BackgroundIn this study, we develop reliable and practical virtual coiling and stenting methods for intracranial aneurysm surgical planning. Since the purpose of deploying coils and stents is to provide device geometries for subsequent accurate post-treatment computational fluid dynamics analysis, we do not need to accurately capture all the details such as the stress and force distribution for the devices and vessel walls. Our philosophy for developing these methods is to balance accuracy and practicality.MethodsWe consider the mechanical properties of the devices and recapitulate the clinical practice using a finite element method (FEM) approach. At the same time, we apply some simplifications for FEM modeling to make our methods efficient. For the virtual coiling, the coils are modeled as 3D Euler–Bernoulli beam elements, which is computationally efficient and provides good geometry representation. During the stent deployment process, the stent–catheter system is transformed according to the centerline of the parent vessel since the final configuration of the stent is not dependent of the deployment history. The aneurysm and vessel walls are assumed to be rigid and are fully constrained during the simulation. All stent–catheter system and coil–catheter system are prepared and packaged as a library which contains all types of stents, coils and catheters, which improves the efficiency of surgical planning process.ResultsThe stent was delivered to the suitable position during the clinical treatment, achieving good expansion and apposition of the stent to the arterial wall. The coil was deployed into the aneurysm sac and deformed to different shapes because of the stored strain energy during coil package process and the direction of the microcatheter.ConclusionsThe method which we develop here could become surgical planning for intracranial aneurysm treatment in the clinical workflow.

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A cohesive zone model (CZM) approach is applied to simulate atherosclerotic plaque delamination experiments in mouse abdominal aorta specimens. A three-dimensional finite element model is developed for the experiments. The aortic wall is treated as a fiber-reinforced, highly deformable, incompressible material, and the Holzapfel-Gasser-Ogden (HGO) model is adopted for the aortic bulk material behavior. Cohesive elements are placed along the plaque-media interface along which delamination occurs. The 3D specimen geometry is created based on images from the experiments and certain simplifying approximations. A set of HGO and CZM parameter values is determined based on values suggested in the literature and through matching simulation predictions of the load vs. load-point displacement curve with experimental measurements for one loading-delamination-unloading cycle. Using this set of parameter values, simulation predictions for four other loading-delamination-unloading cycles are obtained, which show good agreement with experimental measurements. The findings of the current study demonstrate the applicability of the CZM approach in arterial tissue failure simulations.

Background: Intravascular ultrasound (IVUS) provides good insight into lumen boundary and plaques; however, it is still difficult to detect functionally significant stenosis from IVUS images for the guidance of coronary percutaneous intervention (PCI). This study aimed to develop a novel method to estimate fractional flow reserve (FFR) value for determining the functional significance of coronary artery disease through the fusion of IVUS and X-ray angiographic images. Methods:We developed a novel approach to 3D vessel reconstruction by integrating IVUS with X-ray angiographic images. Based on the reconstructed geometry and the inlet flow derived from the thrombolysis in myocardial infarction (TIMI) frame count, a simplified fluid dynamics equation was established to compute the pressure drop and IVUS-derived FFR (AccuFFRivus) was subsequently obtained. To validate the feasibility and performance of this IVUS-based FFR method, we performed AccuFFRivus calculations on 32 coronary vessels with invasive FFR as the reference standard.Results: Great correlation (r=0.86, P<0.001) was observed between AccuFFRivus and FFR. The area under the receiver-operating characteristic curve (AUC) was higher for AccuFFRivus than minimal lumen area (MLA, <4 mm 2 ) and diameter stenosis rate (DS% ≥50%) [0.98 (95% CI: 0.86 to 1.0) vs. 0.78 (95% CI: 0.60 to 0.91) and 0.66 (95% CI: 0.47 to 0.82)]. Bland-Altman plot showed a mean difference value of -0.011 (limits of agreement: -0.156 to 0.134).Conclusions: AccuFFRivus is a novel method for hybridizing IVUS and X-ray angiographic images to identify functionally significant stenosis with FFR ≤0.80. The good diagnostic performance from the initial validation study demonstrates the potential for clinical utilization of physiologically guided decision-making.Further validation is required in future studies with a large number of cases.

Fibrous cap delamination is a critical process during the rupture of atherosclerotic plaque, which often leads to severe life-threatening clinical consequences such as myocardial infarction or stroke. In this study a finite element modeling and simulation approach is presented that enables the study of fibrous cap delamination experiments for the purpose of understanding the fibrous cap delamination process. A cohesive zone model (CZM) approach is applied to simulate delamination of the fibrous cap from the underlying plaque tissue. A viscoelastic anisotropic (VA) model for the bulk arterial material behavior is extended from existing studies so that the hysteresis phenomenon observed in the fibrous cap delamination experiments can be captured. A finite element model is developed for the fibrous cap delamination experiments, in which arterial layers (including the fibrous cap and the underlying plaque tissue) are represented by solid elements based on the VA model and the fibrous cap-underlying plaque tissue interface is characterized by interfacial CZM elements. In the CZM, the delamination process is governed by an exponential traction-separation law which utilizes critical energy release rates obtained directly from the fibrous cap delamination experiments. A set of VA model parameter values and CZM parameter values is determined based on values suggested in the literature and through matching simulation predictions of the load vs. load-point displacement curve with one set of experimental measurements. Using this set of parameter values, simulation predictions for other sets of experimental measurements are obtained and good agreement between simulation predictions and experimental measurements is observed. Results of this study demonstrate the applicability of the viscoelastic anisotropic model and the CZM approach for the simulation of diseased arterial tissue failure processes.