one of the problems encountered when an elongated medical device , such as a retrieval device in a sheath , is used to reach a remote location in the body , is the turns and curves in the body tract that must be negotiated in order to reach the remote body location . as illustrated in fig1 by way of example , a stone 100 lodged in the renal calyx 42 can not be approached via the ureter 40 without encountering at least one curve 102 illustrated by arrow 104 . the rigid elongate member of a medical device can not effectively negotiate curves , such as the one illustrated , without causing tissue trauma in order to reach the remote tissue location . according to the invention , positioning a flexible sheath portion near the distal end of the sheath , addresses this problem . the embodiments of the invention described below , all have the common feature of a flexible sheath portion positioned near the distal end of the elongated sheath . all of the following embodiments of the invention have at least one thing in common , the sheath of the invention , on one hand , has sufficient flexibility in an area adjacent the distal end portion ( at the “ intermediate portion ” of the sheath ) to allow engagement of a stone , tissue , or other material . on the other hand , the sheath has sufficient strength or rigidity at the most distal end portion of the sheath to enclose the object engaging unit in the inoperative or collapsed state and to permit the object - engaging unit to move in and out of the distal end portion of the sheath without the distal end portion of the sheath deforming or failing . referring to fig2 a , 2 b , 3 a , and 3 b , one embodiment of a medical device , according to the invention , includes a handle portion 16 , an actuator 20 , a sheath 14 , a sheath lumen 15 , an elongated member 18 that passes within the sheath lumen 15 , and an object - engaging unit 10 , such as the grasping forceps illustrated in fig2 a and 2b . the handle 16 , the sheath 14 , and the object - engaging unit 10 are not shown in their correct size or proportion to each other . the sheath 14 typically is much longer and narrower than the handle 16 or the grasping forceps 10 to allow insertion into a body cavity or tract . referring to fig4 a , a sheath 14 according to the invention comprises at least three segments : a proximal segment 30 , an intermediate segment 32 , and a distal segment 34 . the proximal segment 30 of the sheath is located nearest to the handle 16 . the distal portion of the sheath 34 is that region of the sheath at the distal end of the medical device opposite to the handle 16 . the intermediate portion 32 of the sheath is positioned distal to the proximal portion 30 of the sheath and proximal to the distal portion 34 of the sheath . the proximal end of the intermediate portion 32 of the sheath is located about 3 inches to 7 inches , preferably 4 . 75 inches , from the distal end 26 of the sheath . the object - engaging unit 10 is collapsed within the distal portion of the sheath 34 for direct entry into the body or for entry into the body via the operating channel of an endoscope or laparoscope . the object - engaging unit 10 can be a grasping - type device , as illustrated in fig2 a and 2b . such grasping type object - engaging units are described in u . s . ser . no . 09 / 064 , 704 , the disclosure of which is expressly incorporated by reference herein . other types of object - engaging units that can be used with the sheath of the invention are retrieval basket - type devices , as illustrated in fig3 a and 3b , such as those described in u . s . ser . no . 09 / 065 , 158 , u . s . ser . no . 09 / 027 , 534 , u . s . ser . no . 09 / 084 , 135 , u . s . ser . no . 09 / 296 , 327 , u . s . ser . no . 09 / 268 , 484 , and u . s . ser . no . 09 / 369 , 226 , the disclosures of which are expressly incorporated by reference herein . other suitable object - engaging units are forceps , probes , retractors , elevators , blades , needles , and the like . referring now to fig2 a , 2 b , 3 a and 3 b , the sheath 14 , according to the invention , has at least one lumen 15 therein , and it extends from the handle 16 to a distal sheath end 26 . in one embodiment , an elongated member 18 , such as a cable , coil , shaft , guidewire , or mandril wire , extends within the lumen 15 from the actuating mechanism 20 in the handle portion 16 to a base 13 of the object engaging unit 10 where the elongated member 18 is joined to the object - engaging unit base 13 . operation of the actuating mechanism 20 by an operator causes the object - engaging unit 10 to move relative to the sheath 14 between a collapsed state within the distal sheath portion 34 , as illustrated in fig3 b , to an extended state outside of the distal end 26 of the sheath 14 where the object - engaging unit 10 is open and extending beyond the distal end 26 of the sheath , as shown in fig3 a . alternatively , in another embodiment of the invention , the actuating mechanism is joined to the sheath . operation of the actuating mechanism 20 by an operator in this embodiment causes the sheath 14 to move relative to the object - engaging unit 10 and the elongated member 18 , such that the object - engaging unit 10 is moved between a collapsed position within the distal sheath portion 34 , illustrated in fig2 b , to an extended position outside of the sheath 14 where the object - engaging unit 10 is open and extended beyond the distal end of the sheath 26 as illustrated in fig2 a . with the object - engaging unit 10 withdrawn into and collapsed within the distal sheath portion 34 , as shown in fig2 b and 3b , the object - engaging unit 10 is inserted into the body directly , or via an endoscope channel , to a remote internal site in the body where the target material is located . the object - engaging unit 10 is then moved relative to the sheath 14 and placed in the extended position illustrated in fig2 a and 3a , such that the object - engaging unit 10 , in its operative position , is manipulated by the operator to engage the target material or tissue in the remote body site . the object - engaging unit 10 can then be used to manipulate the material in the body . following manipulation of the material by the object - engaging unit 10 , the object - engaging unit 10 is at least partially withdrawn into the lumen 15 of the distal sheath portion 34 , as illustrated in fig3 b , by moving the elongated member 18 axially relative to the sheath 14 with the object - engaging unit 10 attached to its distal end , or by moving the sheath 14 axially relative to the object - engaging unit 10 , as illustrated in fig2 b . the medical device , including the object - engaging unit 10 and the sheath 14 , are withdrawn from the body cavity . the overall length of the sheath 14 , according to the invention , can range between 40 inches to 75 inches , preferably about 49 . 5 inches to 52 . 5 inches . the proximal portion 30 of the sheath is 35 inches to 55 inches in length , preferably 44 . 75 inches to 48 . 25 inches in length , the intermediate portion 32 of the sheath is 3 inches to 6 inches in length , preferably 3 . 5 to 4 . 0 inches , and the distal portion 34 of the sheath is 0 . 10 inches to 1 . 0 inch in length , preferably 0 . 75 inches . the outside diameter 11 of the sheath , indicated between the arrows 11 in fig4 a , may or may not be uniform from the proximal end of the sheath 24 to the distal end of the sheath 26 . in general , the outside diameter 11 of the proximal sheath portion 30 may range from 0 . 0315 inches to 0 . 0414 inches , the outside diameter 11 of the intermediate sheath portion 32 may range from 0 . 03 inches to 0 . 0445 inches , and the outside diameter 11 of the distal sheath portion 34 may range from 0 . 0315 inches to 0 . 0445 inches . sheath flexibility varies along the sheath &# 39 ; s long axis from the proximal end 24 of the sheath to the distal end 26 of the sheath . in one embodiment , according to the invention , the intermediate portion 32 of the sheath 14 is more flexible than either the proximal sheath portion 30 or the distal sheath portion 34 . that is , the proximal sheath portion 30 and the distal sheath portion 34 are more rigid than the intermediate sheath portion 32 . the flexibility of the proximal sheath portion 30 and the distal sheath portion 34 can be the same or can differ . however , the proximal sheath portion 30 and the distal sheath portion 34 are less flexible , i . e ., more rigid , than the intermediate sheath portion 32 . the intermediate portion 32 is highly flexible , as illustrated in fig . 4b , and can be flexed to as much as 360 degrees from the long axis of the sheath ( indicated as reference line 100 ). after the sheath of the invention is inserted into a channel of a flexible endoscope , the flexible endoscope with the sheath may flex as much as 180 degrees to 190 degrees . enhanced flexibility of the intermediate portion 32 of the sheath 14 is achieved in several ways . referring to fig4 a , 4 b , 5 a , 5 b , 6 a and 6 b , in one embodiment of a sheath 14 , according to the invention , the sheath 14 is constructed with layers of material extending from the luminal side 19 of the sheath wall 12 to the outside 17 of the sheath wall 12 . the wall 12 of the sheath , according to the invention , includes multiple concentric layers of the same or different materials . the intermediate sheath portion 32 , like the proximal sheath portion 30 and the distal sheath portion 34 , includes multiple concentric layers , however , the intermediate sheath portion 32 has at least one fewer layer or at least one different layer of material than the layers of material in the proximal sheath portion 30 and the distal sheath portion 34 . for example , as illustrated by a cross - section of distal sheath 34 in fig5 a , in one embodiment of the sheath , according to the invention , the distal sheath portion 34 and the proximal sheath portion 30 ( not shown ) are manufactured from four layers of material including , from inside 19 of the sheath wall 12 to outside 17 of the sheath wall 12 , a first layer ( a ) of polytetrafluoroethylene ( ptfe ), a second layer ( b ), of 304 braided stainless steel , a third layer ( c ) of polyimide , and a fourth layer ( d ) of fluorinated ethylenepropylene ( fep ). each material is arranged in a concentric layer around the circumference of the sheath wall 12 . in the same sheath , the intermediate sheath portion 34 , illustrated in fig5 b , has one fewer of the layers a - d than the proximal and distal sheath portions . the materials in intermediate sheath portion 32 , from the inside 19 of the sheath wall 12 to the outside 17 of the sheath wall 12 , include a first inner layer ( a ) of ptfe , a second layer ( b ) of stainless steel braid , no third layer , and a fourth layer ( d ) of fep , each material arranged in a concentric layer around the circumference of the sheath wall 12 . the relative thickness of each layer , illustrated in fig5 a and 5b , is merely intended to be illustrative and is not limited to that illustrated . the thickness of one or more of the layers of the sheath wall 12 may be greater or lesser than the thickness of one or more of the other layers . thus , the outer diameter 11 of the intermediate sheath portion 32 may be less than or the same as the outer diameter 11 of proximal sheath portion 30 and distal sheath portion 34 . however , the internal diameter 13 of the intermediate sheath portion 32 is the same as the internal diameter 13 of proximal sheath portion 30 and distal sheath portion 34 . that is , the diameter of the lumen 15 of the sheath 14 is uniform from the proximal end 24 of the sheath to the distal end 26 of the sheath . by maintaining a constant luminal internal diameter 13 throughout the length of the sheath 14 , the object - engaging unit 10 and the elongated member 18 may move in the lumen 15 relative to the sheath 14 without becoming snagged . in an alternate embodiment , the proximal sheath portion 30 and the distal sheath portion 34 are manufactured from a different combination of materials . for example , the first or inner layer is fep , followed by a second layer of stainless steel braid , followed by a third layer of polyimide , and followed by a fourth , outer layer of ptfe . the intermediate sheath portion 32 of this embodiment of the sheath includes a first inner layer ( a ) of fep , a second layer ( b ) of stainless steel braid , no third layer , and a fourth , outer layer ( d ) of ptfe . in yet another embodiment of the sheath of the invention , the proximal sheath portion 30 , illustrated in fig6 a , and the distal sheath portion 34 each have five layers , each layer made from the same material . in this embodiment of the sheath , the intermediate sheath portion 32 , illustrated in fig6 b , has four layers of material identical to the material used in the five layers of the proximal 30 and distal 34 sheath portions . other materials and different number of layers of the sheath are also contemplated by the invention and are not limited to those illustrated in fig5 a , 5 b , 6 a and 6 b . whatever the combination of materials and numbers of layers , the intermediate sheath portion 32 is always more flexible than the proximal sheath portion 30 and distal sheath portion 34 , and the internal diameter 13 of the sheath is uniform from the proximal end 24 of the sheath to the distal end 26 of the sheath . in another embodiment of the sheath , the intermediate sheath portion 32 has at least two sections 33 , 35 , and at least one of the sections has a different number of layers of material than at least one other of the sections . a section of the sheath is a region of the sheath wall having a different number of layers than an adjacent region of the sheath wall . for example , as illustrated in fig7 a , the wall of the intermediate portion 32 of the sheath 17 can have a section of three layers 35 of material followed by a section of four layers 33 of material , followed by a section of three layers 35 of material , and so on . alternatively , the wall of the intermediate portion 32 of the sheath can have a section of four layers of material , followed by a section of three layers of material , followed by a section of two layers of material , followed by a section of four layers of material , and so on . this pattern may be repeated along the entire length of the intermediate sheath portion 32 or the pattern may be limited to a portion of the intermediate sheath portion 32 . the number and type of sections can be varied and different than the specific arrangements shown . the sections in the intermediate sheath portion 32 can be arranged circumferentially , spirally in a lattice - like or criss - cross pattern , or longitudinally , as illustrated in fig7 a , 7 d , 7 e and 7 f , respectively . in one particular embodiment , the wall of the intermediate sheath portion 32 has a repeating pattern of four layer and three layer sections along its entire length , although other embodiments can have other layers in the sections . in a particular embodiment of the wall of the intermediate portion of the sheath having four layers , one of the four layers is polyimide while the other layers are selected from materials , such as fep , stainless steel braid , ptfe , polyetheretherketone ( peek ), or nitinol . in this embodiment , the polyimide layer is absent in the sections of the wall of the sheath having three layers . in other embodiments , a layer of a different material is absent in the wall of the intermediate sheath portion . a sheath , according to the invention , has the advantage of enhanced flexibility while maintaining sheath column and compression strength . for example , in one embodiment of the sheath of the invention , the proximal sheath portion 30 and the distal sheath portion 34 have four layers in the sheath wall while the intermediate sheath portion 32 , has a repeating pattern of a three layer section 35 followed by a four layer section 33 . alternatively , sections 33 have two , four , or more layers and sections 35 have a different number of layers than sections 33 . in one embodiment of the invention , the arrangement of sections in the intermediate sheath portion 32 may be circumferential as illustrated in fig7 a , 7 b and 7 c . in this embodiment , each section 33 , 35 is a band that wraps 360 ° around the circumference of the sheath wall . at least one of the sections 35 has fewer layers of material than an adjacent section 33 . in another embodiment , as illustrated in fig7 d , adjacent sections 33 , 35 in the intermediate sheath portion 32 are spirally arranged . rather than the sections being circumferentially arranged as illustrated in fig7 a , the sections in this embodiment spiral along all or a portion of the length of the wall of the intermediate sheath portion . in yet another embodiment of the invention , as illustrated in fig7 e , the sections in the intermediate sheath portion 32 are arranged as two intersecting spirals along all or a portion of the intermediate sheath portion 32 . in this embodiment of the intermediate sheath portion 32 , looking at the side of the sheath 17 , spiral sections 33 , 33 ′ appear as a plurality of “ xs ” along all or a portion of the intermediate sheath portion . sections 35 have a different number of layers of material than sections 33 . in still another embodiment of the invention , as illustrated in fig7 f , adjacent sections 33 , 35 in the intermediate sheath portion 32 are arranged longitudinally , paralleling the long axis of the sheath . in this embodiment of the intermediate sheath portion 32 , one or more longitudinal sections 33 , 35 are distributed around the circumference of the sheath along all or a portion of the intermediate sheath portion 32 . the embodiments illustrated in fig7 a - 7f are meant to be illustrative . other arrangements of sections in the intermediate sheath portion are possible . in another embodiment of the sheath , according to the invention , a first polymer having a certain characteristic stiffness is used to manufacture the sheath wall in the intermediate sheath portion 32 and a second polymer having a different characteristic stiffness than the first polymer can be used in the proximal sheath portion 30 and the distal sheath portion 34 ( not shown ). for example , a polymer - metal composition may be used in the intermediate sheath portion 32 whereas a more rigid or stiff type of polymer can be used in the proximal sheath portion 30 and the distal sheath portion 34 . in general , any type of material may be used in the intermediate sheath portion 32 that is a suitable material having the appropriate strength , flexibility and biocompatibility characteristics . other materials that can be included in one or more layers of the sheath are polyetheretherketone . ( peek ), or nickel - titanium ( nitinol ) braid . referring now to fig8 a , in another embodiment , according to the invention , the outer diameter 11 of the sheath wall in the intermediate portion 32 , is less than the thickness of the sheath wall at the proximal portion 30 and the thickness of the sheath wall at the distal sheath portion 34 . as illustrated by cross - sections of proximal sheath portion 30 in fig8 b , and distal sheath portion 34 in fig8 d , the thickness of sheath wall 12 is the same in the proximal sheath portion 30 and distal sheath portion 34 . as illustrated by cross - section of intermediate sheath portion 32 in fig8 c , the thickness of the intermediate sheath portion 32 is less than either the proximal sheath portion 30 illustrated in fig8 b and the distal sheath portion 34 illustrated in fig8 d . the inside diameter 13 of the sheath in the intermediate portion 32 of the sheath , illustrated in fig8 c , is unchanged relative to the inside diameter 13 of proximal sheath portion 30 , illustrated in fig8 b , and distal sheath portion 34 , illustrated in fig8 d . by maintaining a uniform inside diameter 13 from the proximal end 24 of the sheath to the distal end 26 of the sheath , illustrated in fig8 a , an object - engaging unit can slide smoothly in the lumen 15 of the sheath without risk of snagging in dilated or constricted regions of the inner wall 13 of the sheath . in one embodiment , illustrated in fig8 a , the transition in wall 12 thickness along the intermediate portion 32 of the sheath is gradual . in an alternate embodiment , the transition in wall thickness of the intermediate sheath portion 32 , relative to the wall thickness of proximal sheath portion 30 and distal sheath portion 34 , is incremental , i . e ., occurs in multiple stages , segments , or steps as illustrated in fig9 a . the number of possible incremental steps is without limit . the increments in wall thickness can be non - uniformly distributed along the long axis of intermediate sheath portion 32 as illustrated in fig9 b and 9c . the inside diameter 13 of the sheath wall 12 is uniform from the proximal sheath portion 30 , the intermediate sheath portion 32 , to the distal sheath 99 portion 34 . as a result , the diameter of the sheath lumen 15 is unchanged throughout the length of the sheath from the proximal end 24 to the distal end 26 of the sheath 14 . referring to fig9 d , in another embodiment of the sheath of the invention , the external sheath wall 17 of the intermediate sheath portion 32 is thrown into circumferential folds to achieve an accordion - like effect . this accordion - like effect enhances the flexibility of the intermediate sheath portion 32 relative to the rest of the sheath 14 . the inner diameter of the sheath in the intermediate sheath portion 32 is unchanged relative to the inner diameter of proximal sheath portion 30 and distal sheath portion 34 . the diameter of the lumen 15 of the sheath , therefore , is constant from the proximal end 24 of the sheath to the distal end 26 of the sheath . referring to fig1 a - 10c , in another embodiment of the invention , flexibility may be added to the intermediate portion 32 of the sheath by modification of the external sheath wall 17 with slits , grooves , or other depressions . slits , grooves , or depressions can be distributed completely or partially around the circumference of the sheath wall 12 in the intermediate sheath portion 32 as illustrated in fig1 a . as illustrated by a cross - section in perspective of intermediate sheath portion 32 in fig1 b , the modifications in the external sheath wall 17 of the intermediate sheath portion 32 extend part way through the full thickness of the sheath wall 12 and not through the inner sheath wall 19 . sheath all modifications , such as slits or grooves , are oriented with their long axis anywhere from parallel to perpendicular to the long axis of the sheath . as illustrated in fig1 c , in yet another embodiment of the sheath of the invention , scattered dimples or other shapes are introduced into the outer sheath wall 17 of the intermediate sheath portion 32 . like the grooves or slits illustrated in fig1 b , dimples extend from the outer wall 17 partially into the sheath wall 12 but not through the inner sheath wall 19 . thus , as illustrated in fig1 b and 10c , the inner diameter 13 of the sheath and , therefore , the sheath lumen 15 , is uniform throughout the length of the sheath beginning at the proximal end 24 of the sheath , extending through the intermediate portion 32 of the sheath , to the distal end 26 of sheath 14 . the surface of the sheath 14 , from the proximal portion 24 to the distal portion 26 , is made or coated with any suitable material with a low friction coefficient , such as a polymeric material , a polyethylene glycol , a photopolyacrylamide - heparin complex , hyaluronic acid , polyvinylpyrrolidine material , and others . these low - friction materials are materials included in the composition of the sheath wall during manufacturing or applied to the surface of the sheath after the sheath is manufactured . the sheath of the invention provides numerous advantages . for example , the flexible intermediate portion 32 of the sheath allows an increase in the deflection capability of the sheath 14 . when inserted into a flexible scope , for example , the flexible intermediate portion 32 of the sheath 14 overcomes the rigidity of the distal end 26 of the sheath that is necessary for the proper actuation of the object - engaging unit 10 . the flexible intermediate portion 32 coincides and deflects with a bending portion of the flexible scope without substantially impairing the capacity of the endoscope to flex . the distal portion 34 of the sheath holds and surrounds the object - engaging unit 10 when it is in the collapsed state or partially collapsed state , without radial deformation of the sheath 14 . the flexible intermediate portion 32 of the sheath allows more steerability than possible with conventional sheaths . in another aspect , the invention relates to a method for manipulating material or tissue in a body , such as a body tract or body canal , with a medical device including a sheath . the sheath , as part of the medical device , may be introduced directly into the body cavity or may be introduced through a channel in an endoscope or laparoscope . sheaths , according to the invention , provide the requisite rigidity at the proximal sheath portion 30 for effective manipulation by an operator for locating , engaging , and retrieving stones , and the requisite rigidity at the distal sheath portion 34 to enclose the object - engaging unit 10 in the collapsed or partially collapsed state without deformation or distortion of the distal end of the sheath . sheaths of the invention can be introduced into an endoscope or laparoscope without the need for introducers or other means . when the sheath is inserted into a flexible endoscope , the flexible intermediate portion 32 of the sheath allows the endoscope to flex to reach a remote body site . with the sheath inserted into a channel of the endoscope , the endoscope can flex about 180 to 190 degrees . sheaths of variable strengths , according to the invention , are used with medical retrieval devices or a variety of other medical devices . also , the sheaths of the invention can be used in urology , endoscopy , laparoscopy , biliary , and lithotripsy procedures as well as a variety of other applications . referring to fig1 a - 11c , a method for retrieving material from a patient includes inserting a medical device including a sheath according to the invention into the patient . the medical device including the sheath according to the invention may be directly introduced into the patient or may be introduced via a channel 50 of an endoscope or laparoscope as illustrated in fig1 a . for example , the endoscope 50 is advanced by an operator via the lumen of the ureter 40 until the distal end of the endoscope 50 enters the patient &# 39 ; s body site , such as the renal pelvis 42 , where the target material 100 is located . the medical device , including the object - engaging unit 10 collapsed within the distal end portion 34 of the sheath , is passed into the endoscope 50 , until the distal end 26 of the sheath approaches the distal end 51 of the endoscope 50 . as shown in fig1 b , the flexible intermediate portion 32 of the sheath coincides and deflects with the bending portion of the flexible endoscope 50 . the object - engaging unit 10 is extended from the distal end 26 of the sheath 14 to manipulate the material or tissue 100 within the remote body site 42 . the distal end portion 34 of the sheath is of sufficient strength and rigidity to resist deformation of the sheath as the object - engaging unit 10 is moved relative to the sheath . as shown in fig1 c , after the material or tissue 100 within the remote body site 42 is manipulated , the object - engaging unit 10 is withdrawn partially or completely into the distal end portion 34 of the sheath either by axial movement of the elongated member 18 , attached to the base 13 of the object - engaging unit 10 , or by movement of the sheath 14 over the stationary object - engaging unit 10 . the medical device including the sheath according to the invention can be directly inserted ( not shown ) into a body cavity without an endoscope or an introducer . the steps are similar to those described above for use of the medical device in an endoscope . the flexible intermediate portion of the sheath 32 deflects against the wall of the body tract as the sheath housing the object - engaging unit is advanced in the body tract . the object - engaging unit extends from the distal end of the sheath in the manner described above for using the medical device in an endoscope . after the material in the body site is manipulated , the object - engaging unit is withdrawn partially or completely into the distal sheath portion . the medical device including the sheath is withdrawn from the body tract . variations , modifications , and other instrumentations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and scope of the invention as claimed . accordingly , the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims .
a medical device includes a handle , a sheath , and an object - engaging unit . the distal end portion of the sheath is strong enough to resist being deformed by the object - engaging unit , yet another portion of the sheath is flexible enough to bend sufficiently .