PMC4899351_01
1H-MR imaging [T1-weighted fast-low-angle-shot (FLASH)-sequence, left] and 23Na-MR imaging (right) of both lower legs immediately after injury. The left leg shows a half-moon shaped, hyperintense Na+ rich area on the medial side (arrow). Highest muscle Na+ signal could be found in the region of the left medial gastrocnemius muscle (there was a 2.4-fold increase in Na+ concentration compared to the corresponding soft tissue of the contralateral non-affected leg, 43.5 vs. 18.0 mmol/l). The calibration tubes below the lower legs contain 10, 20, 30 and 40 mmol/l NaCl. Gray-scale measurements of the tubes served as calibration standards for 23Na-MRI by relating intensity to a concentration in a linear trend analysis
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Fig1
T1 weighted 1H image (Fig. 1, left), all anatomic compartments can be seen in detail, while all Na+ calibration tubes appear at a similar intensity. The affected left lower leg presented a discrete swelling of the subcutaneous region in comparison to the contralateral leg. The concomitant 23Na-MRI showed a strong hyperintense signal in the affected leg region (Fig. 1, right), indicating increased local Na+ concentration.
1H-MR imaging [T1-weighted fast-low-angle-shot (FLASH)-sequence, left] and 23Na-MR imaging (right) of both lower legs 2 weeks after injury. The area of hyperintense Na+ rich tissue was reduced, but could still be clearly visualized at the level of the left medial gastrocnemius muscle (arrow, Na+ concentration compared to the corresponding soft tissue of the contralateral non-affected leg: 37.5 vs. 18.5 mmol/l). Muscle function of the leg was completely restored by this point
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Fig2
We performed follow-up imaging (Fig. 2). The Na+ concentration of the medial gastrocnemius decreased but was still elevated (Na+ 37.5 vs. 18.5 mmol/l, Fig. 2, right).
1H-MR imaging [T1-weighted fast-low-angle-shot (FLASH)-sequence, left] and 23Na-MR imaging (right) of both lower legs 2 month after injury showed only a marginal Na+ rich region in the medial aspect of the left gastrocnemius muscle (arrow, Na+ concentration compared to the corresponding soft tissue of the contralateral non-affected leg: 21.5 vs. 18.5 mmol/l)
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Fig3
Two months after injury, 23Na-MR imaging showed a barely detectable Na+ rich region in the medial gastrocnemius (Na+ 21.5 vs. 18.5 mmol/l, Fig. 3, right).