Relaxation times and concentrations of ⁷Li in the brain of patients receiving Lithium therapy

The present study describes a protocol for the determination of in vivo absolute molar concentrations of Li⁺ in the human brain using a double tuned ¹H/⁷Li surface coil. The protocol follows the method of Thulborn and Ackerman [J. Mag. Reson. 55, 357–371 (1983)] where the ratio of the signal intensities of ⁷Li and ¹H in the brain is compared to the same ratio in a phantom containing known concentrations of Li⁺. The ⁷Li T₁ values in the brains of five patients receiving lithium therapy were measured. The average result was T₁ = 3.5±0.25s. The phantom solution was adjusted to have this T₁ value. The protocol was applied for eight bipolar patients receiving lithium therapy. The average ratio of brain to serum lithium molar concentration was found to be 0.59±0.12.