Magnetic susceptibility artifacts with superparamagnetic gastrointestinal contrast media

This paper reports on superparamagnetic gastrointestinal contrast agents for MR imaging which have limited effectiveness because of magnetic susceptibility artifacts and image distortion. The authors hypothesize that these artifacts can be circumvented by optimizing the concentration and viscosity of the formulation. Phantom and canine studies (n = 39) were performed with a new superparamagnetic agent (WIN 39996, Sterling Drug). A 250 μg of iron per milliliter aqueous suspension was diluted from 10% - 100% wt/wt (10% increments). Viscosity varied from 1 to 600 CPS (150 CPS increments) using Xanthan gum. MR imaging was performed at 1.5 T with spin-echo (TR/TE 300/15 and 2,000/35,70 with fat saturation) and gradient-echo sequences (25-40/13/30 degrees), initially and after 1 hour of gravitational settling. All concentrations at 1 CPS caused susceptibility artifacts. For 150-600 CPS formulations, 50% - 60% wt/wt concentrations yielded good negative contrast with the same susceptibility changes as air in vitro, and no susceptibility artifacts seen in vivo, even with gradient-echo and fat-saturated sequences, up to 1 hour. Higher concentrations produced artifacts; lower concentrations provided insufficient negative contrast