Fig. 10. Tagged magnetization depicting 3-D strain associated with anterior protrusion of the human tongue. (A) A grid of supersaturated MRI tags was applied to the resting tongue in the mid-sagittal imaging plane, and principal strain depicted for the x, y and z components of the strain tensor in terms of a color-coded pseudosurface smoothed by bicubic splines. A bidirectional contraction in the y- and z-directions resulted in tissue protrusion in the x-direction. (B) Model of bidrectional contraction leading to hydrostatic elongation. Contraction of muscle fibers orthogonally aligned to each other results in hydrostatic elongation in the remaining direction (dashed lines), without a change in tissue volume. (Reproduced with permission from Napadow et al., 1999a.)