the entire disclosure of u . s . patent application ser . no . 08 / 466 , 934 filed jun . 6 , 1995 is expressly incorporated by reference herein . turning now to fig3 the endovascular measuring apparatus 100 of the invention broadly includes a hollow plunger 102 , a wire stent 104 , a hollow sheath 106 , and a hollow inner catheter 108 attached to a hub 109 . the plunger 102 has a proximal end 110 with a first locking hemostasis valve 112 and a distal end 116 which is affixed to the proximal end 118 of the stent 104 . the hemostasis valve 112 includes an o - ring 113 , and a locking cap 114 . the lumen ( not shown ) of the hollow plunger 102 is dimensioned such that it can slide freely over the body of the hollow inner catheter 108 . the hollow inner catheter 108 serves as a guide for a guidewire 144 and as a tether to hold a soft flexible hollow dilator tip 148 in place at the distal end 146 of the catheter 108 . the tip 148 can be adjusted relative to the distal end 116 of the plunger 102 by sliding the inner catheter 108 within the plunger 102 . once the tip 148 is adjusted to accommodate the compressed stent 104 , the inner catheter 108 is locked into place by tightening the cap 114 onto a threaded portion 117 of the first locking hemostasis valve 112 . the cap 114 is effectively a locking mechanism which compresses the o - ring 113 , thereby fixing or locking the plunger 102 relative to the inner catheter 108 and the tip 148 . the body 120 of the plunger 102 contains a calibrated scale 122 having , e . g ., fifty major divisions 124 spaced at calibrated intervals . the scale 122 is calibrated to adjust for the longitudinal length contraction and diameter expansion experienced by the particular stent 104 when being decompressed ; i . e ., the ratio of the length of the stent when in the sheath to the length of the stent when uncompressed . the proximal end 118 of the wire stent 104 is affixed to the distal end 116 of the plunger 102 by any desirable means such as by heat fusing , insert molding , or gluing with epoxy . the body 128 of the wire stent 104 when uncompressed has a diameter larger than that of the plunger 102 and of the sheath 106 . the distal end 130 of the sheath 106 is open , and the sheath 106 has a diameter slightly larger than that of the body 122 of the plunger 102 so as to be translatable along the plunger body . the sheath 106 is further translatable over the stent 104 due to flexible and deformable characteristics of the stent 104 . it will be appreciated that when the sheath 106 is positioned over the wire stent 104 , the stent 104 contracts and elongates in a manner similar to that discussed in the background of the invention and shown at 132 . the proximal end 131 of the sheath 106 is attached to a second hemostasis valve 133 which is preferably provided with external threads 135 . a second threaded cap 138 containing a second compressible o - ring 140 is screwed onto the proximal end of a second locking hemostasis valve 133 . the second threaded cap 138 mates with the threads 135 of the second locking valve 133 to reversibly fasten the sheath 106 to the plunger 102 . the o - ring is used both to prevent inadvertent slippage of the sheath 106 relative to the plunger 102 by acting as a friction - locking mechanism , and to serve as a hemostasis valve during interventional surgical procedures . by pulling the first locking valve 112 away from the second locking valve 133 ( or pushing the sheath 106 relative to the plunger 102 ), the wire stent 104 can be pulled into the sheath 106 and compressed . conversely , by pushing the first locking valve 112 toward the second locking valve 133 ( or pulling the sheath 106 relative to the plunger 102 ), the distal end 126 of the wire stent 104 can be released and will expand towards its relaxed uncompressed configuration until ( and if ) constrained by the blood vessel in which it is being deployed . it will be appreciated that the second locking valve 133 can be positioned and will lock anywhere along the body 120 of the plunger 102 , thus providing the user with a means to control the length of stent 104 to be deployed . by reading the scale 122 at the location of the proximal - most end 142 of the second locking valve 133 , the length of stent required for deployment within the body cavity 202 at any given time can be determined . in particular , since the scale 122 is preferably calibrated to the ratio of the length of the stent 104 when compressed in the sheath 106 to the length of the stent 104 in its uncompressed state , the reading provided on the calibrated scale will inform the practitioner as to the length of uncompressed stent required to bridge any cavity in any path , regardless of the state that the stent will assume when deployed in the cavity . still referring to fig3 it is noted that both the first and second locking hemostasis valves 112 , 133 are preferably provided with flushing lines 115 , 137 . the lines 116 and 137 permit the spaces between the concentric hollow sheath 106 , hollow catheter 108 , and hollow plunger 102 to be flushed with heparinized saline during the insertion procedure . it is also seen that the hollow catheter 108 extends from the proximal hub 109 past the open distal end 126 of the stent 104 . the catheter 108 has an interior lumen ( not shown ) dimensioned for following a guide wire 144 into the body cavity 202 ( see fig4 ) of a patient . the distal end 146 of the catheter 108 is coupled to the hollow dilator tip 148 . the hollow catheter 108 and dilator tip 148 are capable of transporting a radiopaque contrast medium ( not shown ) used for fluoroscopic viewing . the plunger 102 and the sheath 106 of the apparatus 100 can be made from any durable biocompatible material such as nylon , polyurethane , teflon ®, polyester , pvc , polyethylene , polypropylene , etc ., or various combinations of the above , with or without radiopaque fillers such as barium sulfate or bismuth subcarbonate . the dilator tip 148 can be formed of the same materials as the plunger 102 and sheath 106 , but is preferably formed of a softer durometer material such as shore 80 a polyurethane or pebax nylon with a radiopaque filler or a radiopaque marking band . the measuring apparatus 100 of the invention can be made disposable or reusable . the lumen ( not shown ) of the inner catheter 108 or the annular space 150 between the sheath 106 and plunger 102 can be used to inject radiopaque contrast media into the vessel to assist in placement of the apparatus 100 as discussed above . the stent 104 material can be of the same material and of similar geometry as would be used in an evg , or it may be of a more radiopaque material such as tungsten , stainless steel , gold and the like . the apparatus 100 can be used in virtually any cavitous area of the body such as the urethra , esophagus , biliary duct , blood vessels , etc . or in any surgically made duct or shunt such as those made in the liver during transjugular intrahepatic portosystemic shunt procedures . referring now to fig4 - 7 , the apparatus 100 of the invention is seen with reference to the method of the invention . according to the method of the invention , the measuring apparatus 100 of the invention is initially placed in its fully axially extended position ( see fig4 ), with the sheath 106 covering the entire length of the wire stent 104 which is in turn fully compressed . in this configuration , the second locking valve 133 of the sheath 106 is at its furthest distance from the first locking valve 112 of the plunger 102 , and is aligned with the scale 122 such that the proximal most end 142 of the stop coincides with the “ 0 ” mark 204 on the scale 122 . the tip 148 is adjusted to fit into the sheath 106 by loosening the first locking valve 112 and pulling the inner hollow catheter 108 proximally such that the stepped proximal end 143 of the tip 148 fits into the sheath 106 and the distal end 116 of the plunger 102 abuts the proximal end 118 of the compressed stent 104 . tile distal end 206 of the guide wire 144 is located sufficiently past the body cavity 202 to allow proper placement of the measuring apparatus 100 . when positioning the measuring apparatus 100 , the distal ends of the stent 104 and sheath 106 should typically be located slightly past the distal neck 208 of the body cavity 202 in which the stent 100 is to be deployed ( see fig5 ). this is done to compensate for the tendency of the stent 104 to contract in length when going from its compressed configuration in the sheath 106 to its deployed configuration in the vessel 202 . it should be noted that the flexible hollow dilator tip 148 at the distal end 146 of the catheter 108 is radiopaque . thus , a user may monitor the progress and placement of the measuring apparatus 100 by means of a ti fluoroscope ( not shown ). once the measuring apparatus 100 is properly positioned within the body cavity 202 ( as in fig5 ), the sheath 106 is slowly retracted ( see fig6 ) by first loosening the cap 138 on the second locking valve 133 and then , while holding the plunger 102 stationary , pulling the sheath 106 backwards . as the sheath is retracted , the distal end 126 of the stent 104 is released and expands back towards its uncompressed configuration until it engages the distal neck 208 of the cavity 202 . it will be appreciated that , as the distal end 126 of the stent 104 has an at rest uncompressed diameter greater than the distal neck 208 diameter of the body cavity 202 , the distal end 126 of the stent exerts pressure on the distal neck 208 when it is deployed , causing the distal end 126 of the stent 104 to be locked into place . as mentioned above , the overall length of the stent 104 decreases when it goes from its compressed configuration to its less compressed deployed configuration . it is thus important that the user position the distal end 126 of the stent 104 sufficiently past the distal neck 208 of the body cavity 202 to compensate for this shrinkage . it will be noted , however , that should the practitioner discover after the sheath 106 has been retracted that the distal end 126 of the stent 104 is not positioned far enough into the distal neck 208 of the body cavity 202 , the practitioner need only re - extend the sheath 106 fully over the stent 104 and repeat the above steps of positioning . as indicated by fig7 the sheath 106 is further retracted until the user determines , via fluoroscopy , that the stent 104 is sufficiently deployed so as to bridge the length of the body cavity 202 . as shown in fig7 the length of stent 104 as retractably deployed must be slightly longer than the length of the body cavity 202 . in this manner , the proximal end 718 of the length of retractably deployed stent 104 and the distal end 126 of the stent are positioned respectively within the proximal and distal necks 210 , 208 of the body cavity 202 . once the desired length of stent 104 is retractably deployed , the proximal most end 142 of the second locking valve 133 is used as an indicator on the scale 122 of the plunger 102 . as discussed above , the scale 122 is calibrated such that the indicated number 702 represents the uncompressed length of stent needed to fully bridge the body cavity 202 . in this particular case , the scale 122 indicates 27 mm , signifying that a stent having an at rest , uncompressed length of 27 mm must be used to properly bridge the body cavity 202 which may be , e . g ., 20 mm long . once the measurement is taken , the sheath 106 is re - extended over the stent 104 ( as in fig5 ), thus re - compressing it , and the entire measuring apparatus 100 is withdrawn from the body cavity 202 and the patient . the stent 104 may then be detached from the measuring apparatus 100 by cutting it with , for example , scissors , or a new stent or covered stent ( not shown ) having the same properties and pitch angle as the stent 104 of the measuring apparatus 100 , and having an at rest uncompressed length equal to or proportional to the recorded measurement , may be obtained . in the above example , a 27 mm stent of the same diameter and geometry would thus be obtained . this stent is then inserted into the body cavity 202 for deployment via any known means in the art . as the measurement method of the invention has already determined the proper stent length , the user is only left with the task of properly placing the stent within the body cavity 202 . turning now to fig8 a second embodiment of the apparatus 300 of the invention is seen . in this embodiment , the stent 304 of the measuring apparatus 300 is coated with a microporous or non - porous elastomeric membrane . the apparatus 300 has particular advantageous use where the body cavity 301 has several branching vessels 302 , 303 and a saccular aneurysm 308 . with the measuring apparatus 300 deployed inside the body cavity 301 as shown , the organs and tissues ( not shown ) fed by the branch vessels 302 , 303 can be monitored to determine if they are suffering harmful effects as a result of the blocking of the branch vessels 302 , 303 caused by the non porous stent 304 . for example , if the branch vessels 302 , 303 were to represent arteries which nourish the spinal chord , the lower extremities of the patient can be tested and monitored to determine if blocking of these arteries causes paraplegia in the patient . should such a determination be made , the coated stent can either be cut shorter so as to not block the branch vessels , or the procedure terminated altogether . similarly , when proceeding to bridge an aortic aneurysm , the measuring apparatus can be used with a coated stent to determine whether there is a back flow from , for example , a lumbar artery into the aneurysm , which if not occluded can lead to rupture of the aneurysm . if a back flow is detected , interventional blockage of the lumbar artery with an occlusion device may be required prior to stenting the aorta . in accord with yet another aspect of the invention , a detachable hub and detachable hemostasis valve for use in conjunction with methods for loading and deploying a stent or stent - graft are seen in fig9 and 10 . in particular , a detachable hub 310 for use on the endovascular measuring apparatus 100 of fig3 - 8 ( in lieu of hub 109 ) is seen in fig9 having a cap 312 which screws onto threads 314 , an o - ring 316 , a lumen 317 , and a proximal handle 318 having a luer lock 320 capable of connection to a hemostasis valve or the like . the inner catheter 315 is fed through the lumen 317 of the detachable hub 310 and locked into place by tightening the cap 312 onto the threads 314 , thereby compressing the o - ring 316 . similarly , the detachable hemostasis valve 410 of fig1 is intended to replace the valve lock 112 of fig3 - 8 . the detachable hemostasis valve 410 includes a body portion 412 having proximal threads 414 and distal threads 416 , distal and proximal caps 418 , 420 , a lumen 422 , distal and proximal o - rings 424 , 426 , and a flush port 430 . the inner catheter 108 and plunger 120 pass through the lumen 422 , and when in place , the distal cap 420 can be tightened on the distal threads 416 to compress the distal o - ring 424 and lock the valve onto the plunger 120 . similarly , the proximal cap 418 can be tightened on the proximal threads 414 to compress the proximal o - ring 426 to lock onto the inner catheter 108 . the flush port 430 can be used to enable flushing of the annular space between the plunger 120 and the inner catheter 108 with , e . g ., heparinized saline . with the detachable hub 310 and lock 410 as provided in fig9 and 10 , the method of measuring a desired stent length can be carried out as described above with reference to fig3 - 8 . however , in accord with another aspect of the invention , after the measurement , the provided apparatus can be used for loading and deployment of the measured stent or stent - graft . in particular , after the desired stent length has been measured , the entire measuring apparatus is removed from the body of the patient . preferably , all lumens of the apparatus are then flushed with heparinized saline . the detachable hub 310 ( fig9 ) is then detached an removed , and the detachable lock 410 is detached and removed . with the hub 310 and lock 410 removed , the dilator tip 148 is grabbed an pulled distally , such that the inner catheter 108 is removed completely from the hollow plunger 120 . then , the stent 104 is pulled through and entirely out of the sheath 106 . using a waterproof , sterile , felt - tipped pen or the like , or any other desired mechanism , the stent of stent - graft 104 is marked to the desired length from its distal end 126 ( e , g ., 27 mm from the distal end of the stent ). with the stent marked , the proximal end of the plunger 102 , still connected to the stent 104 , is inserted into the sheath , and through the plunger lock 133 until the proximal end 120 of the plunger sticks out of the distal end of the sheath 106 ; i . e ., the plunger is inserted backwards through the sheath . the proximal end of the plunger sticking out to the distal end of the sheath is then pulled such that the stent or stent - graft 104 is pulled into the sheath and out of the distal end of the sheath to the mark . the stent 104 is then cut at , or just proximal to the marking such that the remaining stent ( with the marking ) with the plunger can be discarded , and the stent in the sheath properly loaded . with the sheath loaded , the introducer system is reassembled by inserting the catheter 108 through the sheath and stent , if desired , by providing a plunger to push out the stent or stent - graft 104 when properly located , and , if desired , by reattaching the hub 310 to the catheter , and the lock 410 to the plunger and catheter . it will be appreciated that the plunger utilized with the loaded sheath can be a new plunger used for deploying the stent 104 , or the remaining portion of the stent utilized in the initial measurements with the excess stent removed from the plunger . the loading and deployment method of the invention as set forth above have numerous advantages . it will be appreciated that since the stent is loaded by pulling the stent with the plunger , there is less opportunity for the stent wires to scrape and perforate the wall of the sheath . in addition , funnels usually required to load the stent are eliminate , and the stent loading operation is simple . further , the stent or stent - graft being utilized is the same unit which was used as the measuring devise , thereby rendering the system less expensive . there have been described and illustrated herein several embodiments of a tubular braided stent and a method of manufacturing the stent of the invention . while particular embodiments of the invention have been described , it is not intended that the invention be limited thereto , as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise . thus , while particular stent designs have been disclosed for use with the apparatus of the invention , it will be appreciated that other designs may work as well . for example , while a stent having a homogeneous pitch angle throughout has been disclosed , a stent with a different body and end pitch angle can also be used as disclosed in copending u . s . patent application ser . no . 08 / 388 , 612 , or continuously varying hyperbaloidal stents can be used . furthermore while a particular mechanism for adjusting and locking the sheath relative to the plunger and a similar method for locking the plunger relative to the inner catheter has been disclosed , it will be understood that other mechanisms or no mechanisms may be used as well . also , while a particular type of scale has been disclosed , it will be recognized that any other suitable scales could be used . for example , although a metric scale has been disclosed , an english system scale or any other measurement system scale could also be used . in addition , although a scale has been disclosed printed along the plunger body , the scale may instead include electronic measuring means coupled to an lcd readout . furthermore , although the scale has been disclosed as having a particular calibration , any other calibration could be used . for example , although the scale has been calibrated to account for the contraction experienced by the stent when in an uncompressed configuration , the scale may be calibrated in any other fashion or may be uncalibrated . when uncalibrated , the practitioner can either conduct the necessary mathematics in order to determine the length of uncompressed stent to use , or can cut a stent in its compressed state in a sheath the same diameter as the sheath of the apparatus . in fact , if desired , no scale or calibration is necessarily required on the plunger , as the plunger can be marked by the practitioner during use , and measured afterwards . although this measuring apparatus has been described for use with a self - expanding stent of the wallsten or didcott configuration , it will be appreciated that the measuring apparatus can be calibrated for use with other devices such as balloon expandable palmaz or gianturco stents and the like . the apparatus may also be used to acquire exact measurements of body cavities for data collection and subsequent use for other procedures such as bypass surgery , electrophysical mapping , endoscopic surgery , etc . moreover , while a particular configuration for the dilator tip has been disclosed , it will be appreciated that other configurations or no dilator tip could be used as well . furthermore , while a particular monitoring means has been described for use with the apparatus , it will be understood that any monitoring means can be similarly used . in particular , while the monitoring means were described to be fluoroscopy , other means such as radioscopy and ct scans may also be used . in addition , while a particular method of measuring the deployment length of a stent in a body cavity using the apparatus of the invention has been disclosed , it will be understood by those skilled in the art that details may be altered without changing the nature of the method . it will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided apparatus and method of the invention without deviating from their spirit and scope as so claimed .
an apparatus and method are disclosed for measuring the desired length of a prosthetic device which is to be implanted in a body cavity of a patient . the apparatus generally includes a helically coiled stent formed of a resiliently - deformable material , a plunger which is connected to the proximal end of the stent , a sheath which slides over the plunger and stent when the plunger and sheath are used to insert and removably deploy the stent into the body cavity , and a scale for measuring an indication of the length of the stent once removably deployed in the body cavity . proximal movement of the sheath to partially deploy the stent causes a length to be indicated on the scale . according to the method of the invention , the helically coiled stent of the apparatus is placed and partially deployed within the body cavity by use of the plunger and sheath of the apparatus . once the stent bridges the body cavity , the scale of the apparatus is used to determine the length of the deployed stent . the apparatus is then removed from the body cavity , and a stent similar to the stent of the apparatus is cut to the length indicated on the scale . in a second embodiment of the apparatus and method , the stent of the measuring apparatus is substantially non - porous to allow occlusion of side vessels extending from the body cavity . the patient is then monitored for any ill effects resulting from the occlusion .