Use of AMI-227 as an oral MR contrast agent.

We report the use of an ultrasmall superparamagnetic iron oxide colloid AMI-227 as an oral contrast agent. Due to the small size, AMI-227 has a larger effect on T1 than larger superparamagnetic iron oxides colloids like ferumoxsil. At 2 T, AMI-227 had an R2/R1 of 11.4 compared with an R2/R1 for the superparamagnetic iron oxide ferumoxsil of 179. The R1s of the two agents were 7.1 and 1.6 mM-1 s-1, for AMI-227 and ferumoxsil, respectively. Due to its smaller R2/R1, orally administered AMI-227 can produce brightening or darkening of the lumen of the GI tract, depending on instrument parameters. At 1 mM Fe, image brightening (2 T, TR = 300, TE = 25) or image darkening of the GI tract (2 T, TR = 1500, TE = 80) was obtained. The ability of AMI-227 to produce either image brightening or darkening suggests it may be useful as an MR contrast agent for the GI tract.