3D and 4D characterization of vascular tissue : opportunities and challenges

Cardiovascular diseases (CVDs) are the leading cause of death globally. In order to design better treatments, it is necessary to fully characterize the mechanical behavior of arteries and its relationship with their microstructure. This could be achieved by a novel imaging method, where in situ mechanical testing is combined with contrast-enhanced 3D microfocus X-ray computed tomography (CE-CT); further referred to as 4D CE-CT. The challenge of 4D CE-CT is the need of a constrast enhancing staining agent (CESA) to visualize arteries with good contrast. Indeed, the CESA used should not affect the mechanical properties of arteries. The aim of this master thesis was two-fold. First, an image analysis protocol has been defined in order to fully characterize the microstructure of arteries using CE-CT, such as the inner and outer diameter, the luminal surface and the wall thickness. Moreover, with an appropriate threshold, the elastin lamellae in the media layer have been segmented from the rest of the aorta, and the number of lamellae, their thickness and structure separation have been computed. All results have been compared with values found in the literature. Second, the effect of the CESA staining, of the staining time and of a preservation solution on the mechanical properties of arteries have been characterized. Different samples have been tested under planar biaxial mode. One concluded that sample aging had no effect on the mechanical properties of arteries. However, the staining by the CESA led to a stiffening effect of 20 to 30 kPa for a 15% strain. The staining time had no influences, and no clear conclusion on the effect of the preservation solution could be made. As a conclusion, this study emphasized the challenges of obtaining sufficient contrast for CE-CT imaging and image analysis of the samples without influencing the mechanical properties of arteries. Further perspectives would be to test fresh samples (i.e. non-frozen samples) and to have more samples per condition to confirm and strengthen our findings.