Virtual 3D histology of calcified aortic valves

Details

Supervisors

Kerckhofs, Greet

Faculty

Ecole polytechnique de Louvain

Degree label

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

Abstract

Calcific aortic heart valve stenosis is a valvular disease that consists in the formation of calcifications in the aortic valve leaflets. The progression of the calcifications results from a biological cascade mechanism within the valve that are triggered by biomechanical changes in the micro-environment. As a result, the leaflets gradually get thicker, which hardens the valve and reduces their flexbility and hence their motion. That leads to the progressive narrowing of the aortic valve opening, resulting in the obstruction of the left ventricular outflow of the heart. Aortic stenosis is characterized by a reduction of the aortic valve area and a rise of the transvalvular pressure gradient. However, even though the valve aperture is reduced, it sometimes happens that the pressure gradient stays low and the flow normal. The prognostic significance of normal-flow, low-gradient aortic stenosis (NF-LG AS) is uncertain for cardiologists. Indeed, scientists do not agree on whether patients suffering from this particular case of aortic stenosis require a valve replacement or not. The study had two main objectives. First, we tried to assess more structural and compositional characteristics, such as volume fraction and density, of calcifications than in vivo imaging of aortic valves. Then, we investigated whether these detailed characteristics would bring more insights into NF-LG AS. For this purpose, samples from calcified aortic valves of 28 patients were evaluated using high-resolution microfocus computed tomography (microCT) and compared with clinical data. We found that microCT captures more details about calcifications than in vivo CT, even for short scanning times. First, low-density calcifications generally represent about one third of the total amount of calcifications while the other two thirds are balanced between moderate and high-density calcifications. Then, a low proportion of high-density calcifications reach the core region of the valve while most of the high-density calcifications are located on the edge or intermediate regions of the valve. Finally, there are more and thinner high-density calcification specks on the highly calcified sample compared to the low calcified sample. Moreover, we saw that the relative amount of calcifications is lower for patients diagnosed with NF-LG AS than for those diagnosed with typical severe aortic stenosis. From our data, the density or spatial distribution of the calcifications did not seem specific to patients suffering from NF-LG AS. However, the amount of samples was too limited for the analysis of this particular pathology. Our study showed that microCT is a useful and reliable tool for structural characterization of calcified human heart valves. NF-LG AS should be compared to moderate aortic stenosis to assess whether it is more serious and requires a surgical intervention. We also assessed briefly the potential of contrast-enhanced computed tomography to investigate the soft tissues around the calcifications, and in this way study the impact of the calcification process on the microstructure of the valve.