Ultrasound study of acoustic properties of the normal canine heart: Comparison of backscatter from all chambers

Much effort has recently been directed toward ultrasound characterization of normal and abnormal left ventricular myocardium. The purpose of this study was to evaluate the normal acoustic properties of all four cardiac chambers as a first step toward tissue characterization of the atria and ventricles. The hypothesis was that integrated ultrasound backscatter would follow the pattern of collagen concentration in the cardiac chambers, being higher in the right side of the heart than in the left and in the atria compared with the ventricles. Seven normal canine hearts, perfusion-fixed in 10% formalin, were examined. Sections of the free walls of right and left ventricles and atria were studied in vitro with a 5 MHz transducer positioned at the focal distance from the epicardium. The radio frequency ultrasound signal energy from each specimen was derived, corrected for sample thickness and expressed as integrated backseatter, in decibel units less than the reflected energy from a stainless steel block. The backscatter was higher from the right ventricle than from the left ventricle (−64.5 ± 1.25 [mean ± SEM] [n = 7] versus −73.6 ± 1.32; p < 0.05), higher from the right atrium than from the right ventricle (−58.5 ± 0.83 versus −64.5 ± 1.25; p < 0.05) and higher from the left atrium than from the left ventricle (−62.8 ± 1.14 versus −73.6 ± 1.32; p < 0.05). These data show that backscatter is higher in the right ventricle than in the left ventricle and in the atria compared with the ventricles. This pattern corresponds to known regional collagen concentration, and provides initial data of importance in the acoustic characterization of structural abnormalities of all four cardiac chambers.