The relationship between quantitative magnetic resonance imaging of the ankle plantar flexors, muscle function during walking and maximal strength in people with neuromuscular diseases.

BACKGROUND: Progression of plantar flexor weakness in neuromuscular diseases is usually monitored by muscle strength measurements, although they poorly relate to muscle function during walking. Pathophysiological changes such as intramuscular adipose tissue affect dynamic muscle function independent from isometric strength. Diffusion tensor imaging and T2 imaging are quantitative MRI measures reflecting muscular pathophysiological changes, and are therefore potential biomarkers to monitor plantar flexor functioning during walking in people with neuromuscular diseases. METHODS: In fourteen individuals with plantar flexor weakness diffusion tensor imaging and T2 scans of the plantar flexors were obtained, and the diffusion indices fractional anisotropy and mean diffusivity calculated. With a dynamometer, maximal isometric plantar flexor strength was measured. 3D gait analysis was used to assess maximal ankle moment and power during walking. FINDINGS: Fractional anisotropy, mean diffusivity and T2 relaxation time all moderately correlated with maximal plantar flexor strength (r > 0.512). Fractional anisotropy and mean diffusivity were not related with ankle moment or power (r < 0.288). T2 relaxation time was strongly related to ankle moment (r = -0.789) and ankle power (r = -0.798), and moderately related to maximal plantar flexor strength (r < 0.600). INTERPRETATION: In conclusion, T2 relaxation time, indicative of multiple pathophysiological changes, was strongly related to plantar flexor function during walking, while fractional anisotropy and mean diffusivity, indicative of fiber size, only related to maximal plantar flexor strength. This indicates that these measures may be suitable to monitor muscle function and gain insights into the pathophysiological changes underlying a poor plantar flexor functioning during gait in people with neuromuscular diseases.

Reliability of in vivo determination of forearm muscle volume using 3.0 T magnetic resonance imaging.

PURPOSE: To apply magnetic resonance imaging (MRI) as a tool for quantifying muscle volume of forearm muscles feasibility and reliability of volume estimation of the flexor carpi ulnaris (FCU) and the extensor carpi ulnaris (ECU). MATERIALS AND METHODS: Forearms of 10 subjects were scanned twice. Muscle volumes were calculated from manual outlines on axial slices, slice thickness, and the number of slices. Observer agreement and repeatability were estimated using intraclass correlation, coefficient of variation, and the smallest detectable difference. RESULTS: The average volume of the FCU and ECU was 31.0 mL (SD 11.5 mL) and 16.4 mL (SD 7.7 mL), respectively. Intraclass correlation coefficients of the volumes were all above 0.99 and the coefficient of variation varied between 5.7% and 0.8%. The smallest detectable difference corresponded to approximately 7% of muscle volume. CONCLUSION: MRI muscle volume measurement of forearm muscles is feasible, reproducible, and allows for longitudinal studies where expected responsiveness exceeds 7%.