covered SEMS), or small areas at the ends may be left uncovered (partly covered SEMS) [

The Wallstent is a self-expanding stent made from a biomedical stainless-steel alloy with a radiopaque core, fi laments woven in a tubular fashion, and fl exible construction [ 16, 17 ] . The Wallstent is available in 40-, 60-, 80-, and 100-mm lengths. The available diameters of the fully expanded Wallstent are 8 and 10 mm. The deliv­ery device has an outside diameter of 7.5 Fr and consists of a 0.035-in. guidewire compatible introducer catheter, on which the compressed SEMS is constrained by a hydrophilic-coated outer sheath. The delivery device has a tapered tip to allow ease of passage. The stent is deployed by withdrawing the outer sheath releasing the SEMS in the desired location. The Wallstent is radiopaque (Fig. 6.1 ), and there are four radiopaque markers on the delivery device to guide precision deployment. The stent can be recaptured, if need be, and repositioned to 90% of full stent release. Wallstents can be deployed entirely within the bile duct or in transpapillary position. There is 33% foreshortening of the Wallstent postdeployment. Transpapillary posi­tioned, uncovered Wallstents may be reliably removed within 12–24 h after insertion. Subsequently, the stent becomes embedded into the bile duct wall, and it is more dif fi cult, if not impossible, to remove.

This new SEMS features an improved metal material to form the wire of the stent. Platinol (platinum-cored nitinol) wire achieves a 30–40% reduction in axial force while conferring suf fi cient expandability comparable to that of the Wallstent. This may preclude complications immediately after stent placement, including stent kinking and migration. Furthermore, the stent is designed

aid in repositioning. There is a yellow transition zone on the catheter, four fl uoroscopy markers, and a reconstrainment limit marker on the handle to aid in placement.

The Zilver biliary stent [ 18– 21 ] was the fi rst stent of its kind made of fl exible laser-cut nitinol tub­ing, which makes it an open-cell-design stent. The cells of an open-cell-design stent are simply connected, without the tight weaving or interlock­ing of closed-cell-design stents. Laser cut and polished from solid tubing, this SEMS produces more metal coverage with smaller interstices than previous designs, theoretically impeding tissue ingrowth. Zilver “Z” con fi guration applies uni­form radial strength evenly to the biliary duct. Nitinol, which is inherently kink resistant, allows the stent to conform to the ductal wall while pro­viding reliable patency. Stent ends are atraumatic, potentially reducing the risk of ulceration or per­foration. The four gold markers on each end and 0% foreshortening of the stent assist in precise positioning of the stent. The Zilver stent is, in fact, a modi fi cation of the original Gianturco­Rosch “Z” stent. The “Z” stent was a stainless steel wire bent into a continuous Z-shaped pattern forming a cylinder. This was modi fi ed by string­ing together individual cages by adding small eyelets making the stent more fl exible and com­pressible. This is known as the spiral Z stent. The spiral Z stent is available in 5.7- and 7.5-cm lengths and 10 mm in diameter. There are silver radiopaque markers along the length of the stent. Another modi fi cation of the design, the Za stent, incorporates nitinol in place of stainless steel making the stent more fl exible. The available lengths of the Za stent are 4, 6, and 8 cm with a diameter of 10 mm. There are gold radiopaque markers in the middle and at the end of the Za stent for fl uoroscopic visualization. A novel, self­expanding nonforeshortening metal stent has been developed with a 6-Fr delivery system (Zilver 635; Cook Medical, Winston-Salem, NC) to poten­tially enable simultaneous side-by-side bilateral hilar deployment [ 21 ] . The current commercially

which helps to improve conformability. Three radiopaque markers are fi xed to both ends as well as two at the middle.