Ultrasonic assessment of tissue anisotropy

Two completely separate experiments using the Scanning Laser Acoustic Microscope, operating at an ultrasonic frequency of 100 MHz, assessed the attenuation coefficient and propagation speed of two anisotropic biological materials, viz., human Achilles tendon samples and bovine longissimus striated muscle samples. For the tendon samples, three separate locations were also evaluated (superior, medial and inferior). Anisotropy was evaluated by measuring the samples with the ultrasonic beam propagating either parallel or perpendicular to the tendon muscle fibers. Achilles tendons generally exhibited a greater anisotropy than did skeletal muscle, and for both materials, the parallel orientation of both attenuation coefficient and propagation speed were consistently greater that those of the perpendicular orientation.