Image processing and advanced analysis of contrast-enhanced microCT data to investigate microstructural changes in arteries

Details

Supervisors

Kerckhofs, Greet

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil biomédical, à finalité spécialisée

Abstract

The Ross procedure is performed on patients that have heart diseases like aortic valve stenosis, aortic valve regurgitation or a bicuspid aortic valve. It consists of removing the defective aortic valve. The aortic valve is replaced by the pulmonary valve of the same patient. The pulmonary valve is replaced by a healthy valve of another patient or a synthetic valve. Concretely, a segment of the aorta containing the defective valve is removed and replaced by a new segment coming from the pulmonary artery which contains a healthy valve. This healthy pulmonary segment is called the pulmonary autograft. The pulmonary autograft, when placed in the systemic circulation, is subjected to different hemodynamic conditions than in the pulmonary loop due to differences in pressure, velocity and acceleration rate of the blood. Therefore, mechanotransduction applies to the cells of the arterial wall and leaflet of the new aorta segment leading to the synthesis of collagen. As a result, the arterial wall stiffens. There is also an increase of the amount of elastic fibers, but in much less proportion than the collagen fibers [1]. In some cases, the Ross procedure leads to good remodeling of the pulmonary artery into an aorta. Unfortunately, it is not the case for all pulmonary autografts which fail in some cases. More specifically, a failed pulmonary autograft stays mechanically similar to a native pulmonary artery. Therefore, it will dilate due to the higher pressure and could lead to an aortic aneurysm which has a high risk of rupture. To better understand the Ross procedure, it is crucial to gain more knowledge on the 3D microstructure of the cardiovascular tissues involved. The aim of this Master thesis was to use Cryogenic Contrast-Enhanced MicroCT (cryo-CECT) imaging to characterize the 3D microstructure of cardiovascular tissues with a focus on the aorta. More specifically, this thesis is a first step to understand the behaviour of the elastin fibers of the sheep arterial walls by providing the tools to analyse them, and then to be able to analyse how elastin fibers evolve in sheep that underwent the Ross procedure. This Master thesis contains three parts. First, a denoising and sharpening protocol has been developed in other to distinguish the elastin fibers of the microstructure of the arterial wall of a sheep ascending aorta in datasets imaged with cryo-CECT. The aim of this protocol was to denoise and improve the contrast of elastin fibers in native sheep ascending aorta datasets. Second, a segmentation protocol was developed to extract the elastin fibers from the arterial wall of datasets of a sheep ascending aorta imaged with cryo-CECT. Third, a quantitative structural analysis of the elastin fibers was done on this 3D dataset.