Fig. 1

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