Continuous measurement of aortic dimensions in Turner syndrome: a cardiovascular magnetic resonance study

Background: Severity of thoracic aortic disease in Turner syndrome (TS) patients is currently described through measures of aorta size and geometry at discrete locations. The objective of this study is to develop an improved measurement tool that quantifies changes in size and geometry over time, continuously along the length of the thoracic aorta. Methods: Cardiovascular magnetic resonance (CMR) scans for 15 TS patients [41 +/- 9 years (mean age +/- standard deviation (SD))] were acquired over a 10-year period and compared with ten healthy gender and age-matched controls. Three-dimensional aortic geometries were reconstructed, smoothed and clipped, which was followed by identification of centerlines and planes normal to the centerlines. Geometric variables, including maximum diameter and cross-sectional area, were evaluated continuously along the thoracic aorta. Distance maps were computed for TS and compared to the corresponding maps for controls, to highlight any asymmetry and dimensional differences between diseased and normal aortae. Furthermore, a registration scheme was proposed to estimate localized changes in aorta geometry between visits. The estimated maximum diameter from the continuous method was then compared with corresponding manual measurements at 7 discrete locations for each visit and for changes between visits. Results: Manual measures at the seven positions and the corresponding continuous measurements of maximum diameter for all visits considered, correlated highly (R-value = 0.77, P < 0.01). There was good agreement between manual and continuous measurement methods for visit-to-visit changes in maximum diameter. The continuous method was less sensitive to inter-user variability [0.2 +/- 2.3 mm (mean difference in diameters +/- SD)] and choice of smoothing software [0.3 +/- 1.3 mm]. Aortic diameters were larger in TS than controls in the ascending [TS: 13.4 +/- 2. 1 mm (mean distance +/- SD), Controls: 12.6 +/- 1 mm] and descending [TS: 10.2 +/- 1.3 mm (mean distance +/- SD), Controls: 9.5 +/- 0.9 mm] thoracic aorta as observed from the distance maps. Conclusions: An automated methodology is presented that enables rapid and precise three-dimensional measurement of thoracic aortic geometry, which can serve as an improved tool to define disease severity and monitor disease progression.