Assessment of the relationship between deformation characteristics and the presence of calcification in human atheromatous plaques using uniaxial stretching evaluations with digital image correlation, CT scanning and histological examination

Atherosclerosis is a major cause of mortality and morbidity worldwide. In advanced atheromatous plaques, stiffening is often accompanied by calcification. Although the fibrous cap is more deformable than calcified regions, it is unknown to which extent it deforms with a presence of calcified region. In the present study, we excised human aortas with calcified/noncalcified plaques at autopsy and investigated the correlation between the presence of calcification and the deformation of the luminal surface. Rectangular specimens were stretched uniaxially in the circumferential direction. A digital image correlation (DIC) technique was applied to scattered spots on the specimen surface with an applied strain of 0.04 - 0.05 to obtain the distributions of normal strain in the stretching direction. The distance between the calcified region and the lumen was measured at the location of minimum strain on the luminal surface from cross-sections of computed tomography (CT) images of specimens and photographic images of formalin-fixed specimens. The calcified region was also identified upon histological examination. Our results showed that two calcified plaques had a minimum strain of zero on the luminal surface with calcified regions 10 - 20 μm off the lumen in the fibrous cap and one had a minimum strain of 0.006 with calcified regions 496 μm off the lumen in the lipid core, while two noncalcified plaques had minimum strains of 0.004 and 0.008. These results indicate that the local deformation of the fibrous cap is restricted completely in cases where it is calcified. The average deformation is about one tenth of that observed on the surrounding vascular tissue surface in the cases where calcification is not present, or is present in a deep layer of the fibrous cap or in the lipid core. These findings may facilitate better understanding of calcified plaques, aiding image-based diagnosis.