Estimating Activation of Denervated, Degenerated Muscle after Functional Electrical Stimulation with Magnetic Resonance Imaging

摘要

FES of long-term denervated, degenerated human skeletal muscle has been shown to be a suitable method for improving a number of physiological parameters. The underlying mechanisms of activation of a denervated muscle fiber can be described with suitably modified and extended Hodgin-Huxley type models, coupled with 3D finite element models of the surrounding electrical field. Regions of activation within a muscle can be determined using a 3D computer model. However, simulation results have not yet been validated experimentally. During and immediately after exercise, muscle shows increased T2-relaxation times. It is thus possible to estimate muscle activation non-invasively and spatially resolved with the MRI method of T2-mapping, which was, therefore, chosen as a suitable validation approach. Six patients were scanned prior to FES training with a MSME-sequence at 3 Tesla and then asked to perform one of their regular daily training-sessions (leg extensions). Subjects were then repositioned in the MR-scanner and two to five post-exercise scans were recorded. Pre- and post exercise scans were co-registered and T2-parameter maps were calculated. ROIs were drawn manually around quadriceps femoris and its antagonists. In well trained patients, activation in the quadriceps was found to be considerably higher than in its antagonists. These experimental results will help further improve existing models of FES of denervated degenerated human skeletal muscle.