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Orientation-dependent anisotropy of acoustic properties of tendons at micrometer scale

Tendons are bands of fibrous connective tissue connecting muscles to bones. They are composed of parallel arrays of collagen fibers closely packed together which makes them highly anisotropic. The anisotropy of the acoustic properties of tendons was investigated at an ultra-fine resolution (< 7 μm) using quantitative acoustic microscopy (QAM). Chicken tendons were fixed (formalin) while loaded longitudinally, then cryosectioned (16-µm) at several orientations (every 15 deg) from parallel (i.e., 0 deg) to perpendicular to the fibers (i.e., 90 deg). Two regions of two sections per angle were scanned using a QAM system operating at a center frequency of 250 MHz yielding a total of 28 QAM datasets which were processed to yield two-dimensional (2D) maps of the bulk modulus, mass density, acoustic impedance, and speed of sound for each scanned region. Acoustic parameters were averaged within each 2D map and mean and standard deviations computed at each angle. Results demonstrated a strong acoustical anisotropy. For instance acoustic impedance increased from 1.68 ± 0.08 to 1.87 ± 0.19 MRayl between 0 and 75 deg. Similarly, the speed of sound increased from 1686 ± 90 to 1958 ± 186 m/s between 0 and 75 deg. These results demonstrate the value of QAM to investigate the anisotropy of tissue microstructure and pave the way for using it to characterize other soft tissues with complex three-dimensional fiber orientations. [Work supported in part by NIH Grants EY023966 and EY028662.]Tendons are bands of fibrous connective tissue connecting muscles to bones. They are composed of parallel arrays of collagen fibers closely packed together which makes them highly anisotropic. The anisotropy of the acoustic properties of tendons was investigated at an ultra-fine resolution (< 7 μm) using quantitative acoustic microscopy (QAM). Chicken tendons were fixed (formalin) while loaded longitudinally, then cryosectioned (16-µm) at several orientations (every 15 deg) from parallel (i.e., 0 deg) to perpendicular to the fibers (i.e., 90 deg). Two regions of two sections per angle were scanned using a QAM system operating at a center frequency of 250 MHz yielding a total of 28 QAM datasets which were processed to yield two-dimensional (2D) maps of the bulk modulus, mass density, acoustic impedance, and speed of sound for each scanned region. Acoustic parameters were averaged within each 2D map and mean and standard deviations computed at each angle. Results demonstrated a strong acoustical anisotropy....