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 IF9. A New Method to Quantify Aortic Biomechanics in Vivo Using Four-Dimensional Magnetic Resonance Imaging (4D MRI): Implications for Ascending Aortic Endografts

Rachel Clough, Christian Buerger, Christoph Kolbitsch, Peter Taylor, Claudia Prieto, Tobias Schaeffter
NIHR Comprehensive Biomedical Research Centre of Guy's and St Thomas' NHS Foundation Trust and King's College London, London, United Kingdom.

OBJECTIVES: The thoracic aorta is subject to physiological forces from cardiac and respiratory motion, which have an important effect on endograft failure such as fracture, migration and endoleak. This study's aim was to develop new methodology to accurately measure aortic biomechanics in vivo using 4D MRI and image registration techniques.
METHODS: These consisted of: 1) Development of 4D MRI acquisition schemes; 2) Optimization of non-rigid image registration algorithm and assessment of accuracy (TRE); and 3) Quantification of aortic biomechanics in vivo.
RESULTS: High spatial resolution 4-D dynamic imaging sequences were developed to separately determine the displacement of the aorta caused by cardiac and respiratory motion. The registration algorithm was accurate (TRE-cardiac: 2.05±1.27mm; TRE-respiratory: 1.60±0.88mm) and robust to changes in registration parameters. The biomechanical displacement of the ascending aorta (6.41±1.87mm) was significantly greater than the arch (3.75±0.79mm) (p<0.0001(95%CI 1.7 to 3.6)) and descending aorta (3.64±0.87mm) (p<0.0001(95%CI 1.8 to 3.7)). The motion of the arch was not significantly different to the descending aorta (p=0.68(95%CI -0.4 to 0.6)). The maximum displacement caused by cardiac and respiratory motion was 16.9mm and 7.7mm, respectively. Significant interindividual differences in aortic deformation and dynamic curvature were seen. Maximal displacements occurred at peak systole in the ascending aorta and arch whereas in the descending thoracic aorta there was minimal change with time. In the ascending aorta, there was a large rotational component, demonstrated by large RL (4.71±0.52mm) and AP displacements (2.65±0.76mm).
CONCLUSIONS: We have successfully developed, validated and applied a new method to quantify aortic biomechanics in vivo. The motion of the ascending aorta is complex, multidirectional and significantly greater than the arch and descending aorta. These data will inform ascending aortic endograft design and advance durability and deployment accuracy.
AUTHOR DISCLOSURES: C. Buerger: Nothing to disclose; R. Clough: Nothing to disclose; C. Kolbitsch: Nothing to disclose; C. Prieto: Nothing to disclose; T. Schaeffter: Nothing to disclose; P. Taylor: Nothing to disclose.
Posted April 2013

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