In Vivo Strain Analysis of Dilated Ascending Thoracic Aorta by ECG-Gated CT Angiographic Imaging

Abstract

Accurate assessment of aortic extensibility is a requisite first step for elucidating the pathophysiology of an ascending thoracic aortic aneurysm (ATAA). This study aimed to develop a framework for the in vivo evaluation of the full-field distribution of the aortic wall strain by imaging analysis of electrocardiographic- (ECG) gated thoracic data of 34 patients with ATAA. Seven healthy controls (i.e., non-aneurysmal aorta) from patients who underwent ECG-gated CT angiography for coronary artery diseases were included for comparison. To evaluate the systolic function, ECG-gated computed tomography (CT) angiography was used to generate patient-specific geometric meshes of the ascending aorta, and then to estimate both the displacement and strain fields using a mathematical algorithm. Results evidenced stiff behavior for the aneurysmal aorta compared with that of the healthy ascending aorta of the controls, with patients over 55 years of age displaying significantly lower extensibility. Moreover, the patient risk as quantified by the ratio of in vivo strain to the ruptured one increased significantly with increased systolic blood pressure, older age, and higher pressure-strain modulus. Statistical analysis also indicated that an increased pressure-strain modulus is a risk factor for ATAAs with bicuspid aortic valve, suggesting a different mechanism of failure in these patients. The approach here proposed for the in vivo evaluation of the aortic wall strain is simple and fast, with promising applicability in routine clinical imaging, and could be used to develop a rupture potential criterion on the basis of the aortic aneurysm extensibility.

Statistical Shape Analysis of Ascending Thoracic Aortic Aneurysm: Correlation between Shape and Biomechanical Descriptors

“…CTA images at both end-diastole and peak systole were segmented using semi-automatic thresholding and region growing techniques, combined with manual editing of masks in commercial software (Mimics v20, Materialize NV, Leuven, Belgium) as described previously [19][20][21][22]. The 3D ATAA models were cut near the brachiocephalic artery, to reduce irrelevant shape variability related to the aortic arch and descending aorta.…”

“…Strain analysis of ATAA wall mechanics at peak systole was done using an algorithm previously developed by our group [20,24,25]. For each ATAA, the aortic surface mesh segmented at diastole was projected normally onto the aortic surface mesh at systole, and then the displacement field was achieved as the Euclidean distance between closest points.…”

Three-dimensional thoracic aorta principal strain analysis from routine ECG-gated computerized tomography: feasibility in patients undergoing transcatheter aortic valve replacement

“…A methodology exists to perform in-vivo 3D aortic strain analysis requiring a single segmentation at end-diastole, optically and automatically tracked in 3 dimensions throughout the cardiac cycle relying on a velocity-field reconstructed for the whole dataset by means image-based feature tracking, described by Satriano et al [ 13 ]. Another approach exists leveraging on segmentations performed throughout the cardiac cycle, described by Pasta et al [ 14 ]. In this approach, the point cloud obtained for the end-diastolic aortic luminal surface is projected normally onto the surfaces reconstructed for other cardiac phases [ 14 ].…”

“…Another approach exists leveraging on segmentations performed throughout the cardiac cycle, described by Pasta et al [ 14 ]. In this approach, the point cloud obtained for the end-diastolic aortic luminal surface is projected normally onto the surfaces reconstructed for other cardiac phases [ 14 ]. However, the application of the single-segmentation approach [ 13 ] specifically to multi-phase CTA is previously undescribed.…”

Pre-Operative Modeling of Transcatheter Mitral Valve Replacement in a Surgical Heart Valve Bioprosthesis

“…Volumetric CT images in standard DICOM format were imported in Mimics to reconstruct the left ventricle, left atrium, and aortic root anatomy in terms of the spatial position and dimension by applying different gray values and multiple masks based on different Hounsfield unit thresholds. Segmentation was performed by semi-automatic thresholding operation followed by manual mask editing and morphological operation including cropping, erosion, and smoothing, as done previously by our group [14][15][16][17][18]. The bioprosthetic heart valve was distinctly reconstructed using a different mask.…”