Background:Ascending thoracic aortic aneurysm (ATAA) is a potentially life-threatening dilation of the ascending aorta (AscAo) that often develops without symptoms. The current clinical practice relies on measuring the maximal diameter of the aorta to manage ATAA patients and plan surgeries. However, this approach has limitations as it may not adequately predict the risk of dissection in many patients. Therefore, there is a need for more comprehensive quantitative assessments of aortic morphology and pressure-flow-wall associations in both healthy individuals and patients with ATAA.Methods:We conducted a study involving 17 ATAA patients (average age 64.7±14.3 years, 5 females), along with 17 age- and sex-matched healthy controls (average age 59.7±13.3 years, 5 females), and 13 younger healthy subjects (average age 33.5±11.1 years, 4 females). All participants underwent magnetic resonance imaging (MRI) scans, including 4D flow and 3D anatomical images of the aorta. The 3D anatomical images were used to measure the maximal diameter (iDMAX) and volume of the AscAo, indexed to body surface area. The 4D flow MRI data were analyzed to estimate: 1) local spatial (∆PS) and temporal (∆PT) pressure changes within the AscAo, as well as the distance (∆DPS) and time duration (∆TPT) between local pressure peaks, 2) maximal wall shear stress (WSSMAX) at peak systole, 3) flow vorticity amplitude (VMAX), duration (VFWHM), and eccentricity (VECC) within the AscAo.Results:We found significant associations between various flow and pressure indices and AscAo iDMAX (WSSMAX: r=-0.49, p<0.001; VECC: r=-0.29, p=0.045; VFWHM: r=0.48, p<0.001; ∆DPS: r=0.37, p=0.010; ∆TPT: r=-0.52, p<0.001) as well as indexed volume (WSSMAX: r=-0.63, VECC: r=-0.51, VFWHM: r=0.53, ∆DPS: r=0.54, ∆TPT: r=-0.63, p<0.001 for all). Additionally, intra-AscAo cross-sectional pressure in the 30 healthy subjects (average age 48.3±18.0 years), the difference in local spatial pressure (∆PS) was significantly and positively correlated with both flow vorticity amplitude (VMAX) (r=0.55, p=0.002) and maximal wall shear stress (WSSMAX) (r=0.59, p<0.001). These associations remained significant even after adjusting for maximal diameter (iDMAX), age, and systolic blood pressure. By comparing the ATAA patients to the normal aging trends observed in the healthy subjects, we were able to identify patients exhibiting notably high pressure differences concurrent with AscAo dilation, which may indicate increased risk.