Determinants of echodensity at the intima-media interface with intracoronary ultrasound imaging

A thin, echodense layer (EL) is sometimes observed at the intima-media interface on intravascular ultrasonographic images. We reviewed a series of 119 histologically matched, 30 MHz, in vitro ultrasound cross sections of human coronary arteries for factors determining the occurrence of an EL. ELs were observed in 19 (27%) of 71 images with optimal gain settings, in two (17%) of 12 with high gain settings, and in none of 26 with low gain settings. In 17 (94%) of 18 cross sections with eccentric catheter positions, an EL was visible only in parts of the vessel wall that were perpendicular to the ultrasound beam. ELs were seen behind fibrous, lipid-rich, and mixed lesions but not behind calcified lesions because of acoustic shadowing. The presence or morphologic elements of the internal elastic lamina did not influence the occurrence of an EL. We conclude that the occurrence of an EL at the intima-media interface depends on acoustic factors and gain settings, and it provides no anatomic information per se.