NMR Temperature Measurements Using a Paramagnetic Lanthanide Complex

NMR thermometry has previously suffered from poor thermal resolution owing to the relatively weak dependence of chemical shift on temperature in diamagnetic molecules. In contrast, the shifts of nuclear spins near a paramagnetic center exhibit strong temperature dependencies. The chemical shifts of the thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) complex (TmDOTP^5-) have been studied as a function of temperature, pH, and Ca²⁺ concentration over ranges which may be encountered in vivo. The results demonstrate that the ¹H and ³¹P shifts in TmDOTP^5- are highly sensitive to temperature and may be used for NMR thermometry with excellent accuracy and resolution. A new technique is also described which permits simultaneous measurements of temperature and pH changes from the shifts of multiple TmDOTP^5- spectral lines.