In vivo 3D imaging of human motor units in upper and lower limb muscles

Linda Heskamp; Alexis R Miller; Matthew G Birkbeck; Julie Hall; Ian S Schofield; Andrew M Blamire; Roger G Whittaker

doi:10.1016/j.clinph.2022.05.018

In vivo 3D imaging of human motor units in upper and lower limb muscles

Clin Neurophysiol. 2022 Sep:141:91-100. doi: 10.1016/j.clinph.2022.05.018. Epub 2022 Jun 20.

Authors

Linda Heskamp¹, Alexis R Miller², Matthew G Birkbeck³, Julie Hall⁴, Ian S Schofield⁵, Andrew M Blamire⁶, Roger G Whittaker⁷

Affiliations

¹ Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK. Electronic address: Linda.heskamp@newcastle.ac.uk.
² Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK.
³ Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK; Newcastle Biomedical Research Centre (BRC), Newcastle University, Newcastle Upon Tyne, UK; Northern Medical Physics and Clinical Engineering, Freeman Hospital, Newcastle upon Tyne NHS Foundation Trust, Newcastle upon Tyne, UK. Electronic address: Matt.Birkbeck@newcastle.ac.uk.
⁴ Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK; Department of Neuroradiology, Royal Victoria Infirmary, Newcastle upon Tyne, UK. Electronic address: julie.hall6@nhs.net.
⁵ Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK. Electronic address: ian.schofield@newcastle.ac.uk.
⁶ Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK. Electronic address: andrew.blamire@newcastle.ac.uk.
⁷ Newcastle University Translational and Clinical Research Institute (NUTCRI), Newcastle University, Newcastle upon Tyne, UK. Electronic address: Roger.Whittaker@newcastle.ac.uk.

PMID: 35853787
DOI: 10.1016/j.clinph.2022.05.018

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 (FD_max) did not differ between the lower leg (CSA: 22.4 ± 8.4 mm²; FD_max: 8.7 ± 2.4 mm), forearm (CSA: 23.6 ± 14.1 mm²; FD_max: 9.0 ± 3.3 mm) and hand (CSA: 26.8 ± 12.8 mm² and FD_max: 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.

Keywords: Diffusion weighted imaging; Electromyography; Motor unit; Motor unit MRI; Skeletal muscle.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Electromyography / methods
Humans
Imaging, Three-Dimensional*
Leg / physiology
Lower Extremity
Motor Cortex* / physiology
Muscle, Skeletal / diagnostic imaging

Abstract

Publication types

MeSH terms

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