Retrospective Comparative Study of Side-by-Side and Stent-in-Stent Metal Stent Placement for Hilar Malignant Biliary Obstruction.

BACKGROUND: In patients with unresectable hilar malignant biliary obstruction (MBO), bilateral metal stent placement is recommended. However, treatment selection between partially stent-in-stent (SIS) and side-by-side (SBS) methods is still controversial. STUDY: Clinical outcomes of bilateral metal stent placement by SBS and SIS methods for hilar MBO were retrospectively studied in four Japanese centers. While large-cell-type uncovered metal stents were placed above the papilla in SIS, braided-type uncovered metal stents were placed across the papilla in SBS. RESULTS: A total of 64 patients with hilar MBO (40 SIS and 24 SBS) were included in the analysis. Technical success rate was 100% in SIS and 96% in SBS. Functional success rate was 93% in SIS and 96% in SBS. Early adverse event rates were higher in SBS (46%) than in SIS (23%), though not statistically significant (P = 0.09). Post-procedure pancreatitis was exclusively observed in SBS group (29%). Recurrent biliary obstruction rates were 48% and 43%, and the median time to recurrent biliary obstruction was 169 and 205 days in SIS and SBS, respectively. CONCLUSIONS: Other than a trend to higher adverse event rates including post-procedure pancreatitis in SBS, clinical outcomes of SIS and SBS methods were comparable in patients with unresectable hilar MBO.

Optical Coherence Tomography-Based Modeling of Stent Deployment in Heavily Calcified Coronary Lesion.

In this work, a heavily calcified coronary artery model was reconstructed from optical coherence tomography (OCT) images to investigate the impact of calcification characteristics on stenting outcomes. The calcification was quantified at various cross sections in terms of angle, maximum thickness, and area. The stent deployment procedure, including the crimping, expansion, and recoil, was implemented. The influence of calcification characteristics on stent expansion, malapposition, and lesion mechanics was characterized. Results have shown that the minimal lumen area following stenting occurred at the cross section with the greatest calcification angle. The calcification angle constricted the stretchability of the lesion and thus resulted in a small lumen area. The maximum principal strain and von Mises stress distribution patterns in both the fibrotic tissue and artery were consistent with the calcification profiles. The radially projected region of the calcification tends to have less strain and stress. The peak strain and stress of the fibrotic tissue occurred near the interface with the calcification. It is also the region with a high risk of tissue dissection and strut malapposition. In addition, the superficial calcification with a large angle aggregated the malapposition at the middle of the calcification arc. These detailed mechanistic quantifications could be used to provide a fundamental understanding of the role of calcification in stent expansions, as well as to exploit their potential for enhanced pre- and post-stenting strategies.

Impact of Calcium Quantifications on Stent Expansions.

Severely calcified plaque is of great concern when planning and implementing a stenting intervention. In this work, computational models were developed to investigate the influence of calcium characteristics on stenting outcomes. The commonly used clinical measurements of calcium (i.e., the arc angle, maximum thickness, length, and volume) were varied to estimate stenting outcomes in terms of lumen gain, stent underexpansion, strut malapposition, and stress or strain distributions of the stenotic lesion. Results have shown that stenting outcomes were most sensitive to the arc angle of the calcium. A thick calcium with a large arc angle resulted in poor stenting outcomes, such as severe stent underexpansion, D-shaped lumen, increased strut malapposition, and large stresses or strains in the plaque. This was attributed to the circumferential stretch of the tissue. Specifically, the noncalcium component was stretched significantly more than the calcium. The circumferential stretch ratios of calcium and noncalcium component were approximately 1.44 and 2.35, respectively, regardless of calcium characteristics. In addition, the peak stress or strain within the artery and noncalcium component of the plaque occurred at the area adjacent to calcium edges (i.e., the interface between the calcium and the noncalcium component) coincident with the location of peak malapposition. It is worth noting that calcium played a protective role for the artery underneath, which was at the expense of the overstretch and stress concentrations in the other portion of the artery. These detailed mechanistic quantifications could be used to provide a fundamental understanding of the impact of calcium quantifications on stent expansions, as well as to exploit their potential for a better preclinical strategy.

Improved stent expansion with prolonged compared with short balloon inflation: A meta-analysis.

BACKGROUND: Despite evidence from individual studies suggesting that prolonged inflation improves coronary stent expansion, relatively shorter inflation times are commonly employed in clinical practice. METHODS: We performed an electronic search of PubMed, Web of Science, Cochrane, and CINAHL databases to retrieve outcome studies comparing prolonged versus short inflation times during stent deployment. Outcomes studied included minimal stent diameter (MSD) and minimal stent area (MSA). Standardized mean difference (SMD) was used to estimate the effect sizes for these continuous variables. RESULTS: Seven studies with a total of 341 patients (415 lesions; mean age 67.6 years; 82% male) were included. Drug-eluting stents were used in 89 ± 15% of coronary lesions. Prolonged stent inflation was associated with increased minimal stent diameter (2.93 ± 0.34 mm vs. 2.72 ± 0.28 mm; SMD = 0.42; 95% CI 0.25-0.59; P < 0.001) and minimal stent area (5.99 ± 1.21 mm2 vs. 5.17 ± 0.87 mm2 ; SMD = 0.46; 95% CI 0.19-0.73; P = 0.001) compared with shorter duration stent inflation. This difference remained significant in sensitivity analyses that excluded studies with very prolonged inflation duration or multiple stent balloon inflations. CONCLUSION: Despite differences in duration and methodology, prolonged stent inflation is associated with improved expansion compared with shorter duration. The effect of this optimization recommends randomized trials to determine whether long-term outcomes can be improved by this simple technical modification.

Classification of mechanisms of strut malapposition after angiographically optimized stent implantation: An optical coherence tomography study.

AIMS: To elucidate causes and extent of strut malapposition in angiographically optimized stenting. METHODS AND RESULTS: Using a new classification system for strut malapposition, the mechanisms of stent strut malapposition were classified as localized lumen enlargement, vessel asymmetry, stent undersizing, strut underexpansion and stent deployment issue. Stent implantations (n = 110) in 100 consecutive patients undergoing optical coherence tomography (OCT) after the operator considered the stent as optimally deployed angiographically were reviewed to determine if strut apposition was complete. 127,894 stent struts in 110 stents were analyzed. There were 6,644 struts malapposed (5.2% ±7.3%), with strut malapposition found in 82 of 110 stents (74.5%). Localized lumen enlargement was the most common cause of malapposition (74.4% of malapposition clusters). Stent undersizing was the second most common cause (46.3%) followed by strut under-expansion in 29.3%, stent deployment issue in 18.2%, and vessel asymmetry in 9.7%. CONCLUSION: Malapposition of any degree is common after angiographic stent optimization, occurring in up to three-quarters of stents. The most frequent mechanism was localized lumen enlargement. The second most common cause of strut malapposition was stent undersizing, which was angiographically invisible. Whether performing OCT after angiographic optimization improves short- and long-term outcomes requires further study. © 2017 Wiley Periodicals, Inc.

Comparison and calibration of a real-time virtual stenting algorithm using Finite Element Analysis and Genetic Algorithms.

In this paper, we perform a comparative analysis between two computational methods for virtual stent deployment: a novel fast virtual stenting method, which is based on a spring-mass model, is compared with detailed finite element analysis in a sequence of in silico experiments. Given the results of the initial comparison, we present a way to optimise the fast method by calibrating a set of parameters with the help of a genetic algorithm, which utilises the outcomes of the finite element analysis as a learning reference. As a result of the calibration phase, we were able to substantially reduce the force measure discrepancy between the two methods and validate the fast stenting method by assessing the differences in the final device configurations.

Prolonged high-pressure is required for optimal stent deployment as assessed by optical coherence tomography.

AIMS: Optimizing stent deployment is important for both acute- and long-term outcomes. High-pressure balloon inflation is the standard for coronary stent implantation. However, there is no standardized inflation protocol. We hypothesized that prolonged high-pressure balloon inflation until stabilization of inflation pressure is superior to a rapid inflation/deflation sequence for both stent expansion and strut apposition. METHODS AND RESULTS: A high-pressure rapid inflation/deflation sequence was deployed followed by angiography to assure no residual stenosis. Optical coherence tomography (OCT) was then performed followed by prolonged inflation until balloon pressure was stabilized for 30 sec using the same balloon at the same pressure as the rapid sequence. A second OCT run was then done. Thirteen thousand nine hundred thirteen stent struts were evaluated by OCT in 12 patients undergoing successful stenting. Stent expansion improved with prolonged (206 ± 115 sec) vs. rapid (28 ± 17 sec) inflation for both minimal stent diameter (3.0 ± 0.5 vs. 2.75 ± 0.44 mm, P < 0.0001) and area (7.83 ± 2.45 vs. 6.63 ± 1.85 mm(2) , P = 0.0003). The number of malapposed struts decreased (45 ± 41 vs. 88 ± 75, P = 0.005) as did the maximal malapposed strut distance (0.31 ± 0.2 vs. 0.43 ± 0.2 mm, P = 0.0001). Factors related to strut malapposition after rapid inflation included localized asymmetry in 67%, stent underexpansion in 75%, and stent undersizing in 67%. CONCLUSIONS: These data demonstrate that prolonged inflation is superior to a rapid inflation/deflation technique for both stent expansion and strut apposition. We recommend for routine stent deployment a prolonged inflation protocol as described above to optimize stent deployment.

Effects of percutaneous endovascular angioplasty for severe stenosis or occlusion of subclavian artery.

To investigate the effect and safety of percutaneous endovascular angioplasty (PEA) with optional stenting for the treatment of severe stenosis or occlusion of subclavian artery, patients with severe stenosis ≥ 70% or occlusion of subclavian artery treated with PEA were retrospectively enrolled. The clinical data were analyzed. A total of 222 patients were retrospectively enrolled, including 151 males (68.0%) and 71 females (32.0%) aged 48-86 (mean 63.9 ± 9.0) years. Forty-seven (21.2%) patients had comorbidities. Subclavian artery stenosis ≥ 70% was present in 201 (90.5%) patients and complete subclavian occlusion in 21 (9.5%) cases. Angioplasty was successfully performed in all (100%) patients. Balloon-expandable stents were used in 190 (85.6%) cases, and self-expandable stents in 20 (9.0%) cases. Only 12 (5.4%) cases were treated with balloon dilation only. Among 210 patients treated with stent angioplasty, 71 (33.8% or 71/210) cases underwent balloon pre-dilation, 139 (66.2% or 139/210) had direct deployment of balloon-expandable stents, and 2 (1.0% or 2/210) experienced balloon post-dilation. Distal embolization protection devices were used in 5 (2.3% or 5/222) cases. Periprocedural complications occurred in 3 (1.4%) patients, including aortic dissection in 2 (0.9%) cases and right middle cerebral artery embolism in 1 (0.5%). No hemorrhage occurred. Among 182 (82.0%) patients with 6-month follow-up, restenosis > 70% occurred in 1 (0.5%) patient, and among 68 (30.6%) patients with 12-month follow-up, restenosis > 70% took place in 11 (16.2%) patients. Percutaneous endovascular angioplasty can be safely and efficiently performed for the treatment of severe stenosis ≥ 70% or occlusion of subclavian artery.

Intravascular imaging of angioplasty balloon under-expansion during pre-dilation predicts hyperelastic behavior of coronary artery lesions.

Introduction: Stent-induced mechanical stimuli cause pathophysiological responses in the coronary artery post-treatment. These stimuli can be minimized through choice of stent, size, and deployment strategy. However, the lack of target lesion material characterization is a barrier to further personalizing treatment. A novel ex-vivo angioplasty-based intravascular imaging technique using optical coherence tomography (OCT) was developed to characterize local stiffness of the target lesion. Methods: After proper institutional oversight, atherosclerotic coronary arteries (n = 9) were dissected from human donor hearts for ex vivo material characterization <48 h post-mortem. Morphology was imaged at the diastolic blood pressure using common intravascular OCT protocols and at subsequent pressures using a specially fabricated perfusion balloon that accommodates the OCT imaging wire. Balloon under-expansion was quantified relative to the nominal balloon size at 8 ATM. Correlation to a constitutive hyperelastic model was empirically investigated (n = 13 plaques) using biaxial extension results fit to a mixed Neo-Hookean and Exponential constitutive model. Results and discussion: The average circumferential Cauchy stress was 66.5, 130.2, and 300.4 kPa for regions with <15, 15-30, and >30% balloon under-expansion at a 1.15 stretch ratio. Similarly, the average longitudinal Cauchy stress was 68.1, 172.6, and 412.7 kPa, respectively. Consequently, strong correlation coefficients >0.89 were observed between balloon under-expansion and stress-like constitutive parameters. These parameters allowed for visualization of stiffness and material heterogeneity for a range of atherosclerotic plaques. Balloon under-expansion is a strong predictor of target lesion stiffness. These findings are promising as stent deployment could now be further personalized via target lesion material characterization obtained pre-operatively.

OCTOPUS - Optical coherence tomography plaque and stent analysis software.

Background and objective: Compared with other imaging modalities, intravascular optical coherence tomography (IVOCT) has significant advantages for guiding percutaneous coronary interventions, assessing their outcomes, and characterizing plaque components. To aid IVOCT research studies, we developed the Optical Coherence TOmography PlaqUe and Stent (OCTOPUS) analysis software, which provides highly automated, comprehensive analysis of coronary plaques and stents in IVOCT images. Methods: User specifications for OCTOPUS were obtained from detailed, iterative discussions with IVOCT analysts in the Cardiovascular Imaging Core Laboratory at University Hospitals Cleveland Medical Center, a leading laboratory for IVOCT image analysis. To automate image analysis results, the software includes several important algorithmic steps: pre-processing, deep learning plaque segmentation, machine learning identification of stent struts, and registration of pullbacks for sequential comparisons. Intuitive, interactive visualization and manual editing of segmentations were included in the software. Quantifications include stent deployment characteristics (e.g., stent area and stent strut malapposition), strut level analysis, calcium angle, and calcium thickness measurements. Interactive visualizations include (x,y) anatomical, en face, and longitudinal views with optional overlays (e.g., segmented calcifications). To compare images over time, linked visualizations were enabled to display up to four registered vessel segments at a time. Results: OCTOPUS has been deployed for nearly 1 year and is currently being used in multiple IVOCT studies. Underlying plaque segmentation algorithm yielded excellent pixel-wise results (86.2% sensitivity and 0.781 F1 score). Using OCTOPUS on 34 new pullbacks, we determined that following automated segmentation, only 13% and 23% of frames needed any manual touch up for detailed lumen and calcification labeling, respectively. Only up to 3.8% of plaque pixels were modified, leading to an average editing time of only 7.5 s/frame, an approximately 80% reduction compared to manual analysis. Regarding stent analysis, sensitivity and precision were both greater than 90%, and each strut was successfully classified as either covered or uncovered with high sensitivity (94%) and specificity (90%). We demonstrated use cases for sequential analysis. To analyze plaque progression, we loaded multiple pullbacks acquired at different points (e.g., pre-stent, 3-month follow-up, and 18-month follow-up) and evaluated frame-level development of in-stent neo-atherosclerosis. In ex vivo cadaver experiments, the OCTOPUS software enabled visualization and quantitative evaluation of irregular stent deployment in the presence of calcifications identified in pre-stent images. Conclusions: We introduced and evaluated the clinical application of a highly automated software package, OCTOPUS, for quantitative plaque and stent analysis in IVOCT images. The software is currently used as an offline tool for research purposes; however, the software's embedded algorithms may also be useful for real-time treatment planning.

Assessment of the flow-diverter efficacy for intracranial aneurysm treatment considering pre- and post-interventional hemodynamics.

Endovascular treatment of intracranial aneurysms with flow diverters (FD) has become one of the most promising interventions. Due to its woven high-density structure they are particularly applicable for challenging lesions. Although several studies have already conducted realistic hemodynamic quantification of the FD efficacy, a comparison with morphologic post-interventional data is still missing. This study analyses the hemodynamics of ten intracranial aneurysm patients treated with a novel FD device. Based on pre- and post-interventional 3D digital subtraction angiography image data, patient-specific 3D models of both treatment states are generated applying open source threshold-based segmentation methods. Using a fast virtual stenting approach, the real stent positions available in the post-interventional data are virtually replicated and both treatment scenarios were characterized using image-based blood flow simulations. The results show FD-induced flow reductions at the ostium by a decrease in mean neck flow rate (51%), inflow concentration index (56%) and mean inflow velocity (53%). Intraluminal reductions in flow activity for time-averaged wall shear stress (47%) and kinetic energy (71%) are present as well. However, an intra-aneurysmal increase in flow pulsatility (16%) for the post-interventional cases can be observed. Patient-specific FD simulations demonstrate the desired flow redirection and activity reduction inside the aneurysm beneficial for thrombosis formation. Differences in the magnitude of hemodynamic reduction exist over the cardiac cycle which may be addressed in a clinical setting by anti-hypertensive treatment in selected cases.

Impact of Design and Deployment Technique on the Hydrodynamic Resistance of Flow Diverters : An in Vitro Experimental Study.

PURPOSE: Despite the high efficacy of flow diverters (FD) in treating sidewall intracranial aneurysms, failures are reported. One of the physical factors determining efficacy is the flow reducing capacity of the FD that is currently unknown to the operator. Our aim was to measure the flow reducing capacity expressed as the hydrodynamic resistance (HR), the metallic surface area (MSA) and pore density (PD) of two different FD designs and quantitatively investigate the impact of sizing and the deployment technique on these parameters. METHODS: Altogether 38 Pipeline (Medtronic) and P64 (Phenox) FD­s were implanted in holder tubes by a neurointerventionist in nominally sized, oversized and longitudinally compressed or elongated manners. The tubes were placed in a flow model with the flow directed across the FD through a side hole on the tube. HR was expressed by the measured pressure drop as the function of the flow rate. Deployed length, MSA and PD were also measured and correlated with the HR. RESULTS: Both PD and MSA changed with varying deployment length, which correlates well with the change in HR. Oversizing the device by 1 mm in diameter has reduced the HR on average to one fifth of the original value for both manufacturers. CONCLUSION: This study demonstrates experimentally that different FD designs have different flow diverting capacities (HR). Parameters are greatly influenced by radial sizing and longitudinal compression or elongation during implantation. Our results might be useful in procedure planning, predicting clinical outcome, and in patient-specific numerical flow simulations.

How precise is PreSize Neurovascular? Accuracy evaluation of flow diverter deployed-length prediction.

OBJECTIVE: The use of flow-diverting stents has been increasingly important in intracranial aneurysm treatment. However, accurate sizing and landing zone prediction remain challenging. Inaccurate sizing can lead to suboptimal deployment, device waste, and complications. This study presents stent deployment length predictions offered in medical software (PreSize Neurovascular) that provides physicians with real-time planning support, allowing them to preoperatively "test" different devices in the patient's anatomy in a safe virtual environment. This study reports the software evaluation methodology and accuracy results when applied to real-world data from a wide range of cases and sources as a necessary step in demonstrating its reliability, prior to impact assessment in prospective clinical practice. METHODS: Imaging data from 138 consecutive stent cases using the Pipeline embolization device were collected from 5 interventional radiology centers in the United Kingdom and retrospectively analyzed. Prediction accuracy was calculated as the degree of agreement between stent deployed length measured intraoperatively and simulated in the software. RESULTS: The software predicted the deployed stent length with a mean accuracy of 95.61% (95% confidence interval [CI] 94.87%-96.35%), the highest reported accuracy in clinical stent simulations to date. By discounting 4 outlier cases, in which events such as interactions with coils and severe push/pull maneuvers impacted deployed length to an extent the software was not able to simulate or predict, the mean accuracy further increases to 96.13% (95% CI 95.58%-96.69%). A wide discrepancy was observed between labeled and measured deployed stent length, in some cases by more than double, with no demonstrable correlation between device dimensions and deployment elongation. These findings illustrate the complexity of stent behavior and need for simulation-assisted sizing for optimal surgical planning. CONCLUSIONS: The software predicts the deployed stent length with excellent accuracy and could provide physicians with real-time accurate device selection support.

Can Endovascular Treatment of Fusiform Intracranial Aneurysms Restore the Healthy Hemodynamic Environment?-A Virtual Pilot Study.

Numerous studies assess intracranial aneurysm rupture risk based on morphological and hemodynamic parameter analysis in addition to clinical information such as aneurysm localization, age, and sex. However, intracranial aneurysms mostly occur with a saccular shape located either lateral to the parent artery or at a bifurcation. In contrast, fusiform intracranial aneurysms (FIAs), i.e., aneurysms with a non-saccular, dilated form, occur in approximately 3-13% of all cases and therefore have not yet been as thoroughly studied. To improve the understanding of FIA hemodynamics, this pilot study contains morphological analyses and image-based blood flow simulations in three patient-specific cases. For a precise and realistic comparison to the pre-pathological state, each dilation was manually removed and the time-dependent blood flow simulations were repeated. Additionally, a validated fast virtual stenting approach was applied to evaluate the effect of virtual endovascular flow-diverter deployment focusing on relevant hemodynamic quantities. For two of the three patients, post-interventional information was available and included in the analysis. The results of this numerical pilot study indicate that complex flow structures, i.e., helical flow phenomena and the presence of high oscillating flow features, predominantly occur in FIAs with morphologically differing appearances. Due to the investigation of the individual healthy states, the original flow environment could be restored which serves as a reference for the virtual treatment target. It was shown that the realistic deployment led to a considerable stabilization of the individual hemodynamics in all cases. Furthermore, a quantification of the stent-induced therapy effect became feasible for the treating physician. The results of the morphological and hemodynamic analyses in this pilot study show that virtual stenting can be used in FIAs to quantify the effect of the planned endovascular treatment.

Transcatheter aortic valve replacement in bicuspid valves: The synergistic effects of eccentric and incomplete stent deployment.

Bicuspid aortic valve is a congenital cardiac anomaly and common etiology of aortic stenosis. Given the positive outcomes of transcatheter aortic valve replacement (TAVR) in low-risk patients, TAVR will become more prevalent in the future in the treatment of severe bicuspid valve stenosis. However, asymmetrical bicuspid valve anatomy and calcification can prevent the circular and complete expansion of transcatheter aortic valves (TAVs). In previous studies, examining the impact of elliptical TAV deployment on leaflet stress distribution, asymmetric expansion of balloon-expandable intra-annular devices was studied up to an ellipticity index (long/short TAV diameter) of 1.4. However, such a high degree of eccentricity has not been observed in clinical studies with balloon-expandable devices. High degrees of stent eccentricity have been observed in self-expanding TAVs, such as CoreValve. However, CoreValve is a supra-annular device, and it was not clear if eccentric and incomplete stent deployment at the annulus would alter leaflet stress and strain distributions. This study aimed to assess the effects of eccentric and incomplete stent deployment of CoreValves in bicuspid aortic valves and compare the results to that of SAPIEN 3. Leaflet stress distribution and leaflet kinematics of 26-mm CoreValve and 26-mm SAPIEN 3 devices in bicuspid valves were obtained in a range that was observed in previous clinical studies. The results indicated that elliptical and incomplete stent deployment of TAVs increase leaflet stress and impair leaflet kinematics. The changes were more pronounced in CoreValve than SAPIEN 3. Increased leaflet stress can reduce long-term valve durability, and impaired leaflet kinematics can potentially increase blood stasis on the TAV leaflets. The study provides complementary insights into the mechanics of TAVs in bicuspid aortic valves.

A New Method to Optimize Stent Deployment by High-Definition Intravascular Ultrasound.

OBJECTIVES: Optimal stent deployment by intravascular ultrasound (IVUS) improves outcome, but it can only be achieved in 50% of patients. We investigated the feasibility and effect of a new method of stent optimization on optimal stent deployment. METHODS: IVUS analyses of 168 coronary segments were performed after angiography-guided stenting (AGS) and stent optimization in 29 patients (30 lesions). Minimum stent area (MSA), stent volume index (SVI), lumen area, external elastic membrane (EEM), and plaque burden (PB) were measured. Stent optimization included post-stent dilation with a balloon sized by high-definition (HD)-IVUS to the distal reference EEM diameter for stent underexpansion or malapposition, and stenting of PB >50% or edge dissection. RESULTS: After AGS, stent deployment was suboptimal in 77% of patients. After stent optimization, MSA and SVI were significantly larger than AGS. Adequate stent expansion - defined as MSA ≥5.4 mm² or ≥90% of distal reference lumen area - was significantly higher after stent optimization vs AGS (87% vs 56%, respectively; P=.02). Optimal stent deployment - a composite of adequate stent expansion, no malapposition, PB <50% at the stent edges, and no edge dissection - was markedly higher after stent optimization vs AGS (87% vs 35%, respectively; P<.01). CONCLUSION: After stent deployment and postdilation, stent results were suboptimal in two-thirds of patients. This simple online stent optimization by HD-IVUS was feasible and resulted in optimal stent deployment in the majority of patients. Randomized studies are warranted to compare the rate of optimal stent deployment and outcomes of this strategy vs other techniques.

Influence of the Adopted Balloon Modeling Strategies in the Stent Deployment Procedure: An In-Silico Analysis.

PURPOSE: As the promoter of the stent expansion, the balloon plays a very important role, offering a strong influence on the deployment process. Balloon-artery interaction is pointed as a probable cause of restenosis, stressing the relevance of balloon modeling when simulating the stenting procedure. In this work, an in-silico study of the balloon modeling strategies is performed. METHODS: Ultrasonic-microcasting is a novel technology that allows obtaining stents manufactured in magnesium alloys, being suggested as a promising solution. However, this technique demands superior stent strut thickness, which may have an impact on the stent deployment procedure. The influence of the balloon modeling is studied through the simulation of different balloon geometries (open- or taper-ended) and material constitutive model (linear elastic or hyperelastic) on the expanded configuration of a stent manufactured through ultrasonic-microcasting. RESULTS: The results obtained suggest that the choice of balloon type has small impact in terms of demanded pressure to inflate the balloon and in the stent final radius achieved at fully-expanded configuration. Additionally, it was proved that the balloon-type influences the stent expanded profile along its length and diameter as a result of the different deformation behavior exhibited by the balloon. CONCLUSION: The hyperelastic taper-ended balloon suggests being the model that better correlates with both experimental and clinical results regarding the expanded balloon profile during the procedure.

Finite element evaluation of artery damage in deployment of polymeric stent with pre- and post-dilation.

Using finite element method, this paper evaluates damage in an arterial wall and plaque caused by percutaneous coronary intervention. Hyperelastic damage models, calibrated with experimental results, are used to describe stress-stretch responses of arterial layers and plaque; these models are capable to simulate softening behaviour of the tissue due to damage. Abaqus CAE is employed to create the finite element models for the artery wall (with media and adventitia layers), a symmetric uniform plaque, a bioresorbable polymeric stent and a tri-folded expansion balloon. The effect of percutaneous coronary intervention on vessel damage is investigated by simulating the processes of vessel pre-dilation, stent deployment and post-stenting dilation. Energy dissipation density is used to assess the extent of damage in the tissue. Softening of the plaque and the artery, due to the pre-dilation-induced damage, can facilitate the subsequent stent deployment process. The plaque and the artery experienced heterogeneous damage behaviour after the stent deployment, caused by non-uniform deformation. The post-stenting dilation was effective to achieve a full expansion of the stent, but caused additional damage to the artery. The continuous and discontinuous damage models yielded similar results in the percutaneous coronary intervention simulations, while the incorporation of plaque rupture affected the simulated outcomes of stent deployment. The computational evaluation of the artery damage can be potentially used to assess the risk of in-stent restenosis after percutaneous coronary intervention.

Mechanistic evaluation of long-term in-stent restenosis based on models of tissue damage and growth.

Development and application of advanced mechanical models of soft tissues and their growth represent one of the main directions in modern mechanics of solids. Such models are increasingly used to deal with complex biomedical problems. Prediction of in-stent restenosis for patients treated with coronary stents remains a highly challenging task. Using a finite element method, this paper presents a mechanistic approach to evaluate the development of in-stent restenosis in an artery following stent implantation. Hyperelastic models with damage, verified with experimental results, are used to describe the level of tissue damage in arterial layers and plaque caused by such intervention. A tissue-growth model, associated with vessel damage, is adopted to describe the growth behaviour of a media layer after stent implantation. Narrowing of lumen diameter with time is used to quantify the development of in-stent restenosis in the vessel after stenting. It is demonstrated that stent designs and materials strongly affect the stenting-induced damage in the media layer and the subsequent development of in-stent restenosis. The larger the artery expansion achieved during balloon inflation, the higher the damage introduced to the media layer, leading to an increased level of in-stent restenosis. In addition, the development of in-stent restenosis is directly correlated with the artery expansion during the stent deployment. The correlation is further used to predict the effect of a complex clinical procedure, such as stent overlapping, on the level of in-stent restenosis developed after percutaneous coronary intervention.

Co-registration of pre- and post-stent intravascular OCT images for validation of finite element model simulation of stent expansion.

Intravascular optical coherence tomography (IVOCT) provides high-resolution images of coronary calcifications and detailed measurements of acute stent deployment following stent implantation. Since pre- and post-stent IVOCT image "pull-back" acquisitions start from different locations, registration of corresponding pullbacks is needed for assessing treatment outcomes. In particular, we are interested in assessing finite element model (FEM) prediction of lumen gain following stenting, requiring registration. We used deep learning to segment calcifications in corresponding pre- and post-stent IVOCT pullbacks. We created 1D representations of calcium thickness as a function of the angle of the helical IVOCT scans. Registration of two scans was done by maximizing the cross correlation of these two 1D representations. Registration was accurate, as determined by visual comparisons of 2D image frames. We used our pre-stent calcification segmentations to create a lesion-specific FEM, which took into account balloon size, balloon pressure, and stent measurements. We then compared simulated lumen gain from FEM analysis to actual stent deployment results. Actual lumen gain across ~200 registered pre and post-stent images was 1.52 ± 0.51, while FEM prediction was 1.43 ± 0.41. Comparison between actual and FEM results showed no significant difference (p < 0.001), suggesting accurate prediction of FEM modeling. Registered image data showed good visual agreement regarding lumen gain and stent strut malapposition. Hence, we have developed a platform for evaluation of FEM prediction of lumen gain. This platform can be used to guide development of FEM prediction software, which could ultimately help physicians with stent treatment planning of calcified lesions.