Temporal Changes in the T1 and T2 Relaxation Rates (delta R1 and delta R2) in the Rat Brain Are Consistent With the Tissue-Clearance Rates of Elemental Manganese

Chuang, Kai‐Hsiang, Alan P. Koretsky, and Christopher H. Sotak. "Temporal changes in the T1 and T2 relaxation rates (ΔR1 and ΔR2) in the rat brain are consistent with the tissue‐clearance rates of elemental manganese." Magnetic Resonance in Medicine 61.6 (2009): 1528-1532.

One of the main points of recent MeMRI study was to determine the time course of influx and efflux of manganese in the RVLM following systemic injections of manganese.  As a trace mineral, manganese can be found in multiple forms in the body that effect both its rate of efflux from a cell and its effect on proton relaxation rates.  While we discuss signal intensity in our study as manganese uptake within a cell, signal intensity may also be dictated by the relative state in which the manganese is able to change the proton relaxation rates.  To determine the extent that changes in relaxivity (how effectively manganese is able to change relaxation rates) are contributing to changes in signal intensity MeMRI studies were done in combination with NMR, directly examining manganese concentrations in neuronal tissue.  Initial results showed that T1 and T2 relaxation times, as well as delta R1 and delta R2 peak 1 day after administrations of manganese, which corresponded to greatest concentrations of manganese in neuronal tissue.  In all cases manganese uptake was seen to be greater in the olfactory bulb than in the cortex.  Both relaxation rates and relaxivity levels return to baseline levels 4 and 5 weeks post injections, conclusive with absolutely manganese concentrations also returning to baseline at 4 weeks.  Conclusively, this study was able to show that T1 and T2 relaxation times were mainly influenced by transport of manganese in and out of the cell, compared to manganese taking different forms while remaining in the cell (relaxivity).  This is important, because it further validates manganese enhancement being measured following systemic injections of manganese is an appropriate representation of in vivo neuronal activity.

~JI