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Atrophy of calf muscles by unloading results in an increase of tissue sodium concentration and fat fraction decrease: a 23Na MRI physiology study

Abstract

Purpose

23Na MRI demonstrated increased tissue sodium concentrations in a number of pathologies. Acute atrophy results in muscle fibre volume shrinking that may result in a relative increase of extracellular volume and might affect sodium concentration. Thus, we hypothesized that local unloading of the calf muscles would lead to a decrease in muscle volume and an increase in muscle tissue sodium concentration.

Method

One lower leg of 12 healthy male subjects was submitted to a 60 day long period of unloading using the Hephaistos orthosis, while the other leg served as control. 23Na MRI and 2D PD-weighted Dixon turbo spin echo were obtained from the control and orthosis leg using a 3T scanner. For quantification, a sodium reference phantom was used with 10, 20, 30, and 40 mmol/L NaCl solution.

Result

Tissue sodium concentration (TSC) increased as an effect of unloading in the orthosis leg. Relative increases were 17.4 ± 16.8% (P = 0.005) in gastrocnemius medialis muscle, 11.1 ± 12.5 (P = 0.037) in gastrocnemius lateralis muscle, 16.2 ± 4.7% (P < 0.001) in soleus muscle, 10.0 ± 10.5% (P = 0.009) in the ventral muscle group, and 10.7 ± 10.0% (P = 0.003) in the central muscle group, respectively. TSC in the control leg did not significantly change. In the orthosis leg, muscle volume decreased as follows: medial gastrocnemius muscle: −5.4 ± 8.3% (P = 0.043) and soleus muscle: −7.8 ± 15.0% (P = 0.043).

Conclusion

Unloading atrophy is associated with an increase in muscle sodium concentration. 23Na MRI is capable of detecting these rather small changes.

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Abbreviations

FoV:

Field of view (FoV)

LME:

Linear mixed effects

PD:

Proton density

ROI:

Regions of interest

SNR:

Signal-to-noise ratio

TSC:

Tissue sodium concentration

TSE:

Turbo spin echo

TA:

Acquisition time

TE:

Echo time

TR:

Repetition time

T2 :

Transversal relaxation time

References

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Acknowledgements

K. Schopen received a Helmholtz Space Life Sciences Research School (SpaceLife) Ph.D. scholarship. SpaceLife was funded in equal parts by the Helmholtz Association (Grant No.: VH-KO-300) and the German Aerospace Center (DLR). The NutriHEP study was funded by the DLR internal cost object 2475 101.

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Authors

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Correspondence to D. A. Gerlach.

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Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Conflict of interest

The authors declare that they have no conflict of interest.

Additional information

Communicated by Guido Ferretti.

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Gerlach, D.A., Schopen, K., Linz, P. et al. Atrophy of calf muscles by unloading results in an increase of tissue sodium concentration and fat fraction decrease: a 23Na MRI physiology study. Eur J Appl Physiol 117, 1585–1595 (2017). https://doi.org/10.1007/s00421-017-3647-4

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  • DOI: https://doi.org/10.1007/s00421-017-3647-4

Keywords

  • Sodium
  • MRI
  • 23Na MRI
  • Tissue sodium concentration (TSC)
  • Quantification
  • Muscle unloading