Signal loss in the T₂-weighted magnetic resonance images by using an USPIO-particle contrast agent

We observed a significant signal loss in the T₂-weighted MR (magnetic resonance) images when USPIO (ultrasmall superparamagnetic iron oxide) particles were used as the MRI contrast agent. The mean diameter of the coated ferrite nanoparticles we used for MR imaging was about 38.63 nm. The hydrogen bond between the dextran and the ferrites was checked with an FT-IR spectrometer. Using an aqueous solution of these ferrites as the contrast agent, we observed a 35.2 % signal loss in the T₂-weighted MR images of the liver of a New Zealand white rabbit. We also found that the effect of the contrast agent was the greatest 15 minutes after the injection of the contrast agent and that the MR images recovered their original brightness about 30 minutes after the injection. This tells us that the Kupffer cells retain the ferrites only for about 30 minutes and then release them into the blood. We also found that there was no signal loss at the gallbladder which has no Kupffer cells.