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Comparison of the anisotropy of apparent integrated ultrasonic backscatter from fixed human tendon and fixed human myocardium.

The content and organization of collagen in the cardiac interstitium may represent significant determinants of the ultrasonic scattering properties of myocardium. This study was designed to investigate the anisotropic backscattering properties of a fibrous soft tissue exhibiting an ordered arrangement of fibers similar to myocardium, but possessing a substantially greater content of collagen. Human Achilles tendon was chosen for this study because it possesses a simple unidirectional arrangement of fibers and a high content of collagen compared to normal myocardium. Integrated (frequency-averaged) backscatter was measured from ten formalin fixed samples of tendon as a function of insonifying angle relative to the fiber axis of the tissue. The samples were insonified in a water bath using a 5-MHz center frequency piezoelectric transducer. Maximum backscatter occurred for insonification perpendicular to the fibers, and minimum backscatter occurred for insonification parallel to the fibers. The mean peak to nadir variation, or magnitude of anisotropy, of integrated backscatter for the ten formalin fixed samples of tendon was 36.3 dB. This compares to 14.5 dB for formalin fixed human myocardium measured in an earlier study by our laboratory.