Supersonic Shear Imaging Elastography in Skeletal Muscles: Relationship Between In Vivo and Synthetic Fiber Angles and Shear Modulus

Objectives To verify a relationship between the pennation angle of synthetic fibers and muscle fibers with the shear modulus (mu) generated by Supersonic shear imaging (SSI) elastography and to compare the anisotropy of synthetic and in vivo pennate muscle fibers in the x(2)-x(3) plane (probe perpendicular to water surface or skin). Methods First, the probe of Aixplorer ultrasound scanner (v.9, Supersonic Imagine, Aix-en-Provence, France) was placed in 2 positions (parallel [aligned] and transverse to the fibers) to test the anisotropy in the x(2)-x(3) plane. Subsequently, it was inclined (x(1)-x(3) plane) in relation to the fibers, forming 3 angles (18.25 degrees, 21.55 degrees, 36.86 degrees) for synthetic fibers and one (approximately 0 degrees) for muscle fibers. Results On the x(2)-x(3) plane, mu values of the synthetic and vastus lateralis fibers were significantly lower (P < .0001) at the transverse probe position than the longitudinal one. In the x(1)-x(3) plane, the mu values were significantly reduced (P < .0001) with the probe angle increasing, only for the synthetic fibers (approximately 0.90 kPa for each degree of pennation angle). Conclusions The pennation angle was not related to the mu values generated by SSI elastography for the in vivo lateral head of the gastrocnemius and vastus lateralis muscles. However, a mu reduction with an angle increase in the synthetic fibers was observed. These findings contribute to increasing the applicability of SSI in distinct muscle architecture at normal or pathologic conditions.