Motor units (MUs) play a fundamental role in muscle physiology and disease. Contraction of muscle fibres belonging to a MU induces signal voids on diffusion weighted (DW) images enabling us to image these MUs (MUMRI). We demonstrated that MUMRI can also extract the twitch profile of single MUs. Computational modelling showed that the attenuation of net magnetisation and the cumulative phase changes increase with twitch magnitude. Therefore, we can measure the MU time profile by altering the timing of electrical nerve stimulation relative to the diffusion-encoding gradients. We applied this experimentally and measured in-vivo contraction times of human MUs.
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