EFFECT OF COLLAGEN ON THE ANISOTROPY OF QUASI-LONGITUDINAL MODE ULTRASONIC VELOCITY IN FIBROUS SOFT-TISSUES - A COMPARISON OF FIXED TENDON AND FIXED MYOCARDIUM

The widespread use of echocardiography has generated considerable inte rest in the ultrasonic properties of myocardial collagen. This study w as designed to investigate the effect of collagen on the propagation o f ultrasound by measuring the anisotropy of ultrasonic velocity throug h formalin fixed specimens of bovine Achilles tendon. Tendon was chose n for this study because it possesses a high content of collagen and a well-defined unidirectional arrangement of fibers. Ultrasonic velocit y data were acquired from nine samples of fixed tendon that were each insonified at multiple angles relative to the fibers in 2 degrees incr ements for a full 360 degrees. Analysis of the data revealed a substan tial angular dependence of velocity qualitatively similar to that repo rted for formalin fixed specimens of normal human myocardium, but appr oximately 17 times larger in magnitude. Together with measured values of density, these results were used to compute the elastic stiffness c oefficients C-11 (corresponding to propagation perpendicular to the fi bers) and C-33 (corresponding to propagation parallel to the fibers) o f fixed tendon, yielding 3.08 and 4.51 GPa, respectively.