Abstract:
Methods and apparatus for aiding in support and repair of a thoracic aneurysm of the aortic arch. A stent graft provides a window therein, which enables blood to flow freely into branch vessels which would otherwise be occluded by the stent graft. Additionally, the stent portions of the stent graft are configured to minimize the risk of overexpansion, wherein stents are provided in the window portion.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of PCT/US2006/034340 filed on Sep. 1, 2006; which claims priority to U.S. Provisional Patent Application 60/713,595 filed Sep. 1, 2005, all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is the treatment of vascular abnormalities and defects. 
     BACKGROUND OF THE INVENTION 
     “Thoracic aortic aneurysm” is the term used to describe a condition where a segment of the aorta in the thoracic region is dilated and is treatable when it reaches more than 50% of its original diameter. Thoracic aortic aneurysms are known to be caused by hardening of the arteries (atherosclerosis), high blood pressure (hypertension), congenital disorders such as Marfan&#39;s Syndrome, trauma, or less commonly, syphilis. Atherosclerosis is by far the most common cause. Thoracic aneurysms occur in the ascending aorta (approximately 25% of the time), the aortic arch (approximately 25% of the time) or the descending thoracic aorta (approximately 50% of the time). 
     The thoracic aorta has numerous arterial branches. The arch of the aorta has three major branches extending therefrom, all of which arise from the convex upper surface of the arch and ascend through the superior thoracic aperture to the root of the neck. The brachiocephalic artery originates anterior to the trachea. The brachiocephalic artery divides into two branches, the right subclavian artery (which supplies blood to the right arm) and the right common carotid artery (which supplies blood to the right side of the head and neck). The left common carotid artery arises from the arch of the aorta just to the left of the origin of the brachiocephalic artery. The left common carotid artery supplies blood to the left side of the head and neck. The third branch arising from the aortic arch, the left subclavian artery, originates behind and just to the left of the origin of the left common carotid artery and supplies blood to the left arm. 
     When an aneurysm of the aorta occurs, most patients have no symptoms until the aneurysm begins to leak or expand. Most non-leaking thoracic aneurysms of the aortic arch are detected by tests—usually a chest x-ray or a chest CT scan—that are run for other reasons. Chest or back pain may indicate acute expansion or leakage of the aneurysm. An aortogram (a special set of x-ray images made as a result of injection of dye into the aorta) also may identify the location and extent of the aneurysm and identify any branch arteries of the aorta that are also involved. For patients with thoracic aneurysms of the aortic arch, surgery to replace the aorta may be performed where the aorta is replaced with a fabric substitute in an operation that uses a heart-lung machine. In such a case, the aneurysmal portion of the aorta is removed or opened and a substitute lumen is sewn across the aneurysmal portion. Such surgery is highly invasive, requires an extended recovery period and, therefore, cannot be performed on individuals in fragile health or with other contraindicative factors. 
     Alternatively, the aneurysmal region of the aorta can be bypassed by use of a tubular exclusion device, e.g., by a stent graft placed inside the vessel spanning the aneurysmal portion of the vessel, to seal off the aneurysmal portion from further exposure to blood flowing through the aorta. A stent graft can be implanted without a chest incision, using specialized catheters that are introduced through arteries, usually through incisions in the groin region of the patient. The use of stent grafts to internally bypass, within the aorta or flow lumen, the aneurysmal site, is also not without issues. In particular, where a stent graft is used in a thoracic location, care must be taken so that critical branch arteries are not covered or occluded by the stent graft yet the stent graft must seal against the aorta wall and provide a flow conduit for blood to flow past the aneurysmal site. Where the aneurysm is located immediately adjacent to the branch arteries, there is a need to deploy the stent graft in a location which partially or fully extends across the location of the origin of the branch arteries from the aorta to ensure sealing of the stent graft to the artery wall. However, there is not presently an acceptable paradigm for enabling flow to the branch artery when a stent graft is deployed. 
     Additionally, where an aneurysm develops, an aortic dissection may develop as a side effect of the thinning of the aorta wall during an aneurysmal event or as a consequence of the weakening of the aorta wall which brought on the aneurysmal event. When such dissection occurs, an inner lumen wall layer and an outer lumen wall layer of the aorta become separated, such that a gap may form therebetween. If blood can access this gap, such as through a tear in the inner wall of the aorta, the dissection may increase in size and the inner blood vessel wall layer may extend inwardly of the flow lumen, reducing the flow cross-section for blood flow therethrough and forming a region between the inner and outer lumen wall layers where blood can collect under systemic pressure. This blood may further aggravate the aneurysmal condition, increasing the risk of a rupture of the aneurysm. Such a dissection may occur adjacent to, and extend from, the aneurysmal aortic site, such that the placement of a stent graft to exclude the aneurysm may not address the dissected lumen condition and fresh blood can access the dissection and perhaps, through the region between the lumen walls, supply fresh blood to the aneurysm leading to further progression thereof. 
     Thus, there is a desire in the art to achieve a greater success of aneurysm repair and healing of the aortic arch, and to address the dissected lumen wall condition. 
     SUMMARY OF THE INVENTION 
     Embodiments according to the present invention address aneurysm repair and stabilization. Specifically, a stent graft for use in the treatment of thoracic aneurysms of the aortic arch that spans the aneurysmal region, while not blocking or otherwise impeding the flow of blood to the three arteries that branch off of the aortic arch. 
     Thus, in one embodiment according to the invention there is provided an intravascular treatment device, comprising various embodiments of a window configured stent graft locatable at an aneurysmal site in the aortic arch. The treatment device may, additionally, provide localized radially outward pressure over a dissected area of the lumen, which can extend from the aneurysmal location and may extend adjacent to the branch artery locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of the invention, briefly summarized above, may be had by reference to the embodiments according to the invention described in the present specification and illustrated in the appended drawings. 
         FIG. 1  is an artist&#39;s rendering of a heart and aorta with a thoracic aneurysm of the aortal arch. 
         FIG. 2  is an artist&#39;s rendering of an the heart and aortic arch of  FIG. 1 , wherein the aortic arch is in a healthy condition; 
         FIG. 3  is an artist&#39;s rendering, in cutaway, of the aneurysmal aortic arch of  FIG. 1 , including a dissected portion thereof; 
         FIGS. 4A ,  4 B,  4 C and  4 D are side views of various embodiments of the stent graft according to the present invention. 
         FIG. 5  is a plan view of a preform of the stent portion of the stent graft. 
         FIG. 6  is a perspective view of the preform of  FIG. 5 , further configured as a stent. 
         FIG. 7  is a partial sectional view of a thoracic aneurysm of the aortal arch of  FIG. 3  with the embodiment of the stent graft shown in  FIG. 4B  located therein. 
         FIG. 8  is a partial sectional view of a thoracic aneurysm of the aortal arch with an embodiment of the stent graft shown in  FIG. 4A  placed therein. 
         FIG. 9  is a perspective view of the stent graft of  FIG. 4B , positioning around a delivery catheter in preparation for being compressed and having a delivery catheter moved into position surrounding it. 
         FIG. 10  is a perspective view of the stent graft in  FIG. 9  compressed to a size smaller than the internal circumference of the sheath of a delivery catheter. 
         FIG. 11  is a partial view of a schematic view of the sheath of the delivery catheter, partially cut-away, showing the stent graft received therein. 
         FIG. 12  is a partial cutaway view of an aortic arch undergoing aneurysm, having the guide wire needed to guide a catheter to the aneurysmal location shown extending therethrough. 
         FIG. 13  is a view of the aortic arch of  FIG. 12 , showing a catheter in a position to deploy the stent graft therein. 
         FIG. 14  is a view of the aortic arch as in  FIG. 13 , showing the stent graft partially deployed therein. 
         FIG. 15  is a view of the aortic arch of  FIG. 7 , showing the stent graft of  FIG. 4B  deployed therein and a balloon catheter deployed within the stent graft to additionally configure portions thereof in the aorta. 
     
    
    
     DETAILED DESCRIPTION 
     Methods and apparatus for stabilizing and treating an aneurysm of the aortic arch include positioning an endovascular stent graft with various branch artery aligned window configurations in an aneurysmal site in the aortic arch. The stent graft excludes blood flow to the weakened vessel wall at the aneurysmal site, but, as a result of the window configuration, allows unimpeded blood flow from the aortic arch to the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery. 
     Referring initially to  FIG. 1 , there is shown an aneurysm of the aorta  12 , such that the aorta is enlarged at an aneurysmal site  14 . The aneurysm at the aneurysmal site  14  forms an aneurysmal bulge or sac  18  which is a weakened portion of the aorta wall which is less capable of supporting the systemic blood flow pressure than adjacent regions. As a result of this loss of strength, as well as loss of elasticity, the aorta wall expands outwardly into a bulge or sac  18 . If left untreated, the aneurysmal sac  18  may continue to deteriorate, weaken, increase in size, and eventually tear or burst. The heart  10 , the aortic arch  50 , with three branching arteries, the brachiocephalic trunk ( 52 ), the left common carotid artery ( 54 ), and the left subclavian artery ( 56 ) are shown, such that they are diametrically opposed to, or circumferentially adjacent to, the aneurysmal sac  18 . Typically, an aneurysmal aortic condition is considered to require treatment if the diameter of the aorta, including the aneurysmal sac  18 , exceeds 150% of the diameter of the healthy aorta. The aorta  12  wall extends circumferentially outwardly at the aneurysmal site  14  to form the aneurysmal sac  18 , at which aorta  12  wall location the aorta wall  12  is stretched and weakened, in comparison to the aorta  12  of  FIG. 2 , where no aneurysm is present and the aorta  12  wall remains non-distended such that the diameter of the aorta  12  is relatively uniform as it extends away from the heart in the direction of, and past, the branch arteries,  52 ,  54 , and  56 . 
     Referring now to  FIG. 3 , an artist&#39;s rendition of the aorta  12  of  FIG. 1  is shown with the aneurysmal region of the arch in a cutaway view, such that the effect of the aneurysm upon the aorta wall is clear. In this Figure, the aneurysmal sac  18  is present, in the aorta  12 , intermediate of the heart (not shown, but to the left, in  FIG. 3 ) and adjacent to the branch arteries  52 ,  54 , and  56 . Also present, in this aorta  12 , is a dissected region  58 , where the blood vessel inner wall (layer)  60  has pulled away from the blood vessel outer wall (layer)  62 , in a position in the aorta adjacent to (upstream from) the location of the branch arteries  52 ,  54 , and  56 . Also present is a tear  64 , in the inner aorta wall (layer)  60 , through which blood, under systemic pressure, can reach the gap  66  formed between the inner and outer layers of the aorta wall  60  and  62 . Thus, for treatment of these aortic conditions, a single stent graft will need to span and form a synthetic flow lumen past the aneurysmal sac  18 , seal off blood supply through the tear  64  and may be configured to compress (or press) the aorta inner wall layer  60  with the outer wall layer  62  forming the dissection. 
       FIGS. 4A ,  4 B,  4 C, and  4 D are side views of embodiments of a stent graft according to the present invention, which are capable of providing the sealing off of the aneurysmal sac  18  and the tear  64 , while pressing the aorta inner wall layer  60  toward the outer wall layer  62  adjacent to the tear  64 . In each embodiment of the stent graft shown in these Figures, there is provided a synthetic flow lumen to bypass or exclude the aneurysmal sac  18  and likewise seal off and compress (or press or exert force on) the dissected aorta wall  12  adjacent to the branch arteries  52 ,  54 , and  56  while simultaneously allowing blood flow to the branch arteries  52 ,  54 , and  56 . Generally, the stent grafts of the embodiments can be considered to include one with a single window configured to span the location of all three of the branch arteries ( FIG. 4B ), a configuration with a discrete window for each branch artery ( FIG. 4A ), and configurations where one window accommodates a single one of the branch arteries and a second window accommodates the remaining two of the branch arteries ( FIGS. 4C and 4D ). 
     Referring initially to  FIG. 4B , there is shown generally a stent graft  20  comprising a series of stents  22   a ,  22   b  . . .  22   f . in a cylindrically formed framework, having a graft portion  24 , having a single window  32  therein, disposed over the stents  22   a ,  22   b , etc. To form the stent graft  20 , a plurality of stents  22   a ,  22   b , etc. must be formed, and secured to a tubular graft portion  24  structure which will be described in further detail. To form the stents  22   a  through  22   f , a wire  33  ( FIG. 5 ), in the embodiments shown in  FIGS. 4  ( 4 A to  4 D), made of Nitinol, is formed into a zig-zag pattern such as shown in  FIG. 5 . In this configuration, this forms a plurality of staggered, opposed apexes  26   a ,  26   b , et. seq. separated by substantially straight sections (struts)  28   a ,  28   b , et. seq. terminating in opposed ends  30   a ,  30   b . Once formed as shown in  FIG. 5 , the zig-zag wire is formed into a hoop, as shown in  FIG. 6  (where a plurality of hoop shaped stents are shown), such that ends  30   a  and  30   b  are joined, to create each of stents  22   a , et. seq. 
     To form the graft portion  24  of the stent graft  20  of  FIG. 4B , a length of tubular woven bio-compatible polyester of the length and diameter desired for exclusion of the aneurysmal sac  18  and also of sufficient length to span the branch arteries shown as  52 ,  54 , and  56  in  FIG. 3 , is selected, and the fabric is cut (or otherwise configured) to form a window  32  therethrough as shown in  FIG. 4B . The length and width of the window are selected to ensure that the window  32 , when the stent graft  20  is deployed in the aneurysmal; aorta  12 , spans opening of the branch arteries  52 ,  54 , and  56  from the aorta  12 , yet, the portion of the graft material  24  circumferentially adjacent to the window can push against, and seal against, the aorta wall, to exclude blood flow to the aneurysmal sac  18  as shown in  FIG. 7 . To seal the cut edges of the window  32 , the fabric adjacent thereto is subject to a temperature sufficient to cause the material to reform slightly (or be cauterized or melt). The tubular woven fabric forming the graft may be of a single piece of material, or of multiple pieces of material sewn or otherwise attached together. Once the window  32  is cut or formed in the graft material, the remaining graft material forms first and second hoops  21 ,  23 , and a spanning semi-circumferential portion  25  extending therebetween across the underside, or opposed to, the window  32 . The stents  22   a  through  22   f  are then compressed and placed inside of the graft portion  24 , and allowed to expand against the inner surface of the material forming the graft portion  24 . Each of the stents  22   a - 22   f  is individually sewn to the adjacent graft material, to secure the stents  22   a - 22   f  to the graft portion  24 . As shown in  FIG. 4B , the stents  22   a  and  22   f  are located within, and fully supported against, an enveloping portion of the graft portion  24  formed by first and second hoops  21 ,  23 , and stents  22   b,    22   c,    22   d  and  22   e  are located such that a portion thereof extend about the perimeter of the window  32 , in a position substantially mimicking the position of the graft material removed to form the window  34  as if the graft material were not removed to form the window  34 . Stents  22   b - 22   e  are maintained in the stent graft by being sewn, or otherwise affixed to, the semi circumferential portion  25 . Additionally, spanning wires (connecting bars)  27 , of the same material and diameter of the wire comprising the stents  22   a,  et. seq., may be deployed between adjacent stents, typically between adjacent apexes thereof, in three or four locations about the circumference of the stents  22   a - 22   f,  such as shown between stents  22   a  and  22   b,  and crimped or otherwise affixed thereto, to maintain additional rigidity of the stent graft between the stents  22   a,  et. seq. Further expansion limiting hoop wires or strong durable fibers (not shown) can be employed to assure that the stents positioned in the open area  32  of the graft do not expand substantially beyond the limits of the tubular configuration of the thoracic side opening stent graft whose diameter along its length is approximated by the graft portion  24  surrounding the first and second hoops  21 ,  23 . The expansion limiting hoop wires can be sewn or crimped to the individual stents in the opening or can be part of flexible lattice work that allows the tubular structure to bend as needed to confirm to the aortic arch, but minimizes the chance that a potion of a stent will end up in an undesired position or configuration outside the confines of a curved cylinder that tracks to and through the aortic arch mimicking the aorta itself. 
     The stent graft  20  of  FIG. 4B  is shown, deployed, in  FIG. 7 , wherein the window  34  is aligned with the branch arteries  52 ,  54 , and  56  such that no portion of the graft portion  24  of the stent graft  20  overlays the intersection of the aorta  12  with any one of branch arteries  52 ,  54 , or  56 . The opposed hoops  21 ,  23  of the stent graft  20  are engaged against the inner aorta wall  60  and seal the stent graft aorta wall interface, and the portion of the graft spanning partial-circumferential portion  25  adjacent to the opening of the window  32  through the graft material  24  likewise is expanded against, and seals against, the aorta inner wall  60  to seal off the passage of blood from the interior of the stent graft  20  to the aneurysmal sac  18 . Additionally, the portion of the stent graft  20  overlying the dissected region  58  of the aorta presses the inner wall layer  60  toward the outer wall layer  62  of the aorta  12  (together) and likewise seals the tear  64  in the aorta inner wall  60 . Thus, blood flow through the aorta  12  is excluded from the aneurysmal sac  18 , the dissection region  58  is closed off from fresh blood supply through the tear  64 , and the inner and outer walls of the aorta  12 , otherwise separated at the dissection region  58 , are pushed together. 
     One problematic issue inherent in the in the use of the stent graft  20  shown in  FIG. 4B  is the contact between the partially unsupported portions of stents  22   b,    22   c,    22   d,  and  22   e,  i.e., stents deployed such that the outward extension thereof is not limited by a full hoop of graft material, and the aorta  12  wall. These partially unsupported stents  22   b - 22   e  must provide sufficient circumferential force, when deployed, to seal the portions of the semi-circumferential spanning portion  25  adjacent to the window  32  against the adjacent aorta inner wall  60 , yet they must not overload or overextend (overexpand) into the aorta wall  60  in such a manner as to cause damage thereto. In the embodiment shown in  FIG. 4B , the stents  22   b - 22   e  which are positioned within the window  32  are partially unrestrained, as they are not surrounded and thus not completely bounded and compressed by the graft portion  24  as are stents  22   a  and  22   f . Thus, the stents  22   b - 22   e  may overextend into and damage the aorta  12  wall. In particular, there is a risk, in the event of overextension of the stents  22   b - 22   e,  that an apex such as apex  26   a  may puncture or tear the aorta  12  wall. To prevent this occurrence, (if the hoop wire/lattice work configuration discussed earlier is not used) the relaxed circumference of the partially unrestrained by the graft portion stents  22   b - 22   e  may be smaller than that of the restrained stents  22   a - 22   f . Preferably, the restrained stents  22   a,    22   f  have a relaxed (or unrestrained) circumference larger than that of the inner circumference of the graft portion  24  in the region of the graft portion  24  in which they are to be located, i.e., the first and second hoops  21 ,  23  and the partially unrestrained stents  22   b  to  22   e  have a circumference which is the same size, or slightly smaller, on the order of, or slightly smaller than, the inner circumference of the graft portion  24  in its unbiased by the stent portions  22   a  or  22   f  state or condition. Thus, the maximum extension of the stent portions  22   b - 22   e  is on the order of the free or unbiased circumference of the graft portion  24 , and thus overextension of the stents  22   b  to  22   e  is prevented, yet sufficient force is exerted radially by the stent portions  22   b  to  22   e  against the aorta  12  wall to cause the semi-circumferential spanning portion  25  of the stent graft  20  to seal against the aorta wall at locations where it contacts the aorta  12  wall adjacent to the window  32 . 
     Referring now to  FIG. 4A , there is shown a further embodiment according to the present invention, in which the single window  32  of the embodiment shown in  FIG. 4B  is replaced with a stent graft  100  having a plurality of individual windows  102 ,  104 , and  106 , each one configured to span the opening of each branch artery  52 ,  54 , and  58  from the aorta  12 . To form these windows, graft material  110  having a length sufficient to span an aneurysmal sac  18  and enable sealing of the stent graft  100  with aortic wall tissue at either side thereof is further processed by cutting three generally rectangular or circular segments out of its tubular wall  108 . The windows  102 ,  104 , and  106  are each located in the graft material  110  to correspond, when stent graft  100  is deployed, with a location of one of the branch artery  52 ,  54 ,  56  intersection locations with the aorta  12 . Again, as with stent graft  20 , the location of the cut in the graft material  110  is heat cauterized to prevent fraying. The cutting of the three windows  102 ,  104  and  106  provides, longitudinally adjacent to the windows, a series of continuous hoops of the graft material  110 . These hoops include inlet hoop  112 , outlet hoop  114 , first intermediate hoop  116  and second intermediate hoop  118 . Window  102  is located between inlet hoop  112  and first intermediate hoop  116 , window  104  is located between first intermediate hoop  116  and second intermediate hoop  118 , and window  106  is located between second intermediate hoop  118  and outlet hoop  114 . 
     To prepare stent graft  100 , stents  120 , having the same configuration as the stents described herein with reference to  FIGS. 5 and 6 , are located within the graft material  100  having the windows  102 ,  104 , and  106  previously formed therein. In the configuration of stent graft  100  shown, five stents,  120   a  to  120   e,  are used. Stents  120   a  and  120   e  are shown in phantom, and are fully received within, and restrained by, inlet hoop  112  and outlet hoop  114  respectively. Stent  120   b  spans the window  102 , but its opposed apexes  122 ,  124  are received within, and restrained by, inlet hoop  112  and first intermediate hoop  116 . Likewise stent  120   c  is disposed to span window  104 , such that the opposed apexes  122 ,  124  are located within, and are restrained by, first intermediate hoop  116  and second intermediate hoop  118 . Likewise, stent  120   d  spans window  106 , and the opposed apexes  122 ,  124  thereof are disposed within, and restrained by, second intermediate hoop  118  and outlet hoop  114 . As with the configuration of stent graft  20  of  FIG. 4B , spanning wires (not shown) may be deployed between adjacent stents  120   a ,  120   b , etc. 
     In contrast to the structure of stent graft  20 , wherein their exists a need to differentially size the restrained stents  22   a ,  22   f  as compared to unrestrained stents  22   b - 22   e , the retraining capability provided by the hoops  112 - 118 , and the positioning of the apexes  122 ,  124  of the stents  120   b - 120   d  within these hoops  112 - 118 , helps prevent overextension of the stents  120   b - 120   d  disposed across the windows  102 ,  104  and  106  and thus enables the use of stents of equal circumference throughout the stent graft  100 . Additionally, the hoops  112 - 118  provide additional sealing and pressing capacity to seal against the aorta wall adjacent to and intermediate of the branch arteries  52 ,  54 , and  56 , as shown with the deployed stent  100  in an aneurysmal aorta as shown in  FIG. 8 . However, the use of three individual windows  102 ,  104 , and  106  requires more precision, during deployment, to ensure that each window corresponds to a branch artery location. 
     Referring now to  FIG. 4C , an additional embodiment of a stent graft  200  useful for the treatment of aneurysm of the aortic arch is shown. In this embodiment, the stent graft  200  includes two windows  202 ,  204 , the first window  202  sized to span branch arteries  52  and  54  (the arteries as shown in  FIG. 3 ), and a second smaller window  204  sized to span the position of the intersection of branch artery  56  and the aorta  12  (as such are shown in  FIG. 3 ). As with the embodiments of  FIGS. 4A and 4B , the stent graft  200  of this embodiment is constructed by cutting the windows  202 ,  204 , in a tubular length of graft material  208  of sufficient length to span the aneurysmal sac  18  (as the sac is shown in  FIG. 3 ) and sufficient diameter, when deployed, to seal against the aorta  12  wall. Window  202  is located between an inlet hoop  210  and an intermediate hoop  212 . Window  204  is located between intermediate hoop  212  and an outlet hoop  214 , each of the hoops  210 ,  212  and  214  formed of a continuous circumferential loop of graft material. In this embodiment, five stents  216   a - e  of the construction shown and described with respect to  FIGS. 5 and 6  are used. Stent  216  is fully received within inlet hoop  210 , and stent  216   e  is fully received within exit hoop  214 . Two stents  216   b  and  216   c  are disposed in window  202 , such that the apexes  218  of stent  216   b  are received within and restrained by inlet hoop  210  and apexes  220  thereof within the window  202  are unrestrained, and the apexes  220  of stent  216   c  are received in and restrained by intermediate hoop  212 , but apexes  218  thereof are unrestrained in the window  202 . Each of the stents  216   a - 216   e  is secured in the stent graft  200 , preferably by sewing the stents  216   a - e  to adjacent portions of the graft material  210 . Likewise, spanning wires, not shown, may be used to secure the stents  216   a - e  in a fixed longitudinal or spaced relationship, and provide additional hoop or radial strength to the stent graft  200  structure. Stent  216   d  spans second window  204 , with the opposed apexes  218 ,  220  thereof received within, and restrained by, intermediate hoop  212  and exit hoop  214  respectively. 
     As with the stent graft  20  of  FIG. 4B , the stents  216   b  and  216   c  are, at least partially, unrestrained. Therefore, if lattice work hoop expansion limiting structures (described above) are not used stents  216   b  and  216   c  are preferably sized to have a slightly smaller circumference than the remainder of stents  216   a ,  216   d  and  216   e , on the order of the unbiased by a stent circumference of the graft material  208 . When deployed in an aorta  12  having an aneurysmal condition, the window  202  will span the location of the intersection of the branch arteries  52  and  54 , ( FIG. 3 ), and window  204  will span the location of branch artery  56 . Alternatively, the stents  216   b  and  216   c  may be fully unrestrained, i.e., the apexes thereof not inserted within the adjacent hoops, and of a smaller circumference than stents  216   a, d , and  e  as was discussed with respect to the stent graft  20  of  FIG. 4B . Likewise, an additional stent may be located in the envelope of, and fully restrained by, intermediate hoop  212 . 
     Referring now to  FIG. 4D , an additional embodiment of a stent graft for treatment of ascending aortic aneurysm is shown. In this embodiment, stent graft  300  includes a tubular length of graft material  302 , into which two windows  304 ,  306  have been prepared such as by cutting out rectangular portions of the graft material  202  and heat sealing or cauterizing the cut edges to prevent fraying. Window  304  is sized to correspond with the location of the intersection of a single branch artery  52 , and window  306  is sized to correspond to the location of two branch arteries,  54  and  56 . The remaining graft material forms an inlet hoop  306 , an intermediate hoop  308  and outlet hoop  310 . Stents  312   a - 312   e  are disposed in the tubular segment of graft material  302 , such as by being sewn to adjacent portions of the graft material  302 . The stents  312   a - 312   e  have the general construction of the stents shown and described with respect to  FIGS. 5 and 6 , and stents  312   a  and  312   e  are fully located within, and restrained by inlet hoop  306  and outlet hoop  310  respectively. Stent  312  b spans window  304 , such that the opposed apexes  316 ,  318  thereof are restrained within inlet hoop  306  and intermediate hoop  308 , respectively. Stents  312   c  and  312   d  are disposed in window  306  such that the apexes  320  of stent  312   c  are restrained by intermediate hoop  308  and apexes  322  thereof are unrestrained in the window  306 , and stent  312   d  is positioned such that apexes  322  are held and restrained under exit hoop  310 , whereas the apexes  320  thereof are unrestrained. As in the construction shown in  FIG. 4C , the two stents  312   c ,  312   d  which are unrestrained, are configured of a smaller circumference than those which are restrained, to prevent damage to the flow lumen by overextension of the stents  312   c ,  312   d . Likewise, spanning wires may laterally extend between, and be secured to, adjacent ones of the stents  312   a , et. seq. When deployed in an aorta undergoing an aneurysmal condition, the inlet hoop and outlet hoops  302 ,  310  will seal against the aorta wall, and the graft material  302  is likewise biased to seal against any tears which it overlays and compress together any dissected regions it overlays. As with stent graft  200 , stents  312   c , d may be unrestrained, and of a slightly smaller diameter than stents  312   a, b  and  e , as was described wherein with respect to  FIG. 4B . Likewise, an additional stent may be located within, and fully restrained by, intermediate hoop  308 . 
     Referring now to  FIGS. 9 through 14 , a paradigm for deployment of the stent graft, in this example stent graft  20 , into the aneurysmal aortic arch is shown. To prepare the stent graft  20  for delivery, the stent graft  20  in one loading process is first cooled with air cooled by vapors of liquid nitrogen and positioned over a delivery catheter as shown in  FIG. 9 , and then radially compressed, along its longitudinal axis  330  to the condition shown in  FIG. 10 , such that it has an outer diameter or cross section capable of being fitted into the crossing profile of a delivery sheath or catheter. (In another configuration a camera iris type compression cylinder can surround the device and press it uniformly to a small diameter—without cooling). Prior to compressing of the stent graft  20 , a guidewire sheath central or middle member or catheter  356  is inserted through the inner circumference thereof, such that upon being compressed, the stent graft  20  surrounds and incorporates the middle member  356  extending therethrough. The stent graft  20 , in its still cold state shown in  FIG. 10  and having the middle member  356  disposed therethrough, is then held stationary as the outer sheath  358  of a catheter such as catheter  360  shown in  FIG. 11  is moved into place surrounding the stent graft. A tapered tip  352  is disposed at the end of the middle member  356 , such that the guidewire  350  ( FIG. 13 ) may pass through the middle member  356  and through an open end of the tapered tip  352 , and the tapered tip  352  also moves, with longitudinal movement of the middle member  356  with respect to the catheter outer sheath  358  ( FIG. 14 ). The tapered tip  352  helps reduce the vessel trauma associated with guiding the catheter to the aneurysmal aorta location and, being of a tapered configuration, is more easily guided into and through restricted or smaller diameter regions of the lumen leading to the aneurysmal location than would be a catheter having a continuous diameter of the outer sheath  358 . The middle member  356  also includes, a separate stop  370  (in cutaway of outer sheath  358  in  FIG. 11 ) is fixedly positioned longitudinally on the middle member  356  with, respect to the outer sheath  358 , such that, to deploy the stent graft  20 , the outer sheath  358  is retracted while the stop  370  remains stationary. Thus, the stent graft remains stationary within the aortic arch while the retraction of the outer sheath  358  releases the stent graft  20  therefrom. The stent graft  20  is thus ready for deployment in an aneurysmal aortic arch. 
     For delivery of the stent graft  20  to the aneurysmal location, an incision (not shown) is made, preferably in the patient&#39;s leg or groin and into the femoral artery therein, and a guide wire  350  is guided into the artery through the incision and pushed along the artery in the direction of the aortic arch. The guide wire  350  is initially inserted such that the end  353  thereof passes through the aneurysmal site  14  and past the aneurysmal sac  18  location in the aorta  12  as shown in  FIG. 12 . To enable proper placement of the guide wire  350 , the end  353  thereof may include a radiological marker thereon making the end  353  more easily visible through the use of a fluoroscope, although the guidewire  350  itself may be sufficiently fluoroscopically visible so as not to require the use of a marker. Likewise, the aorta  12  is radiologically marked, such as by injection of a liquid based radiological marker into the aorta  12  as part of the preparation of the patient for the placement of the stent graft  20 , such that the aneurysmal sac  18  and the location of the branch arteries  52 ,  54 , and  56  is readily visualized, with respect to the stent graft  20  and catheter, by the surgeon or other person deploying the stent graft  20 . Thus, by viewing a fluoroscope which is directed to the aorta  12 , the surgeon can properly locate the guide wire  350  and position the end  353  thereof adjacent to, and beyond, the aneurysmal sac  18 . The guide wire  350  is used to guide the catheter  360 , which has a substantially larger cross section than the guidewire  350 , to the aneurysmal location  14  in the aorta  12 . 
     Once the guide wire  350  is located as shown in  FIG. 13 , a catheter  360 , having the compressed stent graft  20  located in a sheath  358  therein as described with respect to  FIG. 11 , is guided through the artery on the guide wire  350  to a position just upstream, of i.e., to the heart side, of the aneurysmal sac  18  as shown in  FIG. 14 . At this point in time, the stent graft  20  may be deployed. Prior to deployment, the tapered tip  352 , on the end of guidewire sheath  356 , may be slightly moved away from the outer sheath  358  as shown in  FIG. 14 , in the direction of the heart, by pushing on the middle member  356  thereby exposing the stent graft  20  through the open end of the outer sheath  358 . To deploy the stent graft  20 , the outer sheath  358  is then pulled back i.e., away from the heart and to the right in  FIG. 14 , while holding the middle member  356  and the stop  370  ( FIG. 11 ) stationary. Thus the stent graft  20  is maintained in a stationary position in the aorta  12  resulting in the stent graft  20  being left behind in the aorta  12 , the first hoop  21  thereof seen emerging from the outer sheath  358  in  FIG. 14 . Because the stent graft according to the present embodiment is constructed of a shape memory material, the stent graft  20  will expand towards its as made state (relaxed—low energy), i.e., as shown in  FIG. 4B , without the need for an inflation device. During deployment, the stent graft  20  must be positioned such that its opposed ends span the aneurysmal sac  18 , and the window  32  thereof must be positioned to span the three branch arteries  52 ,  54 , and  56 . To accomplish this, the stent graft  20  may include radiological markers thereon (not shown), the orientation and position of which, relative to the branch arteries  52 ,  54  and  56  and the aneurysmal sac  18 , are used by the surgeon to properly deploy the stent graft  20 . Once the stent graft  20  is rotationally and longitudinally properly positioned in the aorta  12 , the outer sheath  358  is fully retracted to release the stent graft  20  into the deployed position as shown in  FIG. 7 , and the catheter  360  composed of the guide wire  350 , tapered tip  352 , middle member  356  and outer sheath  358  are removed through the leg incision. 
     After the stent graft  20  is deployed, the surgeon may utilize a balloon catheter  380 , as shown in  FIG. 15 , into the interior of the deployed stent graft  20 , and use a contrast saline solution mix to inflate a balloon  382  contained therein and extendable therefrom, to slightly expand or assure full expansion of the stent graft  20 , and to remove any wrinkles in the graft material  24 . During this procedure, the balloon should only be inflated within the bounds of the first and second hoops  21 ,  23 , so as not to over-extend the stents  22   b - 22   e  into the aorta wall. Once this procedure is completed, the balloon  382  may be deflated, the catheter  380  removed, and the incisions in the artery and leg or groin closed. Each of the embodiments of the stent graft shown and described herein are likewise deployable using this technique, such that the windows therein are alignable with the branch arteries  52 ,  54 , and  56  to prevent the blockage of the branch arteries intersection with aorta  12 . 
     The stent grafts of the embodiments shown and described herein have been described in terms of using a shape memory material as the stent material. Alternatively, other biocompatible materials such as stainless steel could be used to form the stent portions of the stent graft. In such a case, the deployment of the stent graft into the aorta might require the use of an inflation device, positioned within the stent graft, which could be inflated to cause the stent graft to retake it&#39;s as-manufactured (relaxed/unconstrained) form. Such an inflation device can be a balloon, which is located in, and spans the length of, the stent graft within the circumference prescribed by the graft portion, and is attached to a tube extending outwardly therefrom. When the stent graft is compressed and configured for placement in a catheter, the balloon is located therein, and the tube is fed down the catheter such that the surgeon can apply a pressure source to the tube to direct a contrast liquid or other fluid, under pressure, to the balloon, to inflate the stent graft at the appropriate time. Upon completion of the deployment of the stent graft, the balloon is removed with the catheter. 
     While the present invention has been described with reference to specific embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, or process to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the invention. 
     All references cited herein are to aid in the understanding of the invention, and are incorporated in their entireties for all purposes.