Identification of atherosclerotic plaque components with intravascular ultrasound elastography in vivo: A Yucatan pig study

Background - Intravascular ultrasound elastography assesses the local strain of the atherosclerotic vessel wall. In the present study, the potential to identify different plaque components in vivo was investigated. Methods and Results - Atherosclerotic external iliac and femoral arteries (n=24) of 6 Yucatan pigs were investigated. Before termination, elastographic data were acquired with a 20-MHz Visions catheter. Two frames acquired at end-diastole with a pressure differential of ≈4 mm Hg were acquired to obtain the elastograms. Before dissection, x-ray was used to identify the arterial segments that had been investigated by ultrasound. Specimens were stained for collagen, fat, and macrophages. Plaques were classified as absent, early fibrous lesion, early fatty lesion, or advanced fibrous plaque. The average strains in the plaque-free arterial wall (0.21%) and the early (0.24%) and advanced fibrous plaques (0.22%) were similar. Higher average strain values were observed in fatty lesions (0.46%) compared with fibrous plaques (P=0.007). After correction for confounding by lipid content, no additional differences in average strain were found between plaques with and without macrophages (P=0.966). Receiver operating characteristic analysis revealed a sensitivity and a specificity of 100% and 80%, respectively, to identify fatty plaques. The presence of a high-strain spot (strain >1%) has 92% sensitivity and 92% specificity to identify macrophages. Conclusions - To the best of our knowledge, this is the first time that intravascular ultrasound elastography has been validated in vivo. Fatty plaques have an increased mean strain value. High-strain spots are associated with the presence of macrophages.