Anisotropy of ultrasonic backscatter from human tendon compared to that from normal human myocardium

Anisotropy is a characteristic of ultrasonic backscatter observed in a number of materials containing directionally oriented fibers. It has been hypothesized that in heart the fibrous tissue collagen is a major determinant of backscatter. To investigate the effects of the orientation of collagenous fibers on ultrasonic backscatter, the authors studied excised human Achilles tendon, a tissue rich in collagen and exhibiting highly aligned fibers. The magnitude of anisotropy was quantified by measuring the integrated (frequency-averaged) backscatter in the fiber plane of cylindrical biopsy specimens taken from tendons. Tissue samples were insonified in a water bath around their entire circumference in 2° steps with a 5-MHz center frequency piezoelectric transducer. Integrated backscatter was a maximum for insonification perpendicular to the fibers, and a minimum for insonification parallel to the fibers. Measurements of three formalin-fixed specimens revealed an average magnitude of anisotropy of 39±4 dB for tendon compared to 14.5±1.6 dB for normal regions of three fixed autopsied human hearts previously measured by the authors´ laboratory