fig2 illustrates an exemplary micro - catheter 20 for precision stent placement in accordance with the present invention . micro - catheter 20 comprises a flexible tubular catheter body 28 having an internal passage stemming from distal end 22 to proximal end 24 ( at connector 26 ) for delivery of stents or other instruments / devices to a target location within the body . starting from the distal end 22 of the catheter body 28 , the catheter 20 comprises a plurality ( e . g . six ) of radio - opaque markers 30 at spaced apart intervals ( e . g . 10 mm ). the markers 30 act as a ruler to help the physician determine length and location with respect to an internal lumen or vessel . markers 30 may comprise any radio opaque material for visibility within the body under x - ray ( e . g . radiographic or fluoroscopic imaging ). in one embodiment , markers 30 comprise thin - walled tubes placed at spaced - apart locations on catheter body 28 , and are typically made from a high density material such as a metal ( e . g . platinum , gold or tantalum ) for visibility under an x - ray fluoroscope . markers 30 may be embedded with , or adhered to an outside surface of , catheter body 28 . markers 30 may also comprise a radio - opaque coating deposited on the catheter body . the radio - opaque markers 30 may be of various quantity , sizes and intervals from the distal end 22 of the catheter body . for example , catheter 20 may comprise a plurality of radio - opaque markers 30 spaced - apart at 5 mm intervals along a distal segment spanning 3 cm - 5 cm to provide reference for an operator placing a braided stent . the interval of the radio - opaque markers may range from every 1 mm , 2 mm , 3 mm , 4 mm , and 5 mm or more . the length of the radio - opaque marker segment 30 may be 3 mm , 4 mm , 5 mm , 6 mm , 7 mm , 8 mm , 9 mm , and 10 mm or more to provide sufficient visibility under an x - ray fluoroscope . each radio - opaque marker 30 may be shaped similarly , or may be variably shaped , e . g . the 5 mm marker ( from distal end 22 may comprise one band , the 10 mm marker may comprise 3 bands , the 15 mm marker may comprise 4 bands , and so on . in one embodiment , the stent delivery catheter 20 may comprise multiple radio - opaque marker bands 30 spaced apart in a 40 mm distal segment 22 at 5 mm intervals , and may be configured for delivery of a 20 mm long braided stent . the stent would generally elongate in the delivery catheter 20 more than twice as much as its unconstrained length . since the elongated stent in the delivery catheter 20 could not be helpful as a guide to anticipate where the 20 mm long stent ends ( when unconstrained ), the use of the array of radio - opaque markers 30 would indicate the 20 mm point from the catheter tip , enabling better stent positioning . fig3 shows a stent delivery system 50 comprising a stent delivery wire 40 configured with a proximal end 46 and a distal end 42 for supporting stent 38 for delivery to a target treatment location within the body . the stent 38 / delivery wire 40 assembly is delivered through micro catheter 20 ( which may comprise radio - opaque markers 30 as shown in fig2 ) to the target treatment location in the vessel . once the stent is completely pushed out from the distal end 22 of the delivery catheter 20 , it is detached from the delivery wire 40 and is positioned at the target location / lesion permanently . as shown in fig3 , delivery wire 40 comprises a radio - opaque marker 44 a set length l se from the distal end 42 of the delivery wire . l se indicates the true , expanded length of the stent 38 , i . e . from distal end 34 to proximal end 36 . as mentioned previously , stents , and particularly braided stents , are significantly elongated when crimped in a delivery catheter . radio - opaque marker 44 may comprise a ring or coating of size , shape and composition similar to marker 30 described above for fig2 . while delivery wire 40 is typically metallic , it is generally made of stainless steel or nitinol , and the distal end 42 of the delivery wire is generally very thin so as not to generally be very radio - opaque . marker 44 generally comprises radio - opaque metal , such as a platinum band , that is welded or bonded on wire 40 . without the system of the present invention , it is difficult to anticipate where the proximal end 36 of the stent lands in relation to the target anatomy . using system 50 of the present invention , the physician may use the radio - opaque marker 44 on the delivery wire 40 to give an indication where the proximal end 36 of the unconstrained stent 38 would land after delivery through the micro catheter 20 , and thus start extraction of the distal end 34 of stent 38 at the appropriate distance from the target anatomy . for example , a 20 mm long braided stent 38 is crimped and mounted on delivery wire 40 having a radio - opaque marker positioned on the wire at a point that indicates l se = 20 mm from the distal tip 34 of the stent 38 ( which may or may not correspond to the distance from distal end 42 of the wire 40 ). with this marker 44 , the operator can easily anticipate where the proximal end 36 of the stent would land in the tortuous vessel , and select a delivery location of the stent 38 ( generally starting at the distal end 22 of the micro - catheter ) that corresponds to the desired treatment location ( e . g . the aneurysm 52 ). fig4 shows an exemplary radiographic image of the catheter 20 comprising multiple radio - opaque maker bands 30 at 10 mm intervals in use within tissue in accordance with the present invention . as seen in fig4 , the markers 30 are clearly delineated , and provide valuable visualization as a position indicator when placed in a tortuous anatomy . fig5 shows a radiographic image of an expanded stent 38 and stent delivery wire 40 with radio - opaque markers for illustrating expanded and compressed lengths . the image shows a braided stent 38 after it is delivered , but still attached to the delivery wire 40 . the left - most arrowhead shows a maker on the delivery wire 40 that corresponds to the distal end 36 of the stent 38 . the middle arrow indicates an additional radio - opaque marker 44 that represents the unconstrained length ( or location of proximal end 36 when unconstrained ) of the stent 38 . the double arrowheads 48 correspond to the location of the proximal end 36 of the stent 38 when crimped and constrained in the catheter 20 or delivery sheath . the marker 44 therefore guides the treating physician to better anticipate where the proximal end 36 of the stent lands . fig6 illustrates a schematic diagram of a brain artery 54 ( e . g . left internal carotid artery ) and a brain aneurysm 52 as the target treatment anatomy . fig7 through fig1 show a first embodiment of the invention of a stent delivery procedure using the micro - catheter 20 illustrated in fig2 . fig1 through fig1 show a second embodiment of the invention of a stent delivery procedure using the stent delivery system 50 illustrated in fig3 . fig7 illustrates a schematic diagram of the micro - catheter 20 with radio - opaque markers 30 navigated into the brain artery 54 and is placed across the aneurysm 52 neck . the general strategy is to cover the aneurysm 52 neck with a stent . as shown in fig7 , the distal end 22 of the micro - catheter 20 is delivered past the target location 52 and is placed at a location corresponding to the desired extraction of the stent 38 ( e . g . where the distal end 34 of the stent will be located at distal end 22 ). fig8 illustrates a schematic diagram of a braided aneurysm stent 38 ( e . g . 30 mm length ) inserted into the micro - catheter 20 . in general , stents are very radio - opaque so that the entire length is clearly visible even if it is in a micro - catheter 20 . due to the significant elongation , the 30 mm stent is much longer than the true length . this elongation on top of the tortuous anatomy sometimes poses a challenge to the physician for accurate placement . the multiple radio - opaque markers 30 at known intervals on the micro - catheter 20 allow the physician to ignore the elongation and simply use the 30 mm point marker ( e . g . 3 rd marker from distal end 22 at 10 mm spacing ) as a reference . if the stent 38 lands in the vessel 54 as projected , it will span the neck of the aneurism 52 . fig9 illustrates a schematic diagram of the micro - catheter 20 being pulled back as stent 38 is being pushed out of the distal end 22 . distal end 34 of the stent lands at the location of the distal end 22 at extraction , while proximal end 36 is still within the micro - catheter 20 as distal end 22 of the micro - catheter is pulled back to the location of the aneurysm 52 . due to the stent elongation effect in the micro - catheter 20 , the remaining length of the stent 38 in the micro - catheter is significantly different from the length that the stent 38 covers within the artery 54 . fig1 illustrates a schematic diagram of the stent 38 completely extracted from the micro - catheter 20 for completion of the stent placement . the proximal end 36 of the stent 38 lands well beyond the aneurysm 52 neck to fully cover or occlude the target lesion . fig1 illustrates a schematic diagram of a stent delivery micro - catheter 20 navigated into the brain artery and placed across the aneurysm neck . in this configuration , delivery micro - catheter 20 does not have radio - opaque markers 30 as shown in fig2 . however , it is contemplated that markers 30 may also be employed . as with the previous procedure described in fig7 through fig1 , the desired treatment plan is to cover the aneurysm neck 52 with a stent ( e . g . 30 mm length ). fig1 illustrates a schematic diagram of a braided aneurysm stent 38 ( e . g . 30 mm ) inserted into the micro - catheter 20 over a delivery wire 40 so that the distal end 42 of the delivery wire is at or past the distal opening 22 of the micro - catheter 20 . in general , stents are very radio - opaque so that the entire length is clearly visible even it is in a micro - catheter 20 . due to the significant elongation , the 30 mm stent 38 is much longer than the true length . this elongation on top of the tortuous anatomy sometimes poses a challenge to the physician for accurate placement . the radio - opaque marker 44 at known distance l se on the delivery wire 40 allows the physician to ignore the elongation and simply use the point marker 44 ( e . g . 30 mm from the distal end 34 of the stent 38 when positioned on the delivery wire 40 ) as a reference . having the radio - opaque marker 44 that indicates the unconstrained length of the stent 38 , the physician can simply navigate the stent delivery system ( e . g . distal end 22 of micro - catheter 20 ) to the point where the desired stent placement starts in light of the radio - opaque marker 44 that indicates where the proximal end 36 of the stent 38 should land . fig1 illustrates a schematic diagram of the micro - catheter 20 being pulled back as stent 38 and delivery wire 40 are being pushed out of the distal end 22 . distal end 34 of the stent 38 lands at the location of the distal end 22 at extraction , while proximal end 36 is still within the micro - catheter 20 as distal end 22 of the micro - catheter is pulled back to the location of the aneurysm 52 . due to the stent elongation effect in the micro - catheter 20 , the remaining length of the stent 38 in the micro - catheter is significantly different from the length that the stent 38 covers within the artery 54 . nevertheless , the physician can use the radio - opaque marker 44 as a predicted stent 38 ending point . fig1 illustrates a schematic diagram of the stent 38 and delivery wire 40 assembly completely extracted from the micro - catheter 20 for completion of the stent placement . the proximal end 36 of the stent 38 lands well beyond the aneurysm 52 neck at the projected marker location 44 on the delivery wire 40 to fully cover or occlude the target lesion 52 . while the above examples are illustrated with use of a braided stent because of its associated substantial foreshortening , it is appreciated that the systems and methods of the present invention may be used with stents fabricated via any method , including micro - machined metal stents fabricated with laser - machining , photo - etching , electroforming , and micro - electro - discharge machining , and polymeric stents fabricated using injection , compression , or fused deposition molding processes . it is appreciated that the length of the stent 38 while in a completely unconstrained state may be different than ( e . g . smaller ) the length of the stent when “ unconstrained ” in the lumen 54 outside of delivery micro - catheter 20 . for example , a stent may be sized to have a diameter that compresses against the inner wall of the lumen 54 . thus , the lumen 54 may have a constraining effect on the stent 38 that causes it to be slightly larger than when in completely free state outside the body . thus , length l se of the marker location in fig3 , and the incremental spacing between markers 30 in micro catheter 20 of fig2 , may have dimensions that are larger than the unconstrained length of the stent 38 . from the discussion above it will be appreciated that the invention can be embodied in various ways , including the following : 1 . an apparatus for precision delivery of a stent within a lumen of the body , comprising : a delivery wire having a proximal end and a distal end ; wherein the distal end of the delivery wire is configured to support an expandable stent in a compressed , elongated configuration ; wherein the delivery wire comprises a radio - opaque marker disposed at a predetermined distance from the distal end of the delivery wire ; and wherein the predetermined distance corresponds to a length of the stent when the stent is in a shortened , unconstrained state . 2 . an apparatus as in any of the previous embodiments : wherein the predetermined distance corresponds to a length of a braided stent in a shortened , unconstrained state ; and wherein the length of the braided stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within a catheter . 3 . an apparatus as in any of the previous embodiments : wherein the predetermined distance corresponds to a length of a micro - machined stent in a shortened , unconstrained state ; and wherein the length of the micro - machined stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within a catheter . 4 . an apparatus as in any of the previous embodiments : wherein the delivery wire and stent are configured to be delivered through a catheter in the compressed , elongated configuration to a treatment location within the lumen . 5 . an apparatus as in any of the previous embodiments ; wherein the treatment location comprises an aneurysm within a cerebral blood vessel ; and wherein the stent is configured to span across the aneurysm when disposed at the treatment location in the unconstrained state . 6 . an apparatus for precision delivery of a stent within a lumen of the body , comprising : a micro - catheter having a proximal end and a distal end ; wherein the micro - catheter is configured to house an expandable stent in a compressed , elongated configuration for delivery to a treatment location within the lumen ; and wherein the micro - catheter comprises three or more radio - opaque markers disposed at spaced - apart intervals from the distal end of the micro - catheter . 7 . an apparatus as in any of the previous embodiments , wherein the spaced - apart marker intervals correspond to a length of the stent when the stent is in a shortened , unconstrained state . 8 . an apparatus as in any of the previous embodiments , wherein the spaced - apart marker intervals form a ruler visible under radiographic imaging . 9 . an apparatus as in any of the previous embodiments : wherein the spaced - apart intervals correspond to a length of a braided stent in a shortened , unconstrained state ; and wherein the length of the braided stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 10 . an apparatus as in any of the previous embodiments : wherein the predetermined distance corresponds to a length of a micro - machined stent in a shortened , unconstrained state ; and wherein the length of the micro - machined stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 11 . an apparatus as in any of the previous embodiments : wherein the micro - catheter is sized to allow delivery of the stent through the micro - catheter in the compressed , elongated configuration to the treatment location within the lumen . 12 . an apparatus as in any of the previous embodiments : wherein the treatment location comprises an aneurysm within a cerebral blood vessel ; and wherein the stent is configured to span across the aneurysm when disposed at the treatment location in the unconstrained state . 13 . a system for precision delivery of a stent within a lumen of the body , comprising : a delivery wire having a proximal end and a distal end ; wherein the distal end of the delivery wire is configured to support an expandable stent in a compressed , elongated configuration ; a micro - catheter having a proximal end and a distal end ; wherein the micro - catheter is configured to house the expandable stent while in the compressed , elongated configuration on the delivery wire for delivery to a treatment location within the lumen ; wherein the delivery wire comprises a radio - opaque marker disposed at a predetermined distance from the distal end of the delivery wire ; and wherein the predetermined distance corresponds to a length of the stent when the stent is in a shortened , unconstrained state . 14 . a system as in any of the previous embodiments : wherein the predetermined distance corresponds to a length of a braided stent in a shortened , unconstrained state ; and wherein the length of the braided stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 15 . a system as in any of the previous embodiments : wherein the predetermined distance corresponds to a length of a micro - machined stent in a shortened , unconstrained state ; and wherein the length of the micro - machined stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 16 . a system as in any of the previous embodiments : wherein the treatment location comprises an aneurysm within a cerebral blood vessel ; and wherein the stent is configured to span across the aneurysm when disposed at the treatment location in the unconstrained state . 17 . a system as in any of the previous embodiments , wherein the micro - catheter comprises a plurality of radio - opaque markers disposed at spaced - apart intervals from the distal end of the micro - catheter to form a ruler visible under radiographic imaging . 18 . a method for precision delivery of a stent within a lumen of the body , comprising : positioning a distal end of a micro - catheter to a treatment location within the lumen ; delivering an expandable stent in a compressed , elongated configuration on a distal end of a delivery wire through the micro - catheter to the distal end of the micro - catheter ; wherein the delivery wire comprises a radio - opaque marker disposed at a predetermined distance from the distal end of the delivery wire ; and wherein the predetermined distance corresponds to a length of the stent when the stent is in a shortened , unconstrained state ; locating the distal end of the micro - catheter at a delivery location corresponding to the radio - opaque marker and the treatment location ; and extracting the stent from the distal end of the micro - catheter at the delivery location . 19 . a method as in any of the previous embodiments : wherein the predetermined distance corresponds to a length of a braided stent in a shortened , unconstrained state ; and wherein the length of the braided stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 20 . a method as in any of the previous embodiments : wherein the treatment location comprises an aneurysm within a cerebral blood vessel ; and wherein the delivery location is selected such that the stent spans across the aneurysm when disposed at the treatment location in the unconstrained state . 21 . a method for precision delivery of a stent within a lumen of the body , comprising : positioning a distal end of a micro - catheter to a treatment location within the lumen ; delivering an expandable stent in a compressed , elongated configuration through the micro - catheter to the distal end of the micro - catheter ; wherein the micro - catheter comprises three or more radio - opaque markers disposed at spaced - apart intervals from the distal end of the micro - catheter ; and locating the distal end of the micro - catheter at a delivery location corresponding to the radio - opaque marker and the treatment location ; and extracting the stent from the distal end of the micro - catheter at the delivery location . 22 . a method as in any of the previous embodiments , wherein the spaced - apart marker intervals correspond to a length of the stent when the stent is in a shortened , unconstrained state . 23 . a method as in any of the previous embodiments , wherein the spaced - apart marker intervals form a ruler visible under radiographic imaging . 24 . a method as in any of the previous embodiments : wherein the spaced - apart intervals correspond to a length of a braided stent in a shortened , unconstrained state ; and wherein the length of the braided stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 25 . a method as in any of the previous embodiments : wherein the spaced - apart intervals corresponds to a length of a micro - machined stent in a shortened , unconstrained state ; and wherein the length of the micro - machined stent in a shortened , unconstrained state is smaller than the length of the braided stent when in a constrained state within the micro - catheter . 26 . a method as in any of the previous embodiments : wherein the micro - catheter is sized to allow delivery of the stent through the micro - catheter in the compressed , elongated configuration to the treatment location within the lumen . 27 . a method as in any of the previous embodiments : wherein the treatment location comprises an aneurysm within a cerebral blood vessel ; and wherein the delivery location is selected such that the stent spans across the aneurysm when disposed at the treatment location in the unconstrained state . although the description herein contains many details , these should not be construed as limiting the scope of the disclosure but as merely providing illustrations of some of the presently preferred embodiments . therefore , it will be appreciated that the scope of the disclosure fully encompasses other embodiments which may become obvious to those skilled in the art . in the claims , reference to an element in the singular is not intended to mean “ one and only one ” unless explicitly so stated , but rather “ one or more .” all structural , chemical , and functional equivalents to the elements of the disclosed embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims . furthermore , no element , component , or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element , component , or method step is explicitly recited in the claims . no claim element herein is to be construed as a “ means plus function ” element unless the element is expressly recited using the phrase “ means for ”. no claim element herein is to be construed as a “ step plus function ” element unless the element is expressly recited using the phrase “ step for ”.
a micro - catheter delivery system that includes radio - opaque marker bands optimized for the purpose of length reference to assist the operating physician to estimate the length of a tortuous lesion and to anticipate foreshortening of stents with multiple sizes . the radio - opaque maker bands are positioned at the distal end of a stent delivery catheter at a certain intervals acts like a ruler . in another embodiment , a stent delivery system includes a stent delivery wire with one or more radio - opaque markers distanced from the stent distal end for indicating the non - restrained length of the stent when discharged from the delivery catheter .