Hyperpolarized Lithium-6 as a Sensor of Nanomolar Contrast Agents

Lithium is widely used in psychotherapy. The Li-6 isotope has a long intrinsic longitudinal relaxation time T-1 on the order of minutes, making it an ideal candidate for hyperpolarization experiments. In the present study we demonstrated that lithium-6 can be readily hyperpolarized within 30 min, while retaining a long polarization decay time on the order of a minute. We used the intrinsically long relaxation time for the detection of 500 nM contrast agent in vitro. Hyperpolarized lithium-6 was administered to the rat and its signal retained a decay time on the order of 70 sec in vivo. Localization experiments imply that the lithium signal originated from within the brain and that it was detectable up to 5 min after administration. We conclude that the detection of submicromolar contrast agents using hyperpolarized NIVIR nuclei such as Li-6 may provide a novel avenue for molecular imaging. Magn Reson Med 61:1489-1493, 2009. (C) 2009 Wiley-Liss, Inc.