3D ⁷Li magnetic resonance imaging of brain lithium distribution in bipolar disorder

Lithium is a major treatment for bipolar disorder and the likelihood of a favourable response may be determined by its distribution in the brain. Lithium can be directly detected by magnetic resonance (MR), but previous ⁷Li MR spectroscopy studies have demonstrated that this is challenging compared to conventional ¹H MR imaging due to the MR properties of the lithium nucleus and its low concentration in brain tissue, as dictated by therapeutic dose. We have tested and implemented a highly efficient balanced steady-state free precession ⁷Li-MRI method to address these challenges and enable MRI of brain lithium in a short duration scan. We report a 3D ⁷Li-MRI acquisition with 25 mm isotropic resolution in an 8-min scan that demonstrates heterogeneity in lithium concentration within the brain in subjects with bipolar disorder. This represents the direct imaging of a pharmaceutical agent in its target organ and notably expands the repertoire of techniques available to investigate the effects of lithium in man.