Fig. 4.

Representative velocity-encoded, phase-contrast (VE-PC) images that are used for calculation of velocity distribution and displacement of tissue points within the medial gastrocnemius muscle. A: VE-PC MRI provide both magnitude (leftmost) and three velocity images. Anatomical location of the rectangle region of interest can be chosen from the magnitude image. Three sagittal velocity images with velocities encoded in the anterior-posterior (A-P), right-left (R-L), and superior-inferior (S-I) axes, acquired during passive contraction at an angle corresponding to a dorsiflexed position (phase 6 in a time phase of B), are shown on the three images on the right-hand side, respectively. In the velocity images, the gray-scale values represent velocities, with white indicating maximum inferior to superior, and dark indicating maximum velocity in the opposite direction. B: velocity vs. time phase curves during passive (top) and active eccentric (bottom) ankle dorsiflexion-plantar flexion cycle. The positive velocities represent movement toward the posterior side for A-P axis, left side for R-L axis, and inferior side for S-I axis, respectively. Each graph is represented as a mean of 11 subjects. The images, as well as the curves, indicate substantially higher S-I and, to a lesser degree, A-P velocities than through-plane R-L velocities.