Shear wave vibrometry evaluation in transverse isotropic tissue mimicking phantoms and skeletal muscle.

Ultrasound radiation force-based methods can quantitatively evaluate tissue viscoelastic material properties. One of the limitations of the current methods is neglecting the inherent anisotropy nature of certain tissues. To explore the phenomenon of anisotropy in a laboratory setting, we created two phantom designs incorporating fibrous and fishing line material with preferential orientations. Four phantoms were made in a cube-shaped mold; both designs were arranged in multiple layers and embedded in porcine gelatin using two different concentrations (8%, 14%). An excised sample of pork tenderloin was also studied. Measurements were made in the phantoms and the pork muscle at different angles by rotating the phantom with respect to the transducer, where 0° and 180° were defined along the fibers, and 90° and 270° across the fibers. Shear waves were generated and measured by a Verasonics ultrasound system equipped with a linear array transducer. For the fibrous phantom, the mean and standard deviations of the shear wave speeds along (0°) and across the fibers (90°) with 8% gelatin were 3.60  ±  0.03 and 3.18  ±  0.12 m s(-1) and with 14% gelatin were 4.10  ±  0.11 and 3.90  ±  0.02 m s(-1). For the fishing line material phantom, the mean and standard deviations of the shear wave speeds along (0°) and across the fibers (90°) with 8% gelatin were 2.86  ±  0.20 and 2.44  ±  0.24 m s(-1) and with 14% gelatin were 3.40  ±  0.09 and 2.84  ±  0.14 m s(-1). For the pork muscle, the mean and standard deviations of the shear wave speeds along the fibers (0°) at two different locations were 3.83  ±  0.16 and 3.86  ±  0.12 m s(-1) and across the fibers (90°) were 2.73  ±  0.18 and 2.70  ±  0.16 m s(-1), respectively. The fibrous and fishing line gelatin-based phantoms exhibited anisotropy that resembles that observed in the pork muscle.