Patent Publication Number: US-2010131000-A1

Title: System and method for removal of material from a  blood vessel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to commonly assigned copending U.S. patent application Ser. No. 12/098,201, which was filed on Apr. 4, 2008, by Richard M. DeMello, et al. for a SYSTEM AND METHOD FOR REMOVAL OF MATERIAL FROM A BLOOD VESSEL USING A SMALL DIAMETER CATHETER, which is a continuation-in-part of commonly assigned copending U.S. patent application Ser. No. 11/583,873, which was filed on Oct. 19, 2006, now published as U.S. Publication No. US2007-0118165 on May 24, 2007, by Jonathan R. DeMello, et al. for a SYSTEM AND METHOD FOR REMOVAL OF MATERIAL FROM A BLOOD VESSEL USING A SMALL DIAMETER CATHETER, which is a continuation-in-part of U.S. patent application Ser. No. 11/074,827, which was filed on Mar. 7, 2005, now published as U.S. Publication No. US2005-0234474 on Oct. 20, 2005, by Richard M. DeMello, et al. for a SMALL DIAMETER SNARE, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/551,313, which was filed on Mar. 8, 2004, by Richard M. DeMello et al., for a SMALL-DIAMETER SNARE, each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to surgical catheters, and more particularly to devices for removing thrombus, and other blockages and materials from blood vessels. 
     2. Background Information 
     Certain snare and similar devices have become available over recent years for retrieving malfunctioning or misplaced devices or blockages such as plaque and thrombus within the cardiovascular and non-vascular regions of the body. These typically consist of fairly large diameter sheaths, which house a movable central wire or wires whose distal ends are formed into a loop, plurality of loops or other purpose-built shape. The loop is used to ensnare and capture the desired object for withdrawal and removal from the body, while other shapes may be used to grasp or capture softer biological materials. In use, the snare or another distal tool is typically passed through a guiding catheter or other introducing catheter that is placed within the vasculature and is directed to the vessel or area where the misplaced or malfunctioning device is located. The snare/distal tool can then capture the intended device or material and retrieve it out of the body through the introducing catheter or by withdrawing both the snare and the introducing catheter in tandem. 
     Currently available snares and similar distal tools are generally designed using large diameter outer sheaths that require relatively large entry sites. This may result in complications such as excessive bleeding and/or hematomas. Additionally, because of the large diameter, it may be necessary to remove the existing catheters and exchange to other larger devices, resulting in an increase in the overall time and cost of the procedure. A third disadvantage of the old means is that the outer sheath, which is typically made of a plastic material, exhibits little or no torque control, which can make ensnaring the misplaced or malfunctioned device or removing other materials very difficult. Lastly, because of the size and stiff design of these snare/distal tool devices, they have a very sharp distal leading edge which cannot be safely advanced into small diameter vessels such as those in the coronary and cerebral vasculature without risking damage to the vessel wall. 
     An exemplary small-diameter snare design that overcomes many of the concerns above is provided in commonly owned U.S. Pat. No. 6,554,842, entitled SMALL DIAMETER SNARE by Heuser, et al., the teachings of which are expressly incorporated herein by reference. Devices, such as the exemplary Heuser design, are characterized by a small-diameter outer sheath that has a relatively thin wall (for example, approximately 0.0020 inch or less in wall thickness) so as to accommodate an axially movable/rotatable central core wire of approximately 0.008 inch. The structure allows a snare loop attached to the distal end of the core wire and housed within the open distal end of the sheath to be selectively extended from the sheath end, withdrawn and torqued. This sheath is at least partially composed of metal. However, the thinness of the tube, and its metallic content make it susceptible to splitting, fracturing and fatigue failure under stress. In addition, the metal section of the tubular outer sheath tends to experience permanent (plastic) deformation when bent, and once deformed, the central core wire will tend to bind upon the lumen of the sheath, rendering the device inoperable for its intended purpose. In addition, the outer wall of the metal tube section has a lubricious coating, such as PTFE (Teflon), which is typically approximately 0.0010 inch in thickness. This necessitates further downsizing of the sheath overall outer diameter thereby reducing the inner diameter available for accommodating the central core wire and at the same time increasing the risk of inadvertent failure of the device through breakage or plastic deformation. 
     Further considerations arise in the case of a non-snare device used to remove materials from blood vessels. Within the U.S. alone, approximately 700,000 strokes occur every year. The majority of these (83%) are ischemic strokes due to blood clots (thrombus) that become lodged in and block cerebral vessels. It has been documented that if the blockage can be eliminated within a short period of time (up to 8 hours), the patient can experience a full recovery from the stroke. Presently, clot-dissolving drugs can be administered to break up the clot and restore blood flow, however these drugs must be administered within 3 hours of symptom onset as they take considerable time to become effective. Unfortunately, not all patients are medically eligible to receive these drugs and even those who otherwise are eligible often do not arrive for medical treatment within the 3 hour limit. In these patients, mechanical removal of the blood clot has been shown to have a significant positive outcome for such patients. 
     Several devices have been designed to break up and suction-out thrombus in the large vessels of the legs and coronary arteries. These use a variety of therapeutic means to accomplish the breaking up, such as water jets, mechanical maceration, ultrasound or photo-acoustic shock waves, and laser ablation. All of these devices, however, have limitations when working in the cerebral vessels. First, they tend to be large and bulky and very difficult or impossible to navigate above the skull base. Secondly, their therapeutic means can be extremely vigorous, resulting in damage to the delicate blood vessels in the brain. In use, the devices require removal of an already placed microcatheter, and the insertion of a replacement catheter that accommodates the device. 
     One such device that is used to treat blood clots is a mechanical capture device whereby the blood clot is grasped and pulled out of the distal vessels of the brain. The MERCI retrieval device (available from Concentric Medical of Mountain View, Calif.) is a 0.014-inch guidewire that can be passed through a catheter and into the blood clot as a straight wire and then can be remotely shaped into a corkscrew configuration (e.g., by extending the straight wire out of a surrounding sheath, thus “springing” into the pre-shaped corkscrew), becoming intertwined within the blood clot. The wire is then withdrawn from the distal cerebral vessel pulling the blood clot with it. Although this device addresses the ability to navigate above the skull base, it has one major shortcoming, namely, the corkscrew segment of the wire must be very soft and flexible in order to navigate within the brain. This reduces the ability of the device to remain in the cork-screw shape as it is withdrawing the blood clot. During withdrawal, the wire can straighten and the blood clot can be partially or fully released resulting in greater injury to the patient through thromboembolism. A more effective tool for removal of thrombus reduced risk of release or breakup and the ability to navigate smaller blood vessels is highly desirable. 
     SUMMARY OF THE INVENTION 
     This invention overcomes prior disadvantages by providing a device (e.g., a small-diameter device) for removing thrombus and other materials from vascular lumens consisting of a hollow, elongate (e.g., thin-walled) outer sheath, a core/actuating wire, and a capture mechanism. The sheath may be constructed from polymer, e.g., at least at a distal part thereof for enhanced flexibility and can be metal at an adjoining proximal part for added strength. A single central core wire extends through the entire length of the sheath. The outer diameter of the core wire is sized close to the inner diameter of the sheath while allowing for axial sliding, in order to maximize the support to the body portion of the snare device. The distal end of the core wire has a tapered section of reduced diameter or cross section to provide a “guidewire-like” flexibility to the distal portion of the device. Also, a tool tip (or “capture segment”) for removal of thrombus is provided at the distal end of the sheath and core wire that can be controllably expanded to engage a thrombus and remove the thrombus from the blood vessel. In particular, the controllably expansive capture segment may illustratively comprise a braided or meshed screen-like material adapted to open and close around a thrombus. 
     In use, the controllably expansive thrombus removal tool tip is collapsed by pushing on the actuating handle. The device is then advanced into a balloon or guiding catheter until the distal end of the core wire has reached (exited) the distal end of the thrombus. The tool tip is then expanded by pulling the actuating handle backward; and the radially extended (expanded) tool tip is moved to receive and substantially surround (e.g., encompass) the thrombus. The tool tip may then be collapsed again by pushing on the actuating handle to engage (tighten around) the thrombus, and the device may be withdrawn from the patient&#39;s body through the vascular system with the thrombus engaged by the tool tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention description below refers to the accompanying drawings, of which: 
         FIG. 1  is a partial side cross section of a device according to an illustrative embodiment of this invention; 
         FIG. 2  is a partial side cross section of the device including a manipulator handle assembly attached to the proximal end thereof; 
         FIG. 3  is a full cross section in the region of the slide actuator of the handle, taken along line  3 - 3  of  FIG. 2 ; 
         FIGS. 4A-B  illustrate a controllably expansive tool in an expanded orientation for removal of thrombus and other materials according to an illustrative embodiment of this invention; 
         FIG. 5  illustrates an embodiment of the controllably expansive tool in a collapsed orientation according to embodiments of this invention; 
         FIGS. 6A-C  illustrate another embodiment of the controllably expansive tool according to embodiments of this invention; 
         FIG. 7  illustrates another embodiment of the controllably expansive tool according to embodiments of this invention; and 
         FIGS. 8A-D  illustrate a blood vessel and removal of a thrombus therein by a controllably expansive tool according to embodiments of this invention. 
     
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT 
     A. Thrombus Retrieval Device and General Design Details 
       FIG. 1  shows an example (e.g., small diameter) thrombus retrieval device (or snare device)  100  according to an embodiment of this invention. Illustratively, the device  100  includes of a hollow, elongate, thin-walled polymer outer sheath  102 . The sheath  102  may include a radiopaque marker located at or adjacent to the open distal end  104  for visualization under fluoroscopy. The polymer can be any one of a number of acceptable biocompatible polymers with sufficient structural strength to support a thin-walled (approximately 0.0020 inch maximum wall thickness TS) structure without rupture or other failure under normal use conditions. Alternatively or in addition, the thin-walled outer sheath  102  may be made from a metal tube, a metal spring coil with an outer polymer jacket, or a combination of a metal tube proximal portion and a thin-walled polymer tube distal portion (described below). 
     In one embodiment, the sheath is constructed from polyimide with a tungsten filler for radiopacity. The radiopaque filler may be added to the sheath polymer during processing, or a radiopaque material may be added to the outer surface via vapor deposition, plating, ion implantation processes, or the like. Alternatively, radiopaque markers can be applied at the distal end and/or other known locations along the sheath, and thus, an overall tungsten filler/radiopaque coating can be omitted. As discussed further below, the outer surface can include thereon a polytetrafluoroethylene (PTFE or “Teflon”) coating upon some, or all, of its outer surface for enhanced lubricity. Alternatively, the outer sheath coating can be constructed form a hydrophilic material that provides lubricity, instead of a PTFE coating. The sheath polyimide material is commercially available for a variety of vendors and sources and is becoming accepted in a variety of medical device applications. It has the property of allowing a very strong, thin-walled cylindrical-cross section tube to be made therefrom, with wall thicknesses on the order of approximately 0.00075 inch to 0.010 inch in normal applications. Nevertheless, the resulting polyimide tube can withstand high pressures in excess of 750 PSI when employed in the size range of the sheath of this invention. Polyimide also resists high temperatures, as much as 1000 degrees F., or greater. Accordingly, polyimide is desirable as a sheath material based upon all of the above-described superior performance characteristics. Nevertheless, it is expressly contemplated that other equivalent plastic/polymer materials suitable for forming a thin-walled sheath tube with similar or better properties (e.g. high strength, thin wall-thickness limits, small diametric sizing) may also be employed as an acceptable “polymer” herein. 
     The outer sheath  102 , which forms the main support and outer framework of the device  100  has an overall length sufficient to traverse the body&#39;s varied vasculature, and is (for most applications) permissibly in a range of between approximately 20 cm and 500 cm (more typically between 120 cm and 300 cm), such as depending upon (among other factors) the location of the insertion point into the body cavity/vasculature, and the location of the target thrombus, or other material, to be acted upon by the device. The outer diameter DSO of the sheath is, for most applications, in a range of between approximately 0.010 inch to 0.045 inch (more typically between 0.010 inch and 0.021 inch), although the diameter may fall within the range of 0.008 inch to 0.250 inch. In general, where the outer diameter is less than 0.35 inch, the device  100  may fit easily through a standard balloon catheter. 
     A single central core wire (or “actuating wire”)  110  extends through the entire length of the sheath  102 . The outer diameter DC of the body of the core wire is sized close to the inner diameter DSI of the sheath while allowing for axial sliding (double arrow  112 ), in order to maximize the support imparted by the core wire  110  to the body portion/sheath  102  of the snare device  100 . (For instance, example guidewire dimensions are 0.014 inch and 0.035 inch diameters.) The distal end  114  of the core wire  110 , however, may have a tapered section  116  of reduced diameter or cross section to provide a “guidewire-like” flexibility to the distal portion of the device. According to one or more illustrative embodiments, a tool tip or capture segment  122  (shown collapsed) may extend from the end of the sheath configured in a manner described herein so as to increase the ability to ensnare and capture objects (e.g., a thrombus). Capture segment  122  may be attached at a proximal end  126  to the outer sheath  102 , and at a distal end  128  to the distal-most portion  130  of the central core wire  110 , as described further below. For example, depending upon its materials and configuration, the capture segment  122  may be attached at its ends via welding, soldering, brazing (or other high-strength metal-flowing means), adhesives, wrappings, sewing, etc. The core wire  110  may be further secured slideably to the outer sheath (e.g., through a loop, not shown) in order to maintain the core wire&#39;s orientation to one side of the capture segment  122 . 
     The central core wire  110  may be made from metal for flexibility and strength. In one embodiment, the central core wire  110  may be made by connecting a proximal stainless steel portion, for support and stiffness, to a distal nitinol portion, for torqueability and kink resistance. Likewise, it can be made from 300-series stainless steel or a stronger, heat settable material such as 400-series stainless steel, alloy MP35N, a chromium-cobalt alloy such as Elgiloy, or nitinol in its super elastic or linear elastic state. 
     Note, because a thin-walled polymer sheath is illustratively employed, it advantageously allows for a maximized central core wire diameter, which in turn, provides stiffness for torque control and axial pushability of the device. In this and other embodiments described herein, however, the sheath can be all polymer along its entire length, or can be constructed from a combination of polymer and metal. For example, the distal part of the sheath can be the above-described polyimide material (or another appropriate polymer), while the proximal part can be constructed from 300-series stainless steel or any other appropriate metal. This affords the desired flexibility in the distal part, while providing greater strength and rigidity against buckling in the proximal part. Flexure is required less and beam strength (so as to assist in driving the device distally) is required more in the proximal part. The distal part may be joined to the proximal part at a joint (not shown) located at a predetermined distance along the device. The joint can be accomplished using adhesive or any other acceptable joining technique. In one example, the polymer distal part is approximately 40 centimeters in length, while the metal proximal part is approximately 140 centimeters in length. These measurements are widely variable depending upon the overall length of the sheath, the purpose of the device (e.g. where it will be inserted) and the distance of the distal part in which high flexibility is required. 
     After assembly of the core wire  110 , its insertion into the sheath  102 , and the attachment of the capture segment  122 , a second short, hollow tube may be fitted over the proximal end  152  of the central core wire  110  and attached thereto by a filler or adhesive  154  to provide an actuating handle  150  so as to slideably move the central core wire axially (as indicated by double arrow  112 ) within the sheath  102 , thus selectively expanding and contracting the capture segment  122  at the open distal end  104  of the sheath  102 . In one embodiment, the actuating handle  150  may be sized with an outer diameter DOO similarly (or identically) in outer diameter DSO to the main body of the sheath  102 . The exposed proximal end  152  of the core wire  110  may include a narrowed-diameter end  160 , with a special connection so that an additional length of wire  166  can be attached to it, thereby extending the overall length of the snare device. This extension may have a similarly sized outer diameter DA to that of the handle  150  (DOO) and sheath  102  (DSO). The attachment of this similarly small-diameter extension allows for the exchange of one catheter for another catheter over the body of the snare (and extension). The entire device when complete (including the actuating handle  150 ) can be made less than 0.014 inch in overall outer diameter, and is therefore capable of being placed directly through a PTCA balloon catheter or other small-diameter catheter  180 , having a sufficiently large inner diameter CD, that may already be in place within the patient (e.g. CD&gt;DSO). Since the actuating handle is equally small in diameter, it also passes through the small-diameter catheter with an extension piece joined behind the handle to the attachment end  160 , and thereby allowing the device to be guided even deeper into the patient when needed. The capture segment and device may also be passed through the guiding catheter along side of the balloon or access catheter without the need to remove the prior device and, thus, lose temporary access to the site within the patient. For example, the device  100  may be initially passed through the PTCA balloon catheter, which is already located within the target area. The balloon catheter can then be removed and replaced with a larger-inner diameter catheter to allow removal of the object (e.g., thrombus). 
     The actuating handle  150  may consist of a metal or a polymer tube. In an alternate embodiment (not shown) the actuating handle may consist of a tube slideable within a second metal tube that is attached to the proximal end  170  of the sheath to maintain an axial orientation between the proximal end of the core wire  102  and sheath, thereby minimizing permanent bending or kinking of the core wire at or near this proximal location. 
     While the depicted actuating handle  150  is of similar outer diameter as the sheath  102 , it is expressly contemplated (where the handle will not be passed into another catheter) that the actuating handle may be made in a diameter significantly larger than the snare device so that it may also serve as a torquing handle, similar to those utilized in routine small-diameter guidewire placement.  FIG. 2  shows an overall version  200  of the device that includes an enlarged handle attachment  202  attached to the previously described snare device  100  of  FIG. 1  (with like components in  FIGS. 1 and 2  retaining like reference numbers, capture segment  122  now shown expanded). The handle attachment  202  extends over the actuating handle  150 , as discussed in more detail herein. The handle attachment  202  may be made from a polymer material which (in an embodiment of this invention) is injection molded and mechanically attached onto the device or (in another embodiment) may be over molded directly onto the device. 
     The handle attachment  202  includes a base ring  210  that is secured to the outer surface of the proximal end  170  of the sheath  102 . In a detachable-handle embodiment, the ring can consist of a conventional lockable collet structure in which turning of an outer element reduces the diameter of an inner locking element to deliver securing hoop stress to the distal end  170  outer surface of the sheath  102 . The base ring is connected to two or more ribs  212  and  214  that are also shown in cross section in  FIG. 3 . The ribs have a square or rectangular cross-section. 
     A second actuating ring  220  is secured onto the actuating handle  150  either permanently or detachably. Where it is detachable, the ring may also utilize a locking collet structure (not shown) as described above. The ring  220  includes at least two apertures  230  and  232  to allow passage of the respective ribs  212  and  214  through the ring, such that the ring  220 , actuating handle  150  and core wire  110  can slide axially (double arrow  240 ) to move the core wire with respect to the sheath  102 . The ribs, with their square or rectangular cross-section prevent rotation of the ring  220  and interconnected core wire  110  and handle  150  relative to the sheath. The connection is sufficiently strong so that rotation of the handle assembly  202  causes torquing of the entire device so as to rotate the capture segment  122  (in one or more embodiments) into a desired rotational orientation. In an alternate embodiment, the ring  220  may have a non-circular cross-section. In another alternate embodiment (also not shown), the ring  220  may also allow at least limited rotation of the core wire relative to the sheath by utilizing arcuate slots at the ribs. 
     The handle assembly  202  includes a rear gripping member  250  that connects to the proximate ends of the ribs  212  and  214 . The gripping member remains outside the body and is sized to provide an ergonomic hand piece for a practitioner during a procedure. In one embodiment the member  250  has an outer diameter of approximately ½ to ¾ inch and an external length of approximately 4 to 5 inches. However, it is expressly contemplated that both these dimensions are widely variable outside the stated ranges herein. The member  250  defines an inner cylindrical barrel  252  having an inner diameter sized to slideably receive and guide the proximal end of the actuator handle  150 . The barrel  252  is sufficiently long so that its inner end wall  262  (of end cap  260 ) is not struck by the end  160  of the device at maximum withdrawal (as approximately shown) of the core wire  110  into the sheath  102  (for expansion of capture segment  122 , as described below). 
     Coatings can be applied to the outer surfaces of each of the core assembly and the sheath assembly to reduce friction between the core and the tube as well as to enhance movement of the retrieval device within a catheter. In one embodiment, a lubricious coating, such as PTFE (Teflon), hydrophilic, or diamond-like coating (DLC) may be applied to the outer surface of the sheath to reduce friction. Likewise, one of these coatings may be applied to the outer surface of the core wire to reduce friction with respect to the sheath. Since the coating adds a quantifiable thickness to the thickness of the sheath and/or diameter of the core wire, the overall size of components should be adjusted to compensate for the thickness of any lubricating coating. For example, the outer diameter of the sheath may need to be reduced to maintain a desired 0.035-inch or less outer diameter. Likewise, the thickness of the uncoated wall of the sheath may be reduced to maintain the desired inner diameter and create a final wall thickness, with coating, of approximately 0.0020 inch. 
     B. Controllably Expansive Thrombus Retrieval Device 
     Having described the general structure of the device, a more specific description of the braided mesh/screen capture segment is now described with reference to  FIGS. 4A-5  (hereinafter referenced as device  400 ). The device  400  comprises an outer sheath  401 , a core/actuating wire  402 , and a capture segment  403 . The capture segment  403  is shown in an expanded or “open” state in  FIGS. 4A-B , and in a collapsed or “closed” state in  FIG. 5 . An additional distal cap  406 , located at the distal end of core wire  402 , may be rounded to form an atraumatic leading edge to facilitate movement through the blood vessels without causing damage. Illustratively, the capture segment  403  may be formed from a braided, metallic material. For example, suitable materials for screen  403  may comprise nitinol, stainless steel, or cobalt-chromium alloy, although it is conceivable that the braid/screen could also be made from a non-metallic material such as a cloth or polymer fibers. Note that a portion of or the entire mesh/screen segment  403  may be made radiopaque to aid in fluoroscopic visualization, such as by adding marker bands (e.g., at a distal end), electroplating, vapor deposition, or ion-beam bombardment/implantation of a radiopaque material onto the mesh. Also, the screen  403  may be made from a radiopaque material, such as platinum-tungsten wire (e.g., typical of guidewire coils). 
     The proximal end of the braided capture segment  403  may be attached about its periphery to the distal end of the outer sheath  401 , at point  404 , and the distal end of the braided capture segment may be attached at (or along) one side to the distal end  405  of the actuating wire  402 . The distal end of the capture segment thus remains open when the capture segment is in its expanded state, thus creating a void within the capture segment for receiving a thrombus or other material. For example, the mesh/screen material may, though need not, be pre-formed, such by heat setting or other process (e.g., pre-bending), to create a desired shape when expanded (and/or when compressed/collapsed) to optimize capturing ability, such as the open shape as shown. Notably, while a single core wire attachment is shown, a plurality of attachments (e.g., for a split core wire  402 ) may be made, so long as the distal end of the capture segment generally consists of one or more opening that are sufficient in size to capture a thrombus as described herein. Also, while the core wire  402  is shown on the inside of the capture segment  403 , other locations may be possible, such as on the outside of the capture segment or within the capture segment (that is, a part of and thus neither inside nor outside the capture segment) as may be appreciated by those skilled in the art. 
     In operation, as shown in  FIG. 5 , the core/actuating wire  402  is advanced forward such that the braided/screen material is stretched longitudinally causing the body of the braided section to collapse downward against the actuating wire. (For example, this action is similar to that of a known “Chinese finger trap.”) In other words,  FIG. 5  shows one embodiment of the controllably expansive capture segment  403  for a thrombus retrieval device that is in a collapsed orientation/position. When the core/actuating wire  402  is withdrawn backward ( FIGS. 4A-B ), the braided capture segment  403  returns to its expanded shape, whereby a distal most end of the capturing mechanism is in an open (net-like) configuration. 
     In particular, for controlling expandability operation of this embodiment, when the actuating/core wire  402  is advanced forward, as shown in  FIG. 5 , the braided mesh/screen capture segment  403  collapses downward against the core wire (a “collapsed state”) so that the device can be introduced into the body/vessel (e.g., with an outer diameter substantially close to that of the outer sheath  401 ) and directed to the thrombus location. When the core wire  402  is withdrawn within the outer sheath  401  (as in  FIGS. 4A-B ), the capture segment  403 , attached or otherwise restricted from entering the outer sheath  401 , expands outwardly (an “expanded state”) to the desired shape. The capture segment may then be moved into position to surround (encompass) a thrombus. The capture segment thus envelops the thrombus/material, which remains generally intact. Also, as described below, the capture segment  403  may again be collapsed around the surrounded thrombus, by advancing the core/actuating wire  402 . Various techniques may be used to lock or otherwise secure the core wire in position to maintain the capture segment in either the expanded or collapsed state to allow an operator of the device to securely position the capture segment in one or the other state without having to manually apply consistent force (tension) to the actuating/core wire. 
     As noted, in a collapsed state, the OD of the capture segments may be sized substantially similar to the OD of outer sheath itself (e.g., no greater than an ID of a catheter in which the outer sheath/device is meant to traverse). In an expanded state, the capture segment extends to approximately the vessel diameter so that it may be used to capture a thrombus or other material within the vessel. The capture segment may then be collapsed to move the thrombus/material, e.g., removing it from the vessel or otherwise repositioning the thrombus/material to another location. The range of radial extension of a fully-deployed tool tip or other capture segment is highly variable. It can be anywhere from 1 millimeter to 100 millimeters in various embodiments. This radial sizing depends partly upon the size of the space into which the capture segment is being inserted. More typically, a capture segment will have maximum radial extension between approximately 2 millimeters and 35 millimeters. In other words, the radial projection (RT) of the distal tool tip should be sufficient to surround the approximate dimension of the thrombus/material to be cleared, yet remain smaller than the inner diameter of lumen of any vessel through which the deployed tool is expected to carry. This helps to reduce the chance of injury to vascular walls. The distal-to-proximal length (LT) is also highly variable, depending upon the position of the core wire, and the current and/or desired radial projection. 
     Notably, in alternative or additional embodiments a distal atraumatic spring portion may be added to the distal end of the core wire to facilitate movement through the blood vessels without causing damage. In particular, as shown in  FIGS. 6A-C , the core wire  402  may illustratively continue beyond the distal end of the capture segment  403  (e.g., by approximately 1-3 cm), and may taper to a smaller (e.g., more flexible or “softer”) diameter. A radiopaque spring coil  408  fits over the end of the core wire and is secured at its distal end to the distal most portion of the core wire. The proximal end of spring coil  408  is secured to the core wire at the distal end of the capturing segment  403 , and thus the proximate end of the extended core wire. 
     Further, in addition or in the alternative, the outer sheath  401  may contain a flexible coil portion on its distal end. For example,  FIG. 7  shows a further embodiment of a thrombus retrieval device in which the outer sheath  401  has a hollow flexible coil segment  711  added onto its distal end. The coil  711  provides a flexibility at the distal end of the outer sheath that aids in negotiation of the device through constricted portions of the anatomy, such as that found in the brain (e.g., often extremely tortuous). Coil  711  is illustratively attached to the distal end of the outer sheath  401  in a manner that the ID of the coil remains open to allow the actuating/core wire  402  to slide therein. In doing so, coil  711  may be considered as an extension of the outer sheath  401 . In this embodiment, the capture segment  408  may be attached at its proximal end to the coil  711  and at its distal end to the core wire  402 . 
     In each embodiment described herein, the mesh/screen of the capture segment  403  is straightened out and thus collapsed for insertion of the device into the body when the actuating core wire is advanced, and expanded (e.g., enlarged or opened) when the core wire is retracted/withdrawn. The capture segment  403  may then be re-collapsed (e.g., around a thrombus) by advancing the actuating core wire  402 . Also, in use, the actuating wire may be withdrawn or advanced and locked in position as described above, such that the capture segment remains in the capture/collapsed state to remove the thrombus or move the thrombus/material to a desired location, as described below. 
     Note that each of the tool designs described herein is by way of example. For instance, the size of the capture segment can be varied based upon the size of the target vessel, as well as the size and characteristics of the material being engaged. Further, while the capturing segment is illustratively shown as a symmetric design, the segment  403  may be configured in multiple fixed diameters, or as other pre-configured shapes and/or varying diameters not explicitly shown. These illustrations, therefore, are merely representative, and should not be limiting on the scope of the present invention. 
     C. Procedures for Withdrawal of Thrombus and Other Materials with Controllably Expansive Capture Segments 
     Having described the general structure of the device and more specifically an illustrative braided mesh/screen capture segment, a procedure of removing a thrombus or other material from a blood vessel is now described in further detail.  FIG. 8A  shows the insertion of the device  400  into a blood vessel  815  containing a thrombus  806  (or other internal blockage, natural or man-made), which is prevented from traversing the vessel  815  by a constriction  807  (e.g., a plaque build up). Initial insertion of the device can be made via the aorta or another suitable blood vessel, where the device  400  may be advanced into a balloon or guiding catheter  410  until the distal end of the device and capture segment  403  has exited the distal end of the catheter. In particular, with the actuating core wire advanced forward, thus collapsing the capture segment  403 , the device may be advanced into the vessel  815  and maneuvered (e.g., torqued, manipulated, etc.) into a location adjacent to the object to be retrieved, e.g., a thrombus  806 . (Notably, the collapsed capture segment should be constructed and assembled in a manner that reduces drag within the vessel or encapsulating catheter, and prevents snagging/catching along vessel/catheter walls. Also, once deployed, the positions of the core wire  402  with respect to the sheath  401  can be locked using, for example, the above-described handle lock mechanism.) 
     Once positioned adjacent to the thrombus  806 , the core/actuating wire  402  is withdrawn allowing the capture segment  403  to expand into its open state, e.g., substantially sized to the inner diameter of the vessel  815 , as illustrated in  FIG. 8B . The entire device  400  may then be advanced forward and manipulated such that the capture segment  403  is moved over the thrombus  806 , as shown in  FIG. 8C . In this manner, the capture segment  403  surrounds (or encompasses or envelops) the thrombus material, which is generally kept intact, since no portion of the capture segment need pierce or otherwise enter the material/thrombus. 
     Once the thrombus  806  is enclosed within the capture mechanism  403 , the core/actuating wire  402  is re-advanced causing the capture mechanism  403  to collapse around the thrombus  806 , thereby providing a secure capture of the thrombus/material ( FIG. 8D ). Generally, the thrombus material may be sufficiently accretive such that it can be grasped and withdrawn without fragmentation, thus avoiding a thromboembolism or another undesirable effect. As such, all or a large portion of the thrombus  806  is captured and can be withdrawn with the device  400  from the patient&#39;s body. Alternatively, the thrombus may be retrieved back to a larger area within the body, where the thrombus can be safely aspirated out of the body using a large bore catheter and syringe (not shown). 
     The capture segment may instead be maintained in its collapsed state, pushed through and into the thrombus so that the capture segment resides at least partially within the thrombus, and then expanded by withdrawal of the core wire, allowing the capture mechanism to expand outward into the thrombus. The device may then be withdrawn, removing the thrombus from the vessel (e.g., from patient&#39;s body), while maintaining outward pressure from within inside the thrombus. 
     The above-described insertion procedures can be modified to accommodate the characteristics of the particular tool tip shape and size. A variety of additional tools and/or internal scanning devices can be employed to facilitate the procedure in accordance with known medical techniques. Note also that the proximal end of the thrombus-removal device described herein includes a proximal end that allows removal of the actuator handle and addition of a small-diameter extension. When the extension is added, the practitioner can pass another catheter over the inserted device sheath, thereby using the device as a guide for the larger diameter catheter. 
     Notably, the controllably expansive capture segments described above should be substantially sized in its expanded state so that it approximates the vessel diameter. For instance, vessel diameters where such a device may be used can typically range from 1 mm to greater than 35 mm, however, most thrombus retrieval procedures are performed in vessels ranging between 1 mm and 10 mm. In this manner, the capture of the thrombus is assisted by substantially allowing the capture segment to more fully surround and encompass the thrombus. 
     Further, in accordance with one or more embodiments of the present invention, the capture segment may be advantageously coated with a material to attract a thrombus, such as an ionic charge, or may include brushes and/or filaments (not shown). Also, the capture segment may be coated with a thrombus dissolving drug, such as Integrelin®, ReoPro®, or other thrombolytic agents as will be understood by those skilled in the art. Alternatively or in addition, the device may be constructed with a gap between the outer sheath and the actuating/core wire in order that localized drugs (e.g., thrombolytics) may be infused through the outer sheath and delivered directly to the thrombus. 
     The thrombus removal devices described herein may also operate to open the impeded vessel to allow blood flow. While removal of the thrombus is discussed above, the embodiments may instead be maneuvered within or proximate to the thrombus to puncture and/or break up the thrombus. Also, the thrombolytic agents applied to the capture segment may allow the capture segments to more readily enter/pass through the thrombus to puncture and/or break up the thrombus. 
     The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. For example, while specified materials are described, it is expressly contemplated that similar or superior materials may be employed if and when available for the described components of this invention. In particular, a variety of metals, polymers, composite, nano-materials and the like having desirable memory characteristics can be employed for capture segments and other components herein. Likewise, alternate techniques and materials can be employed for joining components. In addition further attachments can be provided to the devices described herein, with appropriate mounting hardware and locations to facilitate other, non-described procedures using the device. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of the invention.