Fig. 4. (A) Ex vivo MRI images of the mice brains injected with IONRs. The location of injected beads of IONRs or controls is shown by red circles. The colour codes the signal intensity which is proportional to the value of T^eff₂ in ms. The signal is shown to decrease in intensity for the 50 ppm and 25 ppm areas confirming the presence of a negative contrast agent which is expected from the IONPs. (B) Comparative curves of the control (left) and IONRs beads (right) showed the drop in signal intensity as a function of echo time, with a steeper change in the case of free IONRs indicating a shorter T^eff₂.