This study aims to validate ultrasonic anisotropy in 2-dimensional echocardiograms by one-toone histological correlation. Thirteen echograms were obtained in vitro from 9 specimens of 2 left ventricles of healthy adult beagle dogs and were correlated with corresponding histology in regard to ultrasound orientation relative to the local fiber direction. Median value of pixel echogenicity (255- rank) was lower in areas with parallel (n = 9, 18 ± 13) than in those with oblique (n = 7, 41 ± 14, P < 0.05) and perpendicular (n = 13, 57 ± 21, P < 0.01) ultrasound orientations. Echogenicity in the proximal part within 0.5 cm from an edge was relatively high (n = 9, 33 ± 15; n = 5, 66 ± 27; n = 8, 65 ± 32, respectively) and was different between parallel and perpendicular orientations (P < 0.05). The ratio of the distal adjacent 0.5-cm part to the proximal part echogenicity was lower for either parallel or oblique orientation (0.35 ± 0.25, 0.51 ± 0.16) than for perpendicular orientation (0.95 ± 0.16, P < 0.01, respectively). Acoustic dropouts appeared beyond myocardial areas with parallel or oblique ultrasound orientation. These results disclosed precise acoustic anisotropy in the 2-dimensional echocardiograms.

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