CHARACTERIZATION OF COLLAGEN BY HIGH-FREQUENCY ULTRASOUND - EVIDENCE FOR DIFFERENT ACOUSTIC PROPERTIES BASED ON COLLAGEN FIBER MORPHOLOGIC CHARACTERISTICS

Fibrous tissue on conventional ultrasound images appears as an echo-br ight area. We have observed that on high-frequency ultrasonography ima ges of thin sections of myocardium, fibrous tissue may appear as eithe r a dark or light area. This study was designed to test the hypothesis that echo characteristics of fibrous tissue on high-frequency ultraso nography are determined by collagen fiber morphologic characteristics. We examined 16 tissue specimens from human beings and rats containing different forms of fibrosis. The specimens were sectioned at 5 mu m, placed on a glass slide, and imaged with a 600 MHz transducer. On ultr asound images, collagen appeared either as a dark amorphous area or a light area that had a fibrillar pattern. The same specimens were then stained with picrosirius red and examined with polarized light. When v iewed with polarized light microscopy, thick collagen fibers appear re d or orange and thin fibers appear green or yellow. Polarized light mi croscopy revealed that dark areas on ultrasound images corresponded to thick collagen fibers that were predominantly longitudinally sectione d. In contrast, light areas corresponded to regions of thin, loosely p acked fibers, or to thick collagen fibers that were obliquely sectione d. Collagen has different appearances on high-frequency ultrasound ima ges depending on collagen fiber morphologic characteristics. If such v ariation in echo intensity also occurs with lower frequency transducer s used in clinical echocardiography, the differentiation between norma l myocardium and immature scar may be difficult.