Human skeletal muscle: sodium MR imaging and quantification-potential applications in exercise and disease.
OBJECTIVE
To use sodium 23 magnetic resonance (MR) imaging to quantify noninvasively total sodium in human muscle and to apply the technique in exercise and musculoskeletal disease.


METHODS
Total [Na] sodium was determined from the ratio of the relaxation-corrected (23)Na signal intensities measured from short echo-time (0.4 msec) (23)Na images to those from an external saline solution reference. The method was validated with the blinded use of saline solutions of varying sodium concentrations. [Na] was measured in the calf muscles in 10 healthy volunteers. (23)Na MR imaging also was performed in two healthy subjects after exercise, two patients with myotonic dystrophy, and two patients with osteoarthritis.


RESULTS
(23)Na MR imaging yielded a total [Na] value of 28.4 mmol/kg of wet weight +/- 3.6 (SD) in normal muscle, consistent with prior biopsy data. Spatial resolution was 0.22 mL, with signal-to-noise ratio of 10-15. Mean signal intensity elevations were 16% and 22% after exercise and 47% and 70% in dystrophic muscles compared with those at normal resting levels. In osteoarthritis, mean signal intensity reductions were 36% and 15% compared with those in unaffected knee joints.


CONCLUSIONS
(23)Na MR imaging can be used to quantify total [Na] in human muscle. The technique may facilitate understanding of the role of the sodium-potassium pump and perfusion in normal and diseased muscle.
Departments of Biomedical Engineering, Johns Hopkins University School of Medicine, 720 Rutland Ave, Traylor Bldg, 6th Floor, Rm 606, Baltimore, MD 21205, USA. constant@bme.jhu.edu
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Constantinides
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Gillen
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Boada
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Pomper
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Bottomley
D000328:Adult; D000465:Algorithms; D000704:Analysis of Variance; D001706:Biopsy; D001847:Bone Diseases / Q000175:diagnosis / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005583:Fourier Analysis; D006801:Humans; D016018:Least-Squares Analysis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism*; D009135:Muscular Diseases / Q000175:diagnosis* / Q000378:metabolism; D009223:Myotonic Dystrophy / Q000175:diagnosis / Q000378:metabolism; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000378:metabolism; D019047:Phantoms, Imaging; D005082:Physical Exertion / Q000502:physiology*; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D016037:Single-Blind Method; D012964:Sodium / Q000032:analysis*; D012965:Sodium Chloride
D012965:Sodium Chloride; D012964:Sodium