Background The relationship between blood flow characteristics and ascending aortic (AA) dilatation has not been studied in patients with a tricuspid aortic valve (TAV) without aortic stenosis. Purpose To evaluate whether 4D flow characteristics determined in MRI are related to AA dilatation by comparing dilated AA and nondilated AA subjects with TAV. Study Type Prospective. Population Twenty patients with dilated AA and 20 age‐matched patients with nondilated AA. Field Strength/Sequence 1.5T/4D flow, 2D flow, and anatomic images. Assessment Altogether, 16 different 4D flow parameters were assessed in 10 planes in the thoracic aorta. Intra‐ and interobserver reproducibility were analyzed. Statistical Tests Independent t‐test for normally distributed and the Mann–Whitney test for skewed distributed parameters were used. A paired‐samples t‐test was used to compare 2D and 4D flow parameters. Intraclass correlation coefficient (ICC) was used in intra‐ and interobserver reproducibility analysis. Results Aortic flow was displaced from the centerline of the aorta in the proximal and tubular planes. Flow displacement (FD) was greatest in the proximal plane of AA and was higher in dilated AA (4.5%, range 3.0–5.8%) than in nondilated AA (2.0%, 1.0–3.0%, P < 0.001). Total wall shear stress (WSS) values were 1.3 ± 0.4 times higher on the displaced side than on the opposite side of the aorta (P < 0.01). The circumferential WSS (WSSC) ratio to total WSS was greater in dilated AA, being 0.48 ± 0.11 vs. 0.32 ± 0.09 in the inner curvature of the proximal AA (P < 0.001) and 0.37 ± 0.11 vs. 0.26 ± 0.07 in the whole aortic ring in the distal AA (P < 0.001). Depending on 4D flow parameters, reproducibility varied from excellent (ICC = 0.923) to very low (ICC = 0.204). Data Conclusion The present study demonstrates that 4D flow measurements help to visualize the pathological flow patterns related to aortic dilatation. Flow displacement and an increased WSSc/WSS ratio are significantly associated with AA dilatation. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:136–145.

Objectives To clarify the prevalence and risk factors of ascending aortic (AA) dilatation according to ESC 2014 guidelines. Methods This study included 1000 consecutive patients scheduled for diagnostic coronary artery computed tomographic angiography. AA diameter was retrospectively measured in 3 planes: sinus valsalva, sinotubular junction, and tubular part. The threshold for AA dilatation was set to > 40 mm which has been suggested as an upper normal limit for AA diameter in ESC 2014 guidelines on aortic diseases. Aortic size index (ASI) using the ratio between aortic diameter and body surface area (BSA) was applied as a comparative measurement. The threshold for AA dilatation was set to the upper limit of normal distribution exceeding two standard deviations (95%). Risk factors for AA dilatation were collected from medical records. Results The patients' mean age was 52.9 ± 9.8 years (66.5% women). The prevalence of AA dilatation was 23.0% in the overall study population (52.5% males) and 15.1% in the subgroup of patients with no coronary artery disease or bicuspid (BAV)/ mechanical aortic valve (n = 365). According to the normal-distributed ASI values, the threshold for sinus valsalva was defined as 23.2 mm/m 2 and for tubular part 22.2 mm/m 2 in the subgroup. Higher BSA was associated with larger AA dimensions (r = 0.407, p < 0.001). Male gender (p < 0.001), BAV (p < 0.001), hypertension (p = 0.009) in males, and smoking (p < 0.001) appeared as risk factors for AA dilatation. Conclusions The prevalence of AA dilatation is high with current ESC guidelines for normal AA dimension, especially in males. Body size is strongly associated with AA dimensions; it would be more reliable to use BSA-adjusted AA diameters for the definition of AA dilatation. Key Points • The prevalence of AA dilatation is high in patients who are candidates for coronary CT angiography. • Body size is strongly associated with AA dimensions.

BackgroundThe relationship between blood flow characteristics and ascending aortic (AA) dilatation has not been studied in patients with a tricuspid aortic valve (TAV) without aortic stenosis. PurposeTo evaluate whether four-dimensional (4D) flow characteristics determined in MRI are related to AA dilatation by comparing dilated AA and non-dilated AA subjects with TAV. Study type Prospective.Population 20 patients with dilated AA, 20 age-matched patients with non-dilated AA. Field Strength/Sequence1.5T/4D flow, 2D flow and anatomic images. AssessmentAltogether 16 different 4D flow parameters were assessed in 10 planes in the thoracic aorta. Intra-and inter-observer reproducibility were analyzed. Statistical testIndependent T-test for normal-distributed and Mann-Whitney-test for skewed distributed parameters were used. Paired-samples T-test was used to compare 2D and 4D flow parameters. Intraclass correlation coefficient (ICC) was used in intra-and inter-observer reproducibility analysis. ResultsAortic flow was displaced from the center line of the aorta in the proximal and tubular planes. Flow displacement (FD) was greatest in the proximal plane of AA and was higher in dilated AA (4.5%, range 3.0-5.8%) than in non-dilated AA (2.0%, 1.0-3.0%, p<0.001). Total wall shear stress (WSS) values were 1.3±0.4 times higher on the displaced side than on the opposite side of the aorta (p<0.01). The circumferential WSS (WSSC) ratio to total WSS was greater in dilated AA, being 0.48±0.11 vs. 0.32±0.09 in the inner curvature of the proximal AA (p<0.001) and 0.37±0.11 vs. 0.26±0.07 in whole aortic ring in the distal AA (p<0.001). Depending on 4D flow parameter, reproducibility varied from excellent (ICC=0.923) to very low (ICC=0.204). Data conclusionThe present study demonstrates that 4D flow measurements help to visualize the pathological flow patterns related to aortic dilatation. Flow displacement and an increased WSSc/WSS ratio are significantly associated with AA dilatation.