Fig. 4

a In muscular sodium channel diseases, a defective sodium channel within the muscular cell membrane leads to a pathological influx of Na⁺ after provocation with typical triggers, e.g. exposition to cold. Results are muscular weakness or muscular stiffness. b STIR weighted ¹H imaging shows elevated signal in the lower leg muscles of this patient suffering from hypokalaemic periodic paralysis type 1. The intracellular Na⁺ accumulation can be visualised nicely with ²³Na (arrows). Observe the reference tubes: 0.3% NaCl solution in the middle, 0.3% NaCl bound with agarose gel on the left-hand side, 0.6% NaCl solution on the right-hand side