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Does the Aorta Expand Elliptically? Shape Changes Analyzed and Visualized with Dynamic MRI

Joffrey van Prehn¹, Joost A. van Herwaarden¹, Koen L. Vincken², Bart E. Muhs³, Hence J. M. Verhagen^1,4, Frans L. Moll¹, Lambertus W. Bartels.^2
1University Medical Center, Utrecht, The Netherlands;²Image Sciences Institute, University Medical Center, Utrecht, The Netherlands;³Yale University School of Medicine, New Haven, Conn.;⁴Erasmus University Medical Center, Rotterdam, The Netherlands.

OBJECTIVES: ECG-triggered dynamic imaging offers insight in changes of the aortic shape throughout the cardiac cycle. Knowledge of aortic morphologic changes may have consequences for endograft design and may offer insight in aneurysm pathophysiology. We utilized dynamic MRI scans to evaluate the changes in aortic shape at different levels in the aneurysm neck in patients with AAA’s.

METHODS: Eleven EVAR-patients (11 men, median age 74, range 63 to 78) were scanned pre-operatively using a retrospectively ECG-triggered balanced gradient echo MRI scan, with 16 reconstructed phases over the cardiac cycle. Transverse scan planes were planned perpendicular to the aorta, both in the coronal and in the sagittal plane. Changes in aortic circumference throughout the cardiac cycle were studied at three levels: (A) 3 cm above the renal arteries, (B) between the renal arteries, and (C) 1 cm below the renal arteries. After segmentation of the aortic lumen in the images, aortic radial changes during the cardiac cycle were determined over 360 degrees and plotted. Radiuses were measured from the center of mass of the aortic lumen. A standard Anterior-Posterior (AP) line with the spinal foramen as anatomic orientation was used as reference for the baseline AP-direction (0°).

RESULTS: Most patients showed an asymmetric expansion with an elliptical shape (Figure 1, typical example of asymmetric elliptical shape change). At level A 7 patients showed elliptical plots, at Level B 6 patients and at level C 8 patients. Above the renal arteries the direction of elliptical expansion showed a tendency to right-anterior (6/7). Asymmetric shape changes were more pronounced when the radial changes over the cardiac cycle were high.

CONCLUSIONS: We were able to visualize shape changes of the aorta throughout the cardiac cycle, in relation to the anatomy. In the majority of the AAA patients we studied, the shape change of the aneurysm neck is elliptical. This observation may have consequences for endograft design as it may affect endograft sealing. Asymmetric shape changes may depend on a combination of blood flow dynamics and aortic wall properties and may be correlated to atherosclerosis and aneurysm development.

AUTHOR DISCLOSURES: J. van Prehn, None; J.A. van Herwaarden, None; K.L. Vincken, None; B.E. Muhs, None; H.J.M. Verhagen, None; F.L. Moll, None; L.W. Bartels, None.