Towards an updated aortic 3D map during EVAR: experimental and computational studies

Recently, the endovascular treatment for abdominal aortic aneurysm, commonly indicated as EVAR, has become a widespread alternative to open surgery, thanks to its lower peri-operative mortality and morbidity. However, it presents some challenges and there is still room for improvement towards a safer procedure. In particular, for the intra-operative visualization of instruments and vessels, EVAR relies on the use of radiation and contrast agent injection, whose amounts increase for complex cases. Radiation exposure is potentially harmful for both patients and clinical personnel, while contrast agent is nephrotoxic. Moreover, traditional image fusion techniques lack a continuous and automatic update of the vessel configuration, which changes due to the insertion of stiff guidewires, that are introduced to enable the delivery of the stent graft to its deployment site. This can impair EVAR navigation, especially for complex geometries (e.g., highly tortuous and long iliac arteries, severe calcifications) leading to higher fluoroscopy time. Furthermore, the pre-operative planning can be affected by the guidewire-induced aortic displacements, leading, for example, to suboptimal choice of stent graft size and landing zones. Today, their prediction relies mainly on the surgeon’s experience. Computer-based models and innovative tracking technologies can help to address these challenges, potentially reducing the risks of intra-operative and postoperative complications. In silico approaches, such as numerical simulations, can be used to predict the guidewire-induced aortic deformations during EVAR, while experiments with deformable patient-specific models can be exploited for validation of computational approaches, training of clinicians and testing of innovative navigation technologies. Among the latter, electromagnetic and shape sensing tracking technologies allow to follow the inserted tool in their path, without the use of fluoroscopy. Hence, the present PhD thesis aims to develop engineering strategies to overcome the above-mentioned challenges. In detail, as ultimate goal, it sought to obtain an updated aortic roadmap, that takes into account the deformations induced by the insertion of tools of different stiffness, to improve EVAR navigation. Three main studies were conducted towards this objective. First, finite element-based analyses of guidewire insertion in models of increasing anatomical complexity, i.e., with the inclusion of intraluminal thrombus and calcifications, were carried out and experimentally validated through ad-hoc manufactured models in a hybrid operating room, equipped with a rotating C-arm cone-beam CT scanner. A good agreement was found between the experimental and the computational studies. Second, to improve the predictions obtained from the sole numerical model, an innovative approach that combines the use of electromagnetic (EM) tracking technology and numerical simulations was investigated. An ad-hoc sensorized tool with three embedded EM sensors was obtained. The simulation that minimized the in silico vs. in vitro discrepancy in terms of sensor positions, gave the most accurate results in terms of aortic displacement. The proposed approach suggests that the EM tracking technology, can be used not only to follow the tool but also to minimize the error in the predicted aortic roadmap, thus paving the way to a safer EVAR navigation. Finally, to overcome the computational cost of high-fidelity simulations and the uncertainties related to the input parameters (e.g., stiffness of the guidewires and aorta, insertion angles), a reduced order model (ROM) trained on parametric finite element simulations of the lumen-guidewire interaction was developed. Once built, the ROM provided accurate and almost real-time estimates of the guidewireinduced aortic displacement field, thus potentially being a promising pre- and intra-operative tool for clinicians. The experimental and numerical studies conducted during this project allowed to shed light on vessel-tool interaction and they can be considered as a first step towards developing a potential radiation-free EVAR procedure. The application of the developed strategies pre- and intra-operatively seems an intriguing upcoming challenge with a potential impact on clinical practice.