Liquid oral magnetic particles as a gastrointestinal contrast agent for MR imaging: efficacy in vivo.

Recent in vitro studies suggested there is an optimal range of concentration and viscosity for a liquid formulation of oral magnetic particles (WIN 39996) for magnetic resonance (MR) imaging of the gastrointestinal (GI) tract. To determine whether this formulation is also effective in vivo and whether differing viscosity and administration regimen affect GI distribution of the contrast agent, a range of concentrations of iron (75, 150, and 200 micrograms/mL) and viscosities (1, 150, and 600 cp) were imaged in dogs at 1.5 T with conventional spin-echo and fat-saturation pulse sequences. The effects of dose regimen (single vs divided dose) and subject position (supine vs right lateral decubitus) were also studied. The 75 and 200 micrograms/mL concentrations were unacceptable for MR imaging, while 150 micrograms/mL was effective. The GI distribution of the contrast agent was affected jointly by viscosity, subject position, and dose regimen. The 150 micrograms/mL formulation produced excellent GI contrast enhancement in vivo for both 150- and 600-cp viscosities. The choice of optimal viscosity may depend on the preferred administration regimen.