Heskamp L, Miller AR, Birkbeck MG, Hall J, Schofield I, Blamire AM, Whittaker RG. In vivo 3D imaging of human motor units in upper and lower limb muscles.
Clin Neurophysiol 2022;
141:91-100. [PMID:
35853787 DOI:
10.1016/j.clinph.2022.05.018]
[Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 05/17/2022] [Accepted: 05/30/2022] [Indexed: 11/24/2022]
Abstract
OBJECTIVE
To assess in-vivo cross-sectional and 3D morphology of human motor units in hand, forearm and lower leg muscles using magnetic resonance imaging (MRI).
METHODS
Diffusion weighted MRI was used with in-scanner electrical stimulation in healthy controls to image motor units at a single slice in lower leg, forearm and hand muscles (n = 6) and multiple slices in the lower leg for 3D assessment (n = 7).
RESULTS
Motor unit cross-sectional area (CSA) and maximum Feret diameter (FDmax) did not differ between the lower leg (CSA: 22.4 ± 8.4 mm2; FDmax: 8.7 ± 2.4 mm), forearm (CSA: 23.6 ± 14.1 mm2; FDmax: 9.0 ± 3.3 mm) and hand (CSA: 26.8 ± 12.8 mm2 and FDmax: 9.6 ± 2.7 mm) (ANOVA; p = 0.487 and p = 0.587, respectively). Lower leg motor units were 8.0 ± 3.8 cm long with largest CSA in the motor unit's middle section. 3D motor unit imaging revealed a complex structure with several units splitting and re-forming along their length.
CONCLUSIONS
Motor unit MRI (MUMRI) can be applied to upper limb muscles, and can reveal the 3D structure of human motor units in-vivo.
SIGNIFICANCE
MUMRI provides the first in-vivo 2D images of upper limb motor units and 3D images of lower leg motor units. 3D imaging suggest a more complex human motor unit structure than previously thought.
Collapse