This paper presents a magnetic resonance imaging (MRI) method for quantifying the spatial concentrations of the paramagnetic species Mn2+ and Mn3+, during pattern formation, in the manganese-catalyzed 1,4-cyclohexanedione-acid-bromate reaction. The relaxivity of each species was measured, which enabled their concentration to be calculated from nuclear magnetic resonance T-2 relaxation times. Images were acquired using the fast spin-echo imaging method RARE. By determining the relation, in these experiments, between signal intensity and T-2 relaxation time, it was possible to produce T2 maps from the images. These T-2 maps were then used to produce concentration maps for the oxidized (Mn3+) and reduced (Mn2+) states of the catalyst.