Direct CSF injection of MnCl2 for dynamic manganese-enhanced MRI

MnCl2 was injected intrathecally through the cisterna magna in rats, allowing infusion of divalent manganese ions (Mn++) into the CSF space and thence into the brain, without breaking the blood–brain barrier (BBB). Mn++ uptake and washout dynamics in the brain were measured by serial T1‐weighted MRI and EPI T1 and T2 mapping for up to 3 weeks after injection. Observations within the first 6 hr after injection demonstrated anterograde and bilateral distribution of the Mn++ within the CSF space, from the olfactory bulb and frontal cortex to the brain stem. Enhancement increased in most brain areas up to 4 days after injection, and then slowly decreased. Relaxation maps at each time point demonstrated higher concentrations of Mn in basal ganglia. Residual concentrations were still observable after 3 weeks in all brain regions. With the use of MnCl2 calibration phantoms, the maximum Mn concentration in the brain was estimated to be approximately 27 ± 16 μM, corresponding to changes in relaxation rates of 0.49 ± 0.30 s−1 for R1 and 3.9 ± 2.4 s−1 for R2. For comparison, an intrathecal GdDTPA injection was performed. This injection showed different distribution dynamics: it remained chiefly within the CSF spaces, and was largely washed out after 1 day. This method shows promise as a means of supplying Mn++ uniformly to the whole brain for a variety of chronic functional activation studies. Magn Reson Med 51:978–987, 2004. © 2004 Wiley‐Liss, Inc.