Optimization of an oral magnetic particle formulation as a gastrointestinal contrast agent for magnetic resonance imaging

Magnetically susceptible iron oxide (MSIO) contrast agents for magnetic resonance imaging (MRI) of the gastrointestinal (GI) tract are limited because they produce magnetic susceptibility artifacts. To determine whether oral magnetic particles (WIN 39996) can be an effective MRI contrast agent without producing induced image artifacts, we optimized a liquid formulation of WIN 39996. A range of concentrations (25-250 micrograms iron/mL) and viscosities (1-600 cP) was imaged in a phantom at 1.5 T using conventional spin-echo and gradient-recalled echo pulse sequences. Some formulations also contained titanium. All concentrations of WIN 39996 at 1 cP produced susceptibility artifacts. For formulations in the 150 to 600 cP range, the 125 to 150 micrograms/mL concentrations produced signal blackening and magnetic susceptibility image distortion comparable to an air control. Concentrations greater than 150 micrograms/mL were unacceptable because they produced significant susceptibility artifacts, while concentrations less than 125 micrograms/mL were undesirable because they produced insufficient signal blackening. These preliminary in-vitro studies suggest that an optimized liquid formulation of WIN 39996 can be produced that yields excellent negative contrast without producing image artifacts.