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Objectives: Synchrotron radiation-based X-ray phase-contrast tomography (XPCT) has proven innovative modality for analyzing 3D morphology and is useful for understanding the pathophysiology of various cardiovascular disease. To elucidate mechanisms of aneurysmal wall enlargement after endovascular aortic repair (TEVAR or EVAR), we evaluated aortic wall samples after TEVAR and EVAR with XPCT. Methods: Human aortic samples of the descending aorta or abdominal aorta were obtained during open aortic repair for aortic aneurysm (Group-A; n=5),and for aneurysm expansion after endovascular repairs (Group-E: n=7). Normal aorta (Group-N: n=10), obtained from autopsy, were also investigated. Effective resolution of XPCT in Japan Synchrotron Radiation Research Institute / SPring-8 is 11.7 μm. Pathological analysis was performed, subsequently. Results: Age of patients was 76.8 ± 5.4 years old in Group-A, 83.4 ± 5.2 in Group-E, and 57.5 ± 9.5 in Group-N. In Group-E, time from endovascular repair to open aortic repair was 64.2 ± 7.2 months, and initial endovascular repair included TEVAR (n=2) and EVAR (n=5). Representative findings of three groups were demonstrated in figures, including XPCT findings (Fig.A), changes of wall density (B), and pathological findings (C). In Group-N, density of the tunica media was not different within tunica media and average of medial density was 1.085 ± 0.003g/cm3. In Group-A, thickness of aortic wall was lower than Group-N, but density of the tunica media was unchanged (1.079 ± 0.022g/cm3). On contrast, in Group-E, density of the tunica media was significantly lower than Group-N (1.063 ± 0.008; p < 0.005), and differences in density within tunica media were well correlated with distribution of elastic fibers and existence of medial necrosis in pathological analysis. Conclusions: X-ray phase-contrast tomography was a cutting-edge modality to understand aortic structures and degeneration of tunica media in aneurysm expansion after endovascular repair was clearly demonstrated. [ABSTRACT FROM AUTHOR]