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Imaging soft biological tissues, such as blood vessels, with X-ray microfocus computed tomography (microCT) is challenging. However, staining tissues with X-ray contrast-enhancing staining agents (CESAs) allows to enhance the X-ray attenuation of the tissue constituents (such as collagen, elastin, etc.) and to distinguish different constituents within the soft tissue. We refer to this as contrast-enhanced microCT (CECT). When CECT is combined with in-situ mechanical testing, i.e. 4D-CECT, microstructural changes of the tissue constituents can be assessed during mechanical loading, allowing to link microstructure with functional behavior. However, for this purpose, a CESA is needed that gives the best contrast properties for the tissue constituents, while preserving the tissue integrity and mechanical properties. Therefore, we investigated the effect of six different CESAs on the mechanical properties of porcine aorta tissue.

Diseases such as hypertension, atherosclerosis, aneurysms, or aortic dissection directly influence the tissue microstructure of the vascular wall and hence its biomechanical response to physiological loading [1]. The relationship between the microstructure and mechanical behavior is key for understanding disease development. The final goal of our study is to understand this relationship by developing an imaging tool that allows to visualize the change in the tissue microstructure during mechanical loading. For this purpose, we combine contrast-enhanced X-ray microfocus computed tomography (CECT) with in-situ mechanical testing, i.e. 4D-CECT. CECT allows the visualization of unmineralized biological tissue through the use of contrast-enhancing staining agents (CESAs). Here, we present the results on optimizing the CESAs for 4D-CECT of vascular tissues; these CESAs should allow accurate visualization of the tissue microstructure, while preserving the mechanical properties of the tissue.

Atherosclerosis is a leading cause of death. To better understand and treat this disease, it is important to evaluate the changes in blood vessel wall microstructure during disease development and to link these structural changes to changes in mechanical properties. Microfocus X-ray computed tomography (microCT) is a powerful technique for assessing, in a non-invasive way, the 3D microstructure of complex materials. To achieve sufficient X-ray attenuation in soft tissues, contrast-enhancing staining agents (CESAs) containing high atomic number molecules are combined with microCT. This technique is referred to as contrast-enhanced microCT (CE-CT). Monolacunary and Hafnium-substituted Wells-Dawson polyoxometalate(Mono-WD and Hf-WD POM respectively) have shown their potential for non-destructive staining of kidney and soft skeletal tissues [1]. Additionally, we have shown with planar biaxial testing that these POMs have a negligible effect on the mechanical properties of the tissue. In this study, both CESAs were evaluated and compared for their staining potential of the porcine aorta. Other types of blood vessels were imaged to show the ability of CE-CT to highlight the vessel wall microstructure, including the different wall layers and their content in elastin and collagen. The novelty of this study lies in the high-detailed comparison of the microstructure of different types of blood vessels(healthy and diseased) in a non-invasive way.