The dependence of ultrasonic attenuation and backscatter on collagen content in dog and rabbit hearts.

To determine whether collagen content may be a determinant of the ultrasonic attenuation and backscatter in myocardium and to identify factors in the measurement of the backscatter coefficient needed for ultrasonic characterization of myocardium in vivo, two series of experiments were conducted. In the first series, the ultrasonic attenuation was measured from 110 regions in 18 dogs studied 2, 4, and 6 weeks after coronary occlusion. The increased slope of the attenuation of regions within zones of infarction correlated closely with regional content of collagen as determined from concentration of hydroxyproline in canine hearts (0.90 in hearts studied at 6 weeks and 0.77 and 0.73 in those studied 4 and 2 weeks after occlusion). In a second series of experiments in which hearts from 21 rabbits were studied from 5 to 7 weeks after coronary occlusion, ultrasonic attenuation, ultrasonic backscatter, and content of collagen within zones of regions of infarction were increased significantly compared to nonischemic regions from the same rabbits (P < 0.001 in each case). To determine whether the increased ultrasonic backscatter depended on the content of intact collagen in regions of infarction, isolated rabbit hearts were perfused with modified Krebs-Henseleit solution and collagenase resulting in a significant reduction of the backscatter coefficient (P < 0.05). Since regional ultrasonic backscatter in the heart appears to be influenced markedly by the regional content of intact collagen, characterization of tissue with reflected ultrasound may permit noninvasive estimation of replacement of myocardium by collagen in vivo facilitating diagnosis and evaluation of the evolution of conditions such as ischemic heart disease and cardiomyopathy. Circ Res 47: 49-58, 1980