ULTRASONIC PROPERTIES OF TENDON - VELOCITY, ATTENUATION, AND BACKSCATTERING IN EQUINE DIGITAL FLEXOR TENDONS

Ultrasound velocity, attenuation, and backscattering were measured in vitro in samples of equine digital flexor tendon sandwiched between pl ane, parallel rexolite buffer rods. The buffer rods were coupled to tr ansmitting and receiving transducers (nominally 10 MHz) mounted in-lin e and facing one another on the jaws of a digital caliper. Six superfi cial digital flexor (SDF) tendons and six deep digital flexor (DDF) te ndons were measured in three orthogonal directions: along the long axi s of the tendon (D), and across the tendon in the dorsal-volar (C), an d lateral (L) directions. Substantial anisotropy was apparent in all t he measured properties. The velocity data, which in both tendons showe d a higher velocity along the fibers than across (e.g., in the DDF ten don at 0 degrees C: 1713+/-9 m/s in the D direction compared with 1650 +/-5 m/s in the C direction), were consistent with a composite compris ing stiff fibers embedded in a less stiff medium of lower speed. The a pparent backscattering coefficient adjusted for the tissue's frequency -dependent attenuation (e.g., in the C direction of the DDF tendon at 0 degrees C: 7.4X10(-3) cm(-1) sr(-1)), was independent of frequency i n both transverse directions and larger than that measured along the l ong axis of the tendon (e.g., in DDF tendon at 0 degrees C: 1.2X10(-3) cm(-1) sr(-1) at 7 MHz) in which direction the apparent backscatterin g was thought to be increased with frequency as f(4.0+/-1.2). The freq uency-independent backscattering was thought to be due to specular ref lection from the boundaries between the fascicles, i.e., the bundles o f fibers making up the tendon, while backscattering along the axis was due to structures of unknown origin, but of a size much smaller than 45 mu m. Attenuation of ultrasound directed along the fibers was highe r than that across (at 7 MHz in DDF tendon at 0 degrees C: 58 dB/cm in the D direction compared with 11.3 dB/cm in the C direction). Calcula tions indicated that the attenuation was primarily caused by absorptio n rather than scattering. (C) 1996 Acoustical Society of America.