Variability of brain lithium levels during maintenance treatment: A magnetic resonance spectroscopy study

In vivo magnetic resonance spectroscopy (MRS) was used to determine the relationship between serum and brain lithium levels in bipolar patients (n = 25). Over the broad range of serum lithium levels observed, the correlation (r = .68) with brain lithium levels was high. This correlation was much weaker (r = .39) when limited to only those patients with serum lithium levels in the range of 0.6–1.0 mmol/l. This variability may account for failure of lithium prophylaxis in some patients who have serum lithium levels in the therapeutic range.