Computer-controlled, MR-compatible foot-pedal device to study dynamics of the muscle tendon complex under isometric,...

To design a computer-controlled, magnetic resonance (MR)-compatible foot pedal device that allows in vivo mapping of changes in morphology and in strain of different musculoskeletal components of the lower leg under passive, isometric, concentric, and eccentric contractions.

A programmable servomotor in the control room pumped hydraulic fluid to rotate a foot-pedal inside the magnet. To validate the performance of the device, six subjects were imaged with gated velocity-encoded phase-contrast (VE-PC) imaging to investigate the dynamics of muscle and aponeurotic structures.

Artifact-free VE-PC imaging clearly delineated different muscle compartments by differences in distribution of mechanical strains. High repeatability of contraction cycles allowed establishing that fascicles lengthened 6.1% more during passive compared with eccentric contractions. Aponeurosis separation during passive (range between three locations: -2.6≈1.3 mm) and active (range: -2.4≈1.6 mm) contractions were similar but significantly different from concentric (range: -0.9≈3.3 mm), with proximal and distal regions showing mostly negative values for the first two modes, but positive for the last.

The device was sufficiently robust and artifact-free to accurately assess, using VE-PC imaging, physiologically important structure and dynamics of the musculotendon complex.