Integrated ultrasonic backscatter has been related to collagen deposition in fibrotic myocardium. The purpose of our study was to measure the integrated ultrasonic backscatter in the right and left ventricles of 10 normal freshly excised canine hearts and five normal formalin-fixed human hearts. A 2.25 MHz, 50% fractional bandwidth transducer was positioned at the transducer focal distance from the epicardium. The radio frequency backscatter signal, excluding specular reflections, was digitized, squared, and integrated to yield the integrated ultrasonic backscatter (in decibels down from a 100% reflector). The segment of myocardium corresponding to the integrated ultrasonic backscatter sample volume was excised and assayed for hydroxyproline, a marker for collagen. A second purpose of our study was to evaluate the influence of fixation with formalin on the backscatter. Regional integrated ultrasonic backscatter was therefore measured in 10 freshly excised canine left ventricles, which were fixed in 10% formalin for 2 weeks. Integrated ultrasonic backscatter measurements were then repeated. In freshly excised canine hearts, the integrated ultrasonic backscatter from right ventricle was higher than that from left ventricle (-60.4 ± 1.6 [SEMI vs -66.9 + 1.0 dB; p < .001). The collagen content of right ventricle was also higher than that of left ventricle (4.40 ± 0.26 [SEMI vs 3.58 ± 0.13 ,g/mg dry weight; p < .005). Similar results were obtained in human hearts. There were no correlations between integrated ultrasonic backscatter and collagen content (r = .28 and .32 for dogs and humans, respectively). The integrated ultrasonic backscatter in freshly excised canine left ventricles was -64.8 ± 0.7 dB, which was not significantly different than the value of -65.6 + 0.7 dB measured after fixation with formalin. We conclude that both integrated ultrasonic backscatter levels and collagen content are higher in the right ventricle than in the left ventricle of normal hearts. Formalin is a suitable fixative for ultrasound studies of the myocardium in vitro. Circulation 69, No. 4, 775-782, 1984. BOTH the importance and limitations of M mode and two-dimensional echocardiography are well known to clinicians.' Current clinical applications of echocardiography depend on specular reflection occurring at tissue interfaces to depict such structures as the epicardium, endocardium, and valve leaflets; standard echocardiographic examinations are not designed to evaluate the myocardium itself. This limitation has prompted interest in other acoustic variables of potential clinical relevance for characterization of structural changes in the myocardium. These HOYT et al. ed that collagen may be an important determinant of backscatter. These investigators found significantly increased backscatter in the hearts of rabbits and dogs 5 to 16 weeks after infarction and in the hearts of rabbit after cardiotoxic doses of doxorubicin.5 9 In both lesions these changes were associated with an increase in the collagen content based...

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