# Volumetric Analysis of Aortic Changes after TEVAR Using Three-Dimensional Virtual Modeling
## 4 Discussion  
TEVAR is a minimally invasive endovascular procedure used to treat DTAAs, and it shows several advantages compared to traditional open surgical repair, such as a lower risk of perioperative complications, shorter hospital stays, and lower mortality rates during follow-up. These advantages make TEVAR an attractive option for many patients who have a DTAA [17; 18; 19]. Stent grafts are designed to cover aneurysms, diverting blood flow away from the weakened, aneurismatic aorta, and restoring normal blood flow. After the positioning of the stent graft, the aorta and the excluded aneurysm undergo a remodeling process, which ideally leads to thrombosis of the excluded aneurysm sac and reduction in or stability of the aortic aneurismatic dilatation (positive aortic remodeling). As this remodeling process is complex and takes time, and with it, the relationship between the stent graft and the aorta or its branches can also change, possibly leading to complications like endoleaks or stent graft migration, life-time imaging follow-up of these patients is recommended, while re-TEVAR is not uncommon [10]. In addition to recognizing the appearance or increase in endoleaks, CTA follow-up is routinely used for monitoring the evolution of the aneurysm and the surrounding aorta. As for any other aortic condition, both in the settings of acute aortic syndromes and chronic conditions, like aneurysm, dissection, or penetrating aortic ulcers, in clinical practice, the aortic dimensions are reported as the maximum diameter perpendicular to the axis of blood flow [20]. Aorta measurements must be repeatable and precise to characterize pre-existent aortic disease and its eventual progression. Measurements should be performed at specific segmental levels, as well as at the site of any aortic pathology. Using multiplanar reformats that are orthogonal to the aortic flow axis is strongly recommended [10]. Still, even in experienced centers, there is some degree of inter-observer variability when reporting aortic diameters, and the need for a more robust and objective way to measure the aortic changes and pathologies has already been expressed in the literature [11; 21]. As the aorta is a cylindrical structure subjected to tortuosity and with changing dimensions or degrees of dilatation along its long course inside the body, a volumetric evaluation can be suitable to better analyze its changes both in the case of chronic aortic pathology or post-surgery/endovascular procedures [22]. A DTAA can be stable at its maximum diameter but still increase in dimension along its path, and these differences may be underestimated by a manual diameter evaluation. As previously suggested by similar experiences of using volumetric analysis to three-dimensionally characterize pathological regions (typically tumors), a 3D-based approach may provide additional information that cannot be extracted from 2D images. Moreover, volumetric analysis, such as the one we propose in this study, allows for objective evaluation of the morpho-dimensional changes in the treated aorta (e.g., the volume of the whole vessel or portions of it), since these parameters are calculated automatically by the implemented algorithms on the 3D reconstructed vascular model (once this is validated by the radiologist). This guarantees repeatable results, regardless of the operator carrying out the assessment. Volumetric evaluation of the aorta after endovascular aortic repair (EVAR) for abdominal aortic aneurysm has already been reported in the literature, with interesting results [23; 24; 25; 26]. As for TEVAR, some studies have shown promising results in the context of type-B aortic dissection or post-surgery type-A residual dissection [27; 28; 29]. To the best of our knowledge, only [PERSON] et al. compared volumetric and diameter analysis in the settings of TEVAR for DTAA correction [30].