Anisotropy of the transverse mode ultrasonic properties of fixed tendon and fixed myocardium

This study investigates the influence of the fiber-reinforced nature of myocardium and tendon on the propagation of transverse mode ultrasonic waves. Formalin fixed specimens of normal human left ventricular cardiac muscle and bovine Achilles tendon were prepared for this study in such a way that transverse mode ultrasonic waves could be propagated perpendicular to the fiber axis of the tissue with the polarization oriented either parallel or perpendicular to the fiber axis. Measurements of velocity and attenuation were made at 3 MHz to assess the degree of anisotropy in these parameters for both tissues. Formalin fixed tendon exhibited a significant anisotropy whereas formalin fixed myocardium displayed a similar trend of more modest magnitude. Results of these measurements were used to compute two elastic stiffness coefficients for each tissue, yielding c44 = 37.2 MPa and c66 = 18.0 MPa for formalin fixed tendon, and c44 = 8.97 MPa and c66 = 8.45 MPa for formalin fixed myocardium. To validate this approach, additional studies were conducted to measure the transverse mode ultrasonic properties of silicone rubber and motor oil.