  $\textbf{Object}$ Neuromuscular electrical stimulation (NMES)-induced
isometric contraction is feasible during MRI and can be combined with
acquisition of volumetric dynamic MR data, in a synchronous and controlled way.
Since NMES is a potent resource for rehabilitation, MRI synchronized with NMES
presents a valuable validation tool. Our aim was to show how minimal
NMES-induced muscle contraction characterization, as evaluated through phase
contrast MRI, differs between senior and young volunteers. $\textbf{Materials
and Methods}$ Simultaneous NMES of the quadriceps muscle and phase contrast
imaging were applied at 3T to 11 senior (75 $\pm$ 3 years) and 6 young
volunteers (29 $\pm$ 7 years). A current sufficient to induce muscle twitch
without knee extension was applied to both groups. $\textbf{Results}$ Strain
vectors were extracted from the velocity fields and strain datasets were
compared with non-parametric tests and descriptive statistics. Strain values
were noticeably different between both groups at both current intensities and
significant differences were observed in the regions of interest between the
two electrodes. $\textbf{Discussion}$ In conclusion, NMES-synchronized MRI
could be successfully applied in senior volunteers with strain results clearly
different from the younger volunteers. Also, differences within the senior
group were detected both in the magnitude of strain and in the position of
maximum strain pixels.
