The muscle twitch profile assessed with motor unit magnetic resonance imaging
| Autor: | Andrew M. Blamire, Ian S. Schofield, Roger G. Whittaker, Linda Heskamp, MG Birkbeck |
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| Rok vydání: | 2020 |
| Předmět: |
Muscle tissue
Adult Male Materials science Contraction (grammar) Time Factors Signal Models Biological 030218 nuclear medicine & medical imaging 03 medical and health sciences Young Adult 0302 clinical medicine medicine contraction time diffusion weighted imaging Humans Radiology Nuclear Medicine and imaging Computer Simulation Muscle Skeletal Spectroscopy Research Articles medicine.diagnostic_test Motor unit Motor unit MRI Relaxation (NMR) Skeletal muscle Magnetic resonance imaging Middle Aged Magnetic Resonance Imaging muscle twitch medicine.anatomical_structure Diffusion Magnetic Resonance Imaging Molecular Medicine Female 030217 neurology & neurosurgery Biomedical engineering Diffusion MRI Muscle Contraction Research Article phase contrast imaging |
| Zdroj: | Nmr in Biomedicine |
| ISSN: | 1099-1492 |
| Popis: | Localised signal voids in diffusion‐weighted (DW) images of skeletal muscle have been postulated to occur as a result of muscle fibre contraction and relaxation. We investigated the contrast mechanism of these signal voids using a combination of modelling and experimental measurements by employing DW and phase contrast (PC) imaging sequences. The DW signal and PC signal were simulated for each time point of a theoretical muscle twitch. The model incorporated compaction (simulating actively contracting muscle fibres) and translation (simulating passively moving surrounding fibres). The model suggested that the DW signal depended on contraction time and compaction whereas the PC signal depended on contraction time, compaction and translation. In a retrospective study, we tested this model with subgroup analyses on 10 healthy participants. Electrical nerve stimulation was used to generate muscle twitches in lower leg muscles; the resulting force was measured using an MR‐compatible force transducer. At current levels causing a visible muscle twitch (~13 mA), the width of the first signal drop in the DW signal (mean ± SD: 103 ± 20 ms) was comparable with the force contraction time (93 ± 34 ms; intraclass correlation coefficient [ICC] = 0.717, P = .010). At current levels activating single motor units (~9 mA), the contraction time determined from the DW signal was 75 ± 13 ms and comparable with the PC contraction time (81 ± 15 ms; ICC = 0.925, P = .001). The maximum positive velocity was 0.55 ± 0.26 cm/s and the displacement was 0.20 ± 0.10 mm. Voxel‐wise analysis revealed localised DW changes occurring together with more widespread phase changes. In conclusion, local signal attenuations in DW images following muscle fibre activation are primarily caused by compaction. The PC sequence also detects translating muscle tissue being passively pulled. The magnitude of the changes in DW and PC images depends on the twitch's contractile properties and percentage contraction. DW imaging and PC imaging can therefore measure twitch profiles of skeletal muscle fibres. Muscle fibre contraction induces signal changes in diffusion weighted and phase contrast images, which we used to extract the twitch time profile of individual motor units with a technique called motor unit MRI (MUMRI). Using modelling and experimental data, we showed that these signal changes depend on the contractile characteristics of the muscle twitch. Furthermore, we found that the diffusion weighted signal represents the active contraction, and the phase contrast measured velocity also detects passively moving muscle fibres. |
| Databáze: | OpenAIRE |
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