adapted to generate control signals for the external magnet to generate a magnetic field to orient a magnetically responsive element in the distal end portion of the medical device, especially to cause the distal end of the medical device to bend in a given direction for improving navigation. The invention is also related to a method for interventional navigation with such a medical device. 
         [0003]    A variety of techniques are available to physicians for advancing elongated medical devices such as catheters, endoscopes and other surgical tools within a patient&#39;s body. When such an elongated medical device is advanced deeper within the patient&#39;s body, the advancing device becomes correspondingly more difficult to control, especially when the distal end has to corner sharply. However, especially during some medical procedures such as cardiac interventions, it is important that the advancing of the elongated medical device occurs in a very controlled and precise manner where the risk of a perforation or injury of the patient is minimized. It is also important that the physician&#39;s fatigue during the medical procedure is minimized. 
         [0004]    A system for performing a medical intervention in a patient&#39;s body is known from EP 2 620 109 A1 and relates to a magnetic clot disruptor comprising a magnetic wire, which is used to disrupt a clot within a body vessel. The wire includes a magnet that is positioned within the patient&#39;s body adjacent the clot. A magnetic driver is positioned outside the patient&#39;s body in proximity to the magnet. When the magnetic field of the magnetic driver is alternated, the wire moves within the body vessel to break up the clot. The control unit alternating the magnetic field switches the direction of the magnetic field between two directions, but since the distal end is positioned near the clot to be destroyed, it is pressed laterally into the clot and breaks it up. No further steering function is disclosed. 
         [0005]    U.S. Pat. No. 8,551,109 B2 relates to an apparatus and method for interventional navigation within a subject&#39;s body in which a medical device having at least one electrostrictive element is adapted to cause the distal end of the medical device to bend in a given direction for improving navigation. The medical device may further comprise at least one magnetically responsive element on the distal end, which may be oriented in the approximate direction of a magnetic field that is applied to the subject&#39;s body. At least one method for navigating a medical device though a subject&#39;s body is provided, by changing the direction of an applied magnetic field to align a magnetically responsive element on the distal end for orienting the distal end, and by applying a voltage to at least one electrostrictive element disposed in the distal portion of the device for causing the distal end to change orientation from that achieved by application of the magnetic field alone. 
         [0006]    Therefore the effect of the external magnetic field is supported and enhanced by an additional force factor provided by electrostrictive elements in the distal end of the medical device. The improvement according to this prior art complicates the work of a physician since he has to control two electro-magnetic actuators, one external magnetic field and one voltage directly acting on the electrostrictive element. 
         [0007]    DE 10 2010 043 481 A discloses a medicine system with aligning control unit that controls the relative position of a magnetic element such that the field axis is parallel to the rotational axis of the magnetic element. The medical system comprises a position detection system and a control unit. The position detection system detects the relative position between the rotation axis of the magnetic element and the field axis. The magnetic field is rotated in a direction that the power or the full torque is fully available for the rotation of the magnetic element. 
         [0008]    WO 2008/003059 relates to a further electrostriction device and method for assisted magnetic navigation by bending the distal end of the medical device comprising a magnetically responsive element in a given direction for improving navigation. A method for navigating a medical device though a subject&#39;s body changes the direction of an applied magnetic field to align the magnetically responsive element on the distal end for orienting the distal end, and by applying a voltage to at least one electrostrictive element disposed in the distal portion of the device the distal end changes orientation from that achieved by application of the magnetic field alone. 
         [0009]    U.S. Pat. No. 6,173,199 B1 relates to a catheter having a distal end portion including a sensor responsive to the presence of a magnetic field or flux of a predetermined strength. The sensor is selected to respond when the distal end portion of the catheter is exposed to a magnetic field, such as provided by the external magnet, sufficient to capture and maneuver the distal end of the catheter. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide an improved system for orienting an elongated medical device, in particular a catheter, which allows for a precise movement based on a single electro-magnetic effector and avoids negative impact from the misalignment between the magnetic field and the magnetic distal end of the medical device, which can, as will be explained in connection with the drawings, lead to a torque based flip of the distal end of the and thus to damaging nearby lumen walls. 
         [0011]    This object is achieved by a system for performing a medical intervention in a subject&#39;s body, comprising a medical device comprising several segments to be navigated through the body lumens or cavities; one or more external magnets; and a control unit connected with the external magnet(s) adapted and configured to generate control signals for the external magnet(s) to generate a magnetic field having a direction to orient a magnetically responsive element in the distal end portion of the medical device, especially to cause the distal end portion of the medical device to bend in a given direction for improving navigation. 
         [0012]    In other words the magnetic field generated through control signals from the control unit has a specific direction which is—in the control mode—not parallel to the distal end of the medical device. If it is parallel at a point in time, then no more bending takes place, and the distal end is directed in the direction as provided by the control unit. Usually, the navigation comprises an advancing (or retreating) of the medical device. The medical device is usually a catheter with a long proximal part extending through, for example, the blood vessel system of a patient. The orientation of proximal part is at that time no longer of interest, since the navigation issues are related to the distal part. There, an initial, sometimes incremental advance always takes place in the direction of the magnetic field. Then the advance necessitates a direction change. The person using the system uses the control unit for the external magnetic field to change the direction of this magnetic field, for example, diverts the direction of the magnetic field from the parallel alignment with the distal end. 
         [0013]    This control change can be performed via a switch, if the new orientation in the 3D space is known and predetermined, or the control change can be performed by incremental changes of the angle of the magnetic field, starting from an alignment with the distal end. These changes starting from the direction defined by the direction of the distal end can be limited to a specific plane or open the entire cone with the cone tip virtually located at the bending point or a portion of the distal end, that is, in its prolongation. 
         [0014]    According to the invention, the control unit is adapted and configured to allow limiting of the generation of control signals for the external magnet in such a way that the direction of the new magnetic field generated after the accomplishment of the orientation change of the magnetic field is limited within a field limiting frame around the longitudinal axis of the distal end portion of the medical device. 
         [0015]    In other words, the control unit, being adjusted to a first magnetic field direction, preferably in the direction of the distal end, now receiving a control input defining a second magnetic field direction, generates control signals for the magnetic field orientation, for example, turning the external magnets or controlling the overlapping magnetic field of several electric magnets, only up to a second magnetic field direction which is inside the predetermined field limiting frame. 
         [0016]    The control unit is configured to store a first direction, especially the current direction of the magnetic field or the current direction of the distal end, as starting direction for the following limitation step. The control unit is configured, for example, through lapse of a time interval or by initiation of a user, to store this first direction temporarily until the next separated bending and advancing step. This storage action can be initiated in common or separately by fixing a field limiting frame for the external magnet. The fixation of the field limiting frame for the external magnet allows the generation of control signals for the external magnet to determine the direction of the magnetic field in such a way that the direction of the magnetic field is limited within such a field limiting frame around the stored first direction, that is, the longitudinal axis of the distal end portion of the medical device at the time of initiating the present bending and advancing step. That is, that the central axis of the cone is predetermined to be in line with the longitudinal axis direction of the magnetic tip or the distal end, respectively, of the medical device, at that initiating step. 
         [0017]    It is preferred that the user of the system can give said calibrating and limiting order by pushing a button, for example or, if after a specific time of having oriented the distal end in a first direction, the calibration automatically takes place in the first direction, and the limiting frame is defined when the user diverts from the original first direction towards a second direction having an angle in comparison to the first direction being beyond a predefined threshold angle, for example, 2 or 5 degrees. 
         [0018]    It is of course possible that there is not only one external magnet; the system can comprise two or more external magnets. 
         [0019]    In an embodiment of the system, the field limiting frame is a cone. It can have an inverted regular form having a regular constant or adjustable opening angle around the central axis of the cone. It can be taken from the group of base surfaces being a circle, an ellipse, the shape of a bone or another simple closed curve. 
         [0020]    A further embodiment of the system has a central axis of the cone which is predetermined to be in line with the longitudinal axis direction of the magnetic tip or the distal end, respectively, of the medical device. 
         [0021]    The control unit can comprise a switch or button to enable or disable the field limiting frame. Then it switches the limiting opening angle on or off. Furthermore, the limiting opening angle can be adjusted from 90° to 140° divergence to the first direction. 
         [0022]    A medical device, especially for use within a system according to the invention, in addition to the magnetic tip, comprises at least one further magnetic segment with non-magnetic flexible shaft portions between magnet segments(s) and/or the magnetic tip, respectively, wherein optionally the field limiting frame is provided with its main axis along the orientation of the magnetic tip. 
         [0023]    A method for moving the distal end of an elongated medical device, in particular a catheter, by means of a magnetic field, is provided. A method of performing a medical intervention in a subject&#39;s body comprises navigation of at least one medical device comprising several segments through the body lumens or cavities, the navigation method comprising the step of applying a magnetic field to orient a magnetically responsive element in the distal end portion of the medical device and advancing the device, and further comprising the step of limiting the direction of the magnetic field within a field limiting frame around the longitudinal axis of the distal end portion of the medical device for any subsequent bending and/or navigating step. Navigating steps are steps where the medical device is pushed or retracted, that is, performs a longitudinal movement. 
         [0024]    Such a method can, according to an embodiment, combine the limiting function with an ablation step wherein the direction of the magnetic field is rotated along the borders of the field limiting frame. This can be done by a rotation along the bordering surface of an inverted cone, wherein the apex is on the main direction of the distal end portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings: 
           [0026]      FIG. 1  shows a schematic side view of a distal end of a medical device influenced by an external magnetic field; 
           [0027]      FIG. 2  shows a schematic side view of the distal end of the medical device of  FIG. 1  influenced by a magnetic field having a higher misalignment with the distal tip than the field of  FIG. 1 ; 
           [0028]      FIG. 3  shows a schematic side view of the distal end of the medical device of  FIG. 1  influenced by a magnetic field with even a higher misalignment than the field of  FIG. 2  and leading to a flip of the distal tip of the medical device; 
           [0029]      FIG. 4  shows a schematic side view of the distal end of the medical device of  FIG. 1  influenced by a magnetic field with a field reference frame avoiding a flip of the distal end of the medical device; 
           [0030]      FIG. 5  shows a side view of the distal end of the medical device of  FIG. 1  touching a lumen wall; 
           [0031]      FIG. 6  shows the situation of  FIG. 5  after a slipping incident; 
           [0032]      FIG. 7  shows the preparatory situation and position of a medical device before a circular ablation of vessel walls; 
           [0033]      FIG. 8  shows the advantage of applying the limiting field alignment in the situation of  FIG. 7 ; and 
           [0034]      FIG. 9  shows a specific multi-segment medical device according to a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]      FIG. 1  to  FIG. 3  show schematic side views of a distal end  20  of a medical device  10  influenced by a magnetic field B having the direction of arrow  40 . The distal end  20  is essentially straight and has one well defined direction  30  along its longitudinal axis. The medical device  10  further comprises a flexible shaft  12  allowing the bending of the distal end  20  compared to the more distant portions  15  of the medical device  20 . 
         [0036]    The distal end  20  comprises a magnetic tip  25 . The magnetic tip  25  can be a solid or a sleeve around a core of the central medical device  10 ; it comprises preferably ferromagnetic material but can be composed of any material which can be influenced by the external magnetic field B having the direction  40 . Magnetic tip  25  is not necessarily at the free end of the medical device  10 , but can also be provided at a short distance from the free end. The length of the magnetic tip  25  can have a length of between 5 and 20 mm, for example, while having a diameter of 3 to 8 mm, for example. 
         [0037]      FIG. 2  shows the medical device  10  of  FIG. 1  influenced by a magnetic field with an orientation according to arrow  40  having a higher misalignment angle  45  than the misalignment angle between the field  40  and the longitudinal direction  30  of the magnetic tip  25  of  FIG. 1 . Reference numeral  50  indicates the torque T influencing the distal tip  25  to follow the direction  40  of magnetic field B leading to a higher bend and curvature of the distal end  20  of the medical device  10 . In other words, the misalignment angle between field direction  40  and magnetic tip  25  increases with increasing device deformation, for example, of a catheter, since even if the medical device  10  is not stiff, it has an increasing resistance against bending with higher bending angles. 
         [0038]    In different situations, a physician is nevertheless obliged to bend the distal portion  20  of the medical device  10  even more, for example, to direct the tip of the medical device into a blood vessel having an angle of more than 90° or 120°, for example, in view of the larger vessel, where the not so distant parts  15  of the medical device  10  are provided.  FIG. 3  shows such a situation where the magnetic tip  25  should even bend more. The misalignment angle  45  between the direction  40  of the magnetic field band and the direction  20  of the distal tip  20  is greater than 90°, whereas the right angle is shown with the axis as dotted line  46  being perpendicular to the general direction  30  of the distal tip  25  of the medical device  10 . In such a case, the direction of torque T according to the arrow  52  flips over and the distal tip  20 , instead of bending further and following the direction of the magnetic field B in its direction  40 , flips over to the opposite direction. This might be dangerous especially if there is a vessel wall on the other side, where the flip occurs. The situation is problematic for the physician, since the distal tip  20  may be scraping along a lumen wall and when freed, flips over. Another problem resides in the fact that the physician has to direct the distal tip  20  in a 3D environment and the misalignment angle  45  in the 2D representation as in  FIGS. 1 to 3  may misguide him in the evaluation of the effective angle of misalignment  45 . Additionally the direction of magnetic field  30  is not visible as such. 
         [0039]      FIG. 4  shows a schematic side view of the distal end of the medical device of  FIG. 1  influenced by a magnetic field B having the orientation  40  with a field limiting frame  60  avoiding a flip of the medical device  10 . The field limiting frame  60  is shown as two lines opening a cone. The cone is a three-dimensional geometric shape that widens from a point  62  called the apex or vertex to a virtual base (frequently, though not necessarily, circular, as shown in  FIG. 7 ). It is preferred that the cone is an inverted regular form having a regular constant opening angle  64  around the central axis of the cone. The axis of the cone is the straight line, passing through the apex, about which the virtual base (not shown) and the whole cone has a rotational symmetry and which is in line with the longitudinal axis direction  30  of the magnetic tip  25  or the distal end  20 , respectively. This is the cone according to the embodiment shown in  FIG. 4 . Of course, it is not necessary that the cone is a regular constant cone, it can have a changing opening angle. For example, the opening angle can provide not a circle as base line but an ellipse or another form. It is also not necessary that the surface of the cone is always convex; it can be any simple closed curve. Furthermore, it is possible that the cone form can be chosen within the control unit beforehand; that is, the cone angle is adjustable. This can also comprise a switch between different cone forms, for example, between a circular base to an elliptic base to a base having the “shape of a bone” or any other simple closed curve. 
         [0040]    In view of the direction  40  of the magnetic field B, the field limiting frame  60  can directly be applied to the axis  30  of the magnetic tip  25 . The magnetic field is controlled through a control unit predetermining the strength and the direction  40  of the magnetic field B. The system according to an embodiment of the invention comprises a field limiting function. This field limiting function can comprise a control button providing a value of a field limiting frame  60  comprising an opening angle fixed in the 3D space around the direction  30  of the distal tip  25  at the moment of actuation of this control button or after the actuation of the control button. 
         [0041]    In other words, the physician evaluates the position of the distal tip  20  and the existing pre-bending condition, for example, before he evaluates next advancing and bending steps of the medical device  10 , if he has to turn the tip  20  of the medical device  10  into a new direction without being guided by the walls of a lumen. According to prior art devices, the physician makes the decision that the turning movement will be feasible without risking the situation of  FIG. 3 . According to the invention, the system allows the limiting directions for the magnetic field direction  30  to be fixed by fixing its opening angle through the field limiting frame  60 . Then the physician can advance the medical device  10  and bend the distal tip  20  through manipulating the direction  40  and or strength of the magnetic field B, since the misalignment angle  45  is limited by the predefined limiting cone angle  64 . The field limiting frame  60  angle  64  can be 90° to 140°, for example. 
         [0042]    In other words, the distal tip  20  is oriented along a first direction  30  through former advancing steps. This can comprise an ongoing bending as shown in  FIG. 4  with a bent flexible shaft  12 . Nevertheless,  FIG. 4  shows a specific point in time before the next control step. Either the control unit senses through measuring a time interval via a threshold of non-action that the current first direction  30  of the distal end is to be taken as originating direction or the user of the system pushes a button to define said first direction  30 . Then the physician makes the decision to turn the distal end for the next treatment or advance step. The field frame limiting decision is either made by the physician through actuation of a button or automatically from the predefined first direction. The control unit, in either case, is built and configured to allow generation of control signals for the orientation of the external magnet in a way that the distal end  20 —after execution of the new orientation of the external magnet—can only be oriented up to a second new direction which is limited by the directions of the field limiting frame  60  or cone around the longitudinal axis of the distal end portion of the medical device prior to the new orientation, which is stored at the calibration step in the control unit for this navigation or bending step. 
         [0043]    In other words, the new direction of the distal tip  25  after the bending is at most the limiting directions provided by the field limiting frame  60  as a cone, for example, or any direction in between. 
         [0044]      FIG. 5  shows a side view of the distal end  20  of the medical device  10  of  FIG. 1  touching a lumen wall  70 .  FIG. 6  shows the situation of  FIG. 5  after a slipping incident, where the final position of the magnetic tip  25  is limited by the (maximum) opening angle of the field limiting frame  60 . Here, the physician recognizes that the tip  25  touches the lumen wall  70  and blocks the motion in the situation of  FIG. 5  before trying to move the distal end  20 . When the slipping incident occurs, the orientation  30  of the distal end  20  cannot go beyond the orientation of the magnetic field B when the direction  40  of the magnetic field B is in line with the angle opening line of the cone as defined before the bending step at the limit engaging step at  FIG. 4  through storing the former direction  30  as first direction and defining direction for the field limiting frame or cone  60  for any new second direction. 
         [0045]      FIG. 7  shows the preparatory situation and position of a medical device  10  before a circular ablation  80  of vessel walls  72 , and  FIG. 8  shows the advantage of applying the field limiting frame  60  in the situation of  FIG. 7 . The medical device  10  is pushed and bent into the opening of a pulmonary vein, for example, so that the direction  40  of the magnetic field B is in alignment with the direction  30  of the magnetic tip  25  of the medical device  10 . Then the control unit is activated to fix the opening angle  64  of the field limiting frame  60 ; here the limited opening angle  64  can be chosen to be smaller so that the use of the maximum misalignment angle exerts a predetermined force. Then the circular ablation is effected and forms the circular ablation edge  80 . 
         [0046]      FIG. 9  shows a specific multi-segment medical device  100  according to a further embodiment of the invention. In addition to the magnetic tip  25 , at least one, here two further magnetic segments  125  are provided with inserted non-magnetic flexible shaft portions  112 . The magnetic segments  125  can be solid segments with non-magnetic flexible shaft portions  112  attached or they can comprise a sleeve attached to a continuous non-magnetic flexible shaft material. 
         [0047]    The segments  25 ,  125  can have a length of 8 to 15 mm, whereas the shaft portions  112  can have the same length or be up to 2 times longer. 
         [0048]    The externally applied magnetic field can be at about 0.1 to 0.15 Tesla, to orient the magnetically responsive tip  25  and magnetic segments  125  of the medical device  10  or  100 . 
         [0049]    The specification incorporates by reference the disclosure of EP 15 154 187.7, filed Feb. 6, 2015. 
         [0050]    The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of Reference Numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 medical device 
               
               
                 12 
                 flexible shaft 
               
               
                 15 
                 distant portion 
               
               
                 20 
                 distal end 
               
               
                 25 
                 magnetic tip 
               
               
                 30 
                 orientation of distal end 
               
               
                 40 
                 orientation of magnetic field 
               
               
                 45 
                 angle of misalignment 
               
               
                 46 
                 90 degree angle 
               
               
                 50 
                 direction of torque 
               
               
                 52 
                 direction of torque 
               
               
                 60 
                 field limiting frame 
               
               
                 62 
                 apex 
               
               
                 64 
                 opening angle 
               
               
                 66 
                 virtual base of the cone 
               
               
                 70 
                 lumen wall 
               
               
                 80 
                 ablation edge 
               
               
                 100 
                 multi-segment medical device 
               
               
                 112 
                 flexible shaft portion 
               
               
                 125 
                 magnetic segment