Intravascular ultrasound insights into plaque composition

Previous studies correlating histomorphology with 20-30 MHz-derived intrava scular ultrasound (IVUS) images showed that IVUS provides to some extent qu alitative information on plaque composition. IVUS imaging proved to define calcifications with high sensitivity and specificity but was found to be le ss accurate in the assessment of soft components. Nevertheless previous stu dies on atherosclerotic plaque characterization were limited by use of low- frequency transducers that did not define accurately soft components. Our g oal was to test the effectiveness of high frequency IVUS transducers in the identification of lipid/necrotic pools in atherosclerotic plaques. Methods: Forty MHz transducers were used for in vitro IVUS assessment of 12 arterial segments (10 coronary arteries and 2 carotid arteries dissected f rom 5 different autopsy cases). IVUS acquisition was performed at a 0.5 mm/ s speed after ligature of the branching points to generate a closed system. Lipid necrotic areas were defined by IVUS as large echolucent intraplaque areas surrounded by tissue with higher echodensity. To obtain histopatholog ic sections corresponding to NUS cross sections, vessels were divided into consecutive 3 mm-long segments using the most distal recorded IVUS image as the starting reference. Then, samples were fixed with 10 % buffered formal in, processed for histopathologic study, serially cut, and stained with the Movat penthacrome method. Results: One hundred twenty-two sections were analyzed. Lipid pools were ob served by histology in 30 cross sections (25 %). IVUS revealed the presence of lipid pools in 19 of 122 cross sections with a sensitivity and specific ity of 67 % and 94 %, respectively. Conclusions: High frequency transducers accurately identify lipid/necrotic pools and open new perspectives on future IVUS characterization of atherosc lerotic plaques.