Figure 2c: (a) In vitro T2 relaxation time MR image of agar-gel-suspended monocytes labeled with USPIO and SPIO at varying iron concentrations in a 96-well plate. The vehicle-treated sample contained unlabeled monocytes. (b) Graph shows R2 relaxation rates of cell samples. (c) Graph shows T2 relaxation times of increasing concentrations of SPIO-labeled monocytes. Data in b and c are presented as mean ± standard error of the mean. * = P < .05 versus vehicle-treated cells, # = P < .05 versus USPIO-labeled cells, 128e0.67x = 128 · ex.