Relationship between collagen and ultrasonic backscatter in myocardial tissue

The relationship between ultrasonic backscatter and collagen concentration estimated on the basis of hydroxyproline concentration was examined in hearts from normal dogs and in hearts from dogs subjected to ischemic injury by coronary occlusion as an approach toward elucidating the physical mechanisms underlying the scattering of ultrasound by soft tissue. Ultrasonic backscatter was found to increase significantly in regions of ischemic injury studied 5--17 weeks following occlusion. The average backscatter coefficient was six time larger in regions of infarct studied 8--10 weeks after occlusion than that in regions of infarct studied 5--6 weeks after occlusion. In contrast, the average hydroxyproline concentration, a quantitative index of molecular collagen content, for regions of infarct was only about 25% larger at 8--10 weeks compared with that at 5--6 weeks after occlusion. These results may suggest that the magnitude of ultrasonic scattering in regions of remote myocardial infarct is sensitive not only to the concentration of molecular collagen but also to the organizational state of this structural protein. In addition, the results of this study may indicate that scattering represents a small fraction of the total attenuation coefficient in a biological system exhibiting either low collagen concentration (normal myocardium) or significant collagen concentration (scarred myocardium).