Patent Publication Number: US-2015080713-A1

Title: Intracorporeal imaging aid (ima)

Description:
RELATED APPLICATIONS 
     The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application 61/623,404 filed on Apr. 12, 2012, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to devices for imaging internal features of the body. 
     BACKGROUND 
     The aortic valve is located in the wall of the left ventricle at the entrance of the aorta and operates to prevent blood pumped by the left ventricle into the aorta from flowing back into the heart. The aortic valve may become leaky or blocked, causing a condition known as aortic insufficiency. In such patients, replacement of the aortic valve may be recommended. Transcatheter Aortic Valve Implantation (TAVI) is a procedure in which a patient&#39;s defective aortic valve is replaced with a prosthetic valve in a procedure using a catheter, rather than in a procedure involving sternotomy, opening the patient&#39;s chest cavity. Advantages of TAVI over sternotomy include reduced risk of medical complication and shorter recovery times. 
     A difficulty in performing TAVI is ensuring proper placement of the prosthetic valve, in the place of the defective valve. Improper placement of the prosthetic heart valve may not cure the patient&#39;s aortic valve complication, and may even cause harm to the patient by blocking proper blood flow and cause additional complications. This difficulty in performing TAVI stems from the fact that heart tissue is difficult to visualize using standard imaging procedures that are typically employed to guide a surgeon in performing the procedure. 
     SUMMARY 
     An aspect of an embodiment of the invention relates to providing apparatus, hereinafter referred to as an intracorporeal imaging aid (IMA), for positioning markers that are readily imaged using a conventional medical imaging modality on a surface of an internal body tissue to aid in identifying and making a location of the surface visible using the imaging modality. The markers may be referred to as tissue markers. An exemplary surface which may be identified using an IMA is the surface of the aortic valve and/or tissue surrounding the aortic valve. 
     In an embodiment of the invention, an IMA comprises a marker support comprising at least three elastically deformable support filaments each comprising at least one tissue marker, and having distal and proximal ends. Each tissue marker may be located on or in the filament substantially midway between the distal and proximal ends of the filament in a region referred to as an abutment region. The marker support may further comprise a cylindrical distal collar, to which the distal ends of the filaments are connected. The marker support may also comprise a cylindrical proximal collar, to which the proximal ends of the filaments are optionally connected. The marker support has a collapsed state and a deployed state. 
     In the collapsed state, the distal and proximal ends of each filament are substantially maximally apart and the filaments lie within a relatively small radial distance from the axis of the marker support. In an embodiment of the invention, the radial distance is small enough so that the IMA may be introduced into the body using a catheter deployment system having dimensions adapted for introduction through the cardiovascular system and passage through the aortic valve. The marker support may be positioned on a guidewire while introduced into the body, and deployment may occur while the marker support is located on the guidewire. 
     The IMA may be brought to the deployed state by moving the distal and proximal ends of the marker support towards each other until they are within a predetermined deployed distance, at which the marker support may be maintained deployed in the stable state. In the deployed state, at initial stages of deployment, the filaments may form loop-like, substantially planar structures whose planes extend along radial directions substantially from the axis of the marker support. Upon further motion of the proximal and distal collars towards each other, the loop-like structures, hereinafter also referred to as “support loops”, contort and rotate away from their initial respective radial directions. When the proximal and distal collars are within the predetermined deployment distance, each of the support loops has a proximal end that comprises the abutment region of the loop&#39;s filament, and projections of the abutment regions on a plane perpendicular to the axis of the IMA lie along the sides of a polygon, hereinafter referred to as a projection polygon. For an IMA in accordance with an embodiment of the invention comprising not more than three support filaments the projection polygon is a projection triangle. Optionally, the projection triangle is substantially an equilateral triangle. The shape of a support loop when the IMA is in the deployment state may be referred to as a “loop deployment shape”. 
     In an embodiment of the invention, each support filament is processed so that upon bringing the proximal and distal ends of the IMA within the deployment distance of each other, the filament naturally assumes the loop deployment shape. Optionally, processing the filament to assume the loop deployment shape comprises annealing the filament on a suitable mandrel or die that maintains the filament in the loop deployment shape during annealing and/or shape setting by heat treatment. In some embodiments of the invention, the filament is formed from a suitable shape memory or superelastic alloy treated to remember the loop deployment shape. 
     An IMA may be introduced in the collapsed state into and positioned inside a body using a suitable catheter and guide wire. In an embodiment of the invention, a deployment tube and guide wire may be used to move the distal and proximal ends of the IMA towards one another and bring the IMA from its collapsed state to its deployed state. In the deployed state inside the body the IMA may be moved proximally toward a tissue surface inside the body to be located so that the abutment regions of the support loops and their respective markers abut the tissue. An image of at least three markers acquired using a suitable medical imaging modality may be used to locate the markers and thereby determine orientation of a plane along which the abutted tissue substantially lies. 
     In an embodiment of the invention an IMA may be used to determine orientation of a planar region of tissue in which the aortic valve of a patient undergoing TAVI is located. Location of the planar region may be determined with relatively small risk of a support loop lodging in a commissure of the aortic valve because the support loops of a deployed IMA lie along sides of a polygon and thereby, in general, transverse to the valve commissures. 
     According to an embodiment of the invention, the marker support may further comprise a proximal deployment marker at its proximal end (either on a filament or on a collar) and a distal deployment marker at its distal end (either on a filament or on a collar.) The distance between the proximal marker and distal marker may be identified using an imaging modality to determine if the marker support is in a deployed state or in a collapsed state. 
     According to an embodiment of the invention, relative motion between proximal marker and distal marker may be identified using an imaging modality to determine if the marker support is properly placed against a surface of an internal body tissue. 
     In the discussion unless otherwise stated, adjectives such as “substantially” and “about” modifying a condition or relationship characteristic of a feature or features of an embodiment of the invention, are understood to mean that the condition or characteristic is defined to within tolerances that are acceptable for operation of the embodiment for an application for which it is intended. Unless otherwise indicated, the word “or” in the specification and claims is considered to be the inclusive “or” rather than the exclusive or, and indicates at least one of, or any combination of items it conjoins. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       Non-limiting examples of embodiments of the invention are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. 
         FIGS. 1A and 1B  show an IMA in closed configuration according to an embodiment of the invention; 
         FIG. 1C  shows an IMA according to an embodiment of the invention in collapsed configuration, in disassembled format; 
         FIG. 1D  shows distal ends of collapsed IMAs according to embodiments of the invention; 
         FIGS. 2A-2I  show cross-sectional views of the left ventricle of a patient with an IMA according to embodiments of the invention, at various stages of deployment. 
     
    
    
     DETAILED DESCRIPTION 
     As mentioned above, IMAs according to embodiments of the invention are useful in imaging a patient&#39;s aortic valve and in aiding in replacement thereof. IMAs according to embodiments of the invention may be used to aid in medical procedures performed in a minimally invasive manner, obviating the need for large incisions. 
     In addition to imaging the aortic valve, various other imaging procedures may be performed using IMAs according to embodiments of the invention. For example, cardiovascular structures such as vessels, arteries, veins, branches, occlusions, blockages, chambers and valves may be visualized. Gastrointestinal structures such as the throat, esophagus, stomach, duodenum, intestines, colon and blockages therein may also be visualized. Pulmonary structures such as trachea, bronchi and thorax may also be visualized. Uro-gynecological structures such as the ureter, bladder, cervix, uterus, fallopian tubes and blockages may also be visualized. 
     In addition to prosthetic valves, other medical devices may be positioned with devices according to embodiments of the invention including but not limited to, stents, catheters, balloon catheters, pace makers, radioactive medicines, therapeutics, cameras, laparoscopes, endoscopes and sterilization devices. 
     IMAs according to embodiments of the invention may be used to direct laparoscopic or endoscopic surgery or to visualize target anatomical structures with directed energy therapies such as radiation therapy. 
     The term distal refers to a direction away from the opening in the body along the axis of the guidewire or catheter used to insert the IMA. The term proximal refers to a direction towards the opening in the body along the axis of the guidewire or catheter. 
     Reference is now made to the figures which illustrate various embodiments of an IMA according to embodiments of the invention, adapted for the performance of TAVI. As shown in  FIGS. 1A ,  1 B and  1 C, (disassembled view) an IMA  10  is shown in a collapsed position. IMA  10  comprises a marker support  12  having a distal collar  14  and a proximal collar  16 . Proximal collar  16  comprises a proximal deployment marker  18 . Distal collar  14  comprises a distal deployment marker  24 . Marker support  12  comprises tissue markers  28 . 
     Marker support  12  is configured to be movably attached, with an ability to slide along a guidewire  30  (guidewire shown in  FIGS. 1B and 1C ). Marker support  12  is fixedly attached at proximal collar  16  to outer deployment tube  20  via connector  22 . Clip connector  26  is fixedly attached to guidewire  30 . Distal collar  14  of marker support  12  may be clipped to clip connector  26  as in  FIG. 1A  or unclipped as in  FIG. 1B . The portion of guidewire  30  shown in  FIGS. 1A-1C  is substantially coincident with the axis of IMA  10 . 
     Guidewire  30  may be coated with envelope  32 , at the distal end of guidewire  30 . 
     Marker support  12  may be formed from metals such as stainless steel, shape memory alloys, superelastic alloys, titanium alloys, surgical steel, zirconium alloys, niobium alloys, tantalum alloys, polymers or other flexible and medically safe materials. According to an embodiment of the invention, marker support  12  is made from a nickel-titanium alloy. Marker support  12  may be formed, for example by cutting filaments using laser cutting techniques or by using wires optionally attached to collars. Marker support  12  may be shaped in its deployed position (shown below in  FIGS. 2E-2H ) by shape setting in its deployed position. After being collapsed, marker support  12  may revert to its deployed position upon release of tension between distal and proximal ends of marker support  12  or by pushing proximal end and distal end towards each other. 
     According to an embodiment of the invention, marker support  12  is shaped, for example by annealing, in a manner that each filament comprises a single strand deformed to a position capable of forming a loop comprising an abutment member. 
     Tissue marker  28 , distal marker  24  and proximal marker  18  may all be formed from a radio-opaque material, preferably material which is easily discernible from native human tissue when using imaging techniques such as fluoroscopy, computed tomography (CT), ultrasound, magnetic resonance imaging (MRI), positron emission tomography (PET). In an embodiment of the invention, a marker may be formed from stainless steel, ceramic, titanium alloy, tungsten, zirconium, silver, platinum, tantalum or gold. 
     Guidewire  30  and outer deployment tube  20  may be formed using guidewires and deployment tubes known in the art. 
     As shown in  FIGS. 1A-1C , IMA  10  is in the collapsed state and has a tubular shape. The distal and proximal ends of each filament are substantially maximally apart and the filaments lie within a relatively small radial distance from the axis of the IMA, the axis being parallel and coincident with the guidewire. In an embodiment of the invention, the radial distance is small enough so that the IMA may be introduced into the body using a catheter deployment system having dimensions adapted for introduction through the cardiovascular system and passage through the aortic valve. 
     With reference to  FIG. 1D , IMA  10  is shown in collapsed state, using an enlarged view of distal collar  14 . Distal collar  14  comprises fingers  36 . Clip connector  26 , which is fixedly attached to guidewire  30 , comprises fingers  34 .  FIG. 1D  shows fingers  34  and  FIG. 36  in partially engaged position. In this partially engaged position, rotational movement of distal collar  14  relative to clip connector  26  (and relative to guidewire  30 , which is fixedly attached to clip connector  26 ) is limited due to the partial engagement of fingers  34  and fingers  36 . Upon applying significant force on marker support  12  in the distal direction, fingers  36  enter apertures formed between fingers  34 , thereby entering engaged position. In engaged position, application of significant force is required to detach clip connector  26  from distal collar  14 . For example, the force required to detach clip connector  26  from distal collar  14  is higher than the force required to transform marker support  12  from a deployed state to a collapsed state. 
       FIG. 1D  also shows IMA  40  according to an embodiment of the invention, with an enlarged view of a distal end of a marker support according to an embodiment of the invention. Marker support comprises fingers  48  and clip connector  46  comprises fingers  44 .  FIG. 1D  shows fingers  44  engaged with fingers  46 , thereby preventing rotational movement of marker support relative to clip connector  46 . Upon movement of marker support  12  in a proximal direction relative to clip connector  46  from the position shown in the figure, fingers  48  will disengage from fingers  44  without significant resistance. 
       FIGS. 2A-I  show cross sectional views of a patient&#39;s left ventricle  62 , surrounded by a left ventricle wall  66  at various stages of deployment of an IMA. 
       FIG. 2A  shows an IMA  10  positioned in collapsed configuration in the patient&#39;s left ventricle. IMA  10  is introduced through an aorta  60  via an aortic valve  64  in need of replacement. IMA  10  may be introduced in a catheter tube (not shown) which is then removed to allow for expansion of marker support  12 . 
     Inset  50  shows a projection of a plane perpendicular to guidewire  30 , viewed along the axis of deployment tube  20  and guidewire  30 , including aortic valve  64 . Aortic valve  64  comprises leaflets  68  which are separated by commissures  72  which separate leaflets  68  when valve  64  is closed. 
     In an embodiment of the invention, envelope  32  may have a curved tip to allow for positioning in the left ventricle as shown in  FIG. 2A , without puncturing heart tissue. In an embodiment of the invention, envelope  32  may be coated with a protective layer, for example, a coated wire, to prevent puncturing of heart tissue. Positioning of envelope  32  limits further movement of guidewire  30  in the distal direction. 
       FIG. 2B  shows an IMA  10  positioned in the patient&#39;s left ventricle, during the initiation of the deployment process. Upon movement of proximal collar  16  and distal collar  14  towards one another by, for example, distal movement of deployment tube  20 , marker support  12  is compressed, separating three deployable filaments, which begin to form loop-like structures. Each deployable filament comprises a tissue marker  28  and an abutment region  27 . 
     Inset  70  shows a projection of abutment regions  27  on a plane perpendicular to guidewire  30 , viewed along the axis of deployment tube  20  and guidewire  30 , including aortic valve  64 . Abutment regions  27  are shown extending in a radial direction from guidewire  30 , each loop defining a plane extending radially from the axis. 
       FIG. 2C  shows an IMA  10  positioned in the patient&#39;s left ventricle, during the deployment process, in a stage following the position shown in  FIG. 2B . Upon further movement of proximal collar  16  in the direction of distal collar  14 , filaments assume a loop-like configuration each loop defining a plane extending radially from the axis. 
     Inset  80  shows a projection of abutment regions  27  on a plane perpendicular to guidewire  30 , viewed along the axis of deployment tube  20  and guidewire  30 , including aortic valve  64 . Projection of abutment regions  27  extend in a radial direction from guidewire  30 . In such a formation, if marker support  12  is applied to aortic valve  64 , abutment regions  27  may enter commissures  72 , thereby providing an inaccurate image of location of aortic valve. 
     Upon further movement of proximal collar  16  and distal collar  14  towards each other, projection of abutment regions  27  begin to move relative to commissures  72  in the clockwise direction as indicated by arrows. 
       FIG. 2D  shows an IMA  10  positioned in the patient&#39;s left ventricle, during the deployment process, in a stage following the position shown in  FIG. 2C . 
     Upon further movement of proximal collar  16  and of distal collar  14  toward each other, marker support  12  is further distorted as loops further rotate away from their initial radial directions, and abutment regions  27  move to point in the proximal direction. 
     Inset  90  shows a projection of abutment regions  27  on a plane perpendicular to guidewire  30 , viewed along the axis of deployment tube  20  and guidewire  30 , including aortic valve  64 . Abutment regions  27  move in the clockwise direction as indicated by arrows. 
     In an embodiment of the invention, abutment regions  27  are moved in the counterclockwise direction upon distal compression of marker support  12 . 
     As mentioned with reference to  FIG. 1D , distal collar  14  of marker support  12  may be partially engaged with clip connector  26 , which is fixedly attached to guidewire  30 , to prevent rotational movement of distal collar  14  relative to clip connector  26  (and relative to guidewire  30 , which is fixedly attached to clip connector  26 .) This configuration allows marker support  12  to be aligned so that deployable elements avoid excessive contact with left ventricle wall  66  while deploying, thereby preventing entanglement of marker support  12  with left ventricle wall  66 . 
       FIG. 2E  shows an IMA  10  positioned in the patient&#39;s left ventricle, during the deployment process, in a stage following the position shown in  FIG. 2D . 
     Upon further movement of proximal collar  16  and distal collar  14  towards each other to a predetermined distance, support loops are rotated so that each loop defines a plane substantially normal to a vector extending radially from the axis. 
     Inset  90  shows a projection of abutment regions  27  on a plane perpendicular to guidewire  30 , viewed along the axis of deployment tube  20  and guidewire  30 , including aortic valve  64 . Projections of abutment regions on the plane form a polygon, in particular a substantially equilateral triangular shape. In the formation as shown in Inset  100 , abutment regions  27  may be placed on aortic valve  64  without the risk of misplacement which may be caused by an abutment region  27  entering a commissure  72 . 
     According to an embodiment of the invention, the projection polygon is a tangential polygon in which all sides of the polygon are tangent to an inscribed circle. According to an embodiment of the invention, the projection polygon is a rectangle, a square, a pentagon, a hexagon or an octagon. According to an embodiment of the invention, the polygon is an equiangular polygon. 
     Once marker support  12  has been deployed as in  FIG. 2E , it may be positioned against aortic valve as in  FIG. 2F . Loops formed by deployable filaments are substantially are pointed in a substantially proximal direction. Marker support  12  may be positioned against aortic valve by moving deployment tube  20  proximally relative to guidewire  30 . A medical practitioner may realize that a marker guide is properly positioned, for example, through feeling increased resistance while moving deployment tube  20  proximally when abutment members  27  of marker support  12  abut against aortic valve. 
     In an embodiment of the invention, proper deployment of marker support  12  may be verified by an imaging modality to determine if distance between the proximal deployment marker  18  and distal deployment marker  24  corresponds to a predetermined distance associated between the markers in deployed state. 
       FIG. 2F  shows abutment region  27  and tissue markers  28  abutted against aortic valve. Proximal deployment marker  18  and distal deployment marker  24  are shown and may be easily visualized relative to each other using imaging techniques. Proper deployment of marker support  12  may be verified by imaging relative motion of proximal deployment marker  18  away from distal deployment marker  24  upon gentle pulling of deployment tube  20  in the proximal direction, thereby slightly compressing marker support  12 . Upon distal motion, for example, by release of deployment tube  20 , and allowing marker support  12  to spring back in the distal direction, proximal deployment marker  18  moves towards distal deployment marker  24 . 
       FIG. 2G  shows a side view of marker support  12  positioned against aortic valve. A dotted line  110  indicates the plane defined by tissue markers  28  abutted against aortic valve. A prosthetic valve may be introduced, for example, using a guide tube external to deployment tube  20   
       FIG. 2H  shows introduction of a collapsed prosthetic valve  104  via valve guide  120 , having a valve marking  102 . Valve marking  102  may be imaged relative to tissue markers  28  to confirm proper alignment of compressed prosthetic valve  104  relative to a plane defined by tissue markers  28 , thereby confirming proper placement of prosthetic valve  104 . 
       FIG. 2I  shows expanded prosthetic valve  106  which is expanded, thereby replacing valve  64  upon verification of prosthetic valve location. Valve guide  120  may then be removed from the patient, and the removal of IMA may be initiated. 
     IMA may be removed by moving deployment tube  20  distally relative to guidewire  30 , thereby moving deployed marker support  12  distally. Upon contact of distal collar  14  with clip connector  26 , distal force may be applied to deployment tube  20  to clip distal collar  14  to clip connector  26 . Upon clipping, deployment tube  20  may be pulled proximally, thereby pulling proximal collar  16  of marker support  12  relative to guidewire  30  thereby closing marker support to a collapsed position as shown in  FIG. 2A . IMA may then be removed by introduction of a catheter external to deployment tube  20  and pulling of guidewire  30  and deployment tube  20  through the catheter. 
     In an embodiment of the invention, a distal collar may be configured to lock with a clip connector by rotation, for example using matching threading on the distal collar and the clip connector. Alternatively, the distal collar may be configured to lock with a clip connector using a quarter-turn locking mechanism. 
     In an embodiment of the invention, an IMA may be formed as in  FIG. 1A  with a modification of an intermediate tube configured to be attached and slidable surrounding the guidewire and beneath the deployment tube. A distal end of a marker support may be fixedly attached to the intermediate tube. A proximal end of a marker support may be fixedly attached to the outer deployment tube. Deployment of the marker support may occur through distal pushing of the outer deployment tube relative to the intermediate tube, or alternatively through proximal pulling of the intermediate tube relative to the outer deployment tube. Closing of the marker support may occur through distal pushing of the intermediate tube relative to the deployment tube, or alternatively by proximal pulling of the deployment tube relative to the intermediate tube. Such a configuration may allow for rapid collapsing and deployment of a marker support without a clip connector affixed to the guidewire. 
     Embodiments of the invention described in the figures showed IMAs comprising marker supports comprising 3 filaments and 3 loop-like structures. Further embodiments of the invention comprise marker supports having 4, 5, 6, 7 or 8 filaments or 4, 5, 6, 7 or 8 loop-like structures which extend to abut a surface of an internal body tissue. 
     In an embodiment of the invention, a marker support may be formed by deployable elements which upon deployment of the marker support, are positioned to form a circumferential formation relative to the guidewire. 
     In an embodiment of the invention, deployable elements may comprise a mesh-like material, comprised of filaments, which is flexible and tubular in collapsed state. Upon deployment, deployable elements may then extend from to form a concentric formation relative to the guidewire. 
     In an embodiment of the invention, deployable elements, upon initial deployment, may be substantially extending in a radial direction from the axis. Deployable elements may be rotated to a formation in which projections of the abutment regions on a plane perpendicular to the axis of the marker support each lie along a side of a polygon, for example, by rotation of a deployment tube by a medical practitioner, relative to a guidewire. 
     Embodiments of the invention described in the figures showed IMAs comprising abutment regions which comprised within them tissue markers. Further embodiments of the invention relate to IMAs comprising a tissue marker located in or on a filament, located a predetermined distance away from an abutment region. A medical practitioner may use an imaging modality to visualize a plane formed by the tissue markers, the plane being located a predetermined distance away from a surface of an internal body tissue. A medical practitioner may then optionally position a valve or device in line with or relative to the imaged plane formed by the tissue markers. 
     There is further provided in accordance with an embodiment of the invention an apparatus for determining a location of a surface of an internal organ of a body, the apparatus comprising: a marker support having proximal and distal ends, an axis, a collapsed state and a deployed state, the marker support comprising: at least three flexible filaments, which in the collapsed state lie within a relatively small radial distance from the axis of the marker support, and in the deployed state, each filament forms a loop, the loops each configured to abut a surface of an internal body tissue at an abutment region of each filament; and at least three tissue markers, each tissue marker located at an abutment region of a filament; wherein projections of each of the abutment regions on a plane perpendicular to the axis of the marker support each lie along a side of a polygon. Optionally, upon initial transition from the collapsed state to the deployed state, the loops define planes which extend along radial directions from the axis of the marker support. Optionally, the marker support further comprises a proximal collar at a proximal end and a distal collar at a distal end, each filament connected to the proximal collar and distal collar. Optionally, bringing the proximal collar closer to the distal collar transforms the marker support from a collapsed state to a deployed state. Optionally, in the deployed state, the tissue markers are configured to abut a surface of an internal body tissue by movement of the marker support in a proximal direction. Optionally, a tissue marker is located substantially midway between the distal and proximal ends of the filament. Optionally, the marker support is in a collapsed state, the radial diameter is small enough so that the marker support may be introduced into a human body using a guiding catheter system having dimensions adapted for introduction through the cardiovascular system and passage through the aortic valve. Optionally, the apparatus further comprising a guidewire and a deployment tube external to the guidewire. Optionally, the marker support is slidably attached to a guidewire. Optionally, the marker support is fixedly attached to the deployment tube at the proximal end of the marker support. Optionally, the apparatus comprises a connector fixedly attached to the guidewire, the connector configured to engage the distal collar of the marker support upon relative motion of the connector in the direction of the distal collar. Optionally, a protrusion on the connector engages the distal collar of the marker support, preventing rotational movement of the distal collar relative to the connector. Optionally, the connector and distal collar interlock via a clipping mechanism located on the connector and the distal collar. Optionally, the apparatus further comprises an intermediate tube between the guidewire and the deployment tube. Optionally, the distal collar is fixedly attached to the intermediate tube and the proximal collar is fixedly attached to the deployment tube. Optionally, when the marker support is in deployed state, it is shaped so that each filament comprises a single strand deformed to a position capable of forming a loop comprising an abutment region. Optionally, the marker support comprises a distal marker on its distal end and a proximal marker on its proximal end configured to be imaged overlapping or at a predetermined distance from each other when the marker support is in its deployed state. Optionally, the surface of an internal body tissue is a surface of the aortic valve. Optionally, the marker support comprises a superelastic alloy. Optionally, the superelastic alloy is nitinol. Optionally, the polygon is a tangential polygon in which all sides of the polygon are tangent to an inscribed circle. Optionally, the polygon is equiangular. Optionally, the polygon is a rectangle, a square, a pentagon, a hexagon or an octagon. Optionally, the tissue markers are radio-opaque markers. Optionally, the tissue markers are made of gold, platinum or tantalum. Optionally, the axis of the marker support lies substantially at the center of the polygon. 
     In the description and claims of the present application, each of the verbs, “comprise,” “include” and “have,” and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of components, elements or parts of the subject or subjects of the verb. 
     Descriptions of embodiments of the invention in the present application are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments utilize only some of the features or possible combinations of the features. Variations of embodiments of the invention that are described, and embodiments of the invention comprising different combinations of features noted in the described embodiments, will occur to persons of the art. The scope of the invention is limited only by the claims.