DEFormable models for the ENdovaScular trEatment and follow-up of abdominal aortic aneurysms
An Abdominal Aortic Aneurysm (AAA) is a condition consisting of a weakening and ballooning of the abdominal aorta, exceeding the normal diameter by more than 50%. If not treated, they tend to grow and rupture with a high risk of mortality. Endovascular Aneurysm Repair (EVAR) is a minimally invasive alternative to open surgical repair involving the deployment and fixation of a stent-graft via catheterism. This excludes the damaged wall from circulation and creates and intraluminal thrombus which tends to shrink after a successful intervention. EVAR is much less aggresive that open surgery and has significantly lower operative mortality but the survival rate after 2 years is almost equivalent. The reason is that the aneurysm is excluded but not removed, leading to some problems, known as endoleaks, due to wrong fixation, recurrent flow into the thrombus area or device wear.
Pre-operative planning is performed on the basis of CTA imaging by performing patient-specific measurements (diameters and lengths) which allow the selection of the most suitable endoluminal device from a catalogue or the design of a patient-specific endograft in the case of complex anatomies. One main problem is that the relative position and deformation of catheter-aorta and endograft-aorta is not known at the planning and design stage. Prediction such behavior by using deformable models may lead to better design and a reduction of the 2-year after EVAR mortality.
In the intra-operative scenario, X-ray Angiography (XA) offers valuable but limited information, and still is difficult for the surgeon to orient himself, visualize relevant structures and compare the current situation with the planning and designed endograft. Deformable models and image registration procedures may help to align pre-operative and intra-operative imaging and models so as to provide more valuable information for image guidance. Furthermore, this information could help validating pre-operative simulation models.
Close follow-up is required after EVAR by performing CTA examinations at least yearly. Correctly excluded aneurysms tend to shrink, which is usually measured by largest diameter. However, aneurysm volume is a better indicator but is not used on routine due to lack of robust thrombus segmentation methods, as this structure is not contrasted and shows fuzzy borders. Furthermore, it would be very useful for clinicians if they could align and compare different post-operative CTA time series in order to assess the evolution of the aneurysm by different shape analysis, migration of the endograft and other changes that could be relevant for assessing the rupture risk. This requires specific research in deformable models and image registration methods in order to align different time series of volumes with changing structures.
One common technical challenge in these three scenarios related to the endovascular intervention on AAAs are the study of deformable models on medical images in this context (CTA deformable model simulation, XA-CTA intra-operative) which is the main objective of the DEFENSE project. These models will be able to characterize the changes and deformations occurring before, during and after the intervention. Furthermore, the study of the deformations involved could lead to new clinical evidence on how to perform the procedures, correct the endograft designs based on the observed geometries and endograft used, and evaluate the rupture risk after the intervention.
Vicomtech will participate in the 3D model generation by segmentation of relevant structures present in CTA or XA images (aortic lumen, thrombus, endoprosthesis, vertebrae...) and in the aneurysm follow-up and rupture risk prediction in the post-operative stage.