Asymmetric Stent Research Articles

Treatment of Bicuspid Aortic Valve Stenosis with TAVR: Filling Knowledge Gaps Towards Reducing Complications

Bicuspid aortic valve (BAV) disease is the most common congenital heart defect worldwide. When severe, symptomatic aortic stenosis ensues, the treatment has increasingly become transcatheter aortic valve replacement (TAVR). The purpose of this review is to identify BAV classification and imaging methods, outline TAVR outcomes in BAV anatomy, and discuss how computational modeling can enhance TAVR treatment in BAV patients. TAVR use in BAV patients, when compared to use in tricuspid aortic valves, showed lower device success rate, and there remains no long-term randomized trial data. It has been reported that BAV patients with severe calcification increase the rate of complications. Additionally, the asymmetrical morphology of BAVs often results in asymmetric stent geometries which have implications for increased thrombosis risk and decreased durability. These adverse outcomes are currently very difficult to predict from routine pre-procedural imaging alone. Recently developed patient specific experimental and computational techniques have the potential to assist in filling knowledge gaps in the mechanisms of these complications and provide more information during preclinical planning for better TAVR selection in low surgical risk BAV patients. Efficacy of TAVR for irregular BAV anatomies remains concerning due to the lack of a long-term randomized trial data, their increased rate of short-term complications, and signs that long-term durability could be an issue. More knowledge on identifying which BAV anatomies are at greater risk for these adverse outcomes can potentially improve patient selection for TAVR versus SAVR in low surgical risk BAV patients.

In-stent restenosis and stent compression following stenting for chronic iliofemoral venous obstruction

ObjectiveIn-stent restenosis (ISR) and stent compression (SC) are problems encountered after stenting for chronic iliofemoral venous obstruction that are responsible for a majority of reinterventions. However, characteristics of ISR and SC, in addition to outcomes after reintervention, have not been explored in detail and represent the focus of this study. MethodsA retrospective analysis of contemporaneously entered electronic medical record data on 578 limbs/patients with initial unilateral iliofemoral venous stents placed from 2014 to 2018 was performed. ISR was estimated from stent and flow channel diameters measured using duplex ultrasound. SC was estimated from rated stent diameter and actual stent diameter on duplex ultrasound. Characteristics evaluated included onset of ISR/SC after stent placement and progression over time. Analysis was performed to evaluate risk factors for the development of ISR and SC. Outcomes after reintervention for ISR/SC were also appraised. ResultsA total of 578 limbs underwent stenting for stenotic lesions (nonthrombotic iliac vein lesion/post-thrombotic syndrome). ISR was noted in 27% of limbs on post-intervention day 1. The prevalence of ISR increased to 74% by 3 months and stabilized thereafter. SC was noted in 80% of limbs on day 1 and plateaued. Of the variables evaluated as potential risk factors for ISR, intravascular ultrasound determined stent inflow luminal area and shear rate were found to be significant. For SC, asymmetric stent sizing was a significant risk factor. Over a median follow-up of 24 months, 95 of 578 (16.4%) limbs underwent reintervention for ISR, SC, or a combination. The median time to reintervention was 11 months. There was no statistically significant difference in the degree of ISR/SC among patients who underwent reintervention vs those who did not (P > .05). However, there was a statistically significant difference in the grade of swelling (P = .006) and visual analog scale pain scores (P < .0001) between those who underwent reintervention and those who did not. Primary, primary assisted, and secondary patencies at 60 months were 70%, 98%, and 84% after reintervention for ISR and 70%, 99%, and 84% for SC, respectively. ConclusionsAlthough ISR and SC are both common after stenting for chronic iliofemoral venous obstruction, neither are relentlessly progressive. Indication for reintervention must be a recurrence of symptoms with impairment of quality of life and not the percentage of ISR or degree of SC. After reintervention good outcomes can be expected both in terms of clinical improvement and stent patency. Further study of the impact of shear rate on stent flow is required to help reduce the incidence of ISR.

An asymmetric surface coating strategy for improved corrosion resistance and vascular compatibility of magnesium alloy stents

Magnesium (Mg) and its alloys are promising materials for biodegradable drug-eluting stent applications, but their rapid corrosion remains a major challenge for clinical practice. Considerable efforts have been made to develop an efficient surface coating that can provide higher Mg stent corrosion resistance, sustained drug-delivery capability, and vascular compatibility. Herein, we introduce poly(ether imide) (PEI) and poly(lactic-co-glycolic acid) (PLGA) as surface coating polymers for WE43 Mg-alloy stent. Using a sequential spray-coating method, we developed a novel asymmetric stent coating comprising an inner surface coated with a PEI single layer and outer/side surfaces coated with sirolimus-loaded PLGA/PEI double layers. PEI coating layer has excellent adhesiveness to WE43 surface and considerably improves WE43 corrosion resistance and in vitro endothelial cell compatibility. PLGA/PEI double coating layer ensures a low release rate of sirolimus and stable surface morphology during drug-release process. Only vascular smooth muscle cells are directly affected by sirolimus owing to the asymmetric geometry of PLGA/PEI double coating, which has a satisfactory anti-proliferation effect. These results indicate that the developed asymmetrically PEI- and PLGA/PEI-coated WE43 stents have significant potential for achieving enhanced re-endothelialization and suppressed in-stent restenosis in vascular stent applications.

Experimentally validated simulation of coronary stents considering different dogboning ratios and asymmetric stent positioning.

In-stent restenosis remains a major problem of arteriosclerosis treatment by stenting. Expansion-optimized stents could reduce this problem. With numerical simulations, stent designs/ expansion behaviours can be effectively analyzed. For reasons of efficiency, simplified models of balloon-expandable stents are often used, but their accuracy must be challenged due to insufficient experimental validation. In this work, a realistic stent life-cycle simulation has been performed including balloon folding, stent crimping and free expansion of the balloon-stent-system. The successful simulation and validation of two stent designs with homogenous and heterogeneous stent stiffness and an asymmetrically positioned stent on the balloon catheter confirm the universal applicability of the simulation approach. Dogboning ratio, as well as the final dimensions of the folded balloon, the crimped and expanded stent, correspond well to the experimental dimensions with only slight deviations. In contrast to the detailed stent life-cycle simulation, a displacement-controlled simulation can not predict the transient stent expansion, but is suitable to reproduce the final expanded stent shape and the associated stress states. The detailed stent life-cycle simulation is thus essential for stent expansion analysis/optimization, whereas for reasons of computational efficiency, the displacement-controlled approach can be considered in the context of pure stress analysis.

Vulnerability analysis on the interaction between Asymmetric stent and arterial layer.

The utilization of Asymmetric stent for recovering atherosclerotic diseases, particularly non-symmetric obstruction, is a quite challenging breakthrough treatment. In terms of eccentric plaque, the non-uniform stiffness of arterial layer causes the increasingly complex issues of vulnerability. This study investigated the vulnerability of the interaction between the Asymmetric stent and the surrounding arterial layer using structural transient dynamic analysis in ANSYS. Four combinations of stent deployment, i.e. the Sinusoidal stent expanded by the offset balloon, the Sinusoidal stent expanded by the ordinary cylindrical balloon, the Asymmetric stent expanded by the offset balloon, and the Asymmetric stent expanded by the ordinary cylindrical balloon, are generated for this comparative study. Multilayer material properties from recent in vitro experiments are adopted for the surrounding arterial layer, such as a fibrous cap, lipid core, diseased-healthy intima, and diseased-healthy media. In order to address plaque vulnerability, the Cauchy stresses and Hencky strains are used for stress measure because of convenience in comparison with the uniaxial/biaxial tension test data. The location-specific threshold value from the diseased human carotid artery is adopted for rupture criteria. The simulation indicated that as regards the eccentric plaque, the plaque vulnerability is caused by the plaque shape and components rather than caused by the geometrical structure of the stent or balloon expansion method. Nevertheless, the non-symmetric inflation of balloon, which leads against the plaque, contributed to an increase in the vulnerability of fibrous cap of fibroatheroma plaque.

THE ASSOCIATION BETWEEN POST-PROCEDURAL STENT ASYMMETRY AND SUBSEQUENT STENT COVERAGE AND NEOINTIMAL HYPERPLASIA ASSESSED BY OPTICAL COHERENCE TOMOGRAPHY: THE EGO-BIOFREEDOM AND OCT-ORION STUDIES

There are limited data regarding the impact of asymmetric stent expansion on subsequent stent coverage and neointimal hyperplasia (NIH) in the contemporary drug-eluting stent era. EGO-BIOFREEDOM (BioFreedom stent in 105 lesions, 99 pts) and EGO-ORION (randomized Resolute vs BioMatrix stent in 119

Development of asymmetric stent for treatment of eccentric plaque.

The selection of stent and balloon type is decisive in the stenting process. In the treatment of an eccentric plaque obstruction, a symmetric expansion from stent dilatation generates nonuniform stress distribution, which may aggravate fibrous cap prone to rupture. This paper developed a new stent design to treat eccentric plaque using structural transient dynamic analysis in ANSYS. A non-symmetric structural geometry of stent is generated to obtain reasonable stress distribution safe for the arterial layer surrounding the stent. To derive the novel structural geometry, a Sinusoidal stent type is modified by varying struts length and width, adding bridges, and varying curvature width of struts. An end ring of stent struts was also modified to eliminate dogboning phenomenon and to reduce the Ectropion angle. Two balloon types were used to deploy the stent, an ordinary cylindrical and offset balloon. Positive modification results were used to construct the final non-symmetric stent design, called an Asymmetric stent. Analyses of the deformation characteristics, changes in surface roughness and induced stresses within intact arterial layer were subsequently examined. Interaction between the stent and vessel wall was implemented by means of changes in surface roughness and stress distribution analyses. The Palmaz and the Sinusoidal stent were used for a comparative study. This study indicated that the Asymmetric stent types reduced the central radial recoiling and the dogboning phenomenon. In terms of changes in surface roughness and induced stresses, the Asymmetric stent has a comparable effect with that of the Sinusoidal stent. In addition, it could enhance the distribution of surface roughening as expanded by an offset balloon.

Effect of Asymmetric Geometry on the Flexibility of Stent

Mechanical characteristic assessment of the new stent design is important to improve the performance during the stenting process. Stent with good performance in geometric assessment should pass several tests in the unexpanded and expanded condition. The FEM assessment is expected to replace the actual mechanical assessment to save the cost and time of the manufacturing. In this study, the FEM assessment is conducted using the structural nonlinear analyses in ANSYS R15.0. The stent type used in the simulation is the Asymmetric stent and the Sinusoidal stent. The assessments included in this study are the flexibility test on the unexpanded condition (single-load and multi-load) and that on the expanded condition under single point loading. The three-point bending test is chosen as the flexibility test, either for the unexpanded or expanded condition, due to its simplicity. To restrain angular deformation and more save the computation process, a symmetry model (due to longitudinal and angular plane) of each stent type is constructed. By utilizing Multi Point Constraint (MPC) element, the loading is subjected over a pilot node at the center line of the stent. The analysis results showed that Asymmetric stent has lower flexibility comparing with a Sinusoidal stent in the unexpanded configurations. In the case of an Asymmetric stent, its inflated-side is more flexible than the fixed-side.

Displacement Forces in Stent Grafts: Influence of Diameter Variation and Curvature Asymmetry

Long-term durability after endovascular aortic repair is influenced by stent graft migration causing types I and III endoleaks. Flow induced displacement forces have been shown to have the potential to cause migration. In this study, the influence of the distal diameter of iliac limb stent grafts and the shape of graft curvature on flow induced displacement forces, were investigated. In an experimental pulsatile flow model mimicking aortic conditions invivo, flow induced displacement forces at the proximal and distal ends of iliac limb stent grafts were studied at different angles (0-90°) and perfusion pressures (145/80, 170/90, 195/100mmHg). Bell-bottomed, tapered, and non-tapered stent grafts and also asymmetric stent graft curvatures at 90° bend were studied. Measurements of graft movement were performed at all studied angulations and graft shapes. For all stent graft diameters, flow induced displacement forces increased with higher pressure and increased stent graft angulation. Forces in the bell-bottom graft were considerably higher than in tapered and non-tapered grafts, with a markedly elevated peak force at the distal end (proximal end, 2.3±0.06N and distal end, 6.9±0.05N compared with 1.7±0.08N and 1.6±0.08N in non-tapered grafts; p<.001 both). Peak forces in tapered and non-tapered grafts were not significantly different between the proximal and distal end. In asymmetric stent graft curvatures, a significant increase in displacement forces was observed in the attachment zone that was closest to the stent graft bend. Graft movement increased with greater displacement forces. Flow induced displacement forces in iliac limb stent grafts are significant and are influenced by distal stent graft diameter and the shape of the graft curvature. The displacement forces are particularly high at the large distal end of bell-bottom grafts. Wide iliac arteries treated with bell-bottom stent grafts may require more vigilant surveillance and improved stent graft fixation.

ASSESSMENT OF OSTIAL LEFT ANTERIOR DESCENDING LESION STENTED FROM LEFT MAIN TO LEFT ANTERIOR DESCENDING BY OPTICAL COHERENCE TOMOGRAPHY

Percutaneous coronary intervention (PCI) with kissing balloon inflation (KBI) for left main (LM) bifurcation disease is often performed in order to secure side branch (SB) patency and SB stenosis. However, several studies have shown that asymmetric stent expansion may affect the pattern of

Impact of final kissing balloon inflation on vessel healing following drug-eluting stent implantation: Insight from the optical coherence tomography sub-study of the J-REVERSE trial

BackgroundWe sought to clarify the impact of final kissing inflation (FKI) after single stenting of bifurcation lesions on vessel healing. MethodsFrom the J-REVERSE registry enrolling 303 bifurcation lesions treated with provisional single stenting using sirolimus- (SES) or everolimus-eluting stent (EES), 65 lesions treated with (n=30) and without (n=35) FKI underwent 9-month follow-up optical coherence tomography. Average stent eccentricity index (SEI: minimum/maximum stent diameter) and neointimal unevenness score (NUS: maximum/average neointimal thickness of the same cross-section) for the proximal, bifurcation, and distal segments were compared between FKI and non-FKI groups. ResultsAt the proximal segment, the FKI group demonstrated significantly larger average stent area with greater asymmetric stent expansion, and average lumen area remained significantly larger at 9-month follow-up despite a tendency toward greater neointimal proliferation. Jailed strut and thrombus incidence were also significantly lower at the side branch orifice, and NUS was significantly smaller at the bifurcation and proximal segments in the FKI group. ConclusionsNine months after SES and EES treatment of bifurcation lesions, FKI reduced proximal-segment luminal narrowing. Considering its homogeneous neointimal distribution and fewer jailed struts, FKI may be beneficial for treating bifurcation lesions.

Impact of Kissing Balloon Inflation on the Main Vessel Stent Volume, Area, and Symmetry After Side-Branch Dilation in Patients With Coronary Bifurcation Lesions: A Serial Volumetric Intravascular Ultrasound Study

Intravascular ultrasound (IVUS) was performed to investigate the impact of kissing balloon inflation (KBI) on the main vessel (MV) stent volume, area, and symmetry after side-branch (SB) dilation in patients with coronary bifurcation lesions (CBL). It remains controversial whether KBI would restore the MV stent area and symmetry loss after SB dilation. A total of 88 serial IVUS examinations of the MV were performed after MV angioplasty, MV stenting, SB dilation, and KBI in 22 patients with CBL. The MV stent was divided into proximal, bifurcation, and distal segments; the stent volume index (SVI), minimal stent area (MSA), stent symmetry index (SSI), and external elastic membrane (EEM) volume index were measured in 198 stent segments and compared after MV stenting, SB dilation, and KBI. In the bifurcation segment, SVI, MSA, and SSI were significantly smaller after SB dilation than after MV stenting and KBI (SVI was 6.10 ± 1.50 mm(3)/mm vs. 6.68 ± 1.60 mm(3)/mm and 6.57 ± 1.60 mm(3)/mm, respectively, p < 0.05; MSA was 5.15 ± 1.30 mm(2) vs. 6.08 ± 1.40 mm(2) and 5.86 ± 1.50 mm(2), respectively, p < 0.05; and SSI was 0.78 ± 0.02 mm(2) vs. 0.87 ± 0.03 mm(2) and 0.84 ± 0.03 mm(2), respectively, p < 0.05). KBI restored the MV SVI, MSA, and SSI after SB dilation. In the proximal segment, SVI, MSA, and EEM volume index were significantly larger, but SSI was smaller after KBI than after MV stenting and SB dilation. In the distal segment, neither SB dilation nor KBI had a significant impact on the MV stent volume or symmetry. This is the first comprehensive volumetric IVUS analysis of CBL, to our knowledge, demonstrating that KBI restores the MV stent volume, area, and symmetry loss after SB dilation in the bifurcation segment, and induces asymmetric stent expansion in the proximal segment.

Bench top evaluation and clinical experience with the szabo technique

The Szabo technique has been described as a method to ensure accurate ostial stent placement. We sought to investigate this novel technique in detail both in vitro and in vivo. The technique was subjected to bench testing and also undertaken in 26 patients. Each step was recorded with cine angiography and the stents imaged by microcomputed tomography. The ostial LAD was treated in 81% and a DES was implanted in 92%. Angiographic success was 88.5% (one case of stent dislodgement). Repeat angiography was performed in 78% and restenosis observed in two patients. MACE rate at 15.5 ± 5.1 months was 13% (1 TLR, 1 MI, 1 cardiac death). Despite a seemingly excellent immediate angiographic result, we report one case of restenosis at follow up and one case of IVUS examination (performed in four patients) in which significant stent protrusion, into the proximal main vessel, was observed. In vitro bench testing confirmed a significant and asymmetric (carina side) stent protrusion into the main branch, with the last cell of the stent undergoing significant deformation. The Szabo technique is not a precise technique to implant a stent at the level of the ostium. The proximal end of the stent undergoes significant and asymmetric deformation, protruding into main branch. Additional concerns with this complex technique include the potential for stent damage or contamination before implantation and the risk of stent dislodgement. We conclude that there are more disadvantages than benefits to this technique which only partially addresses the difficulties encountered in the treating ostial lesions.

Comparisons of the Effects of Stent Eccentricity on the Neointimal Hyperplasia between Sirolimus-Eluting Stent versus Paclitaxel-Eluting Stent

PurposePrevious studies suggested that asymmetric stent expansion did not affect suppression of neointimal hyperplasia (NIH) after sirolimus-eluting stents (SES) implantation. The aim of this study was to evaluate the effects of stent eccentricity (SE) on NIH between SES versus paclitaxel-eluting stents (PES) using an intravascular ultrasound (IVUS) analysis from the randomized trial.Materials and MethodsSerial IVUS data were obtained from Post-stent Optimal Expansion (POET) trial, allocated randomly to SES or PES. Three different SE (minimum stent diameter divided by maximum stent diameter) were evaluated; SE at the lesion site with maximal %NIH area (SE-NIH), SE at the minimal stent CSA [SE-minimal stent area (SE-MSA)], and averaged SE through the entire stent (SE-mean). We classified each drug-eluting stents (DES) into the concentric (≥ mean SE) and eccentric groups (< mean SE) based on the mean value of SE.ResultsAmong 301 enrolled patients, 233 patients [SES (n = 108), PES (n = 125)] underwent a follow-up IVUS. There was no significant correlation between %NIH area and SE-NIH (r = - 0.083, p = 0.391) or SE-MSA (r = - 0.109, p = 0.259) of SES. However, SE-NIH of PES showed a weak but significant correlation with %NIH area (r = 0.269, p < 0.01). As to the associations between SE-mean and NIH volume index, SES revealed no significant correlation (r = - 0.001, p = 0.990), but PES showed a weak but significant correlation (r = 0.320, p < 0.01). However, there was no difference in the restenosis rate between the eccentric versus concentric groups of both DES.ConclusionThis study suggests that lower SE of both SES and PES, which means asymmetric stent expansion, may not be associated with increased NIH.

WE-C-304A-05: Angiographic Analysis of Aneurysms Treated with a Novel Self-Expanding Asymmetric Vascular Stents (SAVS)

Purpose: To quantify hemodynamic modification in animal model aneurysms caused by image‐guided deployment of a new self‐expanding asymmetric vascular stent (SAVS) using x‐ray contrast digital subtraction angiography(DSA) thus providing an indication of expected treatment outcome. Materials and Methods: A novel nitinol‐SAVS containing a low porosity patch to cover only the aneurysm neck was used to treat five rabbit‐model aneurysms. Contrast flow in the aneurysm dome was recorded before‐treatment, and after‐treatment, using rapid‐sequence (15 fps) DSA. The DSAs were analysed using time‐density curves (TDC) measuring the contrast in the aneurysm as a function of frame‐time for each case. The TDCs were normalized to the maximum value of the initial curve (before‐treatment). Results: Before‐treatment TDC's showed clearance of the contrast from the aneurysm dome in less than 3 seconds indicating strong blood flow in the dome. Post‐treatment TDC's showed in 3 of 5 cases negligible contrast entering the aneurysms (almost 100% drop in the TDC peak), 1 of the 5 had strong inflow followed by prologue contrast residence in the dome, and the last of the 5 had moderately reduced flow (75% of the initial peak), fast clearance, however only a remnant neck was observed at 30 day follow‐up. TDC's generated from the DSA acquisitions of the Nitinol‐SAVS‐treated aneurysms indicated drastic reduction of the hemodynamicflow in the aneurysm dome and completely successful treatment except for the one case where incomplete treatment was predicted by only moderate flow modification. Conclusions: Changes in angiographically derived TDC's appear to be a very useful tool to predict treatment outcome. Based on TDC‐analysis, the new Nitinol‐SAVS is a very promising option for treatment of intracranial aneurysms. (Support: NIH‐R01NS43924, NIH‐R01EB002873)

Local Determinants of Thrombus Formation Following Sirolimus-Eluting Stent Implantation Assessed by Optical Coherence Tomography

We conducted this study to assess the prevalence and determinants of subclinical thrombus after sirolimus-eluting stent (SES) implantation. Angioscopic analyses have demonstrated the presence of thrombus is more common than the clinical incidence of SES thrombosis. Fifty-three patients (53 lesions) underwent 6-month follow-up optical coherence tomography. A stent eccentricity index ([SEI] minimum/maximum stent diameter) was determined in each cross section. To evaluate unevenness of neointimal thickness, a neointimal unevenness score ([NUS] maximum neointimal thickness in the cross section/average neointimal thickness of the same cross section) was calculated for each cross section. Average SEI and NUS were calculated for each stent. Major adverse cardiac events were defined as a composite of death, myocardial infarction, and target vessel revascularization. Fourteen cases of thrombus (26%) were detected by optical coherence tomography (thrombus: n = 14 vs. nonthrombus: n = 39). The percentage of thrombus was associated with longer stents (36.4 +/- 20.2 mm vs. 25.1 +/- 9.8 mm; p = 0.008), a larger number of uncovered struts (17 +/- 16 vs. 8 +/- 11; p = 0.03), smaller average SEI (0.89 +/- 0.04 vs. 0.92 +/- 0.03; p = 0.001), and greater average NUS (2.22 +/- 0.24 vs. 2.00 +/- 0.33; p = 0.03). A significant relationship existed between average SEI and average NUS (p < 0.0001, R = 0.68), and between average SEI and the number of uncovered struts (p < 0.0006, R = 0.46). There was no significant difference in major adverse cardiac events during follow-up (median: 485 days, 7.1% vs. 12.8%; p > 0.99). Longer stents and greater asymmetric stent expansion may be important determinants of thrombus formation after SES implantation. In this small cohort, the presence of thrombus did not increase the risk of major adverse cardiac events.

Abstract 4478: Local Determinants and Clinical Significance of Thrombus Formation Following Sirolimus-Eluting Stent Implantation: Insights from Optical Coherence Tomography Analysis

Angioscopic analyses have shown the presence of subclinical thrombus in sirolimus-eluting stents (SES) is more common than the clinical incidence of stent thrombosis. However, the determinants and long term significance of subclinical thrombus remain unknown. Thirty five patients (44 stents) who received SES underwent 6 months follow-up optical coherence tomography (OCT). Patients were divided into 2 groups according to the presence of thrombus by OCT. Cross-sectional images were analyzed every 1mm. Stent eccentricity index (SEI; minimum stent diameter divided by maximum stent diameter) was determined in each cross section (CS). To assess the unevenness of neointimal thickness (NIT), a neointimal unevenness score (NUS) was calculated for each CS as maximum NIT in the CS divided by the average NIT of the same CS. Average SEI and NUS were also calculated for each stent. Major adverse cardiac event (MACE) was defined as a composite of death, myocardial infarction, and target vessel revascularization. Eight cases of thrombus were detected by OCT (18%). The thrombus cases were associated with longer stent length, larger numbers of uncovered struts, smaller average SEI, and greater average NUS (Table ). A significant relationship existed between the average SEI and average NUS ( P &lt;0.0001, R=0.66), as well as between average SEI and the number of uncovered struts ( P =0.005, R=0.47). There was no significant difference in MACE during follow-up (median: 655days) (Thrombus: 0%, Non-thrombus: 7.4%, P=0.43). Based on OCT, longer stents, a larger number of uncovered stent struts, asymmetric stent expansion, and unevenness of NIT may be important determinants of thrombus formation in patients treated with SES. Asymmetric stent expansion may interfere with even neointimal coverage after SES deployment, perhaps a key mechanism for thrombus formation. In this small cohort, the presence of thrombus did not seem to increase the risk of MACE.

Investigation of new flow modifying endovascular image-guided interventional (EIGI) techniques in patient-specific aneurysm phantoms (PSAPs) using optical imaging.

Effective minimally invasive treatment of cerebral bifurcation aneurysms is challenging due to the complex and remote vessel morphology. An evaluation of endovascular treatment in a phantom involving image-guided deployment of new asymmetric stents consisting of polyurethane patches placed to modify blood flow into the aneurysm is reported. The 3D lumen-geometry of a patient-specific basilar-artery bifurcation aneurysm was derived from a segmented computed-tomography dataset. This was used in a stereolithographic rapid-prototyping process to generate a mold which was then used to create any number of exact wax models. These models in turn were used in a lost-wax technique to create transparent elastomer patient-specific aneurysm phantoms (PSAP) for evaluating the effectiveness of asymmetric-stent deployment for flow modification. Flow was studied by recording real-time digitized video images of optical dye in the PSAP and its feeding vessel. For two asymmetric stent placements: through the basilar into the right-posterior communicating artery (RPCA) and through the basilar into the left-posterior communicating artery (LPCA), the greatest deviation of flow streamlines away from the aneurysm occurred for the RPCA stent deployment. Flow was also substantially affected by variations of inflow angle into the basilar artery, resulting in alternations in washout times as derived from time-density curves. Evaluation of flow in the PSAPs with real-time optical imaging can be used to determine new EIGI effectiveness and to validate computational-fluid-dynamic calculations for EIGI-treatment planning.

SU‐FF‐I‐127: Patient Specific Angiography Phantoms for Investigating New Endovascular Image‐Guided Interventional (EIGI) Devices

Purpose: To provide patient‐specific phantoms for investigating new endovascular image‐guided interventional (EIGI) devices such as stents. Methods and Materials: A human cerebral/saccular aneurysm phantom was constructed from a patient's segmented CT‐scan data. The CT‐derived vascular lumen was converted to a standard stereolithography (STL) computer file which was used, through a rapid‐prototyping process, to make a plastic resin (Accura 25) mold of the vessel with the aneurysm. In this process, an ultraviolet laser is used to selectively cure a liquid plastic layer by layer resulting in a highly accurate and very detailed positive model. RTV silicone is placed around this plastic aneurysm, allowed to cure, and then cut in half to create a mold with a cavity in the shape of the aneurysm. This mold is used to make a wax replica of the human aneurysm. The wax replica is then immersed in a silicone elastomer solution, the bubbles removed via vacuum, and the elastomer allowed to cure. The wax is then dissolved using boiling water. Results: The finished product is a clear elastomer model with a patient‐specific aneurysm cavity that may be used in both x‐ray and optical flow experiments. Multiple identical elastomer phantoms can be generated from one mold so that new EIGI devices such as an asymmetric stent with a low porosity patch region to occlude aneurysmal flow can be variously deployed under fluoroscopic guidance and evaluated angiographically. Additionally, the effects of contrast media can be studied by comparisons with optical flow studies. Comparisons of angiographic and optical time‐density curves for an anterior cerebral artery with multi‐lobular aneurysm will be presented. Conclusions: We have developed a unique system for the creation of realistic patient‐specific phantoms which enable the evaluation of detailed vascular flow and experimental EIGI treatment techniques for clinically representative pathology.(Support: NIH R01‐NS43924, R01‐EB002873, Toshiba Corp.).

Method to rotate an endovascular device around the axis of a vessel using an external magnetic field

A magnetic guidance methodology to rotate a device around the catheter axis is proposed. The specific medical application is to intracranial aneurysms. An endovascular device, the asymmetric stent, has a low porosity region that is rotated to cover the aneurysm neck so as to reduce the blood flow into and hence obliterate the aneurysm. The magnetic guidance system consists of a magnetic device attached to the asymmetric stent and an external homogeneous magnetic field of 0.1 T. This magnetic field puts a torque on the magnetic moment of the magnetic device, thereby rotating the stent for proper orientation. For the magnetic device with the required magnetic moment of 0.001 A m2, a cylindrical neodymium permanent magnet is proposed due to its favorable material characteristics while a coil electromagnet with iron core appears impractical due to demagnetizing effects.