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Free keywords:
Brain mapping, Contrast media, Gadolinium-DTPA, Intraventricular injections, Manganese chloride, Subcutaneous injections
Abstract:
Using T1-weighted MRI at two different magnetic
field strengths, the enhanced longitudinal relaxivity
due to paramagnetic manganese ions in mouse brain
in vivo is shown to reflect reduced intracellular mobility.
One day after systemic administration of manganese
chloride, increases of the longitudinal relaxation rate DR1
in several brain regions are significantly higher at 2.35 T
than at 9.4 T. The corresponding relaxivity ratios
100r1/400r1 = 100DR1/400DR1 range from 2.4 (striatum) to
4.4 (cerebellar cortex). In contrast, the DR1 values after
intraventricular administration of gadolinium-DTPA (Gd-
DTPA) are not significantly different between both field
strengths yielding 100r1/400r1 ratios from 1.0 to 1.1. The
same observation holds true for manganese and Gd-DTPA
relaxivities in aqueous solution. The pronounced field
strength dependence of manganese relaxivities indicates a
reduced mobility of manganese ions in vivo by confinement
to a viscous fluid compartment and/or due to macromolecular
binding. Moreover, preferential enhancement
of nerve cell assemblies by manganese ions and the
observation of additional contrast enhancement by magnetization
transfer suggest an intracellular localization of
manganese. This is further supported by a slow release of
manganese from nerve cells postmortem, which occurs
despite a high permeability of damaged cellular membranes
as demonstrated by a rapid uptake of extracellular
Gd-DTPA.
