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Measuring motor unit morphology in upper extremities using motor unit magnetic resonance imaging (MUMRI)

Matthew Birkbeck^1,2,3, Linda Heskamp¹, Ian Schofield¹, Roger Whittaker¹, and Andrew Blamire¹
¹Translational and Clinical Research Unit, Newcastle University, Newcastle upon Tyne, United Kingdom, ²Newcastle Biomedical Research Centre, Newcastle Biomedical Research Centre, Newcastle upon Tyne, United Kingdom, ³Northern Medical Physics and Clinical Engineering, Newcastle upon Tyne NHS Foundation Trust, Newcastle upon Tyne, United Kingdom

MUMRI has been applied for the first time to study in-vivo single human MUs in the forearm and hand muscles and to determine the size and shapes of these MUs. This increases the clinical translatability of the MUMRI technique.

Figure 4: A) MU difference maps overlaid onto the MUMRI images for each of the extracted MUs. Two from the forearm in the flexor carpi ulnaris muscle and one from the hand in the abductor pollicis muscle. B) Bar charts showing MU metrics: cross sectional area (CSA) shown in green, maximum Feret diameter shown in red and minimum Feret diameter shown in blue.

Figure 2: Data processing steps to extract the single MUs. A) MUMRI image B) Images grouped into two data sets: where motor unit is inactive and active (indicated by red arrow). Graph shows single voxel time-series from the MU territory, example alternations where MU inactive (red circle), MU active (green circles). C) MU difference map with no threshold applied. D) MU difference map with 0.5 threshold, showing good agreement with initial size of MU territory in (B).