Establishing an endovascular carotid stent program

FDA approval of carotid stent and distal protection devices has transformed carotid artery stenting (CAS) from an investigational procedure to a practical application. Recent approval by the Center for Medicare Services (CMS) has ensured that CAS will be a part of everyday practice throughout the country. To establish a competitive endovascular carotid stent program, one needs to develop an effective strategy. The key to success is substance and service. A high-quality clinical program with excellent communication between the patient and referring physician is essential. You must first get access to the patient by establishing a clinical practice. As a radiologist, you have the advantage of gaining access by identifying appropriate patients through noninvasive vascular labs, CTA, and MRA. An algorithm-driven evaluation and treatment protocol with good pre- and postoperative care, along with a quality assurance program, will ensure that your carotid stent program has substance and delivers optimal service. With good planning, you will have a firm clinical foundation for treatment of carotid artery stenosis in your community. Putting all of the ingredients together will ensure a successful carotid endovascular program.     

Percutaneous endovascular stents: an experimental evaluation

Percutaneous, expanding, endovascular stents were constructed of stainless steel wire formed in a zig-zag pattern. Stents were placed for varying periods of time in the jugular vein, vena cava, and abdominal aorta in each of five adult dogs. The dilating force of the stents could be controlled by different wire size, number and angle of wire bends, and stent length. In addition, multiple stents could be placed one inside the other or one after the other, depending on the circumstance. The stents distended the vessels and increased their diameter. No flow defects, luminal narrowing, or occlusion were noted in any of the stented vessels, even after 6 months. Side branches bridged by the stents remained patent and showed no indication of narrowing. Stent wires became encased by a proliferation of the tunica intima where they contacted the vessel wall. Encasement was slower and less extensive in the abdominal aorta. No vascular erosion or clot formation was found to be associated with any of the stents.     

Comparison of various cerebral protection devices used for carotid artery stent placement: an in vitro experiment

PURPOSE: To compare the effectiveness of five basic cerebral protection devices designed for carotid angioplasty in an in-vitro bench-top model. MATERIALS AND METHODS: Simulation of embolization from carotid angioplasty (n = 180) was performed with polyvinyl alcohol (PVA) particles (Contour; 150-1,000- micro m) in an open flow model simulating the aortic arch with a carotid bifurcation made from elastic silicone tubes. Particles (150-250 micro m [small], 355-500 micro m [medium], 710-1,000 micro m [large]; 5 mg each) were injected separately into the internal carotid artery (ICA) proximal to the placed protection device. Five devices were tested: the Angioguard (AG), Filter Wire EX (EX(A), EX(B)), Trap, Neuroshield (NS), and GuardWire Plus (GW). Particles getting past the protection device or flowing into the external carotid artery (ECA) were caught in a filter at the end of both arteries and their weight was determined. RESULTS: For small, medium, and large particles, the lowest weight of emboli in the effluent of the ICA was obtained with the NS (0.28 mg, 0.18 mg, and 0.07 mg, respectively; P <.001 compared to all other devices except the GW for small particles only). The GW had the highest embolization rate into the ECA for all particle sizes. When combining the particle weights for the different protection devices, the NS showed the lowest weight of emboli into the ICA filter (0.53 mg/3.5%; P <.001 compared to all [>1.1 mg/7.0%]). The GW revealed the highest weight of emboli into the ECA (1.2 mg/7.6%; P <.001 compared to all [<0.59 mg/0.09%]). Effectiveness of the EX(B) device was enhanced when circumferentially deployed under direct view (EX(B), 0.39 mg/2.58%; EX(A), 1.18 mg/7.81%; P <.001). CONCLUSIONS: In vitro, none of the tested devices or modifications has the ability to prevent embolization completely. An occlusion balloon leads to increased embolization into the ECA. The effectiveness of the EX might be enhanced with design improvements. During this evaluation, the NS was most effective for preventing PVA particle embolization of the three different particle groups within this in-vitro model.     

覆膜支架腔内治疗脾动脉瘤的临床评价

目的 探讨覆膜支架腔内隔绝治疗脾动脉瘤的安全性、可行性及疗效.方法 对4例脾动脉瘤患者,经覆膜支架植入腔内隔绝治疗,术后CT随访1年.结果 4例手术成功,术后无腹痛、发热等不适.随访1年,支架位置良好,脾动脉瘤末见再通,未发生脾梗死.结论 覆膜支架腔内隔绝治疗脾动脉瘤具有创伤小、恢复快、住院时间短、不适反应少等优点,更易被患者接受.长期效果有待更多的病例进一步观察.     

Magnetic resonance monitoring of stent deployment: in vitro evaluation of different stent designs and stent delivery systems

RATIONALE AND OBJECTIVES: To evaluate MR imaging features of commercially available stents before, during, and after in vitro deployment as a step toward MR-guided stent deployment. METHODS: Fourteen stents were deployed in a phantom under MR monitoring at 1.5 T by using a gradient-echo sequence. Device visibility was rated on a four-point scale (excellent, fair, poor, not visible). RESULTS: The Memotherm stent and the rolling membrane (RM) Wallstent showed excellent stent visibility and at least fair scores for artifact-induced narrowing of the stent lumen. Three stents (Palmaz, AVE, Easy Wallstent) showed excellent visibility of the stent but no visible lumen. Five stents (Strecker, Accuflex, Hemobahn, Passager, Sinus) displayed fair visibility. The delivery catheters of four stent systems (Smart, Vascucoil, Symphony, ZA) displayed severe black hole artifacts. CONCLUSIONS: The imaging features of several stent systems might be suitable for MR-guided intervention. The Memotherm and the Wallstent RM combine good visibility of the stent and the lumen.     

Update on multidetector coronary CT angiography of coronary stents: in vitro evaluation of 29 different stent types with dual-source CT

The aim of this study was to test a large sample of the latest coronary artery stents using four image reconstruction approaches with respect to lumen visualization, lumen attenuation, and image noise in dual-source multidetector row CT (DSCT) in vitro and to provide a CT catalogue of currently used coronary artery stents. Twenty-nine different coronary artery stents (19 steel, 6 cobalt-chromium, 2 tantalum, 1 iron, 1 magnesium) were examined in a coronary artery phantom (vessel diameter 3 mm, intravascular attenuation 250 HU, extravascular density −70 HU). Stents were imaged in axial orientation with standard parameters: 32 × 0.6 collimation, pitch 0.24, 400 mAs, 120 kV, rotation time 0.33 s. Image reconstructions were obtained with four different convolution kernels (soft, medium-soft, standard high-resolution, stent-dedicated). To evaluate visualization characteristics of the stent, the lumen diameter, intraluminal density, and noise were measured. The stent-dedicated kernel offered best average lumen visualization (54 ± 8.3%) and most realistic lumen attenuation (222  ± 44 HU) at the expense of increased noise (23.9 ± 1.9 HU) compared with standard CTA protocols (p < 0.001 for all). The magnesium stent showed the least artifacts with a lumen visibility of 90%. The majority of stents (79%) exhibited a lumen visibility of 50–59%. Less than half of the stent lumen was visible in only six stents. Stent lumen visibility largely varies depending on the stent type. Magnesium is by far more favorable a stent material with regard to CT imaging when compared with the more common materials steel, cobalt-chromium, or tantalum. The magnesium stent exhibits a lumen visibility of 90%, whereas the majority of the other stents exhibit a lumen visibility of 50–59%. David Maintz and Matthias Burg contributed equally to this publication.     

In vitro evaluation of coils for endovascular therapy.

PURPOSETo evaluate the physical characteristics and behavior of coils for endovascular therapy.METHODSMechanically detachable coils were constructed with simple helical (4 mm X 10 cm and 8 mm X 30 cm) and pretzel shapes (4 mm X 5 cm) made from three metals using 0.003- and 0.004-in wire. Stiffness or pliability, frictional resistance, shape memory, and coil stability were evaluated in vitro.RESULTSThe 0.004-in wire stock coils proved significantly stiffer when compared with the 0.003-in coils. Tungsten coils proved least pliable; platinum coils were intermediate in stiffness; and nitinol coils were softest. Frictional resistance in the catheter was greatest for stiffer coils. The 5-cm pretzel coil consistently created more frictional force than the 10- or 30-cm simple helical coils. Despite a shorter length, the 4-mm simple helical coil exerted more frictional force than the 8-mm coil. Stiffer metal coils constructed of larger-diameter wire (0.004 in) were more stable than softer coils.CONCLUSIONStiffer coils exert greater frictional forces within the catheter and a greater resistive force during bending but are more stable after placement. Frictional forces also depend on the complex three-dimensional shape of the coil and the diameter of the turns in that shape rather than coil length. These data suggest that a family of coils of different metals is optimal for varied intravascular needs.     

Appearance of vascular stents in computed tomographic angiography: in vitro examination of 14 different stent types

RATIONALE AND OBJECTIVES: To evaluate the appearance of the vessel lumen after implantation of different vascular stents with the use of a computed tomographic (CT) angiography model. METHODS: A vascular phantom was studied with helical CT and different slice thicknesses (2 and 3 mm) and pitch values (1.0, 1.5, and 2.0). Original transverse CT images and coronal reformations were evaluated. Fourteen different stents were analyzed with regard to changes in the stent lumen (attenuation values, noise, and artificial lumen narrowing). RESULTS: Some stents caused artifacts resulting in potential errors during evaluation of their patency. Assessment of the lumen was impaired in two stents (Strecker tantalum and Passager). Increased attenuation values were measured in all stents (increase of 8%-145%). The degree of artificial lumen narrowing was 4.4% to 77.8%. CONCLUSIONS: In most stents, reliable evaluation of the stent lumen seems possible. However, knowledge of the artifacts caused by different stent types is useful for the assessment of stent patency with CT angiography.     

Thrombogenicity of Teflon versus copolymer-coated guidewires: evaluation with scanning electron microscopy

Utilizing the scanning electron microscope, we compared a new guidewire with copolymer coating with standard Teflon-coated, coiled-spring guidewires in both clinical and in vitro settings. Intense thrombogenicity was observed with the Teflon-coated guidewires with formed thrombi ranging in size from 50-100 microns. No formed thrombus was noted on any of the specimens of the copolymer guidewire, although isolated clumps of platelets and erythrocytes without fibrin strands were seen infrequently. We conclude that the copolymer guidewire is markedly less thrombogenic than Teflon-coated guidewires.     

Endovascular stent for use in aortic dissection: an in vitro experiment

Injection of normal saline and contrast material into the walls of aortic specimens from human cadavers created a narrowing of the aortic lumen, simulating aortic dissection. Endovascular stents were applied to expand the aortic lumen. Successful dilatation of the narrowed aortic lumen was demonstrated in all six specimens.     

In vitro evaluation of intravascular stent artifacts in three-dimensional MR angiography

RATIONALE AND OBJECTIVES: To evaluate the intraluminal signal characteristics of various stents and stent-grafts in contrast-enhanced three-dimensional MR angiography (3D MRA) in vitro. METHODS: Fourteen stents made of different materials (steel, nitinol, tantalum, cobalt-based alloy, polyethylene) and six stent-grafts were implanted in plastic tubes simulating the common iliac artery. The tubes were filled with gadopentetate dimeglumine in water at a concentration of 25 mmol/L and positioned in a plastic container filled with water. For imaging, the container was placed in the center of the magnet, parallel, orthogonal, and diagonal to the z axis. A 3D gradient-echo sequence (T1-FFE) was acquired with the following parameters: repetition time 5.3 ms, echo time 1.6 ms, flip angle 50 degrees, slice thickness 1.5 mm, and acquisition matrix 256 with zero filling to 512. To evaluate the influence of the frequency-encoding gradient on the appearance of the artifacts, stents were examined with their axes oriented in all three directions both with the frequency-encoding gradient in the feet-head and right-left directions. The size and pattern of stent-related artifacts were evaluated semiquantitatively for each measurement. RESULTS: Five different components of artifacts could be distinguished: homogeneous signal reduction inside the stent, narrowing of the stent lumen, structures of various shapes inside the stents, signal reduction or signal increase at the ends of the stents, and shift of the intraluminal signal orthogonal to the longitudinal axis of the vessel. The size of the artifacts depended heavily on the material of the stent. The polyethylene stent showed no artifacts, the tantalum stent only minor artifacts. Nitinol stents were characterized by artifacts at both ends and signal reduction intraluminally. Stents made of steel demonstrated the strongest artifacts, characterized by almost complete signal loss intraluminally. The characteristics of the artifacts of all stents depended on the direction of the stent relative to the frequency-encoding gradient. CONCLUSIONS: Three-dimensional MRA follow-up after stent placement may be applicable for stent patency evaluation in all instances. However, grading of stenoses seems to be unrealistic in steel stents and in most nitinol stents.     

Three-year follow-up of fenestrated thoracoabdominal stent graft bridging an endovascular thoracic stent graft and a surgical abdominal aortic graft

This case report describes repair of a type I endoleak at the distal landing zone of a thoracic aortic stent graft by endovascular placement of a thoracoabdominal fenestrated stent graft (Cook, Brisbane, Australia). The fenestrated stent graft was interposed between a previous abdominal aortic aneurysm (AAA) Gelsoft tube graft (Sulzer Vascutek Ltd, Inchinnan, United Kingdom) and two overlapping Zenith thoracic endografts (Cook Inc, Bloomington, Indiana). Placement was made more complex because the distal thoracic endograft had rotated into a horizontal position. At 3-year clinical and computed tomography (CT) follow-up, continued clinical and radiologic success was shown with no further intervention required.     

Determinants of stent expansion in curved stenotic lesions: an in vitro experimental study

PURPOSE: This study compared the expansion parameters of four different new-generation balloon-expandable stents in a curved stenotic phantom model. MATERIALS AND METHODS: Five stents for each length and type, each with a 3.5-mm diameter (AVE, 12 mm and 18 mm; Penta, 13 mm and 18 mm; BX-Sonic, 13 mm and 18 mm; and Jostent Flex Master, 12 mm and 16 mm), were implanted in curved silicon models 3.25 mm in diameter with 58% concentric elastic stenoses. The forces exerted on the inner curvature were continuously registered. Minimal luminal diameter (MLD) and reference luminal diameter (RLD) of the stents, inflated balloon diameter at both ends of the stents during inflation (BD(ref)), and balloon diameter at the stenotic site during inflation (BD(min)) were determined by magnification radiography. RESULTS: The Penta and AVE stents presented greater RLD (Penta, 3.78 mm +/- 0.08; AVE, 3.75 mm +/- 0.13; BX-Sonic, 3.47 mm +/- 0.06; Jostent, 3.28 mm +/- 0.06) and MLD values (Penta, 2.94 mm +/- 0.18; AVE, 3.05 mm +/- 0.19; BX-Sonic, 2.68 mm +/- 0.06; Jostent, 2.53 mm +/- 0.09) than the BX-Sonic and Jostent stents. Displacement forces after stent placement were greater for AVE (0.034 N +/- 0.015) and Penta stents (0.023 N +/- 0.017) than for BX-Sonic (0.013 N +/- 0.007) and Jostent stents (0.009 N +/- 0.007; P <.05). BD(min) was correlated in a linear fashion with MLD (r = 0.84; P <.001), as was BD(ref) with RLD (r = 0.92; P <.001), for all stents. CONCLUSIONS: Inflated balloon diameter was the main determinant of stent expansion. The AVE and Penta stents gained larger MLD values than the BX-Sonic and Jostent stents, but they excessively dilated the nonstenotic region of the model.     

放射性覆膜金属支架制备方法的研究

目的 探索32P放射性覆膜金属支架的制备方法.方法　通过比较聚乙烯醇和聚氨酯以及不同制备工艺制作的放射性膜材料在生理盐水中的32P放射性物质的泄漏率;测量不同聚氨酯涂膜工艺和同一膜不同部分的质量和放射性计数率,测量每部分单位质量的放射性计数率,评价支架膜上放射性物质的均匀性;比较旋转滴涂法和浸涂法在支架上涂膜的不同效果.结果 聚乙烯醇中放射性物质在生理盐水中泄漏率达90%,聚氨酯能有效降低放射性物质在生理盐水中的泄漏,在其表面再涂聚氨酯涂层,泄漏率处于本底水平;不同聚氨酯膜中的放射性物质分布百分差率差异没有统计学意义(非参数检验Mann-Whitney test方法,U=10.0,P=0.602＞0.05),同一膜材料中放射性物质分布平均百分差率为11.76%;旋转滴涂法在支架上形成的膜层不均匀,出现穿孔现象,而浸涂法可形成均匀的膜层.结论 以聚氨酯作为覆膜材料,能有效减低32P放射性物质的泄漏,同时放射性物质在膜材料中的分布亦较均匀.     

Rupture and migration of an endovascular stent in the brachiocephalic trunk causing a vertebral steal syndrome

Delayed stent fracture has been observed in many different arteries and may represent a risk factor for restenosis. We describe the case of a delayed rupture of an endovascular brachiocephalic trunk stent. The complete fracture allowed a fragment to migrate distally and tilt, resulting in a hemodynamic pattern similar to that of a prevertebral stenosis with complete inversion of the homolateral vertebral blood flow. The induced vertebral steal syndrome as well as the risk of cerebral embolism was corrected by an aortobrachiocephalic bypass and resection of the ruptured stent.