Abstract
There has been growing interest in using manganese‐enhanced MRI (MEMRI) to detect neuronal activation, neural architecture, and neuronal connections. Usually Mn^2+^ produces a very wide range of T~1~ change. In particular, in neuronal tract tracing experiments the site of Mn^2+^ injection can have very short T~1~ while distant regions have small T~1~ reductions, primarily due to dilution of Mn^2+^. Most MEMRI studies use T~1~‐weighted sequences, which can only give optimal contrast for a narrow range of T~1~ changes. To improve sensitivity to the full extent of Mn^2+^ concentrations and to optimize detection of low concentrations of Mn^2+^, a fast T~1~ mapping sequence based on the Look and Locker technique was implemented. Phantom studies demonstrated less than 6.5% error in T~1~ compared to more conventional T~1~ measurements. Using center‐out segmented EPI, whole‐brain 3D T~1~ maps with 200‐μm isotropic resolution were obtained in 2 h from rat brain. Mn^2+^ transport from the rat olfactory bulb through appropriate brain structures could be detected to the amygdala in individual animals. The method reliably detected less than 7% reductions in T~1~. With this quantitative imaging it should be possible to study more extensive pathways using MEMRI and decrease the dose of Mn^2+^ used. Magn Reson Med, 2006. Published 2006 Wiley‐Liss, Inc.