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Manganese ion enhances T 1 ‐weighted MRI during brain activation: An approach to direct imaging of brain function
Author(s) -
Lin YiJen,
Koretsky Alan P.
Publication year - 1997
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910380305
Subject(s) - chemistry , stimulation , nuclear magnetic resonance , magnetic resonance imaging , calcium , glutamate receptor , neuroscience , somatosensory system , cerebral blood flow , biophysics , medicine , biology , biochemistry , physics , receptor , organic chemistry , radiology
Present techniques for functional MRI rely on detecting changes in hemodynamics that result as a consequence of brain activation. It would be useful if MRI techniques could be developed that enable imaging of a parameter directly related to neuronal activity. Influx of calcium into neurons is necessary for release of neurotransmitters. Divalent manganese ions (Mn 2+ ) can enter cells through voltage‐gated calcium channels and Mn 2+ is paramagnetic. Mn 2+ accumulation in brain due to activation should alter relaxation times offering an approach to sensitize MRI to calcium influx in the brain. To test this idea, T 1 ‐weighted MRI was obtained from the rat brain in the presence of a continuous intravenous infusion of 3.6 μmol/min MnCl 2 . In the anesthetized rat brain, signal enhancement was detected in regions corresponding to ventricles. Activation of the brain with glutamate led to increase in MRI signal intensity in the brain to 238 ± 23% of the original. This increase in signal was dependent on the presence of MnCl 2 and was not due to changes in blood flow. It was necessary to break the blood brain barrier with mannitol to make Mn 2 accessible to the active sites for efficient detection. Enhancement of MRI signal in the brain was also detected with decreasing anesthesia and with somatosensory stimulation. Due to the slow clearance of Mn 2+ from the stimulated region of the brain, MRI enhancement could also be detected after stimulation that occurred on awake, behaving rats outside the magnet. These data indicate that MnCl 2 shows potential as a MRI contrast agent that is directly sensitive to brain activation.