Improved neuronal tract tracing using manganese enhanced magnetic resonance imaging with fast T(1) mapping.

Chuang KH, Koretsky A.

Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA

There has been growing interest in using manganese-enhanced MRI (MEMRI) to detect neuronal activation, neural architecture, and neuronal connections. Usually Mn²⁺ produces a very wide range of T₁ change. In particular, in neuronal tract tracing experiments the site of Mn²⁺ injection can have very short T₁ while distant regions have small T₁ reductions, primarily due to dilution of Mn²⁺. Most MEMRI studies use T₁-weighted sequences, which can only give optimal contrast for a narrow range of T₁ changes. To improve sensitivity to the full extent of Mn²⁺ concentrations and to optimize detection of low concentrations of Mn²⁺, a fast T₁ mapping sequence based on the Look and Locker technique was implemented. Phantom studies demonstrated less than 6.5% error in T₁ compared to more conventional T₁ measurements. Using center-out segmented EPI, whole-brain 3D T₁ maps with 200-mum isotropic resolution were obtained in 2 h from rat brain. Mn²⁺ 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 T₁. With this quantitative imaging it should be possible to study more extensive pathways using MEMRI and decrease the dose of Mn²⁺ used. Magn Reson Med, 2006. Published 2006 Wiley-Liss, Inc.

PMID: 16470592 [PubMed - indexed for MEDLINE]