基于医学影像的镍钛合金膨出式支架的设计与性能研究

发布时间：2019-01-29 20:56

【摘要】：主动脉夹层是异常凶险的主动脉高危疾病,严重影响人们的健康与正常生活。我国主动脉疾病以主动脉夹层为主。主动脉腔内支架修复术(TEVAR)能够有效封堵夹层近端破口,促进假腔血栓化。主动脉覆膜支架作为TEVAR治疗的主要器械,承担重建血液通路、加快血管重塑等重要作用。夹层患者的医学影像是选择合适的支架规格的重要依据,也是未来个性化支架设计参数的重要来源。覆膜支架植入后的力学性能表现是主动脉疾病疗效的重要评价指标。有限元分析技术作为一种体外模拟研究方法,在医学领域已获得广泛应用。通过有限元分析,能够对支架植入后的受力状态进行较为全面的评价与预测。本课题根据夹层患者术后远端返流的现象,基于患者的医学影像数据,创新性提出一种变截面式镍钛合金覆膜支架,通过膨出段与夹层内膜相互紧贴并对夹层内膜施加一定压迫,加速假腔近端血栓化,达到积极的治疗效果。通过对患者医学影像的提取与处理,能够获得夹层病变的重要尺寸参数与形态参数,能够指导合适支架的设计与选择。通过有限元分析得出几何参数对支架的径向支撑力性能具有重要影响:增加支架丝径与膨出段支架环个数,可以提高膨出段支架的支撑性能,增加膨出段长度则会使支撑性能降低;当膨出段支架的膨出度为8 mm时,其支撑性能为较好水平;几何参数影响程度由大至小依次为丝径、膨出段长度、支架环个数、膨出度。通过静力学计算与误差分析,得到相应支架的理论径向支撑力值与误差范围,对支架的设计与改进提供一定的理论基础与帮助。在本实验条件下,根据设计理念筛选获得的较优组合为丝径中0.5mm,膨出段长度50mm,膨出段上支架环个数3个,膨出度12 mm。通过对夹层内膜的力学性能测试,获得相应的力学性能参数,为支架合理的参数选择提供重要评价标准:通过改变支架几何参数提高支架支撑性能时,其设计径向支撑力不能超过夹层内膜或者主动脉血管壁的生理承受极限,防止因支架力学性能不匹配产生的严重术后并发症。CFD流体动力学的模拟结果表明,远端破口未及时处理时,离支架末端较近的破口有可能成为新入口,持续为下段夹层假腔提供灌注;而膨出式支架能够有效阻断夹层假腔破口的返流现象。体外流体模型的观测结果能够较好地验证CFD流体模拟结果的有效性。
[Abstract]:Aortic dissection is an extremely dangerous high-risk disease of aorta, which seriously affects people's health and normal life. Aortic dissection is the main disease of aorta in China. Endovascular stent repair (TEVAR) can effectively close the proximal break of the dissection and promote pseudo-lumen thromboembolization. As the main instrument of TEVAR, aortic stent graft plays an important role in reconstructing blood pathway and accelerating vascular remodeling. Medical imaging of dissection patients is an important basis for selecting appropriate stent specifications and an important source of personalized stent design parameters in the future. The mechanical performance of stent implantation is an important index to evaluate the curative effect of aortic disease. Finite element analysis, as an in vitro simulation method, has been widely used in the field of medicine. Through finite element analysis, the stress state of the scaffold can be comprehensively evaluated and predicted. According to the phenomenon of distal regurgitation in patients with dissection and based on the medical image data of the patients, a new type of nickel-titanium alloy coated stent with variable cross-section was proposed. In order to accelerate the thromboembolization of the proximal pseudo-lumen, a positive therapeutic effect was achieved by pressing the intima of the dissection by pressing the swelling segment closely to the intima of the dissection. Through the extraction and processing of medical images of patients, the important size parameters and morphological parameters of dissection lesions can be obtained, and the design and selection of suitable scaffolds can be guided. Through finite element analysis, it is concluded that geometric parameters have an important effect on the support performance of the support: increasing the diameter of the wire and the number of rings in the extruding section can improve the support performance of the extruded bracket. Increasing the length of the extruded section will reduce the support performance. When the extruding degree of the extruded bracket is 8 mm, the support performance is better, and the influence degree of geometric parameters from big to small is the wire diameter, the length of the extruded segment, the number of the bracket rings and the expansion degree. Through static calculation and error analysis, the theoretical radial support force and error range of the corresponding support are obtained, which provides a certain theoretical basis and help for the design and improvement of the support. Under the experimental conditions, the optimum combination is 0.5 mm in diameter, 50 mm in length, 3 rings in the extruded segment, and 12 mm. in the extruded section, according to the design concept. The optimum combination is 0.5 mm in diameter, 50 mm in length of extruding segment, 3 in the number of bracket rings on the extruded segment, and 12 mm. in expansion degree. Through testing the mechanical properties of the interlayer inner membrane, the corresponding mechanical performance parameters are obtained, which provides an important evaluation criterion for the reasonable selection of the support parameters: when the support performance is improved by changing the geometric parameters of the scaffold, The designed radial supporting force should not exceed the physiological endurance limit of the dissecting intima or the aortic vascular wall and prevent the serious postoperative complications caused by the mismatch of the mechanical properties of the stent. The simulation results of CFD fluid dynamics show that, When the distal break is not treated in time, the break near the end of the scaffold may become a new entrance, which will continue to provide perfusion for the lower segment of the false chamber. The extruded bracket can effectively block the reflux phenomenon of the break in the false cavity of the interlayer. The observational results of the external fluid model can well verify the validity of the CFD fluid simulation results.
【学位授予单位】：北京有色金属研究总院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R318.08

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