Fig. 3. (a) Dissolution of SPIONs in citrate buffer system at pH 4.5 at 37 °C for 14 days (b) 
solution relaxivity of SPIONs before and after exposure to citrate buffer for 2 days. MR images correspond to a concentration of 0.25 mM as imaged with a MGE sequence at TE = 15.5 ms.
