Quantification of the anisotropy of ultrasonic quasi-longitudinal velocity in normal human and canine myocardium with comparison to anisotropy of integrated backscatter

Measurements of ultrasonic quasi-longitudinal velocity were made in the muscle fiber plane of excised human and canine cardiac tissue. The measurements were carried out in 2° increments through the full 360° relative to the myofibers. In addition, for each tissue specimen, measurements were made at a number of adjacent planes across the left ventricular wall in order to assess the transmural dependence of velocity. The data indicate a 1.0% to 1.5% anisotropy of velocity, with maximum velocity when insonifying along the myofibers and minimum velocity when insonifying perpendicular to the myofibers. The anisotropy of velocity is 90° out of phase with the anisotropy of integrated backscatter, which was also measured. Both velocity and integrated backscatter were found to depend on transmural position. Each exhibited a progressive angular shift of maximal value from the epicardium to the endocardium. This shift in the position of peak in the backscatter and velocity graphs reflects the underlying shift in myofiber orientation