Effect of paramagnetic manganese cations on H-1 MRS of the brain

Manganese cations (Mn2+) call be used as all intracellular contrast agent for structural, functional and neural pathway imaging applications. However, at high concentrations, Mn2+ is neurotoxic and play influence the concentration of H-1 MR-detectable metabolites. Furthermore, the paramagnetic Mn2+ cations may also influence the relaxation of the metabolites under investigation. Consequently, the purpose of this study was to investigate the effect of paramagnetic Mn2+ cations on H-1-MR spectra of the brain using in vivo and phantom models at 4.7T. To investigate the direct paramagnetic effects of Mn2+ canons on the relaxation of N-acetylaspartate (NAA), creatine and choline, T-1 relaxation times of metabolite Solutions. with and without 5% albumin, and containing different Mn2+ concentrations were determined. Relaxivity values with/without 5% albumin for NAA (4.8/28.1 s(-1) nM(-1)), creating (2.8/2.8s(-1) nM(-1)) and choline (1.8/1.1 s(-1) mM(-1)) showed NAA to be the most sensitive metabolite to the relaxation effects of the cations. Using an in vivo optic tract tracing imaging model, we obtained two adjacent regions of interest in the superior colliculi with different water T-1 values (Ma(2+)-enhanced = 1.01 s: unenhanced = 1.14 s) 24 h after intravitreal injection of 3 mu L 50 mM MnCl2. Using phantom and in vivo water relaxation time data, we estimated the in vivo Mn2+ concentration to be 2-8 mu M. The phantom data suggest that limited metabolite relaxation effects would be expected at this concentration. Consequently, this study indicates that. ill this model. the presence of Mn2+ cations does not significantly affect H-1-MR spectra despite possible toxic and paramagnetic effects.