Numerical Simulation Of Balloon-stent System Based On Patient-specific Coronary Remodeling

Coronary artery disease is a narrowing or blockage of the arteries and vessels that provide oxygen and nutrients to the heart, usually due to atherosclerosis(hardening of the arteries), an accumulation of fatty materials on the inner linings of arteries. As CAD is a serious threat to human health, the prevention, diagnosis and treatment has been major issues in clinical researches. Stent implantation is an effective method for the treatment of CAD, and it has been widely used in recent years. The process of stenting is to deliver the stent wrapped on balloon catheter to the vascular lesion site, and then expand it by pressuring the balloon to support the blood vessel. Currently, the deployment of stent, such as length and size of stent,implantation schemes, are mainly based on the information from two-dimensional coronary angiography and clinician’s experiences. Lack of necessary theoretical basis and inability to obtain stented coronary geometry and hemodynamics directly make it unable to evaluate the instant therapeutic effect. On the other hand, due to the differences between individual patients, improper stent deployment may lead to serious postoperative complications such as in-stent restenosis.Considering of the latest researches about treatment of CAD using coronary stent in the world, this thesis intends to establish a balloon-stent model for individual coronary which could more really indicate the expanding and recoiling process of clinical stent in stenosed coronary. This model can also be used in better understanding for deformation and mechanical behavior of stent and vessel, change of coronary lumen geometry, distribution and apposition of stent strut, which provides personalized gaudiness for stent deployment and treatment evaluation.The main jobs of this thesis are as followed:We analyzed the influence of different folded level balloon on the process of stent expanding and recoiling. The simulation results were verified by the pressure-diameter compliance curve of the manufacturer. Besides, the maximum“dog-boning ”、 foreshortening and radial recoil rates were depicted to evaluate different simulation effect. The non-folded balloon expandable stent expanded larger than others with low stress, and all three coefficients were the highest. Six-folded balloon expandable stent behaved well, its pressure-diameter compliance curve perfectly agreed with the manufacturer’s data than tri-folded configuration.Furthermore, its foreshortening and recoil rates were also lower than the former. In the primary design stage of stent, the non-folded configuration can be used to carry out the expansion and recoil simulation of the stent, but considering the transient behavior and the final positioning, the folded level and the conical tip design should be included in the simulation.In the second part(Chapter III) of the paper, right coronary model was reconstructed from individual CTA images based on the six-folded balloon with conical tip discussed in the first part. Mechanical expansion and recoil process of a patient-specific balloon-stent were simulated in this model. Then feasibility of simulation and consistency with clinical outcome were evaluated. The deformation of lumen geometry pre and post stent placement, strain and stress distribution of vessel and stent at maximum expansion and recoil, apposition of stent were also analyzed.Evaluation indicated that the simulation results were in good agreement with clinical imaging. A certain amount of axial deformation occurred in the vessel after stent deployment, vascular lumen diameter and area changed to a large extent accordingly.The maximum principal stress distribution of vessel mainly concentrated in theplaque area and reached the ultimate stress at the maximum expansion moment,making it easier to rupture. The peak Mises stress of the stent occurred in the corner of the strut and at the connection between different crowns. Slight malappositions were found in the proximal end of the stent which may be related to the incomplete recoiling and bended geometric structure.