The effect of paramagnetic manganese cations on H MR spectroscopy of the brain

Introduction The paramagnetic properties of divalent manganese cations (Mn) and their in vivo resemblance to calcium cations (Ca) has led to their use in morphological [1] and neural pathway [2] imaging. Mn is taken up through Ca-channels during neural activity and subsequently transported anterograde along microtubules at a velocity equivalent to fast axonal transport thereby making the metal suitable for neural tract tracing [2]. Mn is an essential trace element found at low concentrations in the brain. Elevated levels of Mn are neurotoxic and influence a range of neurophysiologic and metabolic processes and chronic exposure to Mn may lead to neurodegeneration [3]. The administration of Mn to observe, for example, neural pathways may therefore influence those same pathways due to the high local concentrations of Mn required to provide MRI contrast. As a result, the use of H MRS to obtain a metabolic profile of the brain may be influenced by both Mn-induced metabolic changes and the effect of the paramagnetic metal ion on the relaxation of the metabolites themselves if the Mn cations and metabolites are in the same cellular compartment. Consequently, this study has investigated the effect of Mn on H MR spectroscopy using an in vivo Mn-enhanced optic tract imaging model [2] together with phantom experiments.