In Vivo Quantification of Ascending Thoracic Aortic Aneurysm Wall Stretch Using MRI: Relationship to Repair Threshold Diameter and Ex Vivo Wall Failure Behavior.

Background Ascending thoracic aortic aneurysms (aTAA) can lead to life-threatening dissection and rupture. Recent studies highlighted aTAA mechanical properties as relevant factors associated with progression. The aim of this study was to quantify in vivo aortic wall stretch in healthy participants and aTAA patients using displacement encoding with stimulated echoes (DENSE) MRI. Moreover, aTAA wall stretch between surgical and non-surgical patients were investigated. Finally, DENSE measurements were compared to reference-standard mechanical testing on aTAA specimens from surgical repairs. Methods In total, 18 subjects were recruited, six healthy participants and 12 aTAA patients, for this prospective study. ECG-gated DENSE imaging was performed to measure systole-diastole wall stretch, as well as the ratio of aTAA stretch to unaffected descending thoracic aorta stretch. Free-breathing and breath-held DENSE protocols were used. Uniaxial tensile testing-measured indices were correlated to DENSE measurements in five specimens. Results In vivo aortic wall stretch was significantly lower in aTAA compared to healthy subjects (P=.0004). There was no correlation between stretch and maximum aTAA diameter. The ratio of aTAA to unaffected thoracic aorta wall stretch was significantly lower in surgical candidates compared to non-surgical candidates (P=.0442). Finally, in vivo aTAA wall stretch correlated to wall failure stress and peak modulus of the intima (P=.017 and P=.034, respectively), while the stretch ratio correlated to whole-wall thickness failure stretch and stress (P=.013 and P=.040, respectively). Conclusion Aortic DENSE has the potential to assess differences in aTAA mechanical properties and progressions.

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