3 Tesla ²³Na Magnetic Resonance Imaging During Acute Kidney Injury

Sodium and proton magnetic resonance imaging (²³Na/¹H-MRI) have shown that muscle and skin can store Na⁺ without water. In chronic renal failure and in heart failure, Na⁺ mobilization occurs, but is variable depending on age, dialysis vintage, and other features. Na⁺ storage depots have not been studied in patients with acute kidney injury (AKI).

We studied 7 patients with AKI (mean age: 51.7 years; range: 25-84) and 14 age-matched and gender-matched healthy controls. All underwent ²³Na/¹H-MRI at the calf. Patients were studied before and after acute hemodialysis therapy within 5-6 days. The ²³Na-MRI produced grayscale images containing Na⁺ phantoms, which served to quantify Na⁺ contents. A fat-suppressed inversion recovery sequence was used to quantify H₂O content.

Plasma Na⁺ levels did not change. Mean Na⁺ contents in muscle and skin did not significantly change following four to five cycles of hemodialysis treatment (before therapy: 32.7 ± 6.9 and 44.2 ± 13.5 mmol/L, respectively; after dialysis: 31.7 ± 10.2 and 42.8 ± 11.8 mmol/L, respectively; P > .05). Water content measurements did not differ significantly before and after hemodialysis in muscle and skin (P > .05). Na⁺ contents in calf muscle and skin of patients before hemodialysis were significantly higher than in healthy subjects (16.6 ± 2.1 and 17.9 ± 3.2) and remained significantly elevated after hemodialysis.

Na⁺ in muscle and skin accumulates in patients with AKI and, in contrast to patients receiving chronic hemodialysis and those with acute heart failure, is not mobilized with hemodialysis within 5-6 days.